PAUL SCHERRER INSTITUT ISSN 1 4 2 3 - 7 2 9 6March 2001

Scientific Report 2000Volume I

Particles and Matter

ed. by: J. Gobrecht, H. Gaggeler, D. Herlach, K. Junker, P.-R. Kettle, P. Kubik, A. Zehnder

CH-5232 Villigen PSISwitzerland

Telephone: +41 56 310 21 11Telefax:+ 41 56 310 21 99

http://www.psi.ch

PLEASE BE AWARE THATALL OF THE MISSING PAGES IN THIS DOCUMENT

WERE ORIGINALLY BLANK

TABLE OF CONTENTS

Introduction. i

Laboratory for Particle Physics 3Foreword 4

Particle PhysicsTheoryTheory (I) 5Theory (II) 6Theory (III) 7ExperimentsSearch for muon - electron conversion on gold 8A precise measurement of the K+ —> 7t°e+v decay rate 9Does the KARMEN time anomaly originate from a beam-correlated background 10Precision measurement of the mass of the charged pion 11A precision measurement of the michel parameter % in polarized muon decay 12Precision measurement of singlet (ip capture in hydrogen 13Pionic hydrogen 14Rare A^-decays in flight (Brookhaven AGS E865) 15Higgs candidates in e V interactions at -JJ = 206.6 GeV 16

Nuclear PhysicsTest of supersymmetry using in-beam spectroscopy of1% Au 17Study of 100Ru at the philips cyclotron and at SINQ 18Modelling fission in nuclear reactions: I reaction cross-sections 19Modelling fission in nuclear reactions: II mass distribution 20Measuring itD3He fusion 21

Atomic PhysicsHigh-resolution study of heavy-ion-induced thorium and uranium Ly x-ray spectra 22First direct observation of long-lived 2S-states in muonic hydrogen 23

Detectors and Experimental FacilitiesDevelopment work for the CMS pixel detector 24Development of event triggers for CMS based on the picel detector 25Polarized nuclei in plastic scintillators: New tools for spin physics 26An ultracold neutron facility at PSI 27The low energy muon beam for the muonic hydrogen lamb shift experiment 28

Laboratory for Astrophysics 29Foreword 30The first year of XMM-Newton 31XMM-Newton: from calibration to first results 32Free-floating planets in stellar clusters 33Spatial analysis of solar type III events associated with narrowband spikes at metric wavelengths 34Hard x-rays and decimetric radio correlations 35Shape and geometry of galaxy clusters and the SZ- effect 36Baryonic dark matter in clusters and spiral galaxies 37First data from SREM in space 38Repairing the imaging system of the high-energy solar spectroscopic imager (HESSI) after JPL-mishap 39Star calibration of the HESSI roll angle system (RAS) 40The aspect data proccesor (ADP) for the HESSI imager 41The HESSI solar aspect system (SAS) 42Fabrication of transition edge sensors (TES) devices 43Arrays of superconducting photon detectors 44Transition edge sensors for astronomical applications 45Operating of the proton irradiation facility - concise summary 46Standard radiation environment monitor SREM as a successful example of technology transfer and industrial cooperation 47Comparison of calibration results from PROBA standard radiation environment monitor with Monte-Carlo simulations 48

Laboratory for Muon Spin Spectroscopy 49Foreword 50

SuperconductivityOxygen isotope effect on magnetic penetration depth in underdoped YxPr1.xBa2Cu3O7.7 51Magnetism in tetragonal La2.x.ySrxREyCuO4 52Cation size disorder-induced crossover from superconductivity to magnetic order in Li 85M0.i5CuO4 53Low energy excitations and inhomogeneous magnetism in electron doped cuprates 54Effect of an applied current on the flux line lattuce of NbSe2 55Flux line lattice of 3d superconductors 56

Magnetism (partial overlap with Superconductivity)Magnetic ordering in ammoniated alkali fullerides 57Spin dynamics in novel transition metals 58Effects of dimensionality and quantum criticality on heavy-fermion superconductivity and magnetism 59Glassy spin dynamics in non-fermi-liquid UCu5.xPdx, x = 1.0 and 1.5 60Study of the magnetic properties of Ce3Pd20Si6 and Ce3Pd20Ge6 compounds 61\iSR magnetic studies of the heavy fermion compound Ce7Ni3 62Magnetic properties of CeNiSn doped with Cu or Pt 63\iSR studies of the Kondo insulators Yb!_xLuxB12 64The magnetism of YFe6Al6 65Macroscopic and local magnetic moments in Si-doped CuGeO3 with neutron and [iSR studies 66Spin fluctuations in the triangular antiferromagnet CsNiBr3 67Low temperature spin fluctuations in spin-liquid Yb3Ga5Oi2 68Study of U- and RE-intermetallic compounds exhibiting quadrupolar and magnetic order 69Comparative study of the magnetic properties of rare earth intermetailic compounds,complementing neutron scattering experiments 70Magnetic correlations in one dimensional spin systems 71\iSR and spin-vacancy-induced magnetism in low-dimensional quantum systems 72\iSR studies of the electron-doped C a ^ SmxMnO3 73Zero and longitudinal field relaxation in low doping manganites: search for static and dynamic ferromagnetic clusters 74A [iSR study of the low temperature magnetic properties of the molecular cluster Fe8 75\iSR on monodisperse nano-scale Pd clusters at low temperatures 76Study of the dynamic and structure features of magnetism in holmium 77Spontaneous magnetic ordering in sodium electro sodalite 78Formation of Condon domains in lead at very low temperatures 79

Semiconductors and Liquid CrystalsHSR dynamics of liquid crystals studied by ALC 80HSR in II-VI solar cell materials 81Muon(ium) in nitrogen-rich diamond with H2/H3 centres 82Measurement of relaxation rate and paramagnetic frequency shift of the negative muon spin precession in silicon 83

ChemistryHydrocarbon activation in zeolites; insights through EPR and jiSR 84"The blue-ridge mountains of Virginia" 85ALC-jiSR on aza-cyclohexadienyl radicals in pyridinium salts 86Interactions of cosurfactants with surfactant bilayers 87

Research and Development with Low Energy MuonsDiffusion of muons in metallic multilayers 88Emission of epithermal muons from a patterned moderator 89Thickness dependence of the efficiency of s-Ar and s-N2 moderators 90Anew surface muon beam 91

Laboratory for Micro and Nano Technology 93Foreword 94

Nano Factory and X-ray OpticsRheology and pattern formation during hot embossing of thin polymer films 95Nanofabrication with hot embossing and electroforming 96V-groove replication: a tool for quality control of a compact disc injection molding process 97Laser ablation lithography using diffractive phase masks 98High resolution scanning x-ray fluorescence microscopy 99Tunable wet etched diffractive optics for hard x-rays 100Micromechanical cantilevers for thermal analysis 101

Silicon Based Nanomaterials and NanoelectronicsSingle hole transistor in a p-Si/SiGe quantum well 102Electro- and photoluminescence of C-induced Ge islands embedded in Si 103Optical and structural analysis of Ge quantum dots embedded in strained Si quantum wells grown on patterned substrates 104Modeling of the c(4x4) surface reconstruction 105Strain fields in C-induced Ge dots 106Modifications of the Si (100) surface 107Thermophotovoltaics - system, photocells and potential 108TEM investigation of an ordering phenomenon in Alo.5Gao.5As 109Application of the quantum cascade laser principle to the Si/SiGe material system 110Structural investigations of Si/SiGe cascade samples I l lFormation of arbitrary 3-dimensional nano-structures from strained Si/SiGe double layers 112

Molecular NanotechnologyPhotolithographic generation of protein micropatterns 113Deposition system for single molecule experiments 114Extracellular stimulation of neurons cultured on microelectrode arrays 115Nanostructred chips for the analysis of individual proteins 116Electrochemistry of stacked layers of redox labeled proteins 117Production and redox labelling of antibodies against B-lactam antibiotics 118

Laboratory for Radio- and Environmental Chemistry 119Foreword 120

Heavy ElementsFluoride complexation of rutherfordium (Rf, element 104) 121Thermochemical predictions of the chemical properties of bohrium (Bh, Element 107) 122Stability of group 8 tetroxides MeO4 (Me=Ru, Os, Hs) and their adsorption behavior on quartz 123Evaluation of the enthalpy of adsorption of OsO4 on quartz 124The interaction of element 112 with metal surfaces 125A first attempt to chemically identify element 112 126On-line thermochromatographic studies of radon as a presumable pseudohomologue of the elements 112 and 114 127Vander Waals interaction of atoms of elements 112, 114, and 118 with solid surfaces 128Semi-empirical calculation of adsorption entropies 129Selective gas-phase transport of short-lived, carried-free iodine isotopes from a 252Cf fission source 130a-peak shift in cooled PIN-diode detectors 131

Surface ChemistryTransport yields of selenium nuclides at the SINQ gas-jet facility 132Reaction of HO86Br with sodium bromide aerosol 133The adsorption of NO, NO2 and HONO on ice 134The adsorption of peroxyacetyl nitrate on ice 135The reaction of HNO3 with sea-salt aerosol particles 136Modelling the heterogeneous reaction of NO2 on diesel soot 137Measurement of the HONO emission from a diesel engine 138Significant nitrite formation in diesel exhaust 139

Analytical ChemistryAn Alpine ice-core record of anthropogenic HF and HC1 emissions 140North-South deposition gradients of trace species in the Alps 141Electrical conductivity measurement on an ice core from the Illimani (6430 m, 16°39'S, 67°47'W), Bolivia 142Seasonal record of glaciochemical and isotopic signals in a shallow ice core from Chimborazo, Ecuador 143Glaciological and chemical survey at glaciar Esmeralda, Chile 144The influence of sublimation on stable isotope records recovered from high altitude glaciers in the tropical Andes 146Analysis of dust layers in an ice core from Cerro Tapado, Chile 147First glacio-chemical investigation of Belukha glacier in the Siberian Altai 148Continuous melting and ion chromatographic analyses of ice cores 149Preliminary results of trace element analysis in ice cores by continuous ice melting (CIM) ICP-MS 150First approach to determine concentrations of mercury in ice cores by cold vapour ICP-MS 151Determination of total dissolved silicon for 32Si dating of glacier ice 152Applicability of TXRF for trace element analysis in ice samples 1537Be and 10Be concentrations at the high-alpine site Jungfraujoch 154A new Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) for trace element analyses 155

Cement ChemistryCement Chemistry: Quality control and developments 2000 156

IV

Project Radwas teDetermination of the radionuclide inventory in accelerator waste 157High and intermediate energy nuclear data for accelerator-driven systems (HINDAS) 158Measurement of radionuclide contents in activated graphite 159

Laboratory for Ion Beam Physics i6iForeword 162The PSI/ETH Tandem accelerator facility 163Investigation of natural 10Be/Be ratios with accelerator mass spectrometry (AMS) 164Dendrochronological and radiocarbon dating of the Scythen burial place in the Pazyryk Valley in the Altai Mountains,South Siberia 165Biosphere 2 ocean radiocarbon experiment 166Variations in atmospheric 14C content 40,000 ago and radiocarbon age of Heinrich event 4 167Late Pleistocene sequences of the Black Sea shelf: Calibration by AMS 14C dating 168A Late-Glacial and early Holocene environment and climate history for the Neuchatel region (Switzerland) 169The application of in situ cosmogenic nuclide exposure dating (10Be, 26A1), to glacial deposits of the last deglaciation inthe southern Andes of Chile 170Slip rates of active thrusts at the northeastern margin of Tibet (China) as revealed by 21Ne and 10Be exposure ages ofLate Pleistocene alluvial fans 171Cosmogenic nuclide erosion assessment of tropical highlands (Sri Lanka) 172Can we use cosmogenic nuclides to date stone artifacts? 173A 30,000 year erosion rate record from cosmogenic nuclides in river terrace sediments in the Massif Central, France 174Last major advance of Taylor Glacier into Central Beacon Valley, Antarctica, at least 4 Ma ago 175Constraints for the latest glacial advance on Wrangel Island from surface exposure dating 176Cosmogenic isotope constraints on erosion rates in the Himalaya 177Detection of the 205 year solar cycle during the last ice age 178Air-firn-transfer of 10Be on Polar ice sheets 179Ice core recovery from the South Inilchek Glacier (Kyrghyzstan) 180Paleomagnetic field reconstruction based on cosmogenic 36C1 in the GRIP ice core 181Composition-dependent scavenging of 10Be by marine particles 18210Be sedimentation and transport processes in the South Atlantic 18310Be and Pb-time-series of a Fe-Mn crust from the Tasman Basin, south-western Pacific 18410Be / 7Be ratios at the high-alpine site Jungfraujoch 185129I in rain water near Zurich 186Prospects of 129I as an environmental tracer 187Beryllium liquid alloy ion sources for focused ion beam implantation 188A GePd liquid alloy ion source for focused ion beam implantation 189Nanostructued materials by selective surface activation using focused ion beam implantation 190

List of publications 191

Contributions to conferences and workshops 216

Lectures and courses 243

Awards 245

INTRODUCTION

Our most important resources are people, scientists withinnovative ideas, engineers with an impetus to produce a fi-nal product and technicians with pragmatic solutions to helpus to be faster than the competition and within budget. Wefeel presently the good economy through the difficulty to re-cruit new people at all levels. We have therefore to increasethe training of people and facilitate migrations within the in-stitute.

The year 2000 was the first year under the new regimeof a global budget. This implied a change in the culture ofproject management. Project leaders have to optimize thefull project including at first sight invisible or hidden costsuch as services from the infrastructure and logistic departe-ment. Also the operating costs have to be taken into accountat a much earlier stage. As any change in culture takes itstime we have to improve in the coming years.

A partial answer to the mentioned challenges above is astronger collaboration within the institute. We experiencealready a few excellent examples such as a collaboration ofscientists and technicians from Particle Physics, Micro- andNanotechnology and SLS to produce pixel detectors for useat SLS, the development of advanced x-ray optics for SLSand other light sources by people from Nanotechnology, anincreased collaboration between Radiochemistry and IonBeam Physics. Also collaborations beyond the departementare increasing in strength where we like to mention commonusers meetings of the Muon Spin Rotation (/iSR) andNeutron Scattering communities, the help of the detectorgroup of Particle Physics for instruments at SINQ, andthe collaboration between Molecular Nanotechnology andElectrochemistry from General Energy departement.

Equally, we should further strengthen our link to indus-try. The front page of this report is about one of the high-lights of this year. We could demonstrate the first electrically

stimulated light emission from SiGe-heterostructures with alargely recognized publication in Science and several spon-taneous reactions from semiconductor industries. Also othertechniques and devices could be transferred to industry asfor instance superconducting tunnel junction detectors devel-opped for astrophysics with application in protein Time-of-Flight Mass Spectrometry to mention one.

The Paul Scherrer Institut devotes 60% of its resourcesto the user laboratory function. We consider it as important,that we keep our facilities at the forefront of the technologyand constantly improve on it. It has been decided to rebuildthe yuE4-beam and optimize it for highest intensity of lowenergy muons. A factor of about 5-10 will be achieved in2003/2004 and will serve primarily the ultra low energy //SRfacility, where we can stop fully polarised muons in thin sur-faces. A new international users group for this unique facil-ity has been formed and a significant contribution to this newbeam line has been granted by the German BMBF. PSI likesto thank for this generous support.

The majority of the publications in 2000 address ques-tions in basic research. They pave the way for the long termfuture of science and technology or equal importantly con-tribute to the understanding of nature, the origin of mass andforces or the dynamics of our universe. The price for basicresearch is justified if it is of high quality. In the year 2000three laboratories have been reviewed by a team of inter-national experts; the laboratories of Particle Physics, MuonSpin Rotation, and Micro- and Nanotechnology have demon-strated world class results and received suggestions for fur-ther developments.

L a b o r a t o r y for P a r t i c l e P h y s i c sForeword

Particle Physics

TheoryExperiments

Nuclear Physics

Atomic Physics

Detectors and Experimental Facilities

LABORATORY FOR PARTICLE PHYSICS

Kurt Gabathuler

The year 2000 marked the closing of the Large Electron-Positron Collider LEP at CERN, which ultimately achieveda centre-of-mass energy of 209 GeV. This facility has greatlycontributed to the sharpening of the picture of elementaryparticles and their interactions. A Standard Model fit to thehigh quality data now available allows one to predict themass of the so far elusive standard Higgs boson to withina range between 113.5 GeV/c2 (from direct search) and 170GeV/c2 (95% CL).

At LEP, PSI was a member of a collaboration runningthe L3 detector and contributed to the construction of the for-ward muon chambers. In the last months of running LEP apossible hint of a Higgs signal at 115 GeV/c2 was reported,which led to a one-month extension of LEP operation be-yond the long anticipated shut-down date. A request for afurther extension was however rejected as it seemed ques-tionable that it would be possible to resolve the ambiguouspresent signal at LEP within a reasonable time and cost, andnot cause a delay in the construction of the Large HadronCollider LHC, which is to succeed LEP. Indeed, LHC withits centre-of-mass energy of 14 TeV is not limited in energyand will therefore be able to cover the predicted mass win-dow of the Higgs particle.

PSI is a member of the CMS collaboration, now prepar-ing its multi-purpose experiment at LHC, which is scheduledto become operational in about five years. Our laboratory hasa major responsibility for the development and constructionof the pixel vertex detector and the electromagnetic calorime-ter ECAL. These two subdetectors are particularly suited tothe search for the Higgs around 115 GeV/c2. The mostpromising decay mode of a light Higgs particle is H —> 77,for which a high performance ECAL is mandatory. With ef-ficient, high purity b-tagging by the vertex detector in asso-ciated Higgs production Htt, the main decay mode H —> bbfor the case of a light Higgs could be singled out from thelarge background.

Concerning the experimental programme at the PSI ac-celerator, 2000 was certainly a productive year for all exper-iments seeking high-statistic data. Two experiments involv-ing ordinary muon decay and utilizing polarisation measure-ments completed their data taking phase. This concludes along term programme of looking for effects beyond the Stan-dard Model in this purely leptonic process.

In the last few years, the existence of a neutral parti-cle of 33.9 MeV/c2 has been claimed by the KARMENcollaboration while looking at neutrino induced reactions atthe Rutherford Laboratory. At PSI, this particle was unsuc-

cessfully searched for in pion decay. The anomaly found atRutherford, however, might recently have been explained bymembers of our laboratory, the effect being assigned to a tinyadmixture of nitrogen in the organic scintillator used for de-tection of the neutrino interactions.

A new precision measurement of the pion mass relativeto the muon mass has achieved a statistical accuracy of 1ppm by detecting x-ray transitions in muonic oxygen and pi-onic nitrogen atoms simultaneously. Both x-ray lines couldbe registered by Bragg scattering in the same geometric con-figuration of a crystal spectrometer, thus avoiding system-atic uncertainties. This experiment greatly benefited fromthe new cyclotron trap enhancing the atom formation rate,and from using spherically curved crystals. With the sameapparatus, a preliminary experiment was performed on pio-nic hydrogen, where the rate of registered x-ray transitionscould be enhanced by a factor of 10 with an improved peak-to-background rate, thanks to optimized shielding.

The year 2000 saw two retirements of distinguished SIN/PSI veterans closely related to our laboratory. Milan Locherjoined SIN in 1970 and acted for many years as head of thetheory group. His scientific interest was concentrated on lowenergy hadron interactions. He served, since the seventies,as scientific secretary of our Research Committee, where hiscareful wording of the often very difficult committee recom-mendations were very much appreciated, as well as his ex-pertise in the judging of the many pion- nucleus and pion-nucleon proposals. Wilfred Schoeps joined SIN in 1968 andis known to all experimentalists at the PSI accelerators asthe promoter and designer (together with his group) of stan-dardised, high performance NIM and CAMAC electronics.Hundreds of his NIM and CAMAC modules are still in usetoday in numerous experiments at PSI. In fact, some of thedesigns have been licenced out to commercial firms.

In October, the activities of the Laboratory for ParticlePhysics were presented, both in written and oral form, tothe reviewing Plenary PSI Research Committee (F0K0). Inthe summary of the deliberations and recommendations, thecommittee stated: "Considering the human and financial re-sources, PSI's programme in particle physics is, overall, agood balance between in-house and external engagements...The traditional user lab. function in particle physics can onlybe maintained if new innovative projects at PSI's proton ringare actually implemented in the near future and opportunitiesfor new proposals are kept open." The two new initiatives onthe forbidden decay [i —> e + 7 and on the electric dipolemoment of the neutron are examples of such new innovativeprojects.

THEORY (I)

E. Accomando, C. Alexandrou1, A. Denner, St. Diirr, D. Graudenz2, Th. Jensen3, K. Junker, M. P. Locher4, V. E. Markushin,M. Melles, St. Pozzorini3, R. Rosenfelder, M. Spira, O. Wigger5

1 now: Department of Natural Sciences, University of Cyprus, CY-1678 Nicosia, Cyprus2 now: McKinsey Consulting, Hamburg

3 PhD student4 retired

5 now: Physik-Institut der Universitat Zurich

In this year the Theory group organized again the tra-ditional summer school in Zuoz. The "Phenomenology ofGauge Interactions" was covered and discussed by leadingexperts in this field - both from an experimental and theoret-ical point of view.The scientific proceedings are available as

Proceedings of the Summer School on Phenomenologyof Gauge Interactions, eds. Dirk Graudenz and ValeriMarkushin, Zuoz (Engadin), Switzerland, August 13 -19, 2000, PSI-Proceedings 00-01, ISSN 1019-6447.

At present the Theory group works mainly in the follow-ing fields: exotic atoms (nuclear, atomic and molecular ef-fects), strong interaction physics at low energy (mesonic res-onances, antiprotons), nonperturbative methods in field the-ory (variational methods, lattice gauge theory), and the Stan-dard Model of particle physics (Higgs physics, electroweakradiative corrections) together with its extensions.

Below and in the following contributions a few examples arepresented in more detail; for further topics see the detailedlist of publications which also includes the work done in col-laboration with visitors.

The structure of scalar mesonsThe decay <f> ->• JTTTT has been studied in an exactly solv-

able coupled channel model containing the TTTT, KK, and qqchannels interacting via separable potentials [1,2]. Since the<f> meson is nearly a pure ss state, this decay is an OZI-ruleviolating process which is expected to proceed via a two-stepmechanism with intermediate KK states and therefore iswell suited for probing the KK content of the scalar mesons.It was found that the /o (980) resonance corresponds to one5-matrix pole close to the KK threshold; this pole has a dy-namical origin and represents the molecular-like KK state.The molecular picture of the f0 (980) meson is found to be ina fair agreement with the experimental data (see Fig.l).

The lightest scalar meson, a, has a dynamical origin re-sulting from the attractive character of the effective TTTT inter-action, with a partial contribution from the coupling via theintermediate scalar qq states. The distinction between gen-uine qq states and dynamical resonances, a and /o (980), canbe illuminated by considering the limit Nc —>• oo where theqq states turn into infinitely narrow resonances while the dy-namical states disappear altogether.

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1M^ (GeV)

Figure 1: The calculated nn invariant mass distribution inthe decay <f> —>• 77r°7r°. The experimental points are from theSND and CMD experiments.

The structure of the qq state embedded into the mesoniccontinuum has been analyzed using the calculated quark-antiquark spectral density. The gross structure of the qq spec-tral density p(s) has been found to be related to the /o(1370)resonance. There is also a significant contribution to p(s) inthe low mass region (tr meson) which is related to the strongcoupling between the TTTT and qq channels. This realisticspectral density can be used in QCD sum rule calculationsfor the scalar quark condensate and gives a significant im-provement over the usual narrow-resonance approximation[3].

REFERENCES

[1] V. E. Markushin, Eur. Phys. J. A 8, 389 (2000).

[2] V. E. Markushin,Acta Physica Polonica B 31, 2665 (2000).

[3] M.A. Shifman, A.I. Vainstein, V.I. Zakharov,Nucl. Phys. B 147, 385, 448 (1970);S. Narison, Nucl. Phys. B 509, 312 (1998).

THEORY (II)

E. Accomando, C. Alexandrou, A. Denner, St. Diirr, D. Graudenz, Th. Jensen, K. Junker, M. P. Locher, V. E. Markushin,M. Melles, St. Pozzorini, R. Rosen/elder, M. Spira, O. Wigger

Variational Worldline QEDNon-perturbative methods are urgently needed for many

strong-coupling problems in quantum field theory. FollowingFeynman's successful treatment of the polaron problem incondensed matter physics the same variational principle wasapplied to quenched QED in the worldline formulation. Newfeatures arise from the description of fermions by Grassmanntrajectories, the supersymmetry between bosonic and fermi-onic variables and the much more singular structure of arenormalizable gauge theory like QED in 3 + 1 dimensions.As trial action a general retarded quadratic action is takenwith free retardation functions. From the variational equa-tions for these functions a remarkably simple, non-perturba-tive, gauge-invariant solution for the anomalous mass dimen-sion 7™ (a) in the MS-scheme has been derived [1].

2.0

1.6-

1.2-

0 . 8 -

0.4-

0.0

3-loop/

Dyson—

Schwinger

4-loop\

0.0 0.5 1.0 1.5 2.0 2.5 3.0a

Figure 1: Anomalous mass dimension j m as function of thecoupling constant a in quenched QED. The variational resultis shown as a solid curve while the solution from the Dyson-Schwinger equations in rainbow approximation and Landaugauge is indicated as a dot-dashed line. The curves labeled"n-loop" show the results up to n-loop perturbation theory.The Pade estimation of the 5-loop result is also shown.

For small couplings the variational result can be com-pared with recent four-loop perturbative calculations [2] whileat large couplings one finds that 7 m (a) becomes proportionalto y/a (see Fig. 1). The anomalous mass dimension showsno obvious sign of the chiral symmetry breaking observed in(gauge-dependent) Dyson-Schwinger calculations [3], how-ever it is found that a perturbative expansion of 7 m (a) di-verges for a > 0.7934. The calculation of physical observ-ables or application to bound state problems seems also fea-sible within the variational worldline approach.

MSSM Higgs Boson Production in 77 CollisionsThe heavy neutral Higgs bosons H, A in the minimal su-

persymmetric extension of the Standard Model can be pro-duced as single resonances at high-energy 77 colliders. Theprospects of the search for these particles have been studiedin bb and neutralino-pair final states [4]. The Higgs bosonscan be found with masses up to 70-80% of the initial e±e~collider energy for medium values of tg/?, i.e. in areas of thesupersymmetric parameter space not accessible at other col-liders. In a fine scan of the resonance region the two Higgsbosons A and H can be disentangled at least in part of the su-persymmetry parameter space. This is shown in Fig. 2. If thesupersymmetry parameters ft, M2 are favourable, the steps inthe resonance formation curve are clearly visible. However,this theoretical analysis must be backed by future experimen-tal simulations including detector effects.

4

3.5

3

2.5

1.5

1

0.5

<G(TI -> bE)> [fb]•MA = 300GeV

"A = ±2 GeV /

cos9| < 0.5 /

AJ y

AI/

y^ " N^-A+H

\

' M2/n = 200/-200\

w/o SUSY \

background

-

•

\200/200GeV .

\«-H J

............. ...._* .T..™,.7.._._.^

395 396 397 398 399 400 401

e [GeV]

402 403 404 405

Figure 2: Threshold scans for H, A production as a functionof the e±e~ collider energy with final decay into bb pairs.The cross sections are defined in bb mass bins of ± 2 GeVaround the maximum of the 77 luminosity. Increasing theenergy stepwise from below, the Higgs boson A is producedfirst, followed by the combination of A and H, while finallyH is left before the scan leaves the resonance region.

REFERENCES

[1] C. Alexandrou, R. Rosenfelder and A. W. Schreiber,PSI-PR-00-05; Phys. Rev. D 62, 085009 (2000).

[2] K. G. Chetyrkin, Phys. Lett. B 404,161 (1997); J. A. M.Vermaseren et al, Phys. Lett. B 405, 327 (1997).

[3] V. A. Miransky, II Nuov. Cim. 90 A, 149 (1985);A. Kizilersu et al., hep-th/0010161.

[4] M. M. Miihlleitner, M. Kramer, M. Spira andP. M. Zerwas, PSI-PR-00-19, hep-ph/0101083.

THEORY (III)

E. Accomando, C. Alexandrou, A. Denner, St. Diirr, D. Graudenz, Th. Jensen, K. Junker, M. P. Locher, V. E. Markushin,M. Melles, St. Pozzorini, R. Rosen/elder, M. Spira, O. Wigger

W-pair productionWhile the limelight in the last running period of the elec-

tron-positron collider LEP was on the search of the Higgsboson, other interesting physical processes such as W-pairproduction were studied as well. This allowed one on theone-hand to measure the mass of the W-boson with a preci-sion of 0.5% and on the other hand to investigate the non-abelian gauge interaction at the level of 5%. The total crosssection for W-pair production was measured at the per-centlevel.

These precision measurements require adequate theoreti-cal predictions. Since the W bosons can only be detected viatheir decay products, they have to be treated as resonancesin the full four-fermion processes e+e~ —> W + W~ —> 4 / .Moreover, radiative corrections need to be included. To a-chieve a theoretical accuracy at the per-cent level, the uni-versal radiative corrections, which comprise renormalizationeffects (running or effective couplings), the Coulomb singu-larity at the W-pair-production threshold, and initial-state ra-diation (ISR) in leading-logarithmic approximation, are notsufficient.

During the last years a calculation of non-universal cor-rections was performed at PSI and implemented into a MonteCarlo generator, called RACOONWW [1]. First results ofthis generator had already been published at the end of 1999[2, 3,4]. RACOONWW was further developed during the lastyear. The leading higher-order initial-state corrections havebeen implemented. Within the LEP2 Monte-Carlo workshop[5] the generator was compared with other programs, and itstheoretical uncertainty was estimated. It allows to calculatethe total cross section with an accuracy of 0.4 % and the cor-responding distributions with an accuracy of 1%. Finally, afirst version of RACOONWW has been made available forthe experimentalists. Our results indeed show that the non-universal corrections reduce the cross section by about 2%.

Figure 1 shows the present experimental data points forthe total W-pair-production cross section as given by the LEPElectroweak Working Group [6] for the Summer 2000 con-ferences. The data are in good agreement with the Standard-Model prediction as obtained from RACOONWW and a sim-ilar generator YFSWW [7].

Below a centre-of-mass energy of 170 GeV, the predic-tion in Fig. 1 is continued by GENTLE [8], which does notinclude the non-universal electroweak corrections. GEN-TLE is tuned to reproduce the prediction of RACOONWWand YFSWW3 on the total cross section at LEP2 within afew per mill. Quite recently an improved Born approxima-tion has been implemented into RACOONWW which allowsa similar extrapolation down to the W-pair production thresh-old [9].

LEP20

10

21/07/2000

Preliminary

RacoonWW / YFSWW 1.14

Gentle 2.1 (±0.7%)

4 :<

210

Figure 1: Total W-pair production cross section at LEP2 asgiven by the LEPEWWG [6]

REFERENCES

[1] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,PSI-PR-00-11, Nucl. Phys. B 587, 67-117 (2000).

[2] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,PSI-PR-99-29, Phys. Lett. B 475, 127-134 (2000).

[3] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,PSI-PR-99-30, J. Phys. G 26, 593-599 (2000).

[4] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,PSI-PR-99-34, hep-ph/9912447, EPJdirect Vol.2, C4,1-10 (2000), DOI 10.1007/sl010500c0004.

[5] W. Griinewald, G. Passarino et al., hep-ph/0005309, inReports of the working groups on precision calculationsfor LEP2 physics, eds. S. Jadach, G. Passarino andR. Pittau, CERN 2000-009, p. 1-135.

[6] Homepage of the LEP Electroweak Working Group,http://lepewwg.web.cern.ch/LEPEWWG/.

[7] S. Jadach et al, Phys. Lett. B 417, 326 (1998);Phys. Rev. D 61 (2000) 113010 .

[8] D. Bardin et al., Phys. Lett. B 308, 403 (1993);Comput. Phys. Comm. 104, 161 (1997).

[9] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,PSI-PR-01-01.

SEARCH FOR MUON - ELECTRON CONVERSION ON GOLD

W. Bertl2, R. Engfer3, E. A. Hermes3, T. Kozlowski3, G. Kurz3, J. Kuth1, G. Otter1,F. Rosenbaum2, N. M. Ryskulov2, A. van der Schaaf, P. Wintz3,1. Zychor3

R-87-03, SINDRUM II COLLABORATION: AACHEN1 - PSI2 - ZURICH3

Observations on solar and atmospheric neutrinos indicatethat neutrinos mix so lepton flavor would not be conserved.SINDRUM 11 tests lepton-flavor conservation by a search foryue conversion in muonic atoms. The process would result inelectrons at fixed momentum (depending on atomic number)around 100 MeV/c.

In recent years a dedicated beamline was brought intooperation in the TTE5 area. The major element is a 9 m longsuperconducting magnet. In spring 2000, after a long seriesof modifications, reliable operation of this PMC magnet wasobtained. In the following months data were taken on gold.Conversion on a heavy nucleus might be enhanced relative toa medium Z target, such as titanium [1].

See Fig. 1 for a description of the experimental setup.

SINDRUM run2000: |xe conversion on gold

A exit beam solenoidB gold targetC vacuum wallD scintillator hodoscopeE Cerenkov hodoscope

F inner drift chamberG outer drift chamberH superconducting coilI helium bathJ magnet yoke

1m

SINDRUM II

Figure 1: The SINDRUM II spectrometer during the year2000 measurements. Muons are transported to the gold targetwith the help of a 9 m long superconducting solenoid coupleddirectly to the spectrometer magnet.

Radiative pion capture (RPC), followed by e+e~ pairproduction, can be a major source of background. A pionreaching the gold target has a chance of order 10~5 to pro-duce an electron in the energy region of interest, so the pionstop rate must be below one every ten minutes. At the PMCentrance the beam contains similar amounts of muons andpions. Since the pion range in matter is about half as large asthe corresponding muon range the pion contamination can bereduced strongly with the help of a moderator at the PMC en-trance. Only one out of 106 pions may cross this moderator.Typically 99.9% of them would decay before reaching thetarget. The requirement puts strong constraints on the high-momentum tail transported by the beam line which could bemet after a careful optimization of the beam settings.

During an effective measuring period of 75 days about4 x 1013 muons stopped in the gold target. Figure 2 showsas a preliminary result various momentum distributions. Themain spectrum, taken at 53 MeV/c, shows the steeply failing

histogram:ue conversion at B=10"- u"Au —> e'Au

85 90 95 100 105

e" momentum (MeV/c)

Figure 2: Momentum distributions for three different beammomenta and polarities: (i) 53 MeV/c negative, optimizedfor n~ stops, (ii) 63 MeV/c negative, optimized for n~ stops,and (iii) 48 MeV/c positive, for /x+ stops. The 63 MeV/c datawere scaled to the different measuring times. The /x+ datawere taken at reduced spectrometer field.

distribution expected from muon decay in orbit. Two eventswere found at higher momenta, but just outside the regionof interest. The agreement between measured and simulatedpositron distributions from / i + decay gives us confidence inthe momentum calibration. At present we have no hints aboutthe nature of the two high-momentum events: they might beinduced by cosmic rays or RPC, for example. Both processesresult in flat momentum distributions such as shown by thedata taken at 63 MeV/c (see Fig.2).

Presently we are still studying the various rates and ef-ficiencies that enter the calculation of the new limit on thebranching ratio. As a preliminary result we obtain a single-event sensitivity slightly below 2 x 10~13 which correspondsto a 90% C.L. upper limit below 5 x 10~13. This constitutesan improvement by two orders of magnitude of the previousbest result on a heavy target [2].

REFERENCES

[1] T. S. Kosmas, Z. Ren and A. Faessler,Nucl. Phys. A 665,183 (2000) and references therein.

[2] SINDRUM II Collaboration, W. Honeckeref ah,Phys. Rev. Lett. 76, 200 (1996).

A PRECISE MEASUREMENT OF THE TT+ -»• 7r°e+i/ DECAY RATE

E. Frlez1, J. E. Koglin1, W. Li1, R. C. Minehart1, B. E. Norum1, D. Pocanic1, S. Ritt1''2, O. A. Rondon-Aramayo1, L. C. Smith1,W. A. Stephens1, K.O.H. Ziock1, W. Bertl2, Ch. Broennimann2, J. F. Crawford2, M. Daum2, R. Horisberger2, D. Renker2,

D. Sawannakachorn2, R. Schnyder2, H. P. Wirtz2, T. Kozlowski3, B. G. Ritchie4, V. A. Kalinnikov5, N. V Khomutov5,A. S. Korenchenko5, S. M. Korenchenko5, N. P. Kravchuk5, N. A. Kuchinsky5, D. Mzhavia6, Z. Tsamalaidze6,1. Supek7

R-89-01.1, PIBETA Collab: U. VIRGINIA1 - PSI2 - SWIERK3 - ARIZONA ST.4 - DUBNA5 - TBILISI6 - IRB ZAGREB7

The PIBETA experiment aims to measure the pion betadecay (ir+ ->• ir°e+v) branching ratio to about 0.5 % in itscurrent phase. The best experimental value at present has er-ror limits of ~ 4 %, far exceeding the theoretical uncertaintyof < 0.15%.

During the year 2000 we have successfully continuedtaking data at the ir+ stopping rate of ~ 9 x 105/s. Wehave also: (i) fully automated the timing offset adjustmentand detector gain matching procedures, (ii) implemented thedomino sampling chip readout for all PMT signals, and (iii)completed implementation of near-100 % experiment auto-mation, requiring that only a single experimenter be physi-cally present and on call at the PSI site while running.

2000 Partial 7T/? Analysis Results - Preliminary

E

2000

1000

n

71

3/B>250

s Hi \1 k-/ \/ \

f \/ \

/ VJ 8 >

14500 Events

- 1 0 - 5 10

>) (ns)

2000 Partial 7T/? Analysis Results - Preliminary

^ 1500

E 1000

500

14500 Events

— Simplified GEANT

Veo 165 170 175 180 185

B7l72 (deg)

Figure 1: 7-7 time difference for pion beta decay events (top)and 7-7 opening angle distribution (bottom) projected fromthe analyzed fraction of our 2000 data set. Signal to back-ground ratio exceeds 250.

Our most important accomplishment in 2000 is the ac-quired statistics of clean pion beta (TT/?) decay events, keep-ing the experiment on schedule for the ~ 0.5 % phase. With<40 % of the data replayed and the most stringent off-line

cuts we find > 14,000 clean IT/3 events. Relaxing the soft-ware cuts (presently under study) results in ~ 20 % morefinal events in the current sample. Typical signal-to-back-ground ratio spectra for the n/3 events are shown in Fig. 1.

2000 PartialCO

£600

.2 400

200

V y Analysis Results — Preliminary

1670n*-»eE,>63E.,>1E

0.*,>1

MeV

MeV

*vy Events

/

ji

t'

s\

i

B

\\

1"\\\

1 -Arm HT TriggerS/3-

V

= 13.8

' . . . .*.?::.•*:•:-vt ^ . .

- 1 0 - 5 5 10t(e')-t(7) (ns)

2000 Partial n*—>eVy Analysis Results - Preliminarym

>±j

= 20005

Ez

1000

0

7959 TV*->eEr>53 MeVE.,>53 MeV

***

*i/j Events

/

4

/

'/i-v-v, :•

S*

1 \

B

2—Arm HT Trigger

S/3 > 250

*

-10 - 5 5 10t(e')-t(7) (ns)

Figure 2: e-7 timing difference in a subset of the 1-arm trig-ger 7T+ —> e+vy data (top). Comparable distribution for the2-arm data is virtually background-free (bottom).

We have simultaneously recorded a large set of radia-tive decay events for the processes n+ —>• e+v-f and /i+ —>•e+vvy. In its current phase the PIBETA experiment will in-crease the existing world data set for these processes by morethan an order of magnitude. Fig. 2 illustrates the quality ofour data by showing preliminary results of the partial dataanalysis of the radiative pion decay. We anticipate significantphysics results from the analysis of these data, addressing is-sues of non-(y — A) terms in the weak interaction and pionstructure (FA/FV, polarizability).

In summary, during the year 2000 the apparatus was sta-ble and performed as designed and on schedule. We are cur-rently in the process of evaluating a first ~ 1 % result for thepion beta decay branching ratio.

10

DOES THE KARMEN TIME ANOMALY ORIGINATE FROM A BEAM-CORRELATEDBACKGROUND

F. Atchison1, M. Daum1, P-R. Kettle1, C. Wigger1

R-96-05, PSI1

In a recent letter[l] we present arguments for the exis-tence of a beam-correlated neutron background in the KAR-MEN detector that could contribute to an excess of events,known as the KARMEN time anomaly [2]. The speculativeexplanation was that these events could be generated by hith-erto unobserved neutral massive X-particles originating fromthe ISIS target via the rare pion decay process, TT+ ->• fi+X.

Our basis is that the KARMEN detector can respond tothe 10.8 MeV 7-energy from neutron capture by 14N. Ther-mal neutrons will originate from moderation of fast neutrons(Tn < 10 MeV) in the liquid scintillator. These fast neu-trons are produced from medium energy interactions (Tn >100 MeV) in the KARMEN iron shield. The liquid scintil-lator (PPP) used in the KARMEN detector consists of 75 %(volume) paraffin oil, 25 % pseudocumene and 2 g/1 PMP (1-phenyl-3-mesityl-2-pyrazoline)[3, 4]. The chemical formu-lae of the components are (i) paraffin oil, taken as CnH24,(ii) pseudocumene C9H12, (iii) PMP Ci8H2oN2.

The nuclear densities in the liquid scintillator material(in units of nuclei/A3) are 0.071 for hydrogen, 0.036 for car-bon and 9.1 • 10~6 for nitrogen leading to the ratio of atomicabundances of UH '• nc '• TIN ~ 7800 : 4000 : 1. It is thisnitrogen that can capture neutrons via the reaction

14 N(n,7)1 5N (1)

with an integral 7-energy of 10.8 MeV. The thermal neutroncross-section for this reaction is a «75 mb. The lower en-ergy cut applied to the events in the KARMEN analysis isHMeV[2] with an energy resolution of aE/E = 11.5%/VE[3] (E in MeV), which is 3.5 % or 380 keV for E = 11 MeV.Thus, the 10.8 MeV 7-events from reaction (1) will be ac-cepted with an efficiency of about 30 %; we note that in theenergy distribution of the excess events[5], about 40 % of theanomalous events, which are selected from an energy win-dow between 11 and 35 MeV, are clustered at about 11 MeV.If such a beam-correlated neutron background is present, thesubtraction of purely cosmic background events is not suffi-cient.

For a background estimate, one has to consider that in apulsed neutron spallation source, a beam-correlated neutronbackground has a time structure originating from the dutycycle of the primary proton beam and the kinetic energy ofthe neutrons on their way through the shielding. It has beenshown that the neutron capture rate of a gadolinium absorberdissolved in water measured as a function of time after theinjection of a fast neutron pulse[6] corresponds to a linearrise from zero to about 6 yus followed by a constant rate atlonger times.

The time variation of the neutron capture rate in the liq-uid scintillator is expected to be similar. This behavior hasbeen approximated by the functiony(t) = A • ef-t/2.2^) + B . tjTc for t < Tc a n d

y(t) = A • e(-*/2-2M») + B for t > TC. Here, A is the initialrate of the exponential decay, B is the beam-correlated back-ground from reaction (3), and TC is the linear risetime of theneutron capture rate. A fit to the data of Ref.[2] results in aX2 of 15.5 for 16 DOE

If we restrict our fit to the shorter 5 [is time window, asused in the original analysis[2], in order to be less depen-dent on fluctuations of the background, we obtain a \2 of 8.7for 7 DOE These fits demonstrate that the enhancement re-ported in Ref. [2] is not significant after introducing a beam-correlated background.

10o

250

200 -

50

Figure 1:KARMEN data of Ref. [2] fitted with the function y(t) =A-e-t^-^ + B-t/Tc foxt<Tcandy(t) = A-e-t^-^+Bfor t > TC. The smooth line represents the fitting func-tion. The dashed line is an exponential with TM = 2.2 /is,and the dotted line represents the time dependence of ourestimate of neutron capture in the KARMEN scintillatorfrom reaction (1). The values of the fitted parameters areA = (277 ± 14) events/yus, B = (7.3 ± 2.8)events//ns, andTC = (3.4 ± 0.5) us; the x2 of the fit is 15.5 for 16 DOE

REFERENCES

[1] F. Atchison et al., Phys. Lett. B, to be published (2001).

[2] B. Armbruster et al., Phys. Lett. B 348,19 (1995).

[3] G. Drexlin et al.,

Nucl. Instrum. Meth. A289,490(1990).

[4] H. Giisten et al., J. Phys. Chem. 82, 459 (1978).

[5] Ch. Oehler, PhD-thesis, Uni Karlsruhe, 118 (1999).

[6] K. H. Beckurts, K. Wirtz, "Neutron Physics", SpringerVerlag OHG Berlin, 40Iff, (1964).

11

PRECISION MEASUREMENT OF THE MASS OF THE CHARGED PION

D. F. Anagnostopoulos1, G. Borcheri2, J.-P. Egger3, D. Gotta2, M. Hennebach2, P. Indelicate)4, Y.-W. Liu5, B. Manil4,N. Nelms6, L M. Simons5, A. Wells6

R-97-02, IOANNINA1 - JULICH2 - NEUCHATEL3 - PARIS4 - PSI5 - LEICESTER6

A series of experiments to determine the mass of the neg-atively charged pion was finished by a high-statistics mea-surement in summer 2000 ([1] and expts. R-94.01 and R-97.02). Here, pionic and muonic transitions from nitrogenand oxygen were measured. The muonic line served as en-ergy calibration because the muon mass is known to morethan one order of magnitude better than the pion mass [2].The circular transitions, TTN(5<7—4/) and /j,O(5g—4/), arenot affected by finite-size effects and hence not distorted bystrong interaction. Furthermore, using dilute targets, electronrefilling is suppressed, thus avoiding any energy shifts fromsatellite transitions.

1800

1400

1200-

' 1000

800

• 600

400

200 -I

X- Si 220 reflection *• •

1 200 400 600 800

pixel i 40 .̂m1000 1200

Figure 1: Simultaneously recorded reflections of the 5-4transitions in TTN and /iO using a silicon crystal of 90 mmdiameter. The sensitive area of the CCD array (not drawn inscale) is 48 x 72 mm2.

1000 1200400 600 800

pixel & 40 (Lin

Figure 2: Projection of the TTN and /iO reflections to the axisof dispersion.

The pion beam of the TTE5 channel at PSI was injectedinto the cyclotron trap II [3], the basic idea of which is towind up the range curve in a weakly focusing magnetic field.In the case of pions, deceleration has to be fast because of theshort life time. The energy loss of the pions is then achievedby thick degraders. About 1% are stopped in a thin-walledgas-filled target container in the center of the trap at a pres-sure of 1.4 bar. Length and diameter of the gas cell are220 mm and 60 mm. Muons, originating from pion decayshortly before capture, are slow enough to be stopped in thegas cell as well. With a set-up, optimized for muons, thecount rate for muonic atom X-rays is about 4% of the onefor pionic atoms. Because of the high pion flux of several109s^1, this method is still superior to a direct use of a muonchannnel.

The X-rays were reflected in second order by a spheri-cally bent silicon Bragg crystal cut along the 110 plane andhaving a radius of curvature of 2.985 m. The X-rays wererecorded in a newly set-up large area detector array of 2 x 3Charge-Coupled Devices (CCDs). The sensitive area of onechip is 24 x 24 mm2 or 600 x 600 pixels of 40 yum [4].CCDs allow an efficient background reduction by analyzingthe hit pattern and applying simultaneously a narrow cut onthe deposited charge. Such an analysis is essential for low-rate experiments in accelerator environments [5, 6].

The aim of the experiment is to reach an accuracy ofabout 1 ppm for the mass of the charged pion, which re-quired the accumulation of about 10000 events in each ofthe two fines in a running period of several weeks. With acount rate of about 15 per hour and transition by using anN2/O2 gas mixture of 90%/10%, the simultaneous detectionof both fines (Fig. 1) inherently avoids systematic errors aris-ing from the long-term stability of the experimental set-up.After correcting for the curvature of the image, the reflec-tions are projected to the axis of dispersion (Fig. 2). Thedistance between the pionic and the muonic lines results inthe ratio of the masses of the pion and the muon.

REFERENCES

[1] S. Lenz et al., Phys. Lett. B 416, 50 (1998).

[2] D. E. Groom et al., (PDG), Eur. Phys. J. C 15, 1 (2000).

[3] IKP Annual Report 1997, p. 85 (1997).

[4] EEV, England, CCD22 with frame buffer.

[5] D. Gotta et al., Nucl. Phys. A 660, 283 (1999).

[6] J-P. Egger, Hyperfine Interactions 119, 291 (1998).

12

A PRECISION MEASUREMENT OF THE MICHEL PARAMETER £" IN POLARIZED MUONDECAY

P. Van Hove1, J. Deutsch1, J. Govaerts1, P. Knowles1 ,R. Medve1, A. Ninane1, R. Prieelsx,J. Egger2, F. Foroughi2, X. Morelle2,L. Simons2, N. Danneberg3, W. Fetscher3, M. Hadri3, C. Hubes3, K Kirch3, K Köhler3, A. Kozela3, J. Lang3,

O. Naviliat3,J. Sromicki3.

R-97-06, LOUVAIN1 -PSI2 -ZÜRICH3

Michel parameters describe the various observables in muon-decay. Most of them are known to have values close to theStandard Model (SM) ones with precisions better than a fewpercent. One notable exception is the parameter £", or thecombination (/ = £" /££' - 1) which is zero in the SM. Thiscombination governs the angular and energy dependence ofthe positron longitudinal polarization in polarized muon de-cay:

where 0 < x < 1 is the normalized energy and z = cos 6,6 being the angle between the muon spin and the positronmomentum, the parameters £, £', £" are all equal to 1 in theSM. As can be seen in this formula, values of a; close to 1 andz close to -1 , strongly enhance the impact of a non vanishing(£" /££' — 1) on PL for highly polarized muons.In order to avoid the need to determine the absolute polariza-tion with high precision, we will undertake relative polariza-tion measurements.

Xn polarized)= 1 +

A exp -f (2)unpolarized) ± T ̂ -exp

where Aexp is an energy dependent experimental value andis obtained by :

_ N(Pß(backward))^exp (3)

where N(Pß) is the number of positrons incident on the po-larimeter for a given number of muons having a polarizationPß. Six weeks of measurement are expected to provide alimit of 0.5% o n / .The full setup is described in [1]. Muons from the nE3 beamline at PSI, backward polarized at 95%, are stopped in targetsthat either maintain (Al) or destroy (S) the muon polarization.The most energetic positrons of the Michel spectrum are se-lected using solenoidal magnets. A tracking inside a uni-

Figure 1: Amplitude distribution of signals recorded from A)one p-strip and B) from one n-strip.

# Measurements # Measurements

Figure 2: ANI and Bhabha experimental asymmetry for aseries of 20 measurements of one 1 hour data taking each.Each point corresponds to one foil and is computed fromtwo data files of opposite magnetization. The big dots cor-respond to processes occuring in the 2nd foil. As is clearlyseen, the analyzing power changes sign between Bhabha andANI events

form magnetic field section is performed using three planesof double sided silicon strip detectors resulting in an energyresolution of about 1 MeV FWHM. The figure 1 shows theamplitude distribution of signals from the p side and the nside of one of these detectors.The positron polarimeter, based on the spin dependence ofBhabha scattering (BB) and annihilation in flight (AIF) ofpositrons on polarized electrons, consists of 2 Vacoflux foilswith opposite magnetization and interleaved wire chambersallowing to determine the nature of the interaction and thefoil in which it took place. It should be noted that BB andAIF have opposite analyzing powers.A sample of events recorded in the last test with the com-plete setup were roughly analyzed. The rate asymmetry forBhabha and annihilation events originating from each foilsfor runs with opposite magnetic polarization is show in fig-ure 2.During 6 weeks, in September-August 2000, we performedthe production run of the experiment. The reconstruction ef-ficiency of the positron tracking was close to 80% which isthe highest possible efficiency taking into account the deadregions of the telescope. The wire chambers worked withan efficiency close to 99 %. Due to acquisition adjustmentand beam handling, we recorded about 50% of the expectedstatistic. Data are now under analysis.

REFERENCES

[1] P. Van Hove, Ph. D. Thesis, UCL 2000, unpublished.

13

PRECISION MEASUREMENT OF SINGLET /xp CAPTURE IN HYDROGEN

V.A. Andreev1, D. V. Balin1, T. Case3, K. M. Crowe3, J. Deutsch8, P. U. Dick:2, A. Dijksman2, J. Egger2, D. Fahrni2,A. A. Fetisov1, V. A. Ganzha1, J. Govaerts6, F J. Hartmann5, W. D. Herold'2, V. I. Jatsioura1, P. Kammel4, A. G. Krivshich1,

E. M. Maev1, O. E. Maev1, V. E. Markushin2, C. Petitjean2, G. E. Petrov1, R. Prieels6, S. M. Sadetsky1, G. N. Schapki,inR. Schmidt2, G. G. Semenchuk1, A. A. Vorobyov1, N. I. Voropaev1

R-97-05, GATCHINA1 - PSI2 - BERKELEY3 - URBANA4 - MUNICH5 - LOUVAIN6

In this experiment a 1 % precision measurement of thesinglet capture rate As in the process ßpis —> n + vß isproposed. The rate As is very sensitive to the weak formfac-tors of the nucleón, in particular to the induced pseudoscalarcoupling constant gp. The determination of gp will be a rig-orous test of modern effective field theories of low energyQCD [1]. Previous attempts with liquid H2 targets and directneutron observations could not reach high enough precisionbecause of p¡ip molecule formation in liquid H2 (ortho-paratransitions) and because of limited calibration accuracy ofneutron counters.

Our method is based on a very precise lifetime measure-ment of n~ in hydrogen gas and the comparison with the freeß+ decay constant (Ao). The rate As is then determined asthe difference between the inverse pTp lifetime and Ao. ThepT experiment must be performed in ultraclean, deuterium-depleted H2 gas (protium). Otherwise, the transfer of pT toimpurities would induce distortions of the time slope. Trans-fer to deuterium would lead also to distortions due to verylarge diffusion of ¡id atoms caused by the Ramsauer-Townsendeffect.

To achieve 1% precision in As, the exponential time dis-tribution of //-e decays must be determined with a precisionbetter than 10~5 requiring a statistics of at least 1010 an-alyzed good events. Events from muon stops outside theH2 gas must be strongly suppressed. Moreover, the system-atics of the electronic time measurement must be carefullychecked.

run= 224 event=1282 disp= 26

I I ; I

I *

I I : * I

I I ; I

y(m-F

5 10 15 20 25x (e-PC)

Figure 1 : Display of a diffusion event observed in the TPC

To meet all these challenges, we developed in 1997-2000a time projection chamber (TPC) and several proportionalchambers operating in pure H2 gas of 10 bar and success-fully tested them on the yuE4 beam [2]. A new data collec-tion system with continuously operating deadtime-free TDC

electronics was also developed and tested together with theprototype TPC. As a special example, Fig. 1 shows a 60 /xstime slice with a ß~ stop in the TPC and the decay electronemerging at 5 cm from the muon stop location ("diffusionevent"). This is one of the event types which we must haveunder full control in the final measurement.

Figure 2: Design drawing of the new clean TPC (stereoview),the sensitive volume is 15x12x30 cm3

Based on the experience gained in the test runs and on thedata analysis, we have designed the final apparatus with anultra clean TPC as its center part (Fig. 2). The TPC with 2entrance chambers will be mounted in a hydrogen pressuretank with thin cylindrical Aluminum walls (d~2 mm). Elec-tron detection and tracking will be made outside the tank withtwo Sindrum chambers and a scintillator hodoscope. This ar-rangement removes dangerous electronic cross talk betweenmuon and electron tracks and allows observation of the /xedecays in a cylindrically symmetric geometry with a solidangle of 75%.

Our system is designed to handle muon stop rates up to50 kHz. The electrical field in the TPC is ~2.3 kV/cm, cor-responding to 0.5 cm//js drift velocity. The negative chargesfrom ionizing particles drift down to a plane of 75 anodewires and 32 perpendicular cathode strips where the signalsare amplified and read out. All test runs were made so farwith regular clean hydrogen which is not good enough for thecapture measurement. In the meantime, however, our chem-istry group demonstrated successfully the production of ultraclean protium at impurity levels below 10~8. In fall 2001,we expect to be ready for runs with the final TPC.

REFERENCES

[1] J. Govaerts and J.-L. Lucio-Martinez,Nucl. Phys. A 678, 110 (2000).

[2] PSI Ann. Rep 1997,1, 32; PSI Sci.Rep. 1998,1,20; PSISei. Rep. 1999,1, 15;P. Kammel et al., Nucl. Phys. A 663/A 664, 911c (2000).

14

PIONIC HYDROGEN

D. F Anagnostopoulos1, G. Bordiert2, W. Breunlich3, M. Cargnelli3, H. Fuhrmann3, D. Gotta2, M. Giersch3, A. Gruber3,M. Hennebach2, P. Indelicato4, T. Jensen5'6, Y.-W. Liu6, B. ManilA, V. E. Markushin6, J. Marton6, N. Nelms7, L. M. Simons6,

H. Zmeskal3

R-98-01, IOANNINA1 - JÜLICH2 - VIENNA3 - PARIS4 - ZÜRICH5 - PSI6 - LEICESTER7

The measurement of the hadronic shift and broadeningof the ground state in pionic hydrogen gives access to fun-damental properties of the pion-nucleon interaction. On-going improvement in the calculation of strong-interactionphenomena by Heavy-Baryon Chiral Perturbation Theory al-lows predictions with an accuracy of a few per cent, whichshould be experimentally tested (see [1, 2] and referencestherein).

New techniques that have been originally developed forthe precision spectroscopy of X-rays from antiprotonic hy-drogen [3] and for the determination of the charged pionmass [4] will be used in a new series of measurements[5,6]. The final aim is to achieve an accuracy for the hadronicbroadening Tis of about 1 %, which is an improvement of al-most one order of magnitude as compared to previous pre-cision experiments [7]. A similar improvement is also ex-pected for the hadronic shift eis.

The first goal of the new experiment is to establish a shiftvalue independent of pressure. Such a pressure dependencecould originate from the formation of complex molecularstructures like (irpp)+pee [8]. The irO(6h—5g) transition,which is not affected by the strong interaction, serves as en-ergy calibration. At lower pressures, a simultaneous mea-surement of both the hydrogen 3p-ls and the oxygen line ispossible. This allows an energy calibration basically free ofsystematic errors.

In late 2000, an engineering run took place at the TTE5

high-intensity pion channel at the Paul-Scherrer-Institut (PSI).The experimental set-up was similar to the one used for thepion mass measurement [4]. As target, a cryogenics sys-tem was installed in the center of the cyclotron trap, whereabout 1 % of the incoming pions are stopped in gas at normaltemperature and pressure. Higher densities are achieved bycooling. The X-rays were reflected in first order by a spher-ically bent silicon Bragg crystal cut along the 111 plane. Tokeep aberrations small, the crystal was covered by an aper-ture restricting the reflecting area horizontally to 60 mm. Alarge-area array of Charge-Coupled devices (CCDs) servedas an X-ray detector. The response function of the spectrom-eter was obtained from the TTC12 (5<?—4/) transition, which isclose in energy (2973.8264 eV) to the pure electromagneticir~p(3p-ls) transition energy 2878.808 eV.

With a H2/O2 mixture at a gas density of 3.5 bar equiva-lent, count rates of about 20 per hour were achieved (Fig. 1).The peak-to-background was improved significantly com-pared to the previous experiments. In total, 750 and 1100events were recorded in the oxygen and the hydrogen line.This already yields an accuracy for the shift which is slightlybetter than that of earlier results because of the absence ofsystematic errors in the energy calibration. A preliminaryvalue is

els = 7.080 ± 0.035 eV (attractive) (1)

which is in agreement with the result of the previous experi-ment eu = 7.102 ± 0.038 eV [7].

From the limited statistics of the engineering run, no con-clusions can be drawn on density effects yet. A high-statisticsrun for the shift measurement is foreseen in summer 2001.Further measurements will investigate in detail the pressuredependence of the line widths of various pionic hydrogentransitions to establish the pure hadronic effect with the en-visaged accuracy.

240

Figure 1: Simultaneously recorded reflections of theTTO(6—5) calibration transition and the 7r~p(3—1) transition.The spectrum displays about | of the total statistics accumu-lated for the H2/O2 mixture.

REFERENCES

[1] N. Fettes, U.-G. Meissner,Nucl. Phys. A 676, 311 (2000); hep-ph/0101030.

[2] V. E. Lyubovitskij, A. Rusetsky,Phys. Lett. B 494, 9 (2000).

[3] D. Gotta et al., Nucl. Phys. A 660, 283 (1999).

[4] D. F. Anagnostoploulos et al.,Precision measurement of the mass of the charged pion,experiment R-97-02, this report.

[5] PSI experiment R-98.01.

[6] D. Gotta, TTN Newsletter 15, 276 (1999).

[7] H.-Ch. Schroeder et al., Phys. Lett. B 469, 25 (1999).

[8] S. Jonsell et al., Phys. Rev. A 59, 3440 (1999).

15

RARE K+-DECAYS IN FLIGHT (BROOKHAVEN AGS E865)

R. Appel4, G. S. Atoyan5, B. Bassalleck2, D. R. Bergmann4, D. N. Brown3, N. Cheung3, S. Dhawan4, H. Do4, J. Egger7,S. Eilerts2, C. Felder3, H. Fischer2, M. Gach3, W. D. Herold7, V. V. Isakov5, H. Kaspar4'7, D. E. Kraus3, D. M. Lazarus1,

P. Lichard3, L. Leipuner1, J. Lowe2, J. Lozano4, H. Ma1, W. Menzel6, S. Pislak4'8, A. A. Poblaguev5, V. E. Postoev5,A. Proskurjakov5, P. Rehak1, P. Robmann 8, Alexandre Sher 3, Aleksey Sher 8, /. A. Thompson3, P. Truöl4'8, A. Walid4,

H. Weyere'7, M. E. Zeller4

E-91-02.1, BNL1 - NEW MEXICO2 - PITTSBURGH3 - YALE4 - INR MOSCOW5 - BASEL6 - PSI7 - ZÜRICH8

Experiment E865 at the Brookhaven AGS [1] was setup primarily to search for the lepton flavor violating decayK+ —>• ir+n+e~ (K^ue) [2] with more than an order of mag-nitude increased sensitivity. The flexibility of the apparatusallowed also to obtain high statistics event samples on thefollowing decay modes, where existing data were scarce:

•K ' e ' e (i™) [3]|

7r+7r~e+z/e (Ke4); ß+e+

(K,,,) [4];

'vu ; e + e + e ve

From the K„ßli and the Ke± data we have also extracted con-siderably reduced upper limits for other lepton flavor vio-lating decay modes like 7r+e+\iT, n~/i+e+, n~ß+ß+, and7T-e+e+ [5].

i.28 0.3 0.32 0.34 0.36 0.38Mm [GeV]

Figure 1 : Phase shift difference SQ — S\ as a function of the7T+7T~ invariant mass. The curves shows the result of thefit from which the scattering length was extracted (Geneva-Saclay: ref. [8]).

The analysis of the Kivl, data is still in progress. Pre-liminary results indicate, that we will be able to determinefor the first time separately the electroweak vector and axi-alvector kaon formfactors Fy and FA , while previous exper-iments [6] with real photons in the final state were sensitiveto\FA+ Fv\ only.

Though considerable progress in the reduction of the im-mense amount of data has been made last year (Thesis A.

Sher, University of Zürich), the analysis of the final Kviie

data set taken in 1998 has not been completed yet. We expecthowever to improve the sensitivity by at least a factor of threebeyond our published limit of 2.8 x KT 1 1 [2].

The analysis of the Ke4 data, performed by S. Pislak, hasbeen completed and lead to the new, quite precise value forthe s-wave TTTT scattering length [7]:

ag = 0.228 ± 0.012 (stat.) ± 0.003 (syst.).

Figure 1 shows the phase shift difference ¿§ ~^l a s a functionof the 7T+7T~ invariant mass extracted from our data in com-parison to those from an older experiment [8] with twelvetimes less statistics, which measured a^ = 0.26 ± 0.05.Aside from the scattering length, which agrees well withthe latest prediction from chiral QCD perturbation theory(ChPT) ag = 0.220 ± 0.005 [9], we have also extracted themomentum transfer dependence of the axialvector and vectordecay form factors, which are an essential ingredient for thedetermination of the coefficients of the ChPT Hamiltonian toorder O(p4) [10].

REFERENCES

[1] R. Appel et ai,

submitted to Nucí. Instrum. Meth.,(January 2001).

[2] R. Appel et ai, Phys. Rev. Lett. 85, 2450 (2000).

[3] R. Appel et al, Phys. Rev. Lett. 83, 4482 (1999).

[4] H. Ma et al, Phys. Rev. Lett. 84, 2580 (2000).

[5] R. Appel et al, Phys. Rev. Lett. 85, 2877 (2000).[6] S. Adler et al, Phys. Rev. Lett. 85, 2256 (2000);

S. Heintze et al, Nucl. Phys. A 149, 365 (1979).

[7] S. Pislak ef a/., to be published;M. Zeller, Proc. Chiral Dynamics 2000,TJNL, Newport News, VA (July 2000);P. Truöl, Proc. Int. Conf. Heavy Quarks at Fixed Target

(HQ2K), Rio de Janeiro, Oct. 2000, hep-ex/0012012.

[8] L. Rosselet et al, Phys. Rev. D 15, 574 (1977).

[9] G. Colangelo et al, Phys. Lett. 488, 261 (2000).[10] G. Amoros et al, Phys. Lett. B 480, 471 (2000);

Nucl. Phys. B 585, 293 (2000).

16

HIGGS CANDIDATES IN e+e~ INTERACTIONS AT

A. J. Barczyk1, K. Deiters1

L3 Collaboration, PSI1

= 206.6 GeV

In a search for the Standard Model Higgs, carried out on212.5 pb~x of data collected by the L3 detector [1] at thehighest LEP centre-of-mass energies, including 116.5 pb^1

above T/S = 206 GeV, an excess of candidates for the pro-cess

e+e- ->• Z* ->• HZ

is found for Higgs masses near 114.5 GeV. Smaller produc-tion processes through W+W~ and ZZ fusion, are also con-sidered. All significant signal decay modes are investigated.Four-fermion final states from W- and Z-pair production, aswell as e+e~ —> qq{^), make up the largest sources of back-ground.

10-

d

a> -I

10 -

Data

Background

Signal + Background

0.05 0.1 0.15 0.2

Signal Efficiency

0.25

Figure 1: a) The logarithm of the signal-to-background ra-tio for all channels combined assuming a Higgs mass of114.5 GeV. The total number of events is also indicated, cor-responding to a signal efficiency of 31.4%. b) The number ofevents above a cut on the final discriminant, versus the signalefficiency.

The search for the Standard Model Higgs boson at LEPis based on the study of four distinct event topologies repre-senting approximately 92% of the HZ decay modes: qqqq,qqvV, qql+l~ (l=e,/i,r) and T+r~qq. With the exceptionof HZ —> T+T~ qq7 the analyses for each channel are opti-mized for H —>• bb, since this represents about 74% of theHiggs branching fraction in the mass range of interest. Thedetails of the analysis will be presented in a forthcoming pub-lication.

By combining all the search channels, we compute theconfidence level for the data to be compatible with signalplus background or background only. Our data indicate themost likely mass of the Higgs candidates to be 114.5 GeV.For an assumed Higgs boson of this mass, the confidencelevel to be consistent with a background only hypothesis iscalculated to be 0.09, equivalent to 1.7 standard deviationsfrom the background expectation. The confidence level to beconsistent with signal plus background is 0.62. Figure la)shows the signal-to-background ratio for all channels com-bined assuming a Higgs mass of 114.5 GeV. After a cut onthe final discriminant, Figure lb) displays the number ofevents versus the signal efficiency. The excess of data is con-sistent with the signal expectation.

In data collected with the L3 detector at ^/s = 206.6GeV, we have observed an excess of events above backgroundwhich is compatible with a Standard Model Higgs boson ofmass 114.5 GeV. High-weight events are seen in differentdecay channels qq~v~U and qqqq which are characteristic ofHiggs production together with a Z boson. These data fromL3, together with those of other LEP experiments [2] suggestthe first observation of the Higgs boson.

REFERENCES

[1] L3 Collaboration.,B. Adeva et al., Nucl. Inst. Meth. A 289, 35 (1990);J. A. Bakken et al., Nucl. Inst. Meth. A 275, 81 (1989);0. Adriani et al., Nucl. Inst. Meth. A 302,53 (1991);B. Adeva et al., Nucl. Inst. Meth. A 323, 109 (1992);K. Deiters et al., Nucl. Inst. Meth. A 323, 162 (1992);M. Chemarin et al., Nucl. Inst. Meth. A 349, 345 (1994);M. Acciarri et al., Nucl. Inst. Meth. A 351, 300 (1994);G. Basti et al., Nucl. Inst. Meth. A 374, 293 (1996);A. Adam et al., Nucl. Inst. Meth. A 383, 342 (1996).

[2] LEP Higgs Working Group,"Standard Model Higgs Boson at LEP: Results with the2000 Data, Request for Running in 2001",Submitted to the LEP Committee and the CERN Re-search Board (2000).

17

TEST OF SUPERSYMMETRY USING IN-BEAM SPECTROSCOPY OF 196Au

F. Corminboeuf, M. de Huu1, L. Genilloud1, G. Graw3, J. Groger2, C. Gunther1, J. Jolie1, A. Metz3, N. Warr1, T. WendeP,

Z-95-05, FRIBOURG1 -BONN2-LMUMUNCHEN3

Symmetry is an important concept in physics. In finitemany-body systems, it appears as time reversal, parity androtational invariance but also in the form of dynamical sym-metries. In the field of dynamical symmetries, a remarkablyversatile model was elaborated in the mid seventies by Arimaand Iachello [1]. This Interacting Boson Model considers 2Nvalence nucleons which are coupled to TV nucleon pairs as s(I = 0) and d (I = 2) bosons. The even-even nucleus is, then,described in a space spanned by the irreducible representa-tions (irreps) [N] of UB (6). The model turned out to be verysuccessful for medium-heavy and heavy nuclei. Moreover, anumber of nuclei have low-lying spectra, which resemble indetail one of the three dynamical symmetries of the model.In these cases, the model has an analytic solution.

A further step towards unification was made in the earlyeighties when Iachello and coworkers introduced (dynami-cal) supersymmetry to connect odd-even and even-even nu-clei by embedding a Bose-Fermi symmetry into a graded LiealgebraU(6/M) [2,3]. The supersymmetricirrep [AT}, then,spanned a space that describes both an even-even nucleuswith N bosons and an odd-A nucleus with N — 1 bosons andthe odd fermion. If a common set of parameters describesthe excited states of such two nuclei, one concludes that thenuclei exhibit a (dynamical) supersymmetry. Van Isacker etal. [4] introduced an extension of this model allowing thedescription of a quartet of nuclei, using the same algebraicform of the hamiltonian.

This extended supersymmetry (or neutron-proton super-symmetry) deals with boson-fermion and neutron-proton de-grees of freedom. The quartet of nuclei consists of an even-even nucleus with (J\fv + Af^) bosons, an odd-proton and anodd-neutron nucleus, both with (J\fv +A^) - 1 bosons and anodd-odd nucleus with (Nv + Afv) — 2 bosons. The extendedsupersymmetry relates the often very complex structure ofthe odd-odd nucleus to the simpler ones of even-even andodd-A systems. It was realised from the beginning that theultimate candidate for the test would be the odd-odd nucleus198 Au [4] since the quartet i94,i95pti95,i96Au c o n t a m s t n e

nuclei 194pt-195Pt which are considered to be the best exam-ple of the U(6/12) supersymmetry.

Since the experimental level scheme of 196Au was stillpoorly known, an experimental study of196 Au was started in1995 in a Fribourg/Bonn/Munich collaboration. The exper-imental program included in-beam gamma-ray and conver-sion electron spectroscopy following the reactions 196Pt(d,2n)and 196Pt(p,n) at the cyclotrons of the PSI (Viiligen, Switzer-land) and at the University of Bonn. In parallel high reso-lution transfer experiments were performed at the Tandemaccelerator of the TU/LMU Miinchen using (p,d), polarised

(d, t) and polarised (d, a) reactions [5]. In a later stage 7 — 7coincidences were measured at the Yale WNS tandem ac-cellerator. These studies allowed the observation of manynew excited states, among which 25 excited negative paritystates below 500 keV.

Figure 1 shows the resulting energy spectrum for the low-est negative parity states in 198 Au [6]. The excited states areassigned by combining all experimental data. In view of theextreme complexity of odd-odd nuclei in this mass region,one can conclude that a good agreement between theory andexperiment is obtained. This provides a strong argument forthe existence of dynamical supersymmetry in atomic nuclei.

This work was supported by the Swiss National ScienceFoundation and the DPG (grants IIC4 Gr 894/2 and Gu 179/2).

Figure 1: Comparison between the predicted and measuredlevel scheme of198 Au

REFERENCES

[1] F. Iachello, A. Arima, The interacting boson model,(Cambridge University Press, Cambridge), (1987).

[2] F. Iachello, Phys. Rev. Lett. 44, 772 (1980).

[3] A.B. Balantekin, I. Bars, F. Iachello,Nucl. Phys. A 370, 284 (1981).

[4] P. Van Isacker, J. Jolie, K.L.G. Heyde, A. Frank,Phys. Rev. Lett. 54 , 653 (1985).

[5] A. Metz, J. Jolie, G. Graw , R. Hertenberger, J. Groger,C. Gunther, N. Warr, Y. Eisermann,Phys. Rev. Lett. 83, 1542 (1999).

[6] J. Groger et al., Phys. Rev. C 62 , 064304 (2000).

18

STUDY OF 100Ru AT THE PHILIPS CYCLOTRON AND AT SINQ

F. Corminboeuf1, S. Drissi1, L. Genilloud1, J. Jolie1, J. Kern1, H. Lehmann1, N. Warr1,

Z-96-04, FRIBOURG1

In the framework of the Interacting Boson Model [1], vi-brational nuclei are described by the U(5) dynamical sym-metry. New interest in the study of vibrational nuclei aroseafter experiments on 112Cd isotopes at PSI showed that theyexhibited a multiphonon structure up to high phonon num-bers [2]. The systematics of vibrational nuclei along the nu-clear chart was studied by J. Kern et al. [3] and 100Ru wasproposed as a possible candidate for a vibrational nucleus.This possibility was especially attractive, because this nu-cleus is situated far from a closed shell and as such its struc-ture should be rather free of particle-hole excitations. There-fore a systematic study of 100Ru was undertaken.

The in-beam experiments consisted of the measurementof 7-ray excitation functions, 7-ray angular distributions and77-coincidences. The excited nucleus 100Ru was producedby bombarding a 97.6% isotopically enriched 98Mo target,with a beam of a particles from the Philips variable energycyclotron. In order to also extend the knowledge on high-energy low-spin states a second series of experiments wasstarted using the cold neutron beam at the PGA installationof SINQ. Here a 150 mg 98.1% enriched "Ru target wasused. The detailed set-up is shown in Figure 1.

Neutron beamfrom SINQ

Anti-ComptonSpectrometer

PairSpectrometer

neutron lens

1.11 1 1

Figure 1: PGA set-up used at SINQ to measure the primarycapture gamma rays.

The very small target mass and capture cross section wascompensated by the use of the neutron focusing lens of thePGA installation [4], which permitted to enhance the neutronflux of 6.9x107 on the target by a factor 6.4. The primarygamma-rays were then observed using the pair spectrometerof the PGA installation. These primary gamma-rays, whichattain energies of several MeV, reveal directly the excitedstates in 100Ru, because the capture state at 9.673 MeV has awell-defined energy. Figure 2 shows the observed spectrumin the energy domain of 6.5-8.5 MeV.

To construct the final level scheme, the PSI data were

12600 13000 13400 13800 14200 14600

CHANNELS

Figure 2: Primary gamma-ray spectrum observed using thepair spectrometer of the PGA installation at SINQ.

combined with crystal spectrometer data on secondary gammarays obtained at ILL. In this way 36 new levels could be ob-served [5]. Comparison with the U(5) symmetry revealedno two particle-hole intruding states below 1.7 MeV and theneed for a small SU(3) breaking of the U(5) symmetry [5].

We acknowledge the staff of the Philips cyclotron and ofSINQ for the excellent beams they provided. This work wassupported by the Swiss National Science Foundation.

REFERENCES

[1] F. Iachello, A. Arima, The interacting boson model,(Cambridge University Press, Cambridge), (1987).

[2] M. Deleze, S. Drissi, J. Jolie, J. Kern, J. P. Vorlet,Nucl. Phys. A 554,1 (1993).

[3] J. Kern, P. E. Garrett, J. Jolie, H. Lehmann,Nucl. Phys. A 593, 21 (1995).

[4] M. Crittin, J. Kern, J.-L. Schenker,Nucl. Instrum. Meth. A 449, 221 (2000).

[5] L. Genilloud, H. G. Borner, F. Corminboeuf, Ch. Doll,S. Drissi, M. Jentschell, J. Jolie, J. Kern, H. Lehmann,N. Warr, Nucl. Phys. A 662,3 (2000); A 669,407 (2000)

19

MODELLING FISSION IN NUCLEAR REACTIONS: I REACTION CROSS-SECTIONS

F. Atchison1

1Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland

1 IntroductionSemi-empirical formulae have been developed[l] that yield(i) the ratio of the fission and neutron emission widths in thede-excitation of states over a large range of nuclear charge,mass and excitation-energy and (ii) the nuclear states of theassociated scission products; these allow fission to be treatedconsistently in calculations of nuclear reactions.

Absolute cross-section values are obtained using the fissionformulation in a new evaporation code capable of handlingthe wide range of nuclear states involved. Description ofthe entrance channel is made using either the optical-modeland pre-equilibrium emission routines from the ALICE95[2]code or the MECC7 intra-nuclear cascade code of Bertini[3].

2 Theoretical considerations2.1 General considerationsThe basic assumptions made about the fission process are(i) that it is relatively slow and so competes only with evap-oration and similarly depends only on the immediate nuclearstate and not how it was reached, (ii) it is mainly a collec-tive process but with some influence from shell and singleparticle effects, (iii) it involves barrier penetration; traversalof the fission barrier (and hence determination if the systemwill fission) occurs at deformations well before actual scis-sion, which means that the process can be separated into twoindependent steps, crossing the barrier and formation of thescission products.

An important consequence of the first assumption is that allstages of the de-excitation need to be allowed to contributewhich means that reactions involving high excitation ener-gies (e.g. those induced by medium energy particles) need atreatment of fission for a wide range of nuclear states.

The collective aspects of the fission process are described bythe liquid-drop model; this means that (i) the fissility (Z2/A)is a good parameter for formulae to interpolate/extrapolatefission parameters, (ii) the shape of the deformation energypotential function is parabolic and the penetrability may besolved explicitly. Shell effects are significant at low excita-tion energies and lead to many of the actinides having doublehumped fission barriers.

2.2 Reaction widthChannel widths are calculated from the ratio of the openchannels to contributing states multiplied by some suitablevibration period (Willets[4]). Calculation of the fission widthis reasonably clear near the nuclear ground state and at largeexcitations when it reduces to the standard statistical modeltreatment[5]. In this latter case, values for open parame-ters (level density parameters and fission barriers) have beenfixed by fitting measured excitation functions to formulae de-rived using the statistical model and then constructing poly-nomials, using the fissility as parameter, to derive values forunmeasured nuclear states.

Difficulties occur for low excitation energy states which means

that special treatment is required for large fissility nuclei.These are handled using the Vandenbosch, Huizenga[6] cor-relation to give the asymptotic fission probability, with a double-humped fission barrier and a Fermi distribution for the low-lying neutron states to describe the threshold region.

Calculations of fissioning systemsFull details of the physics, formulae and parameter value se-lection are given in [1] together with a selection of compar-isons between measured and calculated values.

As an example of the capability of the new formulation toreproduce low energy neutron induced fission, the calculatedand experimental values for the fission cross-section in thethreshold region for 238U and 232Th are shown below. Theentrance channels were calculated using the optical modelroutines from [2].

Neutron Energy CMBV>

Figure 1: Calculated and measured total fission cross-sections for neutron interactions with 238U and 232Th.

REFERENCES

[1] F. Atchison, PSI-report 98-12 (1998).

[2] M. Blann, Private communication (1995).

[3] H.W. Bertini, M.P. Guthrie,Nucl. Phys. A169, 670 (1971).

[4] L. Willets, Phys Rev. 116, 372 (1959).

[5] N. Bohr, J.A. Wheeler, Phys. Rev. 56, 426 (1939).

[6] R. Vandenbosch, J.R. Huizenga, Paper P688, Proc 2ndGeneva Conf on the Peaceful use of atomic energy,Vol. 15, Geneva (1958).

20

MODELLING FISSION IN NUCLEAR REACTIONS: II MASS DISTRIBUTION

F. Atchison1

1Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland

IntroductionThe results from a uniquely detailed study of the fission ofW, Au, Pb and Th induced by 190 MeV protons have beenpublishedfl] recently. The particularly interesting featureis the inclusion of production cross-sections for several iso-topes of the same element for the four systems; this allowsa searching test of the predictive powers of the recently de-veloped semi-empirical fission formulae[2] in the mediumenergy range.

2 The selection of scission parametersThe broad features of the partitioning of energy, charge andnucleons between the scission fragments are known from ex-periment. The main features that are incorporated into themodelling are (i) scissions are complete and into two frag-ments, (ii) large fissility nuclides divide their mass asymmet-rically at low excitation energies (the peaks have a width ofseveral AMU with edges that are Gaussian in form but thedistributions are not simple Gaussian functions and the en-ergy partition between the two fragments is non- uniform),(iii) at higher excitation energies competition comes from anincreasing and eventually dominant contribution from sym-metric division (It is assumed that only the symmetric mass-division occurs for elements below Radium), (iv) nuclearcharge selection is made on the basis of "equal displace-ment from stability", with 0.78 charge unit standard devia-tion Gaussian distributions.

Full details of the physics, formulae and parameter value se-lection are given in [2] together with an extensive selectionof comparisons between measured and calculated values.

3 CalculationAbsolute cross-section values for these medium energy inter-actionsfl] have been obtained using the fission formulationin a new evaporation code, which can handle the wide rangeof nuclear states involved, and the MECC7 intra- nuclear cas-cade code of Bertini[3] to calculate the entrance channel.

The accompanying figure shows the calculated and measuredisotopic variation of production cross-section for the samefive elements (Zn, Rb, Y, Nb and Sb) as produced by inter-actions with the Au, Pb and Th targets; the calculated (abso-lute) cross-section values are shown as a continuous curve.The agreement between the experimental results and calcu-lation is rather reasonable.

REFERENCES

[1] M.C. Duijvestijn, AJ. Konig, J.P.M. Beijers, A. Ferrari,M. Gastal, J. van Klinken, R.W. Ostendorf,Phys. Rev. C 59, 776 (1999).

[2] F. Atchison, PSI-report 98-12 (1998).

[3] H. W. Bertini, M. P. Guthrie,Nucl. Phys. A 169, 670 (1971).

85 95 105 115 90 100 110 120 110 120 130 140

Fig. 1. Calculated and measured cross-sections for the production of Zn, Rb, Y, Nb and Sb isotopes in190 MeV proton interactions with Au, Pb and Th.

21

MEASURING /xD3He FUSION

M. Augsburger1, V. F. Boreiko2, V. M. Bystritsky2S, W. Czaplinski5, A. Del Rosso1, C. Donche-Gay1, M. Filipowicz5, O. Huot1,P. Knowles1, F. Mulhauseris, V. N. Pavlov2, F. M. Pen'kov2, C. Petitjean3, N. P. Popov4, V G. Sandukovsky2, L. A. Schaller1,

H. Schneuwly1, V. A. Stolupin2, J. Wozniak5

R-98-02, FRIBOURG1 - JINR2 - PSI3 - MÜNCHEN4 - CRACOW5

The goal of this experiment is to measure the fusion rateof the /id3 He molecule via the reactions

/Lid+3 He ^ [i + a(3.7 MeV) + p(14.6 MeV) (1)

^ /x5Li + 7 +16.4 MeV. (2)

The main process, the production of 14.6 MeV protons, shouldlead to the determination of the fusion rate A/.

In September-October 1999, our collaboration performeda five week experiment in the [iE4 channel at PSI. This timewas planned as one week setup and 4 weeks data production,and this was achieved.

Measurements with pure deuterium, pure helium, and mix-tures of deuterium and 5% 3He were performed. Two dif-ferent pressures were used in the mixture to obtain relativeliquid hydrogen densities $ = 0.0573 and $ = 0.168. Datafor a total of 1.2 x 1010 good muons for the low density mea-surement were collected.

The target was designed for the installation of three(dE/dx — E)-Si detector pairs, namely Sijjp, SIDO, andSIRI, located above, below, and to the right of the beam. The£7—Si detectors are 4 mm thick, whereas the dE/dx-Si de-tectors have a thickness of 360 [im. Using these detectorpairs protons could be separated from other charged parti-cles, like deuterons. Scintillators are located above (Eup),below (Epo), to the left (ELE), and right (ER/ ) of the beam.They detect the muon decay electrons coming from the tar-get. Details about the target and setup can be found in Refs. [ 1,2,3].

Strong evidence for the fusion can be seen in the com-parison of the distribution of events in the dE/dx-E plane(Figs. 1, 2). Of note are the excess of events (i.e., eventsabove the expected background level) in the expected energyregion 9-13 MeV seen in Fig. 2. The excess events, if at-tributed to the fusion reaction Eq. (1), correspond to a fusionrate A/ = 3(2) x 105s~1. Clarifying the provenance of theseevents and reducing the uncertainty on the result is now thefocus of our work on this experiment.

0 5 10 15 20Energy in E (MeV)

Figure 2: The same data as Fig. 1 with the added requirement thata muon decay electron be seen between 0.2 to 5 [is after the protonevent. Contours are spaced 2 counts apart.

10 15 20Energy in E (MeV)

25 30

Figure 1: Events in the dE/dx-E plane between 0.1 [is and 3 [isafter the arrival of the muon. Electrons are seen in the lower left ofthe plot; contours are spaced 200 counts apañ.

In conclusion, we have seen proton events with charac-teristics consistent with the fusion Eq. (1). The analysis iscurrently focusing on the details necessary to prove conclu-sively that the signal is from fusion. The continuation of theexperiment to look for [id + 4He fusion can only be evaluatedafter the complete analysis of the present data.

REFERENCES

[1] A. Del Rosso et ai,Hyperfine Interactions 118, 177 (1999).

[2] M. Augsburger et al.,PSI Sei. Rep. 1999,1, 16.

[3] V. F. Boreiko et al,Nucl. Instrum. Meth. A 416, 221 (1998).

22

HIGH-RESOLUTION STUDY OF HEAVY-ION-INDUCED THORIUM AND URANIUM LjX-RAY SPECTRA

D. Banas1, D. Castella2, D. Chmielewska3, D. Corminboeuf ', J.-Cl. Dousse2,1. Fijal3, J. Hoszowska4, M. Jaskola3, A.Korman3, T. Ludziejewski3, Y.-P. Maillard2, O. Mauron2, M. Pajek1, M. Polasik5, P.-A. Raboud2, J. Rzadkiewicz3 andZ.

Sujkowski3

Z-99-05, KIELCE1 - FRIBOURG2 - SWIERK3 - GRENOBLE4 - TORUN5

In asymmetric collisions of heavy-ions with atoms multi-ple vacancy states are formed as a result of the strong Coulombinteraction between the projectile nuclear charge and the elec-trons of the target atoms. Rich and valuable informationabout the heavy-ion-induced multiple ionization and the dy-namics of the collisions can be gained from the observationof the satellite structure characterizing the target x-ray emis-sion spectra. For studying the M- and ./V-shell multiple ion-ization, the L — N and L — O x-ray transitions are well suitedbecause their energies are strongly influenced by the numberof vacancies in the outer shells.

We report on high-resolution measurements of the satel-lite structure accompanying several Lj x-ray transitions inTh and U metallic targets excited by impact with 230 MeVand 360 MeV oxygen ions. The measurements were per-formed at the variable energy cyclotron of PSI by means ofhigh-resolution x-ray spectroscopy, using the transmissionDumond type bent crystal spectrometer installed in the areaNE-B for the observation of the target x-ray emission. Theinstrumental broadening of about 10 eV of the spectrome-ter allowed us to resolve the M satellites of the L% — N4,L\ — N2 and L\ — N3 transitions in both U and Th. More-over, in the 360 MeV oxygen-thorium collision, resolved TVx-ray satellites of the L-2 — O 4 transition could be observed,to our knowledge, for the first time (Fig. 1).

The measured x-ray spectra contained information on theionization probabilities for M-, N-, and O-shells at the mo-ment of the L-x-ray emission. By applying adequate correc-tions for the vacancy rearrangement processes occuring inthe target atoms prior to the L x-ray emission, the ionizationprobabilities for the direct Coulomb excitation at the momentof the collision can be deduced. The results will be discussedin terms of available theoretical approaches such as the geo-metrical model and the semiclassical approximation (SCA).Energies and intensities of the observed x-ray diagram andsatellite lines will be compared to theoretical predictions ofmulticonfiguration Dirack-Fock (MCDF) calculations.

19.4 19.5 19.6 19.7 19.8 19.9 20.0Energy [keV]

Figure 1: High-resolution L\ — N¡ and Li — O 4 x-ray spec-tra of Th excited by impact of 360 Mev O7 + of 360 MevO7 + ions. Comparison with results of simulation calcula-tions. Note the resolved N- satellites of the L2 - O4 transi-tion. The L2 absorption edge is shown enlarged in the inset.

23

FIRST DIRECT OBSERVATION OF LONG-LIVED 2S-STATES IN MUONIC HYDROGEN

H. Daniel1, F J. Hartmann1, P. Hauser3, F. Kottmann2, V. E. Markushin3, M. Muhlbauer1, C. Petitjean3, R. Pohl2'3, W. Schott1,D. Taqqu3,

R-97-04, TU MUNICH1 - ETH ZURICH2 - PSI3

An experiment is being under preparation at PSI to deter-mine the Lamb shift (25 — 2P energy difference) in muonichydrogen atoms. It is based on the availability of a suffi-ciently high population of long-lived //p(25) atoms. Un-til recently there was only indirect experimental evidencefor their existence. It resulted from the analysis of the upkinetic energy distributions measured at hPa H2 pressureswhich showed that a considerable part of the yup(25) atomsis slowed down below the 25 — 2P energy threshold wherecollisional 25-quenching is forbidden in first order[l].

The principle of the kinetic energy experiment is to mea-sure the time-of-flight (TOF) of yup atoms, produced near theaxis of a 20 cm long cylindrical gas target, to the gold-coatedwall. The muon is there transferred to gold and /iAu X-rays of MeV energies are emitted which are detected by alarge Csl crystal surrounding the target. Various target diam-eters between 7 mm and 58 mm were used. Smaller targetsare more sensitive to smaller kinetic energies, and the use ofdifferent target diameters allows a consistency check of ourmethod [2].

The TOF spectra were fitted with a superposition of Mon-te Carlo generated time spectra for individual kinetic ener-gies. The resulting distribution of kinetic energies extendfrom below 1 eV up to several tens eV, depending on gaspressure. The mean value steadily increases from ~ 2 eVat 0.25 hPa to ~ 6 eV at 16 hPa. The pressure dependencedemonstrates the importance of collision-induced accelerat-ing cascade processes at high n-levels which are attributed toradiationless Coulomb-deexcitations where the muon transi-tion energy is transformed to kinetic energy of the collidingatoms.

Surprisingly the TOF spectra measured at 16 and 64 hPashow a pronounced component at early times, correspond-ing to /ip energies of nearly 1 keV (see Fig. 1). After acareful analysis of these data it became clear that this cor-responds to an effect which was predicted by Froelich andFlores-Riveros [3]: High-energetic (~ 1 keV) /xp(15) atomsare produced by resonant molecule formation from the 25-state and subsequent autodissociation

H2

/up(15)+p

In this process, which has been discussed in more detail inref.[4], the 25 — 15 energy difference of ~ 2keV is sharedamong the /xp(15) and one proton. This results in /up(15)atoms with a kinetic energy of ~ 900 eV.

Similar components of fast //p(15) atoms were also mea-sured at 16 and 4 hPa, where the 25-lifetime is longer. Preli-

a quenched np(2s)b Coul. de-excit. n—>2c Coul. de-excit. n—>3d continuum 1/128..64 eV

Figure 1: Early part of the TOF spectrum taken at 64hPaH2 pressure in the 58 mm diameter target, together with aset of calculated functions fitted to the data. The thick func-tion corresponds to the resonantly quenched //p(25) result-ing in a 900 eV kinetic energy component convoluted witha (fitted) 25 lifetime. The full fit function includes, besidesa "continuum"-energy distribution, some discrete high en-ergies from low-n Coulomb deexcitation. The dashed peakindicates the measured stop time distribution. The measuredbackground and a kinetic energy scale corresponding to theTOF are also shown.

minary results from a detailed analysis confirm the fractionof ~ 1.5% of long-lived /xp(25) atoms previously found bythe indirect method. Simultaneous analysis of the time distri-butions measured at 16 and 64 hPa for 20 and 58 mm targetdiameters will provide also information on the yup(25) life-time.

The present data are the first direct observation of metastableyup(25) atoms. They give also evidence for a new molecu-lar cascade process which is predicted to be important also athigher levels n > 2 for gas pressures above 1 bar [4].

REFERENCES

[1] R. Pohl et al., Hyperfine Interactions 127, 161 (2000).

[2] F. Kottmann et al., Hyperfine Interactions 119, 3 (1999).

[3] P. Froelich and A. Flores-Riveros,Phys. Rev. Lett. 70, 1595 (1993).

[4] S. Jonsell, J. Wallenius, P. Froelich,Phys. Rev. A 59, 3440 (1999).

24

DEVELOPMENT WORK FOR THE CMS PIXEL DETECTOR

C. Amsler3, M. Barbero4'1, R. Baur1, W. Berti1, R. Eichler1, W. Erdmann2, K. Gabathuler1, R. Horisberger1,R. Kaufmann3'1, D. Kotlinski1, B. Meier2, Ch. Regenfus3, J. Rothe1, P. Riedler3, R. Schnyder1, S. Streulï2, L. Tauschet

E-94-09, SWISS CMS PIXEL COLLABORATION PSI1 - ETHZ2 - ZÜRICH3 - BASEL4

The pixel detector as the innermost detector element inCMS has the task of tagging long-lived reaction products,e.g. b quarks and T leptons, and to find secondary vertices.The pixel modules consist of a 6.4cmx 1.6cm Si pixel sensorwith 150 ¿urn square pixels, which are read out by two rows ofeight electronic chips. Each of the 44,096 pixels on the sen-sor is connected via a bump bond to its own readout circuiton the readout chips (pixel unit cell PUC).

Before module production can start in the year 2003, ex-tensive R&D work must be performed, the main part of itconcerning the readout chip. A complete precursor chip inradiation-hard technology with 36x40 pixels has been de-signed and sent to fabrication in July 2000. It features thefull readout architecture for the LHC environment and incor-porates all the functions needed for full luminosity readout.The programming interface and the voltage control section ishowever not yet implemented.

On the chip the PUC's are organized in columns. A "col-umn drain architecture" initiates immediate data transfer fromthe PUC's to a perifery located at the end of the column,where the complex task of data buffering and trigger verifica-tion is performed, allowing to use a rather simple PUC whithonly 140 transistors. The chip dimensions are 5.4mmx 7.8mmwith a transistor count of about 225,000. It is expected to bedelivered in February 2001.

A first pixel module with six readout chips of simplerreadout architecture has been bump-bonded and operated (seeFig. 1). With this module, possible problems arising from in-

Figure 1 : Pixel module with six readout chips on a testboard

terferences between the chips due to large, transient powersurges and from minimal power filtering due to a restrictedmaterial budget could be addressed. Remedy was found witha rather small budget of electric capacitance.

The module was tested with a set of x-ray sources (seeFig. 2). The copper line corresponds to signals of 2220 elec-trons and the spectra were recorded with the pixel thresholdsof about 1000 electrons (however with an increased peakingtime of 45 ns).

Figure 2: Response of pixel module to various x-ray lines(see text)

Concerning the sensors a novel open atoll structure ofp-stop rings around the n-pixels has been implemented. Thisprovides a high resistive path between the pixels, which shouldprevent the charging-up of pixels where the bump bond fails.Measurements with irradiated detectors show a dramatic in-crease of the inter-pixel resistance with fluence. (see Fig. 3.Consequently an unconnected pixel will be at a growing po-

CSEM 7888SR

1O"> -¡

fluence [7t cm"2]

Figure 3: Inter-pixel resistance as a function of pion fluencefor different detector bias voltages

tential with increasing fluence, which could discharge to thePUC over the small distance of 15 /im and disturb the neigh-bourhood. Studies with a point laser are underway to mapthe behaviour of a region of pixels around an unconnectedpixel.

25

DEVELOPMENT OF EVENT TRIGGERS FOR CMS BASED ON THE PIXEL DETECTOR

M. Barbero1'2, R. Horisberger1, D. Kotlinski1, R. Schnyder1,

E-94-09, CMS COLLABORATION, PSI1 - BASEL2

LHC at full luminosity generates around 1000 particlesfrom proton-proton collisions every 25 ns. These producea very large amount of raw data in the detectors, of which,however, only a small fraction is of interest. Therefore aselective filtering must be applied. The high resolution, 3-dimensional space points from the pixel detector, allowingfor precise pattern recognition, are very useful for triggeringinteresting events. Unfortunately the complete pixel detec-tor data cannot be read out at each collision. Therefore twopossible triggering schemes are considered. A 1st level trig-ger which uses reduced pixel information and a 2nd/3rd leveltrigger which uses the full pixel information.

The 1 st level pixel trigger uses the hit multiplicity infor-mation. The readout mechanism of the pixel chip is organ-ised in double-columns; we use this feature to combine thepixels into 300 \im x 8 mm pseudo-strips.

- 100 optical fibres

Pixel reconstruction, h(5OO)—>-c-c, high-luminosity

analog codedchip address

# j e t s ( z, I <p, t\)

' Rate: kHz ?

Figure 1: Schematic of the pixel first level trigger.

Two variables can then be extracted from the readoutchip in a few bunch crossings: J^ double — columns and^2 clusters (a cluster is a group of adjacent hit double-columns).Chip addresses where these variables pass a certain thresholdare read out and fed into a trigger algorithm. The algorithmfinds jets and reconstructs the interaction point (IP). In oneversion of the algorithm, we reconstruct jets using 3 chipsout of 3 layers. For the 150 GeV b-jet event sample an effi-ciency of 33% can be obtained with a a < 100 mrads in the(f> and r\ directions, and a ~ 0.65 cm for the IP position. Inthe second algorithm we tighten the threshold cuts and askfor 2 chips out of 3 layers. An increase of the detection to55% can be achived at the cost of an increase in fake jets anda deterioration of the IP accuracy. A sketch of the pixel 1 stlevel scheme is shown in Figure 1.

After the 1 st level trigger the data rate is sufficiently re-duced and the full pixel information can be read out. We havebeen developing a triggering algorithm which uses pixel hitsto reconstruct all charged tracks above a momentum thresh-old of 1 GeV and finds all primary reaction vertices (PV).

Figure 2: The reconstructed tracks versus pseudo-rapidity.Only pixel hits are used in the track reconstruction of TTevents at the full LHC luminosity. The solid fine shows thereconstructed tracks, the dashed line shows all Monte Carlotracks which have at least 3 pixel hits. The dotted line showsMonte Carlo tracks with at least 1 pixel hit.

With three pixel hits, per particle track, one can find trackseven at the full LHC luminosity with a high efficiency (above90%) for most types of LHC events. This can be seen in Fig-ure 2 where the reconstructed tracks are plotted versus thetrack pseudo-rapidity for the 500 GeV Higgs —>• TT eventsample at the full LHC luminosity. As a comparison allMonte Carlo tracks having at least 3 pixel hits are drawnwith a dashed line. The difference between the solid andthe dashed curves shows the inefficiency of our track findingalgorithm. Also shown (with a dotted line) are Monte Carlotracks with at least 1 hit in the pixel detector. The PV posi-tion can also be found with a high accuracy of about 50 /xmand a high efficiency (above 90%).

Once track candidates are found, they are used to selectinteresting events and to suppress backgrounds. Events witha high momentum lepton are of particular interest and thesetypically appear as an isolated track. One approach to se-lect these is to apply track isolation criteria in a narrow conearound some specified direction indicated by other subdetec-tors, e.g. by the ECAL trigger. Pixel tracks found in the re-gion around this direction are used to perform isolation tests.Simulations show that this method works successfully as a rtrigger (e.g. for r 's coming from Higgs particles), where theT decays into one or three charged particles. The backgroundevents having mostly a larger number of widely spread tracksare strongly suppressed.

26

POLARIZED NUCLEI IN PLASTIC SCINTILLATORS: NEW TOOLS FOR SPIN PHYSICS

B. van den Brandt1, E. I. Bunyatova2, P. Hautle1, J. A. Konter1 and S. Mango1

1 Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland2 Joint Institute for Nuclear Research, Dubna, Head P.O. Box 79, 101000 Moscow, Russia

New possibilities for the measurement of spin-dependentobservables in nuclear and particle physics are offered by thedevelopment of polarizable plastic scintillators. A polarizedscintillating target is an instrument in which the hydrogennuclei (or other nuclei of interest) in a piece of scintillatorcan be dynamically polarized at very low temperatures andthe light produced in the scintillator by scattered particlescan be forwarded to a photomultiplier at room temperature[1, 2]. One such instrument has allowed e.g. to measure theneutron-proton spin correlation parameter at forward anglesat 68 MeV [3] and the analyzing powers in 7rp*-scattering at45-87 MeV [4], thanks to the coincident detection of the lowenergy recoil proton in the target itself.

The light output and the polarization achievable in a blockof scintillator are determined by the doping and productionprocess [2]. We achieve now routinely 80% proton polariza-tion at 2.5 T and below 0.3 K in blocks o f l 8 x l 8 x 5 mmof PS-based scintillator. A nominal concentration of 2 x 1019

paramagnetic centres/gram was found to give high degrees ofpolarization in a reasonable time. For a sample in which 80%and more polarization could be obtained, 85 minutes wereenough to reach + 60% and 135 minutes to reach + 70%. Wemeasured the proton spin-lattice relaxation time T i p of a se-ries of samples with different concentrations of TEMPO atabout 100 mK in magnetic fields of 0.4 and 0.8 T. Sampleswith a TEMPO concentration of 7 x 1018 p.c./g had at 90 mKa proton relaxation time of 70 hours in 0.4 T, and of 230 hoursin 0.8 T, but needed one day and more to reach full polariza-tion at 2.5 T. In 98.7% deuterated polystyrene-based scin-tillator, containing the non deuterated additives p-terphenyl(1.5 wt.%) and l,4-di-(2-(5-phenyloxazolil))-benzene (0.15wt.%), a deuteron polarization of 25% could be obtained at2.5 T.

The scintillation characteristics of the blocks have beendetermined with a 90Sr-source and with protons of energiesranging between 5 and 12 MeV. The light output of the latestprobes reaches up to 30% of the one of the undoped mate-rial. Protons of energy down to 1.5 MeV can be detectedwith an energy resolution degraded to about 25 % of the oneof the untreated material and an almost unchanged timingresolution. The light extracting system has been investigatedwith a raytracing program. Accordingly, an improved targetholder has been constructed (s. fig.l), and the diameter ofthe 1150 mm long lightguide has been increased to 19 mm.The hydrogen-free light collecting quartz transition (diam-eter 19 mm) between the scintillator and the lightguide isvisible above the scintillator, around which the NMR coil iswound. The microwave guide (with white PTFE cone) can beseen in the center of the figure. A rutheniumoxide thermome-ter is hanging below the scintillator. The lightguide is con-tained in a tight-fitting stainless steel tube inside the (white)ceramic bobbin, on which the continuous heatexchanger cap-illary is wound. The system has been operated recently over

Figure 1: A polarizable scintillating block of 18x18x5 mm,mounted in the mixing chamber.

20 40 60time [h]

Figure 2: Time histogram of the proton polarization in a scin-tillating block as shown in fig. 1.

a period of two months, proving to be very robust and reli-able. A reasonable polarization could be achieved (s. fig.2)and the base temperature attained was 65 mK.

REFERENCES

[1] B. van den Brandt, E.I. Bunyatova, P. Hautle,J.A. Konter, S. Mango,Proc. of SPIN96, Amsterdam, Sept. 10-14,1996, 238.

[2] B. van den Brandt, E.I. Bunyatova, P. Hautle,J.A. Konter, S. Mango,Nucl. Instrum. Meth. A 446 , 592 (2000).

[3] S. Buttazzoni et al., PSI Sci. Rep. 1998,1, 23.

[4] R. Bilger et al., PSI Ann. Rep. 1997,1, 22.

27

AN ULTRACOLD NEUTRON FACILITY AT PSI

F Atchison1, B. Van den Brandt1, M. Daum1, W. Gloor1, G. Heidenreich1, R. Henneck1, P. Hautle1, St. Joray1, K. Kohlik1, J. A.Konter1, S. Mango1, H. Obermeier1, Ch. Perret1, U. Rohrer1, H. J. Temnitzer1, A. Fomiri2, S. Kalcheva2, A. Kharitonov2, M.

Lasakov2, V. Mityukhlaev2,1. Potapov2, M. Sazhin2, A. Serebrov2, G. Shmelev2, V. Shustov2, R. Taldaev2, D. Tytz2, V.Varlamov2, A. Vasiliev2, A. Zakharov2, K. Bodek3, J. Smmicki3, P. Geltenbort4, S. Kistryn5, A. Magiern5, D. Pocanice, E. Frleze

R-00-03, PSI1, PNPI2, ETHZ3, ILL4, Cracow5, Virginia6

During the recent years most attention in physics withultracold neutrons has been focused on two experiments, thehigh sensitivity search for time reversal violation via the mea-surement of the electric dipole moment of the neutron (EDM)and the decay asymmetry and lifetime of the neutron. Theseexperiments rely heavily on long observation times of an en-semble of stored neutrons, and were the driving force behindthe development of techniques for the production and storageof ultracold neutrons (UCN), i.e. neutrons with an extremelylow speed (< 8 m/s). The main impact of the search for theneutron EDM is the exclusion of a variety of proposed mech-anisms for CP violation. Solving this puzzle is expected toprovide an access to physics beyond the Standard Model andtherefore it ranks at the highest priority. Recently, theoriesincluding Supersymmetry, multiple Higgs boson exchange,left-right symmetric models, and attempts to understand thebaryon asymmetry in the universe, predict a finite value ofthe neutron EDM in the range between 10~28 and 10~25ecm;this is just at the verge of the present experimental limit of6-lCr26ecm.

These important experiments are hindered by a low den-sity of ultracold neutrons presently available for experiments.Recently, an attractive solution of these problems has beenproposed [1]. It is based on a pulsed spallation source, cus-tomized to the needs of UCN production. The proposedscheme solves a contradiction between the high neutron ther-mal flux flowing into the solid deuterium moderator and anaverage heat load in such a moderator.

At PSI, we are building such a new type of ultracold neu-tron source. The essential elements are a pulsed proton beamwith a high intensity and a very low duty cycle, a heavy el-ement spallation target and a large moderator consisting ofsolid deuterium kept at a temperature of about 8 K. For theProduction of ultracold neutrons, the proton beam is directedfor a time period of the order of few seconds onto a leadspallation target to generate a high density neutron pulse ina moderator assembly dedicated to the production of ultra-cold neutrons. The lead target is cooled by heavy water andsurrounded by a premoderator and neutron reflector consist-ing of ~4 m3 of heavy water. About 301 of solid deuteriumat ~8 K is used as the cold moderator for the production ofultracold neutrons. The emerging neutron gas, with a den-sity reaching saturation level in the solid may be directedto a dedicated experiment located as close to the productiontarget as the secondary radiation field allows [1]. The ultra-cold neutrons are then observed and/or counted over a periodcomparable to the neutron lifetime in the experiments. Af-ter the density of the UCN in the experimental stations hasdropped significantly, a new proton pulse generates the nextultracold neutron packet, and the whole cycle is repeated.

Figure 1:Scheme of the PSI/PNPI Spallation Ultracold Neutron

Source and Neutron EDM spectrometer

Estimations [2] and Monte Carlo studies [3] show thata UCN density of more than 103 UCN/cm3 can be deliv-ered to the experiments using the proposed method. This is~ 2 orders of magnitude more than in experiments at the re-actors in the Institute Laue Langevin, Grenoble and in theSt. Petersburg Nuclear Physics Institute, Gatchina, whichare at present the world leading centers in ultracold neutronresearch. With these improvements at the new facility, weintend to measure the electric dipole moment (EDM) of theneutron with a sensitivity of about 10~27 ecm, an improve-ment by more than one order of magnitude. The Paul Scher-rer Institute with its superior proton beam is an ideal place torealize such a new UCN source, which is a prerequisite for anext leap in the EDM and lifetime experiments.

REFERENCES

[1] A. P. Serebrov, V. A. Mityukhlaev, A. A. Zakharov,T. Bowles, G. Greene and J. Sromicki,JETPLett. 66, 803(1997).

[2] J. Sromicki, A. P. Serebrov, International Symposiumon Weak and Electromagnetic Interactions in Nuclei,WEIN 98, Santa Fe, NM, June 1998, World Scientific,in press.

[3] I. Potapov, V. Kuzminov,contributions to the "First UCN Factory Workshop",Pushkin, Russia, January. 19-22, 1998.

