Some people naturally assume that atomic nuclei are made of protons and neutrons. That is, they are basicly clumps of protons and neutrons that each maintain its separate existence, like pieces of gravel maintain their existence if you mold them together in a ball with mud for a binding force.
This is a natural assumption. A hydrogen nucleus can have one proton as its nucleus. Nuclei can absorb neutrons to become other isotopes. It's natural to assume that nuclei are clumps of protons and neutrons.
Sometimes if an atomic nucleus gets broken by application of large amounts of energy, typically applied with a fast-moving subatomic particle, they might release a neutron or a proton. So for example, smash an alpha particle into a beryllium nucleus and a neutron comes out. Doesn't that imply that the neutron was in there all along, waiting to get out?
But that reasoning implies that electrons, positrons, muons etc are also inside the nucleus all the time, waiting to get out.
There's an idea that protons and neutrons inside a nucleus swiftly transfer charges. This is analogous to a theory from organic chemistry, where sometimes single and double bonds switch back and forth, increasing stability. We could have quarks getting exchanged rapidly between protons and neutrons, increasing stability. I can see that as increasing stability for the nucleus, but I just don't see it as making the protons and neutrons more stable. If ten Hollywood couples get repeated divorces and marry each other's exes, you wouldn't say that the original marriages are stable.
In the extreme, the quarks might just wander around in a nuclear soup, and the protons and neutrons have no more identity than a bunch of used computers disassembled with the parts on shelves for resale. Maybe you could collect enough parts to take a working computer out of the store with you, but it probably won't be one of the old computers.
So -- my question -- is there experimental evidence that strongly implies protons and neutrons maintain their separate identities inside atomic nuclei? Or is there data which can be interpreted that way but which can also be easily interpreted another way?