Definition and overview of radioactive decay

Summary

Radioactive decay (also called nuclear decay or radioactivity) is the process by which an unstable atomic nucleus loses energy by emitting radiation. A material containing unstable nuclei is considered radioactive. The decay is fundamentally random for individual atoms: quantum theory says it is impossible to predict the exact time when a particular nucleus will decay, even if its age is known. For large numbers of identical nuclei, the overall decay behavior becomes predictable using statistical measures such as the decay constant and half-life. The original nucleus is the parent radionuclide, and the decay produces at least one daughter nuclide. Except for gamma decay (and internal conversion from an excited nuclear state), radioactive decay typically changes the nucleus by transmutation, altering the number of protons and/or neutrons and therefore (when protons change) creating a different chemical element. Radioactive half-lives vary enormously, from nearly instantaneous to much longer than the age of the universe.

Key Points

• 1

  Radioactive decay is energy loss by unstable nuclei through radiation emission.

• 2

  At the single-nucleus level, decay time is random and not predictable; at the population level, decay rates follow statistical laws.

• 3

  Parent radionuclides transform into daughter nuclides; most decays involve nuclear transmutation that can change the element.