28

THE LOW ENERGY MUON BEAM FOR THE MUONIC HYDROGEN LAMB SHIFTEXPERIMENT

F Biraben1, C. A. N. Conde2, C. Donche-Gay3, T. W. Hänsch4, F J. Hartmann5, V.-W. Hughes8 O. Huot3, P. Indelicato1,Y.-W. Liu6'7, P. Knowles3, F. Kottmannss, F. Mulhauser3, F Nez1, C. Petitjean7, R. Pohf<s, P. Rabinowitz8, L. Schaller3,

H. Schneuwly3, J. M. F. dos Santos2, L. M. Simons7, W. Schott5, D. Taqqu7, J. F. C.A. Meloso1

R-98-03, PARIS1 - COIMBRA2 - FRIBOURG3 - MPI MUNICH4 - TU MUNICH5 - YALE6 - PSI7 - ETH8 -PRINCETON9

For the realisation of the /ip Lamb shift experimentfl] alow energy muon beam line has been built, tested and op-erated successfully. It consists of the cyclotron trap for theproduction of the low energy muons [2], the muon extractionchannel (MEC) for the transport and the selection of the lowenergy muons and the PSC solenoid with two transmissiondetectors for the muon trigger (Fig. 1).

]Cyclotron Trap

B - 0.15 Tesla

2nd StackSointillator

ExB Plates1st Stack

Figure 1: Set up of the low energy muon channel.

The MEC is a curved magnetic channel where large ad-justable normal conducting coils provide a field that trans-ports particles adiabatically whose momentum is between 1and 3 MeV/c (5 to 45 keV muons). For the efficient elim-ination of the large amount of low energy electrons presentin the initial beam, two special electron beam dumps (notshown in Fig. 1) have been installed downstream and up-stream. The device was tested and adjusted. It provided morethan 90% transmission for the low energy muons. No contri-bution of low energy electrons was detected downstream.

The outcoming muons enter the superconducting 5 T so-lenoid (PSC) where they first cross a new type of transmis-sion detector. It is based on a stack of ultrathin carbon foilswith 1.8 kV voltage between them to compensate for themuon energy loss [3]. Secondary electrons are emitted andaccelerated towards a downstream plastic scintillator con-nected to an external PMT via a long light guide. Betweeenthe stack and the scintillator an E x B drift space induce atransverse drift (greater for the muons than for the electrons)allowing the muons to pass the scintillator. A 70% muon de-tection efficiency could be measured. Further downstreamthe muons cross a second foil stack placed in front of the tar-get. The emitted secondary electrons, accelerated to a few

keV, cross the thin gas target and are detected in a down-stream microchannel plate (MCP) providing a second muonsignal. The TOF information from the two time signals pro-vides optimized triggering on muons stopping in the target.

Figure 2 shows the time spectrum of the second signalrelative to the first one in absence of a target. The first peak,which disappears when the last foil voltage is set to zero,defines the TOF trigger signal. The later signals are inducedby muons stopping in the MCP. The measured muon energyis predominantly between 5 keV and 20 keV.

4000

3500

3000

ts i

n 1

0ns

a>1500

1000

500

n

-

it /

'- i; it_ v i , , , i ,

s l-i with signal in both stacks

¡a. without signal in stack 2

XT ^ ^ ^ ^ electrons

^'T"~Ti-, / from n decay^ — ~ - ,

, , i , , , i , , , i , , , i0 . 6 0 . 8 1.2 1.4 1.6

time/jj.s

Figure 2: Time of flight spectrum measured between firstentrance detector (first foil stack - scintillator - PMT) andsecond detector (foil - MCP). The spectrum can be decom-posed in contributions from TOF trigger electrons , muonsstopping in the MCP and electrons from muon decay in theMCP.

In a seperate measurement, the MCP was replaced by aGe(Li) diode with a Be window. From the measured inten-sity of the yuBe x rays the muon beam intensity was deduced.It agrees with the results of a Monte-Carlo simulation ap-plied to the used foil thickness in the cyclotron trap. It in-dicates that with the fully optimized foil configuration in thecyclotron trap, a beam rate of 100 n~ I ( cm2 . keV . mA . s)will be obtained as predicted. Finally, a 4 mbar gas targetwas introduced and the observation of muonic x rays fromgas stops completed the full operation of the beamline.REFERENCES

[1] R. Pohl et al., Hyperfine Interactions 127, 161 (2000).

[2] P. deCecco et al.,Nucí. Instrum. Meth. A 394, 287 (1997).

[3] M. Mühlbauer et al.,Hypfine Interactions 119, 305 (1999).

29

Laboratory for Astrophysics

30

LABORATORY FOR ASTROPHYSICS

A. Zehnder

Highlights for the Laboratory for Astrophysics (LAP) in 2000 were the delivery of the flight hardware ofHESSI, therepair work following the mishap at Jet Propulsion Laboratory in Pasadena, the successful turn-on of the reflectiongrating spectrometer on board of the XMM-Newton X-ray satellite and the following calibration phase. Thedevelopments of cryodetectors for astrophysical applications, our long-term goal, resulted in the first observation ofvisible light by a superconducting strip detector array.

Following the successful launch of the ESA cornerstonemission XMM-Newton X-ray telescope on Dec. 10, 1999from Kourou by a powerful Ariane 5 rocket, we were eagerto learn how the PSI-subsystem of the reflection gratingspectrometer (RGS) detector housing, the door mechanism,the CCD front-end electronics and the passive CCD coolingsystem were operating in space. All the devices were turnedon without problems, and the commissioning andcalibration phase could start in time. The astrophysicsgroup of LAP was responsible for the key program 'cooland hot stars' and was actively engaged with softwaredevelopment for the in-flight calibrating of the RGSinstrument. Their contribution in the present annual reportentitled The first year of XMM-Newton' and 'XMM-Newton: from Calibration to First Results' give an overviewof this so far very successful mission. The program for theguaranteed observing time started in fall and PSI, the ETH,the University of Zurich and the Observatory of Geneva areprofiting from it. The proposed live time of XMM-Newtonis 10 years and should deliver exciting results, leading to abetter understanding of stellar, galactic and extragalacticastrophysics. The astrophysical contributions, as well as thelist of publications and conference reports of the membersof the small astrophysics group of LAP display theirproductivity that is based on the hardware efforts made atPSI over the last 10 years.

PSI built the imager and the aspect system of the HighEnergy Solar Spectroscopic Imager HESSI. It wasdelivered in time and the integration into the spacecraft waswell under way for the proposed launch of July 2000. Allthe subsystems and the mechanical parts had passed theacceptance tests. However, during the shock tests on thevibration test facility at the Jet Propulsion Laboratory (JPL)that had qualified a number of very famous spacecrafts, anaccident occurred. A malfunction of the apparatus led tosevere damages of the HESSI instrument. The contribution'Repairing the imager of HESSI after JPL-mishap' givesdetails. The repair, re-alignment and re-calibration workkept us busy during 2000. The HESSI contribution of theSolar Aspect System (SAS) and the Roll Angle System(RAS) as well as the Aspect Data Processor (ADP) showthat the system is now well calibrated and well understood.Integration into the spacecraft started again in October2000 and we are looking forward to a successful launch ofHESSI on March 28, 2001.

The third flight hardware, the ESA-financed, PSI-designedand Contraves/Space-built Standard Radiation EnvironmentMonitor (SREM) was successfully launched on Nov. 16, byan Ariane 5 rocket on one of two UK satellites, STRV-lcand STRV-ld. The results received on ground during theinitial phase proved that the SREM design and productionfulfilled the goal. This is shown in the contribution FirstData from SREM in Space'. Unfortunately both UK-satelhtes STRV-lc and -Id stopped transmitting data andaccepting commands owing to unknown reasons. However,ESA additionally procured six SREMs fromContraves/Space and therefore, in the future, we willreceive radiation data from SREM's on satellites likePROBA and INTEGRAL.

The ESA Center of Excellence, the Proton IrradiationFacility (PIF), for the qualification of space electronics andcomponents had again a successful year with a long list ofexternal users from universities, agencies and industries.However, a decision for the relocation of PIF in connectionwith PROSCAN is pending and needs to be taken in orderto guarantee the users long-term operation.

At the beginning of the year 2000, a decision was made tostrengthen the development of cryogenic detectors in favorof further space-borne hardware projects. The work onthese detectors should be expanded from the X-ray into theoptical wavelength region. Moreover, the development of amulti-pixel detector should be initiated. As explainedabove, the HESSI mishap was using up the availablemanpower resources and consequently slowed down thework on cryodetectors. However, as shown in the threecontributions of the group, a 2x8 superconductingtunneling junction (STJ) strip-detector array was producedwith such good characteristics that it could becommercially sold. It produced encouraging results for thedetection of biological macromolecules. With a similar STJstrip detector we observed optical photons for the first time.This was possible by the use of a vastly improved low-noise preamplifier. A few thousand excess charges weremeasured after absorption of a single photon. This resultmust be compared with the few charge carriers produced ina Si-semiconductor after absorption of a photon. It thusclearly demonstrates the potential of STJ detectors.

31

THE FIRST YEAR OF XMM-NEWTON

M. Giidel1, M. Audard1, and the RGS Consortium2'3'4

PSI1 - SRON/NL2 - COL UNIV/USA3 - MSSL/UK4

XMM-Newton has observed various astrophysical objects during its first year. A large amount of the observing timewas spent to perform feasibility tests and to obtain high-quality science data.

Following the inital commissioning and calibration pha-ses, XMM-Newton went through a long series of observa-tions to test the performance of the instrument under realisticconditions. For the Reflection Grating Spectrometer Team,these included, among others: i) testing temperature, ele-mental abundance, and line broadening sensitivity in line-dominated spectra of stellar coronae and wind sources; ii)obtaining a set of complex spectra from active galactic nu-clei to disentangle the different components; iii) testing high-resolution spectroscopy with extended objects, namely su-pernova remnants and galaxy clusters; iv) obtaining fieldswith weak sources to measure background and test spectros-copy at its limits.

Most of these tests provided extremely satisfying results.With the calibration at hand, the RGS stands up to its expec-tations. Measurements of spectral line shifts and broadeningrequires spacecraft stability which was, for the time being,measured by the centroid stability of the EPIC point sourceimages. Most of the time, spacecraft jitter was found below1" over several hours.

The performance verification data were exploited for theirscientific content. The observation of the 'First Light Tar-get' HR1099, a binary star system consisting of two roughlysolar-like stars, resulted in the detection of unexpected ele-mental abundances in the coronal plasma. The abundancesof the elements (relative to the putative photospheric com-position) increase with increasing First Ionization Potential(FIP), which is contrary to previous findings in the solar co-rona, in the solar wind, and in cosmic rays. Our speculationis that high-FIP-enriched flares as occasionally seen in theSun are reponsible for this abundance pattern [1].

A particularly rich XMM observation was devoted to the

7 8 9 10 11 12 13 14 15 IS 17 18

Wavelength (A)

Figure 1: Extract from the RGS spectrum of HR 1099

10 12 14 16 18 20 22 24 26 28

First Ionization Potential (eV)

Figure 2: Elemental abundances (relative to O) in the coronaeof HR 1099 increase with increasing first ionization potential

Castor system [2]. Castor consists of 3 binaries that werefor the first time seen as separate, strongly variable X-raysources. One of the systems, the binary YY Gem, shows to-tal eclipses between its two identical, low-mass stars every9.5 hrs. Through X-ray light-curve inversion covering a fullstellar orbit, the spatial coronal structure of the binary systemwas reconstructed. The main findings were i) rather extendedcoronae, with scale heights that are compatible with the highaverage temperature of 5-10 MK measured by spectroscopicmeans; and ii) inhomogeneities in the corona that are concen-trated at relatively low stellar latitudes (within ±50°). Thelatter geometry corresponds to the Sun but differs from pre-dictions made for this type of star (magnetic fields concen-trated at the poles).

Figure 3: Reconstructed X-ray image of the YY Gem binary.

REFERENCES

[1] A. C. Brinkman, E. Behar, M. Giidel, et aLAstron. Astrophys. 365, L324 (2001).

[2] M. Giidel, M. Audard, H. Magee, et al.,Astron. Astrophys. 365, L344 (2001).

32

XMM-NEWTON: FROM CALIBRATION TO FIRST RESULTS

M. Audard1, M. Gtidel1, and the RGS Consortium2<ZA

PSI1 - SRON/NL2 - COL UNIV/USA3 - MSSL/UK4

After the successful launch of the XMM-Newton Observatory on December 10, 1999, the satellite and its scientificinstruments have been thoroughly tested during a two-month long commissioning phase. We have spent three monthsat SRONin the Netherlands to take part in the calibration and performance verification phase of the RGS instruments.This effort is now ongoing at PSI. The validation of the calibration procedures has been performed on the first datasets and first results have been successfully obtained.

The XMM-Newton Observatory has been successfullylaunched at the end of 1999 [1]. After two months of com-missioning phase during which various tests of functionalityhave been performed, the calibration and performance phasebegan. We actively participated in this phase at SRON, TheNetherlands. Issues addressed were: the wavelength scale,the effective area, the line-spread function, the CCD model.The wavelength scale has been validated and the present ac-curacy is within 8 mA or 4 arcseconds in pointing indepen-dent of off-axis angle [2]. The residual uncertainty is be-lieved to originate from the present non-inclusion of attitudecorrection. We continue to take an active part in the deter-mination of the wavelength scale: we will analyse attitude-corrected data as soon as they become available.

PSI is mainly responsible for the testing and vahdationof the XMM-Newton Science Analysis System (SAS) whichallows for the reduction, cahbration and analysis of XMM--Newton data. Basically, we test all RGS-related tasks (e.g.,RGSFRAMES, RGSANGLES, RGSPROC, RGSRMFGEN, etc),in collaboration with SAS developers. We are also involvedin the EPIC MOS and pn software testing. To further con-tribute to this effort, PSI has been invited to join the XMM-Newton SAS Working Group.

The testing and validation of the cahbration procedureswere performed on various data sets obtained during the threeearly phases of XMM-Newton. Of particular interest wasa large flare that occurred during the observation of the bi-nary system HR 1099, the RGS first-light target [3]. Time-dependent spectroscopy has been performed to derive ele-mental abundances and their variations during the variousstages of the flare. The reconstructed temperature structureof the coronae of HR 1099 suggested two different compo-nents: a very hot plasma (up to 100 MK) that evolves rapidly,and a stable quiescent plasma. The coronal abundance oflow-first-ionization-potential elements such Fe and Si havebeen found to significantly increase during the flare, whilethe Ne (high-FIP) abundance did not show significant varia-tion. This increase of low-FIP elements during the flare is tocontrast with the apparent anti-FIP effect (high-FIP elementshave larger abundances than the low-FIP elements, relative totheir solar photospheric abundance) found in the "quiescent"spectrum of HR 1099 [3, 4].

The high signal-to-noise ratio of the bright star Capellaallowed us to study the faintest features in its X-ray spec-

trum [5]. The reconstructed emission measure distributionpeaked around 7 MK, consistent with previous EUVE andASCA results. For the first time for an X-ray spectrum froma stellar corona, we have applied the temperature diagnos-tics of dielectronic recombination satellite lines to the He-like O vii triplet to constrain the cool plasma temperature.From line ratios of the same triplet, we derived an averagedensity for the cool (2 MK) coronal plasma smaller than109 cm"3. The "hotter" (7 MK) Mg triplet tentatively in-dicated a much higher density around 1012 — 1013 cm"3,suggesting bi-modality of the coronae of Capella.

CAPELLAXMM-Newton/RGS

14 __ 16Wavelength (A)

Figure 1: Extract from the RGS spectrum of Capella. Majoremission lines have been labeled.

REFERENCES

[1] M. Audard, L. Grenacher, M. Giidel, et al.,PSI Sci. Rep. 1999,1, 27 (2000).

[2] J. R. Peterson, M. Audard, RGS-COL-CAL-00011,Columbia Astrophysics Laboratory (2000).

[3] M. Audard, M. Giidel, R. Mewe,Astron. Astrophys. 365, L318 (2001).

[4] A.C Brinkman, E. Behar, M. Giidel, et al.,Astron. Astrophys. 365, L324 (2001).

[5] M. Audard, E. Behar, M. Giidel, et al.,Astron. Astrophys. 365, L329 (2001).

33

FREE-FLOATING PLANETS IN STELLAR CLUSTERS

K.W. Smith1'2

PSI1 - ETH ZURICH2

The discovery of numerous extrasolar planetary systemsin the solar neighbourhood (Mayor & Queloz 1995, Marcy& Butler 1996) has revolutionised our ideas of the planet for-mation process and how it can vary from system to system.Specifically, the fact that most of the systems found containrelatively massive planets at small separations, in contrastto our solar system, has engendered significant research intopossible orbital migration. More recently, the discovery thatthere appear to be no such close systems in the globular clus-ter 47 Tuc (Brown et al 2000, Gilliland et al 2000) impliesa significant difference in planetary formation which couldbe due to the stellar environment. There are three likely ex-planations for this. Firstly, planet formation may not be effi-cient in globular clusters due to their poor metallicity. Sec-ond, UV radiation from clusters of O stars may destroy pro-toplanetary discs at an early stage, as seems to be occurringin the Trapezium (Armitage, 2000). Thirdly, close encoun-ters between stars lead to a lack of close planetary systems.This may be because planetary formation is itself impeded,because the inward migration of planets is hampered subse-quent to planet formation, or because the planetary systemsare destroyed by disruptive encounters (Bonnell et al, 2001).This last scenario could then lead us to expect a populationof liberated planets in the cluster. Recently there has beena reported detection of a population of substellar objects ina Orionis (Zapatero-Osorio et al, 2000) that could be due tostellar encounters.

We have simulated encounters between planetary systemsand single stars in three different clustered environments.These were intended to resemble a globular cluster, opencluster and a young star forming cluster, such as a Orionis.We found that in globular clusters a relatively high fractionof any planetary population with orbits outside 1AU is likelyto be liberated by encounters over the cluster lifetime, andfurthermore that the majority of these systems should be re-tained in the cluster at least until they are lost through twobody relaxation after several thousand crossing times.

In the less dense environments of an open cluster or youngstar forming cluster, planet liberation was found to be less ef-ficient, although still capable of producing a significant pop-ulation of free floating planets. However, it was found thatthese objects were liberated at too high a velocity to remainbound in the cluster. In each case, only a fraction of a per-cent of the planetary population was liberated but remainedbound to the cluster. This suggests that there should not besubstantial numbers of free floating planets in such environ-ments. Furthermore, any such objects which were observedin stellar clusters would be expected to have a higher veloc-ity than the cluster stars, and so to be found predominantlyin the outer regions far from the cluster core.

This result implies that the substellar objects recentlyfound in a Orionis are not after all planets which formed

in a disc around a young star, but must have formed fromindependent collapse.

-100-100 -50 0 50 100

- 5 0

.' 1 ' '

- *1'"'\

-, 1 1 1

. . - - • • •

, i , / , , i ,

T 1 | , , , | 1 1 , _

—

" • ; • :

-20 0 20 40 60 80

0

- 5 0

-100

-150

\ j

1 ' 1 l

•'..' 1 '

'

-_

, , 1 r

0

- 5 0

100

- : . . . r v • • • i • • •

/ .--•

- /- / \:

1 1 L

.... ~

• • ; -

-

-

—

i 1 r

0 50 100 0 50 100

Figure 1: Examples of encounters between planetary systemsand a star. (Clockwise from top left): (a) The planet is liber-ated entirely, (b) The planet is retained by its parent, (c) Theplanet is exchanged, finishing bound to the perturbing star,(d) Finally, the planet is again exchanged, and the final orbitis extremely eccentric.

REFERENCES

[1] P. Armitage,Astron. Astrophys. 362, 968 (2000).

[2] I. A. Bonnell, K. W. Smith, M. B. D. Davies andK. D. Home, MNRAS, in press.

[3] T. M. Brown, et al.,Astron. Astrophys. Suppl. 196, 203 (2000).

[4] R. L. Gilliland, et al.,Astrophys. J. 545, L47 (2000).

[5] G. Marcy and P. Butler,PASP 112, 137 (2000).

[6] M. Mayor, and D. Queloz, Nature 378, 355 (1995).

[7] M. R. Zapatero-Osorio, V. J. S. Bejar, E. L. Martin, R.Rebolo, D. Barrado y Navascues, C. A. L. Bailer-Jonesand R. Mundt, Science 290,103 (2000).

34

SPATIAL ANALYSIS OF SOLAR TYPE III EVENTS ASSOCIATED WITH NARROWBANDSPIKES AT METRIC WAVELENGTHS

G. Paesold1*2, A. O. Benz1, K.-L. Klein3, N. Vilmer3

ETH ZURICH1 - PSI2 - OBS. of PARIS3

The spatial association of narrowband metric radio spikes with type III bursts is analyzed. The analysis addressesthe question of a possible causal relation between the spike emission and the acceleration of the energetic electronscausing the type III burst. The spikes are identified by the Phoenix-2 spectrometer (ETH Zurich) from routine solarobservations in the frequency range from 220 MHz to 530 MHz. Simultaneous spatial information was providedby the Nancay Radioheliograph (NRH) at several frequencies. The 3-dimensional geometry of the single events hasbeen reconstructed by implying different coronal density models.

Millisecond narrowband radio spikes are structures in theradio spectrum of the Sun forming a distinct class of flareemission. The term 'narrowband, millisecond spikes' refersto short (few tens of ms) and narrowband (few percent of thecenter frequency) peaks in the radio spectrogram. They canbe observed in the range of 0.3 to 8 GHz and occur mainlyduring the impulsive phase of a solar flare. Since the spikeemission is often associated with enhanced hard X-ray emis-sion it is generally assumed that spikes are closely related tothe actual process of energy release in solar flares.

A subclass of spikes found at metric wavelengths cor-relates with type III bursts. They have been called 'metricspikes' in the literature (e.g. Giidel & Zlobec [3]). They oc-cur in clusters usually at frequencies slightly higher than thestart frequency of the type III burst and can be shifted in timewith respect to the type III extrapolated in frequency (Benzet al. [1]).

Previously published spatially resolved observations ofmetric spike events (Krucker et al. [4]) found the spike sourcesat high altitudes and suggest a model of energy release tak-ing place in or close to the spike sources. Escaping beamsof electrons cause the type III emission. Thus a scenario isconceivable, in which the spikes may be a direct signature ofthe accelerator.

Using two dimensional spatially resolved data from theNan§ay Radioheliograph (NRH), it is possible to reconstructthe spatial configuration of the event and the relative positionof the spike source with respect to the type III trajectory. Themain purpose of this work is to answer the question whetherthe geometry of the events supports the picture mentionedabove.

Four new events of type III associated metric spike eventshave been found and analyzed. In addition, three separateevents on 92/08/18 that are already published in Krucker etal. ([4]) using VLA observations have been investigated us-ing older data from Nancay.

In all analyzed events the spike sources are always lo-cated at positions coinciding with expected locations fromextrapolated type III trajectories to lower altitudes. Theseobservations thus strongly support a model for radio spikesoccurring in the course of type III beam propagation or nearits origin, consistent with independent spectrogram observa-tions (Benz et al. [2]). They add further evidence for spikesbeing a signature of the mechanism accelerating electronbeams that cause type III bursts. One of the 92/08/18 events

92/08/18, III/IV

-1.0 -0.5 0.0 0.5 1.0E-W coord, in solor rodii

-0.20-0.18-0.16-0.14-0.12-0. IIE-W coord, in solor rodii

Figure 1: Upper right: Observed position of three frequen-cies: triangle - 164.0 MHz, square - 236.6 MHz and x -327.0 MHz. Upper left: side view from far to the West.Lower right: top view from far above the North. Lowerleft: location of upper right panel on the Sun.

exhibits a very suggestive situation: two consecutive type IIIbursts originate in the same spike source. The situation isdepicted in Fig. 1. Energetic electrons appear to be injectedinto different and diverging coronal structures from one sin-gle position. Such a magnetic field geometry is the standardingredient of reconnection. These observations are consistentwith the hypothesis that metric spikes may be a signature ofparticle acceleration.

REFERENCES

[1] A. O. Benz, P. Zlobec, M. Jaeggi,Astron. Astrophys. 109, 305 (1982).

[2] A .0. Benz, A. Csillaghy, M. J. Aschwanden,Astron. Astrophys. 309, 2291 (1996).

[3] M. Giidel, P. Zlobec,Astron. Astrophys. 245, 299 (1991).

[4] S. Krucker, A. O. Benz, M. J. Aschwanden,Astron. Astrophys. 317, 569 (1997).

35

HARD X-RAYS AND DECIMETRIC RADIO CORRELATIONS

Pascal Saint-Hilaire1'2, Arnold O. Benz1

ETH ZURICH1-PSI2

Hard X-rays from the Sun are emitted during the impul-sive phase of flares. They are often accompanied by unpolar-ized type III radio bursts in the decimetric range at the veryonset of the flare, and then pulsating continua appear. Thetemporal relation for one of the observed flares is shown inFigure 1.

Figure 1: BATSE Hard X-ray lightcurve, and PHOENIX-2radiospectrogram (stokes I) from ETH's Bleien Observatory)

In preparation for the Hessi mission, we have started aprojet to compare several such flares, and to find the essentialingredients related to particle acceleration and the generationof hard X-ray emission.

Fig. 2 depicts the same flare that occurred on September8th, 1999 as observed with the TRACE ultraviolet/extreme-ultraviolet satellite. The TRACE image shows a two-ribbonflare (brightest areas), and the early phase of an expandingcoronal mass ejection (CME). The latter can be noticed be-tween the radio sources (contour overlays) and the brightflare. The three radio frequency contours to the right of theactive region correspond to the first pulsating continuum. Thisemission stays mainly on top of the active region through-out the episode of hard X-ray emission. The two lowest fre-quency contours, located further south, correspond to typeIII radio bursts attributed to fast electron beams. The type IIIbursts are present just when the magnetic energy is being re-leased (as evidenced by the hard X-ray rise). Later on, as theCME is expelled towards the upper layers of the corona at aspeed of about 1000 km/s, the radio sources at all frequenciesslowly follow the wake of the CME, way up into the uppercorona.

It is interesting to note that the most important decimetricradio emissions are by the CME itself, and not by the plasmaduring the flare (hard X-ray peak).

There are many more as yet unexplained features, like thepresence of low-frequency type III bursts around UT 12:18shooting out more than 100 arcseconds to the right of theactive region.

This project is pivotal as a preparation for Hessi hard X-ray observations. The image reconstruction using YohkohHXT data as presented here will be refined greatly with Hessi(resolution at this energy range is twice better than HXT's).Hessi will also provide much better hard X-ray spectra (HXTonly has four channels, spanning the 14-93 KeV range).

300

-900 -800 -700X (orcsecs)

-600

Figure 2: TRACE 1600A picture (CI, Fell and somecontinuum), with Hard X-ray overlay from Yohkoh HXT(thin, black contours : 23-33 KeV range), and from theNancay Radioheliograph (thick contours, red=164MHz, or-ange=236.6MHz, yellow=327MHz, green=410.5MHz, pur-ple=432MHz, representing the top two percent of the radioflux at each frequency). The time, 12:15:10, correspondsto the peak of the hard X-ray emission in Figure 1. TheTRACE image shows a two-ribbon flare (brightest areas),and the early phase of an expanding CME. The three radiocontours to the right correspond to the first pulsating contin-uum whereas the radio contours to the south are related totype III radio bursts. The fact that the two hard x-ray foot-points are not precisely located right on top of the two-ribbontracks (they are about 10 arcseconds to the right) can easilybe attributed to the pointing inaccuracy of TRACE.

36

SHAPE AND GEOMETRY OF GALAXY CLUSTERS AND THE SZ EFFECT

L. Grenacher1'2, Ph. Jetzer1'2'3, P. Koch2, R. Piffaretti1'2, D. Puy1'2, M. Signore5

PSI1 - ZURICH2 - ETH ZURICH3 - OBS. of PARIS5

The Sunyaev-Zel'dovich (SZ) effect is the change in en-ergy experienced by cosmic background photons when theyscatter on the hot gas in galaxy clusters. By combining theSZ intensity change and the X-ray emission observations,and solving for the number density distribution of electronsresponsible for both these effects, the angular diameter dis-tance to galaxy clusters can be derived. Assuming a cosmo-logical model, this leads then to an estimate of the Hubbleconstant.Recently, Mauskopf et al. [1] determined the Hubble con-stant from X-ray measurements obtained of the cluster Abell1835 with ROS AT and from the corresponding millimetricobservations of the SZ effect with the SZ Infrared Eperi-ment (SUZIE) multifrequency array receiver. Assuming aninfinitely extended spherical gas distribution with an isother-mal equation of state, they found a value of H°hs = 59±28km s^1 Mpc^1 for the Hubble constant.If we suppose other physical characteristics of the clustersuch as: finite extension or aspherical distribution for thedensity, we find accordingly other estimation of the Comptonparameter y and the surface brightness, and so a relative er-ror with respect to the classical configuration (i.e. sphericaldistribution with an infinite extension). Thus, we define twofamily of relative errors:

• CyXt = 1 — (yi/yoo) where y^ is obtained for an infi-nite extension and yi for a cluster extension I. Here weconsider an isothermal profile and a spherical distribu-tion.

rc

eeyxt (in %)

eeg (in %)

2294

4151

6120.4

89

0.2

107

0.1

• tfom = 1 - ilVsph) where ysph is the Compton

parameter obtained for a spherical distribution and yeuthe one for an ellipsoidal distribution, with an infiniteextension and an isothermal equation of state for thetwo distributions.

Of course, the same analysis for the relative error applies alsoon the surface brightness Sx •

Finite extension of clusters

Since the hot gas in a real cluster has a finite extension, eachof the observed quantities, the Compton parameter and the X-ray surface brightness, will be smaller than those estimatedassuming I —> oo. In Puy et al. [2] we have analysedthe influence of this correction for the simplest cluster case:isothermal fi = 2/3-model with a spherical density profile,and a fine of sight going through the cluster center. In Table 1we give the relative error on the y-parameter and the surfacebrightness for different finite extensions of the cluster.

In Figure la we show the influence of the finite extensionI using the same input parameters of Mauskopf et al. [1]. Fora spherical geometry, Ho displays a strong dependence onthe cluster extension [3]. An extension of I ~ 10, given in

Table 1: Relative errors eeyxt on the {/-parameter and ee

sx^ on the

surface brightness assuming fi = 2/3 and a spherical cluster. rc isthe core radius in kpc.

units of the core radius rc, leads to Ho ~ 45 km s 1 Mpc 1

which is well below the value found by Mauskopf et al. [1].

Geometrical effect

Some observations with ROS AT of rich clusters have revealedthat on large scales the X-ray distribution has an ellipticalshape. The influence of the geometrical shape of the clusterprofile on the investigated quantities induces a relative erroron the y parameter of up to 10%, depending on the line ofsight and the shape of the cluster.The effect on the Hubble constant is shown in Figure (lb) foran ellipsoidal geometry [3] for different axis ratios, where wecompare again with the value obtained by Mauskopf et al.[1].

0 20 40 60

Cluster extension 1 (in units of r )

Figure 1: The Hubble constant as a function of the clusterextension and the axis ratio.

REFERENCES

[1] P. Mauskopf, P. Ade, W. Allen, et al.,Astrophys. J. 538, 505 (2000).

[2] D. Puy, L. Grenacher, Ph. Jetzer, M. Signore,Astron. Astrophys. 363, 415 (2000).

[3] L. Grenacher, Ph. Jetzer, R. Piffaretti, D. Puy,M. Signore, Proceedings of the SZ Toulouse Workshop,astro-ph/0010512

37

BARYONIC DARK MATTER IN CLUSTERS AND SPIRAL GALAXIES

L. Grenacher1 >2

PSI1 - ZURICH2

The thesis, done under the supervision of Prof. Ph. Jet-zer, deals with different footprints of baryonic dark matter.For this purpose we investigate three environments on differ-ent scales:

• the intracluster gas (ICG) is used as a tracer of the darkmatter distribution in galaxy clusters,

• the fate of the gas in cooling flows in the central re-gion of clusters is investigated, as well as the molecu-lar clouds in the cooling flow.

• low-mass stars, observed in microlensing experiments,are used to determine galactic parameters.

We study the Sunyaev-Zel'dovich (SZ) effect and the X-ray surface brightness for clusters of galaxies with a non-spherical mass distribution [1]. In particular, we consider theinfluence of the shape and the finite extension of a cluster,as well as of a polytropic equation of state on the Comptonparameter, on the X-ray surface brightness, and on the de-termination of the Hubble constant HQ . It is found that thenon-inclusion of such effects can induce errors up to 30% inthe various parameters and, in particular, on the Hubble con-stant value, when compared with results obtained under theisothermal, infinitely extended and spherical shape assump-tions. On the other hand, for a given Ho, the temperaturedecrement given by the SZ-effect allows predictions of theX-ray surface brightness and thus gives information on theshape of the density profile of the cluster, which in turn givesimproved constraints on the total mass.

In many clusters of galaxies there is evidence for cool-ing flows in the central regions. The ultimate fate of the gaswhich cools is still unknown. A possibility is that a fractionof the gas forms cold molecular clouds. We discuss the mini-mum temperature which can be reached by clouds in coolingflows by computing the cooling function due to Hi, HD andCO molecules [2]. As an example, we determine the mini-mum temperature achievable by clouds in the cooling flowsof the Centaurus, Hydra and PKS 0745-191 clusters [3] [4].Our results suggest that clouds can reach very low temper-atures - less than ~ 10 K - which would explain the non-detection of high excited CO rotational transitions in theseclusters. We show in Figure 1 the equilibrium distance ofcold molecular clouds in a cooling flow environment with re-spect to the center of the cluster PKS 0745-191. The heatinginduced by the hot ICG is equal to the cooling due to transi-tions between excited rotational levels. The equilibrium posi-tion is shown inside the cooling radius rcooi for different COabundances r/co, given with respect to the Hi abundance.

In the context of microlensing searches in our Galaxy, we

calculate the optical depth and the number of events towardsthe Galactic bulge and some directions towards the spiralarms [5]. Using the events found by the MACHO collabo-ration during their first year of observation towards Baade'sWindow we estimate the mass functions for the bulge anddisk populations following the mass moment method. Wefind that the mass function can be well described by a de-creasing power-law with slope a ~ —2.0 in both cases and aminimal mass of ~ 0.01 M 0 for the bulge and ~ 0.02 M 0

for the disk, respectively. Assuming that the obtained massfunction for the disk is also valid in the spiral arms, we findthat the expected number of events towards the spiral arms isin reasonable agreement with the observations.

S loo

\\

\ \\ \11 \

\ \\\\ v\ \\ ^\ ^\ \\ ^\ ^

. \

rcool

•

6 8 10 12Equilibrium Temperature [K]

Figure 1: Equilibrium distance as a function of cloud tem-perature in the cooling flow environment of the cluster PKS0745-191 for different CO abundances. CO is the maincooling agent in this range of temperature.

REFERENCES

[1] D. Puy, L. Grenacher, Ph. Jetzer, M. Signore,Astron. Astrophys. 363, 415 (2000).

[2] D. Puy, L. Grenacher, Ph. Jetzer,Astron. Astrophys. 345, 723 (1999).

[3] L. Grenacher, Ph. Jetzer, D. Puy, Proceedings of theLarge scale structure in the X-Ray Universe meeting,Atlantisciences 371 (2000).

[4] L. Grenacher, Ph. Jetzer, D. Puy, Proceedings of theClustering at High Redshift conference,ASP Conference Series 200,444 (2000).

[5] L. Grenacher, Ph. Jetzer, M. Strassle, F. De Paolis,Astron. Astrophys. 351, 775 (1999).

38

FIRST DATA FROM SREM IN SPACE

P. Buhler1, C. Eggel1, W. Hajdas1, N. Schlumpf, A. Zehnder1, E. Daly2, A. Mohammadzadeh2, P. Nieminnen2, J. Schneider3

PSI1 , ESA/ESTEC'2 , Contraves Space3

The Standard Radiation Environment Monitor, SREM isa particle detector developed for satellite applications [1]. Itmeasures high energy electrons and protons of the space en-vironment with a fair angular and spectral resolution and pro-vides the host spacecraft with radiation information. SREMwas developed and manufactured by Contraves Space in co-operation with Paul Scherrer Institute under a developmentcontract of the European Space Agency. SREM is the suc-cessor of REM [2].

On 16 November 2000 a first SREM instrument was laun-ched aboard the UK-satellite STRV-lc into space by an Ariane-5 rocket. The satellite reached its foreseen GeostationaryTransfer Orbit, GTO with apogee and perigee altitudes of600 and 39000 km, respectively, an inclination of 6°, and aperiod of approximately 12 h (figure 1). During the check-out of all STRV-lc experiments, SREM has been switchedon and was operated for a short period. The data receivedduring that period indicate that the instrument works well.

2

12

* °

-2

\GEO

/ ^ \ \

/ \

\ A

:/ :

. X si •_GTO" - " " " /

- 2 2 4XSM [RE]

Figure 1: GTO of Strvlc on 22 November 2000. The red dotmarks the position of the satellite at 13:13 when the electronspectrum shown in figure 2 was taken.

The orbit of Strv-1 c is ideal for investigations of the radi-ation belts, because it covers a large spatial area and allowsto trace the radial distribution of the trapped particles. Es-pecially now, during solar maximum it allows to investigatethe influence of spontaneous solar ejections on the Earth'smagnetosphere. The Strv-lc/SREM data promises to be avaluable extension of the database obtained by REM aboardStrv-lb from 1994 to 1998, which covered the last solar min-imum period.

Figure 2 shows an example of an electron spectrum mea-sured by SREM aboard Strv-lc during the commissioningphase. The position of the satellite during the measurementis indicated in figure 1 by a red spot. The satellite is at a dis-tance of 5.3 Rg from the center of the earth, in the outer radi-ation belt zone. The SREM spectrum is plotted in red and isapproximated by an exponential function and a step-function.The black dotted line shows the electron spectrum described

by the radiation environment model AE8 from NASA. Thisexample demonstrates the power of SREM for monitoringand characterizing the electron space radiation environment.

10s

| 106

"B IO 4

(4-(

102

10°

22/11/2000,13:13:01.950

X '•,

X-.

x:-.X, •-

\ • • • . _

SREMX\''-..^

Xri

B. := BO MeVA = 3.10e-;-06 I /cm'TMt-V/^.

i . . . i

R =L =

v x xx.i "^

5.33 [RE] .5.50 [RE]

-

_

4 6Energy [MeV]

Figure 2: Comparison of the differential electron spectrameasured with SREM and predicted with the standard radia-tion environment model AE8 from NASA. In case of SREMthe spectrum is approximated by an exponential function anda step-function.

Prior to launch the instrument was fully calibrated at theProton Irradiation Facility, PIF of PSI. In addition the in-strument including the host spacecraft were simulated withGEANT to accurately determine the response functions toelectrons at energies between 0.5 to 10 MeV and to protonsin the 10 to 600 MeV range. These are needed to compute theincident particle spectra from the measured detector countrates.

In order to ease the exploitation of the scientific datawe developed the Data Management and Analysis System,DMAS. DMAS is a software tool written in PV-WAVE, whichallows to maintain the databases of multiple SREMs but alsoother space science data sets. DMAS is modular and can beupdated to work with new experiment data. It includes instru-ment specific functions for the reduction of the raw data andgeneral functions for e.g. the computation of earth magneticfield parameters and satellite orbits. A GUI allows to de-fine experiment parameters, execute data analysis functions,display the data, and to produce data products for the presen-tation on the Internet.

Further SREMs will be launched aboard Proba in 2001and the ESA M2 mission Integral in 2002. News and datacan be found at

http://wwwl.psi.ch/www_srem_hn/srem_home.html.

REFERENCES

[1] W. Hajdas, PSI Annual Report (1997).

[2] P. Buhler etal.,Nucl. Instrum. Meth. A 368, 825 (1996).

39

REPAIRING THE IMAGING SYSTEM OF THE HIGH-ENERGY SOLARSPECTROSCOPIC IMAGER (HESSI) AFTER JPL-MISHAP

K. Thomsen, F. Burri, R. Henneck, A. Mchedlishvili, P. Ming, J. Welte, A. Zehnder (PSI), A. Bern (ETH-Z), in colla-boration with the Space Science Laboratory Berkeley, Goddard Space Flight Center, and the University of Delft

During the vibration test of the HESSI space craft the satellite was partly destroyed due to malfunctioning of the testfacility; after refurbishment and realignment the imaging system was brought back to a flight-worthy condition

HESSI is a Small Explorer NASA mission with a singleinstrument on a small spin-stabilized spacecraft in lowearth orbit. The primary scientific aim of the mission is toexplore the basic physics of particle acceleration andexplosive energy release in Solar Flares. HESSI willproduce hard X-ray images with an angular resolution asfine as 2 arc-seconds and a temporal resolution on the orderof 10 ms; a detailed image can be obtained in 2 seconds. Atthe same time HESSI will provide energy resolution below1 keV over the range from 3keV to 400 keV. For the firsttime HESSI will perform hard X-ray and gamma-rayimaging above 100 keV with an energy resolution of a fewkeV up to energies as high as 20 MeV.

The imaging capability of HESSI is based on a Fourier-transform technique using a set of 9 pairs of grids spaced1.55m. Transmission through a grid pair is modulated asthe spacecraft rotates around its axis. The different gridpairs have different slit widths. For the finest grid pair arelative twist alignment and its stability to better than 20arcsec is mandatory to yield sufficient modulation depth.Given the exact timing of single photons together with theprecise knowledge of the aspect of the imager it is possibleto reconstruct an image of the source. A Roll Angle SystemRAS and a Solar Aspect System SAS, allow for aspectreconstruction to arcmin and arcsec, respectively.

The energy resolution of the instrument is achieved byusing Ge detectors at liquid nitrogen temperature. HESSIwill have the best angular and spectral resolution of anyhard X-ray or gamma ray instrument flown so far.

21, 2000, the HESSI spacecraft was subjected to a series ofvibration tests at JPL as a part of its flight certificationprogram. The structural qualification test, denoted as thesine-burst test, subjected the spacecraft to a major over testthat resulted in significant structural damage. A stickingbearing of the shaker facility was found to be the culprit ofthe accident. The central imager support ring was broken intwo at about its design load; the imager got almostcompletely loose and started to hammer, which resulted insevere peak loads for the whole imaging system as well asit destroyed two of four solar panels.

IMAGER Ti RINGS complete burst history

-7X(OK) - -10X a 4 kHz (PSI top ring) 11X @4 kHz (PSI bottom)

Fig. 1: Overview of HESSI imager, view of grids expandedon top, Roll Angle System visible at bottom leftOn March

Fig. 2: Accelerations as measured on the imager end rings

The spacecraft was disassembled and the PSI-builtcomponents were sent back to Switzerland for repair. Herethe imager was taken apart and the individual componentswere subjected to detailed investigations and tests. No partwas really destroyed; only the strut fittings, the traymounts, and the mounts of grid #6 were slightly deformed.The surface of the a carbon fiber reinforced plastic (CFRP)imager tube showed two marks from the hammeringagainst the sharp corner of the imager support ring but nodeterioration of its structural integrity could be detected.Strut fittings were successfully reworked manually, the trayand grid mounts were replaced by spares. The RAS as wellas the SAS units were found intact. Functional testsincluding thermal cycling of the RAS and SAS electronicsverified the healthy condition of the aspect systems. Withtheir acceptable status fully confirmed the RAS and theimager components were cleaned anew, reassembled andaligned.

After verification of the alignment with an end-to-endgridlet test the flight hardware was sent to Berkeley forintegration with the rebuilt spacecraft.

40

STAR CALIBRATION OF THE HESSI ROLL ANGLE SYSTEM (RAS)

R. Henneck,, J. Bialkowski, F. Burri, M. Fivian, W. Hajdas, A. Mchedlishvili, P. Ming, K. Thomsen, J. Welte,A. Zehnder, (PSI), G. Hurford (UC Berkeley), D. Curtis (UC Berkeley), D. Pankow (UC Berkeley)

We describe the calibration of the HESSI RAS at the Jungfraujoch. We determined the width of the point spreadfunction (PSF) to be about 0.9 arcmin rms and the sensitivity to be as predicted (weakest object seen has mv=3.65).

The Roll Angle System (RAS) is part of the HESSIinstrument [1] to be launched by March 2001. It willprovide information on the roll angle of the rotatingspacecraft (15 rpm). Precise knowledge (1 arcmin at la) ofthis angle is a necessary ingredient for imagereconstruction. The RAS is a star camera which pointsradially outwards and observes stars at 75° from the sundirection. Stars within a field-of-view of 30° x 1.4° arefocussed by a lens onto a 2048 pixel line CCD. The passageof a star image over the CCD (orthogonally) will produce asignal in several pixels and the timing of this signal definesthe roll angle, once the star has been identified via its pixelposition and amplitude (for more detail see Refs. [2], [3]).

Ground calibration of the assembled flight model wasperformed at the Jungfraujoch Research Station at analtitude of 3600 m. This location combines betteratmospheric ,seeing' with the beneficial side effect ofconvenient CCD cooling. The RAS was mounted on ahorizontally rotating support and could be set to scan thesky continuously over about 50° between two end-switches. Due to a longer delay at one end-switch thecharacteristic periodicity shown in Fig.2 was obtained.

# laser measurement at 670 nm

a planets (Jupiter, Saturn)

^prediction, 'sampled'with 1 pixel resolution

X stars (Aldebaran, Capella)

Fig.l: PSF rms versus angle of incidence.

Focal length adjustment was achieved by minimizing thewidth of the point-spread-function (PSF) upon varying thefocal length. Doing this for several sources with differentspectra resulted in a PSF which is independent of CCDposition, as intended (see Fig.l). The predicted width(triangles) of the PSF as a function of incidence angle,calculated with the CCD responsivity spectrum and.sampled' with 1 pixel resolution agrees reasonably with alab measurement using a red laser collimator (diamonds,with trendline).

Fig.2 shows CCD position versus time, plotted with enoughtime resolution to see the characteristic periodicity of each

object. Although a number of random events are present inthis 'raw data plot' the true celestial objects can be easilyseparated by the requirements (a) of the correct periodicityand (b) to follow a nearly straight line.

2000

c 1000 -

Fig.2: CCD position vs. time for Hipp. 25336 (mv=1.64),Hipp. 30343 (mv=2.89), Hipp. 29655 (mv=3.65),Hipp. 25428 (mv=1.65) together with Hipp. 21421('Aldebaran', mv=0.87)), Jupiter, Saturn and Hipp.23015 (mv=2.69) (from bottom to top). Theperiodic long / short time structure is characteristicfor the azimuth of each object and is due to alonger delay at one end-switch.

Stellar scintillation introduced a large amount of amplitudespread which made the determination of the PSF width andof the RAS sensitivity from weak objects (mv>l)unreliable. For Aldebaran we took 4 measurements forwhich the effective sensitivity varied between 74% and81% of the nominal prediction. We therefore consider 80%a lower limit taking into account the possibility of someresidual haze that we cannot exclude. Thus, the RASsensitivity is as predicted and the required accuracy will beachievable.

REFERENCES:

[1] R.P Lin et al, SPIE Proc. 3442, 2-12 (1998).[2] R. Henneck et al, SPIE Proc. 3765, 518-523 (1999).[3] M. Fivian et al, SPIE Proc. 4012, 518-523 (2000).

41

THE ASPECT DATA PROCCESOR (ADP) FOR THE HESSI IMAGER

A. Mchedlishvili, J. Bialkowski, M. Fivian, R. Henneck, K. Thomsen, A. Zehnder, (PSI), D. Curtis (UC Berkeley).

We describe the design and software of the HESSI Aspect Data Processor (ADP). It controls 4 CCD detector unitsand is capable to do complex processing on an input rate of 2 Mword/s, corresponding to a frame rate of 0.5 kHz.

The ADP is part of the aspect system of the HESSIinstrument [1]. It controls the front-end of the Solar AspectSystem SAS [2] and of the Roll Angle System RAS [2],makes preliminary on-board processing of CCD imagesand controls the data transfer between the front-ends andthe Instrument Data Processing Unit (IDPU).

The SAS data represent intensity profiles of a Sun image,which is intersected by a 2048 pixel line CCD. Three SASCCD are intersection the Sun image at 120°. The ADPdetermines the edges or 'limbs' of this profile by selectingN pixels above/below a selectable threshold, ignoringhowever Sunspots and spurious signals. This is done at128Hz, the resulting pixel positions, amplitudes and timesare sent to ground. The RAS scans the sky for stars imageson a linear CCD, which appear periodically as HESSIrotates at 15 rpm. Snapshots are taken every 10 ms. TheADP selects all pixels above a pixel dependent, selectablethreshold, which correspond to a star image. It ignoresextended 'high' regions caused by the Earth or Moon.Since the timing of a star is the crucial information, thepixel-corresponding amplitudes before and after thetriggering images are recorded as well. Using spatial andtime summation of consecutive pixels and images canimprove the sensitivity.

The ADP creates the different data formats, gets absolutetime from the spacecraft, synchronizes the aspect data,generates status of health information and is ready tocommunicate by messages with the IDPU at any time.The ADP has three independent parts (see Fig.l) with theprocessing power distributed accordingly. It contains a DSP(SMJ320C50GFAM50) for on-line data processing and 3FPGAs (A14100) to realize hardware level of dataprocessing and communication with the IDPU. The centralpart with the DSP also controls and monitors the activity ofthe other two parts.

After initialization, the SAS-RAS I/F acts as anindependent unit and becomes responsible for functioningof the SAS/RAS front-ends.

eventmemory

SASRASI/F

DSP

MUXBus

control

Busi/fPower and

FIFO control

JLTmemory

FIFO Powercontrol

JFigure 1: ADP general scheme.

It is driven by an internal sequencer. Upon request setevery its by incoming SAS/RAS data, the sequencer movesthe data into interface memory, starts the processes to findSolar limbs and star events and if requirements are met thepixel addresses are saved in memory. At the end of eachimage the sequencer generates an interrupt for the DSP,which does general processing and moves the formatteddata into FIFO. The FIFO can accommodate 192 images,sufficient to equalize the data flow, unless the IDPU stopsto acquire data.

The 3rd part has an internal hardware timer, which getsabsolute time from the spacecraft and passes it to the DSPto synchronize all data collection procedures.

B o o t s o f t w a r ef r o m E E P R O M

In i t i a l y z e D S Pa n d h a r d w a r e

S A Sm a g e i m a g e

Figure 2: ADP on-board software structure.

Fig.2 shows the structure of the software. After rebootingand initialisation, the DSP goes in loop and waits for flags.Flags are generated by the end of the SAS/RAS images, bymessages and FIFO operations in corresponding driverprograms, which are speed optimised and can process anyevent in -lits time intervals. To increase the processingrate, bad events are masked and ignored by the drivers.

The processing software contains four independentsubroutines, which are accessed via flags. The subroutinesare not interruptible and single event processing should becompletely finished. However, even with this limitation weachieved full limb and star event determination at 128 Hz,including periodic down-loading of the whole, raw imagesat about 40 Hz. The status of the ADP program iscontrolled and monitored by the IDPU, which can uploadnew software or update old one.

The ADP was found to work properly during all groundcalibration of SAS and RAS and during the full flight-qualification program on the assembled spacecraft.

REFERENCE:[2] M. Fivian et al, SPIE Proc. 4012 518-523 (2000).

42

THE HESSI SOLAR ASPECT SYSTEM (SAS)

M. Fivian1, W. Hajdas1, R. Henneck1, A. Mchedlishvili1, P. Ming1, K. Thomsen1, A. Zehnder1, G. Hurford2, D. Curtis2,B. Dennis3

PSI1 - UC-BERKELEY2 - GSFC- GREENBELT3

We describe the design, performance and the pre-flight calibration of the HESSI Solar Aspect System. It is basedon the optical observation of the Sun image with three linear CCDs and it will provide a position determination withaccuracy < 0.4 arcsec.

The Solar Aspect System (SAS) is part of the HESSI in-strument [1] to be launched by March 2001 at the maximumof Solar activity. In order to reconstruct images with a resolu-tion of 2 arcsec, the relative pointing of the imager has to beknown with a precision of < 0.4 arcsec (on a 1 a level) at anytime. The SAS consists of 3 identical lens/sensor subsystems(spaced at 120 degrees) and provides a high rate (< 128 Hz)of information on the Solar pointing of the rotating spacecraft(15 rpm). Each SAS subsystem is based on focussing the Sunthrough a narrow bandwidth filter (at 670 nm) onto a 2048-element x (13 /xm)2 linear CCD. For each image, there aretwo limb crossings where the Sun image intersects the CCD.After integration of the image for pa 500 /is (programmable),a digital thresholding algorithm is used to select N pixels atthe Solar limb for inclusion in the telemetry. [2]

Ground Based Measurements

For calibration, the imager with the integrated SAS sub-systems was pointed directly at the Sun. Setting an initialpointing ahead of the Sun image motion, the drift of the Sunover the FOV (pa 1 degree) gives a well defined trajectory inthe SAS image plane. Aquiring images for every integrationcycle, Sun profiles were obtained. The Solar limbs (i.e. theangle over which the intensity rises from zero to about 50 %of the maximum intensity) were fitted with an error functionadding a linear background. [3]

before fitting of geometry after fitting of geometry

50 100time [sec]

50 100time [sec]

Figure 1: The left column shows the 6 measured Solar radii(upper plot) and the size of the residual triangle (lower plot),i.e. the square root of the area of the triangle, for the nominalgeometry of the SAS lenses and CCDs. The plots in the rightcolumn show the same variables after fitting of the geometri-cal parameters of the SAS subsystems.

Calibration of the Geometry

For ideal circumstances and with exactly known posi-tions (lens optical center, CCD pixel location), the mid-perpen-dicular of the 3 chords (i.e. the straight line between the twolimbs on each CCD) would intersect in one point, the mo-mentary Sun center position. Given the accuracy of our di-mensional measurements and given thermal and mechanicalinstabilities, the mid-perpendiculars usually do not intersectin one point but form a residual triangle. The best guess forthe Sun center is then the center of gravity of the three inter-sects of the mid-perpendiculars. The size and shape of the tri-angle depend sensitively on the position of lenses and CCDs.Since every momentary Sun center is overdetermined, the sixmeasured radii and the residual triangle form a set of not self-consistent parameters, which can be used for calibration ofthe SAS pointing. Therefore, the following calibration algo-rithm has been designed [4]:

1. Assume that the first lens/CCD subsystem is in correctposition.

2. Minimize the variance of the size of the residual trian-gle by varying the two undefined angles.

3. Minimize the size of the residual triangle by varyingthe shift along the CCD of one of the two other CCDs.

4. Minimize the variance of the radii by varying the threeshifts perpendicular to the CCDs.

As shown in Fig. 1, these three minimization algorithmslead to a set of calibration parameters which is self-consistent.Using the ground based measurements, the geometry of theSAS could easily be calibrated to an accuracy of 5 arcsec forthe angles between the CCDs and 1.5 yum for the componentsof the CCD positions. Therefore, the relative pointing is ex-pected to be better than 0.2 arcsec. The offset to the telescopeaxis and thereby the absolute pointing will be drawn from ourdimensional measurements of all features of the imager.

REFERENCES

[1] R. P. Lin et al, SPIE Proc. 3442,2 (1998).

[2] R. Henneck et al, SPIE Proc. 3765, 771 (1999).

[3] M. Fivian et al, PSI Ann. Report I, 39 (1999).

[4] M. Fivian et al, SPIE Proc. 4012, 518 (2000).

43

FABRICATION OF TRANSITION EDGE SENSOR TES

E. C. Kirk1, J. E. Olsen1, Ph. Lerch1, A. Zehnder1, H. R. Ott2

P S ^ - E T H ZURICH2

This contribution describes the fabrication process of theTES photon detector [1]. The process [2] takes place upon a1 mm x 1 mm x 250 nm thick pre-fabricated silicon nitridemembrane. With cautious handling, the membrane with-stands most normal fabrication steps, e.g. heating to 700degrees C, photoresist spinning, patterning and development,film deposition and wet etching. The fabrication process maynot include steps which touch the membrane (contact lithog-raphy), ultrasonic cleaning or strong jets of air or liquid.

The Mo and Au thermometer bilayer is sputter-depositedacross the entire chip surface in an ultra-high vacuum sys-tem. Mo is a superconductor with a transition temperature(Tc) of 0.92 K. This can be tuned to the lower Tc requiredfor the thermometer by the addition of a layer of Au. Thefilm thicknesses we have used in these devices are 40 nm ofMo and 180 nm of Au. The Mo is deposited at 700 degreesC, after which several hours are required to bring the sub-strate down to room temperature before the Au is deposited.The quality of the interface between the two metals is criti-cal for the strength of the proximity effect and therefore theTc of the thermometer. To achieve a clean, reproducible in-terface, the surface of the Mo is sputter-cleaned immediatelybefore starting the Au deposition. Transmission electron mi-croscopy of a cross-section through the bilayer shows theroughness of the thinnest film (Mo) to be a few percent ofits thickness. A constant film thickness is important for thesharpness of the transition.

The bilayer is etched away to leave a thermometer in thecentre of the membrane.

To connect to the thermometer, superconducting leadsmust be deposited on the chip. The preferred interconnectmaterial is Nb, because its Tc is well above that of the ther-mometer. In order to deposit only where interconnects arerequired, the thermometers and other surface areas are pro-tected by a photoresist mask. At this stage, the excellent ther-mal isolation properties of the silicon nitride membrane, es-sential for functioning of the TES device, present a problem.Nb has too high a melting point to be deposited by thermalevaporation and must be sputtered, a process creating con-siderable heat. Keeping the membrane below the tempera-ture at which the photoresist mask deforms is a challengingtask. Thermally-evaporated Al contacts present fewer depo-sition problems and are currently in use, although they areless satisfactory because of their lower Tc and the step cov-erage where they meet the thermometer.

If the energy of the photon to be detected is high enoughfor it to pass through the device, it may be necessary in a fi-nal processing step to add an absorber in the form of a very

t. -?•:.

Figure 1: Picture of a TES device on its silicon ni-tride membrane: a=thermometer+absorber (smaller square),b=contacts, c=membrane, d=substrate.

Thermometer: Mo/Au bilayer. Size: 420 (lm X 420 (lm X 40 nm Ms,

T c « 120mK, Cv O.epJ/K

Sypereersdueirsg sontaof tay«

_ ™

BUJ

Figure 2: Schematic cross-section of the TES device.

thick (approaching 1 yum) square of Au covering most of thethermometer. For processing reasons this is best not done inthe initial deposition. If an absorber is required, the Mo filmthickness should be chosen such that the maximum Au thick-ness is required to tune it to the final Tc. Figure 1 in [1] showsthat, as the Au thickness is increased, the effect on the Tc ofadding further Au is reduced. Otherwise, the area under theabsorber has a lower Tc than the surrounding thermometermaterial, reducing the sharpness of the measured transition.

REFERENCES

[1] J.E. Olsen, E.C. Kirk, Ph. Lerch, A. Zehnder, H.R. Ott,Sci.Rep.2000,1, this Volume.

[2] E.C. Kirk, Ph. Lerch, J. Olsen, A. Zehnder, H.R. Ott,Nucl. Instrum. Meth. A 444, 201 (2000).

44

ARRAYS OF SUPERCONDUTING PHOTON DETECTORS

Ph. Lerch1, E. C. Kirk1, J. E. Olsen1, A. Zehnder1, H. R. Ott2

P S ^ - E T H ZURICH2

Superconducting tunnel junctions (STJ) have reached per-formances that allow their use in scientific instrumentation.With soft x-rays, individual pixels have shown energy re-solved photon counting with an energy resolution approxi-mately an order of magnitude better [ 1 ] than the one obtainedwith state-of-the-art Ge detectors. Count rates up to 104 cpshave been demonstrated as well. At lower energy, they com-bine a modest energy resolving power with fast response andhigh detection efficiency from the NIR to the EUV band.This makes this type of detector an interesting alternative tothe present generation of detectors used in UV/optical astron-omy, such as CCDs and micro-channel plates.

In order to fully exploit the unprecedented sensitivity ofthis class of detectors, one wishes to be able to pack severalpixels into arrays in order to build an imaging instrument inwhich every pixel has its intrinsic resolution in energy. Atechnology demonstrator including an array of 6 x 6 pixelswith parallel readout has been built by an ESA collaboration[2]. Each pixel counts single visible photons with a resolu-tion of about 10 % at 2 eV.

An STJ is an active device that does not store its infor-mation. Thus, unlike pixels used in CCD cameras, the par-allel readout of N x N pixels requires N2 channels. Sinceevery pixel is operated in a deep cryogenic environment, thethermal load imposed by wiring all the pixels to their read-out channel is going to limit the maximum number of chan-nels. Several readout approaches like the matrix connectionscheme, frequency or time multiplexing are currently inves-tigated worldwide.

By separating the photon collection from the signal mea-surement functions within the device, we hope 1) to reducethe number of STJs without reducing the photon collectionarea in the same proportion and 2) to limit the influence of(still not completely understood) energy resolution degradingprocesses that gain in importance with energy. We built 2 x 8arrays and tested individual elements of them. Each elementis a ID-strip of superconducting material (Nb or Ta) whichacts as photon absorber. The energy of an absorbed photongenerates an electric charge by the break-up of Cooper pairs.This charge diffuses in the absorber, is collected - and am-plified - by 2 STJ devices microfabricated at each end of thestrip. Each STJ delivers a signal proportional to a fraction ofthe "primeval" electric charge that is dependent on the posi-tion of impact in the absorber. Coincidence measurement ofthese two signals enables to measure the energy as well as theimpact location on the absorber [3]. STJs, which have about100 pF of capacitance, are readout by charge sensitive am-plifiers that have best equivalent noise charge of about 1000e. We measured a responsivity of 2500 e/eV at 2 eV (red)with a Nb absorber and obtained an energy resolution of 45eV together with a position resolution of 5 microns on a totallength of 200 microns at 6 keV.

Figure 1: Optical micrograph of a 2 x 8 superconducting tun-neling junction system. The 400 /im long strip absorbers, in-clinated at 45 degrees, are made out of high quality Ta or Nb,the 30 by 30 yum2 junctions placed at each end of the stripsare made out of Al/AlOx/Al/Nb.

One disadvantage of the readout scheme based on thecharge division mechanism is its intrinsic low speed. Thediffusion rate D of quasiparticles in Ta [4] is only 8 to 10cm2/sec. The precise origin of this low diffusion rate remainsunclear. A photon absorbed near one end of a strip of totallength L generates quasiparticles. A large fraction will beregistered by the closest junction, another fraction needs atime r = L2 /D to reach the other STJ where it generates the"coincidence" signal. Using L = 0.1 cm, we obtain r « 1mSec, equivalent to a count rate of 1 kHz.

REFERENCES

[1] S. Friedrich, et al, IEEE Transactions onApplied Superconductivity 9, 3330 (1999).

[2] S. Kraft, P. Verhoeve, N. Rando, A van Dordrecht,A. Poelaert, R. den Hartog, A. Owens, M. Bavdaz,A. Peacock, Nucl. Instrum. Meth. A 436, 238 (1999).

[3] E. C. Kirk, Ph. Lerch, J. Olsen, A. Zehnder, H. R. Ott,Nucl. Instrum. Meth. A 444, 201 (2000).

[4] Th. Nussbaumer, Ph. Lerch, E. Kirk, A. Zehnder,R. Fiichslin, P. F. Meier, H. R. Ott,Phys. Rev. B 61, 9719 (2000).

45

TRANSITION EDGE SENSORS FOR ASTRONOMICAL APPLICATIONS

J. E. Olsen1, E. C. Kirk1, Ph. Lerch1, A. Zehnder1, H. R. Oti2

PSI1 - ETH ZURICH2

We are developing superconducting transition edge sen-sors (TES) for the energy resolved detection of single pho-tons in the energy range from visible to X-Ray. The bestresolution reported with similar /^calorimeters is 4.5 eV at 6keV [1]. These devices are operated around Tb ss 100 mK.

When a photon of energy E1 hits the absorber of knownheat capacity Cy, its energy is transformed into heat. Athermometer is then needed to measure the temperature riseAT = E7/Cy proportional to the collected energy. Thesharp transition (a = dlogR/dlogT m 100) of a supercon-ductor provides such a sensitive thermometer in a small tem-perature range (pa 2 mK). We use superconducting Mo/Aubilayers in which the transition temperature of Mo (Tc = 920mK) has been reduced to about 120 mK by proximity effect[2]. Fine tuning of the deposition parameters is required toestablish reproducible and sharp transitions (figure 1). As analternative, an Ir (bulk Tc = 12 mK) monolayer was used[3].

The bilayer is deposited on a 250 nm thick S13N4 mem-brane (see figure 1 b) in [4]) that provides a weak thermallink (G pa nW/K) to the heat bath (substrate). After an im-pact, the detector returns to equilibrium temperature with itsintrinsic time constant To = Cy/G. To detect higher energyphotons, a Au absorber in good thermal contact with the bi-layer needs to be deposited on top of it.

8 0 0

6 0 0

4 0 0

2 0 0

i \

: \j-

-

H Mo-Au: ds =

A Mo-Au: ds =

™h Mo-Au: ds =

guide1 i i i i i i

fml 1

a

\

m

43

43

51

3 0

2 0

1 0

•

•

1 1 8

Xntti

ntti

nm

\

120 122 124 ;T [mK] ;

•j

X ^ :

50 100 150

d (Au) [nm]2 0 0

Figure 1: Transition temperature of a Mo/Au bilayer as afunction of Au thickness. The inset shows the transition asmeasured with SQUID readout cicuit.

By biasing the detector with a voltage instead of the clas-sical current bias, an electro-thermal feedback (ETF) is achie-ved. For that purpose, a shunt resistor is placed in parallelwith the detector, as shown in figure 2. Its resistance mustbe an order of magnitude smaller than the bilayer's normal

'bias

SQUID-Array Readout

FVFUT=O II I CO

Sensor

2.2 K

ShuntIV 2mQ

100 mK

Figure 2: The TES SQUID readout circuit.

resistance RN ~ 50 mtt. A significant part of the currentflows through the shunt and if Tb < Tc, a dynamical equilib-rium is established. The power permanently dissipated in thethermometer flows to the substrate through the heat link G.This operation mode is called ETF: the increase of the resis-tance of the device due to the deposition of Ey is registeredas a decrease (V = cst) of the current flowing through thesensor. The device will rapidly return to its equilibrium tem-perature. The effective time constant that can be achieved ismuch smaller than To.

ETF requires a low-resistance readout scheme, achievedwith superconducting electronics, e.g. Superconducting Quan-tum Interference Devices (SQUID).

The electrical performances of bilayers deposited on mem-branes were measured, however stray impedances (sa 30 mfl)in the superconducting detection circuit precluded irradiationexperiments to be successfully performed.

REFERENCES

[1] K. D. Irwin, G. C. Hilton, J. M. Martinis,S. Deiker, N. F. Bergren, S. W. Nam, D. A.Rudman, D. A. Wollman,Nucl. Instrum. Meth. A 444, 185 (2000).

[2] U. Nageletal.J. Appl. Phys. 76 (7), 4262 (1994).

[3] M. Frank, D. Dummer, S. Cooper,J. Igalson, F. Proebst, W Seidel,Nucl. Instrum. Meth. A 345, 367 (1994).

[4] E. C. Kirk, J. E. Olsen, Ph. Lerch,A. Zehnder, H. R. Ott,PSI Sci. Report 2000,1, this Volume.

46

OPERATING OF THE PROTON IRRADIATION FACILITY - CONCISE SUMMARY

W. Hajdas, K. Thomsen, A. Zehnder (PSI), R. Harboe-Sorensen (ESA-ESTEC)

All PIF experiments in the year 2000 were conducted in two new areas: NEB and PKC2. Beam activities utilizedmore than 90 shifts giving a 10% increase comparing to 1999. Different experiments were grouped into 42 testblocks resulting in 77 proton and gamma-source exposure days. Majority of tests aimed to qualify and calibratedevices and radiation monitors for forthcoming satellite missions like HESSI, INTEGRAL, PROBA and ROSETTA.

PIF experiments in the year 2000, similarly as in 1999,extended through a long period from 2 February to 15December. Researches from 17 institutes, industrial labs,and space agencies were involved in the irradiation tests.These were arranged into 42 irradiation blocks of variableduration within which about 25 different types of tests andcalibrations were performed. It resulted in more than 90proton beam shifts distributed over about 70 days. Up tonow it is the largest number of shifts in the whole PIFactivity record. It prominently extends behind the originallydesigned upper limit of the beam time set to 60-70 shifts.The most important novelty in the year 2000 was that PIFexposures utilized two new irradiation areas. The high-energy test site moved to the PKC2 area giving room forconstruction works of the PROSCAN project. Similarly,the parasitic use of the OPTIS was replaced by a new standin the NEB area. It made utilizing of beams much easier,prevented interference and lowered waiting time for the set-up. Obviously, the future goal is to merge both low andhigh-energy site together into a single one. This facility willbe more user and operator friendly and cover the wholerange of energies from 0 to 250 MeV. First steps arealready in a design phase in frame of the new biomedicalcyclotron project (PROSCAN) and its test areas.

Table 1: Beam time and test area utilization by PIF

Beam blocks

Shifts

PKC2

22

64

NEB

14

25Y2

"Co

6

6Y2

Total

42

92i/2

IRRADIATION EXPERIMENTS 2000

The most important trend seen in PIF activities in the year2000 is a larger than before participation of groups fromSwitzerland. They represent about a complete spectrum ofconceivable users starting from universities - University ofBern through scientific institutes as CERN and industrythat was represented by ABB and Contraves Space AG. Asusually, the largest amount of beam time was reserved forEuropean Space Agency (ESA) related activities. It wasmainly used to characterize several electronic devices andcalibrate new generation of radiation monitors - SREMs.Several missions either use them already (STRV-lc) or willplace them on board for dose and particle spectrameasurements (INTEGRAL, PROBA, ROSETTA, ISS).The next large activity is motivated by background studiesof the HESSI satellite and relates with spacecraft materialsactivation during passages through the South AtlanticAnomaly. Together with NASA-GSFC and BerkeleyUniversity, the PSI, represented by Laboratory for

Astrophysics, is preparing the HESSI launch in March2001. Industrial research labs also carried out several largeexperiments. The ABB Semiconductors tested sensitivity ofpower devices for upsets induced by ionizing particles onearth. The Marconi Applied Technologies verified numberof Charge Coupled Devices (CCDs) to find best candidatesfor space usage. French firm TRADE, contracted by ESA,irradiated and characterized hundreds of optocouplersforeseen for e.g. telecommunication satellites. In addition,device functionality quick testing (SREM) with 60Co sourcebecame a routine extension to standard PIF operation.

Table 2: Selected PIF experiments

• SREM radiation monitor calibration

• SRAM/DRAMs proton SEU characterization

• Radiation damage of various CCDs

• Dose effects in photo-, laser-, and avalanche diodes

• FPGA total dose and SEE testing

• Optocouplers rad-hardness determination

• Activation measurement of Ta, Ti, Cu, W, and Al

• Radiation damage in crystal frequency shifters

• Radiation effects in power MOSFETs

• Performance studies of PC error correcting software

• Radiation damage in novel solar cell technologies

• Dose effects in power supplies for LHC

Table 3: Users and collaborations

No

1

2

3

4

5

6

7

8

9

10

11

12

13

Research Institution

ESA / ESTEC, The Netherlands

PSI / GSFC / Berkeley University

ETH, Zurich

University of Bern

ABB Semiconductors, Lenzburg

Contraves Space, Zurich

CERN, Genf

HIREX, France

TRAD, France

ALCATEL, France and Norway

ASTRIUM, France and Germany

SAAB, Sweden

Marconi Applied Technologies, UK

47

STANDARD RADIATION ENVIRONMENT MONITOR SREM AS A SUCCESSFULEXAMPLE OF TECHNOLOGY TRANSFER AND INDUSTRIAL COOPERATION

W. Hajdas, P. Biihler, N. Schlumpf, A. Zehnder (PSI), L. Adams, E. Daly, P. Vuilleumier (ESA),HJ. Schneider (CSAG)

The Standard Radiation Environment Monitor (SREM) was developed under a partnership of European SpaceAgency (ESA), PSI and Contraves Space AG (CSAG). Successful teamwork resulted in production of 10 devicesunder an ESA contract. First SREM is by now in space onboard of the STRV-lc satellite and future missions arealready planned. PSI is responsible for response modeling as well as calibration of the whole production batch.

Remarkable achievements of first Radiation EnvironmentMonitors (REMs) that flew on MIR and STRVlb satellitesencouraged continuation of the program and furtherdevelopment of such detectors. ESA issued a bid withspecification requirements for a new monitor while PSIfabricated its reduced model and conducted preliminarytests with particles. Several industrial firms contacted PSILAP acquiring technological details needed for monitordesign and construction. The best proposal came from theSwiss firm Contraves Space AG and was selected by ESA.Near locations of PSI and CSAG allowed for very frequentand productive contacts. The PSI provided expertise infield of electronic design, detector optimization as well asresponse modeling and tests. Close teamwork carriedthrough the whole development phase when our teamattended weekly progress meetings. Contraves fabricatedfirst model of SREM in November 1996 - see Photo 1.

Photo. 1: SREM Engineering Model

The most important improvements in the new SREMdesign are: smaller weight and dimension, lower powerconsumption and capability of detecting very high particlefluxes. The proton and electron spectroscopy is furtherrefined and, in addition, the monitor provides directionalsensitivity. Programmable alarm flags for high/low doserates inform the mission about radiation hazard while a setof external RADFETs enables dose determination at sevendistinct satellite locations.

First engineering and pro-to-flight exemplars of SREMswere intensively tested and characterized by CSAG and,

with respect to requirements of radiation dosimetry andspectroscopy, by PSI. Calibrations were performed usingPSI Proton Irradiation Facility (PIF) and the results werecompared with theoretical response obtained with extensiveMonte Carlo simulations

After successful completion of the first part of the project,ESA decided to use the 1st SREM on board of the STRV-lc mission. The satellite was launched in November 2000by UK Defense Research Agency. In addition, PSI LAPentered a scientific collaboration of the ESA INTEGRALproject (International Gamma-Ray AstrophysicsLaboratory) scheduled for 2002. The INTEGRAL SREM -IREM was quickly adapted to the mission requirements byCSAG and PSI and is already delivered to the prime projectcontractor - ALENIA SPAZIO - for integration.

Because ESA considered having SREMs as a basicradiation monitoring equipment for its missions, a purchaseorder of 8 SREMs was issued to CSAG. PSI LAP wassubcontracted with a task of calibration and verification ofperformances. First two devices for PROBA andROSETTA were already tested. The PROBA - Project forOn-Board Autonomy - spacecraft will fly in summer 2001as a part of the ESA Technological DemonstrationProgram. Another calibrated SREM will conduct radiationmeasurements on board of the ROSETTA mission to besent in 2003 to study the nucleus of comet Wirtanen. OtherESA missions with SREMs are shortly listed below:

• SMART-1 - 1st European mission to the Moon flyingwith use of the Solar Electric Propulsion (2003).

• Mars Express - 1st European flight to Mars (2003)• FIRST - infrared laboratory studying how stars and

galaxies were born (2007)• Mercury Orbiter - (2009)• International Space Station - still under discussion in

frame of the Technology Exposure Facility project

Beside activities related to hardware qualification andcalibration in frame of CSAG-PSI contract, PSI LAP begandetailed preparations towards analysis of data from space.It includes improved SREM response functions in whichthe satellite mass distribution is taken into account.Moreover, software analysis packages are developed for theIntegral Science Data Center in Genf. There is also a firminterest in development of yet another family of radiationmonitors by ESA-CSAG and PSI collaboration. The primegoal is to design a minimum intrusive, light instrument withvery powerful spectroscopic capabilities.

48

COMPARISON OF CALIBRATION RESULTS FROM PROBA STANDARDRADIATION ENVIRONMENT MONITOR WITH MONTE-CARLO SIMULATIONS

C. Eggel, W. Hajdas, A. Zehnder (PSI)

The Standard Radiation Environment Monitor (SREM)for PROBA satellite was calibrated at the Proton IrradiationFacility (PIF) in PSI. For measurements of proton spectra and angular distributions, the detector suite wasirradiated with protons at various energies and different angles. The detector response was compared withcorresponding Monte Carlo Simulations. The agreement between laboratory results and theory is very good.

SREM - Standard Radiation Environment Monitor wasdeveloped in partnership between ESA-PSI and ContravesSpace AG (Zurich). First monitors e.g. for ROSETTA,PROBA and STRVlc missions are already manufacturedby Contraves, calibrated by PSI and delivered to ESA. TheSREM is a space dedicated detector system for on-boardparticle spectroscopy and dosimetry. Its calibrations areperformed using the PSI Proton Irradiation Facility inPKC2 Area, and gamma and electron radioactive sources.They provide a final check of instrument detection systemqualifications, give ultimate verification of the SREMresponse function and provide input for its adjustment. The1st objective is to measure monitor's parameters: energythresholds, detector area and dead time corrections and the2nd one is to provide a reference data for full set of energiesand incoming angles. It is done using the same particlesand spectra as in space and results in having an accuratemodel of the SREM response. An accurate monitor'scomputer model was constructed to compute full responsematrix for protons, electrons and heavier ions for the wholeenergy range met in space.

I. TEST FLOW AND CONFIGURATION

Essential parts of the calibration procedure are shortlylisted below.1. Short Functional Test, "Co and Cosmic Ray check2. Low energy response at 0°3. Thresholds determination

4. Detector area measurement5. Dead-time determination

6. Full response calibration/set of energies and anglesThe high-energy tests are performed with protons usingfive energies in the range 50.8 to 300 MeV whilecalibrations at nine lower energies, 12.5 MeV to 60 MeV,are done using 60 MeV initial energy setup. For the 300MeV setup the detector was irradiated at 12 angularconfigurations covering the whole range polar angles0=(O° -180°) and selected azimuth angles (0°-270°). Thelow energy setup was used for measurements from the frontonly as the collimators cut off protons coming from a side.For flux normalization purposes, measurements at differentenergies are performed with two plastic detectors inpositions corresponding to SREM detector heads, exactlyas during calibration runs. Ionization chambers monitor theproton beam current at the same. It allows for calculationsof normalisation factors so one can relate SREM sealerresponse to the corresponding proton fluence.

II. SIMULATION PROCEDURE

Monte Carlo simulations of the SREM response areperformed using CERN code GEANT. Simulations arecarried out for exactly the same energies as in theexperimental case and with sufficient statistics. Angularposition of the SREM is changed to cover the whole set ofproton incidence angles. Detector areas were first re-measured during the experiment and their values were setfor simulations. Separate computations were done to findout the fluency at the positions of the detectors heads aswell as at the beam center in order to assure the sameconditions as in the experiment. By these means, thecorrectness of computational setup could be verified andSREM sealers values normalized properly.

III. RESULTS COMPARISON

The agreement between experimental data and simulationresults is in general very good - see Fig. 2. Though, in afew cases 10-20% differences can be seen. It is due to fine-tuning of SREM discriminators and its material bulkdistribution as well as beam uniformity and divergence.

Simulation 300 MeV / 0 degExperiment 300 MeV / 0 deg

TC1 SI 2 513 514 515 TC2 525 01 C2 C3 C4 TC3 532 533 S34

Sealer

Fig. 2: Experiment compared to Monte Carlo Simulationfor Proba SREM at energy 300 MeV and angle 0°.

V. CONCLUSIONS

The numerical simulations of the detector response and thecomputer model of the SREM have proven to beadequately exact. They can be used to obtain full SREMresponse matrix. In addition, they greatly support and assistin refined analysis of data from space. Simulations are nowcarried on for the application of SREM on boards ofINTEGRAL and PROBA satellites.

49

Labora to ry forMuon Spin S p e c t r o s c o p y

Foreword

Superconductivity

Magnetism

Semiconductors and Liquid Crystals

Chemistry

Research and Development with Low Energy Muons

50

LABORATORY FOR MUON-SPIN SPECTROSCOPY

D. Herlach

Research at the Laboratory for Muon-Spin Spectroscopy(LMU) uses positive and (occasionally) negative muons (p+,H~) as local magnetic probes in matter. The experimen-tal techniques referred to as [iSR (for Muon-Spin dotation,Relaxation, Resonance or Research) are universally applica-ble since the polarised muons available at meson factoriessuch as the PSI proton accelerator complex can be implantedin any material.

The muon is a very sensitive probe of both static and dy-namic magnetic properties of materials: due to its mean life-time of 2.2 /is and a gyromagnetic ratio of 2?r-135.5 MHz/T,the accessible magnetic fields and widths of field distribu-tions range from ~ 10 /zT to several Tesla, and the time scalesfor dynamic properties from pico- to milliseconds. As a'light isotope' of the proton (mM = 0.1 lmp) the yU+ can formthe hydrogen-like atom Muonium (/i+e~) which may substi-tute for hydrogen in insulators and organic materials, provid-ing a very sensitive spin label.

At present, our laboratory maintains and further devel-ops six state-of-the-art /iSR instruments: three for surface-muons (4.2 MeV /i+) , one for decay-channel muons (7-60MeV / i + or yU~), an avoided-level-crossing (ALC) spectrom-eter, and the unique low-energy-muon beam and spectrome-ter (LE-/xSR) for fj,+ of tunable energy between 0 and 30 keV.Two instruments are permanently installed at the TTM3 beamwhich is equipped with a spin rotator and a beam-sharing de-vice (MORE) that allows one to extract one muon from thebeam upon request of one of the spectrometers, thus provid-ing unique sensitivity to small magnetic field differences andextending the measurable characteristic times into the mil-lisecond range at 1 ns time resolution.

Five of the instruments are operated as a User Facilityfor which the yuSR group provides scientific and technicalsupport. In 2000, 65 research proposals of groups from PSI,Swiss universities and from abroad have been active, usingroughly 50% of the total beam time allocated to approvedexperiments at the target M and E beam lines. About 225scientists from 96 institutions in 21 countries are involved inthe /uSR proposals.

Together with collaboratoring groups from the Universi-ties of Birmingham, Konstanz and Zurich, the Technical Uni-versity of Braunschweig and ETH Zurich - some of whomalso provide funding and manpower and participate in the de-velopment of the LE-//SR technique - the LEM group usestheir unique beam and spectrometer to apply the advantagesof/xSR to thin films and layered structures, near surfaces andas a function of implantation depth on a nm scale.

In 2000, a proposal and design for a new surface-muonbeam to be installed in the present yuE4 channel has beenworked out. This beam - which is expected to provide tentimes the muon flux of the present TTE3 beam - has primarily

been designed to fully exploit the potential of the LE-yuSRtechniqhe but will also be available for other experiments re-quiring highest intensity polarised /x+ beams. The projectfound strong support from the PSI Research Commission(FoKo) and has been approved by the PSI directorate. Theconstruction of this beam, which is planned to be installed in/xE4 in 2003, will be funded to a substantial proportion bythe German Mininistry for Education and Research (BMBF)through the Technical University of Braunschweig and theUniversity of Konstanz, and by the British EPSRC throughthe University of Birmingham.

In October the LMU reported to the plenary FoKo. Theresult of the evaluation was very positive. In particular, thecommission acknowledged the large number of high-qualityyuSR publications, though recommended to take measures forkeeping track of all publications based on work using theyuSR facilities. The FoKo appreciated the presented scien-tific highlights and the demonstration of the complementaryrole of /uSR vis a vis of other experimental techniques, suchas neutron scattering and NMR, and particularly acknowl-edged the original development of bulk /iSR using muons onrequest. The availability of low energy muons opening /iSRto the investigation of surface problems, thin films, layeredstructures, magnetic nanoparticles etc. was highly appreci-ated.

The user programs involve a large variety of topics incondensed matter research. The majority of the proposals isdevoted to magnetism and superconductivity. Effort is put onthe study of new materials such as high spin molecules, lowdimensional magnetic systems, organic superconductors, con-ducting polymers, liquid crystals and novel solar cell materi-als.

During the year 2000, more than one hundred articlesbased on //SR work performed at PSI have been published,of which six in Physical Review Letters. Major achievementshave been obtained in the determination of microscopic prop-erties of superconductors. In particular, evidence has beenfound for ferromagnetic-fluctuations mediated superconduc-tivity in UPt3 and for unconventional superconductivity in(U,Th)Bei3. Another highlight is the observation of a largeoxygen-isotope effect on the magnetic penetration depth inunderdoped Ya;Pri_a;Ba2Cu3O7_5. Low energy muons havebeen used for a direct determination of the depth-resolvedprofile of the magnetic field entering a superconductor (bothinside and outside of the sample) with a few nanometers res-olution. But as the reader may see by going through the fol-lowing 41 reports, there are many other significant contri-butions of yuSR to topics of current interest, some of whichclosely related to environmental and technological problems.

51

OXYGEN ISOTOPE EFFECT ON MAGNETIC PENETRATION DEPTH IN UNDERDOPED

YxPr1_xBa2Cu3O7_ (5

A. Shengelaya1, R. Khasanov1'2, H. Keller1, E. Morenzom2, K. Conder3, and I. M. Savic4

RA-90-07, ZURICH1 - LMU/PSI2 - LNS/PSI3 - BELGRADE4

There is increasing evidence that a strong electron-pho-non coupling is present in cuprates [1], which may lead to theformation of polarons (bare charge carriers accompanied bylocal lattice distortions) [2]. However, it is not clear whetherthese normal-state polaronic carriers condense into Cooperpairs. To show that this occurs, it is necessary to demon-strate that the effective mass of supercarriers m* depends onthe ionic mass M. In conventional superconductors, only the'bare' charge carriers condense into the supercarriers, and thesupercarrier mass is essentially independent of M.

According to the London model the magnetic field pen-etration depth A in superconductors is proportional to theeffective mass m* of the superconducting carriers. Thusthe isotope dependence of m* can be determined from theisotope dependence of the penetration depth. Previous ex-periments indicated that in cuprate superconductors A is in-deed isotope dependent. However, in all these experiments Awas extracted indirectly - from the Meissner fraction [3], andfrom the reversible part of a torque magnetometry signal [4].

l . C

The /uSR technique is one of the most direct and accu-rate methods to determine the penetration depth in super-conductors. Detailed /iSR investigations of polycrystallinehigh-Tc superconductors have demonstrated that A can beobtained from the gaussian muon spin depolarization ratea(T) ~ 1/A2(T), which probes the magnetic field distri-bution in the mixed state. For the highly anisotropic super-conductors (like HTSC-cuprates) A is solely determinated bythe shortest penetration depth Aa& and according to [5]

\ab{nm) = 224/. (1)

We used the transverse-field /iSR technique to measure theisotope dependence of A in Yi_xPrxBa2Cu3O7 samples withtwo oxygen isotopes 16O and 18O.

Fig. 1 shows the temperature dependence of the transverse-field muon spin depolarization rate a for Yo.ePro.4Ba2Cu307sample with two oxygen isotopes. This sample has a Tc of45 K. One can see that below Tc the 16O sample has a higherdepolarization rate compared to the 18O one. We also mea-sured a sample with smaller Pr concentration x=0.3, wherethe isotope effect also exists, but it is smaller compared tothe x=0.4 sample. The calculations of the isotope shift in aand correspondingly in A give Atr/tr = AA~6

2/A~62 = 3.7%

for Pr 0.3 and 6.9% for Pr 0.4 respectively.

o.d

Figure 1: Temperature dependence ofthe/iSR depolarizationrate a for the 16O and 18O samples of Yo.6Pro.4Ba2Cu307.The back exchange data (x) demonstrate the intrinsic char-acter of the oxygen isotope effect. The right vertical axisshows the value of Aa&, calculated from the formula (1).

Our experiments are the first direct demonstration of anisotope effect on the magnetic penetration depth in cupratesuperconductors. This implies that lattice vibrations play animportant role in the occurence of high-Tc superconductivity.

In a further step of research we propose to continue thestudy of the oxygen isotope effect on the penetration depth inYi_a;Pra;Ba2Cu3O7 as a function of Pr doping, and to mea-sure directly the magnetic penetration depth in the Meissnerstate of thin films by low energy yuSR. Such experiments canprovide crucial information about the nature of the doping-induced charge carriers in cuprates.

REFERENCES

[1] Proc. Int. Workshop on Anharmonic Properties oTc Cuprates edited by D. Mihailovic, G. Ruani,E. Kaldis, and K. A. Miiller, 118-146(World Scientific, Singapore, 1994).

[2] A. S. Alexandrov and N. F. Mott,Int. J. Mod. Phys. 8, 2075 (1994).

[3] G. M. Zhao et al., Nature 385, 236 (1997).

[4] J. Hofer et al., Phys. Rev. Lett. 184, 4192 (2000).

[5] P. Zimmerman et al., Phys. Rev. B 52, 541 (1995).

52

MAGNETISM IN TETRAGONAL La2_x_ySrxREyCuO4

H.-H. Klaufi1, W. Kopmann1, D. Baabe1, D. Mienert1, H. Luetkens1, F. J. Litterst1, M. Hucker2, B. Buchner2

RA-93-05, BRAUNSCHWEIG1 - KOLN2

In this proposal we study the magnetic phases in the RareEarth doped high-Tc system La2-xSrxCu04 (LSCO). Thepartial substitution of the La-Ion with Nd or Eu leads to astructural modification at low temperatures: the low temper-ature orthorhombic (LTO) phase is replaced by a tetragonalphase (LTT). In the LTT phase a new kind of incommen-surate stripe like magnetic order was observed [1]. /z+SRas an outstanding method to observe inhomogeneous localmagnetic order has played an important role, e.g. the ex-istence of magnetic order in La2-x-ySrxREyCu04 in anextended carrier doping range (x < 0.20) has been shownin this project and the magnetic phase diagram of the LTTphase has been established [2, 3]. The structural transitionfrom LTO to LTT is accompanied by a change from a su-perconducting to a magnetically ordered ground state withnearly identical transition temperatures. This can be inter-preted as evidence for a common coupling mechanism.

The aim of the experiments in 2000 was to clarify thereason for the charge carrier doping dependent change fromstripe like magnetism to superconductivity. In Lai.g_xEuo.2SrxCuO4 this is observed at a; = 0.20. One possible expla-nation is the gradual decrease of the LTT tilt pattern of theCuOg octahedra with increasing Sr-concentration causing acrossover to the superconducting phase at a Sr concentrationx corresponding to a critical tilt angle [4]. Alternatively theintrinsic charge carrier doping itself might be responsible. Ina comparitive study of different high-T^-systems a commonquantum critical point has been extracted in a number of ex-perimental properties at a hole concentration of 0.19 [5].

We studied a series of La2-x-ySrxREyCu04 samplesat the GPS spectrometer with a fixed carrier concentration ofx = 0.20 and different Europium content y between 0.10 and0.23 thereby increasing only the LTT tilt angle of the CuO@octahedra. We studied the relaxation rate in 2kG transversalfield (TF) experiments as a measure of the magnetic penetra-tion depth A in a bulk superconducting phase and of a criticalmagnetic relaxation at a magnetic phase transition. Figure 1shows the gaussian relaxation rate a oc A~2. For y =0.10 anincrease of a below 22 K indicates the bulk superconductingstate with a small magnetic penetration depth. For increasedy a is reduced between 5 and 20 K indicating a larger fieldpenetration or a reduced superconducting carrier density. Be-low 5 K a strong increase of a is due to magnetic relaxation.This relaxation is strongly enhanced in systems with y = 0.20and 0.23. These data show that it is indeed possible to tunethe electronic behavior from susperconductivity to magneticorder by increasing the LTT tilt angle.

In addition ZF-measurements have been performed to de-rive a sublattice magnetization from the spontaneous muonspin precession in a magnetically ordered state. Figure 2shows some Fourier spectra at base temperature (1.8 K). Thewidth of the observed static local field distribution increases

0 25 30 35 40

Temperature (K) Temperature (K)

Figure 1: Gaussian relaxation rate a in 2kG transverse fieldon Lai.8-ySro.2EuyCu04.

with a stronger Eu-doping. Only for the samples with y = 0.20and 0.23 a nonzero spontaneous muon spin precession couldbe fitted to the time spectrum.

(a.

(L)T 3

H

ft

1(1)

urx

0

iH

A

1 . 5 :

1

0 . 5 •

n

INi: \

i i \

^ \

% *•**. X

y=Y=Y=

. 1 0

. 1 7

. 2 0

. 2 3

X

•*+

-

Q)PS

4 6 8Frequency(MHz)

10

Figure 2: Fourier transforms of zero-field //SR spectra mea-sured on Lai.8_ySro.2EuyCu04 at 1.8 K.

In conclusion the presented data clearly prove that phe-nomenologically the LTT tilt angle of the CuO6 octahedra isresponsible for the change from susperconducting to mag-netic ground state. A quantum critical point at a specificcharge carrier concentration x is not observed in La2- x - y Srx

Eu yCu0 4 .

REFERENCES

[1] J. M. Tranquada et al., Nature 375, 561 (1995);M. von Zimmermann et al.,Europhys. Lett. 41, 629 (1998).

[2] W. Wagener et al., Phys. Rev. B 55, R14761 (1997).

[3] H.-H. KlauB et al., Phys. Rev. Lett. 85, 4590 (2000).

[4] B. Buchner et al., Phys. Rev. Lett. 73, 1841 (1994).

[5] J. L. Tallon and J. W. Loram, cond-mat/0005063 (2000).

53

CATION SIZE DISORDER-INDUCED CROSSOVER FROM SUPERCONDUCTIVITY TOMAGNETIC ORDER IN L185Mo 15C11O4

/. A. McAllister1, J. P. Attfield1, K. Prassides2, S. Rouziere2, A. Lappas3

RA-99-12, CAMBRIDGE1 - SUSSEX2 - FORTH CRETE3

Cation size mismatch (tr2) is known to alter the super-conducting and structural properties of the L1.85M0.15C11O4single-layer high-rc cuprates [1]. Tc decreases as a2 in-creases and structural transitions to the lower temperatureLTO1, LTO2 and LTT forms [2] occur at progressively highertemperatures. Earlier studies suggest that the lowest temper-ature form, LTT, is responsible for the suppression of super-conductivity [3]; this phase has been found to nucleate at theLTOlandLTO2.

A preliminary yU+SR study revealed a fast relaxing com-ponent of the muon spin depolarisation, due to the slowingdown of the spin fluctuations. A more comprehensive studyof this magnetic behaviour was subsequently carried out onthe General Purpose Spectrometer and the Low TemperatureFacility at PSI. The compositions, a2 and 7"c's of the materi-als studied are given in Table 1. Structural behaviour, studiedby neutron diffraction is described elsewhere [1].

A site composition<r j 4> = 1.223ALao.925Sro.o75La0.925Sr0.045Ca0.017Ba0.013Lao.925Sro.030Cao.025Bao.020Lao.925Sro.008Cao.037Bao.030Lao.900Ndo.025Cao.037Bao.038La0.875Nd0.050Ca0.032Ba0.043La0.850Nd0.075Ca0.028Ba0.047<rA> = L232kLa0.925Sr0.019Ba0.056La0.868Nd0.058Ba0.075

aA

0.00060.00120.00150.00200.00250.00290.0033

0.00350.0047

T1 c

35.431.326.224.917.316.0-

32.029.0

No.

1345678

LIL5

Table 1: A-site compositions, (tr2), Tc's and sample numbersof the L1.85M0.15Q1O4 materials studied by /x+SR

Time (us)

Figure 1: ZF-yU+SR data at 2 K for samples 3-8.

In ZF-/i+SR experiments, sample 1 showed only the slowrelaxation expected for a superconducting material, while an

additional fast relaxation, which disappeared on heating wasevident in samples 3 and 4. On the other hand, a sponta-neous precession of the / i + spin at low temperatures was ob-served for samples 5-8, LI and L5, providing unambiguousevidence of the development of long range magnetic order.The frequency of the observed oscillations at 2 K increaseswith a2, as shown in Figures 1 and 2. The fraction of themagnetic component (extracted from the asymmetry) also in-creases with a2 but decreases with increasing temperature(Figure 3).

10 12 14

T(K)

Figure 2: Variation of the zero-field oscillation frequency(UZF) f° r samples 5-8, LI and L5.

T(K)

Figure 3: Fractions of magnetic (closed symbols) and non-magnetic (open symbols) components for samples 3-8, asdetermined from the ZF asymmetries.

Increasing a2 in the L1.85M0.15G1O4 series causes mi-croscopic structural phase separation, with one phase sup-porting magnetic LRO and the other, superconductivity.

REFERENCES

[1] J. A. McAllister et al., Phys. Rev. Lett. 83, 3289 (1999).

[2] D. M. Paul et al., Phys. Rev. Lett. 58, 1976 (1987).M. Onoda etal, Jpn. J. Appl. Phys. 26, 363 (1987).J. D. Axe et al, Phys. Rev. Lett. 62, 2751 (1989).

[3] A. Lappas et al.,J. Phys.: Condens. Matter 12, 3401 (2000).

54

LOW ENERGY EXCITATIONS AND INHOMOGENEOUS MAGNETISM IN ELECTRON

DOPED CUPRATES

D. Baabe1, H.-H. Klaufi1, D. Mienert1, M. Birke1, P. Adelmanri2 and F. J. Litterst1

RA-94-12, BRAUNSCHWEIG1 - KARLSRUHE2

Introduction: Nd2-y Ce^CuC^ (NCCO) is the prototypeelectron-doped high-Tc cuprate crystallizing in the tetrago-nal T' structure. By substitution of Nd3+ with Ce4+ elec-trons with predominantly Cu-3d character are added to thesystem. This affects the Cu-3d magnetism and changes theNd-4f spin system by diluting it. Specific heat measurementson Nd2CuO4 from Brugger et al. [1] have shown a Schottkytype anomaly with a peak maximum at m 1.4 K. With Cedoping the peak maximum is shifted to lower temperaturesand a large Sommerfeld constant develops gradually in nonmagnetic NCCO.

Low energy excitations in non magnetic NCCO: In2000 we performed longitudinal field /i+SR experiments onpolycrystailine specimens of NCCO with y = 0.1575 and 0.19at the LTF spectrometer to study the spin dynamics of theobserved low energy excitations. As reported in 1999 we ob-served an increasing relaxation rate which saturates below w0.5 K for all investigated compounds with y > 0.15 indicat-ing the low energy excitations from the viewpoint of /x+SR.Consequently, the decoupling experiments were performedin this low temperature regime at T m 75 mK. In the fast dy-namic limit the Redfield approach leads to a magnetic fielddependence of the relaxation rate A as

1A a • vc

•B2

with a proportional to the 2nd moment of the static fielddistribution A. The results for NCCO with y = 0.1575 atT = 50 mK are plotted in Fig. 1 (left) and shows good agree-ment with the expected power law. From this diagram thefluctuation rate vc was calculated and plotted in Fig. 1 (right).A moderately fluctuating spin system for NCCO with y = 0.15

Figure 1: 1/A vs. B2atT = 50 mK of NCCO with y = 0.1575(left). Calculated fluctuation rate vc vs. Ce content y of com-pounds NCCO (right).

beyond the antiferromagentic ordered regime (y pa 0.13) isobserved. This mirrors the proximity to the magnetic or-dered regime and still existing short range correlations. Thesurprisingly sharp transition from a vc of MHz to GHz bychanging y from 0.15 to 0.1575 may indicate a quantum crit-ical point.

Inhomogeneous magnetism in magnetic NCCO: Sincean incommensurate stripe-like magnetic order has been foundinLa2-x-yREa:Srj/Cu04 [2], [3] we investigated compoundsof RE2-j/Cej/Cu04 (RE = Nd, Pr, Eu) with y < 0.125. Lastyear we found an anomalous broadening for the 1/8 com-pound below 30 K. In 2000, we have performed an addi-tional set of experiments on polycrystalline (Nd,Pr,Eu)CCOcompounds at the GPD spectrometer. The temperature de-pendence of the ZF spontaneous muon spin precession fre-quency v was observed for compounds NCCO with y = 0.05and 0.10. For NCCO with y = 0.10 a fit with one frequencywas not suited to account for the data. The appearance of asecond frequency at T pa 25 K (Fig. 2) reflects the onset of abroadening of the static field distribution as found for y = 1/8at pa 30 K [4]. Contrarily for NCCO with y = 0.05, no second

50 100

temperature (K)

Figure 2: Spontaneous muon spin precession frequency inzero external magnetic field vs. temperature for NCCO withy = 0.10.

frequency was observed. A comparison with also measuredcompounds Pr2_j/Cej/Cu04 with y = 0.05, 0.10 and 0.125excludes an important role of the Nd magnetic moment onthis anomaly and supports the assumption of an electronicphase separation.

REFERENCES

[1] T. Brugger ef al.,Phys. Rev. Lett. 71, 2481 (1993).

[2] J. M. Tranquada e? aZ.,Nature 375, 561 (1995).

[3] W. Wagenere?a/.,Phys. Rev. B 55, R14761 (1997).

[4] D. Baabe et al.,J. Magn. Magn. Mat., in print (2001).

55

EFFECT OF AN APPLIED CURRENT ON THE FLUX LINE LATTICE OF NbSe2

A. Yaouanc1, P. Dalmas de Reotier1, P. C. M. Gubbens2, C. T. Kaiser2, F. Lefloch1, P. L. Gammel3, A. Amato4

RA-99-10, CEA GRENOBLE1 - TU DELFT2 - BELL LABORATORIES3 - PSI4

In October 1999 we managed to observe the effect of anelectrical current on the flux line lattice in NbSe2. However,the signal arising from the muons implanted outside the sam-ple, i.e. the background signal, was relatively large. In Oc-tober 2000 we attempted to study the effect of a current witha sample configuration designed to drastically reduced thebackground. Unfortunately, because one of the soldering ofthe current wire was damaged, it occurs that any current ofsufficiently large intensity (to be of interest) was heating thesample through the contact resistance. This means that wedid not manage to perform better experiments than last year.

Q

2.0

1.5

1.0

0.5

0.0

i • •

-

-

i , .

i i i i i i i i i i i i i i i i i i i i

•

. . B ex ,=

- . T = 2•

. , i . . , , i . , , . i , . . , i . .

i i i i i i i

-

50 mT ~

I K •

-

40 45 50 55 60 65 70

Magnetic field (mT)

Figure 1: one of the field distribution measured on a singlecrystal of NbSe2. The external field intensity is 50 mT. Afield cooling procedure was used. The observed structure at50 mT arises from the muon implanted outside the sample.

In Fig. 1 we present a typical field distribution deducedfrom a /xSR spectrum using the maximum entropy algorithm.It is visible that the background signal is small. We decidedit was worthwhile to study the disorder of the field distribu-tion by measuring at low temperature the distribution as afunction of the field intensity. Fig. 2 shows that the corre-lation length along the applied field direction increases withthe field and the correlation length perpendicular to the fielddirection is also expected to increase at high field. We arepresently analysing two sets of field scans taken at 2.1K and

4.7 K with the purpose to test the validity of the predictionmade in Fig. 2 concerning the transverse correlation length.Because the yuSR measurements have been done on the sam-ple used for the small angle neutron scattering experiment[1], any direct comparison between the muon and neutrondata is meaningful.

10

1000H(Oe)

Figure 2: The field dependence of the longitudinal corre-lation length £L measured at 4.7 K by small angle neutronscattering these values on a linear plot with theoretical pre-dictions. The dotted line is the prediction for the transversecorrelation length and the open circle is the result of a deco-ration experiment.

REFERENCES

[1] U. Yamn etai,Phys. Rev. Lett. 73, 2748 (1994).

56

FLUX LINE LATTICE OF 3D SUPERCONDUCTORS

P. Dalmas de Reotier1, A. Yaouanc1, P. C. M. Gubbens2, S. J. Harker2, A. Amato3

RA-00-01, CEA GRENOBLE1 - TU DELFT2 - PSI3

The discovery of high temperature superconductivity incuprates has refocussed attention on the nature of the mixedstate of type-II superconductors in general. It is now apparentthat the understanding of the physical properties of the vor-tex state in high Tc superconductors requires a better under-standing of that state for 3D conventional superconductors.In recent years surprising discoveries have been made forthese latter compounds. For example, the small angle neu-tron scatterring (SANS) technique has revealed the squareflux line lattice (FLL) at high field for RENi2B2C [1] andV3Si [2].

The transverse field yuSR technique has confirmed theSTM result [3] that the core size in NbSe2 shrinks as thefield increases in the low field regime [4]. In addition, this/xSR study has proven that the London penetration depth inthe flux line lattice phase is field dependent.

The results obtained recently by the Vancouver /iSR grouphave nicely shown that the yuSR technique can yield essentialinformation on the FLL. Surprisingly, the results obtained bythe /uSR and SANS techniques are not discussed on the samefooting. In particular the effect of disorder is not describedwith the same physical principle: the correlation length con-cept. The purpose of this proposal is to probe the FLL of con-ventional 3D superconductors by the transverse /xSR tech-nique and compare the results obtained by the /xSR and SANStechniques. The effect of disorder on the field distributionwill be modelled using the correlation length concept.

In 2000 we intended to focus our attention on the high-Kcubic superconductor VsSi (Tc ~ 16 K). The reasons areas follows. The physical properties of its FLL is now ofmuch interest. The SANS technique has shown that its crys-tal structure depends on the field orientation and its intensity[2]. These results are largely but not completely in agree-ment with a recent theory which accounts for the nonlocalcharacter of the electrodynamics [5]. A detailed theoreticalprediction has been presented recently for the temperaturedependence at low temperature of the core size (the Kramer-Pesch effect) [6].

However, due to an accelerator breakdown, we managedto record only 8 spectra from 20 K down to 2.1 K usinga field cooling procedure. Some field distributions derivedfrom the spectra using the maximum entropy algorithm arepresented in Fig. 1. The typical expected asymmetry of thedistribution is observed, reflecting the influence of the coresize. The peak at about 75 mT observed for the two distribu-tions recorded in the superconducting regime arises from themuon implanted in the sample holder. We are now analysingthese spectra.

50 60 70 80 90 100 110Magnetic field (mT)

Figure 1: Some field distributions measured on a single crys-tal of V3Si (Tc = 16 K) with the field applied along the [100]crystal direction. The external field intensity is 75 mT. Afield cooling procedure was used.

REFERENCES

[1] P. C. Canfield et al,

Phys. Today 51, No. 10, 40-46 (1998).

[2] M. Yethiraj et al., Phys. Rev. Lett. 82, 5112 (1999).

[3] U. Hartmann et al, SPIE Conf. Proc. 1855, 140 (1993).

[4] J. E. Sonier et al, Phys. Rev. Lett. 79, 1742 (1997).

[5] V. G. Kogan et al, Phys. Rev. Lett. 79, 741 (1997).

[6] N. Hayashi et al., Phys. Rev. Lett. 80, 2931 (1998).

57

MAGNETIC ORDERING IN AMMONIATED ALKALI FULLERIDES

T. Takenobu1,1. Mauriri2, K. Prassides2, A. Lappas3, A. SchenckA, Y. Iwasa1

RA-93-03, JAIST1 - SUSSEX2 - FORTH CRETE3 - ETH ZURICH4

Recent progress in the synthesis of fullerene intercala-tion compounds has afforded a huge variety of materials.Among them, the ammoniated alkali fulleride (NH3)K3C6oprovides a novel opportunity to investigate the correlationbetween molecular rotation and electronic properties, whichis one of the most unique aspects of fullerene based solids.(NH3)K3C6o is synthesized by intercalation of neutral am-monia molecules into fee K3C60, which is a superconductorwith Tc= 19 K. The structure of (NH3)K3C60 is very similarto that of K3C6o except for a slight orthorhombic distortioninduced by ammoniation. Interestingly, despite the similarcrystal structures, the electronic ground state of (NH3)K3C6ois that of an antiferromagnetic insulator with TN= 40 K, asshown by zero-field/longitudinal-field yU+SR [1]. The mag-netic moment is on the order of 0.7 yU^/molecule. The sup-pression of superconductivity and the metal-insulator transi-tion in (NH3)K3C6o are thus associated with effects of mag-netic origin, providing an important analogy with the phe-nomenology in organic and high-Tc superconductors.

Recently, we have succeeded in synthesizing an isostruc-tural series of (NH3)A3C6o compounds, where A is amixtureof K and Rb ions, in which the interfullerene separation isfurther substantially expanded. We observed similar behav-ior between (NH3)K3C60 and (NH3)A3C60 in electron spinresonance (ESR) measurements [2]. Thus the systematic cor-relation between the structure and the magnetic properties inthis series of compounds is crucial in obtaining a compre-hensive understanding of the role of degenerate molecularorbitals in determining the properties of fullerene solids. Inthis work, we have undertaken a preliminary investigation ofthe low-temperature ground state of some members of the(NH3)A3C6o series by the /z+SR technique with the GPSspectrometer.

Fig. 1 shows the time-dependent zero-field //+SR spec-tra of (NH3)KRb2C60 at 5 and 80 K. No oscillating signal ispresent at temperatures of 80 K and above. However, at lowertemperatures, the shape of the /x+ SR spectra changes and weobserve a short-lived oscillating signal. In fitting the data,we employ a strongly-damped oscillating polarization signalsuperimposed on a slowly relaxing component. The observa-tion of a yU+ Larmor precession frequency u^ in zero externalfield indicates the onset of magnetic order, where the spon-taneous magnetization is proportional to v^. The frequency,v^ is 0.57(1) MHz at 5 K, corresponding to a static local fieldat the muon site, < B^ >= 42.1(1) G. In addition, the depo-larization rate of the oscillating component, Ai has a value of2.5(1) fis^1 at 5 K, implying a distribution of local field witha width < 5B2 >1 /2 ss 25 G, only smaller than < B^ > bya factor of 1.6. A similar local field with a large spatial inho-mogeneity is observed in (NH3)K3C6o [1]. Fig. 2 shows thetemperature dependence of the muon precession frequencyand the depolarization rate of the magnetically ordered com-ponent in (NH3)KRb2C6o. The variation of v^ with tem-

0.00-

Figure 1: Evolution of the zero-field (ZF) yU+ spin polariza-tion, P^it) at 5 and 80 K for (NH3)KRb2C60.

perature is described by the equation of the conventional 3DHeisenberg antiferromagnet: v^= v0 [l-(T/TN)]° 33, with1/0= 0.62(2) MHz and TN= 50(1) K.

