Mechanism of the hysteresis effect in rate-dependent photomultiplier gain variations.

The hysteresis effect in rate-dependent photomultiplier gain variations observed in a particular ten-stage tube was extensively studied to clarify the mechanism involved. The transition points or count rates at which abrupt gain changes take place are measured with respect to the anode and ninth dynode pulses as a function of light pulse intensity and applied high voltage. The experimental results show that the transition occurs at constant average currents and is attributed to certain physical processes on the ninth dynode. Besides, extensive measurements of the hysteresis curves are performed with respect to the ninth dynode pulse for various biases applied to the tenth dynode. The results clearly indicate that the transitions are due to sudden changes in surface potential on the ninth dynode, presumably resulting from dielectric breakdown in the dynode surface layer. In accordance with these and other measurements, a possible physical mechanism is proposed to interpret the hysteresis effect. With the proposed mechanism, temperature effect on the transition points and possible dependence of the hysteresis effect on dynode structure are briefly discussed.