The "Packing Fraction" is the fraction of volume in a crystal structure that is occupied by atoms.
Applicable units are those of quantitykind:PackingFraction
http://en.wikipedia.org/wiki/Atomic_packing_factor
The "Packing Fraction" is the fraction of volume in a crystal structure that is occupied by atoms.
$f = \frac{\Delta_r}{A}$, where $\Delta_r$ is the relative mass excess and $A$ is the nucleon number.
http://www.iso.org/iso/catalogue_detail?csnumber=31895