Editing Beta particle

{{short description|Ionizing radiation}}{{More citations needed|date=September 2024}}[[File:Alfa beta gamma radiation.svg|300px|thumb|[[Alpha particle|Alpha radiation]] consists of [[helium]] nuclei and is readily stopped by a sheet of paper. [[Electron|Beta radiation]], consisting of [[electrons]] or [[positron]]s, is stopped by a thin aluminum plate, but [[Gamma ray|gamma radiation]] requires shielding by dense material such as lead or concrete.<ref name=NRC_Radiation>{{cite web |url=https://www.nrc.gov/about-nrc/radiation/health-effects/radiation-basics.html |title=Radiation Basics |date=2017-10-02 |publisher=United States Nuclear Regulatory Com}}</ref>]]

A '''beta particle''', also called '''beta ray''' or '''beta radiation''' (symbol '''β'''), is a high-energy, high-speed [[electron]] or [[positron]] emitted by the [[radioactive decay]] of an [[atomic nucleus]], known as [[beta decay]]. There are two forms of beta decay, β<sup>−</sup> decay and β<sup>+</sup> decay, which produce electrons and positrons, respectively.<ref>{{cite web |title=Beta Decay |url=http://www.lbl.gov/abc/wallchart/chapters/03/2.html |work=Nuclear Wall Chart |author=Lawrence Berkeley National Laboratory |publisher=[[United States Department of Energy]] |date=9 August 2000 |access-date=17 January 2016 |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303195332/http://www2.lbl.gov/abc/wallchart/chapters/03/2.html |url-status=dead}}</ref>

Beta particles with an energy of 0.5 MeV have a range of about one metre in the air; the distance is dependent on the particle's energy and the air's [[density]] and composition.

Beta particles are a type of [[ionizing radiation]], and for [[radiation protection]] purposes, they are regarded as being more ionising than [[gamma ray]]s, but less ionising than [[alpha particle]]s.<!--This is the correct ordering. If you believe otherwise, please cite a reliable source, or discuss on the Talk page.--> The higher the ionising effect, the greater the damage to living tissue, but also the lower the [[Mean free path|penetrating power]] of the radiation through matter.

==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]].

== Interaction with other matter ==

[[File:TrigaReactorCore.jpeg|thumb|250px|Blue [[Cherenkov radiation]] light being emitted from a [[TRIGA]] reactor pool is due to high-speed beta particles traveling faster than the speed of light ([[phase velocity]]) in water (which is 75% of the speed of light in vacuum).]]Of the three common types of radiation given off by radioactive materials, [[Alpha particle|alpha]], beta and [[Gamma ray|gamma]], beta has the medium penetrating power and the medium ionising power. Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of [[aluminium]]. However, this does not mean that beta-emitting isotopes can be completely shielded by such thin shields: as they decelerate in matter, beta electrons emit secondary gamma rays, which are more penetrating than betas per se. Shielding composed of materials with lower atomic weight generates gammas with lower energy, making such shields somewhat more effective per unit mass than ones made of larger atoms such as lead.

Being composed of charged particles, beta radiation is more strongly ionizing than gamma radiation. When passing through matter, a beta particle is decelerated by electromagnetic interactions and may give off [[bremsstrahlung]] [[X-ray]]s.

In water, beta radiation from many [[nuclear fission product]]s typically exceeds the speed of light in that material (which is about 75% that of light in vacuum),<ref>The macroscopic speed of light in water is 75% of the speed of light in vacuum (called ''c''). The beta particle is moving faster than 0.75 c, but not faster than c.</ref> and thus generates blue [[Cherenkov radiation]] when it passes through water. The intense beta radiation from the fuel rods of [[swimming pool reactor]]s can thus be visualized through the transparent water that covers and shields the reactor (see illustration at right).

=== Detection and measurement ===
[[File:Beta radiation in a cloud chamber.jpg|thumb|300px|Beta radiation detected in an isopropanol [[cloud chamber]] (after insertion of an artificial source [[strontium-90]])]]
The ionizing or excitation effects of beta particles on matter are the fundamental processes by which radiometric detection instruments detect and measure beta radiation. The ionization of gas is used in [[ionization chamber|ion chambers]] and [[Geiger counter|Geiger–Müller counters]], and the excitation of [[scintillator]]s is used in [[scintillation counter]]s.
The following table shows radiation quantities in SI and non-SI units:
{{Radiation related quantities}}

* The [[gray (unit)|gray]] (Gy)  is the SI unit of [[absorbed dose]], which is the amount of radiation energy deposited in the irradiated material. For beta radiation this is numerically equal to the [[equivalent dose]] measured by the [[sievert]], which indicates the stochastic biological effect of low levels of radiation on human tissue. The radiation weighting conversion factor from absorbed dose to equivalent dose is 1 for beta, whereas alpha particles have a factor of 20, reflecting their greater ionising effect on tissue.
* The [[rad (unit)|rad]] is the deprecated [[CGS]] unit for absorbed dose and the [[Röntgen equivalent man|rem]] is the deprecated [[CGS]] unit of equivalent dose, used mainly in the USA.

