Boron-10-Doped Polysiloxanes as Matrix Materials for Application in the Simultaneous Detection and Discrimination of Gamma Rays and Fast and Thermal Neutrons

Three boron-10 enriched aromatic molecules have been synthesized and incorporated into two different commercial polysiloxane resins, Shin Etsu KER-6000 and Wacker SilRes H62-C. Scintillating fluorophores, 9,9-dimethyl-2-phenylfluorene (PhF) and 2,5-diphenyloxazole (PPO), were tested in combination with each resin and boron-10 molecule for the simultaneous detection of gamma rays, fast neutrons, and thermal neutrons. The H62-C resin was able to solubilize a large amount of PhF, in excess of 20 wt%. Cure kinetics were controlled through the addition of divinylbenzene (DVB) and phenyl tris(dimethylsiloxy)silane (PTDMSS) crosslinker solution to the H62-C resin, with rheology experiments demonstrating a large reduction in time to gelation when 20 wt% crosslinker solution was added, from more than 4 h to less than 1 h. These polysiloxane resins can be cured in 3 h under air, while common poly(vinyltoluene) scintillators require at least four days of heating and oxygen-free conditions. PhF-doped KER-6000 with tolyl boronate pinacol ester exhibited the best overall performance with a light yield (LY) of 62% relative to EJ-200 and thermal neutron capture at energies up to 103 keVee (84 keVee for EJ254B-5). In addition, four samples exhibited LYs surpassing an industry-standard boron-doped plastic scintillator, Eljen’s EJ254B-5. Over the course of ten months, the KER-6000 samples showed precipitation of dopant molecules, which reduced their LY by 15% on average, while H62-C proved to be more stable with only a 6% reduction.