Timing and Energy Resolution of New Near-UV SiPMs Coupled to ${\rm LaBr}_3$ :Ce for TOF-PET

The high light output and fast decay time of LaBr₃:Ce scintillation detectors leads to excellent timing performance. To realize the potential of timing resolution with LaBr₃:Ce we have investigated the performance with SiPMs, which enable 1-to-1 coupling to individual crystals, and which have been optimized for the near-ultraviolet (NUV) scintillation light emission of LaBr₃:Ce. Coincidence timing resolution (CTR) of 100 ps was measured for a 4 ×4 ×5 mm³ LaBr₃:30%Ce crystal directly coupled to a large-area 4 ×4 mm² NUV-SiPM. Results show very little dependence on temperature, in the range of - 20^° to 20^°C, and bias voltage, from 2 V to 5 V over breakdown. Optimal performance was achieved at an over-voltage (OV) range of 3 V - 5 V, at which high gain and high photon detection efficiency are achieved. Though saturation was evident at 511 keV, an energy resolution of 6.8% was measured after correcting for non-linearity. We also measured a CTR of 110 ps for a 4 ×4 ×5 mm³ LaBr3:5%Ce crystal and 245 ps for a 4 ×4 ×30 mm³ LaBr₃:5%Ce crystal using the NUV-SIPM. The poorer timing measurement for the 30-mm long crystal is due mainly to a systematic shift in the time pick-off as a function of the depth-of-interaction. The excellent temperature stability, fast rise time, high gain, and low noise of the NUV-SiPM make it a practical and highly appealing photodetector for the readout of a LaBr₃:Ce TOF-PET detector.