Energy response of photomultiplier tubes to neutron irradiation

The photomultiplier tube (PMT) responding to direct neutron irradiation has an extreme effect on the scintillation detector design and its practical applications. The response mechanism of a photomultiplier tube interacting with an accelerator neutron source was investigated. ¹⁰B(n, α), ²⁸Si(n, α) and ²⁸Si(n, p) reactions in borosilicate glass of the end window lead to fluorescence yield, and then the fluorescence was converted into electrons by the photocathode. Experiments were carried out with EMI photomultiplier tubes (9815B and 9850B) at 5SDH-2 accelerator and the responses to neutrons with neutron energy ranging between 0.5 MeV and 5 MeV were obtained. The results show that the spectral sensitivities increase with the incident neutron energy. The sensitivity ratio of 9815B to 9850B is about 10², which is in good agreement with the gain ratio between 9815B and 9850B.