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Idea Re: Optical Photon Wave Length Shifting 

Forum: Processes Involving Optical Photons
Re: Question Optical Photon Wave Length Shifting (Eric)
Re: Idea Re: Optical Photon Wave Length Shifting (Benton Pahlka)
Re: Question Re: Optical Photon Wave Length Shifting (Eric)
Date: 17 Dec, 2010
From: Benton Pahlka <Benton Pahlka>

Hi Eric,

Here is some code for (one) implementation of a plastic scintillator. A paper on this subject can be found here:

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Volume 625, Issue 1, 1 January 2011, Pages 20-28

In this implementation:

wlsEmit is the emission spectrum of POPOP (a wavelength shifter). wlsAbsorb is the absorption spectrum of the scintillator including the polystyrene, pTP (primary scintillant), and POPOP (wavelength shifter). Absorb is the absorption spectrum of the polystyrene alone. scintEmit is the emission spectrum of pTP.

I have chosen a light yield of 8000 photons/MeV, but you can set this to something small for testing purposes.

  scintMPT->AddProperty("WLSCOMPONENT",wlsEnergy,wlsEmit,wlsEmEntries);
  scintMPT->AddProperty("WLSABSLENGTH",wlsEnergy,wlsAbsorb,wlsAbEntries);
  scintMPT->AddConstProperty("WLSTIMECONSTANT",4*ns);
  scintMPT->AddProperty("RINDEX",ref_index_Energy,ref_index_value,ref_index_Entries);
  scintMPT->AddProperty("ABSLENGTH",absorbEnergy,Absorb,absorbEntries);
  scintMPT->AddProperty("FASTCOMPONENT",scintEnergy,scintEmit,scintEntries);
  scintMPT->AddProperty("SLOWCOMPONENT",scintEnergy,scintSlow,scintEntries);

  G4double efficiency = 1.0;
  G4double scintRes = 1;
  G4double scintFastconst = 0.9*ns;
  G4double scintSlowconst = 2.1*ns;

  scintMPT->AddConstProperty("EFFICIENCY",efficiency);
  scintMPT->AddConstProperty("SCINTILLATIONYIELD",lightyield/MeV);
  scintMPT->AddConstProperty("RESOLUTIONSCALE",scintRes);
  scintMPT->AddConstProperty("FASTTIMECONSTANT",scintFastconst);
  scintMPT->AddConstProperty("SLOWTIMECONSTANT",scintSlowconst);
  scintMPT->AddConstProperty("YIELDRATIO",1.0);

  scintillator->SetMaterialPropertiesTable(scintMPT);

I read these spectra in from input files containing the spectral properties from 200 nm to 700 nm. I've found that if you specify all your properties with the same range then you don't get the G4 warnings saying that the properties are out of range. My files, for example, contain on each line <wavelength>, <spectral property>. I have an entry for each integer wavelength (so, 500 entries) for each property.

Including "ABSLENGTH" will allow for absorption in the plastic without wavelength shifting absorption. This makes sense because not all of your photons are wavelength shifted...some are absorbed in the plastic. This should agree with what Peter said previously.

Best regards,

Benton

On Thu, 16 Dec 2010 21:52:14 GMT, Eric wrote:

> So, in my DetectorConstruction.cc I have something like:
> 
> -----------------------------------------------------------------
> 
> const G4int nEntries = 2;
> 
> G4double PhotonEnergy[nEntries]= {2.034*eV, 4.136*eV};
> 
> G4double EmissionSpectrum[nEntries] = {.1*cm, .1*cm};
> 
> G4double RefractiveIndex_Det[nEntries] = {2.1, 2.1};
> 
> G4double Absorption_Det[nEntries] = {.5*m, .5*m};
> 
> G4double ScintilFast_Det[nEntries] = {1.00,1.00};
> 
> G4doubl3e ScintilSlow_Det[nEntries] = {0.00, 0.00};
> 
> G4MaterialPropertiesTable&* MPT_Det = new G4MaterialPropertiesTable();
> 
> MPT_Det -> AddProperty("RINDEX", PhotonEnergy, RefractiveIndex_Det,
> nEntries);
> 
> MPT_Det -> AddProperty("WLSABSLENGTH", PhotonEnergy, Absorption_Det,
> nEntries);
> 
> MPT_Det -> AddProperty("FASTCOMPONENT", PhotonEnergy, ScintilFast_Det,
> nEntries);
> 
> MPT_Det -> AddProperty("SLOWCOMPONENT", PhotonEnergy, ScintilSlow_Det,
> nEntries);
> 
> MPT_Det -> AddProperty("WLSCOMPONENT", PhotonEnergy, EmissionSpectrum,
> nEntries);
> 
> MPT_Det -> AddConstProperty("WLSTIMECONSTANT", .5*ns);
> 
> MPT_Det -> AddConstProperty("SCINTILLATIONYIELD", 1/Mev);
> 
> MPT_Det -> AddConstProperty("RESOLUTIONSCALE", 1.0);
> 
> MPT_Det -> AddConstProperty("FSATTIMECONSTANT", 1.e-18*second);
> 
> MPT_Det -> AddConstProperty("SLOWTIMECONSTANT", 1.e-18*second);
> 
> MPT_Det -> AddConstProperty("YIELDRATIO", 1.0);
> 
> Det -> SetMaterialPropertiesTAble(MPT_Det);
> 
> ----------------------------------------------------------------------
> 
> This has both the emission and absorption parts as I understand you to
> be saying?
> 

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