Photomultipliers with the screening grid at the anode for TOF PET block detectors

In spite of the excellent performance of SiPMs in application to the time-of-flight PET detectors, a development of better photomultipliers for PET detectors is of importance. A fast timing with detectors based on the PMT light readout depends mainly on time jitter and quantum efficiency of the PMTs. But several studies in the past showed that a screening grid at the anode improves significantly time resolution measured with scintillation detectors. ADIT Co. has started a development of a 1″ diameter fast PMT with the screening grid at the anode to be applied in the block detectors in TOF PET scanners. In the present studies, we report of the first comparative study of the L25, classical PMT, with that equipped further with the screening grid. It showed a large improvement of time resolution up to 1.2 factor.