Editing Beta particle (section)

==Beta decay modes==

=== β<sup>−</sup> decay (electron emission) ===
{{main|Beta_decay#.CE.B2.E2.88.92_decay|l1=β<sup>−</sup> decay}}
[[File:Beta-minus Decay.svg|thumb|Beta decay. A beta particle (in this case a negative electron) is shown being emitted by a [[Atomic nucleus|nucleus]]. An antineutrino (not shown) is always emitted along with an electron. Insert: in the decay of a free neutron, a proton, an electron (negative beta ray), and an [[electron antineutrino]] are produced.]]

An unstable atomic nucleus with an excess of [[neutron]]s may undergo β<sup>−</sup> decay, where a neutron is converted into a [[proton]], an electron, and an [[electron antineutrino]] (the [[antiparticle]] of the [[neutrino]]):

:{{SubatomicParticle|neutron}} → {{SubatomicParticle|proton}} + {{SubatomicParticle|electron}} + {{SubatomicParticle|electron antineutrino}}

This process is mediated by the [[weak interaction]]. The neutron turns into a proton through the emission of a [[virtual particle|virtual]] [[weak interaction|W<sup>−</sup> boson]]. At the [[quark]] level, W<sup>−</sup> emission turns a down quark into an up quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark).
The virtual W<sup>−</sup> boson then decays into an electron and an antineutrino.

β− decay commonly occurs among the neutron-rich [[Nuclear fission product|fission byproducts]] produced in [[nuclear reactor]]s. Free neutrons also decay via this process. Both of these processes contribute to the copious quantities of beta rays and electron antineutrinos produced by fission-reactor fuel rods.

=== β<sup>+</sup> decay (positron emission) ===
{{main|Positron emission}}
Unstable atomic nuclei with an excess of protons may undergo β<sup>+</sup> decay, also called positron decay, where a proton is converted into a neutron, a [[positron]], and an [[electron neutrino]]:

:{{SubatomicParticle|proton}} → {{SubatomicParticle|neutron}} + {{SubatomicParticle|positron}} + {{SubatomicParticle|electron neutrino}}

Beta-plus decay can only happen inside nuclei when the absolute value of the [[binding energy]] of the daughter nucleus is greater than that of the parent nucleus, i.e., the daughter nucleus is a lower-energy state.

===Beta decay schemes===
[[File:Cs-137-decay.svg|thumb|Caesium-137 decay scheme, showing it initially undergoes beta decay. The 661&nbsp;keV gamma peak associated with <sup>137</sup>Cs is actually emitted by the daughter radionuclide.]]
The accompanying decay scheme diagram shows the beta decay of [[caesium-137]]. <sup>137</sup>Cs is noted for a characteristic gamma peak at 661&nbsp;keV, but this is actually emitted by the daughter radionuclide <sup>137m</sup>Ba. The diagram shows the type and energy of the emitted radiation, its relative abundance, and the daughter nuclides after decay.

[[Phosphorus-32]] is a beta emitter widely used in medicine. It has a short half-life of 14.29 days<ref name="LNHB">{{cite web |title=Phosphorus-32 |url=http://www.nucleide.org/DDEP_WG/Nuclides/P-32_tables.pdf |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/http://www.nucleide.org/DDEP_WG/Nuclides/P-32_tables.pdf |archive-date=2022-10-09 |access-date=28 June 2022 |website=nucleide.org |publisher=Laboratoire Nationale Henri Bequerel}}</ref> and decays into sulfur-32 by [[beta decay]] as shown in this nuclear equation:
:{| border="0"
|- style="height:2em;"
|{{nuclide|Phosphorus|32}} ||→ ||{{nuclide|Sulfur|32|charge=1+}} ||+ ||{{SubatomicParticle|link=yes|Electron}} ||+ ||{{SubatomicParticle|link=yes|Electron Antineutrino}}
|}
1.709&nbsp;[[MeV]] of energy is released during the decay.<ref name="LNHB"/> The kinetic energy of the [[electron]] varies with an average of approximately 0.5&nbsp;MeV and the remainder of the energy is carried by the nearly undetectable [[electron antineutrino]]. In comparison to other beta radiation-emitting nuclides, the electron is moderately energetic. It is blocked by around 1&nbsp;m of air or 5&nbsp;mm of [[acrylic glass]].