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Physics vocabulary · Atomic and Nuclear Physics

Half-life

Meaning in physics, with examples

/ˈhæf laɪf/nounCommon term

In physics, half-life means: The time it takes for half of the radioactive nuclei in a sample to decay, or for its activity to fall to half. It is constant for a given isotope.

In Turkish: yarı ömür, yarılanma süresi

How it is used

Half-lives range from fractions of a second to billions of years. After two half-lives a quarter remains, after three an eighth. Used in carbon dating (carbon-14 has a half-life of about 5730 years) and in choosing safe medical tracers. Plural: half-lives.

Example sentences

  1. Technetium-99m has a half-life of about six hours, which makes it useful in medical imaging.

  2. If the half-life is 8 days, only one eighth of the original sample is left after 24 days.

Common collocations

  • short half-life
  • long half-life
  • measure the half-life
  • radioactive half-life
  • radioactive decayThe random process in which an unstable nucleus breaks down by giving off radiation, such as alpha particles, beta particles or gamma rays, and often turns into a different element.
  • isotopeOne of two or more forms of the same element whose atoms have the same number of protons but different numbers of neutrons. Isotopes behave the same chemically but have different masses.
  • nucleusThe very small, dense centre of an atom, made of protons and neutrons. It contains almost all of the atom's mass and all of its positive charge.
  • scientific notationA way of writing very large or very small numbers as a number between 1 and 10 multiplied by a power of ten, for example 3.0 × 10⁸ instead of 300,000,000.

This word in other fields

The same English word can have a different meaning in another field:

More terms: Atomic and Nuclear Physics

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