Potassium has three isotopes (see Potassium); potassium-40 (40K) is radioactive and decays to both calcium-40 (40Ca) and argon-40 (40Ar). The combined half-life of 40K is 1.25 billion years. The branched decay scheme of 40K is shown in Figure P33. It decays by β- decay to 40Ca and to 40Ar by both electron capture and positron decay (see Potassium-argon decay system). Although 89.52% of the decays produce 40Ca, the system is of somewhat limited use due to the large natural abundance of 40Ca (96.9% of calcium, see Calcium).
Decay scheme of potassium-40, showing relative energies of the parent and daughter nuclides (Firestone, 1996). Decay parameters from Steiger and Jäger (1977).
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Bibliography
Baadsgaard, H. (1987) Rb–Sr and K–Ca isotope systematics in minerals from potassium horizons in the Prairie Evaporite Formation, Saskatchewan, Canada. Chem. Geol. (Isotope Geosci. Sect.), 66, 1–15.
Firestone, R.B. (1996) Table of Isotopes, CD-ROM, 8th edn. New York: Wiley-Interscience.
Kostoyanov, S.I. (1988) The K–Ca method and the excess-argon problem. Geochem. Int., 25, 38–43.
Marshall, B.D. and DePaolo, D.J. (1982) Precise age determinations and petrogenetic studies using the K–Ca method. Geochim. Cosmochim. Acta, 46, 2537–45.
Marshall, B.D. and DePaolo, D.J. (1989) Calcium isotopes in igneous rocks and the origin of granite. Geochim. Cosmochim. Acta, 53, 917–22.
Marshall, B.D., Woodard, H.H. and DePaolo, D.J. (1986) K–Ca–Ar systematics of authigenic sanidine from Waukau, Wisconsin, and the diffusivity of argon. Geology, 14, 936–8.
Nelson, D.R. and McCulloch, M.T. (1989) Petrogenetic applications of the 40K–40Ca radiogenic decay scheme—a reconnaissance study. Chem. Geol. (Isotope Geosci. Sect.), 79, 275–93.
Shih, C.-Y., Nyquist, L.E., Bogard, D.D. and Wiesmann, H. (1994) K–Ca and Rb Sr dating of two lunar granites: relative chronometer resetting. Geochim. Cosmochim. Acta, 58, 3101–16.
Steiger, R.H. and Jäger, E. (1977) Subcommission on geochronology: convention on the use of decay constants in geo-and cosmo-chronology. Earth Planet. Sci. Lett., 36, 359–62.
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Marshall, B.D. (1998). Potassium-calcium decay system . In: Geochemistry. Encyclopedia of Earth Science. Springer, Dordrecht. https://doi.org/10.1007/1-4020-4496-8_260
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