Half-life
Half-life is a measure of the time taken for a quantity to reduce to a half its initial value. The term is found in the medical and nuclear sciences and is expressed by the formula t by 1/2 or t1/2.
In particular it is used to describe the speed at which unstable atoms become less stable through decay, releasing radioactivity in the process, or conversely, how long atoms remain stable.
In medical science the same measure is used to describe the biological life span of drugs and other chemicals in the human body.
It is also more generally used to describe any type of exponential or non-exponential decay.
The converse of half-life (when considering exponential growth) is doubling time.
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