In-situ evaluation of radiation induced optical degradation of candidate scintillator materials for ITER’s gamma and neutron detectors

Abstract

Neutron and gamma detectors will play an essential role during operation of ITER and future fusion reactors. They are required in systems to monitor the total neutron production from the plasma for control and safety. Neutron and gamma detectors being considered employ scintillators that will be exposed to high neutron and gamma radiation levels. In this work a systematic study of the effect of gamma radiation on different types of scintillators (plastics, liquids and single crystal), candidates for detectors in future machines, has been done. The experiments were performed at the CIEMAT Nayade 60Co gamma irradiation facility, measuring in-situ radiation induced optical absorption (RIA) and radioluminescence (RIL) from 370 to 730 nm. The RIA and RIL at 0.2 Gy/s up to 40 kGy and at 1.2 Gy/s to 240 kGy show reduced efficiency with dose, i.e. increased absorption and reduced luminescence. Rapid degradation for the single crystal Stilbene, with a drastic light emission drop by 20 kGy due to self-absorption, has been observed. Of the solid plastic scintillators, BC-418 exhibits the best behaviour. Liquid scintillators for a high radiation environment show negligible radiation induced absorption and emission loss. Details of the RIA and RIL degradation with dose for the different scintillators are presented.