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Why does the asymmetry exist between the proton-proton, neutron-neutron and neutron-proton strong interactions in the nucleus (which results in nuclei preferring equal numbers of neutrons and protons)? Why is the neutron-proton interaction the strongest?

user50229
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  • which results in nuclei preferring equal numbers of neutrons and protons No, this is not the reason why light nuclei have $N\approx Z$. See https://physics.stackexchange.com/questions/323350/what-makes-the-number-of-neutrons-the-number-of-proton-similar . –  Jul 10 '19 at 17:36
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    Why is the neutron-proton interaction the strongest? This is not really true in general, or even a well-defined statement. We do see states like the deuteron in which there is a strong attraction between the proton and neutron, but we can't make an apples-to-apples comparison with, e.g., a pair of neutrons in the same state, because that would be forbidden by the exclusion principle. –  Jul 10 '19 at 17:39
  • https://www.york.ac.uk/physics/research/nuclear/proton-neutron-symmetries/ "For example, it is well known that the nuclear force, at least when measured in free space, is not quite charge symmetric - that is, the neutron-neutron interaction is just a bit stronger than the proton-proton interaction." – user50229 Jul 11 '19 at 19:45
  • @BenCrowell https://en.wikipedia.org/wiki/Nuclear_binding_energy#Semiempirical_formula_for_nuclear_binding_energy "The symmetry correction term -d(N-Z)^{2}/A^{2} takes into account the fact that in the absence of other effects the most stable arrangement has equal numbers of protons and neutrons; this is because the n-p interaction in a nucleus is stronger than either the n-n or p-p interaction." – user50229 Jul 11 '19 at 19:56

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