Question about gluons and nucleon binding

[artis]

The strong force is mediated by gluons which bind quarks together to make protons and neutrons but extends some distance outside the proton, neutron particle boundary and is said to hold nucleons together to form the nucleus. proton electrostatic charge and the electrostatic force tries to push two protons apart , so this is the reason why we can't have a nucleus made of just 2 protons and the only element without atleast a single neutron is Protium?


Because the strong force falls off in strength and the electrostatic force always repels so the strong force cannot "grab" onto two protons, but it can have two protons in a nucleus if it has at least a single neutron in the nucleus forming He 3,
is this because the neutron being neutral (adding no electrostatic force) helps to add the missing energy of the strong force from the two protons and eventually helps to bring the particles together to form a stable element?

So here is where I would like to ask a bit of a speculative (not sure) question , could we say that the neutron is somewhat like a "gluon" for the nucleus , given it doesn't exert repulsive electrostatic forces but adds some extra strong force?

If I'm not mistaken there are plenty of neutron rich nuclei where the number of neutrons outweighs the number of protons but there are 3? nuclei where the proton number is higher by 1 or few than the neutron, so is this for the same reason that I asked above, namely the neutron addition to the strong force without electrostatic repulsion?


thanks

 

[mathman]

Simplified description for elastic scattering: In general (proton) being the exception) the nucleus receives little kinetic energy, so that it simply bounces little more. Furthe in case of a solid the energy gets spread out (as described previously). Protn scattering could give the proton half the K.E. of the neutron and move freely taking the molecule (water?) with it or possibly getting loose.

Inelastic scattering is more complicated and the target nucleus will be in an excited state, where what happens depends on the nucleus.

 

[mfb]

even though this is not directly related to my thread idea

Yes, that would fit better in a different thread. Anyway, it's a common question, you'll find previous discussions with the search function, and the reason deuterium is the only stable nucleus with two nucleons is a bit more complicated. It depends on the spin and is beyond the level of this thread.

 

[artis]

Ok now this thread got tidied up (thanks) but does the general idea of what I asked holds true that the neutron serves as the gluon of the nucleus for it brings additional strong force to the "table" while lacks the repulsion of the proton?

And in general terms is this property also the reason why we see neutron rich elements (higher number of neutrons than protons) but don't see more protons than neutrons for nuclei with more nucleons?

 

[snorkack]

No, neutron is not acting like the gluon here.
A better comparison here might be how for example He atoms bind molecules/clusters. They are bound together by virtual photons... yet while bulk He-3 condenses into liquid near absolute zero, two He-3 atoms, or a He-3 and He-4 atom, will not bind to each other. You cannot get a drop of liquid He-3 of less than about 30 atoms (the exact number was not known back in 2003 - cannot quickly find if there are news).
The key about quantum mechanics is that you cannot bind a quantum particle - whether a boson or a fermion - into a too shallow and narrow potential hole. If you have a broad potential hole like bulk liquid then you can have it arbitrarily shallow and still bind a particle in it. If the hole is narrow then the size of the hole imposes a minimum momentum and energy for the ground state and if the hole is too shallow then no ground state will fit in.
Now, while the potential hole in the atom is created by the charge of the nucleus and is only attraction between opposite charges - electron is attracted to nucleus but another electron is only attracted to the nucleus while repelled from the other electron - the attraction between atoms in a molecule, or nucleons in a nucleus, is multilateral. A molecule added to a drop is attracted to all molecules already in the drop, and attracts them to each other in addition to the attraction they already have between each other.

A neutron and proton of opposite spin are significantly attracted to each other, but not as strongly as a neutron and a proton of same spin. That they are not equally attracted to each other can be seen from a deuteron. Deuteron ground state has spin 1, because neutron and proton have same spin. If you try to flip them, you will not find any excited states of deuteron - adding 2,22 MeV energy breaks deuteron apart altogether rather than form any excited states. If you start from opposite end of free proton and neutron, maybe starting with opposite spins, you just confirm absence of excited states - they either manage to flip their spin and form the ground state or else just bounce off each other.

They do experience strong attraction, though. You will find that the elastic collision has a large cross-section. This is because of the strong attraction, which comes just short of allowing full binding.

 

[Meir Achuz]

The strong force is mediated by gluons which bind quarks together to make protons and neutrons but extends some distance outside the proton, neutron particle boundary and is said to hold nucleons together to form the nucleus.

Pion exchange is the 'mediation' that binds nucleons together.