Performance of Stilbene Bars Coupled to Silicon Photomultipliers Using Different Reflectors

Two 6-mm by 6-mm by 50-mm bars of stilbene were each coupled to a silicon photomultiplier (SiPM) and evaluated for signal-to-noise ratio (SNR), time resolution, and pulse shape discrimination (PSD) capability using specular and diffuse reflectors. To evaluate the SNR at 478 keV, a Cs-137 source was placed between both bars and measured. The average SNR was 38% lower using a specular reflector as compared to using a diffuse reflector. The coincidence resolving time, measured with a Na-22 source, improved by 32% for standard output pulses and 40% for fast output pulses. PSD capability, measured with a Cf252 source, degraded with an increased gamma misclassification rate of about 972% for the light output range of 100-200-keVee. These results show that timing performance can be improved by using a specular reflector, but PSD capability is greatly diminished.