ecns '99 — young scientists forum

*Corresponding author.

Physica B 276}278 (2000) 45}51

ECNS '99 * Young Scientists Forum

Monica Ceretti!, Stefan Janssen", Des McMorrow#, Paolo Radaelli$,Uschi Steigenberger$,*

!Laboratoire Le&on Brillouin, CE Saclay, F-91191 Gif sur Yvette, France"Laboratory for Neutron Scattering, PSI, CH-5232 Villigen, Switzerland

#Department of Solid State Physics, Ris~ National Laboratory, DK-4000 Roskilde, Denmark$ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK

Abstract

The Young Scientists Forum is a new venture for ECNS and follows the established tradition of an active participationby young scientists in these conferences. At ECNS '99 the Young Scientists Forum brought together 30 young scientistsfrom 13 European countries. In four working groups, they discussed emerging scienti"c trends in their areas of expertiseand the instrumentation required to meet the scienti"c challenges. The outcome was presented in the Young ScientistsPanel on the "nal day of ECNS '99. This paper is a summary of the four working group reports prepared by the GroupConvenors. ( 2000 Elsevier Science B.V. All rights reserved.

Keywords: Young Scientists Forum

1. Working group: structures of crystalline, amorphous,liquid and glassy materials

Group Convenor: Paolo Radaelli, ISIS, UK; Mem-bers: LaH szloH Almasy, BNC, Hungary, Stanislaw Baran,Krakow, Poland, Ferdinando Formisano, Firence, Italy,Igor Goncharenko, Saclay, France and Moscow, Russia,Jean-Yves Raty, LieH ge, Belgium, Denis Sheptyakov,Dubna, Russia, Emanuelle Suard, ILL, France.

1.1. Introduction

The new generation of neutron sources now on thedrawing board will endow neutron di!raction witha wealth of new opportunities. Clearly, the projectedincrease of brilliance, up to a factor of 30 over existingsources, is of extreme interest to extend the domain ofcurrent di!raction techniques. However, at least equallyimportant is that complete new suites of instruments,built with state-of-the-art technology and provided withadequate funding for hardware and software develop-

ment, will be built. For example, of the 44 instrumentscurrently planned for the European Spallation Source(ESS), 12 are di!ractometers. This is an acknowledge-ment of the continuing role of neutron di!raction as oneof the supporting pillars of neutron science.

However, the projected 10}15-year scenario, based oncurrent projects and political trends, is not completelyreassuring for neutron scattering in general and neutrondi!raction in particular. For instance, it is expected that,by the year 2012, 75% of the existing research reactorswill be decommissioned. The corresponding loss in neu-tron #ux may be more than compensated by the con-struction of new bright sources like the ESS, but thistransition will imply a dramatic shift of balance fromsteady-state to pulsed sources and from many small na-tional sources to a few large multinational facilities. Upto now, low- and medium-#ux sources have had a para-mount importance, not only as training facilities forfuture neutron scatterers, but also in the development ofstate-of-the-art techniques and instrumentation. An out-standing example of this fact was illustrated at this con-ference by the awarding of the "rst HaK lg price to FerencMezei for his innovative and outstanding contributionsto the science of neutron scattering, mostly originatingfrom his work at the Budapest reactor during the late

0921-4526/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved.PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 5 2 8 - 8

1960s. If this rich diversity is lost, and nothing is put inplace to replace it, the healthy development of neutronscience will be seriously threatened.

1.2. Complementarity between steady-state and pulsedneutron sources

Neutron di!raction in particular has enormously be-ne"ted from the complementarity between steady-stateand pulsed neutron sources, and from the availability ofmany small- and medium-#ux sources. In principle, allthe applications of neutron di!raction can make use ofeither pulsed or constant-wavelength neutrons, providedthat neutrons of the desired wavelength/polarisation canbe produced and changes in momentum/polarisationdetermined. However, in practice, technical issues haveresulted in a signi"cant specialisation of the di!erenttypes of sources in some techniques, with a large overlapin some others. In the "eld of crystallography, magneticdi!raction in general, and polarised neutron di!ractionin particular, have been the almost exclusive monopolyof steady-state reactors, while very high-resolution pow-der di!raction and surveying of Bragg/di!use nuclearscattering on single-crystals have been performed almostexclusively at pulsed sources. Similarly, the biggest im-pact of time-of-#ight liquid and amorphous di!ractionhas been for hydrogenous materials, and wherever it isimportant to achieve very large Q values. It is crucial thatcompetence in some of the most specialised steady-statetechniques is swiftly transferred to pulsed sources. Other-wise, entire areas of neutron di!raction science may be atrisk.

