Editing Caesium (section)

===Isotopes===
{{Main|Isotopes of caesium}}
Caesium has 41 known [[isotope]]s, ranging in [[mass number]] (i.e. number of [[nucleon]]s in the nucleus) from 112 to 152. Several of these are synthesized from lighter elements by the slow neutron capture process ([[S-process]]) inside old stars<ref>{{cite journal |doi=10.1146/annurev.astro.37.1.239 |author=Busso, M. |author2=Gallino, R. |author3=Wasserburg, G. J. |title=Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation |journal=Annual Review of Astronomy and Astrophysics |volume=37 |date=1999 |pages=239–309 |url=http://authors.library.caltech.edu/1194/1/BUSaraa99.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://authors.library.caltech.edu/1194/1/BUSaraa99.pdf |archive-date=10 October 2022 |url-status=live |access-date=20 February 2010 |bibcode=1999ARA&A..37..239B}}</ref> and by the [[R-process]] in [[supernova]] explosions.<ref>{{cite book |first=David |last=Arnett |date=1996 |title=Supernovae and Nucleosynthesis: An Investigation of the History of Matter, from the Big Bang to the Present |publisher=Princeton University Press |page=527 |isbn=978-0-691-01147-9}}</ref> The only [[stable nuclide|stable]] caesium isotope is <sup>133</sup>Cs, with 78 [[neutron]]s. Although it has a large [[nuclear spin]] ({{sfrac|7|2}}+), [[nuclear magnetic resonance]] studies can use this isotope.<ref name="NMR">{{cite journal |doi=10.1016/0277-5387(96)00018-6 |title=Complexation of caesium and rubidium cations with crown ethers in N,N-dimethylformamide |date=1996 |last1=Goff |first1=C. |journal=Polyhedron |volume=15 |pages=3897–3903 |last2=Matchette |first2=Michael A. |last3=Shabestary |first3=Nahid |last4=Khazaeli |first4=Sadegh |issue=21}}</ref>
[[File:Cs-137-decay.svg|thumb|Decay of caesium-137|alt=A graph showing the energetics of caesium-137 (nuclear spin: I={{sfrac|7|2}}+, half-life of about 30 years) decay. With a 94.6% probability, it decays by a 512&nbsp;keV beta emission into barium-137m (I=11/2-, t=2.55min); this further decays by a 662&nbsp;keV gamma emission with an 85.1% probability into barium-137 (I={{sfrac|3|2}}+). Alternatively, caesium-137 may decay directly into barium-137 by a 0.4% probability beta emission.]]
The radioactive [[caesium-135|<sup>135</sup>Cs]] has a very long half-life of about 2.3&nbsp;million years, the longest of all radioactive isotopes of caesium. [[caesium-137|<sup>137</sup>Cs]] and [[caesium-134|<sup>134</sup>Cs]] have half-lives of 30 and two years, respectively. <sup>137</sup>Cs decomposes to a short-lived [[barium-137m|<sup>137m</sup>Ba]] by [[beta decay]], and then to nonradioactive barium, while <sup>134</sup>Cs transforms into <sup>134</sup>Ba directly. The isotopes with mass numbers of 129, 131, 132 and 136, have half-lives between a day and two weeks, while most of the other isotopes have half-lives from a few seconds to fractions of a second. At least 21 metastable [[nuclear isomer]]s exist. Other than <sup>134m</sup>Cs (with a half-life of just under 3&nbsp;hours), all are very unstable and decay with half-lives of a few minutes or less.<ref>{{cite journal |doi=10.1016/0022-1902(55)80027-9 |title=The half-life of Cs137 |date=1955 |last1=Brown |first1=F. |last2=Hall |first2=G. R. |last3=Walter |first3=A. J. |journal=Journal of Inorganic and Nuclear Chemistry |volume=1 |pages=241–247 |issue=4–5 |bibcode=1955PhRv...99..188W}}</ref><ref name="nuclidetable">{{cite web |url=http://www.nndc.bnl.gov/chart/ |title=Interactive Chart of Nuclides |publisher=Brookhaven National Laboratory |author=Sonzogni, Alejandro |location=National Nuclear Data Center |access-date=6 June 2008 |archive-date=22 May 2008 |archive-url=https://web.archive.org/web/20080522125027/http://www.nndc.bnl.gov/chart |url-status=dead}}</ref>

