Study of a triple-discriminating plastic scintillator detector for fast neutrons, thermal neutrons, and gamma rays

TL;DR

This work tackles the challenge of identifying fast neutrons, thermal neutrons, and gamma rays in mixed radiation fields using two compact plastic-scintillator configurations: EJ200+EJ426 and EJ276+EJ426. Energy response is calibrated with three gamma sources, and pulse shape discrimination is employed with an Am-Be neutron source to separate the three radiation types. The EJ200+EJ426 configuration achieves strong thermal-neutron versus gamma discrimination with a peak FOM of 5.34, while the EJ276+EJ426 configuration enables three-way discrimination (fast neutrons, thermal neutrons, gamma rays) above 1 MeV gamma-equivalent energy, with FOMs exceeding 6.12 and 4.39 for the relevant pairs. These results indicate robust neutron–gamma discrimination in mixed fields and point to practical applications in reactor antineutrino experiments, radiation monitoring, and safety contexts where precise identification of radiation types is essential.

Abstract

Detecting fast and thermal neutrons plays a crucial role in neutrino experiments and reactor physics. In this study, we propose a plastic scintillator detector which demonstrates the ability to clearly distinguish fast neutrons, thermal neutrons, and gamma rays within mixed radiation fields, offering a practical approach for multi-radiation detection. Two plastic scintillator assemblies: EJ200+EJ426 and EJ276+EJ426 were setup, and the system energy response was calibrated using three gamma sources(137Cs, 22Na and 60Co). An Am-Be neutron source was employed, and pulse shape discrimination(PSD) was used to separate fast neutrons, thermal neutrons and gamma rays. Using a three-sigma discrimination criterion, the EJ200+EJ426 configuration was found to reliably distinguish thermal neutrons from gamma rays, while the EJ276+EJ426 configuration can effectively discriminate fast neutrons, thermal neutrons and gamma rays at gamma-equivalent energies above 1 MeV.

Figures (14)

• Figure 1: Schematic of the experimental setup .The entire experimental setup is enclosed in a dark box. One end of the plastic scintillator is coupled to the PMT via silicone grease, while the other end is coupled to EJ426. The EJ426 is clamped by PMMA and faces the radiation source. When using an Am-Be neutron source, HDPE of varying thicknesses is added as required to moderate neutrons.
• Figure 2: The side view(left) and top view(right) of the experimental setup.The PMT is wrapped with black tape and coupled with a plastic scintillator .
• Figure 3: Photograph showing the EJ276 (left) and EJ426 (right) EljenEJ426 scintillators
• Figure 4: Schematic of the PMT gain calibration setup.
• Figure 5: Left:The charge-integrated energy spectrum of SPE signals. Right: Relationship between the logarithm of PMT gain and applied voltage.