ioniums

Ionium is an obsolete term used in early radiochemistry to refer to the naturally occurring isotope of thorium with mass number 230, which is written as 230Th. This isotope is a significant member of the uranium-238 decay series. It is formed from the alpha decay of uranium-234 (234U) and decays by alpha emission to radium-226 (226Ra). The half-life of ionium (230Th) is approximately 75,380 years.

The term "ionium" was introduced in the early 20th century due to the belief that it was a distinct element. However, as the understanding of isotopes developed, it became clear that ionium was simply a radioactive isotope of thorium, an element already known. Its significance lies in its role as a long-lived intermediate in the decay chain, and it is used in various dating techniques, such as dating of marine sediments and corals, due to its relatively long half-life and the fact that it is often incorporated into these materials from dissolved uranium. The presence and decay of ionium are crucial for understanding the age and history of geological and oceanic samples.