View source for Isotopes of argon

{{Short description|none}}
{{Infobox argon isotopes}}
{{Use dmy dates |date=July 2020}}
[[Argon]] ({{sub|18}}Ar) has 26 known [[isotope]]s, from {{sup|29}}Ar to {{sup|54}}Ar, of which three are [[stable isotope|stable]] ({{sup|36}}Ar, {{sup|38}}Ar, and {{sup|40}}Ar). On Earth, {{sup|40}}Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are {{sup|39}}Ar with a half-life of 268 years, {{sup|42}}Ar with a half-life of 32.9 years, and {{sup|37}}Ar with a half-life of 35.04 days. All other isotopes have half-lives of less than two hours, and most less than one minute. Isotopes lighter than <sup>38</sup>Ar decay to [[chlorine]] or lighter elements, while heavier ones beta decay to [[potassium]].

The naturally occurring [[Potassium-40|{{sup|40}}K]], with a [[half-life]] of 1.248{{x10^|9}} years, decays to stable {{sup|40}}Ar by [[electron capture]] (10.72%) and by [[positron emission]] (0.001%), and also to stable {{sup|40}}Ca via [[beta decay]] (89.28%). These properties and ratios are used to determine the age of [[rock (geology)|rocks]] through [[potassium–argon dating]].<ref name="iso">
{{cite web
|title=<sup>40</sup>Ar/<sup>39</sup>Ar dating and errors
|url=http://www.geoberg.de/text/geology/07011601.php
|access-date=2007-03-07
|url-status=dead
|archive-url=https://web.archive.org/web/20070509023017/http://www.geoberg.de/text/geology/07011601.php
|archive-date=2007-05-09
}}</ref>

Despite the trapping of {{sup|40}}Ar in many rocks, it can be released by melting, grinding, and diffusion. Almost all argon in the Earth's atmosphere is the product of {{sup|40}}K decay, since 99.6% of Earth's atmospheric argon is {{sup|40}}Ar, whereas in the Sun and presumably in primordial star-forming clouds, argon consists of ~85% {{sup|36}}Ar, ~15% {{sup|38}}Ar and only trace {{sup|40}}Ar. <!--taken from the argon article--> Similarly, the ratio of the isotopes {{sup|36}}Ar:{{sup|38}}Ar:{{sup|40}}Ar in the atmospheres of the [[outer planet]]s is measured to be 8400:1600:1.<ref name="36Ar-Cameron">{{cite journal |last1=Cameron |first1=A.G.W. |author-link1=Alastair G. W. Cameron |title=Elemental and isotopic abundances of the volatile elements in the outer planets |journal=Space Science Reviews |date=1973 |volume=14 |issue=3–4 |pages=392–400 |bibcode=1973SSRv...14..392C |doi=10.1007/BF00214750 |s2cid=119861943}}</ref>

In the Earth's [[atmosphere]], radioactive {{sup|39}}Ar (and to a lesser extent <sup>37</sup>Ar) is made by [[cosmic ray]] activity, primarily from {{sup|40}}Ar. In the subsurface environment, {{sup|39}}Ar is also produced through [[neutron capture]] by {{sup|39}}K or <sup>42</sup>Ca, with proton or alpha emission respectively; <sup>37</sup>Ar was created in subsurface [[nuclear testing|nuclear explosions]] similarly from <sup>40</sup>Ca.<ref name="iso"/> The content of {{sup|39}}Ar in natural argon is measured to be of (8.0±0.6)×10{{sup|−16}} g/g, or (1.01±0.08)&nbsp;Bq/kg weight.<ref name="40Ar-Benetti">
{{cite journal 
|author=P. Benetti
|title=Measurement of the specific activity of <sup>39</sup>Ar in natural argon
|year=2007
|journal=[[Nuclear Instruments and Methods A]]
|volume=574 |issue=1
|pages=83–88
|arxiv=astro-ph/0603131 |bibcode=2007NIMPA.574...83B |display-authors=etal
|doi=10.1016/j.nima.2007.01.106
|s2cid=17073444
}}</ref> The content of <sup>42</sup>Ar (half-life 33 years) in the Earth's atmosphere, though it had previously been reported as a cosmogenic isotope,<ref>For example in {{cite journal |last1=Barabash |first1=A.S. |last2=Saakyan |first2=R.R. |last3=Umatov |first3=V.I. |year=2016 |title=On concentration of 42Ar in the Earth's atmosphere |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |doi=10.1016/j.nima.2016.09.042|arxiv=1609.08890 }}</ref> is lower than 6×10<sup>−21</sup> of the element.<ref name="40Ar-Ashitkov">
{{cite journal
|author=V. D. Ashitkov
|title=New experimental limit on the <sup>42</sup>Ar content in the Earth's atmosphere
|year=1998
|journal=[[Nuclear Instruments and Methods A]]
|volume=416 |issue=1
|pages=179–181
|display-authors=etal |bibcode=1998NIMPA.416..179A
|doi=10.1016/S0168-9002(98)00740-2
}}</ref> Many endeavors require argon depleted in the [[cosmogenic isotope]]s, known as depleted argon.<ref name="36Ar-Back">
{{cite journal
|author=H. O. Back |year=2012
|title=Depleted Argon from Underground Sources
|journal=[[Physics Procedia]]
|volume=37 |pages=1105–1112
|display-authors=etal |bibcode=2012PhPro..37.1105B
|doi=10.1016/j.phpro.2012.04.099 |doi-access=free}}</ref>

