Pile-up discrimination method applied to novel gamma-ray detectors based on SiPMs arrays

Abstract

SiPMs-based gamma ray detectors have shown a significant development impulse in recent years due to a number of advantages, namely: good time response, small size, magnetic field immunity and low cost. We have designed a special SiPM array formed by 12x12 SiPMs of 3x3 mm 2 active area (FB-30035, SensL) that covers a total photosensor area of 5x5 cm 2 for gamma ray detection in PET scanners. When thick crystals are considered, pile-up events increase with the scintillation material volume leading to a loss of events and spatial distortions in the image.We have implemented an analogue approach using existing Analogue to Digital Converters (ADC) to provide pile-up information. The method is based on the characterization of the photon energy pulse using two parameters namely the maximum peak value and the area. As long as the pulse shape is preserved we observed that the ratio of the peak signal to the area remains almost constant, independently of the signal amplitude.We have initially tested the method goodness with position sensitive PMTs (H8500, Hamamatsu). The results have shown the feasibility of pile-up event rejection at high rates. Pilot tests with the above-described SiPM array have also showed encouraging results when applying this technique. A case study varying the impact rate and chosen peak to integral ratio will be presented.