Intrinsic evaluation of n/γ discrimination in organic plastic scintillators

Abstract : This paper is devoted to characterizing plastic scintillators with neutron/gamma (n/γ) discrimination abilities and understanding experimentally the photophysical processes down-stream. This experimental work is divided into two main studies, neutron sources irradiations and optical photoionization on a range of organic scintillators. The commercial liquid and plastic scintillators, respectively BC-501A from Bicron and EJ-200 from Eljen, are used as references in term of respectively extremely high [1] and poor n/γ discrimination efficiency, or more precisely Triplet-Triplet Annihilation rate probabilities after nuclear irradiations. We have characterized a range of organic plastic scintillators including one developped in our laboratory that shows good discrimination efficiency when compared to plastics that discriminate from litterature. For that purpose we use the well known charge comparison as a pulse shape discrimination (PSD) method. We have also studied raw wave forms acquired after neutron irradiation before any kind of treatment was applied and managed to separate two light components, prompt and delayed, thus two particle families. We have demonstrated that by exciting with a 70 femtoseconds pulsed LASER at the femtosecond up to 50 μJ at 260 nm, photoionization was achieved for a range of organic scintillators by observing a delayed light emission in the time decay fluorescence when the LASER energy deposited in the materials was increased. This work is ongoing at CEA in collaboration with the nuclear measurement industry Canberra and the Laboratoire de Chimie Physique from Orsay University.