PHITS computational investigation of the neutron shielding ability of HMPE sheets with B4C and Gd2O3 fillers

Abstract

Photoneutrons are produced by accelerator machines operating at a minimum of 10 MV. These photoneutrons come from the photonuclear interactions between photons produced by machines and high-Z materials specifically at the photon beam targets. When unshielded, these photoneutrons cause an unnecessary increase in dose to the patients or exposure to the workers, resulting in biological hazard. This study computationally investigated the neutron shielding ability of 0.08-cm thick high-modulus polyethylene (HMPE) sheets with varying weight fractions of B₄C or Gd₂O₃ fillers using Particle and Heavy Ion Transport System (PHITS). HMPE on its own can shield neutrons, but the results of this study have shown that the addition of B₄C or Gd₂O₃ fillers increases its neutron shielding ability, especially in the thermal neutron energy region. Moreover, increasing the filler weight fraction from 5% to 20% increased the neutron shielding ability of the HMPE sheets with B₄C or Gd₂O₃ fillers. The HMPE sheets with Gd₂O₃ resulted in the highest neutron dose reduction percentages ranging from 3.43−6.60% for neutron sources with high fast neutron percentages, and 9.55−58.27% for neutron sources with high thermal neutron percentages.