1 1

-

1

I 1 1 1 1

-

1

i

i

1f i i i i

0 10 20 30 40 50 SO 70 SO

Temperature ( K )

Figure 2: Temperature dependence of the ZF muon preces-sion frequency, v^ in (NH3)KRb2C6o.

We also collected time-dependent ZF-yU+SR spectra for(NH3)Rb3C6o as a function of temperature and observe sim-ilar evidence for a transition to a low-temperature LRO mag-netic state around 57 K. More detailed analysis of the data iscurrently in progress.

REFERENCES

[1] K. Prassides et al., J. Am. Chem. Soc. 121,11227 (1999).

[2] T. Takenobu et al., Phys. Rev. Lett. 85, 381 (2000).

58

SPIN DYNAMICS IN NOVEL TRANSITION MAGNETS

R. H. Heffner1, J. E. Sonier1, J. Sarrao1, D. E. MacLaughlin2, G. J. Nieuwenhuys3, O. O. Bernal4

RA-98-04, LOS ALAMOS1 - RIVERSIDE2 - LEIDEN3 - CALIFORNIA STATE4

When La2CuC>4 is doped with Sr, antiferromagnetism(AFM) is destroyed at about 3% Sr content; beyond 3% aso-called spin-glass phase exists, which has been shown byNiedermayer et al. [1] to coexist with superconductivity be-tween about 6 and 10% Sr doping. Recent measurements byPanagopoulos et al. [2] seem to show that this phase may ex-ist as high as 18-19% Sr doping. Both Li doping on the Cusite (Li1+ replaces Cu2+) and Sr doping on the La site de-stroy long-range AFM order at the same rate; e.g., T/v —>0 at about 3% Li doping. [3] Beyond 3%, Li doping inLa2Cui_zLizC>4 also leads to short-range, quasi-static mag-netic order, as found previously by us in both polycrystalsand single crystals with z < 0.10.

There are significant differences in the Li- and Sr-dopedLa2CuC>4 materials, however. Although Sr doping leads tosuperconductivity, Li-doped La2CuC>4 remains an insulatorout to at least z = 0.50. Thus, the similar depression ofT/v is remarkable in view of the very different mobilities ofthe Li- and Sr-doped holes. Furthermore, neutron scatter-ing has established that when sufficient numbers of holes areintroduced into the CuO2 planes the dynamic magnetic cor-relations become incommensurate with the underlying latticein all previously investigated La2-xAxCui_ zB zO4+ y (A =Sr or Nd, B = Zn) materials except B = Li. Recent inelasticscattering on z = 0.10, a; = 0, Li-doped 214 show only com-mensurate magnetic correlations for T > 15 K, the range oftemperatures measured. [4]

Our principal goal during 2000 has been to map out mostof the phase diagram for Li-doped La2CuO4. As shown inFig. 1, we have largely succeeded in doing this, although thefreezing temperatures for the concentrations > 10% Li arenot yet well established. Panagopoulos et al. [2] have ar-gued that there exists a characteristic temperature for the spinfluctuations in Sr-doped La2Cu04 which vanishes above acritical Sr concentration xc = 0.19. This concentration cor-responds to the doping at which the normal state pseudogapalso vanishes. From this they conclude that xc is a pointof quantum criticality associated with the competition be-tween spin fluctuations and superconductivity. In view of thesimilarity between the phase diagrams for Li- and Sr-dopedLa2CuC>4, and the fact that no superconductivity exists inthe Li-doped system, it is very important to pursue this com-parison as far as is feasible.

We also confirmed the coexistence of magnetism and su-perconductivity in La2-xSrxCiii_zLiz04+y, for x = 0.15and y = 0.02.

100

:AFM

10

••A

A

•

T N

T N

T «

Tn

T r

polyxtalpolyxtalxtal

A

"Glass1

10.00 0.04 0.08 0.12

Nominal Li concentration z

Figure 1: Temperature versus Li concentration. T/v = Neeltemperature, TQ or Tp = freezing temperature (glass state).

REFERENCES

[1] Ch. Niedermayer et al, Phys. Rev. Lett. 80, 3843 (1998).

[2] C. Panagopoulos et al., preprint, 2000.

[3] L. P. Le, R. H. Heffner et al.,Phys. Rev. B 54, 9538 (1996);B. J. Suh, et al., Phys. Rev. Lett. 81, 2791 (1998);J. L. Sarrao, et al., Phys Rev. B 54, 12014 (1996).

[4] W. Bao, et al., Phys Rev. Lett. 84, 3978 (2000).

59

EFFECTS OF DIMENSIONALITY AND QUANTUM CRITICALITY ON HEAVY-FERMIONSUPERCONDUCTIVITY AND MAGNETISM

R. H. Heffner1, J. E. Sonier1, J. Sarrao1, D. E. MacLaughlin2, G. J. Nieuwenhuys3, O. O. BernalA

RA-00-16, LOS ALAMOS1 - RIVERSIDE2 - LEIDEN3 - CALIFORNIA STATE4

We have carried out a survey of three materials in a newfamily of heavy fermionmaterials[l]: CeRhIn5 (undergoingmagnetic order at Tm = 3.5 K), Celrlii5 (a superconductorbelow Tc = 0.4 K) and CeRho.5Iro.5In5 (a superconductorbelow Tc = 0.8 K, undergoing magnetic order at Tm = 3.8K). In CeRhlns the Ce moments are AFM aligned in the a-bplane, but rotate 107 degrees for each unit cell distance alongthe c-axis [2]. Our /iSR measurements in CeRhlns show twomuon frequencies below Tm.

In CeRho.5Iro.5In5 our most significant discovery is thatthe magnetism and superconductivity coexist microscopically.Fig. 1 shows the temperature dependence of the spin-latticerelaxation rate 1/Ti, the amplitude of the single observedoscillating signal Aosc, the /xSR frequency v^ and the in-homogeneous linewidth A. All four of these quantities passsmoothly through the superconducting critical temperatureTc = 0.8 K, indicating very little influence of the supercon-ductivity on the magnetism. Between T = 3.5 and 3.9 K,we observe only a Kubo-Toyabe (KT) relaxation rate; i.e.,the oscillating amplitude is too small to be observed and thefluctuations are too fast to damp the nuclear KT rate. Themagnetic structure has not been determined in this system,but is likely to be complicated based on neutron scatteringmeasurements in CeRhlns. Specific heat measurements inour laboratory are consistent with all of the Ce atoms par-ticipating in the superconductivity. Thus, this system is evi-dentially one in which a fraction of the crystal-field ground-state moment is itinerant (and becomes superconducting) anda fraction is localized and magnetically ordered.

We also carried out Knight shift measurements forH = 6 kOe parallel to the c-axis in Celrlns (Fig. 2) andCeRho.5Iro.5In5 from T = 2 -300K.

REFERENCES

[1] J. D. Thompson, R. Movshovich, Z. Fisk, F. Bouquet,N. J. Curro, R. A. Fisher, P. C. Hammel, H. Hegger, M.F. Hundley, M. Jaime, P. G. Pagliuso, C. Petrovic, N. E.Phillips and J. L. Sarrao,J. Magn. Magn. Mat. , to be published.

[2] Wei Bao, private communication, Los Alamos, 2000.

0.2

0.1

0.0

1.0

0.5 -

0.01.0

0.5 -i

0.0

3

2

1

; C e R h o 5 I r o . 5 I n

• • • • •

• • • • •

; • • • • •

TC

i , | ,

• • •

• • •

• • •

i . i

5

•

•

•

• •

H =0 :

app :

T :m

•

• !• • .

• • . :• J

i . i . i . i

i \0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

T(K)

Figure 1: Temperature dependence of zero field fit to/xSR relaxation function Aosc exp(—At) COS(2TTZ^£ + </>M) +

81.4

81.3

8 1 .2

81.1

81.O

8O.9

Celrln5

m

O 5O 1OO ISO 2OO 25O 3OO

Figure 2: Temperature dependence of the two frequenciesobserved in transverse field of 6 kOe.

60

GLASSY SPIN DYNAMICS IN NON-FERMI-LIQUID UCug^Pd,., x = 1.0 AND 1.5

D. E. MacLaughlin,1 O. O. Bernal,'2 R. H. Hejfner3 G. J. Nieuwenhuys,4 M. S. Rose,1 J. E. Sonier3

B. Andraka,5 R. Chau,6 M. B. Maple6

RA-00-15, RIVERSIDE1 - LOS ANGELES2 - LOS ALAMOS3 - LEIDEN4 - GAINESVILLE5 - SAN DIEGO6

Local/-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCus-^Pdj;, x = 1.0 and 1.5, havebeen studied using muon spin-lattice relaxation. The sample-averaged asymmetry function G(t) exhibits the scalingG(t, H) = G(t/H7) expected from glassy dynamics. Our results put an upper bound of ~10~3 /xmagnetism in either alloy above 0.05 K, and strongly suggest quantum spin glass behavior in this system.

ion on static

/xSR and other experiments [1,2] have demonstrated theimportance of structural disorder in the breakdown of Fermi-liquid theory in certain /-electron intermetallic compoundsand alloys. Disorder-driven mechanisms have been consid-ered for the non-Fermi-liquid (NFL) properties of some ofthese systems, and it is natural to consider the possibilityof extremely disordered or "glassy" behavior. On theoreti-cal and experimental grounds it is known that glassy dynam-ics lead to long-time correlations with distinct signatures asthe freezing or "glass" temperature Tg is approached fromabove [3]. In a spin glass the spin autocorrelation functionq(t) = (Sj(t)-Sj(O)) is theoretically predicted to exhibitpower-law (q(t) = ct~a) or "stretched-exponential" (q(t) =cexp[—(Ai)'3]) behavior. Power-law correlation has beenfound in spin-glass AgMn using /iSR [3].

Our /xSR experiments suggest that spin correlations inthe NFL alloys UCu5_xPdx, x = 1.0 and 1.5, are indica-tive of glassy spin dynamics. The sample-averaged muonasymmetry G(t,H), shown in Fig. 1 for UQ^.sPdi.s , isstrongly sub-exponential, indicating a quenched inhomoge-

UCu35Pd15 7= 0.05 K

H=0

8Time t ((is)

Figure 1: Field dependence of sample-averaged muon asym-metry relaxation function G(t) in UCu3.5Pdi.5, T = 0.05 K.

neous distribution of relaxation rates, and obeys a time-fieldscaling relation G(t, H) = G(t/H"<) (Fig. 2) for appliedmagnetic field H between 13 Oe and 1 kOe. The field depen-dence corresponds to a measurement of the Fourier transformof q(t) over the frequency range "j^H^-ir K, 200 kHz-14MHz. Power-law behavior of q(t) is implied by the observa-tion 7 < 1 [3], and also by the temperature-frequency scal-

20UCu3.5Pd,5T=0.05K

£>

10AH=13OeO51 OeY160Oe• 400 Oe• 1.0 kOeA2.5kOe

010-4

10"-2

10t/H

10" 10u

0.7

Figure 2: Data of Fig. 1 plotted versus the scaling vari-able t/H-t, 7 = 0.7.

ing found in the inelastic neutron scattering (INS) cross sec-tion [4], although the connection with glassy dynamics hasnot been previously noted. The present measurements ex-tend by three orders of magnitude the frequency range overwhich power-law correlations are observed in UCus-^Pd;,;.Zero-field /iSR shows no sign of static magnetism or spinfreezing in either alloy down to 0.05 K.

By definition NFL behavior is a property of the lowest-lying excitations of a metal, to which a low-frequency probesuch as /uSR is extremely sensitive. The strong disorder,glassy behavior, and absence of a phase transition inUCus-^Pda; all strongly suggest that these alloys are quan-tum spin glasses [5].

REFERENCES

[1] O. O. Bernal et al, Phys. Rev. B 54, 13000 (1996);D. E. MacLaughlin etal, Phys. Rev. B 58,11849 (1998).

[2] C. H. Booth et al., Phys. Rev. Lett. 81, 3960 (1998).

[3] A. Keren, P. Mendels, I. A. Campbell, and J. Lord,Phys. Rev. Lett. 77, 1386 (1996); D. E. MacLaughlin,Phys. Rev. Lett. 51, 927 (1983).

[4] M. C. Aronson et al., Phys. Rev. Lett. 75, 725 (1995).

[5] D. R. Grempel and M. J. Rozenberg,Phys. Rev. B 60, 4702 (1999).

61

STUDY OF THE MAGNETIC PROPERTIES OF Ce,Pd,nSiß AND Ce,Pd2nGeß COMPOUNDS

A. Amato1, Ch. Baines1, V. N. Duginov2, A. V Gribanov3, K. I. Gritsaj1, D. Herlach1, A. A. Nezhivoy4 V. N. Nikiforov3, V Yu.Pomjakushiri2, A. N. Ponomarev4, Yu. D. Seropegin3, U. Zimmermann1

RA-97-04, PSI1 -DUBNA2 -MOSCOW3 -KURCHATOV4

Ternary rare earth compounds R-T-X (R: rare earth metal,T: transition element, X: Si or Ge) deserved recently con-siderable attention due to their interesting properties suchas heavy fermion state, non-Fermi liquid behaviour, super-conductivity, mixed valence, Kondo phenomena, anomalousmagnetic ordering. Cerium phases are known to exhibit thesefeatures particularly frequently.

The competition between magnetic and Kondo interac-tions was traditionally considered to result in either a mag-netic ground state with full suppression of Kondo features,or in a non-magnetic Kondo ground state. However, in thelast decade it has been found that there are many f-electroncompounds in which magnetic ordering coexists with Kondobehaviour. The Ce3Pd2oX6 (X = Ge, Si) systems belong tothem.

Preliminary results of our previous experiments with thecompound CesPcboSie have been published [1]. Last yearwe concentrated our efforts on Ce3Pd2oGe@. It is knownthat there are two separated cerium subsystems in this com-pound [2]. One of the subsystems involves Ce3+ ions in Ce2positions which form 'small cubes' inside the unit cell. Ionsof each cube make up magnetic 'molecules' with a magneticmoment that increases with decreasing temperature and un-dergo antiferromagnetic-like ordering at Tmagn .

The second cerium subsystem consists of Ce 1 ions. Theseions are less magnetically active because they have Ge asnearest neighbors. The Cel atoms may mostly play the roleof Kondo scattering centers for the conduction electrons.

Zero-field /iSR measurements were undertaken to gaininformation about the magnetic ordering at low temperaturesusing the LTF-setup. The depolarization function was repre-sented by an exponential. The temperature dependence of themuon-spin depolarization rate is shown in Fig. 1 (top). Below0.4 K the increase of the depolarization rate represents the de-velopment of quasi-static ordering of magnetic moments ofelectronic origin most probably randomly oriented.

We observe a recovery of the polarization in longitudinal-field measurements, with fields up to IT (Fig. 1, bottom).This proves the dynamic nature of part of the muon-spin de-polarization. More detailed experiments are planned at lowlongitudinal magnetic field.

We also performed transverse-field //SR measurementsin an external field of 3 kOe. The temperature dependence ofthe magnetic field seen by the muons is similar to the one inCe3Pd2oSÍ6.

0.00.0

3.0

-4.0

COU

3.0

g 2.0

O 1.0acu

Q0.0

0.2 0.4 0.6 0.8 1.0Temperature, K

Ce3Pd20Ge6

T = 50 mK

0.0 0.1 0.2 0.3 0.4Longitudinal field, T

0.5

Figure 1: Top: Temperature dependence of the muon spinrelaxation rate. Bottom: The recovery of the muon spin po-larization in longitudinal magnetic field.

Further experiments at low magnetic fields are requiredfor a detailed study of the dynamic properties of the internalmagnetic field. It seems that all magnetic anomalies can beobserved only at sufficiently low magnetic field.

REFERENCES

[1] V. N. Duginov et al, Physica B 289, 43 (2000).

[2] V. N. Nikiforov et al, Low Temp. Phys. 24, 565 (1998).

62

MAGNETIC STUDIES OF THE HEAVY FERMION COMPOUND Ce7Ni3

A. Kratzer1, D. R. Noakes2, G. M. Kalvius1, E. Schreier1, R. Wdppling3, K. Umeo4, T. TakabatakeA, H. v. Lohneysen5

RA-98-05, TU MUNCHEN1 - VIRGINIA STATE2 - UPPSALA3 - HIROSHIMA4 - KARLSRUHE5

Ce7Ni3 exhibits intermediate valence (IV) at high andheavy Fermion (HF) properties with 7 = 9 J/(mol K2) andan antiferromagnetic (AFM) ground state (T/v pa 1.9 K) atlow temperatures. One distinguishes three different Ce sitesin its hexagonal Th7Fe3 crystal structure, labeled Cei (oneatom/unit cell with trigonal point symmetry), Ce2 and Ce3

(both three atoms/unit cell with monoclinic symmetry). Ithad been suggested that Cei is responsible for AFM order,Ce2 for the HF behavior and Ce3 for the IV contributions[1]. A recent neutron study [2] reports two successive mag-netic transitions at TN = 1.8 K and TM = 0.7 K. Below TN asingle-k incommensurate (IC) spin structure is formed, witha temperature dependent modulation of moments along thec-axis. All three Ce sites are involved but with different rmsmoments (0.46, 0.7 and 0.1/xs for Cei, Ce2, Ce3, respec-tively). Below TM a coexistence of a commensurate and theIC structure is proposed. The AFM order vanishes at appliedpressure of Pc «0.32GPa. Simultaneously non Fermi liquid(NFL) behavior appears [3].

0.5-

g 0.4-

5 0.3-

5 ° -2 '1 0.1-

0.0-

5? Ce7Ni3 ZF

••••-0 c perp Sfl

^ c par Sfl

*

0 1 2 3 4 5 6 7 8 9 10 11 12

Temperature (K)

Figure 1: Temperature dependence of the ZF-relaxation rateabove TJV

spectra were measured at the GPS facility using sin-gle crystalline samples. The data are fully consistent with amagnetic transition at T/v =1.85 K. The ZF relaxation ratefor T > TN (Fig. 1) shows critical behavior (i.e. follows acritical power law) typical for a second order transition. Thecritical exponent was found to be w pa 1. One further no-tices a distinct dependence of relaxation rate on crystal ori-entation, meaning that magnetic anisotropy persists, leadingto non isotropic paramagnetic spin fluctuations in the vicinityof TN. The Knight shift in TF = 0.6 T between 3 K and 300 Kwas studied in a separate set of experiments [4]. Two signals,one with positive, the other with negative Knight shift wereobserved. Both show a simple cosine angular dependencebut with opposite phases. They were interpreted in terms oftwo muon stopping sites. Both are tetrahedrally coordinatedb sites. Their nearest neighbor shells are identical (one Ceiand three Ce3 ions), but the next nearest neighbor shell ( 3 Niions vs. 3 Ce2 ions) are different. The occupation of the twosites by the muon is temperature dependent. As an extensionto this work, the angular dependence of the Knight shift in

low field (TF = 0.025 T) was measured just above T^. Weobserved again two signals with opposite Knight shifts andcosine angular dependences. Their relative separation in fre-quency has increased from 20% at 3 K to 37% at 2K, giv-ing strong evidence for a critical divergence of both Knightshifts

0.5 1.0 1.5

Temperature (K)

SM. The insetFigure 2: Left: ZF-spectrum at 1.8 K for cshows the case for c || SM. Right: Temperature dependenceof the spontaneous precession frequency

Below TN heavily damped oscillatory muon spin preces-sion signals are seen for c _l_ SM (see Fig. 2, left, for an exam-ple). They were fitted with a Bessel type oscillation in accor-dance with the IC spin structure. These types of fits were un-satisfactory. They required a phase shift near 180° and thusmissed the early channels. Adding a monotonically decayingGaussian relaxation remedied the situation, but had no theo-retical base. The likely conclusion is that a more complexspin arrangement than a simple IC modulation exists. An ad-ditional complication are the two muon stopping sites, but,as stated, their immediate neighborhood of magnetic ions isidentical and differences are expected to be small. Indepen-dent of these fit problems one easily derives the temperaturedependence of the precession frequency (Fig. 2, right). Itreflects the order parameter of a second order phase transi-tion. The saturation field is roughly 0.15T, a low value, butin agreement with the comparatively small Ce moments de-tected by neutrons. No significant change in spectral shapewas seen around TM = 0.7 K. If this second transition existsat all, then the spatial arrangement of Ce spins around themuon changes only very little. The inset to Fig. 2, left revealsthat the spontaneous spin precession seen for c _L S^ is ab-sent for c || SM. This confirms that the moments are orientedpredominantly in c direction. Further work is in progress.

REFERENCES

[1] O. Trovarelli et al., Physica B 206, 243 (1995).

[2] H. Kadowaki et al., J. Phys. Soc. Jpn. 69, 2269 (2000).

[3] K. Umeo et al., J. Phys. Cond. Mat. 8, 9743 (1996).

[4] A. Schenck et al., submitted for publication (2000).

63

MAGNETIC PROPERTIES OF CeNiSn DOPED WITH Cu OR Pt

G. M. Kalvius1, E. Schreier1, G. Grosse1, A. Kratzer1, D. R. Noakes2, R. Wäppling3, Y. Echizen4, T. Takabatake4, H. v.Löhneysen5, A. Amato6, Ch. Baines6

RA-99-03, TU MÜNCHEN1 - VIRGINIA STATE2 - UPPSALA3 - HIROSHIMA4 - KARLSUHE5 - PSI6

CeNiSn is a non magnetic Kondo semi-metal. Replac-ing Ni in part by Cu or Pt induces magnetism when a certaincritical concentration is exceeded. The absence of long- oreven short-range magnetism in CeNiSn [1] is due to the dom-inance of Kondo interaction over RKKY coupling (TK >TRKKY)- The magnitude of TK is determined by the de-gree of hybridization of the Ce 4 / state with the conductionelectron sea. The nominal picture is, that the introduction ofCu or Pt widens the unit cell which weakens the hybridza-tion and in turn reduces TK below TRKKY when exceedingthe critical concentration. The transition temperature (TM)into a magnetic state is determined as the temperature wherethe muon spin relaxation rate (in ZF) exhibits a sharp up-turn. For CeNii-^Cu^Sn we had found earlier [2] a crit-ical concentration x^r

u « 0.07. In the present work westudied CeNio.74Pto.26Sn which was found to be magnetic(TM = 1.5 K) while the compound with x = 0.2 is non mag-netic. This leads to x^ K, 0.23. Fig. 1 (which supersedesthe corresponding figure shown in [2]) shows that in order tocreate a magnetic state one needs a volume expansion abouttwice as large when doping with Pt relative to Cu, mean-ing that volume increase is not the only mechanism inducingmagnetism in the CeNiSn series. Pt is isoelectronic to Ni, butCu contains one additional 3d electron. One concludes thatan increase of d electron density helps to move towards theonset of magnetism.

Ico

•JB

CO

œO)CO

8-7-6-5-4-3-2-1-0-

-CeNi lxCuxSnC e N i i - x P t x S n

1 I0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

xo iforCu| |xcrforPt

Volume Increase (%)

is roughly the same as in CeNiSn [3] at base temperature, theabsence of a temperature dependence is a distinct differencesignaling a definite change in electronic structure whose ori-gin may be the loss of coherent AFM spin excitations withcrystallographic disorder [4]. Furthermore, we find a linearfield dependence of the Knight shift, again contrasting the be-havior of CeNiSn where a slight curvature is present. In thepure material the spin correlations at low temperatures areweak and respond to even small external fields. The additionof Cu strengthens the correlations. The corresponding stud-ies for the magnetic compounds with x = 0.08 and 0.2 aresummarized in Fig. 2. The Knight shift in the paramagneticregime of the x = 0.2 compound exhibits a clear tempera-ture dependence, reflecting weak critical behavior. At TM ajump of Knight shift occurs. Both features are barely visi-ble in the x = 0.08 material which obviously is only weaklymagnetic. The TF relaxation rates show little critical behav-ior for both compounds, but a distinct field dependence in theparamagnetic regime which vanishes at the transition point.In the magnetic regime the internal field fully dominates theapplied field in both cases. The ZF spectra at low tempera-tures for x > 0.07 are characterized by a monotonie gaus-sian decay of muon spin polarization, implying a disorderedcluster-type magnetic state [5].

C e N i 0 .8 C U 0 .2 S n

-0.35

-0.4G

-0.451-

in TF=2kG

* 2kG TF» ZF

0.0 0.4 0.8 1.2 1.6 2.0 0

Temperature (K)

Figure 2: //SR Knight shift and TF relaxation data forCeNii-zCu^Sn with x = 0.08 (left) and x = 0.2 (right).The ZF data are taken from previous studies.

Figure 1: Volume dependence of T M for CeNii-^Cu^Sn andCeNii-^Pt^Sn. The numbers at the data points give the val-ues of x.

In addition, we have performed /iSR Knight shift andTF relaxation rate measurements for CeNii-^Cu^Sn com-pounds with x = 0.065,0.08,0.2 (i.e. just below, just abovethe onset of, and well inside the magnetic regime). A smallKnight shift exists for x = 0.065, but without any tempera-ture dependence. Although the magnitude of the Knight shift

REFERENCES

[1] A. Kratzer et ai, Europhysics Lett. 19, 649 (1992).

[2] G. M. Kalvius et al, Physica B 289-290, 256 (2000).

[3] G. M. Kalvius et al, Physica B 206-207, 807 (1995).

[4] A. Briickel et al, Physica B 240,199 (1997).

[5] D. R. Noakes, J. Phys: Cond. Matt. 11,1589 (1999).

64

/LtSR STUDIES OF THE KONDO INSULATORS Yb i_ x Lu x B 1 2

G. M. Kalvius1, E. Schreier1, A. Kratzer1, D. R. Noakes2, R. Wdppling3, F. Iga4, T. Takabatake4, H. v. Lohneysen5

RA-99-04, TU MUNCHEN1 - VIRGINIA STATE2 - UPPSALA3 - HIROSHIMA4 - KARLSRUHE5

High purity single crystalline samples of the Kondo insu-lators Ybi-^LuxB^ (x =0,0.125,0.5,1) were studied be-tween 1.8 and 300 K at the MORE facility with the aim to getinformation on local magnetic properties as a function of gapclosure which is induced by the partial replacement of Yb byLu [1]. Previously published yuSR data [2] of a powder sam-ple of YbBi2 were interpreted in terms of the development ofextremely weak slowly dynamic (~ 60 MHz) magnetic cor-relations of Yb moments of less than 10~2 HB below ~ 10 K.This conclusion was based on LF=200 G relaxation data, theZF spectra being fully dominated by dipolar couplings to thenuclear moment of n B . We were unable to confirm the con-

0.2

£• o.oCD=

| 0.2

0.0

\

\

\

YbB12

»3»B^2K

(*£,20K.

\

0 5 10 15 0 5 10 15 20Time (us)

Figure 1: Raw ZF-yuSR spectra of YbBi2

elusions of [2]. First, we observed significant changes in ZFspectral shape with temperature (Fig. 1). Characteristic tem-peratures for changes are ~20K, ~100K and ~150K. Thiscontradicts the interpretation of [2] using a single site nuclearKubo-Toyabe (KT) relaxation with A ss 0.5 fj,s~1. Second,this single parameter set was not able to reproduce the spectrain low LF (5 to 50 G). Third, we could not confirm the dropin LF=100 (or 200) G relaxation rate near 10 K. In contrast,we found that this rate suddenly peaks sharply at 150 K. Theobservation that for LF > 1000 G the relaxation rate is closeto zero at all temperatures agrees with [2]. It means, onedeals with comparatively slow dynamical effects. Fourth, wefound no systematic differences in the spectra of the variousYbi_a;Lua;Bi2 compounds with Yb content. Similarly, thereis no contrasting behavior in the LF=100 G relaxation rate ofdifferent Ybi_a;Lua;Bi2 compounds (Fig. 2). This excludesmagnetic correlations as its origin. The ZF and low LF spec-tra are difficult to fit. Below ~ 100 K, best results were ob-tained with a sum of two (nuclear) Gaussian KT functions(double relaxing with the additional relaxation present in theLF data) of widths Ai =0.52(1) jus1 and A2 =0.13(l)/xs"1

with temperature (but not field) dependent intensities a\ anda2 of the signal components (see Fig. 3). Above ~100K asingle site static KT function with roughly the weighted av-erage of widths at 100K (A =0.22(1)/L<S"1) fits the spectrawell. All differences in appearance in this regime are due tothe relaxation visible in LF.

0.0050 100 150 200

Temperatur (K)

250 300

Figure 2: Temperature dependence of the LF=100G relax-ation rate in Ybi_a:Lua:Bi2

The probable explanation is fast motional narrowing be-tween the two muon surroundings leading to a single qua-sistatic relaxation function. A site change may be anotherscenario which cannot be excluded. It could be initiated bymolecular rearrangement which would explain the peak inlow LF relaxation rate. In summary, our data suggest that the

20 40 60 80 100 120

Temperature (K)Figure 3: Temperature dependence of the relative intensityai.

features of the /xSR spectra of Ybi_xLuxBi2 arise mainlyfrom molecular dynamics (probably within the B12 clusters)and that Yb carries no detectable moment. This is supportedby recent m Yb NMR measurements [3] where a minimumof 1/Ti was seen around 15 K which ties in with the tem-perature dependence of ZF-//SR spectral shape. The NMRresults on the m Yb sites differs from those at the n B sitesrequiring an additional relaxation process for the B ions.

REFERENCES

[1] F. Iga et al, J. M. M. M. 177-178,156&377 (2000).

[2] A. Yaouanc et al., Europhys. Lett. 47, 247 (1999).

[3] K. Ikushima et al., Physica B 274-275,274 (2000).

65

THE MAGNETISM OF YFe6Al6

E. Schreier1, G. M. Kalvius1, F. E. Wagner1, U. Zimmermann2, D. R. Noakes3, R. Wdppling4, W. Schdfer5,1. Halevy8, J. Gaf

RA-00-04, TU MUNICH1 - PSI2 - VIRGINIA 3 - UPPSALA4 - BONN5 - BEN GURION8

The RFe@Al6 (R = rare earth) spinels crystallize in theThMni2 structure where four lattice sites can be distinguished.Site 2a contains all R ions, site 8i only Al, site 8 / only Fewhile site 8 j is randomly occupied by Fe and Al in equal pro-portion. We had previously studied the R=Tb, Ho, Er com-pounds which are known ferrimagnets (T/v ~ 340 K) andfound evidence for frustration due competing exchange in-teractions [1]. Unpublished neutron diffraction results onYFegAlg gave no indication for the presence of long-rangeorder. In addition, line shape analysis provided even no con-clusive evidence for any short-range order. If correct, theseresults mean that the absence of a magnetic 2a sublattice pre-vents magnetic order altogether, although the Fe containing8/ sublattice is considered the driving force for magnetismin all RFe6Al6 materials. To gain more insight into the sit-uation from a local point of view, we employed yuSR andMossbauer spectroscopies. The yuSR data were taken at theGPS (He-flow cryostat down to 1.8 K) and GPD (N2-flowcryo-oven up to 400 K) facilities.

0.15-

0.10-

0.05-

0 00-

4-

3-

2-

1-

0-

YFeeA ' e

s

a LF=50G* ZF

a GPS LF=50G* GPS ZFX GPD ZF

^ • • > -

!

100 200 300 400Temperature (K)

Figure 1: Temperature dependences of the /iSR signalamplitude (top) and relaxation rate (bottom) in YFegAlg.

A large loss of yuSR signal amplitude occurs around 60 K(see Fig. 1 -top). This points strongly towards an onset oflong-range ordered magnetism. The signal at 50 K and belowcan be understood as the 1/3 longitudinal part of the typical/xSR spectrum of an ordered magnet. The oscillatory trans-verse part is damped too rapidly by excessive field distribu-tions. The variation of muon spin relaxation rate with tem-perature is shown in Fig. 1 - bottom. It shows critical behav-ior on approach to 60 K and thus confirms the conclusion ofpresence of a magnetic transition. The behavior of relaxationrate at lower temperatures reveals the typical approach tothe quasistatic limit of ordered magnetism. Between 60 K<T <320K one observes a relaxation rate much too large fora free paramagnet. At least strong spin correlations must bepresent. The rate drops in the vicinity of 320 K. Whether thisis due to another phase transition or whether muon diffusion

sets in, cannot be decided on yuSR data alone. Mossbauerspectroscopy comes to aid. Typical spectra are shown inFig. 2. We shall not discuss the (still preliminary) fits to thespectra at this stage. At low temperature all iron atoms ex-hibit magnetic hyperfine splittings in accordance with long-range ordered magnetism. A considerable field distributionis visible here as well. The Zeeman splitting of the ma-jority of Fe atoms collapses towards 60 K, but a small por-tion remains unaffected. Up to 320K a coexistence of mag-netically ordered and very short range-ordered, or otherwisehighly correlated paramagnetic states exists. Beyond 320 Kthe Mossbauer spectra show no longer magnetic splittings,the pure paramagnetic state has been reached. The resid-ual quadrupole doublet exhibits a distinct asymmetry whichmost probably arises from slow paramagnetic spin fluctua-tions (paramagnetic relaxation spectrum). Slow spin fluctua-tions tie in with the still large muon spin relaxation rate seenabove the final magnetic transition of 320 K. In summary thelocal magnetic data clearly show the existence of differentkinds of magnetic order in YFegAlg. The discrepancy to theneutron data remains a mystery.

- 4 0 4Velocity (mm/s)

Figure 2: 57Fe Mossbauer spectra of YFegAlg at various tem-peratures.

REFERENCES

[1] G. M. Kalvius et al. Physica B 289-290,225 (2000).

66

MACROSCOPIC AND LOCAL MAGNETIC MOMENTS IN Si-DOPED CuGeO3 WITH

NEUTRON AND /zSR STUDIES

F. Semadeni1, A. Amato1, B. Roessli1, P. Boni1, C. Baines1, T. Matsuda1, K. Uchinokura2, G. Shirane3,

RA-00-10, PSI1 - TOKYO2 - BROOKHAVEN3

Since the first observation that the inorganic compoundCuGeO3 undergoes a spin-Peierls (SP) transition [1], an ex-tensive study of the doped system has been undertaken. Site(Cui_xMxGeO3) [2] and bond (CuGei_xSixO3) doping [3]studies have revealed the existence of a new antiferromag-netic phase below the SP ordering temperature TSP- In thepresent work we report a detailed study of the phase dia-gram of Si-doped CuGeO3 single crystals by means of neu-tron diffraction as well as zero-field field muon spin rota-tion (/iSR). The different signals observed with the neutrons,namely the AF and SP superlattice peaks, are interpreted interms of volume fractions via the analysis of the zero-fieldmuon spectra. Finally, the local magnetic moment measuredby /iSR is compared with the macroscopic order parameterobtained by neutron diffraction. Selected samples (0.82%,1.7%, 2.38% and 3.8%) belonging to the series of singlecrystals measured with neutrons have been investigated bymuon spin rotation spectroscopy in the three temperature re-gions that have been determined with neutron and suscepti-bility measurements, according to the experimental T-x dia-gram presented in Fig. 1. The values obtained from the vari-ous techniques are found to be in good agreement, indicatingthat the muon and the neutrons observe a magnetic orderingat the same transition temperature. The observation of the

14

12

10

g 8H 6

4

2

n

• i •

- ""*= j

T-

-

- 2

X

oo•

in

• •

TN (neutrons)

TN (HSR)

TN (X) JTSp 00TSp (neutrons)

-

—j=s :

• • • •

0.00 0.01 0.02 0.03Si concentration x

0.04 0.05

Figure 1: Temperature-concentration phase diagram of theSi-doped CuGeO3. The AF ordering temperature TJV andthe spin-Peierls transition temperature TSP have been deter-mined by susceptibility [4] and neutron diffraction experi-ments. The Tjy determined by /iSR measurements are alsoreported. The dashed lines are a guide to the eye.

SP dimerisation in susceptibility data for the samples in thelow doping regime is also confirmed by neutrons. The dis-crepancy between both methods is due to the fact that theSP superlattice peak that is measured with neutrons becomesextremely small while approaching the critical concentration.Furthermore, we emphasise that TSP is not observed abovex=1.2%. Below Tjy, the muon signal is found to consist of

0.6

0.5

0.4

Is °-3

0.2

0.1

0.0

O (xeff (neutrons) _

• AOSCA (\iSK)

0.00 0.01 0.02 0.03 0.04Si concentration x

0.6

0.5

0.3

0.2

0.1

0.00.05

Figure 2: The order parameter fj,eff as a function of Si dop-ing x measured with the neutron diffraction method (opencircles). The effective magnetic moment determined by /iSRis also shown. The dashed line is a guide to the eyes.

an oscillating and relaxing part. The good agreement be-tween neutron and /iSR results (see Figs. 1 and 2) allowsto associate the precessing signal, referred to Aosc, with thedimerised-AF phase in the low doping regime, and with theuniform-AF phase in the high doping regime. The purelyrelaxing signal, A r;x, is attributed, for x < 1.23%, to the re-gions where the lattice dimerisation is maximal. However,for higher doping concentrations, this amplitude does notdisappear. It is thought to arise from an increase of staticmagnetic disorder that is induced by high doping. The com-pilation of information provided by neutron and /iSR haveprovided a detailed insight about the origin of the variousmagnetic and non magnetic contributions observed in the Si-doped CuGeO3. The analysis of the zero-field muon spec-tra has confirmed the spatial inhomogeneity of the staggeredmagnetisation that characterises the antiferromagnetic super-lattice peaks observed with neutrons. The variation of themacroscopic order parameter with doping can be understoodby considering the evolution of the local magnetic momentas well as of the various regions contributing to the muonsignal.

REFERENCES

[1] M. Hase et al., Phys. Rev. Lett. 70, 3651 (1993).

[2] See for ex.: S. Coad et al.,J. Phys.: Condens. Matter 8, 6251 (1996).

[3] L. P. Regnault et al., Europhys. Lett. 32, 579 (1995);K. Hirota et al., J. Phys. Soc. Jpn. 67, 645 (1998).

[4] See for eg.: T. Masuda et al.,Phys. Rev. B 61, 4103 (2000).

67

SPIN FLUCTUATIONS IN THE TRIANGULAR ANTIFERROMAGNET CsNiBr3

P. C. M. Gubbens1, P. Dalmas de Reotier2, A. Yaouanc2, D. Visser1 S. J. Harker1

RA-00-08, TU DELFT1 - CEA GRENOBLE2

CsNiBr3 crystallizes in a hexagonal structure with mag-netic chains forming a triangular array in the plane perpen-dicular to the c-axis. This compound displays two magneticphase transitions. The c-component of the Ni magnetic mo-ment orders at TNI ~ 13.7 K, while the transverse compo-nent orders at TN2 ~ 11.6 K. The mutual magnetic momentcanting partially resolves the geometrical magnetic frustra-tion inherent in a crystal structure composed of triangulars.Note that most of the magnetic properties of CsNiBr3 havebeen inferred from NMR results [1].

•a

.2 4

Max

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0

2.0

| 1.5

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cQ.

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-

-

• • i • • • • i

CsNiBr3 :zero field

v _

•

\ TN2 :V :

5 10Temperature (K)

15

Figure 1: Temperature dependence a) of the maximum mag-netic field at the muon site corresponding to the Bessel depo-larization function, b) of the exponential damping rate. Themeasurements are done below TNI , in the magnetically or-dered state of CsNiBr3 with the initial muon spin polarisationparallel to the c-axis.

We started the //SR investigation of CsNiBr3 at ISIS.However, we could only take spectra with the initial beamasymmetry, SM, perpendicular to the c-axis. Thanks to thespin rotator available at the GPS spectrometer, we have beenable to extend the study to the c-axis parallel to SM. The de-polarization function for the two geometries is well describedby the product of a Bessel function with an exponential func-tion. In Figure 1 and Figure 2 we present Bmax(T) and A(T),where £?max(T) is the maximum field of the field distribu-tion corresponding to the Bessel depolarization function and

1.0

CsNiBr3zero field

5 10Temperature (K)

Figure 2: Temperature dependence a) of the maximum mag-netic field at the muon site corresponding to the Bessel depo-larisation function, b) of the exponential damping rate. Themeasurements are done below TN i , in the magnetically or-dered state of CsNiBr3 with the initial muon spin polarisationperpendicular to the c-axis.

A(T) characterizes the additional exponential depolarizationneeded to describe the spectra. Remarkably, A(T) = 0 forTN2 < T < TNI • The need for a Bessel function means theNi magnetic moment is sinusoidally modulated below TNI •The extra distribution below TN2 may be the signature of anadditional modulation of the Ni moment.

The measurements in the paramagnetic region indicatesthat the spin dynamics displays a critical slowing down whenapproaching TNi from above. Therefore, while there is stillthe possibility of recording spectra nearer to TNI , we canalready conclude that magnetic frustration does not quenchthe paramagnetic critical dynamics. This is in sharp contrastto one of the conclusions of the NMR work [1].

REFERENCES

[1] S. Maegawa et al.,Phys. Rev. B 51, 15979 (1995).

[2] P. C M . Gubbens etai.,ISIS Annual Report (2000).

68

LOW TEMPERATURE SPIN FLUCTUATIONS IN SPIN-LIQUID Yb3Ga5Oi2

/. A. Hodges1, P. Dalmas de Reotier2, A. Yaouanc2, P. C. M. Gubbens2, S. J. Harker2

RA-00-22, CEA SACLAY1 - CEA GRENOBLE2 - TU DELFT3

In the garnet YbsGasO^, the Yb3+ ion has a well iso-lated S' = 1/2 crystal field ground state with only a modestanisotropy. Specific heat measurements [1] evidence the ap-pearance of short-range magnetic correlations as the temper-ature is lowered below ~ 0.5 K and a A-anomaly at 0.054 K.Our 170 Yb Mossbauer measurements show that below the A-anomaly, the correlated magnetic moments continue to fluc-tuate at relatively high rates. YbsGasO^ may thus be clas-sified as a correlated spin-liquid. This property is associatedwith the geometrical frustration of the magnetic interactionswhich arises from the geometric arrangement of the Yb3+

ions on corner sharing triangular sublattices.

,—.^HIAI:

*?Bre

pine

£CO

Q

3.0

2.5

2.0

1.5

1.0

0.5

0.0

1

II

I!

;

7

7

1 ,

1 1 1 ' '

Yb3Ga5O12 ;zero-field itSR \

• \

• J• •

0.01 0.1 1 10Temperature (K)

100

Figure 1: Zero-field muon spin relaxation rate, Xz, forYbsGa5Oi2. The Xz increase below ~ 0.5 K is the signatureof the slowing down of the magnetic fluctuations. Above ~0.5 K the fluctuations are uncorrelated. The drop of Xz above100 K could result from muon diffusion.

In Fig. 1 we present the zero-field relaxation rate ver-sus temperature measured at ISIS and PSI. Below ~ 0.5 K,we observe a slowing down of the magnetic fluctuations. Nomagnetic phase transition is detected down to 28 mK. Xzshows no particular behaviour at the temperature of the spe-cific heat A-anomaly. The frequency shift (Fig. 2) shows achange of behaviour near 0.5 K, it becomes temperature in-dependent and again there is no change at the temperature ofthe A-anomaly. Further surprising results are displayed onFig. 3. A^(Sext) is unusual since in a conventional systemwe would expect Xz to decrease monotonically as the field isincreased. Our results seem to indicate the applied externalmagnetic field has a strong influence on the Yb3+ magneticmoment dynamics and this influence is quite different at 0.04and 2.0 K.

h

iitt

(

in

oc0

O"

ive

tiR

elat

0

-20

-40

-60

-80

i i i i

_

-

_ 1 t

Yb3Ga5O12 . "

Bext = 0.6T , / -

yY//

. i l / T

I l r -0.1 1Temperature (K)

Figure 2: Muon frequency shift measured for Ywith B e x t = 0.6 T. The fine is an eye guide.

B

Dam

pin

g r

3.0

2.5

2.0

1.5

1.0

0.5

0.0

i

7

L t: i

1

- \

; \

- ®.

7

-1

• " " 1 • " " " 1 •

I*r\ /\ /\y

. . . i , . . . i ,

• • ' •

Xxx

Yb3

. . i , ,

• • i

•

0

\\

Ga. . i

• • • • '

0.04 K -:

2.00 K J

N ~\ :

U —X_J j

5 o i 2 1, , , . 1

0.0 0.5 1.0 1.5 2.0 2.5External magnetic field (T)

Figure 3: Xz versus Be x t for longitudinal field experi-ments on YbsGa5Oi2. This behaviour of Xz(Bext) does notseem to have been observed previously. Whereas at 0.04 K^z(Bext) starts to decrease as the field increases, at 2.0 K,the opposite is seen. The fines are eye guides.

REFERENCES

[1] J. Filippi et ah,J. Phys. C 13, 13 (1980).

69

STUDY OF U- AND RE- INTERMETALLIC COMPOUNDS EXHIBITING QUADRUPOLARAND MAGNETIC ORDER

A. Schenck1, D. Andreica1, F. N. Gygax1, Y. Onuki2

RA-98-16, ETH ZURICH1 - OSAKA2

This years measurements were focused on the systemsCeAg, PrCu2, GdCu2 and a few measurements on TbCu2,all available as single crystals. The measurements on CeAgcould essentially be completed and the data analysis is nowin progress. In particular we have collected all necessary datato indentify the yU+-stopping site(s) in CeAg. Extensive ZFand LF-measurements show that magnetic correlations set inalready far above To = 5 K, namely below 20 K near thequadrupolar ordering temperature TQ = 15 K. PrCu2 was

0.25

0.20

0.15

0.25

0.20

0.15

0.25

0.20

0.15

0.25

0.20

0.15

0.25

0.20

0.15

0.25

0.20

0.15

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

-0.10

500 G

50 G

VK > y > y ^ / ; > l f ^ ;.\

extensively studied in ZF and LF with the aim to pin downthe spin dynamics observed in parallel to the appearance ofstatic fields below about 60 K. Due to problems with thecryostat on Dolly these measurements could unfortunatelynot be completed. As an example Fig. 1 shows the //SR sig-nal at 20 K in LF with P^ (0) andBext parallel to the crys-tallographic &-axis for Bext ranging from zero to 500 G. Therelaxation rate from the non-oscillating component is shownin Fig. 2 as a function of Bext. It follows a 1/(1 + aB2

xt)dependence. Note that if Bext is replaced by the total fieldat the /i+ (By, = Bext + Bint) no satisfying fit is achieved.We conclude that the observed field dependence is a prop-erty of the Pr-4f spin dynamics. ZF measurements on GdCu2

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Field (T)

Figure 2: Field dependence of the spin lattice relaxation rateat 20 K, deduced from the signals in Fig. 2. The solid linerepresents a fit, see text. Also shown is the field dependenceat 80 K, i.e. above the onset of magnetic order at ~ 60 K.

below T/v — 40 K produced four spontaneous precessionfrequencies which confirm a recent determination of the AF-structure of GdCu2 by neutron scattering.

Figure 1: LF-/xSR signal at 20 K for various applied fields.

70

COMPARATIVE STUDY OF THE MAGNETIC PROPERTIES OF RARE EARTHINTERMETALLIC COMPOUNDS, COMPLEMENTING NEUTRON SCATTERING

EXPERIMENTS

P. Schobinger-Papamantellos1, D. Andreica2, F. N. Gygax2, A. Schencli2, P. Duong3, K. H. J. Buschow3

RA-00-11, LFK-ETHZ1 IPP-ETHZ2 - AMSTERDAM3

The magnetic ordering of the PrCoALi compound hasbeen studied by neutron powder diffraction and magneticmeasurements [1, 2]. Below TN = 17 K only the Pr momentsorder with a longitudinal amplitude-modulated structure con-fined to the c direction. The wave vector q = (0,0,qz) has analmost T-independent length. At 1.5 K the amplitude of thewave is 2.24(4)yUB/Pr atom and qz =0.437(2)= 11/25 givingthe possibility to consider a commensurate phase. ZF-, LF-and TF-/iSR measurements were used to study the magneticordering of a PrCoAl4 single crystal with the aim to check theinterpretation of neutron results. The ZF signal consists of upto four components with amplitudes Ai, A2, A3, A4 depend-ing on the T-range: Above 30 K one observes two compo-nents in the signal (Ai,As). Below 30 K one observes threecomponents (Ai,A3,A4) and below 17 K four components.Only one of the components above 30 K shows a frequencycorresponding to a field of 0.05 T at the lowest T. The thirdcomponent appearing below 30 K is associated with a veryrapid relaxation probably reflecting a very wide field distri-bution and zero average field and the fourth component ap-pearing below 17 K reflects a precession in a much larger in-ternal field of 0.26 T. The T-dependence of the two frequen-cies is displayed in Fig. 1. In contrast to the neutron diffrac-tion results we find two additional critical temperatures at30 K and 90 K.

According to theory [3] long period structures with a wavevector expressed by a rational fraction p/N where N is oddmay display odd and even harmonics. The possible evolu-tion of ferromagnetism in such structures [4] is due to thefact that the number of + and — moments do not match. Inthe case of Pr3+ (having an even number of unpaired elec-trons) the ground state may be non-magnetic if the lowestCrystalline Electric Field level is a singlet; so the observedsinusoidal structure may be stable down to 0 K. This may ex-plain why no higher harmonics were observed at the lowestT in the powder patterns.

The /uSR experiment cannot yet distinguish between longperiod commensurate or incommensurate structures. To de-cide on the structure type it is necessary to determine the yU+

site (foreseen for 2001) and to perform dipolar field calcula-tions. In any case the /iSR signal above 17 K demonstratesthat short-range order sets already in at much higher T. Thiseffect was not clearly evident in the neutron data. To checkon the possible disappearance of the Pr magnetic moment fortemperatures close to 0 K or the appearance of a very weakferromagnetism we intend to extend the /iSR measurementsdown to below 100 mK.

Furthermore the investigation of ErFe4Ge2 and YFe4Ge2

powder samples confirmed the appearance of magnetic or-der below T/v (Fig. 2). The anomaly observed in ErFe4Ge2in the range 30 - 40 K traces the path of the double first or-

10° -

D DV2

:

: v i

7

-

TN=17K

Io

1 1 1

-

JL

Temperature (K)102

Figure 1: T-dependence of the precession frequencies inPrCoAl4.

der magnetostructural transition where the volume portionsof the two coexisting orthorhombic LT phases display thestrongest T dependence as found by x-ray and neutron scat-tering.

16

20 -

E 10

_i i i i | i i i i | i

'- ErFe4Ge

'•

• 1 1 1 1 1 1 1 ' '

T N

P

1 1 '

P

4

1 1 1

1 1 1 1 1

-•--

• i - - -

YFe

, , , i ,

1 1 1 1 1

i ""

, , , i ,

- 12

20 40 T [ K ] 60 80

Figure 2: T-dependence of the ZF amplitudes of the //SRsignal in the ErFe4Ge2 and YFe4Ge2 compounds.

REFERENCES

[1] L. D. Tung, K. H. J. Buschow.J. Alloys Comp. 37, 291 (1999).

[2] P. Schobinger-Papamantelloset ah,J. Magn. Mag. Mater., in Press.

[3] D. Gignoux, D. Schmitt, Phys. Rev. B 48,12682 (1993).

[4] A.R. Ball et al, J. Magn. Mag. Mater. 119, 96 (1993).

71

MAGNETIC CORRELATIONS IN ONE DIMENSIONAL SPIN SYSTEMS

D. Mienert1, H.-H. Klaufi1, D. Baabe1, W. Kopmann1, M. Birke1, H. Luetkens1, F. J. Litterst1, U. Ammerahl2, B. Buechner1'2

and C. Geibel3

RA-99-01, BRAUNSCHWEIG1 -KOLN2 -DRESDEN3

In this work we study the magnetic phases of quasi onedimensional spin- \ -systems as a function of charge carrierand impurity doping in the family of (Sr, Ca, La)i4Cu24O4i.This system contains CuO2 chains and Cu2O3 2-leg ladderstructures [1]. Because of the large spin gap energy of theladders (A ~ 370 K [2]) for all compounds below RT themuon mainly traces the magnetic correlations on the chains.

Starting with Sri4Cu24O4i, a system which exhibits adoping of 0.6 holes per Cu-atom on the chain sites, we inves-tigated the magnetic phase diagram as a function of hole dop-ing on well defined single crystals (Fig. 2). Ca doping leadsto a considerable charge transfer from the chains to the ladderstructures and doping with trivalent elements like La reducesthe number of holes and e.g. forLa6Ca8(...) ((...)=Cu2404i)the chain and ladder structures are nominally undoped [3].

In the nearly undoped compound LasCagO..) a linearscaling of the Knight shift and susceptibility in 0.6 T TF ex-periments between «75 K and RT has been used to extractthe dipolar hyperfine coupling tensor Adip,y and a contactterm Acontact. A comparison of this tensor with dipole cal-culations leads to a muon site (0,0.18, nil) close to the ladderoxygen atoms above the chains Cu sites (Fig. 1).

muon sites

Figure 1: Muon site extracted from 6 kG transversal fieldexperiments.

We investigated several crystals with Ca and La dopingin ZF and LF experiments. The observed magnetic transitiontemperatures are shown in figure 2. In the undoped systemalong the chain ferromagnetic nearest neighbour spin corre-lations originating from a nearly 90 degree superexchangevia oxygen atoms and antiferromagnetic interchain couplingis expected. By doping with spin deficiencies the antiferro-magnetic next nearest neighbour coupling ( JNNN = 11.2 meV)dominates the correlations along the chain.

a1 - NaV2 O5 is discussed as a quarter filled ladder sys-tem with a spin gap below 34 K. It is well established thatthis spin gap formation correlates with a charge ordering.For T > Tco=34 K a single V-site with an average valenceof 4.5 is observed, below Too magnetic V 4 + and nonmag-netic V 5 + sites are concluded from different experiments [5].ZF //SR spectra exhibit a spin freezing like magnetic relax-ation with quasi static order below 10 K similar to the one

LaKCa= —

10-

6 -

4 -

2 -

* L

I

s1

a,Ca.

W L a * C a ' °

' a" of

', "„ °»

Ca i 4

nonmagnetic

Sr ]4

hole doping (holes per chai Cu)

Figure 2: The phase diagram shows three different regimesfor the magnetism of the chains as studied by / i + SR exper-iments. Only Sri4Cu24O4i shows spin freezing below thedisplayed temperature of T=10 K. The other samples seemto be nonmagnetic or show only a weak nuclear dampingdownto 1.8 K.

observed in Sri4(...) [4]. The origin for this observed spinfreezing is still not clear. To exclude impurity spin freezingof paramagnetic spins present in all those samples we haveperformed ZF/LF experiments on two different single crys-tals of a1 — NaV2C>5 with very much different impurity spincontent. The observed relaxation is nearly identical and com-pares well with results in [4] (see figure 4).

A Klauss et al., sample 1• Klauss et al., sample 2D Fudamoto et al.

0 10 20 30 40 50

temperature (K)

Figure 3: Results on two different single crystals ofa1 — NaV2C>5 in comparison to Fudamoto et al. [4].

REFERENCES

[1] K. Kumagai et al, Phys. Rev. Lett. 78, 1992 (1997).

[2] S. Katono et al, Phys. Rev. Lett. 82, 633 (1999).

[3] T. Osafune etal, Phys. Rev. Lett. 78,1980 (1997).

[4] Y. Fudamoto et al, Phys. Rev. Lett. 83, 3301 (1999).

[5] Y. Fagot-Revurat et al, Phys. Rev. Lett. 84,4176 (2000).

72

AND SPIN-VACANCY-INDUCED MAGNETISM IN LOW-DIMENSIONAL QUANTUMSPIN SYSTEMS

A. Lappas1,1. Mastoraki1, A. Schenck2, F. N. Gygax2, K. Prassides3,1. Maurin3

RA-00-09, FORTH CRETE1 - ETH ZURICH2 - SUSSEX3

Haldane suggested that the ground state for half-integersystems can show quasi long-range-order (LRO) whereas, in-teger spin systems have a non-zero energy gap in the spin-excitation spectrum, exhibiting a singlet non-magneticground state. An important problem, which merits furtherinvestigation is related to the question of how the singletground state can be suppressed and give its place to LRO.The GPS spectrometer at the TTM3 beamline was employedto study the issue of the spin-vacancy induced magnetic LROin low-dimensional quantum spin systems of both S=l/2 andS=l. We employed /xSR in its ZF/LF variants to characterisethe physical properties of model spin-gap compounds [1],such as: (a) PbNi2-a;Mga;V2O8 (of quasi-lD NiOg-chains)and (b) S r C u ^ M g ^ B O s ^ (of quasi-2D CuO4-planes),which are critical between spin-singlet and formation of NeelLRO states. By implanting /z+ in such model compounds,one could follow the spin dynamics of the nonmagnetic state,as in the yuSR data of the spin-Peierls CuGeO3 [2].

ZF-yuSR on the Haldane-gap (at T<120 K) PbNi2V2O8

compound was carried out between 2-130 K. In this undopedsystem slowing down of the spin fluctuations (Fig. 1) was de-tected at T/ ~ 11 K indicating some deviations from a spin-singlet nonmagnetic ground state. The static magnetic freez-ing occurs in a subset spin system (~ 40 % of sample vol-ume) different from the majority of the Ni2+ moments whichform singlet pairs. The quasi-static character of this tran-sition was confirmed by LF-//SR. Defects on the Ni chains(due to chain-ends) of the PbNi2V2O8 and/or yU+-perturbation[3] of its ground state could lead to liberation of unpairedspins adjacent to the /u+-site. The response of the PbNi2V2Os

ments. For example, in the heavily Mg-doped compound(x=0.24), at least 3 spontaneous Larmor precession frequen-cies were resolved in ZF-yuSR, corresponding to local fieldsof < Bf, > ~ 20, 120, 220 G. Sizeable field distribution,< AB2 > x / 2 ~ 29 G, appeared to be due to large spatial in-homogeneities. In a preliminar approach, a phenomenolog-ical fit to the 1.82 K ZF data was carried out by the sum ofPM(i) ~ A, cos(uit + <f>) terms («=l-10). In order to addressthis problem we are currently undertaking dipolar field cal-culations to search for the /x+-site in the lattice. In the case

ois

atla

r

o

0.20

0.15

0.10

0.05

0.00

• i «C

1.82 K,

PbNiK, ZF

hi

1 7 e M 9 c 2 4 V2

O s •

•

111,-)||

0 2 4 6 8 10Time (usec)

Figure 2: Time evolution of the ZF-yuSR spectra at T<3.2 K.

of S=l/2 SrCu2_a;Mgx(BO3)2 (x=0, 0.04), no sponatneous/x-spin precession was found. In ZF- and LF-/xSR strongquasi-static relaxation (Fig. 3) was resolved below T/~3.8K. Both in the borates and the undoped vanadate compounds,/xSR has confirmed magnetic spin-freezing in the tempera-ture regime well below the spin-gap opening transitions, asfound before for analogous [3] low-dimensional systems.

Spin Freezing, Tf~11 K

s

o.o 10 15 20 25Temperature (K)

3 0

Figure 1: ZF- and LF-/iSR relaxation rates.

unusual ground state was explored by //SR (ZF/LF) uponchemical substitution of the metal in the NiOg chains by non-magnetic Mg2 + . Three samples with compositions through-out the phase diagram (x=0.04/ T/=2.52 K, x=0.12/T/=3.38K and x=0.24/T/=3.19 K) were found to display extremelyrapid ZF depolarisation. All the zero-time asymmetry waslost in t<2.2 /xs"1 for all samples with x>0.04. Fig. 2 presentsZF spectra below the 3.2 K antiferromagnetic-like transitionfound in DC susceptibility and neutron diffraction experi-

3 0

2.5

2.0

1.5

"5 0.5DC

0.0

' \

SrCu 1 M M

*# . .i

g 0 0 4 ( B O 3 ) 2 .

a LF100G* LF300G "X LF500Go LF800G -« LF2kG

3.8 K

k . . A4 6 8

Temperature (K)10

Figure 3: ZF- and LF-/iSR relaxation rates.

REFERENCES

[1] Y. Uchiyama et al., Phys. Rev. Lett. 83, 632 (1999).H. Kageyama et al., Phys. Rev. Lett. 82, 3168(1999).

[2] A. Lappas et al., Z. Physik B 96, 223 (1994).

[3] D. Andreica et al., Physica B 289, 176 (2000).Y. Fudamoto et al., Phys. Rev. Lett. 83, 3301 (1999).

73

STUDIES OF THE ELECTRON-DOPED C a i_xSmxMnO3

T. Chatterji1, D. Andreicci2, A. Schenck2, F. N. Gygax2, R. Suryanarayanan3, R. Revcolevschi3

RA-99-05, GRENOBLE1 - ETH ZURICH2 - ORSAY3

Following the discovery of colossal magnetoresistance(CMR) properties [1] there has been a lot of research in re-cent years on the hole-doped manganites Lai_xAxMn03 ,where A is a divalent element like Ca, Sr, Ba, Pb. If one con-siders AMnO3 compounds then substituting A by a trivalentrare-earth can be considered to be electron doping. Electron-doped manganites also show CMR effects. Here the purecompound AMnC>3 contains only Mn4+ ions and has no efl

electrons. By doping electrons with trivalent rare-earth el-ements efl levels are occupied and Mn3+ ions are created.The properties of electron-doped manganites are much lessstudied compared to those of hole-doped analogues but it isalready known that the manganites are not symmetric withrespect to the hole and electron doping. Here we report theresults of our /xSR investigations on Cai -x SmxMn03.

We have performed zero-field (ZF) and longitudinal-field(LF) yuSR investigations on the electron-doped manganitesCai-^SnXjMnOs for x = 0.1 and 0.3 on the Dolly and theGPS spectrometers of the Paul Scherrer Institute. The poly-crystalline samples were pressed into cylindrical pellets ofradius of about 10 mm and thickness of about 2 mm by ap-plying high pressure and temperature. These pellets werefixed on a fork-shaped copper sample holder with mylar foils.The sample holder was mechanically fixed to the cold tipof the helium flow cryostat. The incident muon beam wasperpendicular to the sample plate. The initial muon polari-sation was parallel to the beam. The ZF-yuSR signals fromCao.gSmo.iMnOs were recorded on the DOLLY spectrome-ter at several temperatures in the range from 100 K to 120 K.The signal showed no oscillations but relaxation which couldbe fitted by a stretched exponential function Ae^~xt^ fortemperatures above TCG ~ 110 K. The relaxation rate whichis about 10~1

/usec~1 at T = 120 K increases with decreas-

102 -

ing temperature and becomes large (10/isec^1)110 K. Below TCG ~ 110K the muon signal could be fit-ted by two exponential components A\e^Xlt^ + A^e^^^downtoaboutT = 107 K at which the component Aie(~Alt)is lost. The second component A2e^~X2t' survives down to100 K. The asymmetry A of the signal is about 0.26 aboveTCG ~ HO K. Below TCG the asymmetry ofthe two compo-nents are about A\ K, 0.17 and Ai ~ 0.9. The asymmetry ofthe component which survives below 107 K is about one thirdof the total asymmetry and hence represents those fi+ whichexperience internal fields parallel to their spin. We have alsomeasured the temperature dependence of the LF-yuSR sig-nal in a longitudinal field of 0.2 T. The LF-yuSR signal could

COCD

COX

CD

01

10°

10"1

10-2

95

: A fZF A

r O LF

X2

: 5 ° oi i i i i i i i i i i i

"K i4

i\

'LK>i \

cpW •Q •—" •

1 0

0.80.60.4

0.2

-

: P'o :

3-

•=

105 110 115 120 125 •

> T(K) :

Ll • Q rn •

i i i i i i i i i i i i

100 105 110 115 120 125Temperature (K)

Figure 1: Temperature variation of the muon relaxation ratesin Cao.gSmo.iMnOs above and below TCG ~ 110 K. AboveTCG a stretched exponential function Ae^~xt' is used to fitthe muon relaxation whereas below TCG two exponentiallydamped components have been used. The insert displays thetemperature variation of the exponent (3 of the stretched ex-ponential above TCG-

be fitted by a single exponential component Ae^xt\ Therelaxation rate is about 5 x lO^yUS^1. Fig. 1 displays thetemperature variation of these muon relaxation rates. The in-sert shows the temperature variation of the exponent j3 whichdecreases from about 1.0 (pure exponential) to about 0.3 atTCG ~ 110 K. We have also measured the longitudinal fielddependence ofthe yuSR signal at T = 105 and 120 K. Fromthe field dependence at T = 105 K we deduce an internalfield spread experienced by the muon of about 1.4kG. Theobserved strong field dependence at T = 120 K is some-what unusual and is not understood at present. The obser-vation of a stretched exponential relaxation function aboveTCG, implying an inhomogeneous distribution of relaxationrates, could be in line with theoretical considerations that theground state of the manganites may be unstable with respectto the appearance of a phase separation.

REFERENCES

[1] Colossal magnetoresistive oxides, ed. Y. Tokura,Gordon and Breach, Science Publishers (2000)

74

ZERO AND LONGITUDINAL FIELD RELAXATION IN LOW DOPING MANGANITES:SEARCH FOR STATIC AND DYNAMIC FERROMAGNETIC CLUSTERS

R De Renzi1, G. Allodi1, M. Cestelli Guidi1, G. Guidi1, M. Hennion2, L. Pinsard'6, A. CaneiroA, F. Prado4, R. Sanchez4, A.Amato5

RA-99-06, PARMA1 - LBL2 - PARIS SUD3 - BARILOCHE4 - PSI5

The magnetic properties of LaMnO3 and of its low dop-ing derivatives are a key to the understanding of the entiremanganite phase diagram. The interplay of magnetic inter-actions, charge and orbital ordering leads to a very rich phe-nomenology. These features reveal important aspects of themore general transition from the spin-correlated insulating tothe metallic state, hence they are a frontier test of condensedmatter theories.

In our second beam allocation (May 2000) we have stud-ied the following samples: a single crystal of LaMnO3; mo-saics of single crystals of Lai_xCaxMnO3 (x = 0.08,0.125);a polycrystal of KCuF3.

Our main results are summarized below.

0.050 100

T (K)150 0 50 100 150

Temperature (K)

Figure 1: Right: Local fields in LaMnO3; Left: Relaxationrates. Insets show the critical behaviour.

We have identified the two muon sites from dipolar calcu-lations, symmetry arguments and a careful study of the fielddependence of the muon frequencies. This allows us to givean absolute estimate of the Mn moment, which agrees withthe 4[IB detected by neutrons at T ->• 0[l, 4]. Fig. 1 (left)shows the temperature behaviour of the two local fields andthe inset shows the critical behaviour, with critical exponentft = 0.36(2) in agreement with Heisenberg 3D. The relax-ation rates, T^1 and T^1 also show a critical behaviour[l, 4],evidencing a cross-over to an Ising 3D critical exponent valuen = 0.7(1) (Fig. 1, right). The dynamical cross-over is ex-pected, since the ordered material does have a full anisotropy(spin along a axis).

We have taken more data on two Ca dopings, which bothshow an additional magnetic transition at T = Tco (Fig. 2):low temperatures precession frequencies abruptly give wayto a single very fast Kubo-Toyabe relaxation. We have pro-duced preliminary phase diagrams, to be compared with pre-vious self doped LaMnO3+y data[2].

1.0

0.8

•^0.6

>0.4

0.2

0.050 100

T (K)150

0.050 100 150

T(K)

Figure 2: Local fields vs. T (dashed lines are fig.l data).Right: Lao.92Ca0.o8Mn03; Left: La0.88Cao.i2Mn03; Tco

marks charge ordering.

Orbital ordering (OO) plays also an important role inmanganites. In OO the planar orbital configuration of Mn3+

may give rise to alternate perpendicular orientations at neigh-bouring sites. Coherent OO states may have subtle implica-tions on magnetism and transport. To clarify this point weextended or studies to a prototype material for OO, KQ1F3,where Cu2+ has the same local symmetry of Mn3+. It is aquasi-one dimensional antiferromagnet, with weak ferro cou-pling among chains (T/v = 39.5 K, in our sample). Our mainresults consist in the identification of a F-Mu-F center in theparamagnetic state [see J. Brewer et al.7 Phys. Rev. B 33,7813 (1986)] and of its complex quasi-lD spectrum in theordered state. Since we know precisely the muon site, wecan now proceed to a thorough study of magnetism in pureand charge doped materials.

REFERENCES

[1] R. De Renzi, G. Allodi, M. Cestelli Guidi, G. Guidi,M. Hennion, L. Pinsard, A. Amato,Physica B 289, 52 (2000).

[2] R. De Renzi, G. Allodi, G. Amoretti, M. Cestelli Guidi,S. Fanesi, G. Guidi, F. Licci, A. Caneiro, F. Prado,R. Sanchez, S. Oseroff, A. Amato,Physica B 289, 85(2000).

[3] R. De Renzi and S. Fanesi, Physica B 289, 209 (2000).

[4] M. Cestelli Guidi, G. Allodi, R. De Renzi, G. Guidi,M. Hennion, L. Pinsard, A. Amato,Cond. Mat. 0012158.

75

A fiSR STUDY OF THE LOW TEMPERATURE MAGNETIC PROPERTIES OF THEMOLECULAR CLUSTER Fe8

A. Lascialfari1 ,R. De Renzi2,R. Ullu1,

RA-00-19, PAVIA1 - PARMA2

The metal-ion based molecular clusters are constituted ofidentical and almost non-interacting molecules. In this wayone can study the properties of a single molecule by usingmacroscopic amounts of a sample [1]. One of the most in-vestigated systems is the superparamagnet Fe8 [2] which ischaracterized by a magnetic (high-spin) S=10 ground state.At low temperatures the S=10 ground state degeneracy is re-moved by the crystal field and the energy levels can be la-beled by Ms = 0 ,±l , . . . ,±10. Ms, the magnetic quan-tum number, is the projection of the total spin S along thez anisotropy axis. At temperatures well below that corre-sponding to the energy barrier A/ks ~ DMs2 ~ 27 K, byapplying an increasing magnetic field H \\ z7 level crossingconditions among theMs states are produced and phenomenaassociated with the quantum tunneling of the magnetization(QTM) can be singled out[3].

In the present experiment we studied the intramolecularspin dynamics with muons, a local probe, giving informationcomplementary to that obtained by macroscopic techniques.In order to enhance the signal we aligned three single crys-tals resulting together in a total cross section to the beamof about 5 mm2. Each crystal was aligned with Q ~ 0° and,in a second experiment, 0 ~ 40°, where© is the angle be-tween the easy (anisotropy) axis and the external magneticfield. The experiments have been perfomed at T = 1.7 K afterzero-field-cooling of the sample by varying the longitudinalmagnetic field H. The total muon asymmetry was 0.23 andthat of the background was estimated to be around 0.06.

The muon asymmetry recovery curves of the sample havebeen fitted by a sum of two different contributions, namelyAL and As originating from muons coming from two verydifferent sites of the crystal. The muons corresponding tothe AL asymmetry have a long relaxation time, resulting in aflat curve. They are placed far away from the magnetic cen-tral core of Fe8. These could actually correspond to morethan one site, indistinguishable through their muon relax-ation. The muons with As asymmetry have a shorter re-laxation time I/A, giving the only decaying part of the totalasymmetry. They are placed near to the magnetic core.

We focused on the X(H) behaviour at T=1.7K. Fig. 1shows for 6 ~ 0° some anomalies in X(H) at H ~ 0.22,0.44Tesla. These values correspond to the first two energy levelcrossings caused by the applied magnetic field. Analogously,for 0 ~ 40°, we observed an anomaly at H ~ 0.3 Tesla,which corresponds to the theoretically predicted first level

crossing at this angle. This suggests that these anomalies arecaused by the QTM process which induces local spin fluctu-ations seen by the muons.

Fe8:Br single crystal T=1.7K

0.0152000 4000

Field (Gauss)6000

Figure 1: Longitudinal relaxation rate A in Fe8 as a functionof the magnetic field H, for two different angles between Hand the easy-axis. The dashed lines mark the crossing fieldsat the two angles.

REFERENCES

[1] D. Gatteschi, A. Caneschi, L. Pardi and R. Sessoli,Science 265,1054(1994).

[2] C. Delfs, D. Gatteschi, L. Pardi, R. Sessoli, K. Wieghardtand D. Hanke,Inorg. Chem. 32, 3099 (1993).

[3] C. Sangregorio, PhD thesis;C. Sangregorio et al., Phys. Rev. Lett. (1997).

76

/xSR ON MONODISPERSE NANO-SCALE Pd CLUSTERS AT LOW TEMPERATURES

P. C. M. Gubbens1, C. T. Kaiser1, F. M. Mulder1, P. Dalmas de Reotier2, A. Yaouanc2, P. M. Paulus3,L. J. de Jongh3, G. SchmidA

RA-99-07, TU DELFT1 - CEA GRENOBLE2 - LEIDEN3 - ESSEN4

The materials we have studied belong to a class of giantmolecular clusters, in which the metal cores are members of aseries of "magic numbers" obtained by surrounding an atomby successive shells of atoms of its kind [1], [2]. The magicnumbers are 13, 55, 147, 309, 561 and so on. Organic lig-ands are necessary to stabilize the particles and for obtaininga monodisperse particle size. Studies of the magnetic sus-ceptibility and electronic specific heat, which are sensitive tothe electrons at the Fermi level, show a clear size dependenceand an odd/even effect for the 5, 7 and 8 shell Pd clusters [3].

This year we have extended our study of the clusters tothe so-calledPd5 compound, i.e. Pd56iPheng602oo- Becauseonly a limited sample material (300 mg) is available, the "fly-past" set-up of GPS proved to be very useful. Furthermore,the MORE device on GPS has been used to monitor the rela-tively low depolarization rate.

In a first approximation we have fitted the zero-field datawith a single exponential characterized by a depolarizationrate Xz. In Fig. 1 the temperature dependence of Xz is shown.From room temperature down to 75 K, Xz increases untilreaching a plateau. This behaviour is very similar to the Pd2sample, and could be due to muon diffusion in the palladiumcore. However, in contrast to Pd2 for which an additional in-crease of Xz is observed below 15 K, a similar effect is notobserved in Pd5.

The initial asymmetry is reduced, indicating that part ofthe muons form muonated radicals in the ligands surroundingthe cluster core. In an attempt to show that a large fraction ofthe measured signal arises from the Pd core, additional highfield measurements were performed on the Pd5 compoundand the pure ligand sample. In Fig. 2 the areas underneaththe spectra for both the Pd5 and the ligand sample versus ap-plied magnetic field are shown. Both sets of data are clearlydifferent at lower fields, indicating some muons in the Pd5sample do indeed measure an effect of the Pd core. More-over, an increase of the area for Pd5 compound and the lig-and Phen seems to start around 0.5 mT, which is about thesame order of magnitude as observed in Pd2. At very highfields both curves are similar. A preliminary analysis of thisresult indicates that roughly 50% of the muons are located inthe Pd clusters and the other half in the Phen ligands. At lowfield the signal of the muons is mainly composed of the Pdcluster contribution, whereas the contribution of the ligand issmall. Aim of future analysis will be to separate the Pd-corefrom the ligand contribution. This will enable us to obtainboth the correlation time and width of the field distributiondue to the delocalized electron in the Pd core.

NX2,

N

CD

mco'•aN

asoQ.CDQ

0.30

0.25

0.20

0.15

0.10

-

-

; pd5,

i . . . . i .

. . . i . . . . i .

6

0

1Phen*36

Zero-field

. , . i . , . , i .

00

O2OO

1 1 • "

0

<:

, 1 , .

• • 1

-

-

-

0 ;

, . 1

0 50 100 150 200 250 300Temperature (K)

Figure 1: Temperature dependence of the exponential relax-ation rate Xz for Pd5giPhen3602oo in zero-field.

3.0

2.5

a 1.5

* 1.0

0.5

0.0

: • Pd56|Phen*36O200 # :

- oPhen 8 • j: • 0 :••_ 5 K ° J

: 0 :

7 • -.

- • ° '•

: . ° :- • • 0- 0 0 0 -

, ,i 1 1 1

0.1 1 10 100External magnetic field Bext (mT)

Figure 2: Field dependence of the area underneath the spectrafor both Pd5 and Phen at 5K.

REFERENCES

[1] G. Schmid (ed.), Clusters and colloids, from theory toapplications, VHC, Weinheim, 1994.

[2] L. J. de Jongh (ed.), Physics and chemistry of metalcluster compounds, Kluwer, Dordrecht, 1994.

[3] Y. Volokitin, et al, Nature 384 (1996) 621;see also N&V ib 612.

77

STUDY OF THE DYNAMIC AND STRUCTURE FEATURES OF MAGNETISM IN HOLMIUM

V. N. Duginov1, K. I. Gritsaj1, D. Herlach2, A. A. Nezhivoy3, B. A. Nikolsky3, V. G. Olshevsky1, V. Yu. Pomjakushin1*2, A. N.Ponomarev3, U. Zimmermann2

RA-98-01, DUBNA1 - PSI2 - MOSCOW3

It is known that for 20 K < T < 132 K the magnetic struc-ture of holmium is an antiferromagnetic (AF) helicoid whichrestructures into a ferromagnetic (FM) helicoid at Tc = 20 K.

The spiral structure wavelength along the c-axis and thedistance between the basal planes of the crystal lattice are,generally speaking, incommensurate. A phenomenologicaldescription of such an incommensurate helicoid is the modelof a magnetic spin-slip structure, according to which onlysix equivalent directions of magnetic moments in the basalplanes are possible, corresponding to the hexagonal symme-try. According to the spin-slip model, an individual angleceind between the directions of magnetization of two neigh-boring basal planes can assume only two values, 0 (doubletsplanes) or 60° (singlets planes).

In a simple helicoid structure («¿„d = a) all intersti-tial sites are magnetically equivalent, and in a /iSR exper-iment only one muon-spin precession frequency should beobserved at a given temperature. In the spin-slip structure,the interstitial fields in different sections of the helicoid aredifferent and the frequency spectrum of the spin precessionsignal should be more complicated.

Zero field measurements were performed on a texturedsample of holmium and on a the single crystal which was cutoff from the textured sample. High-statistics spectra weremeasured below the Néel temperature near the spin-slip point.The c-axes of the textured sample were oriented parallel tothe polarization of the muon beam. We used the CCR cryo-stat of the GPD spectrometer and performed measurements attemperatures around 96 K, 42 K, and 24 K. At each tempra-ture, about 15-106 events were collected in the 'backward'and 30-108 in the 'forward' detectors, respectively.

The spectra in the AF temperature regime are describedsatisfactorily by a single muon-spin precession frequency.The temperature dependence of the measured precession fre-quencies is shown in Fig. 1.

The spin-slip transition near 42 K seems to be most suit-able for a yuSR study because it is situated at a smoother partof the Brillouin curve, but it is also evident that significantlyhigher precision is needed for the determination of the muon-spin precession frequencies. The spin-slip point near 24 K isdistorted by the proximity of an unexplained drop of the spinprecession frequency not far from Tc [2].

In earlier experiments with the textured sample [1] wehave performed measurements of the form of the muon-spinprecession signal in the FM region. In 2000 we have re-peated this experiment with the single-crystal in the 'deep'FM region. Typical statistics was about 5.5-106 in the 'back-ward' and 12-106 in the 'forward' detectors. At 6 K and8 K the muon-spin precession signal proved to be complex

217

205

132

39 41 43 45 47Temperature, K

11293 95 97 99

T e m p e r a t u r e , K101

Figure 1: Temperature dependence of the muon-spin preces-sion frequencies around the 42 K and 96 K spin-slip temper-ature points.

in the case of the single-crystal sample, too. This may beconnected with the features of the domain structure and/ordifferent magnetic environments for the muons.

In 2001 we are not planning to perform yuSR experimentson holmium because for the data obtained so far a more com-plex analysis and theoretical interpretation is needed first.

REFERENCES

[1] A. N. Ponomarev et al, Physica B 289, 236 (2000).

[2] E. Schreier et al, Physica B 289, 240 (2000).

78

SPONTANEOUS MAGNETIC ORDERING IN SODIUM ELECTRO SODALITE

R. Scheuermann1, E. Roduner1, B. Grofi1, G. Engelhardt1, D. Herlacli2, A. Schenck3, A. Amatd2, W. Waeber2

STUTTGART1 - PSI2 - ETH ZURICH3

Sodium-doped anhydrous sodium sodalite (sodium-elec-tro-sodalite, SES) represents a unique model system of abody-centered cubic (bcc) lattice of paramagnetic clusters,analogous to F centers in ionic solids. The sodalite frame-work is built by an alternating network of corner-sharingAIO4 and SiC>4 tetrahedra, forming truncated octahedral cages(J3- or sodalite cages) arranged on a bcc lattice. The particu-lar type of F center is a Na3+ ionic cluster (four alkali cationsin a tetrahedral geometry sharing one electron) located in-side a /?-cage. At high sodium loadings their large density(« 1021 cm"3) allows one to study their interaction. The ex-change coupling between unpaired electrons leads to an anti-ferromagnetic phase transition, observed in nuclear magneticresonance (NMR), electron paramagnetic resonance (EPR),and static susceptibility measurements [1].

In this work we present results from zero-field muon spinrotation experiments performed at the surface muon beams inarea TTE3 (DOLLY) and TTM3 (GPS) on a powder sample of280 mg black SES (sodium loading « 90 %). As no exter-nal field is applied any muon spin precession is only due tointernal fields, and anisotropy does not play a role. Fig. 1shows the measured forward-backward asymmetry at differ-ent temperatures. Clearly, spontaneous magnetic ordering,reflected in muon spin precession, sets in below pa 50 K.The data were analyzed in the time-domain, best fitted by athree-component polarization function

P(t) = aLe - A t ,aGe •a R e -r t (1)

OL reflects the volume fraction of magnetic domains and de-creases with increasing temperature near the phase transition.The Lorentzian relaxation rate A increases when approachingthe Neel temperature, indicating a non-uniform local mag-netic field near the phase transition ('melting of magnetic do-mains'). Although the specific site of the muon in the latticeis not known, the rather small damping rate of the preces-sion signal leads to the conclusion that the field distributionaround the stopping sites is very homogeneous and the pre-cession signal originates from muons stopped at equivalentsites.

The temperature dependence of the precession frequencyv{T) (equivalent to a magnetization curve) shown in Fig. 2can be fitted perfectly by the expression taken from [2]:

u0 = (1.250 ± 0.003) MHz corresponds to a local magneticfield at the muon site of B\oc K, 92 G. TN = (50.51 ±0.07) K is obtained for the Neel temperature. /? = (0.406 ±0.009) is close to the theoretically predicted value of 0.38for a three-dimensional Heisenberg system [3]. S = (2.59 ±0.07) is a phenomenological parameter and reflecting magnonexcitations [2] (predicted to be 2 for a cubic system [4]).

0 2 4 6f[HS]

Figure 1: Spontaneous muon spin precession in SES at lowtemperatures, polarization fitted to Eq. 1.

1.4-1

1.2-

1.0-

£0.8-1

1,0.6-

0.4-

0.2-

0.00 10 20 30

7[K]40 50

Figure 2: Temperature dependence of the zero-field preces-sion frequency, fitted to Eq. 2.

The second term in Eq. 1 is ascribed to a fraction of non-precessing muons in a local field parallel to their spin direc-tion and/or to muons in paramagnetic regions. The third termis attributed to muonium formation. A decoupling experi-ment at 50.4 K clearly shows the existence of a system akinto muonium. At low magnetic fields (up to 500 G) the dipolarinteraction with the nuclear magnetic moments of 27A1 and23Na leads to a reduction of the observed muonium asymme-try, and GSL + GSQ + 2aR to be less than the full beam asym-metry.

REFERENCES

[1] V. I. Srdanov et ah, Phys. Rev. Lett. 80, 2449 (1998).

[2] A. Schenck etal,J. Phys.: Cond. Matter 10, 8059 (1998).

[3] J. J. Binney et al, The Theory of Critical Phenomena,Oxford University Press, Oxford (1992).

[4] R. Kubo, Phys. Rev. 87, 568 (1952).

79

FORMATION OF CONDON DOMAINS IN LEAD AT VERY LOW TEMPERATURES

G. Solt1, V. S. Egorov2, C. Baines1, D. Herlach1, U. Zimmermann1

RA-94-14, PSI1 - KURCHATOV2

The thermodynamic instability of a uniform system withvery high differential magnetic susceptibility \ = dM/dB >1/4TT leads, in the case of metal single crystals with largeamplitude de Haas-van Alphen (dHvA) oscillations, to thebreak-up of the homogeneous state with the arisal of dia- andparamagnetic domains [1, 2]. In this state, the occupation ofLandau levels and thereby the magnetizations ±MV in thetwo kinds of domains are 'frozen', and the response of thesystem to changes of the applied field consists in varyingmerely the volumes of the oppositely magnetized regions.The domain state reappears periodically with the variationof the external field H, the period and the 'domain section'within the dHvA cycle are related to the electron Fermi sur-face (FS). By the use of /iSR the study of the domain phasein Be has become possible [3, 4]. Also, a first observation ofdomains in white Sn has recently been reported [5]. In fact,for highly pure metal single crystals at sufficiently low tem-perature, Condon domains should always be stable in a givenfield range determined by the FS geometry. The present yuSRresults for Pb shown in Figs. 1 and 2 provide new evidencefor this.

0.20

0.06

23950 23970 23990 24010applied field H (Oe)

24030

Figure 1: Exponential damping rate A (line broadening) ofthe /xSR signal at T = 20 mK. The distance between theperiodical peaks corresponding to centers of the domain sec-tions is AH pa 34 G.

The Pb single crystal plate was oriented normal to the ex-ternal field i f 11 [110]. The period AH PS 34 G correspondsto a dHvA mode with frequency F = H'2/AH Pa 1694 T,near to the known [6] value i<c(110) = 1 8 0 9 T associatedwith the FS sheet in the third Brillouin zone (the differenceis probably due to an angular offset of the sample). The in-dividual domain magnetizations ±M P for this crystal are toosmall to be resolved as a doublet splitting of the muon-spinprecession frequency. Therefore, the difference 8nMp in the

local fields inside the domains appears as a broadening ofthe spectral line (as compared to the uniform state outsidethe domain sections), resulting in the peaks in Fig. 1. Forslightly lower (H < 2.2 T) or higher (H > 2.6 T) fields thesharp peaks of A disappear, indicating that the phase bound-aries for the Condon domain state in the (B, T) plane are,for this 'domain-active' (Q mode, unexpectedly 'steep'. Thequantum oscillations are damped with increasing tempera-ture, and the observed peak height oc 8irMp decreases asshown in Fig. 2.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8temperature T (K)

Figure 2: Peak height (proportional to domain magnetizationMp) as function of the temperature, with H kept constant atthe first maximum of A in Fig. 1.

A more detailed investigation of the domain state and ofthe phase boundaries in Pb are projected.

REFERENCES

[1] J. H. Condon, Phys. Rev. 145, 526 (1966).

[2] D. Shoenberg, Magnetic oscillations in metals,Cambridge University Press, Cambridge 1984.

[3] G. Solt, C. Baines, V. S. Egorov, D. Herlach,E. Krasnoperov, U. Zimmermann,Phys. Rev. Lett. 76, 2575 (1996).

[4] G. Solt, C. Baines, V.S. Egorov, D. Herlach,U. Zimmermann, Phys. Rev. B 59, 6834 (1999).

[5] G. Solt, V. S. Egorov, C. Baines, D. Herlach,U. Zimmermann, Phys. Rev. B 62, R11933 (2000).

[6] J. R. Anderson, W. J. O'Sullivan, J. E. Schirber,Phys. Rev. B 5, 4683 (1972).

80

/xSR DYNAMICS OF LIQUID CRYSTALS STUDIED BY ALC

S. J. Blundell1, B. W. Lovett1, F. L. Pratt2,1. M. Marshall1,1. D. Reid3, W. Hayes1,

RA-97-22, OXFORD1 -ISIS2 -PSI 3

The uniaxial nematic (N) mesophase of a liquid crystal[1] is a state of matter which exhibits symmetry propertiesintermediate between those of a solid (S) and an isotropic liq-uid (I). In the N phase, molecules have translational freedomand orientate preferentially along one particular axis, whichis defined by a unit vector called the director, n. Nuclearmagnetic resonance (NMR) measurements have elucidatedmany of the dynamical properties of the N state. The use-fulness of the positive muon, an alternative local magneticprobe, has recently been established in dynamical studies ofsmall organic molecules and so we wished to apply this tech-nique to liquid crystals.

CO

CD•oD

"5.

<co

CD

oo

400 420 440 460 480 500 520 540

Hyperfine Frequency (MHz)

Figure 1: Structure of 5CB showing four muon positions andcorresponding correlation amplitudes obtained from a TF ex-periment. The cross marks an artifact peak.

To demonstrate the feasibility of applying the muon spinrotation/ relaxation (/iSR) technique to nematics we presentthe results of measurements carried out on the nematic com-pound 4' -n-pentyl-4-cyanobiphenyl (5CB), whose molecularstructure is shown in Fig. 1. It has a S-N transition at 24°Cand a N-I transition at 35°C. It is chemically the simplestnematic mesogen known and is thus a good choice for thisfirst investigation. In 5CB, as in other organic materials, weexpect muonium (Mu = /U+e~) to form by electron capturesoon after implantation. At high magnetic field ( » 20 mT)the eigenstates of the muon-electron system are well approx-imated by the two particle Zeeman states quantized in thefield direction, except in the special case of an avoided level

1.75 1.8 1.85 1.9 1.95 2.0 2.05

29 °C (N)

C(S)

Figure 2: ALC spectra taken from 5CB for four differenttemperatures.

crossing. Thus if the muons are implanted with their spinstransverse to the field, their spins will precess. Two preces-sion frequencies are expected, corresponding to the selectionrule A/ z = ± 1 , ASZ = 0, and are obtained by fast Fouriertransform of the raw muon time spectra and their averagevalue is A^. In a field of 200 mT we identified four pairsof Mu precession frequencies (not shown). By correlatingthese peaks, we obtain a spectrum in A^. Four peaks areclearly visible in this correlation amplitude spectrum in the Iphase, which then broaden with decreasing temperature as isshown in Fig. 1. In the I phase, where D^ is averaged out,the peaks correspond to four values of A^. These are dueto the four possible inequivalent sites for Mu addition to the5CB molecule.

In our ALC studies, we observe four AM = 0 reso-nances, one for each of the four possible Mu addition sites.For the I phase all dipolar parts of the Hamiltonian are aver-aged out, so we expect only the Fermi contact terms to con-tribute. This is not the case for the N and S phases. We use amodel [2] of the molecular dynamics to fit these spectra. Thefitted curves are shown in Fig. 2. Further details and alsolongitudinal-field data are reported elsewhere [2].

REFERENCES

[1] P. G. de Gennes and J. Prost, The Physics of LiquidCrystals, 2nd edition, Clarendon Press, Oxford (1993).

[2] B. W. Lovett, S. J. Blundell, J. StieBberger, F. L. Pratt, T.Jestadt, S. P. Cottrell and I. D. Reid,Phys. Rev. B 63, 054204 (2001).

81

IN II-VI SOLAR CELL MATERIALS

N. Ayres de Campos1, J. M. Gil1, H. V. Alberto1, R. C. Vilao1, J. Piroto Duarte1, A. Weidinger2, Ch. Niedermayer3, S. F. J. Cox4

RA-97-23, COIMBRA1 - HMI BERLIN2 - KONSTANZ3 - ISIS4

1. ZnO

After the discovery of a shallow donor muonium statein CdS [1], a theoretical work predicted the existence of asimilar state in ZnO [2]. Experiments recently conducted atISIS on ZnO powder [3] confirmed the existence of a shallowdonor muonium state, with an isotropic component of the hy-perfine interaction of the order of 500 kHz and an ionisationenergy of 64 meV.

In this project, experiments were conducted in a com-mercially available ZnO single crystal. Transverse-field (TF)measurements were performed in a field of 200 G in the tem-perature range from 2.2 K to 100 K in GPS. The results con-firm the ionisation temperature and energy previously ob-tained for the shallow state. Fig. 1 shows the envelope re-laxation rate corresponding to the hyperfine interaction, theionisation being made visible as a sharp decrease when thediamagnetic signal becomes dominant in the time spectra.

0.30

20 40 60 80Temperature (K)

100

Figure 1: Envelope relaxation rate of the muon-spin preces-sion in a transverse field of 200 G, in a ZnO single crystal.

The shallow muonium signal in the low temperature spec-tra is not sharp enough to allow the desirable characterisa-tion of the hyperfine interaction, possibly due to the presenceof defects in the crystal. The envelope relaxation is seen todecrease with decreasing temperature below 16K, which isprobably due to either a second component or a dynamic ef-fect on the paramagnetic signal.

2. HgOA clear muonium paramagnetic signal was observed on

HgO powder, in a survey of several II-VI compounds. Fig. 2presents an asymmetry time spectrum obtained on HgO pow-der in a 4kG transverse field and at 50 K, in GPS. The hyper-fine interaction is of the order of 16 MHz, considerably lowerthan that of Mug^ in Si, but considerably larger than that ofthe shallow states in CdS and ZnO.

0.2 0.4

Time (|a,s)0.6

Figure 2: Muon-spin precession in a transverse field of 4kGon HgO powder at 50 K.

A temperature scan at a transverse field of 100 G was firstperformed in the HgO powder sample. The diamagnetic frac-tion is observed to increase at the expense of the paramag-netic fraction in the temperature range from 150 to 200 K.This is attributed to the ionisation of the paramagnetic state,as in the case of CdS. The analysis of the data yielded a para-magnetic state ionisation energy E Q = (311 ± 4) meV.

3. ZnSeIn longitudinal field repolarization measurements on ZnSe

at ISIS [4] full polarization could not be recovered at a fieldof 4.5 kG. The high longitudinal field, the high time reso-lution (1.25 ns), and the low temperatures attainable at LTF,were combined to verify the existence of that fast relaxingcomponent, which would justify the still missing fraction. Afast relaxation component was indeed observed in the timespectra at fields from 1.5 T up, at 50 mK. A preliminary anal-ysis of these data leads to a spin exchange rate of 50 MHz inthe slow-exchange limit, considering an isotropic muoniumstate as known from transverse field data.

REFERENCES

[1] J. M. Gil et al, Phys. Rev. Lett. 83, 5294 (1999).

[2] C. G. Van de Walle, Phys. Rev. Lett. 85, 1012 (2000).

[3] RBI2295 DD ISIS experimental report, October 2000.

[4] RBI 1353 ISIS experimental report, April 2000.

82

MUON(IUM) IN NITROGEN-RICH DIAMOND WITH H2/H3 CENTRES

/. Z Machi1, S. H. Cornell2, J. P. F. Sellschop2, K. Bharuth-Ram3

RA-97-24, SOUTH AFRICA1 - WITWATERSRAND2 - DURBAN-WESTVILLE3

Introduction: Much of the understanding of the elec-tronic and dynamical behavior of hydrogen in diamond hascome from /iSR methods. This is made possible by similarchemical properties of muonium (Mu) with those of hydro-gen (H). This allows H states in diamond to be identified byanalogy with the different Mu states. Presented in this workare the prompt fractions (/) and the spin relaxation rates (A),of the /x+ state, after the conversion of some A-centres in anitrogen-rich type la diamond to H2/H3 centres.

Experimental: Characterization of a type la diamond re-vealed the presence of about 600 ppm of A-centres (a pair oftwo adjacent substitutional nitrogen atoms). H2/H3 centreswere produced by irradiating this same sample with 2 MeVgamma photons to a dose of 1019 cm"2, and then anneal-ing at 1270 K for 2 hrs. This procedure results in vacancytrapping at some A-centres to convert them to H2 or H3 cen-tres [1] depending on their charge state. The / and A of the/x+ states were determined in the temperature range 5-300 K,and in applied magnetic fields of 7.5 mT, while those for theMUT state were determined in the range 5-55 K, in 1.0 mT.

Results and Discussion: In our previous work conductedon the current sample (with only A,B-centres), a new para-magnetic muonium species, with less than axial symmetry(termed Max) trapped at the nitrogen related defects wasshown to form [2]. These results, following the production ofH2/H3 centres showed for the first time (in diamond) a non-negligible relaxation of the yU+ signal (see Fig. 1), except thedata of the chemical-vapor-deposited sample [3] which couldnot be linked to the current data. Also, previous measure-ments on vacancy rich samples (even after annealing) did notshow a relaxation of the / i + signal.

twice the value it had before some of the A-centres were con-verted to H2/H3 centres.

The behaviour of the MUT state is not changed from be-fore to after the production of the H2/H3 centres, as the /and the A remain (on average) at about 30% and 4.0 fis^1.

The yU+ has therefore grown at the expense of the missingfraction (MF). The entire strength of the MF is known to beassociated with the Mu trapped at the nitrogen related cen-tres, as Mux [2]. Clearly, the decoration of the A-centres byvacancies has resulted in less paramagnetic M u j , and moreof the / i + species.

The absence of a large value of / for the MuT state inthe previous work had indicated that it was most likely the/x+ species diffused to the nitrogen related centres and thentrapped there, capturing an electron to form the Mux species.It is possible that the trapping of a vacancy at some of thethe nitrogen related defects in the present work enables thetrapped /J,+ to remain in the diamagnetic state. The hint of anALC resonance (see Fig. 2), consistent with trapped /x+ ob-

100

90

80

70

60

50

40

30

"Old muons" (averaged over the time range 4-15 |is)

Temperature = 10K

Resonance at 50 mT

10

Field (mT)

100

100

80

o 60

1U- 40

20

Natural diamond (la)

2 MeV photon irradiated (1019 cm"2

Annealed (1000°C for 2 hrs)

O Prompt Fraction (u.+)

• Relaxation rate (u.+)

Field = 7.5 mT

0.05

0.04

0.03

0.02

0.01

J0.000 40 80 120 160 200 240 280

Temperature (K)

Figure 1: Prompt fractions and spin relaxation rates of the/x+ state in type la diamond with H2/H3 centres.

In addition, the value of / for the /x+ state displayed

Figure 2: Repolarization curve of old" muons in virgin" statetype la diamond.

served in LF-/iSR data for the 'virgin' sample, would there-fore be expected to become more significant in the samplewith some A-centres converted to H2/H3 centres.

Conclusion: These results are therefore interesting inthat they are consistent with the observation of dynamicaleffects involving / i + in diamond.

REFERENCES

[1] Y. Mita et al., J. Phys.: Condens. Matter 2, 8567 (1990).

[2] I. Z. Machi et al., Physica B 289/290, 507 (2000).

[3] K. Bharuth-Ram et al.,Hypfine Interactions 105, 339 (1997).

83

MEASUREMENT OF RELAXATION RATE AND PARAMAGNETIC FREQUENCY SHIFT OFNEGATIVE MUON SPIN PRECESSION IN SILICON

T. N. Mamedov1, D. G. Andrianov2, V. N. Gorelkin3, K. I. Gritsaj1, D. Herlach4, O. Kormann5, J. Major5'8,M. Schefzik6, A. V Stoykov1, U. Zimmermann4

RA-97-25, DUBNA1 - MOSCOW2'3 - PSI4 - STUTTGART5'6

As was shown earlier [1, 2] on n- and p-type silicon withimpurity concentrations from 5101 2 cm"3 to ~1017cm~3,the relaxation rate v of the Al acceptor center magnetic mo-ment depends on temperature as v ~ Tq (qm 3) and is prac-tically independent of the type and concentration of impu-rity. As the impurity concentration increases approachingnc, the critical concentration corresponding to the insulator-metal transition (the Mott transition), there is a deviationof the temperature dependence of v from z/~T 3 . Relax-ation of the acceptor center magnetic moment in Si is due tospin-lattice interaction and exchange scattering of free chargecarriers on the acceptor. Deviation of v{T) from the T3-behaviour at high impurity concentrations could have beencaused by substantial changes in the phonon spectrum of thecrystal or by an increased role of the spin exchange process.

Measurements carried out in the year 2000 were aimingat the study of mechanisms for the relaxation of the acceptorcenter magnetic moment in highly doped silicon. The tem-perature dependence of the negative muon polarization hasbeen investigated for silicon samples with boron (4.1-1018,1.341019,4.91019 cm"3), phosphorus(1.141019 cm"3) andgermanium (91019 cm"3) impurities. The boron and phos-phorus concentrations were above nc. Germanium in siliconis an isoelectronic substitutional impurity - the valency ofGe and Si atoms is the same and equal to four. Accordingly,introduction of Ge atoms in silicon does not change the con-centration of charge carriers.

The measurements were carried out in an external mag-netic field of 0.1 T transverse to the muon-spin direction inthe temperature range 4 - 300 K.

The temperature dependence of the frequency shift of themuon-spin precession Aui(T)/uio for the germanium-dopedsilicon sample does not contradict the 1/T-Curie law (seeFig. 1), thus making it possible to determine the hyperfineinteraction constant in the muonic MA1 atom: Ahf/27r =(23.6±1.5)MHz. This result agrees with Ah{/2n ~ 26 MHz- the averaged value for n- and p-type silicon samples withimpurity concentrations up to ~10 1 7cm- 3 studied earlier.A decrease of the frequency shift with increasing impurityconcentration is observed for boron-doped silicon. AU/UJQ

decreasing is possibly due to antiferromagnetic exchange in-teraction of the hole localized on the M Al acceptor with theholes of neighboring acceptor centers (see, e.g. [3]).

In silicon with a high impurity concentration of germa-nium v depends on temperature as T3 . This behaviour isanalogous to the one for non-degenerate n- and p-type sili-con samples. In silicon highly doped with boron and phos-phorus the temperature dependence of the relaxation rate ofthe acceptor center magnetic moment is weaker than the In-dependence. Thus, the present experimental data evidencethat the change in the temperature dependence of v in de-

generate n- and p-type silicon is caused by interaction of theacceptor magnetic moment with free charge carriers, whilein the case of a low concentration of charge carriers (in non-degenerate Si and in Si with isoelectronic impurity) the mainmechanism for the acceptor relaxation at T < 60 K is the spin-lattice interaction.

The spin-exchange scattering cross-sections of electrons(cre) and holes (<7h) on the Al acceptor in silicon are esti-mated: cre ~ 7-10~15 cm2 and <7h ~ 10~13 cm2 at n- and p-type impurity concentrations close to nc.

In silicon with 1.14-1019 cm"3 phosphorus impurity thereare damped and undamped components of the muon polar-ization at T < 20 K. The presence of the undamped compo-nent of polarization in degenerate n-type silicon is due to [2]the capture of conduction electrons by the neutral acceptorand its ionization with the rate z/tr comparable with the re-laxation rate of the muon spin in the paramagnetic (neutral)state of the acceptor. The ionization rate for this sample isabout4-106s"1 atT = 4.2-10K.

20-

15-

. 10-3

1

'},

o Si:Ge[9*1019cm3]

A Si:B[4.1*10l8cm"3]

• Si:B[1.34*1019cm3;

v Si:B [4.9*10'° cm"3]

5 -

0

* * *

K•H

10 20 30 40

T, K

50 60 70

Figure 1: Temperature dependence of the frequency shift ofthe muon-spin precession for highly doped silicon samples.The dashed curve corresponds to AOJ/UQ = C/T with C =(0.16 ± 0.01) K.

REFERENCES

[1] T. N. Mamedov, K. I. Gritsaj, A. V. Stoykov et.al,Physica B 289-290,574 (2000).

[2] T. N. Mamedov, D. G. Andrianov, D. Herlach et.al.,JETP Lett. 71, 438 (2000).

[3] M. P. Sarachik, D. R. He, W. Le, M. Levy,Phys. Rev. B 31, 1469 (1985).

84

HYDROCARBON ACTIVATION IN ZEOLITES; INSIGHTS THROUGH EPR AND

C. J. Rhodes1, H. Morris1, T. C. Dintinger1,1. D. Reid2, U. Zimmermannz, C. A. Scott4

RA-93-02, LIVERPOOL1 - UCL2 - PSI3 - ISIS4

The activation of hydrocarbons by oxidation and catalyticcracking forms the basis of the petrochemical industry. Thecatalysts in most common use are the zeolites, which are alu-minosilicate nanomaterials containing micropores of molec-ular dimensions: these are generally used in their proton-exchanged forms, although transition-metal exchanged zeo-lites find useful applications, for instance in the transforma-tion of high molecular weight fractions "heavy cuts".

It has been amply demonstrated that such zeolites, whenactivated under thermal oxygen conditions, develop redoxproperties and can oxidise spontaneously a variety of hydro-carbons[l]. Controversy exists for benzene, which thoughreported to form a "dimeric" radical cation in a range of ze-olites, it has not been clear whether this cation is the TT-TT

sandwich complex (with the positive hole shared between 2intact benzene moieties, or is the biphenyl 7r-radical cation,sinceisotropic simulations of their spectra are very similar[2].On the basis of anisotropic simulations, however, far betteragreement is met with the experimental spectrum, showingthat the "dimer" is, in fact, the biphenyl radical cation.

This result demonstrates that C-C a-bond formation canoccur in zeolites by a free-radical mediated route.

Since the reorientational dynamics of neutral free radi-cal intermediates in zeolites are largely inaccessible to EPR/-ENDOR methods, certainly under conditions pertinent to cat-alytic processes, we have utilised an alternative strategy: theLongitudinal Field Muon Spin Relaxation method [3, 4, 5,6, 7]. This employs positive muons as radioactive magneticlabels for radicals, and is extremely sensitive since it usessingle-particle-counting detection.

We have studied cyclohexadienyl radicals and dimethyl-cyclohexadienyl radicals as sorbed in zeolites ZSM5, sili-calite and mordenite. For cyclohexadienyl radicals in ZSM5,silicalite and mordenite, a fraction was detected with a com-mon reorientational activation energy of ca 5 kJ mol~1; how-ever, in both ZSM5 and silicalite there appeared a secondaryfraction with an activation energy of ca 14 kJmol^1. Thiswas absent in mordenite. These differences arise from thediffering internal channel structures of the zeolites, namelythat there are only straight channels in mordenite, hence there

is broadly a single location for sorbed molecules; in ZSM5/-silicalite there are zig-zag channels which provide the lateralinterconnection of the straight channels, and so moleculescan be located both within these separate channels and, pref-erentially, at the channel intersections.

We propose that the fraction exhibiting the low reorien-tational activation energy is located at the more spacious in-tersection sites (d = 9 A), while that at the higher activationenergy is from molecules occupying the channels themselves(d ~ 5.5 A) upon which are imposed greater motional restric-tion.

ACKNOWLEDGEMENTS

We thank Professor A. Lund for providing a copy of hisanisotropic EPR simulation program. Further acknowledge-ments are due to the EPSRC, the Paul Scherrer Institute, theEuropean Union, Unilever Research and John Moores Uni-versity for financial support of this overall programme ofwork; CJR further acknowledges the Royal Society of Chem-istry for the award of a J. W.T. Jones Travelling Fellowship.

REFERENCES

[1] C. J. Rhodes, in Radicals on Surfaces,ed A. Lund and C. J. Rhodes, Kluwer, Dordrecht, 1995.

[2] G. Hiibner and E. Roduner,Magn. Reson. Chem. 37, S23 (1999).

[3] C. J. Rhodes, T. C. Dintinger and C. A. Scott,Magn. Reson. Chem. 38, 62 (2000).

[4] C. J. Rhodes, T. C. Dintinger and C. A. Scott,Magn. Reson. Chem. 38, 729 (2000).

[5] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott,Magn. Reson. Chem. 38, S58 (2000).

[6] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott,Magn. Reson. Chem. 38, 281 (2000).

[7] C.J.Rhodes,Prog. React. Kinet. Mech. 25, 219 (2000).

85

"THE BLUE-RIDGE MOUNTAINS OF VIRGINIA"

C. J. Rhodes1, H. Morris1,1. D. Reid2, U. Zimmermann3

RA-99-15, LIVERPOOL1 - UCL2 - PSI3

The chemistry of the troposphere is dominated by ox-idation reactions, mediated by OH radicals [1]. The plantkingdom emits enormous quantities of hydrocarbons into theatmosphere, especially terpenes from forests. Indeed, the"Blue-Ridge Mountains" (of Virginia), of Laurel and Hardyfame, appear blue behind the haze caused by the troposphericoxidation of pinenes and other terpenes [2]. The processof hydrocarbon oxidation involves the partial oxidation ofminute hydrocarbon droplets, and is incomplete, leading toa carbonaceous aerosol - hence the haze. It is a kind of coldcombustion, involving the formation and diffusion of hydro-carbon radicals within the developing microporous structureof developing carbon particles.

Using Longitudinal Field Muon Spin Relaxation [3, 4, 5,6, 7], we have investigated the formation of radicals from avariety of terpenes and their interaction with a porous carbonmaterial. The results for a-pinene and /3-pinene are repre-sentative of this study. Addition of muonium to either pineneisomer will yield very similar radicals, differing only in therelative position of the muon and a proton. It might be ex-pected, therefore, that the reorientational dynamics of theseradicals would also be very similar.

In both samples two distinct motional regimes are re-vealed, corresponding to radicals sorbed at different sorp-tion sites within the carbon micropores. The activation en-ergies and frequency factors are shown in the table, and areindeed identical within error for both fractions for both iso-mers. We propose that the fraction of lower activation en-ergy (~6kJmol^1) corresponds to molecules that occupythe meso- and macro-pores (i.e. those of dimensions >20 A),while the fraction at higher activation energy (~15 kJ mol"1)is sorbed within the micropores (4-20 A).

A Ea A Ea

(1011 s-1) (kJmor1) (1012 s-1) (kJmor1)a-pinene/3-pinene

8.1±2.44.5±1.1

6.0±0.36.6±0.9

4.8±1.38.1±2.5

13.1±1.716.0±1.2

Table 1: Reorientational activation parameters measured fora-pinene and /?-pinene sorbed in activated carbon powder.

ACKNOWLEDGEMENTS

CJR thanks the Royal Society of Chemistry for the award ofa J.W.T. Jones Travelling Fellowship.

