Editing Xenon (section)

== Isotopes ==
{{Main|Isotopes of xenon}}
Naturally occurring xenon is composed of seven [[stable isotope|stable]] and two [[primordial radionuclide|almost stable]] [[isotope]]s: <sup>126</sup>Xe, <sup>128–132</sup>Xe, and <sup>134</sup>Xe are stable, <sup>124</sup>Xe and <sup>136</sup>Xe have very long half-lives, trillions of times the age of the universe. The isotopes <sup>126</sup>Xe and <sup>134</sup>Xe are predicted by theory to undergo [[double beta decay]], but this has never been observed so they are considered stable.<ref>{{cite journal
| last    = Barabash
| first   = A. S.
| s2cid   = 15146959
| title   = Average (Recommended) Half-Life Values for Two-Neutrino Double-Beta Decay
| journal = Czechoslovak Journal of Physics
| year    = 2002
| volume  = 52
| issue   = 4
| pages   = 567–573
| doi     = 10.1023/A:1015369612904
| arxiv   = nucl-ex/0203001
| bibcode = 2002CzJPh..52..567B
}}</ref> More than 40 unstable isotopes are known. The longest-lived of these isotopes are the [[primordial nuclide|primordial]] <sup>124</sup>Xe, which undergoes [[double electron capture]] with a half-life of {{val|1.8|e=22|u=yr}},<ref name=xenon1T>{{cite journal
| year            = 2019
| title           = Observation of two-neutrino double electron capture in <sup>124</sup>Xe with XENON1T
| journal         = Nature
| volume          = 568
| issue           = 7753
| pages           = 532–535
| doi             = 10.1038/s41586-019-1124-4
| arxiv           = 1904.11002
| last1           = Aprile
| first1          = E.
| last2           = Aalbers
| first2          = J.
| last3           = Agostini
| first3          = F.
| last4           = Alfonsi
| first4          = M.
| last5           = Althueser
| first5          = L.
| last6           = Amaro
| first6          = F. D.
| last7           = Anthony
| first7          = M.
| last8           = Antochi
| first8          = V. C.
| last9           = Arneodo
| first9          = F. |last10=Baudis |first10=L.
| last11          = Bauermeister
| first11         = B.
| last12          = Benabderrahmane
| first12         = M. L.
| last13          = Berger
| first13         = T.
| last14          = Breur
| first14         = P. A.
| last15          = Brown
| first15         = A.
| last16          = Brown
| first16         = A.
| last17          = Brown
| first17         = E.
| last18          = Bruenner
| first18         = S.
| last19          = Bruno
| first19         = G. |last20=Budnik |first20=R.
| last21          = Capelli
| first21         = C.
| last22          = Cardoso
| first22         = J. M. R.
| last23          = Cichon
| first23         = D.
| last24          = Coderre
| first24         = D.
| last25          = Colijn
| first25         = A. P.
| last26          = Conrad
| first26         = J.
| last27          = Cussonneau
| first27         = J. P.
| last28          = Decowski
| first28         = M. P.
| last29          = de Perio
| first29         = P. |last30=Di Gangi |first30=P.
| pmid            = 31019319
| bibcode         = 2019Natur.568..532X
| s2cid           = 129948831
| display-authors = 1
}}</ref> and <sup>136</sup>Xe, which undergoes double beta decay with a half-life of {{nowrap|2.11 × 10<sup>21</sup> yr}}.<ref name="EXO">{{cite journal
| last    = Ackerman
| first   = N.
| s2cid   = 40334443
| title   = Observation of Two-Neutrino Double-Beta Decay in <sup>136</sup>Xe with the EXO-200 Detector
| journal = Physical Review Letters
| year    = 2011
| volume  = 107
| issue   = 21
| pages   = 212501
| doi     = 10.1103/PhysRevLett.107.212501
| pmid    = 22181874
| bibcode = 2011PhRvL.107u2501A
| arxiv   = 1108.4193
}}</ref> <sup>129</sup>Xe is produced by [[beta decay]] of <sup>129</sup>[[iodine|I]], which has a [[half-life]] of 16&nbsp;million years. <sup>131m</sup>Xe, <sup>133</sup>Xe, <sup>133m</sup>Xe, and <sup>135</sup>Xe are some of the [[nuclear fission|fission]] products of <sup>235</sup>[[uranium|U]] and <sup>239</sup>[[plutonium|Pu]],<ref name="caldwell">{{cite web
 |last         = Caldwell
 |first        = Eric
 |date         = January 2004
 |url          = http://wwwrcamnl.wr.usgs.gov/isoig/period/xe_iig.html
 |title        = Periodic Table – Xenon
 |work         = Resources on Isotopes
 |publisher    = USGS
 |access-date  = October 8, 2007
|archive-date = December 13, 2013
|archive-url  = https://web.archive.org/web/20131213053952/http://wwwrcamnl.wr.usgs.gov/isoig/period/xe_iig.html
 |url-status   = dead
}}</ref> and are used to detect and monitor nuclear explosions.

