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Forum: Geometry
Re: Question Holes in a triangular pattern in layered strucutre (Daniel M)
Date: 11 Mar, 2015
From: John Apostolakis <John Apostolakis>

Dear Daniel,

In general, it is better to avoid using Boolean volumes with many constituents if possible, due to their complication (leading to some reduction in robustness) and run-time costs.

Solution 1

In this case the simplest way I see to construct each layer out of several copies (placement physical volumes), each of which is a as simple Boolean solid.  If you cut up the layer (in gray in your picture) into elementary sub-volumes, then your boolean can be created by two subtractions

or potentially three subtractions if you use a slightly larger elementary volume:


In this case, the 'hole' volumes can be created as a single volume each, which allows them to be associated with one sensitive detector.
This is likely to be the simplest way to construct your setup, and associate it with logical volumes, if the layers are not sensitive.

Solution 2

In the setup you describe it should be possible to create the holes as daughter volumes of each rectangular volume.  You will need to create a different logical volume for each of these holes, (one for the ones in the top right corner, one for all the volumes next to its right etc) so that you can associate one sensitive detector with it.
This simple solution works if the layers are of the same thickness.

You do not mention whether this is the case. If not, you would need to create different logical volumes - but my understanding is that you could associate the same sensitive detector with the ones which belong to the same physical hole.

I hope that these suggestion will help.

Best regards,
John Apostolakis,  PH Department, CERN
SFT (SoFTware for Experiments) Group,

On 11 Mar 2015, at 09:52, Daniel M <<>> wrote:

*** Discussion title: Geometry


I have a question about the best way of going about creating a layered
structure of eight (8) layers with alternating materials which also has
cylindrical holes in them in a equilateral triangular pattern, much like
the one you would see in a gas electron multiplier. My first approach
was to make a rectangular box from which 8 cylinders were removed one at
a time from previous resulting boolean solid (see attached image) and
then replicate it to a desired area (in x and y directions, and then
"stacking" such boxes on top of eachother to create the full geometry.
This results in a coumpound boolean solid which i have a feeling isn't
very cheap.

Since i want to be able to gather energy deposited at x,y,z in such
structure, including the holes which are intended to be filled with a
gas mixture, using a sensitive detector i guess i need to be able to
identify the holes somehow, which this geometry probably wont allow.

How do i make something similiar which allows me more freedom to pick
out individual holes (or atleast include all of them) which also go
through several layers?

My gut tells me using a clever parametrisation could be used for this,
but I'm not sure how to do that given that i'm quite new to geant4.

I hope that the problem is clear, please let me know if you need further


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1 None: Re: Holes in a triangular pattern in layered strucutre   (Daniel M - 11 Mar, 2015)
(_ None: Re: Holes in a triangular pattern in layered strucutre   (John Apostolakis - 11 Mar, 2015)
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