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Isotopes of argon

From Wikipedia, the free encyclopedia

Main isotopes^[1]			Decay
Isotope	abundance	half-life(t_1/2)	mode	product
³⁶Ar	0.334%	stable
³⁷Ar	trace	35.01 d	ε	³⁷Cl
³⁸Ar	0.0630%	stable
³⁹Ar	trace	302 y	β⁻	³⁹K
⁴⁰Ar	99.6%	stable
⁴¹Ar	trace	109.61 min	β⁻	⁴¹K
⁴²Ar	synth	32.9 y	β⁻	⁴²K

Standard atomic weightA_r°(Ar)

[39.792, 39.963]^[2]
39.95±0.16 (abridged)^[3]

Argon (₁₈Ar) has 26 knownisotopes, from²⁹Ar to⁵⁴Ar, of which three arestable (³⁶Ar,³⁸Ar, and⁴⁰Ar). On Earth,⁴⁰Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are³⁹Ar with a half-life of 302 years,⁴²Ar with a half-life of 32.9 years, and³⁷Ar 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 than³⁸Ar decay tochlorine or lighter elements, while heavier ones beta decay topotassium.

The naturally occurring⁴⁰K, with ahalf-life of 1.248×10⁹ years, decays to stable⁴⁰Ar byelectron capture (10.72%) and bypositron emission (0.001%), and also to stable⁴⁰Ca viabeta decay (89.28%). These properties and ratios are used to determine the age ofrocks throughpotassium–argon dating.^[4]

Despite the trapping of⁴⁰Ar in many rocks, it can be released by melting, grinding, and diffusion. Almost all argon in the Earth's atmosphere is the product of⁴⁰K decay, since 99.6% of Earth's atmospheric argon is⁴⁰Ar, whereas in the Sun and presumably in primordial star-forming clouds, argon consists of ~85%³⁶Ar, ~15%³⁸Ar and only trace⁴⁰Ar. Similarly, the ratio of the isotopes³⁶Ar:³⁸Ar:⁴⁰Ar in the atmospheres of theouter planets is measured to be 8400:1600:1.^[5]

In the Earth'satmosphere, radioactive³⁹Ar (and to a lesser extent³⁷Ar) is made bycosmic ray activity, primarily from⁴⁰Ar. In the subsurface environment,³⁹Ar is also produced throughneutron capture by³⁹K or⁴²Ca, with proton or alpha emission respectively;³⁷Ar was created in subsurfacenuclear explosions similarly from⁴⁰Ca.^[4] The content of³⁹Ar in natural argon is measured to be of (8.6±0.4)×10⁻¹⁶ g/g, or (0.964±0.024) Bq/kg weight.^[6]

The content of⁴²Ar (half-life 33 years) in the Earth's atmosphere, though it had previously been reported as a cosmogenic isotope,^[7] is lower than 6×10⁻²¹ of the element.^[8] Many endeavors require argon depleted in thecosmogenic isotopes, known as depleted argon^[9] 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 ofargon hydride, was detected in theCrab Nebula supernova remnant during 2013.^[10]^[11] This was the first time anoble molecule was detected inouter space.^[10]^[11]

