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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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