The time taken for the activity of a substance to reduce to half its original level. The term is usually used to refer to the time taken for the level of radiation emitted by a radioactive substance to decay to half its original level. The concept is useful in radiotherapy for assessing how long material will stay radioactive in the body. Half-life is also used to refer to the length of time taken by the body to eliminate half the quantity of a drug.
Half-life |
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