Isotopes of argon

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Isotopes of argon  (18Ar)
Main isotopes [1] Decay
abun­dance half-life (t1/2) mode pro­duct
36Ar0.334% stable
37Ar trace 35 d ε 37Cl
38Ar0.0630%stable
39Artrace268 y β− 39K
40Ar99.6%stable
41Artrace109.34 minβ− 41K
42Ar synth 32.9 yβ− 42K
Standard atomic weight Ar°(Ar)

Argon (18Ar) has 26 known isotopes, from 29Ar to 54Ar and 1 isomer (32mAr), of which three are stable (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 4×10−20 seconds. [4]

Contents

The naturally occurring 40K, with a half-life of 1.248×109 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 rocks through potassium–argon dating. [5]

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. [6]

In the Earth's atmosphere, 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, 40Ar. [7] 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, 40Ar. [8] Many endeavors require argon depleted in the cosmogenic isotopes, known as depleted argon. [9] 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. [10] [11] This was the first time a noble molecule was detected in outer space. [10] [11]

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 nuclear explosions. It has a half-life of 35 days. [5]

List of isotopes

Nuclide [12]
[n 1] 		Z N Isotopic mass (Da) [13]
[n 2] [n 3] 		Half-life
Decay
mode
[n 4] 		Daughter
isotope
[n 5] 		Spin and
parity
[n 6] [n 7] 		Natural abundance (mole fraction)
Excitation energyNormal proportionRange of variation
29Ar [4] 1811~40 zs 2p 27S
30Ar181230.02247(22)<10 ps2p28S0+
31Ar181331.01216(22)#15.1(3) ms β+, p (68.3%)30S5/2+
β+ (22.63%)31Cl
β+, 2p (9.0%)29P
β+, 3p (0.07%)28Si
32Ar181431.9976378(19)98(2) msβ+ (64.42%)32Cl0+
β+, p (35.58%)31S
32mAr5600(100) keVunknown5−#
33Ar181532.9899255(4)173.0(20) msβ+ (61.3%)33Cl1/2+
β+, p (38.7%)32S
34Ar181633.98027009(8)843.8(4) msβ+34Cl0+
35Ar181734.9752577(7)1.7756(10) sβ+35Cl3/2+
36Ar181835.967545105(29) Observationally Stable [n 8] 0+0.003336(4)
37Ar181936.96677631(22)35.011(19) d EC 37Cl3/2+Trace [n 9]
38Ar182037.96273210(21)Stable0+0.000629(1)
39Ar [n 10] 182138.964313(5)268.2+3.1
−2.9 y [14] 		β−39K7/2−Trace [n 9]
40Ar [n 11] 182239.9623831238(24)Stable0+0.996035(4) [n 12]
41Ar182340.9645006(4)109.61(4) minβ−41K7/2−Trace [n 9]
42Ar182441.963046(6)32.9(11) yβ−42K0+
43Ar182542.965636(6)5.37(6) minβ−43K5/2(−)
44Ar182643.9649238(17)11.87(5) minβ−44K0+
45Ar182744.9680397(6)21.48(15) sβ−45K(5/2,7/2)−
46Ar182845.9680374(12)8.4(6) sβ−46K0+
47Ar182946.9727681(12)1.23(3) sβ− (99.8%)47K(3/2−)
β−, n (0.2%)46K
48Ar183047.97608(33)415(15) msβ−48K0+
49Ar183148.98155(43)#236(8) msβ−49K3/2−#
50Ar183249.98569(54)#106(6) msβ−50K0+
51Ar183350.99280(64)#60# ms [>200 ns]β−51K3/2−#
52Ar183451.99863(64)#10# msβ−52K0+
53Ar183553.00729(75)#3# msβ−53K(5/2−)#
β−, n52K
54Ar [15] 1836β−54K0+
This table header & footer:
  1. ↑ mAr – Excited nuclear isomer.
  2. ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ↑ Modes of decay:
    EC: Electron capture
    n: Neutron emission
    p: Proton emission
  5. ↑ Bold symbol as daughter – Daughter product is stable.
  6. ↑ ( ) spin value – Indicates spin with weak assignment arguments.
  7. ↑ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  8. ↑ Believed to undergo double electron capture to 36S (lightest theoretically unstable nuclide for which no evidence of radioactivity has been observed)
  9. 1 2 3 Cosmogenic nuclide
  10. ↑ Used in argon–argon dating
  11. ↑ Used in argon–argon dating and potassium–argon dating
  12. ↑ Generated from 40K in rocks. These ratios are terrestrial. Cosmic abundance is far less than 36Ar.

