Simulating Neutron Interaction in a Shielding Material for Proton Therapy
Abstract
Proton therapy facilities employ two types of beam delivery techniques that use beams of protons with energy up to 250 MeV to treat cancerous tumors. However, during nuclear interactions of these protons with the apparatus in the beam path and also with the patient, stray neutrons can be generated, which have energies ranging up to the maximum energy of the proton beam (250 MeV). Shielding of these neutrons requires a two-stage process which first slow down fast neutrons (> 2 MeV) by collisions with a material to thermal energy (0,025 eV) and then absorbs the thermal neutrons by a high thermal cross section material. The simulated neutron shielding material utilized in this project was concrete enhanced by Polyethylene and Boron-Carbide (B4C) to improve its shielding properties against fast and thermal neutrons respectively. This concrete mixture was e↵ective at thermal neutron energy which absorbed approximately 99% of the incident thermal neutrons. However, for fast neutrons energy especially at 250 MeV, the concrete has low attention properties where around 58% of fast neutrons left the concrete mixture. In addition, a significant fraction of secondary gamma rays was produced during the interaction of primary neutrons with the concrete mixture. The angular distribution of both primary neutrons and secondary gamma rays exiting the concrete were found to be maximum at the forward direction (0°). Future work can be built on this project to improve the concrete performance especially at fast neutron range by adding heavy elements as well as investigating the performance of the required lead layer around the concrete mixture to effectively attenuate outgoing gamma rays.