Message: Stuck Track using very simple geometry and parallel beam model  Not Logged In (login) 
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  G4ExceptionSTART  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 1e07 mm ...Potential overlap in geometry!
*** This is just a warning message. ***  WWWW  G4ExceptionEND  WWWW 
G4WT27 >  WWWW  G4ExceptionSTART  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 1e07 mm ...Potential overlap in geometry!
*** This is just a warning message. ***  WWWW  G4ExceptionEND  WWWW 
G4WT21 >  WWWW  G4ExceptionSTART  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 1e07 mm ...Potential overlap in geometry!
*** This is just a warning message. ***  WWWW  G4ExceptionEND  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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