The problems arising from the loss of small- andmedium #ux reactors is not easily addressed. One of themain advantages of the present situation is the opportun-ity of building dedicated instruments, which open upentire new "elds of investigation. One of the best exam-ples is the LLB programme on magnetic powder di!rac-tion at high pressures, which is now approaching the 0.5Mbar limit. This technique requires extreme real-spacefocussing and very high signal-to-background ratios, andis ideally suited for a constant-wavelength di!ractometerwith highly specialised optics. The medium #ux of theLLB is not an obstacle to the scienti"c excellence of thisprogramme, as long as enough time is available for themeasurements. However, it is at present unclear how thesame science can be performed at a general-purposetime-of-#ight instrument, even with the ESS #ux.

1.3. Powder diwraction

Among the neutron di!raction techniques, neutronpowder di!raction (NPD) has undoubtedly been themost proli"c in the last 20 years. This was due to theavailability, at the beginning of the 1980s, of severalstate-of-the-art di!ractometers at both reactors and pul-

sed sources around the world. As a consequence, NPDhas established itself as the chosen technique for studyingnewly discovered inorganic materials, especially, but notexclusively, oxides. We should not forget, however, thatrelatively &old' materials, such as manganese perovskites,have proved to be extremely rich "elds of investigationfor NPD, as long as technical advancements in the tech-nique could yield su$ciently new insight into their phys-ics. Another strong asset of NPD has been the ability toexplore complex phase diagrams as a function of chem-ical (composition, partial pressures, etc.) and physical(temperature, pressure, magnetic "eld, etc.) parameters,yet always yielding reliable and detailed information.These strong points constitute the basis to build thefuture of NPD. Novel compounds are often producedwith techniques, such as high-pressure synthesis, thatyield tiny amount of material. Therefore NPD must becapable to measure high-quality di!raction patternsfrom a few milligrams of sample. Also, phase diagramswill be explored in far greater detail than it is currentlyavailable, combining high #ux with synchrotron-like res-olution in a variety of special environments.

The current plan is to achieve these goals by com-bining the high #ux available at third-generation pulsedsources with a very large solid angle, covering a signi"-cant fraction of 4p. The latter trend is well illustratedby some of the most recent instrument designs both atpulsed sources (e.g. GEM at ISIS) and at reactors (e.g.SuperD2B at the ILL). The biggest challenge is represent-ed by the need to manage meaningfully and e$ciently anenormous #ux of information.

1.4. Single-crystal diwraction

By comparison with NPD, single-crystal neutron dif-fraction (SXND) has had far fewer highlights in thescienti"c press. The current perception (or prejudice) isthat SXND is a slow technique that requires very largecrystals. This situation is now changing, thanks to theintroduction of detectors capable of mapping large sec-tions of reciprocal space with one crystal orientation.LADI, a quasi-Laue instrument using cylindrical imageplates, is already in service at the ILL and is enjoyinggreat success. The fact that other instruments with com-parable data-acquisition rates will soon follow LADI,suggests that we may be at the edge of a revolution. In thenext decade, SXND may have a scienti"c impact compa-rable to what NPD has had in the 1980s and 1990s.

1.5. Structure determination of liquids and amorphousmaterials

Di!raction on liquid and amorphous substances(L&AD) is distinctively di!erent from the aforemen-tioned techniques, in that it will not fully bene"t from any

46 M. Ceretti et al. / Physica B 276}278 (2000) 45}51

#ux/solid angle increase unless accompanied by equiva-lent gains in stability and reduction of systematic errors.Therefore, the technical challenges for L&AD are fargreater, especially considering that L&AD may have toshare their instrumentation with crystallographer. Ifproperly exploited, however, this dual role can be bene"-cial to both communities.

