isotopes

isotopes Forms of elements with the same chemical properties, differing in atomic mass because of differing numbers of neutrons in the nucleus. Thus, hydrogen has three isotopes, of atomic masses 1, 2, and 3, generally written as ¹H, ²H (deuterium), and ³H (tritium). ¹H is the most abundant isotope of hydrogen; ²H is stable, while ³H is radioactive.

Radioactive isotopes are unstable, and decay to stable elements, emitting radiation in the process. This may be α‐radiation, β‐radiation (electrons), γ‐radiation, or X‐rays, depending on the isotope. The time taken for half the radioactivity to decay is the half‐life of the isotope, and can vary from a fraction of a second, through several days to years (e.g. the half‐life of ³H is 12½ years, that of ¹⁴C is 5200 years).

Stable isotopes can be detected only by their different atomic mass. Since they emit no radiation, they are safe for use in labelled compounds given to human beings. Examples of stable isotopes commonly used in nutrition research include ²H, ¹³C, ¹⁵N, and ¹⁸O.