Editing Xenon (section)

== Occurrence and production ==
Xenon is a [[trace gas]] in [[Earth's atmosphere]], occurring at a volume fraction of {{val|87|1|u=nL/L}} ([[parts per billion]]), or approximately 1 part per 11.5 million.<ref name="kirk">{{cite book
| last      = Hwang
| first     = Shuen-Cheng
| author2   = Robert D. Lein
| author3   = Daniel A. Morgan
| chapter   = Noble Gases
| title     = Kirk-Othmer Encyclopedia of Chemical Technology
| publisher = [[John Wiley & Sons|Wiley]]
| year      = 2005
| edition   = 5th
| doi       = 10.1002/0471238961.0701190508230114.a01
| isbn      = 0-471-48511-X
}}</ref> It is also found as a component of gases emitted from some [[mineral spring]]s. Given a total mass of the atmosphere of {{convert|5.15e18|kg}}, the atmosphere contains on the order of {{convert|2.03|Gt}} of xenon in total when taking the average molar mass of the atmosphere as 28.96&nbsp;g/mol which is equivalent to some 394-mass ppb.

=== The missing Xe problem ===
The concentration of Xe in the atmosphere is much lower than Ar and Kr, a geological mystery known as "the missing Xe problem". Numerous proposals have been made to explain the mystery, including formation of Xe-Fe oxides in the Earth's lower mantle,<ref>{{Cite journal |last=Peng |first=Feng |last2=Song |first2=Xianqi |last3=Liu |first3=Chang |last4=Li |first4=Quan |last5=Miao |first5=Maosheng |last6=Chen |first6=Changfeng |last7=Ma |first7=Yanming |date=October 16, 2020 |title=Xenon iron oxides predicted as potential Xe hosts in Earth’s lower mantle |url=https://www.nature.com/articles/s41467-020-19107-y |journal=Nature Communications |language=en |volume=11 |issue=1 |doi=10.1038/s41467-020-19107-y |issn=2041-1723 |pmc=7568531 |pmid=33067445}}</ref> formation xenon dioxide in silica,<ref>{{Cite journal |last=Brock |first=David S. |last2=Schrobilgen |first2=Gary J. |date=April 27, 2011 |title=Synthesis of the Missing Oxide of Xenon, XeO2, and Its Implications for Earth’s Missing Xenon |url=https://pubs.acs.org/doi/10.1021/ja110618g |journal=Journal of the American Chemical Society |volume=133 |issue=16 |pages=6265–6269 |doi=10.1021/ja110618g |issn=0002-7863}}</ref> and reactions between Xe and Fe/Ni in the Earth's core.<ref>{{Cite journal |last=Zhu |first=Li |last2=Liu |first2=Hanyu |last3=Pickard |first3=Chris J. |last4=Zou |first4=Guangtian |last5=Ma |first5=Yanming |date=July 2014 |title=Reactions of xenon with iron and nickel are predicted in the Earth's inner core |url=https://www.nature.com/articles/nchem.1925 |journal=Nature Chemistry |language=en |volume=6 |issue=7 |pages=644–648 |doi=10.1038/nchem.1925 |issn=1755-4349|arxiv=1309.2169 }}</ref>

=== Commercial ===
Xenon is obtained commercially as a by-product of the [[air separation|separation of air]] into [[oxygen]] and [[nitrogen]].<ref>{{cite journal
| url     = https://www.nevis.columbia.edu/~ju/Paper/Paper-detector/science16.pdf
| title   = Present and future production of xenon and krypton in the former USSR region and some physical properties of these gases
| last1   = Lebedev
| first1  = P. K.
| last2   = Pryanichnikov
| first2  = V. I.
| journal = Nuclear Instruments and Methods in Physics Research A
| volume  = 327
| year    = 1993
| issue   = 1
| pages   = 222–226
| doi     = 10.1016/0168-9002(93)91447-U
| bibcode = 1993NIMPA.327..222L
}}</ref> After this separation, generally performed by [[fractional distillation]] in a double-column plant, the [[liquid oxygen]] produced will contain small quantities of [[krypton]] and xenon. By additional fractional distillation, the liquid oxygen may be enriched to contain 0.1–0.2% of a krypton/xenon mixture, which is extracted either by [[adsorption]] onto [[silica gel]] or by distillation. Finally, the krypton/xenon mixture may be separated into krypton and xenon by further distillation.<ref>{{cite book
| first     = Frank G.
| last      = Kerry
| date      = 2007
| title     = Industrial Gas Handbook: Gas Separation and Purification
| pages     = 101–103
| publisher = CRC Press
| isbn      = 978-0-8493-9005-0
| url       = https://books.google.com/books?id=cXNmyTTGbRIC&pg=PA101
}}</ref><ref>{{cite web
| url          = http://www.c-f-c.com/specgas_products/xenon.htm
| title        = Xenon – Xe
| access-date  = September 7, 2007
| date         = August 10, 1998
| publisher    = CFC StarTec LLC
| archive-date = June 12, 2020
| archive-url  = https://web.archive.org/web/20200612100905/http://www.c-f-c.com/specgas_products/xenon.htm
| url-status   = dead
}}</ref>

