Editing Positron (section)

=== Experimental clues and discovery ===
[[File:Cloud chambers played an important role of particle detectors.jpg|thumb|Wilson [[cloud chamber]]s used to be very important [[particle detector]]s in the early days of [[particle physics]]. They were used in the discovery of the positron, [[muon]], and [[kaon]].]]
{{Antimatter}}
Several sources have claimed that [[Dmitri Skobeltsyn]] first observed the positron long before 1930,<ref>
{{cite book
 |last=Wilson |first=David
 |year=1983
 |title=Rutherford, Simple Genius
 |pages=562–563
 |publisher=Hodder and Stoughton
 |isbn=0-340-23805-4
}}</ref> or even as early as 1923.<ref>
{{cite book
 |last=Close |first=F. |author-link=Frank Close
 |year=2009
 |title=Antimatter
 |pages=50–52
 |publisher=[[Oxford University Press]]
 |isbn=978-0-19-955016-6
}}</ref> They state that while using a Wilson [[cloud chamber]]<ref>
{{cite journal
 |last=Cowan |first=E.
 |date=1982
 |title=The Picture That Was Not Reversed
 |journal=[[Engineering & Science Education Journal|Engineering & Science]]
 |volume=46 |issue=2 |pages=6–28
 |url=http://calteches.library.caltech.edu/3360/
}}</ref> in order to study the [[Compton effect]], Skobeltsyn detected particles that acted like electrons but curved in the opposite direction in an applied magnetic field, and that he presented photographs with this phenomenon in a conference in the [[University of Cambridge]], on 23–27 July 1928. In his book<ref>
{{cite book
 |last=Hanson |first=Norwood Russel
 |year=1963
 |title=The Concept of the Positron
 |pages=136–139
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-05198-9
}}</ref> on the history of the positron discovery from 1963, [[Norwood Russell Hanson]] has given a detailed account of the reasons for this assertion, and this may have been the origin of the myth. But he also presented Skobeltsyn's objection to it in an appendix.<ref>
{{cite book
 |last=Hanson |first=Norwood Russel
 |year=1963
 |title=The Concept of the Positron
 |pages=179–183
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-05198-9
}}</ref> Later, Skobeltsyn rejected this claim even more strongly, calling it "nothing but sheer nonsense".<ref>
{{cite book
 |last1=Brown |first1=Laurie M.
 |last2=Hoddeson |first2=Lillian
 |year=1983
 |title=The Birth of Particle Physics
 |pages=118–119
 |publisher=[[Cambridge University Press]]
 |isbn=0-521-24005-0
}}</ref>

Skobeltsyn did pave the way for the eventual discovery of the positron by two important contributions: adding a magnetic field to his cloud chamber (in 1925<ref>
{{cite journal
 |last=Bazilevskaya |first=G.A.
 |year=2014
 |title=Skobeltsyn and the early years of cosmic particle physics in the Soviet Union
 |pages=61–66
 |journal=Astroparticle Physics
 |volume=53
 |doi=10.1016/j.astropartphys.2013.05.007
 |bibcode=2014APh....53...61B
}}</ref>), and by discovering charged particle [[cosmic ray]]s,<ref>
{{cite journal
 |last=Skobeltsyn |first=D.
 |year=1929
 |title=Uber eine neue Art sehr schneller beta-Strahlen
 |pages=686–702
 |journal=Z. Phys.
 |volume=54
 |issue=9–10
 |doi=10.1007/BF01341600
 |bibcode=1929ZPhy...54..686S
 |s2cid=121748135
}}</ref> for which he is credited in [[Carl David Anderson]]'s [[Nobel Prize|Nobel lecture]].<ref>
{{cite web
 |last=Anderson |first=Carl D.
 |year=1936
 |title=The Production and Properties of Positrons
 |url=https://www.nobelprize.org/prizes/physics/1936/anderson/lecture/
 |access-date=10 August 2020
}}</ref> Skobeltsyn did observe likely positron tracks on images taken in 1931,<ref>
{{cite journal
 |last=Skobeltzyn |first=D.
 |year=1934
 |title=Positive electron tracks
 |pages=23–24
 |journal=Nature
 |volume=133
 |issue=3349
 |doi=10.1038/133023a0
 |bibcode=1934Natur.133...23S
 |s2cid=4226799
}}</ref> but did not identify them as such at the time.

