Editing Chromium (section)

=== Isotopes ===
{{Main|Isotopes of chromium}}

Naturally occurring chromium is composed of four stable [[isotope]]s; <sup>50</sup>Cr, <sup>52</sup>Cr, <sup>53</sup>Cr and <sup>54</sup>Cr, with <sup>52</sup>Cr being the most abundant (83.789% [[natural abundance]]). <sup>50</sup>Cr is [[Stable nuclide#Still-unobserved decay|observationally stable]], as it is theoretically capable of [[radioactive decay|decaying]] to [[Isotopes of titanium|<sup>50</sup>Ti]] via [[double electron capture]] with a [[half-life]] of no less than 1.3{{e|18}} years. Twenty-five [[radioisotope]]s have been characterized, ranging from <sup>42</sup>Cr to <sup>70</sup>Cr; the most stable radioisotope is <sup>51</sup>Cr with a half-life of 27.7 days. All of the remaining [[radioactive]] isotopes have half-lives that are less than 24 hours and the majority less than 1 minute. Chromium also has two [[metastable]] [[nuclear isomer]]s.{{NUBASE2020|ref}} The primary [[decay mode]] before the most abundant stable isotope, <sup>52</sup>Cr, is [[electron capture]] and the primary mode after is [[beta decay]].{{NUBASE2020|ref}}

<sup>53</sup>Cr is the [[radiogenic]] decay product of <sup>53</sup>[[manganese|Mn]] (half-life 3.74&nbsp;million years).<ref>{{cite web|url = https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html|title = Live Chart of Nuclides|website = International Atomic Energy Agency – Nuclear Data Section|access-date = 18 October 2018|archive-date = 23 March 2019|archive-url = https://web.archive.org/web/20190323230752/https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html|url-status = live}}</ref> Chromium isotopes are typically collocated (and compounded) with [[manganese]] isotopes. This circumstance is useful in [[isotope geology]]. Manganese-chromium isotope ratios reinforce the evidence from [[aluminium-26|<sup>26</sup>Al]] and <sup>107</sup>[[Palladium|Pd]] concerning the early history of the [[Solar System]]. Variations in <sup>53</sup>Cr/<sup>52</sup>Cr and Mn/Cr ratios from several meteorites indicate an initial <sup>53</sup>Mn/<sup>55</sup>Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of <sup>53</sup>Mn in differentiated planetary bodies. Hence <sup>53</sup>Cr provides additional evidence for [[nucleosynthesis|nucleosynthetic]] processes immediately before coalescence of the Solar System.<ref name="53Mn53Cr">{{cite journal|journal = Geochimica et Cosmochimica Acta|volume = 63|issue = 23–24|date = 1999|pages = 4111–4117|doi = 10.1016/S0016-7037(99)00312-9|title = <sup>53</sup>Mn-<sup>53</sup>Cr evolution of the early solar system|last1 = Birck|first1 = JL|last2 = Rotaru|first2 = M|last3 = Allegre|first3 = C|bibcode=1999GeCoA..63.4111B}}</ref><!-- {{doi|10.1038/331579a0}} {{doi|10.1016/j.gca.2004.01.008}} {{doi|10.1016/j.epsl.2006.07.036}} ---> <sup>53</sup>Cr has been posited as a proxy for atmospheric oxygen concentration.<ref>{{cite journal|last1 = Frei|first1 = Robert|last2 = Gaucher|first2 = Claudio|last3 = Poulton|first3 = Simon W|last4=Canfield|first4=Don E|s2cid = 4373201|title=Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes|journal = Nature |volume = 461|issue = 7261|pages = 250–253|date = 2009|pmid = 19741707|doi = 10.1038/nature08266|bibcode = 2009Natur.461..250F}}</ref>