Isotopes of potassium

{{Short description|none}} {{Infobox potassium isotopes}} Potassium ({{chem||19|K}}) has 25 known isotopes from {{chem|34|K}} to {{chem|57|K}} as well as {{chem|31|K}}, as well as an unconfirmed report of {{chem|59|K}}.<ref name="neufcourt2019">{{cite journal |last1=Neufcourt |first1=Léo |last2=Cao |first2=Yuchen |last3=Nazarewicz |first3=Witold |last4=Olsen |first4=Erik |last5=Viens |first5=Frederi |title=Neutron Drip Line in the Ca Region from Bayesian Model Averaging |journal=Physical Review Letters |date=14 February 2019 |volume=122 |issue=6 |article-number=062502 |doi=10.1103/PhysRevLett.122.062502 |pmid=30822058 |arxiv=1901.07632 |bibcode=2019PhRvL.122f2502N |display-authors=3}}</ref> Three of those isotopes occur naturally: the two stable forms {{chem|39|K}} (93.26%) and {{chem|41|K}} (6.72%), and the long-lived radioisotope {{chem|40|K}} (0.012%).

Naturally occurring radioactive {{chem|40|K}} decays with a half-life of 1.248×10⁹ years. 89% of those decays are to stable {{chem|40|Ca}} by beta decay, whilst 11% are to {{chem|40|Ar}} by either electron capture or positron emission. This latter decay branch has produced an isotopic abundance of argon on Earth which differs greatly from that seen in gas giants and stellar spectra. {{chem|40|K}} has the longest known half-life for any positron-emitting nuclide.<ref>Of longer ones, only ⁵⁰V and ¹³⁸La are theoretically capable of it, but they are still more forbidden and have very low energy release.</ref> The long half-life of this primordial radioisotope is caused by a highly spin-forbidden transition: {{chem|40|K}} has a nuclear spin of 4, while both of its decay daughters are even–even isotopes with spins of 0.

{{chem|40|K}} occurs in natural potassium in sufficient quantity that large bags of potassium chloride commercial salt substitutes can be used as a radioactive source for classroom demonstrations.{{citation needed|date=May 2018}} {{chem|40|K}} is the largest source of natural radioactivity in healthy animals and humans, greater even than {{chem|14|C}}. In a human body of 70 kg mass, about 4300 nuclei of {{chem|40|K}} decay per second.<ref>{{cite web | vauthors = Rowland RE | url = http://www.rerowland.com/BodyActivity.htm | title = The Radioactivity of the Normal Adult Body | archive-url = https://web.archive.org/web/20110205025628/http://www.rerowland.com/BodyActivity.htm | archive-date=2011-02-05 | work = rerowland.com }}</ref>

The decay of {{chem|40|K}} to {{chem|40|Ar}} is used in potassium-argon dating of rocks. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic {{chem|40|Ar}} that has accumulated. {{chem|40|K}} has also been extensively used as a radioactive tracer in studies of weathering.{{citation needed|date=April 2020}}

All other potassium isotopes have half-lives under a day, most under a minute. The unbound {{chem|31|K}} was discovered in 2019 and emits ''three'' protons; its half-life was measured to be shorter than 10 picoseconds.<ref name="31K-1">{{cite journal |title=A peculiar atom shakes up assumptions of nuclear structure |journal=Nature |volume=573 |issue=7773 |page=167 |date=6 September 2019 |doi=10.1038/d41586-019-02655-9 |pmid=31506620 |bibcode=2019Natur.573T.167. |doi-access=free }}</ref><ref name="31K-2">{{cite journal |doi=10.1103/PhysRevLett.123.092502 |pmid=31524489 |journal=Physical Review Letters |volume=123 |issue=9 |article-number=092502 |last=Kostyleva |first=D. |display-authors=et al. |title=Towards the Limits of Existence of Nuclear Structure: Observation and First Spectroscopy of the Isotope ³¹K by Measuring Its Three-Proton Decay |date=2019|bibcode=2019PhRvL.123i2502K |arxiv=1905.08154 |s2cid=159041565 }}</ref>

Stable potassium isotopes have been used for several nutrient cycling studies since potassium is a macronutrient required for life.<ref>{{Cite web |date=June 2022 |title=Soil potassium isotope composition during four million years of ecosystem development in Hawaiʻi |url=https://par.nsf.gov/servlets/purl/10389596 |website=par.nsf.gov}}</ref>

