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Forum: Processes Involving Optical Photons
Re: Question Optical Photons (Ibrahim)
Date: 03 May, 2010
From: Gumplinger Peter <Gumplinger Peter>

> The question is how do I have to define boundary between the scintillator
> and the world volume?

I MUST NOT specify a LogicalBorderSurface and a LogicalSkinSurface at the same time to a dielectric that is part of an interface (in your case the air)!

> Gd2O2S->SetMaterialPropertiesTable(myMPT1);

> Air->SetMaterialPropertiesTable(myMPT2);

Up to here your code for myMPT1, myMPT2 and Gd202S looks right.

You now have to decide if you need a G4OpSurface at all. If you don't specify one, the simulation will work as if the surface is polished. If that's what you want then no further code is required.

>  G4LogicalBorderSurface* Gd2O2SSurface =
>                                 new G4LogicalBorderSurface("Gd2O2SSurface",
>                                 PhyBox1,PhyWorld,OpGd2O2SSurface);

The Gd2O2SSurface is defined correctly. Every photon going from PhyBox1 to PhyWorld will see this surface. If you also want photons to see the same structured surface in the reverse direction you have to define also:

  G4LogicalBorderSurface* Gd2O2SSecondSurface =
                                 new G4LogicalBorderSurface("Gd2O2SSurface",
                                 PhysWorld,PhyBox1,OpGd2O2SSurface);

You need SetSigmaAlpha, the facet normal distribution parameter, since you set 'ground':

OpGd2O2SSurface->SetSigmaAlpha(sigma_alpha);

You don't need: OpAirSurface (see above)

> OpGd2O2SSurface->SetMaterialPropertiesTable(myST1);

Correct, if you need the UNIFIED reflectivity parameters.

>  const G4int num = 2;
>  G4double Ephoton[num] = {2.038*eV, 4.144*eV};

This better reads:

  G4double Ephoton[num] = {2.0*eV, 3.264*eV};

to cover the range above:

 G4double PhotonEnergy[nEntries] =
           { 2.0*eV, 2.138*eV, 2.297*eV, 2.690*eV,
             2.690*eV, 2.820*eV, 2.953*eV, 3.264*eV,
           };

>  //Optical_Gd2O2S_Surface
> 
>  G4double RefractiveIndex[num] = {2.3, 2.3};

You should only attach an RefractiveIndex to 'backpainted' surface, so NOT in your case.

> what does it mean : 2.038*eV and 4.144*eV ? in my case where can I find
> these valuse are from the example exampleN06!
> 
> and what do the following lines mean?
> 
>  G4double RefractiveIndex[num] = {2.3, 2.3};
>  G4double SpecularLobe[num]    = {0.3, 0.3};
>  G4double SpecularSpike[num]   = {0.2, 0.2};
>  G4double Backscatter[num]     = {0.2, 0.2};

Please, read the Application Developers Guide.

> and what is the meaninig of 2.3, 2.3.Why we have twice 2.3

These properties have to be given as a vector. If they are constant thoughout the range, you give the same value for the range at each end.

>  G4double Reflectivity[num] = {0.3, 0.5};
>  G4double Efficiency[num]   = {0.8, 1.0};

This you need only for dielectric_metal surfaces.

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