Isotopes of argon

{{Short description|none}} {{Infobox argon isotopes}} {{Use dmy dates |date=July 2020}} Argon ({{sub|18}}Ar) has 26 known isotopes, from {{sup|29}}Ar to {{sup|54}}Ar, of which three are 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 302 years, {{sup|42}}Ar with a half-life of 32.9 years, and {{sup|37}}Ar with a half-life of 35.01 days. All other isotopes have half-lives of less than two hours, and most less than one minute. Isotopes lighter than ³⁸Ar decay to chlorine or lighter elements, while heavier ones beta decay to potassium.

The naturally occurring {{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 rocks through potassium–argon dating.<ref name="iso"> {{cite web |title=⁴⁰Ar/³⁹Ar 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 planets 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 ³⁷Ar) 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 ⁴²Ca, with proton or alpha emission respectively; ³⁷Ar was created in subsurface nuclear explosions similarly from ⁴⁰Ca.<ref name="iso"/> The content of {{sup|39}}Ar in natural argon is measured to be of (8.6±0.4)×10{{sup|−16}} g/g, or (0.964±0.024)&nbsp;Bq/kg weight.<ref name="DEAP-39Ar-2023"> {{cite journal | author = P. Adhikari | title = Precision Measurement of the Specific Activity of ³⁹Ar in Atmospheric Argon with the DEAP-3600 Detector | journal = The European Physical Journal C | volume = 83 | issue = 7 | pages = 642 | year = 2023 | doi = 10.1140/epjc/s10052-023-11678-6 | doi-access = free| url = https://doi.org/10.1140/epjc/s10052-023-11678-6 | s2cid = | display-authors = etal | arxiv = 2302.14639 }} </ref>

The content of ⁴²Ar (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 |volume=839 |pages=39–42 |doi=10.1016/j.nima.2016.09.042|arxiv=1609.08890 }}</ref> is lower than 6×10⁻²¹ of the element.<ref name="40Ar-Ashitkov"> {{cite journal |author=V. D. Ashitkov |title=New experimental limit on the ⁴²Ar 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 isotopes, 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> and this may be obtained from underground sources that have been isolated from the atmosphere long enough for these isotopes to decay.

³⁶Ar, 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, ³⁶ArH+, in the Crab Nebula |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 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, IsotopeFRIB |notes=m, unc(), mass#, spin(), spin#, daughter-st, n, p, EC, discoveryname }} |-id=Argon-29 | ²⁹Ar<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 |article-number=064308 |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)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/29.pdf 2018] | | 2p | ²⁷S | 5/2+# | | |-id=Argon-30 | ³⁰Ar | style="text-align:right" | 18 | style="text-align:right" | 12 | 30.02369(19)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/30.pdf 2015] | <10&nbsp;ps | 2p | ²⁸S | 0+ | | |-id=Argon-31 | rowspan=7|³¹Ar | rowspan=7 style="text-align:right" | 18 | rowspan=7 style="text-align:right" | 13 | rowspan=7|31.012125(14)<ref name="chen2025">{{cite journal |last1=Chen |first1=Z. Y. |last2=Yan |first2=X. L. |last3=Hou |first3=S. Q. |last4=Liu |first4=J. B. |last5=Shi |first5=J. Y. |last6=Zhou |first6=X. H. |last7=Zhang |first7=Y. H. |last8=Wang |first8=M. |last9=Zhou |first9=X. |last10=Zhang |first10=M. |last11=Li |first11=H. F. |last12=Sun |first12=M. Z. |last13=Xing |first13=Y. M. |last14=Shuai |first14=P. |last15=Xu |first15=X. |last16=Huang |first16=W. J. |last17=Wang |first17=Q. |last18=Song |first18=Y. N. |last19=Deng |first19=H. Y. |last20=Jiao |first20=H. Y. |last21=Luo |first21=Y. F. |last22=Litvinov |first22=Yu. A. |last23=Blaum |first23=K. |last24=Yamaguchi |first24=T. |title=Precision Mass Measurement of 26 P and 27 S and Their Impact on the 26 P( p , γ ) 27 S Reaction in