Scintillation detector efficiency

I am using Geant4 to model a scintillation detector. I have the scintillator coupled to a photomultiplier tube - is there a way of including in my simulation how the quantum efficiency of the PMT varies with wavelength(energy)? I have modelled the surface of the PMT as an optical surface.

You could count the photons and their energies on the surface of the photocathode and save the result to a root or csv file. Then read the file off line using Root, Matlab/Octave, etc. to form an optical photon spectrum. The latter can then be multiplied by the energy-dependent quantum efficiency in the off line software.

I suppose you could do the last part in the Geant4 simulation too, but I find it much easier to do the PMT response stuff outside Geant4.

Hi John, thank you for your response. I will give that a go. I guess there isn’t a way to do it directly in Geant4 by simply specifying the wavelengths and the corresponding quantum efficiency? (from the PMT data sheet)

As far as I know, there isn’t. There is no reason why you couldn’t code it in the Geant4 program, as I mentioned previously. However, to get the PMT output, you will have interpolate the QE vs energy vector to match the scintillator response, then multiply the two, multiply by a PMT gain factor and convolve with a PMT response function to get the PMT output. It is probably easier to do that in a high level language outside Geant4.

If you’d simply want to model the fractions of photons detected in Geant4, you can do that with the optical surface and the parameter EFFICIENCY. See

and the text above. As John notes, getting the PMT output may be harder.

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