Potassium-40

Potassium-40 (⁴⁰K) is a radioactive isotope of potassium which has a long half-life of 1.25 billion years. It makes up about 0.012% (120 ppm) of the total amount of potassium found in nature.

Potassium-40 is a rare example of a nuclide that undergoes both types of beta decay. In about 89.28% of events, it decays to calcium-40 (⁴⁰Ca) with emission of a beta particle (β−, an electron) with a maximum energy of 1.31 MeV and an antineutrino. In about 10.72% of events, it decays to argon-40 (⁴⁰r) by electron capture (EC), with the emission of a neutrino and then a 1.460 MeV gamma ray. The radioactive decay of this particular isotope explains the large abundance of argon (nearly 1%) in the Earth’s atmosphere, as well as prevalence of ⁴⁰Ar over other isotopes. Very rarely (0.001% of events), it decays to ⁴⁰Ar by emitting a positron (β+) and a neutrino.

Spectrum (Fullscreen)

5 minute measurement with a High Purity Germanium (HPGe) radiation detector.

Metadata

Isotope:	Potassium
Mass number:	40
Atomic number:	19
Neutron number:	21
…	…

Sources and Further Read

• https://en.wikipedia.org/wiki/Potassium
• https://en.wikipedia.org/wiki/Potassium-40