The half-life of a radioactive substance is the amount of time that it takes to lose half its radioactivity.
half-life in British English
noun
1.
the time taken for half of the atoms in a radioactive material to undergo decay
Symbol: τ
2.
the time required for half of a quantity of radioactive material absorbed by a living tissue or organism to be naturally eliminated (biological half-life) or removed by both elimination and decay (effective half-life)
half-life in American English
(ˈhæfˌlaɪf)
noun
the constant time period required for the disintegration of half of the atoms in a sample of some specific radioactive substance
: also half life
Examples of 'half-life' in a sentence
half-life
(Of all the emotions guilt surely has the longest half-life.
Edward Docx THE CALLIGRAPHER (2003)
Had deprived her, condemned her to the purgatory of a half-life without them.
Dobbs, Michael WALL GAMES (2003)
He paused before adding distantly, `Which is just about the half-life of caesium-134.
Stewart, Michael GRACE (2003)
He estimated its half-life to be in the tens of thousands of years.