Problem 148

Problem report by :

 Daniel Elvira
 PAT/CD Fermilab
 daniel@fnal.gov
  (630)840-3604

> Dear Gunter,
>           a few days ago, I switched to GEANT4.2.0. (from 4.1.1). Until
> then, my simulation was running smoothly. Now the same user code is
> crashing with the following message:
>
> Process::SubtractNumberOfInteractionLengthLeft()  negative
> currentInteractionLength
>
> *** G4Exception: Aborting execution ***
> Abort (core dumped)
>
>           I looked at G4VProcess.cc, where
> SubtractNumberOfInteractionLengthLeft() is implemented. The way to
> get that negative value is if currentInteractionLength<0.0.
>           By the way, the crash goes away if I remove the EM physics
> (comment the line ConstructEM(); in the PhysicsList.cc file). I inspected
> my PhysicsList.cc file against the one in 4.2.0 N02 example and did not find
> any difference (except I am not implementing all the physics contained
> there). I then tried directly replacing my PhysicsList.cc file by the one
> in the 4.2.0 N02 example and still got the same crash.
>
>           Let me give you some details: I'm shooting a muon beam (a few
> hundred MeV), through liquid hydrogen, in a magnetic field. Ionization,
> Bremsstrahlung and pair production processes are turned on for muons.
> I'm running on a Linux PC.
>
>           Is it obvious to you what's going on? If I change the 4.2.0
> N02 example to shoot muons instead of protons I don't get any crash.
> Please let me know if you need more information, like my PhysicsList.cc
> for example. Right now I'm switching back to 4.1.1, but I would really
> like not to do that. Thanks for your help,
>
>
>                                                       Daniel
>