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Forum: Geometry
Re: Question strange proton energy loss (Simone)
Date: 09 Jul, 2010
From: michel maire <michel maire>

On Wed, 07 Jul 2010 08:59:45 GMT, Simone wrote:
> hello to everyone,
> 
> in my simulation MIP protons (2 GeV) impact on a thin layer made of
> bismuth. the energy deposited anyway seems not to scale linearly with
> the layer thickness (wich is strange since dE<<E): with 1 cm thickness I
> get a total energy deposition with a peak around 10 MeV, while with 1
> micron i get a energy deposition of ~0.3 keV (while I expected
> 10MeV/10000=~1keV).
> 
> it is surely not due to secondaries escaping the 1 micron layer, since i
> used an extremely high cut value to avoid that effect
> 
> does someone has any suggestion/ideas about this strange behaviour?

  We reproduced your results with testEm5. Macro and plots in attachements.

  The problem comes from the Eloss fluctuation model : when we disconnect it, energy deposit is delta peak independant of thickness, as it must be.

 Geant4 Fluctuation model has intrinsec limit for too small thickness. 1 um Bismuth reach this limit. However, notice that :
 1- at 10 um, distribution is ok.
 2- mean value of distribution is stable at any thickness : about 10.8 MeV/cm
    This can be read on the output of TestEm5

    Cheers,   Michel

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/07/09/18.40-94836-slotti.txt
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/07/09/18.41-94604-1cm.jpg
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/07/09/18.41-15161-10um.jpg
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/07/09/18.41-9630-1um.jpg

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