Isotopes of potassium

Last updated
Isotopes of potassium  (19K)
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
39K93.3% stable
40K 0.0120%1.248×109 y β− 40Ca
ε 40Ar
β+ 40Ar
41K6.73%stable
Standard atomic weight Ar°(K)
  • 39.0983±0.0001
  • 39.098±0.001 (abridged) [1] [2]

Potassium (
19K) 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. [3] 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%)

Contents

Naturally occurring radioactive 40
K decays with a half-life of 1.248×109 years. 89% of those decays are to stable 40
Ca by beta decay, whilst 11% are to 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. 40
K has the longest known half-life for any positron-emitter nuclide. The long half-life of this primordial radioisotope is caused by a highly spin-forbidden transition: 40
K has a nuclear spin of 4, while both of its decay daughters are even–even isotopes with spins of 0.

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 ]40
K is the largest source of natural radioactivity in healthy animals and humans, greater even than 14
C. In a human body of 70 kg mass, about 4,400 nuclei of 40
K decay per second. [4]

The decay of 40
K to 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 40
Ar that has accumulated. Typically, the method assumes that the rocks contained no argon at the time of formation and all subsequent radiogenic argon (i.e., 40
Ar) was retained.[ citation needed ]40
K has also been extensively used as a radioactive tracer in studies of weathering.[ citation needed ]

All other potassium isotopes have half-lives under a day, most under a minute. The least stable is 31
K, a three-proton emitter discovered in 2019; its half-life was measured to be shorter than 10 picoseconds. [5] [6]

Stable potassium isotopes have been used for several nutrient cycling studies since potassium is a macronutrient required for life. [7]

List of isotopes

Nuclide [8]
[n 1] 		Z N Isotopic mass (Da) [9]
[n 2] [n 3] 		Half-life
[n 4] 		Decay
mode
Daughter
isotope
[n 5] 		Spin and
parity
[n 6] [n 4] 		Natural abundance (mole fraction)
Excitation energy [n 4] Normal proportionRange of variation
31
K [5] [6] 		1912<10 ps3p28S
33K191433.00756(21)#<25 nsp32Ar3/2+#
34K191533.99869(21)#<40 nsp33Ar1+#
35K191634.9880054(6)178(8) ms β+ (99.63%)35Ar3/2+
β+, p (.37%)34Cl
36K191735.9813020(4)341(3) msβ+ (99.95%)36Ar2+
β+, p (.048%)35Cl
β+, α (.0034%)32S
37K191836.97337589(10)1.2365(9) sβ+37Ar3/2+
38K191937.96908112(21)7.636(18) minβ+38Ar3+
38m1K130.50(28) keV924.46(14) msβ+38Ar0+
38m2K3458.0(2) keV21.95(11)  μs IT 38K(7+)
39K192038.963706487(5)Stable3/2+0.932581(44)
40K [n 7] [n 8] 192139.96399817(6)1.248(3)×109 yβ− (89.28%)40Ca4−1.17(1)×10−4
EC (10.72%)40Ar
β+ (0.001%) [10]
40mK1643.639(11) keV336(12) nsIT40K0+
41K192240.961825258(4)Stable3/2+0.067302(44)
42K192341.96240231(11)12.355(7) hβ−42Ca2−Trace [n 9]
43K192442.9607347(4)22.3(1) hβ−43Ca3/2+
43mK738.30(6) keV200(5) nsIT43K7/2−
44K192543.9615870(5)22.13(19) minβ−44Ca2−
45K192644.9606915(6)17.8(6) minβ−45Ca3/2+
46K192745.9619816(8)105(10) sβ−46Ca2−
47K192846.9616616(15)17.50(24) sβ−47Ca1/2+
48K192947.9653412(8)6.8(2) sβ− (98.86%)48Ca1−
β−, n (1.14%)47Ca
49K193048.9682108(9)1.26(5) sβ−, n (86%)48Ca(3/2+)
β− (14%)49Ca
50K193149.972380(8)472(4) msβ− (71%)50Ca0−
β−, n (29%)49Ca
50mK171.4(4) keV125(40) nsIT50K(2−)
51K193250.975828(14)365(5) msβ−, n (65%)50Ca3/2+
β− (35%)51Ca
52K193351.98160(4)110(4) msβ−, n (74%)51Ca2−#
β− (23.7%)52Ca
β−, 2n (2.3%)50Ca
53K193452.98680(12)30(5) msβ−, n (64%)52Ca(3/2+)
β− (26%)53Ca
β−, 2n (10%)51Ca
54K193553.99463(64)#10(5) msβ− (>99.9%)54Ca2−#
β−, n (<.1%)53Ca
55K193655.00076(75)#3# msβ−55Ca3/2+#
β−, n54Ca
56K193756.00851(86)#1# msβ−56Ca2−#
β−, n55Ca
57K [11] [3] 1938β−57Ca
59K [3] [n 10] 1940β−59Ca
This table header & footer:
  1. ↑ mK – 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. 1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. ↑ Bold symbol as daughter – Daughter product is stable.
  6. ↑ ( ) spin value – Indicates spin with weak assignment arguments.
  7. ↑ Used in potassium-argon dating
  8. ↑ Primordial radionuclide
  9. ↑ Decay product of 42Ar
  10. ↑ Discovery of this isotope is unconfirmed

See also

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<span class="mw-page-title-main">Isotopes of silicon</span> Nuclides with atomic number of 14 but with different mass numbers

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References

  1. ↑ "Standard Atomic Weights: Potassium". CIAAW. 1979.
  2. ↑ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN   1365-3075.
  3. 1 2 3 Tarasov, O.B. (2017). "Production of very neutron rich isotopes: What should we know?".
  4. ↑ "Radioactive Human Body" . Retrieved 2011-05-18.
  5. 1 2 "A peculiar atom shakes up assumptions of nuclear structure". Nature. 573 (7773): 167. 6 September 2019. Bibcode:2019Natur.573T.167.. doi: 10.1038/d41586-019-02655-9 . PMID   31506620.
  6. 1 2 Kostyleva, D.; et al. (2019). "Towards the Limits of Existence of Nuclear Structure: Observation and First Spectroscopy of the Isotope 31K by Measuring Its Three-Proton Decay". Physical Review Letters. 123 (9): 092502. arXiv: 1905.08154 . Bibcode:2019PhRvL.123i2502K. doi:10.1103/PhysRevLett.123.092502. PMID   31524489. S2CID   159041565.
  7. ↑ "Soil potassium isotope composition during four million years of ecosystem development in Hawai'i". par.nsf.gov. June 2022.
  8. ↑ 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.
  9. ↑ 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.
  10. ↑ Engelkemeir, D. W.; Flynn, K. F.; Glendenin, L. E. (1962). "Positron Emission in the Decay of K40". Physical Review. 126 (5): 1818. Bibcode:1962PhRv..126.1818E. doi:10.1103/PhysRev.126.1818.
  11. ↑ 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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