Simulation of Neutron Moderating Materials Performance Based on BNCT of 2.5 MeV Proton Accelerator

Boron Neutron Capture Therapy (BNCT) based on accelerator neutron source is a new generation of radiation therapy. As an important part of the BNCT facility, Beam Shaping Assembly (BSA) aims to moderate the fast neutron beam in the neutron source to the epithermal neutron energy region (0.5 ev~10 keV), and to minimize the components of fast neutron, thermal neutron and \gamma ray during the treatment. The ⁷Li(p, n)⁷Be reaction with a 2.5 MeV/10 mA proton intensity was taken as the method for generating neutrons. In this paper, the Monte Carlo software package Geant4 (Geometry and Tracking) was used to study and analyze the effects of different thicknesses of AlF₃, Fluental, Al₂O₃ and Al as moderator materials on the epithermal neutron flux rate, epithermal neutron flux to thermal neutron flux ratio, fast neutron and \gamma ray components at the beam exit. The results show that when AlF₃ with a thickness of 25 cm is selected as the moderator material, the neutron beam parameters of the epithermal neutron beam after shaping and moderation all meet the recommended value by the International Atomic Energy Agency (IAEA).