Scintillator-Based SiPM Detector: Improved Performance by Equalization of Pulse Arrival Times

A desired temporal accuracy of scintillator-based detectors is less than 100 ps. In medical imaging, this is necessary for successful time-of-flight positron emission tomography (TOF-PET) measurements. In high-energy physics, the calorimeter time resolution must also be on the order of tens of picoseconds. In this work, we describe a way to achieve such a high level of performance for a detector consisting of a monolithic scintillator that distributes light over several cells of an analog silicon photomultiplier (SiPM) array. Each of the cells is read and analyzed separately, applying a waveform sampling (WFS) technique combined with a nonlinear rise approximation (nLRA). Initially, due to a specific spatiotemporal distribution of photons in the scintillator, as well as saturation and recovery effects inherent to SiPMs, the spread of arrival times deduced from signals of different cells can exceed 1 ns for the same array and the same event. To improve the timing performance, we propose a method of equalization of arrival times for predominantly illuminated cells in the same SiPM array. This results in a coincidence time resolution (CTR) below 100 ps full width at half maximum (FWHM) for a pair of identical detectors.