Silicon photomultiplier (Si-PM) comparisons for low-energy gamma ray readouts with BGO and CsI (Tl) scintillators

We studied herein the low-energy performances of three multi-pixel photon counters (MPPCs, silicon photomultipliers, Si-PMs), namely, S13360-6050VE, S13360-6050CS, and S14160-6050HS, provided by Hamamatsu K.K. to read 1 cm3 BGO and CsI (Tl) scintillators. S13360s had 1/4 lower dark currents, while S14160-6050HS had 25% higher quantum efficiency and 1.5× higher gain with a lower operational voltage. S13360-6050VE and S14160-6050HS were used for surface mounting, while S13360-6050CS was in a black ceramic case. We changed the overvoltage and found that the best performances are achieved at overvoltages of +4 V and +2.5 V for S13360s and S14160-6050HS, respectively. In the case of the BGO scintillator, S13360-6050VE obtained a lower threshold of 6 keV compared to 9 keV of S14160-6050HS. Both surface-mounting Si-PMs achieved an energy resolution of ∼35% at 59.5 keV of the 241Am source. The threshold and the energy resolution of S13360-6050CS were the worst, because the black case absorbed approximately half of the scintillation photons. The CsI (Tl) scintillator yielded a number of scintillation photons that was 6× higher than the BGO. The same trends were measured for the three MPPCs. This result is attributable to the lower threshold determined by the dark current, and the energy resolution mainly dominated by the statistical fluctuation of the scintillation photons.