Potassium: isotope data

Although Potassium only has two stable isotopes (K-39 and K-41), the long-lived radioisotope K-40 is often also regarded as a stable isotope. Potassium isotopes, mainly K-40 and K-41, are used to study the impact of potassium on the growth of plants and of the human cardiovascular system.

Naturally occurring isotopes

This table shows information about naturally occuring isotopes, their atomic masses, their natural abundances, their nuclear spins, and their magnetic moments. Further data for radioisotopes (radioactive isotopes) of potassium are listed (including any which occur naturally) below.
Isotope Mass / Da Natural abundance (atom %) Nuclear spin (I) Magnetic moment (μ/μN)
39K 38.9637074 (12) 93.2581 (44) 3/2 0.3914658
40K 39.9639992 (12) 0.0117 (1) 4 -1.298099
41K 40.9618254 (12) 6.7302 (44) 3/2 0.2148699

In the above, the most intense ion is set to 100% since this corresponds best to the output from a mass spectrometer. This is not to be confused with the relative percentage isotope abundances which totals 100% for all the naturally occurring isotopes.

Radiosotope data

Further data for naturally occuring isotopes of potassium are listed above. This table gives information about some radiosotopes of potassium, their masses, their half-lives, their modes of decay, their nuclear spins, and their nuclear magnetic moments.
Isotope Mass / Da Half-life Mode of decay Nuclear spin Nuclear magnetic moment
37K 36.9733769 EC to 37Ar 3/2 0.2032
38K 37.969080 7.63 m EC to 38Ar 3 1.37
40K 39.9639987 1.277 x 109 y EC to 40Ar 4
42K 41.9624031 12.36 h β- to 42Ca 2 -1.1425
43K 42.96072 22.3 h β- to 43Ca 3/2 0.163
44K 43.96156 22.1 m β- to 44Ca 2 -0.856
45K 44.96070 17.8 m β- to 45Ca 3/2 0.1734
46K 45.96168 1.8 m β- to 46Ca 2 -1.05
47K 46.96551 17.5 s β- to 47Ca 1/2 1.93
48K 47.96551 6.8 s β- to 48Ca; β- + n to 47Ca 2
49K 48.96745 1.26 s β- to 49Ca; β- + n to 48Ca

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  1. Naturally occurring isotope abundances: Commission on Atomic Weights and Isotopic Abundances report for the International Union of Pure and Applied Chemistry in Isotopic Compositions of the Elements 1989, Pure and Applied Chemistry, 1998, 70, 217. [Copyright 1998 IUPAC]
  2. For further information about radioisotopes see Jonghwa Chang's (Korea Atomic Energy Research Institute) Table of the Nuclides
  3. Masses, nuclear spins, and magnetic moments: I. Mills, T. Cvitas, K. Homann, N. Kallay, and K. Kuchitsu in Quantities, Units and Symbols in Physical Chemistry, Blackwell Scientific Publications, Oxford, UK, 1988. [Copyright 1988 IUPAC]

NMR Properties of potassium

Common reference compound: KI/D2O, 0.1 M.

Table of NMR-active nucleus propeties of potassium
  Isotope 1 Isotope 2 Isotope 3
Isotope 39K 40K 41K
Natural abundance /% 93.2581 0.0117 6.7302
Spin (I) 3/2 4 3/2
Frequency relative to 1H = 100 (MHz) 4.666373 5.802018 2.561305
Receptivity, DP, relative to 1H = 1.00 0.000476 0.000000612 0.00000568
Receptivity, DC, relative to 13C = 1.00 2.79 0.00359 0.0333
Magnetogyric ratio, γ (107 rad T‑1 s-1) 1.2500608 -1.5542854 0.68606808
Magnetic moment, μ (μN) 0.50543376 -1.4513203 0.27739609
Nuclear quadrupole moment, Q/millibarn 58.5 -73 71.1
Line width factor, 1056 l (m4) 46 5.2 67


  1. R.K. Harris in Encyclopedia of Nuclear Magnetic Resonance, D.M. Granty and R.K. Harris, (eds.), vol. 5, John Wiley & Sons, Chichester, UK, 1996. I am grateful to Professor Robin Harris (University of Durham, UK) who provided much of the NMR data, which are copyright 1996 IUPAC, adapted from his contribution contained within this reference.
  2. J. Mason in Multinuclear NMR, Plenum Press, New York, USA, 1987. Where given, data for certain radioactive nuclei are from this reference.
  3. P. Pyykkö, Mol. Phys., 2008, 106, 1965-1974.
  4. P. Pyykkö, Mol. Phys., 2001, 99, 1617-1629.
  5. P. Pyykkö, Z. Naturforsch., 1992, 47a, 189. I am grateful to Professor Pekka Pyykkö (University of Helsinki, Finland) who provided the nuclear quadrupole moment data in this and the following two references.
  6. D.R. Lide, (ed.), CRC Handbook of Chemistry and Physics 1999-2000 : A Ready-Reference Book of Chemical and Physical Data (CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, Florida, USA, 79th edition, 1998.
  7. P. Pyykkö, personal communication, 1998, 204, 2008, 2010.

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