Design of Beam Shaping Assembly for an Accelerator-based Multi-terminal BNCT Facility

Boron Neutron Capture Therapy (BNCT) is a new treatment of precision radiotherapy. Beam shaping assembly (BSA) is one of the key components in the facility of BNCT and of vital importance in producing neutron beams appropriate for BNCT treatment. BSA is used to moderate and fast neutrons to suitable energy range, reduce other unwanted ingredients, and meet the requirements for BNCT. In this work, based on a neutron source which produced by a 2.5 MeV/30 mA proton accelerator, the Monte Carlo simulation software MCNP was employed to design BSAs. A multi-terminal BSA scheme was designed to slow down the fast neutron beam generated by proton bombarded Li target to the thermal neutron energy range (<0.5 eV) and the epithermal neutron energy range (0.5 eV~10 keV). The proposed thermal neutron BSA scheme uses D₂O as moderator, BeO as reflector, Bi as \gamma filter, and for epithermal BSA, MgF₂ was used as moderator, Pb as reflector, and ⁶LiF as thermal neutron filter. All the parameters of the thermal and epithermal neutron beams at the exit ports of the designed BSAs both meet the recommended values proposed by the International Atomic Energy Agency (IAEA).