| Summary: | Volume assignment with multiple-scattering does not correspond to point for a very small volume | ||
|---|---|---|---|
| Product: | Geant4 | Reporter: | Pedro.Arce |
| Component: | processes/electromagnetic | Assignee: | Vladimir.Ivantchenko |
| Status: | RESOLVED FIXED | ||
| Severity: | major | CC: | Gabriele.Cosmo, John.Apostolakis |
| Priority: | P4 | ||
| Version: | 9.3 | ||
| Hardware: | PC | ||
| OS: | Linux | ||
| Attachments: | events visualisation | ||
The fact that the problem occurs only when multiple-scattering is involved, suggests that is cannot be a pure geometry problem. PS: in order to make sure that the point is indeed outside the volume, you should increase the precision of the output to show more mantissa... Indeed I also found eBrem or eIoni processes, although it is true that msc is the first one. For example (with a geometry 0. 10.*um 125.*um)
Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName
0 0 0 0 3 0 0 0 NanoPin initStep
1 0.00928 0.00372 0.057 2.9 0.0954 0.0643 0.0643 NanoPin msc
2 -0.00233 0.0625 0.047 2.77 0.139 0.0643 0.129 NanoPin msc
3 -0.0059 0.0959 -0.00318 2.66 0.105 0.0643 0.193 NanoPin msc
4 0.0112 0.135 -0.0459 2.55 0.113 0.0643 0.257 NanoPin msc
5 0.0602 0.148 -0.0778 2.31 0.242 0.0643 0.322 NanoPin msc
6 0.0908 0.198 -0.0769 2.22 0.09 0.0643 0.386 NanoPin msc
7 0.074 0.208 -0.132 2.11 0.103 0.0643 0.45 NanoPin msc
8 0.0976 0.203 -0.186 2.02 0.0917 0.0643 0.514 NanoPin msc
9 0.13 0.16 -0.207 1.85 0.169 0.0643 0.579 NanoPin msc
10 0.158 0.158 -0.256 1.78 0.0765 0.0643 0.643 NanoPin msc
11 0.181 0.209 -0.268 1.68 0.095 0.0643 0.707 NanoPin msc
12 0.165 0.262 -0.26 1.59 0.0954 0.0643 0.772 NanoPin msc
13 0.133 0.303 -0.241 1.41 0.171 0.0643 0.836 NanoPin msc
14 0.14 0.33 -0.193 1.31 0.101 0.0668 0.903 NanoPin msc
15 0.144 0.352 -0.139 1.2 0.115 0.0731 0.976 NanoPin msc
16 0.169 0.38 -0.0917 1.1 0.101 0.0799 1.06 NanoPin msc
17 0.136 0.424 -0.0644 0.986 0.112 0.0855 1.14 NanoPin msc
18 0.108 0.457 -0.11 0.842 0.144 0.0958 1.24 NanoPin msc
19 0.155 0.431 -0.136 0.655 0.187 0.104 1.34 NanoPin msc
20 0.164 0.457 -0.153 0.0902 0.133 0.0474 1.39 NanoPin eBrem
21 0.164 0.457 -0.154 0 0.0902 0.0152 1.4 NanoPin eIoni
P.S: you can see that the tube extends from -0.125 to 0.125 in Z, and 0.01 in radius, so it is clearly outside. This can also be seen looking at the scattering points in the figure I attached
The problem sems to be the multiple scattering model. With WentzelVI and GoudsmitSaunderson ut does not appear, while with Urban90, Urban92 and Urban93 it does. Hello Pedro, I need tar file with the problematic application. In fact, I not yet understand what it is and is there real problem or all is a problem of the printout. VI Hi Vladimir, You just have to take examples extended/persistency/P03 and replace g4geom.txt by :ROTM RM0 0. 0. 0. :VOLU world BOX 1.*um 1.*um 1.*um G4_Galactic :VIS world OFF :VOLU NanoPin TUBE 0.*nm 250./26.*nm 250./2.*nm G4_Ta :PLACE NanoPin 1 world RM0 0. 0. 