|Message: Re: strange proton energy loss||Not Logged In (login)|
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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
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