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An Inexpensive Circuit for Pulsing-Off a Side-Window Photomultiplier Tube

Volume 41, Number 2 (Feb. 1987) Page 308-311

Carney, Kevin P.; Goldberg, Joel M.


In many applications, photomultiplier tubes (PMTs) must be operated at high gains in order for one to obtain adequate detection of low-light-level signals. However, when an intense light pulse immediately precedes the low-level light signal, the PMT may be promoted into a state of saturation. Saturation is the nonlinear enhancement of the anode current with respect to the intense photon flux incident upon the photocathode. This is caused by the redistribution of the biasing potential across the dynode chain. The last dynodes are unable to be sustained at a constant potential because of space charge depletion of the dynode surfaces. Further illumination of the photocathode results in a nonlinear increase in photocurrent. Saturation effects may last up to several microseconds, rendering the photomultiplier tube inoperable. In the extreme, intense light pulses may result in permanent damage to the MPT.