Editing Positron (section)

== Natural production ==
{{main|Positron emission}}
Positrons are produced, together with [[neutrino]]s naturally in [[Β+ decay|β<sup>+</sup> decays]] of naturally occurring radioactive isotopes (for example, [[potassium-40]]) and in interactions of [[photon|gamma quanta]] (emitted by radioactive nuclei) with matter. [[Antineutrino]]s are another kind of antiparticle produced by natural radioactivity (β<sup>−</sup> decay). Many different kinds of antiparticles are also produced by (and contained in) [[cosmic rays]]. In research published in 2011 by the [[American Astronomical Society]], positrons were discovered originating above [[thunderstorm]] clouds; positrons are produced in gamma-ray flashes created by electrons accelerated by strong electric fields in the clouds.<ref>
{{Cite news
 |last=Palmer |first=J.
 |date=11 January 2011
 |title=Antimatter caught streaming from thunderstorms on Earth
 |journal=BBC News
 |url=https://www.bbc.co.uk/news/science-environment-12158718
 |access-date=11 January 2011
 |archive-url=https://web.archive.org/web/20110112080623/http://www.bbc.co.uk/news/science-environment-12158718
 |archive-date=12 January 2011 
 |url-status=live
}}</ref> Antiprotons have also been found to exist in the [[Van Allen Belt]]s around the Earth by the [[Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics#Results|PAMELA module]].<ref>
{{cite journal
 |last1=Adriani |first1=O.
 |display-authors=etal
 |date=2011
 |title=The Discovery of Geomagnetically Trapped Cosmic-Ray Antiprotons
 |journal=[[The Astrophysical Journal Letters]]
 |volume=737 |issue=2 |pages=L29
 |arxiv=1107.4882
 |bibcode=2011ApJ...737L..29A |bibcode-access=free
 |doi=10.1088/2041-8205/737/2/L29 |doi-access=free
}}</ref><ref>
{{cite news
 |last=Than |first=K.
 |date=10 August 2011
 |title=Antimatter Found Orbiting Earth—A First
 |url=http://news.nationalgeographic.com/news/2011/08/110810-antimatter-belt-earth-trapped-pamela-space-science/
 |archive-url=https://web.archive.org/web/20111010014111/http://news.nationalgeographic.com/news/2011/08/110810-antimatter-belt-earth-trapped-pamela-space-science
 |url-status=dead
 |archive-date=10 October 2011
 |publisher=[[National Geographic Society]]
 |access-date=12 August 2011
}}</ref>

Antiparticles, of which the most common are antineutrinos and positrons due to their low mass, are also produced in any environment with a sufficiently high temperature (mean particle energy greater than the [[pair production]] threshold). During the period of [[baryogenesis]], when the universe was extremely hot and dense, matter and antimatter were continually produced and annihilated. The presence of remaining matter, and absence of detectable remaining antimatter,<ref>
{{cite web
 |date=29 May 2000
 |title=What's the Matter with Antimatter?
 |url=https://science.nasa.gov/headlines/y2000/ast29may_1m.htm
 |publisher=[[NASA]]
 |access-date=24 May 2008
 |archive-url=https://web.archive.org/web/20080604155823/https://science.nasa.gov/headlines/y2000/ast29may_1m.htm
 |archive-date=4 June 2008 
 |url-status=dead
}}</ref> also called [[baryon asymmetry]], is attributed to [[CP-violation]]: a violation of the CP-symmetry relating matter to antimatter. The exact mechanism of this violation during baryogenesis remains a mystery.<ref>{{cite web
 |date=19 October 2017
 |title=Riddle of matter remains unsolved: Proton and antiproton share fundamental properties
 |url=http://www.uni-mainz.de/presse/aktuell/3027_ENG_HTML.php
 |publisher=Johannes Gutenberg University Mainz
 |access-date=21 September 2019
 |archive-date=21 September 2019
 |archive-url=https://web.archive.org/web/20190921212147/http://www.uni-mainz.de/presse/aktuell/3027_ENG_HTML.php
 |url-status=dead
 }}</ref>

