For a nucleus with A nucleons, including Z protons and N neutrons, a semi-empirical formula for the binding energy (E B) per nucleon is: E B A ⋅ ⋅ MeV = a − − b A 1 / 3 − − c Z 2 A 4 / 3 − − d ( N − − Z ) 2 A 2 ± ± e A 7 / 4 where the coefficients are given by: a = 14.0 ; b = 13.0 ; c = 0.585 ; d = 19.3 ; e = 33 .