REFERENCES

[1] R. P. Wayne, Chemistry of Atmospheres,Clarendon Press, Oxford (1985).

[2] R. P. Turco, Earth Under Siege,Oxford University Press, Oxford (1997).

[3] C. J. Rhodes, T. C. Dintinger and C. A. Scott,Magn. Reson. Chem. 38, 62 (2000).

[4] C. J. Rhodes, T. C. Dintinger and C. A. Scott,Magn. Reson. Chem. 38, 729 (2000).

[5] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott,Magn. Reson. Chem. 38, S58 (2000).

[6] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott,Magn. Reson. Chem. 38, 281 (2000).

[7] C.J.Rhodes,Prog. React. Kinet. Mech. 25, 219 (2000).

86

A L C - M S R ON AZA-CYCLOHEXADIENYL RADICALS IN PYRIDINIUM SALTS

B. Beck1, E. Roduner1, H. Dilger1, R. Scheuermann1, P. Czarnecki2

RA-OO-21-a, STUTTGART1-POZNAN2

Avoided-Level-Crossing Muon-Spin-Resonance (ALC-has proven to be an appropriate tool to investigate re-

orientational dynamics of aza-cyclohexadienyl radicals in py-ridinium tetrafluoroborate (PyBF4) [1]. As a variant of mag-netic resonance, ALC-//SR interprets the relaxation of a po-larized muon spin-label in the radical as a function of a longi-tudinally applied magnetic field being scanned through avoid-ed crossings of magnetic energy levels. Muonium (Mu =/x+e~) is chemically a light hydrogen isotope in which thenucleus is a polarized muon. The hyperfine coupling con-stants in the Mu adduct are related to the resonance fields.Changes in the reorientational dynamics of the radical resultin changes of the line shape of the resonances [2].

PyBF4 shows two solid-solid phase transitions of order-disorder character at 7\ = 238.7 K and T2 = 204 K. Thefirst transition is paraelectric-ferroelectric and of second or-der, which is exceptional for multidimensional ferroelectrics[3]. Pyridinium perchlorate (PyClO4), belonging to the samefamily as the tetrafluoroborate, also reveals two solid-solidphase transitions — but in contrast to the PyBF4 of first order— taking place at 7\ = 248 K and T2 = 232 K [4]. Simi-lar symmetry of the involved phases is thought to be at leastpartially responsible for the continuous character of a phasetransition. But factors driving a transition in a discontinuousway although in a structurally comparable compound are stillunknown. Adding muonium to pyridinium cations in the or-tho, meta and para position with respect to the nitrogen atomresults in three different aza-cyclohexadienyl radical cations(C5H6NMU"1"). The radicals are expected to perform fast ro-tation around the axis perpendicular to the molecular plane[3, 4].

In the range of 1.8 T to 2.8 T both compounds yield sixstrong resonances which are identified as Ai and méthylèneAo lines of each radical. The coupling constants for themuons and the méthylène protons calculated from the res-onance positions are identical for both salts. In fig. 1, the or-tho Ai resonance of both compounds and the correspondingline width analysis are displayed. From the Dzz values, char-acterizing the line width, and the line shape we deduce thatabove 7\ the cations perform fast uniaxial rotation around theaxis perpendicular to the molecular plane in both salts. Incase of the tetrafluoroborate we observe a dramatic changeof the reorientational dynamics of the aza-cyclohexadienylradical between 233 K and 240 K. The evolution of the Dzz

values is very smooth, reminiscent of the continuous char-acter of the first phase transition, and indicates a restrictionof rotational dynamics with temperature. The perchlorate re-veals this change in dynamics between 244 K and 245 K. Incontrast to the tetrafluoroborate the alteration is limited to avery small temperature range and is steplike here, remindingus of the discontinuous transition. The similar Dzz valuesfor both compounds above T\ demonstrate identical reorien-tational dynamics in the paraelectric phase and therefore an-

ion independence. The totally different development of lineshape around the first phase transitions in contrast leads tothe conclusion that a differentiation of phase transition typeswith ALC-//SR is possible. Up to now it is not clear whetheronly the ordering of the ions is responsible for the ferroelec-tricity appearing in the low temperature phases, or whetherthe conventional mechanism of anion lattice displacement to-wards the cation lattice contributes here as well.

(a) PyBF4

1.85 1.9 1.95 270 280 290 300

Figure 1: ALC-yuSR spectra of ortho Ai resonance (left)and axial hyperfine anisotropy of all Ai resonances (right)of PyBF4 (a) andPyClO4 (b).

REFERENCES

[1] B. Beck et al, Physica B 289-290, 607 (2000).

[2] (a) E. Roduner, Chem. Soc. Rev. 22, 337 (1993).(b) E. Roduner, Appl. Magn. Res. 13,1 (1997).

[3] I. Szafraniak et al.,J. Phys.: Condens. Matter 12, 643 (2000).

[4] J. Wasicki et al, Molecular Physics 98, 643 (2000).

87

INTERACTIONS OF COSURFACTANTS WITH SURFACTANT BILAYERS

R. Scheuermann1, E. Roduner1, H. Dilger1, B. Beck1,1. M. Tucker2, E. J. Staples2

RA-00-21-b, STUTTGART1 - UNILEVER RESEARCH PORT SUNLIGHT2

Surfactants are amphiphiles which by nature form aggre-gates in order to satisfy the enthalpic and entropic require-ments derived from their structure. Depending on the rela-tive magnitudes of the hydrophilic headgroup and hydropho-bic tail, the molecule will tend to form curved or planar in-terfaces. At low concentrations, surfactant self-aggregationleads to the production of' micelles'. However, when presentat sufficiently high concentrations, molecules with small head-group areas and long chains prefer to form bilayer planar in-terfaces which result in one-dimensional lamellar type struc-tures. Temperature and molecular geometry thence dictatewhether the lamellar phase is 'simple' (fig. la), tilted (fig. lb),or 'interdigitated' (fig. lc).

(a) (b) (c)

Figure 1: Schematic arrangements of surfactant molecules indifferent configurations of lamellar phase.

Dialkyl chain systems readily form lamellar phases. Thealkyl chains can be considered 'liquid' (La) above a definedtemperature. Below this the system is said to be in the L^state with more ordered packing of the hydrocarbon chains.In the L a state the mixing of surfactant components is nearlyideal. In the Lp state considerable mixing is possible leadingto the formation of defective lamellar phases. In this workavoided level crossing (ALC) /iSR is used to contrast the in-teraction of a cosurfactant, phenylethanol (PEA), with bothsimple and interdigitated lamellar structures. The muonatedcyclohexadienyl radical derived from PEA exists in three iso-mers (ortho-, meta-, para-PEA-Mu), each of them gives atypical signature in an ALC spectrum (fig. 2).

From the appearance/disappearence of the Ai resonancelines or a sudden change of the hyperfine coupling (and hencethe resonance field) the local environment of the muonatedradical may be deduced. In this instance this means whetherPEA resides in an ordered state (co-aligned with the mole-cules in the surfactant bilayer) or in an isotropic environment.In liquid solution of pure PEA a spectrum which is typical ofPEA in its rotationally averaged environment is observed, theresonance positions shift to higher field values in an aqueousenvironment, and to lower field values in an environment ofalkyl chains (fig. 2).

Interdigitated and simple lamellar phase dispersions wereprepared at constant phase volume in water and were mixedwith identical levels of PEA. For the simple bilayer (fig. 3a)there is no evidence of anisotropy (Ai resonances) until acritical temperature of 55 °C is reached. This is the tempera-ture at which the alkyl chains of the surfactant 'melt' (LafLpphase transition). The implication is that in the simple lamel-lar phase below the transition temperature the chains are suf-

para- meta-PEA-Mu19500 20000 20500

magnetic field [G]21000

Figure 2: Ao resonances of the three isomers of themuonated cyclohexadienyl radical PEA-Mu in a solution ofPEA in liquid octadecane (top), pure liquid PEA (middle),and in a solution of PEA in water (bottom) at T = 35 °C.In the 'aqueous' environment the resonance positions areshifted to higher fields. The solid lines represent the resultof a fit of three Lorentzians to the data.

ficiently close packed that the cosuractant cannot penetratethe bilayer. For the interdigitated bilayer (fig. 3b) the aniso-tropy is present even at room temperature, indicating that thetracer molecule is axially aligned within the bilayer. The rel-ative intensities of the Ai fines are much larger than observedwith the simple lamellar structure, revealing a significantlyhigher order of PEA in the interdigitated bilayer.

(a) A

20000magnetic field [G]

18000 20000magnetic field [G]

Figure 3: ALC spectra of a PEA solution in a surfactantforming a simple lamellar phase (a) or an interdigitatedbilayer (b). The solid fines in (a) serve to visualize theshift/step of the Ao resonance positions with temperature.

These results demonstrate the potential of ALC-/xSR instudies of systems where the variation of the tracer moleculeenvironment with temperature is dramatic.

DIFFUSION OF MUONS IN METALLIC MULTILAYERS

H. Luetkens1'2, E. M. Forgan3, H. Glückler2, B. Handke5, R. Khasanov2'6, H. Keller6, J. Korecki5, F J. Litterst1, E.Morenzoni2, Ch. Niedermayer4, M. Pleines'2'4, T. Prokscha2, G. Schatz4, T. Slezak5

RA-94-15, BRAUNSCHWEIG1 - PSI2 - BIRMINGHAM3 - KONSTANZ4 - KRAKOW5 - ZÜRICH6

The development of the low energy muon beam at PSIopens the possibility to study the muon diffusion in artificiallayered structures of a few ten run thickness [1]. Here, we re-port on the first muon diffusion experiments done in 1999 ona single 10 nm Cr / 40 nm Au / 10 nm Cr epitaxial trilayer.The motivation of these studies is threefold: first, as a ba-sic experiment to understand muon diffusion in such systemsit is a necessary prerequisite for further LE-//SR studies onmagnetic multilayers. Second, they allow to study muon dif-fusion without introducing magnetic impurities in the speci-men as it is normally done in muon diffusion studies of non-magnetic metal hosts. Third, they allow to investigate inter-face effects like diffusion barriers due to different enthalpiesof solution, preferential diffusion due to epitaxial strain andthe role of disorder at the interface for sputtered samples.The principle of the experiment is shown in Fig. 1.

= f o - e-Ea/kT(1)

Cr Au A Cr

Depth (nm)

Figure 1 : Initial muon implantation profile (solid line) andtime dependent muon distribution due to thermally activateddiffusion (dashed line). Muons reaching one of the magnetic(SDW) Cr interfaces immediately loose their spin polariza-tion [2]. The depolarization of the LE-//SR signal thereforedirectly reflects the time dependent fraction of muons withinthe non-magnetic Au.

The measured yuSR spectra are well described by a sin-gle exponentially damped signal. The temperature dependentdepolarization rate A is shown in Fig. 2. At 125 K, the on-set of muon diffusion across the plane boundaries is detectedby the increase of A. The decrease of A at 285 K indicatesthe magnetic phase transition of 10 nm Cr at a reduced Néeltemperature compared to bulk Cr due to the size effect [2].

Monte Carlo calculations were performed to reproducethe experimental data. In these calculations, Arrhenius likehopping between the octahedral interstitial lattice sites of thefee Au lattice is assumed. For this thermally activated pro-cess the jump rate / at temperature T is given by:

Here, Ea is the activation energy, k is the Boltzmann con-stant, and /o is the attempt frequency. For a realistic initialstopping distribution the Monte Carlo code TRIM.SP [3] hasbeen used. The calculated time dependent fraction of muons

50 100 150 200 250 300 350

Figure 2: Measured and calculated depolarization rates A asa function of temperature T.

in the Au layer is well reproduced by an exponential deflationof muons from the Au layer. As a first approximation we ne-glected any additional interface barriers resulting in infinitelypermeable interfaces. The calculated depolarization rates arecompared to the experimental data in Fig. 2. It is visible thatthe diffusion to the Cr layers is strongly suppressed comparedto the literature values of muon diffusion in bulk Au. Thedata could only be reproduced by using extremly small at-tempt frequencies, clearly showing that interface effects arenot neglectable. The energy barrier at the interface is ex-pected to strongly depend on the enthalpy of solution, H, formuons in the two connected metals. Since H is related to theinteratomic spacing in the metal lattice it is reasonable to as-sume the same qualitative behaviour for muons and protons.First promising results are obtained using proton enthalpiesof solution at infinite dilution in the Monte Carlo code givinga repelling potential for muons at the interface.

REFERENCES

[1] E. Morenzoni, Appl. Magn. Reson. 13, 219 (1997).

[2] H. Luetkens et al, Physica B 289-290, 326 (2000).

[3] W.Eckstein,Computer Simulation of Ion-Solid Interactions,Springer Verlag Berlin (1991).

89

EMISSION OF EPITHERMAL MUONS FROM A PATTERNED MODERATOR

T. Prokscha and E. Morenzoni, PSI

The emission of epithermal (~ 15 eV ) positive muons(/i+) from a solid argon (s-Ar) moderator is essentially a sur-face process since the escape depth of these /x+ is of the orderof a some ten nanometers [1,2]. Therefore, an increased sur-face should yield a larger moderation efficiency emod. Forthe geometry shown in Fig. 1, we observe a gain of 1.48(3)of emod compared to a flat moderator [3]. This is about 15%less than the surface enlargement factor of 1.73.

A2AAdA>

Figure 1: SEM image of a structured silicon moderatorsubstrate with ridge distance d = 30 /im, ridge heighth = 20 yum, and angle 2a = 70.5°. The right side showsa front view of the substrate with a 3 x 3 cm2 pattern in thecenter. The thickness of the s-Ar layer deposited on the cold(~ 10 K) substrate is typically a few hundred nm. The in-coming surface / i + beam is directed upwards from the planeof view.

It can be shown geometrically that the gain in emod equalsthe gain in surface only, if the angular distribution of theepithermal / i + inside the moderator layer is isotropic, seeFig. 2. For an extreme forward directed distribution emoddoes not change when increasing the surface. In case of anisotropic distribution, some /z+ will impinge on the adjacentmoderator layer. If the absorption probability for those fi+

were unity, emoa would also not change with increasing sur-face.

We performed a Monte Carlo simulation to investigatein detail the consequences of various angular distributionsand backscattering probabilities on the emission of epither-mal / i + from a patterned moderator. The simulation gener-ates epithermal particles with homogenous stop density andangular distribution Fin{&) with respect to the beam axisin a flat and patterned moderator layer. The cumulative ef-fect on the angular distribution arising from collisions withthe moderator atoms is taken into account by the appropriatechoice of the functional dependence of Fin (0) . In the case ofthe patterned moderator, the angular distribution of particlesbackscattered from the adjacent groove wall is assumed tobe cos 0 ra, where 0 ra is the angle with respect to the surfacenormal. The angular distribution of backscattered /x+ calcu-lated with the program TRIM.SP [4], which has been shownto predict reliably the distribution of backscattered protons,supports this assumption. Only for grazing incidence at an-gles larger than 70° with respect to the surface normal, specu-lar reflection is favored. Due to the geometry of the V-shapedgrooves this case is very unlikely because only the small frac-tion of yU+ starting near the bottom of the groove can impinge

b)

: moderatorlover

: direction ofepithermal

Figure 2: (a) For an isotropic distribution, the escape depthd9

e of the moderator grating is equal to d{, the escape depthof the flat moderator. The active moderation volume Va, andtherefore the moderation efficiency, is increased by the sur-face enlargement factor G, Va oc d9

e • A? • G, where A? isthe area of the flat moderator surface, (b) For an extremeforward distribution, the escape depth d9

e is reduced with re-spect to d{,d9

e = d(/G. Therefore, a larger surface does notproduce a larger yield of epithermal /x+, because the activevolume does not change.

under large angles onto the neighbouring wall.The results of the simulation are summarized in Tab. 1.

Forward directed distributions like ^ ^ ( 0 ) = (1 + cos 0)™with n > 1 yield a gain < 1.48 for R = 1 and can be ex-cluded. The program TRIM.SP yields R = 89% for normalincidence of a 15 eV yU+ on s-Ar. We conclude, that theobserved gain in emod for a patterned moderator is a conse-quence of i) a nearly isotropic distribution of epithermal fi+

inside the layer, and ii) a reflection coefficient R ~ 90%.

Table 1: Simulated gain of emod for different angular dis-tributions Fin(@). F0Ut(Q) is the distribution of those /x+

which are emitted from the moderator and not absorbed inthe V-groove walls. The backscattering probability R for asingle collision is derived from the experimental gain of 1.48.

Fm(Q)1 (isotropic)

(l + ±cos0)(l + |cos0)

gain1.731.581.52

Fout{®)cos©

COS1'2 0COS1'3 0

R[%]789096

REFERENCES

[1] E. Morenzoni, Physics and applications of low energymuons, in Muon Science, S. Lee et al. (Eds.),IOP Publishing (1999).

[2] T. Prokscha et al, PSI Scientific Report 2000, Vol. 1.

[3] T. Prokschaetal, Appl. Surf. Sc. 172, 235 (2001).

[4] W Eckstein, Computer Simulation of Ion-Solid Interac-tions, Springer Verlag Berlin (1991).

90

THICKNESS DEPENDENCE OF THE EFFICIENCY OF s-Ar AND s-N2 MODERATORS

T. Prokscha1, H. Gluckler1, R. Khasanov1'4, H. Luetkens1'2, E. Morenzoni1, Ch. Niedermayer3, M. Pleines1'3

PSI1 - BRAUNSCHWEIG2 - KONSTANZ3 - ZURICH4

The efficiency of a condensed van der Waals gas moder-ator, measured as a function of the moderator thickness, re-veals information on the processes involved in the generationof epithermal ( ~ 15 eV) positive muons (//+). We investi-gated the epithermal /i+ yield NSJOW/N™ of solid argon (s-Ar) and solid nitrogen (S-N2) moderators in dependence onthe layer thickness. The number of epithermal muons N^ow

is determined by a time-of-flight (TOF) measurement, andN™ denotes the number of incoming surface muons.

As moderator substrate we used a patterned Ag foil as de-scribed in [1]. Research purity gas was condensed onto theblank substrate (T ~ 10 K). The gas pressure during layerdeposition was ~ 10~6 mbar resulting in a deposition rateof ~ 0.1 nm/s. The deposition rate was calibrated offline bymounting a micro balance at the moderator position and re-peating the evaporation procedure under the same pressureconditions. After measuring the epithermal / i + yield for onethickness additional gas was deposited on top of the existinglayer. This procedure was repeated until reaching the satura-tion of the yield.

The results for s-Ar and S-N2 are shown in Fig. 1. With-out moderator layer a yield of ~ 10~6 is observed in theTOF spectrum. This is due to the flat tail at the lower endof the energy spectrum of the fi+ beam penetrating the sub-strate. After adding a few nm of a moderator layer the yieldshows a step followed by a smooth increase which saturatesat ~ 120 nm for s-Ar, and at ~ 60 nm for S-N2.

Assuming a diffusion like motion of epithermal yU+ in-side the moderator the dependence of the yield on the layerthickness d can be written as [2]

jyTSloW-(d) =Nstop-Pe! L-tanh(-) (1)

where Nstop is the stop density in the moderator, Pesc is theprobability that an epithermal yU+ escapes into vacumm, L isthe escape depth, and N° denotes the offset at d ~ 0.

The fit of Eq. 1 to the data yields escape depths of ~ 36nm and ~ 15 nm for s-Ar and S-N2, respectively. This meansthat the "production" volume for epithermal /i+ in s-Ar is 2.4times larger than in S-N2 which should directly translate intoa higher epithermal yU+ yield. However, experimentally theyield of s-Ar is only ~ 20% larger. This difference is causedby i) a larger Pesc, and ii) a larger N° for s-N2.

The fit yields (NstopPesc)N* > (NstopPesc)

Ar. This re-quires a larger Pesc for S-N2 because in S-N2 Nstop is ~ 15%smaller than in s-Ar due to the lower density of S-N2. Thereare mainly two contributions that determine Pesc: the angu-lar distribution of the / i + (which is to good approximationisotropic [1], so that < 50% of the / i + escape into vacuum),and the probability of fi+ to form muonium (Mu) at epither-mal energies. Since the angular distributions are the same ins-Ar and S-N2 the epithermal (prompt) Mu fraction in S-N2must be smaller than in s-Ar. A more detailed analysis yields

2500

2000

1500

1000

500

0

.....

s-Ar: I _

», , , , i , , , , i , , , ,

xVndf 1PI :

"pi":P 3 :

1

(3.6 / 177.636.1344

^ *

0 :7 ± : 0.89146± : oISi;7 ± I 6.12

I

0 25 50 75 100 125 150 175 200

2500

2000

1500

1000

500

- [ | | • z _ ^ _ 4 -

i s-N2 i ^Jf^^ \- L 2 L &£L...± L...

xVndf

pi :

P3 I

- \-<f~ \ \ (•••

- [ I I I -

31.57 i' 21119.2 ±:i4.56±1720.1 ±

: 3.326: 0J530i 15.62

d(nm)

Figure 1: Measured epithermal /x+ yield N^ow /N™ as afunction of the moderator layer thickness d. The solid linesrepresent fits of Eq. 1 to the s-Ar and s-N2 data. PI = Nstop •Pesc [1/nm], P2 = L [nm], and P3 = 7V°. The offset for theblank substrate (d = 0) is 100(10)/108iV™.

a prompt Mu fraction of ~ 65% for s-Ar, and of ~ 45% fors-N2.

The physical significance of N° can be understood in thefollowing way. The / i + beam exiting the Ag substrate at ep-ithermal energies consists mainly of Mu (90%). A condensedgas layer reduces this fraction by stripping off electrons fromMu. A new charge state equilibrium builds up within a fewmean free paths for charge exchange which is of the order ofnm here. The larger value of 7V° for s-N2 is a consequenceof its larger cross section for electron loss.

Within the scope of this model the generation of epither-mal /i+ starts at small d's by stripping off electrons from Mucoming out of the substrate. The "true" moderation process(epithermal yU+ moving in the layer and escaping into vac-uum due to missing efficient energy loss channels) shows upin the smooth increase until saturation.

REFERENCES

[1] T. Prokscha et al, Appl. Surf. Sci. 172, 235 (2001).

[2] E. Morenzoni, Physics and applications of low energymuons, in Muon Science, S. Lee et al. (Eds.),IOP Publishing (1999).

91

A NEW SURFACE MUON BEAM

E. Morenzoni1, T. Prokscha1, F. Foroughf, K. Deiters2, M. Daunt", D. Renter3, D. Herlach1, C. Petitjean3

PSI: L M L ^ - A E A ^ L T P 3

Over the past years, a beam of polarized low energy mu-ons (LEM), which can be implanted at very small and con-trollable depths on a nm scale below the surface of a sample,has been developed at our institute. In order to definitely es-tablish the emerging LE-//+SR technique, to strengthen theleading role of PSI in this field and to cope with the increas-ing demand from external users, we have designed and pro-posed to set up a new surface muon beam line optimized todeliver the highest intensity on a small beam spot.

The main motivation for this development was to increasethe intensity of low energy muons, which is directly propor-tional to the flux of incoming surface muons on a 30x30 mm2

area. However, also other programs, such as bulk //+SR andparticle physics experiments using low momentum positiveand negative muons will profit from the availability of such abeam.

Optimum surface and cloud muon intensity and lowerpositron contamination are obtained with a 90 degree extrac-tion with respect to the target production surface as in thepresent TTE3 and /iE4 beam lines.

After studying different variants the //E4 beam area turnedout to suit our purposes best. In order to keep costs andwork within reasonable limits we only considered designsleaving the target E region (including the vacuum chamber)untouched and minimizing the impact on other beam lines.This implies that the external dimension of the first focusingelement and its distance from target E are fixed at 90 cm and60 cm, respectively and that the existing shielding channelhas to be used to a large extent.

A schematic overview of the proposed version is shownin Fig. 1, together with the new area layout. A significant in-crease of the channel acceptance with respect to TTE3, whichis limited by the use of a quadrupole of small aperture, isachieved by the use of a normal conducting, radiation-hardsolenoid as first focusing element, which rotates the imageof target E by about 45°.The solenoid is followed by a beamline consisting of bending magnets (ASK's with increasedgap) and large aperture quadrupoles (QSF). Positron separa-tion is achieved by using a wide gap ExB filter at the end ofthe beam line. The first bending magnet must be positionedat a distance of 3-3.5 m from target E in order to fit into theexisting channel.

The beam has been calculated with TRANSPORT andthe parameters optimized with TURTLE and ray tracing pro-grams. The comparison of the acceptances between TTE3 andthe new beam yields an increase of the muon rate by a factorof 10 for the full beam spot, starting with an initial rectangu-lar momentum distribution of 3% (which corresponds to theuseable momentum width for low-energy muon production).Also in the central region, the gain in muon rate amounts toa factor of 10. The suppression factor of positrons over a3x3 cm2 area is better than 100. The new beam area is largeenough to accommodate and render accessible for develop-ment and tests the LEM apparatus also during periods thatare used by other users to perform experiments in this area.

After positive review of the PSI research committee theconstruction of the beam line has been approved. A largefraction (~40%) of the total investment will be funded bythe Technical University of Braunschweig and the Univer-sity of Konstanz through the German Ministry for Educationand Research, BMBF. The new beam line will require a newinjection chamber and moderator cryostat for the LEM appa-ratus, which will be developed and funded in collaborationwith the University of Birmingham.

Figure 1: Schematic layout (bold lines and filled outlines ofbeam-line elements) of the new /iE4 beam line and area forhighest intensity surface muons.

93

Laboratory for

Micro and Nano TechnologyForeword

Nano Factory and X-ray Optics

Silicon Based Nanomaterials and Nanoelectronics

Molecular Nanotechnology

94

LABORATORY FOR MICRO- AND NANOTECHNOLOGY

J. Gobrecht

The Laboratory for Micro- and Nanotechnology in 2000 achieved several breakthrough-results in its core researchactivities. At the same time a significant number of new academic and industrial users could be served by theadvanced technological services. LMN's overall performance was ranked excellent by external auditors.

In 2000 the LMN continued in its efforts to focus theresearch activities in the areas of light emission fromsilicon (Si) based nanomaterials and molecularNanotechnology for applications in the life-sciences. At thesame time, our base-laboratory services to externalacademic and industrial users as well as other PSI projectswere intensified.

I am happy to report some major advances and highlightsof our research work during the last year:

After having set "light-emission" as the major goal for thearea of Si-based nanomaterials, we now can reportelectrically stimulated photon-emission from Si-Gequantum cascade structures - to our knowledge the firstever reported from this material. Also the luminescencefrom Ge quantum dots can now be stimulated electrically.After tedious solving of technological problems we wererewarded with exciting results from our "single holetransistor" in Si/Si-Ge, also the first of its kind everrealised. In a fruitful cooperation with PSFs energyresearch department we were able to realise a thermo-photovoltaic energy conversion demonstrator with a world-record system efficiency of 2.1%.

In the neuroinformatics project, we observed electro-physiological signals from living neural cells cultivated onstructured microchips. In the search for an amprometricimmunosensor, control was gained over the unexpectedlycomplex chemistry of penicillin. In order to bring themolecular nanojunction-experiments into operation wecould move to a new lab and start assembling the UHVequipment.

In micro- and nanostructuring, an increasingly intensiveand fruitful cooperation with the SLS team in the area of X-ray optical devices and detectors developed. For ouradvanced, submicron "hot embossing lithography" and"nano injection moulding" processes a broad industrialinterest was observed leading to a number of interestingindustry research contracts with high potential fortechnology transfer. A poster on a joint project with theenergy department of PSI on structuring of polymersurfaces using diffractive optics was awarded at theesteemed MNE conference.

Next to all the highlights and successes we are happy toreport on in the following pages, there are also a number ofproblems which have to be solved in order to furtherenhance our performance: probably the most urgent one isthe difficulty in recruiting qualified PhD students, who areand always have been a cornerstone of our scientificresearch work. If this situation does not improve in 2001,

several of our research projects will be delayed or evenmore seriously endangered. The other concern is the slowbut unavoidable ageing of our process equipment whichconsumes an increasing part of our resources formaintenance and repairs. A major investment isunavoidable in the coming years since we have to keeppace with the rapidly moving developments in micro-processing technologies. This is a prerequisite for appliedresearch at the forefront of micro- and nanotechnology.

In 2000 an audit of the LMN was requested by thedirectorate of PSI. This was conducted in September bythree internationally recognised external scientists from thefields of Si-Ge electronics, molecular sciences andnanostructuring. In short, the results and recommendationscan be summarized as follows:

• LMN's overall performance is ranked excellent.

• Industrial cooperation should be increased in someareas, particularly in the Si-Ge nanostructures area.

• Some projects should be reinforced to become over-critical, in particular in Molecular Nanotechnology.

We are satisfied with this very positive outcome and esteemthe valuable recommendations by the auditors.

Our scientific output in 2000 not only increased in respectto refereed papers, but we also initiated or participated infour patent applications. Another remarkable changeoccurred in respect to our research partners. Due to theending of the SPP "MINAST" in Dec. 99, the six projectswith LMN participation were finished as was thecooperation with 10 academic and 9 industrial partners.Due to intensive marketing and launching of new proposalswe were able to compensate this with the start of severalnew projects in 2000 with numerous new research partners.It seems we are proceeding well towards our goal ofbecoming one of the recognised and preferred researchpartners in nanotechnology [1].

I would like to take the opportunity to thank all LMN stafffor their engaged scientific work, for successful fundraising and for taking great care about our academic andindustrial partners. Equally I thank the PSI directorate forthe continuous support and all our research partners for thefruitful cooperation.

Enjoy reading the following pages!

REFERENCE

[1] Vision 4, Dec. 2000, supplement "Mikrotechnik in derSchweiz", p. 18

95

RHEOLOGY AND PATTERN FORMATION DURINGHOT EMBOSSING OF THIN POLYMER FILMS

L.J. Heyderman, M. Aufder Maur, J. Gobrecht, B. Haas, B. Ketterer and H. Schift (PSI)

We investigated the viscous flow of thin PMMA films into microcavities during hot embossing in order to optimisethe moulding of nanostructured surfaces. The cavities fill by lateral flow of PMMA from the borders of the cavities,and compressive and capillary effects are important. Under certain conditions, periodic patterns form which arestrongly influenced by the stamp geometry. Rapid expansion of air results in fractal viscous fingering patterns.

The hot embossing process is a low cost, fast method forthe replication of structures at the micro- and nanoscaleover large areas. In Hot Embossing Lithography, a thinlayer of thermoplastic material is used as a resist forsubsequent pattern transfer; it is heated above the glasstransition temperature so that it assumes a viscous state andcan then be shaped under pressure by imprinting with ahard master. Once the polymer has exactly conformed tothe shape of the stamp, it is hardened by cooling and themaster is demolded. In order to optimise the embossingprocess for more complex stamp geometries, an insight intothe way in which the nano- and microcavities fill duringembossing is important. The thin film environment alsoprovides a model system where fundamental effects can bestudied.

AFM profile of partially filled cavity

Position of cavityduring embossingwidth: 20 umheight: 175 nm

Schematic Representation of Polymer Flow

STAMP

POLYMER

SUBSTRATE

compression

t ft t t t

Fig. 1: Squeeze flow of polymer into stamp cavity.

Under ordinary conditions, a microcavity is continuouslyfilled from the borders during hot embossing of thinpolymer films. AFM measurement reveals that bothcapillary effects, causing the polymer to flow up the cavitywalls, and compressive effects, seen as a bowing of thecentral region, are apparent (see Fig. 1).

The formation of periodic pillar arrays in thin polymerfilms can be induced when a charged mask is placed inclose proximity to the molten polymer film. It is knownthat the period depends on the size of the electrostatic field,surface tension, Van der Waals interaction, and the polymerviscosity, thickness and molecular weight. We have shownthat it is possible to tailor the shape and size of the polymerpillars by using a specific stamp cavity size and shape. Linesections, dots and rings have been isolated and an exampleof this is given in Fig. 2.

Fig. 2: Polymer pillars formed in stamp cavity. Originalstamp geometry in black (cavity) and white.

At the high pressures used for embossing, the air in thecavities is compressed and is not observed in the finalembossed structures. However, if the embossing pressure isapplied rapidly or the embossing pressure is released beforecooling, an explosive behaviour of the air occurs and aviscous fingering pattern is formed. The final pattern isfractal in nature due to the high air expansion velocitiesinvolved. In the presence of a structured stamp, there is ananisotropic growth of the finger pattern which prefers togrow along the structure edges (see Fig. 3).

Fig. 3: Viscous fingering with structured stamp.

The observation of pattern formation in polymer thin filmsis proving to be important for the understanding ofstructure formation in the micro- and nanorange, and willhelp to improve stamp design and processing.

FUNDING: SNF (NFP36), PSI.

REFERENCES[1] L.J. Heyderman, H. Schift, C. David, J. Gobrecht,

T. Schweizer Micro. Eng., Accepted (2001).

[2] H. Schift, LJ. Heyderman, M. Auf der Maur,J. Gobrecht Nanotechnology, Accepted (2001).

96

NANOFABRICATION WITH HOT EMBOSSING AND ELECTROFORMING

L.J. Heyderman, M. Aufder Maur, D. Bdchle, C. David, F. Glaus, J. Gobrecht, B. Haas, M. Horisberger,P. Hdberling, B. Ketterer, T. Neiger and H. Schift (PSI), R. Bischofberger (Applied Microswiss)

The nano- and microstructuring possibilities of electroforming in combination with hot embossing lithography aredemonstrated. Periodic structures down to 120 nm and feature sizes < 50 nm were replicated. Electrode devices,several mm long, were fabricated with various line widths and heights. Overplating provided a means to increaseaspect ratios and decrease gapwidths, and daughter molds with nanoscale fidelity were fabricated by backplating.

Hot Embossing Lithography (HEL), also referred to asNanoimprint Lithography (NIL), can be used to replicatemicro- and nanostractures for a variety of applications, forexample electrode structures, Fresnel zone plates and highdensity magnetic recording media. One of the mainadvantages of conformal molding over other replicationtechniques, is that structures with high aspect ratios can bedirectly reproduced by embossing a thermoplastic material.

Lines Dots HolesHeight: 35 nm Height: 35 nm Depth: 150 nm

Structured stamp

Embossed thinpolymer filmSeed layerSubstrate

HI

(i) Aspect RatioPreserved

(ii) Overplating

(Hi) Backplating

Fig. 1: Process scheme for HEL with electroforming.

To maintain this advantage in subsequent pattern transfer,electroforming rather than lift-off is used because metalstructures can be generated with a considerable height anda good surface quality. The possibilities for electroformingof resist structures with an underlying seed layer are shownin Fig. 1. After embossing the residual resist layer isremoved by oxygen reactive ion etching (RIE), openingseed layer windows for plating. Depending on the extent ofelectroplating, either the structure height can be preservedor increased. Daughter stamps can be manufactured byextending the overplating to form a substantial supportingbase, providing a robust metal stamp.

We used a Cr/Ge seed layer which provided a good startingmaterial for subsequent nickel electroplating. Periodicarrays of lines and dots with periods down to 120 nm andfeature sizes <50 nm were faithfully replicated, andexamples of 400 nm period nickel structures are given inFig 2. The surface of the electroplated nickel is smoothwith a roughness comparable to that of the electroplatingseed layer. Nickel daughter stamps, backplated to athickness of 100 to 400 u,m, were produced with resolutionmatching that of the original and were successfully used toreplicate structures in polycarbonate.

400 nm

Fig. 2: 400 nm period electroformed structures (originalpolymer mask height: 50 nm).

Cross-section images of some electroplated electrodes aregiven in Fig. 3. Here, electrode lines with periods of 1 (J,mwere overplated to heights up to six times greater than theoriginal polymer galvanoform (45 nm thick), resulting in adecrease in the interelectrode gap from 150 nm to 40 nm.Following removal of the Cr/Ge between the nickel linesby RIE, electrical measurements showed that the longparallel electrode fingers were isolated.

Fig. 3: Electroplated nickel lines for electrode device.

HEL and electroforming is of interest, for example forelectronic devices where a small gap is required or forcreating metal sieves with nanoscale holes. It seems likelythat the dimensions of the electroformed structures can befurther decreased for future nanoscale applications.

FUNDING: SNF (NFP36), PSI.

REFERENCE[1] L. J. Heyderman, H. Schift, C. David, B. Ketterer,

M. Auf der Maur and J. Gobrecht, MicroelectronicEngineering, Accepted for Publication (2001).

97

V-GROOVE REPLICATION: A TOOL FOR QUALITY CONTROL OF A COMPACTDISC INJECTION MOLDING PROCESS

H. Schift, F. Glaus, J. Gobrecht, B. Haas and B. Ketterer (PSI), A. D'Amore, D. Simoneta and W. Kaiser(FHAargau and KATZ), M. Gabriel (AWM Werkzeugbau), W. Haese (Bayer AG)

Polymer molding is highly suitable for the mass fabrication of high precision micro- and nanostructures. It requiresthermoplastic polymers with good molding properties at moderate process temperatures. We show a quantitativeapproach to the analysis of the molding properties of polymers in the nanorange and indicate which parameters aremost important for achieving a good replication fidelity.

Thermal injection molding is a key technology for thefabrication of devices with nano structured surfaces. Itcombines a very high resolution capability with low-cost,mass production potential. In our previous work [1] it hasbeen shown that the replication limit has not yet beenreached and that the molding process can be very fast. Forfuture high precision applications it is necessary to broadenour understanding of how nanostructures are molded andwhich kind of polymers are best suited for nanoreplication.

Fig. 1: V-groove etched into monocrystalline silicon

Our aim was to generate microstructures on a mold withvariable size and defined shape, and to examine a physicalproperty in the nanorange which can be easily measured onthe molded structure. Particularly suitable as masterstructures for this are V-grooves, which can be fabricated inmonocrystalline silicon substrates by anisotropicalchemical wet etching. This process yields grooves withvery smooth walls and a sharp V-shaped bottom edge (seefig. 1). Gratings with periods ranging from 120 nm to 5 Limwere fabricated. The silicon master was inserted into aCompact Disc molding tool from AWM and severalhundred discs with a diameter of 80 mm were producedwith cycle times down to 10 sec (see fig. 2). The polymersused were polycarbonates from Bayer AG.

The degree of molding of replicated V-groove structureswas compared for different process parameters, sizes andorientations. The dominant factor which influences themolding fidelity is the strong dependence of the meltviscosity with the mold temperature. Within thetemperature range given by the molding tool the height ofthe A-ridges increases constantly up to temperaturesslightly below the glass transition temperature of the

lliil

Fig. 2: Injection molded A-ridges on a Compact Disc

polymer (see fig. 3). The aspect ratio (relative height) of themolded structures is nearly constant for different structuresizes on the same molded disc.

70

60

40-

£ 303

10

I

I

I

I ' ' - " !

y

i

100 105 110 115 120

mold temperature [°C]125 130

Fig. 3: Structure height of an injection molded A-ridgedependent on the mold temperature (structurewidth 200 nm).

Using molds with V-grooves new materials can be testedand the fidelity of the molding in the micro- and nanorangecan be improved. With this knowledge the already largepotential of the injection molding technique for the massfabrication of nano structured devices can be increased.

FUNDING: SNF (NFP36), PSI, FHA, AWM.

REFERENCE

[1] H. Schift, A. D'Amore, C. David, M. Gabriel,J. Gobrecht, W. Kaiser and D. Simoneta,J. of Vac. Sci. Technol. B 18 (6) (2000).

98

LASER ABLATION LITHOGRAPHY USING DIFFRACTIVE PHASE MASKS

C. David, T. Neiger, P. Haberling, J. Wei, T. LippertandA. Wokaun (PSI)

We investigated a fast parallel method for the fabrication of continuous profile structures in polymer surfaces usinga XeCl excimer laser. The used quartz phase masks consist of phase gratings with varying duty cycles to control thetransmitted zero order flux for different positions on the mask. Using this method, blazed diffractive optical elementswere ablated in polyimide films.

Intense UV laser pulses can be applied to pattern polymersurfaces. The ablated depth per laser pulse depends on thefluence and the sensitivity of the polymer. Complexpatterns over larger areas can be generated by projecting ademagnified image of a mask onto the substrate.Conventional photo masks consisting of absorber structuresoften suffer from radiation damage. We developed phasemasks consisting of gratings etched into quartz substrates.The patterned areas diffract the light out of the aperture ofthe projection lens without absorption or damage (Fig.l).

Photomask withdiffracting structures

Substrate(polymer)

Fig. 1: Set-up for the patterning of polymer surfaces bylaser ablation using diffractive masks.

The masks are generated using electron beam lithographyand reactive ion etching (Fig. 2). The transmitted zero orderflux propagating through the lens onto the substrate can bevaried by changing the line width and thus the duty cycle ofthe diffracting structures. This is achieved by a continuouschange of the focal setting of the electron-beam lithographytool [1]. To achieve an accurate control of the ablateddepth, the threshold and the non-linear response of theablated polymer was measured and pre-compensated in themask design. The correction algorithm was implemented inthe mask data preparation software.

I I

Fig. 2: SEM micrograph of diffractive grey tone phasemask structures with varying duty cycle etchedinto quartz.

Fig. 3: SEM micrographs of an array of diffractive microlenses. Each lens has a size of 0.8 x 0.8 mm2 andis generated using only a few shots of the excimerlaser.

The described method opens up the possibility for efficientfabrication of diffractive optical elements with continuousstructure profiles [2]. As an example, a micro lens arrayablated into a spin-coated polyimide film on a glasssubstrate is shown in figure 3. The array was formed in astep-and repeat scheme by exposing each lens with a fewlaser pulses. The lower image shows the desired sphericalshape and the steep edges of the polyimide lenses.

FUNDING: SNF, PSI.

REFERENCES

[1] C. David and D. Hambach, MicroelectronicEngineering 46 (1999) 219-222.

[2] C. David, J. Wei, T. Lippert, A. Wokaun,submitted to Microelectronic Engineering.

99

HIGH RESOLUTION SCANNING X-RAY FLUORESCENCE MICROSCOPY

C. David, F. Glaus, T. Neiger (PSI), B. Kaulich, R. Barrett, M. Salome and J. Susini (ESRF)

Using Fresnel lenses optimised for operation near the sulphur absorption edge at 2472eV photon energy, it waspossible to perform X-ray fluorescence microscopy experiments with unprecedented spatial resolution andsensitivity. By imaging zinc sulphide (ZnS) test structures specially fabricated for this experiment, we were able toresolve features with lateral dimensions below 100 nm and to detect sulphur quantities down to 3-10l6g.

For many samples the fluorescent X-ray emission resultingfrom absorption of the incident beam offers usefulchemically sensitive information about the system understudy. In particular, the vastly reduced Bremsstrahlungspectral background has a trace element sensitivity whichcan be significantly better than that possible using electronexcitation. On the other hand, it is also of interest forconcentrated systems as the use of fluorescence emissionallows the study of bulk, non-conducting samples whichcannot be prepared in suitably thin sections for standardabsorption contrast microscopy. The characteristics of theESRF ID21 X-ray microscopy beamline make it well suitedto applying X-ray fluorescence microscopy for studies ofsulphur content using both spectrometric and spectroscopicmethods in applications such as geochemistry and humanbiology.

The experimental methods being developed depend uponthe quality of the microfocussing optics, which mustdeliver high fluxes into the smallest possible probe size. Tomeet these demands, the lens diameter has to be matched tothe spatial coherence of the undulator source, and itsoutermost zone structures should be as small as possible.Furthermore, the zone structures have to provide a gooddiffraction efficiency. Fresnel lenses especially optimisedfor this purposes have been fabricated using electron beamlithography and reactive ion etching. The 300 |j,m diameterlenses consist of 900 nm high germanium structures with100 nm outermost zone width on a Si3N4 membrane [1].

To investigate the limits of sulphur fluorescencemicroscopy, a test pattern consisting of 26 nm thick ZnSstructures was used. To minimise the background signal agermanium substrate was used. Figure 1 shows scanningelectron microscopy (SEM) images of these structures.

".*. •

Fig. 1: SEM images of a ZnS Siemens star. The structuresare 26 nm thick, the width ranges from 1 itm downto 50 nm (half pitch). The right image showsstructure widths from 75 nm to 175 nm.

Fig. 2: The ZnS test structures imaged at the ESRFscanning x-ray microscope in sulphur-fluorescence mode. The lower image shows azoom of structure widths ranging from 75 nm to175 nm.

The sample was scanned with radiation just above thesulphur K-absorption edge at 2472 eV. The sulphur K-linesX-ray fluorescence (2307-2464 eV) was collected using anenergy dispersive high-purity Ge detector. Figure 2 showsthe resulting scanning x-ray fluorescence microscopeimages. Even though the fluorescence yield for S K-lineemission is only 0.078, structure widths below 100 nm canbe resolved. Taking into account the sulphur content of thetest structures, this corresponds a sensitivity of better than300ag(3-1016g).

Further high resolution scanning x-ray fluorescenceinvestigations on biological specimens are currentlyongoing.

FUNDING: PSI, ESRF.

REFERENCE

[1] C. David, B. Kaulich, R. Barrett, M. Salome,J. Susini, Appl. Phys. Lett. 77, 3851 (2000).

100

TUNABLE WET ETCHED DIFFRACTIVE OPTICS FOR HARD X-RAYS

C. David, B. Nohammer, B. Haas, J.F. van der Veen (PSI), J. Hoszowska, E. Ziegler, M. Drakopoulos,F. Zontone (ESRF), J.H.H. Bongaerts, M.J. Zwanenburg (Univ. Amsterdam)

Electron beam lithography and vertical selective wet etching of silicon has been applied to fabricate linear transmissionFresnel zone plates. By tilting the lens it is possible to increase the effective structure height and to optimise thediffraction efficiency over a wide range of photon energies. Measurements using the lenses as collimators for x-raywaveguiding experiments resulted in a flux enhancement by a factor of 50.

Focusing elements for hard x-rays are used either toprovide a small spot of radiation for spatially resolvingtechniques or to concentrate the radiation in order toenhance the flux density in a small region of interest. Themain problem with producing highly efficient diffractivelenses for hard x-rays is that the phase shift of matter issmall, which means that extreme aspect ratios are requiredfor sub-micron structure widths. This is particularly true formaterials consisting of light elements, and is therefore whysilicon was formerly considered as unsuited for thefabrication of diffractive transmission hard x-ray optics.However, single crystal silicon offers a unique possibilityto fabricate very high aspect ratio structures using a simplewet etching process shown in figure 1.

ra) membrane definition

Vc) 30 nm Cr lift-off

b) eleclron-beam exposure.mil development

d) orientation-selectivewet etching and removal of Cr

Fig. 1: Schematic view of the lens manufacturingprocess. On <110> Si substrates, lines in <112>direction can be wet etched with vertical side

The hard x-ray lenses shown in figure 2 were fabricatedusing this method [1]. The outermost zone width is 324 nm,the zone height is 12 (am, corresponding to an aspect ratioof 40. To increase the aspect ratio even further, the linearlenses can be tilted with respect to the x-ray beam as shownin figure 3. This trick also enables us to vary the effectivestructure height in order to match the resulting phase shift

•CO

Fig. 2: SEM images of a linear Fresnel lens fabricated byelectron beam lithography and wet chemicaletching of <110> oriented silicon substrates.

Fig. 3: The effective structure height of adiffractive lens can be increased by tilting.

linear

over a wide range of photon energies [1]. The diffractionefficiency of a 5.5 |j,m high silicon lens was measured as afunction of tilt angle for photon energies up to 29 keV (seefigure 4). The measured values are in good agreement withcalculations based on scalar diffraction theory; they show,that it is indeed possible to tune the lens over a wide energyrange.

The lens has been applied to focus 13.3 keV radiation inwaveguiding experiments on ordering phenomena ofcolloid suspensions [2]. An increase in flux by a factor of50 was measured compared to measurements performedwithout a lens.

Aspect ratio of outermost zone structures16 20 30 50 100 200

10 20 30 40 50 60 70 80

Fig. 4: Calculated and measured efficiency of a 5.5 iimhigh silicon lens as a function of tilt angle.

FUNDING: PSI, ESRF.

REFERENCES

[1] C. David, B. Nohammer, E. Ziegler:submitted to Appl. Phys. Lett.

[2] M. J. Zwanenburg et al.:Phys. Rev. Lett. 85, 5154 (2000).

101

MICROMECHANICAL CANTILEVERS FOR THERMAL ANALYSIS

J.H. Fabian, C. Padeste, J. Gobrecht, Ph. Lerch (PSI), L. Scandella (NanosurfAG), E. Meyer (Univ. Basel)

Micromechanical cantilever devices have been designed and fabricated. Heated cantilevers are used as athermo gravimetric sensor for the analysis of nanogram weight samples and achieve picogram mass accuracy. Todemonstrate the excellent features of the fabricated devices, the thermal gravimetric analysis of 2.7 ng calciumoxalate monohydrate is presented.

Analytical chemistry routinely uses thermal gravimetricanalysis (TGA) in order to study the change in mass ofsamples undergoing desorption, adsorption or decom-position processes. We have developed a method based onjoule heated micromechanical cantilevers to investigate thethermal behaviour of samples whose masses range betweenabout 100 picograms and several hundred nanograms.

Micromechanical cantilevers were attached to a piezo-electric actuator and the bending amplitude measured by anoptical beam deflection technique adapted from scanningforce microscopy. In the experimental setup (Fig. 1) theresonance frequency of a cantilever with the depositedsample (Fig. 2) is tracked while the cantilever is heated up.

vacuum pump

Fig. 1: In the experimental setup, the cantilevers'deflection can be determined with < 1 nmaccuracy while the device is operated undervacuum or inert gas conditions.

A variation of the mass of a cantilever-sample systeminduces a shift in the resonance frequency. Since thetemperature of the silicon cantilever can be controlled bythe electrical power dissipated into the device, a sensitivethermobalance is realised.

For that purpose, complete arrays of U-shaped cantileverswith a p-doped top layer in which joule heat is dissipatedwere micro-machined [1]. In order to optimise the designof the cantilevers for thermogravimetric applications, finiteelement simulations of the micro-electro-mechanical devicewere performed [2].

To demonstrate the performance of our thermobalance, wemeasured the thermal decomposition curve of calciumoxalate monohydrate. The chemical reaction occurring inthree steps can be described as follows:

Fig. 2: 2.7 ng of calcium oxalate were deposited with amicromanipulator on the cantilever device.

CaC2O4 H2O (s) <-»CaC2O4 (s) + H2O (g)CaC2O4 (s) -> CaCO3 (s) + CO (g)CaCO3 (s) <-> CaO (s) + CO2 (g)

In the measured TGA curve (Fig. 3) the threedecomposition steps can be well resolved; only a smalldiscrepancy in the second step is observed in comparisonwith the theory.

-1,4200 400 600temperature (°C)

800

Fig. 3: Temperature dependence of the mass changefollowing the decomposition of 2.7 ng calciumoxalate monohydrate.

The major advantages of a cantilever based systemcompared with conventional thermal analytical instrumentsare the high mass sensitivity, the low power consumptionfor heating the device up to several hundred degreesCelsius, and the short thermal response time which allowsus to thermally cycle the device in the kHz range.

FUNDING: SPP MINAST NOSE, PSI.

REFERENCES

[1] J.H. Fabian er al., Ultramicroscopy 82, 69 (2000).

[2] J.H. Fabian et al., Proceedings of the 18th CAD-FEMUsers' Meeting, International Conference on FEMTechnology, A 1.4.5 (2000).

102

SINGLE HOLE TRANSISTOR IN A p-Si/SiGe QUANTUM WELL

U. Dotsch, U. Gennser, C. David, G. Dehlinger, D. Griitzmacher (PSI), T. Heinzel, S. Luscher, K. Ensslin (ETHZ)

A single hole transistor is created in a p-Si/SiGe quantum well by applying voltages to nanostructured top gate elec-trodes. The gating is achieved by oxidizing the etched semiconductor surface and the mesa walls prior to evapora-tion of the top gates. Pronounced Coulomb blockade (CB) effects are observed at small coupling of the transistorisland to source and drain.

Transport through small islands defined in semiconductorshas been of considerable interest recently. When the islandis only weakly coupled to reservoirs via tunnel barriers, theCoulomb blockade effect determines the carrier transport.Single hole transistors out of p-doped Si/SiGe quantumwells are of particular interest for several reasons: (i) thematerial has a large g-factor of geJ= 6.7 and a large effectivemass (m = 0.25 me), (ii) the interaction parameter rs, de-fined as the ratio between the Coulomb energy of two holesat their average separation, and the Fermi energy, is verylarge, i.e., rs ~ 4 for typical carrier densities.

jot'

Fig. 1: Schematic cross section through the processedhetero structure.

The top gate (10 nm Ti and 20 nm Al) was patterned byelectron beam lithography and subsequent lift-off usingthermal evaporation. In Fig.2 the island geometry is shown.Three split gate electrodes (point contact gates pel, pc2, aswell as the center gates define the dot with a lithographicsize of 500 nm x 800 nm. For pel and pc2, a gap width of150 nm was chosen.

0.010

0.008

0.006

0.004

0.002

pel: -180mVpc2:+145mV

0.002

43 44gate voltage (mV)

35 40 45 50gate voltage (mV)

55 60

However, p-SiGe has been notoriously difficult to gate, dueto leakage currents across the Schottky barrier. Here, wepresent the fabrication and characterization of a gated sin-gle hole transistor in a p-SiGe quantum well. Tests haveindicated that in our samples, large leakage currents be-tween the top gate and the 2-dimensional hole gas can flowacross the mesa edge. Therefore, we have deposited a layerof SiO2 by thermal evaporation right after the reactive ionetch which defines the mesa, as shown in Fig. 1.

Fig. 2: Scanning electron micrograph of the gate geome-try. The Ti/Al gates appear as bright areas.

Fig. 3: Conductance G through the island as a function ofVg, showing CB oscillation. Inset: blow-up of thepeak at Vg =43 mV (crosses), fitted to a thermallybroadened CB resonance (solid line). For thesemeasurements, the temperature was 90 mK

At sufficiently large split gate voltages Vpcl and Vpc2, CBoscillations are observed as a function of the center gatevoltage V,s.[Fig. 3]. Here, Vsomdmin was kept at 100 jxV. Themeasured CB resonances can be fitted well to the expres-sion

G(VTh) = Gmax cosh"2 [rj • (F - Fmax)/ kjh ]

describing a thermally smeared CB peak in the multileveltransport regime. G ^ and Vmai denote the amplitude and theposition of the CB resonance, respectively.

FUNDING: SPP MINAST (SIMNAD), PSI.

REFERENCE

[1] U. Dotsch et al., Appl. Phys. Lett. 78, 341 (2001).

103

ELECTRO- AND PHOTOLUMINESCENCE OF C-INDUCED GE ISLANDSEMBEDDED IN SI

A. Beyer, E. Miiller, S. Stutz, H. Sigg, D. Grutzmacher (PSI), K. Ensslin (ETHZ)

The deposition of a sub-monolayer carbon on a Si (001) surface and the subsequently growth of Ge leads to an im-mediately 3-dimensional nucleation of small Ge islands. These islands show intense photoluminescence (PL). Theexternal quantum efficiency (EQE) increases with a decrease of the excitation power density from 4xlO'4 to 1.4xlO'2

for an optimised sample. Electroluminescence from Ge islands was observed with an EQE in the 10" range.

A promising way to improve the optical properties in indi-rect semiconductors like silicon is the localisation of chargecarriers. The resulting enhanced uncertainty in the momen-tum of the charge carriers allows optical transitions withoutthe use of phonons. In order to realise a distinct carrierlocalisation, Ge islands were prepared on the C alloyed Si(001) surface. This technique leads to extremely small Geislands (<15 nm) at moderate deposition temperatures [1].

We have grown these islands by molecular beam epitaxy ata substrate temperature of 460°C using e-beam evaporationof Si and Ge. The carbon was evaporated from a pyrolithicgraphite filament. Photoluminescence (PL) measurementsat 1.8 K were performed on samples with a stack of 10island layers. These layers were separated from each otherby 8 to 32 nm Si. An annealing step in a H/N2 ambience at650°C for 10 minutes was applied after the growth in orderto enhance the PL intensity due to healed up point defects.

U5CCD

0.9 1.0energy [eV]

1.1 1.2

Fig. 1: PL at various excitation power densities. Inset:Integrated PL of the Ge dots and the Si TO peak.

The amount of C and Ge per island layer was varied from0.1 to 0.3 monolayer (ML) and from 0 to 3.4 ML, respec-tively. The strongest PL intensity was found for islandsformed by 0.2 ML of C and 2 ML of Ge grown in layerswhich were separated by 16 nm Si. The PL for such a struc-ture at different excitation power densities is shown infigure 1. The large broad peak around 1.0 eV stems fromthe Ge islands. The Si cause to smaller narrow peaks athigher energies, such as the TO phonon related (Si TO) lineat 1.09 eV. The external quantum efficiency of the Ge is-

land related PL increases with a decrease of the excitationpower density from 4-10"4 to 1.4-102. The inset in figure 1compares the integrated PL from the Ge islands and the SiTO peak in dependence of the excitation power. The slopeof 0.5 and 0.97 suggests that Auger recombination in theislands and impurity levels in the silicon are the dominantnon-radiative recombination paths.

H .6V / 30mAJ

voltage / current

-2.6V / 309mA

-2.4V/245mA

-2.2V/182mA

-2.0V/124mA

1.4V/9mA

0.85 0.90 0.95 1.00 1.05

energy [eV]1.10 1.15

Fig. 2: Electroluminescence (EL) at various bias voltages.Inset: Integrated EL and external quantum effi-ciency (EQE) at various current densities.

For the electroluminescence (EL) measurements, deviceswere fabricated from samples containing a stack of 30island layers with the PL optimised structure grown on a n-type Si wafer and capped with a 200 nm wide p-doped Silayer. On the front side of the devices aluminium fingercontacts were fabricated, with a width of 4 iim and spacedby 3 (im covering a device area of 0.134 mm2.

The EL measurements at 15K shown in figure 2 reveal anbroad peak from the Ge islands at 1.04 eV. The externalquantum efficiency is plotted in the inset for the variouscurrent densities and is generally rather low in the 106

range. Improvements can be expected by using transparentconductive oxide (TCO) contacts instead of the Al fingercontacts on the front side.

FUNDING: SNF, PSI.

REFERENCE[1] O. G. Schmidt, C. Lange, K. Eberl, O. Kienzle, and

F. Ernst, Appl. Phys. Lett. 71, 2340 (1997).

104

OPTICAL AND STRUCTURAL ANALYSIS OF GE QUANTUM DOTS EMBEDDED INSTRAINED SI QUANTUM WELLS GROWN ON PATTERNED SUBSTRATES

A. Beyer, E. Miiller, S. Stutz, H. Sigg, C. David, D. Grutzmacher (PSI), K. Ensslin (ETHZ)

Ge quantum dots embedded in strained Si quantum wells (QW) were investigated. The dislocation density in the re-laxed SiGe buffer layer was reduced by deposition on mesa lines possibly permitting an elastically strain relaxation.Intense PL signals were observed from Ge dots in the stained Si QW's. It was proven, that these PL stems from thequantum structures by comparing samples before and after etching the Si QW and the Ge dots.

Ge quantum dots embedded in silicon have been used in thepast to improve the opto-electronic properties of Si basedmaterials. The idea is to overcome the limitation of theindirect band gap of Si by strong localisation of the carriersin quantum dots. However, the Ge quantum dots provide astrong carrier confinement only for the holes, the electronsare only weakly confined in the Si. We embedded the Gequantum dots in strained Si quantum wells (QW) grown onrelaxed SiGe buffer layers. The strained Si QW provide aconfinement of the electrons in the vicinity of the Ge dots.

The structures were deposited on planar and patterned sub-strates by MBE. The pattern was created by e-beam lithog-raphy on Si (001) wafers. 2 Lim deep and 1.5 itm widetrenches were etched to define line shaped mesas withwidths ranging from 0.5 |im to 4.5 (J,m. The lines werealigned parallel and 15, 30 and 45° off to the [110] direc-tion. Si and Ge were deposited by e-beam evaporationusing a substrate temperature of 620°C. First a 1.2 (j,m thickSi08Ge02 step graded buffer layer was grown. On top of thisbuffer layer Ge islands have been deposited using 7monolayer of pure Ge, followed by a 2.5 nm thick siliconlayer and a 20 nm thick Si08Ge02 spacer layer. These threegrowth steps were repeated 10 times.

0.9 1.0

energy [eV]

1.1

Fig. 1: PL at 1.8K of Ge dots in strained Si QW (blackline). The etched and the planar sample confirmour assignments (see text).

The PL from a patterned and a planar sample are comparedin figure 1. The planar sample exhibits intense dislocationrelated PL lines. These lines are strongly reduced in thecase of patterned substrates [1]. An intense PL signal la-beled with X^ dominates the spectra from the patternedsample in figure 1. In the planar sample these signal is

quenched, presumably because of the high dislocationdensity in the SiGe buffer layer. These PL is assigned to thequantum structures grown on top of the relaxed bufferlayer. We have proved this assumption by removing thequantum structures by an reactive ion etching step in a SF6

plasma. The PL spectra from the remaining SiGe bufferlayer is plotted as a gray line in figure 1. The X^ line isquenched due to the etching. Consequently these line isattributed to the quantum structures. Unfortunately, the PLdata do not permit an exact assignment of the recombina-tion path, which give rise to the X^ line.

Fig. 2: TEM images from structure grown on top of theline shaped mesa. An silicon enrichment on the topcorner forms an vertical silicon quantum well.

The sample with the smallest mesa width shows an unusualfeature in the TEM image in figure 2. A vertical bright thinline through the center of the mesa structure is visible,indicating an enrichment of silicon. Apparently, the growthrate of si is larger on the top than on the adjacent facets.Consequently, we have grown a self assembled verticalsilicon rich quantum well with a width of about 20 nm.This vertical QW acts as an efficient collector for electronsand improves the confinement of the electrons in the vicin-ity of the Ge islands, leading to intense PL lines.

FUNDING: SNF, PSI.

REFERENCE

[1] D. Grutzmacher, R. Hartmann, O. Leifeld,U. Gennser, C. David, E. Miiller, J.-C. Panitz, SPIEVol. 3630, 171 (1999).

105

MODELING OF THE C(4X4) SURFACE RECONSTRUCTION

C. Guedj, O. Leifeld, D. Griitzmacher (PSI), P. Kelires (FORTH), E. Kaxiras and I. Remediakis (Univ. Harvard)

The C(4x4) surface reconstruction previously observed by STM was modelled with anharmonic Keating modelling,Monte Carlo modelling, and full Ab Initio quantum mechanics calculations. The lowest energy configuration as wellas good agreement with STM data is obtained with a configuration involving surface carbon atoms positioned insecond nearest neighbours.

Carbon-induced Ge dots can exhibit interesting photolumi-nescence and electroluminescence properties, which maylead to further opto-electronic applications if the techno-logical and economical requirements are fulfilled. Thecontribution of carbon is essential but its exact distributionduring and after growth is not precisely known. Carbonpre-deposition onto Si(001) lead to the c(4x4) surface re-construction domains, which were previously interpretedwith a model involving surface carbon atoms in first nearestneighbours.[l] However, this model turned out to be in-compatible with recent XPD experiments.[2],[3],[4] There-fore, we searched for another structural arrangement ofatoms compatible with all available experiments. Threecomplementary theoretical tools also indicate that thismodel, involving carbon atoms in second nearestneighbours, is the most stable among those considered.

This structure is represented at the atomic scale in figure 1.

oo

aCO

§tn

b

3 -

0 1 2 3 4Distance along [110] (nm)

Fig. 1: Top view of the arrangement of atoms considered toexplain the c(4x4) surface reconstruction. Atomicpositions are obtained from anharmonic Keatingmodelling.

In this newly suggested configuration, carbon atoms arearranged in second nearest neighbour positions, thereforethey locally form a zinc-blende silicon carbide. This con-figuration is a local cubic 3C-SiC nanostructure on silicon,which is more stable than a surface diamond nanocluster.For bulk Si-C solid solutions, it is known that stoechiomet-ric SiC is the only stable compound of the phase diagram.In our case, anharmonic Keating modelling, Monte Carlosimulations and full ab initio Quantum mechanics simula-tions demonstrate that this model has a lower energy thanthe one involving surface carbon atoms in first nearestneighbors. Moreover, a reasonable match is found for thecalculated STM image and the experimental one, as illus-

trated in figure 2. The calculated distance between spots(0.64 nm) is reasonably close to the experimental one (0.59nm). In this respect the model described in [1] gives betteragreement, however, the asymmetry between spots is wellreproduced, as opposed to the modelling suggested in [1].Moreover, the overall agreement by this new model with allavailable experimental data is satisfactorily.

Fig. 2: Comparison between experimental STM image andsimulated image (top left) obtained from full abinitio calculations.

The STM resolution is difficult to estimate and depends onmany factors such as tip radius, voltage step resolution,resolution of the A/D converter in addition to electrical andmechanical noise. A conclusive answer to the atomic posi-tion of the C atoms in the C alloyed Si surface may beobtained from grazing incidence x-ray diffraction data.

FUNDING: BBW/EU (SiGeNET), PSI.

REFERENCES[1] O. Leifeld, D. Gratzmacher, B. MuTler, K. Kern,

E. Kaxiras and P. C. Kelires,Phys. Rev. Lett. 82, 5 (1999).

[2] R. Kosugi, S. Sumitani, T. Abukawa, Y. Takakuwa,S. Suzuki, S. Sato, S. Kono,Surf. Sci. 412/413,125 (1998).

[3] M. Ikeda, T. Maruoka, N. Nagashima,Surf. Sci. 416,240 (1998).

[4] M. Stoffel, L. Simon, D. Aubel, J.L. Bischoff,L. Kubler, Surf. Sci. 454-456, 201 (2000).

106

STRAIN FIELDS IN C-INDUCED GE DOTS

C. Guedj, E. Muller, A. Beyer, D. Griitzmacher (PSI), K. Eberl (MPI Stuttgart)

Optical properties of solid-state nanostructures are usually correlated to the amount of strain at the atomic level.Local stresses modify the orbitals shapes and the energy levels. The exact distribution of strain in a heterogeneousmedium is usually difficult to estimate. Analysis of high-resolution TEM images may help to get a better insight intothe local distortions in various nanostructures. The example of carbon-induced Ge dots is particularly interesting.

Electronic-Device properties are directly linked to the mi-crostracture of the material, at the atomic scale. In lowdimensional heterostractures, interatomic distances mayrapidly change from the substrate to the active layers, andthe mapping of these distortions is of high interest to under-stand the resulting physical properties. Carbon-induced Gedots are particularily relevant to illustrate this principle,because rapid fluctuations of strain occur in these nanos-tructures, and photoluminescence energies depend on thespatial distribution of stresses. The direct correlation be-tween the strain map and the optical properties is a key tocontrol the final optoelectronic properties of the device.Therefore, we performed an investigation of strain fields inthese nanostructures.

This analysis uses digitized high-resolution transmissionelectron microscopy images to analytically extract a strainmap after proper atomic scale modeling. In parallel, wehave also implemented a self-Moire technique to obtain arapid qualitative insight into the strain fluctuations, withoutthe counstraints of extensive analytical calculations. Wefound that the two methods give basically the same results.An example is represented in figure 1.

I/J1]

Fig. 1: Self Moire pattern of a carbon-induced Ge dot epi-taxially grown on Si(001). The Moire process istuned to highlight the distortions of the parallel lat-tice parameter.

With this newly developped technique, we can choose tohighlight the distortions in the directions either parallel orperpendicular to the substrate. For example, the verticallines of figure 1 are linked to the distortion of the parallellattice parameter. When a deviation from perfect lateralperiodicity occurs, then the Moire lines bend. We can see

that the local increase of parallel lattice parameter is maxi-mal at the peripheral base of the dot. This area correspondsto the maximal distortions, where defects are most likely tooccur. These regions also fix the size of the dot; they repre-sent the "elastic fences" where the island would need toomuch energy to grow bigger. The picture is simpler in thecase of 2D systems. For a single layer of Si, xGex epitaxiallygrown on silicon with a thickness below the onset of misfitdislocations, the layer is called pseudomorphic when itsparallel lattice parameter is equal to the one of the sub-strate. In that case, the Moire pattern of figure 1 wouldconsist of a series of parallel lines whithout bending.

The picture obtained for the perpendicular distortions ispresented in figure 2.

"'. •••'"•**: [°01]

-• ; , - ; •. *'"•*>.... [ T ! O ] ^ J

if: •

Fig. 2: Self Moire pattern of a carbon-induced Ge dot epi-taxially grown on Si(001). The Moire process istuned to highlight the distortions of the perpen-dicular lattice parameter.

The spacing between the Moire lines is inversely propor-tional to the actual interplanar distance. The highest per-pendicular lattice parameter is obtained at the top of theGe-rich dot, where Ge atoms are likely to segregate. Thedot is in compression. In the underlying matrix, there is aninverse distortion, with a broader spatial extention: this areais tensially strained. The dot elastically differs from itssubstrate, and the mutual adaptation gives this complexpattern, both in the parallel and perpendicular directions.The simple 2D analysis does not apply anymore, and 3Dband structure calculations must be implemented to calcula-te the resulting band offsets. It may be possible to obtainquasi-discrete levels at the peripheral base of the dots,which should noticeably influence the optoelectronic prop-erties of the system. The tensially strained channel belowthe dot may be used for a new type of device, calledDOTFET, and recently invented by K. Eberl.

FUNDING: BBW/EU-(SiGeNET), PSI.

107

MODIFICATIONS OF THE SI(100) SURFACE

O. Kirfel, D. Grutzmacher (PSI), K. Kern (MPI Stuttgart)

The deposition of C-induced Ge dots on pre-structured surfaces is expected to lead to the self organised formation ofsmall (-10 nm diameter) Ge dots. Theoretical model calculations show that the reduction in size of the dots mightlead to an increase of the radiative recombination processes.' As the size of the dots is of strong importance, the ex-act control of their nucleation and growth is crucial and their formation has to be studied in detail.

Previous experiments with Ge deposition on C pre-coveredSi(100) showed, that pre-deposition of a 0.11 ML of Cprevents the formation of a Ge wetting layer. Ge dots withirregular shape can be found in the C-poor areas after thedeposition of 2.5 ML Ge. This could be attributed to anundulating surface strain field caused by the submonolayerof carbon.2 In contrast, the deposition of Ge on bare Si(100)leads to a wetting layer, until a critical thickness of about 4ML is reached and faceted hut-clusters are formed (Stran-ski-Krastanov growth mode)/ As the growth of Ge clustersand therefore their size is strongly influenced by the pre-deposition of carbon, we started to study the influence ofthe amount of carbon on the Si(100) surfaces.

To analyse the impact of carbon on the Si(100) surfaces,samples with a lOOnm Si buffer (750°C) and a sub-monlayer of C (460°C; 0.05ML, 0.11ML; 0.2ML, 0.3ML)were grown in a MBE and transferred under UHV condi-tion into a STM.

A general feature of the pre-deposition of carbon is theenhancement of surface roughness with increasing C cov-erage, demonstrated in figure 1. At a C coverage of 5% of amonolayer there are terraces with buckled Si dimers whichoften occur when impurities are present. On top of theseterraces are a small number of paired bright spots. Thisspots are characteristic for the c(4x4) reconstruction of theSi, initiated by the C. At a coverage of 0.11ML patches ofareas with a c(4x4) recontruction appear, separated by areasrevealing buckled dimmer rows (fig l.b). After depositing0.2ML almost the complete surface is covered by thec(4x4) reconstructed areas. Buckled Si dimers can hardlybe found. Besides the c(4x4) reconstruction, there are areasvisible where the reconstruction seems to be modified. Twoareas exhibiting this modification are circled in figure lc.Similar to the c(4x4) reconstruction this modified surfaceexhibits paired bright spots, but the correlation of thesepaired spots is different and might be written as a 2x4 re-construction based on the Si lattice. At a coverage of0.3ML the roughness has increased again. No c(4x4) re-construction and no Si dimers can be found. Generally thesurface is much less ordered and no clear reconstruction isvisible.

To summarize, these results show, that first, the Si dimerschange to buckled ones accompanied by the first c(4x4)reconstruction at 0.05 ML C. Increasing the amount of C,the reconstruction of the surface gradually changes fromthe c(4x4) reconstruction at 0.1 ML to the 2x4 reconstruc-tion at 0.2 ML. The areas with c(4x4) reconstruction growand only small areas with buckled Si dimers were found at0.11 ML C. After this, the buckled Si

Fig. 1: All Samples are Si(lOO) with a submonolayer ofC. a) 0.05ML C: First occurrence of c(4x4) recon-struction indicate by white arrows, b) 0.11ML C:Areas with elongated pairs of bright spots exhibit ac(4x4) structure, c) 0.2ML C: Most of the surfaceis c(4x4)-reconstructed. d) 0.3ML C: No c(4x4)reconstruction and no Si-dimers.

dimers disappear and the c(4x4) reconstruction starts to beextruded by a modified reconstruction at 0.2 ML C. At 0.3ML C the c(4x4) reconstruction is completely extruded andonly a less ordered surface can be seen. The increase of Ccoverage is accompanied by an increase in surface rough-ness. The larger amount of C itself with the change in thesurface reconstruction and also the change in roughnesswill impact the surface diffusion length of ad-atoms on theC-modified Si (100) surface. Thus the amount of C pre-deposited allows to control the size of the Ge dots, which isa crucial parameter in the process of optimising the emissi-on of photons.

FUNDING: SNF, PSI.

REFERENCES

[1] B. Delley and E. F. Steigmeier,Phys. Rev. B 47 (3), 1397 (1993).

[2] O. Leifeld, E. Miiller, D. Grutzmacher, B. Miiller, andK. Kern, Appl. Phys. Lett. 74 (7), 994 (1999).

[3] Y.W.Mo, D. E.Savage, B. S.Swartzentruber, andM.G.Lagally, Phys. Rev. Lett. 65 (8), 1020 (1990).

108

THERMOPHOTOVOLTAICS - SYSTEM, PHOTOCELLS AND POTENTIAL

B. Bitnar, G. Palfinger, W. Durisch, D. Griitzmacher, J. Gobrecht (PSI)

Thermophotovoltaics is a technique which converts heat into electricity by using a radiation emitter and photocells.We built a small TPV prototype system, which reached a world record system efficiency of 2.1 %. The usability ofdifferent photocells in a TPV system is discussed based on IV- measurements. One application of TPV is the integra-tion in residential gas heating systems. We present a cost estimate of the electricity generated by TPV.

A TPV prototype system was developed based on a1.35 kW butane burner, a selective emitter made fromYb2O3 and silicon photocells. With this system, componentsare tested for future use in a larger demonstration system[1].

Fig.l shows the prototype system mounted onto a conven-tional butane gas cylinder. The burner in the centre of thecylindrical configuration is surrounded by the radiation

emitter, which producesradiation in a narrow emis-sion band around 1 jxmwavelength. We measuredan emitter temperature of1735 K and a maximumemissivity of 0.85 [2]. Acluartz gl a s s tube protectsthe photocells from the hotexhaust gas. The tempera-ture of the cells, which areglued onto water-cooledcopper blocks, is below30°C.

This system produces29 W electrical power with1.35 kW thermal inputpower. This corresponds to

a world record system efficiency of 2.1 %. The photocellgenerator is made from commercially available silicon solarcells from TESSAG (Heilbronn).

Table 1 shows the result of IV (Current/Voltage)-measurements of different single photocells under AM 1.5solar irradiation and Yb2O/Er2O3 emitter radiation.

Table 1: IV-characteristics of different photocells.

Fig. 1: TPV prototype system

cell

TESSAG

PSI

CESI Ge

radiationspectrumAM 1.5

Yb,O,AM 1.5Yb,O,AMOEr,O3

Isc[mA/cm2]

37.414629.713749.5117

[mV]595630630679204243

Pmx

[mW/cm2]16.050.814.564.23.3810.7

A photocell optimised for the TPV was produced at PSI.Tab.l shows that this cell has an efficiency by Yb2O3 irra-diation about 26 % higher than the TESSAG cell.

Selective Er,O3 emitters have an emission band at 1.55 Jimwavelength and reach in principle a higher radiation powerthan Yb2O3 emitters at a temperature around 1700 K. Tab.l

also shows first IV-results for a germanium photocell fromCESI (Segrate, Italy) illuminated with Er2O3 emitter radia-tion. The electrical power is still low, but probably thiscombination has a large potential for improvements.

In order to roughly estimate the cost of electricity producedby TPV, the cost of the components of a the 20 kW TPVsystem was calculated for three different scenarios:

1. Based on an efficiency of 2.1 % already reached by the1.35 kW system, the geometry of the current system,the prices of commercially available monocrystallinesolar cells, quartz tube, an emitter and copper blocksfor cooling the cells.

2. An improved system efficiency of 3 %, which shouldbe feasible without any major breakthrough in technol-ogy, a reduction of the system diameter and the photo-cell area and using a DURAN glass tube.

3. A system efficiency of 5 %.

Scenario 1 should be achievable by producing a small se-ries of TPV systems with the current technology. Scenario2 presumes the availability of a high efficiency concentra-tor cell. Scenario 3 marks a technological breakthrough likea low bandgap cell with an efficiency and price comparableto silicon photocells.

Table 2 shows the results of the calculation assuming a life-time of 20 years, a burner running 1800 hours/year at12 kW, an interest rate of 4V4 % and yearly maintenancecosts of 1% of the investment. Expecting the market break-through of TPV at an investment cost of 1000 to1500 Euro/kWpeak, an economic large scale production ofelectricity by decentralised TPV generators could be reach-able within the next years.

Table 2: Cost estimate for a 20 kW TPV system.

Scenario

cost of cells [EUR]cost of quartz/DURAN glass tube [EUR]cost of emitter [EUR]cost of cell cooling (copper) [EUR]total investment [EUR]EUR/kW,,,tEUR/kWh excluding gasEUR/kWh including gas

1

1171876212148819360.0920.127

2

59596260

240666

0.0320.067

3

59596260240400

0.0190.054

FUNDING: PSI, BFE.

REFERENCES[1] J. C. Mayor et al, PSI annual report 2000.

[2] B. Bitnar et. al, 28"1 IEEE PVSC 2000.

109

TEM INVESTIGATION OF AN ORDERING PHENOMENON IN Al05Ga05As

E. Muller and B. Patterson (PSI)

Two types of ordering have been observed in Al05Ga0SAs grown on GaAs (110) substrate. Transmission electron dif-fraction proved the presence of a homogeneous but incomplete CuAu I type ordering while high resolution transmis-sion electron microscopy (HRTEM) revealed compositional striation parallel to the interface.

Al05Ga05As grown on GaAs (110) substrate by MolecularBeam Epitaxy is one of the materials known to show order-ing effects. An ordering of Al and Ga (Fig. 1) in the CuAu Itype structure [1] as well as quasi-periodic compositionvariations [2] are reported in the literature. Only one of thetwo phenomena used to be present at a time, however. In asample grown at the former PSI Zurich, an ordering of theCuAu I type was observed by synchrotron X-ray scattering.The additional TEM investigation aimed at a more localcharacterisation of the ordered material.

bo

Fig. 1: Ordering of Al and Ga in the CuAu I type structure.Ga : dark circles, As : bright circles, Al: gray cir-cles

Towards the bottom of the layer the number of such stack-ing faults appears to be much higher, resulting in strongerstreaking relative to the {110}-spots (Fig. 4). In the diffrac-tion pattern of the substrate neither of the additionalintensities is observed. The presence of a homogeneouslybut imperfectly ordered structure of the CuAu I type musttherefore be concluded. The quality of the ordering in-creases towards the top of the layer. This was confirmed byX-ray measurements at a thicker sample.

Fig. 4: Electron diffraction patterns from the bottom of theGaAlAs-layer (left) and from the GaAs substrate(right)

Fig. 2: TEM micrograph of a GaAlAs layer (dark gray) onGaAs (HO)-substrat (black)

The AlGaAs layer consisted of flat parts and a relativelylarge number of pyramids (Fig. 2). Diffraction patternstaken at a constant distance from the GaAs substrate showhardly any variation. Parallel to the growth direction, how-ever, two phenomena can be distinguished: Diffractionpatterns from the top of the pyramids (Fig. 3) contain"zincblende-forbidden" intensities at {110}-positions.These prove the presence of the CuAu I type ordered struc-ture. Diffraction patterns from the top of the flat part of thelayer show strong {110}-ordering reflections and weakstreaking through these spots along the growth direction(Fig. 3). The streaking is due to the presence of stackingfaults within the ordered structure.

Subsequently, the samples were investigated with high-resolution transmission electron microscopy (Fig. 4). Stria-tions running parallel to the interface have been observedover the whole length of the electron transparent part of thesample (~ 10 |j,m).

Fig. 3: Electron diffraction patterns from the top of apyramid (left) and from the top of a flat part (right)

_ -- 20 nm

Fig. 4: TEM image: horizontal composition striation in theAlGaAs layer (top), but not in the GaAs (bottom)

Calculating the autocorrelation function, two values result:a short-range correlation (1.5 nm), indicating random stack-ing faults [1], and weaker, quasi-periodic oscillations (20nm) due to composition variations [2]. It is the first timethat both ordering phenomena have been observed in thesame sample.

REFERENCES

[1] T.S. Kuan et al., Phys. Rev. Lett. 54, 201 (1985).

[2] P.M. Petroff et al., Phys. Rev. Lett. 48,170 (1982).

110

APPLICATION OF THE QUANTUM CASCADE LASER PRINCIPLE TO THESi/SiGe MATERIAL SYSTEM

L. Diehl, G. Dehlinger, H. Sigg, U. Gennser, D. Grutzmacher, E. Mttller, S. Stutz (PSI), J. Faist (Univ. Neuchatel),K. Ensslin (ETHZ)

The principle of intersubband emission is applied to the Si/SiGe material system, using hole intersubband transitionin structures grown pseudo-morphic on Si by molecular beam epitaxy. Cascade structures consisting of three timesfour repetitions of a five quantum well sequence are investigated. We observed a good agreement between theoreti-cal and experimental transition energies. The present investigation shows that Si/SiGe quantum cascade LEDs havesufficiently narrow linewidths and - in certain cases - high efficiency to be promising candidates for laser applica-tions.

The combination of Si technology for both electronics andactive optical components has always attracted a great dealof interest, but so far, the indirect bandgap of this group IVmaterial prevented the fabrication of an efficient light emit-ter. This obstacle can be circumvented by adopting theconcept of the Quantum Cascade Laser (QCL) [1] to theSi/SiGe material system. QCLs rely on intersubband tran-sitions and tunneling, which are not dependent on the typeof the bandgap. While the non-polar character of SiGealloys is an advantage, the large lattice mismatch betweenSi and Ge, small band offsets in the complex valence band,and large effective masses for holes are severe drawbacksfor the fabrication of Si-based QCL that has to be over-come.

The structure is a repetition of twelve periods consisting ofone injector region and one optically active quantum welleach. As shown in Fig. 1, two heavy hole (HH) states andone light hole (LH) state are confined in the optically activequantum well. The aim of the injector is to fill the upperlevel HH2 with carriers, which then make a radiative transi-tion down to the ground state HH1. Holes can escape fromthis level via tunneling through a miniband provided by theinjector region of the subsequent period.

0.1

-0.3

-0.4

Injector (n+1)

HH2

LHstates

Valence band edge

HHLH

100 0 -100 -200 -300 -400 -500 -600

Position (A)

Fig. 1: Valence band structure of one period of a typicalSi/SiGe quantum cascade structure.

Several intersubband luminescence structures, whose maindifference is the Ge content and width of the optical activewell, were grown by low temperature molecular beamepitaxy. TEM pictures and x-ray measurements confirmed

the good quality of the samples (see next report). For theemission experiments, the devices were mounted into a He-cooled flow cryostat and held at a temperature of 4 K. Thelight was collected by f/0.8 optics, sent into a Fourier trans-form infrared spectrometer (FTIR) and detected by a cooledHgCdTe detector. An electrical current with a frequency of100 kHz and a pulse width of 5 (is was supplied to the0.4x0.4 mm2 large mesa structures.

zed)

norm

ali

>,

tens

i

c

Ligh

1.0

0.5

0.0

i \i

Mi \

I

ed E

L e

nerg

y

1\ °

180

160

140

120

/

- A

-

100 120 140 160 180 200

HH2-HH1 (meV)A_ A A n

50 100 150 200 250 300 350 400Energy (meV)

Fig. 2: Electroluminescence spectra for the three differentsamples. Inset: Measured versus calculated transi-tion energy.

The electroluminescence signal shows a strongly TM-polarized peak close to the calculated transition energy.This peak could be detected up to temperatures of 200 K. Aclear confinement shift is observed, Fig 2. The FWHM ofabout 25 meV is comparable to the best value reported sofar in absorption measurements on Si/SiGe QWs. Theradiative efficiency of the best of the SiGe is found to becomparable to GalnAs/AlInAs quantum cascade LEDs [2].

FUNDING: SNF, PSI.

REFERENCES

[1] J. Faist, F. Capasso, D. L. Sivico, C. Sitori, A.L. Hutchison, A. Y. Cho, Science 264, 553 (1994).

[2] G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist,K. Ensslin, D. Grutzmacher, and E. Miiller,Science 290, 2277 (2000).

I l l

STRUCTURAL INVESTIGATIONS OF Si/SiGe CASCADE SAMPLES

D. Griltzmacher, E. Miiller, G.Dehlinger (PSI), T. Roch, J. Stangl, G. Bauer (Uni. Linz)

The structural peculiarities of Si/SiGe quantum cascade structures have been carefully analysed using transmissionelectron microscopy, x-ray diffractometry and x-ray reflectivity. Special emphasis was put on the determination ofstrain, the interface roughness and the reproducibility of the well and barrier widths within the stacks of Si/SiGecascades. An interface roughness of 2 to3 monolayers and a correlation length of 300 +200 nm was established.

The large lattice mismatch between Si and Ge of 4% putssevere constrains on the design and the process window forthe fabrication of quantum cascade structures. In order toachieve a large confinement potential high Ge concentra-tions are desired. In addition thin Si barriers are required toallow for efficient hole tunnelling from the ground state ofthe active well into the adjacent SiGe wells. Each cascadecontains a SiGe active well and 4 SiGe quantum wellsseparated by 2 nm wide Si barriers from each other. Those4 wells form a mini-superlattice, with a miniband, which isaligned under proper bias conditions to the ground state ofthe active well of one cascade and to the excited state of theactive well of the adjacent cascade.

Fig.l shows strain situations, which occur during the depo-sition of the Si/SiGe quantum cascade structures on Si(100) substrates. The curves separate the regimes for pseu-domorphic growth (below lower line) and lattice relaxationvia formation of dislocations (above upper line). The re-gime of meta-stable growth Between these curves is acces-sible by low temperature deposition. The data a)-e) markthe situation after a) the growth of a single SiGe activewell, b) two wells separated by a Si barrier, c) one cascade(5 wells, 4 barriers), d) a block containing 4 cascades ande) the whole structure except the topmost Si contact layer.In particular for the latter situation the figure demonstratesthe huge amount of strain incorporated in the structure. Thedeposition temperature was therefore reduced to 350°C.Molecular beam epitaxy permits deposition of single crystalSi/SiGe layers at these low temperatures.

m isf i l d i s loca l io n

Fig. 1: Critical thickness of SiGe vs. the Ge content; dem-onstrating the strain situation during deposition ofa Si/SiGe quantum cascade structure

Fig.2 : TEM dark field image of the complete cascadestructure, containing 3 stacks of 4 cascades, sepa-rated by 100 nm wide Si layers.

To determine the interface roughness and the reproducibil-ity of the cascade sequence x-ray diffractometry and re-flectivity measurements have been performed. Fig. 3ashows a reciprocal space map of the (113) reflex. Anylattice relaxation would lead to a deviation of the (1U) line,i.e. the sattelite peaks would not line up with the substratepeak located at (113). Hence the reciprocal space mapclearly proves that the structure is completely strained.

Fig.3b) depicts a reflectivity space map. The reflectivitymeasurements performed at the HASYLAB and at theUniversity of Linz indicate an interface roughness of 2-3ML for the topmost quantum wells and slightly lower val-ues for the wells at the bottom of the structure. The spacemaps, showing the diffusive scattering, indicate a correla-tion length of 300 ± 200 nm. This confirms the excellentreproducibility of layer thicknesses and Ge contents in thegrown cascade structures.

a) 0.54 -

Despite the severe strain in the structures and the low depo-sition temperature no extended defects were obtained bytransmission electron microscopy (TEM). Fig. 2 shows across sectional dark field image of the complete structure.

Fig. 3: a) Reciprocal space map of (113) reflex and b)reflectivity space map of a cascade structure

FUNDING: SNF, BBW (EU), PSI.

112

FORMATION OF ARBITRARY 3-DIMENSIONAL NANO-STRUCTURES FROMSTRAINED Si/SiGe DOUBLE LAYERS

V. Prinz, A. Beyer, C. David, E. Deckardt, B. Haas, B. Ketterer, F. Glaus, D. Grutzmacher (PSI)

Complex 3-dimensional nano-structures can be formed by scrolling strained doublelayers. The simplest structuresconsists of a sacrificial layer, a thin compressively strained SiGe layer and a thin Si cap layer. By etching the sacri-ficial layer the asymmetric strain field in the underetched SiGe/Si bilayer leads to scrolling of these film. Dependingon the shape and orientation of the mesa which is underetched a large variety of 3-d nano objects are created.

Recently it has been demonstrated that nanotubes and othernano-objects with cylindrical geometry can be formed byscrolling strained films such as III/V compounds andSi/SiGe structures [1]. In this study we extended this ap-proach to the formation of arbitrary 3-dimensional nano-objects, which may open up numerous paths for new appli-cations of semiconductor nano-structures.

On top of a Si (100) substrate a thick heavily Boron dopedfilm has been deposited, followed by a 10 nm wide un-doped Si layer forming the sacrificial layer. The structure iscompleted by the growth of a SiGe/Si p-type double-layer.Using e-beam lithography and wet chemical etching mesasof specific shapes were etched. The trenches defining themesa structures were etched through the 3 topmost layers,including the sacrificial layer. Using a solution of NH3OHin water (3.7%) the undoped sacrificial layer is selectivelyetched against the heavily doped Si and SiGe layers. Due tothe strain relaxation in the double layer these films start tobend up. The curvature will depend on the amount ofstrain, i.e. of the Ge concentration in the SiGe film, and theindividual Si and SiGe film thickness', as given by:

DdAa

with D=diameter of curvature, d=thickness of the doublelayer, a lattice constant of Si, and Aa difference in the lat-tice constant averaged over the double layer. Fig.l showsschematically the structure and driving forces for the scroll-ing of the epitaxial double layer.

material for further shaping of the objects by additionallithography or overgrowth.

Fig.2: Scrolled Si/SiGe heterostructures with D = 5|j,m

Figure 3 depicts two examples of structures fabricated byunderetching V-shaped mesa structures. The helical spiralshown in Fig 3 a is fabricated by a thin, highly strainedSiGe/Si double-layer, whereas the tips in figure 3b are theresult of underetching rather thick epitaxial layers with asmall lattice mismatch. Those structures might be useful formicromechanical as well as optical structures. Since the tipshave atomically sharp edges, use as field emission tipsshould be possible.

,- * f • ••*" k -*

Etch

p - Si

Fig. 1: Schematic view of the scrolling mechanism

Figure 2 shows two examples of rings fabricated by thismethods. Fig. 2a shows three rings, which are connected atthe front end and Fig. 2b shows a top view of a ring whichhas been manipulated in such a way, that it forms a cylinderstanding on the substrate surface. This might be the starting

Fig. 3: a) helical spiral and b) tips fabricated from V-shaped mesa structures

FUNDING: PSI.

REFERENCE

[1] V. Ya. Prinz, S. V. Golod, V. I. Mashanov and A.K. Gutakovsky, Inst. Phys.S er. No. 166, 26thInt. Symp. Comp. Semicond. Berlin, 203 (1999).

113

PHOTOLITHOGRAPHIC GENERATION OF PROTEIN MICROPATTERNS

C. Padeste, H. Sorribas, L. Tiefenauer (PSI)

Positive resist photolithography in combination with oxygen plasma etching has been explored for the generation ofmicropatterns of covalently immobilised functional proteins. After plasma etching the surface adjacent to the proteinpattern is chemically modified, or a second protein is immobilised resulting in a complementary protein pattern.

Patterns of proteins and other molecules on varioussurfaces are of increasing interest for biosensors and forneurobiological applications. Lines of adhesion proteins onsurfaces have been shown to guide neurite outgrowth inpredifined patterns. Photolithographic techniques are wellestablished to produce patterns with a resolution better than0.5 (xm. However, development and removal of theirradiated resist are done in organic solvents or alkalinesolutions which may denature proteins. We have furtherdeveloped a published technique for the production ofprotein patterns using positive resist photolithography,where the protein layer is protected with a sucrose film toavoid direct contact with solvents. The technique allows theimmobilisation of a second substance, thus creatingcomplementary patterns on one surface.

Fig. 1: Complementary line patterns of rabbit-IgG (tophalf) and of streptavidin (bottom). Line widths are5 |im (left) and 2 |im (right).

The patterning process consists of several steps. A proteinis covalently immobilised on a glass or oxide surface usinga silane and a crosslinker. The protein film is embedded ina sucrose layer, which is spin dried at high rotation speedand cured in an oven. A photoresist is applied to the surfaceand structured using a lithographic mask. After develop-ment of the irradiated photoresist, exposed sucrose andprotein is removed from the surface in an O2-plasmaetching step. A second protein can now be immobilised onthe etched areas. A final lift-off step removes thephotoresist.

Complementary lines of different widths were created onone surface. The used proteins rabbit-IgG and streptavidin(SAv) were visualised by binding rhodamine labelledantibodies and fluoresceine labelled biotin, respectively.The successful specific binding confirmed the biochemicalfunctionality of the protein patterns. The limit of resolutionof the process sequence is in the range of 1 \im (Fig.l).

For neuron culture applications it is of interest to createinert areas adjacent to a protein pattern. Silanes differing inhydrophilicity were investigated to produce differentbackground areas: a polyethyleneglycol-silane (PEG), afluorinated alkyl silane (tridecafluorosilane, TFS) and along chain alkyl silane (octadecyltrichlorosilane, ODS).Plasma treated glass surfaces were modified with thecorresponding silane and contact angles and adsorption ofradiolabelled rlgG were measured. Streptavidin covalentlyimmobilised on glass served as the control surface.

PEG SAv ODS SAv

Fig. 2: Spreading of water droplets on glass chips withimmobilised SAv (right half) and modified withPEG-silane and ODS, respectively (left half).

A correlation of adsorption of IgG with the surfacehydrophobicity was found (Table 1). Protein adsorptionwas ranging from a few percent of a monolayer for theplasma and PEG-treated surfaces to values exceeding acomplete monolayer (600 ng/cm2 adsorbed IgGcorresponds about to a dense monolayer of protein).

Table 1: Contact angles and non specific adsorption ofrlgG on glass surfaces.

Treatment

SAv

O,-Plasma

PEG

ODS

TFS

H2O contactangle [deg]

42 ±2

17 ±4

33 ±3

131±4

104 ±3

AdsorbedIgG [ng/cm2]

125 ± 10

22 ±10

28 ±10

861 ±110

524 ± 27

Using the presented techniques patterns of adhesionmolecules can be generated combined with complementaryPEG-silane areas to suppress non-specific proteinadsorption. Such structured surfaces will be useful toestablish cultures of dissociated neurons with guidance ofneurite outgrowth by the protein pattern.

FUNDING: PSI, SPP Biotech, Module Neuroinformatics.

114

DEPOSITION SYSTEM FOR SINGLE MOLECULE EXPERIMENTS

T.A. Jung, R. Schelldorfer (PSI), S. Berner, F. Meisinger, M. Brunner (Univ. Basel),H. Suzuki IFP (Univ. Basel and KARC)

Molecular material in monolayer or submonolayer surface coverage exhibits distinctively different physical andchemical properties than in solution or in the bulk. Here we describe a system to handle sub-monolayer coverages ofmolecules like fullerenes and porphyrins. This effort aims at the detailed characterisation of molecular properties atsurfaces using Scanning Probe Microscopy(SPM) experiments synchrotron based photoelectron diffraction andspectroscopy techniques. The main goal of this research is to understand structure and properties of molecules atsurfaces and interfaces, for example in future molecular devices.

A two chamber molecular deposition system wasdevelopped complementary to a pre-existing multi-chambervacuum system with sample preparation and surfacecharacterization (AES, XPS, STM, LEED, ...) techniques.Molecular sublimation sources on ,button heaters' andsamples can be interlocked without breaking vacuum(Fig.l).

top edge of the steps, and self-organize in almostequidistant spacings. This gives some evidence for residualmobility at the room temperature used for the preparationand observation of these molecules on the Ag(100)substrate.

r[j HI in

f-rl tni ti i n f - i fit

; | oia*m

1-4 n j i^j

fca. •*-- t f — p l -

1 ! |illl |L,Int^t.i It-r m"l>- h- in- ilirnt i ~:~> i i f r i |L intfi I- w - a\. n i

Fig.l: Schematic representation of the sublimationchamber: In vacuum button heaters withsublimation sources and samples can betransferred and operated next to a quarz crystalmicrobalance to enable precise depositions.

Fig.2: Chemical Structure of Cun-tetra-(di-tertiary-butylphenyl) porphyrin (Cu-TBPP).

Fig.3: STM image of some percent of a monolayer Cu-TBPP on Ag(100). The individual molecules arevisible as they are lined up at the substrate stepswith monoatomic height.

Cu-TBPP (Fig.2) has been sublimed onto atomically cleanAg(100) substrate. In a Scanning Tunneling Microscopyimage (STM), the porphyrin molecules appear as brightspots which are lined up along step edges like pearls on anecklace (see Fig.3). Molecules preferentially adsorb to the

Preferential adsorption [1] and the correspondingconformational flexure [2] of molecules when deposited onatomically clean substrates are crucial determinants ofmolecular properties. Molecular flexure and moleculesubstrate interactions affect any physical, chemical, optical,and electronic property. This is important for ourunderstanding of contacted molecular devices.

FUNDING PSI, SNF, University Basel, KARC Japan.

REFERENCES

[1] H. Rauscher et. al. Chem. Phys. Lett 303, 363 (1999).

[2] T. Jung et. al. Nature 386, 696 (1997).

115

EXTRACELLULAR STIMULATION OF NEURONS CULTURED ONMICROELECTRODE ARRAYS

H. Sorribas, L. Tiefenauer (PSI), C. Strieker (Univ. Zurich /ETHZ)

Microelectrode arrays have been fabricated, functionalised with cell adhesion molecule and cultures of dissociatedneurons established. Cells on electrodes were extracellularly stimulated and the electrophysiological cell responsewas measured with patch clamp techniques.

Microelectrode arrays for extracellular stimulation andrecording from neural cells have been developed by severalgroups. Such devices can be used to study neuralprocessing, plasticity and learning, and have also foundapplications as sensing devices for pharmacologic drugscreening. The low signal intensity recorded withextracellular electrodes is partially due to loose sealing ofthe neuron membrane onto the electrode. Functionalisationof the electrode surface with cell adhesion proteins hasbeen tried in order to improve the sealing. Results onextracellular stimulation with extracellular gold electrodeson a microstructured chip are presented.

Chips with extracellular electrodes were fabricated withconventional thin film technology. Gold tracks wereinsulated with a 200 nm silicon oxide and a 400 nm siliconnitride layer. The chip was mounted on a printed circuitboard. The contact pads on the chip were connected to theprinted board via Al-wire bonds. The printed board and thebond wires were embedded in PDMS which isbiocompatible (Fig. 1). The surface of the chip wasfunctionalised with a cell adhesion molecule to promoteneurite outgrowth. Dissociated chicken dorsal root ganglianeurons were cultured on such chips for 4-7 days.Electrophysiological activity of neuron cells on or close tothe electrodes was first tested with whole-cell patch clamp.The electrode was then connected to a stimulus generatorand currents between 50 and 350 |J,A were applied during50-100 |is. The response of the cell was recorded with theintracellular patch electrode.

Fig. 1: Chip bonded into printed board for stimulation viaextracellular electrodes.

Neurons were cultured on RGDC treated chips. With theapplied cell density 5 - 8 of 50 electrodes were coveredwith a neuron. Higher cell densities prevented neuriteoutgrowth. Neuron cells for stimulation were chosenaccording to morphologic aspects (size, shape, membrane

smoothness). Electrophysiological characterisation of theneurons with whole cell patch clamp confirmed that thesecultured neurons were electrically active. The membranepotential was about -65 mV. Upon stimulation themembrane was depolarised in two phases to a value ofabout 60 mV. Extracellular stimulation with 130 (iA pulsesduring 100 |is was necessary to generate an action potentialin the neuron which was recorded with the intracellularelectrode (Fig. 2). Stimulation with pulses higher than 350(J.A led to electrochemical reactions on the electrode surfaceresulting in damage of the electrode and of the cell.

stimulating extracellular gold electrode

V • -66 mV

intracellularly recordedaction potential

recordingglass microelectrode

Stimulation100 jis with 130jiA

Fig. 2: Action potential recorded intracellularly afterextracellular stimulation

These preliminary results show that the fabricatedmicrostructured electrode array chip can be used forstimulation of cultured neurons. It remains to be shown ifextracellular recording is feasible with these chips.Measurement of the gap distance between the neuron cellmembrane and the electrode surface with fluorescenceinterference contrast microscopy revealed that a minimalcell-surface distance of 37 nm can be obtained when theadhesion protein axonin-1 or the peptide RGDC is on thesurface [1]. This gap is larger for neurons grown onNgCAM (47 nm) or laminin (91 nm). Whether the tightcontact induced by axonin-1 will result also in an improvedextracellularly recorded signal has to be shown.

FUNDING: SPP Biotechnology, PSI.

REFERENCE

[1] H. Sorribas, D. Braun, L. Leder, P. Sonderegger andL. Tiefenauer, J. Neurosci. Met. 104, 133 (2001).

116

NANOSTRUCTRED CHIPS FOR THE ANALYSIS OF INDIVIDUAL PROTEINS

L. Tiefenauer, B. Ketterer, B. Haas, H. Schift, L. Heyderman, J. Gobrecht (PSI), O. Dubochet, P. Surbled,T. Hessler (Leister Process Technol.)

The aim of this feasibility study is to produce nanochips used for the investigation of individual proteins by lightmicroscopes as well as scanning probe techniques. The regularly arranged openings with diameters from 100 to400 nm will permit an unhindered mass transport through individual protein assemblies present in biologicalmembranes. Nanoreplication techniques will be developed and transferred to industry.

Proteins in biological membranes are crucial for the vitalfunctions of life, especially by regulating intercellularcommunication and transport of molecules into the cells.Elucidating the structure of individual membrane proteinsin their natural environment is therefore an important steptowards a better understanding of their functions. Scanningprobe microscopy (SPM) techniques are unique tools toimage individual proteins. However, membrane proteinsare usually mobile (see (1) in Fig. 1) in the membrane anddifficultly to visualize by SPM. Furthermore, masstransport phenomena (2) cannot be investigated, if theinside of the natural membrane is lying flat on a surface (3).

2

Outside

Inside

Fig. 1: Mass transport through membranes (2) requires freeaccess from the inside (3).

We have therefore designed a nanochip (Fig. 2), whichessentially consists of a 300 nm thick silicon nitridemembrane in which pores in diameters of 100 to 400 nmare regularly arranged. The pores are arranched ininvestigation fields, which are in the dimensions suitablefor SPM-investigations.

The challenge of this project is to produce nanosizedstructures in a sufficient quantity. Lateral dimensions downto 100 nm cannot be generated by conventionalphotolithography processes. Thus, we have first written thenanostructures by e-beam lithography and produced asilicon master stamp (Fig. 3). In a second step the sharprelief is replicated in a resist coated onto a silicon nitridelayer using hot embossing. The procedure used forpreparing silicon nitride layer on silicon determines themechanical stability of the final thin membrane and musttherefore carefully be optimised. The feasibility of thenanoembossing technique has earlier been demonstrated,but further developments are required as it will be done inthe synergic nanoreplication project. Resist windows areopened on the substrate using reactive ion etching. In afinal wet etching process a free standing membrane isobtained.

••••

D

••

D •

•

investigation-fields

o o o o o oo o o o o oo o o o o oo o o o o oo o o o o o

• • •

I 300 run chip membrane

CH-

membrane length 0.5 mm

cell membrane protein

I?

30 nm

Fig. 2: Layout of the nanochip. Note that dimensions frommm- to nm-range must be controlled.

The processes are developed in close collaboration with theindustrial partner. The product-oriented procedure isfavorized by TopNANO 21 and will facilitate thetechnology transfer from the research to production places.

Production processes

1. Stamp production

2. Nanoreplication: stamping

3. Etching processes

Fig. 3: Production process: Hot embossing of a resist isfollowed by dry and wet etching steps.

FUNDING: TopNANO21, PSI.

117

ELECTROCHEMISTRY OF STACKED LAYERS OF REDOX LABELED PROTEINS

B. Steiger, C. Padeste, A. Grubelnik, L. Tiefenauer (PSI)

Streptavidin-ferrocene conjugates were synthesised and utilised as functional building blocks to derivatise electrodesurfaces. The analysis of the cyclic voltammograms of the electrodes provided evidence for the biochemical andelectrochemical functionality of the conjugates and for the formation of spatially ordered multilayers.

The avidin (Av)-biotin technology is a universal molecularanchoring system in the biological sciences. Av-ferroceneconjugates immobilised on electrodes can provide a multi-functional base for electrochemical biosensors [1]. The useof the egg white protein avidin, however, is often restricteddue to its high isoelectric point and presence of sugarmoieties, which may lead to nonspecific interactions.Streptavidin (SAv), a protein isolated from Streptomycesavidinii, is remarkably similar to Av, especially in terms ofbiotin-binding, but it is only slightly anionic and containsno sugar groups. SAv-ferrocene conjugates (Fc16SAv,Fig. 1) have been synthesised and the SAv-biotin bindingwas used to form assemblies on gold electrodes.

* ,

V*'<>

t " t

Fig. 1: Polypeptide backbone of the SAv tetramermodified with ferrocenes. Arrows indicate theposition of the four biotin binding pockets. Thetyrosines located at the bottom of the pockets areshown as black stick models.

The initial step was the chemisorption of 2-aminoethane-thiol on a gold disk electrode, followed by the reaction ofthe amino groups with sulfosuccinimidyl-6-(biotin-amido)hexanoate. The next step was the binding of Fc16 SAv to theimmobilised biotin groups. Fig. 2 shows that the coveragerFcl6SAv reaches a limiting value of about 3 pmol/cm2 uponincreasing reaction time, indicating the formation of acomplete monolayer. T was calculated from the area underthe ferrocene redox peaks (Fig. 4, N=l).

100 120 140

Fig. 2: Quantities of Fc16SAv immobilised on a biotincovered Au electrode, T, at various times after theelectrode was exposed to 200 jig/ml of Fc16SAv.

IMM1 LSLffLl LSLffLl

rww^ rww] rwwi rwwi

//////////////////

= Ferrocenylated Streptavidin

Fig. 3: Schematic picture of the multilayer structure.

This monolayer provided the base for the assembly ofsuccessive Fc16SAv layers via biotin-dimers (Fig. 3). Toprevent intramolecular bridging, the biotin-dimer wassynthesised in situ by first binding 5-(biotinamido) pentyl-amine to the immobilised Fc16SAv layer and then reactingthe amino groups with sulfosuccinimidyl-6-(biotinamido)hexanoate. This procedure was repeated after immo-bilisation of a next Fc16SAv layer.

400 300 200 1

Potential (V vs Ag/AgCI)

Fig. 4: Cyclic voltammograms (CV) of a Au electrode ina pH 7.4 buffer at 0.1 V/s during the assembly ofFc16SAv multilayers.

CVs were recorded to monitor the growth of the multi-layers. rFcl6SAv as a function of the number of layers gavelinear plots with a slope close to 3 pmol/cm2 per layer. Anelectrode with 4 layers exhibited reasonable stability, thedecrease in the CV response being ca. 10% after 7 days.

FUNDING: PSI.

REFERENCE

[1] C. Padeste, A. Grubelnik and L. Tiefenauer,Biosensors and Bioelectronics, 15, 431 (2000).

118

PRODUCTION AND REDOX LABELLING OF ANTIBODIES AGAINST fi-LACTAMANTIBIOTICS

A. Grubelnik, C. Padeste, J.-J. Hefti, L. Tiefenauer (PSI)

Antibodies against the fi-lactam antibiotics benzylpenicillin and cloxacillin have been produced and tested in anenzyme immunoassay. In various food samples, we have determined these antibiotics in concentrations below themaximum residue limits of the European community. After purification, the antibodies have been redox labelled withmicroperoxidase 8 (MP8)for use in an amperometric immunosensor.

The (3-lactam antibiotics, in particular the penicillins, aremost frequently used in veterinary medicine. A sensitive,quick and cheap assay would be important for routineanalysis of samples in food industry as well as for govern-mental food control. We are developing an amperometricimmunosensor that could fulfil these requirements. Theimmunological recognition is very sensitive and specificand can in principle be applied to any analyte of interest, aslong as a suitable antibody is available. The directamperometric detection has a lot of advantages, but itrequires the redox labelling of the antigen or the antibody.

The production of sensitive antisera against benzyl-penicillin and cloxacillin, two commonly used antibiotics inveterinary medicine, turned out to be difficult. Since the(3-lactam ring is very reactive, the antibiotic haptensundergo chemical modifications during immunisation andthe resulting antisera are insensitive and unspecific.

hydrolysed form of the antibiotic

R =

cloxacillin benzylpenicillin

Fig. 1: Structures of benzylpenicillin and cloxacillin,hydrolysis with penicillinase and synthesis of theirBSA conjugates.

