Half-life

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Half-life (T½)

Half-life (pronunciation: /ˈhaf ˌlīf/) is a term used in nuclear physics and pharmacology to describe the time required for a quantity to reduce to half of its initial value. The term is commonly used in relation to radioactive decay where it denotes the period of time after which half of a sample of a radioactive substance remains active, or in pharmacology, where it refers to the duration it takes for the concentration of a drug in the body to be reduced by half.

Etymology

The term "half-life" is derived from the two English words "half" and "life", indicating the period of time during which half of something is lost or used up. The term was first used in the early 20th century in the field of radioactivity.

Related Terms

  • Decay constant: The decay constant is the probability that a nucleus will decay per unit time. It is inversely proportional to the half-life.
  • Radioactive decay: A process by which an unstable atomic nucleus loses energy by radiation.
  • Pharmacokinetics: The study of how an organism affects a drug, including absorption, distribution, metabolism, and excretion.
  • Biological half-life: The time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity.

See Also

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