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Question sigma_alpha properties 

Forum: Processes Involving Optical Photons
Date: 11 Jul, 2006
From: Francesca Ciocia <Francesca Ciocia>

Dear All, could you please help me to clarify a doubt that I have? In mail of Peter Gumplinger:

--------

Base:  Geometry
Re: Question wrapped cerenkov (andreas battaglia)
Date: Mon, 17 Oct 2005 21:04:12 GMT
From: Peter Gumplinger <gum@triumf.ca>
--------

he describes some surface properties; in particular he writes:

"Note,

OpSurface -> SetSigmaAlpha(sigma_alpha);

SMPT -> AddProperty("SPECULARLOBECONSTANT",pp,specularlobe,NUM);

SMPT -> AddProperty("SPECULARSPIKECONSTANT",pp,specularspike,NUM);

SMPT -> AddProperty("BACKSCATTERCONSTANT",pp,backscatter,NUM);

concern the interface between your detector and the thin dielectric layer between it and the wrapping, while:

SMPT -> AddProperty("REFLECTIVITY",pp,reflectivity,NUM);

and 'polishedbackpainted' or 'groundbackpainted' concern the wrapping. "

In my Geant4 program I have the following:

  G4OpticalSurface* OpYapSurface = new
G4OpticalSurface("YapSurface");
  OpYapSurface->SetModel(unified);
  OpYapSurface->SetType(dielectric_dielectric);
  OpYapSurface->SetFinish(groundbackpainted);
  OpYapSurface->SetSigmaAlpha(1.0); 
//
  G4double RefractiveIndex[num] = {1.0, 1.0};
  G4double SpecularLobe[num]    = {1.0, 1.0};
  G4double SpecularSpike[num]   = {0.0, 0.0};
  G4double Backscatter[num]     = {0.0, 0.0};
  G4double Reflectivity11[num] = {0.0, 0.0};

If revetment reflectivity is zero, all photons are absorbed by the wrapping. If sigma_alpha is a property of the interface detector-dielectric layer and groundbackpainted is a property of the wrapping, and if photons are all absorbed by the wrapping, then why sigma_alpha acts only if the wrapping is grounbackpainted and not polishedbackpainted?

Thanks in advance for your kindly reply.

Best regards, Francesca

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