Recent advances on the VESUVIO Recent advances on the VESUVIOSpectrometer: High energy InelasticSpectrometer: High energy Inelastic

Neutron ScatteringNeutron Scattering

Roberto SenesiUniversita’ degli Studi di Roma Tor Vergata-Dipartimento di Fisica

and Istituto Nazionale per la Fisica della Materia ITALY

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SUMMARYSUMMARY•• Kinematic requirements for eV neutron spectroscopyKinematic requirements for eV neutron spectroscopy

•• VESUVIO in The RD VESUVIO in The RD configurationconfiguration: : the e.VERDI projectthe e.VERDI project

–– Gamma detector Gamma detector technologies fortechnologies for EEnn = 1 = 1 eV eV - 100 - 100 eVeV.–– VLAD VLAD bank with bank with RD RD unit unit (e.g. YAP (e.g. YAP γγ-detector + U -detector + U foilsfoils))

prototype prototype ((22θθ=2=2oo- 5- 5oo) ad final () ad final (22θθ=1=1oo- 5- 5oo) ) versionsversions

•• benchmark experiment benchmark experiment (RD) (RD) from from VLAD VLAD prototypeprototype::–– O-H O-H stretching stretching density of density of states states in Hin H22O at 300 KO at 300 K

•• high high energy excitations energy excitations in in diamond diamond and and PrPr

•• high high energy excitations energy excitations : future : future perspectives perspectives on VESUVIOon VESUVIO

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Kinematical space

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High energy excitationsHigh energy excitations

• (DINS):- <Ek>- n(p)

• (HINS):-high energy excitations

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Example:HH22O or Metal O or Metal hydridehydride

If the above measurements can be done simultaneouslyThen a compact spectrometer for single particle dynamics is realized (momentum distribution+vibrational spectroscopy)

1) Momentum distribution and kinetic energy: n(p); <EK>2) Reconstruction of Born-Oppenheimer potentials (recently determined for KDP)1) Hydrogen projected density of states (for hω > 0.3 eV )

H2O 300 KQ=(52±2) Å-1

pQ (Å-1)

n(p Q

) (Å

)

+

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��HINS on VESUVIOHINS on VESUVIO

High energy excitations at low qHigh energy excitations at low q

q < 10 Å-1 , hω > 0.3 eV;

(10-6 ps ÷10-3 ps)Examples include:high lyinghigh lying vibrational vibrational state in molecular systems,state in molecular systems,high energy excitations in magnetic systems andhigh energy excitations in magnetic systems andsemiconductors.semiconductors.

Require low scattering anglesRequire low scattering angles

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1°2°

3°

4°

6°

7°

8°

9°

0.5 1.0 1.5 2.0 2.5 3.00

2

4

6

8

10

238U, Ef = 6.67 eV

q [A-1]

hω [eV]

((q,q,hhωω) range ) range

for HINSfor HINS

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0.50°

1.0°

1.5°

2.0°

2.5°

0.5 1.0 1.5 2.0 2.5 3.00

2

4

6

8

10

238U, Ef = 102.6 eV

q [A-1]

hω [eV]

((q,q,hhωω) range for HINS) range for HINS at high Eat high E11almostalmostconstant constant q q scansscans

((q,q,hhωω) range for HINS) range for HINS

22θθ=1=1o o

149149SmSm E E1 1 = 0.872 = 0.872 eV eV ((- -- -))185185ReRe E E1 1 = 2.16 = 2.16 eV eV ((- -- -)) 238238UU E E1 1 = 6.671 = 6.671 eV eV ((______))150150SmSm E E1 1 = 20.7 = 20.7 eV eV ((______))149149ErEr E E1 1 = 79.7 = 79.7 eV eV ((______))

EE1 1 > 6 > 6 eVeV

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Schematics of the VESUVIO spectrometer and principles of the Resonance Foil (RF)and Resonance Detector (RD) techniques .

VLAD array, with YAP γ detectors

6Li glass neutron detectors

Scattering sample

n

n’22θθ=2=200-5-500

RD

RF

YAP scintillator

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RD unit on VLAD - prototype developmentRD unit on VLAD - prototype development• RD response to scattered neutrons and background

depends on choice of analyzer foil and photon detector.

• Mostly used foil: natural uranium (238U).

• 238U gammas: from 12 keV to 4.06 MeV. Also X-rays.

• YAP detector

YAP teleYAP telescopic detector arrangementscopic detector arrangement

11Detector rings at 2°, 3°, 4° and 5°.

Prototype VLAD: Prototype VLAD: LL0 0 =11 m=11 m, , LL1 1 =2 m=2 m , , 6 sectors of 606 sectors of 60°°, array, arraydiameter diameter ~~40 cm, 40 cm, 238238U analyzer foils U analyzer foils at at T= 298 KT= 298 K

YAP detector

��∆hω ~ 140 meV FWHM forO-H stretching at 0.42 eV

Ice Ih at 2θ=2° Simulated data O-H stretching

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∆∆q q resolution resolution ��q range q range forforO-H stretching at 0.42 O-H stretching at 0.42 eVeV�

YAP detectors located at 2θ=2°, 3.5°, 5°

HINS measurementsDensity of states from

polycristalline Ice Ih

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First VLAD prototype results at 2°Ice Ih sample (270 K)

YAP detectors at 2θ=2°, 3.5°, 5°

No contamination from beam halo - IT WORKS.

