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Glossary of Plasma Physics and Fusion Energy Research

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  Term: Half-life
  Definition: For a given quantity of a radioactive isotope, there is a time period in which half the nuclei will decay to a different state; this period is called the half-life. Measured half-lives range from less than millionths of a second (for very short-lived isotopes) to billions of years (for isotopes which are almost stable, but not quite). The time in which half the atoms of a particular radioactive isotope disintegrate to another nuclear form. By analogy, "half-life" can also be used to describe similar time-periods for other sorts of exponential decay phenomena.

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