If the (3-lactam ring is used to conjugate the antibiotic to thecarrier protein (BSA), a stable immunogen is formed(Fig. 1). This immunogen is similar to the hydrolysedantibiotic and will induce antibodies against this form. Inthe enzyme immunoassay, the intact antibiotic can now behydrolysed with penicillinase and thus be detected by theantibody. We could demonstrate the sensitivity of thismethod by analysing milk and honey samples spiked withbenzylpenicillin or cloxacillin in concentrations as low as0.1 ng/ml.

In a second step, these sensitive antibodies have beenlabelled with a redox centre for amperometric detection. Asredox marker we have chosen microperoxidase 8 (MP8),which catalyses the electrochemical reduction of hydrogenperoxide.

Fig. 2: Structure of the synthesised MP8-DSS conjugate(NHS-activated MP8) used to label the antibodies.

In a complex procedure we are able to label the antibodieswith up to eight MP8 molecules. This procedure includes aprotein G purification of the antiserum, labelling of thepurified IgG with an activated MP8 derivative (Fig. 2) andsubsequent purification of the labelled antibodies on anaffinity column. During the labelling step, the binding sitesof the antibody have to be blocked with an antigenderivative to protect them against chemical modification.With this method, the antibody molecules retain most oftheir biological activity and are electrocatalytically activeas is shown in Fig. 3.

Fig 3: Electrocatalytic reduction of H2O, in a flowinjection system using gold electrodes withcovalently immobilised MP8, IgG-MP8 and IgG.

FUNDING: PSI.

119

Laboratory forRadio- and

Environmental ChemistryForeword

Heavy Elements

Surface Chemistry

Analytical Chemistry

Cement Chemistry

Project Radwaste

120

LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY

H.W. Gaggeler (Univ. Bern & PSI)

In the field of heavy element research much effort wasdevoted to the development of a novel system, IVO (In-situVolatilization and On-line detection) coupled to a "4-TIthermochromatography" detector operated at cryo-temperatures. Such a technique is mandatory for theplanned new heavy element adventures such as attempts tostudy, for the first time, the chemical properties of hassium(element 108) - in form of its very volatile tetroxide - andof element 112 - presumably a very volatile metal. Thescientific steering committee of the Gesellschaft furSchwerionenforschung approved during its summermeeting a proposal to investigate element 112 produced inthe bombardment of a 244Pu target with 48Ca particles.

Our environmental research efforts included the partici-pation in several field campaigns. In July, an exploratoringdrilling was performed on a glacier close to the Belukhasummit in the Altai region. This campaign is the result of ajoint project between the Siberian branch of the RussianAcademy of Sciences in Barnaul and PSI. Based on the iso-topic and chemical interpretation of the drilled shallow-firncore we decided to continue this project with a deep drillingnext year.

Besides Siberia, several people from our unit travelled todifferent places in South America, first, to Patagonia(Chile) - unfortunately the drilling campaign was notsuccessful due to poor weather conditions - second, to theCerro Tapado and Cerro del Plomo (Chile) and, third, to theChimborazo (Ecuador) in collaboration with Frenchcolleagues. Obviously, next year much effort will bedevoted to laboratory work in order to analyze all these firnand ice samples.

Research in the field of surface chemistry with radioactivespecies celebrated several "breakthroughs". It was possibleto produce 13N-labelled peroxyacetyInitiate (PAN) atextremely low carrier concentrations. With this tracer,thermochromatography experiments were conducted thatproved to be instrumental in understanding the interactionof PAN with ice crystals in the upper troposphere and lowerstratosphere.

In addition, the SINQ-gas-jet device was successfully usedfor production of labelled HOBr and allowed to investigatethe kinetics of the interaction of this molecule with NaBraerosol particles. This laboratory study should yieldimportant information on heterogeneous processes in thearctic atmosphere.

The planning and construction phase of the projectPROTRAC came to a positive end. This gives hope that inthe first half of the coming year this new device will startoperation.

The cement chemistry group fulfils R&D work for nuclearpower plants and is mostly financed by external sources.The high competence of this group was recognized byexternal companies resulting in several new projects.Research results gained in the field of waste disposal led toa patent application.

The group Radwaste Analytics continued the radiochemicalanalyses of irradiated accelerator parts, e.g. targets, beamdump samples and shielding materials. Additionally, firstsamples of radioactive SINQ targets (zircalloy and lead)were prepared for analysis. The group cooperates in theEU-Project "High and Intermediate Energy Nuclear Datafor Accelerator-driven Systems".

121

[HNO3]0.10.10.10.10.10.030.010.010.010.003000

[HF]0.010.030.050.510.50.010.050.50.50.010.10.5

logKd(Hf)2.12.12.02.12.22.22.12.32.52.72.52.72.8

log Kd (Rf)0.80.90.80.90.71.71.01.61.61.72.72.41.8

FLUORIDE COMPLEXATION OF RUTHERFORDIUM (Rf, ELEMENT 104)

E. Strub, J.V. Kratz, A. Kronenberg, A. Nahler, P. Thorle (Universitat Mainz), W. Briichle, E. Jager, Z. Li, M. Schadel,B. Schausten, E. Schimpf (GSI Darmstadt),D. Jost, A. Turler (PSI), H.W. Gaggeler (Univ. Bern & PSI), J.P. Glatz (ITU

Karlsruhe)

The sorption studies of Rf and on-line produced Hf on Anionic Ion Exchangers have been continued by systematicallyvarying the HNOj and the HF concentration. Rf shows typical group 4 behavior but its sorption is influenced by thepresence of counter ions like NOj and/or HF2.

The distribution coefficient (IQ) of 261Rf on ion exchangeresins at various HNO3/HF concentrations had been studied[1]. Rf was eluted at higher HF concentrations from CIXthan Zr and Hf and rather resembled Th. Up to 1 M HF, Rfwas not retained on the AIX also resembling its pseudo-homolog Th.Th is known to form no anionic fluoride complexes, whileZr and Hf are forming complexes of the type [MF§]2" in HFsolutions and therefore can be resorbed on AIX resins.We have continued these studiesNow of Rf and on-lineproduced Hf by systemetically varying both the HNO3 andthe HF concentration. If Rf is resembling Th, there shouldexist no concentration range in which Rf is adsorbed on theAIX.261Rf was produced in the ^ C m ^ O ^ n ) reaction at the PSIPhilips Cyclotron. A 730 |Jg/cm2 248Cm target was bombar-ded with a 0.5 |xApart

18O3+ beam. The target contained 10%Gd thus producing simultaneously short-lived Hf isotopes.Rf and Hf were transported by a He(KCl) gas jet and col-lected for 90 s by impaction on a slider in the AutomaticRapid Chemistry Apparatus ARCA II. The residue wasdissolved in 200 \A 0.1 M HNO3/x M HF (x variable) andfed onto the AIX. The effluent was evaporated to dryness assample 1. In order to elute remaining Rf from the column, asecond fraction (200 |ji) was collected which is known toelute group 4 elements from the column (2 M HC1/0.01 MHF). This fraction was prepared as sample 2. 78-s 261Rf wasdetected by a-spectroscopy. The counting time was 12 min.Every 8th pair of samples was monitored by additional y-spectroscopy to determine the distribution of Hf. From theratio of the counting rates, the Kd values were calculated.The results are shown in in the table and are also plotted inthe 3D graphs below (some values in the plot are interpo-lated).

It is obvious that the behavior of Rf and Hf in the examinedsystem are remarkably different. While the Kd values of Rfare varying strongly with both HF and HNO3 concentration,the dependence of the Hf IQ values on the acid concentra-tions is rather weak.

Strong adsorption of both elements onto AIX can only beobserved in pure HF solutions with concentrations [HF] >0.01 M. This indicates the presence of anionic complexesunder this condition which is in agreement with [3].

On the other hand, the sorption of the complexes on AIXseems to be influenced by the presence of other anionsacting as counter ions on the exchanger resin (NO3~ and/orHF2", see [2]).

Thus, Rf shows the typical behavior of group 4 (formationof anionic fluoride complexes), but the interaction of thesecomplexes with different counter ions is enhanced withrespect to Zr and Hf.

REFERENCES[1] E. Strub et al., Radiochimica Acta 88, 265 (2000).[2] E. Strub, Dissertation Universitat Mainz (2000).[3] Szeglowski et al., Radiochim. Acta 51, 71 (1990).

2,75

2,S

2,25

1,f?

0,'ri

U.U1

P.CS

[HF] 1 , 1

• 2,5-2,75

• 2,25-2,5

• 2-2,25

11,75-2

• 1,5-1,75

11,25-1,5

• 1-1,25

• 0,75-1

• 0,5-0,75

logKd~f

'!•:'&

(=.0:

DHNQ,]

0-5 0.10.1

Fig. 1: Sorption on Hf in HNO3/HF solutions on an AIX Fig. 2:resin (Aminex A27 or Riedel de Haen).

Sorption on Rf in HNO3/HF solutions on an AIXresin (Aminex A27 or Riedel de Haen).

122

THERMOCHEMICAL PREDICTIONS OF THE CHEMICAL PROPERTIES OFBOHRIUM (Bh, ELEMENT 107)

R. Eichler (Univ. Bern & PSI)

Extrapolative and empirical correlation methods have been used to predict thermochemical properties of gaseous andsolid Bh compounds, which can be formed with Bh in reactive gas mixtures ofO2(g)/H2O(g) and O2(g)/HCl(g).

Thermochemical predictions of the behaviour of Bh in gaschromatographic studies with reactive gas mixtures ofO2(g)/H2O(g) and O2(g)/HCl(g) are essential for the prepa-ration and the interpretation of experimental studies of Bh.

The presented predictions of the volatility of Bh com-pounds are based on the assumption that Bh is a typicalmember of group 7 of the periodic table and thus homo-logous to Tc and Re. The results obtained in gasadsorption chromatographic experiments with Tc and Re[1-3] are used to estimate unknown enthalpies of formationof oxide, oxyhydroxide, and oxychloride compounds of Tcand Re in the solid or gaseous state. Analogous topredictions made for seaborgium (Sg, element 106)compounds [4] the present approach employs an empiricalcorrelation between the formation data and the knownsublimation enthalpies of metallic Tc and Re [5] (e.g.Fig. 1). Subsequent extrapolations of these correlationsusing predicted sublimation enthalpies of metallic Bh [6,7]yield the formation enthalpies of Bh compounds in solidand gaseous states (Table 1).

— — — - _

Tc Bh*

—• -

Re

MO a

MO ,C 1

-— H M ° 4

Bh

600 700 800 900

A ^ M , , , ) [kJ/mol]

Fig. 1: Empirical correlation of AfH0(g) of different

compounds of group 7 elements with the standardformation enthalpies of the gaseous state of themetal (AfH°(M(g))). Extrapolations for AfH°(s) ofBh compounds were carried out using AfH

0(Bh(g))[6]andAfH°(Bh*(g))[7].

Finally, the standard adsorption enthalpies of single mole-cules of Bh compounds on quartz surfaces were deducedfrom the macroscopic standard sublimation enthalpies em-ploying the well established correlations between the sub-limation enthalpies of different oxide and oxychloridecompounds and their standard adsorption enthalpies onquartz surfaces [3,4].

In addition, the standard sublimation enthalpy of BhO3Cl(Table 1, BhO3Cl (rel)) is also predicted by correlating thecalculated relativistic molecular properties of MO3C1(M=Tc, Re, and Bh) [8] with the sublimation enthalpies ofthe compounds (Fig. 2).The estimated adsorption enthalpy of Bh oxychloride onquartz surface, AHads(BhO3Ci)=-74+12 kJ/mol, was in-

strumental in selecting the experimental conditions in gaschemical investigations of BhO3Cl [9]. The predictionsrevealed BhO3Cl to be thermodynamically more stable andless volatile than TcO3Cl and ReO3Cl [10].

OP (M=O) •

00 -

80 -

60 -

0.6 0.8 1.0

V T C

/

2

/

/

/Re1

MO3C

2.0

/' Bh

-5

2.2

' /

2.4

Re

H[D] •

Fig. 2: Empirical correlation of AHsuW of oxychlorides ofgroup 7 elements with calculated dipole moments(|i) and molecular overlap populations (OP) of themolecules MO3C1 (M=Tc,Re) [8]. Extrapolation ofAHsubi (BhO3Cl) using |i(BhO3Cl) and OP(BhO3Cl)from [8].

Table 1: Predicted thermochemical formation data of dif-ferent Bh compounds in their solid and their gaseous state.

Compound

BhO2

Bh*O2

BhO3

Bh*O3

HBhO4

HBh*O4

BhO3ClBh*O3Cl

BhO3Cl (rel)

AfH°(s)[kJ/mol]

-444-436-671-576-837-738-650-588

AfH°(g)[kJ/mol]

4833

-385-339-710-628-561-528

AHsuW

[kJ/mol]4924693582371271108960

75...100

AHads

[kJ/mol]-341±21-325±20-250±18-168+15-93+11-81+11-74±12-58±12

REFERENCES[1] R. Eichler et al., Radiochim. Acta 87,151-159(1999).[2] T.Hafeli, Diploma thesis, University of Bern (1999).[3] R. Eichler et al., Radiochim. Acta 86, 87-93 (2000).[4] B. Eichler et al., J.Phys.Chem. A103 (46), 9296 (1999).[5] O. Knacke et al., Thermochemical Properties of Inor-

ganic Substances, 2nd ed., Springer-Verlag, Berlin(1991).

[6] B. Eichler, Kernenergie 19 (10), 307 (1976).[7] G.V. Ionova et al., Sov. Radiochem 37, 282 (1995).[8] V. Pershina et al., J. Chem. Phys. A 113,1441 (2000).[9] R. Eichler et al., Nature 407, 63(2000).[10] For more details see: wwwl.psi.ch/www_lch_hn/Bh_

chemistry_prediction.pdf.

123

2500 ;

| 2000

1 1500

o! . 1000%

i :*? 500 ;

0 ^600

B—"

•

Ru

650

= = =

j =

700

AH

O s H s l

750 800

°298(M(g)) [kJ/mol]

_ •—9

•

•

Hsll

, , ,850

MeO4(8)

MeO3(g)

MeO2 (S)

MeO2(g)

MeO (a)

9C

STABILITY OF GROUP 8 TETROXIDES MeO4 (Me=Ru, Os, Hs) AND THEIRADSORPTION BEHAVIOR ON QUARTZ

Ch.E. Dullmann, R. Eichler, A. Tiirler (Univ. Bern & PSI), B. Eichler (PSI)

In view of a first gas-phase chemistry experiment with hassium (Hs, Z=108) the high volatility of the tetroxides ofgroup 8 elements ruthenium (Ru) and osmium (Os) indicates that an isolation ofHs as volatile HsO4 is currently themost promising approach. The atomic formation enthalpies of oxides of group 8 elements Ru and Os werecalculated on the basis of known thermodynamical properties and extrapolations for Hs and its oxides wereperformed. The trends of stability and the enthalpy of sublimation were evaluated from these extrapolations and theadsorption enthalpies evaluated using an empirical correlation which holds for several oxides.

1 INTRODUCTIONWell-known volatile compounds of group 8 elementsruthenium (Ru) and osmium (Os) are their tetroxides, RUO4and OSO4, respectively. Due to the coordinative saturationof the metal ions in symmetrical molecular geometries suchas the tetrahedral RUO4 and OSO4, the molecule - surfaceinteraction of these compounds is dominated byphysisorptive forces. The high volatility of RuO4 and OsO4

is related to this effect and makes these molecules suitablefor gaschromatography experiments. The transactinideelement hassium (Hs, Z=108) is expected to behomologuous to Ru and Os and should therefore also forma very volatile tetroxide, HsO4. It is important to have anotion about the volatility of this compound in order to planan experimental set-up for the chemical separation andinvestigation of Hs as tetroxide. We have thereforecalculated the sublimation enthalpy AHsuW on the basis ofan extrapolation along the memebers of group 8 andevaluated the adsorption enthalpy AHads on quartz surface.

2 CALCULATIONS / RESULTSAs reference for the extrapolation, the standard enthalpiesof the gaseous monoatomic elements AH°298(Me(g)) wereused. Since an estimation of the error of this value isdifficult, a realistic range limited by two values forAH°(Hs(g)), denoted by Hs I (790 kJ/mol [1]) and Hs II (842kJ/mol [2]) was chosen. Then, the atomic formationenthalpies of the gaseous and solid oxides MeOx(&S) weredetermined with

AH*(MeOx(g))=AH0298(MeOx(g))-AH0

298(Me(g))-x-AH0298(O(g))

AH*(MeOx(s))=AH0298(MeOx(s))-AH°298(Me(g))-x-AH°298(O(g))

and are shown in Fig. 1 as a function of the standardenthalpy of the gaseous metals. In a correlation ofAH*(MeOX(gS)) against AH°298(Me(g)) for elements of a givengroup, the stability of the compound MeOx increases withincreasing atomic number if the slope of the correlation lineis greater than 1. That is because the AH°298(Me(g)) valuesare already included in the quantities of AH (MeOx(gS)). Theslope of the linear regression of the values of the gaseoustetroxides is 2.06, indicating increasing stability from RuO4

to OsO4. Consequently, HsO4 is expected to bethermodynamically even more stable.In a next step, the standard sublimation enthalpies werecalculated from the atomic formation enthalpies accordingtoAH°subl=AH*(MeOx(g))-AH*(MeOx(s)).

Fig. 1: Atomic formation enthalpies of the gaseous andsolid oxides of group 8 elements as a function ofthe standard enthalpy of the gaseous metals. Thestraight lines are linear regressions.

Values of (52±8) kJ/mol (RuO4 [3]) and 56.6 kJ/mol (OsO4

[4]) are taken from the literature. 57 kJ/mol are calculatedfor Hs I and 58 kJ/mol for Hs II. Comparison between thestandard sublimation enthalpy of macroscopic amounts andthe adsorption enthalpy of carrier-free oxides showed thatthere exists a good linear correlation between these twoquantities. An updated correlation taking into account alsomore recent experiments [5] resulted in

-AHads=(6.271±7.780)+(0.680±0.028)-AHsubl

Adorption enthalpies of (-41±9) kJ/mol for RuO4, (-45±9)kJ/mol for OsO4, (-45±9) kJ/mol for Hs I and (46±9) kJ/molfor Hs II, respectively, are calculated with this correlation.Comparison of these values clearly shows that theadsorption behavior of HsO4 on quartz is expected to be thesame as the one of OsO4 and therefore HsO4 is consideredto be suitable for a first ever chemical investigation of Hs.

REFERENCES

[1] B. Eichler, Kernenergie 19 (10), 307 (1976).

[2] B. Fricke, Structure and Bonding, Springer-Verlag,Berlin, Heidelberg, New York, 1975, Vol. 21, p. 92.

[3] J.A. Rard, Chem. Rev. 85, 1 (1985).

[4] H. Oppermann et al., Z.Naturforsch. 53b, 1352(1998).

[5] R. Eichler et al., Radiochim. Acta 87, 151 (1999).

124

EVALUATION OF THE ENTHALPY OF ADSORPTION OF OsO4 ON QUARTZ

Ch.E. Dullmann, R. Eichler, H.W. Gdggeler, A. Tttrler (Univ. Bern & PSI), B. Eichler, D.T. Jost, D. Piguet (PSI)

Short-lived Os-isotopes were produced in heavy ion reactions at the PHILIPS Cyclotron at PSI. Highly volatile Os-tetroxide was synthesized directly in the recoil chamber and transported to a quartz chromatography column kept atan isothermal but variable temperature. By measuring the yield at different temperatures, the retention time of thecompund in the column was evaluated. Thus, an enthalpy of adsorption of AHJOsO4)=(-38.0±1.5) kJ/mol wasdetermined using two different approaches.

1 INTRODUCTIONOsmium (Os) is a member of group 8 of the periodic tableof the elements and thus serves as a model for thetransactinide element hassium (Hs, Z=108) which isexpected to be also a member of group 8 and shouldtherefore exhibit similar chemical properties. The highlyvolatile tetroxide of Os (OsO4) is one of the best knowncompounds of this element and is extensively used as anoxidizing agent in organic chemistry. Due to its highvolatility (boiling point: 135 °C) it is suitable for adsorptiongaschromatographic investigations. We have determinedthe enthalpy of adsorption of OSO4 on quartz surface usingshort-lived carrier-free Os-isotopes.

2 EXPERIMENTALShort-lived Os isotopes were produced at the PHILIPSCyclotron in the reaction 162Er(18O, 6-7n)173174Os at a beamenergy of 116 MeV in the middle of the target and beamintensities of 100 particle-nA. The apparatus for In-situVolatilization and On-line detection (IVO) which isdescribed in detail elsewhere [1,2] was used to synthesizeOsO4 in-situ in the recoil chamber and to separate it frominterfering by-products which were produced in transferreactions or in reactions of the beam with impurities in thetarget, backing or target assembly. As carrier gas, 500ml/min helium and 50 ml/min oxygen were used. OSO4 wastransported from IVO via a 5 m long PFA teflon capillary(i.d.=2 mm) to a quartz chromatography column(length=1.5 m, i.d.=2 mm) kept at a variable isothermaltemperature. After passing through this column, themolecules were transported through a 2 m long PFA tefloncapillary (i.d. 2 mm) to the cluster chamber.For further transport, an aerosol was produced from moltenlead (Pb) in argon (500 ml/min), since earlier experimentsat FLNR in Dubna [3] and at PSI [1] have shown that a leadsurface strongly adsorbs OsO4, presumably via its reducingsurface to form less volatile Os compounds. Optimumtransport yields of OsO4 were found if the molten Pb waskept at 820 °C and then passed through a container of 3 1volume in order to allow the formation of agglomerates ofappropriate size. The aerosol was fed into the clusterchamber and the adsorbed Os compounds were transportedto ROMA [4] for final counting. The isothermaltemperature of the chromatography (IC) column was variedbetween ambient temperature and -80 °C to evaluate theretention time of OsO4 on quartz.

9o

0)

Experimental Data- Monte-Carlo Simulation AHa(te=-38.0 kJ/mol-•±1.5 kJ/mol

-100 -80 -60 -40 -20 0

Isothermal temperature [°C]

Fig. 1: Relative yield vs. isothermal temperature curve for173OsO4 (T =22.4 s).

3 RESULTSFig. 1 shows the relative yield vs. isothermal temperaturecurve for 173Os (Ti/2=22.4 s). The solid line is the result of aMonte-Carlo simulation of the experiment [5] assuming anenthalpy of adsorption AHads of -38.0 kJ/mol. The dashedlines indicate the la-error range of ±1.5 kJ/mol. Analysis ofthe experimental data using the model of mobile adsorption[6] yielded AHa(OsO4)=(-37±l) kJ/mol.

REFERENCES

[1] Ch.E. Dullmann et al., Nucl. Instrum. Meth. A, inpress.

[2] Ch.E. Dullmann et al., Ann. Rep. Univ.Bern & PSI1999, p. 13

[3] B. L. Zhuikov, et al., Report JINR Dubna, USSR,P7-86-322 (1986).

[4] K. Siimmerer et al.,

GSI Ann. Rep. 1983/84-1, 246 (1984).

[5] I. Zvara, Radiochim. Acta 38, 95 (1985).

[6] B. Eichler et al., Radiochim. Acta 30, 233 (1982).

125

THE INTERACTION OF ELEMENT 112 WITH METAL SURFACES

B. Eichler (PSI)

The enthalpies of solution, of net adsorption, and of segregation have been calculated for the interaction of element112 with selected metal surfaces. The effect of these thermochemical values are discussed.

INTRODUCTION

The net adsorption enthalpy and the enthalpy of segregationare thermochemical values, which characterize thebehaviour of a metal element at the surface of anothermetal. The partial molar net adsorption enthalpy at zerosurface coverage is a measure for the interaction of singleatoms of metal A with the surface of metal B. The sum ofthe partial molar net adsorption enthalpy and the subli-mation enthalpy of A yields the enthalpy of adsorption ofthe gaseous metal A on B. The probabilities, both of thesurface enrichment in the case of implantation of A into thebulk phase of B and vice versa of the penetration of A intothe bulk phase of B from the surface are characterized bythe enthalpy of segregation. A surface enrichment ispossible if the enthalpy of segregation is large and negative(<-50 kJ/mol). A dissolution of A in B can be assumed atsmall absolute and at positive values of the segregationenthalpy in the case of no diffusion hindrance. The enthalpyof solution and the enthalpy of segregation are both ofexceptional importance for the selection of adsorbensmaterials in order to prepare thin and stable samples, whichare required for high resolution a- and SF- decaymeasurements.

CALCULATION

The partial molar enthalpy of solution, the net adsorptionenthalpy and the enthalpy of segregation have beencalculated using [1] and applying extrapolated values ofelectron density at the Wigner-Seitz cell boundaries, of theelectronegativity parameter [2]. The extrapolations [2]yielded six consistent data sets for the calculations. Theresults for the corresponding enthalpies of element 112 as afunction of melting points of the adsorbens metals B areshown in figure 1 a-c.

DISCUSSION

The behaviour of element 112 at the selected metal surfacesis determined by contrary acting effects. Therefore, acontinuous linear function can not be expected. Twoobserved dependencies are remarkable: For high meltingmetals B a low solubility, a high surface enrichment, andthus, a high adsorption, and for low melting metals B a highsolubility, a low surface enrichment and a low adsorptioninteraction can be expected. This sequence is a well knownempirical rule for adsorption phenomena on metal surfaces.The influence of the enthalpy of solution is partiallyoverruling this sequence. This influence is for examplevisible at the Pd surface. It is well known that Pd formsvery stable compounds with s- and p- metals. For element112 in contrast to other d-metals small enthalpy of solutionin Pd has been calculated. A limited solubility of element112 in the solid phase of Pd can therefore be expected. Thecalculated data can be used for the selection of optimalmaterials in experimental studies of the chemical behaviourof element 112.

350-

300-

250-

200-

150-

100-

5 0 -

0 -

-50-

Cd

iPb

FeAWoD

A

Cu f

1 N 1 T J

* •~~~Ag~ f ~ ~Pd

Nb

D

1

AVo

Mo

A

D

Ir

ASD

Ta

AwoD

Re

±

°nw

1000 1500 2000 2500

T (K)

3000 3500 4000

a)2 0 -

0 -

-20-

-40-

-60-

-80-

-100-

-120-

-140-

Cd

D

Pb

n „Ag "°

F eoS

-L -

Ti

Mo

ID

Ir

a

- :

a

Ta*

a

500 1000 1500 2000 2500 3000 3500 4000

Tm(K) b)0-

-50-

-100-

-150-

-200-

-250-

-300-

-350-

-400-

-450-

C d , Ag

Au

|

Cu

Pd

TiP t

Ni «SS Nb7Q D* * &

A A1 * <^

Fe

Ir

B TaJMO D

I AR06W

* x s

500 1000 1500 2000 2500 3000 3500 4000

T (K)C)

Fig. 1: Enthalpies of solution (a), net adsorption (b) andsegregation (c) as function of Tm of adsorbensmetals.

REFERENCES

[1] B. Eichler, H. Rossbach:Radiochim. Acta 33,12 (1983).

[2] B. Eichler, Metallchemie der Transaktinoide,PSI Bericht Nr. 00-09 (2000).

126

A FIRST ATTEMPT TO CHEMICALLY IDENTIFY ELEMENT 112

A.B. Yakushev, G.V. Buklanov, M.L. Chelnokov, V.l. Chepigin, S.N. Dmitriev, V.A. Gorshkov, V.Ya. Lebedev,O.N. Malyshev, Yu.Ts. Oganessian, A.G. Popeko, E.A. Sokol, S.N. Timokhin, V.M. Vasko, A.V. Yeremin,

I. Zvara (FLNR Dubna), S. Hübener (FZ Rossendorf), A. Türler (PSI & Univ. Bern)

A first experiment to chemically identify a previously discovered long-lived superheavy isotope of element 112 wasconducted at the U-400 cyclotron of Flerov Laboratory of Nuclear Reactions, Dubna. Eventhough the experimentreached a sensitivity of a few picobarns, no decay that could be attributed to an isotope of elment 112 was observed.

1 INTRODUCTION

The relatively long half-lives of isotopes of super-heavyelements obtained in 48Ca induced reactions, allow for thefirst time to study their chemical properties. The chemicalidentification of the proton number is very important, sincenone of the members of the observed decay chains areknown. The nuclide 283112 (Ti/2 = 3 min) can be producedin the reaction 238U(48Ca, 3n) with a cross section of about 5pb [1]. Element 112 (El 12) should belong to group 12 ofthe periodic table like Zn, Cd, and Hg and exhibit someunique chemical properties. Some theoretical works predict,that El 12 is very volatile and chemically inert andresembles thus more Rn than Hg [2]. Two differentapproaches are thus necessary. In a first step we developeda separation and detection method for Hg, expecting El 12to behave similarly and thus to strongly adsorb on somemetal surfaces due to intermetailic bonds.

2 EXPERIMENTAL

Tests with both long- and short-lived Hg isotopes showed,that an almost quantitative transport through a 30 m longteflon capillary is possible at room temperature. Next, thechemisorption of Hg on various metal surfaces in pure Hewas studied at room temperature or slightly below it, inorder to deposit El 12 directly on metal coated Si detectorsurfaces. Adsorption of Hg was quantitative on Au, Pt orPd. The rate of chemisorption was highest on Au. Only 1cm2 of Au or Pd surface sufficed for quantitativechemisorption of Hg from He at room temperature and flowrates up to 1 1/min. The adsorption yield of Hg on Au at -30°C decreased to 50%. For the experiments with short-lived Hg isotopes at the U-400 cyclotron a flow-throughdetection chamber was constructed with a pair of square(2x2 cm) PIPS (passivated ion-implanted planar silicon)detectors, which were coated with about 40 |J,g/cm of Auor Pd. The distance between the detectors was 1 mm, whichresulted in a detection efficiency of 80% at a resolution ofabout 100 keV for 6 MeV a-particles. The residence timeof the gas in each detector chamber was only a fraction of asecond. Several chambers were connected in series withshort PTFE capillaries.

A first attempt to chemically identify El 12 was performedat the Dubna U-400 cyclotron in January 2000. A 2-mg/cm238U3O8 target containing 100 ug of natural Nd on a 2 ¡̂ mHAV AR foil (which served also as vacuum window) wasirradiated with 6.85xl017 48Ca ions (Elab=230-244 MeV).Recoils were thermalized in pure He at atmosphericpressure and transported through a 25 m long PTFEcapillary to the detection apparatus. The transport time was25 s at a gas flow rate of 500 ml/min. Eight detectionchambers were connected in series. Detectors 1 through 6were coated with Au, the last two chambers contained Pdcoated detectors. The chambers were positioned inside anassemblage of 84 He-filled detectors (in a moderator) toregister neutrons form spontaneous fission decays. Thedetection efficiency for a single neutron was about 50%.Decay events in the fission fragment energy range triggeredthe measurement of prompt neutrons, which lasted 128 ¡O.S.Neutrons were detected in this period with a time resolutionof 1 \\s. The a-decay count rate in a single detector(Ea > 6 MeV) was 4.5 min"1. All peaks in the spectra wereidentified and attributed to the decay of 211'220Rn and itsdescendants.

3 RESULTS AND DISCUSSION

In our experiment no SF events were observed. If theefficiencies measured for Hg held for El 12, we could haveexpected detection of some 3 events based on a 5 pbproduction cross section. This experiment undoubtedlyshowed the possibility of chemical identification of nucleiproduced with picobarn cross sections. The experimentdoes not give an unambiguous answer about physical andchemical properties of element 112. In a next step, we planto increase the beam dose by at least a factor of two and toupgrade our detector system to measure a-decays and SFevents in the gas exiting the chambers with the PIPSdetectors using a special ionization chamber.

REFERENCES

[1] Yu.Ts. Oganessian et al., EPJ A5, 63 (1999).

[2] K. S. Pitzer, Chem. Phys. 63, 1032 (1975).

127

ON-LINE THERMOCHROMATOGRAPHIC STUDIES OF RADON AS APRESUMABLE PSEUDOHOMOLOGUE OF THE ELEMENTS 112 AND 114

R. Eichler (Univ. Bern & PSI), B. Eichler (PSI)

Thermochromatographic low temperature separations of 220Rn have been carried out using various metals, polar,and nonpolar materials as stationary phase. The expected dependence of the adsorption interaction of radon on thedifferent polarizabilities of the stationary phase materials was approved experimentally.

1 INTRODUCTIONFrom theoretical relativistic calculations of atomicproperties of the heaviest elements noble gas behaviour ofthe elements 112, 114, and 118 can be expected [1].According to [2] for the fictitious noble gas elements 112and 114 a high volatility and a less adsorption interactionwith metal surfaces can be expected. The scientific goal ofexperimental approvals of either metallic or non-metallicproperties of elements 112 and 114 will be the confirmationof established rules manifested in the periodic table or theobservation of deviations of chemical properties ofelements 112 and 114 due to relativistic effects in theirelectron orbitals. In order to approve the model described in[2], we studied in this work the adsorption of Rn as anelement with a nearly homologous behaviour compared tothe possible noble gas elements 112 and 114 on variouspolar, nonpolar materials, and metals as stationary phase inon-line thermochromatography experiments.

2 EXPERIMENTAL

V~7

IIFig. 1: On-line low temperature thermochromatography

setup with:1 50 ml/min He carrier gas flow; 2 oven with232U3O8 at 400°C; 3 drying unit (SICAPENT®); 4getter oven at 1000°C with Ta metal; 5 column; 6temperature gradient setup from 50 - -193°C with

Heating the source to 400°C supports the emanation of220Rn from the 232U3O8 source. The carrier gas He(50 ml/min) was loaded with 220Rn. Subsequently, in orderto remove traces of O2 and H2O, the gas mixture was passedthrough a gas drying unit, filled with Sicapent®, and througha Ta metal getter (at 1000°C). The getter was placeddirectly into the thermochromatography column. Thematerials used as stationary phase in the columns are listedin table 1. The metal columns have been prepared usingmetal foils, which were applied into a quartz tube(0, = 3 mm) and covered the entire inner surface of thequartz column. The surfaces of these "metal" columns werereduced and cleaned in a separate oven at 800°C in aflowing gas mixture of He/H2 (Vol%-94/6). The possible H2

coverage was removed at the same temperature of 800°C ina gas flow of Ar. The deposition position of 220Rn along the

temperature gradient was determined measuring its decayproduct 2l2Bi after each experiment of 1 h duration using aGeiger-Muller counter and a 1 cm lead collimator.

3 RESULTS AND DISCUSSIONThe thermochromatogram of 220Rn on Ni is shown in Figure2. Typically, in all metal columns two deposition peaks or apronounced tailing to higher deposition temperatures havebeen observed. This effect can be explained by anadsorption of Rn first on a clean metal surface, which led toa deposition at higher temperatures (Tl), and after sometime the metal surface is covered by ice. The Rn adsorptionon ice is weak (-20 kJ/mol) [3] and led in our experimentsto a deposition at lower temperatures (T2). The adsorptionenthalpies AHaexp(l,2) have been calculated from themeasured deposition temperatures using the mobileadsorption model [4]. The estimated adsorption enthalpiesfrom T2 agree very well with data obtained in [3]. TheAHam(xl calculated with the model from [2] seem to agreewell with the results of our experiments.

40 50

Fig. 2: Thermochromatogram of 220Rn on Ni.

Table 1: Deposition temperatures and deduced adsorptionenthalpies in (kJ/mol) together with adsorption enthalpiesAHam(xl calculated using the model in [2].

SurfacePdPtCuAgAuNiWSiO,A1ATeflon81

T1°C-110-149-73-147-115-130-157

AHa^l-37-29-46-29-36-33-27

T2°C-163-186-181-191-188-176-181-181-172-183

AHa,Tr2-25-20-21-19-19-23-21-21-24-20

AHa_33.534.932.131.735.431.932.7

REFERENCES[1] K.S. Pitzer, J. Chem. Phys. 63, 1032 (1975).[2] B. Eichler et al., this Annual Report.[3] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000).[4] B. Eichler, I.Zvara, Radiochimica Acta 30, 233 (1982).

128

VAN DER WAALS INTERACTION OF ATOMS OF ELEMENTS 112,114, AND 118WITH SOLID SURFACES

B. Eichler (PSI), R. Eichler, H.W. Gaggeler (Univ. Bern & PSI)

The interaction of the "fictitious" noble gases 112, 114, and 118 with metal surfaces has been estimated as a functionof polarizability, ionization energy, and the distance to the surface.

METHOD

For gaseous atoms and nonpolar symmetrical molecules theVan der Waals interaction E with a solid surface nearlyequals the adsorption enthalpy. The Van der Waals interac-tion can be calculated as a function of the polarizability a(A3), of the distance between the atom or molecule and thesurface r (A), and of the characteristic energies of the atomsor molecules EA and the surface material EB using eq. 1 [1] :

E= oc g EA EB (8r (EA+EB)) (1)

For metals is g = 1. We used for EAB the average dipoletransition energy and substituted EAB with eq. 2 [2]:

EAB = 1.57* IPAB (IPAB ionization potentials [1,7]) (2)

With the predicted extremely high promotion energies forelement 118 and also for elements 112 and 114 a noble gaslike behaviour can be expected [3]. Therefore, their interac-tion with solid surfaces should be exclusively of Van derWaals nature. The correlation of the polarizabilities [1,4,5]with the radii of largest orbital which can be found for thelighter noble gases from He to Rn (eq. 3) is supposed to bevalid for these elements too:

a = f(rmax3) (3)

As rmai we used the the maximum radial probability densityof the electrons in the outer orbitals in the ground stateconfiguration of elements 112, 114, and 118, obtained fromrelativistic calculations [6].

This correlation is shown in Figure 1 for the noble gasesand element 112, 114, and 118.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Fig. 1: Correlation of polarizabilities with rmax for noblegases, and extrapolation of rmax for elements 112,114, and 118.

The analysis of the distances of the lighter noble gases todifferent solid surfaces, calculated with eq. 1 on the basis ofliterature data of adsorption enthalpies [8] yielded a sur-prising result: a nearly constant distance (r) of 2.47 A hasbeen calculated independent from the noble gas and fromthe nature of the solid surface. Applying this distance the

adsorption enthalpies of elements 112, 114, and 118 onselected metal surfaces can be calculated. The results areshown in Figure 2.

o

"—'

-AH

50-.

45-

4 0 -

3 5 -

3 0 -

2 5 -

118

114

•o

112

•

a

o

m

a

O

•

•o

•

•

o

•

D

o

•

•o

Cu Pd Pt Au

Fig. 2: Adsorption enthalpies of elements 112, 114 and118 on different metal surfaces.

DISCUSSION

Evidently, these results are approximated values. Neverthe-less they give a real picture of a possible adsorption be-haviour of the "fictitious" noble gas elements 112, 114, and118 is given. However, only the experiment can prove ifthese elements are supposed to form colourless non con-ducting solids in a fictitious condensed phase as would beexpected for noble gas-like elements. For elements 112 and114 this would be a distinct break of the rules manifested inthe periodic table. Experimentally this break could be ob-served in gas adsorption chromatographic investigationswith metallic stationary phases. If this elements do not formintermetallic bonds, a noble gas behaviuor can be assumed.

REFERENCES

[1] Handbook of Chemistry and Physics, ed. 79,CRC Press (1998).

[2] L. Pauling, Sience 134, 3471 (1961).[3] K.S. Pitzer, J. Chem. Phys. 63, 1032 (1975).[4] C.K. Jorgensen in Structure and Bonding, Springer

Verlag, Berlin 1966, 243.[5] B. Eichler, H. P. Zimmermann, H. W. Gaggeler,

J. Phys. Chem. A 104, 3126 (2000).[6] J. P. Desclaux,

Atomic and Nuclear Data Tables 12, 311 (1973).[7] O. L. Keller, G. T. Seaborg,

Ann. Rev. Nucl. Sci. 27, 139 (1977).[8] A. R. Miedema, B. E. Nieuwenhuys,

Surface Science 104, 491 (1981).

129

SEMI-EMPIRICAL CALCULATION OF ADSORPTION ENTROPIES

S. Taut, S. Hubener (FZRossendorf), B. Eichler (PSI)

Adsorption entropies can be calculated using statistical thermodynamics model, an empirical correlation betweenforce constants and adsorption enthalpies, and the long known compensation effect between To and the adsorption en-thalpy.

SYMBOLSA

d

fJhindr

gh

J

k

m

<?2,™,s

R

t

T

To

Tad!

T<lm

ua

V

V

*o

A S " ,

molar standard surface area of adsorbed substance

inner co lumn diameter

force constant

hindrance factor

temperature gradient along the chromatography column

Planck constant

electron system magnetic quantum number

Boltzmann constant

mass of adsorpt atom

partition function of two-dim, translation

gas constant

chromatography time

temperature

ambient temperature

adsorption temperature

temperature at starting position

carrier gas speed at ambient temperature To

molar standard volume of substance to be adsorbed

adsorpt vibration frequency normal to surface

frequency factor in the FRENKEL equation

differential molar standard adsorption enthalpy

differential molar standard adsorption entropy

CALCULATION OF ADSORPTION ENTROPIES

Applying statistical partition functions for both gaseous andadsorbed state [1] and considering the non-ideal behaviourof the two-dimensional adsorpt gas [2], an expression forthe entropy of mobile adsorption was derived:

2Jads+l2/ ..+1

V-(kT-ln-i

l -exp -h-v

kT

In [3] was shown that experimental adsorpt stretching fre-quencies follow the oscillation equation:

L

An empirical correlation between force constants and ad-sorption enthalpies was derived from literature data:

lo = -1.78 - 0.0036 • AH^ [U /moll

The stretching frequency can now be calculated. The hin-drance factor considers the non-ideal and ideal translation ofthe two-dimensional gas on the surface:

Jhindr ~Qllmns.adsmoh

It can be calculated from the frequency factor t0 of theFRENKEL equation [2]

exp -h-v

kT-\l-

and from experimental adsorption entropies with the equa-tion derived above. Thus, the well-known compensation ef-fect between experimental % and adsorption enthalpy val-ues [4] can be used to establish a correlation betweenhindrance factor and adsorption enthalpy with literature ad-sorption data of lanthanoids and actinoids on bcc metals:

log (fhindr) = 1.79 + 0.0062 • AHads [kj/mol]

CALCULATIONS OF ADSORPTION ENTHALPIES

Adsorption enthalpies can be calculated from thermochro-matographic data [5]:

To T, TTf 1• - -exp ——/ T I RT

• or

As has been shown, the adsorption entropy is not a simpleparameter, but a function of the adsorption enthalpy. Theprogram TECRAD [6] was modified such that its iterationloop for the enthalpy calculation considers the dependenceof the adsorption entropy on the adsorption enthalpy.

ACKNOWLEDGMENTS

We gratefully acknowledge the support by BMBF, contract06 DR 824.

REFERENCES

[1] P.W.Atkins, "Physikalische Chemie"; 2nd edition,Weinheim 1996, p. 640.

[2] J. H. De Boer, Advances in Catalysis 8, 17 (1956).

[3] C. Astaldi, et. al.,Solid State Commun. 75, 847 (1990).

[4] E. Bauer, "Chemisorption Systems", eds. Woodruff, D.P., King, D. A.; Elsevier 1984, p. 51.

[5] B. Eichler, I. Zvara, Radiochim. Acta 30, 233 (1982).

[6] H. Funke, et. al., Report FZR-43, 53 (1994).

130

SELECTIVE GAS-PHASE TRANSPORT OF SHORT-LIVED, CARRIER-FREEIODINE ISOTOPES FROM A 252CF FISSION SOURCE

S. Soverna (Univ. Bern), Ch.E. Dullmann, H.W. Gdggeler, A. Tilrler (Univ. Bern & PSI), M.Ammann (PSI)

A selective gas-phase transport of carrier-free iodine nuclides from a 2S2Cf fission source was accomplished by usinga moist (H2O) carrier gas (He/N2) (free of aerosol particles). The transported volatile iodine compound is tentativelyidentified as hypoiodous acid HOI.

1 INTRODUCTION

Iodine containing compounds play an important role in thehalogen activation and the ozone loss in the marine boun-dary layer [1]. To investigate the iodine compounds andtheir reactions in the atmosphere in model experiments atthe naturally occurring low concentration levels, the use ofradioactively labelled iodine reservoir species is veryadvantageous. The 252Cf fission source called Miss Piggy[2] provides among other fission products [3] short-livediodine nuclides as primary fission fragments. To use theseiodine isotopes as tracers a rapid selective chemicalisolation of the iodine isotopes is necessary.

2 EXPERIMENTAL

The transport of the fission products was accomplishedwith a gasjet system [4]. Since it is expected that iodinenuclides form volatile compounds, carrier gases free ofaerosol particles were used. The nuclides were transportedwith the carrier gases He, He/N2 or Ar/N2 from the recoilchamber of Miss Piggy [2] through a perfluoroalkoxy tube(2 m) and finally collected on activated charcoal filters atroom temperature. The filters were impervious for iodinecompounds from Miss Piggy. In search of the best selectivetransport of the iodine isotopes O2 and/or H2O vapour wereadded to the carrier gases. In other experiments O2 and/orH2O vapours were excluded from the gases.

3 RESULTS

The iodine isotopes "2I, "3I, "4I, "5I, "% l36mI, and I38I wereeasily separated from other fission products by using carriergases without aerosols (see Fig. 1 and Fig. 2). The iodinecompounds could not be separated from the volatile Tccompounds and the fission nobel gas Xe. Selectivetransport of iodine nuclides was observed for all testedcarrier gas mixtures but the yield of the iodine nuclidesamounted only to about 30 % compared to the yieldobtained by carrier gases seeded with carbon aerosolparticles. Adding up to 34'000 ppm of H2O vapour to theHe/N2 carrier gas a good selective transport was obtainedwith a yield of iodine nuclides of 215 % compared tocarbon aerosol transport. We did not observe the sameresult using Ar/N2 saturated with H2O vapours as carrier gaswhich we do not yet understand, because we obtained thesame yield of iodine for the two carrier gases He/N2 andAr/N2 without H2O vapour.

It appears from literature data [1] that the hypoiodous acidHOI is the iodine compound which is transported fromMiss Piggy to the filters. In order to from HOI, the iodineoxide IO radical has to be formed first by the reaction:

I + O3 -> IO' + O2

The iodine radical I is generated in the fission process, O3 isproduced in the recoil chamber by the radiative chemical

decomposition of O2. It seems as if just a few ppm of O2 areneeded in the carrier gas to form sufficient amounts of O3.IO is a relatively unstable compound and rapidly reactswith other radicals or compounds. One of the reactionpartners of IO is the peroxyradical HO 2:

IO + HO 2 -» HOI + O2

HO2 is produced by the radiative chemical decompositionof H2O and O2. With this reaction HOI is formed, which is arelatively stable compound and is transported to thedetection system.

Counts /10 min

16000 •

4000 •

12000 •

0000-

8000 •

6 0 0 0 -

4000 •

2000 •

0-

10>Nb,'°Tc,1<4Ba

l l rMnili

""Nb, ""Mo,• '"Rh, l4sCe

/ ""Rh

"Mi<b

ill

600 800 1000 1200 1400 1600 181

Energy [keV]

Fig. 1 : y-spectrum of fission products from Miss Piggytransported with graphite aerosols. The spectrumwas measured during a 10 min collection time.

Counts /10 min

2500 •

2000 •

1500 •

000 •

500 •

0 •

l 4 l X e

I \ '"Tc

N k I i •l4lXe '"K

^•IJ i l l , J | „0 200 400 600 800 1000 1200 1400 1600 1800 2000

Energy [keV]

Fig. 2 : y-spectrum of fission products from Miss Piggytransported with a moist carrier gas withoutaerosol particles. The spectrum was measuredduring a 10 min collection time.

REFERENCES

[1] R. Vogt et al., J. Atmosph. Chem. 32, 375 (1999).

[2] D. T. Jost et al., PSI-Ann. Rep. 1998, 2 (1999).

[3] Ch. E. Dullmann et al., PSI-Ann. Rep. 1998, 3 (1999).

[4] R. J. Silva et al., Nucl. Inst. Meth. 147, 371 (1977).

131

oc-PEAK SHIFT IN COOLED PIN-DIODE DETECTORS

D. T. Jost, D. Piguet (PS)

This study shows the influence of temperature on the pulse height of small PIN-diodes used as a-particle detectors.

1 INTRODUCTION

It is planned to use inexpensive PIN-diodes to construct athermochromatographic device for the investigation ofchemical properties of superheavy elements. In thetraditional approach to thermochromatography the chemicalspecies was passed through a quartz column at a constanttemperature and a detection system at the exit of thecolumn. Repeating this experiment at various temperatureslead to a so-called breakthrough curve. Given the very lowproduction yields for the super heavy elements (Element108: 1 atom per day), it is necessary to improve the overallefficiency of the system. Our approach is to combine thechromatographic retention part with the detection system.In the case of element 108 it is expected that the 108-tetroxyde will be adsorbed on a quartz surface at about -80°C. We are planning to build a system with a temperaturegradient from -10°C to -120°C. Two times 36 detectors of10mm length will be used to form this system giving atemperature difference of about 3K per detector. This studywas conducted in order to test functioning of the PIN-diodes at the low temperatures and evaluate the influenceon the energy resolution if three adjacent detectors arecoupled to a common amplifier chain.

Fig. 1: PIN-diode test setup. A) PIN-diode, B) Peltierelement, C) Copper coldfinger, D) Copper braid,E) detector support, F) a-source, G) vacuumenclosure.

comparing the pulse height of the 5.806MeV a-line ofMCm with the value at 20°C. The amplifier chain consistedof a Canberra 2001 preamplifier and an Ortec 855 dualamplifier. One main amplifier was set to 0.5|J,s shaping timeand the other to 3.0(Xs.

3 RESULTS

Fig. 2 shows the temperature dependence of the pulseheight. The most striking feature is the very large shift at -160°C with 0.5(0.s shaping time while with a 3.0|̂ s settingwe did not observe this dramatic change. Observing thepreamplifier output pulse with an oscilloscope showed asignificantly slower rise time at -160°C than at 20°C. Thiseffect can be explained by either the slower chargecollection or with a change in the electrical capacity of thedetector/preamplifier input stage due condensation or smallchanges in the geometry caused by the different thermalexpansion coefficients of the involved materials. With the3.0(0.s shaping time the shift is about -0.4 keV/K at5.8MeV. Within three adjacent detectors the temperaturechanges about 10K giving rise to a decrease in energyresolution of approximately 4keV at 5.8 MeV.

10.0

9.5 -

CO

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

-160 -140 -120 -100 -80 -60 -40 -20 011

20

Temperature [°C]

Fig. 2: Temperature dependence of the pulse height of aHamamatsu PIN-diode used as a-particle detector.

2 SETUP

A lOxlOmm PIN-Diode (Hamamatsu S3590-2) wascoupled with the cold side of a Peltier element (Melcor CP1,4-35-045 L) and this assembly was in turn mounted in anold y-detector cryostat. The detector temperature wasmeasured with a thermocouple in contact with the ceramicssupport of the PIN-diode. The Peltier element was used tovary the detector temperature and gain some experiencewith relatively high currents close to the detector. Fig. 1shows the schematic setup of the detector assembly. A 3-nuclide source (239Pu, 241Am, 248Cm) was used as calibrationstandard. The temperature dependence was determined by

4 CONCLUSIONThe decrease in energy resolution due to a 10K differencein detector temperature is acceptable for our purposes. Evenfor 9MeV a-particles the decrease is less than lOkeV andcomparable to the effects caused by electrically couplingthree detectors.

132

TRANSPORT YIELDS OF SELENIUM NUCLIDES AT THE SINQ GAS-JET FACILITY

M. Wachsmuth, B. Eichler, M. Ammann (PSI), F.L. Hdnssler, H.W. Gdggeler (Univ. Bern & PSI)

The chemical interaction of different reactive gases (O2, H2, CO, C3H$ and only He) with short-lived seleniumnuclides and the transport properties of the resulting products have been investigated using the SINQ gas-jet facility.

INTRODUCTION

The use of short-lived bromine nuclides as tracers inlaboratory studies of heterogeneous reactions of brominecompounds such as hypobromous acid (HOBr) enablesexperiments under atmospherically relevant conditions. Asbromine nuclides, though produced with high efficiency inthermal neutron induced fission of 235U, are not efficientlytransported in the gas-jet facility at the Spallation neutronsource (SINQ) under a variety of gas conditions, theselective transport of its precursor selenium is of interest. Ithas already been shown that by adding CO to the inertcarrier gas (He), selenium nuclides can be transported to thelaboratory, where the daughter bromine nuclides could beseparated under Br2 carrier addition [1]. However, it turnedout that the presence of CO had a negative impact on thephotochemical conversion of the product molecules(labelled Br2) to HOBr. Therefore, other gas mixtures weretested with respect to transport efficiency of Se nuclideswhich depends on the volatility and stability againstreaction with wall materials of the molecules formedbetween the recoil atom and the added gas. In addition, thesuitability of these gas mixtures for separation of Brnuclides in a useful chemical form was tested.

EXPERIMENTAL

The experimental set-up was the same as described in [1].Activated charcoal was used to trap all gaseous nuclides inthe laboratory and to compare the transport yields of the Senuclides. Carbon monoxide (750 ppm CO in He), propene(650 ppm C3H6 in He), oxygen (5 % O2 in He), hydrogen (1% H2 in He) and pure helium (99.9999%) were used. To getfurther information about the chemical identity and stabilityof the transport species, the decomposition temperatureswere determined by cracking the transport molecules in thetube furnace described in [1].

6000

5000-

.1" 3000-

"* 2000-

1000-

—•— Se-84He

—§§— Se-84 02

Se-84H2

H Se-84 CO

—*—Se-84 C3H6

5000 10000

Time [s]

15000 20000

Fig. 1: Saturation activities of 84Se (Ti/2= 3.1 min), col-lected on a activated charcoal trap and measuredwith a HPGe detector, as a function of time.

RESULTS

Fig. 1 compares saturation activity of 84Se for the differentgas mixtures, and Table 1 lists the decompositiontemperature obtained for each system. The highest yieldwas obtained in the case of C3H6. H2 and CO led to a fivetimes smaller yield, while for O2 and He, a saturatingactivity of only around 300 Bq was obtained. The resulting84Br activity from the (3-decay of 84Se was around twotimes higher. No difference in the Se transport yieldbetween pure helium and 5 % O2 in He is apparent.However, after decomposition, bromine could only beseparated in carrier free form in presence of oxygen (Fig.2). From the ability of the bromine compound to beabsorbed on basic surfaces, to pass over solid CBr4 and toreact with solid sodium bromide, it was tentativelyidentified as HO84Br.

6000

390 400 410 420

Energy [keV]

Fig. 2: Comparison of a direct catch (dotted line) and adecomposition/separation experiment (solid line)using 5 % O2 in He as transport gas.

Table 1: Results of decomposition experiments.

Gas

He

H2 (1 % in He)

O2 (5 % in He)CO (650 ppm in He)

C3H6 (650 ppm in He)

Transportmolecule

H2nSe

H2nSeO3

OC"Se

C3H6"Se

Td

[°C]700

900

750

800

1050

After separation

--

--

HO°BrnBr-Br *

--

Td: Decomposition temperature; n: 83, 84, 85, 86;—: daughter bromine nuclide could not be mobilised fromthe tube furnace; *: could only be mobilised after additionof 500 ppb Br2 as carrier.

ACKNOWLEDGEMENTThis project is funded by the Swiss National ScienceFoundation (No. 20-58775.99).

REFERENCES

[1] M. Wachsmuth et al., Radiochim. Acta, in press(2000).

133

REACTION OF HO86Br WITH SODIUM BROMIDE AEROSOL

M. Wachsmuth, M. Ammann (PSI), H W. Gdggeler (Univ. Bern & PSI)

The reaction of gaseous hypobromous acid (HO mBr), available via the SINQ gasjet facility, with deliquescentsodium bromide (NaBr) aerosol particles has been investigated in an aerosol flow tube study. The reaction is fast,and at these low concentrations, the product, gaseous Br2 remains aerosol bound on the short time-scale.

INTRODUCTION

The heterogeneous reaction of bromine compounds, andparticularly of hypobromous acid (HOBr), with sea-saltbromide belongs to the key processes sustaining nearsurface ozone depletion events in the arctic at polar sunrise[1]. Only in one previous study, uptake of HOBr tosuspended aerosol particles have been measured in thelaboratory [2]. The aim of the present work is to investigatethe HOBr(g) - aerosol bromide interaction at extremely lowconcentrations using the short-lived isotope 86Br of bromineavailable from the gas-jet facility at SINQ.

EXPERIMENTAL

HO86Br was produced from thermal decomposition of a86Se compound available from the SINQ gas-jet facility [3].NaBr aerosol particles were produced by nebulising anaqueous sodium bromide solution (-0.2 M) and drying theresulting droplets in a diffusion dryer. The particles werethen humidified to well above the deliquescence point(85%). The size distribution was obtained from aDifferential Mobility Analyser (DMA) coupled to aCondensation Nucleus Counter (CNC).

go 2E+11 -

U 1E+11 -

I"I 5E+1O -

1 10 100 1000Midpoint diameter [nm]

Fig. 1: The size distribution of deliquescent NaBr aerosolat 50% relative humidity after it had beenhumidified to 85%.

HO86Br and the aerosol was mixed in a PFA flow tube(perfluoroalkoxy copolymer). The reaction time was variedby changing the position at which the HO86Br is mixed withthe aerosol. The total concentration of HO86Br is on theorder of 1000 cm"3. After the flow tube, HOBr(g) wasabsorbed onto the walls of a denuder coated withTetrabutylammonium hydroxide (TBAH), whereas theparticles passed the denuder and were retained in a particlefilter behind. From the measurement of the activity due tothe decay of 86Br at the denuder and the filter with a y-detector, the partitioning between HOBr(g) and paniculatebromine was derived. To distinguish between HOBr(g) andBr2(g), the expected product of the reaction, an additionaldenuder coated with CBr4, was mounted in front of theTBAH denuder, or after the particle filter, to absorb Br2 insome experiments.

RESULTS

In Fig. 2, the partitioning of the 86Br activity between theTBAH denuder and the particle filter is shown as a functionof reaction time. With a long enough reaction time,complete uptake onto the aerosol was observed, and norelease of a gas-phase product occurs. If a CBr4 denuderwas mounted behind the particle filter only a very smallfraction of 86Br from release of Br2 was found on thisdenuder. The desorption life-time from the deliquescentbromide solution seems to be longer than the half-life of86Br, 55s, probably due to the significant solubility of Br2.However, when the NaBr particles were not humidifiedabove the deliquescence point, i.e. when the NaBr onlycontained adsorbed water at about 10% relative humidity,all HO86Br taken up on the aerosol was immediatelyconverted to and released as 86BrBr and observed in theCBr4 denuder in front of the TBAH denuder (data notshown). For the case of deliquescent NaBr particles, asshown in Fig.2, the increase of particulate bromine and thedecrease of HOBr(g) are consistent with very fast uptake.According to mass transfer calculations, including diffusionin the gas-phase, the uptake coefficient, i.e., the probabilitythat a collision of HOBr(g) with the surface results inuptake, is larger than 0.5.

2,a• -

M

ntin

3Ou

Is=3

Part

£u

oB

100

80

60

40

20

0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Reaction time [s]

Fig. 2: The reaction of gaseous HOBr with NaBr aerosolsas a function of time shown as partitioning of the86Br activity between the TBAH denuder and theparticle filter after the flow tube.

ACKNOWLEDGEMENT

This project is funded by the Swiss National ScienceFoundation (No. 20-58775.99).

REFERENCES

[1] R. Vogt et al., Nature 383, 327 (1996).

[2] J. P. D. Abbatt, G. C. G. Waschewsky, J. Phys. Chem.A 102, 3719 (1998).

134

THE ADSORPTION OF NO, NO2 AND HONO ON ICE

M. Ammann, T. Bartels, B. Eichler, P. Zimmermann (PSI) andH. W. Gdggeler (Uni. Bern & PSI)

The adsorption of NO, NO2 and HONO on ice was investigated by means of thermo-chromatography and labellingwith the short-lived radioactive tracer I3N. All species undergo a reversible adsorption process during migrationthrough packed ice columns. Adsorption enthalpies were estimated for all three species.

INTRODUCTION

Nitrogen oxides largely determine the budget of ozone inthe atmosphere. As ice is a significant surface interactingwith air masses containing nitrogen oxides in the uppertroposphere, alpine, arctic and polar regions, the adsorptionproperties of nitrogen oxides on ice are of considerableinterest for the chemistry in ice clouds and snow packs [1].

EXPERIMENTAL

To investigate the interaction of nitrogen oxides with ice,its chromatographic retention in a column packed with icespheres was observed using "N labelled molecules. I3NOwas produced through 160(p,oc)l3N in a gas target at thePhilips cyclotron of the Paul Scherrer Institute [2]. Passinghumidified 13NO over solid CrO3 resulted in 13NO2. HO13NOwas produced by passing 13NO2 over solid n-1-Naphtyldiethylenediamine. Rapidly freezing water dropletsin liquid nitrogen and crystallizing them at 253 K resultedin ice spheres with a specific surface of about 0.01 lm2g',which where packed into a column. The column was placedinto a thermo-chromatograph, a device in which a negativetemperature gradient from 253 K to 80 K was maintained[3]. From the warm end, the carrier gas containing the 13Nlabelled molecules passed the column for 30 minutes, theflow rates were between 1.7 and 5.0cm3s"1. After theexperiment, the column was removed from the thermo-chromatograph and submersed into liquid nitrogen. Thedeposition zones of the different 13N-species were recordedby scanning the column with a gamma detector.

RESULTS

Each experiment resulted in a chromatogram as shown inFig. 1, for NO2, and in Fig. 2, for HONO and NO. In allcases, distinct peaks were observed for all species, whichindicates that reversible adsorption is the process governingmigration of each species along the column. Underotherwise identical experimental conditions, the depositiontemperature did not depend on whether any of the specieswas present alone or in a mixture. Therefore, nocompetitive adsorption process seems to be relevant. Also,no indications for decomposition or oxidation reactionsover ice were evident. The absolute concentration of eachspecies was usually below 3ppb. No shift in the depositiontemperature was observed at concentrations up to lOOppb.At the deposition zone, where the molecules accumulated,the surface coverage on ice was at maximum about 1 % of aformal monolayer. Nevertheless, it can not be completelyruled out that in the case of NO2 the adsorbed species wasN2O4.

Based on the assumptions of ideal linear chromatographyand adsorption equilibrium, the adsorption enthalpies canbe derived from the experimental parameters and the

adsorption entropy, which can be estimated from statisticalthermodynamics [4]. Based on the assumption that themolecules do not lose rotational degrees of freedom duringthe adsorption process, for NO, NO2, and HONO theadsorption enthalpies were -22, -28 and -40kJ/mol,respectively.

0 20 40

Position [cm]

Fig. 1: Deposition of 13N labelled NO2 at 110K after athermo-chromatography experiment on ice. NO2

was fed to the column from the warm end at 0cm.

8000

„ 6000

& 4000 •

"* 2000 •

0

\

1

—

\ r

\ ,\

280

260

240

220

• 160

• 140

• 120

• 100

0 20 40

Position [cm]

Fig. 2: Deposition of 13N labelled HONO at 155K and NOat 80K after a thermo-chromatography experimenton ice. The carrier gas was fed to the column fromthe warm end at 0cm.

REFERENCES[1] A. E. Jones et al.,

Geophys. Res. Lett. 27, 345-348 (2000).[2] M. Ammann et al., Nature 395,157 (1998).[3] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000).[4] B. Eichler et al., Radiochim. Acta 68, 41 (1995).

135

THE ADSORPTION OF PEROXYACETYL NITRATE ON ICE

T. Bartels, M. Ammann (PSI), H. W. Gaggeler (Univ. Bern & PSI)

The adsorption of PAN on ice was investigated by means of thermo-chromatography of PAN labelled with the short-lived radioactive tracer nN {W2 = 10 min). First results show no decomposition of PAN on ice and an adsorptionenthalpy of - 36 kJ/mol.

Peroxyacetyl nitrate (PAN) is an atmospheric reservoir andtransport species of NOx (NO and NO2). As NOx largelydetermines the budget of ozone in the upper troposphere, itis important to understand the chemistry of PAN. Besidesthermal decomposition, heterogeneous processes may playan important role. A substrate for heterogeneous processingof PAN in the upper troposphere may be ice crystals incirrus clouds.Currently, it is not known to what degree PAN partitionsbetween the ice and gas phase through reversible adsorptionand whether PAN decomposes to NOx on the ice phase.

To investigate the interaction of PAN with ice, itschromatographic retention in a column packed with icespheres was observed using radioactively labelledmolecules. Rapidly freezing water droplets in liquidnitrogen and crystallizing them at 253 K resulted in icespheres, which where packed into a column. The columnwas placed into a thermo-chromatograph, a device in whicha negative temperature gradient from 253 K to 80 K wasmaintained [1]. From the warm end an N2-carrier gascontaining 13N-PAN passed the column for 30 minutes. The13N-PAN was synthesised by photolysis of acetone vapourat 254 nm in presence of I3NO and O2 The "NO wasproduced through 160(p,oc)l3N in a gas target at the Philipscyclotron of the Paul Scherrer Institute [2].

Excess

Acetone (-160°C)

Fig. 1: Experimental set-up of the flow system.TC: Thermo Chromatograph, CLD: NOx Analysis,hv: photolysis cell

After the experiment, the deposition zone of various I3N-species was deduced using a very sensitive gamma detectoryielding a chromatogram as can be seen in Fig. 2. As thetemperature gradient along the column is known, thedeposition temperature of 13N-PAN could be determined.

Based on ideal linear chromatography and the adsorptionequilibrium, the following relation between experimentalfactors - on the left hand side of the equation -, andthermodynamic functions as well as the depositiontemperature on the right hand side, holds [3]:

t - a u .

S ' l

R T

-AHL

ASU

aR

•p.

- A H U

aR T

a

with t: duration of the experiment, a: temperature gradient,u0: linear gas velocity, s: column surface, To: startingtemperature, R: gas constant, Ta: adsorption temperature,AH°a: standard adsorption enthalpy, AS°a: standardadsorption entropy.

Column Length [cm]

Fig. 2: Chromatogram and temperature gradient (dots).The gas enters from the warm end at 50 cm. PANdeposited at 25 cm / 185 K and NO2at 19 cm / 140K.

Thus, based on the experimentally determined depositiontemperature, the adsorption enthalpy can be calculated.Obviously, the result depends on the choice of entropychange associated with adsorption. The entropy change caneasily be calculated based on statistical thermo dynamicalconsiderations for a symmetrical molecule. For PAN theadsorption entropy at the deposition temperature wasestimated to be -171 J/K.A typical experiment with a gas flow through the column of95 ml/min, a geometrical diameter of the ice spheres of1515 |xm, and experimental time of 30 minutes yields anadsorption enthalpy of -36 kJ/mol.

ACKNOWLEDGEMENT

This work forms part of the EU project CUT-ICE (EVK2-CT-1999-00005) funded by the Swiss Federal Office forEducation and Science.

REFERENCES

[1] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000).

[2] M. Ammann et al., Nature 395, 157 (1998).

[3] B. Eichler et al., Radiochim. Acta 68,41 (1995).

136

THE REACTION OF HNO3 WITH SEA-SALT AEROSOL PARTICLES

M. Ammann, F. Arens, L. Gutzwiller, E. Rossler (PSI), H.W. Gaggeler (Univ. Bern & PSI)

UN labelled HNO3 was reacted with sea-salt aerosol particles, and formation of particulate nitrate was measured asa function of reaction time, HNO^ concentration. The reaction probability derived from the results is about 0.07.

INTRODUCTION

Nitrogen oxides control the ozone abundance over largeareas of the troposphere. The oxidation to HNO3, anduptake of the latter to aerosol particles or cloud dropletsconstitutes their main removal pathway. Only in oneprevious study, uptake to suspended aerosol particles havebeen measured in the laboratory [1]. Using sea salt aerosolparticles as an example, first results for the reaction withHNO3 at very low concentrations are shown here.

EXPERIMENTAL

Similar to our previous aerosol studies [2] we used 13Nlabelled NO2, humidified to 8% relative humidity at 20°C.The mixture was irradiated with 172nm UV radiation forOH production, which rapidly converted 80% of the NO2 toHN03. Sea salt aerosol was produced by nebulising asolution of commercially available synthetic sea salt. Thetotal aerosol surface to volume ratio varied from 10"4 to 10~3

cmVcm3, as measured by a scanning mobility particle sizer.The aerosol and HNO3 flows were mixed in a small aerosolflow tube. By changing the length of the flow tube theinteraction time between the aerosol and HN03 was varied.Immediately after, the resulting flow passed a narrowparallel plate diffusion denuder with selectively coatedwalls absorbing HNO3(g) and NO2(g), respectively,followed by a particle filter collecting the particles withHN03 or its product on them. The amount of labelledmolecules absorbed in each of these traps is measured usinga scanning coincident counting system consisting of twoopposite y-detectors.

Time (min)

Fig. 1: On-line record of HNO3(g), NO2(g), and HNO3

attached to the aerosol particles leaving the flowtube for a typical experiment at 5 ppb HNO3. Thenumber of "N-labelled molecules of each speciesabsorbed in its respective trap is plotted. AfterlOmin, the UV lamp is switched on to convert NO2

to HNO3, the aerosol is switched on and off at 15and 25 min, respectively.

Fig. 1 shows a typical on-line record of HNO3 andparticulate nitrate during an experiment. Each experimentas shown there leads to one data point in Fig. 2 displayingthe number of labelled particulate nitrate leaving the flowtube as a function of the interaction time. The solid linedisplays a best fit of a model describing mass transfer to theaerosol particles including diffusion yielding a preliminaryvalue of 0.07 for the uptake coefficient. This is higher thanon pure bulk NaCl [3], but lower than Abbatt andWaschewsky [1] observed on deliquescent NaCl aerosol. Inour system, the aerosol was dried to below 10% relativehumidity and rehumidified to 30% probably not leading todeliquescent particles.

The measurements presented here show the power of themethodology to determine the uptake kinetics of HNO3 toaerosol particles under atmospheric conditions with respectto concentration and humidity.

0 0.5 1 1.5 2

Residence time in flow reactor (s)

Fig. 2: Amount of 13N labelled molecules leaving theaerosol flow tube attached to the particles,presumably in the form of nitrate, as a function ofthe residence time in the flow tube. The relativehumidity was 30%, the temperature 300 K, and theHN03 concentration 3ppb.

REFERENCES[1] J. P. D. Abbatt and G. C. G. Waschewsky,

J. Phys. Chem. A 102, 3719 (1998).[2] M. Kalberer et al., Journal of Geophysical Research

104, 13825 (1999).[3] J. A. Davies and R. A. Cox,

J. Phys. Chem. A 102, 7631 (1998).

137

MODELLING THE HETEROGENEOUS REACTION OF NO2 ON DIESEL SOOT

F. Arens, M. Ammann, L. Gutzwiller, U. Baltensperger (PSI), H.W. Gdggeler (Univ. Bern & PSI)

Nitrous acid (HONO) may be formed via a reaction between nitrogen dioxide (NO2) and soot particles. Based onresults obtained earlier using nN labelled NO2, a surface chemical model was developed to calculate atmosphericHONO formation rates.

Nitrous acid (HONO) may be important because of itspotential role in initiating daytime photochemistry by itsrapid photolysis yielding OH radicals. The source ofHONO in the atmosphere has not yet been conclusivelyidentified. Several studies have recently identified soot aspossible reactive surface for reaction with NO2 leading toHONO [1,2].

Sampling, characterisation and exposure of diesel sootsamples to "N labelled NO2 is described in detail elsewhere[3]. In these experiments, the formation of HONO as afunction of NO2 concentration and relative humidity wasfollowed over time.

The reaction rates of HONO increased with increasing NO2

concentration (Fig. 1) and did not depend on relativehumidity. HONO formation decreased with time (Fig. 2),indicating consumption of reactive surface species. Due toother experiments, here not explained in detail, we assumethat HONO formation is caused by reduced organic species(RnH) on the soot surface oxydisable by NO2. On the basisof the results, HONO formation was interpreted in terms ofa Langmuir-Hinshelwood model involving two overallsurface reactions in parallel (reactions 1-3).

NO2(g)+S(S) NO2»S (S)

(S)

NO2'S(S)+R2H

(H2O) k,

(H20) k2l ( S ) ~

' ( S )

>S(s)+HONO(g)+R2(S)

(1)

(2)

(3)

For a noncompetitive Langmuir adsorption the equilibriumcoverage of NO2 molecules on the soot surface is given by

e =[NO2»S] KxX NO2

(l + KxXN02)with K = f (4)

des

where [NO2»S] denotes a physisorbed precursor state, XN02denotes NO2 in the gas phase and Ns is the maximumnumber of sites S available. The resulting HONO formationrate involving two surface reactions can be written as

d\HONO] r l 1+k2x[R2H\(t)y

with(f) (t=0)

=\RIH]

[R2H\ =[R2H]

xNsx0 (5)

(f = 0)Applying these equations to the experimental data, valuesfor the unknown constants K, [RjH]^, [/?//](t=0), (Nsx kj)and (Nsx k2) were determined. This parameterisationderived allows to predict the atmospheric HONO formationon diesel soot particles for a time scale up to several hours.

5e+10

10 15 20 25 30 35 40NO2(ppb)

Fig. 1: Initial HONO formation rate on diesel soot particlesas a function of the NO2 mixing ratio (r.h. = 30%)and the corresponding inverse data (insert).

8 ppb NO2 9 ppb NO2

18 ppb NO2

0 10 20 30 40 0 10 20 30 40 50

t im e (m in)

Fig. 2: HONO formation rates as a function of time fordifferent NO2 mixing ratios (r.h. = 30%).

ACKNOWLEDGEMENT

This work forms part of the Eurotrac-2 project CMD(Chemical Mechanism Development) and has beensupported by the 'Komission fur Technologie undInnovation (KTI)'.

REFERENCES

[1] M. Ammann et al., Nature 395,157 (1998).

[2] M. Kalberer et al., JGR 104, 13.825 (1999).

[3] F. Arens et al., submitted toEnviron. Sci. Technol. (2001).

138

MEASUREMENT OF THE HONO EMISSION FROM A DIESEL ENGINE

J. Kleffmann, J. Heland, R. Kurtenbach, J. C. Lorzer, P. Wiesen (Universitdt Wuppertal), M. Ammann, L. Gutzwiller(PSI), M. Rodenas Garcia, M. Pons, K. Wirtz(CEAM, Valencia), V. ScheerandR. Vogt (Ford, Aachen)

HONO emission indices of a commercial diesel engine were measured under varying operating conditions andusing differently formulated fuel. The four different measuring methods applied show good agreement.

Nitrous acid (HONO) is formed during night time andphotolysed to OH and NO at sunrise, thus initiatingphotooxidation processes early in the morning. However,the mechanism of HONO formation is badly understood inspite of intensive research in this field. Direct emissionsfrom vehicles are contributing to atmospheric HONOlevels. Emission measurements were performed in theEuropean Photoreactor EUPHORE in Valencia, Spain. Acommercial 1.8 1 Diesel engine (44 kW, indirect fuelinjection) was used for exhaust generation. About one tenthof the exhaust gas was transferred to the chamber through aheated transfer line and rapidly diluted in the chamber(dilution ratio -1:1000). This set-up preventedagglomeration of particles and the condensation of waterand semi-volatile organic hydrocarbons on the particlessimilar to "real world" conditions of driving a vehicle on aroad.

Five differently formulated fuels were used in the study:European standard Diesel, Biodiesel (RME) and threeDiesel fuels with different content of aromatichydrocarbons and low sulphur content (aromatics < 25%, <15% and < 5%). While the European standard Dieselcontained significant amounts of di- and poly-aromatics and425ppm sulfur, the diesel fuels with < 5%, < 15% and <25% aromatics were formulated almost only with mono-aromatics and 45ppm sulfur.

HONO measurements were performed with different wellestablished techniques and a newly developed instrument:

(1) A wett effluent diffusion denuder (WEDD) [1];

(2) A DO AS spectrometer [2];

(3) HPLC technique [3];

(4) Additional HONO measurements were performed witha long path absorption photometer (LOPAP) [4].

Emission indices (El: g HONO per kg fuel burnt) werederived from the ratio of the weighted mean HONOincrease measured by all instruments per CO2 increase afterexhaust gas injection. It was observed that the HONOemission indices are almost independent of fuel formulationand engine load, although the sulphur and aromatichydrocarbon content of the fuel varied significantly.Accordingly, from all emission data obtained a mean valueof EIH0N0 = (0.11±0.04) g/kg was derived. This value is ingood agreement with the value of -0.1 g/kg for Dieselengines from a recent tunnel study (Becker et ah, 2000).

o

• stand. Diesel• BiodieselH < 5% aromaticsM < 15% aromaticsE < 25% aromatics

ONm 30 Nm 70 Nm ONm 30 Nm 70Noi 70Noi accel. accel.

hot)

engine condition

Fig. 1: HONO emission indices for different engineconditions using different diesel fuels.

The corresponding HONO/NOx ratio of HONO/NOx =(7±2)xl0~3 is in agreement with [5] but still does not explainthe observed ratios before sunrise. Therefore, in theatmosphere, HONO is not formed through emission fromdiesel engines, but rather by secondary processes onsurfaces.

ACKNOWLEDGEMENT

This study formed part of the EU project DIFUSO (ENV4-CT97-0390) supported by the Swiss Federal Office forEducation and Science.

REFERENCES

[1] C. Zellweger, M. Ammann, P. Hofer,U. Baltensperger, Atmos. Environ. 33, 1131 (1999).

[2] T. Etzkorn, R. Volkamer and U. Platt in:Becker. K. H. (ed.): Final Report of the EC-ProjectEUPHORE, 65 (1996).

[3] X. Zhou, H. Qiao, G. Deng and K. Civerolo,Environ. Sci. Technol. 33, 3672 (1999).

[4] J. Heland, J. Kleffmann, R. Kurtenbach, P. Wiesen,Environ. Sci. Techno/, in preparation (2001).

[5] K.H. Becker, J.A.G. Gomes, J. Kleffmann,R. Kurtenbach, J. C. Lorzer, M. Spittler, P. Wiesen,R. Ackermann, A. Geyer and U. Platt,Atmos. Environ, in preparation (2001).

139

SIGNIFICANT NITRITE FORMATION IN DIESEL EXHAUST

L. Gutzwiller, F. Arens, M. Ammann (PSI)

The aqueous reduction of NO, by species contained in diesel exhaust is quantified and may account for hithertounexplained HONO to NOx levels in the atmosphere before sunrise.

Nitrous acid (HONO) is formed during night time andphotolysed to OH and NO at sunrise, thus initiatingphotooxidation processes early in the morning. Accordingto a model study, HONO accounts for a five fold increasein OH concentration at 06:00h and a 16% increase in netphotochemical ozone formation [1].

In a recent study, Arens et al. [2] showed that about 1017

HONO molecules are formed per mg diesel soot. This is thehighest conversion ratio cited in the literature for theNOx/soot system so far, although the soot particles werecollected after stripping gas phase components from theexhaust. Instead of examining the role played by sootparticles, we focus in the present study on possible HONOformation by (semi volatile) species contained in the gasphase of hot exhaust; once dissolved in water, these speciesmay react with NO2. The following reactions are implicatedin the aqueous phase formation of nitrite, i.e. dissolvedHONO:

• 2 NO2 (aq) => 2 H+ + NO3" + NO2" (1)

• 2 NO2 (aq) + HSO3- (aq) => 2 NO2" + 3 H+ + SO42" (2)

• NO2 (aq) + ArO" (aq) + H+ => NO2" + ArO + H+ (3)

Reactions (1) and (2) are well known but account onlypartially for the observed nitrite formation in the interactionof diesel exhaust with wet surfaces. Our hypothesis is thatreactions analogous to (3) involving phenols (ArOH) orsimilar reducing agents may form additional nitrite.

synthetic air&NO2

Fig. 1: Schematic design of the experimental set-up.

The principle of the wetted wall flow tube (WWFT)corresponds to the one described in detail by Zellweger etal. [3]. In short, a constant air flow of 0.48 1 min1 wasdrawn through a parallel plate diffusion denuder and fedinto a NOX analyser. The denuder effluent (0.56 ml/min,residence time 20sec) was preconcentrated on ion exchangecolumns and analyzed by ion chromatography. Theduration of the preconcentration was 7 min. The rateconstant of reaction (1) was confirmed with our set-up.This means that the water film of our WWFT is well mixed,thus allowing aqueous phase kinetic measurements. Hot

diesel exhaust (above 120°C) was injected into the flowtube so that the first cold surface seen by the exhaust gaswas the water film itself. The NO2 concentration was variedin order to determine the total amount of nitrite formingspecies. The contribution of reactions (1) and (2) weresubtracted from the total nitrite signal in order to obtain theamount of nitrite attributed to reaction (3) involvingadditional species.

16000

14000 •

12000

g 10000

O 8000 •

X 6000

4000 •

2000

0

NO2 (ppb)

Fig. 2: Equivalent gas phase HONO formation from thereaction of an organic species contained in theexhaust with NO2. Squares and diamondscorrespond to 1 and 3kW load, respectively.

Under atmospheric conditions, these species contained inthe exhaust may also be adsorbed on wet surfaces and reactwith NO2 to nitrite and hence HONO as atmosphericaqueous phases tend to be acidic. Thus, volatile organicspecies in the exhaust may account for higher HONO toNOX ratios at night than expected from the reaction of NO2

on soot or HONO emissions, only.

ACKNOWLEDGEMENTThis work was supported by the Swiss Federal Office forEducation and Science (contribution to the EU-projectNITROCAT, EVK2-CT-1999-00025).

REFERENCES

[1] M. E. Jenkin, R. A.Cox, and D. J. Williams,Atmos. Environ. 22, 487 (1988).

[2] F. Arens, L. Gutzwiller, U. Baltensperger,H. W. Gaggeler, M. Ammann,submitted to Environ. Sci. Technol. (2001).

[3] C. Zellweger, M. Ammann, P. Hofer,U. Baltensperger, Atmos. Environ. 33, 1131 (1999).

140

AN ALPINE ICE-CORE RECORD OF ANTHROPOGENIC HF AND HCl EMISSIONS

A. Eichler (Univ. Bern & PS1), M. Schwikowski (PS1), H.W. Gaggeler (Univ. Bern & PS1)

Ice-core records of an Alpine glacier from the southern Swiss Alps were used to reconstruct sources of inorganic Fand Cl' in precipitation. Our results suggest that on average 16% of the Cl' deposition and most of the F depositionin the period 1937-94 were due to HCl and HF emissions from anthropogenic sources.

Concentrations of F and Cl" were analysed in an Alpine icecore from Grenzgletscher in order to investigate emissionsources of both species and the anthropogenic influence onprecipitation chemistry in the Alpine region. The ice corecovers the time period 1937-94 [1].

F and Cl concentration records consist of a total of 2320samples. The observed strong correlation between [Cl~] and[Na+] on the one hand and between [Cl~] and [Ca2+] on theother hand revealed that the main source of Cl in the sou-thern Swiss Alps is sea salt originally transported togetherwith mineral dust from the Saharan area. The non-sea-saltfraction of Cl (nssCl) was calculated using a C17Na+ molarconcentration ratio of 1, which is assumed to represent thesea-salt ratio at this glacier site [2]. The record of nssClconcentrations (5-year averages) is shown in Figure 1A,revealing a strong increase between 1960 and 1985, fol-lowed by a steep decrease. The contribution of nssCi to thetotal Cl" amounts to 50% at the most with a mean value of16% for the entire time period.

1-12

-10

OI

-800

-600 c-

-400 |

-200

0.00-1930 1940 1950 1960 1970

Year

1980 1990

Fig.1: 5-year average concentration records of nssCl" (A)and F (B) (lines) together with historical emissionestimations of HCl and HF for Switzerland in theperiod 1935-1990 (dashed lines). Diamonds repre-sent emissions from coal burning, while stars indi-cate total emissions, derived from [4].

Sources of nssCl" could be direct HCl emissions fromindustrial sources. The largest sources of anthropogenicHCl emissions in western Europe are estimated to be coalcombustion (about 75% in 1983) and waste incineration [3].

In contrast to other western European countries wasteincineration is the largest national source of anthropogenicHCl emissions in Switzerland, because most domesticwaste is burned. Estimates of historical HCl emissions inSwitzerland show a strong increase compared to the coalburning level in the period 1960-85 due to rising wasteincineration and the large amounts of PVC in waste ([4],Fig. 1A). Because of the installation of flue gas scrubbersas a consequence of air pollution control measures a declinein emissions has occurred since 1985. The good agreementin the trend between estimated Swiss HCl emissions andour data (Fig. 1A) indicates that the nssCl" concentrationrecord at the drilling site is mainly determined by local HClemissions.

Regarding the F record no significant correlation with anyother major ionic species was observed, suggesting that adifferent source was responsible for the major contributionto the F budget over the last 60 years at this site. Thedevelopment of the F concentrations (5-year averages) overthe period 1937-94 is shown in Figure IB. The profileexhibits a steep increase until 1965, followed by a steadydecrease. F measurements in a Greenland ice core indicatethat coal burning is the most important source ofanthropogenic F at this site [5]. However, historical HFemission estimates for Switzerland [4] reveal that the con-tribution of HF emissions from coal burning is less than17% over the last 60 years (Fig. IB). Increasing HF emis-sions up to 1970 are due to increasing aluminum productionin nearby plants at Chippis and Martigny in the Rhonevalley, which are about 40 km distant from the drilling site.As a consequence of the installation of waste-airpurification systems a steep decrease in HF emissionsoccurred after 1970. By comparing our data with the trendin historical emission estimates (see Fig. IB) we concludethat similar to nssCl the major part of F originated from anearby local source. This is in agreement with the expectedshort lifetimes of HCl and HF in the atmosphere due totheir high water solubility, leading to a complete uptake bycloud droplets and subsequent wet deposition close tosources.

Our results indicate a strong impact of emissions of short-lived atmospheric species such as HCl and HF on local andregional precipitation chemistry.

REFERENCES

[1] A. Eichler et al., J. Glaciol., in press.

[2] A. Eichler et al., Geophys. Res. Lett. 27, 3225 (2000).

[3] Lightowlers et al., Atmos. Environ. 22, 7 (1988).

[4] BUWAL, Schriftenreihe Umweltschutz 256 (1995).

[5] de Angelis et al., J. Geophys. Res. 99, 1157 (1994).

141

NORTH-SOUTH DEPOSITION GRADIENTS OF TRACE SPECIES IN THE ALPS

A. Eichler (Univ. Bern & PSI), M. Schwikowski, M. Furger (PSI), H.W. Gaggeler (Univ. Bern & PSI)

North-South deposition gradients of trace species in the Alps were investigated based on the seasonally resolvedanalysis of ice cores from two sites in the Alps. No gradients were found for species of anthropogenic origin, whiledust- and sea-salt-related species show a different behaviour at the two sites due to the different transport patterns tothe Alps.

Due to their extent the Alps act as a barrier for air massflow, and therefore a north to south gradient of the air pol-lution impact on the high-alpine environment is expected.In order to assess the geographical and seasonal trends ofthe deposition of trace components, glaciochemical recordsfrom two Alpine glaciers (Fieschergletscher, northern Alpsand Grenzgletscher, southern Alps) were used.

Ice-core records of the main aerosol-related species (NH4+,

NO3", SO42", Ca2+, Mg2+, Na\ K+, Cl") were compared for the

time period 1945-83, which is covered by both ice cores[1], [2]. Correlation analyses performed for the logarithmicconcentrations revealed the main sources for the tracespecies:(1) NH/ , NO3, SO4

2: Anthropogen,(2) Ca2+, Mg2+: Dust,(3) Na\ K\ Cl: Sea-salt.

In contrary to the Fieschergletscher concentrations of dust-and sea-salt-related species are well correlated for theGrenzgletscher [1], [2]. Thus, the transport of Saharan dust,which is the main source of mineral dust at theGrenzgletscher [1], to the southern Alpine chain is coupledto the transport of sea-salt.

-10-

-12-

-14-

-16-

-18-

-20-

-22-

-12

12-

10-

Wi Fr So He Wi Wi Fr So He Wi

O 8-

2.0-

0.8-

Wi Fr So He Wi Wi Fr So He Wi

Fig. 1:Annual cycle of the 818O-values, NH4+-, Ca2+-, and

Na+-concentrations for Fieschergletscher (circles)and Grenzgletscher (triangles) in the period 1974-83. 818O values are shown in comparison to thetemperature at Col du Gd. St. Bernard (2480m asl).

Concentration records of trace species were compared on aseasonal time scale for the period 1974-83 (Fig. 1). Basedon the temperature dependent parameter S18O samples wereclassified in winter-, spring-, summer- and autumn samples[1]. The good agreement between the seasonal cycle of the818O-values at both places and of the air temperature at theCol du Gd. St. Bernard (2480 m asl, Fig. 1) indicates thatthe different classes indeed represent the actual seasons.

Concentrations of species of anthropogenic origin show anaccordant seasonal cycle with two to three times highersummer- than winter concentrations. This can be explainedby precipitation from the same air masses at both sites.These are convective precipitation in summer from aerosolrich air, when trace species from the planetary boundarylayer can reach the Alps and advective precipitation in win-ter from aerosol poor air, representing conditions of the freetroposphere. On the other hand species of dust- and sea-salt-origin show a completely different seasonal behaviourat both sites. While the concentrations of these speciesexhibit a pronounced seasonal pattern at the southernAlpine chain, concentrations are constant throughout theyear for the northern Alps. The different seasonality ofdust-related species is due to the different seasonalbehaviour of the transport of Saharan dust to the sites (Fig.2). This becomes obvious by comparing the Ca2+

concentrations at Fiescher- and Grenzgletscher with thenumber of filters with visible Saharan dust deposit at thenearby stations Jungfraujoch and Plan Rosa, respectively.

O 4_

GG

10-

8-

enQ_

•12 ; rin

^ 6-

s °CO

JFJ

FG

Wi Fr So He Wi Wi Fr So He Wi

Fig. 2: Annual cycle of the Ca2+ concentrations (dashed li-nes) at Grenzgletscher (GG) and Fieschergletscher(FG) along with the number of filters with Saharandust (lines) observed at nearby stations Plan Rosa(PR, 1968-77, [3]) and Jungfraujoch (JFJ, 1995-99, [4]).

The similar annual cycle of the concentrations of dust-related and sea-salt species at the Grenzgletscher isexplained by their coupled transport to the southern Alps(see above). The constant concentrations of sea-salt speciesthroughout the year at the Fieschergletscher, however, canbe explained by the transport of sea-salt with westerlywinds from the Atlantic Ocean to the northern Alps. Theseconditions are uniformly distributed throughout the year.

REFERENCES

[1] A. Eichler, Ph. D. Thesis, University Bern (2000).

[2] M. Schwikowski et al.,J. Geophys. Res. 104, 13709 (1999).

[3] Prodi and Fea,Veroff. Schweiz. Meteorol. Anstalt 40, 179 (1978).

[4] C. Zellweger-Fasi, private communication (2000).

142

ELECTRICAL CONDUCTIVITY MEASUREMENT ON AN ICE CORE FROM THEILLIMANI (6430 m, 16°39'S, 67°47'W), BOLIVIA

St. Knttsel (Univ. Bern & PSI), J.-D. Taupin (IRD, Montpellier), J.-R. Petit (LGGE, Grenoble),U. Schotterer (Univ. Bern), M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI)

For a first dating, the electrical conductivity was measured on an ice core from Illimani. By this fast method, acontinuous signal over the whole ice core is received, from which maxima in conductivity can be assigned tovolcanic events and annual layers can be counted. The preliminary dating obtained by annual layer counting and iceflow modelling agreed well, indicating that several hundred years of palaeoclimate information are preserved by thisglacier.

INTRODUCTION

In June 1999, two ice cores were drilled down to bedrock at138 and 136 m, respectively, on Illimani, Bolivia, by a jointPSI/IRD expedition [1]. To perform a first dating and tointerrelate the two ice cores, the electrical conductivity wasmeasured [see e.g. 2].

The non-destructive electrical conductivity method (ECM)gives an indication about acidity in the ice, and is appliedbefore cutting the ice. It serves as a screening for apreliminary detection of seasonal layers as well as for a firstdating by identifying volcanic events. This allowsdetermining a suitable depth resolution for the subsequentanalysis.

EXPERIMENTAL PART

The electrical conductivity measurements were performedat the Laboratoire de Glaciologie et Geophysique del'Environnement (LGGE) in Grenoble, France.

The electrical conductivity was measured after cutting off a8 mm section in longitudinal direction of the core. Afterpolishing, two electrodes slide over the ice core and thecurrent is measured in dependence of the depth.

RESULTS AND DISCUSSION

The raw ECM data were averaged over 1 cm and theaveraged data versus depth are shown in Fig. 1. Seasonallayers were identified by their characteristic two minima,possibly corresponding to the dry seasons. Annual layercounting was performed down to a depth of 40 mwaterequivalent (m weq.). From the accumulation of the

40 60Depth [mweq]

to the Pinatubo eruption in 1992) an average accumulationrate of 0.67 m weq. y"1 was derived. This accumulation rateand an ice thickness of 111.2 m weq. was used to model theice flow with a one-dimensional model [3].

2000

1950-

1900-

Jf 1850-

1800-

1750-

1700

. St.' Hdens 1980 or H Chichon 1982TritiumPeakl96t

Agung 190*$%!? Tritium Peak 1959

ffldal94'Annual layerscounting

Ice flow model

Santa Maria 19Krakatau 1883

Extrapolation of the Ice flow model

Iceflowmodel:t = [3]

laid ( ^

Cctopaxil768C*k

Tatumail739(^

20 40 60

Depth |niwq]

Fig. 2: Age-depth relationship for an Illimani ice coreobtained by annual layer counting, ice flowmodelling, and identification of volcanicevents.

The obtained age-depth relationship is shown in Fig. 2,along with the result of annual layer counting, the locationof the two maxima in tritium activity (attributed to the years1959 and 1964), and ECM peaks assigned to volcanicevents [4]. The different dating methods agree well andindicate that the ice core from Illimani covers a time periodof several hundred years.

In future, 210Pb activity will be measured and trace elementswith stronger seasonal cycles will be analysed to confirmthis first dating.

REFERENCES

[1] B. Zweifel et al.,

Ann. Rep. Univ. Bern & PSI 1999, p.39.

[2] K. Taylor et al., J. Glaciology 38, 325 (1992).

[3] J.F. Nye, J. of Glaciology 4 (36), 785-789 (1963).[4] T. Simkin et al., Volcanoes of the world,

Smithsonian Institution, 1983.

first six years (confirmed by a maximum conductivity due

Fig. 1: 1-cm average ECM data versus depth.

143

SEASONAL RECORD OF GLACIOCHEMICAL AND ISOTOPIC SIGNALS IN ASHALLOW ICE CORE FROM CHIMBORAZO, ECUADOR.

P. Ginot (Univ. Bern & PSI), U Schotterer (Univ. Bern), W. Stickler (GSF-Inst. for Hydrology, Neuherberg),B. Francou (IRD, Quito), R. Gallaire (IRD, La Paz), M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI).

First results from a shallow ice core drilled at the summit of Chimborazo indicate the possibility to reconstructnormal seasonal climate conditions as well as the ENSO influenced variability from this region for several decades.

In December 1999, a 16-meter ice core was recovered fromthe summit of Chimborazo (6310 m a.s.l., 1°28'S,78°50'W, Ecuador, fig. 1) to explore the suitability of thisglacier as palaeoatmosphere and climate archive. TheChimborazo is located at a borderline influenced by twodifferent source regions of atmospheric moisture, thePacific, and the Amazon basin. The meteorologicalconditions in this region are also affected by thedisplacement of the Intertropical Convergence Zone(ITCZ), and by El Nino/La Nina events which mayinfluence the interannual variability. The displacement ofthe ITCZ results in a bimodal precipitation regime,characterized by two wet periods in the year. Stableisotopes in monthly composites of precipitation in Ecuadorclearly showed this shape. Similar results were obtained byevent-based precipitation sampling in the frame of theISOHYC project which aims at following the isotopicfingerprints of ENSO in a transect over the Andes. Up tonow, the ENSO modulated variability could only bechecked by the long-term isotope record of Izobamba,where it is less pronounced as in coastal regions [1; 2].

, <4V ^ *C"*'.

Fig. 1: Chimborazo: Peak Whymper (6310 m) seen fromPeak Ventimilla (6250 m), the drilling site.

In fact, not only the stable isotope record shows large sea-sonal variations along the Chimborazo core, but also thechemical constituents. The bimodal shape is clearlyobservable in most of the years. We averaged the individualvalues according to more wet and dry periods, identified onthe basis of 8I8O seasonality for three consecutive yearsmodulated by the displacement of the ITCZ to examine thebehaviour of atmospheric constituents (fig.2).

The most depleted 818O values are associated with themaximum of precipitation during the southward movementof ITCZ from February to May, the second maximumduring "veranillo" (Oct. to Jan) is less pronounced in the

averaged isotope values. The bimodal shape of some majorions (i.e. calcium, magnesium, nitrate, sulphate,ammonium) is intensified by enrichment due tosublimation, dry deposition, and riming during the lesshumid periods of the year [3]. Sodium and chloride arehighly correlated (r2=0.9), but sea salt concentrationdifference don't show the "distance from the coast" effectat the drilling site (Pacific/Atlantic is 200km/4000km) assource indicator for atmospheric moisture.

Nevertheless, methanesulfonate (MSA) with a short lifetime in the atmosphere and produced by the oceanicbiosphere shows higher concentrations during the Februaryto May period which could indicate a major Pacificmoisture source. Formate on the other hand originatesmainly from vegetation cover and shows a differentbehaviour which is not in phase with MSA. This again maypoint to a predominant source from the Amazon basin(fig-2).

(°/J MSA (ppb) (ppb)-20-18-16-14-12 o 10 20 0 100 200 300

3600

3900

4200

: 4500 •

4800 •

• 5100 •

5400 •

5700

6000

6300

CalciumNitrate

1

CM

1Y

ea

1

Dly2

Dry]

Wet)

D,y2

Wai 2

Dlyt

Well

Dly 2

Wet 2

Dly \

Well

0 200 400 600Formiate (ppb)

Fig. 2: Seasonal variations of 818O and chemical speciesfrom a section of the 1999 Chimborazo ice core.

These encouraging results finally led to the decision toperform a bedrock drilling on Chimborazo. In Nov./Dec.2000 in total 140 m of ice cores were recovered. Thelongest reached at a depth of 55 meters. More informationis available under: www.inamhi.gov.ee/Chimborazo2000

REFERENCES:

[1] M. Garcia, Villalba, F., Araguas-Araguas, L., andRozanski, K., Proc. Symp. IAEA, Vienna 1998.

[2] U. Schotterer et al., in preparation.[3] P. Ginot et al., submitted to J. Geophys. Res.

144

GLACIOLOGICAL AND CHEMICAL SURVEY AT GLACIAR ESMERALDA, CHILE

M. Schwikowski, S. Briltsch (PSI), G. Casassa, M.A. Godoi (Univ. de Magallanes), A. Giannini, A. Rivera(Geografi'a, Univ. de Chile), E. Vera, R. Adaros (Geofi'sica, Univ. de Chile), St. Kniisel (Univ. Bern & PSI),

Ch. Kull (Univ. Bern)

On 11th December 2000, snow samples were collected and a glaciological survey was performed at the upper part ofglaciar Esmeralda on Cerro del Plomo in the Central Chilean Andes in order to explore the suitability of this glacieras palaeoatmosphere and climate archive. Glaciochemical results and the observed maximum ice thickness of about100 m indicate that this glacier is a potential archive.

1 INTRODUCTIONThe Cerro del Plomo (33°14'S, 70°13'W, 5424 m asl) islocated in an area influenced by the Westerlies circulationsystem and is therefore assumed to receive precipitationformed by humidity from the Pacific. Thus, its glaciers arepotential archives for the reconstruction of the climatephenomenon El Nino. In addition, also the history of airpollution from Santiago might be accessible frompalaeorecords, since the distance between Cerro del Plomoand Santiago is only 40 km.

2 GLACIOCHEMICAL STUDYEight surface snow samples and six snow pit samples of 2cm thickness were collected from the upper, flat part ofglaciar Esmeralda at an elevation of about 5300 m. Thesamples were transported back to the laboratory in pre-cleaned polyethylene tubes, and concentrations of majorionic species were analysed by ion chromatography.Table 1 shows median ionic concentrations of the snow pitsamples in comparison to results of an analogous snow pitfrom Cerro Tapado, which is located about 500 km furtherto the North [1]. For calculating the medians, the surfacelayer affected by post-depositional processes such assublimation and dry deposition [1] was not considered.Concentrations at glaciar Esmeralda are significantly lowerfor all species except F, Mg2+, and Ca2+. This differencemight be due to a larger amount of snow precipitation at thesouthern site, leading to a dilution of atmospheric speciesscavenged by snow.The crusty snow surface present indicated that sublimationinfluences glaciar Esmeralda. However, this effect seemsless strong compared to Cerro Tapado, since the glaciersurface was flat and no penitents were formed. As alreadydescribed for the Cerro Tapado glacier [1], post-depositional effects such as sublimation and dry depositionresult in a strong enrichment of most ionic species in thetopmost snow layer. This is also observed at glaciarEsmeralda as indicated by the enrichment ratios (ER) inTable 1, which are defined as ratios of the surface snow andthe snow pit median concentrations. In agreement withresults from Cerro Tapado, hydronium (H+) as well as theorganic acids acetate (H3CO2) and formate (HCO2) werelost from the surface due to sublimation, as indicated bylow ER values. Chloride (Cl), calcium (Ca2+), sodium(Na+), and ammonium (NH4

+) were most strongly enriched,caused by sublimation as well as dry deposition, whereaspotassium (K+), fluoride (F), nitrate (NO3), magnesium(Mg2+), and sulphate (SO4

2) showed an intermediatebehaviour.

3 GLACIOLOGICAL SURVEYThe radar system used is a portable HF impulse-type,developed at Universidad de Magallanes and usedsuccessfully in glaciers of north-central Chile [2], Patagonia[3] and Antarctica [4]. The transmitter was a Narod model[5], powered by a 12 V battery, which generates a pulse of1100 V, a rise time < 2 ns and a pulse repetition rate of 512pulses/s. Two 8 m-long dipole antennas loaded withresistors were connected to the transmitter, generating anelectromagnetic wave with a central frequency of about 6MHz. Wires were inserted inside webbing tape, thusprotecting the antennas and allowing to use them as regularmountain ropes [6]. The receiver consisted of a TektronicsTHS-720 digital storage oscilloscope, connected toreceiving antennas (of the same characteristics as thetransmitting ones) by means of a balun. Data were stored inthe field with a Husky MP 2500 portable PC connected tothe oscilloscope through the RS-232 port. Averaging of 16traces was performed using the oscilloscope, storing oneaveraged trace every 4 s.Surface coordinates were recorded every 1 sec with a singleGPS receiver Trimble Geoexoplorer II, with single-frequency C/A code, which gave an accuracy of about +10m in horizontal coordinates, and ± 20 m in elevation.Two profiles were measured at the upper part of glacierEsmeralda (Fig. 1), at an elevation of ca. 5330 m. The"transverse" profile started at the right (southeast) marginof the glacier and ended at the left margin (northwest), witha length of 390 m. The "diagonal" profile with a length of290 m started ca. 100 m from the left margin, ended at theupstream margin of the glacier, about 20 m from the rockridge of Cerro del Plomo. Both profiles intersected near thecentral point of the upper dome of glaciar Esmeralda.Surface gradient is small in this section of the glacier, withan average slope of 3 % for the diagonal profile, and 5 %for the transverse profile. A raster display of the radar datais shown in Fig. 2, corresponding to the transverse profile.The glacier bed is shown as a V-shaped valley with amaximum ice thickness near the centre of the profile. Dueto the shallow ice thickness, bed echoes are strong, but inpart masked by the direct airwave. Radar data wereprocessed to attenuate the direct airwave, and then migratedto correct for the geometric effect due to the strong bedslope of the glacier. As expected, the bed appears as a U-shape valley in the migrated profiles, with two-way traveltimes which are about 18 % larger than the non-migratedtravel times, and migrated ice thickness values about 8 %larger than the non-migrated values.

Considering the migrated results, and 170 m/|̂ s for theelectromagnetic wave speed in ice, maximum ice thicknessin the transverse profile was 98 m, corresponding to a two-

145

way travel time of 1.17 |J.s. In the diagonal profile,maximum ice thickness was 106 m, corresponding to a two-way travel time of 1.26 [is. From these results, a deep basinwith ice thickness of about 100 m is found in the centralpart of the upper section of glaciar Esmeralda. Steep bedslopes exist within this basin, with maximum values of 47%(transverse profile) and 59% (diagonal profile).Precision of the radar results can be assessed by comparingthe migrated ice thickness at the intersection of bothprofiles. According to the transverse profile, the icethickness at the intersection is 90 m, and according to thediagonal profile it is 114 m. The average value at theintersection is therefore 102 ± 12 m (± 13%). This errorvalue is considered to be an adequate estimate of the icethickness error. The relatively large error value of 13 % isdue to the steep bed slopes present in the study area. Amore complex 3D migration could reduce substantially thiserror, but to achieve that, a complete gridded set of radardata would be needed.

ACKNOWLEDGEMENTS

The work was supported by the Swiss National ScienceFoundation, Project 2100-050854.97. Part of the radar workwas funded through project FONDECYT 1980293. Wethank Cesar Acufia who drew the map and Carlos Cardenasand Jose Araos for their help with the radar figures.

REFERENCES[1] P. Ginot et al., submitted to J. Geophys. Res.[2] A. Rivera et al., Ann. Rep. Univ. Bern & PSI 1999,

p. 38.[3] G. Casassa, A. Rivera, Anales Instituto Patagonia,

Serie Cs. Nat. (Chile) 26, 129 (1998).[4] G. Casassa et al., FRISP Report 12, 7 (1998).[5] B. B. Narod, G. K. Clarke,

J. Glaciology 40, 190 (1994).[6] A. Gades, PhD thesis, University of Washington,

(1998), p. 192.

Table 1: Median concentrations in |a.eq 1' of ionic species in snow pits from glaciar Esmeralda and Cerro Tapado. Enrichmentratios (ER, ratio between medians of surface snow and snow pit samples) al glaciar Esmeralda are also shown.

EsmeraldaTapadoER

H+

2.57.91.7

H,CO,0.040.731.39

HCO,0.110.702.09

K"0.090.253.77

F0.0J0.024.40

NO,1.306.164.86

Mg-0.250.347.05

SO,"2.105.907.32

a0.371.6210.7

Ca3*1.29L63UA

Na"0.25

o.sa15,1

NH;0.050.4722,]

TOPOGRAPHY OF CERRO DEL PLOMO GLACIER

WITH THE LOCATION OF THE RADAR PROFILES

TRANSVERS E

ininHIziioXH

I-00luu 2UU 3UO

DISTANCE (m)

Fig. 2: Non-migrated raster image of radar datacorresponding to the transverse profile. The glaciersurface (time zero) appears flat because it has notbeen corrected using the GPS elevation data. Theglacier bed is the V-shaped reflection whichappears dark on the image, with a maximummigrated depth of 107 m. Time represents non-migrated two-way travel time. Thickness iscalculated from the migrated travel time.

Fig. 1: Map showing the transverse and diagonal radarprofiles. Glacier extensions are taken from the1:50.000 scale map of Instituto Geografico Militar,and include some areas of rock covered by snow.Glaciar Esmeralda and glaciar el Plomo areseparated by a rocky ridge at ca. 5350 m. Theupstream end of glaciar Esmeralda is indicated bythe broken line "ice limit".

146

THE INFLUENCE OF SUBLIMATION ON STABLE ISOTOPE RECORDSRECOVERED FROM HIGH ALTITUDE GLACIERS IN THE TROPICAL ANDES

U. Schotterer (Univ.Bern), W. Stickler (Institute for Hydrology, Neuherberg), K. Frohlich (Vienna), P. Ginot(Univ.Bern & PSI), Ch. Kull (Univ.Bern), H.W. Gdggeler (Univ.Bern & PSI), B. Pouyaud, (IRD, Lima).

Sublimation dominates the ablation process on cold, high-altitude glaciers in the tropical Andes. By altering theisotopic composition of the surface snow layers this process may disturb the climatic information. On Cerro Tapado(Chile) it could be demonstrated that in general the isotopically enriched surface layers are constantly sublimatedand the downward flux of enriched isotope species is blocked by re-condensation of moisture during night.

To reveal information about past physical and chemicalchanges in the atmosphere from glaciers in the tropicalAndes the influence of sublimation has to be ruled out first.Transport of water vapour through the firn and exchangewith ambient humidity alter the stable isotope composition(and the chemistry) of the surface layers. As an example,seasonal changes in evaporation of snow may remarkablyamplify seasonal changes in S18O (1). To assess post-depo-sitional influences on ice cores from arid environments likeon Cerro Tapado (5536 m, 30°08' S, 69°55' W) asublimation experiment was carried out [Stickler et ah,submitted].

The main features of the model include the description ofthe isotopic enrichment at the surface by a net diffusive fluxof 82H and 818O into the interior of the firn profile.Moreover, a time-dependent co-ordinate system (its originis defined by the firn surface) accounts for the firn loss atthe surface in terms of an apparent advective movement ofthe firn layers towards the surface. The velocity of thismovement, equal to the sublimation rate, reproduced theexperimental data of the latter in the same order ofmagnitude. (Mass loss obtained by sublimation pans doesnot include the re-condensation of water vapour fromdeeper layers).

Fig. 1 : For uniform conditions the uppermost 7cm fromthe pit were removed for the experiment.

