I think my learning's gone awry:

Somewhere along the way, I picked up the notion that there exists two separate valence structures within the nucleus (one structure composed of protons, the other of neutrons) responsible for the stability of He-4 and Pb-208 (because both valence structures are simultaneously fulfilled). From a young age, I learned the binding force between nucleons was the strong force, so I assume(d) that this valence structure developed as a bound state between individual nucleons interacting via the strong force with "the nucleus" (akin to the electronic valence structure).

But now that I'm learning more about chromodynamics, I'm starting to wonder if I'm full of BS. Do quarks composing different nucleons in the same nucleus have strong interactions? If so, is color charge swapped (mediated via gluons) strictly within the three quarks of a given nucleon, or is it being exchanged between all the quarks of a nucleus? If so, can you really even describe a nucleus as having individual nucleons, or is it more a sea of up & down quarks (in some ratio) swapping color charge/having strong interactions/with a ton of virtual gluons flying around? If so, is there really any "valance structure" (and if so, how does that develop/what is the bound state that gives these waveforms?)

EDIT: one more: If the nucleus is a relatively structureless sea of color-confined quarks, can it be considered just a massively big colorless meson?

I am perplexed & wikipedia is mostly unhelpful. What on earth does the nucleus of a multiple-nucleon atom look like? If it's a sea of undistinguished quarks, how is it that the nuclear shell model is descriptive of the nucleus?


1 Answer 1


Individual quarks between different nucleons do interact with each other. The inside of a proton (or neutron) is a "soup" of quarks and gluons. The probability with which a quark inside a nucleon interacts with other particles is described by the parton distribution functions (PDFs for short), while the interaction itself is described by the cross section of the process. We have equations that explain how these PDFs evolve with the energy scale of the theory (called DGLAP equations), and what we find is that the higher is the scale with which you "probe" the theory, the more gluons and quark-antiquarks pairs you see inside the nucleons.

  • $\begingroup$ Thanks! Why are He-4 and Pb-208 more stable than other nuclei? $\endgroup$
    – neph
    Dec 6, 2021 at 17:10

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