Abstract
The development of silicon photomultipliers (SiPMs) with a large number of APD cells and improved linearity of the pulse height response prompted interest in their application to gamma spectrometry with scintillators. Hamamatsu MPPC sensors equipped with 3600 and 14400 APD cells were chosen in our study because of their well pronounced single photoelectron spectra, which allowed us to precisely measure the photoelectron numbers (PHE) or fired APD cells and then to discuss, in a quantitative manner, the obtainable energy resolution. The studied detectors were first characterized in direct detection of laser light pulses and then in gamma spectroscopy with LFS and CsI:Tl crystals. In the study with the laser light pulses the linearity of the MPPC response versus a light pulse intensity monitored with PMT was measured. Two different methods were used for an evaluation of the MPPC response expressed in the number of photoelectrons (PHE) generated by light illumination. The direct method (PHEdir), based on the comparison of the light peak position to that of the single photoelectron peak, determined the upper limit of the PHE. The lower limit of the PHE was derived from an analysis of the measured pulse height resolution under the assumption of Poisson statistics and MPPC excess noise factor (ENF) of 1. Furthermore, the ENF of the MPPC is discussed with respect to the contributions of device dead time, optical cross-talk and after-pulses to the results obtained. In the scintillation tests, measurements of energy resolution and non-proportionality of the light yield were performed with LFS and CsI:Tl crystals, and both types of 3 × 3 mm MPPC detectors were used for light readout. The results are discussed in a quantitative manner based on the measured PHE.