Trial of eV Neutron Diffraction KEK M.Arai & T.Yokoo 1) - - PowerPoint PPT Presentation

eV neutron WS at ICANS2005

KEK M.Arai & T.Yokoo 1) Diffraction on highly absorbing materials

K.Kuwahara, M.Kohgi Tokyo Cosm.U

2) Diffraction on pulsed high magnetic field

H.Nojiri, M.Motokawa Tohoku Univ

3) Use of resonance effects (Breit-Wigner) (extracting partial structure factor)

Y.Kawakita, S.Takeda Kyushu Univ.

4) Use of energy dependent cross-section (recoil effects, potential energy, energy contrast)

T.Yokoo , K.Iwasa KEK

5) Pilot Instrument for epithermal neutrons (EXCED)

T.Yokoo KEK Y.Inamura

• Univ. Tokyo

M.Nakamura JAERI

Trial of eV Neutron Diffraction

eV neutron WS at ICANS2005

L1=6.4m, L2=3m Collimation Δθ=0.1°

• 5° < 2θsmall< 10°, Δd/d=0.1

37°< 2θhigh < 95°, Δd/d=0.01 2meV < Ei < 100eV

1.4+1.6m Steel Collimator L1=6.4m L2=3m

(adjustable)

EXCED at KENS

(designed for single crystal diffraction)

high angle PSD small angle PSD

eV neutron WS at ICANS2005

1) good collimation for epithermal neutron

• --> 1.4 +1.6 m long steel (σ~11 barns) collimator section

2) high counting rate with good spatial resolution for epithermal neutrons

• -> 4 layers of 3He-PSD

(10atm, 60cm long, Δr ~ 4mm, 4000 pixels, 70% at 1eV) 3) low background

• -> Vacuum scattering tank with B4C layer

Requirement on the instrument and detector Disadvantage of EXCED Lorentz factor ~ (λ/Q)2 Intensity decreases at small angle scattering for the same Q by using small λ !

eV neutron WS at ICANS2005

d d

• 2

= cot

( )

2 +

• 2

For magnetic scattering most Bragg peak appears at or < Q = 2π/d ~ 1Å-1 with Ei = 2eV (λ~0.2Å) --> 2θ ~2° (SANS with epithermal neutrons) Δd/d ~ 0.1 is required @ 2θ ~2° --> Δθ=0.1° (good value for single crystal) Detector segment size is Δr~4mm (commercially available, cf. RS- 1/2”-60cm PSD) Hence, L2 ~ 3m ---> Δθ =Δr/2L2 < 0.1° dominant negligible

Resolution

eV neutron WS at ICANS2005

Four layered 3He-1D-PSD(10atm) detecting efficiency 70% for 1eV spatial resolution 4mm Pixel Segmentation keeps good spatial and time resolution

Detector system (RS 1/2” PSD)

Intensity at each layer

high angle PSD bank small angle bank

eV neutron WS at ICANS2005

Bragg Peak appears at 4layers 1st layer 2nd layer 3rd layer 4th layer direct-beam background

LabView panel

at 1eV

TOF Angle

Slice along

Angle

eV neutron WS at ICANS2005

EXCED photoes

Scattering Tank(from behind) Sample gonio (top view) B4C slit system Cryo-magnet (Oxford 7T)

eV neutron WS at ICANS2005

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• /-3418./6616+8-9/0111?@3.06A

B0+.CD111?+EA

at Epithermal neutron region ~@1eV the absorption cross-section decreases by 4 order of magnitude

Cross-section as a function of energy

high intensity at the epithermal region( 1Å<λ)

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*+,-./01 *+,-./01 20-+034-51 20-+034-51 6-1 6-1 74-+8-/.1 74-+8-/.1 9/34-4/01 9/34-4/01 401 401 :;<:7 :;<:7 *+,-./0120-+034-5111=6%,%>

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slowing down region (Epithermal) Storage region (Maxwellian, Thermal) Neutron Intensity at a pulsed source Diffraction on highly absorbing materials

eV neutron WS at ICANS2005

１）GdB6 understanding magnetic structure without Quadru-pole interaction (in comparison with CeB6) ２）GdGa2 Magnetic structure and moment rotation to understand the phase diagram

Ei=1.3eV 2θ=2.6°

Example of measurement

eV neutron WS at ICANS2005

for Vertical Field for Horizontal field achieved 32T in 1998 It lasts 100,000 pulses. Development on pulsed high field magnets at KENS

eV neutron WS at ICANS2005

Capacity 1.2mF Voltage(Vc) 10kV Current(I3) 20kA Power 60kJ Time duration 1ms Time repetition 2s Dimension 2x2x4m3 Time Averaged power 1kW(@1ms x 2s) (6 degree increase for 10litter/min cooling water)

DC power Ignitron

Capacitor Bank Specification

5 10 15 20 25 30 0.2 0.4 0.6 0.8 1 B (T) Time (msec)

eV neutron WS at ICANS2005

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01)2-" !"#"$#%&4 >1.5"# ( ) >1.5"# L1 ?"@#&%5*0%@&$" L1 L1+L2 L2 >1.5"#($*,("-3 Bragg Peak 1 d = 2 sin

