Half-life (t½) 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.
Read more about Half-life: Probabilistic Nature of Half-life, Formulas For Half-life in Exponential Decay, Half-life in Non-exponential Decay, Half-life in Biology and Pharmacology
Famous quotes containing the word half-life:
“I could draw Bloom County with my nose and pay my cleaning lady to write it, and I’d bet I wouldn’t lose 10% of my papers over the next twenty years. Such is the nature of comic-strips. Once established, their half-life is usually more than nuclear waste.”
—Berkeley Breathed (b. 1957)