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Neutron scattering lengths and cross sections of the elements and their isotopes have been taken from NIST.
Enter a composition as a molecular formula of elements or isotopes. For example, basic elements might be H, Fe or Si, etc. A molecular formula of elements might be H4-N2-C3, which corresponds to a molecule with 4 Hydrogen atoms, 2 Nitrogen atoms and 3 Carbon atoms. Each element in a molecular formula is followed by the number of the atoms for that element, specified without a hyphen, because each element is separated from other elements using a hyphen.
The number of atoms can be integer or float, but must start with a digit, e.g. 0.6 is fine but .6 is not. This can be used to set elemental ratios within a chemical composition. For example 95.1% Vanadium 4.9% Niobium can be expressed as V0.951 Nb0.049. Warning: Using this representation will calculate all properties except for SampleNumberDensity which must be set manually if required
Isotopes may also be included in a material composition, and can be specified alone (as in (Li7)), or in a molecular formula (as in (Li7)2-C-H4-N-Cl6). Note, however, that No Spaces or Hyphens are allowed in an isotope symbol specification. Also Note that for isotopes specified in a molecular expression, the isotope must be enclosed by parenthesis, except for two special cases, D and T, which stand for H2 and H3, respectively.
Each of the cross sections () are calculated according to
where . A concrete example for the total
cross section of D2 O
The number density is defined as
It can can be generated in one of three ways:
where is the mass density,
is the Avogadro constant, and
the relative molecular mass.
The low- limit of
is
where
is called the normalized Laue term
The data used in this algorithm comes from the following paper.
Category: Concepts