| Summary: | Mulitscattering of Ions form a ringstructure | ||
|---|---|---|---|
| Product: | Geant4 | Reporter: | christoph.gruener |
| Component: | processes/electromagnetic | Assignee: | Vladimir.Ivantchenko |
| Status: | ASSIGNED --- | ||
| Severity: | minor | CC: | christoph.gruener, daren.sawkey |
| Priority: | P4 | ||
| Version: | 10.6 | ||
| Hardware: | Other | ||
| OS: | Linux | ||
| Attachments: |
Plot of Pb206 distribution in x-y plane after first simulation step
Plot of Pb206 distribution in x-y plane after first simulation step |
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Created attachment 863 [details]
Plot of Pb206 distribution in x-y plane after first simulation step
Comment on attachment 862 [details]
Plot of Pb206 distribution in x-y plane after first simulation step
This was the wrong png
Hello, this situation is expected. Even in option4 configuration of EM physics we cannot guarantee good results for all cases and circumstances. What you are reporting is likely a situation that by default ion make only one step. Multiple scattering is called at each step, so you see that it is active but in reality your problem is in one step simulation for low energy ion. It is problem of step limitation. Both ionisation and multiple scattering does not provide more number of steps. In order to force an ion to more number of steps one can use UI command /process/eLoss/StepFunctionIons 0.01, 0.1 um here I propose to decrease both values of the Step function in 10 times. Alternatively it is possible to add step limiter for volume of interest. VI Thank you for your time and your reply. I can also observe this ring for a starting energy of 10 GeV. (With 10 GeV 40+ steps are simulated until the ions are stopped.) I thought that, in one step, multiscatterin scatters each ion differently and not all by the same value? Therefor already after the first simulation step, all the ions should be scattered in different directions with different deviations from their initial path in the Z-direction. Probably I misunderstood it? Can you suggest a starting value this ring should not be visible when interrupting the simulation after the first simulation step? I tried to use the StepLimiter too. With a limit of 10 nm and a starting energy of 2 MeV I also was able to see the ring in the first step. Hello Christoph, can you, please, try out : /process/msc/MuHadLateralDisplacement true VI |
Created attachment 862 [details] Plot of Pb206 distribution in x-y plane after first simulation step I recently had some strange behavior when using multiscattering for low energetic ions. I use G4EmStandardPhysics_option4. I shoot Pb206 with a kinetic energy of 5 MeV inside G4_Si in Z-direction. I then extract the changes in each simulation step of the Pb206 ion applied by msc from the logfile. (i used the maximal tracking/verbose value) The extracted spatial data after the first simulation step can be seen in the appended png. What I can observe: All Pb206 will be transported in z-direction by the Transportation Process. All Pb206 get shifted by the same amount normal to the z-direction by msc (the shifts differ only at a scale of ~1e-14) For 5 MeV the Pb206 ions will be stopped after one simulation step by G4ionIon. A ring can also be seen if Pb206 is not stopped after first step. I tested it with 10 MeV, 100 MeV and 1,000 MeV. The diameter of the ring was smaller for this energies but was still observable. It also seems like this ring structure can be observed in further simulated steps too. Is Multiscattering calculating just one scattering angle per energy for the tested energies? Is my observation correct and if yes, is this intended?