=== Beta spectroscopy ===
The energy contained within individual beta particles is measured via ''beta spectrometry''; the study of the obtained distribution of energies as a [[spectrum]] is ''beta spectroscopy''. Determination of this energy is done by measuring the amount of deflection of the electron's path under a magnetic field.<ref>{{cite web |last1=Boeglin |first1=Werner |title=4. Beta Spectroscopy — Modern Lab Experiments documentation |url=https://wanda.fiu.edu/boeglinw/courses/Modern_lab_manual3/beta_spectroscopy.html |website=wanda.fiu.edu}}</ref>

== Applications ==
Beta particles can be used to treat health conditions such as [[Eye neoplasm|eye]] and [[Bone tumor|bone cancer]] and are also used as tracers. [[Strontium-90]] is the material most commonly used to produce beta particles.

Beta particles are also used in quality control to test the thickness of an item, such as [[paper]], coming through a system of rollers. Some of the beta radiation is absorbed while passing through the product. If the product is made too thick or thin, a correspondingly different amount of radiation will be absorbed. A computer program monitoring the quality of the manufactured paper will then move the rollers to change the thickness of the final product.

An illumination device called a ''[[Beta light|betalight]]'' contains [[tritium]] and a [[phosphor]]. As tritium [[Radioactive decay|decays]], it emits beta particles; these strike the phosphor, causing the phosphor to give off [[photon]]s, much like the [[cathode-ray tube]] in a television. The illumination requires no external power, and will continue as long as the tritium exists (and the phosphors do not themselves chemically change); the [[Radiant flux|amount of light produced]] will drop to half its original value in 12.32 years, the [[half-life]] of tritium.

Beta-plus (or [[positron]]) decay of a [[radioactive tracer]] [[isotope]] is the source of the positrons used in [[positron emission tomography]] (PET&nbsp;scan).

== History ==
[[Henri Becquerel]], while experimenting with [[fluorescence]], accidentally found out that [[uranium]] exposed a [[photographic]] plate, wrapped with black paper, with some unknown [[radiation]] that could not be turned off like [[X-ray]]s.

[[Ernest Rutherford]] continued these experiments and discovered two different kinds of radiation:

* [[alpha particles]] that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper
* beta particles which are 100 times more penetrating than alpha particles.

He published his results in 1899.<ref>{{cite journal |author=E. Rutherford |url=https://books.google.com/books?id=ipMOAAAAIAAJ&pg=PA109 |title=Uranium radiation and the electrical conduction produced by it |journal=Philosophical Magazine |volume=47 |issue=284 |pages=109–163 |doi=10.1080/14786449908621245 |date=8 May 2009 |orig-year=Paper published by Rutherford in 1899|url-access=subscription }}</ref>

In 1900, Becquerel measured the [[mass-to-charge ratio]] ({{math|''m''/''e''}}) for beta particles by the method of [[J. J. Thomson]] used to study cathode rays and identify the electron. He found that {{math|''e''/''m''}} for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron.

== Health ==
Beta particles are moderately penetrating in living tissue, and can cause spontaneous [[mutation]] in [[DNA]].

Beta sources can be used in [[radiation therapy]] to kill cancer cells.

== See also ==
* [[Common beta emitters]]
* [[Electron irradiation]]
* [[Particle physics]]
* [[neutron radiation|n (neutron) rays]]
* [[delta ray|δ (delta) rays]]

== References ==
{{reflist}}

== Further reading ==
* [http://www.oasisllc.com/abgx/radioactivity.htm Radioactivity and alpha, beta, gamma and X&shy;rays]<!-- some company going out of business? -->
* [http://galileo.phys.virginia.edu/classes/252/rays_and_particles.html Rays and Particles] University of Virginia Lecture
* [http://www.physics.isu.edu/radinf/hist.htm History of Radiation] {{Webarchive|url=https://web.archive.org/web/20170506071143/http://www.physics.isu.edu/radinf/hist.htm |date=2017-05-06 }} at Idaho State University
* [http://www.lbl.gov/abc/Basic.html Basic Nuclear Science Information] {{Webarchive|url=https://web.archive.org/web/20061205215708/http://www.lbl.gov/abc/Basic.html |date=2006-12-05 }} at the Lawrence Berkeley National Laboratory

{{Radiation}}

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[[Category:Ionizing radiation]]
[[Category:Radioactivity]]