Assessment of Performance of New-Generation Silicon Photomultipliers for Simultaneous Neutron and Gamma Ray Detection

Significant interest in silicon photomultipliers (SiPMs) over the last decade has spurred impressive growth in their technology, both in terms of performance and selection of SiPMs with differing characteristics. Nuclear nonproliferation and safeguards is a field of particular relevance for the development of SiPMs as they have been shown to be capable of simultaneously detecting gamma rays and neutrons when coupled with organic scintillators and utilizing pulse-shape discrimination (PSD). As such, an assessment of the state of the art in SiPM technology and study of the impact certain SiPM characteristics have on performance in different applications is required. This paper characterizes the performance of 20 different SiPMs from five manufacturers with pixel sizes ranging from 3 to 6 mm and microcell size ranging from 15 to $75~\mu \text{m}$ . Emphasis is placed on the ability to discriminate between neutrons and gamma rays when coupled to organic scintillator stilbene as a function of overvoltage, as well as the noise. Comparison with a fast photomultiplier tube (PMT) shows that current generation SiPMs perform competitively with PMTs in PSD, and it is found that SiPMs with larger microcells tend to have more effective neutron–gamma ray discrimination capability.