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Question Distribution of Optical Photons 

Forum: Processes Involving Optical Photons
Date: 03 Dec, 2017
From: Angus HOLLANDS <Angus HOLLANDS>

Hi all. I'm modelling an Ortec 905-4 NaI(Tl) scintillator, initially with a 60Co source. The resultant optical photon distribution does not, however, resemble the expected Gaussian distribution.

Instead I seem to have a weighted Gaussian, which has a tail in the higher energies. My experimental setup is as follows:

EMLowEP + FTFP_BERT + Decay + RadioactiveDecay + OpticalPhysics 1mm cut value

1.1 MeV Gamma beam NaI(Tl) scintillator + Bialkali PMT

I'm using the Python bindings to configure the simulation, with a helper module to make it easier to create new simulations w/o introducing duplication mistakes. Therefore, although I am sharing the code, it is more use for inspection than actually being run.

The actual volumes in the scene are thus: * Scintillation detector, based on the Ortec 905 design, with an Al wall (.02" thick) + end cap, 3" (diameter, length) crystal, and an air gap on the sides of the crystal. Behind the crystal is the bialkali photocathode.

A ground tyvek surface is defined between the end cap (Al) and the crystal, and the air and the crystal.

The PMT has an optical surface with a nonzero efficiency,

https://gist.github.com/agoose77/baa1fa580795ffa4720ba778f6aab722

Can anyone perhaps shed some light on why this might be happening?

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2017/12/03/12.36-47384-dist1.1_sarc.png

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1 None: Re: Distribution of Optical Photons   (Angus HOLLANDS - 03 Dec, 2017)
2 None: Re: Distribution of Optical Photons   (Daren Sawkey - 13 Dec, 2017)
1 None: Re: Distribution of Optical Photons   (Angus HOLLANDS - 10 Jan, 2018)
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