A particle of neutral
electric charge and approximately the same
mass as the
proton. Outside the nucleus of an atom it is unstable and has a half-life of about 15 minutes, decaying by emitting an
electron and
antineutrino to become a proton. The same decay method (β-decay) occurs in some nuclei. Particles inside the nucleus are typically resonances between neutrons and protons, which transform into one another by the emission and absorption of pion
?s. A neutron contains two down
quarks and one up
quark.
See also particle physics and chemistry.