Isotopes of potassium
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Standard atomic weight Ar°(K) | |||||||||||||||||||||||||||||||||
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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%)
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. 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]
Various potassium isotopes have been used for nutrient cycling studies because potassium is a macronutrient required for life.[citation needed]
List of isotopes
Nuclide[7] [n 1] |
Z | N | Isotopic mass (Da)[8] [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 proportion | Range of variation | |||||||||||||||||
31 K[5][6] |
19 | 12 | <10 ps | 3p | 28S | ||||||||||||||
33K | 19 | 14 | 33.00756(21)# | <25 ns | p | 32Ar | 3/2+# | ||||||||||||
34K | 19 | 15 | 33.99869(21)# | <40 ns | p | 33Ar | 1+# | ||||||||||||
35K | 19 | 16 | 34.9880054(6) | 178(8) ms | β+ (99.63%) | 35Ar | 3/2+ | ||||||||||||
β+, p (.37%) | 34Cl | ||||||||||||||||||
36K | 19 | 17 | 35.9813020(4) | 341(3) ms | β+ (99.95%) | 36Ar | 2+ | ||||||||||||
β+, p (.048%) | 35Cl | ||||||||||||||||||
β+, α (.0034%) | 32S | ||||||||||||||||||
37K | 19 | 18 | 36.97337589(10) | 1.2365(9) s | β+ | 37Ar | 3/2+ | ||||||||||||
38K | 19 | 19 | 37.96908112(21) | 7.636(18) min | β+ | 38Ar | 3+ | ||||||||||||
38m1K | 130.50(28) keV | 924.46(14) ms | β+ | 38Ar | 0+ | ||||||||||||||
38m2K | 3458.0(2) keV | 21.95(11) μs | IT | 38K | (7+) | ||||||||||||||
39K | 19 | 20 | 38.963706487(5) | Stable | 3/2+ | 0.932581(44) | |||||||||||||
40K[n 7][n 8] | 19 | 21 | 39.96399817(6) | 1.248(3)×109 y | β− (89.28%) | 40Ca | 4− | 1.17(1)×10−4 | |||||||||||
EC (10.72%) | 40Ar | ||||||||||||||||||
β+ (0.001%)[9] | |||||||||||||||||||
40mK | 1643.639(11) keV | 336(12) ns | IT | 40K | 0+ | ||||||||||||||
41K | 19 | 22 | 40.961825258(4) | Stable | 3/2+ | 0.067302(44) | |||||||||||||
42K | 19 | 23 | 41.96240231(11) | 12.355(7) h | β− | 42Ca | 2− | ||||||||||||
43K | 19 | 24 | 42.9607347(4) | 22.3(1) h | β− | 43Ca | 3/2+ | ||||||||||||
43mK | 738.30(6) keV | 200(5) ns | IT | 43K | 7/2− | ||||||||||||||
44K | 19 | 25 | 43.9615870(5) | 22.13(19) min | β− | 44Ca | 2− | ||||||||||||
45K | 19 | 26 | 44.9606915(6) | 17.8(6) min | β− | 45Ca | 3/2+ | ||||||||||||
46K | 19 | 27 | 45.9619816(8) | 105(10) s | β− | 46Ca | 2− | ||||||||||||
47K | 19 | 28 | 46.9616616(15) | 17.50(24) s | β− | 47Ca | 1/2+ | ||||||||||||
48K | 19 | 29 | 47.9653412(8) | 6.8(2) s | β− (98.86%) | 48Ca | 1− | ||||||||||||
β−, n (1.14%) | 47Ca | ||||||||||||||||||
49K | 19 | 30 | 48.9682108(9) | 1.26(5) s | β−, n (86%) | 48Ca | (3/2+) | ||||||||||||
β− (14%) | 49Ca | ||||||||||||||||||
50K | 19 | 31 | 49.972380(8) | 472(4) ms | β− (71%) | 50Ca | 0− | ||||||||||||
β−, n (29%) | 49Ca | ||||||||||||||||||
50mK | 171.4(4) keV | 125(40) ns | IT | 50K | (2−) | ||||||||||||||
51K | 19 | 32 | 50.975828(14) | 365(5) ms | β−, n (65%) | 50Ca | 3/2+ | ||||||||||||
β− (35%) | 51Ca | ||||||||||||||||||
52K | 19 | 33 | 51.98160(4) | 110(4) ms | β−, n (74%) | 51Ca | 2−# | ||||||||||||
β− (23.7%) | 52Ca | ||||||||||||||||||
β−, 2n (2.3%) | 50Ca | ||||||||||||||||||
53K | 19 | 34 | 52.98680(12) | 30(5) ms | β−, n (64%) | 52Ca | (3/2+) | ||||||||||||
β− (26%) | 53Ca | ||||||||||||||||||
β−, 2n (10%) | 51Ca | ||||||||||||||||||
54K | 19 | 35 | 53.99463(64)# | 10(5) ms | β− (>99.9%) | 54Ca | 2−# | ||||||||||||
β−, n (<.1%) | 53Ca | ||||||||||||||||||
55K | 19 | 36 | 55.00076(75)# | 3# ms | β− | 55Ca | 3/2+# | ||||||||||||
β−, n | 54Ca | ||||||||||||||||||
56K | 19 | 37 | 56.00851(86)# | 1# ms | β− | 56Ca | 2−# | ||||||||||||
β−, n | 55Ca | ||||||||||||||||||
57K[10][3] | 19 | 38 | β− | 57Ca | |||||||||||||||
59K[3][n 9] | 19 | 40 | β− | 59Ca | |||||||||||||||
This table header & footer: |
- ^ mK – Excited nuclear isomer.
- ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
- ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
- ^ a b c # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- ^ Bold symbol as daughter – Daughter product is stable.
- ^ ( ) spin value – Indicates spin with weak assignment arguments.
- ^ Used in potassium-argon dating
- ^ Primordial radionuclide
- ^ Discovery of this isotope is unconfirmed
See also
References
- ^ "Standard Atomic Weights: Potassium". CIAAW. 1979.
- ^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
- ^ a b c Tarasov, O.B. (2017). "Production of very neutron rich isotopes: What should we know?".
- ^ "Radioactive Human Body". Retrieved 2011-05-18.
- ^ a b "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.
- ^ a b 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.
- ^ 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. - ^ 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.
- ^ 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.
- ^ 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.