I know outside a nucleus, neutrons are unstable and they have
half life of about 15 minutes. But when they are together with
protons inside the nucleus, they are stable. How does that
happen? I got this from wikipedia: When bound inside of a
nucleus, the instability of a single neutron to beta decay is
balanced against the instability that would be acquired by the
nucleus as a whole if an additional proton were to participate
in repulsive interactions with the other protons that are
already present in the nucleus. As such, although free neutrons
are unstable, bound neutrons are not necessarily so. The same
reasoning explains why protons, which are stable in empty space,
may transform into neutrons when bound inside of a nucleus. But
I don't think I get what that really means. What happens inside
the nucleus that makes neutrons stable? Is it the same thing
that happens inside a neutron star's core? Because, neutrons
seem to be stable in there too.