See also

Related Research Articles

Argon–argondating is a radiometric dating method invented to supersede potassium–argon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes. 40Ar/39Ar dating relies on neutron irradiation from a nuclear reactor to convert a stable form of potassium (39K) into the radioactive 39Ar. As long as a standard of known age is co-irradiated with unknown samples, it is possible to use a single measurement of argon isotopes to calculate the 40K/40Ar* ratio, and thus to calculate the age of the unknown sample. 40Ar* refers to the radiogenic 40Ar, i.e. the 40Ar produced from radioactive decay of 40K. 40Ar* does not include atmospheric argon adsorbed to the surface or inherited through diffusion and its calculated value is derived from measuring the 36Ar and assuming that 40Ar is found in a constant ratio to 36Ar in atmospheric gases.

Fluorine (9F) has 18 known isotopes ranging from 13
F
 to 31
F
 and two isomers. Only fluorine-19 is stable and naturally occurring in more than trace quantities; therefore, fluorine is a monoisotopic and mononuclidic element.

There are 42 isotopes of polonium (84Po). They range in size from 186 to 227 nucleons. They are all radioactive. 210Po with a half-life of 138.376 days has the longest half-life of any naturally-occurring isotope of polonium and is the most common isotope of polonium. It is also the most easily synthesized polonium isotope. 209Po, which does not occur naturally, has the longest half-life of all isotopes of polonium at 124 years. 209Po can be made by using a cyclotron to bombard bismuth with protons, as can 208Po.

Lead (82Pb) has four observationally stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay chains: the uranium series, the actinium series, and the thorium series, respectively; a fourth decay chain, the neptunium series, terminates with the thallium isotope 205Tl. The three series terminating in lead represent the decay chain products of long-lived primordial 238U, 235U, and 232Th. Each isotope also occurs, to some extent, as primordial isotopes that were made in supernovae, rather than radiogenically as daughter products. The fixed ratio of lead-204 to the primordial amounts of the other lead isotopes may be used as the baseline to estimate the extra amounts of radiogenic lead present in rocks as a result of decay from uranium and thorium.

There are seven stable isotopes of mercury (80Hg) with 202Hg being the most abundant (29.86%). The longest-lived radioisotopes are 194Hg with a half-life of 444 years, and 203Hg with a half-life of 46.612 days. Most of the remaining 40 radioisotopes have half-lives that are less than a day. 199Hg and 201Hg are the most often studied NMR-active nuclei, having spin quantum numbers of 1/2 and 3/2 respectively. All isotopes of mercury are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed. These isotopes are predicted to undergo either alpha decay or double beta decay.

Naturally occurring platinum (78Pt) consists of five stable isotopes (192Pt, 194Pt, 195Pt, 196Pt, 198Pt) and one very long-lived (half-life 4.83×1011 years) radioisotope (190Pt). There are also 34 known synthetic radioisotopes, the longest-lived of which is 193Pt with a half-life of 50 years. All other isotopes have half-lives under a year, most under a day. All isotopes of platinum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed. Platinum-195 is the most abundant isotope.

