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Forum: Physics List
Re: Question A question about RegisterPhysics (Huagang Yan)
Date: 07 Dec, 2016
From: John Apostolakis <John Apostolakis>

The creator of each physics list is responsible to make sure

i) that the processes registered provide complete coverage of the energy 
range, and

ii) there are no overlaps - only one Geant4 process is responsible for a 
particular interaction of a particle at each energy.  (  Hadronic models 
will overlap - e.g. FTF and Bertini - in an energy range, with a clear 
fraction of interactions being dispatched to each one depending on the 
low & high energy limit of the overlap. )

So there must not be two Compton processes registered to a gamma - 
except if they have separate energy ranges, and know that they must only 
contribute to the cross section in the energy range of their responsibility.

It is possible for different physics constructors to collaborate - e.g. 
one may provide elastic interactions for some (or all) hadrons, whereas 
another may provide their inelastic interactions.  Beyond this 
registered two constructors for the same type of physics will simply 
double count the relevant cross section, and cause unphysical results.

John

On 06/12/16 22:39, Huagang Yan wrote:
> *** Discussion title: Physics List
>
> Hi experts,
>
> I have been puzzled by the use of RegisterPhysics. I have two questions
> about it.
>
> 1) Is the argument of RegisterPhysics representing a physics list, which
> specifies the particle definition, the associated processes, and models?
>
> 2) Suppose the answer to the first question is yes. When two physics
> lists are registered, what will happen if they overlap? For instance,
> RegisterPhysics(new xxx()); RegisterPhysics(new yyy()); What will happen
> if xxx and yyy contain the same particle and processes, but use
> different models?
>
> -------------------------------------------------------------
> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at:
> http://hypernews.slac.stanford.edu/HyperNews/geant4/get/phys-list/957.html

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