Worldwide production of xenon in 1998 was estimated at {{convert|5,000–7,000|m3}}.<ref name="ullmann">{{cite book
| last1     = Häussinger
| first1    = Peter
| author2   = Glatthaar, Reinhard
| author3   = Rhode, Wilhelm
| author4   = Kick, Helmut
| author5   = Benkmann, Christian
| author6   = Weber, Josef
| author7   = Wunschel, Hans-Jörg
| author8   = Stenke, Viktor
| author9   = Leicht, Edith
 |author10= Stenger, Hermann
| chapter   = Noble Gases
| title     = Ullmann's Encyclopedia of Industrial Chemistry
| publisher = Wiley
| year      = 2001
| edition   = 6th
| doi       = 10.1002/14356007.a17_485
| isbn      = 3-527-20165-3
}}</ref> At a density of {{Convert|5.894|g/L}} this is equivalent to roughly {{Convert|30 to 40|t}}. Because of its scarcity, xenon is much more expensive than the lighter noble gases—approximate prices for the purchase of small quantities in Europe in 1999 were 10&nbsp;[[Euro|€]]/L (=~€1.7/g) for xenon, 1&nbsp;€/L (=~€0.27/g) for krypton, and 0.20&nbsp;€/L (=~€0.22/g) for neon,<ref name="ullmann" /> while the much more plentiful argon, which makes up over 1% by volume of earth's atmosphere, costs less than a cent per liter.

=== Solar System ===
Within the Solar System, the [[nucleon]] fraction of xenon is {{val|1.56|e=-8}}, for an [[Abundance of the chemical elements|abundance]] of approximately one part in 630&nbsp;thousand of the total mass.<ref>{{cite book
| first     = David
| last      = Arnett
| date      = 1996
| title     = Supernovae and Nucleosynthesis
| publisher = [[Princeton University Press]]
| location  = Princeton, [[New Jersey|NJ]]
| isbn      = 0-691-01147-8
| url       = https://books.google.com/books?id=PXGWGnPPo0gC&pg=PA30
}}</ref> Xenon is relatively rare in the [[Sun]]'s atmosphere, on [[Earth]], and in [[asteroid]]s and [[comet]]s. The abundance of xenon in the atmosphere of planet [[Jupiter]] is unusually high, about 2.6 times that of the Sun.<ref name="mahaffy">{{cite journal
| last1      = Mahaffy
| first1     = P. R.
| last2      = Niemann
| first2     = H. B.
| last3      = Alpert
| first3     = A.
| last4      = Atreya
| first4     = S. K.
| last5      = Demick
| first5     = J.
| last6      = Donahue
| first6     = T. M.
| last7      = Harpold
| first7     = D. N.
| last8      = Owen
| first8     = T. C.
| title      = Noble gas abundance and isotope ratios in the atmosphere of Jupiter from the Galileo Probe Mass Spectrometer
| journal    = Journal of Geophysical Research
| date       = 2000
| volume     = 105
| issue      = E6
| pages      = 15061–72
| bibcode    = 2000JGR...10515061M
| doi        = 10.1029/1999JE001224
| doi-access = free
}}</ref>{{efn | Mass fraction calculated from the average mass of an atom in the Solar System of about 1.29 atomic mass units.}}  This abundance remains unexplained, but may have been caused by an early and rapid buildup of [[planetesimal]]s—small, sub-planetary bodies—before the heating of the [[solar nebula|presolar disk]];<ref>{{cite journal
| last1      = Owen
| first1     = Tobias
| last2      = Mahaffy
| first2     = Paul
| last3      = Niemann
| first3     = H. B.
| last4      = Atreya
| first4     = Sushil
| last5      = Donahue
| first5     = Thomas
| last6      = Bar-Nun
| first6     = Akiva
| last7      = de Pater
| first7     = Imke
| s2cid      = 4426771
| title      = A low-temperature origin for the planetesimals that formed Jupiter
| journal    = Nature
| year       = 1999
| volume     = 402
| issue      = 6759
| pages      = 269–70
| bibcode    = 1999Natur.402..269O
| doi        = 10.1038/46232
| pmid       = 10580497
| hdl        = 2027.42/62913
| url        = https://deepblue.lib.umich.edu/bitstream/2027.42/62913/1/402269a0.pdf
| hdl-access = free
}}</ref> otherwise, xenon would not have been trapped in the planetesimal ices.  The problem of the low terrestrial xenon may be explained by [[covalent bond]]ing of xenon to oxygen within [[quartz]], reducing the [[outgassing]] of xenon into the atmosphere.<ref>{{cite journal
| last            = Sanloup
| first           = Chrystèle
| s2cid           = 31226092
| display-authors = etal
| title           = Retention of Xenon in Quartz and Earth's Missing Xenon
| journal         = Science
| year            = 2005
| volume          = 310
| issue           = 5751
| pages           = 1174–7
| doi             = 10.1126/science.1119070
| pmid            = 16293758
| bibcode         = 2005Sci...310.1174S
}}</ref>