1.6. Conclusion

In conclusion, the most important step to be takenfrom now to ensure future excellence in neutron di!rac-tion is to promote exchanges of ideas and expertise be-tween the communities of neutron di!ractionists operat-ing at steady-state and pulsed sources, in the "elds ofcrystallography and liquid/amorphous physics. The in-teraction between facility-based scientists and users isparticularly important. One of the many ways to achievethis goal is to invest e!ort and resources in the develop-ment of `Open Virtual Instrumentsa, not only as tools forinstrument scientists, but also as user-friendly desktopprogrammes enabling even the casual user to performa virtual experiment on a virtual sample. This will enablefuture performances to be predicted in a much more re"nedway, and will motivate the communities into a far deeperparticipation in the instrument development process.

2. Working group: materials science, engineeringand industrial applications

Group Convenor: Monica Ceretti, Saclay, France;Members: Mark Daymond, ISIS, UK, Erwin Jericha,Wien, Austria, Gyorgy Kali, BNC, Hungary, TorbenLorentzen, Ris+, Denmark, Dimitar Neov, Rez, CzechRepublic, Pavel Strunz, Rez, Czech Republic.

2.1. Introduction

The strength of neutrons for investigations in the "eldof materials research and industrial applications is basedon the possibility of relatively large penetration depthinto or through a sample, magnetic scattering, the use ofpolarised neutrons, contrast variation, the high sensitiv-ity to hydrogen and a relative non-destructiveness. Neu-trons should be used in all the "elds where they eitherprovide unique information or complement synchrotronradiation results. The higher #ux of a new generationneutron source would certainly extend already broadareas of their utilisation.

2.2. Scientixc opportunities

The scienti"c aspects of materials science and engin-eering research at possible new sources were summarisedwith the new possibility to measure real components in

real time and in real environments. Investigations of highlyabsorbing materials (due to the material character or thelength of the #ight paths through the sample) can beextended with the help of higher #ux. It also meansa possibility to perform non-destructive testing of the usedexpensive components with a consequent estimation ofthe residual lifetime (e.g. turbine blades). The study oftime-dependent processes (also real time operation ofcomponents) is one of the declared goals for scienti"cinvestigations at new generation sources. These measure-ments are only made possible by their unprecedentedneutron #ux. Examples are the formation, solution andevolution of precipitates in structural materials observedby small-angle scattering and real-time investigation ofoperating machinery. This also includes investigation ofmicrostructures near interfaces in the bulk heterogeneousmaterials (e.g. interface metal}thermal coating) or inmaterials inside which a gradient of some measurableparameter is expected. In situ studies (e.g. fatiguebehaviour, thermal cycling stresses, stresses in rotatingmachines) will be enhanced.

An Engineering Research Development and TestCentre at the new generation high #ux neutron sourceswill be able to meet the demands made by industrialengineering applications. As such, the centre will greatlyincrease the range of experiments available to the engin-eering community. However, a strong collaboration be-tween the engineering and material science communitiesis essential: this centre will act as a catalyst for technologyand skill transfer from the engineering community tomaterials science researchers and vice versa.

In the last years, many scienti"c aspects have beendeveloped in material science that will enormously pro"tfrom the high neutron #ux and from which the engineer-ing world has to take advantage. These future themesinclude:

f Understanding of fundamental deformation mecha-nisms, e.g. intergranular stresses and microstrains eval-uation connected with the fatigue behaviour and crackpropagation.

f Understanding of some aspects connected with phasetransformation, e.g. superplasticity in shape memoryalloy used in smart structures.

f Interface characterisation (thick coatings and plasmasprayed materials used as thermal barrier coatings).

f Characterisation of advanced materials such as Ni-based superalloys used in turbine blades or compositematerials.

The developments of all these aspects demand a highneutrons #ux, which o!ers, on the other hand, a highresolution, either spatial (necessary for example to char-acterise interfaces) and instrumental (necessary for ex-ample to characterise microstrains and multiple phasesmaterials).