238U foil E1 = 6.671 eV

Kinematical spaceE1 = 6.671 eV

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HRMECS measurements (IPNS Argonne National Laboratory)

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1

( ) 8E

Eg dω ω =∫ ± 0.1 atoms/cell

2.0 Å-1 ≤ q ≤ 5 Å-1q > 6 Å-1

C. Andreani et al. Appl. Phys. Lett 5, 5454 (2004)

First result on VLAD

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1

( ) 9E

Eg dω ω =∫ ± 2 atoms/cell

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High High Energy excitations Energy excitations ininPraseodimiumPraseodimium

A.D.Taylor, R.Osborn, K.A.McEwen, W.G.Stirling,Z.A.Bowden, W.G. Williams,E.Balcar, S.W.Lovesey,“Intermultiplet Transitions inPraseodymium Using NeutronSpectroscopy”,PRL 61/11 (1988),1309.

dipolar transition3H4 3H5

at 260 meV.non-dipolar transitions

3F2, 3F3 and 3F4

multiplets at 578, 747 and 809meV respectively.

EXAMPLE 1

Neutron scattering cross section of praseodymium at 17 K, measuredOn HET at an angle of 5° , E1 = 1300 meV

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Future measurements planned in 2005 on VESUVIO

HIGH ENERGY EXCITATIONS IN PRASEODYMIUM

Objectives:Objectives:

measure measure intermultiplet intermultiplet spectra on an inverse geometry spectrometer spectra on an inverse geometry spectrometer

observe new transitions in Praseodymium at energies above 800 observe new transitions in Praseodymium at energies above 800 meV meV

Proposing team: Prof K A McEwen (University College London) et al.2005

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238U, Ef = 6.67 eV

HHigh igh energy excitations energy excitations in in Pr Pr - - Kinematical regionsKinematical regions

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EXAMPLE 2 Interband Interband electronic electronic transition spectrum in diamondtransition spectrum in diamond..

Band structure calculated in thedensity functional theory

framework within the local densityapproximation.

Neutron-electron scattering double-Neutron-electron scattering double-differential cross-section differential cross-section for for interbandinterband

transitions in diamond requirestransitions in diamond requires

ELECTRONIC BAND STRUCTUREELECTRONIC BAND STRUCTUREcalculations calculations ((energies and wave functionsenergies and wave functionsand the matrix elements for the orbital andand the matrix elements for the orbital and

spin interactionsspin interactions))

Indirect band gap at E=5.46 eV

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Diamond - Neutron-electron scattering double-differential cross-sectionDiamond - Neutron-electron scattering double-differential cross-section

Interband Interband transition cross section for two different values of transition cross section for two different values of qq:: 2.6 2.6 ÅÅ-1-1 9 9 ÅÅ-1-1

• For greater values of For greater values of Q (unit of 2Q (unit of 2ππ/a)/a) loss of intensity of the double loss of intensity of the double differential cross section observed.differential cross section observed.

•• orbital contribution dominates for smaller orbital contribution dominates for smaller QQ

•• spin term is predominant spin term is predominant for greater for greater QQ..

2.6 Å-1 9 Å-1

Cross section Intensity profilemodified for _Q = 1 Å-1 FHWM(i.e. almost one Brillouin zone,

being 2�/a _ 1.7 Å-1).

∆Q INTERBAND ELECTRONICINTERBAND ELECTRONICTRANSITIONS IN DIAMONDTRANSITIONS IN DIAMOND

Future measurements planned in 2005 on VESUVIO

INTERBAND ELECTRONIC TRANSITIONS IN DIAMONDINTERBAND ELECTRONIC TRANSITIONS IN DIAMOND

Objectives:Objectives:

measure the inelastic neutron scattering cross section formeasure the inelastic neutron scattering cross section for interband interband electronic electronictransitions in diamondtransitions in diamond

compare the results with a parallel theoretical study ofcompare the results with a parallel theoretical study of interband interband transition transitionspectra.spectra.

Proposing team: Dr. V. Garbuio (University of Rome Tor Vergata) et al.2005

�HINS on VLAD�∆ω resolution185185ReRe E E1 1 = 2.16 = 2.16 eV eV ((- -- -))

149149SmSm E E1 1 = 0.872 = 0.872 eV eV ((- -- -)) 238238UU E E1 1 = 6.671 = 6.671 eV eV ((____))150150SmSm E E1 1 = 20.7 = 20.7 eV eV ((____))149149ErEr E E1 1 = 79.7 = 79.7 eV eV ((____))

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THE EXPERIMENTAL TEAMTHE EXPERIMENTAL TEAM

• ISIS Facility– T. Abdul-Redah, Z. Bowden, J. Mayers, N. J. Rhodes, E. M.

Schooneveld

• University of Milano-Bicocca– G. Gorini, E. Perelli Cippo, M.Tardocchi

• University of Rome Tor Vergata– C. Andreani, D. Fernandez Canoto, A. D’Angelo, S. Imberti,

V. Garbuio, A. Pietropaolo, C. Pantalei, R. Senesi

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High energy excitation inDiamondVLAD kinematics and qresolution

238U analyser foilE1=102.6 eV E1=79.9 eV