Light-Based Fast Timing in Bulk CsPbBr3 Crystals for TOF-PET and Proton Range Verification.

Halide perovskite semiconductors such as CsPbBr3 (CLB) are emerging gamma-ray detectors for applications requiring very high energy resolution and potential for fine detector segmentation. Semiconductor detectors typically offer poor time resolution due to the long drift times. Recently, we proposed to use the Cherenkov light component in partially transparent semiconductors to boost the timing capability of such detectors. Cherenkov light produced upon 511 keV gamma-ray interaction with CLB was investigated by means of optical simulations and experimental measurements. The timing capability of a pair of identical CLB crystals ( 3 x 3 x 5 mm3) coupled to NUV- MT silicon photomultipliers was measured. On average, 9.5 Cherenkov photons are produced in CLB between 555 and 900 nm for 511 keV photoelectric interactions based on our simulation framework. Experimentally, we observe 2-to-3 times more photons detected than in the simulation. The two most likely explanations for these additional detected optical photons are either the partial transparency of CLB in the UV, or a mild scintillation light emitted by CLB at room temperature. A coincidence time resolution (CTR) of 419 ps FWHM was obtained by triggering on more than 2 fired SiPM cells and after time walk correction. The measured CTR confirms the feasibility to use the Cherenkov light-component for fast timing applications on top of the charge readout, toward full 3D localization.