KEK Measurement of thermal neutron and 41 Ar at KEK Linac T. Oyama, - PowerPoint PPT Presentation

KEK Measurement of thermal neutron and 41 Ar at KEK Linac T. Oyama, H. Iwase, A. Toyoda, T. Sanami, and Y. Namito Radiation science center, KEK, Japan

1. Purpose - Air activation by electron accelerator 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 - ratio of evaluated air activation production Nuclide Halflife Reaction Threshold (MeV). in whole linac tunnel 12.3y 53.3d 20.4m 9.96m 2.04m 37.2m 55.5m 1.82h thermal neutron a pair of pump and stack Experimental study on 41 Ar production - 2

PFAR 1.2 KEK Linac SUPE 6.5GeV R e- KEKB e- PF 2.5Ge V e+ Dumping e- Ring e+ maximum beam power e- Linac e- 10 GeV 625nA ~ 6.3kW on target (future x1.5) e- 3.3 GeV 800nA ~ 2.6kW e+ production target 3

1.3 KEK-Linac positron production target Beam e- 3.3 GeV, 100 nA Target W 1cm and other components (thick target) T. Kamitani (KEK) ~15cm cabity e- by RF gun york target 4

Target shield final ver. (3.3 GeV 1250nA e-) Target shield 2015 (Radsynch15) KEK controlled controlled KEK controlled (max 1.5 uSv/h) controlled Distance 430cm Distance 700cm Distance 555cm Concrete 250cm Concrete 400cm Concrete 320cm Iron 59cm Iron 72cm Iron 70cm ground level public (max klystron room 0.2 uSv/h) lystron room controlled controlled (max 20 uSv/h) concrete concrete keep out keep out

2. Methods 6

2.1 Experiment-A - 40 Ar gas direct irradiation Target 3.3GeV e- X Y Z (0m) (15m) (35m) 40 Ar gas packages were set in tunnel at positions of X, Y, and Z 7

2.2 Experiment-B - Thermal neutron fluence Φ Target 3.3GeV Z X Y e- (35m (0m) (15m) ) Thermal neutron fluence Φ in tunnel was measured by the Gold foil activation with/without Cadmium cover JENDL-4.0 JENDL-4.0 8

2.3 Experiment-C - Thermal neutron spatial distribution target e- 30m Thermal neutron fluence Φ in tunnel was measured by the Gold method at different positions of upstream and downstream from the target 9

3 Result1 - Experiments A and B Target 3.3GeV Z X Y e- (35m (0m) (15m) ) A: Ar gas B: Gold foil (Bq/cm 3 /kW) (Bq/cm 3 /kW) X(0m) 9.2 ± 1.4 9.2 ± 0.7 kW) Y(15m) 0.73 ± 0.14 0.56 ± 0.034 Z(35m) 0.077 ± 0.016 0.038 ± 0.0015 10

3.2 Result2 - Thermal neutron spatial distribution target e- 30m measurements PHITS 3D Monte Carlo ± 30m from target simulation covers 99% of total integration ratio to total range amount ± 15m 91% ± 20m 96% 11 ± 30m 99%

40 Ar (n, γ) 41 Ar reaction Neutron energy spectrum in tunnel around target PHITS capture Monte Carlo simulation 41Ar productions induced below 1 eV neutron (10-6 MeV) account for 98.7% of total 12

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 41 Ar production • the answer is yes

Neutron energy spectra from 20cm Fe target by 1 GeV e- Thermal neutron source around KEK Linac target High energy GDR thermal neutron ( <1eV) track length plot around the target 14

Comparison to theoretical evaluation Standard method to estimate thermal neutron fluence for electron accelerator (1) GDR neutron production Yn by Mao ’ s formula Y n = 8 × 10 −6 E 0 ( Z 0.5 + 0.12Z 1.5 − 0.001Z 2.5 ) 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) I t 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/cm 2/nA/sec) compared to experiment (4.42e-3) calculation agrees well => 41Ar = 4.95e-3 (Bq/cm3/nA) 15 (due to (2) is estimated by experience)

5. Conclusion 16