High energy Inelastic Neutron High energy Inelastic Neutron - - PowerPoint PPT Presentation

Perspectives of eV neutron spectroscopy - 23th April 2005

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:

VESUVIO in The RD configuration: the e.VERDI project the e.VERDI project

– – Gamma detector technologies for Gamma detector technologies for E

En

n = 1

= 1 eV eV - 100

• 100 eV

eV.

– – VLAD VLAD bank bank with RD unit (e.g. YAP with RD unit (e.g. YAP γ γ-detector + U foils)

• detector + U foils)

prototype ( prototype (2 2θ θ=2 =2o

• - 5
• 5o
• ) ad final (

) ad final (2 2θ θ=1 =1o

• - 5
• 5o
• ) 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

• DINS

DINS: :

• <

<E Ek

k>

>

• n(p)

n(p)

• HINS

HINS: :

• high

high energy energy excitations excitations

❀ ❀ HINS on VESUVIO HINS on VESUVIO

High energy excitations at low q High energy excitations at low q q < 10 Å-1 ,  ω > 0.3 eV; (10-6 ps ÷10-3 ps)

Examples include: 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 requirements for HINS for HINS

Contour plot of iso-q loci vs E1

Contour plot of iso-q loci vs E1 and 2θ For fixed  ω=1.5 eV

1° 2° 3° 4° 6° 7° 8° 9°

0.5 1.0 1.5 2.0 2.5 3.0 2 4 6 8 10

238U, E f = 6.67 eV

q [A

• 1]

h [eV]

(

(q, q,  ω ω) range ) range for HINS for HINS

Perspectives of eV neutron spectroscopy - 23th April 2005

0.50° 1.0° 1.5° 2.0° 2.5°

0.5 1.0 1.5 2.0 2.5 3.0 2 4 6 8 10

238U, E f = 102.6 eV

q [A

• 1]

h [eV]

(

(q, q,  ω ω) range for HINS ) range for HINS

at high E at high E1

1almost

almost constant constant q q scans scans ( (q, q,  ω

ω) range for HINS ) range for HINS 2

2θ θ=1 =1o

• 149

149Sm

Sm E E1

1 = 0.872 eV (

= 0.872 eV (- -

• -)

)

185 185Re

Re E E1

1 = 2.16 eV (

= 2.16 eV (- -

• -)

) 238

238U

U E E1

1 = 6.671 eV (

= 6.671 eV (___

___)

)

150 150Sm

Sm E E1

1 = 20.7 eV (

= 20.7 eV (___

___)

)

149 149Er

Er E E1

1 = 79.7 eV (

= 79.7 eV (___

___)

) E E1

1 > 6 eV

> 6 eV

Perspectives of eV neutron spectroscopy - 23th April 2005

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’ 2 2θ θ=2 =20

0-5

• 50

RD RF

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

YAP tele YAP telescopic detector arrangement scopic detector arrangement

Perspectives of eV neutron spectroscopy - 23th April 2005

Detector rings at 2°, 3°, 4° and 5°.

Prototype VLAD: Prototype VLAD: L

L0

0 =11 m

=11 m, , L L1

1 =2 m

=2 m , , 6 sectors of 60°, array 6 sectors of 60°, array diameter diameter ~ ~40 cm, 40 cm, 238

238U analyzer foils

U analyzer foils at at T= 298 K T= 298 K

YAP detector

Perspectives of eV neutron spectroscopy - 23th April 2005

2° < θ < 5°

YAP’s support frame

The VLAD bank of VESUVIO

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 HINS on VLAD Δ

Δ  ω / ω /  ω ω resolution

resolution

185 185Re

Re E E1

1 = 2.16 eV (

= 2.16 eV (- -

• -)

)

149 149Sm

Sm E E1

1 = 0.872 eV (

= 0.872 eV (- -

• -)

) 238

238U

U E E1

1 = 6.671 eV (

= 6.671 eV (__

__)

)

150 150Sm

Sm E E1

1 = 20.7 eV (

= 20.7 eV (__

__)

)

149 149Er

Er E E1

1 = 79.7 eV (

= 79.7 eV (__

__)

)

E E1

1

149 149Er

Er

150 150Sm

Sm

238 238U

U

149 149Sm

Sm

185 185Re

Re

Perspectives of eV neutron spectroscopy - 23th April 2005

T= 298 K, L T= 298 K, L1

1 =11 m

=11 m T= 77 K, L T= 77 K, L1

1 =20 m

=20 m T= 298 K, L T= 298 K, L1

1 =20 m

=20 m T= 77 K, L T= 77 K, L1

1 =11 m

=11 m

VLAD

Δ  ω vs  ω

HINS on VLAD: HINS on VLAD: Total Total Δ Δ ω ω and individual components and individual components Δ Δ E E1

