Improving neutron/gamma pulse shape discrimination (PSD) of EJ-276 plastic scintillation detectors for nuclear security applications using Monte Carlo simulations

Plastic scintillators capable of neutron/gamma pulse shape discrimination (PSD) offer a low-cost alternative to organic liquids and crystals for detecting neutrons in mixed radiation fields for nuclear security applications. While liquid and crystal scintillators have been used for neutron detection, difficulties with handling and transporting such detectors for large-area field applications have motivated a search for solid-state alternatives without losing detection capabilities. Plastic scintillators are robust and easily manufactured in various geometries. However, commercially available PSD-capable plastic scintillators generally show poorer PSD performance when scaled up to larger sizes. This work reports on Monte Carlo simulation studies conducted to explore the impact of scintillator geometry on the temporal pulse shapes extracted from EJ-276, a PSD-capable plastic scintillator developed by Eljen Technologies. The optical physics capabilities of GEANT4 have been used to simulate the generation and transportation of scintillation photons up to their detection at the photodetector surface. Results show that changes in scintillator size introduce distortion into the pulse shapes, reducing pulse shape discrimination between neutron and gamma pulses. The ability to accurately simulate the temporal pulse shapes from PSD-capable plastic scintillation detectors offers the potential to assess the PSD performance of these detectors before fabrication.