Investigation of GSO, LSO and YSO scintillators using reverse avalanche photodiodes

The performance characteristics of GSO, LSO and YSO scintillators coupled to new "reverse" avalanche photodiodes (ReAPD) were investigated and compared to those of EGO. The energy and timing resolutions were measured as a function of photodiode bias and amplifier shaping time constant While the performance of EGO and GSO is critically dependent on these operating parameters because the signal-to-noise ratio is degraded by the dark and excess noise from the ReAPD, that of the high-luminosity LSO and YSO scintillators is not The energy resolution in these crystals is demonstrated to be limited by the scintillator resolution. Further analysis indicates that excess variance in the number of photons generated in the crystal is mostly responsible for their disappointing energy resolution. This feature appears to be related to the important non-linearity in scintillation response as a function of incident gamma-ray energy observed for these high-luminosity scintillators.