A dynode is an electrode that emits secondary electrons when struck by an incoming electron. A photomultiplier arranges successive dynodes at increasing potentials so that photoelectrons are accelerated and multiplied through a cascade.
If the mean multiplication factor per stage is and there are comparable stages, the idealized mean gain is . Fluctuations in secondary emission contribute to output noise. Excessive current can disturb the electrode voltages or create space-charge effects, so gain calibration and linearity need experimental checks.
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