4,  we have seen that for average mass
nuclei the binding energy per nucleon is  approximately 8 MeV, which is
much larger than the binding energy in atoms Therefore, to bind a
nucleus together there must be a strong attractive force of a totally
different kind It must be strong enough to overcome the repulsion
between the (positively charged) protons and to bind both protons and
neutrons into the tiny nuclear volume We have already seen
that the constancy of binding energy per nucleon can be
understood in terms of its short-range