M. Ceretti et al. / Physica B 276}278 (2000) 45}51 47

Even though having the high #ux, the neutrons shouldbe used as e$ciently as possible. This means, for example,to optimise instruments in advance (e.g. by Monte Carlosimulations). Another topic related to the e$cient use ofthe high #ux is the changing, positioning and aligning ofsamples. With the expected short measuring times forroutinely applied standard con"gurations, the through-put of samples will be considerably high and samplehandling needs to be optimised. This includes pre-align-ment of samples (e.g. with X-ray or light/laser opticalmethods) within a standardised sample environment, fullautomatisation of sample changing and software control-led positioning and alignment of the samples with respectto the neutron beam. This is of particular importancefor the industrial users. Applications are seen for three-dimensional stress analysis and neutron tomography. Inany case, the ratio of measuring time versus sample align-ment time should be kept as large as possible.

2.3. Instrumentation

The following instruments are identi"ed as relevant forthe "eld of materials science, engineering and industrialapplications:

f di!ractometer for residual stress measurements (withan option for texture measurements);

f small-angle scattering instruments;f radiography/tomography facility;f re#ectometry;f neutron activation methods.

One of the key considerations for new instrument designis the e$cient use of the neutron #ux, regarding beampreparation and neutron detection. The development ofactive beam forming components and large-area de-tectors with high resolution and good e$ciency shouldbe given high priority.

2.4. Diwractometer for residual stresses

The aspects of intensity versus resolution play a keyrole in instrument design and experimental procedures.At a high #ux new generation neutron source the aspectof high resolution should be emphasised (e.g. new engin-eering materials will enable the study of phase transitionsor materials with multiple phases). Spatial resolutionbelow 0.5 mm in each direction is important, especiallyfor materials science but also for certain industrial ap-plications (e.g. study of interfaces). Gauge volumes withdimension of order 0.1 mm3 should be easily accessibleby the new instruments. The possibility of high spatialresolution should be intrinsically implemented in theinstrument design, using neutron optics elements forbeam focusing. Detectors have to be fast, with high res-olution and two-dimensional position sensitivity (PSD).

Backscattering detectors and two-dimensional transmis-sion-PSD are considered to be an important addition tothe instrument. The installation of c-ray detectors view-ing collimated c-rays from the sample will allow to obtainan element distribution map together with the corre-sponding stress map of the sample.

2.5. Small-angle scattering

Three types of instruments were discussed: the stan-dard pinhole SANS instrument, the double crystalBonse}Hart camera and the new development of the spinecho SANS instrument. With the high #ux, the study oftime-dependent sample behaviour (e.g. the formation,solution and evolution of precipitates in structural ma-terials) will be feasible. On the other hand, the highspatial resolution allows investigations by scanning thesample (interesting in the case of interface or defect gradi-ents in real components characterisation).

2.6. Radiography

Radiography can take advantage of the pulsed sourcecharacter by characterising elements via Bragg edges(long wavelengths) or nuclear resonances (short wave-lengths). There also exists the possibility of stroboscopicmeasurements (in time-dependent sample environment)in synchronisation with the periodicity of the neutronsource. The high neutron #ux will enable real-time stud-ies of time-dependent processes and the routine opera-tion of neutron tomography. The readily understandableresults and the clearly visible complementarity to X-rayradiographs will guarantee industrial interest in this typeof instrument.

2.7. Reyectometry

Neutron re#ectometry has become an important tech-nique for the study of surfaces and interfaces. Industrialinterest for this method is seen in the study of magnetic"lms.

New developments in this "eld are the techniques ofphase re#ectometry and spin-echo re#ectometry. A char-acteristic feature of both methods is the possibility to usefull divergent neutron beams and the fact that angularchanges are detected in the scattered beam which aremuch smaller than the angular range of the incomingneutron beam.

