| Summary: | e+ tracking becomes infinite loop in Cerenkov production | ||
|---|---|---|---|
| Product: | Geant4 | Reporter: | Scott Nutter <nutters> |
| Component: | processes/electromagnetic | Assignee: | Daren Sawkey <daren.sawkey> |
| Status: | RESOLVED FIXED | ||
| Severity: | minor | CC: | daren.sawkey |
| Priority: | P4 | ||
| Version: | 10.3 | ||
| Hardware: | PC | ||
| OS: | Linux | ||
UPDATE: I had production cuts set to one micron. When increased to five microns, problem was gone. At two microns, problem still occurred. Hello Scott, it seems to be a real problem. Thank you very much for pointing to it. How we can reproduce it in a simple example or you can provide a tar with your application? Vladimir Hi Scott, Thanks for reporting this. I haven't been able to reproduce this problem. I do see similar small steps limited by Cerenkov, but only for a few steps at a time (see below). Could you please provide more information. What material does this occur in? What physics list are you using? Regards -- Daren. G4WT0 > 6 118 um -11.6 um -10.3 um 155 keV 1.77 keV 5.87 um 119 um Tank eIoni G4WT0 > 7 143 um -16.2 um -11.5 um 150 keV 5.57 keV 25.6 um 145 um Tank Cerenkov G4WT0 > 8 145 um -16.6 um -11.7 um 149 keV 324 eV 2.43 um 147 um Tank Cerenkov G4WT0 > 9 146 um -16.8 um -11.7 um 149 keV 268 eV 1.1 um 148 um Tank Cerenkov G4WT0 > 10 146 um -16.8 um -11.7 um 149 keV 0.191 eV 7.85 Ang 148 um Tank Cerenkov G4WT0 > 11 146 um -16.8 um -11.7 um 149 keV7.89e-06 eV 32.4 fm 148 um Tank Cerenkov G4WT0 > 12 146 um -16.8 um -11.7 um 149 keV3.11e-10 eV 0.00128 fm 148 um Tank Cerenkov G4WT0 > 13 147 um -17 um -11.7 um 149 keV 47.2 eV 714 nm 149 um Tank eIoni Sorry I haven't followed up on this. It's part of a large codeset that I need to cull down and check that the problem still occurs. I was tracking in plastic scintillator. I got around the problem by lengthening the steps. I hope to spend some time on this next month. Scott It turns out that this appears only for certain materials, for example, G4_POLYETHYLENE. A fix is available and will be in the next patch release. Scott, thanks for reporting this. |
I am having this problem occur reliably now, each time in the same material and at the same energy, but not every time. The material has optical properties defined, and scintillation and cerenkov physics turned on in the physics list for relevant particles. NOTE: The problem occurs at the threshold energy for Cerenkov production, which makes me suspect it is a GEANT4 problem. My guess is it is a precision problem associated with determining the step length. An e+ loses energy down to KE = 0.149 MeV in a normal manner through eIoni. At 0.149 MeV (threshold for Rindex = 1.58) it loops continuously on the Cerenkov process with very small dE and StepLength. See below: * G4Track Information: Particle = e+, Track ID = 96731, Parent ID = 96394 ********************************************************************************************************* Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 0 58 123 -76 2.92 0 0 0 BCDscin_phy initStep 1 57.9 123 -76.2 2.89 0.029 0.232 0.232 BCDscin_phy eIoni ... 20 57.2 123 -77.7 2.6 0 0 1.91 BCDscin_phy initStep 21 57.2 123 -77.7 2.6 0.00264 0.0217 1.93 BCDscin_phy eIoni ... 180 51.8 125 -81 0.151 0 0 24.1 BCDscin_phy initStep 181 51.8 125 -81 0.149 0.00133 0.00464 24.1 BCDscin_phy eIoni ... Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 184 51.8 125 -81 0.149 0 0 24.1 BCDscin_phy initStep 185 51.8 125 -81 0.149 0 8.06e-05 24.1 BCDscin_phy Cerenkov 186 51.8 125 -81 0.149 1.06e-05 8.06e-05 24.1 BCDscin_phy Cerenkov 187 51.8 125 -81 0.149 9.33e-06 3.78e-05 24.1 BCDscin_phy Cerenkov 188 51.8 125 -81 0.149 5.78e-10 2.34e-09 24.1 BCDscin_phy Cerenkov 189 51.8 125 -81 0.149 2.48e-14 1e-13 24.1 BCDscin_phy Cerenkov 190 51.8 125 -81 0.149 1.37e-17 5.55e-17 24.1 BCDscin_phy Cerenkov 191 51.8 125 -81 0.149 1.37e-17 5.55e-17 24.1 BCDscin_phy Cerenkov 192 51.8 125 -81 0.149 1.37e-17 5.55e-17 24.1 BCDscin_phy Cerenkov 193 51.8 125 -81 0.149 1.37e-17 5.55e-17 24.1 BCDscin_phy Cerenkov ... 5059156 51.8 125 -81 0.149 1.37e-17 5.55e-17 24.1 BCDscin_phy Cerenkov The job does not progress amymore, and at this point I must kill the job. I am at a loss as to how to debug this. Material has constant optical Rindex = 1.58 defined from 3.44 eV to 2.38 eV. Scott