1,

, Δ Δ L Lo

• ,

, Δ Δt t, , Δ Δ L L1

1

238 238U

U analyser analyser foil foil E E1

1 =

= 6.67 6.67 eV eV

T= 298 K, L T= 298 K, L1

1 =11 m

=11 m

Perspectives of eV neutron spectroscopy - 23th April 2005

HINS on VLAD Δq resolution at 2θ=1° q ± Δq/2

149Sm 168Er 238U 238U

Δ Δq q< < 1 1 Å Å-1

• 1

for for ħ ħω ω > > 1 1 eV eV Δ Δq q< < 1 1 Å Å-1

• 1

Δ Δq q< < 1 1 Å Å-1

• 1 for

for ħ ħω ω > 0.3 > 0.3 eV eV 2 2 Å Å-1

• 1 <

<Δ Δq q < < 5 5 Å Å-1

• 1 for

for 1 1 eV eV ≤ ≤ ħ ħω ω ≤ ≤ 7 7 eV eV

Perspectives of eV neutron spectroscopy - 23th April 2005

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 space E1 = 6.671 eV

Perspectives of eV neutron spectroscopy - 23th April 2005

O-H stretching mode at 0.42 eV Δ ω ~ 120 meV FWHM for

238U foil E1 = 6.671 eV (- - -)

ALSO SHOWN Δ ω / / ω

149Sm foil E1 = 0.872 eV (__) 185Re foil E1 = 2.16 eV (…)

Perspectives of eV neutron spectroscopy - 23th April 2005

Δ ω ~ 120 meV FWHM for

O-H stretching at 0.42 eV Ice Ih at 2θ=2° Simulated data

O-H stretching

Perspectives of eV neutron spectroscopy - 23th April 2005

Δ Δq q resolution resolution q range q range for for O-H stretching at 0.42 O-H stretching at 0.42 eV eV

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

HINS measurements Density of states from polycristalline Ice Ih

Perspectives of eV neutron spectroscopy - 23th April 2005

HRMECS measurements (IPNS Argonne National Laboratory)

2 1

( ) 8

E E g

d

• =
• ± 0.1 atoms/cell

2.0 Å-1 ≤ q ≤ 5 Å-1 q ≈ 4 Å-1

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

First result on VLAD

2 1

( ) 9

E E g

d

• =
• ± 2 atoms/cell

Perspectives of eV neutron spectroscopy - 23th April 2005

High High Energy excitations Energy excitations in in Praseodimium Praseodimium

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

dipolar transition

3H4

3H5 at 260 meV. non-dipolar transitions

3F2, 3F3 and 3F4

multiplets at 578, 747 and 809 meV respectively.

EXAMPLE 1

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

• Future measurements planned in 2005 on VESUVIO

HIGH ENERGY EXCITATIONS IN PRASEODYMIUM

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

• bserve new transitions in Praseodymium at energies
• bserve new transitions in Praseodymium at energies

above 800 above 800 meV meV

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

• al. 2005

Perspectives of eV neutron spectroscopy - 23th April 2005 238U, Ef = 6.67 eV

H High igh energy excitations energy excitations in in Pr Pr -

• Kinematical regions

Kinematical regions

Perspectives of eV neutron spectroscopy - 23th April 2005

EXAMPLE 2 Interband

Interband electronic electronic transition spectrum in diamond transition spectrum in diamond.

.

Band structure calculated in the density functional theory framework within the local density approximation. Neutron-electron scattering double- Neutron-electron scattering double- differential cross-section differential cross-section for for interband interband transitions in diamond requires transitions in diamond requires ELECTRONIC BAND STRUCTURE ELECTRONIC BAND STRUCTURE calculations calculations (

(energies and wave functions energies and wave functions and the matrix elements for the orbital and and the matrix elements for the orbital and spin interactions spin interactions) )

Indirect band gap at E=5.46 eV

Perspectives of eV neutron spectroscopy - 23th April 2005

Diamond - Neutron-electron scattering double-differential cross-section Diamond - 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 q q: : 2.6 Å 2.6 Å-1

• 1 9

9 Å Å-1

• 1
• For greater values of

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

• rbital contribution dominates for smaller
• rbital contribution dominates for smaller Q

Q

• spin term is predominant

spin term is predominant for greater for greater Q Q. .

