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Forum: Processes Involving Optical Photons
Re: Question case when child volume not entirely inside mother volume (Athreya Shankar)
Re: More Re: case when child volume not entirely inside mother volume (Athreya Shankar)
Date: 03 Jul, 2012
From: Gumplinger Peter <Gumplinger Peter>

Hi Athreya,

I didn't understand the paragraph just before the following (but it doesn't matter). The important point is that geant4 does not allow for daughter volumes to protrude out of the mother volumes!!!

> However, this does not enable me to keep the fibers half protruding from
> the scintillator - I read that geant4 does not allow for daughter
> volumes to protrude out of the mother volumes. So, is the only way I can
> achieve this is by using G4SubtractionSolid to remove semi-circular
> portions on the slab surface and then place the fibers there (their
> mother volume now being "world") ?

Yes, that is one solution. Another solution is to make your fibers of two halves. One half below the surface, placed inside the daughter, the other half outside placed inside the world volume. You make the two halves from the same material, of course. Now, the disadvantage is that tracking photons inside the fiber will see this artificial boundary but not much is lost because the G4OpBoundaryProcess skips immediately when the media or the index of two media are the same. Still, the number of steps taken are doubled.

It is not wrong for you to adopt the solution in the bug report, for G4Navigator, but it does not pertain to your immediate situation or issue. The suggested fix has not been approved by the G4 experts yet but it sure works quite well for me.

Peter

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