There are two natural isotopes of iridium (77Ir), and 37 radioisotopes, the most stable radioisotope being 192Ir with a half-life of 73.83 days, and many nuclear isomers, the most stable of which is 192m2Ir with a half-life of 241 years. All other isomers have half-lives under a year, most under a day. All isotopes of iridium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

Naturally occurring xenon (54Xe) consists of seven stable isotopes and two very long-lived isotopes. Double electron capture has been observed in 124Xe and double beta decay in 136Xe, which are among the longest measured half-lives of all nuclides. The isotopes 126Xe and 134Xe are also predicted to undergo double beta decay, but this has never been observed in these isotopes, so they are considered to be stable. Beyond these stable forms, 32 artificial unstable isotopes and various isomers have been studied, the longest-lived of which is 127Xe with a half-life of 36.345 days. All other isotopes have half-lives less than 12 days, most less than 20 hours. The shortest-lived isotope, 108Xe, has a half-life of 58 μs, and is the heaviest known nuclide with equal numbers of protons and neutrons. Of known isomers, the longest-lived is 131mXe with a half-life of 11.934 days. 129Xe is produced by beta decay of 129I ; 131mXe, 133Xe, 133mXe, and 135Xe are some of the fission products of both 235U and 239Pu, so are used as indicators of nuclear explosions.

Bromine (35Br) has two stable isotopes, 79Br and 81Br, and 32 known radioisotopes, the most stable of which is 77Br, with a half-life of 57.036 hours.

Calcium (20Ca) has 26 known isotopes, ranging from 35Ca to 60Ca. There are five stable isotopes, plus one isotope (48Ca) with such a long half-life that for all practical purposes it can be considered stable. The most abundant isotope, 40Ca, as well as the rare 46Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 99,400 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar system anomalies. The most stable artificial radioisotopes are 45Ca with a half-life of 163 days and 47Ca with a half-life of 4.5 days. All other calcium isotopes have half-lives measured in minutes or less.

Potassium has 26 known isotopes from 31
K to 57
K, with the exception of still-unknown 32
K, as well as an unconfirmed report of 59
K. Three of those isotopes occur naturally: the two stable forms 39
K (93.3%) and 41
K (6.7%), and a very long-lived radioisotope 40
K (0.012%)

Chlorine (17Cl) has 25 isotopes, ranging from 28Cl to 52Cl, and two isomers, 34mCl and 38mCl. There are two stable isotopes, 35Cl (75.8%) and 37Cl (24.2%), giving chlorine a standard atomic weight of 35.45. The longest-lived radioactive isotope is 36Cl, which has a half-life of 301,000 years. All other isotopes have half-lives under 1 hour, many less than one second. The shortest-lived are proton-unbound 29Cl and 30Cl, with half-lives less than 10 picoseconds and 30 nanoseconds, respectively; the half-life of 28Cl is unknown.

Although phosphorus (15P) has 22 isotopes from 26P to 47P, only 31P is stable; as such, phosphorus is considered a monoisotopic element. The longest-lived radioactive isotopes are 33P with a half-life of 25.34 days and 32P with a half-life of 14.268 days. All others have half-lives of under 2.5 minutes, most under a second. The least stable known isotope is 47P, with a half-life of 2 milliseconds.

Sulfur (16S) has 23 known isotopes with mass numbers ranging from 27 to 49, four of which are stable: 32S (95.02%), 33S (0.75%), 34S (4.21%), and 36S (0.02%). The preponderance of sulfur-32 is explained by its production from carbon-12 plus successive fusion capture of five helium-4 nuclei, in the so-called alpha process of exploding type II supernovas.

Aluminium or aluminum (13Al) has 22 known isotopes from 22Al to 43Al and 4 known isomers. Only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2×105 y) occur naturally, however 27Al comprises nearly all natural aluminium. Other than 26Al, all radioisotopes have half-lives under 7 minutes, most under a second. The standard atomic weight is 26.9815385(7). 26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of sediment transport, deposition, and storage, as well as burial times, and erosion, on 105 to 106 year time scales. 26Al has also played a significant role in the study of meteorites.