Positron production from radioactive {{Subatomic particle|beta+}} decay can be considered both artificial and natural production, as the generation of the radioisotope can be natural or artificial. Perhaps the best known naturally-occurring radioisotope which produces positrons is potassium-40, a long-lived isotope of potassium which occurs as a [[primordial isotope]] of potassium. Even though it is a small percentage of potassium (0.0117%), it is the single most abundant radioisotope in the human body. In a human body of {{Convert|70|kg|lb|abbr=on}} mass, about 4,400 nuclei of <sup>40</sup>K decay per second.<ref>
{{cite web
 |title=Radiation and Radioactive Decay. Radioactive Human Body
 |url=http://www.fas.harvard.edu/~scdiroff/lds/QuantumRelativity/RadioactiveHumanBody/RadioactiveHumanBody.html
 |access-date=18 May 2011
 |publisher=Harvard Natural Sciences Lecture Demonstrations
}}</ref> The activity of natural potassium is 31 [[Becquerel|Bq]]/g.<ref>
{{cite book
 |last1=Wintergham |first1=F. P. W.
 |date=1989
 |title=Radioactive Fallout in Soils, Crops and Food
 |url=https://books.google.com/books?id=KRVXMiQWi0cC&pg=PA32
 |page=32
 |publisher=[[Food and Agriculture Organization]]
 |isbn=978-92-5-102877-3
}}</ref> About 0.001% of these <sup>40</sup>K decays produce about 4000 natural positrons per day in the human body.<ref name=Engelkemeir>
{{cite journal
 |last1=Engelkemeir |first1=D. W.
 |last2=Flynn |first2=K. F.
 |last3=Glendenin |first3=L. E.
 |date=1962
 |title=Positron Emission in the Decay of K<sup>40</sup>
 |journal=[[Physical Review]]
 |volume=126 |issue=5 |page=1818
 |bibcode=1962PhRv..126.1818E
 |doi=10.1103/PhysRev.126.1818
}}</ref> These positrons soon find an electron, undergo annihilation, and produce pairs of 511 [[keV]] photons, in a process similar (but much lower intensity) to that which happens during a [[PET scan]] [[nuclear medicine]] procedure.{{citation needed|date=April 2016}}

Recent observations indicate [[black hole]]s and [[neutron star]]s produce vast amounts of positron-electron [[Plasma (physics)|plasma]] in [[astrophysical jets]]. Large clouds of positron-electron plasma have also been associated with neutron stars.<ref>{{Cite web|url=http://pc.astro.brandeis.edu/pdfs/elec-pos.pdf|title=Electron-positron Jets Associated with Quasar 3C 279}}</ref><ref>
{{cite web
 |url=http://www.nasa.gov/centers/goddard/news/topstory/2007/antimatter_binary.html
 |title=Vast Cloud of Antimatter Traced to Binary Stars
 |publisher=NASA
}}</ref><ref>{{Cite AV media |url=https://www.youtube.com/watch?v=Sw-og52UUVg |title=Science With Integral |date=1 September 2008 |type=Video |time=4:00 |archive-url=https://web.archive.org/web/20130727160716/https://www.youtube.com/watch?v=Sw-og52UUVg |archive-date=27 July 2013 |url-status=dead |quote=Sagittarius produces 15 billion tons/sec of electron-positron matter}}</ref>

=== Observation in cosmic rays ===
{{main|Cosmic ray}}
Satellite experiments have found evidence of positrons (as well as a few antiprotons) in primary cosmic rays, amounting to less than 1% of the particles in primary cosmic rays.<ref>{{cite journal |last1=Golden |title=Measurement of the Positron to Electron Ratio in Cosmic Rays above 5 GeV |journal=Astrophysical Journal Letters |date=February 1996 |volume=457 |issue=2 |doi=10.1086/309896 |bibcode=1996ApJ...457L.103G |hdl=11576/2514376 |s2cid=122660096 |url=https://ui.adsabs.harvard.edu/abs/1996ApJ...457L.103G/abstract |access-date=19 October 2021|hdl-access=free }}</ref> However, the fraction of positrons in cosmic rays has been measured more recently with improved accuracy, especially at much higher energy levels, and the fraction of positrons has been seen to be greater in these higher energy cosmic rays.<ref>{{cite journal |last1=Boudaud |title=A new look at the cosmic ray positron fraction |journal=Astronomy & Astrophysics |date=19 December 2014 |volume=575 |pages=A67 |url=https://www.aanda.org/articles/aa/full_html/2015/03/aa25197-14/aa25197-14.html |access-date=19 October 2021 |doi=10.1051/0004-6361/201425197 |doi-access=free|arxiv=1410.3799 }}</ref>

These do not appear to be the products of large amounts of antimatter from the Big Bang, or indeed complex antimatter in the universe (evidence for which is lacking, see below). Rather, the antimatter in cosmic rays appear to consist of only these two elementary particles. Recent theories suggest the source of such positrons may come from annihilation of dark matter particles, acceleration of positrons to high energies in astrophysical objects, and production of high energy positrons in the interactions of cosmic ray nuclei with interstellar gas.<ref>{{cite web |title=Towards Understanding the Origin of Cosmic-Ray Positrons |url=https://ams02.space/physics/towards-understanding-origin-cosmic-ray-positrons |website=The Alpha Magnetic Spectrometer on the International Space Station |access-date=19 October 2021}}</ref>

