Design study of neutron flux intensity monitor between ten and several hundred keV for BNCT

Abstract

Based on the activation method using 71Ga(n,γ)72Ga reaction, two spherical monitors with gallium nitride (GaN) wafers as activation material were designed by Monte Carlo simulations to precisely measure the absolute integral neutron flux intensity between ten and several hundred keV. The two monitors are almost the same in shape and have an absorber/moderator/absorber/GaN arrangement from outside to inside. The differences between the two monitors are the kind of materials, the thicknesses of the absorbers and the diameter of the moderator. By making difference of the sensitivities between these two monitors, the contributions of thermal, epithermal and very high energy fast neutrons were removed completely, and constant monitor sensitivity to neutrons between ten and several hundred keV was extracted. The simulation results and related analysis indicated that the absolute integral neutron flux intensity between ten and several hundred keV could be precisely measured by the presently designed two monitors.