Are high energy proton beams ideal for AB‐BNCT? A brief discussion from the viewpoint of fast neutron contamination control

• The fast neutron contamination profiles of 3 different moderator materials were discussed.
• D2O, PbF4 and Fluental™ were tested as standalone moderators.
• Standalone moderator cannot effectively suppress fast neutrons higher than 1 MeV.
• AB-BNCT by high energy proton beam suffers serious fast neutron contamination.
• The use of high energy protons (>8 MeV) for AB-BNCT should be carefully evaluated.

High energy proton beam (>8 MeV) is favorable for producing neutrons with high yield. However, the produced neutrons are of high energies. These high energy neutrons can cause severe fast neutron contamination and degrade the BNCT treatment quality if they are not appropriately moderated. Hence, this study aims to briefly discuss the issue, from the viewpoint of fast neutron contamination control, whether high energy proton beam is ideal for AB-BNCT or not. In this study, D2O, PbF4, CaF2, and Fluental™ were used standalone as moderator materials to slow down 1-, 6-, and 10-MeV parallelly incident neutrons. From the calculated results, we concluded that neutrons produced by high energy proton beam could not be easily moderated by a single moderator to an acceptable contamination level and still with reasonable epithermal neutron beam intensity. Hence, much more complicated and sophisticated designs of beam shaping assembly have to be developed when using high energy proton beams.