Performance Characterization of a Plastic-Scintillator Sensor for Fast-Neutron, Thermal-Neutron, and Gamma-Ray Discrimination

Abstract

Discrimination of fast neutrons, thermal neutrons, and $\gamma$ rays in mixed radiation fields is important for radiation monitoring, reactor-related measurements, and background suppression in nuclear experiments. In this work, we investigate a compact plastic-scintillator sensor composed of EJ276 or EJ200 optically coupled to an EJ426 thermal neutron screen and read out by a single photomultiplier tube (PMT). The $\gamma$ equivalent energy response of the detector assemblies was calibrated using $^{137}$Cs, $^{22}$Na, and $^{60}$Co sources through Compton edge analysis, and pulse shape discrimination was evaluated with an AmBe neutron source under different moderator thicknesses. The EJ200+EJ426 assembly provides a well separated discrimination between thermal-neutron capture events and $\gamma$ dominated events over the measured range, with a figure of merit greater than 5. In contrast, the EJ276+EJ426 assembly produced three identifiable signal populations associated with $\gamma$ rays, fast neutrons, and thermal neutrons. These results show that the proposed sensor architecture is a promising compact approach for mixed field radiation applications