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None Tracking problem with tori (followup of message #556) 

Forum: Geometry
Date: 10 Oct, 2006
From: Alexey Tkachenko <>

This message continues the message #556 (and problem report #872) where I reported about tracking problem with policapillary tubes and tori. After Geant 4.8.1. release I have received following:

1. The tracking problem in policapillary tube was resolved in this release. I have tested my geometry with different gamma incidence angles and I have not found any problems with gamma reflections.

2. The problem still remains for tori based geometry. I have tried to simplify this geometry and it has appeared that the problem is observed even for single torus.

I am shooting gamma to this torus at a small incident angle (~1 arc. min). For backscattering of gamma I'm using the our own GammaBoudaryProcess based on G4OpBoundaryProcess. This process changes the momentum of reflected gamma at the boundary.

In most cases the reflection is working properly. The momentum of the gamma is reversed in our GammaBoudaryProcess, the Navigator does a zero length step from Torus through the boundary and then the gamma returns to the Word volume. But approximately in 5% of cases the navigator does not do a zero length step and gamma remains inside torus volume.

For testing I run the program with verbose level 4 for ( /geometry/navigator/verbose, /event/verbose, and /tracking/verbose)

Unfortunately I have not understood the message of the navigator. The log-files with various types of gamma backscattering is here:

Wrong backscattering:

Normal backscattering:

Strange case:

The code of the program can be taken here:

Kind regards, Alexey Tkachenko

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