=== Nuclear spin ===
Nuclei of two of the stable [[isotopes of xenon]], <sup>129</sup>Xe and <sup>131</sup>Xe (both stable isotopes with odd mass numbers), have non-zero intrinsic [[angular momentum|angular momenta]] ([[Spin (physics)|nuclear spins]], suitable for [[nuclear magnetic resonance]]). The nuclear spins can be aligned beyond ordinary polarization levels by means of circularly polarized light and [[rubidium]] vapor.<ref>{{cite journal
| last       = Otten
| first      = Ernst W.
| s2cid      = 51224754
| date       = 2004
| title      = Take a breath of polarized noble gas
| journal    = Europhysics News
| volume     = 35
| issue      = 1
| doi        = 10.1051/epn:2004109
| pages      = 16–20
| bibcode    = 2004ENews..35...16O
| doi-access = free
}}</ref> The resulting [[spin polarization]] of xenon [[atomic nucleus|nuclei]] can surpass 50% of its maximum possible value, greatly exceeding the thermal equilibrium value dictated by [[paramagnetic]] statistics (typically 0.001% of the maximum value at [[room temperature]], even in the strongest [[magnet]]s). Such non-equilibrium alignment of spins is a temporary condition, and is called ''[[hyperpolarization (physics)|hyperpolarization]]''. The process of hyperpolarizing the xenon is called ''optical pumping'' (although the process is different from [[optical pumping|pumping a laser]]).<ref>{{cite journal
| journal = Physical Review Letters
| volume  = 96
| issue   = 5
| page    = 053002
| year    = 2006
| title   = Optical Pumping System Design for Large Production of Hyperpolarized <sup>129</sup>Xe
| first   = I. C.
| last    = Ruset
| author2 = Ketel, S.
| author3 = Hersman, F. W.
| doi     = 10.1103/PhysRevLett.96.053002
| pmid    = 16486926
| bibcode = 2006PhRvL..96e3002R
}}</ref>

