High energy Inelastic Neutron High energy Inelastic Neutron Scattering on VESUVIO Scattering on VESUVIO Carla Andreani Universita’ degli Studi di Roma Tor Vergata-Dipartimento di Fisica e Istituto Nazionale per la Fisica della Materia Perspectives of eV neutron spectroscopy - 23th April 2005
SUMMARY SUMMARY Kinematic requirements for eV neutron spectroscopy Kinematic requirements for eV neutron spectroscopy • • • VESUVIO in The RD configuration: the e.VERDI project the e.VERDI project • VESUVIO in The RD configuration: eV . E n = 1 eV eV - 100 - 100 eV E n = 1 – Gamma detector technologies for Gamma detector technologies for – γ -detector + U foils) with RD unit (e.g. YAP γ – VLAD VLAD bank bank with RD unit (e.g. YAP -detector + U foils) – θ =2 θ =1 2 θ 2 θ prototype ( prototype (2 =2 o o - 5 - 5 o o ) ad final ( ) ad final (2 =1 o o - 5 - 5 o o ) versions ) versions • Resolution in High energy Inelastic Neutron Scattering • Resolution in High energy Inelastic Neutron Scattering (HINS) (HINS) • benchmark experiment (RD) from VLAD prototype: • benchmark experiment (RD) from VLAD prototype: – O-H stretching density of states in H2O at 300 K O-H stretching density of states in H2O at 300 K – • high energy excitations in diamond and Pr • high energy excitations in diamond and Pr • high energy excitations : future perspectives on VESUVIO • high energy excitations : future perspectives on VESUVIO Perspectives of eV neutron spectroscopy - 23th April 2005
Kinematical space Perspectives of eV neutron spectroscopy - 23th April 2005
High energy excitations High energy excitations ❀ HINS on VESUVIO ❀ HINS on VESUVIO High energy excitations at low q High energy excitations at low q • DINS DINS: : • - < <E E k > - k > q < 10 Å -1 , ω > 0.3 eV; - n(p) n(p) - (10 -6 ps ÷10 -3 ps) • HINS HINS: : • - high high energy energy - Examples include: excitations excitations high lying vibrational state in molecular systems, high lying vibrational state in molecular systems, high energy excitations in magnetic systems and semiconductors. high energy excitations in magnetic systems and semiconductors. Require low scattering angles Require low scattering angles Perspectives of eV neutron spectroscopy - 23th April 2005
Kinematic Kinematic ( requirements ω ω ) range requirements ( q, q, ) range 10 for HINS for HINS for HINS for HINS 9° 8 Contour plot of iso- q loc i vs E 1 and 2 θ 8° For fixed ω =1.5 eV 7° 6 6° -1 ] q [A 4° 4 3° 2° 2 238 U, E f = 6.67 eV 1° 0 0.5 1.0 1.5 2.0 2.5 3.0 h � [eV] Contour plot of iso- q loc i vs E 1 Perspectives of eV neutron spectroscopy - 23th April 2005
( q, q, ω ω ) range for HINS ( ) range for HINS 2 2 θ θ =1 =1 o o 149 Sm 149 = 0.872 eV ( - - - - ) Sm E E 1 ) 1 = 0.872 eV ( 185 Re 185 = 2.16 eV ( - - - - ) Re E E 1 ) 1 = 2.16 eV ( 238 238 U U E E 1 = 6.671 eV ( ___ ___ ) ) 1 = 6.671 eV ( E 1 > 6 eV E 1 > 6 eV 150 Sm 150 = 20.7 eV ( ___ ___ ) Sm E E 1 1 = 20.7 eV ( ) 149 Er 149 ___ ) = 79.7 eV ( ___ ) Er E E 1 1 = 79.7 eV ( 10 2.5° 2.0° 8 1.5° 6 -1 ] q [A ω ω ) range for HINS ( ) range for HINS ( q, q, 1.0° 4 at high E 1 almost at high E 1 almost 0.50° 2 constant q q scans scans constant 238 U, E f = 102.6 eV 0 0.5 1.0 1.5 2.0 2.5 3.0 Perspectives of eV neutron spectroscopy - h � [eV] 23th April 2005
Schematics of the VESUVIO spectrometer and principles of the Resonance Foil (RF) and Resonance Detector (RD) techniques . 6 Li glass neutron detectors VLAD array, with YAP γ detectors n θ =2 2 θ =2 0 0 -5 -5 0 0 2 n’ Scattering sample RF RD YAP scintillator Perspectives of eV neutron spectroscopy - 23th April 2005
RD unit on VLAD - prototype development RD 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 ( 238 U). • 238 U gammas: from 12 keV to 4.06 MeV. Also X-rays. • YAP detector Perspectives of eV neutron spectroscopy - YAP telescopic detector arrangement scopic detector arrangement YAP tele 23th April 2005
Prototype VLAD: L Prototype VLAD: L 0 =11 m, , L L 1 =2 m , , 6 sectors of 60°, array 6 sectors of 60°, array 0 =11 m 1 =2 m diameter ~ ~40 cm, 40 cm, 238 238 U analyzer foils U analyzer foils at at T= 298 K T= 298 K diameter YAP detector Detector rings at 2°, 3°, 4° and 5°. Perspectives of eV neutron spectroscopy - 23th April 2005