List of isotopes

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Nuclide ^{[n 1]}	Z	N	Isotopic mass(Da)^[12] ^{[n 2]}^{[n 3]}	Half-life^[1]	Decay mode^[1] ^{[n 4]}	Daughter isotope ^{[n 5]}	Spin and parity^[1] ^{[n 6]}^{[n 7]}	Natural abundance(mole fraction)
Nuclide ^{[n 1]}	Excitation energy			Half-life^[1]	Decay mode^[1] ^{[n 4]}	Daughter isotope ^{[n 5]}	Spin and parity^[1] ^{[n 6]}^{[n 7]}	Normal proportion^[1]	Range of variation
²⁹Ar^[13]	18	11	29.04076(47)#		2p	²⁷S	5/2+#
³⁰Ar	18	12	30.02369(19)#	<10 ps	2p	²⁸S	0+
³¹Ar	18	13	31.012125(14)^[14]	15.0(3) ms	β⁺, p (68.3%)	³⁰S	5/2+
					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
³²Ar	18	14	31.9976378(19)	98(2) ms	β⁺ (64.42%)	³²Cl	0+
³²Ar	18	14	31.9976378(19)	98(2) ms	β⁺, p (35.58%)	³¹S	0+
³³Ar	18	15	32.98992555(43)	173.0(20) ms	β⁺ (61.3%)	³³Cl	1/2+
³³Ar	18	15	32.98992555(43)	173.0(20) ms	β⁺, p (38.7%)	³²S	1/2+
³⁴Ar	18	16	33.980270092(83)	846.46(35) ms	β⁺	³⁴Cl	0+
³⁵Ar	18	17	34.97525772(73)	1.7756(10) s	β⁺	³⁵Cl	3/2+
³⁶Ar	18	18	35.967545106(28)	Observationally Stable^{[n 8]}			0+	0.003336(210)
³⁷Ar	18	19	36.96677630(22)	35.011(19) d	EC	³⁷Cl	3/2+	Trace^{[n 9]}
³⁸Ar	18	20	37.96273210(21)	Stable			0+	0.000629(70)
³⁹Ar^{[n 10]}	18	21	38.9643130(54)	302(10) y^[15]^[16]	β⁻	³⁹K	7/2−	8×10⁻¹⁶^[17]^{[n 9]}
⁴⁰Ar^{[n 11]}	18	22	39.9623831220(23)	Stable			0+	0.996035(250)^{[n 12]}
⁴¹Ar	18	23	40.96450057(37)	109.61(4) min	β⁻	⁴¹K	7/2−	Trace^{[n 9]}
⁴²Ar	18	24	41.9630457(62)	32.9(11) y	β⁻	⁴²K	0+
⁴³Ar	18	25	42.9656361(57)	5.37(6) min	β⁻	⁴³K	5/2(−)
⁴⁴Ar	18	26	43.9649238(17)	11.87(5) min	β⁻	⁴⁴K	0+
⁴⁵Ar	18	27	44.96803973(55)	21.48(15) s	β⁻	⁴⁵K	(5/2−,7/2−)
⁴⁶Ar	18	28	45.9680392(25)	8.4(6) s	β⁻	⁴⁶K	0+
⁴⁷Ar	18	29	46.9727671(13)	1.23(3) s	β⁻ (>99.8%)	⁴⁷K	(3/2)−
⁴⁷Ar	18	29	46.9727671(13)	1.23(3) s	β⁻,n? (<0.2%)	⁴⁶K	(3/2)−
⁴⁸Ar	18	30	47.976001(18)	415(15) ms	β⁻ (62%)	⁴⁸K	0+
⁴⁸Ar	18	30	47.976001(18)	415(15) ms	β⁻, n (38%)	⁴⁷K	0+
⁴⁹Ar	18	31	48.98169(43)#	236(8) ms	β⁻	⁴⁹K	3/2−#
					β⁻, n (29%)	⁴⁸K
					β⁻, 2n?	⁴⁷K
⁵⁰Ar	18	32	49.98580(54)#	106(6) ms	β⁻ (63%)	⁵⁰K	0+
					β⁻, n (37%)	⁴⁹K
					β⁻, 2n?	⁴⁸K
⁵¹Ar	18	33	50.99303(43)#	30# ms [>200 ns]	β⁻?	⁵¹K	1/2−#
					β⁻, n?	⁵⁰K
					β⁻, 2n?	⁴⁹K
⁵²Ar	18	34	51.99852(64)#	40# ms [>620 ns]	β⁻?	⁵²K	0+
					β⁻, n?	⁵¹K
					β⁻, 2n?	⁵⁰K
⁵³Ar	18	35	53.00729(75)#	20# ms [>620 ns]	β⁻?	⁵³K	5/2−#
					β⁻, n?	⁵²K
					β⁻, 2n?	⁵¹K
⁵⁴Ar	18	36	54.01348(86)#	5# ms [>400 ns]	β⁻?	⁵⁴K	0+
					β⁻, n?	⁵³K
					β⁻, 2n?	⁵²K
This table header & footer: view

^^mAr – Excitednuclear isomer.
^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
^Modes of decay:
EC: Electron capture

n: Neutron emission
p: Proton emission
^Bold symbol as daughter – Daughter product is stable.
^( ) spin value – Indicates spin with weak assignment arguments.
^# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^Believed to undergo double electron capture to³⁶S (lightest theoretically unstable nuclide for which no evidence of radioactivity has been observed)
^^a ^b ^cCosmogenic nuclide
^Used inargon–argon dating
^Used inargon–argon dating andpotassium–argon dating
^Generated from⁴⁰K in rocks. These ratios are terrestrial. Cosmic abundance is far less than³⁶Ar.

