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Question Problem with reflection of optical photons 

Keywords: optical, reflection, problem
Forum: Processes Involving Optical Photons
Date: 01 Apr, 2008
From: Justin Dingley <dinglj@rpi.edu>

Hello all,
I am trying to model a scintillator surrounded by reflective material (Aluminium)
on all sides except one. The side w/o a reflector is in contact with a
different volume (PMT). I have defined the materials and reflective surfaces
as follows:

//material properties
G4MaterialPropertiesTable* myMPT1 = new G4MaterialPropertiesTable();
myMPT1->AddProperty("RINDEX", PhotonEnergy, RefractiveIndex1, nEntries);
myMPT1->AddProperty("ABSLENGTH", PhotonEnergy, Absorption1, nEntries);
myMPT1->AddProperty("FASTCOMPONENT", PhotonEnergy, ScintilFast, nEntries);

myMPT1->AddConstProperty("SCINTILLATIONYIELD",100./MeV);
myMPT1->AddConstProperty("RESOLUTIONSCALE",1.0);
myMPT1->AddConstProperty("FASTTIMECONSTANT", 3.2*ns);
//myMPT1->AddConstProperty("YIELDRATIO",0.8);
DetectorMater->SetMaterialPropertiesTable(myMPT1);
G4MaterialPropertiesTable* myMPT2 = new G4MaterialPropertiesTable();
myMPT2->AddProperty("RINDEX", PhotonEnergy, RefractiveIndex2, nEntries);

G4MaterialPropertiesTable* myMPT3 = new G4MaterialPropertiesTable();
myMPT3->AddProperty("RINDEX", PhotonEnergy, RefractiveIndex2, nEntries);

PMTMater->SetMaterialPropertiesTable(myMPT2);
DefaultMater->SetMaterialPropertiesTable(myMPT3);
...

//Reflective surface

G4OpticalSurface* OpScintSurface = new G4OpticalSurface("ScintSurface");
OpScintSurface->SetType(dielectric_metal);
OpScintSurface->SetFinish(polished);
OpScintSurface->SetModel(unified);
G4LogicalBorderSurface* ScintSurface = new G4LogicalBorderSurface("ScintSurface",
physiDetector,physiReflector,OpScintSurface);

const G4int num = 2;
G4double Ephoton[num] = {2.37*eV, 3.11*eV};
G4double Reflectivity[num] = { 0.97, 0.97};

G4MaterialPropertiesTable* myST1 = new G4MaterialPropertiesTable();
myST1->AddProperty("REFLECTIVITY", Ephoton, Reflectivity, num);
OpScintSurface->SetMaterialPropertiesTable(myST1);


I have only defined one reflective interface, but during the simulation
I am seeing reflection from the PMT volume- this material was set to
vacuum with a refractive index of 1.00 for all photons:

*********************************************************************************************************
* G4Track Information: Particle = opticalphoton, Track ID = 27, Parent ID = 25
*********************************************************************************************************
Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName
06.2821.8 27.1 2.99e-06 0 0 0 Detector initStep
1 58.6 24.5 -28.7 2.99e-06 0 76.6 76.6 Reflector Transportation
2 58.6 24.5 -28.7 2.99e-06 0 0 76.6 Detector Transportation
3 52.1 18.5 -38.1 2.99e-06 0 12.9 89.5 PMT Transportation
4 52.1 18.5 -38.1 2.99e-06 0 0 89.5 Detector Transportation
5 -0.69 -29.7 38.1 2.99e-06 0 104 194 Reflector Transportation
6 -0.69 -29.7 38.1 2.99e-06 0 0 194 Detector Transportation
7 -29.7 -56.1 -3.74 2.99e-06 0 57.4 251 Reflector Transportation
8 -29.7 -56.1 -3.74 2.99e-06 0 0 251 Detector Transportation
9 -25.1 -24.2 -38.1 2.99e-06 0 47.1 298 PMT Transportation
10 -25.1 -24.2 -38.1 2.99e-06 0 0 298 Detector Transportation
11 -15 46.5 38.1 2.99e-06 0 104 403 Reflector Transportation



Should this be happening? I would have thought any photon reaching the
PMT volume would be transported straight through it. If anyone can help
me it would be greatly appreciated.

Cheers,

Justin Dingley
Rensselaer Polytechnic
Nuclear Engineering
dinglj@rpi.edu

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1 Feedback: Re: Problem with reflection of optical photons   (Peter Gumplinger - 10 Apr, 2008)
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