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Question Logical volume mass calculation -- non-identical results? 

Forum: Geometry
Date: 15 Feb, 2011
From: Michael H. Kelsey <Michael H. Kelsey>

I have a geometry with a number of duplicated components, each of which is relatively complex in internal structure, including sensitive detectors. In order to assign unique copy-numbers to each of the SDs across my whole geometry, I instantiate and place multiple copies, rather than doing parametrized placements or something similar.

To help support our engineering effort, I just added diagnostic output of each component's mass during the Construct() process. This gave me a bit of a surprise, as the supposedly "identical" objects (all generated via the same function, over and over again) have different masses!

For example, the innermost component is a cylindrical puck with flats taken off the sides. The code to construct it is:

  G4VSolid* zipShape = new G4Tubs("ZipDisk", 0, ZipRad, ZipThick/2., 0, 360*deg)
;

  G4Box* zipCutBox = new G4Box("ZipCutBox", ZipAxis1Len/2., ZipAxis2Len/2.,
                               (ZipThick+tolerance)/2.);
  zipShape = new G4IntersectionSolid("ZipShape", zipShape, zipCutBox);

  G4LogicalVolume* logicalZip =
    new G4LogicalVolume(zipShape, mat, "LogicalZip", 0, 0, 0);

where "mat" is typically germanium ("G4_Ge" from the NIST database).

Imagine my surprise when my diagnostic messages started printing:

  ZIP mass 0.598565 kg
  ZIP mass 0.597912 kg
  ZIP mass 0.59815 kg
  ZIP mass 0.598027 kg
  ZIP mass 0.598105 kg
  ZIP mass 0.597936 kg

and so on. All 84 values were different! All pretty close to 0.6 kg, as I'd expect for the dimensions, but not identical.

Does the G4LogicalVolume::GetMass() function have difficulty with Boolean solids? If so, is there some guidance on what problems to expect (e.g., are subtracted solids worse than intersections or unions?), and of what magnitude?

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1 None: RE: Logical volume mass calculation -- non-identical results?   (Asai, Makoto - 15 Feb, 2011)
1 None: Re: Logical volume mass calculation -- non-identical results?   (Mike Kelsey - 16 Feb, 2011)
(_ Question: Re: Logical volume mass calculation -- non-identical results?   (Kareem Kazkaz - 27 Aug, 2014)
(_ Feedback: Re: Logical volume mass calculation -- non-identical results?   (Michael H. Kelsey - 27 Aug, 2014)
2 None: Re: Logical volume mass calculation -- non-identical results?   (John Apostolakis - 16 Feb, 2011)
1 None: Re: Logical volume mass calculation -- non-identical results?   (Mike Kelsey - 16 Feb, 2011)
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