General considerations for effective thermal neutron shielding in detector applications

Abstract

For thermal neutron detectors, effective shielding is a crucial aspect of signal-to-background optimization. This is especially important for cold to thermal neutrons, as the detectors are most sensitive in this energy range. In this work, a few common shielding materials, such as cadmium, B4C and epoxy-Gd2O3 mixtures, are analytically evaluated based on interaction cross sections extracted from Geant4. For these materials, the neutron absorption and scattering dependence on material thickness and incident neutron energy are examined. It is also considered how the absorption and scattering change with different material compositions, such as 10B-content in B4C, and component ratio in epoxy-Gd2O3 mixtures. In addition, a framework is introduced to quantify the effectiveness of the neutron shielding, comparing the relationship between absorption and scattering of different shielding materials. The aim is to provide a general tool kit, which can be used to quickly identify an appropriate shielding material, with the required thickness, to reach a desired thermal neutron shielding performance. Finally, as an example, the developed tool kit is applied to the specific shielding application for the Multi-Grid CSPEC detector, currently in development for the European Spallation Source.