Natural elements description
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PyDrag is primarly based on a set of IRSN calculation procedures, written in CLE-2000. An extract of this reference can be found on this GitHub repository Therefore, these procedures have been used as the main reference for the PyDrag development, especially on the non-regression tests done by developers. This issue highlights a known approximation that the user should be aware of.
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The description of natural elements made in PyDrag is following this pattern :
- if the natural element is available in the nuclear data library, its "natural" molar mass is used
- if not, the molar mass is calculated as the weighted sum of its isotopes
However, the IRSN reference does not follow this exact algorithm : some molar mass of natural elements are equal to the molar mass of one of its isotope.
This leads to some differences on isotopic composition of mixtures between PyDrag and the reference (as the molar masses of each isotopes are used in the renormalization process).
For non-regression purpose, these approximations are kept during the current developpement of PyDrag, as a list of exceptions directly written in the source code.