Fatigue Effects on the Area Sensitivity, Dynode Gain, and Anode Output for Several End-on Photomultipliers.
Instrumentation was developed to determine the time dependent effect of incident illumination on the area sensitivity and the gain stability of photomultipliers. Five end-on, S-11 photomultipliers were tested (6292, 2020, 6342A, 6655A, and 8053). The anode current variations were measured for a period of 3 h, the last three dynode gains were calculated, and the area sensitivity maps of these photomultipliers were recorded for several levels of illumination. It was found that: (1) with a constant light input to the multipliers tested, the output (anode current) varied up to 10% for the most stable tube (6342A) to over 400% for the most unstable tube (6292); (2) the relative sensitivity over each tube face (photo-cathode) area remained unchanged; (3) the photomultipliers can recover to more than one internal state (the condition of the dynode surfaces); (4) the variation of photomultiplier gain with time depends on the dynode structure and coating; (5) the earlier stages contribute as much to gain instability as do the last three stages; (6) the focus electrode voltage producing the most uniform area sensitivity differs slightly (~5%) from the voltage for maximum anode current.
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