Definition of half-life in US English:



  • 1The time taken for the radioactivity of a specified isotope to fall to half its original value.

    • ‘The small, lead-shielded canisters contain pellets or a fine powder of caesium 137, which emits powerful gamma radiation with a half-life of 30 years.’
    • ‘Radioactive depleted uranium has a half-life of 4500 million years.’
    • ‘Tritium is radioactive, with a half-life of 12.26 years.’
    • ‘In addition, the plants would produce 7,313 tonnes of highly radioactive waste with a half-life of 24,000 years.’
    • ‘The FDA recommends keeping a fourteen-day supply on hand; radioactive iodine has a half-life of eight days.’
    1. 1.1 The time required for any specified property (e.g. the concentration of a substance in the body) to decrease by half.
      • ‘Prealbumin, also known as transthyretin, has a half-life of only 1 to 2 days.’
      • ‘It stays in the body for a lifetime, it has a half-life of 28, 29 years and it gets into the bone, it's taken up just like calcium.’
      • ‘At age 18, caffeine has a half-life of 4.5 hours, which increases with age.’
      • ‘Frova may represent an important advancement in the treatment of migraine headache as no other currently marketed treatment has a half-life of more than six hours.’
      • ‘This constitutes the main long-term threat in the area as the chemical has a half-life of 30 years.’



/ˈhaf ˌlīf//ˈhæf ˌlaɪf/