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Forum: Geometry
Re: Question Tracking problem with policapillary tubes and tori (Alexey Tkachenko)
Date: 24 May, 2006
From: Gumplinger Peter <Gumplinger Peter>

Alexey,

The way I understand your problem, let's not for the moment worry about the geometry, is that in one case the momentum of the gamma is reversed in your 'X-ray boundary Process', the Navigator does a zero length step as for total internal reflection in G4OpBoundaryProcess, then the gamma returns to the air channel from the interface with the fiber. In the other case, the Navigator does not do a zero length step but continues in the fiber where the gamma is quickly absorbed by photoelectric effect.

Since you modified G4OpBoundaryProcess you should be able to debug in detail what is going on. You can check what normal is returned; is it correct (see the G4DEBUG_OPTICAL in G4OpBoundaryProcess::PostStepDoIt) Are you setting the momentum direction correctly; i.e. is it in fact reversed when the Navigator makes step 3 in your second not working example. The default stepping print-out isn't telling us anything about the momentum direction. Was this statement in your process executed:

aParticleChange.ProposeMomentumDirection(NewMomentum);

What happened to the proposed momentum direction? The fact that it works in one geometry and not in another may be as a result of the real problem. The question to ask is why does the Navigator not do the zero length step at the boundary when it should; i.e. when the point is at the boundary and the direction points across it.

Peter

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1 More: Re: Tracking problem with policapillary tubes and tori   (Alexey Tkachenko - 25 May, 2006)
(_ None: Re: Tracking problem with policapillary tubes and tori   (Makoto Asai - 25 May, 2006)
(_ Feedback: Re: Tracking problem with policapillary tubes and tori   (Alexey Tkachenko - 25 May, 2006)
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