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Question Re: Can I have a shared surface between mother and daughter volume? 

Forum: Geometry
Re: Question Can I have a shared surface between mother and daughter volume?
Date: 27 Oct, 2015
From: <Fabio_Zeiser>

Dear Peter,

thanks a lot for you informative answer. I had a look at some other posts
again, and I wondered whether one of them seemed to be in conflict to your
answer.

If I understand your answer correctly, you say that there is no problem with
shared surfaces between mother and daughter volumes.

When reading the following post, I got the impression, that this was only true
if the surfaces are along planes in the X,Y or Z axis. Am I wrong or has maybe
something changed in the implementation in Geat4 in the meantime?
 
From this forum here:
Re: Question Daughter volume sharing a surface with its mother (Andrea Conti)
Date: 07 Dec, 2014
From: Michael H. Kelsey <Michael H. Kelsey> 

http://hypernews.slac.stanford.edu/HyperNews/geant4/get/geometry/1384/1.html?inline=-1

>> But this way the daughter will share a surface with the mother (that is,
>> the mouth of the hole, on the same plane as the host material's surface)
>> and nobody addressed this problem: is it acceptable ? Or are there going
>> to be problems with the consistency of the geometry ?
> 
> If the surfaces are simple planes along X, Y or Z, then you can do 
> this safely as the coordinate of the surface will be floating-point 
> identical in the two cases. If the surface (even a plane) is not 
> exactly on-axis, you are likely to have situations where the computation 
> of the two surfaces do not coincide. In these cases, particles can get 
> "trapped" between the surfaces, or you can have unexpected boundary
> interactions, etc. This is why we generally discourage shared surfaces, 
> because the cases where they are safe are quite limited. 

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