Investigation of instabilities of photomultiplier tubes for multi-element detector systems

Abstract

This paper presents an investigation into response of instabilities of EJ-309 liquid scintillator detectors. A brief review of common instabilities associated with the photomultiplier tubes (PMTs) is presented. The energy response, relative efficiency, energy linearity and warmup duration of sixteen EJ-309 detectors coupled to PMTs tested is presented. A single-channel mixed-field analyser digitiser system was used for data acquisition. Furthermore, timing information of the common instability behaviours is presented alongside suggestions on how to correct for such instabilities. The results show that the relative efficiencies amongst the detectors can vary up to 7%; a multi-energy energy calibration must be performed to ensure energy linearity; the detectors must be warmed-up by ~45 minutes before stable response is achieved; the re-warmup duration depends on the duration of the high voltage supplied to the PMT being switched off. The results indicate that the PMTs take approximately 2 hours to reach "cold" state, where a full warm-up duration must be applied. The reported instability effects will be taken into account when developing a sophisticated auto-calibration methodology for a multi-element detector system.