Definitions for half-life-ˌlaɪvz
This page provides all possible meanings and translations of the word half-life
Random House Webster's College Dictionary
or half′ life`
the time required for one half the atoms of a given amount of a radioactive substance to decay.
the time required for the activity of a substance taken into the body to lose one half its initial effectiveness.
Origin of half-life:
half life, half-life(noun)
the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.
In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
Half-life is the time required for a quantity to fall to half its value as measured at the beginning of the time period. In physics, it is typically used to describe a property of radioactive decay, but may be used to describe any quantity which follows an exponential decay. The original term, dating to Ernest Rutherford's discovery of the principle in 1907, was "half-life period", which was shortened to "half-life" in the early 1950s. Half-life is used to describe a quantity undergoing exponential decay, and is constant over the lifetime of the decaying quantity. It is a characteristic unit for the exponential decay equation. The term "half-life" may generically be used to refer to any period of time in which a quantity falls by half, even if the decay is not exponential. For a general introduction and description of exponential decay, see exponential decay. For a general introduction and description of non-exponential decay, see rate law. The converse of half-life is doubling time. The table on the right shows the reduction of a quantity in terms of the number of half-lives elapsed.
U.S. National Library of Medicine
The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacologic, physiologic, or radiologic activity.
Dictionary of Military and Associated Terms
The time required for the activity of a given radioactive species to decrease to half of its initial value due to radioactive decay. The half-life is a characteristic property of each radioactive species and is independent of its amount or condition. The effective half-life of a given isotope is the time in which the quantity in the body will decrease to half as a result of both radioactive decay and biological elimination.
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