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Forum: Physics List
Re: Question no compton scattering (Athreya Shankar)
Date: 06 Jul, 2011
From: Zach Hartwig <Zach Hartwig>

Hi Athraya,

A few suggestions:

1. Have you tried one of the included Geant4 physics lists (built with the
"physics builder" approach), such as QGSP_BERT? Or copied one of the physics
lists from $G4INSTALL/examples/extended/electromagnetic/? These lists have been
extensively validated and could eliminate one potential source of error for you.

2. Your NaI spectrum looks "too good" to be true, i.e., it appears that
photoabsorption that leads to full energy deposit in the scintillator is the
dominant mechanism, overwhelming the expected Compton edge and continuum
(assuming you have registered Compton scattering correctly).

This may be a result of a) too high NaI material density b) unexpectedly large
NaI cylinder (so large that it becomes an "ideal" detector with no Compton
scattered gamma able to escape the detection volume c) or incorrect scoring of
the energy deposited in the NaI.

How are you scoring energy deposition? You should be summing the total ionizing
energy deposited in the NaI volume only per incident Co-60 gamma per event.

Hope this helps.

~ZSH

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1 Question: Re: no compton scattering   (Athreya Shankar - 07 Jul, 2011)
(_ Idea: Re: no compton scattering   (Vladimir Ivanchenko - 27 Jul, 2011)
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