Stable nuclide

Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes.

The 80 elements with one or more stable isotopes comprise a total of 254 nuclides that have not been known to decay using current equipment (see list at the end of this article). Of these elements, 26 have only one stable isotope; they are thus termed monoisotopic. The rest have more than one stable isotope. Tin has ten stable isotopes, the largest number known for an element.

Definition of stability, and naturally occurring nuclides

Most naturally occurring nuclides are stable (about 254; see list at the end of this article); and about 34 more (total of 288) are known radioactives with sufficiently long half-lives (also known) to occur primordially. If the half-life of a nuclide is comparable to, or greater than, the Earth's age (4.5 billion years), a significant amount will have survived since the formation of the Solar System, and then is said to be primordial. It will then contribute in that way to the natural isotopic composition of a chemical element. Primordially present radioisotopes are easily detected with half-lives as short as 700 million years (e.g., ²³⁵U), although some primordial isotopes have been detected with half-lives as short as 80 million years (e.g., ²⁴⁴Pu). However, this is the present limit of detection, as the nuclide with the next-shortest half-life (niobium-92 with half-life 34.7 million years) has not yet been detected in nature.