Simulation of Combined Metal-Hydrogenous-Composite Materials for Multilayer Shielding of High Energy Proton Radiation Using Monte Carlo Code PHITS

Abstract

Multilayer shielding scenarios for proton radiation with secondary neutron and gamma radiation have been investigated using the Monte Carlo simulation method through Particle Heavy Ion Transport System (PHITS). This research aims to evaluate shielding effectiveness with variations of layer structure from a combination of metal, hydrogenous, and composite materials and determine the optimum shielding thickness that follows the radiation protection standard. The simulation uses a 230 MeV proton source, 1 nA beam current, and water target as the tissue equivalent. The shielding consists of three layers of beam dump from iron (Fe), Portland concrete, and Borated Polyethylene (BPE) materials. The parameters measured in this study are fluence distribution, ambient dose equivalent H*(10) rate, and induced radioactivity assessment. The simulation results show that the configuration with the iron material on the first layer can attenuate high proton and neutron radiation energy and reduce energy effectively. However, it produces a high dose build-up effect with higher gamma radiation from inelastic scattering reaction, which causes the consideration of additional radiation exposure to the gantry room. On the other hand, placing Fe in the second layer between BPE and concrete (BPE Fe-concrete or Concrete-Fe-BPE) should be an excellent option with modest H*(10) and minimum gamma exposure in front of shielding. The estimation of induced radioactivity in the multilayer shielding was performed by predicting a neutron capture and neutron spallation reaction process. The optimum thickness of each layer for the scenario of 1 m distance from the target is BPE (30 cm), Fe (90 cm), and concrete (110 cm).