The isotope <sup>135</sup>Cs is one of the [[long-lived fission product]]s of [[uranium]] produced in [[nuclear reactor technology|nuclear reactors]].<ref>{{cite conference |conference=Seventh Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation |date=14–16 October 2002 |place=Jeju, Korea |first1=Shigeo |last1=Ohki |first2=Naoyuki |last2=Takaki |title=Transmutation of Cesium-135 with Fast Reactors |url=http://www.oecd-nea.org/pt/docs/iem/jeju02/session6/SessionVI-08.pdf |access-date=26 September 2010 |archive-date=28 September 2011 |archive-url=https://web.archive.org/web/20110928005357/http://www.oecd-nea.org/pt/docs/iem/jeju02/session6/SessionVI-08.pdf |url-status=dead}}</ref> However, this [[fission product yield]] is reduced in most reactors because the predecessor, [[xenon-135|<sup>135</sup>Xe]], is a potent [[neutron poison]] and frequently transmutes to stable [[xenon-136|<sup>136</sup>Xe]] before it can decay to <sup>135</sup>Cs.<ref>{{cite report |chapter-url=http://canteach.candu.org/library/20040720.pdf |title=CANDU Fundamentals |publisher=[[CANDU Owners Group]] Inc. |chapter=20 Xenon: A Fission Product Poison |access-date=15 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110723231319/http://canteach.candu.org/library/20040720.pdf |archive-date=23 July 2011}}</ref><ref>{{cite journal |journal=Journal of Environmental Radioactivity |title=Preliminary evaluation of <sup>135</sup>Cs/<sup>137</sup>Cs as a forensic tool for identifying source of radioactive contamination |first1=V. F. |last1=Taylor |first2=R. D. |last2=Evans |first3=R. J. |last3=Cornett |doi=10.1016/j.jenvrad.2007.07.006 |volume=99 |issue=1 |date=2008 |pages=109–118 |pmid=17869392}}</ref>

The [[beta decay]] from <sup>137</sup>Cs to <sup>137m</sup>Ba results in [[gamma ray|gamma radiation]] as the <sup>137m</sup>Ba relaxes to ground state <sup>137</sup>Ba, with the emitted photons having an energy of 0.6617 MeV.<ref>{{cite web |url=http://www.epa.gov/rpdweb00/radionuclides/cesium.html |title=Cesium {{pipe}} Radiation Protection |publisher=U.S. Environmental Protection Agency |date=28 June 2006 |access-date=15 February 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110315034747/http://www.epa.gov/rpdweb00/radionuclides/cesium.html |archive-date=15 March 2011}}</ref> <sup>137</sup>Cs and [[strontium-90|<sup>90</sup>Sr]] are the principal [[medium-lived fission product|medium-lived]] products of [[nuclear fission]], and the prime sources of [[radioactive decay|radioactivity]] from [[spent nuclear fuel]] after several years of cooling, lasting several hundred years.<ref>{{cite report |url=http://www.ieer.org/reports/transm/hisham.html |title=IEER Report: Transmutation – Nuclear Alchemy Gamble |publisher=Institute for Energy and Environmental Research |date=24 May 2000 |access-date=15 February 2010 |first=Hisham |last=Zerriffi |archive-date=30 May 2011 |archive-url=https://web.archive.org/web/20110530074834/http://www.ieer.org/reports/transm/hisham.html |url-status=live }}</ref> Those two isotopes are the largest source of residual radioactivity in the area of the [[Chernobyl disaster]].<ref>{{cite report |url=http://www.iaea.org/Publications/Booklets/Chernobyl/chernobyl.pdf |title=Chernobyl's Legacy: Health, Environmental and Socia-Economic Impacts and Recommendations to the Governments of Belarus, Russian Federation and Ukraine |publisher=International Atomic Energy Agency |access-date=18 February 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100215212227/http://www.iaea.org/Publications/Booklets/Chernobyl/chernobyl.pdf |archive-date=15 February 2010}}</ref> Because of the low capture rate, disposing of <sup>137</sup>Cs through [[neutron capture]] is not feasible and the only current solution is to allow it to decay over time.<ref>{{cite journal |doi=10.3327/jnst.30.911 |title=Transmutation of Cesium-137 Using Proton Accelerator |first1=Takeshi |last1=Kase |first2=Kenji |last2=Konashi |first3=Hiroshi |last3=Takahashi |first4=Yasuo |last4=Hirao |volume=30 |issue=9 |date=1993 |pages=911–918 |journal=Journal of Nuclear Science and Technology |doi-access=free}}</ref>

Almost all caesium produced from nuclear fission comes from the [[beta decay]] of originally more neutron-rich fission products, passing through various [[isotopes of iodine]] and [[isotopes of xenon|xenon]].<ref>{{cite book |isbn=978-1-56032-088-3 |publisher=Taylor & Francis |date=1992 |first=Ronald Allen |last=Knief |chapter-url=https://books.google.com/books?id=EpuaUEQaeoUC&pg=PA43 |page=42 |chapter=Fission Fragments |title=Nuclear engineering: theory and technology of commercial nuclear power |access-date=8 May 2021 |archive-date=5 March 2024 |archive-url=https://web.archive.org/web/20240305132927/https://books.google.com/books?id=EpuaUEQaeoUC&pg=PA43#v=onepage&q&f=false |url-status=live }}</ref> Because iodine and xenon are volatile and can diffuse through nuclear fuel or air, radioactive caesium is often created far from the original site of fission.<ref>{{cite journal |title=Release of xenon-137 and iodine-137 from UO2 pellet by pulse neutron irradiation at NSRR |last1=Ishiwatari |first1=N. |last2=Nagai |first2=H. |pages=843–850 |volume=23 |issue=11 |journal=Nippon Genshiryoku Gakkaishi |osti=5714707}}</ref> With [[nuclear weapons testing]] in the 1950s through the 1980s, <sup>137</sup>Cs was released into the [[atmosphere of Earth|atmosphere]] and returned to the surface of the earth as a component of [[nuclear fallout|radioactive fallout]]. It is a ready marker of the movement of soil and sediment from those times.<ref name="USGS"/>