The VLAD bank of VESUVIO 2° < θ < 5° YAP’s support frame detector positions Perspectives of eV neutron spectroscopy - 23th April 2005
Resolution of an indirect geometry Resolution of an indirect geometry spectrometer VLAD position spectrometer VLAD position Resolution calculation performed by expressing q and ω as a function of the experimental variables: uncertainties on the experimental variables denoted by: Perspectives of eV neutron spectroscopy - 23th April 2005
HINS on VLAD resolution HINS on VLAD ω resolution Re E E 1 = 2.16 eV (- - - -) ) Δ Δ ω / ω / ω 185 Re 185 1 = 2.16 eV ( 149 149 Sm Sm E E 1 1 = 0.872 eV ( = 0.872 eV (- - - -) ) 238 U E E 1 = 6.671 eV ( __ ) 238 U 1 = 6.671 eV ( __ ) 150 150 Sm Sm E E 1 1 = 20.7 eV ( = 20.7 eV ( __ __ ) ) 149 Er Er 149 149 Er Er E E 1 1 = 79.7 eV ( = 79.7 eV ( __ __ ) ) 149 150 Sm 150 Sm 238 U 238 U 149 Sm Sm 149 185 185 Re Re E 1 E 1 Perspectives of eV neutron spectroscopy - 23th April 2005
Δ ω Total Δ ω HINS on VLAD: and individual components and individual components HINS on VLAD: Total Δ E Δ L Δ Δ t Δ L Δ Δ Δ E 1 1 , , L o o , , t, , L 1 1 T= 298 K, L 1 T= 298 K, L 1 =11 m =11 m T= 298 K, L 1 T= 298 K, L 1 =20 m =20 m T= 77 K, L 1 T= 77 K, L 1 =11 m =11 m T= 298 K, L 1 =11 m T= 298 K, L 1 =11 m T= 77 K, L 1 T= 77 K, L 1 =20 m =20 m VLAD U analyser analyser foil foil 238 U 238 6.67 eV eV E 1 = 6.67 E 1 = Δ ω vs ω Perspectives of eV neutron spectroscopy - 23th April 2005
HINS on VLAD Δ q resolution at 2 θ =1 ° Δ q Δ Δ Δ q q< < 1 1 Å Å -1 -1 q< < 1 1 Å Å -1 -1 ħ ω ω for ħ > > 1 1 eV eV for 149 Sm 238 U Δ Δ q ħ ω ω q< < 1 1 Å Å -1 -1 for for ħ > 0.3 > 0.3 eV eV < Δ Δ q 2 Å Å -1 -1 < q < < 5 5 Å Å -1 -1 for for 2 ω ħ ω 1 eV eV ≤ ≤ ħ ≤ ≤ 7 7 eV eV 1 238 U 168 Er q ± Δ q/2 Perspectives of eV neutron spectroscopy - 23th April 2005
First VLAD prototype results at 2° Ice Ih sample (270 K) Kinematical space E 1 = 6.671 eV 238 U foil E 1 = 6.671 eV YAP detectors at 2 θ =2 °, 3.5°, 5° No contamination from beam halo - IT WORKS . Perspectives of eV neutron spectroscopy - 23th April 2005
ALSO SHOWN Δ ω / / ω O-H stretching mode at 0.42 eV 149 Sm foil E 1 = 0.872 eV ( __ ) Δ ω ~ 120 meV FWHM for 185 Re foil E 1 = 2.16 eV ( … ) 238 U foil E 1 = 6.671 eV (- - -) Perspectives of eV neutron spectroscopy - 23th April 2005
Ice Ih at 2 θ =2° Simulated data O-H stretching Δ ω ~ 120 meV FWHM for O-H stretching at 0.42 eV Perspectives of eV neutron spectroscopy - 23th April 2005
HINS measurements Density of states from polycristalline Ice Ih Δ q Δ q resolution resolution q range for for q range O-H stretching at 0.42 eV eV O-H stretching at 0.42 YAP detectors located at 2 θ =2°, 3.5°, 5° Perspectives of eV neutron spectroscopy - 23th April 2005
HRMECS measurements ( IPNS Argonne National Laboratory) First result on VLAD E � � � = 2 ± 2 atoms/cell E E g ( ) d 9 � � � = 2 ± 0.1 atoms/cell E g ( ) d 8 1 1 q ≈ 4 Å -1 2.0 Å -1 ≤ q ≤ 5 Å -1 Perspectives of eV neutron spectroscopy - C. Andreani et al. Appl. Phys. Lett 5, 5454 (2004) 23th April 2005
High Energy excitations Energy excitations in in EXAMPLE 1 High •Future measurements planned in 2005 on VESUVIO Praseodimium Praseodimium A.D.Taylor, R.Osborn, K.A. HIGH ENERGY EXCITATIONS IN PRASEODYMIUM McEwen, W.G.Stirling, Z.A.Bowden, W.G. Williams, E.Balcar, S.W.Lovesey, Objectives: Objectives: “Intermultiplet Transitions in Praseodymium Using Neutron Spectroscopy ”, measure intermultiplet spectra on an inverse geometry intermultiplet spectra on an inverse geometry measure PRL 61/11 (1988),1309. spectrometer spectrometer dipolar transition 3 H 4 3 H 5 at 260 meV. observe new transitions in Praseodymium at energies observe new transitions in Praseodymium at energies non-dipolar transitions above 800 meV meV above 800 3 F 2 , 3 F 3 and 3 F 4 multiplets at 578, 747 and 809 meV respectively. Proposing team: Prof K A McEwen (University College London) et Neutron scattering cross section of praseodymium at 17 K, measured al. 2005 Perspectives of eV neutron spectroscopy - On HET at an angle of 5° , E 1 = 1300 meV 23th April 2005
High igh energy excitations energy excitations in in Pr Pr - - Kinematical regions Kinematical regions H 238 U, E f = 6.67 eV Perspectives of eV neutron spectroscopy - 23th April 2005
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