Simulation study of a wide energy range neutron beam monitor for TMSR-PNS

To address the issue of beam instabilities in the Thorium-Based Molten Salt Reactor-Power Neutron Source (TMSR-PNS) during operation, caused by beam drop or arcing phenomena, it is necessary to develop a neutron beam monitor with high counting rates, low neutron beam sensitivity, and high neutron/gamma discrimination performance. Based on the Monte Carlo simulation software Geant4, this study investigated the effects of key parameters such as the thickness of the neutron conversion layer, the thickness of the scintillator, and the window material on the performance of thin-film plastic scintillator neutron monitors. The analysis showed that a neutron conversion layer thickness of approximately 2 μm provided a relatively suitable intrinsic detection efficiency. Additionally, when the scintillator thickness was 0.5 mm and the discrimination threshold was set to 0.8 MeV, the monitor exhibited gamma-ray insensitivity. Furthermore, through comparisons of the effects of different window materials on the production of electrons and neutron scattering, aluminum was chosen as the window material due to its low electron production and minimal neutron scattering. The study results provide theoretical guidance for the subsequent fabrication of neutron beam monitors.