Borated polyethylene is an effective neutron moderator and absorber in medical linear accelerator shielding; however, there is limited data regarding the required material thickness for adequate neutron attenuation. To address the gap in shielding data, our study systematically quantifies first and equilibrium tenth-value layers (TVL1 and TVLe) for polyethylene containing 0%, 5% and 30% natural boron by weight across neutron energies ranging from thermal to fast. Comprehensive Monte Carlo simulations (n = 3504) were performed to estimate TVL thicknesses from thermal to 20 MeV neutrons. A current tally was used to count neutrons exiting the shield and determine thicknesses corresponding to 10% and 1% transmission. Sixteen energies and 73 thicknesses of materials were modelled with statistical uncertainties below 3%. TVL thicknesses were independently validated with PHITS using identical simulation parameters. We found that TVL values ranged from 1.3 mm for thermal neutrons in borated polyethylene, to 50 cm for 20 MeV neutrons in pure polyethylene. In all cases, adding boron to polyethylene reduced the TVL, with the greatest effect at thermal energies, and a smallest effect at 12 MeV. Here we provide the first comprehensive characterization of borated polyethylene's ability to attenuate neutrons, supporting shielding design for medical linear accelerators.
Bellamy et al. (Mon,) studied this question.
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