Assessing the time resolution of an integrated front-end for solid state radiation detectors

Abstract

Many factors influence the timing accuracy and precision of a TOF-PET system. In particular, the light yield and the decay time constant of the scintillating crystal used, the depth of interaction of the γ-photon within the crystal, the statistical fluctuations of the photon emission process and the light propagation within the crystal appear to be the most relevant ones connected to the detector. When the overall timing performance of the system has to be assessed, it is important also to estimate the influence of the front-end (FE) electronics on it, to find out suitable criteria for the correct choice of the main specifications which affect the timing accuracy. In this contribution Monte Carlo simulations have preventively been employed to evaluate a number of realistic sets of arrival times for the first scintillating photons on a Silicon Photo Multiplier (SiPM), once the geometrical and physical characteristics of the system are known and taking into account the statistical dispersion of the photon emission process of the scintillator and the light propagation mechanisms within the crystal. Then, the elementary current pulses produced by the SiPM coupled with the FE electronics in response to each incident low energy photon have been summed up, according to the respective arrival times, resulting in a realistic set of waveforms for the overall output current pulse in response to a scintillation event. Preliminary lab experiments have been used to validate the equivalent circuit model of the photo-detector coupled to the FE electronics which has been exploited to evaluate its response to a single photon excitation. When the overall output current pulse, is applied to a leading edge current discriminator, the described procedure allows estimating how the performance parameters of the FE electronics affect the timing accuracy of the detection system.