Mass number & Atomic Number of the most stable member of an isobaric series
A = Mass number; Z= Atomic Number = Number of protons present in the nucleus
This equation has been deduced from the semi-emperical mass equation : mN = Z.mP + (A-Z)mN - (NBE)/931. NBE is the total nuclear binding energy. The above equation relates the mass number and the number of protons of a stable nucleus. With this equation, one can obtain the most stable nuclide corresponding to a certain mass number. For example the most stable nuclide with A=180 would have 72 protons in its nucleus.