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

A compact single-PMT composite scintillation detector was developed and characterized for discrimination of γ rays, fast neutrons, and thermal neutrons in mixed radiation fields. The detector assemblies consisted of either EJ200 or EJ276 plastic scintillators optically coupled to an EJ426 thermal neutron screen and read out by a single photomultiplier tube (PMT). The γ−equivalent energy response of the detector assemblies was calibrated using 137Cs, 22Na, and 60Co sources through Compton edge analysis, and pulse shape discrimination was evaluated with an Am–Be neutron source under different moderator thicknesses. The EJ200+EJ426 assembly provides a well-separated discrimination between thermal neutron capture events and γ 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 γ rays, fast neutrons, and thermal neutrons. These results show that the proposed sensor architecture is a promising compact approach for mixed-field radiation applications.