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Forum: Processes Involving Optical Photons
Re: Question queries regarding border surfaces (Athreya Shankar)
Date: 05 Dec, 2011
From: Davinder Siwal <Davinder Siwal>

On Sat, 03 Dec 2011 17:44:38 GMT, Athreya Shankar wrote:
> Hello all,
> I am trying to incorporate WLS fibers in my scintillator.For the purpose
> of testing, I made my detector material out of vacuum, and simulated the
> passage of a single photon and visualised it. I have the following
> questions:
> 1. Following the LXe example, I covered the scintillator with a
> reflective coating :glisur model, polished, dielectric_metal. The
> coating works very well- but my doubt is whether it is valid to specify
> dielectric_metal here, as the scintillator and the experiment hall are
> both composed of vacuum? I tried using dielectric_dielectric, but it
> does not seem to be working (the photons just pass through the
> scintillator boundary).

In case if you surround the scintillator with dielectric material such as teflon then you need to specify dielectric_dielectric on the other hand if matrial is Al reflector you need to give dielectric_metal along with the reflection coefficients, these values helps geant4 to understand the boundary characteristics. I am attaching one presentation to make you more understand about the different models used in geant4.

> 2. I tried to model a PMT, and so I set the efficiency of the
> photocathode surface to 1 for a range of wavelengths. But still in the
> visualisation, I can see the photons getting reflected at this boundary
> and travelling back. Is this to be expected? I thought the photons would
> just get absorbed.

By setting detection efficiency equals to 1 doesn't means that it absorb all the photons infact it does so in a probalistic manner for the photons whose momentum values lies in the absorption region defined by the imaginary refractive index of photocathode material.

> 3. In all the trial runs, the photon(s) is directly incident on the WLS
> fiber's surface. But sometimes, the photon just gets absorbed by the WLS
> outer cladding, and does not have any further trajectory. in some other
> cases, it just passes through the WLS fiber. But also in quite a number
> of cases it gets trapped in the WLS fiber and it undergoes wavelength
> shifting. Why does the photon not undergo OpWLS every time?
> Thanks in advance, Athreya

As I said geant4 calculates the probability of the different processes and accordingly it transport the photons.


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1 Question: Re: queries regarding border surfaces   (Athreya Shankar - 05 Dec, 2011)
(_ Feedback: Re: queries regarding border surfaces   (Gumplinger Peter - 05 Dec, 2011)
(_ None: Re: queries regarding border surfaces   (Athreya Shankar - 06 Dec, 2011)
(_ Feedback: Re: queries regarding border surfaces   (Gumplinger Peter - 06 Dec, 2011)
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