Natural nitrogen (7N) consists of two stable isotopes: the vast majority (99.6%) of naturally occurring nitrogen is nitrogen-14, with the remainder being nitrogen-15. Thirteen radioisotopes are also known, with atomic masses ranging from 9 to 23, along with three nuclear isomers. All of these radioisotopes are short-lived, the longest-lived being nitrogen-13 with a half-life of 9.965(4) min. All of the others have half-lives below 7.15 seconds, with most of these being below 620 milliseconds. Most of the isotopes with atomic mass numbers below 14 decay to isotopes of carbon, while most of the isotopes with masses above 15 decay to isotopes of oxygen. The shortest-lived known isotope is nitrogen-10, with a half-life of 143(36) yoctoseconds, though the half-life of nitrogen-9 has not been measured exactly.

Potassium-40 (40K) is a radioactive isotope of potassium which has a long half-life of 1.25 billion years. It makes up about 0.012% of the total amount of potassium found in nature.

<span class="mw-page-title-main">Primordial nuclide</span> Nuclides predating the Earths formation (found on Earth)

In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present; 286 such nuclides are known.

<span class="mw-page-title-main">Radiogenic nuclide</span>

A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive or stable.

An alpha nuclide is a nuclide that consists of an integer number of alpha particles. Alpha nuclides have equal, even numbers of protons and neutrons; they are important in stellar nucleosynthesis since the energetic environment within stars is amenable to fusion of alpha particles into heavier nuclei. Stable alpha nuclides, and stable decay products of radioactive alpha nuclides, are some of the most common metals in the universe.

References

  1. ↑ Kondev, 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.
  2. ↑ "Standard Atomic Weights: Argon". CIAAW. 2017.
  3. ↑ 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.
  4. 1 2 Mukha, I.; et al. (2018). "Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains". Physical Review C. 98 (6): 064308–1–064308–13. arXiv: 1803.10951 . Bibcode:2018PhRvC..98f4308M. doi:10.1103/PhysRevC.98.064308. S2CID   119384311.
  5. 1 2 "40Ar/39Ar dating and errors". Archived from the original on 9 May 2007. Retrieved 7 March 2007.
  6. ↑ 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.
  7. ↑ P. Benetti; et al. (2007). "Measurement of the specific activity of 39Ar in natural argon". Nuclear Instruments and Methods A . 574 (1): 83–88. arXiv: astro-ph/0603131 . Bibcode:2007NIMPA.574...83B. doi:10.1016/j.nima.2007.01.106. S2CID   17073444.
  8. ↑ V. D. Ashitkov; et al. (1998). "New experimental limit on the 42Ar 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.
  9. ↑ 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 .
  10. 1 2 Quenqua, Douglas (13 December 2013). "Noble Molecules Found in Space". The New York Times . Retrieved 13 December 2013.
  11. 1 2 Barlow, 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.
  12. ↑ Half-life, decay mode, nuclear spin, and isotopic composition is sourced in:
    Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  13. ↑ Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF). Chinese Physics C. 41 (3): 030003-1–030003-442. doi:10.1088/1674-1137/41/3/030003.
  14. ↑ Golovko, Victor V. (15 October 2023). "Application of the most frequent value method for 39Ar half-life determination". The European Physical Journal C. 83 (10). arXiv: 2310.06867 . doi:10.1140/epjc/s10052-023-12113-6. ISSN   1434-6052.
  15. ↑ Neufcourt, L.; Cao, Y.; Nazarewicz, W.; Olsen, E.; Viens, F. (2019). "Neutron drip line in the Ca region from Bayesian model averaging". Physical Review Letters. 122 (6): 062502–1–062502–6. arXiv: 1901.07632 . Bibcode:2019PhRvL.122f2502N. doi:10.1103/PhysRevLett.122.062502. PMID   30822058. S2CID   73508148.
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