|Message: hits not produced for G4Polyhedra in G4.9.3.p02||Not Logged In (login)|
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I have an old simulation that was in Geant4.9.3.p02. Most of the physics extracted from it so far was simple minimum ionizing particle tracking, so the move to newer versions is important but not the first priority.
There was however a tracking bug that appeared when moving to (more realistic) hexagonal cell models for a gas detector I am modeling. The cells are hexagonal close-packed arrays cut out of an aluminium "tube" (see attached picture). The tube is made of aluminium and constructed with G4ExtrudedSolid, and then 8 G4Polyhedra (made to hexagons) are placed inside of it.
The symptom in Geant4.9.3.p02 is that some of the muon tracks seem to "disappear" inside some of the hexagonal cells in that they produce no muon hits there (although they should be producing boundary-crossings and continuous energy depositions). The electrons that they occasionally eject, however, are seen. This can be seen in one of the attached pictures -- black and red points are muon hits while green points are electron hits. Some cells are devoid of muon hits in Geant4.9.3.p02.
The tracking problems seem to be cleared up by going to Geant4.9.5.p02 (see attached figures). I was not able to precisely track the origin of these problems in the code, but nor was I able to understand the release notes at a sufficient level to be confident that this symptom was recognized as a bug (if indeed it is a bug!) and specifically fixed by some update.
Could someone tell me if this was a known problem that has been resolved? If not I still worry a bit that by upgrading this was fixed "by accident" and it was maybe a symptom of a deeper problem.
Other weird things occur as well, for example, if (when using Geant4.9.3.p02) I increase OR decrease the radii of the hexagonal cells, the problem apparently goes away. This I find hard to understand.
Attachment: http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/06/30/19.02-15899-vetotubeReal_numbered.png http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/06/30/19.02-13460-lSensitive_G4.9.3.p02.png http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/06/30/19.02-69978-lSensitive_G4.9.5.p02.png