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High Energy Neutron Shielding for High Yield Proton PCB Exposure: A Monte Carlo Study

S Zimmerman*, D Moyer , E Wolf , D Ionascu , M Lamba , University of Cincinnati, Cincinnati, OH


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To investigate and quantify the neutron shielding required to reduce neutron damage in sensitive components in a proton accelerator gantry performing industrial PC Board (PCB) irradiation using TOPAS Monte Carlo.

Methods: TOPAS (v3.1) was used to model a pencil beam of protons of varying energies (100-250 MeV) directed at a thin copper foil (1 mm) to simulate PCB irradiation. A cylindrical graphite plug sufficient to completely stop 250 MeV protons was modeled directly behind the copper foil. A 5 percent borated polyethylene cylinder was modeled around the carbon plug to absorb neutrons produced in the foil and the plug. The entire shield was 1 m radius, 1 m length. The neutron fluence in four 25 cm segments along the z-axis was tallied as a function of radial distance. The neutron fluence exiting the shield was characterized based on its energy.

Results: For 250 MeV protons the maximum neutron fluence in the shield was 90 n/mm²/10� protons just radially beyond the carbon plug closest to the source. The fluence exiting the shield radially was 0.028, 0.026, 0.019, 0.011 n/mm²/10�p at the 1st (closest to the source) to 4th segments, respectively. The fluence exiting the distal end of the shield was 0.43 n/mm²/10�p. The energies with the highest fluence exiting the shield radially and distally were 40 and 50 keV, respectively, with a lower fluence peak at 4.4 MeV.

Conclusion: 250 MeV protons striking a PCB backed with a graphite plug/borated polyethylene shield reduced the neutron fluence exiting the shield to an average of 0.021 n/mm²/10�p. The maximum fluence was reduced to 6.0E-04 n/mm²/10�p for 100 MeV protons.


Shielding, Monte Carlo, Protons


Not Applicable / None Entered.

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