The TOF-USANS Instrument for Japanese SNS - Spallation Neutron ...

The TOF-USANS Instrument for Japanese SNS
JAERI, Kazuya Aizawa

J-PARC (Japan Proton Accelerator Research Complex)
JSNS
Joint project of JAERI and KEK
Joint Project between JAERI and KEK, 2001~2006( construction period)
400-600 MeV Linac
(Superconducting)
400 MeV Linac
(Normal Conducting)
R&D for Nuclear
Transmutation
3 GeV PS
(333µA, 25Hz)
・1MW, Δt

Time Averaged Intensity (n/cm 2 /eV/sr)
10 16
10 15
10 14
10 13
10 12
10 11
Intensity of JSNS moderator
JSNS
Joint project of JAERI and KEK
Time Averaged Intensity (for CM) :1/4 of ILL’s Cold source
Pulse Peak Intensity (for CM) :~100 of ILL’s Cold source
ILL cold (56 MW)
SNS 2 MW
coupled
JRR-3M cold
KENS (CH4)
JSNS 1 MW
coupled
decoupled
decoupled
(poison)
10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1
Energy (eV)
Pulse Peak Intensity(n/cm 2 /s /sr/eV/pulse)
10 17
10 16
10 15
10 14
10 -4
10 -3
Decoupled
Poisoned
(center)
10 -2
Coupled
ILL cold (56 MW)
10 -1
Energy (eV)
Hg Target
Be reflector
1MW 25Hz
10 0
10 1

Proposed JSNS low-q instruments
Concept : cover wide q-range by several instruments
(1) High Intensity SANS (HI-SANS)
q = 0.01 - 100 nm -1
pin hole collimator, magnetic, lens,
converging collimator
(2) High Resolution SANS (HR-SANS)
merge into HI-SANS
(3) Double Crystal SANS (DC-SANS)
q = 0.00002 - 0.5 nm -1
polymer, alloy, ceramic…

Preliminary layout of JSNS
Muon science facility
proton
Double crystal SANS (TOF-USANS)
Neutron scattering facility

Feature
(1) Use of harmonics (M. Agamalian et al.,SPIE’s 47 th
Annual Meeting, Seattle, 2002)
lower minimum q
higher maximum q
(2) Reduction/measurement of
quasi-elastic scattering, inelastic scattering
Non-dispersive
symmetric Bragg case
Principle of TOF-USANS
y = θ −θ ( B)sin2θ
B −V ()E 0
V( G)
E ∆θn = 2 FN G ( ) ⎛ λ
⎜
πvcsin2θ ⎝ B n
⎞
Reduced angular parameter y
Width of total reflection
⎟
⎠
( )
( )= 2πh2 F N G
V G
mvc θB : Bragg angle, E : neutron energy
h = h
, h : Planck's constant
2π
FN ( G):
nuclear structure factor
Extend reactor
USANS q-range
m : neutron mass, v c : volume of unit cell
(H. Rauch and D. Petrascheck, in: Neutron Diffraction,
ed., H. Dachs, Topics in Current Physics 6 (1978) 303
(Springer, Heidelberg, Berlin, Göttingen))
q minimum q maximum
qmin,n ≈ 2π ⎛ ∆θ ⎞ n
⎜ ⎟
λ n⎝
2 ⎠
( )
= 2 FN G ⎛ λ
⎜
vcsin2θ ⎝ B n
⎞
⎟
⎠
2
G
O
Dispersion surf ace
Maximum scattering angle of
measurement
∆θmax,n = ~ 2000 µrad
= const
λ/ 4
λ/ 3
λ/ 2
λ
qmax,n = 2π ⎛ ∆θ ⎞ max
⎜
λ n ⎝ 2 ⎠
= π∆θ max
λ
n

Schematic drawing of USANS
insturment at JSNS
(1) The instrument is located No.13 port (coupled liquid H 2 moderator).
In order to share the port with other instrument, pre-monochromator is used.
(2) Si crystals are mounted in vacuum chamber.
Because, temperature control of many samples
is carried out.
(3) We use thin type channel cut Si crystals.
~4m
Const ant t emperat ure room
Goniometer in
vacuum chamber
1st channel cut Si,
3 bounce
Beam stop / monitor
2nd channel cut Si,
3 bounce
3 He detector
~3m
Sheild
Coupled moderator
Pulsed neutron
T0 chopper
Pre-monochromator
Slit
Slit
Guide tube
Sample goniometer,
t emperat ure cont rol
Goniometer in
vacuum chamber
Beam st op
Vibration free table
7.5 m
20 m
other instrument

Time averaged intensity (n/cm2/sr/nm)
Characteristic of No. 13 port and selected wavelength
Liquid H 2 coupled moderator
10 14
10 13
10 12
10 11
10 10
10 9
10 8
Calculation codes
NMTC/JAERI97
MCNP4a
0.001 0.01 0.1 1
Wavelength (nm)
Si (111)
0.255 nm
Intensity (n/cm2/sr/nm/pulse)
10 15
10 13
10 11
10 9
0.0001 0.01 1
Time (msec)
0.255 nm
0.0283 nm
λ/9
0.0283 nm Pulse shape for λ and λ/9 at 25Hz, 1MW
Time averaged neutron intensity
FWHM (µsec)
1000
100
10
1
0.1
0.001 0.01 0.1 1
Wavelength (nm)
FWHM of pulse shape as a function of wavelength

