Argon (₁₈Ar) has 26 known isotopes, from ²⁹Ar to ⁵⁴Ar and 1

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

(^32mAr), of which three are

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(³⁶Ar, ³⁸Ar, and ⁴⁰Ar). On the Earth, ⁴⁰Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are ³⁹Ar with a half-life of 268 years, ⁴²Ar with a half-life of 32.9 years, and ³⁷Ar 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. The least stable is ²⁹Ar with a half-life of approximately seconds. The naturally occurring ⁴⁰K, with a half-life of 1.248 years, decays to stable ⁴⁰Ar by electron capture (10.72%) and by positron emission (0.001%), and also transforms to stable ⁴⁰Ca via beta decay (89.28%). These properties and ratios are used to determine the age of

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through potassium–argon dating. Despite the trapping of ⁴⁰Ar in many rocks, it can be released by melting, grinding, and diffusion. Almost all of the argon in the Earth's atmosphere is the product of ⁴⁰K decay, since 99.6% of Earth atmospheric argon is ⁴⁰Ar, whereas in the Sun and presumably in primordial star-forming clouds, argon consists of < 15% ³⁸Ar and mostly (85%) ³⁶Ar. Similarly, the ratio of the three isotopes ³⁶Ar:³⁸Ar:⁴⁰Ar in the atmospheres of the outer planets is measured to be 8400:1600:1. In the Earth's

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, radioactive ³⁹Ar (half-life 268(8) years) is made by cosmic ray activity, primarily from ⁴⁰Ar. In the subsurface environment, it is also produced through neutron capture by ³⁹K or alpha emission by calcium. The content of ³⁹Ar in natural argon is measured to be of (8.0±0.6)×10⁻¹⁶ g/g, or (1.01±0.08) Bq/kg of ^{36, 38, 40}Ar. The content of ⁴²Ar (half-life 33 years) in the Earth's atmosphere is lower than 6×10⁻²¹ parts per part of ^{36, 38, 40}Ar. Many endeavors require argon depleted in the cosmogenic isotopes, known as depleted argon. Lighter radioactive isotopes can decay to different elements (usually chlorine) while heavier ones decay to potassium. ³⁶Ar, in the form of argon hydride, was detected in the

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supernova remnant during 2013. This was the first time a noble molecule was detected in outer space. Radioactive ³⁷Ar is a synthetic radionuclide that is created from the neutron capture by ⁴⁰Ca followed by an alpha particle emission as a result of subsurface

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. It has a half-life of 35 days.