The measurements of a newly created surface at 7cm depth(sampled twice a day for 31/2 days) showed the samestrong enrichment in 82H and 818O as the original surfacelayers down to that depth. Concerning the deuterium excessd, the strong decrease occurred at daytime while during thenight the values remained comparatively constant. Atdaytime the sublimation is enhanced due to the highermoisture deficit of the ambient air accompanied byrelatively high firn surface temperatures. Low surfacetemperatures at night cause condensation of water vapour inthe firn pores near the surface and thus inhibit penetrationof the isotopically enriched surface front into deeper firnlayers. This explanation was not only supported by theisotope profile obtained from the little snow pit throughdetailed sampling down to 38cm; the modification of theisotopic composition at the surface could be describedquantitatively by a model too.

l i - ' i - n Fi'< •-. • i I v a i

Fig. 2 : Measured and calculated change in 8 O anddeuterium excess at the firn surface versus time.

The results of this study suggest that under comparableenvironmental conditions the influence of sublimation onthe isotope record of ice cores is rather limited and of minorimportance. In any case simultaneous measurements of S2Hand 8I8O (change in slope) may help to identify suspiciouslayers deeper in a core which remained influenced due todifferent environmental conditions. However, majorconsequences are to be expected for the interpretation of thevariability of chemical species. The large differencesbetween volatile, soluble, and insoluble components causedby sublimation and obtained by the same experiment arediscussed in detail elsewhere [Ginot et al., submitted].

REFERENCE

[1] P. M. Grootes, M. Stuiver, L. G. Thompson, andE. Mosley-Thompson, Oxygen Isotope Changes inTropical Ice, Quelccaya, Peru, J. Geophys. Res. 94,No. Dl, 1187(1989).

147

ANALYSIS OF DUST LAYERS IN AN ICE CORE FROM CERRO TAPADO, CHILE

S. Olivier (Univ. Bern), H.W. Gaggeler, P. Ginot (Univ. Bern & PSI), M. Schwikowski (PSI)

The concentrations of insoluble particles in an ice core from Cerro Tapado were measured with a Coulter Counter.In order to determine the occurrence of certain mineral dust tracers (aluminium (Al), calcium (Ca), iron (Fe),magnesium (Mg), and mangan (Mn)), the ice samples were additionally analysed with ICP-OES (InductivelyCoupled Plasma - Optical Emission Spectrometry).

The precipitation regime at the Cerro Tapado (5536 m,30°08'S, 69°55'W, Chile) is discontinuous: wet seasonduring the austral winter, and a long dry season fromSeptember to April. As a consequence, mineral dust layersare formed on the glacier surface during austral summer asa result of post-depositional processes like dry deposition ofdust or ice sublimation [1]. Using these horizons it shouldtherefore be possible to identify annual layers for datingpurposes.

In order to detect the dust layers, the suitability of the twofollowing methods was tested:

First, the number of insoluble particles (1-30 Jim) in the icecore section from 13.7 to 16.6 m water equivalent (w.eq.)was determined with a Coulter Counter Z2. The Coultermethod of counting and sizing is based on the detection andmeasurement of changes in electrical resistance producedby a particle suspended in a conductive liquid passingthrough a small aperture.

Second, the melted and acidified samples of the samesection were analysed with ICP-OES. The concentrations ofinsoluble Al, Ca, Fe, Mg, and Mn were used as mineral dusttracers. In order to determine the insoluble fractions, thesoluble fractions were subtracted from the overallconcentrations. For the measurement of the solublefractions, a part of each ice sample was filtered through a0.2 |J,m membrane. Al and Fe were found almostexclusively in the insoluble fractions (all filtrateconcentrations were below the detection limit, which is 20ppb for Al and 10 ppb for Fe). On the other hand, solubleCa, Mg, and Mn contributed up to 95% to the totalconcentration of these elements.

The records of the particle number concentration (PN) andof the concentrations of insoluble Al and Fe are shown inFigure 1.

Fig. 1: Records of the concentrations of insoluble Fe(dashed line) and Al (continuous line) and of theparticle number PN (bold line). Weighted runningmeans over approx. 0.1 m (3 samples) are shown.The arrows indicate assigned dust layers.

A good correlation between the particle number and theconcentrations of the insoluble mineral dust tracers Al andFe (but also Mg, Mn, and Ca) is observed. Assuming thatthe dust layers are due to the dry seasons, a mean annualaccumulation of water over the analysed ice section of 0.41± 0.21 m w.eq. results, which is in agreement with the 0.31m w.eq. determined for the upper 10.5 m w.eq. of the icecore [2].

The record of insoluble particles was compared with therecord of soluble Ca [3] determined by ion chromatography(IC), which has already been used as a tracer for the dryperiod. Ca is assumed to be irreversibly deposited andenriched due to ice sublimation and dry deposition duringthe austral summer [1] (Figure 2).

soluble Ca

insoluble Al

14.8 15.3 15.7

Cbre-depth [mw.eq.]

Fig. 2: Records of the concentration of soluble calcium(bold line) determined by IC and of insolublealuminium (continuous line) determined with ICP-OES. Weighted running means over approx. 0.1 m(3 samples) are shown.

Contrary to the signature of the dust tracers (e.g. insolublealuminium or particle number), soluble calcium shows onlyone significant peak at 14.1 m w.eq. and a smaller one at15.2 m w. eq.. In conclusion, the selected mineral dusttracers can be used for dating purposes even in coresections with a missing seasonal stratigraphy of soluble Ca.Thus, the application of these tracers opens up thepossibility of dating by annual layer counting of ice coresfrom glaciers with a discontinuous precipitation regime.

REFERENCES

[ 1 ] P. Ginot et al., submitted toJ. ofGeophys. (2000).

[2] U. Schotterer, personal communication.

[3] P. Ginot, personal communication.

148

FIRST GLACIO-CHEMICAL INVESTIGATION OF BELUKHA GLACIER IN THESIBERIAN ALTAI

M. Schwikowski, A. Schmitz, S. Brütsch, F. Stampfli (PSI), H.W. Gäggeler (Univ. Bern & PSI), M.Funk (VAW),U. Schotterer (Univ. Bern), T. Papina, St. Eyrik, S. Temerev (IWEP, Barnaul), A. Saprykin, O. Shuvaeva (IIC,

Novosibirsk), V. Galakhov (Altai State University)

In an exploratory study a shallow firn core was recovered and a glaciological survey was undertaken at Belukhaglacier in the Siberian Altai. Chemical records along with a sufficient ice thickness indicate the suitability of thisglacier as palaeoatmospheric archive. Thus, a deep drilling is planned for summer 20001.

The Central Eurasian Altai mountain range is located onthe boundary between East Kazakhstan, Southwest Siberia,Northwest China, and Mongolia. It forms a natural barrierfor trans-boundary transport of air pollutants emittedespecially from heavy metal mining and metallurgicallyused areas of East Kazakhstan and Southwest Siberia aswell as of radionuclides released into the atmosphere by theSemipalatinsk nuclear test site.

For the reconstruction of air pollution levels in the Altairegion, glacier ice cores are among the privileged paleoarchives. Although the Altai mountain range isconsiderably glaciated, most of the glaciers are located atelevations significantly below 4000 m asi and are thereforeassumed to be affected by meltwater percolation. The aimof this study was therefore the search of a suitable, i.e. coldglacier and the drilling of an exploratory shallow firn coreat the selected site. The main purpose of analysing thisshallow core was the identification of possible meltfeatures and of seasonal layers.

The Belukha is the highest mountain in the Altai (4506 masi) and a glacier located immediately west of Belukha(49°48'49"N, 86°32'29"E, 3895 m asi) was selected forthe first glacio-chemical investigation. On 12 July 2000, a6 m firn core was drilled and snow samples were collectedfrom a 1.5 m deep snow pit. Radio echosounding wasperformed to determine glacier thickness and thetemperature in the borehole at 6 m depth was measured.Firn core and snow pit samples were transported in frozencondition to the Institute of Inorganic Chemistry inNovosibirsk, where the firn core was cut into 3.5 cmsegments and packed in pre-cleaned containers. FromNovosibirsk to PSI samples were also transported in frozencondition, cooled with dry ice.

In firn core and snow pit samples concentrations of majorionic species and of insoluble particles were analysed byion chromatography and by the Coulter Counter technique.The stable isotope ratios 818O and 8D were determined byisotope-mass spectrometry, pH and conductivity by pH-electrode and conductivity cell. Concentrations of NH4

+ andSO4

2" in the 6 m firn core fluctuated largly, but both werehighly correlated (Fig. 1). Since a study on an Alpine icecore showed that meltwater percolation influenced theconcentration of SO4

2~ significantly, whereas thestratigraphy of NH4

+ remained undisturbed [1], we assumethat melting processes were of minor importance in the top-most 6 m firn layer. Especially the concentrations of Ca2+

and insoluble particles show a pronounced maximumbetween 0.5 and 2.5 m depth (Fig. 1). Both species arenormally associated with mineral dust and we thereforeassume that the maximum is related to summer

precipitation. In summer, atmospheric transport to high-mountain sites is enhanced and the non-vegetated areassurrounding the glacier are snow-free, both facilitatingmineral dust deposition. Because only one summermaximum is observed in the record, we assume that the 6m of firn represent approximately the precipitation of oneyear.

The maximum ice thickness measured was 150 m, and thefirn temperature at 6 m depth was -1.4°C. With thisrelatively high temperature, the occurrence of meltwaterformation can't be excluded. However, as discussed above,the stratigraphy of chemical species seems to be essentiallyunaffected by melting processes.

35-

30-

AmmoniumSulphate

120

Insoluble particles

-3E+05

•4E+05

COCL

-1E+05

1 2 3 4 5Depth below snow surface (m)

Fig. 1: Concentrations of NH4+ and SO4

2 (upper panel) aswell as of Ca2+ and insoluble particles (lowerpanel) along the 6 m firn core.

REFERENCE

[1] A. Eichler et al., Tellus, in press.

149

CONTINUOUS MELTING AND ION CHROMATOGRAPHIC ANALYSES OF ICECORES

T. M. Huber, H.W. Gaggeler (Univ. Bern & PSI), A. Gaschen, M. Schwikowski (PSI)

With the continuous melting and ion chromatographic analyses, a new method was developed which combines theadvantages of the continuous flow analysis with ion chromatography as a multi-component analysis technique. Thenew method is well suited to quantify the overall amounts of ionic impurities in ice and to resolve their concentrationpatterns.

The common way of analyzing ice cores is to remove thepossibly contaminated outer parts, cut the inner cores inpieces, melt them and analyze each piece separately (see e.g[1, 2]). This procedure is time-consuming and prone tocontamination. By continuously melting and analyzing theice cores, these two effects can be reduced. This so calledcontinuous flow analysis (CFA) [3] was successfullyapplied for recording concentration profiles of differenttracers in Greenland and Antarctica [4, 5]. However, theCFA technique requires a separate detector for every spe-cies analyzed. Not for every species of interest a detectionreaction sensitive enough exists. Thus, the number ofpossible analytes is limited. Udisti et al. [6] used a meltingdevice coupled with an ion chromatograph in order to de-termine chloride, nitrate and sulfate. However, only semi-continuous data sets could be achieved.

Our approach is to take advantage of the full potential ofion chromatography as a multicomponent analytical methodand to couple it to a melting device in order to determinecontinuously organic anions (acetate, formate, oxalate andmethanesulfonate) as well as inorganic anions (fluoride,chloride, nitrate and sulfate) and cations (sodium, ammo-nium, potassium, magnesium and calcium). A detaileddescription of the setup can be found in [7].

In order to verify the new continuous melting and analysismethod, a 95.5 cm long section of an ice core (density0.87 g cm"1) from Grenzgletscher (Swiss Alps, Monte RosaMassif, 4200 m asl.) was analyzed and the results comparedto those obtained by the conventional technique. The reso-lution for the continuous melting at a melting head tem-perature of 35 °C was 3 cm, while the resolution for theconventional analysis was 5 cm.

The concentration profiles of chloride, formate and ammo-nium obtained with the two different methods are shown inFig. 1 as examples. The profiles for chloride and ammo-nium agree well, i. e. both the absolute values and the spa-tial patterns are reproduced by the two methods. The con-centrations of formate determined by the new method tendto be lower, particularly for concentrations below 20 (Xg I"1.This is attributed to a higher blank value of the conven-tional technique, indicating contamination during samplepreparation and contact with laboratory air.

In order to compare the performance of the two methods forall species analyzed, the total amounts of ions in a hypo-thetical sub-core of 1 cm2 cross-section and 95.5 cm lengthwere calculated. The amounts calculated for both methodsagree well (linear regression: correlation coefficient 0.991,slope 0.991, intercept -0.575). Thus, the newly developedmethod is well suited for the analysis of ice cores.

200

'M 15°

% 100

U0

i- 210DXI

^ 140

I 70

^ 0"I- 400

M

" 300

•a 200eS loo

< 0

Coitveittsonal AnalysisContinuous Meltingand Analysis

20 40 60

Depth [cm]80 100

Fig. 1: Concentration profiles of chloride, formate andammonium determined by continuous melting andanalysis (black curve) and conventional analysis(gray curve).

REFERENCES

[1] M. Legrand et al., J. Chromatogr., 640, 251 (1993).

[2] M. Schwikowski, Chimia, 51, 786 (1997).

[3] K. Fuhrer et al., Atmos. Enivron., 27A, 1873 (1993).

[4] A. Sigg et al., Environ. Sci. Technol., 28, 204 (1994).

[5] R. Rothlisberger et al.,

Environ. Sci. Technol., 34, 338 (2000).

[6] Udisti et al., Annals of Glaciology 30, 20 (2000).

[7] T. Huber et al., submitted to J. Chromatogr. (2000).

150

PRELIMINARY RESULTS OF TRACE ELEMENT ANALYSIS IN ICE CORES BYCONTINUOUS ICE MELTING (CIM) ICP-MS

St. Knusel, T. Huber (Univ. Bern & PSI), M. Schwikowski (PSI) and H.W. Gaggeler (Univ. Bern & PSI)

In order to analyse a set of trace elements in ice cores, a new method, continuous ice melting inductively coupledplasma mass spectrometry (CIM-ICP-MS) has been developed. The main advantages are a less time-consumingsample preparation, a reduced risk of contamination, and the possibility to obtain a higher spatial and thereforetemporal resolution of the trace element records.

INTRODUCTION

Aerosol related chemical trace species deposited with snoware the key parameters to identify air mass origin. Usingtypical chemical signatures, marine, volcanic, arid or vege-tated terrestrial, biomass burning, and anthropogenicsources of air masses can be identified and temporalchanges of the contributions of the various sources can beinvestigated. In order to reconstruct historical El Nino andLa Nina periods using an ice core from Illimani, Bolivia(6430 m, 16°39'S, 67°47'W) [1], one approach is to char-acterise air mass origins related to precipitation formationduring this periods. For this purpose, a set of trace elementswill be analysed in the ice samples by ICP-MS.

The conventional procedure of preparing ice samples fortrace element analyses is a mechanical decontaminationunder clean room conditions at -20°C [2]. The outer layersare removed by chiselling, which is a time-consumingprocess with a high risk of contamination. An additionaldisadvantage of this procedure is the limitation in spatialand subsequently temporal resolution. Therefore, a newmethod has been developed: the coupling of a melting de-vice [3] with an ICP-MS (ELEMENT, Finnigan MAT),which allows a continuous decontamination and melting aswell as analysis of the ice core.

THE PRINCIPLE OF THE MELTING

The continuous ice melting (CIM) ICP-MS consists of anice-melting device, which was developed for continuousmelting and ion chromatographic analyses of ice cores [3,4], and which has now been coupled to the ICP-MS.

. Deep TTIXVLT. -20"C

Infusion pump

NO

Degaser

ICP-MS

Mixing Tee Nebulizer

Fig. 1: Schematic of CIM-ICP-MS.

The melting head separates the melt water in an inner, un-contaminated flow and in an outer, possibly contaminatedflow. As illustrated in Fig. 1, the inner melt water is, afterpassing a degaser, acidified (0.1 M HNO3) and an internalstandard (103Rh) for the analysis by ICP-MS is added.Afterwards, the melt water is introduced in the ICP-MS byan HPLC pump.

FIRST RESULTS

The CIM-ICP-MS method was tested by analysing a 60 cmice core from the Alps, and comparing the results withthose from conventional analyses. Although the concentra-tion patterns could be reproduced by the new method for apart of elements, as illustrated in Fig. 2 for 79Br, the abso-lute concentrations obtained by CIM-ICP-MS were signifi-cantly lower. Possible reasons are adsorption processes onthe walls of the capillaries, connecting the melting-headwith the nebulizer of the ICP-MS, differently filtered sam-ples, insufficient acidification, and contamination of con-ventionally prepared samples.

4TO0 -

3500 -

3 3TO0 -

& 2'500 -

g| 21300 -

S 1500 -

U 1TO0 -

500 -

0

Br-79, CIM -»-Br-79, conventional

0 10 20 30Depth [cm]

40 50 60

Fig. 2: Depth profile of Br in an ice core from the Alps,comparison CIM-ICP-MS with conventionalanalysis.

In future, the dead volume will be significantly reduced inorder to minimise adsorption processes. In addition, thecontamination will be controlled and the acid strength, ifnecessary, adapted.REFERENCES

[1] St. Knusel et al., this Annual Report.[2] L. Tobler et al., Ann. Rep. Univ. Bern & PSI 1999,

p. 42.[3] T.M. Huber et al.,submitted to J. Chromatography A.[4] T.M. Huber et al., this Annual Report.

151

FIRST APPROACH TO DETERMINE CONCENTRATIONS OF MERCURY IN ICECORES BY COLD VAPOUR ICP-MS

S. Eyrikh (IWEP), L. Tobler, M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI)

The very low concentrations of Hg expected in snow and ice samples require an extremely sensitive and accurateanalytical technique as well as a contamination-free methodology. The potential of Cold Vapour ICP-MS for Hgdetermination was tested and first experiments on standard and sample handling were conducted.

1 INTRODUCTION

One of the major questions connected with the presentenvironmental mercury problem is the historical trend.Some attempts to estimate global "pre-industrial" emissionsto the atmosphere have been made from Greenland ice coredata. High mercury concentrations (10-230 ppt) reported inearlier studies of ice cores and snow from polar region arelikely incorrect [1]. During recent years new analyticaltechniques have become available, these include ultra-sensitive and specific analytical equipment andcontamination-free methodologies. Concentrations of Hg aslow as 0.19-2.21 ppt were reported from a Greenland icecore [2], whereas higher values were found in snowsamples collected on the ice cover and on the hillsurrounding the Lake Baikal, Siberia (8.6-60 ppt) [3]. Inboth studies, sampling was carried out followingrecommendations of a protocol for ultra-clean work. Hgconcentrations in our snow samples, which were collectedat Belukha glacier in the Siberian Altai [4], should be in theabove-mentioned range (as low as few ppt).

2 ANALYTICAL TECHNIQUE

Inductively coupled plasma mass spectrometry (ICP-MS) isvalued for its multi-element capability and its excellentdetection limits for many elements. However, in case of Hgit suffers from bad transport and ionisation efficiencies,which can be greatly improved by using cold vapourgeneration. There, Hg gas is separated from the liquidsample, and is effectively transferred into the plasma,where ionisation takes place under very dry conditions notloaded with aerosol. In this study we equipped our ICP-MS(ELEMENT, Finnigan MAT) with a Hydrogen Generatorhaving a membrane gas-liquid separator design [5] andoptimised the analysis parameters such as pump speed andwash time for Hg determination.

3 METHODOLOGY SET-UP

Both contamination and loss of Hg are possible duringstorage. The instability of Hg solutions is explained by thespecific Hg properties: high volatility of Hg°; ability ofdissolved Hg2+ to be reduced to Hg°; adsorption of dissolvedHg on suspended particles and vessel walls; contaminationfrom vessel, reagents, and from air diffusing through theplastic vessels. Normally, Hg solutions are stabilised byacidification with HNO3. Therefore, the influence of acidconcentration on the intensity of the Hg signal was tested.In addition, the stability of Hg solution kept at 4°C in arefrigerator was studied.

4 RESULTS

Various HNO3 concentrations were applied on a blank, andon standards with concentrations of 20 ppt and 100 ppt Hg.A strong dependence of the obtained Hg signal on acid

concentration was observed, as shown in Fig. 1. Theintensity of the Hg signal increased steadily until the acidconcentration reached 0.5 to 1 N HNO3, where it becamesufficiently stable. Thus, we consider 0.7 N HNO3 asoptimal acid concentration.

The reproducibility for 200Hg and 202Hg in the same sample(10 determinations) was RSD=3.0 and 2.7%, and in 20different blank samples RSD=3.1 and 3.4%, respectively.

In a solution of 100 ppt Hg, a loss of Hg after 17 days ofstorage at 4°C was observed as shown in Fig. 2. The losswas most pronounced for Hg solutions with low acidconcentrations. Thus, the most important process seems tobe the loss of Hg onto the walls of the sample tubes, andnot contamination.

250000 -|

Q. 200000o

isity

AV

,

^ * ^ 2 0 p p t H g , —^^100 ppt Hg

j-i-a- °—

0 0.5 1 1.5Concentration of nitric acid, N

•

2 2.5

Fig. 1: Dependence of 2

tion.

2 Hg signal on HN03 concentra-

0.1 0.15 0.3Concentration of nitric acid, N

Fig. 2: Loss of 202Hg from standard solution after 17 daysof storage at 4°C.

REFERENCES

[1] H. Appelqvist et al., Nature 273, 657 (1978).

[2] J.M. Vandal et al., Nature 362, 621 (1993).

[3] M. Leemakers et al., in: Global and regional mercurycycles, W. Baeyens, R. Ebinghaus, O. Vasiliev (eds.),Kluwer Academic Publishers, p. 307 (1996).

[4] M. Schwikowski et al., this Annual Report.

[5] B. Klaue, J.D. Blum, Anal. Chem., 71, 1408 (1999).

152

DETERMINATION OF TOTAL DISSOLVED SILICON FOR3 Si DATINGOF GLACIER ICE

U. Morgenstern (GNS, New Zealand), L. Tobler, M. Schwikowski (PSI), H.W. Gdggeler (Univ. Bern & PSI)

Cosmogenic J2Si has potential for dating ice cores in the time range of 50-1000 years. Accelerator mass spectrometry(AMS) is used for measurement of the 31Si/Si ratio, and to derive 32Si concentrations, independent analysis of stablesilicon is necessary. Results of Si determination in NZ glacier snow and ice by high resolution ICP-MS arepresented.

1 INTRODUCTION

Ice cores provide a wealth of palaeoclimate information,and low- to mid-latitude glaciers offer a unique opportunityto study regional patterns of climate change over recentmillennia. However, most stratigraphies of mountainglaciers are incomplete, and dating techniques based oncounting annual layers are limited.Cosmogenic 32Si, with half-life of ca. 140 years, is ideallysuited to provide the necessary time information. However,only accelerator mass spectrometry (AMS) is able toprovide the required high sensitivity for ice core analysis.Recently this technique became available for measurementof 32Si/Si in natural samples [1]. 32Si/Si ratios above theAMS detection limit are found only in snow and icesamples with low total Si. For 32Si dating, one difficulty isthe AMS measurement of the 32Si/Si ratio. The otherchallenge is to determine accurately such low Siconcentrations.

2 EXPERIMENTAL

We analysed snow and ice samples from the Franz Josefglacier, New Zealand (43°S, 170°E, ca. 2,200 m a.s.l.), fortotal dissolved Si. NZ's glaciers contain very little dust inthe region of snow accumulation. Si concentrations weretherefore expected to be below 10 ppb, too low to bedetermined directly with any method. Thus, Si was pre-concentrated by ion exchange [1] to shift the Siconcentration into a range were it can be analysed with atleast 5% accuracy. To keep the initial amount of sample forSi analysis small (< 100 g), an analytical method with highsensitivity is necessary such as high resolution ICP-MS.The analysis of silicon (three stable isotopes withabundances 28Si 92.23%, 29Si 4.67%, 30Si 3.10%) by aquadrupole ICP-MS is not possible due to interferencemainly from N2 and CO2 on all three Si-masses. Table 1 liststhe possible interferences of the 3 Si-isotopes and theresolution needed to resolve them.

Table 1: Interferences of the 3 stable Si isotopes

Isotope Interferences Resolution

!8Si!9Si)0Si

I2C16O+, 14N2+

I2C16OH+, 15N14N+

14N16O+, 12C18O+, 13C16OH+

1556, 9581104,10861238, 1181,927

A double focussing ICP-MS (Elementl, Finnigan MAT)was used to determine silicon in medium resolution (R =m/Am = 3500).Silicon from the glass material (spraychamber, torch etc),the ultrapure water and acids, used to dilute standards andto wash sample containers, and from the sample containerspresent a blank problem in the determination of ultra low Si

concentrations. After a washout time of 3 h of the ICP-MSan overall blank of 14 ppb Si was obtained, with a detectionlimit of 5 ppb (3a criterion).Additional to silicon, the sulphur concentration wasdetermined in the ice samples. Sulphur recovery in the ionexchange process was not calibrated at the time ofextraction, but we assume it to be similar to Si. Becausesulphur is the main interference for 32Si AMS measurement,an estimate of the sulphur concentration in the sample canindicate the demands on chemical purification of the AMSsamples.

3 RESULTS

In Fig.l the concentrations for Si and S in the ice samplesare presented. For many samples Si cone, is below 2 ppb.These were the samples with no visible dust in themeltwater. All the samples with Si > 5 ppb had visible dustin the meltwater. We assume, therefore, that the increasedSi concentrations are due to dissolution of Si from dust.

a.

§

60

50

40

30

20

10

0

• Si

• • • • • • » • •

Fig. 1: Si and S concentration (dissolved) in snow and icesamples from Franz Josef Glacier (NZ).

The concentration of sulphur in the ice and snow samples istypically 5-10 times that of silicon. Therefore, total sulphursuppression in the sample material (containing only a fewug Si) of > 1016 is necessary for AMS analysis. Suppressionof ca. 10" can be achieved within AMS systems with a gas-filled magnet. Therefore, sulphur concentration in the targetmaterial must be reduced by a factor > 105 prior to AMSmeasurement, which might be achieved by heating thesample material to more than 1000°C in hydrogenatmosphere.

REFERENCE

[1] U. Morgenstern, L. K. Fifield , A. Zondervan,Nucl. Instrum. Meth. B 172, 605 (2000).

153

APPLICABILITY OF TXRF FOR TRACE ELEMENT ANALYSIS IN ICE SAMPLES

N.L. Misra, L. Tobler, M. Schwikowski (PSI)

Total Reflection X-ray Fluorescence (TXRF) Spectrometry has been used to analyse trace elements in ice sample.The results were compared with the results of ICP-MS. For some samples and elements agreements in results ofICP-MS and TXRF are satisfactory but for others the difference is significant, probably due to heterogenity of thesamples because of presence of insoluble matter.

Ice samples from glacier ice cores contain elements in awide range of concentrations. As an illustration, Ca in icesamples analysed in this laboratory varied from 1.5 to 6400ppb whereas U varied from 0.2-30 ppt. Though ICP-MS isa technique, which has excellent detection limits, and isbeing used for ice sample analysis, there are some problemswhen samples contain insoluble particles. In recent yearsTXRF has been used in trace elements analysis of variousenvironmental samples and has been proven to be capableto analyse solutions as well as suspensions up to a certainextent [1,2]. In the present work the possibility of usingTXRF for trace element analysis in ice samples wasexplored.

A TXRF spectrometer developed at PSI [3] was used. Twomodes of element excitation, Mo tube having mainly MoKa (55 kV, 10 mA) and W tube with mainly continuum (40kV, 10 mA) were used. Relative sensitivities for elements P(Z=15) - Y (Z=39), Pb, U and Th were determined usingsuitable multielement standards (MES). Detection limits ofthe elements were determined using these data. They variedfrom 2.3 ppm to 10 ppb and 1 ppm to 56 ppb for S (Z=16) -Y (Z=39) using Mo and W excitations, respectively. Amultielement standard with concentrations of 20 ppm of theelements P, K, Ca, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Rband Sr was analysed using Y as internal standard. Theresults were within 15% of the expected values except forK, Fe and Zn. Similarly with the W tube MES containingthe elements P, S, K, Ca, Sc, V, Cr, Mn, Fe, Cu, Zn, Ga,As, Se, Y, Zr, Nb, Hg and U were analysed using Y and Coas internal standards. The results were within 20% of theexpected values.

TXRF spectra of ice samples show very weak intensities ofX-ray lines indicating that pre-concentration is necessarybefore analysis. Preconcentration studies were made underclass 100 clean room conditions on a multielement standardcontaining S, Ca, Cr, Co, Ge, Hg, Rb and Nb withconcentration of 0.74 ppb for each element. The solutionwas subjected to evaporation under an IR lamp. Therecovery for the elements varied up to 20% from theexpected values, except for Hg with a variation above 30%.Preconcentration studies on ice samples showed a variationof 15% in recovery for elements present in higherconcentrations (e.g. Ca). However, the recovery for lowatomic number elements or elements present in very lowconcentrations showed large differences from the expectedvalues. Four ice samples from Colle Gnifetti glacier (SwissAlps) were analysed for the elements P, S, K, Ca, Mn, Fe,Ni, Cu, Zn, Br, Rb, Sr, Pb, Th and U using Mo tube.Similarly, eight samples were analysed using W tube. Outof these eight ice samples, four were the same as measuredwith Mo tube, but the specimens were freshly prepared. Theresults obtained by Mo and W tube showed in general agood agreement. As some of the elements in these samples

were earlier analysed by ICP-MS a comparison betweenthese analysis results was made. The agreement betweenTXRF and ICP-MS results was in many cases notsatisfactory. For the elements Ca, Mn, Zn, Pb, Rb and Srgenerally the ratio of their amounts determined by TXRF(W Tube) and ICP-MS varied between 0.30-3.00. For theelements Sc, V, Cr, Ni, Th and U this ratio was far awayfrom unity. A scatter plot of concentrations of Cadetermined by ICP-MS and by TXRF (W tube) is shown inFigure 1.

1400

1200

jr 1000

•i 800

S 600

•f 400

200

1:1

0 200 400 600 800 1000 1200 1400

Ca (ppb) by W Tube

Fig. 1: Comparison of results of Ca analysis in eight icesamples by TXRF (W Tube) and ICP-MS

Although the agreement between TXRF results using W orMo tube is satisfactory, the discrepancy between TXRF andICP-MS results is obvious. This discrepancy might beexplained by a non-uniformity of the ice samples, possiblydue to insoluble particles present in the ice, or by problemsin the preconcentration step. Thus, future work is needed tobe able to explain the disagreement between TXRF andICP-MS.

ACKNOWLEDGEMENT

Financial support for the work from ICSC-World Labora-tory is kindly acknowledged. We thank F. Hegediis for hishelp in operating the TXRF spectrometer.

REFERENCES

[1] R. Klockenkamper,Total Reflection X-ray Fluorescence Analysis,John Wiley & Sons, Inc. New York (1997).

[2] L. M. Muia, F. Lahatra Razafindramisa, and R.E.VanGrieken, Spectrochim. Acta 46 B, 1421 (1991).

[3] F. Hegediis, Chimia 46, 477 (1992).

154

7Be AND 10Be CONCENTRATIONS AT THE HIGH-ALPINE SITE JUNGFRAUJOCH

L. Tobler, P.W. Kubik, M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI), C. Schnabel (Univ. Bern & ETHZ)

The atmospheric concentrations of the cosmogenic radionuclides 7Be and 10Be have been measured at Jungfraujoch(3580 m a.s.l) within the EU project STACCATO (Influence of Stratosphere-Troposphere Exchange in a ChangingClimate on Atmospheric Transport and Oxidation Capacity). The isotopic ratio wBe / 7Be is used as a probe for theintrusion of relatively old stratospheric air masses into the troposphere.

Stratospheric-tropospheric exchange (STE) is one of thefactors controlling the budgets of ozone, water vapour andother substances in the lower stratosphere and thetroposphere. Cosmogenic radionuclides, which areproduced by cosmic ray particles in the atmosphere, couldprovide valuable information on STE. In the framework ofthe EU project STACCATO, particle bound 7Be and l0Beare collected on glass fibre filters (using a HIVOL airsampler) at the Jungfraujoch with a time resolution of 48 hby the NABEL network [1].Half of the filters are used to measure the 7Be activity (Tl/2 =53.12 d) through its characteristic y-radiation (Ey: 478 keV,Iy: 10.52 %) in a well-type Ge-detector.Fig. 1 shows monthly arithmetic mean values of theatmospheric concentration of 7Be at the Jungfraujoch. Thevalues of the year 2000 are in general lower by a factor ofabout 1.2 compared to the values for 1996 and 1997. Theselower values may be explained by a maximum of solaractivity in 2000, due to the 11-year solar cycle, whichdecreases the production rate of 7Be. The value of July 2000is very low, which might be due to bad weather conditionswith frequent precipitation leading to strong wet scavengingof particles during this time period.

Aug Sep Oct

Fig. 1: Comparison of monthly arithmetic mean activityconcentrations for 7Be at the Jungfraujoch for thetime period January to October 2000(STACCATO), respectively for April 1996 toOctober 1997(previous project VOTALP [2]).

Whereas wet scavenging can affect 7Be and l0Beconcentrations, the ratio 10Be / 7Be is unaffected by suchprocesses. Consequently, Raisbeck et al. [3] proposed touse this isotopic ratio as a probe for atmospheric transportprocesses. Raisbeck et al. [3] and Dibb et al. [4] both foundhigher 10Be/7Be ratios in the lower stratosphere than in theupper one. They explained this by a relatively slowdownward transport of air masses from the upperstratosphere (7Be decays faster than l0Be). These higher10Be/7Be ratios in the lower stratosphere, which clearlyexceed 10Be/7Be ratios of approx. 2.2 measured by Dibb etal. [4] for tropospheric air masses, can be used to determine

intrusions of relatively old stratospheric air into thetroposphere.Within the STACCATO project, 10Be has been measuredusing accelerator mass spectrometry at the PSI/ETHfacility. 10Be/7Be ratios on filter samples collected at theJungfraujoch between 19/2 and 4/4/00 are shown in Fig. 2.

25 T

_ 20

S, 15

J°

qd

qd

Date

Fig. 2: Particle bound 10Be/7Be ratios from air filtersamples from the Jungfraujoch.

The very high l0Be/7Be ratios at the end of February 2000indicate a stratospheric intrusion confirmed by ozone dataand relative humidity. Luder [5] also measured a highmonthly mean isotopic ratio in precipitation at theJungfraujoch in March 1984. However, he attributed thisratio to dust contamination rather than to an intrusion ofvery old stratospheric air masses. That we tend to exclude,since Ca concentrations, measured as a dust parameterduring this time, did not show enhanced concentrations [6].The slow decrease of the very high 10Be/7Be ratios is due toadditional intrusion events during March 2000, which wereobserved by other groups, measuring high ozone and 7Beconcentrations, and low relative humidity at other Alpinesites.

ACKNOWLEDGMENTThis study is part of the EU research project STACCATO(EVK2-CT1999-00050) and is funded by the Bundesamtfur Bildung und Wissenschaft (BBW) of Switzerland. Thesampling and the surrender of the filters by the EMPA(operator of the NABEL network) are highly appreciated.

REFERENCES[1] NABEL Luftbelastung 1999, BUWAL SRU-316 (2000).[2] S. Hubener et al., Ann. Rep. Univ. Bern & PSI (1999),

p. 16.[3] G.M. Raisbeck etal.,

Geophys. Res. Lett. 8,1015 (1981).[4] J.E. Dibb et al., J. Geophys. Res. 99, 12855 (1994).[5] R. Luder, Lizentiatsarbeit, Universitat Bern (1986).[6] S. Henning, personal communication.

155

A NEW INDUCTIVELY COUPLED PLASMA OPTICAL EMISSION SPECTROMETER(ICP-OES) FOR TRACE ELEMENT ANALYSES

R. Keil, M. Schwikowski (PSI)

Our sequential ICP-OES (3410, ARL) was replaced by a new simultaneous ICP spectrometer (Varian Vista). Mainadvantages of the new instrument are lower detection limits for most of the elements, shorter analysis times, andhigher precision.

Since 1988 Inductively Coupled Plasma Optical EmissionSpectrometry (ICP-OES) has been extensively used in theanalytical chemistry group of our laboratory for analyses oftrace elements in a wide range of different samples fromcustomers representing nearly all PSI units [1, 2]. The in-strument used for more than twelve years (3410, AppliedResearch Laboratory) was replaced in November 2000 by anew generation device (Varian Vista). Characteristics ofthis new ICP-OES are:

• A simultaneous spectrometer using an echellepolychromator

• A Charged Coupled Device (CCD) detector• An axially viewed plasma• A compact design, bench-mounted.

The benefits of the new spectrometer include better detec-tion limits due to the axial viewing as well as higher preci-sion and shorter analysis time due to simultaneous meas-urements of all element wavelengths. The improvementresulting from better detection limits is demonstrated forthe case of trace element analysis in ultra-pure water usedin an autoclave. In Table 1 results of analysis of 15 traceelements in two ultra-pure water samples (SI and S2) areshown, along with the detection limits, defined as 3a ofbackground. For comparison, detection limits obtained withthe former ICP-OES are also given, and the factor of im-provement is shown. Detection limits with the new ICP-OES are lower by factors of 1-40, depending on the ele-ment.

With the new ICP-OES, pure analysis times (withoutevaluation of the results) could be reduced to about 1minute, including wash-time, for manual sample introduc-tion. The use of an autosampler increases the analysis time,since a longer wash and sample transport time is required.For comparison, the analysis time with the sequential ICP-OES was dependent on the number of elements, e.g., ananalysis of 15 elements took about 5 minutes.

REFERENCES

[1] R. Keil, Ann. Rep. Univ. Bern & PSI 1994, p. 36.

[2] R. Keil, M. Schwikowski,Ann. Rep. Univ. Bern & PSI 1996, p. 23.

Table 1: Results of trace element analyses in ultra-purewater (samples SI and S2) using the Varian Vista ICP-OES. "<" means that the concentration is below detectionlimit. For comparison detections limits (DL, defined as 3oof background) obtained by the two ICP-OES using ultra-sonic nebulizers (ARL AA81467 and CETAC U5000AT+)are given, along with the factor of improvement (F).

Element

Al

Ba

Ca

Co

Cr

Cu

Fe

Mg

Mn

Mo

Na

S

Si

Sr

Zn

SI

(Mgl"')

0.7

1.05

2.51

<

0.12

1.71

4.85

0.560

0.034

0.13

0.91

5.0

6.0

0.051

0.99

S2

0-igi"1)

<

0.049

2.53

<

<

0.41

1.01

0.334

0.050

<

1.71

5.0

4.0

0.011

0.11

DL(3410,ARL)

Oigi1)

0.5

0.05

0.002

0.8

0.3

0.4

0.3

0.005

0.05

2.0

0.3

2.0

2.0

0.02

0.3

DL(VarianVista)

Oigi1)

0.1

0.002

0.02

0.1

0.05

0.05

0.05

0.05

0.005

0.05

0.02

2.0

2.0

0.002

0.05

F

5

25

10

8

6

8

6

10

10

40

15

1

1

10

6

156

CEMENT CHEMISTRY: QUALITY CONTROL AND DEVELOPMENTS 2000

H.P. Zimmermann, M. Patorski, L. Dohring, M. Egloff(PSI)

This report gives a short summary of the projects and developments in our group during 2000.

This year was mostly dedicated to product control andfinishing already running projects. We received orproduced 25 radioactive and 6 inactive sample-sets. Theamount of samples to be tested depends strongly on theproduction schedules in the power plants and onmodifications of recipes etc. Therefore, we had a somewhatlower number of compressive strength (about 245) and y-spectrometric measurements (about 700 including glasssamples, see below) [1].

During the last cementation campaign of incinerator ashesat PSI sample sets for product control have been takenovercoming the difficulties caused by lumps bigger than 4mm in diameter. These would hamper the compressivestrength measurements using our usual sample cylinders of20 mm diameter and 40 mm height. A simple gadgetcomposed of a vibrated sieve with 4 mm mesh and a funnelallowed to take representative samples with out the biggerparticles.

We made some progress in our endeavour to set up qualitycontrol procedures for the products of the ZWILAG plasmaincinerator. The y-spectrometric measurements of theliquids from the leaching tests of activated slag sampleswere finished. A preliminary data evaluation showed thatthe order of magnitude of the leaching rates at roomtemperature can be determined by our 'normal standardleaching procedure' but the following y-spectrometricmeasurements will be very time consuming (3-5 days atleast, even with an acceptable detector efficiency and a lowbackground). The leaching rates of this first tested samplewere well below the limits required by the guideline HSK-R-14 of the Swiss Federal Nuclear Safety Inspectorate.

We also tried a perhaps unusual approach to determine thesurface area of a piece of slag with an irregular surfacegeometry. S. Baechler and his colleagues of the Departmentof Physics of the University of Fribourg performed aneutron tomography of a piece of slag at SINQ (spallationinduced neutron source) and produced a 3D image of it. Butat the moment we still have to search for an easy method tocalculate the surface area itself using the data of the image.

Meanwhile, during the commissioning of the incinerator atZWILAG some other inactive slag samples with a differentcomposition and other surface properties were produced onsite. A successful test was performed to obtain samples bycore drilling without a cooling liquid and cutting the 'core'with a diamond equipped blade in pieces of a define regulargeometry. It was decided to repeat the neutron activationwith the pneumatic tube transport system of the SINQ(spallation induced neutron source) isotope production andthe leaching tests with these samples but the work is still atthe beginning.

Routine product control was the main activity for thenuclear power plants. At last we could finish some work forKKG or at least bring it close to the end like someconsiderations concerning sedimentation processes inbitumen matrices or leaching experiments in dependence ofthe salt contents of the matrix. In 2001 we will have tooptimise the recipe for solidification of the dirt collected ina now dismantled oil separator of KKB.

Also the dismantling of the former research reactorDIORIT is still in progress. It is planned for 2001 toprepare the graphite for solidification with cement.

Infrastructure

NAGRA

PSI

Fig. 1 : Distribution of working capacity between ourcustomers. (KKW: all Swiss nuclear power plants).

ACKNOWLEDGEMENTS

We want to thank S. Baechler and his colleagues of theDepartment of Physics of the University of Fribourg fortheir spontaneous help and H.-U. Aebersold for theirradiations at SINQ/PSI.

REFERENCE

[1] H.P. Zimmermann et al., Ann. Rep. Univ. Bern & PSI1999, p. 51.

157

DETERMINATION OF THE RADIONUCLIDE INVENTORY IN ACCELERATORWASTE

R. Weinreich, M. Argentini, S. Stallone (PSI)

As an essential part of waste management the nuclide inventories of radioactive waste which has been generated inthe PSI facilities must be determined. Chemical separation methods leading to pure solutions of long-livedradionuclides useful for accelerator mass spectrometry have been developed and tested on waste of dismantledtargets BX2 and BMA and the beam dumps of the targets E, BX 2 and BMA. Conditions for separation of cations byion chromatography were optimized.

According to the irradiation of materials with accelerators,radioactivity is induced. By the primary beam, the targets,their beam dumps and beam lining elements are activated.By the induced secondary radiation, mostly by high-energyneutrons, the surroundings of the target equipment areactivated, including its shielding. Thus, when acceleratorfacilities are decommissioned or when an acceleratorequipment or its elements are changed technically,dismounted activated parts must be disposed, and anappropriated concept should be developed before.

At Paul Scherrer Institute, smaller activated parts of theaccelerators were cast in concrete troughs which were usedfor shielding walls. Such pieces proved to be a safe interimdisposal. Recently, however, highly activated targets andbeam dumps were dismantled. In detail, these elementsrefer to the beam dump and construction materials of TargetE (16 years in use), the biomedical 7t-meson target BMA (8years) and its beam dump and the 72 MeV target equipmentBX2 (15 years in use). Moreover, several graphitedegraders were dismounted which should contain 3H and14C, and some activated aluminum parts are also to beanalyzed. Last but not least, samples of activated parts ofSINQ-targets were taken consisting of zirkalloy and lead,respectively.

Formally, all radionuclides with a sufficient long half-lifeare interesting for disposal problems or for handling beforedisposal. The analytical separation steps of the samplesshould lead to pure solutions of long-lived cations usefulfor accelerator mass spectrometry (AMS). In the progressof this work, the isocratic separation of the most usefulcations in mono-, di- and three-valent states by highperformance ionic chromatography was investigated.

For separation of mono- and divalent elements, an universalcation exchange column (100x4.6 mm) was used. Theisocratic elution was performed with 2.0 mM tartaric acid /0.9 mM oxalic acid, at a flow of 1.5 ml/min. Under theseconditions, the sequence of the eluted cations was: Li+, Na+,K+, Cs+, Zn2+, Be2+, Mn2+, Ca2+, Sr2+, Ba2+; all peaks werecompletely separated. The three-valent cations wereseparated on a Waters Spherisorb 5 SCX column (150x4.6mm). The isocratic elution war performed with 3.0 mM oc-HIBA / 4.0 mM glycolic acid; the solution was adjusted topH 4.0 with HN03. The sequence of the eluted cations werethen Lu3+, Yb3+, Tm3+, Er3+, Ho3+, Dy3+, Tb3+, Gd3+, Eu3+,Sm3+, Nd3+, Pr3+, Ce3+, La3+. All elements are separatedcompletely, only the peaks of Gd and Eu show a smalloverlapping.

By this ionic chromatographic procedure, the followinglong-lived radionuclides should be separated: 1.6-106-a10Be, 2.6-a 22Na, 7.2-105-a 26A1, 1.3-109-a 40K, 1.0-105-a41Ca, 3.7-106-a 53Mn, 10.5-a 133Ba, 6-104-a 137La, 13.3-a152Eu, 150-a 157Tb and 1.37-a 173Lu/3.31-a 174Lu.

158

HIGH AND INTERMEDIATE ENERGY NUCLEAR DATA FOR ACCELERATOR-DRIVEN SYSTEMS (HINDAS)

R. Michel (Univ. Hannover), R. Weinreich (PSI), HA. Synal (ETH-PSI), N. Olsson (Univ. Uppsala), H.Schuhmacher (PTB Braunschweig), U. Herpers (Univ. Koln)

The joint EU-project should deliver data useful for the treatment of nuclear waste produced by power reactors. Inthe frame of this project, the group is measuring cross sections for residual nuclide production induced by neutronsand protons in the energy region of 20-200 MeV.

An accelerator-driven system (ADS) consists of the cou-pling of a high energy intense proton beam (~1 GeV) with aspallation target and a subcritical core. The spallation mod-ule, the window between the target and the accelerator, andthe surrounding materials are subject to a wide variety ofnuclear reactions induced by particles with energies muchhigher than in conventional fission reactors, and even fu-sion reactors. The detailed engineering design of an ADSwill require that the performance of the spallation target andall the problems related to the existence of high-energyparticles can de predicted with sufficient accuracy.

The 1-2 GeV proton beam that is incident on the ADS tar-get (e.g. lead or lead-bismuth eutectics) will create a largeamount of spallation products, mainly neutrons and protons,with energies covering the full range up to the GeV region.At present, there are still a lot of missing data in the 20-200MeV region, especially for the neutron induced reactionsand above 800 MeV, where data are scarce and fragmen-tary. Since measuring of all these reactions would be time-consuming and expensive, it is necessary to use computa-tional tools and models, which properly describe all thenuclear reactions that take place in the spallation module ofan ADS.

The intention to describe these reactions by appropriatemodels and to validate the model data by radioanalyticalmeasurements is equivalent to the handling of the PSI rad-waste; the chemical problems are nearly identical. The mainemphasis in both projects is to develop high-efficientchemical separation methods for long-lived radionuclideswhich should be measured mainly by accelerator massspectrometry. The routine determination of long-lived nu-clides 10Be, 26A1 and 36C1 should be supplemented by heav-ier nuclei like 32Si, 53Mn and/or 60Fe.

In year 2000, many irradiations of lead and uranium targetsand target stacks have been performed by 72 MeV protonsat the PSI Philips Cyclotron, by 200 MeV protons at Uni-versity of Uppsala and with neutrons of different energies atboth Uppsala and the University of Louvain-la-Neuve. They-Spectra of the irradiated targets have been measured. Thechemical treatment will be performed in the next years.

159

MEASUREMENT OF RADIONUCLIDE CONTENTS IN ACTIVATED GRAPHITE

M. Argentini, R. Weinreich (PSI)

The radionuclide content of a graphite target irradiated for 3 years was measured. After a appropriate cooling time,this type of waste should not pose problems in waste management.

Target E consisted of graphite, the investigated copy be-came operational on June 1991 and was dismounted onJune 1994, after 10D73 hours of operation, with an inte-grated beam current of 3.98 Ah. After a cooling time ofmore than 5 years, the samples were prepared on September1999.

The following radionuclides were measured: 12.3-a 3H,53.3-d 7Be, 5730-a 14C, 2.6-a 22Na and 312.2-d 54Mn. Thefirst four radionuclides are produced in the target itself,while 54Mn probably is produced from copper contamina-tions which might accumulate during the operation time.7Be, 22Na and 54Mn were measured by y-spectroscopy with-out chemical treatment, 3H and 14C, however, were sepa-rated before measuring by classical chemical procedures.-

The graphite sample was oxidized at 900°C in a furnaceunder a flow of dried oxygen which is free from carbondioxide. The oxidation process was generally completedwithin 3 hours. The released gas mixture passed three flaskscontaining calibrated amounts of bi-distilled water andsodium hydroxide (6.68 g per 1 g graphite to be oxidized).55 % of the tritium activity were collected in the first flaskand 40 % in the second. 14C was collected quantitatively inthe first flask (94-97 %).

In this solution, tritium activity was measured directly bylow-level counting between 0.0 and 18.6 keV (Hionic-Fluorcocktail, Packard). Since it could be shown that 3H wasyielded in great access compared with 14C, special attentionmust be paid to avoid tritium contamination of 14C:

In a round flask, the aqueous solution was carefully evapo-rated to dryness and further dried for some hours in vacuo.The flask was then connected to a distillation apparatuswhich was kept continuously under dry nitrogen, free fromcarbon dioxide. The dried substance was dissolved in di-luted sulfuric acid by careful dropwise addition. The re-leased gases were passed through two traps filled withcone, sulfuric acid and collected in a calibrated amount ofIN sodium hydroxide as described above. Finally, the 14Cactivity was measured in this solution by (3-counting in theenergy range between 2 and 265 keV.

Although the main amount of tritium has been evaporatedduring cyclotron operation, the handling of the target isdefined by the tritium content. After an appropriate coolingtime, the other nuclides are not of importance for handling.The irradiated graphite targets might be a source of 7Be and(not yet measured) 10Be.

Table 1: Results (Bq/g) (EOB = End of Bombardment, June 1994)

Nuclide

3H7Be*

> 4 C

22Na54Mn

Sample 1

EOB

7.99 • 106

8.54 • 10"

7.84

253

76 + 28

Dec.31,1999

5.81 • 106

2730

7.83

57.3

0.82 + 0.30

Sample 2

EOB

1.17 • 107

9.25 • 1014

10.2

262

31 + 16

Dec. 31,1999

8.55 • 106

2960

10.2

59.4

0.34 + 0.17

Sample 3

EOB

4.20 • 105

3.47 • 1013

<1

8.58

27+12

Dec. 31,1999

3.45 • 105

111

< 1

1.95

0.30 + 0.13

* due to low counting rate, measurement must be repeated

161

Laboratory forIon Beam Physics

162

LABORATORY FOR ION BEAM PHYSICS

M. Suter (ETHZ &PSI)

Our main research interests are related to ion beamtechniques, which are used to determine elementalcompositions of materials and for the analysis of traceelements and rare long-lived radionuclides. For theseactivities, we have now available two electrostatic tandemaccelerators, both located in our laboratory at ETHHonggerberg

About 80 % of our research are related to accelerator massspectrometry (AMS). With this very sensitive detectiontechnique we can measure isotopic ratios or trace elementconcentrations at very low levels. Typical isotopic ratiosfound in the natural environment are in the range of 10l0 to10l5. Presently, we routinely use AMS for the detectionlong-lived radionuclides l0Be, I4C, 26A1, 36C1, 4lCa and l2%which are primarily produced by cosmic rays. Underspecial conditions these radionuclides can be used fordating, but they also play an important role as naturaltracers in environmental research to study exchangeprocesses in atmosphere and the oceans of the present andthe past.

We recognizes the following trends in our applicationsprogram:

1) The demand for radiocarbon dating in archeology andthe arts is still increasing.

2) Exposure dating of surface rocks starts to play anessential role in the fields of geology and glaciology.

3) The application of AMS to biomedical research, inwhich long-lived radionuclides are used as tracers, isbeing recognized.

4) Increasing interest in the monitoring of the release anddistribution of I29I from nuclear fuel reprocessing plantsis shown.

In order to be competitive and to play a leading role in thefield of AMS, continuously upgrading the equipment isnecessary and innovative developments are essential.During the last few years, we concentrated our efforts onthe development of very small and compact AMS systems.Based on a new concept for the elimination of molecularinterferences, it was possible to design a small radiocarbondating facility operating at a terminal voltage of only a fewhundred kV. Presently, the potential of this new techniquefor other radionuclides such as 26A1, 4lCa and I29I is beingstudied intensively. Promising results have been obtained,indicating a potential much larger than originallyenvisioned. Several improvement and modification of oursmall system are still needed for optimized operatingcondition and to minimize background problems.

In the materials sciences part of our research, our activitieswere mainly concentrated on new applications of themicro-focused AMS ion source, the development of newtypes of point ion sources and the investigation of fluorinediffusion as an indicator of exposure age. The number ofmeasurements performed in collaborations and partly as aservice for industrial research laboratories has again grown.In order to increase the throughput we installed a newautomated irradiation station, increased the capacity of ourion beam analysis chamber and developed software forbatch processing.

There is clearly a growing demand among most users ofour facilities for precision analysis of light element contents(H, C, N, O) in materials. We therefore concentrate onfurther development of nuclear methods capable ofsatisfying these requests.

5000i

4000-

3000

2000-

1 000 -

0 -J

980 k

• 14C

• 10Be

• 26AI,36CI,41and 1291

CMOO CO5 C

O35 98

e,

Ca

—

988 | I 066 99

2 |f

i

994 | -is

dl

996 i -1

998 i

[

1 11

ooo

if

a

**•

Fig. 1: Development of the number of AMS measurements at the PSI/ETH AMS facility during the last 20 years.

163

THE PSI/ETH TANDEM ACCELERATOR FACILITY

H.-A Synal, M. Döbeli, H. Fuhrmann, P.W. Kubik (PSI), G. Bonani, M. Grajear, I. Hajdas, S. Ivy-Ochs, S. Jacob,C. Maden, R. Mühle, J. Santos, J. Scheer, C. Schnabel, M. Suter, S. Tschudi (ETHZ)

The year 2000 operation of the PSI/ETH tandem accelerator at ETH Hönggerberg is summarised in a detailed com-pilation consisting of beamtime allocation and the number of measured AMS samples for the various radionuclidesand the major fields of research.

AMS Be-10C-14

Al-26Cl-361-129

Heavy ElementsSubtotalMaterials SciencesAccelerator SIMSTestsConditioningTotal

Hours199847588110316111181

1812416171119257

2775

19993738424831310399

177835719357344

2729

2000503103912912716949

201626540090191

2962

%199817.131.73.75.84.02.965.315.06.24.39.3100

199913.730.91.811.53.83.665.213.17.12.112.6100

200017.035.14.44.35.71.7

68.18.913.53.06.4100

199810981755231401291

2

3778

Samples1999118717688362332712

4000

20001664205525927541523

4691

Beamtime statistics 1998-2000

Research FieldOceanographyIce Core SamplesLimnologyAtmosphereEnvironmental MonitoringExposure Age Dating, OthersEarth Sciences (Total)Meteorite/Cross SectionsArchaeologyOthers, TestsSubtotalStandardsBlanksTotal

Be-102903966163

219102933

240273229133

1664

C-14102

1354

149318

6706541324296117

2055

Al-26

848424

1061303411

259

Cl-36

140

34

28202

32322813

275

1-129

20

1314947247

8

63717423415

Total392556742824952718806567010951830661297

4668

8%12%2%6%1%11%40%1%14%23%39%14%6%

100%

Compilation of measured AMS samples at the PSI/ETH AMS facility in 2000

The PSI/ETH tandem accelerator operated last year for2962 hours, an increase of approximately 10% over 1999.Also the total number of analysed AMS samples increasedagain. With 4691 samples, the year 2000 was the most suc-cessful year since we began routine AMS measurements in1982. Of the total beamtime, 68 % was devoted to AMS,9% to the material sciences and 13 % was used to measurestable trace elements in connection with the focused ionbeam sputter source. For tests and accelerator conditioningonly 10 % of the total beamtime was needed.

For 10Be, the number of samples measured has increased byas much as 40 % mainly due to several new projects con-nected to exposure age studies. For the first time, more than2000 individual 14C samples were analysed in one year.Again, a large number of 10Be and j6Cl measurements were

related to analyses of polar and Alpine ice cores. For 129I,environmental monitoring and studies related to atmos-pheric transport phenomena continued. The microbeam ionsource was used in connection with experiments to evaluatedetection limits of platinum group elements and of 10Besamples prepared without any carrier addition.

The new small AMS system for radiocarbon dating wasused for 14C dating measurements as well as for studies offundamental processes in AMS at low beam energies. Thedetection of radionuclides heavier than 14C has been inves-tigated. For the first time, 26A1/A1 and 41Ca/Ca isotopic ratiomeasurements have successfully been performed at beamenergies below 1 MeV. The overall efficiencies are compa-rable to those at large accelerators.

164

INVESTIGATION OF NATURAL °Be/Be RATIOS WITH ACCELERATOR MASSSPECTROMETRY (AMS)

C. Maden, M. Frank, M. Suter (ETHZ), P.W. Kubik, M. Dobeli (PSI)

An AMS method for measuring natural 10Be/Be ratios has been developed at the PSI/ETH AMS facility. Because no9Be carrier is added during sample preparation, samples of the order of 100 ng are obtained. They can be analysedusing a finely focussed Cs+ primary ion beam. Standard samples have been measured, and it has been shown thatthe method can compete with techniques such as SIMS and the combination of conventional 10Be AMS and ICP-MS.

For some applications in the geological sciences, such asdating of manganese crusts, it is the natural 10Be/Be ratio ofa sample that is of interest. Conventional 10Be AMS is astandard method for measuring 10Be/Be ratios. However, sofar only the absolute concentration of 10Be in the originalsample can be determined, because several hundred micro-gramms of "Be carrier are added during sample preparation.Using a preparation method that does not add 9Be carrier[1], samples of a few hundred nanogramms in size and with10Be concentrations orders of magnitude higher than forconventional 10Be AMS are obtained. These can be ana-lyzed with the finely focussed Cs+ primary ion beam pro-duced by the Atomika Cs431 source of the PSI/ETH AMSfacility. The Cs beam has a spot size of about 100 jxm andis operated with beam currents of around 600 nA. The sec-ondary BeO ions are extracted into the main beamline ofthe AMS facility and are analysed the identical way as inconventional l0Be AMS measurements.For standard samples, the Be is in a 1000 ppm solution ei-ther as BeNO, or as BeSO4. By pipetting some tenths of amicroliter of the solution onto a silicon wafer, evaporatingthe solvent at 70 °C and baking the silicon wafer at a tem-perature of 800 °C for two hours, the nitrate or the sulfate isreduced to an oxide and a spot of a few hundrednanogramms of BeO is left on the silicon wafer. To avoidmass fractionation due to the geometrical shape of the BeOgrain sitting on the silicon the BeO grain is pressed into ahighly pure sheet of aluminium and then coated with about20 nm of Gold to reduce electrical charging of the sampleby the Cs beam. Figure 1 shows a schematic cross sectionthrough a prepared sample.

Au

as a function of measuring time. The nominal 10Be/Be ratioof the sample is 1.08109. The measured mean l0Be/l6O ratiois 0.82-10' with a statistical error of 5.3%.

500 |im

Fig. 1: Schematic cross section through a sample preparedfor measurement.

So far, BeSO4 standard solutions with known l0Be/Be ratiosranging from 10"6 down to 10l0 [2] have been analysed withthe new method. Reproducible measurements of the iso-topic ratios have been performed. An example of a meas-urement is shown in Fig. 2. Both the I6O5+ current comingfrom the break-up of the 9Bel6O molecule in the tandem ac-celerator as well as the measured l0Be/l6O ratio are plotted

0 200 400 600 800 1000 1200 1400 1600

Time (s)

Fig. 2: Measurement of a standard sample with a nominal10Be/Be ratio of 1.0810".

With repeated measurement on different spots of the sam-ple it has been demonstrated that a sufficient analysing cur-rent can be extracted from a 200 ng sample for longer thantwo hours. Transmission, ion source yield and total effi-ciency are almost identical to values of conventional 10BeAMS (Transmission: 16.5% and 7.0% for 9Be3+ and 16O5+ re-spectively; ion source yield: 1%; total efficiency: 0.1%).The suppression of interferences is the same for both meth-ods which would theoretically allow one to measure naturalratios of lower than 10"12. But demanding that a measure-ment with statistical error of 10% should be performed in 1hour the detection limit rises to 1-10l0.

In summary, it can be said that the new AMS method formeasuring natural l0Be/Be ratios is able to compete with al-ready existing methods in sensitivity as well as precision[3] and will be tested on samples from manganese crusts inthe near future.

REFERENCES

[1] F. v. Blankenburg et al.,Chem. Geol., 129,93 (1996).

[2] H.J. Hofman et al.,Nucl. Instrum. Meth. B 29, 32 (1987).

[3] N.S. Belshaw et al., Int. J. of Mass Spectrometry andIon Processes, 142, 55 (1995).

165

DENDROCHRONOLOGICAL AND RADIOCARBON DATING OF THE SCYTHENBURIAL PLACE IN THE PAZYRYK VALLEY IN THE ALTAI MOUNTAINS, SOUTH

SIBERIA

G. Bonani, I. Hajdas (ETHZ), U. Rouff (Bilro fur Archdologie, Zurich), M. Seifert (Archaologischer DienstGraubilnden, Haldenstein), V. Molodinand I. Sljusarenko (Institute of Archaeology and Ethnology, Nowosibirsk)

Fourteen kurgans (burial mounds) have been found in thePazyryk valley, 1600 meters above sea level in the Altairegion in the heart of the Eurasian landmass. The first kur-gan was excavated in 1929 by a Russian specialist in Sibe-rian archaeology. A further seven burial mounds wereopened in the 1940s. Five of the excavated tombs are ofvery large size and have distinct constructions. In theyoungest kurgan (no. 5), the world's most famous and old-est pile rug was discovered. The contents of the barrowswere preserved because the water inside the burial pit hadfrozen, as a result both of local climatic conditions and ofthe construction of the tombs itself. The time of origin ofthe Pazyryk carpet as well as the dating of the wholePazyryk culture were uncertain up to now. The kurganswere thought to have been built in the 5th-4th centuries BC,but the culture of their builders and users, given the name'Pazyryk', has been identified as early nomadic, of Scythentype with many local peculiarities.

Between 1996 and 1998 more than 250 samples fromtombs of different regions in the Altai Mountains were in-vestigated. The tree ring patterns of wood samples frommore than 20 kurgans of different burial places could besynchronized (Fig. 1). As no dendrochronological mastercurve is available for this region, the I4C profiles of twotimbers from two different mounds were measured. Everyother set of 10 tree rings was selected for the measure-ments. The two profiles obtained from 18 respectively 12dates (weighted means of two, respectively four independ-ent measurements) were then synchronized with the radio-carbon master calibration curve of the last 10'000 years [1](Fig. 2). The synchronization allows the absolute dating ofthe tombs between BC 350±5 and BC 240±5.

CALIBRATION CURVE

• KURGAN ULANDRVK 4

O KURGAN PAZYRIK 2

-700 -650 -600 -550 -500 -450 -400 -350 -300CALBC

Fig. 2: 14C profiles of two different mounds, kurganULANDRYK 4 (18 dates) and kurgan PAZYRIK2 (12 dates), synchronized with the radiocarbonmaster calibration curve.

The world's most famous and oldest pile rug, the so-calledPazyryk carpet (Fig. 3) is exhibited in the Hermitage Mu-seum of St. Petersburg (Russia). It was also dated at theETH/PSI accelerator facility, yielding a calibrated calendarage (95 % confidence limit) of BC 383 - 332 (25.4 %) orBC 328 - 200 (74.6 %). In combination with the tree ringstudies of wood samples from the different kurgans, an ab-solute age of BC 260 - 250 could be determined.

Fig. 1: Examples of synchronization of tree ring patternsof wood samples from three different burial fields.

Fig. 3: Pazyryk carpet: wool, 200 x 183 cm (Hermit-age Museum of St. Petersburg)Lab. No.: ETH-18906;Radiocarbon age: 2245±35 y BP;Calibrated age ranges at BC 383 - 332 (25.4 %)95 % confidence limit: BC 328 - 200 (74.6 %)Absolute age: BC 260 - 250

REFERENCE

[1] M. Stuiver et al., Radiocarbon 35 No. 1, 35 (1993).

166

BIOSPHERE 2 OCEAN RADIOCARBON EXPERIMENT

W.S. Broecker, C. Longdon, A. Sanyal (LDEO, Columbia Univ.), I.Hajdas, G. Bonani (ETHZ)

The results of a radiocarbon spike experiment are summarised in this report. We have evidence for a roughly five-fold enhancement of the rate of CO2 gas exchange over that expected from a O, and SF6 gas exchange experiment.This suggests that catalysis of HCO} to CO2 must be occurring as the result of the release of carbonic anhydrasefrom biota. With its high ratio of biota to water volume, Biosphere 2's ocean is the ideal place to study this effect.

On January 12th, 2000 several microcuries of radiocarbon

(in HCO3 form) were added to the Biosphere 2 ocean. This

addition raised the I4C to C ratio in the dissolved inorganiccarbon from 0.56 to 4.56 of the pre-industrial ratio in theEarth's atmosphere. Then, over the period of half a year,the I4C to C ratio drifted back down to 0.85 of the pre-industrial ratio (see Table 1 and Figure 1 for summary).

Table 1: Summary of radiocarbon measurements on dis-solved inorganic carbon. (* T.I.A.: Time after input of 14C;+: (14C/C)/(14C/C)1850-0.56; **: Average of 5 measurements)

Date

19 July 9910 January 0012 January 0021 January 0017 February 0009 March 0017 April 0015 June 00

T.A.I.*

Days

09365796155

14c/c14c/c

WM8500.540.564.563.251.681.300.95

0.85**

Excess+

--

4.002.691.120.740.390.29

Two ways exist for this reduction. One is the exchange ofCO, between the ocean and the overlying atmosphere. Theother is via respiration carbon stored in the organic mattermaking up the organisms inhabiting the ocean bottom. Wehave carried out gas exchange experiments using SF6 andO2 which yield gas residence time of about 2 days. Becausethe ratio of total dissolved carbon (LCO2) to CO2 in theocean is about 100 (i.e., 2000 umol/L ZCO2 to 20 umol/LCO2), the I4C residence time would be expected to be about200 days. Thus, it is clear that the rapid reduction in I4C canbe due to CO2 exchange with the overlying air only, if thereis a very large enhancement of CO2 exchange through thecatalysis of the HCO 3 to CO, reaction by carbonic anhy-drase leaked from biota. Based on the O2 consumption rateduring dark periods (mean 1.8103 mol/L/hr), the rate of in-put of respiration CO2 can be estimated (-40-10"3

mol/L/day). This rate is high enough to explain only abouthalf of the decline of the initial ratio of 14C to C. An upperlimit on the amount of active biomass can be obtained byassuming that the entire is the result of the addition of res-piration CO2. In this case the ratio of biomass carbon to dis-solved inorganic carbon would be 4.00 divided by 0.29 or13.8. The amount of carbon in the ocean is 2 mol/m3 or 8mol/m2. Hence, the amount of biota carbon would be 110

mol/m2 or 0.13g/cm2. As shown in Figure 1, the halvingtime for the I4C excess steadily increased. This surely re-flects the respiration of I4C -tagged organics. As statedabove, based on the dark hour O, drawdown rate, the initialhalving time would be expected to be 30 days (as opposedto the observed 17 days). This leads us to suspect that car-bonic anhydrase-driven enhancement of CO2 exchange istaking place.

Our next step will be to make a simple air-water-biota 3-box model in attempt to confirm the seeming anomaly be-tween the nighttime O2 data and the initial I4C decline rate.We will also determine what spectrum of residence times(i.e., time between production of organic matter and its de-struction by respiration) would fit the decline of the I4C toC ratio. If, as we suspect, the O2 data explains only part ofthe decline, then we have to find means to estimate the roleof catalysis by carbonic anhydrase. The obvious way to goabout this will be to measure the rate of I4C build-up in airspace over the ocean. As the residual excess of I4C is nowquite small, this will be done when we add a second spikeof I4C to the ocean. One thing should be kept in mind. If thestorage of I4C in the biota is assumed to explain the entireI4C drawdown, then the residence time of the excess I4C inthe ocean-biota reservoir will be closer to 2500 days. Thisopens the possibility of using the ocean as a steady sourceof I4C for terrestrial experiments in the mangrove and sa-vanna of Biosphere 2.

50 100 150DAYS AFTER ADDITION

200

Fig. 1: Decline of excess I4C in the dissolved inorganiccarbon of Biosphere 2's ocean addition of tracer14C. As can be seen, the first halving was accom-plished in 17 days and the second in 23 days.

167

VARIATIONS IN ATMOSPHERIC 14C CONTENT 40,000 AGO ANDRADIOCARBON AGE OF HEINRICH EVENT 4

/. Hajdas, G. Bonani (ETHZ), J. McManus (WHO1), M. Mendelson, S. Hemming (LDEO, Columbia Univ.)

Distinct layers of ice rafted debris observed in deep sea sediments from the North Atlantic have been correlated withclimatic events in this region. Here, we present results of AMS 14C dating of one of the layers in ODP 984 core re-covered south of Iceland. To reconstruct variations in atmospheric I4C content, a second independent record of thelacustrine section from Wilson Creek (CA) was dated.

The atmospheric content of 14C changes due to variations inthe 14C production rate and the exchange between the car-bon reservoirs of ocean, atmosphere and biosphere. The ra-diocarbon calibration curve reconstructs the relationshipbetween radiocarbon age and calendar age of the last11,600 calendar years. However, the application of the ra-diocarbon method in dating climate records extends back to40 kyr BP. Beyond the range of the calibration curve(>11,600) and Cariaco chronology (>14,500 cal BP) [1],the INTCAL98 data set [2] is available but the resolution ofthis data is low. Therefore, fast changes in 14C content simi-lar to the one observed during the Younger Dryas cannot bereproduced and taken into account in data analysis.In 1988, Heinrich [3] observed 6 massive layers of icerafted debris in North Atlantic sediments which were de-posited during the last glaciation. He suggested that the de-bris were brought by armadas of icebergs, which surgedfrom the ice sheets. New studies at various locations in theNorth Atlantic region as well as correlation with climate re-cords of Greenland ice cores were published in the early1990's [4]. An important aspect for the correlation betweenrecords is chronology. Most deep-sea sediments are datedusing AMS 14C dating of foraminifera shells. Although theradiocarbon ages of the Heinrich Events HE1 (14.3 kyrBP), HE2 (21 kyr BP), HE3 (27 kyr BP) and HE4 (ca. 35kyr BP) are established [4], discrepancies in chronologieshave been reported [5].Our results of dating the HE4 layer in high sedimentationODP 984 core, which was recovered south of Iceland, showthat the age of this event can be difficult to assess for vari-ous reasons. First of all, records typically studied are deep-sea sediments with low sedimentation rates on an order of afew cm/kyr. Because of that, it might be difficult to collectsufficient amount of material (foraminifera shells) neededfor an AMS sample. Secondly, sediment layers of Heinrichevents are known to be poor in foraminifera. This fact ismaking the dating even more difficult. The third complica-tion is characteristic for HE4. The age of 35 kyr BP is closeto the limit of the radiocarbon dating method. Thereforeany contamination with modern or younger carbon (secon-dary calcite) can result in ages which are too young. More-over, dramatic changes in atmospheric 14C might add tothose problems.Recently, an increased atmospheric 14C/12C ratio at ca. 40kyr BP has been observed in U/Th dated spaleothems anddeep-sea cores. The timing of this excursion is close toHE4 and can influence the radiocarbon chronology of stud-ied records. In order to reproduce the reported excursion,ostracode shells from the Wilson Creek exposure north ofMono Lake (CA) were dated. Both records show an in-

crease in 14C content. Based on the North Atlantic recordwe can say that the excursion precedes HE4 and, as alreadydiscussed, might add to the problems of dating that event.

25000 30000 35000 40000

14/

820

45000 50000

'CageBP

Fig. 1: Radiocarbon chronologies of ODP 984 core andWilson Creek are plotted on the same radiocarbontime scale. The data sets are shifted because of dif-ferent sedimentation rates, but the interesting fea-ture of the I4C excursion is visible in both recordsas a decrease in radiocarbon age from ca. 35,000to 31,000 and an increase of ages back to 34,000-35,000 BP.

REFERENCES

[1] K. Hughen et al., Science 290,1952 (2000)

[2] M. Stuiver et al., Radiocarbon 40,1041 (1998)

[3] H. Heinrich., Quat. Res. 29,143 (1988)

[4] G. Bond et al., Nature 365,143 (1993)

[5] L. Vidal et al.,Earth and Planet. Sci. Lett. 146,13 (1997)

168

LATE PLEISTOCENE SEQUENCES OF THE BLACK SEA SHELF:CALIBRATION BY AMS 14C DATING

C. O. Major, W. B. F. Ryan (LDEO, Columbia Univ.), I. Hajdas, G. Bonani (ETHZ)

Radiocarbon dates of mollusk shells and bulk organic carbon can be used to reconstruct the rate and amplitude ofBlack Sea sea level changes from the Last Glacial Maximum (18,000 BP) to the present.

The Black Sea is a large, semi-enclosed brackish to marinewater body, whose water budget has varied dramaticallyon glacial-interglacial time scales. During glacial stages,lower world sea levels results in the loss of marine waterinput via the shallow Bosporus and Dardanelles sills. Con-tinued fresh water input via large Eurasian and Anatolianrivers transformed the Black Sea to a fresh to brackish wa-ter body during these times. The transition from the lastfreshwater stage (Neoeuxine) to the modern marine stageis marked by a change in the benthic faunal assemblagesand the onset of sapropel formation in the deep basin.Our study seeks to determine the rate and amplitude ofBlack Sea sea level changes from the Last Glacial Maxi-mum (-18 ky BP) to the present, and the degree to whichthe sea level is controlled by varying river input, climatechange, and connection with the world oceans. Forty-onesamples, including shells and bulk organic material, weresubmitted to ETH for radiocarbon dating. The ages of mol-lusk shells from the base of the upper Neoeuxine unit con-firmed a transgression of Black Sea sea level between -20and 7.6 ky BP (all reported ages are unconnected for reser-voir effect). This transgressive unit onlaps an interbeddedbarren unit, which is dated by bulk organic carbon to ap-proximately 23 to 27 ky BP. This basal unit, which is seenin seismic profiles to have a seaward dipping geometryand a truncated upper surface, is interpreted as a low standdelta of the Danube River. Mollusk shells from the mid-shelf region, between 60 and 80 m, were reworked intolarge dune-like bedforms between 7.65 and 7.1 ky BP,suggesting a brief regression of Black Sea sea level in theearly Holocene or intensive submarine sediment transport.In addition, we have found that glacial-interglacial transi-tion, marked by a change in sediment composition to morecalcium carbonate and smectite-rich sediments as well as apositive shift in the 818O of mollusk shells, appears be-tween -13 and 7 ky BP. The preceding period in our re-cord appears to have been characterized by high sedimen-tation rates in the deep basin and continental slope and wi-despread erosion of the Black Sea shelf.A remaining question is the degree to which the Black Seasea level rose and fell independently of world sea levelduring its isolated phase. The Caspian Sea, another en-closed brackish water body, experienced base levelchanges of up to 80 m over the last glacial cycle [1]. Thesechanges are ascribed to changes in the river/precipitationinput versus water loss by evaporation and periodic over-flow to the Black Sea. We seek to resolve whether theBlack Sea transgression during the late Pleistocene was the

result of increased freshwater input from melting glaciersor the reflection of early marine leakage into the BlackSea, which would necessitate a synchronous rise of BlackSea and world sea levels.

Table 1: Summary of dating results from Black Sea cores

Depth (cm)

23111414152233333438394145526093

94.5110.5114115

118.5127130

154.5161

176.5186.5215704840

Dated material

DreissenaDreissenaDreissenaDreissenaDreissenaDreissenaDreissenaMytilusDreissenaDreissenaDreissenaDreissenaDreissenaDreissenaBulk organic materialBulk organic materialMonodacnaTurricaspiaMonodacnaBulk organic materialDreissenaDreissenaDreissenaMonodacnaDreissenaDreissenaDreissenaDreissenaDreissenaDreissenaDreissena

14C Age (uncor-rected) BP

8275 ± 7010430 ± 8010260 ± 9510560 ± 7510090 ± 13012310 ± 958305 ± 806750 ± 707940 ± 758660 ± 75

20490 ± 1508360 ± 758300 ± 70

10250 ± 9023630 ± 18024980 ±2007655 ± 75

10640 ± 807865 ± 70

26630 ±23014010 ± 10011410 ±110

24160 ± 1909580 ± 80

12790 ±1108345 ± 708360 ± 70

12820 ± 10014950 ± 10017760 ± 13020580 ± 150

REFERENCE

[1] A.A. Svitoch, Oceanology 39, 94 (1999).

169

A LATE-GLACIAL AND EARLY HOLOCENE ENVIRONMENT AND CLIMATEHISTORY FOR THE NEUCHATEL REGION (SWITZERLAND)

N. Thew, P. Hadorn, (Service cantonal d'archeologie, Neuchdtel), G. R. Coope (Univ. of London),G. Lemdahl (Vaxjo Univ.), I. Hajdas, G. Bonani (ETHZ)

Radiocarbon chronology of the site Hauterive/Rouges-Terres was established using AMS dating of terrestrial plantmacrofossils. This chronology provides a basis for absolute dating of climatic events of the last deglaciation and be-ginning of Holocene (14,000 to 8,000 yr BP). Environmental changes such as fluctuations of lake level, response offlora (pollen) and fauna (insects and molluscs) to the climatic change were studied.

The site of Hauterive/Rouges-Terres, situated near thenorthwestern part of Lake Neuchatel (Switzerland), wasdiscovered in 1992 in the deep construction trench for theA5 motorway. Field investigations were carried out duringthe summers of 1992 and 1993. Fifteen profiles covering130 m of horizontal stratigraphy have been drawn, de-scribed and sampled for sediment, pollen, plant macrofos-sil, insect and mollusk analyses. Careful cleaning of thewhole section allowed layers to be followed and correlatedbetween the 15 profiles permitting lithostratigraphic unitsto be established for all of the documented sediments.These deposits formed in an embayment at the margin ofLake Neuchatel, with lake sediments predominating to-wards the deeper part of the depression, passing laterallyinto lake margin and supra-littoral marsh and colluvial de-posits. Pollen analysis on four of the profiles have con-firmed field hypotheses that these deposits represent acomplex sequence of Late Glacial to middle Holocenesediments. These sediments are reflecting changing condi-tions in the local environment (linked to lake level varia-tions, and phases of stability and instability of the adjoiningterrestrial land surface) determined by regional scale pat-terns of climate change. Despite the variable nature of thesesediments, the pollen sequence fits very well with the re-gional pollen zones published for the Swiss Plateau [1]. Anabsolute chronology has also been established for thesefour profiles, based on more than 60 AMS dates rangingfrom 14,200 to 8,000 BP. Sediments of the Oldest Dryasbiozone were dominated towards the edge of the depressionby colluvial gravels with alternating layers of silts andsands. The gravel contained many frost-shattered pebbles.Notable deformation structures (several phases) could beobserved, resulting from solifluction and possibly cryotur-bation. Low pollen concentrations show rapid sedimenta-tion during the Oldest Dryas biozone but, despite this, thefiner sediments were found to contain remarkable concen-trations of plant macro-remains, insects and molluscs. Theplant material consists of leaves, fruits, seeds, bud-scalesand twigs that reflect an arctic and alpine Oldest Dryasflora [2]. Among the identified remains are aquatic species,plants typical of lake shore marshes, alpine meadows andloose rocks, as well as dwarf shrubs (Betula nana, Dryasoctopetala, Salix retusa). Insect analyses indicate extremelycold conditions throughout the Oldest Dryas biozone. Themolluscs include alpine, arctic and Siberian species [3].The insects clearly show a sudden and intense temperaturewarming at the very end of the Betula nana phase just be-fore the reforestation by juniper and tree birch, whichmarks the beginning of the B0lling biozone. This warming

coincided with a change in sedimentation (alternating siltsand sands gave way to organic silts) which seems to indi-cate a rise in lake level. The plant remains show subsequentcolonization by tree birches, willows and poplars. TheBetula phase of the B0lling was marked by the depositionof silty marls. A significant lowering of the lake level dur-ing the Youngest Dryas biozone (leading to the formationof pebble beaches and sand layers) caused the erosion of allsediments dating from the Aller0d biozone, and the forma-tion of loading structures. The insects indicate a return tocolder climatic conditions. At the start of the Preboreal anabrupt climatic warming coincided with a major rise in lakelevel and the subsequent deposition of silty marls, silts andfine sands. The Boreal and Atlantic biozones were markedby sediments rich in oncoliths.

Table 1: Radiocarbon chronology of the Rouges-Terresclimatic record

Regionalpollenzones

Boreal

Preboreal

YoungerDryas

B0lling

OldestDryas

Inferred vegetation

Deciduous forest, hazel,elm, oak, lime

Pine and birch forest, ar-rival hazel, elm, oak

Hiatus, erosion of the Al-ler0d, open pine forestwith birch

Reforestation by juniper,buckthorn, birch, willow

Meadows with arctic andalpine herbs, treeless

Radiocarbonage

ca. 8000 BP

9200-10,000BP

<10,000-11,000 BP

<12,000-12,500 BP

12,500-14,500BP

REFERENCES

[1] B. Ammann et al., Boreas 18,109 (1989).

[2] G. R. Coope et al., J. Quat. Sci. 15,157 (2000).

[3] G. Lang, Quartare Vegetationsgeschichte Europas.Fischer, Jena, Stuttgart, New York, p. 462 (1994).

170

THE APPLICATION OF IN SITU COSMOGENIC NUCLIDE EXPOSURE DATING(10Be, 26A1), TO GLACIAL DEPOSITS OF THE LAST DEGLACIATION IN THE

SOUTHERN ANDES OF CHILE

C. Fogwill, W.M.Phillips (Univ. of Edinburgh), P.W. Kubik(PSI)

This report presents preliminary results from AMS measurement of the in situ produced nuclides 10Be and 26Al in gla-cial landforms in Fuego, Patagonia. This data provides some of the first reliable independent chronological controlsof the glaciation of this region during the last glacial transition.

The timing of high frequency - low amplitude climaticvariations during the last glacial/interglacial transition isimportant to our understanding of the nature of interhemi-spheric leads and lags in global climate signalling. To thisend, the measurement of in situ produced cosmogenic nu-clides by AMS provides geomorphologists with an indis-pensable tool for dating the emplacement of geographicalfeatures. These are related to the advance and retreat of gla-ciers in response to climate [1].

Fuego Patagonia is one of the only large landmasses to ex-tend beyond 55° south (see Figure 1). It has been suggestedthat glacial dynamics in this region are controlled by the lo-cation, moisture content and intensity of the westerlies [2,3], which are themselves controlled by global pressure sys-tems. Knowledge of the timing of glaciation therefore indi-cates both precipitation and temperature regimes at varyinglatitudes throughout Patagonia. By constructing an accuratechronology, the nature of interhemispheric climate changeduring the last glacial termination can be elucidated. This iscurrently a contentious topic, which continues to be widelydebated [4, 5, 6].

This project applies cosmogenic exposure dating to a vari-ety of glacial landforms. These landforms are a product ofadvancing glaciers during the last glacial cycle. Two siteswere selected in southernmost South America; Paine andMagellan (Fig. 1) based on the findings of geomorphologi-cal field studies in this region [7]. These previous studieshave identified a series of glacial limits. Attempts to pro-duce a reliable radiocarbon chronology for the Paine andMagellan regions have yielded few useful bracketing datesdue to the lack of preserved organic material. A prelimi-nary radiocarbon chronology has been developed from thiswork. This provides an ideal testing ground for cosmogenicdating.Initial results with 10Be have dated a number of large errat-ics in the Magellan Region. The dates are 21- 24,000 yrsBP using a production rate of 5.1 ± 0.2 10Be atoms g"1 y"1 atsea level [8]. These dates are from a giant rockfall deposit,which occurred on to the advancing ice sheet and whichwas then transported supraglacially before final depositionon the eventual limit of the terminal position of the icesheet at this time.

This data provides the first evidence of glaciation in thisregion contemporaneous with the Last Glacial Maximum.A total of thirty samples have been taken in all, in an at-tempt to produce a reliable chronology of this region.

Fig. 1: Map of southern-most South America, with pre-sent day ice fields (shaded areas), and samplingareas in boxes.

REFERENCES

[1] S. Ivy-Ochs,Ph.D. thesis #11763, ETH Zurich (1996).

[2] A. Hubbard,Earth and Planet. Sci. Lett. 22, 79 (1997).

[3] G.H. Dentonefa/.,

Geog. Ann. 81 A (2), 107 (1999).

[4] T. Blunier et al, Nature 394,739 (1998).

[5] T.V. Lowell et al., Science 269,1541 (1995).

[6] R.M. McCulloch et al.,J. Quaternary Sci. 15,409 (2000).

[7] CM. Clapperton et al.,Quat. Res. 44,133 (1995).

[8] J. Stone, J. Geophys. Res. 10, 23753 (2000).

171

SLIP RATES OF ACTIVE THRUSTS AT THE NORTHEASTERN MARGIN OFTIBET (CHINA) AS REVEALED BY 21Ne AND 10Be EXPOSURE AGES OF LATE

PLEISTOCENE ALLUVIAL FANS

R. Hetzel, S. Niedermann (GFZPotsdam), P.W. Kubik (PSI), S. Ivy-Ochs (ETHZ), M. Tao (CAS, China)

Late Pleistocene 10Be and 21Ne exposure ages obtained from an alluvial fan located at the NE margin of Tibet con-strain the vertical slip rate of an active thrust fault at 0.3-0.5 mm/yr. Our results demonstrate that previous slip rateestimates, which were based on the assumption that tectonically offset surfaces have formed during early Holocenewarming, are doubtful. Slip rate determinations should include rigorous dating of the surfaces affected by faulting.

This ongoing project aims to quantify slip rates of activethrusts at the front of the Qilian Shan, in order to betterconstrain the Late Pleistocene/Holocene deformation his-tory at the northeastern margin of the Tibetan Plateau.Seismically active thrusts and strike-slip faults demonstratethat the 5500 m high Qilian Shan is an actively growingNE-vergent thrust-and-fold belt [1]. There exist only fewslip rate estimates of active thrusts in the Qilian Shan.These estimates are based on the assumption that surfaces,tectonically offset by faults, have formed during earlyHolocene warming and deglaciation as a result of increasedsurface runoff. Ages of 10±2 ka and 11±3 ka have been as-signed to alluvial fan surfaces offset by thrust faults [1,2].In contrast to this assumption, our first 10Be and 21Ne expo-sure ages demonstrate that surfaces considerably older thanHolocene are preserved in the Qilian Shan.The studied Yumen thrust is a NNE-dipping thrust fault lo-cated -10 km north of the steep mountain front of the Qil-ian Shan at an elevation of 2000 m (97°45'E, 39°50'N). Ithas displaced the surface of an alluvial fan and forms a30 km long south-facing fault scarp (Fig. 1). At two studysites, topographic profiles demonstrate that the thrust has avertical displacement of 40 m and 57 m, respectively. As-suming an early Holocene age of -10 ka for the fan surfacewould translate into a vertical slip rate of 4-6 mm/a.

Fig. 1: Corona-image of the western part of the Yumenthrust. Intermittent streams flowing north have in-cised into the uplifted hanging wall of the thrust.Quartz clasts were collected from the surface ofthe fan.

To constrain the age of the tectonically uplifted fan surfacewe sampled quartz clasts from the surface of the fan at both

sites. Since cosmogenic nuclides are not only produced in-situ, but also prior to the deposition of the clasts during ex-humation and transport, this inherited component (also re-ferred to as "geological blank"; [3]) must be taken into ac-count. Therefore, we also collected clasts from intermittentstreams that cross the fault scarp line (see Fig. 1). As indi-vidual clasts contain different amounts of the inheritedcomponent, we followed the amalgamation approach ofAnderson et al. [4] and include 30-40 individual clasts intoone sample.At site 1 (40 m vertical uplift), a surface sample yields a21Ne age of 132±17 ka and a 10Be age of 118+18 ka (2a),both ages being in excellent agreement. At site 2 (57 m ver-tical uplift), a surface sample gave a 21Ne age of 320±22 kathat is considerably older than the 10Be age of 188±25 ka.This discrepancy is interpreted to be caused by a neon com-ponent that deviates from the neon composition of air. Thisnon-atmospheric component is most likely present in fluidinclusions and results in an anomalously old Ne age. There-fore, only the Be age is interpreted as geologicallymeaningful at site 2. The ages mentioned so far have notyet been corrected for a "geological blank". A 10Be and a21Ne analysis of two different samples from active streamssuggest that the inherited cosmogenic component is only arelatively small fraction of the total cosmogenic component(less then a quarter). A detailed consideration of the inher-ited component must await further analyses. However, theages that have already been obtained demonstrate that theaverage rate of vertical tectonic uplift along the Yumenthrust is at both sites only some 0.3-0.5mm/a. This is an or-der of magnitude smaller than the rate that would be ob-tained assuming an early Holocene age of the alluvial fansurface. Thus, rigorous dating of tectonically offset sur-faces is a prerequisite for determining reliable rates of tec-tonic faulting.

REFERENCES

[1] B. Meyer et al., Geophys. J. Int. 135, 1 (1998).

[2] P. Tapponnier et al.,Earth Planet. Sci. Lett. 97, 382 (1990).

[3] E.T. Brown et al.,Geol. Soc. Am. Bull. 110, 377 (1998).

[4] R.S. Anderson, et al., Geology. 24, 47 (1996).

172

COSMOGENIC NUCLIDE EROSION ASSESSMENT OF TROPICAL HIGHLANDS(SRI LANKA)

A.L. T. Hewawasam, F. von Blanckenburg, M. Schaller (Univ. Bern), P. W. Kubik (PSI)

Present-day soil erosion rates have been compared to cosmogenic erosion rates for the Upper Mahaweli catchment,Sri Lanka. Our study reveals that cosmogenic erosion rates solely represent the rates of natural erosion. More im-portantly, the technique can be used to infer the influence of deforestation on soil erosion, when used in conjunctionwith present-day erosion rates. To date, these man-made changes have remained difficult to quantify.

In szYw-produced cosmogenic nuclides are generated inminerals at the earth's surface mainly due to neutron spalla-tion and muon capture reactions. Their concentration is afunction of time and of the surface lowering rate. In an en-tire landscape, large-scale erosion rates can be determinedfrom quartz in river sediment if the rate of nuclide produc-tion equals that of nuclide loss through sediment transportin a river. We employed this concept to quantify large-scaleerosion rates for an integrated time period in a tropicalhighland.10Be and 26A1 concentrations were measured in pure quartzfrom river sediments of six small tributaries of the Ma-haweli river, Sri Lanka. The tributaries are draining amountain range of 600-2500 m altitude which is underlainby crystalline rocks. The catchment areas had been coveredwith thick forest until the 19* century. Later, the forestcover had been removed on a large scale, principallythrough two phases of agricultural plantation. Only a fewisolated patches of the original rain forest remain. Conse-quently, the area is experiencing severe soil erosion today.At present, the spatially averaged soil erosion rates for thesix catchments can be calculated from suspended and dis-solved load data. The present-day soil erosion is severeand ranges from 100 mm/ky to 500 mm/ky.In contrast, erosion rates for the six catchments based onmeasured 10Be concentrations range from 10 mm/ky to 30mm/ky. Measured erosion rates based on 26A1 concentra-tions for five randomly selected samples are consistent withthose of calculated by 10Be concentrations. Moreover, sev-eral very small catchments (both agricultural and originalforest) were also sampled in the Upper Mahaweli catch-ment for the erosion study. The measured erosion rates forsediment and surface soil from both original forests and ag-riculturally utilised area are similar to the large-scale ero-sion from the six catchments of Mahaweli. This suggeststhat the cosmogenic technique is not sensitive to recenthuman effects (Figure 1). This is because the cosmogenicnuclide-derived erosion rates average over a period of 10 to50 kys. Therefore, this novel technique can be used as aneffective tool to quantify natural erosion, which is essen-tially controlled by climate and tectonics.

100-

10-

•oAo

A

Six Small Catchments (RG)Sediments from Six Small Catchments (CN) ""Very Small Forest Catchments (CN) ' 'Very Small Agricultural Catchments (CN)

i 1

A ° ? ?-S

ooo

A

I \

1

100 1000

Drainage Area [km ]

Fig. 1: Erosion rates derived from sediments from sixMahaweli River tributaries, small forest catch-ments, and small agricultural catchments (RG:river gauging, CN: cosmogenic nuclides)

The difference between the low cosmogenic nuclide de-rived erosion rates (10-30 mm/ky) and those from present-day river-load gauging (100 mm/ky to 500 mm/ky) sug-gests that deforestation and plantation agriculture has in-creased the present-day soil erosion by a factor of 10 to 20over the island's natural erosion.

173

CAN WE USE COSMOGENIC NUCLIDES TO DATE STONE ARTIFACTS?

S. Ivy-Ochs (ETHZ), R. Wiist (Univ. Vancouver), P.W. Kubik (PSI), H. Mttller-Beck (Univ. Tubingen),C. Schluchter (Univ. Bern)

Two chert artifacts from the Thebes Mountains near Luxor, Egypt, have yielded concentrations of cosmogenie 10Bethat allow calculation of nominal exposure ages of around 300,000 years. Tools associated with the flakes can beattributed to the Late Acheulean or early Middle Paleolithic. These exposure ages represent composite ages,comprised of exposures both before and after working.

Lithic artifacts can be dated by determining absolute ageson associated geological materials (using 14C, U-series,electron spin resonance, 40Ar/j9Ar, luminescence) or directlydated with luminescence techniques. We present here firstresults of an attempt to use surface exposure dating withcosmogenic nuclides to date siliceous artifacts [1]. Therestricting caveats are that the artifacts must have beencontinuously exposed since fabrication but must not havebeen exposed earlier. Otherwise, earlier exposure must bedeterminable independently.

Both artifacts were collected atop limestone benches of theEocene Thebes Formation which form cliffs along the westside of the Nile. The site is at elevation 240 m (150 mabove the present elevation of the Nile and about 15 kmaway from it). This area, where abundant chert noduleshave weathered out, has been a collection, extraction andfabrication site since the Early Paleolithic (since at least400,000 years ago [2]. The two artifacts we have analyzedthus far are flakes made during the knapping process; theyare not themselves tools. Both artifacts were severely wind-polished and bore a well-developed mottled dark brown toblack patina of desert varnish.

•••• " • " « -

2"m

K

Fig. 1: Sampling site on resistant benches of Thebeslimestone.

Our first results are for two different artifacts. The l0Beconcentrations allow calculation of nominal exposure agesof around 300,000 years (using the production rate ofKubik et al. [3] and the scaling factors of Lai [4]). Theseexposure ages are composite ages made up of:

1. the time the chert nodule was enclosed in the limestonebed rock and gradually getting closer to the surface asthe limestone around it eroded away, plus

2. the time that the eroded out chert cobble was lying onthe plateau surface prior to being worked on, plus

3. the time after the flake was chipped from a cobble.

The crucial question is what proportion of the exposure wasacquired before the cobbles were worked? Had the cobblesbeen exposed for a few thousand years, for tens ofthousands of years or for longer? One approach that mayhelp to narrow down the time range is to analyze chertnodules located close to collected worked pieces but stillembedded in the limestone bedrock. From this we shouldbe able to estimate the erosion rate affecting the removal ofoverlying bedrock. This should provide a further steptowards deconvolution of the three time periods of thecomposite exposure.

Is it possible that the calculated composite exposure agesare the actual exposure ages for these artifacts? Is such anage reasonable for the typology exhibited by the flakes andassociated tools? The two dated pieces belong to the moreheavily varnished artifacts known from the Luxor areacollections. They are connected with more archaic LaterAcheulean inventories, before more refined MiddlePaleolithic sites with less varnished tools appear. The'dates' measured are well in accordance with the olderrange of the estimated time window for the Early to MiddlePaleolithic transition. Acheulean artifacts from middleEgypt are known to date from at least 400,000 years ago,with the Final Acheulean at 350,000-400,000 years ago [2].The Early Middle Paleolithic is centered on 150,000 to200,000 [2]. It is the transition of the Early to MiddlePaleolithic which is difficult to pinpoint. For example,McBrearty and Brooks [5] quote the introduction of MiddleStone Age technology at 250,000 to 300,000 years ago.

These preliminary results are intriguing and highlight theexciting potential of surface exposure dating of siliceousartifacts.

REFERENCES

[1] S. Ivy-Ochs et al., submitted to Radiocarbon s (2001).

[2] P.M. Vermeersch, Paleolithic Living Sites in Upperand Middle Egypt.Leuven University Press, Leuven, Belgium (2000).

[3] P.W. Kubik etal.,Earth and Planet. Sci. Lett. 161, 231 (1998).

[4] Lai, Earth and Planet. Sci. Lett. 104, 424 (1991).

[5] S. McBrearty and A.S. Brooks, J. Human,Evolution 39 (5), 453 (2000).

174

A 30,000 YEAR EROSION RATE RECORD FROM COSMOGENIC NUCLIDES INRIVER TERRACE SEDIMENTS IN THE MASSIF CENTRAL, FRANCE

M. Schaller, F. von Blanckenburg (Univ. Bern), A. Veldkamp (Wageningen Univ.), P.W. Kubik (PSI),N. Hovius (Univ. of Cambridge)

The concentration of cosmogenic nuclides in sediment of terraces with known age can be used to calculate time-integrated paleo-erosion rates for entire river catchments. The erosion rates obtained for Late Pleistocene toHolocene terraces of the Allier river in the Massif Central, France, range from 33-55 mm/ky. These rates agree wellwith rates inferred from sediment accumulation in Lac Chambon situated within the upper Allier basin.

The quantification of past continental erosion is a challengeof principal importance to studies of tectonics andenvironmental change. Existing techniques are 1)thermobarometry of metamorphic belts; 2) fission trackanalysis; and 3) sediment accumulation budgets of naturalbasins. We have used a new technique, exploitingcosmogenic nuclides in dated river terraces, to quantifycatchment-wide rates of "paleo erosion". Quartz sand inriver terraces can be used to determine the time-integratederosion rates concomitant with terrace formation. Measuredcosmogenic 10Be concentrations in quartz are corrected forpost-depositional irradiation using the known terrace age.The remaining nuclide inventory is attributed to irradiationin the source area of the sediments. Erosion rates can thenbe calculated using the steady-state assumption of Lai [1]and making use production rates scaled for the meanaltitude and latitude of the upstream area.

This approach has been tested on the Late Pleistocene andHolocene terraces of the Allier and Dore rivers in theMassif Central, France. These terraces have beenextensively studied, dated, and modelled [2]. In addition,very precise estimates of Late Pleistocene to Holoceneerosion rates exist for Lac Chambon, based upon sedimentaccumulation in the basin [3]. Erosion rates based on 10Beconcentrations have been calculated with the productionrate of Kubik et al. [4] and the altitude/latitude scaling ofLai [1], both modified for the muon production rate valuesof Heisinger [5]. The erosion rates are all between 33 and55 mm/ky for the Late Pleistocene to Holocene terracesamples. These rates are very similar to those measuredwith 10Be in sands from the active Allier and Dore channels(31-59 mm/ky). They are also in agreement with the long-term estimates based on sediment accumulation in LacChambon (50-160 mm/ky). A quantitative model is used tocalculate apparent erosion rates expected from cosmogenicnuclides using as input erosion rates derived from sedimentaccumulation rates in the basin of Lac Chambon. Themodel demonstrates that strong, short-term fluctuations in"real" erosion are damped in the cosmogenic record due tothe considerable lag time (ca. 20 ky) required for thecosmogenic nuclide budget to settle back into steady-stateafter a change in erosion rate. Erosion rates of 50-160mm/ky from the sediment accumulation in the basin of LacChambon are damped to values of 50-70 mm/ky in thismodel calculation. Model results are in good agreementwith the erosion rates derived from the 10Be concentrationin the river terraces.

These results present a plausible explanation for the excesscosmogenic erosion rates measured in recent river sedimentwith respect to estimates based upon river load gauging inthe same streams: recent river-borne quartz contains amemory of the Late Pleistocene to Holocene erosionhistory. Importantly, the cosmogenic nuclide approachmakes it possible to determine changes in time-integratederosion rates from previous climate cycles, or intectonically active regions.

200-|

175-

150-

125-

100-

75-

50-

25-

Fig. 1:

0 5000 10000 15000 20000 25000 30000 35000

Time Before Present (y)

Cosmogenic nuclide-derived erosion ratesmeasured in terrace sediments of the Allier andDore basin (squares). Erosion rates measured bysediment accumulation in the basin of LacChambon back to 12,600 years ([3], solid line). Amodel simulation represents the cosmogenicnuclide-derived erosion rates expected from riversediment at any point back through time basedupon integration through time of the Lac Chambonerosion history (dashed line).

REFERENCES

[1] D. Lai, Earth Planet. Sci. Lett. 104,424 (1991)

[2] A. Veldkamp and S.B. Kroonenberg,Geologie en Mijnbouw 72,179 (1993).

J J Macaire et al., Earth Surface Processes andLandforms 22,473 (1997).

P.W. Kubik etal.,Earth Planet. Sci. Lett. 161, 231 (1998).

[5] B.P. Heisinger, Ph.D. Thesis,. TU Munchen (1998)

[3]

[4]

175

LAST MAJOR ADVANCE OF TAYLOR GLACIER INTO CENTRAL BEACONVALLEY, ANTARCTICA, AT LEAST 4 MA AGO

S. Tschudi, C. Schluchter (Univ. Bern), S. Ivy-Ochs, J.M. Schafer (ETHZ), P.W. Kubik(PSI),N. Potter (Dickinson College), G.H. Denton (Univ. of Maine), D. R. Marchant (Boston Univ.)

Surface exposure dating with cosmogenic nuclides provides absolute chronological information for Granite drift, aglacigenic sediment deposited by a Taylor Glacier advance into central Beacon Valley, Antarctica. Our analysisyields a minimum exposure age of ~ 4.0 Ma indicating a simple exposure history. It supports the contention thatburied remnant ice underlying the floor of central Beacon Valley is at least mid Pliocene, maybe Miocene in age.

Beacon Valley, Antarctica, is a crucial site for thereconstruction of Antarctic paleoglaciations and landscapeevolution. The valley acts like an "overflow basin" of theEast Antarctic Ice Sheet (EAIS), which makes glacialsediments in Beacon Valley an important archive for pastfluctuations of Taylor Glacier and hence Taylor Dome.Although a relative stratigraphy of surficial glacialsediments in Beacon Valley is well defined [e.g. 1, 2], anabsolute chronology is lacking. Underlying the valley floor,a remnant body of ice is buried, which is suggested to beMiocene in age [3]. This age determination has beenquestioned [4] and is presently under further discussion [5].

The goal of this study was to date Granite drift, a glacialsediment deposited by a major advance of Taylor Glacierinto central Beacon Valley [1], by means of surfaceexposure dating with cosmogenic l0Be, 26A1 and 2lNe.Dating this drift also provides a minimum age fordeposition of the stratigraphically older deposits of theSirius Group at Mt. Feather [e.g. 2], and it would shed lighton the discussion of the age of the buried body of ice.

10'

Be [atoms / g]

Fig. 1: Two-nuclide plot of all measured samples. Theconcentrations are normalized to sea level andhigh latitude using the production rates of Kubik etal. [6] (for details see [7].

Six granitic clasts on the valley floor from the surface ofGranite drift near its outer margin were sampled andanalyzed for l0Be, 26A1 and partly also for 2lNe. Theminimum exposure ages for these clasts range from 0.9 ±0.1 Ma to 4.0 ± 0.2 Ma [7], calculated with the productionrates of Kubik et al. [6] scaled after Lai [8]. These ages are

strictly minimum ages, as no erosion or coverage has beentaken into account. l0Be, 26A1 and 2lNe results being inagreement argue for a simple history of exposure.Therefore, Taylor Glacier deposited the Granite drift intocentral Beacon Valley sometime prior to 4.0 Ma. This isconsistent with the correlation of Granite drift withQuartermain I and II drifts in Arena Valley as suggested byMarchant et al. [2]. This age also suggests an early Plioceneor older age for the Sirius Group deposits at Mt. Feather,which is in accord with [9, 10]. From our multi-nuclideanalysis one can conclude that Taylor Glacier neverreached this part of Beacon Valley again and Granite drifttherefore represents the last major advance. Thiscontradicts an overriding of high-altitude sites by the EAISwithin the Dry Valleys at 3.1 Ma ago, as proposed byWebb et al. [11]. Moreover, our data strongly support thecontention that ash deposits on top of Granite drift are insitu and that the underlying remnant ice is indeed severalmillion years in age [3].

This work was partly funded by Swiss National ScienceFoundation grants 21-043469.95/1 and 21-053942.98 andby the United States Division of Polar Programs of theNational Science Foundation.

REFERENCES

[I] G. H. Denton et al., Geogr. Ann. 75 A, 155 (1993).

[2] D. R. Marchant et al., Geogr. Ann. 75 A, 269 (1993).

[3] D. E. Sugden et al., Nature 376, 412 (1995).

[4] R.C.A. Hindmarsh et al.,Geogr. Ann. 80 A, 209 (1998).

[5] J. M. Schafer etal.,Earth and Planet. Sci. Lett. 179, 91 (2000).

[6] P.W. Kubik etal.,

Earth and Planet. Sci. Lett. 161, 231 (1998).

[7] S. Tschudi et al., submitted to Geology, (2001).

[8] D. Lai, Earth and Planet.Sci. Lett. 104, 424-439 (1991).

[9] S. Ivy-Ochs et al., in: The Antarctic Region:Geological Evolution and Proceses, ed. C.A. Ricci,Terra Antarctica Publication, Siena, Italy, 1153(1997).

[10] J.M. Schaferetal.,Earth and Planet. Sci. Lett. 167, 215 (1999).

[II] P. N. Webb et al., Geology 12, 287 (1984).

176

CONSTRAINTS FOR THE LATEST GLACIAL ADVANCE ON WRANGEL ISLANDFROM SURFACE EXPOSURE DATING

S. Tschudi, C. Schluchter (Univ. Bern), P.W. Kubik (PSI), J. Karhu, M. Saarnisto (Geol. Survey of Finland)

From Wrangel Island, bedrock and loose rock samples were collected for surface exposure dating. Especially thebedrock surface samples were expected to provide new constraints for the chronology of glaciations on the island.Minimum exposure ages based on 10Be suggest that no major glaciations have affected Wrangel Island or theadjacent shelf area after about 65 ka, which seems to rule out a major glaciation during the Last Glacial Maximum.

Wrangel Island is well known for the abundance ofmammoth skeletal remains. A number of bones, teeth andtusks have been radiocarbon dated and the ages seem tocover the whole period from about 30'000 to 4'000 yearsBP [1, 2] with some data coincident with the Last GlacialMaximum (LGM). These results suggest that during theLGM this part of the continental shelf was ice-free,although globally the period is characterized by themaximum ice volume of the last glacial cycle [3].However, Grosswald [4, 5] proposed an extensive EastSiberian ice sheet, which covered most of the northeasternRussian shelf during the LGM, including Wrangel Island.

To determine a glacial chronology, rock samples forsurface exposure dating were collected (see Fig. 1) fromexposed bedrock (samples Wra 1 and Wra 4) and looseboulders (sample Wra 2) to be analyzed for 10Be [6].

WraL'2

V

Wra1

Fig. 1: The Bering Strait region and a sketch map ofWrangel Island (W) with sample localities.

The calculation of exposure ages follows the formalism ofLai [7]. For the production rates of in-situ 10Be, we havechosen the value of Kubik et al. [8]. All our calculations arebased on the production rate depth dependency of Masarikand Reedy [9]. Geometric shielding of surrounding hills, aswell as Quaternary uplift of Wrangel Island due to tectonicsor isostatic rebound (e.g. [10]) influences the productionrate on the order of < 1% and have therefore been not takeninto account here. Similarly, the influence of vegetation andsnow coverage can be neglected.

The minimum exposure age estimate for the bedrocksurface sample Wra 1 would suggest no major glacialadvances in this area later than about 65 ka [6]. This age,however, could also reflect a complex exposure history

with repeated periods of exposure and shielding during thepast. Bedrock samples reflect the deglaciation time of thelast glacial event only, if the advancing glacier erodedenough material from the bedrock surface to reset thecosmogenic "chronometer". Sample Wra 2 bears arelatively young exposure age (about 12 ka, [6]), whichcould indicate that the sampled boulder has suffereddisintegration and possibly rotation due to frost action.Sample Wra 4 has a minimum exposure age estimate ofabout 26 ka [6]. Here, field evidence excludes a formercoverage by valley glaciers. Thus, any major advances ofglacial ice sheets should have occurred before this date.

These minimum exposure age estimates indicate that,excluding local valley glaciers, no major growth of glacialice occurred on Wrangel Island during the LateWeichselian glaciation and possibly even during theMiddle Weichselian.

