Evaluation of a LiI(Eu) neutron detector with coincident double photodiode readout

Abstract Previous work showed that enriched 6 Li halide scintillation crystal is a good candidate for portable neutron-sensitive detectors. Photodiodereadout is a good alternative to PMT in compact devices. These detectors are often required to work in presence of a strong gamma background. Therefore, great discrimination against gamma rays is crucial. Because of the high Q- valueof the 6 Li(n,α) 3 H reaction, the light yield of a neutron capturesignal corresponds to 3–4 MeV gamma equivalent in spite of the quenching effect of heavily charged particles. As a result, energy discrimination is quite effective against gamma signals generated in thin crystals. However, direct gamma interactions inside the photodiodecan create pulses whose amplitude is large enough to interfere with thermal neutron peak. This study shows an innovative design based on coincident readout to solve this problem. In this design, two photodiodesare attached on both sides of the LiI crystal. The output signal is only accepted when both photodiodesgive out coincident output. The method is proved to effectively suppress background in the neutron window in a 420 mR/h 137 Cs field down to the level of natural background.