A measurement of transit time spread of photomultiplier tube with Cherenkov light

Using coincidence method, transit time spread (TTS) is measured with Cherenkov light produced by cascade gamma radioactive source, Co-60 on photocathode window of photomultiplier tube (PMT). Transit time distributions with single and multi-photon electrons are fitted to Poisson convoluted with Gaussian, and TTS are obtained. The study to XP2020 and XP2020Q PMTs shows that TTS is consistent with data supplied by Philips. TTS is inversely proportional to the square root of number of photoelectrons. The method is feasible when single and multi-photon electrons can be distinguished.