Stellar X-Ray Bursts |journal=The Astrophysical Journal |date=1 December 2025 |volume=994 |issue=2 |pages=270 |doi=10.3847/1538-4357/ae1470 |doi-access=free }}</ref> | rowspan=7 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/31.pdf 1986] | rowspan=7|15.0(3)&nbsp;ms | β⁺, p (68.3%) | ³⁰S | rowspan=7|5/2+ | rowspan=7| | rowspan=7| |- | β⁺ (22.63%) | ³¹Cl |- | β⁺, 2p (9.0%) | ²⁹P |- | β⁺, 3p (0.07%) | '''²⁸Si''' |- | β⁺, p, α? (<0.38%) | ²⁶Si |- | β⁺, α? (<0.03%) | ²⁷P |- | 2p? (<0.03%) | ²⁹S |-id=Argon-32 | rowspan=2|³²Ar | rowspan=2 style="text-align:right" | 18 | rowspan=2 style="text-align:right" | 14 | rowspan=2|31.9976378(19) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/32.pdf 1977] | rowspan=2|98(2)&nbsp;ms | β⁺ (64.42%) | ³²Cl | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁺, p (35.58%) | ³¹S |-id=Argon-33 | rowspan=2|³³Ar | rowspan=2 style="text-align:right" | 18 | rowspan=2 style="text-align:right" | 15 | rowspan=2|32.98992555(43) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/33.pdf 1964] | rowspan=2|173.0(20)&nbsp;ms | β⁺ (61.3%) | ³³Cl | rowspan=2|1/2+ | rowspan=2| | rowspan=2| |- | β⁺, p (38.7%) | '''³²S''' |-id=Argon-34 | ³⁴Ar | style="text-align:right" | 18 | style="text-align:right" | 16 | 33.980270092(83) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/34.pdf 1966] | 846.46(35)&nbsp;ms | β⁺ | ³⁴Cl | 0+ | | |-id=Argon-35 | ³⁵Ar | style="text-align:right" | 18 | style="text-align:right" | 17 | 34.97525772(73) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/35.pdf 1940] | 1.7756(10)&nbsp;s | β⁺ | '''³⁵Cl''' | 3/2+ | | |-id=Argon-36 | ³⁶Ar | style="text-align:right" | 18 | style="text-align:right" | 18 | 35.967545106(28) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/36.pdf 1920] | colspan=3 align=center|'''Observationally Stable'''<ref group="n">Believed to undergo double electron capture to '''³⁶S''' (lightest theoretically unstable nuclide for which no evidence of radioactivity has been observed)</ref> | 0+ | 0.003336(210) | |-id=Argon-37 | ³⁷Ar | style="text-align:right" | 18 | style="text-align:right" | 19 | 36.96677630(22) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/37.pdf 1941] | 35.011(19)&nbsp;d | EC | '''³⁷Cl''' | 3/2+ | Trace<ref group="n" name="c"/> | |-id=Argon-38 | ³⁸Ar | style="text-align:right" | 18 | style="text-align:right" | 20 | 37.96273210(21) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/38.pdf 1934] | colspan=3 align=center|'''Stable''' | 0+ | 0.000629(70) | |-id=Argon-39 | ³⁹Ar<ref group="n">Used in argon–argon dating</ref> | style="text-align:right" | 18 | style="text-align:right" | 21 | 38.9643130(54) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/39.pdf 1950] | 302(10)&nbsp;y<ref name="DEAP-39Ar-HalfLife-2025"> {{cite journal | author = P. Adhikari | title = Direct Measurement of the Half-Life of ³⁹Ar from 3.4 Years of Data with the DEAP-3600 Detector | journal = The European Physical Journal C | volume = 85 | issue = 7 | pages = 728 | year = 2025 | doi = 10.1140/epjc/s10052-025-14289-5 | display-authors = etal | doi-access = free }} </ref><ref>This appears reliable but the NUBASE2020 value is 268(8) years and the discrepancy is yet to be explained.</ref> | β⁻ | '''³⁹K''' | 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 | ⁴⁰Ar<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) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/40.pdf 1920] | colspan=3 align=center|'''Stable''' | 0+ | 0.996035(250)<ref group="n">Generated from ⁴⁰K in rocks. These ratios are terrestrial. Cosmic abundance is far less than ³⁶Ar.