kaliumin40

Kaliumin40, often written as K-40, is a radioactive isotope of potassium. Naturally occurring potassium contains a small but significant fraction of this isotope, approximately 0.0117%. This makes K-40 a common source of natural radioactivity found in the Earth's crust and in living organisms. Potassium is an essential element for life, playing a crucial role in muscle and nerve function, and therefore is present in all plant and animal tissues.

The decay of K-40 can occur through two primary pathways. The most common decay mode, accounting for about 89.3% of decays, is beta decay, where a neutron in the nucleus is converted into a proton, emitting an electron and an antineutrino. This results in the formation of the stable isotope calcium-40. The other decay mode, representing about 10.7% of decays, is electron capture. In this process, an electron from an inner shell of the atom is captured by a proton in the nucleus, forming a neutron and emitting a neutrino. This leads to the formation of the stable isotope argon-40. K-40 also undergoes a very rare direct positron emission.

The presence of K-40 is a significant contributor to the background radiation dose that humans receive. Its concentration in the body depends on dietary intake of potassium. The long half-life of K-40, approximately 1.25 billion years, means it has been present since the formation of the Earth and continues to be a widespread natural radioisotope.