List of isotopes

, - , ²⁹Ar , style="text-align:right" , 18 , style="text-align:right" , 11 , , ~ s , 2p , ²⁷S , , , , - , ³⁰Ar , style="text-align:right" , 18 , style="text-align:right" , 12 , 30.02247(22) , <10 ps , 2p , ²⁸S , 0+ , , , - , rowspan=4, ³¹Ar , rowspan=4 style="text-align:right" , 18 , rowspan=4 style="text-align:right" , 13 , rowspan=4, 31.01216(22)# , rowspan=4, 15.1(3) ms , β⁺, p (68.3%) , ³⁰S , rowspan=4, 5/2+ , rowspan=4, , rowspan=4, , - , β⁺ (22.63%) , ³¹Cl , - , β⁺, 2p (9.0%) , ²⁹P , - , β⁺, 3p (0.07%) , ²⁸Si , - , rowspan=2, ³²Ar , rowspan=2 style="text-align:right" , 18 , rowspan=2 style="text-align:right" , 14 , rowspan=2, 31.9976378(19) , rowspan=2, 98(2) ms , β⁺ (64.42%) , ³²Cl , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺, p (35.58%) , ³¹S , - , style="text-indent:1em" , ^32mAr , colspan="3" style="text-indent:2em" , 5600(100) keV , unknown , , , 5−# , , , - , rowspan=2, ³³Ar , rowspan=2 style="text-align:right" , 18 , rowspan=2 style="text-align:right" , 15 , rowspan=2, 32.9899255(4) , rowspan=2, 173.0(20) ms , β⁺ (61.3%) , ³³Cl , rowspan=2, 1/2+ , rowspan=2, , rowspan=2, , - , β⁺, p (38.7%) , ³²S , - , ³⁴Ar , style="text-align:right" , 18 , style="text-align:right" , 16 , 33.98027009(8) , 843.8(4) ms , β⁺ , ³⁴Cl , 0+ , , , - , ³⁵Ar , style="text-align:right" , 18 , style="text-align:right" , 17 , 34.9752577(7) , 1.7756(10) s , β⁺ , ³⁵Cl , 3/2+ , , , - , ³⁶Ar , style="text-align:right" , 18 , style="text-align:right" , 18 , 35.967545105(29) , colspan=3 align=center, Observationally StableBelieved to undergo double electron capture to ³⁶S (lightest theoretically unstable nuclide for which no evidence of radioactivity has been observed) , 0+ , 0.003336(4) , , - , ³⁷Ar , style="text-align:right" , 18 , style="text-align:right" , 19 , 36.96677631(22) , 35.011(19) d , EC , ³⁷Cl , 3/2+ , , , - , ³⁸Ar , style="text-align:right" , 18 , style="text-align:right" , 20 , 37.96273210(21) , colspan=3 align=center, Stable , 0+ , 0.000629(1) , , - , ³⁹ArUsed in argon–argon dating , style="text-align:right" , 18 , style="text-align:right" , 21 , 38.964313(5) , 268(8) y , β⁻ , ³⁹K , 7/2− , Trace Cosmogenic nuclide , , - , ⁴⁰ArUsed in argon–argon dating and potassium–argon dating , style="text-align:right" , 18 , style="text-align:right" , 22 , 39.9623831238(24) , colspan=3 align=center, Stable , 0+ , 0.996035(4)Generated from ⁴⁰K in rocks. These ratios are terrestrial. Cosmic abundance is far less than ³⁶Ar. , , - , ⁴¹Ar , style="text-align:right" , 18 , style="text-align:right" , 23 , 40.9645006(4) , 109.61(4) min , β⁻ , ⁴¹K , 7/2− , , , - , ⁴²Ar , style="text-align:right" , 18 , style="text-align:right" , 24 , 41.963046(6) , 32.9(11) y , β⁻ , ⁴²K , 0+ , Trace , , - , ⁴³Ar , style="text-align:right" , 18 , style="text-align:right" , 25 , 42.965636(6) , 5.37(6) min , β⁻ , ⁴³K , 5/2(−) , , , - , ⁴⁴Ar , style="text-align:right" , 18 , style="text-align:right" , 26 , 43.9649238(17) , 11.87(5) min , β⁻ , ⁴⁴K , 0+ , , , - , ⁴⁵Ar , style="text-align:right" , 18 , style="text-align:right" , 27 , 44.9680397(6) , 21.48(15) s , β⁻ , ⁴⁵K , (5/2,7/2)− , , , - , ⁴⁶Ar , style="text-align:right" , 18 , style="text-align:right" , 28 , 45.9680374(12) , 8.4(6) s , β⁻ , ⁴⁶K , 0+ , , , - , rowspan=2, ⁴⁷Ar , rowspan=2 style="text-align:right" , 18 , rowspan=2 style="text-align:right" , 29 , rowspan=2, 46.9727681(12) , rowspan=2, 1.23(3) s , β⁻ (99.8%) , ⁴⁷K , rowspan=2, (3/2−) , rowspan=2, , rowspan=2, , - , β⁻, n (0.2%) , ⁴⁶K , - , ⁴⁸Ar , style="text-align:right" , 18 , style="text-align:right" , 30 , 47.97608(33) , 415(15) ms , β⁻ , ⁴⁸K , 0+ , , , - , ⁴⁹Ar , style="text-align:right" , 18 , style="text-align:right" , 31 , 48.98155(43)# , 236(8) ms , β⁻ , ⁴⁹K , 3/2−# , , , - , ⁵⁰Ar , style="text-align:right" , 18 , style="text-align:right" , 32 , 49.98569(54)# , 106(6) ms , β⁻ , ⁵⁰K , 0+ , , , - , ⁵¹Ar , style="text-align:right" , 18 , style="text-align:right" , 33 , 50.99280(64)# , 60# ms 200 ns, β⁻ , ⁵¹K , 3/2−# , , , - , ⁵²Ar , style="text-align:right" , 18 , style="text-align:right" , 34 , 51.99863(64)# , 10# ms , β⁻ , ⁵²K , 0+ , , , - , rowspan=2, ⁵³Ar , rowspan=2 style="text-align:right" , 18 , rowspan=2 style="text-align:right" , 35 , rowspan=2, 53.00729(75)# , rowspan=2, 3# ms , β⁻ , ⁵³K , rowspan=2, (5/2−)# , rowspan=2, , rowspan=2, , - , β⁻, n , ⁵²K , - , ⁵⁴Ar , style="text-align:right" , 18 , style="text-align:right" , 36 , , , β⁻ , ⁵⁴K , 0+ , ,

References

External links

Argon isotopes data from ''The Berkeley Laboratory Isotopes Project's''
{{Authority control Argon Argon

List of isotopes

See also

References

External links