ASSESSMENT OF THE PHOTOELECTRON NUMBER FOR PHOTOMULTIPLIERS UNDER CONDITIONS OF LOW LIGHT INTENSITIES

The traditional method of assessing the mean photoelectron number from the distribution of anode pulses from a photomultiplier is discussed. The various corrections that need to be incorporated to account for dynode fluctuations and nonuniformities are considered in turn. A completely independent method is derived utilising the number of zero responses resulting from interruptions in the dynode multiplication process. Both methods are applied to an EMI 9623B 17.2 cm tube, their regions of validity are defined and the results compared. The method using zero responses is seen to be particularly useful at very low light intensities where the other method fails. A high gain RCA C70133B tube with clearly visible single photoelectron peaks is used to verify the reliability of the above two methods.