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Forum: Event and Track Management
Re: Question Negative Current Interaction Length with Photonuclear interaction, and other problems (Giles Reid)
Date: 06 Jun, 2005
From: Vladimir IVANTCHENKO <vnivanch@mail.cern.ch>

On Mon, 6 Jun 2005, Giles Reid wrote:

> *** Discussion title: Event and Track Management
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/eventtrackmanage/338"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> Hello,
> 
> I'm trying to simulate magnetic monopoles in GEANT. I am currently using
> a modified mu+ with charge 68.5 and mass of around 300GeV.
> 
> I've been trying to get the Photonuclear interaction process to work,
> using the base of the MuonProcess example, but when I add the process I
> get the following error:
> 
> *** G4Exception : Negative currentInteractionLength
>       issued by : G4VProcess::SubtractNumberOfInteractionLengthLeft()
> 
> All of the PostStepDoIt outputs above this error contain nans for
> various parameters like momentum and total energy.
> 
> So my first question is, can the Muon Photonuclear code be expected to
> work for high charges and masses, or would it need to be rewritten?
> 
> I have been able to modify the PairProduction model to include extra
> factors of the monopole charge and this appears to give reasonable
> results. I have also found that the MuIoni process doesn't work very
> well, but the hIoni one does. The problem is, I can't make pair
> production and ionisation work simultaneously, because when I use hIoni
> with the Muon along with Pair Production I get a segmentation fault in
> the line:
> 
> theDEDXTable->GetFlag(i)
> 
> in G4VEnergyLossProcess.cc.
> 
> I realise that having hadronic and muon processes may be causing the
> problem. However, in order to make the simulations realistic I need to
> have the Pair Production and Photonuclear Processes working, and as far
> as I can tell there is no hadronic equivalent to these processes in
> GEANT.
> 
> Any help would be greatly appreciated.
> 
> Giles Reid.
> 

Hello,

There is little information to make a conclusion but too many things 
changed in official processes/particles, so I am not suprised that it 
crashes.  

Few obvious advices:

1) Never modify official code of G4. If you need to change something - 
make a copy of G4 class, rename it , introduce your changes and use in 
your application.

2) Muon example has specific - all secondary particles are killed, because
it intends not for simulation of all processes but only to demonstrate
muon cross sections and energy loss. If one needs simulation of
secondaries, PHysicsList should be extended by including hadron processes.

3) Both ionisation models muIoni and hIoni are not adequate to monopole,
because monopole ionisation is different. However, if one defines mass and
change of heavy particle they have to work, if PhysicsList is written
correctly.

VI

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1 None: Re: Negative Current Interaction Length with Photonuclear interaction, and other problems   (Giles Reid - 06 Jun, 2005)
(_ None: Re: Negative Current Interaction Length with Photonuclear interaction, and other problems   (Vladimir IVANTCHENKO - 07 Jun, 2005)
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