Back Kalium-40 Afrikaans Potassi 40 Catalan Draslík-40 Czech Potasio 40 Spanish پتاسیم-۴۰ Persian Kalium-40 Finnish Potassium 40 French カリウム40 Japanese 칼륨-40 Korean Калиум-40 Macedonian
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| General | |
|---|---|
| Symbol | 40K |
| Names | potassium-40, 40K, K-40 |
| Protons (Z) | 19 |
| Neutrons (N) | 21 |
| Nuclide data | |
| Natural abundance | 0.0117(1)% |
| Half-life (t1/2) | 1.251(3)×109 y |
| Isotope mass | 39.96399848(21) Da |
| Spin | 4− |
| Excess energy | −33505 keV |
| Binding energy | 341523 keV |
| Parent isotopes | Primordial |
| Decay products | 40Ca (β−) 40Ar (EC, γ; β+) |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| β− | 1.31109 |
| EC, γ | 1.5049 |
| Isotopes of potassium Complete table of nuclides | |
Potassium-40 (40K) is a long lived and the main naturally occurring radioactive isotope of potassium. Its half-life is 1.25 billion years. It makes up about 0.012% (120 ppm) of natural potassium.
Potassium-40 undergoes four different types of radioactive decay, including all three main types of beta decay: electron emission (β−) to 40Ca with a decay energy of 1.31 MeV at 89.6% probability, positron emission (β+ to 40Ar at 0.001% probability,[1] electron capture (EC) to 40Ar* followed by a gamma decay emitting a photon[Note 1] with an energy of 1.46 MeV at 10.3% probability and direct electron capture (EC) to the ground state of 40Ar at 0.1%.[2][3][4] Both forms of the electron capture decay release further photons,[Note 2] when electrons from the outer shells fall into the inner shells to replace the electron taken from there.
The EC decay of 40K explains the large abundance of argon (nearly 1%) in the Earth's atmosphere, as well as prevalence of 40Ar over other isotopes.
- ^ 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.
- ^ Stukel, M.; et al. (KDK Collaboration) (2024). "Rare 40K Decay with Implications for Fundamental Physics and Geochronology". Physical Review Letters. 131 (5): 052503. arXiv:2211.10319. doi:10.1103/PhysRevLett.131.052503.
- ^ Hariasz, L.; et al. (KDK Collaboration) (2024). "Evidence for ground-state electron capture of 40K". Physical Review C. 108 (1): 014327. arXiv:2211.10343. doi:10.1103/PhysRevC.108.014327.
- ^ "Physicists Observe Rare Nuclear Decay of Potassium Isotope". Sci.News. 2024-05-08. Retrieved 2024-05-08.
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