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Question opticalsurface definition problem 

Forum: Processes Involving Optical Photons
Date: 01 Mar, 2009
From: hemiao <hemiao>

hello,

I'm simulating optical photon transportation in the crystal like CsI,
what the problem I encountered  is the parameter of ABSLENGTH during defining G4MPT,
two values were used to calculate collection efficiency of optical photons: 17cm and 100cm .
ABSLENGTH Value    collection eff.
17cm                       40%
100cm                      80%
difference too much, right? 
my questions are :
1) what's meaning the ABSLENGTH in the G4MaterialPropertiesTable(G4MPT)
2) how to assign the value of ABSLENGTH for CsI crystal at 2eV of photon_Energy 
    Is it right that different initial gamma energy will have a different ABSLENGTH?

another problem of the surface parameter: the CsI crystal is wrapped by reflection material, and the G4OpticalSurface is defined. groundbakcpainted, ground and polished are selected for the surface Finish type ,which resulted in different collection efficiency as following:

Finish-type collection eff. ground 30% groundbackpainted 80% polished 30% ( sigma_alpha=0.0)

as I understand, when sigma_alpha=0.0, should be similar with polished type, but results shows that most of optical photons are out of crystal.

what's the problem? who can give some advises to continue calculation about surface parameters.

thanks in advance.

//following codes are part of my program 
//------------------------------------------------------------------------
// CsI G4MPT definition
  const G4int NUMENTRIES = 1; 
  G4double photon_Energy[]    = {  2.0*eV   };  
  G4double Scnt_FAST[] = {0.1  };
  G4double Scnt_SLOW[] = {0.00010};
  G4double RInd[]  = { 1.78};
  G4double AbsLength[]  = {  100*cm  }; 
  G4MaterialPropertiesTable* CsI_mt;
  CsI_mt = new G4MaterialPropertiesTable();
  CsI_mt->AddProperty("FASTCOMPONENT", photon_Energy, Scnt_FAST, NUMENTRIES);
  CsI_mt->AddProperty("SLOWCOMPONENT", photon_Energy, Scnt_SLOW, NUMENTRIES);
  CsI_mt->AddProperty("RINDEX",        photon_Energy, RInd,  NUMENTRIES);
  CsI_mt->AddProperty("ABSLENGTH",     photon_Energy, AbsLength,  NUMENTRIES);
  CsI_mt->AddConstProperty("SCINTILLATIONYIELD",58000/MeV);
  CsI_mt->AddConstProperty("RESOLUTIONSCALE",1.0);
  CsI_mt->AddConstProperty("FASTTIMECONSTANT",10.*ns);
  CsI_mt->AddConstProperty("SLOWTIMECONSTANT",1000*ns);
  CsI_mt->AddConstProperty("YIELDRATIO",0.8);
  CsI->SetMaterialPropertiesTable(CsI_mt);

//-------------------------------------------------------------------- //G4OpticalSurface definition

   const G4int num = 1;
   G4double Ephoton[] = {2*eV};   
   G4double SpecularSpike[]={0.};
   G4double SpecularLobe[]={1.0};
   G4double Backscatter[]={0.};   
   G4double RIndex[]={1.53};

  G4MaterialPropertiesTable* scintHsngPT = new G4MaterialPropertiesTable();   
  scintHsngPT->AddProperty("RINDEX",Ephoton, RIndex, num);  
   scintHsngPT->AddProperty("SPECULARLOBECONSTANT", Ephoton,SpecularLobe,num);
   scintHsngPT->AddProperty("SPECULARSPIKECONSTANT", Ephoton,SpecularSpike,num);
   scintHsngPT->AddProperty("BACKSCATTERCONSTANT", Ephoton,Backscatter,num);

  G4OpticalSurface* OpScintHousingSurface =  new G4OpticalSurface("HousingSurface",unified,  groundbackpainted ,dielectric_dielectric ); 
  //or defined as 
  // G4OpticalSurface* OpScintHousingSurface =  new G4OpticalSurface("HousingSurface",unified,          ground ,dielectric_dielectric ); 
 //or as
  //G4OpticalSurface* OpScintHousingSurface =  new G4OpticalSurface("HousingSurface",unified,  polished ,dielectric_dielectric ); 

  OpScintHousingSurface->SetSigmaAlpha(0.05);

  OpScintHousingSurface->SetMaterialPropertiesTable(scintHsngPT); 

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1 Feedback: Re: opticalsurface definition problem   (Gumplinger Peter - 10 Mar, 2009)
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