References

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^^a ^b ^c ^d ^eKondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021)."The NUBASE2020 evaluation of nuclear properties"(PDF).Chinese Physics C.45 (3) 030001.doi:10.1088/1674-1137/abddae.
^"Standard Atomic Weights: Argon".CIAAW. 2017.
^Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022)."Standard atomic weights of the elements 2021 (IUPAC Technical Report)".Pure and Applied Chemistry.doi:10.1515/pac-2019-0603.ISSN 1365-3075.
^^a ^b"⁴⁰Ar/³⁹Ar dating and errors". Archived fromthe original on 9 May 2007. Retrieved7 March 2007.
^Cameron, A.G.W. (1973). "Elemental and isotopic abundances of the volatile elements in the outer planets".Space Science Reviews.14 (3–4):392–400.Bibcode:1973SSRv...14..392C.doi:10.1007/BF00214750.S2CID 119861943.
^P. Adhikari; et al. (2023)."Precision Measurement of the Specific Activity of³⁹Ar in Atmospheric Argon with the DEAP-3600 Detector".The European Physical Journal C.83 (7): 642.arXiv:2302.14639.doi:10.1140/epjc/s10052-023-11678-6.
^For example inBarabash, A.S.; Saakyan, R.R.; Umatov, V.I. (2016). "On concentration of 42Ar in the Earth's atmosphere".Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.839:39–42.arXiv:1609.08890.doi:10.1016/j.nima.2016.09.042.
^V. D. Ashitkov; et al. (1998). "New experimental limit on the⁴²Ar content in the Earth's atmosphere".Nuclear Instruments and Methods A.416 (1):179–181.Bibcode:1998NIMPA.416..179A.doi:10.1016/S0168-9002(98)00740-2.
^H. O. Back; et al. (2012)."Depleted Argon from Underground Sources".Physics Procedia.37:1105–1112.Bibcode:2012PhPro..37.1105B.doi:10.1016/j.phpro.2012.04.099.
^^a ^bQuenqua, Douglas (13 December 2013)."Noble Molecules Found in Space".The New York Times. Retrieved13 December 2013.
^^a ^bBarlow, M. J.; et al. (2013). "Detection of a Noble Gas Molecular Ion,³⁶ArH+, in the Crab Nebula".Science.342 (6164):1343–1345.arXiv:1312.4843.Bibcode:2013Sci...342.1343B.doi:10.1126/science.1243582.PMID 24337290.S2CID 37578581.
^Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*".Chinese Physics C.45 (3) 030003.doi:10.1088/1674-1137/abddaf.
^Mukha, I.; et al. (2018). "Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains".Physical Review C.98 (6) 064308: 064308–1–064308–13.arXiv:1803.10951.Bibcode:2018PhRvC..98f4308M.doi:10.1103/PhysRevC.98.064308.S2CID 119384311.
^Chen, Z. Y.; Yan, X. L.; Hou, S. Q.; Liu, J. B.; Shi, J. Y.; Zhou, X. H.; Zhang, Y. H.; Wang, M.; Zhou, X.; Zhang, M.; Li, H. F.; Sun, M. Z.; Xing, Y. M.; Shuai, P.; Xu, X.; Huang, W. J.; Wang, Q.; Song, Y. N.; Deng, H. Y.; Jiao, H. Y.; Luo, Y. F.; Litvinov, Yu. A.; Blaum, K.; Yamaguchi, T. (1 December 2025)."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".The Astrophysical Journal.994 (2): 270.doi:10.3847/1538-4357/ae1470.
^P. Adhikari; et al. (2025)."Direct Measurement of the Half-Life of³⁹Ar from 3.4 Years of Data with the DEAP-3600 Detector".The European Physical Journal C.85 (7): 728.doi:10.1140/epjc/s10052-025-14289-5.
^This appears reliable but the NUBASE2020 value is 268(8) years and the discrepancy is yet to be explained.
^Lu, Zheng-Tian (1 March 2013). "What trapped atoms reveal about global groundwater".Physics Today.66 (3):74–75.Bibcode:2013PhT....66c..74L.doi:10.1063/PT.3.1926.

