A Comparative Study of Fast Photomultipliers for Timing Experiments and TOF PET

The new 1 inch and 1.5 inch in diameter photomultipliers for timing applications from Photonis and Hamamatsu have been tested. Time resolution of XP1020, XP3060, R9800 and R9420 was measured with a $10\times 10\times 5\ {\hbox {mm}}^{3}$ LSO crystal in coincidence experiments with 511 keV annihilation quanta from $^{22}{\hbox {Na}}$ gamma source. Results were discussed in terms of measured photoelectron number and time jitter. Single photoelectron spectra were recorded and excess noise factor for each tube was also calculated. The final comparison of the tested tubes and their timing properties were presented in relation to large amount of experimental data of various types of PMTs collected during last few years. Especially, observed linear dependency between the time resolution normalized to the number of photoelectrons and time jitter was pointed out. Inconsistency of the data collected with the Hamamatsu R9420 PMT resulting from the overestimated photoelectron number was reported and further studied. Additional experiments with LED light source and different experimental set-ups were discussed and comparison of the two methods of the photoelectron number measurements was performed.