Science glossary film: Half-life

Originally used in relation to radioactivity, describing the time required for half the atoms of a radioactive substance to decay. It's now applied to other processes too, referring to the time taken for the amount of a particular substance to reduce by half, such as the declining activity of a drug in the body, or the concentration of a chemical in a biological system.

It's now applied to other processes too, referring to the time taken for the amount of a particular substance to reduce by half, such as the declining activity of a drug in the body, or the concentration of a chemical in a biological system.