Benchmark experiments for cyclotron-based neutron source for BNCT

In the previous study, we found the feasibility of a cyclotron-based BNCT using the Ta(p,n) neutrons at 90° bombarded by 50 MeV protons, and the iron, AlF3, Al and 6LiF moderators by simulations using the MCNPX code. In order to validate the simulations to realize the cyclotron-based BNCT, we measured the epithermal neutron energy spectrum passing through the moderators with our new spectrometer consisting of a 3He gas counter covered with a silicon rubber loaded with natB and polyethylene moderator and the depth distribution of the reaction rates of 197Au(n,γ)198Au in an acrylic phantom set behind the rear surface of the moderators. The measured results were compared with the calculations using the MCNPX code. We obtained the good agreement between the calculations and measurements within 10% for the neutron energy spectra and within 20% for the depth distribution of the reaction rates of 197Au(n,γ)198Au in the phantom. The comparison clarified a good accuracy of the calculation of the neutron energy spectrum passing through the moderator and the thermalization in a phantom. These experimental results will be a good benchmark data to evaluate the accuracy of the calculation code.