[stephengillie]

The underlying mechanics are highly theoretical, but it has something to do with the quarks that compose protons and neutrons. The Strong force is theorized to be caused by color-charge attraction. It would be the same situation as if photons (light, etc) were highly magnetic, they'd attract molecules; in this way the charge carriers of the 3-way color force are highly (and mutually) attracted to quarks for their color-charge.

There's a radius for color-charge interaction. This radius is thought to be one cause for larger elements being less likely to be stable; when protons are too far apart to exchange color-charge carriers, their magnetic repulsion can disrupt nucleic stability.

And different quarks have different energies. Every neutron has 2 Down quarks and 1 Up quark (UDD); every proton has 1 Down quark and 2 Up quarks (UUD). Down quarks are more energetic (massive) than Up quarks. After about 5 minutes, a neutron (UUD) decays into a proton (UDD), an electron, and an electron neutrino. This would seem to imply that an electron and a neutrino would equal the difference between an Up and Down quark.

All protons and neutrons have 3 quarks. There are other particles with 2, but they're much more rare. Nuclei with an odd number of nucleons (protons and neutrons) would have to have an even number of quarks. There may be something to the number of quarks, research into that is difficult because the act of pulling quarks apart requires so much energy that it just creates new quarks.

[1]http://en.wikipedia.org/wiki/Neutron