Hi, there. I was trying to prove a relation about the most stable situtation for a nucleus. According to the semiempirical mass formula, the less mass a nuclei has, the most binding energy has and, of course, the most stable is. I followed the "liquid drop model" (Weizsacker) for the binding energy, and I found where nuclear mass becomes minimum. That happens for Z=A/2 (N=Z). But that's true ONLY for small nuclei (A<=20). How can I prove that N=1.5Z for heavy nuclei?