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Feedback Re: the local time goes back -- the true step length is negative 

Forum: Processes Involving Optical Photons
Re: None the local time goes back -- the true step length is negative (khoi nguyen)
Date: 03 Aug, 2012
From: Gumplinger Peter <Gumplinger Peter>

Dear Khoi,

You are bringing up at least two unrelated issues. The first one, is not an issue really. You found the code:

http://www-geant4.kek.jp/lxr/source/track/src/G4ParticleChange.cc#L546

that writes the warning to your screen.

> 3. G4eIonisation 1, G4Scintillation 1, G4OpWLS 1 : i shoot a test
> electron with energy E and let it create some scintillation photons.
> 
>     i. if E < 30 keV --> fine !
> 
>     ii. E >= 40 keV --> GEANT4 complains :  
>          a. G4ParticleChange::CheckIt : "the local time goes back !!"
> 
>          b. G4VParticleChange::CheckIt : "the true step length is negative !!"
> 
>          c. G4Exception: ... step length and/or energy deposit was illegal

From your attachement it looks like the CheckIt warning is written when a optical photon is tracked. So, there is no causal connection between the original electron and the resulting optical photons, once the latter is being tracked. I don't know why you would find a relationship.

Moreover, the G4OpWLS process does only a few things wrt G4ParticleChange:

  aParticleChange.Initialize(aTrack);
  aParticleChange.ProposeTrackStatus(fStopAndKill);

and when there are WLS photons to be produced:

  aParticleChange.SetNumberOfSecondaries(NumPhotons);
  aParticleChange.AddSecondary(aSecondaryTrack);

I think your underlying problem is this: "the true step length is negative !!"

I dont' know why your scintillation photon will take a negative steplength step in Transportation. You'll need to understand how this can come about... I don't know.

Peter

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1 None: Re: the local time goes back -- the true step length is negative   (khoi nguyen - 03 Aug, 2012)
(_ None: Re: the local time goes back -- the true step length is negative   (khoi nguyen - 07 Aug, 2012)
(_ Feedback: Re: the local time goes back -- the true step length is negative   (Gumplinger Peter - 07 Aug, 2012)
(_ None: Re: the local time goes back -- the true step length is negative   (khoi nguyen - 14 Aug, 2012)
(_ None: Re: the local time goes back -- the true step length is negative   (khoi nguyen - 14 Aug, 2012)
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