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Forum: Processes Involving Optical Photons
Re: Question Optical Photons (Ibrahim)
Date: 23 Mar, 2010
From: Gumplinger Peter <Gumplinger Peter>

Sorry, I can't do any better than the Manual (concentrating on your difficulties):

"The optical properties of the medium which are key to the implementation or optical processes are stored as entries in a G4MaterialPropertiesTable. These properties may be expressed as a function of the photon's energy (wavelength). G4MaterialPropertyVectors being sorted in ascending order of photon energy."

You give these properties (like the index of refraction) at discrete bins (32 in the example): nEntries = 32

G4double ppckov[NUMENTRIES] = {2.034*eV, ......, 4.136*eV};

G4double rindex[NUMENTRIES] = {1.3435, ......, 1.3608};

How the program accepts and stores these is technical and explained in the manual. It involves the user to code lines like this:

G4MaterialPropertiesTable *MPT = new G4MaterialPropertiesTable();

MPT -> AddProperty("RINDEX",ppckov,rindex,NUMENTRIES};

scintillator -> SetMaterialPropertiesTable(MPT);

The optical property can also be a constant. In this case:

MPT -> AddConstProperty("SCINTILLATIONYIELD",100./MeV);

Now, as far as the scintillation process is concerned:

"A scintillator is also characterized by its photon emission spectrum. In GEANT4 the scintillator can have a fast and a slow component. It is sufficient to specify in the user's DetectorConstruction class a relative scintillation spectral distribution as a function of photon energy for the scintillating material (again at discrete points)."

As for the Birks Constant - in organic scintillators the energy deposit is not necessarily equal to the 'visible energy'; e.g. the energy that leads to the scintillation yield. Google "Birks Law scintillator"

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