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, 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.

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. [4]

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. [5]

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. [6] 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. [7] Many endeavors require argon depleted in the cosmogenic isotopes, known as depleted argon. [8] 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. [9] [10] This was the first time a noble molecule was detected in outer space. [9] [10]

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. [4]

List of isotopes


Nuclide
[n 1] 		Z N Isotopic mass (Da) [11]
[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)
Excitation energyNormal proportion [1] Range of variation
29Ar [12] 181129.04076(47)# 2p 27S5/2+#
30Ar181230.02369(19)#<10 ps2p28S0+
31Ar181331.01216(22)#15.0(3) ms β+, p (68.3%)30S5/2+
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
32Ar181431.9976378(19)98(2) msβ+ (64.42%)32Cl0+
β+, p (35.58%)31S
33Ar181532.98992555(43)173.0(20) msβ+ (61.3%)33Cl1/2+
β+, p (38.7%)32S
34Ar181633.980270092(83)846.46(35) msβ+34Cl0+
35Ar181734.97525772(73)1.7756(10) sβ+35Cl3/2+
36Ar181835.967545106(28) Observationally Stable [n 8] 0+0.003336(210)
37Ar181936.96677630(22)35.011(19) d EC 37Cl3/2+Trace [n 9]
38Ar182037.96273210(21)Stable0+0.000629(70)
39Ar [n 10] 182138.9643130(54)268.2+3.1
−2.9 y [13] 		β−39K7/2−8×10−16 [14] [n 9]
40Ar [n 11] 182239.9623831220(23)Stable0+0.996035(250) [n 12]
41Ar182340.96450057(37)109.61(4) minβ−41K7/2−Trace [n 9]
42Ar182441.9630457(62)32.9(11) yβ−42K0+
43Ar182542.9656361(57)5.37(6) minβ−43K5/2(−)
44Ar182643.9649238(17)11.87(5) minβ−44K0+
45Ar182744.96803973(55)21.48(15) sβ−45K(5/2−,7/2−)
46Ar182845.9680392(25)8.4(6) sβ−46K0+
47Ar182946.9727671(13)1.23(3) sβ− (>99.8%)47K(3/2)−
β−, n? (<0.2%)46K
48Ar183047.976001(18)415(15) msβ− (62%)48K0+
β−, n (38%)47K
49Ar183148.98169(43)#236(8) msβ−49K3/2−#
β−, n (29%)48K
β−, 2n?47K
50Ar183249.98580(54)#106(6) msβ− (63%)50K0+
β−, n (37%)49K
β−, 2n?48K
51Ar183350.99303(43)#30# ms
[>200 ns]		β−?51K1/2−#
β−, n?50K
β−, 2n?49K
52Ar183451.99852(64)#40# ms
[>620 ns]		β−?52K0+
β−, n?51K
β−, 2n?50K
53Ar183553.00729(75)#20# ms
[>620 ns]		β−?53K5/2−#
β−, n?52K
β−, 2n?51K
54Ar183654.01348(86)#5# ms
[>400 ns]		β−?54K0+
β−, n?53K
β−, 2n?52K
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.

Related Research Articles

<span class="mw-page-title-main">Argon</span> Chemical element with atomic number 18 (Ar)

Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934%. It is more than twice as abundant as water vapor, 23 times as abundant as carbon dioxide, and more than 500 times as abundant as neon. Argon is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust.

<span class="mw-page-title-main">Stable nuclide</span> Nuclide that does not undergo radioactive decay

Stable nuclides are isotopes of a chemical element whose nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The nuclei of such isotopes are not radioactive and unlike radionuclides do not spontaneously undergo radioactive decay. When these nuclides are referred to in relation to specific elements they are usually called that element's stable isotopes.

<span class="mw-page-title-main">Nucleosynthesis</span> Process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium remains small, so that the universe still has approximately the same composition.

Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium is a common element found in many materials, such as feldspars, micas, clay minerals, tephra, and evaporites. In these materials, the decay product 40
Ar
 is able to escape the liquid (molten) rock but starts to accumulate when the rock solidifies (recrystallizes). The amount of argon sublimation that occurs is a function of the purity of the sample, the composition of the mother material, and a number of other factors. These factors introduce error limits on the upper and lower bounds of dating, so that the final determination of age is reliant on the environmental factors during formation, melting, and exposure to decreased pressure or open air. Time since recrystallization is calculated by measuring the ratio of the amount of 40
Ar
 accumulated to the amount of 40
K
 remaining. The long half-life of 40
K
 allows the method to be used to calculate the absolute age of samples older than a few thousand years.

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.

<span class="mw-page-title-main">Isotopes of hydrogen</span>

Hydrogen (1H) has three naturally occurring isotopes: 1H, 2H, and 3H. 1H and 2H are stable, while 3H has a half-life of 12.32(2) years. Heavier isotopes also exist; all are synthetic and have a half-life of less than 1 zeptosecond (10−21 s). Of these, 5H is the least stable, while 7H is the most.

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 it is for all practical purposes 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, 41Ca, with half-life 99,400 years. Unlike cosmogenic isotopes that are produced in the air, 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 strong enough. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar system anomalies. The most stable artificial isotopes are 45Ca with half-life 163 days and 47Ca with half-life 4.5 days. All other calcium isotopes have half-lives of minutes or less.

Potassium has 25 known isotopes from 34
K to 57
K as well as 31
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.

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 23 known isotopes from 21Al 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.

Beryllium (4Be) has 11 known isotopes and 3 known isomers, but only one of these isotopes is stable and a primordial nuclide. As such, beryllium is considered a monoisotopic element. It is also a mononuclidic element, because its other isotopes have such short half-lives that none are primordial and their abundance is very low. Beryllium is unique as being the only monoisotopic element with both an even number of protons and an odd number of neutrons. There are 25 other monoisotopic elements but all have odd atomic numbers, and even numbers of neutrons.

<span class="mw-page-title-main">Standard atomic weight</span> Relative atomic mass as defined by IUPAC (CIAAW)

The standard atomic weight of a chemical element (symbol Ar°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, isotope 63Cu (Ar = 62.929) constitutes 69% of the copper on Earth, the rest being 65Cu (Ar = 64.927), so

<span class="mw-page-title-main">Potassium-40</span> Radioactive isotope of potassium

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">Thermochronology</span> Study of the thermal evolution of a region of a planet

Thermochronology is the study of the thermal evolution of a region of a planet. Thermochronologists use radiometric dating along with the closure temperatures that represent the temperature of the mineral being studied at the time given by the date recorded to understand the thermal history of a specific rock, mineral, or geologic unit. It is a subfield within geology, and is closely associated with geochronology.

<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">Beta-decay stable isobars</span> Set of nuclides that cannot undergo beta decay

Beta-decay stable isobars are the set of nuclides which cannot undergo beta decay, that is, the transformation of a neutron to a proton or a proton to a neutron within the nucleus. A subset of these nuclides are also stable with regards to double beta decay or theoretically higher simultaneous beta decay, as they have the lowest energy of all isobars with the same mass number.

<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.

The Mattauch isobar rule, formulated by Josef Mattauch in 1934, states that if two adjacent elements on the periodic table have isotopes of the same mass number, one of these isotopes must be radioactive. Two nuclides that have the same mass number (isobars) can both be stable only if their atomic numbers differ by more than one. In fact, for currently observationally stable nuclides, the difference can only be 2 or 4, and in theory, two nuclides that have the same mass number cannot be both stable, but many such nuclides which are theoretically unstable to double beta decay have not been observed to decay, e.g. 134Xe. However, this rule cannot make predictions on the half-lives of these radioisotopes.

References

  1. 1 2 3 4 5 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 "40Ar/39Ar dating and errors". Archived from the original on 9 May 2007. Retrieved 7 March 2007.
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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 .
  9. 1 2 Quenqua, Douglas (13 December 2013). "Noble Molecules Found in Space". The New York Times . Retrieved 13 December 2013.
  10. 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.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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): 930. arXiv: 2310.06867 . Bibcode:2023EPJC...83..930G. doi:10.1140/epjc/s10052-023-12113-6. ISSN   1434-6052.
  14. ↑ 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.
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