The large-angle scattering reaction cross sections for materials relevant to the design of fusion reactors are not necessarily consistent between nuclear data libraries. The cross section must be known at large angles in order to accurately model scenarios such as neutron streaming. To confirm the accuracy, our research group developed a benchmark experimental method focusing on backscattering reaction cross sections. Although neutrons via backscattering reaction were able to be successfully extracted and visualized using an activation detector, it was found that the experimental results did not agree with the calculated results.

In this study, we numerically examined the discrepancy using the MCNP5 code in order to determine the source of the discrepancy and allow for quantification of the neutron backscattered by the benchmark target. As a result, it was found that the cause of the disagreement is due to the modeling of the experimental arrangement. This means the benchmark experiment can correctly estimate the backscattering contribution, even if there are elements in the irradiation room that cannot be modeled precisely, such as an accelerator, as long as no unnecessary elements are arranged in the vicinity of the activation detector.