β⁻ decay

In β^⁻ decay, the weak interaction converts a neutron (n) into a proton (p) while emitting an electron (e^⁻) and an electron antineutrino (ν_e):

n

→

p

+

e⁻

+

νe

At the fundamental level (as depicted in the Feynman diagram below), this is due to the conversion of a down quark to an up quark by emission of a W^⁻ boson; the W^⁻ boson subsequently decays into an electron and an electron antineutrino.

β⁻ decay in an atomic nucleus. The intermediate emission of a virtual W⁻ boson is omitted.

The Feynman diagram for β⁻ decay of a neutron into a proton, electron, and electron antineutrino via an intermediate W⁻ boson

β^⁻ decay generally occurs in neutron rich nuclei.

β⁺ decay

See also: Positron emission

In β⁺ decay, energy is used to convert a proton into a neutron, a positron (e⁺) and a neutrino (ν_e):

energy

+

p

→

n

+

e+

+

νe

So, unlike β^⁻, β⁺ decay cannot occur in isolation, because it requires energy, the mass of the neutron being greater than the mass of the proton. β⁺ decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.