Problem 2205

Summary:	Possible geometry bug
Product:	Geant4	Reporter:	Jake <gunshinuja>
Component:	geometry	Assignee:	Gabriele Cosmo <Gabriele.Cosmo>
Status:	RESOLVED INVALID
Severity:	normal	CC:	John.Allison
Priority:	P4
Version:	10.5
Hardware:	Other
OS:	Linux
Attachments:	Build and run exampleB1 (vis.mac) to observe possible geometry bug

Description Jake 2019-11-17 10:01:57 CET

Created attachment 595 [details]
Build and run exampleB1 (vis.mac) to observe possible geometry bug

This is a possible bug with geometry, as described in this thread on the Geant4 forums: https://geant4-forum.web.cern.ch/t/possible-bug-with-geometry/1264

In short, the simulation is not registering that photons are passing through the barrier. While the photons correctly "see" the barrier for 180 < phi < 270 (i.e. one quadrant of the barrier), they do not see the barrier for all other phi.

I have attached a reasonably minimal example (though not very elegant). Please run exampleB1 (vis.mac) to observe the apparent bug. 

Also note that the problem goes away if the "detector" volume is removed.

I have produced this using Geant4 versions 10.05 and 10.05.p01, both on CentOS Linux release 7.6.1810 (Core). I am using VMs from http://geant4.in2p3.fr/spip.php?rubrique8&lang=en

Comment 1 John.Allison 2019-11-17 13:08:03 CET

I have had look at this. The world volume is tight up against all volumes. We recommend the world volume is more generous. When I add

  // Safety
  G4double safety = 2.;
  world_sizeXY *= safety;
  world_sizeZ *= 2.;

and place the detector well inside:

  G4ThreeVector(0., 0., 0.5*world_sizeZ - 0.5*detector_sizeZ - 1.*cm),

all is well. (I suggest place the detector relative to the barriers.)

OK. Problem solved.

Comment 2 Gabriele Cosmo 2019-11-18 16:20:41 CET

Thanks John!  Marking this as invalid report...