How nuclear hadrons combine

[csmyth3025]

We all accept the notion that a hydrogen atom consists of a lone proton "orbited" by an electron and that an atom of deuterium consists of a proton and a neutron "stuck together" in the nucleus. Likewise, the nuclei of heavier elements and isotopes are a combination of protons and neutrons.

I'm sure there are sound reasons why two neutrons don't "stick together" in the same way that a neutron and a proton does in the nucleus of deuterium. I haven't been able to find an explanation for this in laymans terms. Can anyone enlighten me on this?

It seems obvious that a purely neutron "nucleus" would not be capable of forming an atom since such a nucleus would have no charge, so I'm guessing that there is a rule of sub-atomic particles that prohibits neutrons from "sticking together" (except, perhaps, within the confines of a neutron star - which relies on the crushing force of gravity rather than the binding energy of the strong nuclear force).

Chris

 

[ramparts]

Nucleons (i.e. protons and neutrons) are bound by the so-called nuclear force, which you can read about here:

http://en.wikipedia.org/wiki/Nuclear_force

(I'm no expert in this stuff!) (yet )

But from what I gather it sounds like the answer is essentially this: neutrons are unstable outside of atomic nuclei, they decay to a proton, electron, and electron antineutrino after only about 15 minutes. (In fact, this provides huge constraints on big bang nucleosynthesis, as it gives us an upper limit for the formation time of hydrogen atoms in the early universe.) In a neutron-neutron nucleus, the neutrons would still be unstable - the instability only goes away when they're in atomic nuclei with protons, because that instability is then balanced against the greater instability that would result from charge imbalance if another proton ended up in the nucleus from neutron decay. Check out the stability section (particularly the last paragraph) of the neutron article on Wiki:

http://en.wikipedia.org/wiki/Neutron#St ... beta_decay