• Neutron diffraction with pulsed field

Disadvantage Neutron production freq.; 20Hz Pulsed field freq.; 0.5Hz --> 1/40 of normal intensity

eV neutron WS at ICANS2005

0.5 1 1.5 5 10 15 20 25 30 (1/3,1/3,0) Calc (1/3,1/3,0) (1/3,1/3,0.85) Calc(1/3,1/3,0.085)

Spin structure and Bragg Peak intensity in Mag. Field CsCuCl3 Spin structure based on Quantum effect

Magnetic Field in Tesla Intensity of magnetic peaks (Triangular structure with one-dimensional nature, spin=1/2)

eV neutron WS at ICANS2005

Coverage of pulsed field

1ms EXCED Epithermal neutron at 2θ=2°

1ms

Previous experiment 10meV neutron at 2θ=10° Diffraction with epithermal neutron --> effectively broaden pulsed field (diffraction time range is very short) Remark: intensity reduction due to Lorentz factor at small angle

magnetic field profile

eV neutron WS at ICANS2005

Energy dependent cross-section

1 2 3 4 1 2 3 4 5

H n=0,1,2

sigmaT(0) sigmaT(1) sigmaT(2) sum

Cross-section with recoiling effect

t = 0 4E

• M

m

• 1

n! dxx nex

x (n) x+ (n)

• n
• n : E = n0 1+

m Mmol

• x±(n) = m

M 1 0 1+ '

( )

2 E1 2 ± E n0 1+ '

( ) { }

1 2

[ ]

2

t = 0 4E M m

• 1 exp

4mE M0 1+ '

( )

2

• n=0

n=1

t = 0 4E M m

• x+ +1

( ) exp x+ ( ) x +1 ( ) exp x ( )

[ ]

E/ωo

Potential Energy

ωo 2ωo

eV neutron WS at ICANS2005

TiCrMo TiCrMo(V)D (V)D

・Ti0.45Cr0.45Mo0.1D1.8 (TCMD) ・Ti0.48Cr0.32V0.2D1.8 (TCVD) (Hydrogen storage material) M D

・Hydrogen extaction Temperature TCMD ~ 100 ˚C (32meV) TCVD ~ 200 ˚C (41meV)

・<b>~0 for metal atoms →Peaks from H(D) only

2000 4000 6000 8000 1 10

1.2 10

2 4 6 8 10 12

Ti45Cr50Mo5Dx Intensity [a.u.] Q [A

• 1]

Sirius

Powder sample (3g)

eV neutron WS at ICANS2005

Bragg peak intensity change with energy

0.5 1.5 2.5 3.5 2 4 6 8 10

NOR_TCMD Normalized Intensity Q [A

• 1]

10-125seg 16PSDs T=24 K

1) Can it give energy landscape in various crystal directions from various Bragg diffractions ? (energy-surface observation from powder diffraction ?) 2) Gives Caution on powder diffraction analysis. 3) Can apply energy contrast variation ? 4) Importance of angle dispersive diffraction (energy dispersive analysis) ! (importance of continuous angle coverage of powder diffractometer)

eV neutron WS at ICANS2005

s = 1 k 2

n(Eres Ei)

4(Eres Ei)

2 + o 2

a = 1 k n

• 4(Eres Ei)

2 +

• 2

Breit-Wigner Cross-section (resonance scattering)

Resonance Scattering Cross-section Resonance Absorption Cross-section

10

• 1

10 10

1

10

2

10

3

10

4

10

• 3

10

• 2

10

• 1

10 10

1

10

2

109Ag elastic & absorption cross section

elastic cross section absorption cross section

109Ag Cross Section [barn]

Neutron Energy [eV]

Extraction of partial structure factor

b

2S(Q) = bAbASAA (Q) + 2bAbBSAB(Q) + bBbBSBB (Q)

If A-atom has a resonance scattering, SAA(Q) can be extracted.

eV neutron WS at ICANS2005

2 4 6 8 10 12

S(Q) Q (A

• 1)

X=0.00 X=0.09 X=0.17 X=0.23 X=0.33

S(Q) of (AgI)x(Ag2S)x(AgPO3)1-2x glass

• bserved by high-angle detector bank of SWAN

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1 1.5 2 2.5 3 3.5 4 4.5 5 1 2 3 4 5 領域A 領域C

Intensity Q [A

• 1]

10

• 1

10 10

1

10

2

10

3

10

4

0.1 1

109Ag elastic & absorption cross section (lambda)

elastic cross section absorption cross section

109Ag Cross Section [barns] lambda [A] A B C

Diffraction pattern

Example of Resonance Scattering

(AgI)-(Ag2S)-(AgPO)3 (super-ionic conductor) Ag-Ag correlation could be extracted At 2.5A-1

eV neutron WS at ICANS2005

Summary

1) Epithermal neutron is usefule for highly absorbing materials 2) Epithermal neutron is very useful for pulsed field experiments. 3) Use Breit-Wigner cross-section to extract partial structure factor. 4) Use energy dependent cross-section to study recoil effects, potential energy landscape and could apply energy contrast

eV neutron WS at ICANS2005