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Idea Re: New to Ray tracing 

Forum: Processes Involving Optical Photons
Re: Question New to Ray tracing (Steve Asztalos)
Date: 13 Jun, 2012
From: Michael <Michael>

Geant4 has a scintillation process which I've used before to model similar problems; I was looking at the timing and intensity of scintillation produced in BC422 from an ICF X-ray background signal.

You can create a material table within detector construction and add properties such as the 'light yield' (photons per MeV), scintillaton time/decay constants and the spectral intensity shape. You can then add this material table to your scintillation material. Note you will also have to add a refractive index to the material table or the light won't transport. This is all present in the LXe example. I pretty much copied and pasted it in to my model.

What is the original source of the scintillation? Neutrons / protons/ ions / gammas? If you have the scintillation process invoked the scintillation photons are emitted according to the light yield per Mev that you specifiy in the detector construction. Note this is related to 'energy deposited' so it can come from protons / ions / electrons etc. If your original source is neutrons; scintillation will mostly come from proton/ion/electron energy deposition following knock on reactions (assuming you have the relevant hadronic and electromagnetic processes turned on).

If you're interested in mapping PMT photons as a function of position; you could define an isotropic point optical photon source at varying positions within the crystal and map out the parameter space that way? I assume with the positional mapping you only care about 'relative' intensities so defining an optical photon source would be fine...?

Remember you'll also need to consider the optical properties i.e. reflection / refraction of the grease and casing as this will affect your PMT response. Dielectric-dielectric and dielectric-metal boundaries are well covered in the application developer guide and refraction is well described in the LXe example and also the guide.

Hope that helps?!


On Mon, 11 Jun 2012 23:03:54 GMT, Steve Asztalos wrote:

> I wish to study the effect of photon interaction location on the number
> of photons recorded by a PMT for a wrapped, right cylindrical
> scintillator. Specifically, I would like to count the number of optical
> photons incident on my sensitive detector surface (PMT) per each 1 MeV
> photoelectric absorption event inn my crystal. I will then move the
> interaction location around to map position versus light output.
> I have plenty of experience with MEGAlib and electromagnetic processes,
> but this is the first time I've run optical photon generators in GEANT4
> (MEGAlib doesn't do optical transport). I have read and run examples
> extended/optical/LXe and novice/NO6 but don't see their immediate
> utility for what I want to accomplish.
> I imagine that the scintillator+wrapping+can+optical grease+PMT problem
> has been modeled innumerable times. Is anyone aware of of a reasonable
> jumping off point.
> Thanks - Steve

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