Beam quality deterioration related to target cooling in neutron-producing target station of AB-BNCT

Abstract For the research of the accelerator-based boron neutron capture therapy (AB-BNCT), higher therapeutic beam intensity and better beam quality remain the aim of the neutron-producing target station, which is a coupled structure of the neutron target and the beam shaping assembly (BSA). To improve the efficiency of the target station, it is crucial to analyze the loss of epithermal neutron and the deterioration of other key beam parameters that are related to the neutron target, for which the cooling is of particular importance. Based on Monte Carlo simulation, we discuss this problem with two points: (1) the neutron leakage at the proton tube, which depends on the cooling limit of the target, and (2) the over-moderation by the cooling water in the target. It is found that these two points significantly deteriorate the epithermal neutron intensity as well as other beam parameters. Possible methods of improvement are proposed.