Why do standard photomultiplier tubes have a limited temperature range where they are useful?

Question

anonymous · Answer

I think I might have answered my own question, but can someone verify this for me please?

The Quantum Efficiency of a PMT is defined as the average number of electrons released from the cathode per second. As a photomultiplier tube cools, it loses quantum efficiency and so the cooler it is, the fewer electrons it will release into the dynode stack.

If this is the case, then would increasing conductivity to the cathode be an effective way of increasing the temperature range at which it can operate at? Increased conductivity would surely mean more electrons could be released as a result of the photoelectric effect?

anonymous · Answer

I think the issue is the thermal emission of electrons, constituting "noise,"  with more emitted the hotter the tube gets.

anonymous · Answer

Mm, that makes sense. Would this then cause there to be a trade off between noise and QE, where decreasing one would thusly increase the other?

anonymous · Answer

Seems plausible, but I do not know. Eliminating noise is what I understood the reason for cooling to be.

anonymous · Answer

No worries. You've cleared a couple of things up so thanks for your help.