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Question change to dielectric_dielectric routine in geant4.9.3.p01 

Forum: Processes Involving Optical Photons
Date: 25 Aug, 2010
From: Jessica Cook <Jessica Cook>

Our group has just switched from using geant4.9.2.p02 to geant4.9.3.p01, and we noticed the change referenced at "http://hypernews.slac.stanford.edu/HyperNews/geant4/get/opticalphotons/321.html". Our code contains a dielectric_dielectric interface with front surface roughness using the unified model and a ground back paint. Previously we had the reflectivity and the sigma_alpha tuned to give the correct reflections (sigma_alpha = 0.08, reflectivity = 0.74), but we noticed with geant4.9.3.p01 we are getting more absorptions.

We noticed on site: "http://geant4.cern.ch/support/ReleaseNotes4.9.3.html" it was stated that one could not get absorptions off non-front painted dielectric_dielectric interfaces using geants before geant4.9.3.p01. Based on our experience this isn't true. For our purposes the DielectricDielectric function took care of everything.

Also in your comment "http://hypernews.slac.stanford.edu/HyperNews/geant4/get/opticalphotons/321/1.html" you mentioned the new absorption routine is supposed to simulate 'dirt' on the front surface. The problem we have with this is it appears to use the same variable as the reflectivity of the back painted surface. Shouldn't they be different? Shouldn't we be able to set the reflectivity of our back painted surface <1 without adding dirt to our front surface?

Below is the reflection code from DetectorConstruction which we have been using:

  G4OpticalSurface* OpReflectorSurface = new  G4OpticalSurface("ReflectorSurface");
  OpReflectorSurface->SetType(dielectric_dielectric);   
  OpReflectorSurface->SetFinish(groundbackpainted);     
  OpReflectorSurface->SetModel(unified);                
  G4double sigma_alpha = 0.08;                       
  OpReflectorSurface->SetSigmaAlpha(sigma_alpha);

  G4LogicalBorderSurface* ReflectorSurface = 
                                 new G4LogicalBorderSurface("ReflectorSurface",
                                 physiActiveLXe,physiReflector,OpReflectorSurface);

  const G4int nEntries = 3;  
  G4double PhotonEnergy[nEntries] = {6.5*eV, 7.*eV, 7.5*eV};

  G4double RefractiveIndex[nEntries] = {1.4, 1.4, 1.4}; 
  G4double SpecularLobe[nEntries]    = {1., 1., 1.};    
  G4double SpecularSpike[nEntries]   = {0., 0., 0.};    
  G4double Backscatter[nEntries]     = {0., 0., 0.};    
  G4double Reflectivity[nEntries]    = {0.74, 0.74, 0.74};  

  G4MaterialPropertiesTable* myST1 = new G4MaterialPropertiesTable();

  myST1->AddProperty("RINDEX",                PhotonEnergy, RefractiveIndex, nEntries);
  myST1->AddProperty("SPECULARLOBECONSTANT",  PhotonEnergy, SpecularLobe,    nEntries);
  myST1->AddProperty("SPECULARSPIKECONSTANT", PhotonEnergy, SpecularSpike,   nEntries);
  myST1->AddProperty("REFLECTIVITY",          PhotonEnergy, Reflectivity,    nEntries);
  myST1->AddProperty("BACKSCATTERCONSTANT",   PhotonEnergy, Backscatter,     nEntries);

  OpReflectorSurface->SetMaterialPropertiesTable(myST1);

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1 Warning: Re: change to dielectric_dielectric routine in geant4.9.3.p01   (Gumplinger Peter - 27 Aug, 2010)
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