Beta decay
In nuclear physics, beta decay ("β"-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in so-called "positron emission". Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energetically possible, the energy release (see below) or "Q" value must be positive.

Beta decay is a consequence of the weak force, which is characterized by relatively lengthy decay times. Nucleons are composed of up quarks and down quarks, and the weak force allows a quark to change its flavour by emission of a W boson leading to creation of an electron/antineutrino or positron/neutrino pair. For example, a neutron, composed of two down quarks and an up quark, decays to a proton composed of a down quark and two up quarks.

Electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. In electron capture, an inner atomic electron is captured by a proton in the nucleus, transforming it into a neutron, and an electron neutrino is released.
Q81197
nuclear physics
Concept
Q11448
radioactive decay
Concept
Q103531
beta particle
Concept
Q2225
electron
Concept
Q3229
positron
Concept
Q37147
atomic nucleus
Concept
Q108149
nuclide
Concept
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isobar
Concept
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neutron
Concept
Q2294
proton
Concept
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antineutrino
Concept
Q2126
neutrino
Concept
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positron emission
Concept
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ratio of protons to neutrons
UNK
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nuclear binding energy
Concept
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valley of stability
UNK
None
see below
UNK
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"Q" value
UNK
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weak force
Concept
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up quark
Concept
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down quark
Concept
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quark
Concept
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flavour
Concept
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W boson
Concept
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Electron capture
Concept
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Beta decay
Concept
studies
subclass of
subclass of