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

Measurement of thermal neutron and 41Ar at KEK Linac

KEK

• T. Oyama, H. Iwase, A. Toyoda, T. Sanami, and Y. Namito

Radiation science center, KEK, Japan

• 1. Purpose - Air activation by electron accelerator

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• 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 9.96m 2.04m 37.2m 55.5m 1.82h thermal neutron

a pair of pump and stack ratio of evaluated air activation production in whole linac tunnel

1.2 KEK Linac

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e+ Dumping Ring

Linac

e- e- e+ e+ production target e- e-

maximum beam power e- 10 GeV 625nA ~ 6.3kW

• n target (future x1.5)

e- 3.3 GeV 800nA ~ 2.6kW

SUPE R KEKB PFAR 6.5GeV PF 2.5Ge V

1.3 KEK-Linac positron production target

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Beam e- 3.3 GeV, 100 nA Target W 1cm and other components (thick target)

target york cabity

e- by RF gun

• T. Kamitani (KEK)

~15cm

lystron room

klystron 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 555cm Concrete 320cm Iron 70cm Distance 430cm Concrete 250cm Iron 59cm Distance 700cm Concrete 400cm Iron 72cm

ground level controlled controlled KEK controlled

• 2. Methods

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2.1 Experiment-A - 40Ar gas direct irradiation

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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

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Thermal neutron fluence Φ in tunnel was measured by the Gold foil activation with/without Cadmium cover

JENDL-4.0 JENDL-4.0

3.3GeV e-

X (0m)

Target

Y (15m) Z (35m )

2.3 Experiment-C - Thermal neutron spatial distribution

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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

3 Result1 - Experiments A and B

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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

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target

e-

30m

±30m from target covers 99% of total

integration range ratio to total amount ±15m 91% ±20m 96% ±30m 99%

PHITS 3D Monte Carlo simulation

measurements

40Ar (n, γ) 41Ar reaction

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capture

Neutron energy spectrum in tunnel around target

PHITS Monte Carlo simulation

41Ar productions induced 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

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

Comparison to theoretical evaluation

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(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

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