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Idea Re: Use of NIST material database through GDML? 

Forum: Persistency
Re: None Use of NIST material database through GDML? (Jonathan Wrobel)
Re: Idea Re: Use of NIST material database through GDML? (Jonathan Wrobel)
Date: 28 Oct, 2014
From: Jonathan Wrobel <Jonathan Wrobel>

Also, I wanted to pass along some additional information that I received from Gabriele Cosmo and Witold Pokorski in case it helps others get on their way to using GDML (rephrased below):

Mixtures can be made using NIST materials, but it is necessary to define these materials using "fraction" instead of "composite", as the NIST materials are directly treated as materials. Example:

   <material formula="HDPE" name="HDPE" state="solid">
     <D value="0.95" unit="g/cm3"/>
     <fraction n="0.144" ref="G4_H"/> <!-- 4x H:1.008 amu = 4.004 amu-->
     <fraction n="0.856" ref="G4_C"/> <!-- 2x C:12.01 amu = 24.02 amu-->
   </material> <!-- Total: 28.052 amu-->

While this will still produce a validation error (e.g. G4GDML: VALIDATION ERROR! ID attribute 'G4_N'...), it is ok to disregard this error. It simply means that from the XML validation point of view the file is incomplete because it refers to materials that are not defined within the file, but everything works fine because Geant4 finds those materials in the NIST database. GDML does not allow materials to be defined as 'empty' objects... this however is not really a problem, it is still possible to exchange the GDML file conforming with the schema, if you export your geometry description; in this case materials will be exported with their full description down to isotope level.

To get information on the loaded materials, you can always use the UI command "/material/g4/printMaterial material-name" and this should give you the details of the material of interest.

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