  The key numbers useful for describing the fission process are the mass number
of the primordial cluster of the fissioning system and the magic mass numbers
82 and 126 of the nascent light and heavy fragments. The mean mass number and
the mean atomic number of the light fragments are linked to the mass number and
to the atomic number of the primordial cluster by simple relationships. The
value 54 of the mean atomic number of the heavy fragments is predicted by the
nucleon phase model.