== List of isotopes == {{Anchor|Potassium-32|Potassium-32m|Potassium-33|Potassium-58}}

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{{Isotopes table |symbol=K |refs=NUBASE2020, AME2020 II, IsotopeFRIB, IsomerFRIB |notes=m, unc(), hl#, mass#, exen#, spin(), spin#, daughter-st, daughter-hst, discoveryname }} |-id=Potassium-31 | {{chem|31|K}} | style="text-align:right" | 19 | style="text-align:right" | 12 | 31.03678(32)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/31.pdf 2019] | <10&nbsp;ps | p | ³⁰Ar | 3/2+# | | |-id=Potassium-34 | ³⁴K<ref>{{cite journal | last1=Dronchi | first1=N. | last2=Charity | first2=R. J. | last3=Sobotka | first3=L. G. | last4=Brown | first4=B. A. | last5=Weisshaar | first5=D. | last6=Gade | first6=A. | last7=Brown | first7=K. W. | last8=Reviol | first8=W. | last9=Bazin | first9=D. | last10=Farris | first10=P. J. | last11=Hill | first11=A. M. | last12=Li | first12=J. | last13=Longfellow | first13=B. | last14=Rhodes | first14=D. | last15=Paneru | first15=S. N. | last16=Gillespie | first16=S. A. | last17=Anthony | first17=A. K. | last18=Rubino | first18=E. | last19=Biswas | first19=S. | title=Evolution of shell gaps in the neutron-poor calcium region from invariant-mass spectroscopy of ^37,38Sc, ³⁵Ca, and ³⁴K | journal=Physical Review C | volume=110 | issue=3 | date=2024-09-12 | issn=2469-9985 | doi=10.1103/PhysRevC.110.L031302 | osti=2441307 }}</ref> | style="text-align:right" | 19 | style="text-align:right" | 15 | 33.998404(18) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/34.pdf 2024] | | p | ³³Ar | | | |-id=Potassium-35 | rowspan=2|³⁵K | rowspan=2 style="text-align:right" | 19 | rowspan=2 style="text-align:right" | 16 | rowspan=2|34.98800541(55) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/35.pdf 1976] | rowspan=2|175.2(19)&nbsp;ms | β⁺ (99.63%) | ³⁵Ar | rowspan=2|3/2+ | rowspan=2| | rowspan=2| |- | β⁺, p (0.37%) | ³⁴Cl |-id=Potassium-36 | rowspan=3|³⁶K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 17 | rowspan=3|35.98130189(35) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/36.pdf 1967] | rowspan=3|341(3)&nbsp;ms | β⁺ (99.95%) | '''³⁶Ar''' | rowspan=3|2+ | rowspan=3| | rowspan=3| |- | β⁺, p (0.048%) | '''³⁵Cl''' |- | β⁺, α (0.0034%) | '''³²S''' |-id=Potassium-37 | ³⁷K | style="text-align:right" | 19 | style="text-align:right" | 18 | 36.97337589(10) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/37.pdf 1958] | 1.23651(94)&nbsp;s | β⁺ | ³⁷Ar | 3/2+ | | |-id=Potassium-38 | ³⁸K | style="text-align:right" | 19 | style="text-align:right" | 19 | 37.96908111(21) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/38.pdf 1937] | 7.651(19)&nbsp;min | β⁺ | '''³⁸Ar''' | 3+ | | |-id=Potassium-38m1 | rowspan=2 style="text-indent:1em" | ^38m1K | rowspan=2 colspan="3" style="text-indent:2em" | 130.15(4)&nbsp;keV | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/19/38K-1.pdf 1953] | rowspan=2|924.35(12)&nbsp;ms | β⁺ (99.97%) | '''³⁸Ar''' | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | IT (0.0330%) | ³⁸K |-id=Potassium-38m2 | style="text-indent:1em" | ^38m2K | colspan="3" style="text-indent:2em" | 3458.10(17)&nbsp;keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/19/38K-2.pdf 1974] | 21.95(11)&nbsp;μs | IT | ³⁸K | (7)+ | | |-id=Potassium-39 | ³⁹K | style="text-align:right" | 19 | style="text-align:right" | 20 | 38.9637064848(49) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/39.pdf 1918] | colspan=3 align=center|'''Stable''' | 