Bismuth-Loaded Plastic Scintillators for Gamma Spectroscopy and Neutron Active Interrogation

Bismuth-loaded plastic scintillators capable of gamma spectroscopy are being scaled up to multiple cubic inch sizes. High light yields of >30,000 Ph/MeV are obtained with Iridium-complex fluors due to efficient harvesting of both singlet and triplet excitons, providing energy resolution of similar to 10% at 662 keV for 3 in(3) scintillators. Although singlet fluors provide a poorer light yield of similar to 12,000 Ph/MeV and resolution at 662 keV of 14% in the Bismuth-loaded plastics, the fast decay time of <100 ns and the low neutron capture cross-sections of the constituent elements lend themselves to applications in neutron active interrogation. Measurements of the scintillation light yield non-proportionality reveal that exciton-exciton annihilation is suppressed in Iridium-complex activated plastic, in contrast with the singlet fluor activated plastic.