2.8. Neutron activation methods (neutron depth proxling,neutron radiative capture2)

This group of methods is not based on neutron scat-tering but on the use of nuclear reactions. It should bepresent at new neutron sources because of the importance


of applications of these non-destructive analyticalmethods in materials research and in industry:

f determination of concentration of some elements invarious biological, industrial, geological and agricul-tural materials,

f determination of damage pro"le of ion-irradiatedpolymers, metallic or carbon samples,

f distribution of boron, lithium or other elements intechnologically important materials.

More intense neutron sources will enable thesemethods to be extended, including three-dimensionalanalysis.

3. Working group: soft condensed matter, polymersand biology

Group Convenor: Stefan Janssen, PSI, Switzerland;Members: Arantxa Arbe, San SeH bastian, Spain, MikhailAvdeev, Dubna, Russia, Wim Bouwman, IRI Delft, TheNetherlands, Mirko Kreitschmann, FZ JuK lich, Germany,SteH phane Longeville, Saclay, France and MuK nchen, Ger-many, Jan Skov Pedersen, Ris+, Denmark, John Webster,ISIS, UK.

3.1. Introduction

Soft condensed matter physics is amongst the mostpromising and developing "elds in nowadays physics andneutron scattering plays an essential role for studyingthis class of matter due to its spatial and temporal resolu-tion and in particular due to its unbeatable advantagesrelated to deuteration techniques. In our summary, wewould like to pick up a few trends in the "eld of softcondensed matter studies which recently came up andseem to have a great potential and impact for futureexperiments. Additionally, a few aspects of the requiredinstrumentation will be discussed related to small-angleneutron scattering (SANS) and re#ectometry on the onehand, and to classical inelastic or quasielastic experi-ments with time-of-#ight (TOF), backscattering (BS), andspin-echo (NSE) techniques on the other.

3.2. SANS and reyectometry

At the moment three major trends are visible, namelytowards highly complex systems, towards sophisticatedsample environment, and towards &real time' and &in situ'studies. The systems studied mostly at the end of thismillennium are multicomponent systems, micelles,microemulsions, surfactants, polymers with highly com-plex architectures-like hyperbranched or starlike molecu-les, self-assembling systems, etc. When we also includebiologically relevant systems like, e.g. proteins or ribo-

somes obviously the conclusion has to be drawn that anintense co-operation between neutron scattering andchemistry will become more important because there isa strong need for well-de"ned model systems. External"elds such as shear, stress, pressure, electric "elds, etc.will be needed even more intensely than today to studysystems under realistic conditions. Besides its funda-mental interest such studies will also have a great impacton future applications emerging from the "eld. Hence atleast the instruments at the major neutron sources shouldbe equipped with sample environment devices thatroutinely can make use of external "elds. &Real time'studies allow for the in situ investigation of, e.g. phasetransitions, chemical reactions, or stop #ow processes.Only reversible phase transitions can be investigated inaccumulation by repetitive experiments. Otherwise, thetemporal &snap shots' have to be taken in a single run.Hence especially the performance of real time studies onSANS machines and re#ectometers de"nitely requireshigh #ux sources.

Further to an increase of neutron #ux also the reduc-tion of background is an essential instrumental require-ment. Hence the use of polarised neutrons and contrastvariation techniques will be of growing importance.Looking at instrumental components we think thata major task will be the development of a new generationof 2D-multidetectors that can stand the high count ratesof future neutron sources. Very promising seems to be thedevelopment of focussing SANS techniques providingaccess to Q-values of some 10~4 As ~1 as well as recentprogress in the technique of &Spin-Echo SANS' that de-couples the instrumental resolution from the incidentbeam collimation.

3.3. Time-of-yight, backscattering, neutron spin echo

The understanding of the &glass transition' and itsrelated topics is at present one of the major problems oftheoretical physics. Here the microscopic understandingof the various relaxation processes in glass-forming poly-mers such as the a- and b-relaxation, the fast dynamics,and vibrational modes related to the &Boson-peak' is anessential task for future neutron scattering experiments.For a more detailed picture of these processes an exten-sion of the accessible (Q, u)-phase space towards largerQ's and longer relaxation times is needed. In this contextit should be mentioned that the Fourier-time of a NSEexperiment is strongly dependent on the wavelength(q&j3). Hence a high availability of especially longwavelength neutrons is strongly requested. To investigatethe spatial crossover between the various processesa high Q-resolution in the order of 0.1 As ~1 is needed. Itcould be provided by the use of advanced TOF tech-niques at pulsed neutron sources which should provide2}3 orders of magnitude in intensity compared to now-adays cold neutron TOF instruments. Another very


promising technique is the separation of coherent andincoherent scattering by the use of polarised neutronswith energy resolutions beyond that of the presentD7/ILL.

