Designing the front-end electronics of a SiPM based γ-ray detection system for optimal time resolution

It is generally recognized that the main factors affecting the timing accuracy of a typical γ-ray detection system based on SiPM´s coupled to fast scintillators are related to the statistical properties of the scintillation light, to the parameters of the SiPM and to the performance of the front-end electronics used to read out the detectors. In our study, Geant4 Monte Carlo simulations have been exploited to reproduce the statistical characteristics of the photon emission from the scintillator in response to the photoelectric absorption of a γ-ray. Each Monte Carlo trial provides the incidence times of the emitted photons on the surface of the detector. A comprehensive electrical model of the SiPM coupled to the front-end electronics allows finding the waveform of the elementary current pulses produced by each single photon which triggers the avalanche breakdown in a micro-cell of the SiPM, taking into account also the interconnection parasitics. Combining the available information for each Monte Carlo trial, the overall pulse waveform, obtained in response to the photoelectric interaction of a y-ray in the scintillator, is reconstructed. In case a leading edge discriminator is used to generate the signal which marks the arrival of the event, it is possible to study the accuracy of this timing signal as a function of the threshold level, considering also the contribution from the electronic noise of the front-end. Using this procedure, it is possible to distinguish the contribution of each individual parameter affecting the timing accuracy of the detection system and, in particular, to obtain useful indications for an effective choice of the specifications of the front-end electronics.