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Measurement of thermal neutron and 41Ar at KEK Linac
KEK
T. Oyama, H. Iwase, A. Toyoda, T. Sanami, and Y. NamitoRadiation science center, KEK, Japan
1. Purpose - Air activation by electron accelerator
2
- e- facilities have less air activation than hadron facilities- However modern e- accelerators will have higher power- More accurate evaluation of air activation is required
- Experimental study on 41Ar production
Nuclide Halflife Reaction Threshold (MeV). 12.3y
53.3d
20.4m
9.96m2.04m37.2m55.5m1.82h thermal neutron
a pair of pump and stack
ratio of evaluated air activation productionin whole linac tunnel
1.2 KEK Linac
3
e+ DumpingRing
Linace-
e-e+
e+ productiontarget
e-
e-
maximum beam powere- 10 GeV 625nA ~ 6.3kW
on target (future x1.5)e- 3.3 GeV 800nA ~ 2.6kW
SUPER
KEKB
PFAR6.5GeV
PF2.5Ge
V
1.3 KEK-Linac positron production target
4
Beam e- 3.3 GeV, 100 nATarget W 1cm and other components
(thick target)
targetyork
cabitye- by RF gun
T. Kamitani (KEK)
~15cm
lystron roomklystron room
concrete concrete
controlled(max 20 uSv/h)controlled
keep out
keep out
public(max
0.2 uSv/h)
KEK controlled (max 1.5 uSv/h)
Target shield 2015 (Radsynch15)Target shield final ver. (3.3 GeV 1250nA e-)
Distance 555cmConcrete 320cmIron 70cm
Distance 430cmConcrete 250cmIron 59cm
Distance 700cmConcrete 400cmIron 72cmground level
controlledcontrolled
KEKcontrolled
2. Methods
6
2.1 Experiment-A - 40Ar gas direct irradiation
7
40Ar gas packages were set in tunnel at positions of X, Y, and Z
3.3GeV e-X
(0m)
Target
Y(15m)
Z(35m)
2.2 Experiment-B - Thermal neutron fluence Φ
8
Thermal neutron fluence Φ in tunnel was measured by the Gold foil activation with/without Cadmium cover
JENDL-4.0JENDL-4.0
3.3GeV e- X(0m)
Target
Y(15m)
Z(35m
)
2.3 Experiment-C - Thermal neutron spatial distribution
9
targete-
30m
Thermal neutron fluence Φ in tunnel was measured by the Gold methodat different positions of upstream and downstream from the target
3 Result1 - Experiments A and B
10
A: Ar gas(Bq/cm3/kW)
B: Gold foil(Bq/cm3/kW)
X(0m) 9.2±1.4 9.2±0.7
Y(15m) 0.73±0.14 0.56±0.034
Z(35m) 0.077±0.016 0.038±0.0015
3.3GeV e- X(0m)
Target
Y(15m)
Z(35m
)
kW)
3.2 Result2 - Thermal neutron spatial distribution
11
targete-
30m
±30m from target covers 99% of total
integrationrange
ratio to totalamount
±15m 91%
±20m 96%
±30m 99%
PHITS 3D Monte Carlo simulation
measurements
40Ar (n, γ) 41Ar reaction
12
capture
Neutron energy spectrum in tunnel around target
PHITSMonte Carlosimulation
41Ar productionsinduced below 1 eV neutron (10-6 MeV)account for 98.7% of total
Gold foil can be used instead of Gas?
• Experiment-C indicates that thermal neutrons distribute in certain range of ±20m (or ±30m)
• The discrepancy of the Experiment-A(Gas) and B (Gold foil) can negligible in case to obtain integral number of 41Ar production
• the answer is yes
Thermal neutron source around KEK Linac target
14
thermal neutron (
Comparison to theoretical evaluation
15
(1) GDR neutron production Yn by Mao’s formula
Yn = 8 × 10−6 E0 (Z0.5 + 0.12Z1.5 − 0.001Z2.5 )
where Yn GDR neutron production per e-, E0 e- energy (MeV),
and Z atomic number of thick target.
If Z=74(W) Yn=1.0, and Z=29(Cu) Yn=0.52. => 0.76 (n/e-) in average
(2) GDR neutron reduction R by components (shielding effect)
It is difficult to predict by hand-calculation. For example
set R to 1/2. => R Yn = 0.76/2 = 0.38 (n/e-)
(3) Neutron thermalization formula by Patterson
Φ = C R Yn / S
where C is a constant of 1.25, and S is total area of the tunnel (cm2)
Φ = 2.1e4 (1/cm2/nA/sec)
=> 41Ar = 4.95e-3 (Bq/cm3/nA)
Standard method to estimate thermal neutron fluence for electron accelerator
compared to experiment (4.42e-3) calculation agrees well (due to (2) is estimated by experience)
5. Conclusion
16
投影片編號 11. Purpose - Air activation by electron accelerator1.2 KEK Linac1.3 KEK-Linac positron production target投影片編號 52. Methods2.1 Experiment-A - 40Ar gas direct irradiation2.2 Experiment-B - Thermal neutron fluence Φ2.3 Experiment-C - Thermal neutron spatial distribution3 Result1 - Experiments A and B3.2 Result2 - Thermal neutron spatial distribution40Ar (n, γ) 41Ar reactionGold foil can be used instead of Gas?Thermal neutron source �around KEK Linac targetComparison to theoretical evaluation5. Conclusion