Study and understanding of n/γ discrimination in organic plastic scintillators

This study specifically evaluates organic plastic scintillators abilities to discriminate gamma (γ) from neutrons (n) in comparison with other organic media. It also explores different approaches that would allow to explain photo physical processes brought into play after nuclear interactions to understand the differences in discrimination efficiencies. As a matter of fact liquid and crystal media are known to have significantly higher efficiencies than plastics, and the main goal is to understand the reasons originating these differences. Experimental results, both nuclear and optical are presented and demonstrate respectively, by using pulse shape discrimination methods (PSD), that organic plastic scintillators can achieve, rather high neutron/gamma (n/γ) discrimination efficiency, and by performing nanosecond Laser photolysis up to 30 mJ, that Triplets (T) excited states can be created but no T-T annihilation (TTA) can occur at this intensity of the photon flux. Alternative experiments are considered since obtaining time resolved luminescence and transient absorption results allowing the observation of energy transfers occurring after nuclear interactions for photophysical processes understanding and excited state nature determination, is a crucial investigation for plastic scintillators industrial development to replace liquids, crystals being non-adapted alternatives, especially cost wise. This work is ongoing at CEA in collaboration with the nuclear measurement industry AREVA/Canberra. (authors)