|Message: Re: 1-2 MeV protons are NOT scattered, 3 and more MeV are scattered||Not Logged In (login)|
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On Sun, 22 Oct 2006, Gorelick Sergey wrote: > *** Discussion title: Hadronic Processes > Email replies to PublicHyperNews@slac.stanford.edu must include: > In-Reply-To: <"/hadronprocess/588"@geant4-hn.slac.stanford.edu> > Subject: ...change this to be about your reply. > > Hello, > > I am trying to simulate passage of proton beam through a series of > apertures. I got some weird results using Geant4.8.0.p01. When a proton > has relatively low energy (some 1 MeV to 2 MeV) the particle goes in the > matter in a rather straight path without any scattering or changing > direction, even in the end of the range. A result of such proton-passage > (1 and 2 MeV proton) through Tantalum can be seen on the image: > > http://img.photobucket.com/albums/v140/samppa/Geant4/range1MeV.jpg > > http://img.photobucket.com/albums/v140/samppa/Geant4/range2MeV.jpg > > However, when the energy is risen, the proton path in the matter starts > to resemble the real, or the more physical path, with significant > scattering and broadening in the end of the range. An example of such > "more real" results are shown in the images below for 3, 4, 5 and 6 MeV > protons in Tantalum: > > http://img.photobucket.com/albums/v140/samppa/Geant4/range3MeV.jpg > > http://img.photobucket.com/albums/v140/samppa/Geant4/range4MeV.jpg > > http://img.photobucket.com/albums/v140/samppa/Geant4/range5MeV.jpg > > http://img.photobucket.com/albums/v140/samppa/Geant4/range6MeV.jpg > > To simulate passage of proton in matter I used > > //contruct proton as a baryon > G4Proton::ProtonDefinition(); > //used physics for the proton > #include "G4hIonisation.hh" > #include "G4MultipleScattering.hh" > > Which is the initiated by: > > pmanager->AddProcess(new G4MultipleScattering,-1, 1,1); > pmanager->AddProcess(new G4hIonisation, -1, 2,2); > > Now, the ranges of the protons in Tantalum seem to be OK, as they > correlate very well with the values obtained from SRIM, but the strange > behavior of 1-2 MeV protons that are not scattered and go straightly in > the matter until they are completely stopped (and the range is > well-correlated with the SRIM results) are very confusing and I cannot > find out what could be the problem. Please, help me find out what the > problem is and how to resolve it. Maybe, it could be related somehow to > the default cut values, but I am not sure. > > Thank you. > Hello Sergey, Thanks for the intresting plots. The problem you is demonstrating connect with fact that simulation has finite step. At the last step when proton stop we do not sample lateral displacement and multiple scattering in order to save some CPU. From our point of view there is no much sence to do that, because in G4 each step is inside one and only one volume, so independently where proton stop it will be stopped in the volume where it is started, so dose calculation will provide the same result. If it is needed to have more detailed description of proton trajectory one need to use smaller cut value and/or extra step limitation. In particular, in this case it is worce trying to define low cut and step limit inside the foil on level 1 um. VI
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