Another major trend is the investigation of dynamicsin highly complex and functional systems like mem-branes, micelles, brushlike molecules, etc. which is mainlyaddressed to the dynamical range of NSE experiments.These machines will bene"t strongly from the enhanceduse of 2D-multidetectors. From the "eld of biology theinvestigation of internal modes, di!usion behaviour, orthe hydration functionality of protein systems seems tobe best developed right now as far as it concerns neutronspectroscopy. Both, science and scattering techniqueswould bene"t strongly from a more pronounced futureco-operation.

3.4. Conclusions

The essential demand for the investigation of soft con-densed matter with neutron scattering is a high availa-bility of cold neutrons at future sources like the ESS.Hence a dedicated 10 Hz ESS target station for coldneutron applications is mostly favourable due to itsreduced frame overlap and enlarged free wavelengthband and should be taken into consideration with highpriority.

4. Working group: magnetic excitations

Group Convenor: Des McMorrow, Ris+, Denmark;Members: Nordal Cavadini, PSI, Switzerland, Niels vanDijk, Delft, The Netherlands, Roger Eccleston, ISIS, UK,Sergey Gavrilov, Gatchina, Russia, Arno Hiess, ILL,France, Philippe Bourges, Saclay, France.

4.1. Magnetic excitations and the case for neutronscattering

The study of magnetic excitations remains at the fore-front of solid-state physics. This is due to two factors. The"rst is that magnetic #uctuations play a decisive role indetermining the physical properties of many classes ofnew materials. Examples range from heavy-fermion ma-terials, through to high-temperature superconductors,and more recently to the colossal magneto-resistive ma-terials. Secondly, the study of magnetic excitations inmodel systems, such as one- and two-dimensional mater-ials, provides an arena in which to test modern many-body theories. One particularly important emerging newarea is the study of quantum phase transitions, and italready seems clear that progress in this "eld will dependon being able to perform experiments to elucidate thenature of the magnetic #uctuation spectrum in the sys-tems of interest.

Magnetic excitations may be studied by one of severalprobes, such as NMR, neutron scattering, light scatter-ing, etc., each of which has its own particular advantagesand disadvantages. Neutron scattering has the followingdistinct advantages:

f The cross-section measured in an experiment is dir-ectly related to the frequency and wave-vector depen-dent susceptibility, viz.,

d2pdE dX

JsA(Q, u)

and in this way the results of experiments may bedirectly related to theory.

f Compared with other probes sA(Q, u) can be deter-mined over large ranges of both Q and u. For example,using a combination of neutron spectrometers it ispossible to study magnetic #uctuations on energyscales ranging from neVs to several eVs.

f The use of polarisation techniques allows the magneticnature of a signal to be unambiguously assigned.

For these reasons the study of a given system is rarelycomplete until it has been investigated with neutrontechniques.

The main disadvantage of the technique is that thescattering is weak. At existing sources this means that thematerial of interest must be available in single crystalform of at least 1 cm3. Even then the experiments arenearly always #ux limited. For this reason tremendouse!orts have been made over the years to improve theperformance of instruments for the study of magneticexcitations at existing sources. If anything, the pace ofinnovation has quickened in the last decade, and somerecent examples are outlined in the next section, whichwe believe, will also have an impact on the design ofinstrumentation at future sources.

4.2. Optimal use of existing sources

Like all areas of neutron scattering, the instrumenta-tion for magnetic excitations has bene"ted tremendouslyfrom the many technical advances that have been madein the individual components that make up a completeinstrument. These include supermirror guides, 3He polar-ising "lters, position sensitive detectors, etc. As outlinedbelow, the design of instruments bene"ts greatly bya cross-fertilisation of ideas between development pro-grammes at reactor and pulsed sources.