Width ( µrad)
Calculated characteristic of TOF-USANS for JSNS -1-
10
1
0.1
0.01
0.01
λ/1=0.255 nm
(111)
(220)
λ/9
λ/8
λ/7
λ/5
λ/4
2 3 4 5 6 7
λ (nm)
λ/3
λ/3
0.1
λ/2
2 3 4
Darwin width for Si (111) and Si (220) setting.
Si (111)
wavelength λ λ/3 λ/4 λ/5 λ/7 λ/8 λ/9
notation (111) (333) (444) (555) (777) (888) (999)
λ
λ
q min (nm -1 )
10 -4
10 -5
2
7
6
5
4
3
2
0.01
λ/1=0.255 nm
(111)
(220)
Si (220)
wavelength λ λ/2 λ/3λ/4 λ/5 λ/6 λ/7
notation (220) (440) (660) (880) (10 10 0) (12 12 0) (14 14 0)
2 3 4 5 6 7
λ (nm)
0.1
2 3 4
q min for Si (111) and Si (220) setting

Si (111)
Si (220)
Calculated characteristic of TOF-USANS for JSNS -2-
Intensity (arb. units)
Intensity (arb. units)
10 12
10 11
10 10
10 9
10 8
10 7
10 6
10 5
10 12
10 11
10 10
10 9
10 8
10 7
10 6
10 5
-10
-10
Central part of 2nd Si rocking curve
-5
-5
0
0
5
10
θ−θΒ (µrad)
5
10
θ−θΒ (µrad)
λ/1=0.255 nm
15
(111)
(333)
(444)
(555)
(777)
(888)
(999)
20
λ/1=0.255 nm
15
(220)
(440)
(660)
(880)
(10 10 0)
(12 12 0)
(14 14 0)
20
25
25
Intensity (arb. units)
Intensity (arb. units)
10 12
10 11
10 10
10 9
10 8
10 7
10 6
10 5
10 12
10 11
10 10
10 9
10 8
10 7
10 6
10 5
Central part of 2nd Si rocking curve in q-scale
10 -6
10 -6
10 -5
10 -5
10 -4
q (nm -1 )
10 -4
q (nm -1 )
λ/1=0.255 nm
10 -3
10 -3
(111)
(333)
(444)
(555)
(777)
(888)
(999)
λ/1=0.255 nm
(220)
(440)
(660)
(880)
(10 10 0)
(12 12 0)
(14 14 0)
We assumed that the reflectivity of the pre-monochrometer to the neutron which diffracts dynamically on Si crystals was equal.
10 -2
10 -2

Intensity (arb. units)
10 13
10 11
10 9
10 7
10 5
Measurement diagram
~ -2000 µrad step scan
~2000 µrad
first frame
elastic scattering
(444)
(555)
(777)
(888)
(999)
-100 -50 0 50 100
θ−θ Β (µrad)
(333)
(111)
fine step
inelastic scattering
Central part of step scan for 2nd Si rocking curve
1
larger step
Flight distance (m)
20
15
10
5
0
0
40
TOF (msec)
10
10
20
TOF (msec)
25 Hz
λ/1=0.255 nm
30
(111)
(333)
(444)
(555)
(777)
(888)
(999)
Flight distance - TOF diagram
detector
sample
T0 chopper
moderator
40

10 -5
pulse
Performance of TOF-USANS
case of Si (111) setting
10 -4
reactor
10 -3
q (nm -1 )
10 -2
λ=0.255nm
(111)
10 -1
(333)
(999)
(555)
(444)
(888)
(777)
λ/1=0.255nm
10 0
Calculated q-range of TOF-USANS and reactor-USANS
TOF-USANS
q =~ 2×10 −5 − 0.5 nm −1
Gain ~
( )
m Ip n
∑ =~12,
n=1
I r
n =1,3,4,5,7,8,9
Ip n
I r
() : neutron flux for nth order reflection
at pulsed source
: neutron flux at reactor source
Reactor-USANS
q =~ 2×10 −4 − 0.05 nm −1

Intensity (cps)
1000
100
10
0.001
1
0.1
0.01
10 -5
Performance of Reactor USANS at JRR-3
B.G level
10 -4
10 -3
q (nm -1 )
λ = 0.2 nm
Rocking curve
Ewald curve
10 -2
10 -1
Rocking curve of 2nd channel cut Si-crystal of thin type
Thin type channel cut Si
effective for background reduction
S/N ratio : 2 ~ 2.6 ×10 5
neut ron
Thick type
0.25 nm
10 110
10
5 bounce
Thick - thin type
Cd
130
Cd
2 15 2
19
unit mm

Moderator
Repetition
T0 chopper
L1
(L2)
Pre-monochromator
Crystal
Temperature control
Table
Detector
DC-SANS parameters
Coupled liquid H 2
25 Hz
~7.5m
~21 m
(~1.0m)
Bent PG/Bent Si
Si 111, Si 220,triple-triple bounce
Constant temp. room + chamber
Vibration free table
3 He proportional counter