This work was partly funded by the Swiss National ScienceFoundation grant 21-043469.95/1. The Geological Surveyof Finland and the Academy of Finland funded theexpedition to Wrangel Island by J. Karhu and M. Saarnisto(1997).

REFERENCES

[1] S. L. Vartanyan et al., Radiocarbon 37, 1 (1995).

[2] L. D. Sulerzhitsky and F. A. Romanenko,Ambio28, 251 (1999).

[3] N. J. Shackleton,Quaternary Sci. Reviews 6, 183 (1987).

[4] M. G. Grosswald,Polar Geography and Geology 12, 239 (1988).

[5] M. G. Grosswald, in: World Atlas of Snow and IceResources, ed. V.M. Kotlyakov, Russian Acadamy ofSciences, Moscow, Russia, 385-386 (1997).

[6] J. A. Karhu et al.,Global and Planetary Changes, in press (2001).

[7] D. Lai,Earth and Planet. Sci. Lett. 104, 424 (1991).

[8] P.W. Kubik etal.,Earth and Planet. Sci. Lett. 161, 231 (1998).

[9] J. Masarik and R. C. Reedy,Earth and Planet. Sci. Lett. 136, 381 (1995).

[10] D. A. McManus and J. S. Creager,Quaternary Research 21, 317 (1984).

177

COSMOGENIC ISOTOPE CONSTRAINTS ON EROSION RATES IN THE HIMALAYA

D. Vance (Univ. of London), M. Bickle (Univ. of Cambridge), S. Ivy-Ochs (ETHZ), P.W. Kubik (PSI)

10Be and 26Al concentrations have been measured in quartz separated from river sediment sampled along the upperreaches of the Ganges catchment in the Himalaya. The data, along with Nd isotopic data, demonstrate that theapproach provides a reliable estimate of erosion rates in a mountain catchment, even when erosion rates areextremely rapid (several mm per year).

Erosion is a critical process for the structural and thermalevolution of continental crust involved in collisionalorogens and is probably a prime control on chemicalweathering rates. Quantification of time-integrated,spatially-averaged riverine particulate loads hastraditionally proved difficult, however [1, 2]. Present-dayerosion rates can be derived by direct measurement ofsediment fluxes but only provide an instantaneous snapshotthat may be biased by short-term fluctuations andanthropogenic activity. Time-integrated erosion rates canbe estimated from the volumes of sediments in molassebasins but these do not provide information on spatialvariations of rates within mountain belts. Cosmogenicisotope concentrations of river sediment provide ameasurement of the integrated erosive flux from acatchment above the sampling point [e.g. 1]. Here, wereport estimates of 10Be and 26A1 measurements on quartz inriver bed sediments from the headwaters of the Ganges.

The estimation of erosion rates from the cosmogenicisotope inventory of river sediments depends on severalassumptions that have been detailed elsewhere [2]. Themost serious potential problem for this study is that ofcontamination of 10Be analyses by rain-water derived Bebecause the high erosion rates in the Himalaya result in lowcosmogenic isotope concentrations (1 to 2 x 104 atoms10Be/g). As a result samples of quartz greater than 100 gneed to be rigorously cleaned. Samples in this study havebeen cleaned by a combination of repeated magnetic andheavy liquid mineral separation alternating with etching incold HF until Al concentrations are less than 100 ppm. Ourdata display 26Al/10Be ratios that are within error of theproduction ratio [3]. In addition, duplicate samples in twolocalities have 10Be concentrations within analytical error.We are fortunate in that different geological units withinthe Himalaya have different Nd isotopic compositions andthat the boundaries of these geological units alsocorrespond to major topographic boundaries within themountain belt. These differences in Nd isotopiccomposition are mirrored in the sediment and allow thecalculation of relative sediment yields from different partsof the mountain belt that can be compared with estimatesderived from cosmogenic isotope-derived estimates oferosive fluxes.

The 10Be concentration in the sediment allows calculationof two different erosion rates: 1) an average erosion rate forthe whole catchment above that point; 2) average erosionrates for sub-catchments from subtraction of the fluxesfrom upstream sub-catchments. In one tributary, theAlaknanda, the calculated erosion rates are 1.5 mm/yr in a

sub-catchment draining the Tibetan plateau, 4.1 mm/yr in asub-catchment which drains the steepest topography in themain part of the Himalayan range, and 1.3 mm/yr in alower altitude sub-catchment which drains vegetatedfoothills. These data imply that the single most importantfactor affecting erosion rates in these areas is the slope. Theaverage erosion rate for the entire catchment of a secondtributary, the Bagirathi, is 1.4 mm/yr.

For the Alaknanda, the relative inputs calculated from the10Be analyses (62% from the plateau and mountain belt,38% from the foothills) are close to the estimates of relativefluxes from Nd isotope compositions (54% from theplateau and mountain belt and 46% from the foothills). Thesediment balance between the Alaknanda and Bagirathisub-catchments derived from the 10Be measurements (22%Bagirathi and 78% Alaknanda) is broadly consistent withthe fact that the Bagirathi drains 36% of the total area. The10Be estimates are also consistent with the balancesuggested by the Nd isotopic composition of the twotributaries and that of the river sediment beneath theconfluence. The results from the lowest point sampled inthe Ganges, at Rishikesh where the river leaves the foothillsand enters the Ganges plain, are more complex. The erosiveflux at Rishikesh is less than the combined sum for theBagirathi and the Alaknanda at the confluence of the twotributaries. These discrepancies may result from sedimentstorage in the region just above Rishikesh or be due toanthropogenic disturbances. Calculations suggest thatstorage times of the order of 100 years would be required.

REFERENCES

[1] D.E. Granger et al., J. Geology 104, 249 (1996).

[2] P. Bierman and E.J. Steig, Earth Surface Proc. andLandforms 21,125 (1996).

[3] P.W. Kubik etal.,Earth Planet. Sci. Lett. 161, 231 (1998).

178

DETECTION OF THE 205 YEAR SOLAR CYCLE DURING THE LAST ICE AGE

/. Beer, G. Wagner, R. Muscheler (EAWAG), P.W. Kubik (PSI)

A cycle of 205 years has been found in the l0Be record from the GRIP ice core (Greenland) for the glacial period25'000 to 50'000 years before present. There are clear indications that this cycle is due to solar modulation of thegalactic cosmic radiation.

Cosmogenic radionuclides in ice cores offer the uniqueopportunity to detect solar cycles over time scales ofmillennia. Solar physicists are interested in the long-termbehaviour of the length and the amplitude of the cycles inorder to understand the underlying mechanisms that drivethe solar dynamo [1]. Climatologists on the other handcompare climate records with long records of solarvariability in order to investigate what role solar variabilityplays in climate change [2]. The well known 11-yrSchwabe cycle was found in l0Be ice core records [3] andcould be extended considerably compared to theobservational sunspot record that covers about 400 years.

The l0Be concentration data from the GRIP ice core isbased on ice samples of 55 cm length. In the time intervalfrom 25 to 50 kyr BP, this corresponds to a mean timeresolution of about 45 yr.

The analysis of the l0Be flux record using various spectralanalysis techniques reveals a dominant period of 205 ± 5 yr[4]. The same periodicity was previously found in 14C datameasured in tree rings covering the past 10'000 years [5].

sz

B!ZJ

9-

a3

35 40Age [kyrBP]

45 50

Fig. 1: Upper panel: Bandpass-filtered 10Be flux [(215 yr)"1

< x < (195 yr)"1] over the time period of 25 to 50kyr BP in relative units.Lower panel: paleomagnetic field intensitiesduring the last ice age based on remanencemeasurements of several North Atlantic sedimentcores [6]. The record is low pass filtered (cutofffrequency = 1/3 kyr"1) to obtain a time resolutioncomparable to the envelope of the bandpass-filtered 10Be flux.

How do we know whether this cycle is of solar or climaticorigin? Assuming that the l0Be flux reflects the mean globall0Be production rate [7] and using publishedpaleogeomagnetic field variations [6] the geomagneticmodulation effect on the 205 yr cycle can be investigated.The main trends of the geomagnetic field intensity duringthe last ice age are fairly well known. In the lower panel ofFigure 1 the paleogeomagnetic field intensity is presentedrelative to the level of today. This curve is based onremanence measurements from six sediment cores from theNorth Atlantic [6]. The figure shows in the upper panel thebandpass-filtered l0Be flux with a frequency range between(215 yr)' and (195 yr)"1. During the minimum of themagnetic field at about 38.5 kyr BP the amplitude of the205 yr cycle is significantly higher than during timeperiods, when the geomagnetic field intensity was similarto today's. Taking into account that the amplitude of solaractivity cycles changes with time (e.g. sunspot cycle) [2],the agreement between the envelope of the filter output(upper panel) and the geomagnetic field intensity (lowerpanel) is good. This geomagnetic modulation of theamplitude strongly points to a solar origin of the periodicityof approximately 205 yr in the l0Be flux.

REFERENCES

[1] J. Beer et al., Solar Physics 181, 237 (1998).

[2] J. Beeretal.,

Quaternary Science Reviews 19, 403 (2000).

[3] J. Beer et al., Nature 347, 164 (1990).

[4] G. Wagner et al.,Geophys. Res. Let. 28 (2), 303 (2001).

[5] M. Stuiver et al., Radiocarbon 40,1041 (1998).

[6] C. Laj et al., Philos. Trans. R. Soc. London,Ser. A 358, 1009 (2000).

[7] G. Wagner etal.,Nucl. Instr. and Meth. B172, 597 (2000).

179

AIR-FIRN-TRANSFER OF 10Be ON POLAR ICE SHEETS

A. Stanzick, M. Huke, D. Wagenbach (Univ. Heidelberg), P.W. Kubik (PSI), S. Kipfstuhl (AWI, Bremerhaven)

Recent spatial trends of10Be have been investigated infirnfrom central Greenland and Antarctica. We found that thegeographical variations of mBe in Greenland are controlled by the spatial distribution of the mean snowaccumulation rate. In Antarctica, first measurements indicate a comparable mechanism. Thus, the higher 10Beconcentrations there compared to Greenland seem to be the result of the higher dry deposition fraction relative tothe total deposition flux.

Polar ice sheets constitute important archives for aerosolrelated species allowing ice core based reconstruction ofpaleoclimatic and paleoenvironmental conditions. In thiscontext, the cosmogenic radioisotope 10Be (half-life 1.5 Ma)is an important tool for the reconstruction of solar activityand geomagnetic field variations. However, ice corerecords of 10Be are also influenced by changes of theatmospheric transfer from the source regions (stratosphereand upper troposphere) and by locally varying depositionconditions.

Therefore, we investigated the second influence, the air-firntransfer of sub-micron aerosol species by utilizing thespatial variations of 10Be firn concentrations in large areasof Greenland and Antarctica to simulate the temporallyvarying deposition conditions.

In central Greenland, 18 shallow firn cores comprising theyears 1950-1995 were analyzed for their 10Beconcentrations along two traverses, the North GreenlandTraverse (NGT) [1, 2] and the EGIG (ExpeditionGlaciologique Internationale Groenland) Traverse [3].Supplemented by earlier measurements [4, 5] adjusted tothe above period, a factor of 2-3 for the spatial variation ofthe central Greenland ice sheet was found. As illustrated inFigure 1, the 10Be concentrations in firn show a cleardependence on the inverse accumulation rate. This could beexplained by a simple macroscopic deposition model [1]taking into account different deposition mechanisms (dryand wet) leading to nearly constant means for the drydeposition 10Be flux and the 10Be concentration in freshsnow for the entire central Greenland ice sheet. As a result,the dry deposition fraction of 10Be amounts to ca. 50 % forthe low accumulation area ( -10 cm water equivalent / yr)in the northeast of Greenland and to 35 % for Summit.

To date, in Antarctica, only few 10Be concentrations in thesurrounding areas of the deep drilling locations of Dome C(74°S, 124°E) and DML [6] and at the German Antarcticresearch station Neumayer [7] have been measured. Recent10Be concentrations in firn lie between 1.2 and 5.2104at/gand indicate also a linear correlation between 10Beconcentrations in firn and the inverse accumulation rate.Long-term 10Be observations at the German Antarcticstation Neumayer [7] show similar mean 10Beconcentrations in air relative to Summit, Greenland(performed during the winter campaign 1997/1998) andsimilar scavenging ratios. We therefore propose that thehigher concentrations in Antarctic firn are mainly the resultof lower accumulation rates compared to Greenland leadingto much higher dry deposition fractions in Antarctica.

We expect that ongoing studies focusing on 10Be in firn andair of central Antarctica will confirm these results and willalso give new and more detailed insights into the air-firnrelationship at deep ice-core drill sites.

so

a©

A

•V•

NGT EastNGT WestEGIG EastOthers

-Linear fit

0.0

2.5 5.0 7.5 10.0

1 / Accumulation Rate [a / m.w.e.]

Fig. 1: l0Be average firn concentrations versus inverseaverage snow accumulation rates for NGT, EGIGand earlier measurements [4, 5] for centralGreenland, (m.w.e. = meter water equivalent)

REFERENCES

[1] H. Fischer et al., J. Geophys. Res. 103 D17, 21,927-21,934 (1997).

[2] H. Fischer et al., Geophys. Res. Lett. 25, 1749-1752(1998).

[3] H. Fischer et al., J. Glaciol. 41, 515-527 (1995).

[4] J. Beer et al., Nature 347, 164-166 (1990).

[5] J. Beer et al.: Proc. 18th Int. Cosmic Ray Conf.,Bangalore, India, 9, 317-320, Tata Institute ofFundamental Research, Bombay (1983).

[6] H. Oerter et al., Ann. Glaciol. 30, 27-34 (2000).

[7] D. Wagenbach et al., J. Geophys. Res. 103 D9,11,007-11,020(1998).

180

ICE CORE RECOVERY FROM THE SOUTH INILCHEK GLACIER(KYRGHYZSTAN)

H.-A. Synal (PSI), D. Cecil, J. Green, D. Naftz (US Geological Survey), J. Santos (Univ. Sevilla), J. Beer(EAWAG), K. Kreutz (Univ. Maine), C. Wake (Univ. New Hampshire), Vladimir B. Aizen (Univ. Santa Barbara)

An expedition to the South Inilchek Glacier in the Tien Shan Mountains has been successfully completed. Two deepice cores, 167 m and 162 m in length, could be recovered. At the PSI/ETH AMS facility the concentration of thelong-lived radionuclides 10Be, 36Cl and 129I are now being measured in the first 100 m of one core. To recoverinformation on climate changes the cores are being analyzed both for important trace elements and for their isotopiccomposition.

Ice cores are unique archives preserving precipitation overlong periods of time. In the recent past, such archives havebeen exploited to obtain information on past climatechanges. Most important are the deep polar ice corerecords, which can cover time periods of several hundredthousand years. However, information derived from polarregions cannot necessarily be taken as being representativefor changes that have taken place at mid-latitudes. In orderto better understand the link between observations made atpolar sites and the information derived from regions at mid-latitudes Alpine glacier archives play a key role.

Fig. 1: Drill site at an elevation of 5085 m on the SouthInilchek Glacier in the Tien Shan Mountains(42°N, 80°E). At this location an ice core of 167 mlength was recovered.

The U.S. Geological Survey is conducting a collaborativeisotopic research program on mid-latitude glaciers aroundthe world. Three of the glaciers being studied are theInilchek Glacier located in the Tien Shan Mountains on theborders of Kyrghyzstan, Kazakzstan, and China, theNangpai Gosum Glacier located in the HimalayanMountains of Nepal, and the Upper Fremont Glacierlocated in the Wind River Mountain Range of Wyoming,U.S.A.

During the field campaign 2000 on the South InilchekGlacier, two deep ice cores were recovered. The first core(167 m) has in part (100 m) been prepared in the field forthe analysis of the radionuclides 10Be, j6Cl, 129I and lj7Cs.The ice of the core, allocated to recover the radionuclide

records, was shipped to Zurich and is now being processedfor the analysis with AMS.

The radionuclide records will be used to

• establish time markers of fallout events from thenuclear weapons tests in the 1950's and 1960's,

• reconstruct the fallout distribution of 36C1 at mid-

latitudes,

• evaluate ice accumulation rates,

• establish a time scale in combination with stableisotope and major trace element data,

• reconstruct the anthropogenic increase of ml in centralAsia.

To achieve these tasks the following procedure is applied.For the radionuclides 36C1 and I29I the first 100 meters willbe analyzed with a resolution of 1 m per sample usingaccelerator mass spectrometry. This should correspond to aroughly annual time resolution. It is planned to obtaincomplete information on the past 60 years, reaching backwell into pre-nuclear times. A suite of samples is plannedto recover the pre-nuclear concentration of 36C1. In parallelto the AMS analysis, the samples will be measured withgamma spectrometry to obtain information on the l37Csfallout, which peaked in 1953 and 1963.

PRESENT STATUS

Since a large number of different nuclides will bemeasured, a complex chemical sample preparation protocolhas to be followed. It has been decided to test this protocolwith a first set of samples. For this test, 20 samples havebeen prepared. Starting at a core depth of 10 m, the samplesare taken from every 3rd m. Preparation of the I29I sampleswas completed and the measurements took place inDecember 2000. A preliminary ml profile shows the riseand fall of anthropogenic I29I produced during the nuclearweapons tests. The preparation of the 36C1 samples will befinished by January 2001 and the measurements arescheduled for February 2001. The l37Cs measurements arein progress. Based on the results of the first set of samples,the chemical separation protocol will be optimized. Samplepreparation, AMS and gamma measurements will thenproceed.

181

PALEOMAGNETIC FIELD RECONSTRUCTION BASED ON COSMOGENIC 36C1 INTHE GRIP ICE CORE

G. Wagner, J. Beer, R. Muscheler (EAWAG), C. Laj, C. Kissel (CEA/CNRS), H.-A. Synal (PSI)

A distinct peak has been discovered in the 36Cl data from the GRIP ice core between the Dansgaard Oeschger events6 and 7 at approximately 32 kyr BP. This peak can be attributed to a minimum in the geomagnetic field associatedwith the Mono Lake event. Furthermore the 36Cl peak provides an additional time marker similar to a peak foundearlier corresponding to the Laschamp event at about 40 kyr BP.

The cosmogenic radionuclide 36C1 is produced ininteractions of cosmic ray particles with the Ar atoms of theatmosphere [1,2]. The production varies inversely with theEarth's geomagnetic field intensity, which modulates thecosmic ray flux entering the atmosphere, and it is sensitivemainly to the geomagnetic dipole field and not the non-dipolar components. The radionuclide production rate isespecially sensitive to low geomagnetic fields because itincreases non-linearly for a decreasing geomagnetic field.

Mono Lakeevent

Laschampevent

COEoCD

CD30 32 34 36 38 40 42

Age BP [kyr]

Fig. 1: Upper panel: %C1 concentrations [4] (grey linewith circles) as a function of the time scale ofJohnsen et al. [5]. In the same panel the 8ISO datais shown with the usual numbering scheme for theDansgaard-Oeschger events [7].Lower panel: two paleomagnetic fieldreconstructions based on 36C1 (solid line) and onocean sediments of the North Atlantic [4, 6](dotted line).

Polar ice sheets represent the most direct archive for theproduction of %C1 [e.g. 2, 3]. Here, we present the

reconstruction of the geomagnetic field using thecontinuous 36C1 record in the GRIP ice core of Greenlandfor the time period between 30 and 43 kyr BP [4]. Theupper panel of Figure 1 shows the 36C1 concentrations (greyline with circles) from the GRIP ice core. In the same panelthe 8ISO data (black line, inversely plotted) are shown [5].In the lower panel the solid black line shows thegeomagnetic field reconstruction derived from the 36C1 fluxdata which are low pass filtered with a cutoff frequency of(2000 years)'. The dotted line shows the recently publishedpaleomagnetic field data from deep-sea sediments in theNorth Atlantic [4, 6]. The shaded area around the dottedline depicts the uncertainties (± 2 o). Overall, the twocompletely independent geomagnetic field reconstructionsagree very well. Two prominent minima of thegeomagnetic field intensity, the Mono Lake event and theLachamp event, are present in both data sets.

The fact that the Mono Lake event can be detected in the36C1 data shows that this event is a global phenomenon dueto changes in the geomagnetic dipole field. Furthermore the36C1 peak between Dansgaard Oeschger events 6 & 7 hasseveral important implications. I4C dating of the last ice agehas to be discussed in terms of this newly discovered 36C1peak, because the 36Cldata is a direct measure of the I4Cproduction rate_[l, 2]. Finally, the Mono Lake event visiblein geomagnetic field intensity and 36C1 records provides anadditional time marker to synchronise different climatearchives such as ice and sediment cores.

REFERENCES

[1] J. Masarik and J. Beer, J. Geophys. Res. 104, 12099 -12111 (1999).

[2] G. Wagner et al., Nucl. Instr. Meth. B 172, 597 - 604(2000).

[3] S. Baumgartner et al., Science 279, 1330 -1332(1998).

[4] G. Wagner et al., Earth and Planet. Sci. Lett. 181, 1 -6 (2000).

[5] S. J. Johnsen et al., Tellus 47B, 624 - 629 (1995).

[6] C. Laj et al., Phil. Trans. Royal Soc. Lond. A 358,1009 - 1025 (2000).

[7] P. M. Grootes and M. Stuiver, J. Geophys. Res. 102,26455 - 26470 (1997).

182

COMPOSITION-DEPENDENT SCAVENGING OF °Be BY MARINE PARTICLES

R. F. Anderson, Z. Chase, M. Q. Fleisher, (LDEO, Columbia Univ.), P.W. Kubik (PSI), M. Suter (ETHZ)

Many elements are removed from ocean water by scavenging onto particles. The affinity of particles for eachdissolved species depends on particle composition. Fractionation during scavenging of10Be and230Th varies with theopal/CaCO 3 ratio of particles. J0Be/30Th ratios in marine sediments may therefore serve as a geochemical proxy tohelp assess the role of climate-related changes in ocean ecology as an agent regulating atmospheric CO2.

Ice core records demonstrate a striking correlation betweenthe CO2 content of the atmosphere and Earth's climate overthe past 400,000 years [1]. The efficacy of the ocean'sbiological pump as an agent partitioning CO2 between theatmosphere and the deep sea depends in large part on therelative abundance of calcareous and siliceous (primarilydiatoms) plankton [2]. Consequently, there is a widespreadinterest in reconstructing the structure of planktonicecosystems under past climate regimes to establish the roleof ocean biogeochemistry in regulating atmospheric CO2.Microfossil remains of planktonic organisms are poorlypreserved in marine sediments. Furthermore, preservationis highly variable in time and space, and it cannot beevaluated a priori. It is desirable, therefore, to develop asimple geochemical proxy with which to reconstruct theinitial opal/CaCO, ratio of planktonic material sinking intothe deep sea, prior to any modification by dissolution.

as a partition coefficient, K(N) = (atoms/gparticles)/(atoms/ gseawater). Fractionation among nuclides is expressed as theratio of their K values; F(Th/Be) = K(Th)/K(Be). We findthat F(Th/Be) depends strongly on the opal/CaCO3 ratio ofparticles (Figure 1). The composition dependence of thisfractionation during scavenging is so strong that itoverwhelms much smaller effects due to spatial variabilityin dissolved loBe/230Th ratios. Consequently, the annualaverage paniculate l0Be/23OThxs ("xs" = unsupported by 234U)ratio delivered to sediments is a strong function of thepaniculate opal/CaCO, ratio (Figure 2). We are stillexploring this newly-discovered relationship to determine,if loBe/230Thxs ratios, which are preserved during earlydiagenesis when biogenic materials are regenerated, can beused as a tool to reconstruct past changes in the structure ofplanktonic ecosystems.

10'CD

DQ

LL

10"

(

O

U1

o

oo

on

o

oa

AESOPSEqPac

10u 10'opahcarbonate (%:%)

10'

Fig. 1: Relative affinity of marine particles for scavengingof dissolved 230Th and l0Be, expressed as the ratioof their partition coefficients (F), related to particlecomposition. EqPac = equatorial Pacific at 140°W;AESOPS = Southern Ocean at 170°W.

By comparing the nuclide content of particles collected intime-series sediment traps with the dissolved concentrationof each nuclide in the overlying water column, we haveestablished that the affinity of particles for scavenging ofTh (Be) decreases (increases) with increasing opal contentof particles, whereas the affinity of particles for Th (Be)increases (decreases) with increasing CaCO3 content. Theaffinity of particles for each nuclide (N) can be expressed

10'

EQ.

TS05 1

=°o10

5*10°

o'•c

-10

oo

o-

o • • NE PacificO O AESOPS• • EqPac

10" 10u

opakcarbonate (%:%)

Fig. 2: Annual average loBe/230Thxs ratio in marine particlescollected by sediment traps related to opal/CaCO3

ratio. Individual samples depicted in Fig. 1 havebeen combined to create annual averages.Additional northeastern (NE) Pacific Ocean resultsare from Lao et al. [3].

REFERENCES

[1] J. R. Petit et al., Nature 399,429-436 (1999).

[2] D.M. Sigman and E.A. Boyle, Nature 407, 859-869(2000).

[3] Y. Lao et al., Geochim. Cosmochim. Acta. 57, 205-210(1993).

183

10Be SEDIMENTATION AND TRANSPORT PROCESSES IN THE SOUTH ATLANTIC

M. Christl, C. Strobl, S. Siegle, A. Mangini (Heidelberg Academy of Science), P.W. Kubik (PSI)

The production of 10Be is controlled by the flux of galactic cosmic rays which are (on a millenial timescale)modulated by the shielding of the Earth's magnetic field. If all factors influencing the depositional flux of'°Be intodeep sea sediments can be quantified or estimated by model calculations, it will be possible to obtain an individualrecord of the Earth's magnetic field from 10Be fluxes.

Deep sea sediments were suggested as archives for thereconstruction of the changes of the Earth's magnetic fieldin the past by measuring profiles of the cosmogenicradionuclide10Be[l,2].

The aim of our study is to quantify the factors influencingthe depositional flux of 10Be in the deep sea such as: (i)sediment redistribution (focussing and winnowing), (ii)changes of biological productivity at ocean boundaries, and(iii) glacial to interglacial changes of ocean circulation.Whereas focussing and winnowing can be corrected for bynormalizing to 230Thex, points (ii) and (iii) require modelcalculations. We use a two-box model [3] and aredeveloping a simple multi-box model to investigate thesensitivity of 10Be to changes in water circulation andbioproductivity in the South Atlantic.

First results obtained by modelling the Pacific Ocean showthat the measured 10Be depositional flux (even if normalizedto 2j°Thex) can be up to 3.5 times higher than the productionvalue, if the sediment core is located at an ocean marginarea. On the other hand, the flux in the central Pacific mayamount to 2/3 (230Thex normalized) of the production value.

Figure 1 shows the calculated depositional fluxes of 10Be,231Pa and 230Th in the Pacific Ocean as a function of waterresidence time Tres using the model of [3]. The vertical rainrates (RR) in the open Pacific Ocean are taken fromsediment core data [4], the values for the margin box wereestimated to be tenfold the open ocean value. In the centralPacific Ocean the residence time of water is more than 500years. In this case, the 10Be flux is not very sensitive tochanges in water circulation. The model derivedscavenging factors can be used to correct the (^Th^normalized) 10Be depositional flux. Our results applied tothe Holocene data of [4] match within the uncertainty theproduction value of 1.2-106 Atoms/cm2 yr [5].

In the present study we selected core 1089B to investigatel0Be sedimentation and transport processes on a highresolution time scale in the Southern Ocean. During OceanDrilling Program Leg 177 sediments in the southeastAtlantic sector of the Southern Ocean were sampled tostudy the paleoceanographic history of the Antarctic regionon short (millennial) to long (Cenozoic) time scales. Sevensites were drilled along a north-south transect across theAntarctic Circumpolar Current [6]. Site 1089 is locatednorth of the Agulhas Ridge at a water depth of 4620 m. Theaverage sedimentation rate over the last 450 thousand yearsis about 15 cm/ka providing a high temporal resolution. Inthe future we will apply our models to the South AtlanticOcean with its even more complex hydrography.

Fa/Fp(Pa) / Fa/Fp(Th)

Fa/Fp(Be) / Fa/Fp(Th)

- - - Fa/Fp(Th)

1.00 •

0.95 -

0.90

0.85

0.80 -

0.70 •

0.65 -

0.60 -

OPEN OCEAN

•

, / _ ^ . _ "

MarginRR= 15

O p e n R R - 1.5

- - - Fa/Fp(Th)

Fa/Fp(Pa) / Fa/Fp(Th)

Fa/Fp(Be) / Fa/Fp(Th)

•• V ——^^"—•' v — - "

Fig. 1: Model calculations applied to the Pacific Ocean.The following parameters were used:volumes: (margin / open ocean) = 0.1bioproductivity: vertical rain rate [g/cm2 kyr] in

margin box =15open ocean box =1.5

X-Axis: water residence time in open ocean boxY-Axis: calculated depositional flux / production:

for 230Th: Fa/Fp(Th)forlcke:Fa/Fp(Be)/Fa/Fp(Th)for231Pa:Fa/Fp(Pa)/Fa/Fp(Th)

REFERENCES

[1] L. Lao et al., EPSL 113,173 (1992).

[2] M. Frank et al., EPSL 149, 121 (1997).

[3] T. Asmus et al., Marine Geology 159, 63 (1999).

[4] B. Schwarz, PhD thesis Univ. Heidelberg (1996).

[5] M. Monaghan et al.,Earth Planet. Sci.Lett 76, 279 (1985/86).

[6] Proc. of the Ocean Drilling Program 177, (1999).

184

°Be AND Pb-TIME-SERIES OF A Fe-Mn CRUST FROM THE TASMAN BASIN,SOUTH-WESTERN PACIFIC

T. van de Flierdt, M. Frank, A.N. Halliday (ETHZ), P.W. Kubik (PSI)

So36 63 KD, a ferromanganese crust from the southwestern Pacific Ocean, was analyzed for 10Be by AMS and forlead isotopes by MC-ICPMS. The preliminary 10Be derived growth rate of the crust is 1.8 mm/Ma. The Pb isotopetime series reflects an isotopic variations of the ambient deep water caused by changes of the sources of weatheringinput and ocean circulation over the past ~ 22 Ma.

The isotopic composition of Pb in the ocean is influencedby continental weathering, hydrothermal inputs andcirculation of water masses. It varies within and betweenthe oceans, consistent with its short residence time inseawater (50 years in the Atlantic and up to 200-400 yearsin the Pacific [1]). Ferromanganese crusts, which havegrown by direct precipitation of Mn and Fe hydroxidesfrom ambient deep water, incorporate its Pb isotopiccomposition and record variations over millions of years.

Fe-Mn crust 63 KD was recovered during cruise Sonne 36from the Tasman Basin in the southwestern Pacific Ocean(28°34.0'S, 163°00'E) in a water depth of 1700 m. Aprofile of this 35 mm thick crust was taken to obtain achronology based on the decay profile of cosmogenic 10Be(tl/2= 1.5 Ma). A growth rate of 1.8 mm/Ma is derived fromthe 10Be data of the uppermost 16.5 mm of the crust. Below16.5 mm depth, the 10Be data do not show an exponentialdecay which points to rapid growth. This needs to beverified by normalization to stable 9Be for the samesamples. These measurements will be made in the nearfuture.

o1.00

0.10-

0.014 8 12 16 20 24 28 32

depth [mm]36

Fig. 1: 10Be data for Fe-Mn crust 63 KD from the TasmanBasin, southwestern Pacific. For the time series(Fig. 2) the growth rate of 1.8 mm/Ma has beenextrapolated to the base of the crust.

A higher resolution record was sampled and analyzed forvariations in Pb isotope composition by MC-ICPMS(Figure 2). The external reproducibility was obtained byrepeated measurements of the NBS 981 standard. Allmeasured sample ratios were normalized to the acceptedvalue for the standard [2]. Figure 2 shows the time series ofthe 207Pb/206Pb ratio in comparison to other crusts from thePacific Ocean. The time series of crust 63 KD shows a

general increase in the 207Pb/206Pb ratios from -19 Ma to thepresent. This general increase has not been continuous.Two steps where the Pb isotope ratios increased abruptlyare observed at 7.1 Ma and 2.9 Ma.

0.839

0.838

0.836 H

£ 0.834

0.832-

0.830

0.837

-0.835

- 0.833

-0.831

0 20

Fig. 2: 207Pb/206Pb time series of crust 63 KD measured byMC-ICPMS (data points are shown as filleddiamonds). For comparison 3 profiles of crustsfrom the central Pacific are shown, which weremeasured by LA-MC-ICPMS [3] and by MC-ICPMS [4].

The 207Pb/206Pb ratios of crust 63 KD are generally lowerthan for crusts in the equatorial Pacific. This is due to thestronger influence of Circum Antarctic water masses,which have a 207Pb/206Pb ratio of ~ 0.828 before entering thePacific Basin. During the past ~ 6 Ma the Pb isotope timeseries shows trends comparable with the equatorial Pacificdata sets, which points to similar input sources. Prior to 6Ma the difference between crust 63 KD and the equatorialPacific was much larger. This gives evidence for thedominance of local input sources at these locations andsuggests a weaker water mass exchange and mixingbetween 19 and 6 Ma. To validate these interpretations atime series of Nd isotopes will be measured. Nd has alonger residence time in the ocean and is therefore lessinfluenced by local sources.

REFERENCES

[1] B. K. Schaule and C. C. Patterson,Earth Planet. Sci. Lett. 54, 97 (1981).

[2] W. Todt et al., Gephys. Monogr. 95, 429 (1996).

[3] J.N. Christensen et al., Science 277, 913 (1997).

[4] K. David et al., Chem. Geol. (2001), in press.

185

10Be / 7Be RATIOS AT THE HIGH-ALPINE SITE JUNGFRAUJOCH

C. Schnabel (Univ. Bern & ETHZ), L. Tobler, P. W. Kubik, M. Schwikowski (PSI), H. W. Gdggeler (Univ. Bern &PS1)

The particle bound atmospheric concentrations of the cosmogenic radionuclides 7Be and 10Be have been measuredat the Jungfraujoch (3580 m a.s.l). The isotopic ratio l0Be /1 Be can be used as a probe for the intrusion of relativelyold stratospheric air masses into the troposphere.

Stratospheric-tropospheric exchange (STE) is one of thefactors controlling the budgets of ozone, water vapour andother substances in the lower stratosphere and thetroposphere. Cosmogenic radionuclides, which areproduced by cosmic ray particles in the atmosphere, couldprovide valuable information on STE. A stratosphericintrusion into the troposphere gives rise to an increase of7Be and ozone concentrations as well as to a decrease ofrelative humidity in the affected tropospheric area.However, a maximum in 7Be can also result from othermeteorological processes. If such a process takes place,10Be will be affected to the same extent as 7Be.Consequently, Raisbeck et al. [1] proposed to use theisotopic ratio 10Be/7Be as a probe for atmospheric transportprocesses. Raisbeck et al. [1] and Dibb et al. [2] both foundhigher 10Be/7Be ratios in the lower stratosphere than in theupper one. They explained this by a relatively slowdownward transport of air masses from the upperstratosphere (7Be decays faster than 10Be). These higher10Be/7Be ratios in the lower stratosphere, which clearlyexceed 10Be/7Be ratios of approx. 2.2 measured by Dibb etal. [2] for tropospheric air masses, can be used to determineintrusions of relatively old stratospheric air into thetroposphere.

In the framework of the EU project STACCATO (Influenceof Stratosphere-Troposphere Exchange in a ChangingClimate on Atmospheric Transport and OxidationCapacity), particle bound 7Be and 10Be are collected onglass fibre filters (using a HIVOL air sampler) at theJungfraujoch with a time resolution of 48 h by the NABELnetwork [3]. Half of the filters are used to measure the 7Beactivity (T1/2 = 53.12 d) through its characteristic y-radiation in a well-type Ge-detector and the 10Beconcentration using accelerator mass spectrometry at thePSI/ETH facility.10Be/7Be ratios measured on filter samples collected at theJungfraujoch between Feb. 19 and April 4, 2000 are shownin Fig. 1.

Date

Fig. 1: Particle bound 10Be/7Be ratios in air filter samplesfrom the Jungfraujoch (3580 m a.s.l.).

The very high 10Be/7Be ratios at the end of February 2000indicate a stratospheric intrusion, which has beenconfirmed by ozone and relative humidity data. Luder [4]also measured a high monthly mean isotopic ratio inprecipitation at the Jungfraujoch in March 1984. However,in that case the uncertainty of the isotopic ratio was verylarge and a minimum in 7Be concentration suggested dustcontamination as explanation. We tend to exclude thisexplanation for our case, since Ca concentrations, measuredas a dust indicator, did not show enhanced concentrations[5] and since a maximum in 7Be concentration was found.The slow decrease of the very high 10Be/7Be ratios shouldbe due to additional intrusion events during March 2000,which were reported by other groups taking part in theSTACCATO project measuring high ozone and 7Beconcentrations and low relative humidity at the Zugspitze(Germany) [6], the Sonnblick (Austria) [7] and MonteCimone (Italy) [8]. However, for this period severalsamples were combined obscuring the temporal finestructure. In terms of ozone concentrations alone, anintrusion event that took place from March 20 to March 22,2000 was more pronounced at least at the Zugspitze [6] andat Monte Cimone [8] than that one at end of February.Therefore, the period from March 19 to March 26, 2000has been chosen for a detailed case study. Both Be isotopeswill be measured with the same time resolution as the filtercollection (2 days).

ACKNOWLEDGMENT

This study is part of the EU research project STACCATO(EVK2-CT1999-00050) and is funded by the Bundesamtfur Bildung und Wissenschaft (BBW) of Switzerland. Thesampling and the delivery of the filters by the EMPA(operator of the NABEL network) are highly appreciated.

REFERENCES

[1] G.M. Raisbeck etal.,Geophys. Res. Lett. 8, 1015 (1981).

[2] J.E. Dibb et al., J. Geophys. Res. 99, 12855 (1994).

[3] NABEL Luftbelastung 1999,BUWAL SRU-316 (2000).

[4] R. Luder, Lizentiatsarbeit, Universitat Bern (1986).

[5] S. Henning, pers. comm.

[6] T. Trickl and E. Scheel, pers. comm.

[7] M. Mandl, pers. comm.

[8] P. Cristofanelli, pers. comm.

186

129I IN RAIN WATER NEAR ZURICH

C. Schnabel (ETHZ & Univ. Bern), S. Szidat (Univ. Hannover & Univ. Bern & PSI), H.-A. Synal (PSI), J.M. Lopez-Gutierrez (Univ. Sevilla), J. Beer (EAWAG)

I291 concentrations in precipitation at Diibendorf/Ziirich have been determined with monthly resolution duringalmost three years in the mid 1990s. The results confirm that annual mean I29I concentrations in precipitation incentral Europe have remained about constant since the late 1980s. Some evidence for a substantial contribution ofthe gaseous emissions from nuclear fuel reprocessing plants to 129I in the precipitation in central Europe ispresented.

129I is a long-lived (T1/2=15.7 Ma) radionuclide whoseconcentrations in the environment have been elevated byseveral orders of magnitude due to human activities, mainlyby emissions from nuclear fuel reprocessing plants. After anearly continuous increase of 129I concentrations from 1950to the mid 1980s, which is reflected in an ice core from theSwiss Alps [1], the environmental 129I concentrations incentral Europe seemed to have remained stable in the 1990s[2]. One of the main goals of the present work is to verifythis observation using precipitation samples fromSwitzerland.

Our data show a large month-to-month variability of afactor of about 100 between the lowest and the highestmonthly 129I atom concentration. A similar variation wasobserved by Krupp and Aumann in rainfall in Germany [3].A comparison of our annual mean 129I concentrations withliterature data for central Europe from the late 1980s to thelate 1990s is shown in Fig. 1. It confirms the statement ofSzidat et al. [2] that 129I concentrations in precipitation incentral Europe have not increased further since the late1980s.

The question, whether gaseous or liquid emissions from thetwo major European nuclear fuel reprocessing plants, LaHague and Sellafield, dominate 129I in precipitation, isaddressed in detail by Schnabel et al. [4]. Here, just a fewaspects of this question are briefly discussed. Although theliquid emissions exceeded the gaseous ones by a factor of30 from 1991-1996, an upper limit of only 1.37 kg isestimated for the mass of 129I that is transferred annuallyfrom the sea to the atmosphere due to a low iodineevaporation from the marine into the atmosphericcompartment. This upper limit can preliminarily becompared to the 6.5 kg 129I emitted per year directly intothe atmosphere during the same period [4].

Another approach to address the question is to compare thetime dependence of 129I concentration in precipitation withthose of the gaseous and liquid releases from the twoplants. The respective data are also shown in Fig. 1. Thefact that the gaseous releases correlate much better with the129I concentrations in central Europe suggests a substantialcontribution of gaseous releases to 129I in the precipitation.However, we were not yet able to explain quantitatively thelarge month-to-month scatter in the concentrations and cantherefore not definitely answer the question about thedominant 129I source.

Liquid emissions (1988=1)

Gaseous emissions (1988=1)

A Bachhuber & Bunzl, Bavaria [5]

o Dijbendorf / Zurich [This work]

~O~ Krupp & Aumann, South. Germany[3]

-O- Szidat et al., Lower saxony, inland[6]

1988 1990 1998 2000

Fig. 1: Liquid and gaseous 129I emissions from La Hagueand Sellafield normalized to their 1988 values (forreferences see [4]). One scale unit corresponds to50.5 kg 129I liquid and to 6.89 kg gaseousemissions. 129I concentrations in precipitation arenormalized to the 1988 value of Bachhuber andBunzl [5]. One scale unit equals 3.75-109 atoms129I/kg. A vertical line indicates a range of annualmeans from different locations.

ACKNOWLEDGMENT

The preparation of some of the samples by S. Bollhalder-Liick (EAWAG) is gratefully acknowledged.

REFERENCES

[1] M.J.M. Wagner etal.,Nucl. Instrum. Meth. B 113, 490 (1996).

[2] S. Szidat et al.,Nucl. Instrum. Meth. Phys. Res. B172, 699 (2000).

[3] G. Krupp, D. C. Aumann,

J. Environ. Radioactivity 46, 287 (1999).

[4] C. Schnabel et al., subm. to Radiochim. Acta, (2001).

[5] H. Bachhuber and K. Bunzl,J. Environ. Radioactivity 16, 77 (1992).

[6] S. Szidat, Ph.D. thesis, University Hannover (2000).

187

PROSPECTS OF 129I AS AN ENVIRONMETAL TRACER

S. Szidat (Univ. Hannover & Univ. Bern & PSI), T. Ernst, R. Michel (Univ. Hannover),C. Schnabel (Univ. Bern & ETHZ), H.-A. Synal (PSI), J.M. Lopez-Gutierrez (Univ. Sevilla)

In a systematic study, the distribution of the long-lived radionuclide ]29I together with the only stable iodine isotope,127I, was investigated in precipitation, surface and shallow groundwaters in Lower Saxony, Germany. Estimatedresidence times of iodine in the surface soil zone surpass water residence times by one to three orders of magnitude.

The natural abundances of I have changed by severalorders of magnitude as a consequence of civil and militaryuse of nuclear fission. The anthropogenic signal of 129I canbe used to study environmental processes [1-3]. Due to thebiophilic character of iodine, l29yl21\ isotopic ratios mayshow the significance of organic matter in the surface soilzone for the iodine transport [3].

In a systematic study, we analyzed 127I and 129I in open-field precipitation, surface and shallow groundwaters inLower Saxony, Northern Germany (Tab. 1). The area wasdivided into four regions, namely I (NW): North Seacoastal area, II (SW): Northern German lowlands, III (SE):Harz Mountains area, and IV (NE): Valley of the riverElbe. 127I was measured with ICP-MS at University ofHannover, 129I with accelerator mass spectrometry (AMS)at the PSI/ETH tandem facility. For details of samplepreparation, measurements and quality assurance see [2-4].

Table 1: 129i/127I in several Lower Saxonian natural watersfrom 1997-1999 as geometric means with standarddeviations of the observed values.

Sample Region12V27i[1010]

Precipitation

(open-field)

I

II

III

IV

10

9

8300

6200

4600

3700

16001400210016003800210022001400

Surfacewater

Groundwater

I

II

III

IV

I

II

III

IV

12

1211

12

3

4

4

5

460 !

220 !60 !

120 !

ioo !220 !30 !

2 +

490240130804030

12060

5030

120802815102

The deposition of atmospherical " I is the most importantsource in the upper terrestrial environment in centralEurope. A survey of central European precipitation of thelast 20 years [2-4] indicated a dramatic increase of 129I/127Iratios until the middle 1980s, followed by a nearly constantvalue of about 6.5-10"7 until now.

When using these precipitation values as an input functionin a simple exponential model [5] for the transfer of iodinein the surface of a catchment, one can estimate mean iodine

residence times in the surface soil. In this model, meantransition times rare calculated according to

T = -t

In (1 -Hit))

with the time t of constant input and the fraction H(t) of theinput signal that is observed in the investigatedcompartment, t characterizes the time span between thesampling time of a sample and 1986, the interpolatedbeginning of the constant input; H(t) is given as the ratio of129I/127I in the examined sample and the mean precipitationvalue of 6.5-10"7. r i s calculated for every single sampleand geometric means are given in Tab. 2 with standarduncertainties of the mean.

Table 2: Mean iodine residence times in surface soil zonesand characteristic time constants of water transfer intogroundwater with standard uncertainties.

Sample

Surface

water

Ground

water

Region

III

III

IV

III

III

IV

^iodine

[a]biased by sea water

360 !1290 !670 !830 !360 !

2700 !40000 !

5050

2101801601302101708070

1000700

4600021000

712

9

19

tritium

[a]

———

-

± 5± 1

± 4

± 2

This modelling suggests a horizontal and vertical iodinetransport delayed by one to three orders of magnitudecompared to water movements. Surface and ground waterresidence times agree within their expanded uncertainties(95 %) except for region IV where an impermeable zone atthe ground water sampling site is assumed.

REFERENCES

[1] A. Schmidt et al., Sci. Total Environ. 223, 131 (1998).

[2] S. Szidat et al.,

Nucl. Instrum. Meth. B 172, 699 (2000).

[3] S. Szidat, Ph.D. Thesis, Univ. Hannover (2000).

[4] S. Szidat et al., Kerntechnik 65,160 (2000).[5] A. Zuber in: ed P. Fritz, J. C. Fontes, Handbook of

environmental istope geochemistry,Vol. 2B, p. 1 Elsevier, Amsterdam (1986).

188

BERYLLIUM LIQUID ALLOY ION SOURCES FOR FOCUSED ION BEAMIMPLANTATION

R. Mtihle (ETHZ, PSI), M. Dobeli (PSI)

AuBe and AuBeSi liquid alloy ion sources have been developed for focused ion beam implantation. The alloys wereproduced by melting in an evacuated quartz ampoule followed by quenching in water. The melting property of thealloys were investigated by pyrometric temperature measurements. We have investigated the source currentstability, the current-voltage characteristics, and the mass spectrum as a function of the source current.

Liquid metal ion sources (LMIS) and especially liquid alloyion sources (LAIS) have found extensive use as ion sourcesof high brightness in focused ion beam (FIB) systems witha wide range of applications such as microfabrication bymicromachining and deposition, focused ion beamlithography and ion implantation as well as microanalysisof materials [1]. The development of LAIS for Be and Siare important for the implantation in compoundsemiconductors, as for example GaAs and GaP.

The alloys were prepared by melting the constituents inevacuated quartz ampoules, followed by a water quench atroom temperature. The aim was to prepare eutecticcompositions, namely Au795Be2l5 with a liquidustemperature of 580 °C [2] and Au70Bel5Sil5 with a liquidustemperature of 610 °C [3]. The indices stand for atomicpercent. An ion source consists of a tungsten needleemitter, which is wetted with the alloy, and an extractionelectrode with a hole diameter of 1 mm at a distance of 0.6mm from the needle tip. Both sources were investigated ina time-of-flight spectrometer [4]. Their characteristics weredetermined as a function of the temperature, which wasmeasured from outside of the vacuum chamber with anoptical two-colour pyrometer.

Table 1: Ion flux fractions (IFF) in % of the AuBe andAuBeSi LAIS at a source current of 5 |iA.

Ion

Be++

Be+

srsr

Au+ +

Au+

Au2+

Au3+

IFF / %

AuBe

2.0

0.6

1.5E-2

3.0E-3

17.6

66.1

7.1

3.1

IFF / %

AuBeSi

1.9

1.6

4.6

1.7

2.9

72.1

5.3

1.1

The AuBe LAIS could be operated in a stable way at asource current as low as 0.54 uA for a heating current of2.8 A and a temperature of 610 °C. The measured ion fluxfractions of the main peaks at a source current of 5 |JA are

given in Tab. 1. The fraction of Be ions is lower thanexpected. Nevertheless, the source is suitable for ionimplantation purposes because of the low operationtemperature and its high stability. A small percentage of Siions was found in the mass spectrum of the AuBe LAISdue to reactions between beryllium and the quartz ampoule.

The AuBeSi LAIS could be operated in a stable way at asource current as low as 1 LIA at a heating current of 2.4 Aand a temperature of 630 °C. The mass spectrum for asource current of 5 \xA is shown in Fig. 1 and thecorresponding ion flux fractions for this source current aregiven in Tab. 1. The summation over all peaks in the massspectrum gives the following ion flux fractions in atom-%for Au/Be/Si: 93.1/6.8/0.1 for the AuBe LAIS and86.6/6.5/6.9 for the AuBeSi LAIS.

1.E+06

1.E+05 -

c 1.E+04 -

1.E+03 -

1.E+02

1.E+01500 2500 3000

Fig. 1: Mass spectrum of the AuBeSi liquid alloy ionsource for a source current of 5 |iA, obtained witha time-of-flight spectrometer [4].

REFERENCES

[1] J. Melngailis, J. Vac. Sci. Technol. B 5,469 (1987).

[2] Phase Diagrams of Binary Gold Alloys,ed. H. Okamoto and T. B. Massalski (ASM,Metals Park, OH, USA) (1987).

[3] D. F. Reich et al., Microelectron. Eng. 5, 171 (1986).

[4] R. Miihle et al.,J. Phys. D: Appl. Phys. 32,161 (1999).

189

A GePd LIQUID ALLOY ION SOURCE FOR FOCUSED ION BEAM IMPLANTATION

R. Muhle (ETHZ, PSI), A. Spiegel (EPFL), M. Dobeli (PSI)

A GePd liquid alloy ion source has been developed for selective surface activation by focused ion beamimplantation. The alloy was produced by melting in an evacuated quartz ampoule followed by quenching in water.The melting property of the alloy was investigated by pyrometric temperature measurements. We have investigatedthe source current stability, the current-voltage characteristics, and the mass spectrum as a function of the sourcecurrent.

New pathways are now explored to sensitize single crystalsurfaces for selective chemical or electrochemicalnanogrowth or nanostructuring by focused ion beamimplantation [1]. This necessitates the development of ionsources for the required ion species. Our first experimentshave been made with Ga ions from a Ga liquid metal ionsource (LMIS) and Au ions from a AuSi liquid alloy ionsource (LAIS). For the implantation of Pd ions a GePdLAIS was developed using a eutectic alloy with 36 atomicpercent palladium and a liquidus temperature of 725 °C [2].

The alloy was prepared by melting the constituents in anevacuated quartz ampoule followed by a water quench atroom temperature. This procedure ensures that the alloysolidifies congruently and is therefore nearly homogeneous.The ion source consists of a tungsten-needle emitter, whichis wetted with the alloy, and an extraction electrode with ahole diameter of 1 mm at a distance of 0.6 mm from theneedle tip. The source was investigated in a time-of-flightspectrometer [3]. Its characteristics were determined as afunction of the temperature, which was measured with anoptical two-colour pyrometer.

The GePd LAIS could be operated in a stable way at asource current as low as 0.86 iiA for a heating current of2.7 A and a temperature of 750 °C. The mass spectrum isshown in Fig. l . Flux fractions of selected ions are listed inTab.l for a source current of 5 |iA.

Tab. 1: Ion flux fractions

Ion

IFF / %

Pd+

28.9

Pd++

1.0

(IFF) of the first peaks

Ge+

14.4

Ge++

19.9

GePd+

14.5

in Fig. 1.

GePd++

9.3

Each peak in the mass spectrum is composed from severalsub-peaks due to the many isotopes of Ge and Pd.Germanium has 5 isotopes and palladium 6. This results in13 peaks for the GePd+ and GePd++ molecular ions (seeFig. 2 for the GePd++ molecules). As for the case of AuGeand CoGe LAIS, Ge, ions could not be observed. Thesummation over all peaks in the mass spectrum yields 51.4at-% Ge and 48.6 at-% Pd. This composition and the ionflux fractions change with source temperature and sourcecurrent. The energy width of the different peaks was alsodetermined as a function of source current.

At a source current of 5 \iA the Pd+ peak has an relativeintensity of nearly 30 %. In conclusion, the developedGePd liquid alloy ion source is well suited for theimplantation of Pd with the focused ion beam.

1.E+05

1.E+04 -

1.E+03

1.E+02

1.E+01

500 1000

channel

1500 2000 2500

Fig. 1: Mass spectrum of the GePd liquid alloy ion sourcefor a source current of 5 |iA, obtained with thetime-of-flight spectrometer.

200 400 600channel

800 1000 1200

Fig. 2: Mass spectrum of the GePd++ molecules from theGePd liquid alloy ion source for a source currentof 2.5 jxA, obtained with the time-of-flightspectrometer.

REFERENCES

[1] A. Spiegel et al., This annual report.

[2] H. Okamoto, J. of Phase Equilibria 13, 410 (1992).

[3] R. Miihle et al.,J. Phys. D: Appl. Phys. 32,161 (1999).

190

NANOSTRUCTURED MATERIALS BY SELECTIVE SURFACE ACTIVATION USINGFOCUSED ION BEAM IMPLANTATION

A. Spiegel (EPFL), R. Miihle (ETHZ, PSI), M. Dobeli (PSI), P. Schmuki (Univ. ofErlangen-Nurnberg, Germany)

Ion beam induced surface damage on semiconductors may promote local electrochemical reactions which can beused to deposit material selectively at the damaged sites. Cu and Au have been elctrochemically deposited onfocused ion beam written patterns on Si wafers with a spatial resolution of <300 nm. The sub-100 nm range iswithin reach.

The aim of this work is to explore new pathways to achieveselective chemical or electrochemical nanogrowth ornanostructuring of materials on locally sensitized singlecrystal silicon surfaces. In earlier work [1,2] this effect hasbeen used to locally dissolve and porosify the substrate byoxidation. Sensitization is carried out by a direct writingprocess using the focused ion beam (FIB) system installedat the Laboratory for Micro- and Nanotechnology (PSI). Atactivated surface locations a subsequent chemical orelectrochemical reaction will be triggered selectivelyleading to the nanosize material or functionality. Fig. 1shows current-voltage curves of an intact and a damagedsilicon surface in a Cu containing electrolyte. The onset ofCu deposition causes a current increase (electrons have toget from the Si surface to the Cu2+ ions in the electrolyte inorder to reduce it to metallic Cu, which will thenprecipitate). The point where the current increase begins iscalled 'deposit formation potential' (DFP;). It can be seeneasily that the DFP is shifted to higher potentials E for theFIB-damaged surface; we call this shifted DFP for defectsurfaces DFPd. We assume that this shift is due to afacilitated Schottky barrier breakdown at the defect sites.

EXPERIMENTAL DETAILS

For ion implantation we used the FIB system installed inthe LMN cleanroom at PSI.

1 0 s

10""

10"7

10"8

^ i

intactd efect

I I I

j >

DFP

SelectiveDeposition

D

i , , , i , , , i

ik

-8000 -6000 -4000 -2000E vs SCE [mV]

Fig. 1: Current-voltage behavior of intact and damaged Si(idealized).

We have been working with Au-Si (for Au2+ ions) and Gaion sources built inhouse. Different acceleration voltages(23 and 30 keV) as well as implant doses (1011 - 1017

ions/cm2) have been used. These parameters were varied inorder to determine their influence on the electrochemicalbehavior. All electrochemical experiments were carried outusing a standard three-electrode setup (sample as workingelectrode, Pt counter electrode, standard calomel referenceelectrode SCE) under potentiostatic or -dynamic conditions.

Different electrolytes were used (0.1 M CuSO4 + 0.05 MH2SO4 and 0.01 M CuSO4 + 0.05 M H2SO4 for Cudeposition and 0.01 M KAu(CN)2 + 1 M KCN for Audeposits) under varying electrochemical conditions(potentiostatic with varying exposure times and potentialsand potentiodynamic with varying scanning velocity andstart as well as end potentials).

RESULTS AND CONCLUSION

We have been able to selectively deposit both gold andcopper in the sub-micrometer range on FIB-induced surfacedamage patterns.

Fig. 2:

. ' . ( :

Au deposited on FIB-written damage template(optical micrograph).

Fig. 2 shows the sample surface after electrochemicaltreatment. It can be seen clearly that Au deposition hasoccurred. Subsequent analysis by electron microscopy andatomic force microscopy showed that the Au crystalliteshave an average size of roughly 100 nm and that thesmallest structures were in the 300 nm range. In the nearfuture we will further optimize the process in order toachieve higher resolution (<100 nm) as well as morehomogeneously distributed particles (especially when usingCu electrolytes).

REFERENCES

[1] P. Schmuki et al., Phys. Rev. Lett. 80, 4060 (1998).

[2] A. Spiegel et al.,J. Electrochem. Soc. 147, 2993 (2000).

191

LIST OF PUBLICATIONS

LABORATORY FOR PARTICLE PHYSICS

R-87-12J. Arnold, B. van den Brandt, M. Daum, Ph. Demierre, M. Finger, M. Finger,Jr., J. Franz, N. Goujon-Naef,P. Hautle, R. Hess, A. Janata, J. A. Konter, H. Lacker, C. Lechanoine-Leluc, F. Lehar, S. Mango, D. Rapin, E.'Rossle,P. A. Schmelzbach, H. Schmitt, P. Sereni, M. Slunecka, A. Teglia, B. VuaridelMeasurement of spin observables in neutron-proton elastic scatteringPart I: Correlation parametersEur. Phys. J. C 17, 67 (2000).

J. Arnold, B. van den Brandt, M. Daum, Ph. Demierre, M. Finger, M. Fingerjr., J. Franz, N. Goujon-Naef,P. Hautle, R. Hess, A. Janata, J. A. Konter, H. Lacker, C. Lechanoine-Leluc, F. Lehar, S. Mango, D. Rapin, E.'Rossle,P. A. Schmelzbach, H. Schmitt, P. Sereni, M. Slunecka, A. Teglia, B. VuaridelMeasurement of spin observables in neutron-proton elastic scatteringPart II: Rescattering parametersEur. Phys. J. C 17, 83 (2000).

R-87-13M. Planinic, D. Androic, G. Backenstoss, D. Bosnar, T. Dooling, M. Furic, P. A. M. Gram, N. K. Gregory, A. Hoffart,C. H. Q. Ingram, A. Klein, K. Koch, J. Khler, B. Kotlinski, M. Kroedel, G. Kyle, A. Lehmann, A. O. Mateos, K. Michaelian,T. Petkovi, R. P. Redwine, D. Rowntree, N. Simicevic, R. Trezeciak, H. Ullrich, H. J. Weyer, M. Wildi, and K. E. WilsonPion absorption on 4-He into the ppdfinal state.Phys. Rev. C 61 054604,1 (2000).

R-96-05M. Daum, M. Janousch, P.-R. Kettle, J. Koglin, D. Pocanic, J. Schottmuller, C. Wigger, Z. G. ZhaoKARMEN Time Anomaly: Search for a neutral particle of mass 33.9 MeV in pion decayPhys. Rev. Lett. 85, 1815 (2000).

R-97-02D. F. Anagnostopoulos, G. Borchert, D. Chatellard, J.-P. Egger, D. Gotta, M. Hennebach, P. Indelicate,Y.W. Liu, B. Manil, N. Nelms and L. M. SimonsMass of the charged pionActa Phys. Pol. B 31, 2219 (2000).

T. Siems, D. F. Anagnostopoulos, G. Borchert, D. Gotta, P. Hauser, K. Kirch, L. M. Simons, P. El-Khoury,P. Indelicate, M. Augsburger, D. Chatellard, J.-P. EggerFirst direct observation of Coulomb explosion during the formation of exotic atomsPhys. Rev. Lett. 84, 4573 (2000).

R-97-03Ch. Brian§on, V. B. Brudanin, J. Deutsch, V. Egorov, T. Filipova, M. Kudoyarov, V. Lobanov, T. Mamedov,A. Pasternak, R. Prieels, A. Salamatin, Yu. Shitov, Ts. Vylov, I. A. Yutlandov, Sh. Zaparov.The spin-neutrino correlation revisited in 28Si muon-capture : A new determination of the inducedpseudosaclar coupling gp/gaNucl. Phys. A671, 647 (2000).

R-97-05P. Kammel, A. Adamczak, V. A. Andreev, D. V. Balin, T. Case, K. M. Crowe, J. Deutsch, P. U. Dick, A. Dijksman,J. Egger, A. A. Fetisov, V. A. Ganzha, J. Govaerts, F. J. Hartmann, W. D. Herold, V. I. Jatsoura, A. G. Krivshich, E. M. Maev,O. E. Maev, V. E. Markushin, J. Martino, C. Petitjean, G. E. Petrov, R. Prieels, S. M. Sadetsky, G. N. Schapkin, R. Schmidt,W. Schoeps, W. Schott, G. G. Semenchuk, A. A. Vorobyov, N. I. Voropaev,Precision measurement of /ip capture in a hydrogen TPCNucl. Phys. A 663/664,911c (2000).

192

R-98-02B. Gartner, P. Ackerbauer, W.H. Breunlich, M. Cargnelli, P. Kammel, R. King, B. Lauss, J. Marton, W. Prymas,J. Zmeskal, C. Petitjean, M. Augsburger, D. Chatellard, J.-P. Egger, T. von Egidy, F. J. Hartmann, A. Kosak,M. Mühlbauer, F. Mulhauser, L.A. Schaller, L. Schellenberg, H. Schneuwly, Y.-A. Thalmann, S. Tresch, A. WerthmüllerGround state muon transfer from deuterium to 3He and 4HePhys. Rev. A 62, 012501 (2000).

R-98-03R. Pohl, F. Biraben, C.A.N. Conde, C. Donche-Gay, T. W. Haensch, F. J. Hartmann, P. Häuser, V. W. Hughes,O. Huot, P. Indelicate, P. Knowles, F. Kottmann, Y.-W. Liu, F. Mulhauser, F. Nez, C. Petitjean, P. Rabinowitz,J.M.F. dos Santos, L.A. Schaller, H. Schneuwly, W. Schott, L. M. Simons, D. Taqqu, F. Trehin, J. F. C. A. Veloso,Experiment to measure the Lamb shift in muonic hydrogenHyperfine Interactions 127, 161 (2000).

Z-91-01P. E. Garrett, H. Baltzer, M. Bertschy, D. G. Burke, M. Deleze, S. Drissi, C. Guenther, J. Jolie,J. Kern, H. Lehmann, S. J. Mannanal, J. Manns, U. Mueller, J. P. Vorlet, N. Warr, T. Weber,Nuclear levels in 190/r studied with the 192Os(p,3nry) and 192Os(d,4ne~) reactionsNucl. Phys. A 662, 235 (2000).

Z-95-02J. Hoszowska, J.-Cl. Dousse, D. Castella, D. Corminboeuf, J. Kern, Y.-P. Maillard and P.-A. Raboud,Influence of the chemical environment on the Si KL x-ray satellite spectra of transition metal suicidesbombarded by 43 MeY neon ionsJ. Phys. B : At. Mol. Phys. 33, 3165 (2000).

Z-95-06 and Z-97-04J. Groeger, J. Jolie, R. Kreucken, C.W. Beausang, M. Caprio, R. F. Casten, J. Cederkall, J. R. Cooper, F. Corminboeuf,L. Genilloud, G. Graw, C. Guenther, M. De Huu, A.I. Levon, A. Metz, J. R. Novak, N. Warr, T. Wendel,Nuclear structure of196Au: More evidence for its supersymmetric descriptionPhys. Rev. C 62, 064304 (2000).

Z-95-10J. Rzadkievicz, D. Chmielewska, T. Ludziejewski, P. Rymuza, Z. Sujkowski, D. Castella, D. Corminboeuf,J.-Cl. Dousse, B. Galley, Ch. Herren, J. Hoszowska, J. Kern, M. Polasik, M. Pajek,Double K-shell ionization in collisions of fast ions with mid-Z atomsActa Phys. Pol. B 31, 501 (2000).

Z-96-04L. Genilloud, H.G. Borner, F. Corminboeuf, Ch. Doll, S. Drissi, M. Jentschel, J. Jolie, J. Kern, H. Lehmann, N. Warr,Study of the vibrational nucleus 100Ru by the 98Mo(a,2n 7) and "Rufn,^ ReactionsNucl. Phys. A 662, 3 (2000); A 669,407 (2000).

Z-97-02M. Kavcic, M. Budnar, A. Mühleisen, P. Pelicon, Z. Smit, M. Zitnik, D. Castella, D. Corminboeuf,J.-Cl. Dousse, J. Hoszowska, P.-A. Raboud, K. Tökesi,L-shell ionization in near-central collisions of heavy ions with low Z targetsPhys. Rev. A 61, 052711-1 (2000).

R-89-01 : PSI, PIBETA COLLABORATIONE. Frlez et al.,Cosmic muon tomography of pure cesium iodide calorimeter crystalsNucl. Instrum. Meth. A 440, 57 (2000).

BROOKHAVEN AGS, E865 COLLABORATIONR. Appel et al.An Improved limit on the rate of the decay K+ —>• 7r + / i + e~Phys. Rev. Lett. 85, 2450 (2000).

193

R. Appel et al.Search for lepton flavor violation in K+ decays into a charged pion and two leptonsPhys. Rev. Lett. 85, 2877 (2000).

J. Egger, W. Herold, H. Kaspar, H. WeyerH. Maetal.,A new measurement of the rare decay K+ —> n+/x+ n~Phys. Rev. Lett. 84, 2580 (2000).

CERN, L3 CollaborationM. Acciarri et ah,A. J. Barczyk, K. DeitersSearch for charged Higgs bosons in e+e~ collisions at centre-of-mass energies up to 202 GeVPhys. Lett. B 496, 34 (2000).

Measurement of the Wpair production cross section and Wdecay branching fractions in e+e~ interactions at yfs = 189 GeVPhys. Lett. B 496, 19 (2000).

Measurement of Bose-Einstein correlations in e+e~ —> W+W~ at yfs &189 GeVPhys. Lett. B 493, 233 (2000).

Search for anomalous couplings in the Higgs sector at LEPPhys. Lett. B 489,102 (2000).

Measurement of the W+W~j cross section and direct limits on anomalous quartic gauge boson couplings at LEPPhys. Lett. B 490, 187 (2000).

Search for a Higgs boson decaying into two photons in e+e~ interactions at y /s= 189 GeVPhys. Lett. B 489,115 (2000).

Determination ofj/Z interference in e+e~ annihilation at LEPPhys. Lett. B 489, 93 (2000).

Production of single W bosons at yfs = 189 GeV and measurement ofW+W~/y gauge couplingsPhys. Lett. B 487, 229 (2000).

QCD studies in e+e~ annihilation from 30 GeV to 189 GeVPhys. Lett. B 489, 65 (2000).

Search for manifestations of new physics in fermion pair production at LEPPhys. Lett. B 489, 81 (2000).

Search for anomalous ZZ*j and ZJJ couplings in the process e+e~ —>• Zj at LEPPhys. Lett. B 489, 55 (2000).

Measurements of the bb production cross section and forward-backward asymmetry at centre-of-mass energiesabove the Zpole at LEPPhys. Lett. B 485, 71 (2000).

Search for an invisibly decaying Higgs boson in e+e~ collisions at yfs = 183 GeV to 189 GeVPhys. Lett. B 485, 85 (2000).

Measurement of the photon structure function at high Q2 at LEPPhys. Lett. B 483, 373 (2000).

Measurement of the lifetime of the tau leptonPhys. Lett. B 479, 67 (2000).

Inclusive S + and E° production in hadronic Z decaysPhys. Lett. B 479, 79 (2000).

194

Measurements of cross sections and forward-backward asymmetries at the Z resonance and determination ofelectroweak parametersEur. Phys. J. C 16, 1 (2000).

Search for charginos with a small mass difference with the lightest supersymmetric particle at ^/s = 189 GeVPhys. Lett. B 482, 31 (2000).

Measurement of the e+e~ —>• Z77 cross section and determination of quartic gauge boson couplings at LEPPhys. Lett. B 478, 39 (2000).

Hard-photon production and tests ofQED at LEPPhys. Lett. B 475,198 (2000).

Measurement of the running of the fine-structure constantPhys. Lett. B 476, 40 (2000).

Measurement ofhadron and lepton-pair production at 130 GeV < ^fs < 189 GeV at LEPPhys. Lett. B 479,101 (2000).

Direct observation of longitudinally polarized W+W~ bosonsPhys. Lett. B 474, 194 (2000).

Measurement of the probability ofgluon splitting into charmed quarks hadronic Z decaysPhys. Lett. B 476, 242 (2000).

CERN, CPLEAR COLLABORATIONA. Apostolakis et al.,P. Bargassa, F. Blanc, P.-R. Kettle, T. Nakada, O. WiggerA detailed description of the analysis of the decay of neutral kaons to n+ir~ in the CPLEAR experimentEur. Phys. J. C 18, 41 (2000).

A. Apostolakis et al.,P. Bargassa, F. Blanc, P.-R. Kettle, T. Nakada, O. WiggerMeasurement of the energy dependence of the form-factor f(+) in K0(e3) decay,Phys. Lett. B 473, 186 (2000).

DESY, HI COLLABORATIONC. Adloffetal.,S. Egli, R. Eichler, K. Gabathuler, J. Gassner, R. HorisbergerA search for excited fermions at HERAEur. Phys. J. C 17, 567 (2000).

Measurement of elastic electroproduction of<j> mesons at HERAPhys. Lett. B 483, 360 (2000).

Elastic photoproduction ofJ/'ip and Y mesons at HERAPhys. Lett. B 483, 23 (2000).

Measurement ofdijet cross-sections in photoproduction and photon structurePhys. Lett. B 483, 36 (2000).

Search for compositeness, leptoquarks and large extra dimensions in eq contact interactions at HERAPhys. Lett. B 479, 358 (2000).

Investigation of power corrections to event shape variables measured in deep inelastic scatteringEur. Phys. J. C 14, 255 (2000).

Measurement of neutral and charged current cross-sections in positron-proton collisions at large momentum transferEur. Phys. J. C 13, 609 (2000).

195

Measurement of transverse energy flow in deep inelastic scattering at HERAEur. Phys. J. C 12, 595 (2000).

Elastic electropwduction of p mesons at HERAEur. Phys. J. C 13, 371 (2000).

Measurement ofdijet cross-section at low Q2 and the extraction of an effective parton density for the virtual photonEur. Phys. J. C 13, 397 (2000).

D. Pitzl et al.,M. Biddulph, R. Eichler, K. Gabathuler, J. Gassner, R. Horisberger, H. NiggliThe HI Silicon vertex detectorNucl. Instrum. Meth. A 454, 334 (2000).

THEORY GROUPC. Alexandrou, R. Rosenfelder and A. W. Schreiber,Non-perturbative mass renormalization in quenched QED from the worldline variational approachPhys. Rev. D 62,085009 (2000).

A. Borici,Chiral fermions and multigridPhys. Rev. D 62, 017505 (2000).

A. Borici,Lanczos approach to the inverse square root of a large and sparse matrixJ. Comput. Phys. 162, 123 (2000).

A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,O(a) corrections to e+e~ —> WW —> 4 fermions (+/y): first numerical results from RACOONWWPhys. Lett. B 475, 127 (2000).

A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,Electroweak radiative corrections to e+e~ —>• WW —> 4 fermions in the double pole approximation: the RACOONWWapproachNucl. Phys. B 587, 67 (2000).

A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,W-pair production at future e+e~ colliders: precise predictions from RACOONWWEPJdirect Vol.2, C 4,1 (2000), DOI 10.1007/sl010500c0004

A. Denner, S. Dittmaier, M. Roth and D. Wackeroth,Fourfermion production with RACOONWWJ. Phys. G 26, 593 (2000).

S. Diirr and J. Kambor,Two point function of strangeness carrying vector currents in two loop chiral perturbation theoryPhys. Rev. D 61, 114025 (2000).

S. Diirr and S. R. Sharpe,IR divergence and anomalous temperature dependence of the condensate in the quenched Schwinger modelPhys. Rev. D 62, 034506 (2000).

S. Diirr,Topologically unquenched QCD: prospects from an explorative study in two-flavor two-dimensional QEDPhys. Rev. D 62, 054502 (2000).

V. S. Fadin, L. N. Lipatov, A. D. Martin and M. Melles,Resummation of double logarithms in electroweak high-energy processesPhys. Rev. D 61, 094002 (2000).

196

M. C. Fujiwara et ah, V. E. Markushin,Resonant formation ofD/iT molecules in deuterium: an atomic beam measurement ofmuon catalyzed DT fusionPhys. Rev. Lett. 85, 1642 (2000).

K. Junker, V. A. Kuz'min, A. A. Ovchinnikova and T. V. Tetereva,The sensitivity ofmuon capture to the ratios of nuclear matrix elementsPhys. Rev. C 61, 044602 (2000).

P. Kammel et al., V. E. Markushin,Precision measurement of/ip capture in a hydrogen TPCNucl. Phys. A 663,911 (2000).

V. E. Markushin,The radiative decay $ —>• JTTTT in a coupled channel model and the structure of /o (980)Eur. Phys. J. A 8, 389 (2000).

M. Melles,Mass gap effects and higher order electroweak Sudakov logarithmsPhys. Lett. B 495, 81 (2000).

M. Melles,The static QCD potential in coordinate space with quark masses through two loopsPhys. Rev. D 62, 074019 (2000).

R. Rosenfelder,Coulomb corrections to elastic electron-proton scattering and the proton charge radiusPhys. Lett. B 479, 381 (2000).

S. von Rotz, M. P. Locher and V. E. Markushin,Higher order two-step mechanisms in nucleon-antinucleon annihilation and the OZI ruleEur. Phys. J. A 7, 261 (2000).

197

LABORATORY FOR ASTROPHYSICS

M. Fivian, J. Bialkowski, W. Hajdas, R. Henneck, A. Mchedlishvili,P. Ming, K. Thomsen, A. Zehnder, G. Hurford, D. Curtis, D. Pankow,Calibrating the aspect systems of the high-energy solar spectroscopic imager (HESSI)SPIE Proc. 4012,518 (2000).

K. Thomsen, J. Bialkowski, F. Burri, M. Fivian, W. Hajdas,A. Mchedlishvili, P. Ming, J. Welte, A. Zehnder, and The HESSI Team,Calibrating the imaging system of the high-energy solar spectroscopic imager (HESSI)SPIE Proc. 4012,524 (2000).

St. E. Boggs, R. P. Lin, B. R. Dennis, N. W. Madden, P. von Ballmoos, K. Thomsen,G. Hurford, K. C. Hurley, D. M. Smith, P. Jean, J. Kndelseder, R. M. Milan,The Cyclone Hard X-Ray ObservatorySPIE Proc. 4110,166 (2000).

K. A. Moldosanov, R. Henneck, A. M. Skrynnikov, V. A. Kashirin,V. P. Makarov, G. A. Kobtsov, M. A. Samsonov and L. S. Kim,Reflectivities of light-absorptive coatings within visible wavelength rangeSPIE Proc., San Diego 2000.

E. C. Kirk, Ph. Lerch, J. Olsen, A. Zehnder, H. R. OttImpact of the absorber and absorber/trap interface quality on the resolving power ofSTJ x-ray spectrometersNucl. Instrum. Meth. A 444, 201 (2000).

J. Olsen, E. C. Kirk, K. Thomsen, B. van den Brandt, Ph. Lerch, L. Scandella,A. Zehnder, S. Mango, H. R. Ott, M. Huber, G. C. Hilton, J.M. MartinisFirst steps towards small arrays ofMo/Au microcalorimetersNucl. Instrum. Meth. A 444, 253 (2000).

Th. Nussbaumer, Ph. Lerch, E. Kirk, A. Zehnder R. Fiichslin, P. F. Meier, H. R. OttQuasiparticle diffusion in tantalum using superconducting tunnel junctionsPhys. Rev. B 61, 9719 (2000).

M. Audard, M. Giidel, J. J. Drake, V. L. Kashyap,Extreme-ultraviolet flare activity in late-type starsAstrophys. J. 541, 396 (2000).

A. J. Beasley, M. Giidel,VLBA imaging of quiescent radio emission from UXArietisAstrophys. J. 529, 961 (2000).

J. C. Brown, S. Krucker, M. Giidel, A. O. Benz,Mechanisms for dynamic coronal mass supply via evaporative solar" Micro-Events"Astron. Astrophys. 359, 1185 (2000).

C. Erd, M. Audard, A. J. den Boggende, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam,L. Dubbeldam, M. Giidel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. Paerels,J. R. Peterson, A. P. Rasmussen, I. Sakelliou, J. Spodek, K. Thomsen, C. de Vries, A. Zehnder,In-flight calibration of the XMM-Newton reflection grating spectrometersSPIE 4140, 13(2000).

E. J. Gaidos, M. Giidel, G. A. Blake,The faint young sun paradox: An observational test of an alternative solar modelGeophys. Res. Lett. 27, 501 (2000).

198

J. W. den Herder, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, A. J. den Boggende,L. Dubbeldam, C. Erd, M. Güdel, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. Paerels,I. Sakelliou, A. P. Rasmussen, J. Spodek, K. Thomsen, C. P. de Vries,Description and performance of the reflection grating spectrometeron board of XMM-NewtonSPIE 4012, 102 (2000).

M. R. Pestalozzi, A. O. Benz, J. E. Conway, M. Güdel,VLBI observations of two single dMe stars: Spatial resolution and astrometryAstron. Astrophys. 353, 569 (2000).

K. W. Smith, I. A. Bonnell, J. P. Emerson, T. Jenness,NGC 1333/IRAS 4: A multiple star formation laboratoryMon. Not. R. Astron. Soc. 319, 991 (2000).

F. De Paolis, G. Ingrosso, Ph. Jetzer, M. RoncadelliGamma ray emission from a baryonic dark haloNew Journal of Physics 2, 12 (2000).

D. Puy, L. Grenacher, Ph. Jetzer, M. SignoreAsphericity of galaxy clusters and the Sunyaev-ZeV dovich effectAstron. Astrophys. 363, 415 (2000).

Ph. JetzerGamma rays from the galactic haloProceedings of the TAUP99 Meeting,Paris, France, september 1999,Nucí. Phys. B 87 (Proc. Suppl.), 430 (2000).

L. Desorgher, E. Flückiger, P. Bühler and A. Zehnder,Modelling of the outer electron belt flux dropout and losses during magnetic storm main phaseAdvances in Space Research 26, 167 (2000).

Desorgher, L., Bühler, P., Zehnder, A., and Flückiger, E.Simulation of the outer radiation belt electron flux decrease during the March 26, 1995, magnetic stormJ. of Geophys. Res. 105 A 9, 21211 (2000).

Harboe-Sorensen, R., Guerre, FX., Constans, H., van Dooren, J., Berger, G., Hajdas W.,Single event transient characterisation of analog IC'sfor ESA's satellites1999 Fifth European Conference on Radiation and Its Effects on Components and Systems,RADECS 99 xxviii, 573 (2000).

W. Hajdas, J. Bialkowski, U. Wyser, L. Adams, A. Mohammadazdeh, R. Nickson, B. O'Connell,Sensitivity of the SREM RADFET dosimeters for STRV-1C to various proton and gamma radiation environments1999 Fifth European Conference on Radiation and Its Effects on Components and Systems,RADECS 99 xxviii, 110 (2000).

199

LABORATORY FOR MUON SPIN SPECTROSCOPY

RA-86-07D. G. Fleming, M. Shelley, D. J. Arseneau, M. Senba, J. J. Pan, E. Roduner, S. R. KreitzmanHfcs of the CQHQMU radical in NaY zeolitesPhysica B 289-290,603 (2000).

B. Beck, E. Roduner, H. Dilger, P. Czarnecki, D. G. Fleming, I. D. Reid, C. J. RhodesReorientational dynamics of aza-cyclohexadienyl radicals in pyridinium tetrafluoroboratePhysica B 289-290, 607 (2000).

RA-90-02F. N. Gygax, G. Soit, A. Amato, I. S. Anderson, M. Pinkpank, A. Schenck, T. J. UdovicLight hydrogen isotope / i + in Se and a-ScHx solid solutionsPhys. Rev. B 61, 168 (2000).

RA-90-03A. M. Mulders, C. T. Kaiser, P. C. M. Gubbens, A. Amato, F. N. Gygax, M. Pinkpank, A. Schenck,P. Dalmas de Réotier, A. Yaouanc, K. H. J. Buschow, F. Kayzel, A. MenovskyPositive muon diffusion and localization sites in GdNi§Physica B 289-290,451 (2000).

RA-90-05D. E. MacLaughlin, R. H. Heffner, G. J. Nieuwenhuys, P. C. Canfield, A. Amato, C. Baines,A. Schenck, G. M. Luke, Y. Fudamoto, Y. J. UemuraMuon spin relaxation and nonmagnetic Kondo state in PrInAg-2Phys. Rev. B 61, 555 (2000).

D. E. MacLaughlin, R. H. Heffner, J. E. Sonier, G. J. Nieuwenhuys, R. Chau, M. B. Maple,B. Andraka, G. M. Luke, Y. Fudamoto, Y. J. Uemura, A. Amato, C. BainesMuon spin rotation and non-Fermi liquid behavior in UCu^PdPhysica B 289-290,15 (2000).

D. E. MacLaughlinDisorder-Driven Non-Fermi-Liquid Behavior in Heavy-Fermion SystemsJ. Phys. Soc. Jpn. 69, Suppl. A, 33 (2000).

J. E. Sonier, R. H. Heffner, D. E. MacLaughlin, G. J. Nieuwenhuys, O. Bernai, R. Movshovich,P. G. Pagliuso, J. Cooley, J. L. Smith and J. D. ThompsonH+ Knight shift measurements in Uo.965Tho.o3sBei3 single crystalsPhys. Rev. Lett. 85, 2821 (2000).

J. E. Sonier, R. H. Heffner, D. E. MacLaughlin, J. L. Smith, J. Cooley, G. J. NieuwenhuysAnomalous Knight shift in the superconducting state o/UBei3Physica B 289-290,20 (2000).

RA-90-16A. Schenck, N. K. Sato, G. Solt, D. Andreica, F. N. Gygax, M. Pinkpank, A. AmatoStudy of the positive muon Knight shift in UNÍ2AI3: evidence for a tetravalent UA+-state and crystalline electric field splittingEur. Phys. J. B 13, 245 (2000).

A. Amato, D. Andreica, F. N. Gygax, M. Pinkpank, N. K. Sato, A. Schenck, G. SoltMuon tunneling around a ring-shaped orbit in UNÍ2AI3Physica B 289-290,447 (2000).

200

RA-90-17U. Himmer and E. RodunerThe addition reaction ofX to O2 (X = Mu, H, D): Isotope effects in intra- and intermolecular energy transferPCCP 2, 339 (2000).

RA-90-18E. Schreier, M. Ekström, O. Hartmann, R. Wäppling, G. M. Kalvius, F. J. Burghart,S. Henneberger, A. Marelius, A. KratzerInternal fields in magnetically ordered dysprosium, holmium and erbiumPhysica B 289-290, 240 (2000).

E. Schreier, M. Ekström, O. Hartmann, R. Wäppling, G. M. Kalvius, F. J. Burghart,A. Kratzer, L. Asch, F. J. LitterstHigh pressure ßSR studies on elemental rare earth metalsPhysica B 289-290, 244 (2000).

RA-92-01A. Lappas, K. Prassides, F. N. Gygax, A. SchenckMagnetic and structural instabilities in the stripe-phase region of La\^^BaQ.r25-ySryCu0i (0< y< 0.1)J. Phys.: Condens. Matter 12, 3401 (2000).

RA-93-02C. J. RhodesDuplicity ofthiyl radicals in toxicology: Protector and Foe in:Toxicology of the Human Environment - the Critical Role of Free RadicalsC. J. Rhodes, ed., Taylor and Francis, London, 2000, p285.

C. J. Rhodes, T. C. Dintinger, C. A. ScottDynamics of cyclohexadienyl radicals in zeolite X, by longitudinal field muon relaxationMagn. Reson. Chem. 38, 62 (2000).

C. J. Rhodes, T. C Dintinger, C. A. ScottSorption of benzene in cation-exchanged zeolite X, as measured by muon spin relaxation (LF-MuSRx)Magn. Reson. Chem. 38,729 (2000).

P. F. Kelly, A. Soriano-Rama, P. T. Wood, I. D. Reid, T. A. Claxton, C. J. Rhodes,U. A. JayasooriyaMuonium addition to sulfur-nitrogen chainsMagn. Reson. Chem. 38, S65 (2000).

C. J. RhodesRadiotracer studies of free radicals using muonium (the Second Hydrogen Radioisotope)Prog. React. Kinet. Mech. 25, 219 (2000).

RA-93-05H.-H. Klauss, W Wagener, M. Hillberg, W Kopmann, H. Waif, F. J. Litterst, M. Hücker and B. BüchnerFrom antiferromagnetic order to static magnetic stripes: The phase diagram of (La, Eu)2-xSrxCu04Phys. Rev. Lett. 85, 4590 (2000).

RA-93-06F. L. Pratt, S. J. Blundell, Th. Jestädt, B. W Lovett, R. M. Macrae, W. HayesMuon radical states in some electron donor and acceptor moleculesMagn. Reson. Chem. 38, S27 (2000).

B. W Lovett, S. J. Blundell, F. L. Pratt, Th. Jestädt, W. Hayes, S. Tagaki, M. KurmooSpin fluctuations in the spin-Peierls compound MEM(TCNQ)2 studied using ¡iSRPhys. Rev. B 61, 12241 (2000).

201

F. L. Pratt, S. J. Blundell, A. Husmann, I. M. Marshall, B. W. Lovett, W. Hayes, S. L. Lee, C. Äger, F. Y. Ogrin,T. Sasaki, S. Endo, N. Toyota, K. Kanoda, V. N. Laukhin, E. Laukhina, I. Watanabe, K. NagamineBEDT-TTF superconductors studied by ßSRPhysica B 289-290,396 (2000).

B. W. Lovett, S. J. Blundell, F. L. Pratt, Th. Jestädt, W. Hayes, S. Tagaki, M. KurmooVery low temperature muon relaxation in an organic spin-Peierls compoundPhysica B 289-290,145 (2000).

S. J. Blundell, A. Husmann, Th. Jestädt, F. L. Pratt, I. M. Marshall, B. W. Lovett, M. Kurmoo, T. Sugano, W. HayesMuon studies of molecular magnetismPhysica B 289-290,115 (2000).

RA-93-10M. Schefzik, R. Scheuermann, L. Schimmele, A. Seeger, D. Herlach, O. Kormann, J. Major, A. RockA vacancy-related muon species in crystalline siliconPhysica B 289-290,511 (2000).

M. Schefzik, L. Schimmele, A. Seeger, D. Herlach, O. Kormann, J. Major, A. RockOxygen-related muon species in crystalline siliconPhysica B 289-290, 521 (2000).

RA-93-12F. L. Pratt, S. J. Blundell, Th. Jestädt, B. W. Lovett, A. Husmann, I. M. Marshall, W. Hayes,A. Monkman, I. Watanabe, K. Nagamine, R. Martin, A. B. Holmes¡iSR of conducting and non-conducting polymersPhysica B 289-290,625 (2000).

RA-94-01F. N. Gygax, M. Pinkpank, A. Schenck, M. Decroux, 0. FischerßSR spectroscopy on superconducting Chevrel phase compoundsPhysica B 289-290, 381 (2000).

RA-94-03G. J. Nieuwenhuys, N. G. Patil, H. Noijons, D. G. Tomuta, D. E. MacLaughlin, R. H. Heffner, A. AmatoDetermination of the muon site in URh^Ge-iPhysica B 289-290, 228 (2000).

RA-94-04F Y. Ogrin, S. L. Lee, C. Ager, C. M. Aegerter, E. M. Forgan, S. H. Lloyd, P. G. Kealey, T. Riseman, R. Cubitt, G. WirthVortex studies in heavy-ion irradiated BÍ2.i§SrittCaCu2O%+$ probed by ßSR and small-angle neutron scatteringPhysica B 289-290, 355 (2000).

RA-94-07Eve M. Martin, E. Schreier, G. M. Kalvius, A. Kratzer, O. Hartmann, R. Wäppling,D. R. Noakes, K. Kröp, R. Ballou, J. DeportesMagnetic properties ofGdMn^from ßSRPhysica B 289-290,265 (2000).

RA-94-08F J. Burghart, W Potzel, G. M. Kalvius, E. Schreier, G. Grosse, D. R. Noakes, W Schäfer,W. Kockelmann, S. J. Campbell, W. A. Kaczmarek, A. Martin, M. K. KrauseMagnetism of crystalline and nanostructured ZnFe^O^Physica B 289-290,286 (2000).

202

RA-94-14G. Solt, C. Baines, V. S. Egorov, D. Herlach, U. ZimmermannObservation ofdia- and paramagnetic domains in beryllium and white tin by muon spin rotation spectroscopyJ. Appl. Phys. 87, 7144 (2000).

G. Solt, V. S. Egorov, C. Baines, D. Herlach, U. ZimmermannEvidence for Condon domains in white tin with two de Haas-van Alphen periodsPhys. Rev. B 62, R11933 (2000).

RA-95-03M. Pinkpank, A. Amato, D. Andreica, F. N. Gygax, H. R. Ott, A. SchenckDynamic magnetic properties of GdBaiCuzO^x as function of the oxygen contentPhysica B 289-290,295 (2000).

M. Pinkpank, A. Amato, D. Andreica, F. N. Gygax, H. R. Ott, A. SchenckTime effects induced by the muon point charge in the antiferromagnetically ordered phase of HoBa^Cu^OiPhysica B 289-290,316 (2000).

RA-95-10V. Yu. Pomjakushin, A. M. Balagurov, A. A. Zakharov, F. N. Gygax, A. Schenck, A. Amato, D. HerlachConcomitance of magnetic ordering and superconductivity in low oxygen mobility La^CuO^+x single crystalPhysica C 341-348,2153 (2000).

RA-95-15A. Yaouanc, P. Dalmas de Reotier, F. N. Gygax, A. Schenck, A. Amato, C. Baines, P. C. M. Gubbens,C. T. Kaiser, A. de Visser, R. J. Keizer, A. Huxley, A. A. MenovskyEvidence for a two component magnetic response in UPt^Phys. Rev. Lett. 84, 2702 (2000).

P. Dalmas de Reotier, A. Yaouanc, P. C. M. Gubbens, C. T. Kaiser, A. M. Mulders, F. N. Gygax, A. Schenck,A. Amato, C. Baines, A. de Visser, R. J. Keizer, P. Bonville, P. J. C. King, A. Huxley, A. A. MenovskyMagnetism and superconductivity of UPt% by muon spin techniquesPhysica B 289-290,10 (2000).

RA-95-17D. Herlach, T. Albrecht, C. Biihrer, D. M. Herlach, D. Platzek, J. Reske, K. Maier[iSR on Coi-xPdx, an alloy exhibiting ferromagnetism in the liquid phasePhysica B 289-290,232 (2000).

D. Herlach, C. Kottler, T. Wider, K. MaierHydrogen embrittlement of metalsPhysica B 289-290,443 (2000).

RA-95-18A. Schenck, R. J. Keizer, A. de Visser, A. Amato, D. Andreica, F. N. Gygax,M. Pinkpank, P. Estrela, M. J. Graf, A. A. Menovsky, J. J. M. FranseMuon localization site in U(Pt,Pd)zPhysica B 289-290,455 (2000).

A. de Visser, M. J. Graf, P. Estrela, A. Amato, C. Baines, D. Andreica, F. N. Gygax, A. SchenckMagnetic quantum critical point and superconductivity in UPt^ doped with PdPhys. Rev. Lett. 85, 3005 (2000).

RA-96-07T. Blasius, Ch. Niedermayer, D. M. Pooke, D. R. Noakes, C. E. Stronach, E. J. Ansaldo, A. Golnik, C. BernhardLow-temperature vortex structures of the mixed state inPhysica B 289-290,365 (2000).

203

RA-96-09C. J. Rhodes, T. C. Dintinger, H. A. Moynihan, I. D. ReidSpin-labelling with the Second Hydrogen Radioisotope: Radicals formed from squalene by muonium additionFree Radical Research 33, 75 (2000).

C. J. Rhodes, T. C. Dintinger, H. A. Moynihan, I. D. ReidRadiolabelling studies of free radical reactions using muonium (the Second Hydrogen Radioisotope):Evidence of a direct antioxidant role for vitamin K in repair of oxidative damage to lipidsMagn. Reson. Chem. 38, 646 (2000).

M. C. R. Symons, C. J. Rhodes, I. D. ReidEvidence for the solvation of hydrogen atoms by waterMagn. Reson. Chem. 38, 823 (2000).

C. J. Rhodes, T. C. Dintinger, C. S. Hinds, H. Morris, I. D. ReidHydrogen radioisotopic labelling studies using muonium:Properties ofthiyl radicals potentially relevant to cellular membrane damageMagn. Reson. Chem. 38, S49 (2000).

RA-96-10D. Andreica, N. Cavadini, H. U. Giidel, F. N. Gygax, K. Kramer, M. Pinkpank, A. SchenckMuon-induced break-up of spin-singlet pairs in the double-chain compound KCuClzPhysica B 289-290,176 (2000).

RA-96-11P. Schobinger-Papamantellos, N. P. Duong, K. H. J. Buschow, D. Andreica, F. N. Gygax, M. Pinkpank, A. SchenckComparative study of the magnetic properties ofTbFe^Alg, and YFe^Als compoundsPhysica B 289-290,277 (2000).

RA-97-01B. Heisel, R. Hempelmann, O. Hartmann, R. Wappling[iSR-experiments on proton-conducting oxidesPhysica B 289-290,487 (2000).

RA-97-03E. V. Raspopina, A. M. Balagurov, V. Yu. Pomjakushin, V. V. Sikolenko, A. V. Gribanov, A. Amato, A. SchenckMagnetic structure ofU{Pd\-xFex)-2Ge-2 studied by muSR: comparison with neutron diffraction dataPhysica B 289-290,282 (2000).

V. Yu. Pomjakushin, A. M. Balagurov, E. V. Raspopina, V. V. Sikolenko, A. V. Gribanov,A. Schenck, A. Amato, U. Zimmermann, I. S. LyubitinModulated magnetic structure of U(Pd\-xFex)2Ge2 studiedby /iSRJ. Phys.: Condensed Matter 12, 7969 (2000).

RA-97-04V. N. Duginov, K. I. Gritsaj, A. Amato, C. Baines, D. Herlach, V. Yu. Pomjakushin, U. Zimmermann,A. N. Ponomarev, I. A. Krivosheev, A. A. Nezhivoy, A. V. Gribanov, V. N. Nikiforov, Yu. D. SeropeginStudy of the magnetic properties of CezPd2oSie compoundPhysica B 289-290,43 (2000).

RA-97-06Z. Salman, A. Keren, P. Mendels, A. Scuiller, M. VerdaguerQuantum fluctuations of the magnetization in high spin molecules - a [iSR studyPhysica B 289-290,106 (2000).

RA-97-12K. W. Klamut, B. Dabrowski, R. Dybzinski, Z. Bukowski, A. Shengelaya, R. Khasanov, S. Dottinger, H. KellerMuon-spin rotation study of the magnetic correlations in La2-xCai+xCu2Oe+s superconductorsJ. Appl. Phys. 87, 5558 (2000).

204

RA-97-15R. M. Macrae, I. D. Reid, J. U. von-Schütz, K. NagamineOrder-disorder transition in anthracene/tetracyanobenzene probed by muonium-substituted radicalsPhysica B 289-290,616 (2000).

RA-97-17F. N. Gygax, P. Vajda, D. Andreica, M. Pinkpank, A. SchenckPositive muons in rare-earth dideuteridesPhysica B 289-290, 273 (2000).

RA-97-19I. M. Marshall, S. J. Blundell, A. Husmann, Th. Jestädt, B. W. Lovett, F. L. Pratt,J. Lago, P. D. Battle, M. J. RosseinskySpin dynamics in high oxidation state iron oxides displaying colossal magnetoresistancePhysica B 289-290, 89 (2000).

A. Husmann, S. J. Blundell, Th. Jestädt, B. W. Lovett, I. M. Marshall, F. L. Pratt,L. E. Spring, P. D. Battle, M. J. RosseinskyEffect of dimensionality on the magnetic properties of Ruddlesden-Popper manganitesPhysica B 289-290, 69 (2000).

A. I. Coldea, L. D. Noailles, I. M. Marshall, S. J. Blundell, J. Singleton, P. D. Battle, M. J. RosseinskyEnhancement of the magnetoresistance at the Curie temperature of the ferromagnetic insulator Lai.^SrPhys. Rev. B 62, R6077 (2000).

RA-97-22B. W. Lovett, J. S. Stießberger, S. J. Blundell, Th. Jestädt, A. Ardavan,I. M. Marshall, F. L. Pratt, I. D. ReidDirector fluctuations in a nematic liquid crystal probed using ALC spectroscopyPhysica B 289-290, 612 (2000).

RA-97-23J. M. Gil, H. V. Alberto, R. C. Viläo, J. Piroto Duarte, P. J. Mendes, N. Ayres de Campos,A. Weidinger, J. Krauser, Ch. Niedermayer, S. F. J. CoxShallow-level muonium centre in CdSPhysica B 289-290,563 (2000).

RA-97-24I. Z. Machi, S. H. Connell, J. P. F. Sellschop, K. Bharuth-Ram, B. P. Doyle,R. D. Maclear, J. Major and R. ScheuermannQuantum diffusion of tetrahedral interstitial muonium in diamondPhysica B 289-290,468 (2000).

RA-97-25T. N. Mamedov, D. G. Andrianov, D. Herlach, K. I. Gritsaj, V. N. Gorelkin,O. Kormann, J. Major, A. V. Stoikov, M. Schefzik, U. Zimmermann¡i-spin rotation study of the temperature dependent relaxation rate of acceptor centers in siliconJETP Lett. 71, 438 (2000).

T. N. Mamedov, K. I. Gritsaj, A. V. Stoikov, D. G. Andrianov, D. Herlach,U. Zimmermann, V. N. Gorelkin, O. Kormann, J. Major, M. Schefzikß~SR investigations in siliconPhysica B 289-290, 574 (2000).

RA-97-26O. Kormann, J. Major, I. D. Reid, A. Rock, M. Schefzik, L. Schimmele, A. Seeger, D. HerlachRadio-frequency ßSR investigations on paramagnetic muonium centres in crystalline siliconPhysica B 289-290, 530 (2000).

205

R. Scheuermann, J. Major, A. Seeger, L. Schimmele, J. Schmidl, D. HerlachThe interaction of positive muons with photogenerated charge carriers in crystalline siliconPhysica B 289-290, 534 (2000).

J. Major, I. D. Reid, A. Rock, M. Schefzik, R. Scheuermann, J. Schmidl,U. Zimmermann, D. Herlach, O. KormannA novel time-differential /JSR data-acquisition systemPhysica B 289-290,702 (2000).

RA-97-28I. D. Reid, S. F. J. CoxMuons in sulphurPhysica B 289-290,620 (2000).

I. D. Reid, S. F. J. Cox, U. A. Jayasooriya, G. A. HopkinsMuon-spin spectroscopy in seleniumMagn. Reson. Chem. 38, S3 (2000).

RA-98-01A. N. Ponomarev, I. G. Ivanter, I. A. Krivosheev, A. A. Nezhivoy, B. A. Nikolsky, V. N. Duginov,K. I. Gritsaj, V. G. Olshevsky, D. Herlach, V. Yu. Pomjakushin, U. ZimmermannMagnetic fields acting on muons in textured and single crystalline holmiumPhysica B 289-290,236 (2000).

RA-98-03G. Wiesinger, Ch. Reichl, E. Gratz, P. Mietniowski, H. FigielMuon diffusion and relaxation in YC02Physica B 289-290,307 (2000).

RA-98-04R. H. Heffner, J. E. Sonier, D. E. MacLaughlin, G. J. Nieuwenhuys, G. Ehlers, F. Mezei,S.-W Cheong, J. Gardner, H. RoderObservation of two time scales in the ferromagnetic manganite Lai_xCaxMn03, x ~ 0.3Phys. Rev. Lett. 85, 3285 (2000).

R. H. Heffner, J. Sonier, D. E. MacLaughlin, G. J. Nieuwenhuys, Y. J. Uemura, G. M. Luke, S.-W CheongEvidence for a distributed ferromagnetic transition in (La, Ca)MnO3Physica B 289-290,61 (2000).

R. H. HeffnerMuon spin relaxation studies of Small-Moment Heavy Fermion Systems,in: Magnetism in Heavy Fermion Systems, (Ed. Harry Radousky, World Scientific, Nov. 2000).

RA-98-06A. Schenck, D. Andreica, F. N. Gygax, M. Pinkpank, K. A. McEwen, A. AmatoAnomalous temperature dependence of the n+-Knight shift and the phase diagram of UPd^Physica B 289-290, 311 (2000).

RA-98-07D. Andreica, A. Amato, F. N. Gygax, M. Pinkpank, A. SchenckChemical pressure effects in the Yb(Cui-xNix)2Si2 systemPhysica B 289-290, 24 (2000).

RA-98-16W. A. MacFarlane, P. Mendels, J. Bobroff, A.V. Dooglav, A.V. Egorov, H. Alloul,N. Blanchard, G. Collin, P. G. Picard, A. Keren, P. J. C. King, J. LordAntiferromagnetism in water doped YBa2CuzOe+x for x 6.5)Physica B 289-290, 291 (2000).

206

RA-98-18H. Dilger, E. Roduner, R. Scheuermann, J. Major, M. Schefzik,R. Stösser, M. Päch, D. G. FlemingMass and temperature effects on the hyperfine coupling of atomic hydrogen isotopes in cagesPhysica B 289-290,482 (2000).

R. Scheuermann, H. Dilger, E. Roduner, J. Major, M. Schefzik,A. Amato, D. Herlach, A. Raselli, I. D. ReidA novel set-up for fast muon-spin-rotation experimentsPhysica B 289-290, 698 (2000).

RA-98-20U. Staub, B. Roessli, A. AmatoMagnetic ordering in LÍ2CUO2 studied by muSR techniquePhysica B 289-290,299 (2000).

RA-99-03G. M. Kalvius, A. Kratzer, G. Grosse, D. R. Noakes, R. Wäppling,H. v. Löhneysen, T. Takabatake, Y. EchizenTJie onset of magnetism in CeNi\-xTxSn(T=Cu,Pt)Physica B 289-290, 256 (2000).

RA-99-05D. Andreica, F. N. Gygax, M. Pinkpank, A. Schenck, T. Chatterji,R. Suryanarayanan, G. Dhalenne, A. RevcolevschiCharge / orbital and antiferromagnetic ordering in LaSr^Mn^ O7Physica B 289-290,65 (2000).

RA-99-06R. De Renzi, G. Allodi, M. C. Guidi, G. Guidi, M. Hennion, L. Pinsard, A. AmatoMagnetic order in pure LaMnO-¡ and in Ca-doped single crystalsPhysica B 289-290, 52 (2000).

R. De Renzi, G. Allodi, G. Amoretti, M. C. Guidi, S. Fanesi, G. Guidi,F. Licci, A. Caneiro, F. Prado, R. Sanchez, S. Oseroff, A. AmatoPhase diagram of low doping manganitesPhysica B 289-290, 85 (2000).

RA-99-09V. S. Egorov, G. Solt, C. Baines, D. Herlach, U. ZimmermannSuperconducting intermediate state in white tin near Hc: new results by ¡iSRPhysica B 289-290, 393 (2000).

RA-99-15C. J. Rhodes, T. C. Dintinger, I. D. Reid, C. A. ScottMobility of dichloroethyl radicals sorbed in kaolin and silica:Models of heterogeneous environmental processesMagn. Reson. Chem. 38, 281 (2000).

C. J. Rhodes, T. C. Dintinger, I. D. Reid, C. A. ScottSpin-labelling studies of benzene sorbed in carbon particles using muonium:A molecular view of sorption by environmental carbonMagn. Reson. Chem. 38, S58 (2000).

207

LOW ENERGY MUONS

T. J. Jackson, C. Binns, E. M. Forgan, E. Morenzoni, Ch. Niedermayer, H. Glückler, A. Hofer,H. Luetkens, T. Prokscha, T. M. Riseman, A. Schatz, M. Birke, J. Litterst, G. Schatz, H. P. WeberSuperparamagnetic relaxation in iron nanoclusters measured by low energy muonsJ. Phys.: Condensed Matter 12,1399 (2000).

T. J. Jackson, T. M. Riseman, E. M. Forgan, H. Glückler, T. Prokscha, E. Morenzoni,M. Pleines, Ch. Niedermayer, G. Schatz, H. Luetkens, J. LitterstDepth resolved profile of the magnetic field beneath the surface of a superconductor with a few nm resolutionPhys. Rev. Lett. 84, 4958 (2000).See also Phys. Rev. Focus 5, Story 22, 15 May (2000).

E. M. Forgan, T. J. Jackson, T. M. Riseman, H. Glückler, E. Morenzoni, T. Prokscha, H. P. Weber,A. Hofer, Ch. Niedermayer, G. Schatz, M. Birke, H. Luetkens, J. Litterst, A. Schatz, C. BinnsA low-energy muon study of thermal activation in single-domain iron particlesPhysica B 289-290,137 (2000).

H. Glückler, E. Morenzoni, T. Prokscha, M. Birke, E. M. Forgan, A. Hofer, T. J. Jackson,J. Litterst, H. Luetkens, Ch. Niedermayer, M. Pleines, T. M. Riseman, G. SchatzRange studies of low-energy muons in a thin Al filmPhysica B 289-290,658 (2000).

H. Luetkens, J. Korecki, H. Glückler, E. Morenzoni, T. Prokscha, A. Schatz,M. Birke, E. M. Forgan, B. Handke, A. Hofer, T. J. Jackson, M. Kubik, F. J. Litterst,Ch. Niedermayer, M. Pleines, T. M. Riseman, G. Schatz, T. Slezak, H. P. WeberMagnetism of thin chromium films studied with low-energy muon spin rotationPhysica B 289-290,326 (2000).

E. Morenzoni, H. Glückler, T. Prokscha, H. P. Weber, E. M. Forgan, T. J. Jackson, H. Luetkens,Ch. Niedermayer, M. Pleines, M. Birke, A. Hofer, J. Litterst, T. Riseman, G. SchatzLow-energy ßSR at PSI: present and futurePhysica B 289-290,653 (2000).

M. Pleines, E. M. Forgan, H. Glückler, A. Hofer, E. Morenzoni, Ch. Niedermayer, T. Prokscha,T. M. Riseman, M. Birke, T. J. Jackson, J. Litterst, H. Luetkens, A. Schatz, G. SchatzTemperature dependence of the magnetic penetration depth in an YBa^Cu^Oi-ifilmPhysica B 289-290,369 (2000).

T. M. Riseman, T. J. Jackson, M. W. Long, E. M. Forgan, E. Morenzoni, H. Glückler, T. Prokscha,H. P. Weber, Ch. Niedermayer, A. Hofer, M. Pleines, G. Schatz, J. Litterst, H. Luetkens, A. SchatzMeasurements of the penetration depth of an YBÜ2CU-¡OT-S thin film with low-energy muonsPhysica B 289-290, 334 (2000).

A. Schenck, F. N. Gygax, D. Andreica, M. Pinkpank, G. J. Nieuwenhuys, J. Aarts, S. Freisem,M. Hesselberth, J. A. Mydosh, E. Morenzoni, H. Glückler, Th. Prokscha, A. AmatoLow-energy muon study ofCMR and spin-glass filmsPhysica B 289-290, 331 (2000).

208

LABORATORY FOR MICRO AND NANO TECHNOLOGY

J.A. Anna Selvan, D. Griitzmacher, M. Hadorn, B.Bitnar, W. Durisch, S. Stutz, T. Neiger and J. GobrechtTuneable plasma filters for TPV systems unsing transparent conducting oxides of tin doped indium oxide and Al dopedzinc oxideJames and James Science-Publ. 2000, Eds.: M. Scheer, B. McNelis, W. Palz, H. A. Ossenbrink, P. HelmProc. 16th European Photovoltaic Solar Energy Conf., 187 (2000).

A. Beyer, O. Leifeld, E. Miiller, H. Sigg, S. Stutz, K. Ensslin and D. GriitzmacherSize Control of Carbon-Induced Ge Quantum DotsAppl. Phys. Lett. 77, 3218 (2000).

A. Beyer, O. Leifeld, S. Stutz, E. Miiller and D. GriitzmacherIn-situ STM analysis andphotoluminescence of C-induced Ge dotsNanotechnology 11, 298, (2000).

A. Beyer, O. Leifeld, E. Miiller, S. Stutz, H. Sigg and D. GriitzmacherPhotoluminescence of carbon-induced Ge islands in siliconThin Solid Films 380, 246 (2000).

Y. C. Bonetti and J. GobrechtRotating shutters: A mechanical way of flattening Gaussian beam profiles in time averageApplied Optics 39, 5806 (2000).

B. Bitnar, W. Durisch, D. Griitzmacher, J.-C. Mayor, F. von Roth, J. A. Anna Selvan, H. Sigg and J. GobrechtPhotovoltaic cells for a thermophotovoltaic system with a selective emitterJames and James Science-Publ. 2000, Eds.: M. Scheer, B. McNelis, W. Palz, H. A. Ossenbrink, P. HelmProc. 16th European Photovoltaic Solar Energy Conf. 2000, 191 (2000).

