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Forum: Processes Involving Optical Photons
Re: None Scintillation photons leaking through refelctive surface (Geertje)
Date: 30 Apr, 2014
From: Gumplinger Peter <Gumplinger Peter>

Dear Geertje,

> Dear all, I'm simulating a plastic scintillator which is wrapped with a
> reflective foil on three sides, the unwrapped forth side is directly
> coupled to the PMT. For testing reasons I set the refl_foil = 0, so that
> all photons should be absorbed at the foil boundary. If a start an
> electron within the scinillator everything is working as supposed to:
> scintillation light is produced, photons get absorbed on the foil or
> detected by the PMT.

OK, great.

> BUT: If I start the electron outside the the setup
> I find that half of the produced scintillation photons leak through the
> plastic/foil boundary ( and it looks like at the point where the primary
> particle enters the setup).

Well, there is nothing in G4 which would magically alter the surface to make it transparent when an electron goes through it.

> I attached my scintillator detector
> construction with all necessary optical propterties but I can't see
> where I'm going wrong. From my understanding the two things happening
> could be 1) scintillation light is produced in the foil, but that
> shouldn't be possible as I haven't defined any scinillation properties
> for this material

I see that you correctly defined the surface between foil and scintillator in both directions: "Scinti->Foil" and "Foil->Scinti"

I see:

matFoil->SetMaterialPropertiesTable(mptFoil);

and also:

opSFoilScintillator->SetMaterialPropertiesTable(mptFoil);

Don't attach mptFoil to the bulk material matFoil. This may not be your problem but the code does not foresee "REFLECTIVITY" to be associated with a bulk medium. You may also want to change:

G4OpticalSurface* opSFoilScintillator = new G4OpticalSurface("Dielectric-Metal", glisur, polished,dielectric_metal)

but, again, this should not be your problem.

> 2) the border surfaces are not correctly recognized by
> the step but I don't see a reason why. The physics list I'm using is the
> shielidngList where I added G4OpticalPhysics manually.

OK, so you also have the G4Cerenkov process. Does the worldVolume have a material with an index of refraction. If so, the outside electron will generate Cerenkov photons...

Still, photons should not be able to enter the scintillator. They may enter the foil, though that too shouldn't happen since the foil material doesn't have an index of refraction.

I can only suggest at this point, that you turn on tracking verbose and the verbosity of G4OpBoundaryProcess and tell us for one incoming photon - into the scintillator - what the step debugging tells you.

/tracking/verbose 1 /optics_engine/selectOpProcess OpBoundary /optics_engine/setOpProcessVerbose 1

For good measure also set:

/optics_engine/selectOpProcess Cerenkov /optics_engine/setOpProcessUse false

I think that you have perhaps Cerenkov photons stopped at the foil and scintillation photons inside for electrons that enter the scintillator but you actually don't have an individual optical photon go across the surface.

Peter

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1 Feedback: Re: Scintillation photons leaking through refelctive surface   (Geertje - 30 Apr, 2014)
(_ Feedback: Re: Scintillation photons leaking through refelctive surface   (Gumplinger Peter - 30 Apr, 2014)
(_ Ok: Re: Scintillation photons leaking through refelctive surface   (Geertje - 01 May, 2014)
(_ Feedback: Re: Scintillation photons leaking through refelctive surface   (Gumplinger Peter - 01 May, 2014)
(_ Question: Re: Scintillation photons leaking through refelctive surface   (Geertje - 01 May, 2014)
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