Semi-empirical Mass Formula
Carl F. von Weizsacher, 1930's
Assume that nucleus is a collection of interacting particles in the form of a liquid drop.
Semi-empirical ® the numerical values
Binding energy = Volume term + Surface term + Coulomb term + Symmetry term + Pairing term
aV = 14 MeV Binding energy is approximately the sum of all interactions between nucleons due to short range nature of nuclear force.
aA = 13 MeV Surface nucleons do not have saturated interactions. Contribution proportional to R2, hence A2/3 dependence.
Coulomb term Change in energy due to adding a charge dq to a solid sphere of radius r. Self energy is subtracted, yielding Z(Z-1) dependence.
aS = 19 MeV Without Coulomb force, binding energy is a minimum for Z = N. Note that (N-Z)2 >0
0 for odd
-D for odd-odd
D = 33MeV*A-3/4