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Forum: Geometry
Re: Question Stuck Track using very simple geometry and parallel beam model (Youming Yang)
Date: 19 Aug, 2016
From: Gabriele Cosmo <Gabriele Cosmo>

I suggest you to upgrade to 10.1.p03 or to the latest release, where
the problem should be fixed, and if persisting, submit a problem report
in Bugzilla.

Cheers, Gabriele

------------------
On Mon, 25 Jul 2016 04:28:24 GMT, Youming Yang wrote:
> Hello,
> 
> I am getting a stuck track when using a simple voxelized model (using
> PVReplica) 1mm^3 voxels, and a G4GPS parallel beam of photons.
> 
> I am using Geantv4.10.01p02
> 
> The code for the geometry is:
>     dx=dy=dz=1*mm;
>     nx=ny=nz=401;
>     detx=dx*nx;
>     dety=dy*ny;
>     detz=dz*nz;
> 
>     G4String detName("Det");
>     G4VSolid* sDet = new G4Box(detName,detx/2.,dety/2.,detz/2.);
>     lDet = new G4LogicalVolume(sDet, G4Water, "sDet", 0, 0, 0);
>     new G4PVPlacement(0, G4ThreeVector(), lDet, "lDet", logicWorld, false,0,true);
> 
>     //XBOX
>     G4String xName("xRep");
>     G4VSolid* sXRep = new G4Box(xName,dx/2.,dety/2.,detz/2.);
>     lXRep = new G4LogicalVolume(sXRep, G4Water, xName , 0, 0, 0);
>     new G4PVReplica(xName,lXRep,lDet,kXAxis,nx,dx);
> 
>     //Y SLICE
>     G4String yName("yRep");
>     G4VSolid* sYRep = new G4Box(yName,dx/2.,dy/2.,detz/2.);
>     G4LogicalVolume* lYRep =new G4LogicalVolume(sYRep,G4Water,yName);
>     new G4PVReplica(yName,lYRep,lXRep,kYAxis,ny,dy);
> 
>     G4String zName("zRep");
>     G4VSolid* sZRep = new G4Box(zName,dx/2.,dy/2.,dz/2.);
>     G4LogicalVolume* lZRep =new G4LogicalVolume(sZRep,G4Water,zName);
>     new G4PVReplica(zName,lZRep,lYRep,kZAxis,nz,dz);
> 
> And the input for G4GPS is:
> 
>     /gps/particle gamma
> 
>     /gps/pos/type Plane
>     /gps/pos/shape Square
>     /gps/pos/halfx 2.5 cm
>     /gps/pos/halfy 2.5 cm
> 
>     /gps/ene/type Mono
>     /gps/ene/mono 2 MeV
>     /gps/pos/centre 0 0 -21 cm
>     /gps/direction 0 0 1
> 
> I get "warning" messages such as:
>     G4WT30 > 
>     -------- WWWW ------- G4Exception-START -------- WWWW -------
>     *** G4Exception : GeomNav1002
>           issued by : G4Navigator::ComputeStep()
>     Track stuck or not moving.
>               Track stuck, not moving for 10 steps
>               in volume -zRep- at point (-33.3568,-151.5,-64.5)
>               direction: (0.020471,-0.879251,-0.475918).
>               Potential geometry or navigation problem !
>               Trying pushing it of 1e-07 mm ...Potential overlap in geometry!
> 
>     *** This is just a warning message. ***
>     -------- WWWW -------- G4Exception-END --------- WWWW -------
> 
>     G4WT27 > 
>     -------- WWWW ------- G4Exception-START -------- WWWW -------
>     *** G4Exception : GeomNav1002
>           issued by : G4Navigator::ComputeStep()
>     Track stuck or not moving.
>               Track stuck, not moving for 10 steps
>               in volume -zRep- at point (-33.3568,-151.5,-64.5)
>               direction: (0.020471,-0.879251,-0.475918).
>               Potential geometry or navigation problem !
>               Trying pushing it of 1e-07 mm ...Potential overlap in geometry!
> 
>     *** This is just a warning message. ***
>     -------- WWWW -------- G4Exception-END --------- WWWW -------
> 
>     G4WT21 > 
>     -------- WWWW ------- G4Exception-START -------- WWWW -------
>     *** G4Exception : GeomNav1002
>           issued by : G4Navigator::ComputeStep()
>     Track stuck or not moving.
>               Track stuck, not moving for 10 steps
>               in volume -zRep- at point (-6.92026,30.5,-13.5)
>               direction: (0.531012,-0.777328,-0.337325).
>               Potential geometry or navigation problem !
>               Trying pushing it of 1e-07 mm ...Potential overlap in geometry!
> 
>     *** This is just a warning message. ***
>     -------- WWWW -------- G4Exception-END --------- WWWW -------
> 
> This issue only occurs when I use a photon beam (changing particle type
> to protons shows no issues, and the simulation completes successfully.
> However my photon simulation has been running for an order of magnitude
> longer without any output. I am under the impression it may be due to
> the parallel photon beams having initial trajectories collinear with
> voxel boundaries.
> 
> Does anyone have experience/suggestions for this situation?
> 
> Thank you, Ming
> 

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