Definition of Half-life

1. 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).

Exact synonyms: Half Life
Generic synonyms: Period, Period Of Time, Time Period

Definition of Half-life

1. Noun. (physics) The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay. ¹

2. Noun. (chemistry) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value. ¹

3. Noun. (medicine) The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity. ¹

4. Noun. The time it takes for an idea or a fashion to lose half of its influential power. ¹

¹ Source: wiktionary.com

Medical Definition of Half-life

1. 1. The period over which the concentration of a specified chemical or drug takes to fall to half its original concentration in the specified fluid or blood. 2. The time required to reduce the amount of a radionuclide to one-half the amount originally present. Physical or radioactive half-life refers to reduction of activity by radioactive decay, biological half-life refers to biological elimination from the body and effective half-life refers to the combined action of radioactive decay and biological elimination. (16 Dec 1997)

Lexicographical Neighbors of Half-life

half-hitch
half-holiday
half-hour
half-hourlong
half-hourly
half-inch
half-inched
half-inches
half-inching
half-inferior
half-integer
half-integers
half-intensity
half-jacket
half-length
half-life (current term)
half-light
half-line
half-lives
half-long vowel
half-mast
half-measure
half-metal
half-metallic
half-monthly
half-moon
half-moons
half-naked
half-nephew
half-niece

Literary usage of Half-life

Below you will find example usage of this term as found in modern and/or classical literature:

1. A Lifelong Passion: Nicholas and Alexandra: Their Own Story by Andrei Maylunas (2005)
"The half-life of Penk mRNA levels (about 12 h), however, seems not to be affected by histamine as suggested by measurement of the subsequent decay of Penk ..."

2. Proceedings of the Society for Experimental Biology and Medicine (1903)
"The relationship of body weight to disappearance half-life was examined in each cir- rhotic subject by linear regression analysis. ..."

3. Potential Groundwater Contamination from Intentional and Nonintentional by Robert Pitt, Shirley Clark, Keith Parmer (1994)
"The volatilization half-life of BCEE in streams was estimated to be about 4 ... The overall half-life of BCIE was estimated to vary between 3 and 30 days in ..."

4. Fission Gas Behaviour in Water Reactor Fuels: Seminar Proceedings, Cadarache by OECD Nuclear Energy Agency (2002)
"At the end of irradiation, 242Cm (half-life of 163 days) accounts for ... After this, the plutonium isotopes with long lifetimes - 239Pu (half-life: 24 110 ..."

5. Oxygen/Nitrogen Radicals and Cellular Injury edited by Kenneth B. Adler, Robert D. Devlin, Val Vallyathan (2000)
"IL-4 Prolongs iNOS mRNA Half-Life in Human Airway Epithelial Cells IL-4 inhibits iNOS expression in some studies and induces 'NO production in other studies ..."

6. Mount Omi and Beyond: A Record of Travel on the Thibetan Border by Archibald John Little (1901)
"... from our Coolies—Thousand Buddhas Precipice— Figures half Life Size—Indian Type—Bamboos acting as Sounding- boards—Thirteen-storied Pagoda—Junction with ..."

7. The Three Gifts of Life: A Girl's Responsibility for Race Progress by Nellie May Smith (1913)
"Usually these little half-lives are lost; but if one meets the sperm, or male half-life, before leaving the womb, and unites with it, from that moment the ..."

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