Because a <sup>129</sup>Xe nucleus has a [[Spin (physics)|spin]] of 1/2, and therefore a zero [[electric field|electric]] [[quadrupole moment]], the <sup>129</sup>Xe nucleus does not experience any quadrupolar interactions during collisions with other atoms, and the hyperpolarization persists for long periods even after the engendering light and vapor have been removed. Spin polarization of <sup>129</sup>Xe can persist from several [[second]]s for xenon atoms dissolved in [[blood]]<ref>{{cite journal
| first      = J.
| last       = Wolber
| author2    = Cherubini, A.
| author3    = Leach, M. O.
| author4    = Bifone, A.
| title      = On the oxygenation-dependent <sup>129</sup>Xe t<sub>1</sub> in blood
| year       = 2000
| journal    = [[NMR in Biomedicine]]
| volume     = 13
| issue      = 4
| pages      = 234–7
| doi        = 10.1002/1099-1492(200006)13:4<234::AID-NBM632>3.0.CO;2-K
| pmid       = 10867702
| s2cid      = 94795359
| doi-access = free
}}</ref> to several hours in the [[gas phase]]<ref>{{cite journal
| first   = B.
| last    = Chann
| author2 = Nelson, I. A.
| author3 = Anderson, L. W.
| author4 = Driehuys, B.
| author5 = Walker, T. G.
| title   = <sup>129</sup>Xe-Xe molecular spin relaxation
| year    = 2002
| journal = Physical Review Letters
| volume  = 88
| issue   = 11
| pages   = 113–201
| doi     = 10.1103/PhysRevLett.88.113201
| pmid    = 11909399
| bibcode = 2002PhRvL..88k3201C
}}</ref> and several days in deeply frozen solid xenon.<ref>{{cite encyclopedia
| first     = Gustav Konrad
| last      = von Schulthess
| author2   = Smith, Hans-Jørgen
| author3   = Pettersson, Holger
| author4   = Allison, David John
| year      = 1998
| title     = The Encyclopaedia of Medical Imaging
| page      = 194
| publisher = Taylor & Francis
| isbn      = 1-901865-13-4
| url       = https://books.google.com/books?id=zvDY5unRC4oC&pg=PA194
}}</ref> In contrast, [[isotopes of xenon|<sup>131</sup>Xe]] has a nuclear spin value of {{frac|3|2}} and a nonzero [[quadrupole moment]], and has t<sub>1</sub> relaxation times in the [[millisecond]] and [[second]] ranges.<ref>{{cite journal
| first   = W. W.
| last    = Warren
| author2 = Norberg, R. E.
| title   = Nuclear Quadrupole Relaxation and Chemical Shift of Xe<sup>131</sup> in Liquid and Solid Xenon
| year    = 1966
| journal = Physical Review
| volume  = 148
| issue   = 1
| pages   = 402–412
| doi     = 10.1103/PhysRev.148.402
| bibcode = 1966PhRv..148..402W
}}</ref>

=== From fission ===
Some radioactive isotopes of xenon (for example, <sup>133</sup>Xe and <sup>135</sup>Xe) are produced by [[neutron]] irradiation of fissionable material within [[nuclear reactor]]s.<ref name="lanl" /> [[Xenon-135|<sup>135</sup>Xe]] is of considerable significance in the operation of [[nuclear reactor|nuclear fission reactors]]. <sup>135</sup>Xe has a huge [[Neutron cross-section|cross section]] for [[thermal neutron]]s, 2.6×10<sup>6</sup>&nbsp;[[Barn (unit)|barns]],<ref name="stacey">{{cite book
| first     = Weston M.
| last      = Stacey
| date      = 2007
| title     = Nuclear Reactor Physics
| page      = 213
| url       = https://books.google.com/books?id=y1UgcgVSXSkC&pg=PA213
| publisher = Wiley-VCH
| isbn      = 978-3-527-40679-1
}}</ref> and operates as a [[neutron absorber]] or "[[nuclear poison|poison]]" that can slow or stop the chain reaction after a period of operation. This was discovered in the earliest nuclear reactors built by the American [[Manhattan Project]] for [[plutonium]] production. However, the designers had made provisions in the design to increase the reactor's reactivity (the number of neutrons per fission that go on to fission other atoms of [[nuclear fuel]]).<ref>{{cite web
| author       = Staff
| url          = http://www.cfo.doe.gov/me70/manhattan/hanford_operational.htm
| archive-url  = https://web.archive.org/web/20091210094859/http://www.cfo.doe.gov/me70/manhattan/hanford_operational.htm
| archive-date = December 10, 2009
| title        = Hanford Becomes Operational
| work         = The Manhattan Project: An Interactive History
| publisher    = U.S. Department of Energy
| access-date  = October 10, 2007
}}</ref>

