Neutron

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.