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Question UnionSolid Strange behaviour 

Forum: Geometry
Date: 16 Jan, 2014
From: Rafayel Paremuzyan <Rafayel Paremuzyan>

Dear experts,

I meet with a strange behaviour with UnionSolid.

In order to  obtain a target, one end of which is spherical, I did a Union Solid a half sphere (phi:0-360, theta:0-90) with a cylinder.
Visually this looks correct (see attached figures), and z axis is the central axis of target.
However when particles were produced in the (x=0:y=0) inside the end-cap part of the target, then it seems that 
particles doesn't interact at all with the target. 

Then I tried to make a unionsolid of the cylinder with a full sphere (phi:0-360, theta:0-180), which in principle should give the same thing.
In this case, particles start to interact.

We concluded this from two things, 
1st: is visualisation, where one can see only production point in the 1st figure (half_sphere case),
and 2 points inside the target (full Sphere case). Figures are nor good quality, but if one zoom it, can see yellow interaction points.

2nd fact is the output from Geant4 with /tracking/verbose 3

*************************Output from Half-Sphere case********************************
      -----------------------------------------------------------------------
        StepPoint Information               PreStep            PostStep
      -----------------------------------------------------------------------
         Volume Name         :              expHall             expHall


*************************Output from Full-Sphere case********************************
      -----------------------------------------------------------------------
        StepPoint Information               PreStep            PostStep
      -----------------------------------------------------------------------
         Volume Name         :          target_phys         target_phys


It show different volumes for production point from these two cases.

In order for you to read it easily, I reproduced this geometry in N01 example,
where all default geometry was deleted, and this target was built.

So the only difference between two figures is 
lines 98/99 of src/ExN01DetectorConstruction.cc
 I put source codes in this link https://userweb.jlab.org/~rafopar/Geant4/N01_v3.tar

This issue I meet with Geant4.9.5.2, however I was able to reproduce it in a latest 10.00 version.
I also tried with heavy materials e.g. lead (with all EM process included), and it showed same behaviour for half-sphere case.

Rafo

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/01/16/08.48-54734-Half_Sphere.png
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/01/16/08.48-66941-Sphere.png

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1 None: Re: UnionSolid Strange behaviour   (Tatiana Nikitina - 18 Feb, 2014)
(_ None: Re: UnionSolid Strange behaviour   (Rafayel Paremuzyan - 19 Feb, 2014)
(_ None: Re: UnionSolid Strange behaviour   (John Apostolakis - 19 Feb, 2014)
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