Research on perturbation of neutron fluence rate in a closed thermal neutron field due to medium materials

The neutron radiation field has vital applications in areas such as biomedicine, geology, radiation safety, and many others for neutron detection and neutron metrology. Correcting neutron fluence rate perturbation accurately is an important yet challenging problem. This study proposes a correction method that analyzes three physical processes. This method, which transforms the detection process from point detection to area detection, is based on a novel physical model and has been validated through theoretical analyses, experiments, and simulations. According to the average differences between the calculated and experimental results, the new method (1.67%) demonstrated better accuracy than the traditional simulation (2.17%). In a closed thermal neutron radiation field, the detector or strong neutron absorption material significantly perturbs the neutron fluence rate, whereas its impact on the energy spectrum shape and neutron directionality is relatively minor. Furthermore, based on the calculation results of the perturbation rate formula for medium materials with different compositions and sizes, the larger the volume and capture cross section of the medium, the higher the perturbation rate generated in the closed radiation field.