Likewise, in 1929 [[Chung-Yao Chao]], a Chinese graduate student at [[Caltech]], noticed some anomalous results that indicated particles behaving like electrons, but with a positive charge, though the results were inconclusive and the phenomenon was not pursued.<ref name="MehraRechenberg">
{{cite book
 |last1=Merhra |first1=J. |author-link1=Jagdish Mehra
 |last2=Rechenberg |first2=H. |author-link2=Helmut Rechenberg
 |year=2000
 |title=The Historical Development of Quantum Theory, Volume 6: The Completion of Quantum Mechanics 1926–1941
 |url=https://books.google.com/books?id=9l61Dy9FBfYC&q=Chung-Yao%20Chao%20positron&pg=PA804
 |page=804
 |publisher=Springer
 |isbn=978-0-387-95175-1
}}</ref> Fifty years later, Anderson acknowledged that his discovery was inspired by the work of his Caltech classmate [[Chung-Yao Chao]], whose research formed the foundation from which much of Anderson's work developed but was not credited at the time.<ref name="Chinese">{{Cite journal|last=Cao|first=Cong|date=2004|title=Chinese Science and the 'Nobel Prize Complex'|url=http://china-us.uoregon.edu/pdf/Minerva-2004.pdf|journal=Minerva|language=en|volume=42|issue=2|page=154|doi=10.1023/b:mine.0000030020.28625.7e|s2cid=144522961|issn=0026-4695}}</ref>

Anderson discovered the positron on 2 August 1932,<ref>
{{cite journal
 |last=Anderson |first=C. D.
 |date=1933
 |title=The Positive Electron
 |journal=[[Physical Review]]
 |volume=43 |issue=6 |pages=491–494
 |bibcode=1933PhRv...43..491A
 |doi=10.1103/PhysRev.43.491
 |doi-access=free
}}</ref> for which he won the [[Nobel Prize in Physics|Nobel Prize for Physics]] in 1936.<ref name="nobel">
{{cite web
 |title=The Nobel Prize in Physics 1936
 |url=http://nobelprize.org/nobel_prizes/physics/laureates/1936/index.html
 |access-date=21 January 2010
}}</ref> Anderson did not coin the term ''positron'', but allowed it at the suggestion of the ''[[Physical Review]]'' journal editor to whom he submitted his discovery paper in late 1932. The positron was the first evidence of [[antimatter]] and was discovered when Anderson allowed cosmic rays to pass through a cloud chamber and a lead plate. A magnet surrounded this apparatus, causing particles to bend in different directions based on their electric charge. The ion trail left by each positron appeared on the photographic plate with a curvature matching the [[mass-to-charge ratio]] of an electron, but in a direction that showed its charge was positive.<ref name="Penny_Gilmer_6-19-11">
{{cite web
 |last=Gilmer
 |first=P. J.
 |date=19 July 2011
 |title=Irène Jolit-Curie, a Nobel laureate in artificial radioactivity
 |url=http://www.chem.fsu.edu/~gilmer/PDFs/Ch%202_Irene_Curie_Penny_Gilmer_6-19-11_pg_mh.pdf
 |page=8
 |access-date=13 July 2013
 |archive-url=https://web.archive.org/web/20140519131211/http://www.chem.fsu.edu/~gilmer/PDFs/Ch%202_Irene_Curie_Penny_Gilmer_6-19-11_pg_mh.pdf
 |archive-date=19 May 2014
 |url-status=dead
}}</ref>

Anderson wrote in retrospect that the positron could have been discovered earlier based on Chung-Yao Chao's work, if only it had been followed up on.<ref name="MehraRechenberg"/> [[Frédéric Joliot-Curie|Frédéric]] and [[Irène Joliot-Curie]] in Paris had evidence of positrons in old photographs when Anderson's results came out, but they had dismissed them as protons.<ref name="Penny_Gilmer_6-19-11"/>

The positron had also been contemporaneously discovered by [[Patrick Blackett]] and [[Giuseppe Occhialini]] at the Cavendish Laboratory in 1932. Blackett and Occhialini had delayed publication to obtain more solid evidence, so Anderson was able to publish the discovery first.<ref name="AM">
{{cite web
 |date=2011–2014
 |title=Atop the Physics Wave: Rutherford Back in Cambridge, 1919–1937
 |url=http://www.aip.org/history/exhibits/rutherford/sections/atop-physics-wave.html
 |website=Rutherford's Nuclear World
 |publisher=[[American Institute of Physics]]
 |access-date=19 August 2014
 |archive-date=21 October 2014
 |archive-url=https://web.archive.org/web/20141021094704/http://www.aip.org/history/exhibits/rutherford/sections/atop-physics-wave.html
 |url-status=dead
}}</ref>