3/2+ | 0.932581(44) | |- | rowspan=3|⁴⁰K<ref group="n">Used in potassium-argon dating</ref><ref group="n">Primordial radionuclide</ref> | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 21 | rowspan=3|39.963998165(60) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/40.pdf 1935] | rowspan=3|1.248(3)×10⁹&nbsp;y | β⁻ (89.28%) | '''⁴⁰Ca''' | rowspan=3|4− | rowspan=3|1.17(1)×10⁻⁴ | rowspan=3| |- | EC (10.72%) | rowspan=2|'''⁴⁰Ar''' |- |- | β⁺ (0.001%)<ref>{{Cite journal | volume = 126 | issue = 5 | page = 1818 | last1 = Engelkemeir | first1 = D. W. | last2 = Flynn | first2 = K. F. | last3 = Glendenin | first3 = L. E. | title = Positron Emission in the Decay of K40 | journal = Physical Review | date = 1962 | doi = 10.1103/PhysRev.126.1818 |bibcode = 1962PhRv..126.1818E }}</ref> |-id=Potassium-40m | style="text-indent:1em" | ^40mK | colspan="3" style="text-indent:2em" | 1643.638(11)&nbsp;keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/19/40K-1.pdf 1968] | 336(12)&nbsp;ns | IT | '''''⁴⁰K''''' | 0+ | | |-id=Potassium-41 | ⁴¹K | style="text-align:right" | 19 | style="text-align:right" | 22 | 40.9618252561(40) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/41.pdf 1921] | colspan=3 align=center|'''Stable''' | 3/2+ | 0.067302(44) | |-id=Potassium-42 | ⁴²K | style="text-align:right" | 19 | style="text-align:right" | 23 | 41.96240231(11) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/42.pdf 1935] | 12.355(7)&nbsp;h | β⁻ | '''⁴²Ca''' | 2− | | |-id=Potassium-43 | ⁴³K | style="text-align:right" | 19 | style="text-align:right" | 24 | 42.96073470(44) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/43.pdf 1949] | 22.3(1)&nbsp;h | β⁻ | '''⁴³Ca''' | 3/2+ | | |-id=Potassium-43m | style="text-indent:1em" | ^43mK | colspan=3 style="text-indent:2em" | 738.30(6) keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/19/43K-1.pdf 1975] | 200(5)&nbsp;ns | IT | ⁴³K | 7/2− | | |-id=Potassium-44 | ⁴⁴K | style="text-align:right" | 19 | style="text-align:right" | 25 | 43.96158698(45) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/44.pdf 1954] | 22.13(19)&nbsp;min | β⁻ | '''⁴⁴Ca''' | 2− | | |-id=Potassium-45 | ⁴⁵K | style="text-align:right" | 19 | style="text-align:right" | 26 | 44.96069149(56) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/45.pdf 1964] | 17.8(6)&nbsp;min | β⁻ | ⁴⁵Ca | 3/2+ | | |-id=Potassium-46 | ⁴⁶K | style="text-align:right" | 19 | style="text-align:right" | 27 | 45.96198158(78) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/46.pdf 1965] | 96.30(8)&nbsp;s | β⁻ | '''⁴⁶Ca''' | 2− | | |-id=Potassium-47 | ⁴⁷K | style="text-align:right" | 19 | style="text-align:right" | 28 | 46.9616616(15) | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/47.pdf 1964] | 17.38(3)&nbsp;s | β⁻ | ⁴⁷Ca | 1/2+ | | |-id=Potassium-48 | rowspan=2|⁴⁸K | rowspan=2 style="text-align:right" | 19 | rowspan=2 style="text-align:right" | 29 | rowspan=2|47.96534118(83) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/48.pdf 1972] | rowspan=2|6.83(14)&nbsp;s | β⁻ (98.86%) | '''''⁴⁸Ca''''' | rowspan=2|1− | rowspan=2| | rowspan=2| |- | β⁻, n (1.14%) | ⁴⁷Ca |-id=Potassium-49 | rowspan=2|⁴⁹K | rowspan=2 style="text-align:right" | 19 | rowspan=2 style="text-align:right" | 30 | rowspan=2|48.96821075(86) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/49.pdf 1972] | rowspan=2|1.26(5)&nbsp;s | β⁻, n (86%) | '''''⁴⁸Ca''''' | rowspan=2|1/2+ | rowspan=2| | rowspan=2| |- | β⁻ (14%) | ⁴⁹Ca |-id=Potassium-50 | rowspan=3|⁵⁰K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 31 | rowspan=3|49.9723800(83) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/50.pdf 1972] | rowspan=3|472(4)&nbsp;ms | β⁻ (71.4%) | ⁵⁰Ca | rowspan=3|0− | rowspan=3| | rowspan=3| |- | β⁻, n (28.6%) | ⁴⁹Ca |- | β⁻, 2n? | '''''⁴⁸Ca''''' |-id=Potassium-50m | style="text-indent:1em" | ^50mK | colspan=3 style="text-indent:2em" | 172.0(4) keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/19/50K-1.pdf 2010] | 125(40)&nbsp;ns | IT | ⁵⁰K | (2−) | | |-id=Potassium-51 | rowspan=3|⁵¹K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 32 | rowspan=3|50.975828(14) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/51.pdf 1983] | rowspan=3|365(5)&nbsp;ms | β⁻, n (65%) | ⁵⁰Ca | rowspan=3|3/2+ | rowspan=3| | rowspan=3| |- | β⁻ (35%) | ⁵¹Ca |- | β⁻, 2n? | ⁴⁹Ca |-id=Potassium-52 | rowspan=3|⁵²K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 33 | rowspan=3|51.981602(36) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/52.pdf 1983] | rowspan=3|110(4)&nbsp;ms | β⁻, n (72.2%) | ⁵¹Ca | rowspan=3|2−# | rowspan=3| | rowspan=3| |- | β⁻ (25.5%) | ⁵²Ca |- | β⁻, 2n (2.3%) | ⁵⁰Ca |-id=Potassium-53 | rowspan=3|⁵³K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 34 | rowspan=3|52.98680(12) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/53.pdf 1983] | rowspan=3|30(5)&nbsp;ms | β⁻, n (64%) | ⁵²Ca | rowspan=3|3/2+ | rowspan=3| | rowspan=3| |- | β⁻ (26%) | ⁵³Ca |- | β⁻, 2n (10%) | ⁵¹Ca |-id=Potassium-54 | rowspan=3|⁵⁴K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 35 | rowspan=3|53.99447(43)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/54.pdf 1983] | rowspan=3|10(5)&nbsp;ms | β⁻ | ⁵⁴Ca | rowspan=3|2−# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵³Ca |- | β⁻, 2n? | ⁵²Ca |-id=Potassium-55 | rowspan=3|⁵⁵K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 36 | rowspan=3|55.00051(54)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/55.pdf 2009] | rowspan=3|10#&nbsp;ms<br />[>620&nbsp;ns] | β⁻? | ⁵⁵Ca | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵⁴Ca |- | β⁻, 2n? | ⁵³Ca |-id=Potassium-56 | rowspan=3|⁵⁶K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 37 | rowspan=3|56.00857(64)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/56.pdf 2009] | rowspan=3|5#&nbsp;ms<br />[>620&nbsp;ns] | β⁻? | ⁵⁶Ca | rowspan=3|2−# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵⁵Ca |- | β⁻, 2n? | ⁵⁴Ca |-id=Potassium-57 | rowspan=3|⁵⁷K | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 38 | rowspan=3|57.01517(64)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/57.pdf 2018] | rowspan=3|2#&nbsp;ms<br />[>400&nbsp;ns] | β⁻? | ⁵⁷Ca | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵⁶Ca |- | β⁻, 2n? | ⁵⁵Ca |-id=Potassium-59 | rowspan=3|⁵⁹K<ref group="n">Discovery of this isotope is unconfirmed.</ref> | rowspan=3 style="text-align:right" | 19 | rowspan=3 style="text-align:right" | 40 | rowspan=3|59.03086(86)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/19/59.pdf 2018] | rowspan=3|1#&nbsp;ms<br />[>400&nbsp;ns] | β⁻? | ⁵⁹Ca | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁵⁸Ca |- | β⁻, 2n? | ⁵⁷Ca {{Isotopes table/footer}}

== See also == *Banana equivalent dose '''Daughter products other than potassium''' * Isotopes of calcium * Isotopes of argon * Isotopes of chlorine * Isotopes of sulfur

== References == {{Reflist}}

{{Navbox element isotopes}}

Category:Isotopes of potassium Category:Potassium Potassium