Atom Fraction

Support atom fractions.

Given the following, what is the atom density? adensity = 13.546 afracs{ afrac ( hg-196 ) = 0.00146535 % atom fraction sum to one afrac ( hg-198 ) = 0.09839167 % atom fraction sum to one afrac ( hg-199 ) = 0.16732845 % atom fraction sum to one afrac ( hg-200 ) = 0.23027355 % atom fraction sum to one afrac ( hg-201 ) = 0.13204386 % atom fraction sum to one afrac ( hg-202 ) = 0.30064148 % atom fraction sum to one afrac ( hg-204 ) = 0.06985561 % atom fraction sum to one } TODO - capture the conversion formula.