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Question Re: Optical photons stopping at boundary of scintillator 

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Re: None Optical photons stopping at boundary of scintillator (Mario)
Re: Feedback Re: Optical photons stopping at boundary of scintillator (Gumplinger Peter)
Date: 19 Nov, 2010
From: Mario <Mario>

Hello Peter,

thanks for your answer. My next questions i will post in the Optical Physics Forum, thats for sure :)

Regarding to my simulation:

I have now added n=1 to my Air (do'h!) and use G4LogicalBorderSurface: It works! My photos can leave the scintillator.

So my next step is to simulate the wrapping around our scintillator for total internal refection.

I tried this using your advice "new G4LogicalSkinSurface("TiO2Surface",scintillator_log,TiO2Surface);"

The problem: When I do place a sensitive detector on a side of my scintillator, my HitCount is zero, because no photons can leave my scintillator. Thats a little bit too much internal reflection...

My next ansatz would be to place boxes of reflecting material on the 5 sides of my scintillator which should be reflecting. But I'm sure there is in geant4 a more dapper way than this...

Thanks for any advise!


On Thu, 18 Nov 2010 21:07:42 GMT, Gumplinger Peter wrote:

> Dear Mario,
> Your luck, I also monitor this Forum, but you are more guarantied to get
> a response to this kind of question on the 'Optical Physics Forum'.
> I see that you define two types of surfaces:
>       OpScintSurface->SetType(dielectric_dielectric);
>       G4LogicalBorderSurface* ScintSurface
>                      new G4LogicalBorderSurface("OpScintSurface",                                             
>                          scintillator_phys,experimentalHall_phys,OpScintSurface);
>       new G4LogicalSkinSurface("TiO2Surface",scintillator_log,OpScintSurface);
> Now, I think, this is partly because you wanted to toggle between a
> dielectric_dielectric surface and a dielectric_metal one. So, the
> second, should read:
>         new G4LogicalSkinSurface("TiO2Surface",scintillator_log,TiO2Surface);
> BUT, one of the two definitions needs to be commented out. You cannot
> have two definitions for essentially the same real surface. You have to
> decide between one or the other. With both assigned, the logic in
> G4OpBoundaryProcess gives precedent to the G4LogicalBorderSurface. Now,
> a dielectric_dielectric, has to have a material on the outside that has
> an index of refraction - your "Air". You have failed to assign n=1 to
> the "Air". This is the reason that your photons just stop. Snell's Law
> cannot be evaluated.
> If you'd used the G4LogicalSkinSurface, instead, with the above change,
> everything should also work, though you'd get only absorption/reflection
> (no refraction) even if the "Air" has no refractive index because, in
> that case, none is required for the tracking.
> Hope this helps, Peter

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