radioactive decay

gradual reduction in the number of radioactive atoms in material

"Radioactive" and "Radioactivity" redirect here. For other uses see Radioactive (disambiguation).For decay rate in a more general context see Particle decay. Radioactive decay is the process in which an unstable  atomic nucleus  loses energy by emitting radiation in the form of particles or electromagnetic waves. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter.") This is a random process on the atomic level, in that it is impossible to predict when a particular atom will decay, but given a large number of similar atoms, the decay rate, on average, is predictable.
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The decrease in the radiation intensity of any radioactive material with respect to time. 1/3/73

Diminution de l'intensité du rayonnement d'une matière radioactive en fonction du temps. 1/3/73

Spontaneous change in an atom by emission of of charged particles and/or gamma rays; also known as radioactive disintegration and radioactivity.

The spontaneous disintegration of certain atomic nuclei by emission of either 2 protons bound with 2 neutrons (a helium nucleus), known as alpha decay , or of an electron, known as beta decay . If the emitted beta particle is the antimatter positive electron the disintegration process is termed positron emission. Radioactive decay is sometimes accompanied by the emission of gamma rays and is always accompanied by the transmutation of the atomic nucleus into another element which is more stable. The rate of decay, known as the halflife , together with the energy of the emitted particle, is unique to the radionuclide (the species of unstable nucleus).