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Forum: Processes Involving Optical Photons
Re: Question Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber? (matthew)
Date: 25 Mar, 2015
From: Gumplinger Peter <Gumplinger Peter>

> Problem in brief: I am trying to model the trapping efficiency of a
> scintillating optical fiber and the efficiency I measure is more than
> 10x the manufacturer's value.

You trap photons that are produced inside the fiber. The Cherenkov photons even have a specific cone distribution relative to the radiating particle's direction. To understand your situation it would be best to eliminate the Cherenkov photons (no such process) in your simulation for the moment.

> I am trying to model the scintillation and Cherenkov light for a Bicron
> BCF-10 scintillating fiber. factory values for the refractive indices of
> the fiber are n2 = 1.49 (cladding), and n1= 1.6 (fiber core).
> Calculating the trapping efficiency using the equation eff =
> 0.5(1-n2/n1) gives eff = 3.44%, which is the manufacturer stated value.

Real fibers aren't perfectly smooth. A little roughness introduced changes the situation dramatically.

> Strangely, when I calculate eff = (# photons absorbed in PMT)/(# of
> scintillation photons + # of Cherenkov photons produced), i get eff =
> 37%. (steppingAction used to keep track of produced and absorbed photons
> is attached.)

Looks ok.

> Do I misunderstand something in the opticalPhysics process? Shouldn't
> the number of photons trapped in the fiber and transported to the PMT be
> equal to the value calculable based on the ratio of refractive indices
> of the cladding and the fiber? I understand that value only describes
> the meridial rays, but the skew rays only add a few percent.

I would think that almost all of your rays are skew rays. Why do you think the opposite?

Peter

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1 Question: Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (matthew - 25 Mar, 2015)
2 None: Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (matthew - 30 Mar, 2015)
1 None: Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (Erik Dietz-Laursonn - 15 Apr, 2015)
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