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Feedback Re: Optical photons and Shashlik calorimeter 

Forum: Processes Involving Optical Photons
Re: None Optical photons and Shashlik calorimeter (Alessandro Berra)
Re: Feedback Re: Optical photons and Shashlik calorimeter (Gumplinger Peter)
Re: None Re: Optical photons and Shashlik calorimeter (Alessandro Berra)
Date: 10 Nov, 2015
From: Gumplinger Peter <Gumplinger Peter>

Hi Alessandro,

> thank you very much for your help. I didn't think about the possibility
> to create SkinSurfaces on the volumes around the scintillator tiles
> because I feared that the surface has an order with respect to the
> crossed volumes.

Yes, that's true for G4LogicalBorderSurface. Here, the surface used is the one that corresponsed to the ordered pair of G4VPhysicalVolumes.

> Instead you are telling me that a "ground" SkinSurface
> (for example) assigned to the fiber hole logical volume is seen in the
> same way by an optical photon crossing from the scintillator tile to the
> hole and vice-versa?

Yes, correct! But that very same surface is also seen when a photon leaves the cladding of the fiber (and, thinking about it, this is probably not what you want). A skin surface is always "seen" - either direction - unless some other surface has higher presidence.

> Regarding the piece of code you have posted me, I understood the logic
> behind it, but I am not sure where to put it: as far as I understood is
> a check performed every step, so I have to put it in my SteppingAction
> class?

NO! You (the user) don't have to 'put it' anywhere. This code is in G4OpBoundaryProcess::PostStepDoIt where to program decides which surface to use.

> I have another (hopefully) last question: at the moment I am using the
> following values for the ground surface: sigma_alpha=0.2,
> specular_lobe=0.3, backscatter=0.3, specular_spike=0.1 (lambertian
> should be calculated by difference and thus be equal to 0.3). I am
> wondering if I have to add also a "reflectivity" parameter to the ground
> surface. In principle I would say no (the surface is not painted) but I
> want to be sure.

No, you don't.

Peter

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