2.6 Å-1 9 Å-1

Perspectives of eV neutron spectroscopy - 23th April 2005

Cross section Intensity profile modified for ΔQ = 1 Å-1 FHWM (i.e. almost one Brillouin zone, being 2π/a ~ 1.7 Å-1).

ΔQ

INTERBAND ELECTRONIC INTERBAND ELECTRONIC TRANSITIONS IN DIAMOND TRANSITIONS IN DIAMOND

• Future measurements planned in 2005 on VESUVIO

INTERBAND ELECTRONIC TRANSITIONS IN DIAMOND INTERBAND ELECTRONIC TRANSITIONS IN DIAMOND

Objectives: Objectives:

measure the inelastic neutron scattering cross section for measure the inelastic neutron scattering cross section for interband interband electronic transitions in diamond electronic transitions in diamond compare the results with a parallel theoretical study of compare the results with a parallel theoretical study of interband interband transition spectra. transition spectra.

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

Perspectives of eV neutron spectroscopy - 23th April 2005

Diamond indirect band gap at about 6 Diamond indirect band gap at about 6 eV eV - Contour plots of constant angle scans

• Contour plots of constant angle scans

 ω ω ( ( __

__ )

) and and q q (- - ) (- - ) vs vs tof tof at at 2 2θ θ= =1 1° ° for three E for three E1

1

238

238U foil:

U foil:

E1 = 20.9 eV - left, E1 = 79.7 eV - center E1 = 102.6 eV - right Vertical lines Vertical lines correspond correspond to to 

ω

ω

= 6 = 6 eV eV. .

Perspectives of eV neutron spectroscopy - 23th April 2005

High energy excitation in Diamond VLAD kinematics and q resolution

238U analyser foil

E1=102.6 eV E1=79.9 eV

Perspectives of eV neutron spectroscopy - 23th April 2005

HINS on VLAD Δω resolution

185 185Re

Re E E1

1 = 2.16 eV (

= 2.16 eV (- -

• -)

)

149 149Sm

Sm E E1

1 = 0.872 eV (

= 0.872 eV (- -

• -)

) 238

238U

U E E1

1 = 6.671 eV (

= 6.671 eV (__

__)

)

150 150Sm

Sm E E1

1 = 20.7 eV (

= 20.7 eV (__

__)

)

149 149Er

Er E E1

1 = 79.7 eV (

= 79.7 eV (__

__)

)

Perspectives of eV neutron spectroscopy - 23th April 2005

High energy excitations at low High energy excitations at low q q

YAP scintillator fro DINS and HINS

Perspectives of eV neutron spectroscopy - 23th April 2005

THE EXPERIMENTAL TEAM THE 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

Perspectives of eV neutron spectroscopy - 23th April 2005

Perspectives of eV neutron spectroscopy - 23th April 2005

DAE DAE

FOIL FOIL SAMPLE SAMPLE M M

2Θ

n Detector n Detector

VESUVIO VESUVIO

n1(p1)

DAE DAE

SAMPLE SAMPLE M M

2Θ n Detector

n Detector

Chopper Chopper Instrument Instrument N(p)

10 12 14 16 18 20 22 24 26 28 30 120 140 160 180 200

Scattering angles (deg)

Energy Transfer (eV) Q(Å

• 1)

100.0 120.0 140.0 160.0 180.0

Chopper Chopper

q(A q(A-1

• 1)

)

E ( E (eV eV) )

Perspectives of eV neutron spectroscopy - 23th April 2005

EXAMPLE 2

Interband electronic Interband electronic transitions in diamond transitions in diamond.

.

Double differential cross section for interband transitions in semiconductors by high inelastic neutron scattering is given by two contribution:

• an orbital contribution

an orbital contribution, proportional to 1/q2, dominates at smaller values of dominates at smaller values of q q. .

• a spin contribution

a spin contribution dominates at larger values dominates at larger values

• f
• f wavevector

wavevector transfer transfer

Neutrons can be scattered by electronic transitions between valence and conduction states

Perspectives of eV neutron spectroscopy - 23th April 2005

This band structure calculated in the density functional theory framework within the local density approximation.

Electronic band structure of diamond: diamond lattice constant a=3.57 Å, so that the minimum gap, at 0.8 of the Brillouin zone in the (1,0,0) direction, corresponds at a wave vector transfer of about 1.4 Å-1

The evaluation of the cross section for interband transitions in diamond implies calculations of the electronic energies and wave the electronic energies and wave functions and the matrix elements for functions and the matrix elements for the orbital and spin interactions the orbital and spin interactions.

.