Radiation field characterization with emphasis on the collimator configuration at the compact neutron source RANS-II facility

The RIKEN Accelerator-driven compact Neutron Source-II (RANS-II) based on the 7Li(p,n)7Be reaction with 2.49 MeV proton injection was installed in a small area of the experimental hall, where the scattered radiation is expected to strongly influence experiments. Therefore, we have begun to study the radiation characteristics of the RANS-II hall by simulation with the Particle and Heavy Ion Transport code System (PHITS) and by experiments to clearly identify the scattered component. In addition, to suppress the background, a collimator is studied with respect to its size, shape, and materials. With the use of the ϕ30 mm borated polyethylene collimator, we found that the background becomes less than 1% of the extracted neutron beam intensity 1.0 m from the Li target. For the experiment, neutron suppression was characterized by measuring the neutron dose rate with a neutron dosimeter and a collimator. The suppression ability of the neutron beam was confirmed by comparing the results of simulations with those of experiments.