Dark Current in Photomultipliers

A study has been undertaken to determine the nature of the processes that contribute to dark current in photomultipliers. Extensive measurements have been made on a number of production-type photomultipliers and on a series of experimental tubes that were designed to minimize leakage and regeneration. Variations in the dark current pulse-height distribution and counting rate with applied voltage, cathode temperature, and residual gas pressure were measured. The experimental method and preliminary results will be discussed.