What can be defined as a proper calibration process for such an instrument?
The PMT itself ? Or integrated in an instrument ?
In pulse mode, what would give you the "calibration" of a PMT is the quantum efficiency as a function of wavelength. That can be done by having a weak light source of variable wavelength, and calibrating the count rate against the count rate of a PMT with known quantum efficiency for instance.
How about a PMT connected to an NaI detector, and a nim with an amplifier and a SCA + counter...
Calibrations are performed on SCAs and MCAs, not the probes (ie. the NaI probe)themselves. Since this is an SCA, you want to create a relationship between the knob that increases voltage and the energy of the photons being detected. This is done by creating a region of interest (ROI) and finding which setting of the knob creates the highest count rate in that ROI. Typically its performed with cesium-137 and an ROI of 612keV to 712 keV.
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