Why is it that neutrons evaporate from nuclei more easily than protons do?
Intuitively, since protons are electrostatically repelled (in addition to whatever nuclear forces they have in common with neutrons), one would expect protons to be ejected more readily than neutrons. (Maybe this is even what does happen for small nuclei, but apparently not large nuclei.)
It seems to be said in common parlance that the Coulomb force/barrier acts to contain the protons. Which is counter-intuitive.
On the other hand, at least some textbooks acknowledge the coulomb force trying to push protons away from others in the nucleus, and so they infer that the nuclear force (e.g., residual strong force) must act more strongly on protons than what it does on neutrons. (At least in big nuclei, "beta stable nuclei", nuclei with an excess of neutrons..) So how does this nuclear force distinguish between protons and neutrons?
Best Answer
Your intuition about the charge repulsion and strong force acting on Protons more is less important that you think. The strong nuclear force is a few orders of magnitude greater than electromagnetism so coulomb repulsion just doesn't contribute much.
What matters most is the nuclear binding energy to separate a proton from the nucleus. If the resulting system is below the proton separation energy it's possible for the proton to tunnel out. See Proton emission and Proton drip line for more information about this. It does happen but remember Neutron emission is also rare. $\beta^+$ and $\beta^-$ and Alpha emission are much more common.