A neutronic study on accelerator-based hyper-thermal neutron irradiation system for neutron capture therapy

Hyper-thermal neutrons are the thermal neutrons with a high-temperature Maxwellian-like distribution of thousand-order K. In neutron capture therapy (NCT), hyper-thermal neutron irradiation is expected for treating tumors from surface to 5-cm depth, because it can make the intermediate dose distribution between thermal and epi-thermal neutron irradiations. A neutronic study of the accelerator-based hyper-thermal neutron irradiation system was performed. From the parametric surveys, 7Li(p,n)7Be reaction and 6-MeV proton energy was selected for the neutron source. It was found that the combination of the 35-cm-thick heavy-water moderator with 300 K (room temperature) and the 10-cm-thick graphite moderator with 2000 K was advantageous for hyper-thermal neutron generation.