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Forum: Physics List
Re: Question TestEm15 (Georgia de Nolfo)
Date: 07 Mar, 2011
From: michel maire <michel maire>

On Fri, 04 Mar 2011 15:55:25 GMT, Georgia de Nolfo wrote:
> I'm having trouble understanding the output of TestEm15. If I run the
> example in its default mode, I force MSC to occur at every step.
> However, if I "activate" ionization and Bremms in the electron.mac
> example, every step is associated with either an eIoni or Bremm and
> there are no MSC processes registered. Presumably, this means that the
> pathlength for eIoni and Bremm are much shorter than MSC --when I
> increase the density of water, MSC events do occur even with ionization
> & bremm turned on.

  Yes, this is correct. However /tracking/verbose print only the process responsible of the step lenght. But several processes may be applied at that step; it is the meaning of 'alongStep' action. In perticular MSC is always applied, at each step.

 In TestEm15, event is killed at the first step. Therefore Ionis or Brem act only as a step limiter. 
> I guess I don't understand the relevance of "forcing" MSC at each step.
> I also don't understand the importance of the "ratings" in the processes
> (see below).
>       pmanager->AddProcess(new G4eIonisation,        -1, 1, 1);
>       pmanager->AddProcess(new G4eBremsstrahlung,    -1, 2, 2);
> Doesn't GEANT4 determine the next process by determining the smallest
> physical step size? What is the numbering scheme meant to do in
> AddProcess?

  I attach a tutorial. See slides 6-9
> I'm actually interested in determining the interactions of electrons in
> a thin target, say a gas at 1 atm. Is there a specific model in GEANT4
> that I should invoke for this application?
 Normally, no. But it may depend of the thickness of target, and energy of incident particle.



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