Problem 633

When using a geometry constructed with the G4PVReplica method,
the Transportation process sometimes returns a 0 step length and
the particle remains stuck at the same place forever.

I wrote a small example to reproduce the problem in
ftp://guest:time@ftp.metas.ch/voros/totabs.tgz

It is a water cylinder surrounded by air, and the cylinder is
divided into Z-Phi-R replica. For each event an e- of 5.332 MeV located
at -3.2 cm is shot along the Z axis towards the cylinder surface
located at 0 cm.

I tried to avoid "usual" errors with replica (i.e., not filling
the entire mother volume, etc.), so this must be something else,
and DAVID/DAWN did not detect any overlapping volume.
I'm using Geant4.6.0.p01 on a Linux RedHat 9.0 PC.

This small example works similarly as the Geant4 examples : define
the usual Geant4 environment variables, then 'cd' to the 'totabs'
directory, 'gmake' and execute it. The vis.mac file will be
executed first (it uses the OGLIX viewer), and then you can give
the command '/run/beamOn 8'. I get the "desired" problem in the
last event:

Step#      X         Y         Z        KineE    dEStep   StepLeng  TrakLeng
Volume     Process
    0      0 fm      0 fm   -3.2 cm   5.33 MeV     0 eV      0 fm      0 fm
World    initStep
    1      0 fm      0 fm      0 fm   5.33 MeV  6.91 keV   3.2 cm    3.2 cm
World  Transportation
    2      0 fm      0 fm      0 fm   5.33 MeV     0 eV      0 fm    3.2 cm
AbsorberRPhiZDiv  Transportation
    3      0 fm      0 fm      0 fm   5.33 MeV     0 eV      0 fm    3.2 cm
World  Transportation
    4      0 fm      0 fm      0 fm   5.33 MeV     0 eV      0 fm    3.2 cm
AbsorberRPhiZDiv  Transportation
    5      0 fm      0 fm      0 fm   5.33 MeV     0 eV      0 fm    3.2 cm
World  Transportation
........

So the particle seems to oscillate between the World and
AbsorberRPhiZDiv (the replicated) volumes in this case, but I
also saw it remain stuck at an other boundary between two replica
when using a slightly different setup.

I also tested a couple of changes in the geometry, like R-Z-Phi replica instead
of Z-Phi-R, using G4PVDivision instead of G4PVReplica, changing the granularity
in the totabs/src/totabsDetectorConstruction.cc file, but the problem remains
the same.

Thanks a lot for any help.
SĂĄndor