<sup>36</sup>Ar, in the form of [[argon hydride]], was detected in the [[Crab Nebula]] [[supernova remnant]] during 2013.<ref name="NYT-20131213">{{cite news |last=Quenqua |first=Douglas |title=Noble Molecules Found in Space |date=13 December 2013 |work=[[The New York Times]] |url=https://www.nytimes.com/2013/12/17/science/space/noble-molecules-found-in-space.html |access-date=13 December 2013}}</ref><ref name="SCI-2013">
{{cite journal
|last=Barlow |first=M. J.
|year=2013
|title=Detection of a Noble Gas Molecular Ion, <sup>36</sup>ArH+, in the Crab Nebula
|journal=[[Science (journal)|Science]]
|volume=342 |issue=6164 |pages=1343–1345
|display-authors=etal |arxiv=1312.4843
|bibcode=2013Sci...342.1343B |pmid=24337290
|doi=10.1126/science.1243582
|s2cid=37578581
}}</ref> This was the first time a [[noble gas compound|noble molecule]] was detected in [[outer space]].<ref name="NYT-20131213"/><ref name="SCI-2013"/>

==List of isotopes==
{{Anchor|Argon-32m}}

<!--Please delete anchor(s) from the list above or table below if adding a dedicated isotope section(s).-->

