Nuclear Shell Model - pp bound states?

[sk1105]

I have looked around for help with this, including on existing threads, but I can't quite find what I'm looking for.

I know that in the nuclear shell model we fill the shells in the same way as with electrons, so 2 protons in the first and 6 in the second etc, with the same being true for neutrons. I take this to mean that the 1s shell, for example, can contain 2 protons and 2 neutrons. Do I have the right idea? If so, does this not contradict with the fact that proton-proton bound states are not observed in nature? Theoretically could we not have Helium-2, with pp in the 1s shell?

 

[Vanadium 50]

What do you mean by "theoretically". No theory that attempted to explain nature would predict this, because it is known from experiment that the diproton is unbound. Indeed, since the dineutron is unbound, and since the diproton adds the repulsive electrostatic force on top of that, it's guaranteed to be unbound.

 

[mfb]

If you try to fill the proton shell only, you'll get a total energy above the energy of two free protons - the state is extremely unstable.

 

[sk1105]

Sorry, I was unscientific with my words. I was hypothesising based on my incorrect understanding of the model. But both answers were helpful, thanks! :)