4.3. The emergence of time-of-yight for single-crystalexperiments

One of the key developments in the study of magneticexcitations within the last decade has been the use of


time-of-#ight methods for the study of single crystals,pioneered principally at ISIS. At the turn of the decadethe consensus was that the triple-axis spectrometer ata steady source was the perfect instrument for single-crystal spectroscopy, and that time-of-#ight methodsworked well only for powders. A series of experiments,"rst on one, and then two, and "nally three-dimensionalmaterials have challenged this position. It now seemsclear that there is a need for both triple-axis and time-of-#ight spectrometers, with each having its own advant-ages depending on the problem at hand.

4.4. RITA style instruments

Presently, there are parallel programmes at many reac-tor centres aimed at making more optimum use of theavailable #ux, of which the RITA project at Ris+ is butone example. The essential idea behind the project isto use a multi-analyser system in combination witha two-dimensional area detector, with the completeanalyser/detector system sitting in a large vacuumtank. The main advantage of this type of spectrometer isthat it is completely #exible, and the analyser can becon"gured in a number of di!erent modes depending onthe experiment.

It is clear that the continued vitality of the "eld de-pends on the development programmes at the variouslabs. The following programmes are either underway orshould start in the near future, and each should representa signi"cant step forward:

f The millennium programme at ILL.f FMR II at Munich.f ISIS 300 lA, and ISIS II.

In addition, collaborations between European neutronfacilities provides an opportunity to accelerate the devel-opment of technologies, such as guides and polarising"lters, which could have a dramatic impact on the perfor-mance of the spectrometers. Collaborative programmesalready exist and have been shown to be e!ective, but insome cases inter-facility interactions take place at toosenior a level to be e$cient. We suggest that the NeutronRound Table provides an ideal forum to further stimu-late inter-facility collaborations at all levels.

4.5. The user base

The size of the magnetic excitations community doesnot re#ect the power of neutron scattering as a probe ofcondensed matter. One of the most important reasonswhy this is the case is that inelastic neutron scattering has

to a great extent remained the preserve of experts: experi-ments require careful planning which often requiresa profound knowledge of neutron scattering, and dataanalysis is di$cult and time consuming. In order toexpand the user base facility sta! will need to act as &theneutron expert' in a collaborative team, and be preparedto provide advice and guidance during the planning,execution and analysis of an experiment. This involvesa considerable time commitment on the part of facilitysta! when their time is already under pressure.

Other measures that we consider important forstrengthening the user base, and making the use of beamtime more e$cient, are the adoption of a common dataformat such as NEXUS, collaborations on the develop-ment of analysis and visualisation software and greateruse of the internet for data retrieval and analysis.

4.6. Future sources

As far as the study of magnetic excitations is concerneda new source such as the ESS would bring tremendousgains. The additional #ux could be used in a number ofways. For example, it would be possible to trade #ux forresolution. Whenever this is done in other "elds, such asX-ray scattering, new physics emerges. The additional#ux could also be used to bring about a more funda-mental paradigm shift in the way that the study of mag-netic excitations is viewed. The additional #ux could beused to speed up experiments, ease the sometimes pro-hibitive constraint on sample size, and allow parametricstudies to be made in a reasonable time. In this wayneutron scattering would have a greater impact onemerging areas of science, and would become more at-tractive to new users (such as NMR spectroscopists) whoare used to getting results on the time scale of a fewweeks, rather than several months or more. We haveinsu$cient space here to give a detailed description ofwhat is required of the next generation source. It isdi$cult, however, to imagine that it will be possible tokeep up the great momentum in the "eld of neutronscattering if a clear path to the construction of a newsource such as the ESS does not emerge in the nearfuture. In this context, the state of neutron scatteringshould be compared with the X-ray world. Having builtthe ESRF, there are now concrete plans for the develop-ment of a free-electron laser project at HASYLAB to beoperational within the next decade.

Acknowledgements

Moral and "nancial support from ENSA and the Neu-tron Round Table are gratefully acknowledged.


ecns '99 — young scientists forum

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