Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.
  • noun The time required for half the quantity of a drug or other substance deposited in a living organism to be metabolized or eliminated by normal biological processes.
  • noun The time required for the radioactivity of material taken in by a living organism to be reduced to half its initial value by a combination of biological elimination processes and radioactive decay.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Physics) the time it takes for one-half of a substance decaying in a first-order reaction to be destroyed. For radioactive substances, it is the time required for one-half of the initial amount of the radioactive isotope to decay. The half-lifeis a measure of the rate of the reaction being observed. For processes that are true first-order processes, such as radioactive decay, the half-life is independent of the quantity of material present, and it is thus a constant. The time it takes for one-half the remaining quantity of a radioactive isotope to decay will be the same regardless of how far the decay process has advanced. Some chemical reactions are also first order, and may be characterized as having a half-life. However, for chemical reactions the half-life will depend upon temperature and in some cases other environmental conditions, whereas for radioactive isotopes the rate of decay is largely independent of the environment.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun physics The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.
  • 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.
  • noun medicine The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
  • noun The time it takes for an idea or a fashion to lose half of its influential power.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • 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)
  • 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)

Etymologies

from Wiktionary, Creative Commons Attribution/Share-Alike License

half- +‎ life

Examples

  • Everyone metabolizes caffeine at a different a rate, but in general it takes approximately three to seven hours for the body to eliminate half of the total amount of caffeine also called the half-life.

    The Fiber35 Diet

  • One of the properties that govern isotopes is a phenomenon called half-life.

    Egonomics

  • Everyone metabolizes caffeine at a different a rate, but in general it takes approximately three to seven hours for the body to eliminate half of the total amount of caffeine also called the half-life.

    The Fiber35 Diet

  • But on closer inspection, I discovered that many were also struggling with what I now call the half-life of eating disorders.

    The Full Feed from HuffingtonPost.com

  • One sample of konago caught Friday contained twice the permissible level of radioactive iodine-131, which has a half-life of eight days and which can accumulate in the thyroid in humans, possibly raising the risk of thyroid cancer.

    Tiny Fish Spur Widening Worry

  • You can abandon a half-life of self-pity and embrace a life filled with purpose and enhanced character development.

    Recovering From Religious Abuse

  • With a half-life of 30 years, Cs-137 gives off potentially hazardous external penetrating radiation.

    Robert Alvarez: America's Nuclear Spent-Fuel Time Bombs

  • By looking to God for the future rather than blaming Him for the past, I chose life over the debilitating half-life of bitterness.

    Recovering From Religious Abuse

  • The cesium, with a half-life of 30 years, is likely the main long-term health threat from Fukushima, although prevailing winds during the March accident blew most of it out to sea.

    Past Haunts Tally of Japan's Nuke Crisis

  • Three different types of cesium were discovered, one of which has a half-life of 30 years.

    Tiny Fish Spur Widening Worry

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  • if i'm right this is a game title. my aunt plays it all the time it is kind of cool.

    May 28, 2009