{{Isotopes table
|symbol=Ar
|refs=NUBASE2020, AME2020 II
|notes=m, unc(), mass#, spin(), spin#, daughter-st, n, p, EC,
}}
|-id=Argon-29
| <sup>29</sup>Ar<ref name="p-excursion">{{cite journal |last=Mukha |first=I. |display-authors=et al. |title=Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains |date=2018 |journal=Physical Review C |volume=98 |issue=6 |pages=064308–1–064308–13 |arxiv=1803.10951 |bibcode=2018PhRvC..98f4308M |doi=10.1103/PhysRevC.98.064308 |s2cid=119384311}}</ref>
| style="text-align:right" | 18
| style="text-align:right" | 11
| 29.04076(47)#
|
| [[proton emission|2p]]
| <sup>27</sup>S
| 5/2+#
|
|
|-id=Argon-30
| <sup>30</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 12
| 30.02369(19)#
| <10&nbsp;ps
| 2p
| <sup>28</sup>S
| 0+
|
|
|-id=Argon-31
| rowspan=7|<sup>31</sup>Ar
| rowspan=7 style="text-align:right" | 18
| rowspan=7 style="text-align:right" | 13
| rowspan=7|31.01216(22)#
| rowspan=7|15.0(3)&nbsp;ms
| [[Beta decay|β<sup>+</sup>]], p (68.3%)
| <sup>30</sup>S
| rowspan=7|5/2+
| rowspan=7|
| rowspan=7|
|-
| β<sup>+</sup> (22.63%)
| <sup>31</sup>Cl
|-
| β<sup>+</sup>, 2p (9.0%)
| <sup>29</sup>P
|-
| β<sup>+</sup>, 3p (0.07%)
| '''<sup>28</sup>Si'''
|-
| β<sup>+</sup>, p, [[alpha decay|α]]? (<0.38%)
| <sup>26</sup>Si
|-
| β<sup>+</sup>, α? (<0.03%)
| <sup>27</sup>P
|-
| 2p? (<0.03%)
| <sup>29</sup>S
|-id=Argon-32
| rowspan=2|<sup>32</sup>Ar
| rowspan=2 style="text-align:right" | 18
| rowspan=2 style="text-align:right" | 14
| rowspan=2|31.9976378(19)
| rowspan=2|98(2)&nbsp;ms
| β<sup>+</sup> (64.42%)
| <sup>32</sup>Cl
| rowspan=2|0+
| rowspan=2|
| rowspan=2|
|-
| β<sup>+</sup>, p (35.58%)
| <sup>31</sup>S
|-id=Argon-33
| rowspan=2|<sup>33</sup>Ar
| rowspan=2 style="text-align:right" | 18
| rowspan=2 style="text-align:right" | 15
| rowspan=2|32.98992555(43)
| rowspan=2|173.0(20)&nbsp;ms
| β<sup>+</sup> (61.3%)
| <sup>33</sup>Cl
| rowspan=2|1/2+
| rowspan=2|
| rowspan=2|
|-
| β<sup>+</sup>, p (38.7%)
| '''<sup>32</sup>S'''
|-id=Argon-34
| <sup>34</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 16
| 33.980270092(83)
| 846.46(35)&nbsp;ms
| β<sup>+</sup>
| <sup>34</sup>Cl
| 0+
|
|
|-id=Argon-35
| <sup>35</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 17
| 34.97525772(73)
| 1.7756(10)&nbsp;s
| β<sup>+</sup>
| '''<sup>35</sup>Cl'''
| 3/2+
|
|
|-id=Argon-36
| <sup>36</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 18
| 35.967545106(28)
| colspan=3 align=center|'''[[Observationally Stable]]'''<ref group="n">Believed to undergo double electron capture to '''<sup>36</sup>S''' (lightest theoretically unstable nuclide for which no evidence of radioactivity has been observed)</ref>
| 0+
| 0.003336(210)
|
|-id=Argon-37
| <sup>37</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 19
| 36.96677630(22)
| 35.011(19)&nbsp;d
| [[electron capture|EC]]
| '''<sup>37</sup>Cl'''
| 3/2+
| Trace<ref group="n" name="c"/>
|
|-id=Argon-38
| <sup>38</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 20
| 37.96273210(21)
| colspan=3 align=center|'''Stable'''
| 0+
| 0.000629(70)
|
|-id=Argon-39
| <sup>39</sup>Ar<ref group="n">Used in [[argon–argon dating]]</ref>
| style="text-align:right" | 18
| style="text-align:right" | 21
| 38.9643130(54)
| {{val|268.2|3.1|2.9}}&nbsp;y<ref>{{cite journal |last=Golovko |first=Victor V. |title=Application of the most frequent value method for <sup>39</sup>Ar half-life determination |journal=The European Physical Journal C |volume=83 |issue=10 |date=2023-10-15 |page=930 |issn=1434-6052 |arxiv=2310.06867 |bibcode=2023EPJC...83..930G |doi=10.1140/epjc/s10052-023-12113-6}}</ref>
| β<sup>−</sup>
| '''<sup>39</sup>K'''
| 7/2−
| {{val|8e-16}}<ref name="zheng-tian">{{cite journal |last1=Lu |first1=Zheng-Tian |title=What trapped atoms reveal about global groundwater |journal=Physics Today |date=1 March 2013 |volume=66 |issue=3 |pages=74–75 |bibcode=2013PhT....66c..74L |doi=10.1063/PT.3.1926}}</ref><ref group="n" name="c">[[Cosmogenic nuclide]]</ref>
|
|-id=Argon-40
| <sup>40</sup>Ar<ref group="n">Used in [[argon–argon dating]] and [[potassium–argon dating]]</ref>
| style="text-align:right" | 18
| style="text-align:right" | 22
| 39.9623831220(23)
| colspan=3 align=center|'''Stable'''
| 0+
| 0.996035(250)<ref group="n">Generated from <sup>40</sup>K in rocks. These ratios are terrestrial. Cosmic abundance is far less than <sup>36</sup>Ar.</ref>
