Nonlinearity Simulation of Digital SiPM Response for Inhomogeneous Light

Currently, we are developing a neutron scintillation detector prototype using silicon photomultipliers (SiPMs) as the photodetector. In order to reconstruct the position of single neutron events to an accuracy better than the pixel pitch of the SiPM, a very accurate photon count is required. Each pixel consists of 3200 microcells, operated in Geiger mode. A cell which is already triggered cannot detect any following photons hitting the cell, until it is recharged. This leads to a nonlinearity in the pixel's response for a higher photon density impinging across the pixel. Previous studies provided a correction factor to estimate the saturation, by assuming a homogeneous photon distribution density and comparing it to the number of microcells. In our specific application, the photon distribution is not homogeneous, which is why we examined the influence of the homogeneity on the saturation. In this work, we present a case study for difference in nonlinearity effect for an inhomogeneous and homogeneous photon distribution density, given the light intensity is equal. The simulation results suggest that the effect could be higher for an inhomogeneous distribution. Therefore, care must be taken when using the established correction factor for saturation and an analysis of the photon distribution homogeneity is necessary.