Preliminary results from the presently operating [[Alpha Magnetic Spectrometer]] (''AMS-02'') on board the [[International Space Station]] show that positrons in the cosmic rays arrive with no directionality, and with energies that range from 0.5 [[Wiktionary:gigaelectron volt|GeV]] to 500 GeV.<ref>
{{cite journal
 |last1=Accardo |first1=L.
 |collaboration=[[Alpha Magnetic Spectrometer#AMS-02|AMS Collaboration]]
 |date=2014
 |title=High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–500 GeV with the Alpha Magnetic Spectrometer on the International Space Station
 |url=http://ams.nasa.gov/Documents/AMS_Publications/PhysRevLett.113.121101.pdf
 |journal=[[Physical Review Letters]]
 |volume=113 |issue=12
 |page=121101
 |bibcode=2014PhRvL.113l1101A
 |doi=10.1103/PhysRevLett.113.121101
 |pmid=25279616
 |doi-access=free
}}</ref><ref>
{{Cite journal|last1=Schirber |first1=M.
 |title=Synopsis: More Dark Matter Hints from Cosmic Rays?
 |journal=Physical Review Letters
 |volume=113
 |issue=12
 |pages=121102
 |doi=10.1103/PhysRevLett.113.121102
 |pmid=25279617
 |year=2014
 |arxiv=1701.07305
 |bibcode=2014PhRvL.113l1102A
 |url=https://cds.cern.ch/record/1756487
 |hdl=1721.1/90426
 |s2cid=2585508
 }}</ref> Positron fraction peaks at a maximum of about 16% of total electron+positron events, around an energy of 275 ± 32 GeV. At higher energies, up to 500 GeV, the ratio of positrons to electrons begins to fall again. The absolute flux of positrons also begins to fall before 500 GeV, but peaks at energies far higher than electron energies, which peak about 10 GeV.<ref>
{{cite web
 |title=New results from the Alpha Magnetic Spectrometer on the International Space Station
 |url=http://ams.nasa.gov/Documents/AMS_Publications/ams_new_results_-_18.09.2014.pdf
 |website=AMS-02 at NASA
 |access-date=21 September 2014
}}</ref><ref>{{Cite web|url=http://www1b.physik.rwth-aachen.de/~pebs/?PEBS_physics:Positron_fraction|title=Positron fraction|access-date=22 July 2018|archive-date=22 July 2018|archive-url=https://web.archive.org/web/20180722184917/http://www1b.physik.rwth-aachen.de/~pebs/?PEBS_physics:Positron_fraction|url-status=dead}}</ref> These results on interpretation have been suggested to be due to positron production in annihilation events of massive [[dark matter]] particles.<ref name="physrevltrs413">
{{Cite journal 
 |last1=Aguilar |first1=M.
 |display-authors=etal
 |year=2013
 |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV
 |journal=[[Physical Review Letters]]
 |volume=110 |issue=14 |pages=141102
 |bibcode=2013PhRvL.110n1102A
 |doi=10.1103/PhysRevLett.110.141102
 |pmid=25166975
 |url=https://boa.unimib.it/bitstream/10281/44680/1/2013_PhysRevLett.110.141102_positron_fraction.pdf|doi-access=free
}}</ref>

Positrons, like anti-protons, do not appear to originate from any hypothetical "antimatter" regions of the universe. On the contrary, there is no evidence of complex antimatter atomic nuclei, such as [[antihelium]] nuclei (i.e., anti-alpha particles), in cosmic rays. These are actively being searched for. A prototype of the ''AMS-02'' designated ''AMS-01'', was flown into space aboard the {{OV|103}} on [[STS-91]] in June 1998. By not detecting any [[Antihelium#Antihelium|antihelium]] at all, the ''AMS-01'' established an upper limit of 1.1×10<sup>−6</sup> for the antihelium to helium [[flux]] ratio.<ref>
{{cite journal
 |last1=Aguilar |first1=M.
 |display-authors=etal
 |collaboration=[[Alpha Magnetic Spectrometer#AMS-02|AMS Collaboration]]
 |date=2002
 |title=The Alpha Magnetic Spectrometer (AMS) on the International Space Station: Part I – results from the test flight on the space shuttle
 |journal=[[Physics Reports]]
 |volume=366 |issue=6 |pages=331–405
 |bibcode=2002PhR...366..331A 
 |doi=10.1016/S0370-1573(02)00013-3
 |hdl=2078.1/72661
 |s2cid=122726107
}}</ref>