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None Two stacked scintillators and energy conservation 

Forum: Processes Involving Optical Photons
Date: 02 Nov, 2014
From: Steve Asztalos <Steve Asztalos>

I am vexed by a problem with energy conservation in a two stacked scintillator detector. In an earlier incarnation, I had a phoswich design with a hollow sphere with a thin shell of the scintillator BC404 embedded in a larger tube of the scintillator CsI. Xenon gas decays within the sphere emitted electrons that traversed the thin layer of BC404 and with sufficiently high energy would come to rest in the CsI. Such a trajectory would cause scintillation in both the BC404 and CsI. My output confirmed that the electron energy deposited in the BC404+CsI was less than or approximately equal to the emitted energy, and scintillation light generated in the two regions in proportion to the light yield. So far so good.

In a latter design I replaced the embedded sphere with a thin tube of BC404 placed at the end of the CsI tube. The source is now external and, at sufficiently high energies, deposits energy in both scintillators. The problem is that now a) the sum of the electron energy deposited in the BC404+CsI exceeds the beam energy, and I have found that this discrepancy grows as I manually increase the light yield.

I read the manual on optical processes and am not counting the optical photon energies (though the fact the amount that total deposited energy exceeds the beam energy depends on the value I choose for the light yield bothers me). Do I need to explicitly specify the boundary between the two dielectrics (the manual seems to indicate no - in that case it is only a matter of the different indices of refraction). In the outside chance that this is indeed the case, why did I not have to do it when the scintillating sphere was embedded in the Xe tube?

I have attached my detector construction file,

Thanks - Steve Asztalos

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/11/02/22.02-23145-chDetectorConstruction.cc

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