Neutron/Gamma Pulse Shape Discrimination in Plastics Scintillators: From Development to Commercialization

Radiation detection requires instruments which can detect nuclear radiation, having at the same time the ability to discriminate among different types of nuclear particles. Formany decades, neutron detection has been based on He-3 proportional counters sensitive primarily to thermal neutrons. The most common methods for the detection of fast neutrons have been based on liquid scintillators with pulse shape discrimination (PSD). A decade of studies conducted at Lawrence Livermore National Laboratory (LLNL) led to the development of new materials, among which are the first PSD plastics for fast neutron detection manufactured based on high concentrations of 2,5-diphenyloxazole (PPO) dissolved in aromatic polymers. More advantages were introduced by plastics doped with B-10 and Li-6 that enable combined detection of both thermal and fast neutrons, offering, in addition, a unique "triple" PSD for discrimination between fast neutrons, thermal neutrons, and gamma rays. Studies conducted with these and more recently introduced materials prepared with multiple dyes alternative to PPO produced a deeper understanding of energy transfer and excited state interaction phenomena. Research led to the commercial production of PSD plastics which, due to the deployment advantages and ease of fabrication, create a basis for the replacement of liquid scintillators and widespread use of solid-state scintillators as large-volume and low-cost neutron detectors.