Wait, this cannot be right... the neutron has no charge, so it's supposed to
be its own antiparticle.
Well, the story is somewhat more complex. A neutron is made of three quarks:
one Up (with a charge of +2/3*1.606*10-19 C)and two Down (-1/3*1.606*10-19 C),
so its total charge is, in fact, zero.
However, if you put together one Anti-Up and two Anti-Down quarks you get an antineutron.
Both the neutron and its antiparticle are unstable when outside of an atomic nucleus, but
the antineutron decays into an antiproton, a positron and a neutrino
instead of the usual proton-electron-antineutrino.
Also, while protons and neutrons live together in perfect harmony, side by side in
every nucleus, protons and antineutrons clash violently, releasing gamma rays and a pion.
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