In the diagram of nuclear binding energy per nucleon Eb/A (vertical axis) and mass number A (horizontal axis), Fe-56 has one of the highest values. Many authors state that nuclear fusion can only produce energy going from lighter nuclei towards the iron peak, but not beyond the iron peak. Going beyond the iron peak, we end up with a nucleus having less binding energy per nucleon. Why would that prohibit energy production by fusion?
As an example, suppose an Fe-56 nucleus captures an alpha particle, resulting in a Ni-60 nucleus. Fe-56 and He-4 have a rest mass 55.9349+4.0026=59.9375 u which is more than 59.9308 u for Ni-60 (using three atomic masses so we have as many electrons before and after; ignoring the electron binding energy). Because some mass is lost, this "fusion beyond the iron peak" would seem to be possible and to produce energy. Where do I go wrong?
I understand that this fusion requires a very high temperature in the core of a massive star at the end of Si-burning because of the high Coulomb barrier, and that photodesintegration would quickly destroy the Ni-60. But my question is: is energy production through fusion beyond the iron peak possible in principle?