Argon 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% (9340 ppmv). It is more than twice as abu ...

(Ar) has 26 known

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

s, from Ar to Ar, of which three are

stable A stable is a building in which working animals are kept, especially horses or oxen. The building is usually divided into stalls, and may include storage for equipment and feed. Styles There are many different types of stables in use tod ...

(Ar, Ar, and Ar). On Earth, Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are Ar with a half-life of 268 years, Ar with a half-life of 32.9 years, and 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 K, with a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 1.248 years, decays to stable Ar by

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

(10.72%) and by

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron emi ...

(0.001%), and also to stable Ca via

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

(89.28%). These properties and ratios are used to determine the age of

rocks In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...

through potassium–argon dating. Despite the trapping of 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 K decay, since 99.6% of Earth's atmospheric argon is Ar, whereas in the Sun and presumably in primordial star-forming clouds, argon consists of < 15% Ar and mostly (85%) Ar. Similarly, the ratio of the isotopes Ar:Ar:Ar in the atmospheres of the

outer planet The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

s is measured to be 8400:1600:1. In the Earth's

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

, radioactive Ar (half-life 268(8) years) is made by

cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...

activity, primarily from Ar. In the subsurface environment, it is also produced through

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

by >K or

alpha emission Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an atom ...

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

. The content of Ar in natural argon is measured to be of (8.0±0.6)×10 g/g, or (1.01±0.08) Bq/kg of 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 isotope Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an '' in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom ...

s, known as depleted argon. Lighter radioactive isotopes can decay to different elements (usually

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

) while heavier ones decay to

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

. ³⁶Ar, in the form of

argon hydride Argonium (also called the argon hydride cation, the hydridoargon(1+) ion, or protonated argon; chemical formula ArH+) is a cation combining a proton and an argon atom. It can be made in an electric discharge, and was the first noble gas molecul ...

, was detected in the

Crab Nebula The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus (constellation), Taurus. The common name comes from a drawing that somewhat resembled a crab with arm ...

supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...

during 2013. This was the first time a noble molecule was detected in outer space. ³⁷Ar is a synthetic radionuclide that is created via

of ⁴⁰Ca followed by

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...

emission, as a result of subsurface nuclear explosions. It has a half-life of 35 days.

List of isotopes

, -id=Argon-29 , ²⁹Ar , 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, , 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, , 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, , 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 , style="text-align:right" , 18 , 35.967545106(28) , colspan=3 align=center,

Observationally Stable 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 radionuc ...

Believed 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 Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede Potassium-argon dating, potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measur ...

, style="text-align:right" , 18 , style="text-align:right" , 21 , 38.9643130(54) , y , β⁻ , ³⁹K , 7/2− ,

Cosmogenic nuclide Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an '' in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom ...

, , -id=Argon-40 , ⁴⁰ArUsed in

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, , 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, , 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, , 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, , 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, , 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, , 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, , 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, , rowspan=3, , - , β⁻, n? , ⁵³K , - , β⁻, 2n? , ⁵²K

References

External links

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

List of isotopes

See also

References

External links