Isotopes of argon#Argon-40

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 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.

The naturally occurring Potassium-40, 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.

{{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

}}

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 < 15% {{sup|38}}Ar and mostly (85%) {{sup|36}}Ar. 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.{{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}}

In the Earth's atmosphere, radioactive {{sup|39}}Ar (half-life 268(8) years) is made by cosmic ray activity, primarily from {{sup|40}}Ar. In the subsurface environment, it is also produced through neutron capture by {{sup|39}}>K or alpha emission by calcium. 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) Bq/kg of {{sup|36, 38, 40}}Ar.

{{cite journal

|author=P. Benetti

|title=Measurement of the specific activity of ³⁹Ar 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

}} 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.

{{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

}} Many endeavors require argon depleted in the cosmogenic isotopes, known as depleted argon.

{{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}} 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 Crab Nebula supernova remnant during 2013.{{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}}

{{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

}} This was the first time a noble molecule was detected in outer space.

³⁷Ar is a synthetic radionuclide that is created via neutron capture of ⁴⁰Ca followed by alpha particle emission, as a result of subsurface nuclear explosions. It has a half-life of 35 days.

List of isotopes

{{Isotopes table

|symbol=Ar

|refs=NUBASE2020, AME2020 II

|notes=m, unc(), mass#, spin(), spin#, daughter-st, n, p, EC,

}}

|-id=Argon-29

| ²⁹Ar{{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}}

| style="text-align:right" | 18

| style="text-align:right" | 11

| 29.04076(47)#

| 2p

| ²⁷S

| 5/2+#

|-id=Argon-30

| ³⁰Ar

| style="text-align:right" | 18

| style="text-align:right" | 12

| 30.02369(19)#

| <10 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|31.01216(22)#

| rowspan=7|15.0(3) ms

| β⁺, p (68.3%)

| ³⁰S

| rowspan=7|5/2+

| 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|98(2) ms

| β⁺ (64.42%)

| ³²Cl

| rowspan=2|0+

| 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|173.0(20) ms

| β⁺ (61.3%)

| ³³Cl

| rowspan=2|1/2+

| rowspan=2|

| β⁺, p (38.7%)

| ³²S

|-id=Argon-34

| ³⁴Ar

| style="text-align:right" | 18

| style="text-align:right" | 16

| 33.980270092(83)

| 846.46(35) ms

| β⁺

| ³⁴Cl

| 0+

|-id=Argon-35

| ³⁵Ar

| style="text-align:right" | 18

| style="text-align:right" | 17

| 34.97525772(73)

| 1.7756(10) s

| β⁺

| ³⁵Cl

| 3/2+

|-id=Argon-36

| ³⁶Ar

| style="text-align:right" | 18

| 35.967545106(28)

| 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(210)

|-id=Argon-37

| ³⁷Ar

| style="text-align:right" | 18

| style="text-align:right" | 19

| 36.96677630(22)

| 35.011(19) d

| EC

| ³⁷Cl

| 3/2+

| Trace

|-id=Argon-38

| ³⁸Ar

| 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

| ³⁹ArUsed in argon–argon dating

| style="text-align:right" | 18

| style="text-align:right" | 21

| 38.9643130(54)

| {{val|268.2|3.1|2.9}} y{{cite journal |last=Golovko |first=Victor V. |title=Application of the most frequent value method for ³⁹Ar 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}}

| β⁻

| ³⁹K

| 7/2−

| {{val|8e-16}}{{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}}Cosmogenic nuclide

|-id=Argon-40

| ⁴⁰ArUsed in argon–argon dating and potassium–argon dating

| style="text-align:right" | 18

| style="text-align:right" | 22

| 39.9623831220(23)

| colspan=3 align=center|Stable

| 0+

| 0.996035(250)Generated from ⁴⁰K in rocks. These ratios are terrestrial. Cosmic abundance is far less than ³⁶Ar.

|-id=Argon-41

| ⁴¹Ar

| style="text-align:right" | 18

| style="text-align:right" | 23

| 40.96450057(37)

| 109.61(4) min

| β⁻

| ⁴¹K

| 7/2−

| Trace

|-id=Argon-42

| ⁴²Ar

| style="text-align:right" | 18

| style="text-align:right" | 24

| 41.9630457(62)

| 32.9(11) y

| β⁻

| ⁴²K

| 0+

|-id=Argon-43

| ⁴³Ar

| style="text-align:right" | 18

| style="text-align:right" | 25

| 42.9656361(57)

| 5.37(6) min

| β⁻

| ⁴³K

| 5/2(−)

|-id=Argon-44

| ⁴⁴Ar

| style="text-align:right" | 18

| style="text-align:right" | 26

| 43.9649238(17)

| 11.87(5) min

| β⁻

| ⁴⁴K

| 0+

|-id=Argon-45

| ⁴⁵Ar

| style="text-align:right" | 18

| style="text-align:right" | 27

| 44.96803973(55)

| 21.48(15) s

| β⁻

| ⁴⁵K

| (5/2−,7/2−)

|-id=Argon-46

| ⁴⁶Ar

| style="text-align:right" | 18

| style="text-align:right" | 28

| 45.9680392(25)

| 8.4(6) 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|1.23(3) s

| β⁻ (>99.8%)

| ⁴⁷K

| rowspan=2|(3/2)−

| 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|415(15) ms

| β⁻ (62%)

| ⁴⁸K

| rowspan=2|0+

| 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|236(8) ms

| β⁻

| ⁴⁹K

| rowspan=3|3/2−#

| 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|106(6) ms

| β⁻ (63%)

| ⁵⁰K

| rowspan=3|0+

| 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|30# ms
[>200 ns]

| β⁻?

| ⁵¹K

| rowspan=3|1/2−#

| 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|40# ms
[>620 ns]

| β⁻?

| ⁵²K

| rowspan=3|0+

| 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|20# ms
[>620 ns]

| β⁻?

| ⁵³K

| rowspan=3|5/2−#

| 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|5# ms
[>400 ns]

| β⁻?

| ⁵⁴K

| rowspan=3|0+

| rowspan=3|

| β⁻, n?

| ⁵³K

| β⁻, 2n?

| ⁵²K

References

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]

Category:Argon

Argon