=== Stellar ===
Unlike the lower-mass noble gases, the normal [[stellar nucleosynthesis]] process inside a star does not form xenon. Nucleosynthesis consumes energy to produce nuclides more massive than [[iron-56]], and thus the synthesis of xenon represents no energy gain for a star.<ref>{{cite book
| first      = Donald D.
| last       = Clayton
| date       = 1983
| title      = Principles of Stellar Evolution and Nucleosynthesis
| publisher  = [[University of Chicago Press]]
| isbn       = 0-226-10953-4
| url        = https://archive.org/details/principlesofstel0000clay
| url-access = registration
| page       = [https://archive.org/details/principlesofstel0000clay/page/604 604]
}}</ref> Instead, xenon is formed during [[supernova]] explosions during the [[r-process]],<ref name="heymann">{{cite conference
| last      = Heymann
| first     = D.
| author2   = Dziczkaniec, M.
| title     = Xenon from intermediate zones of supernovae
| work      = Proceedings 10th Lunar and Planetary Science Conference
| pages     = 1943–1959
| publisher = Pergamon Press, Inc.
| date      = March 19–23, 1979
| location  = Houston, Texas
| bibcode   = 1979LPSC...10.1943H
}}</ref> by the slow neutron-capture process ([[s-process]]) in [[red giant]] stars that have exhausted their core hydrogen and entered the [[asymptotic giant branch]],<ref>{{cite journal
| author  = Beer, H.
| author2 = Kaeppeler, F.
| author3 = Reffo, G.
| author4 = Venturini, G.
| s2cid   = 123139238
| title   = Neutron capture cross-sections of stable xenon isotopes and their application in stellar nucleosynthesis
| journal = Astrophysics and Space Science
| volume  = 97
| issue   = 1
| date    = November 1983
| pages   = 95–119
| doi     = 10.1007/BF00684613
| bibcode = 1983Ap&SS..97...95B
}}</ref> and from radioactive decay, for example by [[beta decay]] of [[extinct radionuclide|extinct]] [[iodine-129]] and [[spontaneous fission]] of [[thorium]], [[uranium]], and [[plutonium]].<ref name="caldwell" />

=== Nuclear fission ===
[[Xenon-135]] is a notable [[neutron poison]] with a high [[fission product yield]]. As it is relatively short lived, it decays at the same rate it is produced during ''steady'' operation of a nuclear reactor. However, if power is reduced or the reactor is [[scram]]med, less xenon is destroyed than is produced from the beta decay of its [[parent nuclide]]s. This phenomenon called [[xenon poisoning]] can cause significant problems in restarting a reactor after a scram or increasing power after it had been reduced and it was one of several contributing factors in the [[Chernobyl nuclear accident]].<ref>{{cite web
| url   = http://hyperphysics.phy-astr.gsu.edu/hbase/NucEne/xenon.html
| title = "Xenon Poisoning" or Neutron Absorption in Reactors
}}</ref><ref>{{cite web
| url   = https://world-nuclear.org/information-library/safety-and-security/safety-of-plants/appendices/chernobyl-accident-appendix-1-sequence-of-events.aspx
| title = Chernobyl Appendix 1: Sequence of Events – World Nuclear Association
}}</ref>

Stable or extremely long lived isotopes of xenon are also produced in appreciable quantities in nuclear fission. Xenon-136 is produced both as a fission product and when xenon-135 undergoes [[neutron capture]] before it can decay. The ratio of xenon-136 to xenon-135 (or its decay products) can give hints as to the power history of a given reactor or identify a nuclear explosion, as xenon-135 is mostly produced by successive beta decays of more neutron-rich fission products. These short-lived nuclides do not share its neutron-absorbing prowess, and so absorb fewer neutrons during the brief moment of a nuclear explosion, lowering the ratio of mass-136 to mass-135 products.<ref>{{Cite journal
| doi        = 10.1016/j.net.2016.04.006
| title      = Development of Industrial-Scale Fission 99Mo Production Process Using Low Enriched Uranium Target
| year       = 2016
| last1      = Lee
| first1     = Seung-Kon
| last2      = Beyer
| first2     = Gerd J.
| last3      = Lee
| first3     = Jun Sig
| journal    = Nuclear Engineering and Technology
| volume     = 48
| issue      = 3
| pages      = 613–623
| doi-access = free
}}</ref>

The stable isotope xenon-132 has a fission product yield of over 4% in the [[thermal neutron]] fission of {{chem|235|U}} which means that stable or nearly stable xenon isotopes have a higher mass fraction in [[spent nuclear fuel]] (which is about 3% fission products) than it does in air. However, there is as of 2022 no commercial effort to extract xenon from spent fuel during [[nuclear reprocessing]].<ref>{{Cite web
| url   = https://news.mit.edu/2020/novel-gas-capture-approach-advances-nuclear-fuel-management-0724
| title = Novel gas-capture approach advances nuclear fuel management
| date  = July 24, 2020
}}</ref><ref>{{Cite web
| url   = https://energyfromthorium.com/2010/06/22/whats-in-spent-nuclear-fuel-after-20-yrs/
| title = What's in Spent Nuclear Fuel? (After 20 yrs) – Energy from Thorium
| date  = June 22, 2010
}}</ref>