or half life, half·life
noun, plural half-lives [haf-lahyvz, hahf-] /ˈhæfˌlaɪvz, ˈhɑf-/.
British Dictionary definitions for biological half life
Word Origin and History for biological half life
also halflife, half life, 1864, with meaning "unsatisfactory way of living;" the sense in physics, "amount of time it takes half a given amount of radioactivity to decay" is first attested 1907.
Medicine definitions for biological half life
Science definitions for biological half life
Culture definitions for biological half life
In physics, a fixed time required for half the radioactive nuclei in a substance to decay. Half-lives of radioactive substances can range from fractions of a second to billions of years, and they are always the same for a given nucleus, regardless of temperature or other conditions. If an object contains a pound of a radioactive substance with a half-life of fifty years, at the end of that time there will be half a pound of the radioactive substance left undecayed in the object. After another fifty years, a quarter-pound will be left undecayed, and so on.