Fast and Efficient Detection of 511 keV Photons using Cherenkov Light in PbF$_2$ Crystal with MCP-PMT and SAMPIC Digitization Module

We study the possibility to use the Cherenkov light for the efficient detection of 511 keV photons with the goal to use it in TOF-PET. We designed and tested two detection modules consisting of PbF$_2$ crystals attached to Planacon MCP-PMT XP85012. Amplified PMT signals are digitized by the SAMPIC module with high read-out rate, up to ~$10^5$ events/s, and a negligible contribution to the time resolution, below 20 ps (FWHM). We developed a fast 2D scanning system to calibrate the PMT time response and studied in details the timing characteristics of Planacon PMT. Using a radioactive $^{22}$Na source we measured the detection efficiency of 24% for 511 keV photons in a 10 mm thick crystal and a CRT values of 280 ps. We analyzed the main factors limiting the time resolution of the large-surface detection module and proposed solutions to improve it, which will be tested in our future project.