<sup>135</sup>Xe reactor poisoning was a major factor in the [[Chernobyl disaster]].<ref>{{cite book
| title     = Modern Physics: An Introductory Text
| date      = 2000
| first     = Jeremy I.
| last      = Pfeffer
| author2   = Nir, Shlomo
| pages     = 421 ff
| publisher = [[Imperial College Press]]
| isbn      = 1-86094-250-4
| url       = https://books.google.com/books?id=KmMYWP56t98C&pg=PA421
}}</ref> A shutdown or decrease of power of a reactor can result in buildup of <sup>135</sup>Xe, with reactor operation going into a condition known as the [[iodine pit]]. Under adverse conditions, relatively high concentrations of radioactive xenon isotopes may emanate from cracked [[fuel rod]]s,<ref>{{cite book
| first     = Edwards A.
| last      = Laws
| date      = 2000
| title     = Aquatic Pollution: An Introductory Text
| page      = 505
| publisher = John Wiley and Sons
| isbn      = 0-471-34875-9
| url       = https://books.google.com/books?id=11LI7XyEIsAC&pg=PA505
}}</ref> or fissioning of uranium in [[Water cooling|cooling water]].<ref>{{cite news
| author       = Staff
| date         = April 9, 1979
| title        = A Nuclear Nightmare
| magazine     = [[Time (magazine)|Time]]
| url          = http://www.time.com/time/magazine/article/0,9171,920196-4,00.html
| archive-url  = https://web.archive.org/web/20071012190713/http://www.time.com/time/magazine/article/0,9171,920196-4,00.html
| url-status   = dead
| archive-date = October 12, 2007
| access-date  = October 9, 2007
}}</ref>

Isotope ratios of xenon produced in [[natural nuclear fission reactor]]s at [[Oklo]] in Gabon reveal the reactor properties during chain reaction that took place about 2 billion years ago.<ref name="Meshik PRL 2004">{{cite journal
| last1   = Meshik
| first1  = A. P.
| last2   = Hohenberg
| first2  = C. M.
| last3   = Pravdivtseva
| first3  = O. V.
| title   = Record of Cycling Operation of the Natural Nuclear Reactor in the Oklo/Okelobondo Area in Gabon
| journal = Phys. Rev. Lett.
| volume  = 93
| date    = 2004
| issue   = 18
| page    = 182302
| issn    = 0031-9007
| doi     = 10.1103/physrevlett.93.182302
| pmid    = 15525157
| bibcode = 2004PhRvL..93r2302M
}}</ref>

=== Cosmic processes ===
Because xenon is a tracer for two parent isotopes, xenon isotope ratios in [[meteorite]]s are a powerful tool for studying the [[formation of the Solar System]]. The [[Iodine–xenon dating|iodine–xenon method]] of [[Radiometric dating|dating]] gives the time elapsed between [[nucleosynthesis]] and the condensation of a solid object from the [[solar nebula]]. In 1960, physicist [[John Reynolds (physicist)|John H. Reynolds]] discovered that certain [[meteorite]]s contained an isotopic anomaly in the form of an overabundance of xenon-129. He inferred that this was a [[decay product]] of radioactive [[iodine-129]]. This isotope is produced slowly by [[cosmic ray spallation]] and [[nuclear fission]], but is produced in quantity only in supernova explosions.<ref name="Clayton 1983 75">{{cite book
| first      = Donald D.
| last       = Clayton
| date       = 1983
| title      = Principles of Stellar Evolution and Nucleosynthesis
| page       = [https://archive.org/details/principlesofstel0000clay/page/75 75]
| edition    = 2nd
| url        = https://archive.org/details/principlesofstel0000clay
| url-access = registration
| publisher  = University of Chicago Press
| isbn       = 0-226-10953-4
}}</ref><ref name="Bolt, B. A. 2007">{{cite web
| author      = Bolt, B. A.
| author2     = Packard, R. E.
| author3     = Price, P. B.
| year        = 2007
| url         = http://content.cdlib.org/xtf/view?docId=hb1r29n709&doc.view=content&chunk.id=div00061&toc.depth=1&brand=oac&anchor.id=0
| title       = John H. Reynolds, Physics: Berkeley
| publisher   = [[The University of California, Berkeley]]
| access-date = October 1, 2007
}}</ref>

