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Forum: Physics List
Re: Question Physics processes and appearance of primary photons (Sourav Tarafdar)
Date: 27 Mar, 2015
From: John Apostolakis <John Apostolakis>

Dear Sourav,

One simple way to see whether particles are primary or secondaries is to use the 'verbose' capabilities of Geant4.

So long as this is a frequent occurrence, you could use
/tracking/verbose 2
to enable the printing of the secondaries in the step in which they are generated.

I would suggest to use also a simple way to double check your input - e.g. printing all the primaries at the start of the step using a cout in your primary generator action.

The more robust way to check whether a secondary is created with an incorrect parent is to create a G4VUserStackingAction. Please look in the Geant4 documentation regarding how to do this.  It allows you to filter (or simply check) the secondaries which are created by each track, before they are handed back to the Geant4 kernel for further simulation.

Best regards,
John
===================================================
John Apostolakis,  PH Department, CERN

> On 27 Mar 2015, at 13:41, Sourav Tarafdar <sourav.pheonix@gmail.com> wrote:
> 
> 
> *** Discussion title: Physics List
> 
> Dear experts,
> 
> Recently I noticed appearance of primary photons while running Geant4
> for my defined geometry. My geometry consist of a long hollow cylinder
> filled with vacuum. The hollow part of the cylinder is filled with
> uniform magnetic field in Y direction. Then I transported nuclear
> fragments (including protons and neutrons) from Heavy Ion collisions. I
> used standalone generator for generating these to be transported nuclear
> fragments. While looking at the output of Geant4 the Parent ID of these
> nuclear fragments is assigned "0" which is what I expect. However the
> output of Geant4 also shows photons with Parent ID as "0" though I
> *absolutely did not* transport any photons through my Geant4 geometry. I
> used "FTFP_BERT" as physics process while running Geant4. The photons
> seems to appear in the magnetic field region. Any idea what could be the
> reason of appearance of primary photons ?
> 
> Further is there any way of dumping out what kind of processes are
> involved in production of secondaries in Geant4 ? Looking at
> https://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/ch05.html
> it seems that there is a way in "G4StepPoint" but somehow I did not
> manage to figure out how to do it. If anyone can point to be a working
> example it will be really helpful.
> 
> Thanks -Sourav
> 
> -------------------------------------------------------------
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