Positron sometimes says it's 'annihil'ating but do not do so and continue to exist (and no two 511-keV gammas are emitted). At first I observed such events in my own simulation (with either of QBBC or FTFP_BERT+G4EmLowEPPhysics()) based on basic/exampleB1 of geant4-v11.0.2. Then we confirmed that such events also occur in pristine/unmodified basic/exampleB1 of geant4-v11.1.1. For example, 6-MeV gamma primary (as in run2.mac of the example) sometimes yields the following strange positron track, which was observed with exampleB1 of geant4-v11.1.1 by setting `/tracking/verbose 1`: ********************************************************************************************************* * G4Track Information: Particle = e+, Track ID = 3, Parent ID = 1 ********************************************************************************************************* Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 0 5.491 cm 4.39 cm 14.25 cm 3.876 MeV 0 eV 0 fm 0 fm Envelope initStep 1 5.526 cm 4.625 cm 14.65 cm 2.89 MeV 936.3 keV 4.688 mm 4.688 mm Envelope eBrem 2 5.64 cm 4.68 cm 14.91 cm 2.42 MeV 470.3 keV 2.952 mm 7.641 mm Envelope annihil 3 5.7 cm 4.695 cm 15 cm 2.272 MeV 147.4 keV 1.145 mm 8.786 mm Envelope Transportation 4 6.887 cm 4.341 cm 16.29 cm 2.264 MeV 2.074 keV 1.788 cm 2.667 cm World eIoni 5 8.364 cm 3.989 cm 18 cm 2.261 MeV 2.863 keV 2.289 cm 4.956 cm World OutOfWorld That is, the positron was said to be 'annihil'ating but didn't do so (and no new gamma tracks were created). The frequency of occurrence of such events in exampleB1 is 150-200 times for 10^8 6-MeV primaries. Such events occur in single-threaded as well as multi-threaded versions (with single- or multi-thread runs) of G4. I think something is wrong/strange... Discussion in the forum: https://geant4-forum.web.cern.ch/t/positron-annihilation-w-o-two-gammas-and-even-annihilating/10418/22 Thanks in advance. Kazuyoshi
Hello, thank you for this post. In Geant4 it is allowed to define a track step by some process but before sampling of final state PostStep some conditions are checked and a decision to continue tracking may be made. One of the reasons for that - so called "integral approach for tracking", which allows to take into account dependence of a cross section on energy due to energy loss of a particle at the step. So, likely what you observe is normal, with low probability this may happens. Let us think how to double check this assumption before closing this bug report. For example, you may use UI command: "/process/em/integral false". If in such run this type of events does not happens anymore, then my explanation is correct. Vladimir
Hello, It is understood that it is a normal situation, so nothing to fix. Think you for making bug report indeed, because unclear points should be resolved. VI
