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Forum: Processes Involving Optical Photons
Re: Question Energy deposited is larger than the energy of the primary gamma beam (Martin Kocan)
Re: Feedback Re: Energy deposited is larger than the energy of the primary gamma beam (Gumplinger Peter)
Date: 30 Jan, 2014
From: Martin Kocan <Martin Kocan>

Hi Peter,

thank you very much for your reply.

I was able to find some more information regarding my simulation.

1. Regarding the larger energy deposition than the energy of the primary beam in a NaI scintillator, the code counted energy deposition also for opticalphotons that step from a physical volume of NaI (PreStepPoint) to photonDet (PostStepPoint). These minor increments in energy deposition caused the energy deposited to be larger than the energy of the primary beam. I hard-coded an if statement in SensitiveDetector.cc to count the energy deposition only if the physical volume for PreStepPoint and PostStepPoint of a particle comes from NaI physical volume only. In this way the code counts only energy deposition from e- particles stepping in NaI physical volume (I haven't observed any other particles causing energy deposition in my simple example of one gamma event with energy of 1MeV). Not sure it this the right way of doing things but it seems to work for my simple example. Would you have any comments to my observation?

Snap shot of the geometry is pictured in the attached png image file. The scintillator consists of a NaI volume (blue) & a photon detector (red) (made of a metallic disc positioned at the back of NaI volume). Both volumes are housed within a mother AlHousing cylinder volume (white). 1MeV gamma beam outside of the AlHousing is shown in green and the opticalphotons generated in NaI are shown also in green.

2. Regarding the necessity of refractive index definition for AlHousing, my understanding was to define this physical quantity for both materials that form a boundary interface described via G4LogicalBorderSurface.

3. Regarding the reflectivity of 94% for NaI internal walls instead of 100%: since we don't know what the reflector in a real NaI scintillator is made of, the value of 94% seems to show the best agreement with spectral measurement.

4. Regarding the number of detected opticalphotons: thank you for your explanation and guidance.

Thank you.

Martin.

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/01/30/21.16-55563-NaIdet_with_Gamma1MeV.PNG

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1 Agree: Re: Energy deposited is larger than the energy of the primary gamma beam   (Gumplinger Peter - 31 Jan, 2014)
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