</ref> | |-id=Argon-41 | ⁴¹Ar | style="text-align:right" | 18 | style="text-align:right" | 23 | 40.96450057(37) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/41.pdf 1936] | 109.61(4)&nbsp;min | β⁻ | '''⁴¹K''' | 7/2− | Trace<ref group="n" name="c"/> | |-id=Argon-42 | ⁴²Ar | style="text-align:right" | 18 | style="text-align:right" | 24 | 41.9630457(62) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/42.pdf 1952] | 32.9(11)&nbsp;y | β⁻ | ⁴²K | 0+ | | |-id=Argon-43 | ⁴³Ar | style="text-align:right" | 18 | style="text-align:right" | 25 | 42.9656361(57) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/43.pdf 1969] | 5.37(6)&nbsp;min | β⁻ | ⁴³K | 5/2(−) | | |-id=Argon-44 | ⁴⁴Ar | style="text-align:right" | 18 | style="text-align:right" | 26 | 43.9649238(17) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/44.pdf 1969] | 11.87(5)&nbsp;min | β⁻ | ⁴⁴K | 0+ | | |-id=Argon-45 | ⁴⁵Ar | style="text-align:right" | 18 | style="text-align:right" | 27 | 44.96803973(55) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/45.pdf 1974] | 21.48(15)&nbsp;s | β⁻ | ⁴⁵K | (5/2−,7/2−) | | |-id=Argon-46 | ⁴⁶Ar | style="text-align:right" | 18 | style="text-align:right" | 28 | 45.9680392(25) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/46.pdf 1974] | 8.4(6)&nbsp;s | β⁻ | ⁴⁶K | 0+ | | |-id=Argon-47 | rowspan=2|⁴⁷Ar | rowspan=2 style="text-align:right" | 18 | rowspan=2 style="text-align:right" | 29 | rowspan=2|46.9727671(13) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/47.pdf 1985] | rowspan=2|1.23(3)&nbsp;s | β⁻ (>99.8%) | ⁴⁷K | rowspan=2|(3/2)− | rowspan=2| | rowspan=2| |- | β⁻, n? (<0.2%) | ⁴⁶K |-id=Argon-48 | rowspan=2|⁴⁸Ar | rowspan=2 style="text-align:right" | 18 | rowspan=2 style="text-align:right" | 30 | rowspan=2|47.976001(18) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/48.pdf 2004] | rowspan=2|415(15)&nbsp;ms | β⁻ (62%) | ⁴⁸K | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁻, n (38%) | ⁴⁷K |-id=Argon-49 | rowspan=3|⁴⁹Ar | rowspan=3 style="text-align:right" | 18 | rowspan=3 style="text-align:right" | 31 | rowspan=3|48.98169(43)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/49.pdf 1989] | rowspan=3|236(8)&nbsp;ms | β⁻ | ⁴⁹K | rowspan=3|3/2−# | rowspan=3| | rowspan=3| |- | β⁻, n (29%) | ⁴⁸K |- | β⁻, 2n? | ⁴⁷K |-id=Argon-50 | rowspan=3|⁵⁰Ar | rowspan=3 style="text-align:right" | 18 | rowspan=3 style="text-align:right" | 32 | rowspan=3|49.98580(54)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/50.pdf 1989] | rowspan=3|106(6)&nbsp;ms | β⁻ (63%) | ⁵⁰K | rowspan=3|0+ | rowspan=3| | rowspan=3| |- | β⁻, n (37%) | ⁴⁹K |- | β⁻, 2n? | ⁴⁸K |-id=Argon-51 | rowspan=3|⁵¹Ar | rowspan=3 style="text-align:right" | 18 | rowspan=3 style="text-align:right" | 33 | rowspan=3|50.99303(43)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/51.pdf 1989] | rowspan=3|30#&nbsp;ms<br>[>200&nbsp;ns] | β⁻? | ⁵¹K | rowspan=3|1/2−# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵⁰K |- | β⁻, 2n? | ⁴⁹K |-id=Argon-52 | rowspan=3|⁵²Ar | rowspan=3 style="text-align:right" | 18 | rowspan=3 style="text-align:right" | 34 | rowspan=3|51.99852(64)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/52.pdf 2009] | rowspan=3|40#&nbsp;ms<br>[>620&nbsp;ns] | β⁻? | ⁵²K | rowspan=3|0+ | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵¹K |- | β⁻, 2n? | ⁵⁰K |-id=Argon-53 | rowspan=3|⁵³Ar | rowspan=3 style="text-align:right" | 18 | rowspan=3 style="text-align:right" | 35 | rowspan=3|53.00729(75)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/53.pdf 2009] | rowspan=3|20#&nbsp;ms<br>[>620&nbsp;ns] | β⁻? | ⁵³K | rowspan=3|5/2−# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵²K |- | β⁻, 2n? | ⁵¹K |-id=Argon-54 | rowspan=3|⁵⁴Ar | rowspan=3 style="text-align:right" | 18 | rowspan=3 style="text-align:right" | 36 | rowspan=3|54.01348(86)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/18/54.pdf 2018] | rowspan=3|5#&nbsp;ms<br>[>400&nbsp;ns] | β⁻? | ⁵⁴K | rowspan=3|0+ | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵³K |- | β⁻, 2n? | ⁵²K {{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 Argon