|
|-id=Argon-41
| <sup>41</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 23
| 40.96450057(37)
| 109.61(4)&nbsp;min
| β<sup>−</sup>
| '''<sup>41</sup>K'''
| 7/2−
| Trace<ref group="n" name="c"/>
|
|-id=Argon-42
| <sup>42</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 24
| 41.9630457(62)
| 32.9(11)&nbsp;y
| β<sup>−</sup>
| <sup>42</sup>K
| 0+
|
|
|-id=Argon-43
| <sup>43</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 25
| 42.9656361(57)
| 5.37(6)&nbsp;min
| β<sup>−</sup>
| <sup>43</sup>K
| 5/2(−)
|
|
|-id=Argon-44
| <sup>44</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 26
| 43.9649238(17)
| 11.87(5)&nbsp;min
| β<sup>−</sup>
| <sup>44</sup>K
| 0+
|
|
|-id=Argon-45
| <sup>45</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 27
| 44.96803973(55)
| 21.48(15)&nbsp;s
| β<sup>−</sup>
| <sup>45</sup>K
| (5/2−,7/2−)
|
|
|-id=Argon-46
| <sup>46</sup>Ar
| style="text-align:right" | 18
| style="text-align:right" | 28
| 45.9680392(25)
| 8.4(6)&nbsp;s
| β<sup>−</sup>
| <sup>46</sup>K
| 0+
|
|
|-id=Argon-47
| rowspan=2|<sup>47</sup>Ar
| rowspan=2 style="text-align:right" | 18
| rowspan=2 style="text-align:right" | 29
| rowspan=2|46.9727671(13)
| rowspan=2|1.23(3)&nbsp;s
| β<sup>−</sup> (>99.8%)
| <sup>47</sup>K
| rowspan=2|(3/2)−
| rowspan=2|
| rowspan=2|
|-
| β<sup>−</sup>, [[neutron emission|n]]? (<0.2%)
| <sup>46</sup>K
|-id=Argon-48
| rowspan=2|<sup>48</sup>Ar
| rowspan=2 style="text-align:right" | 18
| rowspan=2 style="text-align:right" | 30
| rowspan=2|47.976001(18)
| rowspan=2|415(15)&nbsp;ms
| β<sup>−</sup> (62%)
| <sup>48</sup>K
| rowspan=2|0+
| rowspan=2|
| rowspan=2|
|-
| β<sup>−</sup>, n (38%)
| <sup>47</sup>K
|-id=Argon-49
| rowspan=3|<sup>49</sup>Ar
| rowspan=3 style="text-align:right" | 18
| rowspan=3 style="text-align:right" | 31
| rowspan=3|48.98169(43)#
| rowspan=3|236(8)&nbsp;ms
| β<sup>−</sup>
| <sup>49</sup>K
| rowspan=3|3/2−#
| rowspan=3|
| rowspan=3|
|-
| β<sup>−</sup>, n (29%)
| <sup>48</sup>K
|-
| β<sup>−</sup>, 2n?
| <sup>47</sup>K
|-id=Argon-50
| rowspan=3|<sup>50</sup>Ar
| rowspan=3 style="text-align:right" | 18
| rowspan=3 style="text-align:right" | 32
| rowspan=3|49.98580(54)#
| rowspan=3|106(6)&nbsp;ms
| β<sup>−</sup> (63%)
| <sup>50</sup>K
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β<sup>−</sup>, n (37%)
| <sup>49</sup>K
|-
| β<sup>−</sup>, 2n?
| <sup>48</sup>K
|-id=Argon-51
| rowspan=3|<sup>51</sup>Ar
| rowspan=3 style="text-align:right" | 18
| rowspan=3 style="text-align:right" | 33
| rowspan=3|50.99303(43)#
| rowspan=3|30#&nbsp;ms<br>[>200&nbsp;ns]
| β<sup>−</sup>?
| <sup>51</sup>K
| rowspan=3|1/2−#
| rowspan=3|
| rowspan=3|
|-
| β<sup>−</sup>, n?
| <sup>50</sup>K
|-
| β<sup>−</sup>, 2n?
| <sup>49</sup>K
|-id=Argon-52
| rowspan=3|<sup>52</sup>Ar
| rowspan=3 style="text-align:right" | 18
| rowspan=3 style="text-align:right" | 34
| rowspan=3|51.99852(64)#
| rowspan=3|40#&nbsp;ms<br>[>620&nbsp;ns]
| β<sup>−</sup>?
| <sup>52</sup>K
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β<sup>−</sup>, n?
| <sup>51</sup>K
|-
| β<sup>−</sup>, 2n?
| <sup>50</sup>K
|-id=Argon-53
| rowspan=3|<sup>53</sup>Ar
| rowspan=3 style="text-align:right" | 18
| rowspan=3 style="text-align:right" | 35
| rowspan=3|53.00729(75)#
| rowspan=3|20#&nbsp;ms<br>[>620&nbsp;ns]
| β<sup>−</sup>?
| <sup>53</sup>K
| rowspan=3|5/2−#
| rowspan=3|
| rowspan=3|
|-
| β<sup>−</sup>, n?
| <sup>52</sup>K
|-
| β<sup>−</sup>, 2n?
| <sup>51</sup>K
|-id=Argon-54
| rowspan=3|<sup>54</sup>Ar
| rowspan=3 style="text-align:right" | 18
| rowspan=3 style="text-align:right" | 36
| rowspan=3|54.01348(86)#
| rowspan=3|5#&nbsp;ms<br>[>400&nbsp;ns]
| β<sup>−</sup>?
| <sup>54</sup>K
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β<sup>−</sup>, n?
| <sup>53</sup>K
|-
| β<sup>−</sup>, 2n?
| <sup>52</sup>K
{{Isotopes table/footer}}

== See also ==
*[[Banana equivalent dose]]
'''Daughter products other than argon'''
* [[Isotopes of potassium]]
* [[Isotopes of chlorine]]
* [[Isotopes of sulfur]]
* [[Isotopes of phosphorus]]

==References==
{{Reflist}}

==External links==
*[https://web.archive.org/web/20070731013637/http://ie.lbl.gov/education/parent/Ar_iso.htm Argon isotopes data from ''The Berkeley Laboratory Isotopes Projects'']

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[[Category:Argon]]
[[Category:Isotopes of argon| ]]
[[Category:Lists of isotopes by element|Argon]]