Neutron Decay

Neutrons isolated outside of an atomic nucleus
have a half-life of about 10.3 minutes. Naturally
they will decay by the weak force when a down
quark changes flavor to an up quark. Charge is
conserved by a W- boson, which quickly decays
into an electron and electron antineutrino.
This is known as beta-minus decay, and in some
cases extra energy will be radiated away from the
W- boson as a high energy photon.