An Etymological Dictionary of Astronomy and Astrophysics
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Possessing, or pertaining to, → radioactivity.

→ radio + → active.

Determining the age of an object from the → radioactive decay of its constituting material. The technique consists of comparing the → abundance ratio of a → radioactive isotope to its → decay product. This will yield the number of half-lives that have occurred since the sample was formed. More specifically, if an object is made up of 50 % decay product then it has gone through 1 → half-life. 75% decay product equals 2 half-lives, 87.5% decay product equals 3 half-lives, 93.76% decay product equals 4 half-lives, and so on. For example, the decay product of → uranium-238 (²³⁸U) is → lead-206 (²⁰⁶Pb). The half-life of ²³⁸U is 4.5 billion years. Hence, if the sample has gone through two half-lives, it is 9 billion years old. See also: → radiocarbon dating.

→ radioactive; → dating.

Spontaneous emission by a nucleus of photons or particles.

→ radioactive; → decay.

A → nuclide that is radioactive.

→ radioactive; → isotope.

A → nuclide that disintegrates by emitting radiation and transforms into another nuclide. Same as → radionuclide.

→ radioactive; → nuclide.

The radioactive by-products from the operation of a nuclear reactor or from the reprocessing of depleted nuclear fuel. Also known as nuclear waste.

→ radioactive; → waste.