External links

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Argon isotopes data fromThe Berkeley Laboratory Isotopes Projects

Isotopes of thechemical elements

Group	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Period	Hydrogen and alkali metals	Alkaline earth metals													Pnictogens	Chalcogens	Halogens	Noble gases
①	Isotopes § List H 1																	Isotopes § List He 2
②	Isotopes § List Li 3	Isotopes § List Be 4											Isotopes § List B 5	Isotopes § List C 6	Isotopes § List N 7	Isotopes § List O 8	Isotopes § List F 9	Isotopes § List Ne 10
③	Isotopes § List Na 11	Isotopes § List Mg 12											Isotopes § List Al 13	Isotopes § List Si 14	Isotopes § List P 15	Isotopes § List S 16	Isotopes § List Cl 17	Isotopes § List Ar 18
④	Isotopes § List K 19	Isotopes § List Ca 20	Isotopes § List Sc 21	Isotopes § List Ti 22	Isotopes § List V 23	Isotopes § List Cr 24	Isotopes § List Mn 25	Isotopes § List Fe 26	Isotopes § List Co 27	Isotopes § List Ni 28	Isotopes § List Cu 29	Isotopes § List Zn 30	Isotopes § List Ga 31	Isotopes § List Ge 32	Isotopes § List As 33	Isotopes § List Se 34	Isotopes § List Br 35	Isotopes § List Kr 36
⑤	Isotopes § List Rb 37	Isotopes § List Sr 38	Isotopes § List Y 39	Isotopes § List Zr 40	Isotopes § List Nb 41	Isotopes § List Mo 42	Isotopes § List Tc 43	Isotopes § List Ru 44	Isotopes § List Rh 45	Isotopes § List Pd 46	Isotopes § List Ag 47	Isotopes § List Cd 48	Isotopes § List In 49	Isotopes § List Sn 50	Isotopes § List Sb 51	Isotopes § List Te 52	Isotopes § List I 53	Isotopes § List Xe 54
⑥	Isotopes § List Cs 55	Isotopes § List Ba 56	Isotopes § List Lu 71	Isotopes § List Hf 72	Isotopes § List Ta 73	Isotopes § List W 74	Isotopes § List Re 75	Isotopes § List Os 76	Isotopes § List Ir 77	Isotopes § List Pt 78	Isotopes § List Au 79	Isotopes § List Hg 80	Isotopes § List Tl 81	Isotopes § List Pb 82	Isotopes § List Bi 83	Isotopes § List Po 84	Isotopes § List At 85	Isotopes § List Rn 86
⑦	Isotopes § List Fr 87	Isotopes § List Ra 88	Isotopes § List Lr 103	Isotopes § List Rf 104	Isotopes § List Db 105	Isotopes § List Sg 106	Isotopes § List Bh 107	Isotopes § List Hs 108	Isotopes § List Mt 109	Isotopes § List Ds 110	Isotopes § List Rg 111	Isotopes § List Cn 112	Isotopes § List Nh 113	Isotopes § List Fl 114	Isotopes § List Mc 115	Isotopes § List Lv 116	Isotopes § List Ts 117	Isotopes § List Og 118
⑧	Isotopes § List Uue 119	Isotopes § List Ubn 120

			Isotopes § List La 57	Isotopes § List Ce 58	Isotopes § List Pr 59	Isotopes § List Nd 60	Isotopes § List Pm 61	Isotopes § List Sm 62	Isotopes § List Eu 63	Isotopes § List Gd 64	Isotopes § List Tb 65	Isotopes § List Dy 66	Isotopes § List Ho 67	Isotopes § List Er 68	Isotopes § List Tm 69	Isotopes § List Yb 70
			Isotopes § List Ac 89	Isotopes § List Th 90	Isotopes § List Pa 91	Isotopes § List U 92	Isotopes § List Np 93	Isotopes § List Pu 94	Isotopes § List Am 95	Isotopes § List Cm 96	Isotopes § List Bk 97	Isotopes § List Cf 98	Isotopes § List Es 99	Isotopes § List Fm 100	Isotopes § List Md 101	Isotopes § List No 102