Half life
Half-life
Half-life (pronounced: /ˈhæf laɪf/, from the Old English healf meaning "half" and lif meaning "life") 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 nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. In pharmacology, it is used to describe the rate at which the body metabolizes drugs.
Etymology
The term "half-life" was first used in the early 20th century by scientists studying radioactivity. It is derived from the Old English words healf (half) and lif (life), reflecting the concept that the "life" or existence of something is reduced by "half" over a certain period of time.
In Nuclear Physics
In nuclear physics, the half-life is the time required for half of the atoms in a radioactive substance to undergo decay. The half-life of a radioactive substance is a characteristic constant that does not depend on the amount of substance or its physical state.
In Pharmacology
In pharmacology, the half-life of a drug is the time it takes for the concentration of the drug in the body to be reduced by half. This is an important factor in determining the dosing interval of a drug. Drugs with a short half-life need to be taken more frequently than drugs with a long half-life.
Related Terms
- Radioactive decay: The process by which an unstable atomic nucleus loses energy by radiation.
- Pharmacokinetics: The study of how the body absorbs, distributes, metabolizes, and excretes drugs.
- Elimination (pharmacology): The process of removing a drug from the body.
External links
- Medical encyclopedia article on Half life
- Wikipedia's article - Half life
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