0. :COLOR NanoPin 0 0 1 and run.mac by /tracking/verbose 1 /run/initialize /gun/particle e- /gun/energy 30 keV /run/beamOn 10 I have also tried with geant4.9.4.beta01. The visualisation confirms that the track is outside the tube, while the printing says it is in the tube volume. Hi Pedro, The problem connect with not correct value of safety, so should be discussed with geometry working group members. Your example emphasize the problem which has low probability in other geometries. VI I made an inspection of the safety in the Tubs - and the estimation appears valid. The problem appears to be due to Multiple Scattering rounding down the displacement to the value of the safety. Because of the cylinder geometry this means that the point arrives at the surface with high probability (if the original endpoint is on the axis.) As the Multiple Scattering does *not* change the volume ( to keep it consistent ), the Navigation after this is confused. This is a preliminary conclusion - but an improvement of the relevant code is being prepared. The fix path Geant4 testing and will appear in the next reference version. |
Created attachment 84 [details] events visualisation I build a very small geometry with the text file utility: :ROTM RM0 0. 0. 0. :VOLU world BOX 1.*um 1.*um 1.*um G4_Galactic :VIS world OFF :VOLU NanoPin TUBE 0.*nm 250./26.*nm 250./2.*nm G4_Ta :PLACE NanoPin 1 world RM0 0. 0. 0. :COLOR NanoPin 0 0 1 Then I send an electron of 30 keV : /gun/particle e- /gun/energy 30 keV /tracking/verbose 1 /run/beamOn 10 It tells me often that msc happens in the NanoPin volume, while the coordinates are outside: Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 0 0 0 0 0.03 0 0 0 NanoPin initStep 1 7.92e-06 -5.46e-06 8.12e-05 0.0299 7.73e-05 9.97e-05 9.97e-05 NanoPin msc 2 3.04e-05 -1.66e-05 0.000168 0.0299 1.73e-05 9.97e-05 0.000199 NanoPin msc 3 5.49e-07 -6.57e-05 0.000239 0.0295 0.000399 9.97e-05 0.000299 NanoPin msc 4 -7.1e-05 -9.48e-05 0.000286 0.0295 4.89e-05 9.97e-05 0.000399 NanoPin msc 5 -0.000139 -0.00012 0.00034 0.0293 0.000199 9.97e-05 0.000499 NanoPin msc 6 -0.000182 -0.000195 0.000368 0.0287 0.000514 9.97e-05 0.000598 NanoPin msc 7 -0.00021 -0.00026 0.000423 0.0264 0.00234 9.97e-05 0.000698 NanoPin msc 8 -0.000173 -0.000341 0.00042 0.0249 0.00152 9.97e-05 0.000798 NanoPin msc 9 -0.000185 -0.000428 0.000412 0.0237 0.00114 9.97e-05 0.000897 NanoPin msc 10 -0.000137 -0.000493 0.000445 0.021 0.00275 9.97e-05 0.000997 NanoPin msc 11 -0.000126 -0.000577 0.000459 0.0188 0.00224 0.000101 0.0011 NanoPin msc 12 -0.000208 -0.000561 0.000419 0.0176 0.00116 0.000115 0.00121 NanoPin msc 13 -0.000274 -0.000537 0.000378 0.0164 0.00118 9.97e-05 0.00131 NanoPin msc 14 -0.000324 -0.000593 0.000355 0.0146 0.00184 9.97e-05 0.00141 NanoPin msc 15 -0.000377 -0.000621 0.000303 0.0132 0.00142 0.000106 0.00152 NanoPin msc 16 -0.00035 -0.000563 0.000268 0.0125 0.000633 9.97e-05 0.00162 NanoPin msc 17 -0.000322 -0.000519 0.000218 0.0116 0.000896 9.97e-05 0.00172 NanoPin msc 18 -0.000309 -0.000543 0.000282 0.0112 0.000437 0.000101 0.00182 NanoPin msc 19 -0.000249 -0.00058 0.000258 0.0104 0.000824 0.000115 0.00193 NanoPin msc 20 -0.000188 -0.000608 0.000268 0.00838 0.00199 0.000106 0.00204 NanoPin msc 21 -0.000222 -0.000562 0.000266 0.00773 0.000645 9.97e-05 0.00214 NanoPin msc 22 -0.000218 -0.000554 0.000239 0 0.00773 0.000298 0.00244 NanoPin eIoni If a use a gamma it is always right 0 0 0 0 0.03 0 0 0 NanoPin initStep 1 0 0 0.000125 0.03 0 0.000125 0.000125 world Transportation 2 0 0 0.001 0.03 0 0.000875 0.001 OutOfWorld Transportation = If I change the energy to 3 MeV and the dimensions of the tube to 0. 10.*um 125.*um it still happens, while if I change the dimensions to 0. 100.*um 125.*um I do not see any problem in 100 events. The visualisation confirms that msc is happening outside the tube.