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Forum: Geometry
Re: None overlapping volumes (sergi)
Date: 13 Nov, 2013
From: John Apostolakis <John Apostolakis>

Dear Esteban,

Please see below for a brief answer to your inquiry.

On Nov 13, 2013, at 4:24 PM, Esteban wrote:

> I want to build a quite complicated geometry and I need to know a few things about material's overlapping:
> - If I define two independent boxes (of different material) with the same mother volume and there is a overlaping between this two boxes, which is the material of the overlap volume?

This geometry is erroneous.  The results are not guaranteed.  In some conditions, the geometry modeler may not be able to give reliable results or may even crash in extreme or particularly pathological cases.

In case the overlap is small, ( such as those caused by imperfect rotation matrices related to numerical precision errors), then we expect that the code is robust, and will not crash.

But the material of *any* overlap region is never well defined.  It could be one or the other of the materials, depending on the history of the particle, the direction the original particle entered the first volume it encountered and many other factors.

In other words: avoid this, if at all possible, and define your geometry correctly.  For example use the G4SubtractionSolid to take out any region of other volume from one of them.

> - If the two materials from the daughter's volumes are the same, is it a problem for the simulation this kind of overlaps?

The behaviour of the geometry modeler cannot be guaranteed in this case either.  It may give erroneous results, in particular for macroscopic overlaps.

Use the overlap checking tools to ensure that your geometry is OK up to a reasonable tolerance - of order say 10-100 microns if it the size of your setup is in the region of meters, and you do not have more stringent precision requirements due to your application.

> - I assume that if I put a daughter volume inside a mother volume, the material of the daughter is not the mother's material but is the daughter material, right?

You must give the daughter volume a material. ( It cannot be null. ) So that is the one that will be used.

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1 Ok: Re: overlapping volumes   (Esteban - 13 Nov, 2013)
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