Timing performance of organic scintillators coupled to silicon photomultipliers

Abstract

Abstract This work compares the time resolution obtained from coincidence measurements using combinations of four types of silicon photomultipliers (SiPMs), five types of organic scintillators, and two timing algorithms. Organic scintillators in combination with SiPMs have shown to have equivalent or better time resolution and pulse shape discrimination (PSD) capability than with photo-multiplier tubes (PMTs). In addition, SiPMs are more compact and require low operating voltage. These factors have made them suitable for the development of compact neutron scatter cameras (NSCs) and potentially low-cost positron emission tomography (PET) systems. The following measurements analyze combinations of organic scintillators and SiPMs that could be used for these applications. Measurements and analyses assessed the time resolution of standard-output and fast-output pulses of the various scintillator and SiPM combinations. The coincidence measurements were performed using a Na-22 source to characterize time resolution where all coincident events above about a 40 keVee threshold were analyzed. Uncertainties were determined by applying bootstrapping to the acquired data sets. The full width at half maximum (FWHM) of the time difference distribution for each combination is reported as the time resolution of the system. For standard-output pulses, we found that using a digital implementation of analogue constant fraction discrimination (DIACFD) improved timing resolution greater than a single standard deviation for six of the fourteen tested combinations compared to using digital constant fraction discrimination (DCFD). Conversely, for fast-output pulses, DCFD with a moving average filter produced the best timing resolution. Among the tested non-PSD capable organic scintillators, EJ-228 coupled to a MicroFJ-SMA-60035 SensL SiPM yielded the best time resolution of 303\xa0±\xa04 ps for standard-output pulses and 227\xa0±\xa04 ps for fast-output pulses. The best time resolution found for PSD capable organic scintillators was obtained using Inrad Optics stilbene coupled to a MicroFJ-SMA-60035 SensL SiPM which yielded a time resolution of 428\xa0±\xa06 ps for standard-output pulses and 293\xa0±\xa04 ps for fast-output pulses.