Editing Selenium (section)

===Isotopes===
{{Main|Isotopes of selenium}}

Selenium has seven naturally occurring [[isotope]]s. Five of these, <sup>74</sup>Se, <sup>76</sup>Se, <sup>77</sup>Se, <sup>78</sup>Se, <sup>80</sup>Se, are stable, with <sup>80</sup>Se being the most abundant (49.6% natural abundance). Also naturally occurring is the long-lived [[primordial radionuclide]] <sup>82</sup>Se, with a [[half-life]] of 8.76×10<sup>19</sup> years.{{NUBASE2020|ref}} The non-primordial radioisotope [[Selenium-79|<sup>79</sup>Se]] also occurs in minute quantities in [[uranium]] ores as a product of [[nuclear fission]]. Selenium also has numerous unstable [[synthetic isotope]]s ranging from <sup>64</sup>Se to <sup>95</sup>Se; the most stable are <sup>75</sup>Se with a half-life of 119.78&nbsp;days and <sup>72</sup>Se with a half-life of 8.4&nbsp;days.{{NUBASE2016|ref}} Isotopes lighter than the stable isotopes primarily undergo [[beta plus decay]] to [[isotopes of arsenic]], and isotopes heavier than the stable isotopes undergo [[beta minus decay]] to [[isotopes of bromine]], with some minor [[neutron emission]] branches in the heaviest known isotopes.

{| class="wikitable"
|+Selenium isotopes of greatest stability
! Isotope
! Nature
! Origin
! Half-life
|-
|<sup>74</sup>Se
|Primordial
|
|Stable
|-
|<sup>76</sup>Se
|Primordial
|
|Stable
|-
|<sup>77</sup>Se
|Primordial
|Fission product
|Stable
|-
|<sup>78</sup>Se
|Primordial
|Fission product
|Stable
|-
|<sup>79</sup>Se
|Trace
|Fission product
|{{val|1=327000}} yr<ref>{{cite web |url=https://www.ptb.de/en/org/6/nachrichten6/2010/60710_en.htm |title=The half-life of <sup>79</sup>Se <!-- title=Physikalisch-Technische Bundesanstalt (PTB) --> |date=2010-09-23 |publisher=Physikalisch-Technische Bundesanstalt |access-date=2012-05-29 |df=dmy-all |archive-url=https://web.archive.org/web/20110927042432/http://www.ptb.de/en/org/6/nachrichten6/2010/60710_en.htm |archive-date=2011-09-27}}</ref><ref>{{cite journal |last2=Bühnemann |first2=Rolf |last3=Hollas |first3=Simon |last4=Kivel |first4=Niko |last5=Kossert |first5=Karsten |last6=Van Winckel |first6=Stefaan |last7=Gostomski |first7=Christoph Lierse v. |date=2010 |title=Preparation of radiochemically pure <sup>79</sup>Se and highly precise determination of its half-life |journal=Applied Radiation and Isotopes |volume=68 |issue=12 |pages=2339–2351 |doi=10.1016/j.apradiso.2010.05.006 |pmid=20627600 |last1=Jörg |first1=Gerhard |bibcode=2010AppRI..68.2339J |display-authors=3}}</ref>
|-
|<sup>80</sup>Se
|Primordial
|Fission product
|Stable
|-
|<sup>82</sup>Se
|Primordial
|Fission product*
|8.76{{e|19}} yr{{NUBASE2020|ref}}{{efn|For all practical purposes, <sup>82</sup>Se is stable.}}
|}