Photomultiplier Single-Electron Statistics

Our measurements of the amplitude distribution of photomultiplier anode pulses due to the emission of single-electrons from the cathode consistently show a peak. It is significant that the peak position agrees with that of a calculated distribution based on a Poisson distribution of secondary electrons at each dynode. The integral distribution, obtained by counting single-electron pulses, tends to show a plateau. In low-light-level counting applications, one can set the discriminator so that a majority of photomultiplier single-electron pulses will be counted. Further increase in the sensitivity will eventually increase the noise rate faster than the counting efficiency. The techniques for measuring photomultiplier single-electron statistics are useful for obtaining comparative collection efficiencies. By single-electron measurements, one can adjust focusing-electrode potentials to maximize overall collection efficiency. It is believed that there is some correlation be. tween the amplitude and time distributions. Further work is necessary to show the extent of the correlation.