Rutherford's estimate for the maximum radius of a nucleus  :  

Mass and energy :  E = m c²

The mass of the separated nucleons is always greater than the mass of the combined nucleons in the nucleus.

The mass defect, Dm, of a nucleus is defined as the difference between the mass of the separated nucleons and the combined mass of the nucleus

The binding energy of a nucleus is defined as the work done on the nucleus to separate it into its constituent neutrons and protons.

     The binding energy, B.E. ,equals the energy equivalent of the mass defect

     B.E. = (Dm) c²

     1 u = 931 MeV