Packing fraction is a term used in nuclear physics and chemistry to describe the degree of increase or decrease of the total mass present in an assemblage of nucleons or atoms, respectively. It is a way of expressing the variation of isotopic mass from the whole mass number (atomic mass) .
Parity, on the other hand, is a concept in nuclear physics that refers to the symmetry of a nucleus with respect to spatial inversion. A nucleus is said to have even parity if it remains unchanged under spatial inversion, and odd parity if it changes sign under spatial inversion.
