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Hi Peter, You have made everything clear! thanks a lot! Cheers. Michele. 2013/5/15 Gumplinger Peter <firstname.lastname@example.org> > > *** Discussion title: Processes Involving Optical Photons > > Hi Michele, > > > suppose that you want to propagate optical photons through two > > consecutive volumes, that are put in contact each other (they belong to > > the same mother volume). In general I know that some issues can be > > caused by decimal precision loss in volume definition if you don't keep > > them slightly spaced. > > I don't know what codes you are talking about, but in Geant4, you have > to absolutely put the two volumes abut next to each other!!! There must > not be any space between them. > > > I think it's a quite common problem, but it's not > > clear to me how and if propagation of optical photon is affected by > > that. > > If the G4Navigator 'detects' that it is leaving the daughter into the > mother (the space between your two volumes) you'll get the index of > refraction of the daughter and the mother; e.g. you'll have a small gap > made up of the mother's material. > > > I was wondering if in Geant4 there any options to set volume boundary > > crossing precision to say: "if two volumes are closer that X*mm then > > they really share a surface". In principle this could definitely avoid > > any problem with optical photon propagation between different volumes. > > Or Geant4 has a different approach for this kind of problems? > > One way to overcome issues with two volumes 'touching' each other is to > make one volume the daughter of the other - if that's possible within > your geometry definition. In that case, the boundary crossing is unique. > A track leaving the daughter will enter the mother and a track > encountering the daughter will go in. As well, when the daughter shares > a surface with the mother, the G4Navigator will determine that the track > - coming from the outside of the mother - will go directly into the > daughter. > > If you want to know what is the navigation tolerance for surfaces in > your simulation, print: > > G4cout << "Computed tolerance = " > > << G4GeometryTolerance::GetInstance()->GetSurfaceTolerance()/mm > << " mm" << G4endl; > > See: > > > http://www-geant4.kek.jp/lxr/source/global/management/src/G4GeometryTolerance.cc#L107 > > The default is 1E-9*mm > > Peter > > ------------------------------------------------------------- > Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or > unsubscribe) at: > > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/opticalphotons/507/1.html > -- Michele Gabusi UniversitÓ degli Studi di Pavia Dipartimento di Fisica Nucleare e Teorica via A. Bassi 6, Pavia Tel. +39 0382 987593 (Office) Tel. +39 0382 987637 (Lab) [ MIME part of type text/html without a name stripped ]