A Study on Optimized Neutron Beam Generation by Analysis of Neutron Angular Distribution from 7Li(p,n)7Be Reaction for Accelerator-Based BNCT

Perpendicular neutrons (i.e., solid angle bin of 50-150 .deg. ) among ones generated from 7Li(p,n)7Be reaction, which are focused on the relative low energy regions, was used to produce optimized epithermal neutron beam for Accelerator-based BNCT. By this time, most of the studies for generating the therapeutic neutron beam have used the neutrons emitted to the collinear with the incoming proton. However, it is very difficult to produce the high quantity of epithermal neutrons due to the relative high energy neutrons to be used. In this study, it was found that perpendicular neutrons (solid angle 50-150 .deg. ) include about two times as many neutrons in the energy range of 100 - 300 keV as the existing studies. In particular, epithermal neutron beam from the dual beam port assembly was simulated by MCNPX: this assembly was designed for using the neutrons in optimized neutron angle bin (solid angle 50-150 .deg. ). As the results of the IAEA recommendations for all parameters, and moderation length could be reduced. The advantage depth (AD) and dose rate in the mathematical phantom are calculated to evaluate the dosimetric characterization of the designed epithermal neutron beams. It was recognized that the tumor positioned at the maximum depth of 70 mm from skin could be treated, and tumor at 60 mm depth is approximately taken with only a treatment of a few minutes by using the beam from the dual beam port assembly. It is therefore expected that the neutrons emitted into the solid angle bin of 50 - 150 .deg. from 7Li(p,n)7Be reaction are very effective to produce epithermal neutron beam for BNCT. The new dual beam port assembly which is possible to generate the therapeutic neutron beam satisfies with the IAEA recommendations at each beam port and can be used for reference study of epithermal neutron beam design