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It is all doable with simple shapes. How do I place inner/outer vacuum if I have tessellated solids from CAD? iSveta > On Apr 17, 2016, at 6:30 PM, Michael H. Kelsey <email@example.com> wrote: > > > *** Discussion title: Geometry > >> On Sun, 17 Apr 2016 19:28:21 GMT, Svetlana Shasharina wrote: >> >> I have been doing simple test runs calculating fluence of gammas on a >> hollow Al sphere irradiated by electrons. To my surprise, the gamma >> fluence to the sphere was not zero. I assume now that gammas come from >> the sphere from the inside and get into the sphere again (if I make the >> sphere solid, the fluence becomes 0). >> >> If I add Va volumes just outside of the sphere (1mm off compared to 30cm >> radius of the sphere) and just inside the sphere (1mm off again), I see >> that almost all gammas coming from the sphere enter the vacuum volumes >> (the fluence from the sphere is close to the sum of fluences to the >> vacuum shapes). The number is the same as in the simulation with just Al >> sphere. If I make vacuum volumes match the sphere radius, the gamma >> fluence comes to zero. >> >> Is it ok to make one shape have outer radius be equal to the inner >> radius of another shell? Why the results are so different compared to >> the case with a little offset? > > How are you counting fluence? From what you describe, it sounds like > you're using a stepping action to count boundary crossings from World > into your Al sphere. That would exactly explain what you see: the hollow > sphere by itself has _World_ in the inner hollow, because that hollow > isn't part of the aluminum ball. When you place some other material into > that hollow region, it's a sibling volume to the Al ball, with a > possibly matching surface. > > To avoid your counting problem without having to write different code, > you can do what you've done, or you can make your Al sphere solid, and > then place another vacuum sphere inside it as a daughter volume. > > -- Michael Kelsey > > ------------------------------------------------------------- > Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at: > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/geometry/1466/1.html >