Problem 924

Summary:	Electron is stuck on boundary
Product:	Geant4	Reporter:	Bertalan.Juhasz
Component:	processes/transportation	Assignee:	John Apostolakis <John.Apostolakis>
Status:	RESOLVED WORKSFORME
Severity:	normal	CC:	Gabriele.Cosmo
Priority:	P2
Version:	other
Hardware:	PC
OS:	Linux
URL:	http://www.smi.oeaw.ac.at/juhasz/hbar_bug.tar.gz

Description Bertalan.Juhasz 2007-01-15 02:46:51 CET

In version 8.2 (but not in 7.1), sometimes an electron is stuck on the surface
between two volumes (one of them vacuum (world, G4Box), the other is steel
(G4Cons)). There it makes ~10^5 (!) steps, each infinitesimally small [0 or
10^-(20-30) mm)], "bouncing" between the two volumes, until finally somehow
escapes and tracking continues. This happenes 3-4 times in every 100 events.
FYI, I use a global magnetic field, but the bug occurs with both zero and
non-zero fields.

See the URL for the application in which the bug occurs. This application
already contains a workaround for the bug (see hbarStepAction.cc). However, to
compile, you need a slightly modified GEANT4, so contact me for further information.

Comment 1 John Apostolakis 2007-02-12 10:48:59 CET

We are tracking a couple of similar problems.  A candidate fix is in
preparation for the case of geometries with overlaps and a magnetic field.
We will continue to investigate, and try to extend to the non-field case also.

Comment 2 Gabriele Cosmo 2008-09-19 14:31:51 CEST

The problem should be fixed in the most recent patched versions of Geant4.
If still persisting for the specific use-case, please open a new problem
report with all the details. Thanks.