Design of a mixed material moderator in a beam-shaping assembly for proton accelerator-based boron neutron capture therapy

Boron Neutron Capture Therapy is being promoted with the development of accelerator neutron sources, and many new accelerator-based BNCT facilities are being built. In Particle Accelerator Facility project of Sun Yat-sen University, we plan to build a terminal for BNCT research based on an 8 MeV, CW 3 mA proton accelerator. In this paper, we present a beam-shaping assembly for this proton accelerator with such low 24 kW beam power, using composite moderator materials composed of five elements: Mg, Al, F, O, and Li. The calculation result of FLUKA with ENDF/B and JENDL libraries shows that the epithermal neutron beam flux is 1.57×109n/cm2/s with the CW 3 mA proton beam. The fast neutron component and the gamma ray component under free-air condition are 1.49×10−13Gy∙cm2 and 8.12×10−14Gy∙cm2 respectively, in line with IAEA-TECDOC-1223 design recommendations. The thermal analysis shows that the maximum temperature of beryllium target is 706.5 K, and the structure materials of BSA do not melt. •The study focused on a neutron source using an 8 MeV, 3 mA linear proton accelerator and a 3-layer target for BNCT.•Based on the neutron target, a combination of moderator materials and a beam-shape assembly were designed.•The neutron beam meets the IAEA requirements with such low proton beam power (24 kW).