# Why does stability come from binding energy and not mass

The mass of a nucleus is given by: $$Mc^2=n M_n c^2+zM_pc^2-B(z,n)$$ And we were told that nuclei want to maximise the binding energy per nucleon. However, I don't see why they don't want to minimise mass per nucleon, that seems more logical to me.

• $E = mc^2$, maximize bounding energy $\equiv$ minimize mass ? – patta Apr 17 at 8:47
• They are almost the same, but the small difference in the mass of the proton and neutron do change things slightly – Toby Peterken Apr 17 at 8:58
• ok, now I understand the problem; why all neutrons do not decay to proton? – patta Apr 17 at 9:11
• I understand that, you have the asymmetry term. My question is, why is stability at the maxima of $B$ not at a minima of $Mc^2$ (I doubt they always coincide) – Toby Peterken Apr 17 at 15:07