C. David, C. Musil, A. Souvorov and B. KaulichNanofabrication of custom x-ray optical componentsX-ray microscopy, Proc. 6th Int. Conf., Eds.: W. Meyer-Ilse, T. Warwick, and D. Attwood,American Institute of Physics, 704 (2000).

C. DavidFabrication of stair-case profiles with high aspect ratios for blazed optical elementsMicroelectronic Engineering 53, 677 (2000).

C. David, B. Kaulich, R. Barrett, M. Salome and J. SusiniHigh resolution lenses for sub-100 nm X-ray fluorescence microscopyApplied Physics Letters 77, 3851 (2000).

A. D'Amore, D. Simoneta, M. Gabriel, W. Kaiser and H. SchiftSpritzgiefien im Nanobereich - Kalibrierstrukturen fur RastersondenmikroskopeKunststoffe 6/2000, 52 (2000).

G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist, K. Ensslin, D. Griitzmacher and E. MiillerIntersubband-electroluminescencefrom Si/SiGe quantum cascade structuresScience 290, 2277 (2000).

G. Dehlinger, U. Gennser, D. Griitzmacher, T. Ihn, E. Miiller and K. EnsslinInvestigation of the emitter structure in SiGe/Si resonant tunneling structuresThin Solid Films 369, 390 (2000).

J.-H. Fabian, L. Scandella, H. Fuhrmann, R. Berger, T. Mezzacasa, Ch. Musil, J. Gobrecht and E. MeyerFinite Element Calculations and Fabrication of Cantilever Sensors for Nanoscale DetectionUltramicroscopy 82, 69 (2000).

S. Gehrsitz, F. K. Reinhart, C. Gourgon, N. Herres, A. Vonlanthen and H. SiggThe refractive index ofAlxGa/.xAs below the bandgap: Accurate determination and empirical modelingJ. Appl. Phys. 87, 7825 (2000).

209

S. Graf, H. Sigg, K. Kohler and W. BachtoldDirect observation of dynamical screening of the intersubband resonanceProceed. ISQW'99, Bad Ischl, M. Helm Ed., Physica E 7/1-2, 200 (2000).

S. Graf, H. Sigg, K. Kohler and W. BachtoldDirect observation of the depolarisation shift of the interband resonancePhys. Rev. Lett. 84, 2686 (2000).

S. Graf, H. Sigg and W. BachtoldHigh frequency electrical pulse generation using optical rectification in bulk GaAsAppl. Phys. Lett. 76, 2647 (2000).

S. Graf, H. Sigg, K. Kohler and W. BachtoldPhoton Drag investigations of current relaxation processes in a two-dimensional electron gasPhys. Rev. B 62, 10 301 (2000).

J. Gobrecht, H. Schift, C. David, W. Kaiser, A. D'Amore, D. Simoneta and L. ScandellaInjection molded plastic chip for calibration of scanning probe microscopesPTB Bericht F-39, Braunschweig, 1-8, Jan. (2000).

L. J. Heyderman, H. Schift, C. David, J. Gobrecht and T. SchweizerFlow behaviour of thin polymer films used for hot embossing lithographyMicroelectronic Engineering 54, 229 (2000).

O. Leifeld, A. Beyer, E. Miiller, K. Kern and D. GriitzmacherFormation and ordering effects of c-induced Ge dots grown on Si (001) by molecular beam epitaxyMater. Sci. Eng. B 74, 222 (2000).

O. Leifeld, A. Beyer, E. Miiller, D. Griitzmacher and K. KernNucleation ofGe dots on the C-alloyed Si(001) surfaceThin Solid Films 380, 176 (2000).

E. Miiller, F. KrumeichA simple and fast TEM preparation method utilizing the pre-orientation in plate-like, needle-shaped and tubular materialsUltramicroscopy 84, 143 (2000).

C. Padeste, A. Grubelnik and L. TiefenauerFerrocene-avidin conjugates for bioelectrochemical applicationsBiosensors and Bioelectronics 15, 431 (2000).

R. Prins, M. Schildenberger, Y.C. Bonetti and J. GobrechtNanotechnology and Model Catalysis: The Use of Photolithography for Creating Active SurfaceChimia 54, 63 (2000).

C. Rosenblad, M. Kummer, A. Dommann, E. Miiller, M. Gusso, L. Tapfer and H. von KanelVirtual substrates for the n- andp-type Si-MODFET grown at very high ratesMater. Sci. Eng. B 74, 113 (2000).

C. Rosenblad, H. von Kanel, M. Kummer, A. Dommann, E. MiillerA plasma process for ultrafast deposition ofSiGe graded buffer layersAppl. Phys. Lett. 76, 427 (2000).

C. Rosenblad, J. Stangl, E. Miiller, G. Bauer, H. von KanelStrain relaxation of graded SiGe buffers grown at very high ratesMater. Sci. Eng. B 71, 20 (2000).

H. Schift, C. David, M. Gabriel, J. Gobrecht, LJ. Heyderman, W. Kaiser, S Koppel and L. ScandellaNanoreplication in polymers using hot embossing and injection moldingMicroelectronic Engineering 53, 171 (2000).

210

H. Schift, C. David, J. Gobrecht, A. D'Amore, D. Simoneta, W. Kaiser and M. GabrielQuantitative analysis of the molding of nanostructuresJ. Vac. Sci. Technol. B 18, 3564 (2000).

M. Schildenberger, Y.C. Bonetti, J. Gobrecht and R. PrinsNano-pits: supports for heterogeneous model catalysts prepared by interference lithographyTopics in Catalysis 13, 109 (2000).

V. Senz, T. Ihn, T. Heinzel, K. Ensslin, G. Dehlinger, D. Griitzmacher and U. GennserAnalysis of the Metallic Phase of Two-Dimensional Holes in SiGe in Terms of Temperature Dependent ScreeningPhys. Rev. Lett. 85, 4357 (2000).

V. Senz, T. Heinzel, T. Ihn, K. Ensslin, G. Dehlinger, D. Griitzmacher and U. GennserCoexistance of weak localization and a Metallic Phase in Si/SiGe Quantum wellsPhys. Rev. B 61, R5082 (2000).

F. Schwesinger, R. Ros, T. Stranz, D. Anselmetti, H.-J. Giintherodt, A. Honegger, L. Jermutus, L. Tiefenauer andA. PliickthunUnbinding forces of single antibody-antigen complexes correlate with their thermal dissociation rateProc. Natl. Acad. Sci. USA 97, 9972 (2000).

H. von Kanel, C. Rosenblad, M. Kummer, E. Miiller, T. Graf and T. HackbarthFast deposition process for graded SiGe buffer layersJpn. J. Appl. Phys. 39 (Part 1), 2050 (2000).

D. Wiesmann, C. David, R. Germann, D. Erni and G. L. BonaApodized surface corrugated gratings with varying duty cyclesIEEE Photon. Technol. Lett. 12, 639 (2000).

211

LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY

HEAVY ELEMENTSB. Eichler, H. P. Zimmermann, H.W. GäggelerAdsorption of radon on ice surfacesJ. Phys. Chem. A104, 3126 (2000).

B. Eichler, J.V. KratzElectrochemical deposition of carrier-free radionuclidesRadiochimica Acta 88, 475 (2000).

B. EichlerMetallchemie der TransaktinoidePSI-Bericht 00-09 (2000).

R. Eichler, B. Eichler, H.W. Gäggeler, D. T. Jost, D. Piguet, A. TürlerGas phase chemistry of technetium and rhenium oxychloridesRadiochim. Acta 88, 87 (2000).

R. Eichler, W. Briichle, R. Dressier, Ch. E. Diillmann, B. Eichler, H.W. Gäggeler, K. E. Gregorich, D. C. Hoffman,S. Hübener, D. T. Jost, U. W. Kirbach, C. A. Laue, V. M. Lavanchy, H. Nitsche, J. B. Patin, D. Piguet, M. Schädel,D. A. Shaughnessy, D. A. Strellis, S. Taut, L. Tobler, Y. S. Tsyganov, A. Türler, A. Vahle, P. A. Wilk, A. B. YakushevChemical characteriszation ofbohrium (element 107)Nature 407, 63 (2000).

H.W. GäggelerBohrium finds aplace in the TableCERN Courier 40 (1), 9 (2000).

E. Strub, J.V. Kratz, A. Kronenberg, A. Nähler, P. Thörle, S. Zauner, W. Brüchle, E. Jäger, M. Schädel,B. Schausten, E. Schimpf, Li Zongwei, U. Kirbach, D. Schumann, D. Jost, A. Türler, A. Asai, Y. Nagame,M. Sakama, K. Tsukada, H.W. Gäggeler, J.P. GlatzFluoride complexation of rutherfordium (Rfi element 104)Radiochim. Acta 88, 265 (2000).

SURFACE CHEMISTRYM. Wachsmuth, B. Eichler, L. Tobler, D.T. Jost, H.W. Gäggeler, M. AmmannOn-line gas-phase separation of short-lived bromine nuclides from precursor seleniumRadiochim. Acta 88, 873 (2000).

C. Zellweger, M. Ammann, B. Buchmann, P. Hofer, M. Lugauer, R. Rüttimann, N. Streit, E. Weingartner,U. BaltenspergerSummertime NOy speciation at the Jungfraujoch, 3580 m above sea level, Switzerland.J. Geophys. Res. 105, 6655 (2000).

ANALYTICAL CHEMISTRYA. Eichler, M. Schwikowski, H.W. Gäggeler, V. Furrer, H.-A. Synal, J. Beer, M. Sauer, M. FunkGlaciochemical dating of an ice core from the upper Grenzgletscher (4200 m a.s.l.)J. Glaciology 46, 507 (2000).

A. Eichler, M. Schwikowski, H.W. GäggelerAn Alpine ice core record of anthropogenic HF and HCl emissionsGeophys. Res. Lett. 27, 3225 (2000).

M. Hoelzle, D. Vonder Mühll, M. Schwikowski, H.W. GäggelerHochalpine Gletscher als Zeugen der Geschichte der LuftverschmutzungDie Alpen 10, 25 (2000).

212

M. Lugauer, U. Baltensperger, M. Furger, H.W. Gaggeler, D.T. Jost, S. Nyeki, M. SchwikowskiInfluences of vertical transport and scavenging on aerosol particle surface area and radon decay product concentrationsat the Jungfraujoch (3454 m asl)J. Geophys. Res. 105, 19869 (2000).

S. Nyeki, M. Kalberer, I. Colbeck, S. De Wekker, M. Furger, H.W. Gaggeler, M. Kossmann, M. Lugauer, D. Steyn,E. Weingartner, M. Wirth, U. BaltenspergerConvective boundary layer evolution to 4 km asl over high-Alpine terrain: Airborne Lidar observations in the AlpsGeophys. Res. Lett. 27, 689 (2000).

P. Schleppi, L. Tobler, J.B. Bucher, A. WyttenbachMultivariate interpretation of the foliar chemical composition of Norway spruce (Picea abies)Plant and Soil 219, 251 (2000).

U. Schotterer, Th. Stacker, H. Biirki, J. Hunziker, R. Kozel, D. A. Grasso, J.-P. TripetDas Schweizer Isotopen-Messnetz: Trends 1992-1999Gwa 10, (2000).

W. Stichler, U. SchottererFrom accumulation to discharge: modification of stable isotopes during glacial and post-glacial processesHydrol. Process. 14, 1423 (2000).

N. Streit, E. Weingartner, C. Zellweger, M. Schwikowski, H.W. Gaggeler, U. BaltenspergerCharacterisation of size-fractionated aerosol from the Jungfraujoch (3580 m asl) using Total Reflection X-RayFluorescence (TXRF)Int. J. Environ. Anal. Chem. 76, 1 (2000).

B. Tenberken-Potzsch, M. Schwikowski, H.W. GaggelerAnalysis of size-classified ice crystals by capillary electrophoresisJ. Chromatogr. A 871, 391 (2000).

B. Tenberken-Potzsch, M. Schwikowski, H.W. GaggelerA method to sample and separate ice crystals and supercooled cloud drops in mixed phased clouds for subsequentchemical analysisAtmos. Environ. 34, 3629 (2000).

A. Wyttenbach, L. ToblerThe concentrations ofFe, Zn and Co in successive needle age classes of Norway spruce [Picea Abies (L.) Karst.]Trees 14, 198 (2000).

PROJECT RAD WASTER. G. Blasberg, U. Roelcke, R. Weinreich, B. Beattie, K. von Ammon, Y. Yonekawa, H. Landolt, I. Guenther,N.E.A. Crompton, P. Vontobel, J. Missimer, R. P. Maguire, J. Koziorowski, E. J. Knust, R. D. Finn, K. L. LeendersImaging Brain Tumor Proliferative Activity with [124I]IododeoxyuridineCancer Res. 60, 624 (2000).

D. F. Dos Santos, M. Argentini, R. Weinreich, H.-J. HansenLabelling of Carbaboranyl Compounds with a Selenium Atom with a View to Applications in Boron-Neutron-CaptureTherapy (BNCT) and Positron-Emission Tomography (PET)Helv. Chim. Acta 83, 2926 (2000).

213

LABORATORY FOR ION BEAM PHYSICS

A. Albrecht, C. Schnabel, S. Vogt, S. Xue, G.F. Herzog, F. Begemann, H.W. Weber, R. Middleton, D. Fink, and J. KleinLight noble gases and cosmogenic radionuclides in Esthervilleßudulan, and other mesosiderites: Implications forexposure histories and production ratesMeteoritics and Planet. Sei. 35, 975 (2000).

A. Blinov, S. Massonet, H. Sachsenhauser, C. Stan-Sion, V. Lazarev, J. Beer, H.-A. Synal, M. Kaba, J. Masarik and E.NolteAn excess ofi6Cl in modern atmospheric precipitationNucl. Instram. Meth. B 172, 537 (2000).

B. Brijs, J. Deleu, T. Conard, H.De Witte, W. Vandervorst, K. Nakajima, K. Kimura, I. Genchev, A. Bergmaierd,L.Goergens, P Neumaier, G. Dollinger, M. DöbeliCharacterization of Ultra Thin Oxynitrides, a General ApproachNucl. Instrum. Meth. B 161-163, 429 (2000).

W. S. Broecker, E. Clark, J. Lynch-Stieglitz, W. Beck, L. D. Stott, I. Hajdas and G. BonaniLate glacial diatom accumulation at 9° S in the Indian OceanPaleoceanography 15, 348 (2000).

P. De Almeida, R. Schäublin, A. Almazouzi, M. Victoria, M. DöbeliQuantitative long-range-order measurement and disordering efficiency estimation in ion-irradiated bulk Ni^Al usingcross-sectional conventional transmission electron microscopyAppl. Phys. Lett. 77, 2680 (2000).

A. Eichler, M. Schwikowsky, H. W. Gäggeler, V. Furrer, H.-A. Synal, J. Beer, Saurer and M. FunkGlaciochemical dating of an ice core from upper Grenzgletscher (4200 m a.s.l.)J. Glaciology 46, 507 (2000).

M. Frank, R. Gersonde, M. Rutgers van der Loeff, G. Bohrmann, C. Nürnberg, P.W. Kubik, M. Suter and A. ManginiSimilar glacial and interglacial export bioproductivity in the Atlantic sector of the Southern Ocean: Multiproxy evidenceand implications for atmospheric CO2Paleoceanography 15, 642 (2000).

J. R. Green, L. De Wayne-Cecil, H.-A. Synal, K. J. Kreutz, C. P. Wake, D. L. Naftz and S. K. FrapeChlorine-36 and cesium-137 in ice-core samples from mid-latitude glacial sites in the Northern HemisphereNucl. Instrum. Meth. B 172, 812 (2000).

I. Hajdas, G. Bonani, and B. ZolitschkaRadiocarbon dating ofvarve chronologies: Soppensee and Holzmaar after Ten YearsRadiocarbon 42, 349 (2000).

S. A. W. Jacob, M. Suter and H.-A. SynalIon beam interaction with stripper gas - Key for AMS at sub MeVNucl. Instrum. Meth. B 172, 235 (2000).

I. Leya, H.-J. Lange, M. Lüpke, U. Neupert, R. Daunke, O. Fanenbruck, R. Michel, R. Rösel, B. Meltzow, T. Schiekel,F. Sudbrock, U. Herpers, D. Filges, G. Bonani, B. Dittrich-Hannen, M. Suter, P. W. Kubik and H.-A. SynalSimulation of the interaction of galactic cosmic-ray protons with meteoroids: On the production of radionuclides in thickgab bro and iron targets irradiated isotropically with 1.6 GeV protonsMeteoritics and Planet. Sei. 35, 287 (2000).

N. Liphschitz and G. BonaniDimensions of olive (olea europaea) stones as a reliable parameter to distinguish between wild and cultivated varieties:further evidenceTel Aviv (J. Inst. of Archaeology of Tel Aviv Univ.) 27, 23 (2000).

J. M. López-Gutiérrez, M. García-León, R. García-Tenorio, C. Schnabel, M. Suter, H.-A. Synal and S. Szidati29j/i27j raffos ancj

n9i concentrations in a recent sea sediment core and in rainwater from Sevilla (Spain) by AMSNucl. Instrum. Meth. B 172, 574 (2000).

214

J. M. Lopez-Gutierrez, M. Garcia-Leon, C. Schnabel and H. A. SynalDeterminación de 129I en muestras ambientales mediante espectrometría de masas con aceleradores (AMS)Anales de Fisica 95, 32 (2000).

J. M. Lopez-Gutierrez, H.-A. Synal, M. Suter, C. Schnabel and M. Garcia-LeonAccelerator mass spectrometry as a powerful tool for the determination of1291 in rainwaterAppl. Radiât. Isotop. 53, 81 (2000).

J.M. Schäfer, D.R. Marchant, G.H. Dentón, R. Wieler, S. Ivy-Ochs, C. SchliichterThe oldest ice on Earth in Beacon Valley, Antarctica: New evidence from surface exposure datingEarth and Planet. Sei. Lett. 179, 91 (2000).

C. Schnabel, I. Leya, R. Michel, J. Csikai, Z. Dezso, J.M. Lopez-Gutierrez, H.-A. SynalInstrumental and radiochemical determination of the neutron-induced production cross section of 1-129 from and otherneutron-induced cross sections on Te at 14.7 MeVRadiochimica Acta 88,439 (2000).

C. Shen, J. Beer, F. Heller, P. W. Kubik, M. Suter and T. Liu10Be-susceptibility model and quantitative estimates ofpedogenic ferromagnetic material flux in Chinese loessNucl. Instrum. Meth. B 172, 551 (2000).

F.Sudbrock, U.Herpers, S.M.Qaim, J.Csikai, P.W.Kubik, H.-A.Synal and M.SuterCross sections for the formation of long-lived radionuclides wBe, 26Al and 36Cl in 14.6 MeV neutron induced reactionsdetermined via accelerator mass spectrometry (AMS)Radiochimica Acta 88, 829 (2000).

M. Suter, S. W. A. Jacob and H.-A. SynalTandem AMS at sub-MeV energies - Status and prospectsNucl. Instrum. Meth. B 172, 144 (2000).

M. SuterParticle accelerators for radiocarbon dating in archaeologyEurophysics News 31/6, 16 (2000).

H.-A. Synal, S. Jacob and M. SuterNew concepts for radiocarbon detection systemsNucl. Instrum. Meth. B 161-163, 29 (2000).

H.-A. Synal, S. Jacob and M. SuterThe PSI/ETH small radiocarbon dating systemNucl. Instrum. Meth. B 172, 1 (2000).

S. Szidat, A. Schmidt, J. Handl, D. Jakob, W. Botsch, R. Michel, H.-A. Synal, C. Schnabel, M. Suter, J. M. López-Gutiérrez and W. StädeIodine-129: Sample preparation, quality control and analyses ofpre-nuclear materials and of natural waters from LowerSaxony, GermanyNucl. Instrum. Meth. B 172, 699 (2000).

S. Szidat, A. Schmidt, J. Handl, D. Jakob, R. Michel, H.-A. Synal, Ch. Schnabel, M. Suter and J.M. Lopez-GutierrezRNAA and AMS of Iodine-129 in environmental Materials - comparison of analytical methods and quality assuranceKerntechnik 65, 160 (2000).

D. Terribilini, O. Eugster, G. F. Herzog, and C. SchnabelEvidence for common break-up events of the acapulcoites/lodranites and chondritesMeteoritics and Planet. Sei. 35,1043 (2000).

S. Tschudi, S. Ivy-Ochs, C. Schlüchter, P. Kubik and H. Raino10Be dating of Younger Dryas Salpausselkä I formation in FinlandBoreas 29, 287 (2000).

215

G. Wagner, J. Beer, C. Laj, C. Kissel, J. Masarik, R. Muscheler and H.-A. SynalChlorine-36 evidence for the Mono Lake event in the Summit GRIP ice coreEarth and Planet. Sci. Lett. 181,1 (2000).

G. Wagner, J. Masarik, J. Beer, S. Baumgartner, D. Imboden, P. W. Kubik, H.-A. Synal and M. SuterReconstruction of the geomagnetic field between 20 and 60 kyr BPfrom cosmogenic radionuclides in the GRIP ice coreNucl. Instram. Meth. B 172, 597 (2000).

G. Wagner, J. Beer, C. Laj, C. Kissel, J. Masarik, R. Muscheler, and H.-A. SynalPaleomagnetic field reconstruction based on cosmogenic isotopes of the GRIP ice coreIn: Terra Nostra 2000/10, From Secular Variation to Paleomagnetism - A new View of the Dynamic Geomagnetic Field,115,(2000).

P. R. Wilhnott, F. Antoni, M. DobeliKinetic, Crystallographic and Optical Studies of GaN and AlxGat.xN Thin Films Grown on Si(lll) by Pulsed ReactiveCrossed-Beam Laser Ablation Using Liquid Alloys and N2 or NH3J. Appl. Phys. 88, 188 (2000).

216

CONTRIBUTIONS TO CONFERENCES AND WORKSHOPS

LABORATORY FOR PARTICLE PHYSICS

A. Ackens, et al., - R-97-02 CollaborationA high-rate X-ray detector for exotic-atom spectroscopyDPG Spring meeting, Dresden (Germany), March 20 - 24, 2000.

D Anagnostopoulos, et al., - R-97-02 CollaborationCharged Pion Mass Determination and Energy-Calibration Standards based on Pionic X-ray TransitionsHydrogen Atomll: Precise physics of simple atomic systems (PSAS 2000),Castiglione della Pescaia (Italy), June 1 - 3, 2000.

D. Anagnostopoulos et al., - R-98-01 CollaborationPionic Hydrogen: Status and OutlookHydrogen Atom II: Precise physics of simple atomic systems, PSAS 2000,Casiglione della Pescaia (Italy), June 1-3, 2000.

R. Baur - CMS CollaborationReadout of the CMS Pixel DetectorInternational Workshop on Semiconductor Pixel Detectors for Particles and X-rays PIXEL2000,Genova (Italy), June 5 - 8 , 2000.

M. Daum - New Heavns Collaboration (PSI-Virginia-Beijing)The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33.9 MeV in Pion DecayNeutrino 2000, XIX International Conference on Neutrino Physics and Astrophysics,Sudbury (Canada), June 16 - 21, 2000.

M. Daum - UCN-Collaboration (PSI-PNPI-ETHZ)An Ultracold Neutron Facility at PSITagung der Schweizerischen Physikalischen Gesellschaft, Montreux (Switzerland), March 16 - 17, 2000.

M. Daum - UCN-Collaboration (PSI-PNPI-ETHZ)An Ultracold Neutron Facility at PSICIPANP, 7th Conference on the Intersections of Particle and Nuclear Physics,Quebec City (Canada), May 22 - 28, 2000.

M. Daum - UCN-Collaboration (PSI-PNPI-ETHZ)An Ultracold Neutron Facility at PSIUCN Workshop Los Alamos (USA), September 6 - 8, 2000.

D. GottaPrecision determination if the nN s-wave scattering Lengths from Pionic Hydrogen: A new Proposal at PSISeminar, Inst. fur theoretische Physik, Universitat Bern (Switzerland), January 18, 2000.

D. GottaPionic HydrogenVIII. International Oberjoch meeting on Broken Symmetries and Meson Nuclear Physics,Oberjoch (Germany), September 4 - 9, 2000.

R. Horisberger - CMS CollaborationReadout architectures for pixel detectorsInternational Workshop on Semiconductor Pixel Detectors for Particles and X-rays PIXEL2000,Genova (Italy), June 5 - 8 , 2000.

217

P. Indelicato and L.M. SimonsCrystal Spectroscopy and Exotic AtomsQED 2000 2nd Workshop on frontier tests of Quantum Electrodynamics and Physics of the Vacuum,Trieste (Italy), October 6 - 10, 2000.

C.H.Q.Ingram.Pion Absorption Results from the Meson Factories.Invited (plenary) talk at 16th International Conference on Few-Body Problems in Physics,Taipei (Taiwan), March 6 - 10, 2000.

T.S. JensenStark Mixing and Elastic Scattering in Pionic and Muonic HydrogenThe XVII European Conference on Few-Body Problems in Physics, Few Body 2000,Evora (Portugal), September 11-16, 2000.

M. Kavcic, et al., - Z-97-02 - collaborationL-shell ionization in near-central collisions of heavy ions with low Z targets16th International Conference on the Application of Accelerators in Research and Industry (CAARI 2000),Denton, 76203-1427 TX (USA), November 1 - 4, 2000.

P.-R. Kettle - NewHeavns CollaborationThe KARMEN Time Anomaly, Search for a Neutral Particle of Mass 33.9 MeV in Pion DecayICHEP2000, XXXth International Conference on High Energy Physics,Osaka (Japan), July 27 - August 2, 2000.

B. Kotlinski - CMS CollaborationThe CMS Pixel DetectorInternational Workshop on Semiconductor Pixel Detectors for Particles and X-rays PIXEL2000,Genova (Italy), June 5 - 8, 2000.

B. Kotlinski, R. Baur, K. Gabathuler, R. Horisberger, R. Schnyder, W Erdmann. - CMS CollaborationReadout of the CMS Pixel Detector6th Workshop on Electronics for LHC Experiments,Cracow (Poland), September 11-15, 2000.

F. KottmannLaser spectroscopy of the Lamb shift in muonic hydrogenStatus report at the PSI Users Meeting, PSI, Villigen (Switzerland), January 17, 2000.

F. KottmannTowards a Lamb shift measurement in muonic hydrogenSecond workshop on frontier tests of QED and physics of the vacuum,Trieste (Italy), October 6 - 10, 2000.

Y.-W. LiuLaser spectroscopy of exotic atomsThe Fourth Asian International Seminar on Atomic and Molecular Physics,Taipei (Taiwan), October 13 - 18, 2000.

Y.-W. LiuThe laser system for the muonic hydrogen Lamb shift measurementXVII International Conference on Atomic Physics, ICAP 2000,Florence (Italy), June 4 - 9, 2000.

V.E. Markushin and T.S. JensenAtomic Cascade and X-ray Yields in light exotic Atoms7th International Conference on Hypernuclear and Low Energy Kaon Physics,Torino (Italy), October 23 - 27, 2000.

218

X. Morelle et al., - R-97-06 CollaborationMeasuring the Michel Parameter Xi" in Polarized Muon DecaySpin Physics Symposium, SPIN2000, Osaka (Japan), Oktober 16 - 21, 2000.

M. Pajek et al., - Z-99-05 CollaborationHigh-resolution measurements ofTh and U L-y x-rays induced by energetic O ions10th International Conference on the Physics of Highly Charged Ions (HCI 2000),Berkeley, CA 94710 (USA), July 30 - August 3, 2000.

R. PohlTowards a measurement of the Lamb shift in muonic hydrogenInternational conference "Hydrogen Atom II",Castiglione (Italy), June 1-3, 2000.

R. Prieels et al., - R-97-06 CollaborationA Precision Measurement of the Michel parameter x"Proceedings of the 7th Conference on the Intersections of Particles and Nuclear Physics,CIPANP 2000, Quebec (Canada), May 22 - 28, 2000.

L.M. SimonsMuonic HydrogenVIII. International Oberjoch meeting on Broken Symmetries and Meson Nuclear Physics,Oberjoch (Germany), September 4 - 9, 2000.

C. Wigger - New Heavns Collaboration (PSI-Virginia-Beijing)The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33.9 MeV in Pion DecayTagung der Schweizerischen Physikalischen Gesellschaft, Montreux (Switzerland), March 16 - 17, 2000.

THEORY GROUPC. Alexandrou, P. de Forcrand and M. D'EliaThe relevance of center vorticesContribution to the 17th International Symposium on Lattice Field Theory (LATTICE 99),Pisa (Italy), June 29 - July 3, 1999; Nucl. Phys. (Proc.Suppl.) 83, 437 (2000).

C. Alexandrou, P. de Forcrand and M. D'EliaThe role of center vortices in QCDContribution to the 15th International Conference on Particle and Nuclei (PANIC 99),Uppsala (Sweden), June 10 -16, 1999; Nucl. Phys. A 663/664,1031c (2000).

C. Alexandrou, P. de Forcrand and M. D'EliaImproved multiboson algorithmContribution to the 17th International Symposium on Lattice Field Theory (LATTICE 99),Pisa (Italy), June 29 - July 3, 1999; Nucl. Phys. (Proc.Suppl.) 83, 765 (2000).

A. Bori§iTruncated overlap fermionsContribution to 17th International Symposium on Lattice Field Theory (LATTICE 99),Pisa (Italy), June 29 - July 3, 1999; Nucl. Phys. (Proc. Suppl.) 83, 771 (2000).

A. Denner, S. Dittmaier, M. Roth, D. WackerothPrecise predictions for W-pair production at LEP-2 with RACOON WWContribution to the 35th Rencontres de Moriond: Electroweak Interactions and Unified Theories,Les Arcs (France), March 11-18, 2000; hep-ph/0005074

A. Denner, S. Dittmaier, M. Roth, D. WackerothRadiative corrections to e+e~ —> WW —> 4 fermions with RACOONWWContribution to the Zeuthen Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field Theory,Konigstein-Weissig (Germany), April 9 - 14, 2000; hep-ph/9912447, Nucl. Phys. (Proc. Suppl.) 89, 100 (2000).

219

A. Denner, S. Dittmaier, M. Roth, D. WackerothElectroweak precision physics at e+e~ colliders with RACOONWWContribution to the 22nd Annual MRST (Montreal-Rochester-Syracuse-Toronto) Meeting: Conference on TheoreticalHigh Energy Physics, Rochester, New York (USA), May 8 - 9, 2000; hep-ph/0007245; in: 'Theoretical High EnergyPhysics, MRST2000', ed. C.R. Hagen, (American Institue of Physics, Melville, New York (USA), 2000), p. 40.

A. Denner, S. Dittmaier, M. Roth, D. WackerothElectroweak radiative corrections to off-shell W-pair productionContribution to DPF 2000: The Meeting of the Division of Particles and Fields of the American Physical Society,Columbus, Ohio (USA), August 9 - 12, 2000; hep-ph/0011119

S. DiirrThe phase transition in the multiflavor Schwinger modelContribution to the International Conference on Quantization, Gauge Theory, and Strings: Conference Dedicated tothe Memory of Professor Efim Fradkin, Moscow (Russia), June 5 - 10, 2000; hep-th/0009094

S. DiirrTesting the Leutwyler-Smilga prediction regarding the global topological charge distribution on the latticeContribution to the International Euroconference in Quantum Chromodynamics: 15 Years of the QCD - MontpellierConference (QCD 00), Montpellier (France), July 6 - 13, 2000; hep-ph/0009139

S. DiirrStudy of the Leutwyler-Smilga regimes: lessons for full QCD simulationsContribution to the 18th International Symposium on Lattice Field Theory (Lattice 2000),Bangalore (India), August, 17 - 22, 2000; hep-lat/0010037

M. W. Griinewald et al.7 E. Accomando, A. DennerFourfermion production in electron-positron collisionsReport of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000; hep-ph/0005309

S. Hay wood et al, A. DennerElectroweak physicsProceedings of the Workshop on Standard Model Physics (and more) at the LHC, Geneva (Switzerland),October 14 -15,1999; eds. G. Altarelli and M.L. Mangano, 117 (2000); hep-ph/0003275

V. A. Kuz'min, T. V. Tetereva, K. JunkerOn the strength of spin-isospin transitions in A = 28 nucleiContribution to the BLTP International Conference on Nuclear Structure and Related Topics (NSRT 2000),Dubna (Russia), June 6 - 10, 2000; nucl-th/0009061

V. A. Kuz'min, T. A. Tetereva, K. Junker and A. A. OvchinnikovaThe Total Rates of Ordinary Muon Capture - Microscopic Calculations for Heavy NucleiContribution to the Annual Conference on Nuclear Spectroskopy and Nuclear Structure,St. Petersburg (Russia), June 2000; Dubna preprint E4-2000-202

M. P. Locher, V. E. Markushin, S. von RotzAntiproton-nucleon annihilation, multistep processes and the OZI ruleContribution to the 16th IUPAP International Conference on Few-Body Problems in Physics,Taipei (Taiwan), March 6 - 10, 2000.

V. E. MarkushinThe structure of the light scalar mesons and QCD sum rulesProceedings of the Workshop on Production, Properties, and Interaction of Mesons, (MESON'2000),Cracow (Poland), May 19 - 23, 2000; Acta Physica Polonica B 31, 2665 (2000); hep-ph/0008096.

V. E. Markushin and T. S. JensenAtomic Cascade and X-ray yields in light exotic atomsContribution to the 7th International Conference on Hypernuclear and Low Energy Kaon Physics,Torino (Italy), October 23 - 27, 2000.

220

M. MellesPrecision Higgs physics at a 77 colliderContribution to the International Workshop on High-Energy Photon Colliders (GG 2000),Hamburg (Germany), June 14 - 17, 2000; hep-ph/0008125

M. MellesTwo loop mass effects in the static position space QCD potentialContribution to the International Euroconference in Quantum Chromodynamics: 15 Years of the QCDMontpellier Conference (QCD 00), Montpellier (France), July 6 - 13, 2000; hep-ph/0009085

M. MellesElectroweak Sudakov correctionsContribution to the 5th International Linear Collider Workshop (LCWS 2000), Fermilab,Batavia, Illinois (USA), October 24 - 28, 2000; hep-ph/0012196

M. MellesThe Standard Model Higgs in 77 collisionsContribution to the 5th International Linear Collider Workshop (LCWS 2000), Fermilab,Batavia, Illinois (USA), October 24 - 28, 2000; hep-ph/0012195

R. RosenfelderCoulomb Corrections to Elastic Electron-Proton Scattering and the Proton Charge RadiusContribution to Hydrogen II - Precise Physics of Simple Atomic Systems, Castiglione della Pescaia,Tuscany (Italy), June 1 - 3, 2000.

A. W. Schreiber, R. Rosenfelder, C. AlexandrouWhat Can We Learn from QED at Large Couplings ?Proceedings of the 3rd International Symposium on Symmetries in Subatomic Physics,Adelaide (Australia), March 13 -17, 2000; hep-th/0007182

A. W. Schreiber, R. RosenfelderThe Feynman Variational Approach to Relativistic Quantum Field TheoryContribution to the 14th National Congress of the Australian Institute of Physics,Adelaide (Australia), December 10 -15, 2000.

LABORATORY FOR MUON SPIN SPECTROSCOPY

D. Andreica, A. Amato et al., RA-98-07 CollaborationliSR under pressure, first results on CeRh2ShESF Conference on Non Fermi Liquid Effects in Metallic Systems with Strong Electronic Correlation,Newton Institute, Cambridge (UK), January 5 - 8, 2000.

D. Andreica, A. Amato et al., RA-98-07 CollaborationliSR under pressure, first results on CeRh^Sh18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society,Montreux (Switzerland), March 14-18, 2000.

E. Morenzoni et al., PSI-Birmingham-Leicester-Braunschweig-Konstanz CollaborationUse of polarized muons for investigations on the scale of nm18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society,Montreux (Switzerland), March 14-18, 2000.

G. Solt et al., RA-94-14 CollaborationMagnetic (Condon) domains in s-p metals: beryllium and white tin18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society,Montreux (Switzerland), March 14-18, 2000.

221

W. B. WaeberElectron hyper-state representation of strongly correlated systems18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society,Montreux (Switzerland), March 14-18, 2000.

H. Luetkens et al, PSI-Braunschweig-Cracow-Birmingham-Konstanz CollaborationMagnetism of thin Chromium filmsNuclear Methods in Magnetism, NMM 2000, Rio de Janeiro (Brasil), August 2 - 4, 2000.

E. Morenzoni (invited)Muon spin rotation and relaxation experiments on thin filmsNuclear Methods in Magnetism, NMM 2000, Rio de Janeiro (Brasil), August 2 - 4, 2000.

D. Andreica, F. N. Gygax, A. Schenck, A. Amato et al., RA-98-07 Collaboration[iSR studies of the nonmagnetic-magnetic transition in highly correlated electron systemsInternational Conference on Magnetism, ICM 2000, Recife (Brasil), August 6 - 1 1 , 2000.

H. Luetkens et al., PSI-Braunschweig-Cracow-Birmingham-Konstanz CollaborationMagnetism of thin chromium filmsInternational Conference on Magnetism, ICM 2000, Recife (Brasil), August 6 - 1 1 , 2000.

E. Morenzoni et al., PSI-Birmingham-Leicester-Braunschweig-Konstanz CollaborationSuperparamagnetic relaxation in Fe clusters measured by low energy muon spin rotationInternational Conference on Magnetism, ICM 2000, Recife (Brasil), August 6 - 1 1 , 2000.

E. Morenzoni et al., PSI-Leiden-Braunschweig-Konstanz-Ziirich CollaborationFinite size effects in single layers spin-glass films studied by LE-muon spin relaxationInternational Conference on Magnetism, ICM 2000, Recife (Brasil), August 6 - 1 1 , 2000.

A. Schenck, D. Andreica, F. N. Gygax, A. Amato et al., RA-98-06 CollaborationUnusual static and dynamical magnetic features in PrCu^ as observed by /iSR spectroscopyInternational Conference on Magnetism, ICM 2000, Recife (Brasil), August 6 - 1 1 , 2000.

H. LuetkensMagnetism of thin chromium films studied with low energy muon spin rotationDPG Friihjahrstagung, Regensburg (Germany), March 27-31 , 2000.

M. PleinesMeasurements of the Penetration Depth in both the Meissner and the Mixed States of a YBaiCu^O-j-^,Thin Film with Low Energy MuonsDPG Friihjahrstagung, Regensburg (Germany), March 27-31 , 2000.

D. Andreica, F. N. Gygax, A. Schenck, A. Amato et al., RA-98-07 Collaboration/iSR studies of the nonmagnetic-magnetic transition in YbCu^-xAlx

FERLIN Workshop, II Ciocco (Italiy), October 5 - 7, 2000.

V. N. Duginov et al.,A. Amato, C. Baines, D. Herlach, U. Zimmermann, RA-97-04 CollaborationStudy of the magnetic properties of CesPd2oSie34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

V. S. Egorov, G. Solt, C. Baines, D. Herlach, U. Zimmermann, RA-99-09 CollaborationSR investigation of the topological phase transition in the type-I superconductor white tin34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

222

T. N. Mamedov et al., D. Herlach, U. Zimmermann, RA-97-25 CollaborationThe /iSR method and acceptor centers in Si34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

T. N. Mamedov et al.,D. Herlach, U. Zimmermann, RA-97-25 CollaborationThe magnetic moment of the negative muon in IS states of different atoms34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

A. N. Ponomarev et al.,D. Herlach, U. Zimmermann, RA-98-01 CollaborationMagnetic fields acting on muons in textured and single crystalline holmium34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

T. ProkschaExperiments with low-energy muons at PSI34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

G. Solt, V. S. Egorov, C. Baines, D. Herlach, U. Zimmermann, RA-94-14 CollaborationDiamagnetic domains in Sn?34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science,Repino (Russia), February 14 - 20, 2000.

H. GliicklerReichweite niederenergetischer Myonen in MetallenWorkshop Energiereiche Atomare Stosse, Riezlern (Austria), January 30, 2000.

H. GliicklerliSR an Oberfldchen und diinnen Schichten,3-NMR und /J,SR Treffen, Braunschweig (Germany), April 2000.

H. LuetkensExperimente mit niederenergetischen MyonenBMBF-Verbundtreffen Wasserstoff und Myonen in niederdimensionalen Systemen,Bochum (Germany), May 26-27, 2000.

M. PleinesExperimente mit niederenergetischen Myonen:Bestimmung der Londonschen Eindringtiefe in diinnen supraleitenden FilmenBMBF-Verbundtreffen Wasserstoff und Myonen in niederdimensionalen Systemen,Bochum (Germany), May 26-27, 2000.

H. GliicklerLE-fiSR: eine neue Methode zur Erforschung von Magnetismus an Oberfldchen und diinnen SchichtenBESSY, Berlin (Germany), 2000.

R. KhasanovOxygen isotope effect on in-plane penetration depth in underdoped Y\-xPrxBa-2CuzO~!-?,LMU Seminar, PSI, Villigen (Switzerland), November 21, 2000.

E. MorenzoniThin film studies with polarized low energy muonsPhysikalisches Kolloquium, Zurich (Switzerland), June 14, 2000.

E. MorenzoniMyonen als Sonden im OberfldchenbereichSeminarreihe Industrienahe Entwicklungen und Methoden, PSI, Villigen (Switzerland), November 3, 2000.

223

LABORATORY FOR ASTROPHYSICS

D. Amato, D. Pankow, K. Thomsen,Force limited vibration test test ofHESII imager,International Institute of Acousitcs and Vibration's 7th International Congress on Sound and Vibration,V-2527, Gramisch-Partenkirchen (Germany), July 4-7, 2000.

M. Audard, M. Giidel, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. S. Kaastra,R. Mewe, A. J. J. Raassen, C. de Vries, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels,J. R. Peterson, A. P. Rasmussen, M. Sako, G. Branduardi-Raymont, I. Sakelliou, C. Erd,Stellar coronae with XMM-Newton RGS. II, X-Ray VariabilityX-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000.

M. Audard, M. Giidel, R. Mewe, A. J. J. Raassen, E. Behar,Stellar coronae with XMM-Newton RGS Toulouse X-Ray Astronomy Workshop,Toulouse (France), September 2000. Proceedings of the workshop : Sept. 2000, Toulouse.

E. Behar, A. P. Rasmussen, J. Cottam, S. M. Kahn, F. B. S. Paerels,J. R. Peterson, M. Sako, A. C. Brinkman, A. J. den Boggende, J. W. den Herder,C. P. de Vries, C. Ferrigno, J. S. Kaastra, R. Mewe, T. Tamura, K. J. van der Heyden,G. Branduardi-Raymont, I. Sakelliou, M. Audard, M. Giidel, C. Erd,Modeling ofNon Equilibrium Ionizing Plasmas: Applications and Comparisonwith Supernova Remnant Observations by the RGS Spectrometer2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.

J. J. Bochanski J. M. DePasquale, L. E. DeWarf, P. V. DiTuro,E. f. Guinan, G. P. McCook, M. Giidel, J. Hargis, I. RibasThe Sun in Time: Starspots and Luminosity Variations of the Solar-type Stars of Different Ages196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000.Bull. Am. Astron. Soc. 196, 46.07.

G. Branduardi-Raymont, M. J. Page, I. Sakelliou, S. Zane,A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. S. Kaastra, R. Mewe,C. de Vries, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson,A. P. Rasmussen, M. Sako, M. Audard, M. Giidel, M. Kuster, J. Wilms, C. ErdXMM-Newton RGS Observations ofMCG -6-30-15 andMrk 766:Evidence for emission lines from a relativistic accretion diskX-Ray Astronomy 2000, Palermo (Italy), September 4 - 8 2000.

J. C. Brown, S. Krucker, M. Giidel, A. O. Benz,Mechanisms for Coronal Mass Supply by Evaporative Micro-Events.Recent Insights into the Physics of the Sun and Heliosphere,Highlights from SOHO and other Space Missions.IAU General Assembly, Manchester (UK), August 7 -11 , 2000.

J. Cottam, A. J. den Boggende, G. Branduardi-Raymont, A. C. Brinkman,C. Erd, M. Giidel, S. M. Kahn R. Mewe, F. B. S. Paerels, A. P. Rasmussen,I. Sakelliou, M. Sako, C.P. de Vries,High Resolution Spectroscopy ofEXO 0748-67 with the RGS on XMM196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000.Bull. Am. Astron. Soc. 196, 34.18.

J. J. Drake, V L. Kashyap, M. Audard, M. Giidel,Active Stellar Coronae: Lots of Little Flares?196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000.Bull. Am. Astron. Soc. 196,54.07.

S. A. Drake, N. E. White, M. Giidel, J. S. Kaastra, R. Mewe, T. Simon, K. P. Singh,A Chandra HETG Observation of the Active Binary Algol: Flaring and Quiescent Spectra2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.AAS Bulletin 32 (3), 42.08.

224

L. Grenacher, Ph. Jetzer, R. Piffaretti, D. Puy, M. Signore,Shape and geometry of galaxy clusters and the SZ effectProceedings of the SZ in Toulouse workshopToulouse (France), 29-30 June 2000.e-proceedings Toulouse observatory, astro-ph/0010512

L. Grenacher, Ph. Jetzer, D. Puy,Cold clouds in cooling flowsProceedings of the Workshop on Large Scale Structure in the X-ray Universe,Santorini (Greece), September 20 - 22,1999.Atlantiscience Eds., 371 (2000).

L. Grenacher, Ph. Jetzer, D. Puy,Molecular Clouds in Cooling Flow Cluster of GalaxiesProceedings of the Clustering at high redshift conference,Marseille (France), June 29 - July 2, 1999.ASP Conference Series vol. 200,415 (2000).

L. Grenacher,Microlensing and the galactic mass functionsIX Marcel Grossmann Meeting, Rome (Italy), July 4, 2000.

L. Grenacher, P. Jetzer, D. Puy,Thermal Equilibrium of Cold Clouds in PKS 0745-191Proceedings of the Workshop on Large Scale Structure in the X-ray Universe,Santorini (Greece), September 20 - 22, 1999.Atlantiscience Eds., 373 (2000).

M. Giidel,Characteristics of the RGS data and calibrationsXMM-Newton Science Advisory Group (SAG) Meeting, Leicester (UK), May 10, 2000.

M. Giidel,First Results from XMM/RGSXMM-Newton Science Survey Centre Consortium Meeting, Leicester (UK), May 11, 2000.

M. Giidel,X-ray Spectroscopy of Stellar CoronaeA New Decade of Cosmic X-Ray Spectroscopy, Utrecht (Netherlands), July 7, 2000.

M. Giidel,X-Ray Spectroscopic Studies of Stars - Invited Review,New Vistas from X-Ray Observatories, Warsaw (Poland), July 16 - 23, 2000.

M. Giidel, M. Audard, E. F. Guinan, J. J. Drake, V. L. Kashyap, R. Mewe, I. Y. Alekseev,AD Leo from X-Rays to Radio: Are Flares Responsible for the Heating of Stellar Coronae?X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000.

M. Giidel, M. Audard, A. J. den Boggende, A. C. Brinkman,J. W. den Herder, J. S. Kaastra, R. Mewe, A. J. J. Raassen, C. P. de Vries,E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson,A. P. Rasmussen, M. Sako, G. Branduardi-Raymont, I. Sakelliou, C. Erd,Stellar Coronae with XMM-Newton RGS. I, Coronal StructureX-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000.

225

M. Güdel, M. Audard, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels,J. R. Peterson, A. P. Rasmussen, G. Branduardi-Raymont, I. Sakelliou,A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. Kaastra, R. Mewe,T. Tamura, C. P. de Vries, C. Erd and the XMM Collaboration,Stellar Coronal Spectroscopy with the XMM-Newton RGS2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.AAS Bulletin 32 (3), 45.03.

M. Güdel,Roentgenastronomie mit XMM-Newton: Erste ResultatePhysikalischen Kolloqium, Universität Gießen (Germany), December 18, 2000.

W. Hajdas,Proton Irradiation Facility at PSI1999-2000ESA/ESTEC Final Presentation Day, Noordwijk (Netherlands), January 26, 2000.

W. Hajdas, N. Frey, O. Morath, K. Thomsen, A. Zehnder and W. Wittwer,Experimental Study of Space Proton Environment Effects on HESSI Detector BackgroundNuclear and Space Radiation Effects Conference NSREC, Reno (USA), 2000.

W. Hajdas, P. Buehler, A. Zehnder, R. Harboe-Sorensen,Proton Irradiation Facility and Space Radiation Monitoring1st International Workshop on Space Radiation Research and11th annual NASA Radiation Health Investigators Meeting, Arona (Italy), May 28-31 , 2000.

R. Henneck,Die High Energy Solar Spectmscopic Imager (HESSI) Mission,Frühjahrstagung "Extraterrestrische Physik" der DPG, Bremen (Germany), March 21 - 24, 2000.Verhandlungen der DPG, ISSN 0420-0195,2/2000, p.94.

J. W. den Herder, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam,A. J. den Boggende, L. Dubbeldam, C. Erd, M. Güdel, J. S. Kaastra,S. M. Kahn, R. Mewe, F. B. Paerels, I. Sakelliou, A. P. Rasmussen,J. Spodek, K. Thomsen, C. P. de Vries,Description and Performance of the Reflection Grating Spectrometer on board of XMM-NewtonSPIE Conference, Munich (Germany), Spring 2000.SPIE Proceedings, vol. 4012, 102 (2000).

Ph. Jetzer,Dunkle Materie in der MilchstrassePhysikalische Chemie, Universität Zürich (Switzerland), January 20, 2000.

Ph. Jetzer,Gravitational lensingSIGRAV Graduate School in Contemporary Relativity and Gravitational Physics,Villa Olmo, Como (Italy), May 8 - 13, 2000.

Ph. Jetzer,Gravitationslinseneffekt und dunkle Materie in der MilchstrasseUniversity of Köln (Germany), July 11, 2000.

Ph. Jetzer,Dark matter and microlensingCAPP 2000 Meeting, Verbier (Switzerland), July 18, 2000.

J. S. Kaastra, M. Audard, M. Güdel, A. J. den Boggende, A. C. Brinkman,J. W. den Herder, R. Mewe, A. J. J. Raassen, C. P. de Vries, E. Behar,J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen,M. Sako, G. Branduardi-Raymont, I. Sakelliou, C. Erd,X-ray Spectroscopy ofClusters of Galaxies with XMMX-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000.

226

V. L. Kashyap, J. J. Drake, M. Audard, M. Giidel,Flare Distributions and Coronal Heating on FKAqr196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000.Bull. Am. Astron. Soc. 196, 13.05

E. C. Kirk, J. Olsen, E. Miiller, A. Al Mazouzi, Ph. Lerch, A. Zehnder, H.R. Ott,Micro structural examination ofTES multilayersTrends in Condensed Matter Physics, Monte Verita (Italy), September 3 - 8 , 2000.

Ph. Lerch, E.C. Kirk, J. Olsen, A. Zehnder, H.R. Ott,Energy and time resolved imaging with cryogenic detectors18th General Conference of the Condensed Matter Division of the European Physical Society,Montreux (Switzerland), March 13-17, 2000.

Ph. Lerch, E. C. Kirk, J. Olsen, A. Zehnder,Readout issues with 1D/2D arrays ofSTJProc. Int. Workshop on Superconducting Detectors and Bolometers, Napoli (Italy), October (2000).

M. A. Leutenegger, M. Audard, E. Behar, A. J. den Boggende, A. C. Brinkman, G. Branduardi-Raymont,J. Cottam, C. Erd, C. Ferrigno, M. Giidel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, H. Magee, R. Mewe,F. B. S. Paerels, R. Pallavicini, J. R. Peterson, A. P. Rasmussen, G. Rauw, M. Sako, T. Tamura, I. Sakelliou,K. Thomsen, C. de Vries,High-Resolution X-Ray Spectroscopy ofZeta Puppis and Eta Carinae with the RGS on XMM2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.AAS Bulletin bf 32 (3), 42.01.

J. Olsen, E. C. Kirk, Ph. Lerch, A. Zehnder, H. R. Ott,Mo/Au Microcalorimeters for the detection of radiation and particlesTrends in Condensed Matter Physics, Monte Verita (Italy), September 3 - 8 , 2000.

F. B. S. Paerels, M. Audard, E. Behar, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, A. J. F. den Boggende,J. W. den Herder, C. P. de Vries, C. Erd, C. Ferrigno, M. Giidel, H. W. Hartmann, J. S. Kaastra, S. M. Kahn, R. Mewe,J. R. Peterson, A. P. Rasmussen, I. Sakelliou, M. Sako, T. Tamura, K. J. van der Heyden,High Resolution Spectroscopy of the Stellar Photosphere ofCal 83 with XMM-Newton/RGSX-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000.

F. B. S. Paerels, M. Audard, E. Behar, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, A. J. den Boggende,J. W. den Herder, C. de Vries, C. Ferrigno, M. Giidel, J. S. Kaastra, S. M. Kahn, R. Mewe, J. R. Peterson,A. P. Rasmussen, I. Sakelliou, M. Sako, T. Tamura, K. van der Heyden,High Resolution Spectroscopy of the Nuclear Region ofNGC1068 with XMM-Newton/RGS2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5-10, 2000.AAS Bulletin 32 (3), 1.05.

G. Paesold and A. O. Benz,Electron Firehose Instability and Acceleration of Electrons in Solar FlaresXXV EGS General Assembly, Nice (France), April 2000.

G. Paesold, A. O. Benz, K.-L. Klein, N. Vilmer,Spatial Analysis of Solar Type III Events Associated with Narrowband Spikes at Metric WavelengthAGU Fall Meeting, San Francisco (USA), December 2000.

F. De Paolis, G. Ingrosso, Ph. Jetzer, M. Roncadelli,A gamma ray halo around the Milky WayProceedings of the meeting The Chaotic Universe,Rome and Pescara (Italy), February 1-5,1999.World Scientific (Singapore), 414 (2000).

227

J. R. Peterson, M. Audard, E. Behar, A. J. den Boggende, A. C. Brinkman, G. Branduardi-Raymont,J. Cottam, C. Erd, C. Ferrigno, M. Giidel, J. W. den Herder, J. G. Jernigan, J. S. Kaastra, S. M. Kahn, R. Mewe,F. B. S. Paerels, A. P. Rasmussen, M. Sako, T. Tamura, I. Sakelliou, K. Thomsen, C. P. de Vries,X-ray Spectroscopy of Clusters of Galaxies with XMM-Newton2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.AAS Bulletin 32 (3), 13.22.

D. Puy,The Sunyaev-Zel'dovich effectPaul Scherrer Institut-LAP, Villigen (Switzerland), March 23, 2000.

D. Puy,The Sunyaev-Zel'dovich effect for cluster of galaxies, implications for cosmologyUniversity of Bern (Switzerland), May 10, 2000.

D. Puy,Cosmológica! Thermal decoupling and primordial moleculesJENAM 2000 meeting, Moscow (Russia), May 31, 2000.

D. Puy,Shape and geometry of galaxy clusters and the SZ effectObservatory of Toulouse (France), June 29, 2000.

D. Puy,Cosmochemistry in the early UniverseICTP conference 2000, Trieste (Italy), September 22, 2000.

A. P. Rasmussen, M. Audard, E. Behar, J. A. M. Bleeker, A. J. den Boggende, G. Branduardi-Raymont, A. C. Brinkman, J.Cottam, L. Dubbeldam, C. Erd, M. Güdel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. S. Paerels, J. R. Peterson,C. P. de Vries, I. Sakelliou, K. Thomsen, A. Zehnder,XMM/RGS High Resolution Spectroscopy of the Magellanic Cloud Supernova Remnant Sample: 1E0102-72.3 and the OthersX-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000.

A. P. Rasmussen, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, M. Sako, J. A. M. Bleeker, A. J. den Boggende,A. C. Brinkman, J. W. den Herder, K. J. van der Heyden, J. Kaastra, R. Mewe, T. Tamura, C. P. de Vries, G. Branduardi-Raymont,I. Sakelliou, M. Audard, M. Güdel, C. Erd,The Magellanic Cloud Supernova Remnant Sample as Observed by XMM/Newton RGS2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.AAS Bulletin 32 (3), 40.03.

M. Sako, M. Audard, E. Behar, A. J. den Boggende, Th. Boiler, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, C. Erd,C. Ferrigno, M. Güdel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, A. Lagostina, R. Mewe, F. B. S. Paerels, J. R. Peterson, M.Pierre, E. M. Puchnarewicz, A. P. Rasmussen, T. Tamura, I. Sakelliou, K. Thomsen, C. P. de Vries,XMM-Newton Observation of the Complex Absorbing Medium in IRAS 13349+24382000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000.AAS Bulletin 32 (3), 2.03.

K. W. Smith, I. A. Bonnell, J. P. Emerson, T. Jenness,SCUBA Observations of NGC1333/IRAS4Colloquium at Onsala Space Observatory (Sweden), June 2000.

K. W. Smith, I. A. Bonnell,Free Floating Planets in Stellar ClusterPresentation at the Asgård Users Day, December 2000.

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LABORATORY FOR MICRO AND NANO TECHNOLOGY

J. A. Anna Selvan, D. Griitzmacher, E. Miiller and J. GobrechtComparison of growth of Si thin films on low temperature amophous substrates by MBE and PECVDMaterials Research Society Spring meeting., San Fransisco (USA), May 2000.

J. A. Anna Selvan, D. Grutzmacher, M. Kummer, H von Kanel, M. Rebien, E. Miiller, E. Ortelli and J. GobrechtDevelopment of Si films by new methods of DC PECVD techniques for thin film solar cell applications16th E.C. Photovoltaic Solar Energy Conf., Glasgow (UK), Mai 2000.

J. A. Anna Selvan, D. Grutzmacher, M. Hadorn, B. Bitnar, W. Durisch, S. Stutz, T. Neiger and J. GobrechtTuneable plasma filters for TPV systems using transparent conducting oxides of tin doped indium oxide andAl doped Zinc Oxide16* E.C. Photovoltaic Solar Energy Conf., Glasgow (UK), Mai 2000.

B. Baumeister, T.A. Jung and L. ScandellaFracture Mechanics and Erosive Wear of Microfabricated SiO2-Nanotowers on Si:SPM Studies and New Experimental Modes4* International Conference on the Development and Technological Application of Scanning Probe Methods (SXM4),Minister (Germany), September 25 - 27, 2000.

S. Berner, M. Brunner, H. Suzuki, T.A. Jung and H.-J. GuentherodtDeposition System for Single Molecule STM Experiments4th Hasliberg Workshop on Nanoscience, Hasliberg (Switzerland), October 16 - 20, 2000.

S. Berner, M. Brunner, H. Suzuki, T.A. Jung and H.-J. GuentherodtSingle Molecule Physics, Molecular Epitaxy and Layering: The Experimental Approach4th International Conference on the Development and Technological Application of Scanning Probe Methods (SXM4),Minister (Germany), September 25 - 27, 2000.

S. Berner, M. Brunner, H. Suzuki, T.A. Jung and H.-J. GuentherodtMolecular Patterning in UHV: From Deposition to STM ExperimentsWorkshop on Scanning Probe Microscopies and Organic Materials IX, Hannover (Germany), October 9 - 1 1 , 2000.

J.H.H. Bongaerts, C. David, G. H. Wegdam, M. A. de Vries and J. F. van der VeenFocusing an x-ray beam onto a planar waveguide using a Fresnel zone plateSLS Workshop, Les Diablerets (Switzerland), October 16 - 20, (2000).

M. Brunner, S. Berner, H. Suzuki, T.A. Jung and H.-J. GuentherodtStructure and Confirmation of Single Molecules from UHV-STMWorkshop on Scanning Probe Microscopies and Organic Materials IX, Hannover (Germany), October 9 - 1 1 , 2000.

A. Beyer, O. Leifeld, S. Stutz, E. Miiller and D. GriitzmacherIn-situ STM analysis andphotoluminescence of C-induced Ge dotsInternational Symposium on "Nanostructures: Physics and Technology", St. Petersburg (Russia), June 19 -23, 2000.

A. Beyer, O. Leifeld, G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, E. Mtiller, S. Stutz and D. GrutzmacherLuminescence enhancement from Si using SiGe and SiGeC quantum confinement structuresSeminar: Centre de recherche sur les mechanismes de la croissance cristalline, CRNS, Marseille (France), July 28, 2000.

A. Beyer, O. Leifeld, O. Kirfel, G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, E. Mtiller, S. Stutz and D. GrutzmacherSi-Ge-(C) Nanostrukturen - Moglichkeiten der Lichtemission aus SiSeminar: Walter-Schottky-Institute, Technical University Miinchen (Germany), November 7, 2000.

A. Beyer, O. Leifeld, O. Kirfel, G. Dehlinger, U. Gennser, H. Sigg, E. Miiller, S. Stutz and D. GriitzmacherSi technology off the beaten path: Molecular beam epitaxy of low dimensional Si/SiGeC structuresSeminar: Institute for Semiconductor Physics, Johannes Keppler Universitat Linz (Austria), December7, 2000.

C. DavidNanofabrication of diffractive optical elements by low voltage electron beam lithographyInstitute of Microtechnology, University of Neuchatel (Switzerland), January 26, 2000.

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C. David, D. Wiesmann, R. Germann, F. Horst, B. J. Offrein, R. Beyeler, H.W.M. Salemink and G. L. BonaApodised Bragg gratings in planar waveguides for add-drop filtersMicro and Nanoengineering MNE 2000, Jena (Germany), September 19, 2000.

C. David, L. Heyderman, B. Ketterer, E. Deckardt, U. Dötsch and B. NöhammerThe LION at PSIELBUM Meeting, Jena (Germany), September 22, 2000.

C. DavidNano fabrication of diffractive x-ray opticsSLS Workshop, Les Diablerets (Switzerland), October 18, 2000.

C. DavidX-ray lensesGray Laboratories, Northwood (UK), November 15, 2000.

C. David, J. Wei, T. Lippert and A. WokaunDiffractive grey tone masks for laser ablation lithographyMicro and Nanoengineering MNE 2000, Jena (Germany), September 19, 2000.

J.-H. Fabian, L. Scandella, R. Berger, J. Gobrecht, Ph. Lerch and E. MeyerA Micromechanical Device for Thermal Analysis ofNanogram Sample Quantities12* International Congress on Thermal Analysis and Calorimetry, International Confederation for Thermal Analysis andCalorimetry ICTAC, Copenhagen (Danemark), August 14 - 18, 2000.

J.-H. Fabian, L. Scandella, H. Fuhrmann, J. Gobrecht, E. Meyer and Ph. LerchFinite Element Calculations of Micromechanical Cantilever Sensor-Arrays for Nanoscale Thermal Analysis18th CAD-FEM Users' Meeting, International Congress on FEM Technology,Friedrichshafen (Germany), September 20 - 22, 2000,

J. Gobrecht, H. Schift, C. David, W. Kaiser, A. D'Amore, D. Simoneta and L. ScandellaInjection molded plastic chip for calibration of scanning probe microscopesInvited talk, 4th Seminar on Quantitative Microscopy QM 2000, Semmering (Austria), January 12 - 14, 2000.

J. Gobrecht and H. SchiftFunctional Nanostructures on Surfaces: from „ Manufacture " to Mass Production "Invited talk, 16th meeting Schweiz. Gesellschaft für Oberflächentechnik, Fribourg (Switzerland), January 27, 2000.

J. GobrechtNanotechnology - Between Science Fiction and Real World ApplicationsInvited talk, Unisys Users Association 2000 Conference, The Hague (NL), May 15 - 18, 2000.

J. GobrechtMicro- and nanostructuring of Surfaces for non-electronic applicationsInvited talk, 6th Annual Meeting of the Swiss Society of Biomaterials, Davos (Switzerland), June 8 - 9 , 2000.

J. GobrechtNanotechnologieInvited seminar talk, Zentralinstitut für Biomedizinische Technik, Friedrich-Alexander Universität,Erlangen-Nürnberg (Germany), July 20, 2000.

J. GobrechtKristallines Silizium: Fortschritte und Zukunft beim Arbeitspferd der PhotovoltaikNationale Photovoltaik-Tagung, Neuchatel (Switzerland), November 7 - 8 , 2000.Proc.(ed. S. Novak, BfE), 56 (2000).

J. GobrechtNanotechnologie - Perspektiven für neue Werkstoffe und Methoden in der biomedizinischen Technik34. Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaft für Biomedizinische Technik,Lübeck (Germany), September 28 - 30, 2000.

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J. Gobrecht, L. Heyderman and H. SchiftSubmicron- and Nanostructuring of Surfaces for Non-Electronic ApplicationsSwiss-Japanese Workshop on Nanoscience, Riken (Japan), October 27 - 28, 2000.

J. GobrechtMikro- und Nanostrukturtechnikfür Oberflächen: Beschichten - strukturieren - charakterisierenPSI-Seminarreihe „Industrienahe Entwicklungen", Seminar „Oberflächentechnologie",Vilügen (Switzerland), November 3, 2000.

A. Grubelnik, C. Padeste and L. TiefenauerAmperometric immunosensor for penicillin in milkBiosensors 2000, San Diego (USA), May 24 - 26, 2000.

D.GrützmacherStrukturierung im nm-BereichSeminar: Fakultät für Elektrotechnik, Technische Universität Ilmenau (Germany), July 20, 2000.

D. GrützmacherNanostrukturen: Neue Wege für die Lichtemission aus SiliziumSeminar: Fakultät für Elektrotechnik, Technische Universität Ilmenau (Germany), July 20, 2000.

L. J. Heyderman, H. Schift and J. GobrechtMicro- and Nanorheological Aspects of Thin Thermoplastic Films during Hot Embossing6* MELARI /NID Workshop on Printing, Univ. of Twente (Netherlands), June 25 - 28, 2000.

L. J. Heyderman, H. Schift and J. GobrechtNanoreplication at the Paul Scherrer InstituteMESA-Insitute, Univ. of Twente (Netherlands), June 28, 2000.

L. J. Heyderman, H. Schift, C. David, B. Ketterer, M. Auf der Maur and J. GobrechtNano fabrication using hot embossing lithography and electroformingMNE'2000, Jena (Germany), September 20 - 22, 2000.

L. J. Heyderman, H. Schift and J. GobrechtMicro- and nanorheological aspects of thin thermoplastic films during hot embossingEPS-CMD Montreux (Switzerland), March 13 - 17, 2000.

L. J. Heyderman, H. Schift, C. David and J. GobrechtMicro- and nanorheological study of thin thermoplastic films during hot embossingHasliberg workshop on Nanoscience, Hasliberg (Switzerland), October 16 - 20, 2000.

T. A. JungSingle molecules at surfaces: Will there be molecular devices after microelectronics?Invited Seminar, University of Nijmegen (Netherlands), September 12, 2000.

T. A. Jung, H. Yanagi and H. SuzukiMolecular Nanoscience: The Science for future TechnologiesJapanese Swiss Workshop on Nanoscience, Riken (Japan), October 26 - 29, 2000.

T. A. Jung, S. Berner, M. Brunner, B. Baumeister and H. SuzukiThe Physics and Chemistry of Molecules at Interfaces: Where is the single molecular device?Invited presentation, University of Ulm (Germany), November 24, 2000.

T. A. Jung, S. Berner, M. Brunner and H. SuzukiMolecular Nanoscience at Surfaces and Interfaces: What's different from Molecular Biology and what's needed forMolecular Devices?Invited Seminar, University of Neuchatel (Switzerland), December 4, 2000.

T. A. JungThe Role of Physics for the Future of our Global SocietyInvited Presentation at the World Conference of Physical Societies, held in Conjunction with the Max Planck CentennialWeek, Berlin (Germany), December 15 - 16, 2000.

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O. Leifeld, A. Beyer, E. Miiller, D. Griitzmacher and K. KernNucleation ofGe dots on the C-alloyed Si(OOl) surfaceEuropean Materials Research Society Spring Meeting, Strasbourg (France), May 5 - June 2, 2000.

C. PadesteMolekulare Architektur fur die elektrochemische BiosensorikDFG-Workshop ,,Reaktion und Stabilitat von Nanopartikeln", Dresden (Germany), April 2 - 4, 2000.

C. Padeste, A. Grubelnik and L. TiefenauerMolecular architecture for electrochemical biosensorsBiosensors 2000, San Diego (USA), May 24 - 26, 2000.

F. Pfeiffer, T. Salditt, C. David and P. H0gh0jX-Ray WaveguidesSLS Workshop, Les Diablerets (Switzerland), October 16 - 20, (2000).

F. Pfeiffer, T. Salditt, P. Hoghoj and C. DavidNewly designed x-ray waveguides45th SPIE Annual Meeting, San Diego (USA), August 3, 2000.

R. Ros, F. Schwesinger, T. Stranz, A. Pliickthun, H-J. Giintherodt and L. TiefenauerCharacterization of antibody-antigen complexes using force spectroscopy44th Ann. Meet. Biophys., New Orleans (USA), February 12 - 16, 2000.

H. SchiftReplication of micro- and nanostructures using molding techniquesLecture given at the CSEM Colloquium Series on Applications on Nanosciences, Neuchatel (Switzerland), April 28, 2000.

H. Schift, A. D'Amore, C. David, M. Gabriel, J. Gobrecht, W. Kaiser and D. SimonetaQuantitative analysis of the molding of nanostructuresEIPBN'2000, Palm Springs (USA), May 30 - June 2, 2000.

H. Schift, L J. Heyderman, M. Auf der Maur and J. GobrechtPattern formation in hot embossing of thin polymer filmsTNT'2000, Toledo (Spain), Octoberl6 - 20, 2000.

H. SchiftThe nano replication toolbox: from mastering to mass fabricationTOP Nano 21 meeting, Bern (Switzerland), October 24, 2000.

H. Schift, A. D'Amore, M. Gabriel, J. Gobrecht, L. J. Heyderman, W. Kaiser and D. SimonetaReplication of micro- and nanostructures using molding techniquesUS-Swiss Forum on Nano Bio Sciences, Princeton (USA), December 14 - 15, 2000.

H. Schift, L J. Heyderman and J. GobrechtNanoreplication in polymers using hot embossing and injection moldingNFP36 closing meeting, Bern (Switzerland), November 13 - 14, 2000.

H. Sigg, S. Gehrsitz and F-K ReinhartVegards law in the AlGaAs systemGroup seminar IBM Forschungslabor, Riischlikon (Switzerland), June 20, 2000

H. Sigg, G. Dehlinger, L. Diehl, U. Gennser, J. Faist, K. Ensslin, D. Griitzmacher and E. MiillerPossibilities of a Si-based quantum cascade laser ?Seminar at Physik Institut Universitat Linz (Austria), December 12, 2000

H. Sorribas, D. Braun, C. Padeste, P. Sonderegger and L. TiefenauerNeurite outgrowth on surfaces treated with neural adhesion molecules2nd MEA Conference, Reutlingen (Germany), July 22 - 23, 2000.

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H. Sorribas, C.Padeste, P. Sonderegger and L. TiefenauerPatterns of adhesion molecules for cell guidanceAnn. Meet . Swiss Soc. Biomaterials , Davos (Switzerland), June 8 - 9 , 2000.

H. SorribasNeurons on microstructured biofunctionalised surfacesAO Research Institut, Davos (Switzerland), January 28, 2000.

H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung and H.-J. GiintherodtRotational behaviour in orientation of sub-phtalocyanine overlayer on Ag sufaceFirst International Conference on Molecular Electronics and Bioelectronics (M&BE1),Awaji Yumebutai International Conference Center (Japan), March 5 - 7, 2000.

H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung and H.-J. GiintherodtCharacterization of molecular overlayers on metal surface in dynamic equilibrium by scanning tunneling microscopeInternational Conference on Nanomolecular Electronics, Kobe (Japan), December 5 - 7 , 2000.

H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, H. Rauscher, F. J. Himpsel,K. Muellen, T. A. Jung and H.-J. GuentherodtSingle Molecule Mechanics and Electronics of Individual Molecules at Contacting InterfacesInvited Presentation at Molelecular Electronics 2000, Organizer: United Engineering Foundation, Inc.Kailua - Kona (USA), December 10 - 14,. 2000.

H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung and H.-J. GiintherodtComparative Analysis of Various Porphyrin Compounds from Scanning Tunneling Microscopy andSpectroscopy with Sub-Molecular ResolutionSecond International Conference on Scanning Probe Spectroscopy, Hamburg (Germany), July 19 - 22, 2000.

L. Tiefenauer, A. Grubelnik, R. Ros, H. Sorribas and C. PadesteMicrostructuring and functionalization of surfaces for biosensors and related applicationsCHI-Conference on ,,Lab-chips and microarrays", Zurich (Switzerland), January 17 -19, 2000.

L. TiefenauerMolecular Nanotechnology: Functional molecules on structured surfacesSeminar Inorg. Chemistry, ETH Zurich (Switzerland), April 28, 2000.

L. TiefenauerForce spectroscopy for investigating biorecognitionUS-Swiss Forum on Nano Bio Science, Princeton University NJ (USA), December 13 -16, 2000.

L. Tiefenauer, A. Grubelnik and C. PadestePrevention of protein adsorption to active gold electrodesWorld Biomaterials Congress, Kamuela (USA), May 15 - 20, 2000.

LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY

HEAVY ELEMENTSCh.E. DullmannIVO - ein neuer Separator fur In-Situ Verfluchtigung und On-line DetektionSeminar Radio- und Umweltchemie, Universitat Bern (Switzerland), April 14, 2000.

Ch.E. Dullmann, A. Tiirler, D.T. Jost, D. Piguet, H. Blumer, B. Eichler, R. Eichler, H.W. GaggelerIVO - new apparatus for In-situ Volatilization and On-line detection of transactinide elements5th International Conference on Nuclear and Radiochemist ry (NRC5) , Pontresina (Switzerland), September 3 - 8 , 2000 .

B . EichlerInteraction of transactinides Z=104-116 with metal surfaces5th International Conference on Nuclear and Radiochemist ry (NRC5) , Pontresina (Switzerland), September 3 - 8 , 2000 .

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R. Eichler, H. Gaggeler, A. Tiirler, K.E. Gregorich, D.C. Hoffman, H. Nitsche, C.A. Laue, M. Schadel, A.B. YakushevFirst chemical characterization ofbohrium (element 107)220th ACS meeting, Division of Nuclear Chemistry & Technology, Washington D.C. (USA), August 20 - 24, 2000.

R. EichlerGasphase chemistry ofbohrium (element 107)5th International Conference on Nuclear and Radiochemistry (NRC5) , Pontresina (Switzerland), September 3 - 8 , 2000 .

H.W. GaggelerChemistry ofTransactinide ElementsWorkshop on "Sciences with low energy radioactive beams", IPNS/KEK, Tokyo (Japan), March 10, 2000.

H.W. GaggelerGas Phase Chemistry of the Transactinide ElementsJAERI, Tokai (Japan), Macrh 12, 2000.

H.W. GaggelerStatus of the Spoliation Neutron Source SINQJAERI, Tokai (Japan), March 12, 2000.

H.W. GaggelerDas Wettrennen am obersten Ende des Periodensystems: Chemie versus PhysikPhysikalisches Kolloquium, ETHZ/Univ. Zurich (Switzerland), April 5, 2000.

H.W. GaggelerGas Phase Chemistry of TransactinidesChemical and Nuclear Properties of the Heaviest Elements - A Symposium in Memory of Glenn T. SeaborgACS Meeting, Washington (USA), August 20 - 24, 2000.

H.W. Gaggeler5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3 - 8 , 2000 (organizer).

H.W. GaggelerRadioactivity measurements at JungfraujochNDSC steering committee meeting, Hotel Seepark, Thun (Switzerland), September 12 - 14, 2000.

H.W. Gaggeler1st das Ende des Periodensy stems erreicht?Tagung der Schweiz. Gymnasiallehrer, Baden (Switzerland), September 26, 2000.

H.W. GaggelerNew Results from Heavy Element ResearchSeminar Section TEM, Paul Scherrer Institut, Villigen (Switzerland), November 10, 2000.

A. TiirlerHeavy Element Research at the Paul Scherrer InstituteNuclear Physics Forum, 88" Cyclotron, Lawrence Berkeley National Laboratory, Berkeley (USA), April 27, 2000.

A. TiirlerChemistry and Physics of Heavy and Superheavy ElementsCyclotron Institute Colloquium, Cyclotron Institute, Texas A&M University, College Station (USA), May 16, 2000.

A. TiirlerHeavy Element Research at the Paul Scherrer InstituteNuclear Chemistry Division Seminar, Nuclear Chemistry Division, Lawrence Livermore National Laboratory,Livermore (USA), May 25, 2000.

A. TiirlerAnwendungen kurzlebiger RadionuklideSeminar fiir Kern- und Radiochemie, Institut fur Kernchemie, Universitat Mainz (Germany), June 26, 2000.

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A. Türler, P. A. Wilk, R. Eichler, K. E. Gregorich, D. T. Jost, C. A. Laue, V. Ninov, J. L. Adams, W. Brüchle,R. Dressier, Ch. E. Diillmann, B. Eichler, H.W. Gäggeler, D. C. Hoffman, S. Hübener, U. W. Kirbach, M. R. Lane,V.M.H. Lavanchy, D. M. Lee, H. Nitsche, J. B. Patin, M. Schädel, D. A. Shaugnessy, D. A. Strellis, S. Taut, L. Tobler,Yu. Tsyganov, A. Vahle, A. B. YakushevTwo new isotopes of element 107:266Bh and 267Bh7th International Conference on Nucleus Nuc leus Coll is ions, Strasbourg (France), July 3 - 7 , 2000 .

A. TiirlerNuclear Chemistry Studies of Superheavy ElementsSymposium on Future Physics with Exotic Nuclei, GSI Darmstadt (Germany), July 10 - 11, 2000.

A. TürlerHalides and Oxyhalides of the Transactinide Elements Rf Db, and S g5th International Conference on Nuclear and Radiochemis t ry (NRC5) , Pontresina (Switzerland), September 3 - 8 , 2000 .

A. TürlerChemie mit kurzlebigen RadionuklidenInstitut für Radiochemie, TU München, Garching (Germany), November 21, 2000.

SURFACE CHEMISTRYM. Ammann, F. Arens, L. Gutzwiller, U. Baltensperger, H.W. GäggelerThe reaction ofNO2 with diesel soot: a significant source ofHONO?European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000.

M. Ammann, L. Gutzwiller, U. Baltensperger, H.W. GäggelerMeasurement ofHONO with a wett effluent diffusion dénuder and possible implications for nitrite formationin aqueous solution in presence of diesel exhaustFinal Meeting of the EU-project DIFUSO, CEAM, Valencia (Spain), July 24, 2000.

M. Ammann, L. GutzwillerThe heterogeneous reaction ofNO2 with organic compounds representative of VOC photooxidation productsKick-off Meeting of the EU Project NITROCAT, Wuppertal (Germany), May 5, 2000.

M. AmmannShort-lived radiotracers for surface chemical studies.Invited lecture 5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3 - 8 , 2000.

M. Ammann, T. Bartels, M. Wachsmuth, H.W. GäggelerAdsorption of nitrogen oxides on iceAmerican Geophysical Union Fall, Meeting, San Francisco (USA), December 15 - 19, 2000.

M. Ammann, T. Bartels, P. Zimmermann, B. Eichler, H.W. GäggelerThe adsorption of NO and NO2 on iceEuropean Geophysical Society, XXV General Assembly EGS2000, Nizza (France), April 25 - 29, 2000.

M. Ammann, T. BartelsAdsorption of trace gas species on iceKick-off meeting of the EU Project Cut-ice, Mainz (Germany), March 13 -14, 2000.

F. Arens, M. Ammann, L. Gutzwiller, U. Baltensperger, H.W. GäggelerFormation of HONO from the reaction ofNO2 with diesel sootEuropean Aerosol Conference, Dublin (Ireland), September 3 - 8, 2000. J. Aerosol Sei. 31, S1035 (2000).

F. Arens, L. Gutzwiller, T. Bartels, M. Wachsmuth, H.W. Gäggeler, M. AmmannThe reaction ofHNO3 with sea salt aerosol particlesChemical Mechanism Development, EC/Eurotrac-2 Joint Workshop, Lausanne (Switzerland), September 11 - 13, 2000.

F. Arens, M. Ammann, L. Gutzwiller, U. Baltensperger, H.W. GäggelerThe reactivity of NO, with diesel soot and OH substituted PAHsEurotrac-2 Symposium 2000, Garmisch-Partenkirchen (Germany), March 27-31 , 2000.

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T. BartelsAdsorption von Peroxyacetylnitrat aufEisSeminar Radio- und Umweltchemie, Universitat Bern (Switzerland), December 8, 2000.

T. Bartels, H.W. Gaggeler, M. AmmannAdsorption of PAN on ice5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3 - 8 , 2000.

T. Bartels, H.W. Gaggeler, M. AmmannAdsorption of PAN on iceChemical Mechanism Development, EC/Eurotrac-2 Joint Workshop, Lausanne (Switzerland), September 11 - 13, 2000.

J. N. Crowley, R. A. Cox, M. Ammann, G. Poulet, A. Horn, R. Zellner, M. J. Rossi, P. Mirabel, F. DomineChemistry of the upper troposphere: laboratory studies of heterogeneous processes on iceAviation, Aerosols, Contrails and Cirrus clouds, Seeheim (Germany), July 10 - 12, 2000.

L. GutzwillerImpact of diesel exhaust on atmospheric processesDepartment of Chemistry, Universidad Nacional Autonoma de Mexico (Mexico), March 3, 2000.

L. GutzwillerHONO Bildung an Dieselruss in einer Smogkammer im Rahmen des Projekts DIFUSOSeminar Radio- und Umweltchemie, Universitat Bern (Switzerland), April 14, 2000.

L. Gutzwiller, U. Baltensperger, M. AmmannAqueous reduction of nitrogen dioxide to nitrite at gas phase concentrations below lppm NO2

European Geophysical Society, XXV General Assembly EGS2000, Nizza (France), April 25 - 29, 2000.

L. Gutzwiller, F. Arens, M. AmmannThe HONO formation capacity of diesel exhaustChemical Mechanism Development, EC/Eurotrac-2 Joint Workshop, Lausanne (Switzerland), September 11 - 13, 2000.

L. Gutzwiller, F. Arens, M. AmmannThe HONO formation capacity of diesel exhaustEnergy Technologies for a Sustainable Future, Paul Scherrer Institute, Villigen (Switzerland), November 23 - 24, 2000.

L. GutzwillerWhy should we measure HONO in Mexico City?Centro de Ciencias de la Atmosfera, Universidad Nacional Autonoma de Mexico (Mexico), March 3, 2000.

M. Wachsmuth, B. Eichler, L. Tobler, D.T. Jost, H.W. Gaggeler, M. AmmannOn-line gas-phase separation of short-lived bromine nuclides from precursor selenium5th Nuc lea r and Rad iochemis t ry Conference ( N R C 5 ) Pont res ina (Switzer land) , Sep tember 3 - 8 , 2000 .

ANALYTICAL CHEMISTRYA. Eichler, M. Schwikowski, H.W. Gaggeler, U. Schotterer, M. AmmannReconstruction of historical aerosol concentrations in Europe from Alpine ice coresEUROTRAC-2 Symposium 2000, Garmisch-Partenkirchen (Germany), March 27-31 , 2000.

A. EichlerInterpretation chemischer Signale in einem Eisbohrkern vom Grenzgletscher (Walliser Alpen)Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), April 14, 2000.

A. Eichler, M. Schwikowski, H.W. Gaggeler, U. SchottererHigh resolution paleo atmospheric records from ice cores of the northern and southern AlpsEuropean Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000.

A. Eichler, M. Schwikowski, H.W. Gaggeler, V. Furrer, H.-A. Synal, J. BeerHistorical deposition records of radioactive isotopes from an Alpine Ice Core5th In ternat ional Conference on Nuc lea r and Rad iochemis t ry ( N R C 5 ) , Pont res ina (Switzer land) , Sep tember 3 - 8 , 2000 .

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H.W. GaggelerSnow and ice from the Alps as environmental archivesObservatoire de Geneve, Geneva (Switzerland), January 11, 2000.

H.W. GaggelerGlaziologische NaturgefahrenWorkshop, Glaziologische Kommission und Naturforschende Gesellschaft Oberwallis der Schweiz.Akademie der Naturwissenschaften (SANW), H.W. Gaggeler and H. Schmidt (Organizers),Brig (Switzerland), January 13, 2000.

H.W. GaggelerAlpengletscher als UmweltarchiveNaturforschende Gesellschaft Solothurn, Solothurn (Switzerland), February 21, 2000.

P. Ginot, U. Schotterer, M. Schwikowski, W. Stichler, H.W. GaggelerGlaciochemical evidence of past El Nino events in an ice core from Cerro Tapado, ChileEuropean Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000.

P. GinotCerro Tapado Ice Core: El Nino record and importance of post deposition effectsSeminar Radio- und Umweltchemie, Universitat Bern (Switzerland), June 16,2000.

P. Ginot, C. Kull, U. Schotterer, M. Schwikowski, H.W. GaggelerEffects of post depositional processes on glaciochemical records derived from Andean Cerro Tapado glacier17. Geowissenschaftliches Lateinamerika-Kolloquium, Stuttgart (Germany), October 11-13, 2000.

T. M. HuberKontinuierliches Schmelzen und Analysieren von Eisbohrkernen im Vergleich mit konventioneller AnalysentechnikSeminar Radio- und Umweltchemie, Paul Scherrer Institut, Villigen (Switzerland), May 12, 2000.

T. M. HuberKontinuierliche Analyse von Eisbohrkernen mittels lonenchromatographieAnwendertreffen Ionenchromatographie, Dionex, Olten (Switzerland), May 23, 2000.

T. M. Huber, M. Schwikowski, H.W. GaggelerContinuous Melting and Ion Chromatographic Analyses of Ice CoresInternational Ion Chromatography Symposium, Nice (France), September 11-14, 2000.

S. Kniisel, T. M. Huber, M. Schwikowski, H.W. GaggelerAnalyse von Schwermetallen im Gletschereis mit kontinuierlicher Schmelzmethode und doppelfokussierendemICP-MS5. Symposium: Massenspektrometrische Verfahren der Elementspurenanalyse, Jiilich (Germany), September 18 - 21,2000.

S. KniiselAnalysis of trace elements in ice cores by CIM-ICP-MSSeminar Radio- und Umweltchemie, Paul Scherrer Institut, Villigen (Switzerland), November 10, 2000.

V.H.M. Lavanchy, U. Baltensperger, G. Bonani, U. Schotterer, M. Schwikowski, M. Suter, H.W. GaggelerHistorical record of carbonaceous particles from an ice core from the Alps and a first attempt for their 14C datingEuropean Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000.

N.L. MisraSome studies on the applicability of Total Reflection X-ray Fluorescence (TXRF)for trace element analysisin ice samplesSeminar des Kompetenzzentrums Analytische Chemie der ETH Zurich, Zurich (Switzerland), November 30, 2000.

U. SchottererIsotopen im Wasserkreislauf als Klimaindikator: Bedeutung des Messnetzes der Landeshydrologie und -geologiefur GrundwasseruntersuchungenJahrestagung der Gesellschaft fur Hydrogeologie: Isotopen im Grundwasser, ETH Zurich (Switzerland), April 14, 2000.

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U. SchottererThe isotopic fingerprint of El Nino in precipitation and ice cores from the tropical AndesSeminar Lab. des Sciences du Climat et de l'Environnement, C.E. Saclay, Gif-sur-Yvette (France), April 27, 2000.

U. SchottererIsotopic fingerprints for detecting El Nino in ice coresSeminar Radio- und Umweltchemie, Universitat Bern (Switzerland), June 16, 2000.

M. Schwikowski, P. Ginot, H.W. Gaggeler, U. Schotterer, M. Funk, R. Gallaire, B. Pouyaud, A. Rivera,F. Stampfli, W. StichlerPalaeo atmospheric chemistry and climate records from Cerro Tapado glacier, Norte Chico, Chile,Ice Fields Scientific Task Force, March 24 - 28, 2000, sailing on board the "Aquiles" to the Ice Fields,CECS Valdivia (Chile), March 29, 2000.

M. Schwikowski, B. Tenberken-Potzsch, M. AmmannSampling and Separation of ice crystals and supercooled cloud dropletsEUROTRAC-2 Symposium 2000, Garmisch-Partenkirchen (Germany), March 27-31 , 2000.

M. Schwikowski, H.W. Gaggeler, U. Schotterer, A. Dallenbach1000 year palaeo record of the European atmosphere from an alpine ice core (Colle Gnifetti, Swiss Alps),European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000.

M. Schwikowski, H.W. Gaggeler, U. SchottererEcological studies in the Alps and AndesInt. Conf. on social-oriented environmental problems of contiguous territories of Altai-Sayany Region,Polyex Hotel, Aya Gorni Altai (Russia), July 3 - 7, 2000.

M. SchwikowskiHochalpine Gletscher als Archive fiir Klima- und AtmospharenforschungASE-Seminar, Paul Scherrer Institut, Villigen (Switzerland), November 7, 2000.

M. SchwikowskiFirst glacio-chemical investigation of Belukha glacier in the Siberian AltaiSeminar Radio- und Umweltchemie, Paul Scherrer Institut, Villigen (Switzerland), November 10, 2000.

M. SchwikowskiAnalyse von chemischen Spurenstoffen in Eis zur Rekonstruktion der LuftverschmutzungUniversitat Hamburg, Institut fur Anorganische und Angewandte Chemie, Hamburg (Germany), November 24, 2000.

W. Stichler, U. SchottererClimate Variability in Europe as derived from the GNIP data baseWorkshop ,,In Momoriam Hans Oeschger: Towards an Isotope Climatology",Max Planck Institut fur Meteorologie, Hamburg (Germany), September 4 - 6 , 2000.

N. Streit, E. Weingartner, M. Schwikowski, F. Hegediis, H.W. Gaggeler, U. BaltenspergerTotal reflection X-ray fluorescence (TXRF) as a method of ambient aerosol analysisApplica 2000, Zurich (Switzerland), September 26 - 28, 2000.

L. Tobler, E. Lehmann, H.W. GaggelerThe Irradiation Facility for Neutron Activation at the Spoliation Neutron Source SINQ5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3 - 8 , 2000.

L. Tobler, M. Schwikowski, H.W. GaggelerHistorische Entwicklung von Bleikonzentrationen und Blei-Isotopenverhdltnissen in einem alpinen Eisbohrkern5. Symposium: Massenspektrometrische Verfahren der Elementspurenanalyse, Julich (Germany), September 18 - 21,2000.

L. ToblerMeasuremMeeting EU STACCATO-Project, Thessaloniki (Greece), October 3 0 - 3 1 , 2000.Measurement of7Be and 2l0Pb activity concentrations at the Jungfraujoch

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PROJECT RAD WASTEM. Argentini, R. WeinreichMeasurement of Radionuclide contents in activated graphite5th International Conference on Nuclear and Radiochemist ry (NRC5) , Pontresina (Switzerland), September 3 - 8 , 2000 .

R. Weinre ichBestimmung des Radionuklid-Inventars in BeschleunigerabfalienSeminar der Abteilung ASE/96 des PSI, Villigen (Switzerland), March 15, 2000.

R. Weinreich, M. ArgentiniDetermination of the Radionuclide inventories in Accelerator Waste5 t h I n t e r n a t i o n a l C o n f e r e n c e o n N u c l e a r a n d R a d i o c h e m i s t r y ( N R C 5 ) , P o n t r e s i n a ( S w i t z e r l a n d ) , 3 - 8 S e p t e m b e r 2 0 0 0 .

LABORATORY FOR ION BEAM PHYSICS

G. Bonani, I. Hajdas, U. Rouff, M. Seifert, V. Molodin and I. SljusarenkoDendrochronological and radiocarbon dating of the scythen burial place in the Pazyrik vally in the Altai montains,South Siberia17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

M. DobeliHochauflosende FlugzeitspektrometrieSeminar, Max Planck Institut fur Plasmaphysik, Garching (Germany), February 17, 2000.

M. DobeliThermal Stability of Implanted Fission Product Elements in Yttria Stabilized ZirconiaSpring Meeting of the European Materials Research Society, Strasbourg (France), May 30, 2000.

H. Haas, G. Bonani, Z. Hawass, M. Lehner, S. Nakhla, J. Nolan, R. Wenke and W. WolfliRadiocarbon dating of Egyptian old kingdom monuments17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

I. Hajdas, G. Bonani, J. Beer, G. Bonino and G.C. CastagnoliAn anomalous rise in the I4C activity 40 kyr ago17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

I. Hajdas, G. Bonani, D. Aritztegui and P. MorenoRadiocarbon chronologies of the late glacial cold reversal in Huelemo, Chile and Mascardi, Argentina17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

S. Ivy-OchsSurface exposure dating of boulders on moraines with 10Be, 26Al and 36Cl: the Last Glacial Maximum to the PreborealSeminar, Universitat Wien, Vienna (Austria), October 19, 2000.

S. Ivy-Ochs, R. Wiist, P.W. Kubik, C. SchliichterDating of stone tools from the Luxor region, Egypt, using 10Be17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

S.W.A. JacobBeschleunigermassenspektrometrie bei tiefen Energien:Innovation, Probleme, LosungenKernphysikseminar, ETH Zurich (Switzerland), May 9, 2000.

S.W.A. JacobBeschleunigermassenspektrometrie bei tiefen EnergienSeminar, Universitat Wien, Vienna (Austria), November 23, 2000.

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P.W. KubikLanglebige kosmogene Nuklide an der Erdoberfläche: Werkzeuge zur Charakterisierung von LandschaftsentwicklungenSeminar, Universität Wien, Vienna (Austria), June 15, 2000.

C. Maden, M. Döbeli, M. SuterAnalyse von '0Be/'Be-Verhältnissen mit AMSFrühjahrstagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), April 3 - 7 , 2000.

C. Maden, M. Döbeli, M. SuterInvestigation of natural '0Be/'Be-ratios with Accelerator Mass SpectrometryDoktorandenseminar, ETHZ / Universität Zürich (Switzerland), October 3 - 5 , 2000.

C. Maden, M. Döbeli, P.W. Kubik, M. Suter, M. FrankInvestigation of natural '0Be/'Be-ratios with Accelerator Mass SpectrometryConference on the Application of Accelerators in Research and Industry CAARI 2000,Dentón (USA), November 1 - 4, 2000.

C. Maden, M. Döbeli, P.W. Kubik, M. Suter, M. FrankAnalyse von natürlichen '"BefBe-Verhältnissen mit AMSSeminar, Universität Wien, Vienna (Austria), December 7, 2000.

R. Muscheler, J. Beer, G. Wagner, P.W. Kubik, C. Laj, J. Masarik14 C and wBe - System and Production Effects17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

M. Schaller, F. von Blanckenburg, N. Hovius and P. W. KubikLarge-scale, long-term erosion rates determined from wBe in European river sedimentsGoldschmidt 2000 Conference, Oxford (UK), September 3 - 8, 2000.

J.A. Scheer, S.W.A. Jacob, M. Suter, H.-A. SynalMessung von 26Al bei tiefen EnergienFrühjahrstagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), April 3 - 7 , 2000.

C. SchnabelIod-129 im Niederschlag in Mitteleuropa - woher kommt es?Seminar, Zentrum für Strahlenschutz und Radioökologie, Universität Hannover, Hannover (Germany), June 15, 2000.

C. Schnabel, S. Xue, P. Ma, G.F. Herzog, K. Fifield, R.G. Cresswell, M.L. di Tada, P. Hausladen, and R.C. Reedy,Nickel-59 in surface layers of lunar basalt 74275: implications for the solar alpha particle fluxLunar and Planetary Science Conference, Houston (USA), March 13 -17, 2000.

C. Schnabel, J.M. Lopez-Gutierrez, H.-A. Synal, M. Gloris, R. Michel, J. Kuhnhenn, and U. Herpers,Determination of production cross sections and production rates of iodine-129 in order to model its production fromtellurium63rd Annual Meeting of the Meteoritical Society, Chicago (USA), August 28 - September 1, 2000.

C. Schnabel, J.M. Lopez-Gutierrez, S. Szidat, J. Beer, and H.-A. SynalI29I in rain water near Zurich5th International Conference on Nuclear and Radiochemistry, Pontresina (Switzerland), September 3 - 8 , 2000.

C. Schnabel, L. Tobler, P.W.Kubik, H.W. Gäggeler7Be, wBe and 2l0Pb activity concentrations at the JungfraujochMeeting of the EU project STACCATO, Thessaloniki (Greece), October 30-31 , 2000.

M. SuterNew developments in accelerator mass spectrometry and their impacts on biomédical studiesSeminar, Nestle Research Center, Lausanne (Switzerland), February 15, 2000.

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M. SuterAltersbestimmungen mit TeilchenbeschleunigernAstronomische Gesellschaft, Luzern (Switzerland), May 8, 2000.

M. SuterStatus and Prospects of Accelerator Mass Spectrometry17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000.

M. SuterBeschleunigermassenspektrometrie - Neue Techniken und AnwendungenSeminar, Universitat Basel, Basel (Switzerland), December 7, 2000.

H.-A. SynalMoglichkeiten und Anwendungen von AMS Messungen mit 36ClSeminar, Universitat Hannover, Hannover (Germany), January 5, 2000.

H.-A. SynalNachweis langlebiger Radionuklide mit BeschleunigermassenspektrometrieSeminar, Universitat Bern, Berne (Switzerland), January 21, 2000.

H.-A. SynalLanglebige Radionuklide: Ultrasensitive Nachweismethoden und AnwendungenSeminar, Bergakademie Freiberg, Freiberg (Germany), February 8, 2000.

H.-A. SynalCa measurements @ the Zurich AMS System

OSTEODIET-Meeting, Cork (Ireland), February 18, 2000.

H.-A. SynalMoglichkeiten und Anwendungen von AMS Messungen mit 36ClFriihjahrstagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), April 4, 2000.

H.-A. SynalNew Directions in Accelerator Mass SpectrometrySeminar, Purdue University, West Lafayette (USA), April 17, 2000.

H.-A. Synal, S. Jacob and M. SuterStatus of Radiocarbon Detection at Low Energies17th International Radiocarbonconference, Judean Hills (Israel), June 18-23, 2000.

H.-A. Synal, S. Jacob and M. SuterThe PSI/ETH Small AMS System: New Results15th Conference on Applications of Accelerators in Research and Industry, Denton Texas (USA), November 3, 2000.

H.-A. SynalAMS of long-lived Radionuclides: New Developments and ApplicationsSeminar, US Geological Survey, Idaho Falls (USA), November 7, 2000.

S. Szidat, R. Michel, T. Ernst, J. Handl, D. Jakob, H.-A. Synal, C. SchnabelStatus and trends of iodine-129 abundances in the European environment5 th Internat ional Conference on Nuclea r and Radiochemis t ry , Pont res ina (Switzer land) , Sep tember 3 - 8 , 2000 .

S. TschudiAnwendungKernphysikseminar, ETH Zurich, Zurich (Switzerland), November 28, 2000.Anwendungsmoeglichkeiten von kosmogenen Nukliden ('"Be, 26Al und 2lNe) in der Eiszeitgeologie

S. TschudiExpositionsaltersbestimmung in Finnland und Russland: Schwierigkeiten-Resultate-ZukunftBerner Quartargesprache, University of Berne, Berne (Switzerland), March 29, 2000.

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F. von Blanckenburg, M. Schaller and P.W. KubikA new geochemical method for the determination of large-scale erosion rates, and its comparison toconventional river load gauging

Annual Meeting of the Deutsche Geologische Vereinigung, Vienna (Austria), April 14 -17, 2000.

F. von Blanckenburg, M. Schaller, T. Veldkamp, N. Hovius and P. W. KubikLate Pleistocene to Holocene erosion rate variations from cosmogenie nuclides in river terrace sedimentsGoldschmidt 2000 Conference, Oxford (UK), September 3 - 8, 2000.

D. Vance, M. Bickle. S. Ivy-Ochs and P. KubikCosmo genie isotope measurements of erosion rates in the HimalayaGoldschmidt 2000 Conference, Oxford (UK), September 3 - 8, 2000.

G. Wagner, J. Beer, C. Laj, C. Kissel, R. Muscheler, J. Masarik, H.-A. SynalDetection of the Mono Lake event in the Cl-36 flux in the GRIP ice core, European Geophysical SocietyXXV General Assembly, Nice (France), April 25 - 29, 2000.

G. Wagner, J. Beer, R. Muscheler, J. Masarik, H.-A. SynalDetection of solar cycles in the Cl-36 record from the GRIP ice core, European Geophysical SocietyXXV General Assembly, Nice (France), April 25 - 29, 2000.

G. Wagner, J. Beer, C. Laj, C. Kissel, J. Masarik, R. Muscheler, H.-A. SynalPaleomagnetic field reconstruction based on cosmogenic isotopes of the GRIP ice core,Workshop at the GeoForschungsZentrum, Potsdam (Germany), November 9 - 1 1 , 2000.

G. Wagner, J. Beer, R. Muscheler C. Laj, C. Kissel, J. Masarik, H.-A. SynalReconstruction of the snow accumulation rate of central Greenland during the last ice age using the cosmogenicradionuclides Cl-36 & Be-10 and geomagnetic field intensity dataAmerican Geophysical Union Conference, December 2000.

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PUBLICATIONS AND LECTURES FOR GENERAL PUBLIC

R. EichlerForschung am Paul Scherrer InstitutRotary Club Zurich, PSI-Forum, 6. Marz 2000

R. EichlerForschung am Paul Scherrer InstitutRegionalplanungsgruppe Brugg, PSI19. April 2000.

R. EichlerPhysikvorlesung fur KinderPSI-Brunch, PSI-Forum, 14. Mai 2000.

M. GiidelXMM-Newton Measures the Hot UniverseCern Courier 40 (7), 17-20 2000.

Ph. JetzerMateria oscura e lenti gravitazionaliLiceo Cantonale di Lugano, PSI-Forum, 2. Marz 2000.

A. ZehnderRontgenastronomiePhysikdepartement Tagung, ETH-Zurich, 16. Juni 2000.

A. ZehnderHESSIPhysik. Gesellschaft Zurich, ETH-Zurich, September 2000.

A. ZehnderSonne und Sterne im RontgenlichPSI Pensioniertenvereinigung, PSI, 5. Dezember 2000.

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LECTURES AND COURSES

Prof. Dr. R. EichlerETH Zurich, SSOO:• Physikpraktikum fur Vorgeriickte• Particle Physics Seminar (with others)• Physikalisches Kolloquium (with others)

• Teilchenphysikpraktium am PSI

ETH Zurich, WS00/01:• Physik I fur Mathematiker und Physiker• Physikpraktikum fur Vorgeriickte• Particle Physics Seminar (with others)• Physikalisches Kolloquium (with others)

LABORATORY FOR ASTROPHYSICS

Dr. M. GtidelETH Zurich und Universitat Zurich, WS00/01:• Hochenergie-Astrophysik (with Prof. A. Benz)

PD Dr. Ph. JetzerUniversitat Zurich, SSOO:• Einfiihrung in die Astro-Teilchenphysik

Universitat Zurich, WS00/01:• Mitwirkung an der Organisation des Theorie-Seminars (gemeinsam mit der ETH)ETH Zurich, WS00/01• Mitwirkung am Proseminar in Theoret. Physik

LABORATORY FOR MICRO AND NANO TECHNOLOGYDr. J. GobrechtETH Zurich, WS00/01:• Vorlesung und Ubungen ,,Grundlagen der Mikro- und Nanotechnik"

Dr. D. GrutzmacherUniversitat Konstanz, WS00/01:• Vorlesung "Optik" (Main lecturer: Prof. P. Leiderer)

Dr. T.A. JungUniversitat Basel, WS00/01:• Vorlesung "Einfiihrung in die Nanowissenschaften" (with others)

Dr. H. SiggUniversitat Zurich, SSOO:• "VP Halbleiterpraktikum" (together with Prof. B. Patterson)

LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY

Prof. Dr. H.W. GaggelerUniversitat Bern, SSOO:• Physikalische Chemie IV• Instrumentalanalytik II• Seminar in anorganischer und physikalischer Chemie (with others)• Seminar in Radio- und Umweltchemie (with Dr. M. Ammann), in collaboration with Paul Scherrer Institut

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Universitat Bern, WSOO/01:• Anwendung von Radioisotopen• Radiochemiepraktikum (with PD Dr. A. Tiirler)• Seminar in anorganischer und physikalischer Chemie (with others)• Seminar in Radio- und Umweltchemie (with Dr. M. Ammann), in collaboration with Paul Scherrer Institut

Dr. M. SchwikowskiUniversitat Bern, SSOO:• Instrumentalanalytik II (with Prof. H.W. Gaggeler)

PD Dr. A. TurlerUniversitat Bern, WSOO/01:• Eigenschaften schwerster Elemente

LABORATORY FOR ION BEAM PHYSICSProf. Dr. M. SuterETH Zurich, SSOO:• Seminar Kernphysik mit Anwendungen (with others)• Doktorierendenseminar iiber Kern- und Teilchenphysik (with others)

ETH Zurich, WSOO/01:• Kernphysik II, Wahlfachvorlesung• Seminar Kernphysik mit Anwendungen (with others)

LABORATORY FOR PARTICLE PHYSICS

THEORY GROUP

PD Dr. A. DennerETH Zurich, SSOO:• Proseminar Theoretische Physik (with others)• Das Standardmodell der elektroschwachen Wechselwirkung und dessen Erweiterungen

PD Dr. D. GraudenzETH Zurich, SSOO:• Einfiihrung in die Quantenchromodynamik

PD Dr. K. JunkerTechnische Universitat Wien, SSOO:• Einfiihrung in die theoretische Mittelenergiephysik

Dr. M. MellesETH Zurich, SSOO and WSOO/01:• Seminar iiber Physik der Elementarteilchen (with A. Denner)

PD Dr. R. RosenfelderETH Zurich, WSOO/01:• Solitonen, Instantonen und Monopole

Titels:

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AWARDS

C. David

Ph. Jetzer

K. Thomsen

HESSI / PSI Team

Award for second best posterDiffractive grey tone masks for laser ablation lithographyMicro and Nanoengineering MNE 2000, Jena, 19. Sept. 2000

Titularprofessor at Universitat Zurich

ES A personal award to Knud Thomsen "in recognition of his outstanding contributionto the XMM-Newton programme"

NASA Award to HESSI PSI Team: "Goddard space flight center group achievement award"for oustanding teamwork

Habilitation:

E. Morenzoni: Title of thesis:Generation and applications of polarized low energy muonsPSI and ETH Zurich

Doctoral Thesis:

B. Artur: Title of thesis:Measurement of WW Production Cross Section and Mass of the W bosonPSI

Thesis advisors:Prof. Dr. H. Hofer / Dr. M. Pohl (ETH Zurich)Dr. M. Fabre (PSI)

Y. Bonetti: Title of thesis:Laserinterferenz-Lithographie zur Herstellung von Modell-KatalysatorenPSI

Thesis advisors:Prof. Dr. R. Prins (ETH Zurich)Dr. J. Gobrecht (PSI)

A. Eichler: Title of thesis:Deposition von Spurenstojfen in Firn und Eis alpiner Gletscher, Untersuchung vonNord-SudgradientenPSI/Universitat Bern

Thesis advisors:Prof. Dr. H.W. Gaggeler (Universitat Bern & PSI)Dr. M. Schwikowski (PSI)

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R. Eichler: Title of thesis:Die chemische Charakterisierung des Transactinoids Bohrium (Bh, Element 107)Universitat Bern/PSI

Thesis advisors:Prof. Dr. H.W. Gaggeler (Universitat Bern & PSI)Prof. Dr. B. Eichler (PSI)

H. A. Fuhrmann: Title of thesis:Herstellung von sub-jim CoSi2-Strukturen mit dem fokussierten IonenstrahlETH Zurich

Thesis advisors:Prof. Dr. H. R. Ott (ETH Zurich)Dr. M. Dobeli (PSI)

S. Graf: Title of thesis:Photon drag spectroscopy of the two-dimensional electron gas inGaAs/AlGaAs quantum well systemsPSI

Thesis advisors:Prof. Dr. W. Bachthold (ETH Zurich)Dr. H. Sigg (PSI)

L. Grenacher: Title of thesis:Baryonic Dark Matter in Clusters and Spiral GalaxiesPSI/Universitat Zurich

Thesis advisors:Prof. Dr. N. Straumann (Universitat Zurich)Prof. Dr. Ph. Jetzer (PSI & Universitat Zurich)

J. Koglin: Title of thesis:The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33,9 MeVin Pion DecayPSI

Thesis advisors:Prof. Dr. D. Pocanic (Universitat Virginia)Dr. M. Daum (PSI)

M. Pinkpank: Title of thesis:Rare Earth Magnetism in CupratesPSI

Thesis advisors:Prof. Dr. H. R. Ott (ETH Zurich)PD Dr. A. Schenk (ETH Zurich)

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R. Ros: Title of thesis:Kraftmessungen an einzelnen AntikorpermolekulenPSI

Thesis advisors:Prof. Dr. H.-J. Giintherodt (Universitat Basel)Dr. L. Tiefenauer (PSI)

N. Streit: Title of thesis:Chemical and Physical Characterization of Ambient Aerosols in Source and SinkPSI

Thesis advisors:Prof. Dr. H.W. Gaggeler (Universitat Bern & PSI)PD Dr. U. Baltensperger (PSI)

M. Strassle: Title of thesis:Contributions to the Electrodynamics of Compact Objects and theDark Matter Search in the UniversePSI

Thesis advisors:Prof. Dr. N. Straumann (Universitat Zurich)PD Dr. Ph. Jetzer (PSI)

S. Tschudi: Title of thesis:Surface exposure dating: a geologist's view with examples from both hemispheresUniversitat Bern / PSI

Thesis advisors:Prof. Dr. C. Schliichter (Universitat Bern)Dr. P. W. Kubik (PSI)