Because the half-life of <sup>129</sup>I is comparatively short on a cosmological time scale (16 million years), this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the <sup>129</sup>I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the [[Solar System]], because the <sup>129</sup>I isotope was likely generated shortly before the Solar System was formed, seeding the solar gas cloud with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud.<ref name="Clayton 1983 75" /><ref name="Bolt, B. A. 2007" />

In a similar way, xenon isotopic ratios such as <sup>129</sup>Xe/<sup>130</sup>Xe and <sup>136</sup>Xe/<sup>130</sup>Xe are a powerful tool for understanding planetary differentiation and early outgassing.<ref name="kaneoka">{{cite journal
| last    = Kaneoka
| first   = Ichiro
| s2cid   = 128502357
| title   = Xenon's Inside Story
| journal = Science
| year    = 1998
| volume  = 280
| issue   = 5365
| pages   = 851–852
| doi     = 10.1126/science.280.5365.851b
}}</ref> For example, the [[atmosphere of Mars]] shows a xenon abundance similar to that of Earth (0.08&nbsp;parts per million<ref>{{cite web
| last         = Williams
| first        = David R.
| date         = September 1, 2004
| url          = http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
| title        = Mars Fact Sheet
| publisher    = NASA
| access-date  = October 10, 2007
| archive-url  = https://web.archive.org/web/20100612092806/http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
| archive-date = June 12, 2010
| url-status   = dead
}}</ref>) but Mars shows a greater abundance of <sup>129</sup>Xe than the Earth or the Sun. Since this isotope is generated by radioactive decay, the result may indicate that Mars lost most of its primordial atmosphere, possibly within the first 100 million years after the planet was formed.<ref>{{cite web
| last         = Schilling
| first        = James
| url          = http://humbabe.arc.nasa.gov/mgcm/HTML/FAQS/thin_atm.html
| title        = Why is the Martian atmosphere so thin and mainly carbon dioxide?
| publisher    = Mars Global Circulation Model Group
| access-date  = October 10, 2007
| url-status   = dead
| archive-url  = https://web.archive.org/web/20100528010109/http://humbabe.arc.nasa.gov/mgcm/HTML/FAQS/thin_atm.html
| archive-date = May 28, 2010
}}</ref><ref>{{cite journal
| last    = Zahnle
| first   = Kevin J.
| title   = Xenological constraints on the impact erosion of the early Martian atmosphere
| journal = [[Journal of Geophysical Research]]
| year    = 1993
| volume  = 98
| issue   = E6
| pages   = 10,899–10,913
| doi     = 10.1029/92JE02941
| bibcode = 1993JGR....9810899Z
| url     = https://zenodo.org/record/1231333
}}</ref> In another example, excess <sup>129</sup>Xe found in [[carbon dioxide]] well gases from [[New Mexico]] is believed to be from the decay of [[Mantle (geology)|mantle]]-derived gases from soon after Earth's formation.<ref name="caldwell" /><ref>{{cite journal
| last    = Boulos
| first   = M. S.
| author2 = Manuel, O.K.
| s2cid   = 28159702
| title   = The xenon record of extinct radioactivities in the Earth
| journal = [[Science (journal)|Science]]
| volume  = 174
| issue   = 4016
| pages   = 1334–6
| date    = 1971
| doi     = 10.1126/science.174.4016.1334
| pmid    = 17801897
| bibcode = 1971Sci...174.1334B
}}</ref>