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## Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?

Forum: Processes Involving Optical Photons
Date: 24 Mar, 2015
From: matthew <matthew>

 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. 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. I do believe i am accurately counting the production of both scintillation and cherenkov photons. I am "detecting" photons with a glass detector (named "PMT") at one end of the fiber by counting the number of absorbed photons inside the PMT. (plot of geometry is attached) 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.) 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. Have a forgotten to account for something? any thoughts would be greatly appreciated.    Attachment:       http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2015/03/24/14.13-34968-OpFiberSteppingAction.cc       http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2015/03/24/14.13-30060-FiberGeometry.png

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1 Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (Gumplinger Peter - 25 Mar, 2015)
1 Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (matthew - 25 Mar, 2015)
2 Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (matthew - 30 Mar, 2015)
1 Re: Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?   (Erik Dietz-Laursonn - 15 Apr, 2015)
 to: "Does GEANT4 accurately model the trapping efficiency for a scintillating optical fiber?"
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