Time Resolution Measurements of EJ-232Q With Single- and Dual-Sided Readouts

Abstract

In view of its importance to applications in high-energy physics, nuclear security, and time-of-flight positron emission tomography (TOF-PET), the time resolution of 0.5% benzophenone-quenched EJ-232Q plastic scintillators of various lengths was studied using a fast waveform digitizer and fast photomultiplier tubes (PMTs). The scintillator sizes were 5 mm $\times 5$ mm $\times10$ , 25, 50, 75, or 100 mm. First, the timing measurements were performed by using a single PMT reading out one end. The degradation in time resolution with increasing scintillator length was studied. The irradiation geometry was also observed to have a nonnegligible impact on the time resolution due to the variation of depth-of-interaction (DOI) positions, especially for the scintillators with a high aspect ratio. Second, two PMTs were employed for a dual-sided readout. This readout together with the mean time method was demonstrated to be an effective approach to improve the timing performance since the DOI-related effect was considerably mitigated. A time resolution of 79 ± 1 ps (full-width at half-maximum) has been achieved for the $5 \times 5 \times 10$ mm3 scintillator. The $5\times 5\,\,\times100$ mm3 scintillator can still provide a time resolution as good as 172 ± 1 ps. The energy range used for each was between 340 and 450 keVee. In addition, the time information from individual PMTs in a dual-sided readout was able to show a time resolution almost identical to that determined with the mean-time-based technique after correcting for the DOI variation for the 100-mm-long scintillator.