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Longman Dictionary of Contemporary English
▪ These effects are less marked with fentanyl because of its shorter serum half-life.
▪ The daily intake should be divided into at least three doses because of the short half-life.
▪ The third isotope of hydrogen, hydrogen-3 or tritium, is highly radioactive and has a very short half-life.
▪ But it has a half-life of just 140 days so there can be little delay manufacture and its incorporation into a bomb.
▪ No one has a long half-life as the star of the program.
▪ The daily intake should be divided into at least three doses because of the short half-life.
▪ The more complete descriptive term is drug elimination half-life.
▪ The time it takes for a dose of a drug to wear off is measured by a value called a half-life.
▪ The time taken for half of the atoms of a radioactive isotope to decay is called its half-life.
▪ These effects are less marked with fentanyl because of its shorter serum half-life.
▪ With a half-life of 12 years, tritium could build up in the Tamar estuary and eventually enter the human food chain.
The Collaborative International Dictionary

Half-life \Half"-life`\ (h[aum]f"l[imac]f`), n. (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.

Douglas Harper's Etymology Dictionary

also halflife, half life, 1864, with meaning "unsatisfactory way of living;" the sense in physics, "amount of time it takes half a given amount of radioactivity to decay" is first attested 1907.


n. 1 (context physics English) The time required for half of the nucleus in a sample of a specific isotope to undergo radioactive decay. 2 (context chemistry English) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value. 3 (context medicine English) The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity. 4 The time it takes for an idea or a fashion to lose half of its influential power.


n. 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) [syn: half life]

Half-Life (video game)

Half-Life (stylized as HλLF-LIFE) is a science fiction first-person shooter video game developed by Valve L.L.C., released in 1998 by Sierra Studios for Microsoft Windows. It was Valve L.L.C.'s debut product and the first in the Half-Life series. Players assume the role of Dr. Gordon Freeman, who must fight his way out of a secret research facility after a teleportation experiment goes disastrously wrong, fighting enemies and solving puzzles.

Unlike many other games at the time, Half-Life features no cutscenes; the player has uninterrupted control of Freeman, and the story is told through scripted sequences seen through his eyes. Valve L.L.C. co-founder Gabe Newell said the team had wanted to create an immersive world rather than a "shooting gallery". The game's engine, GoldSrc, is a heavily modified version of the Quake engine licensed from id Software.

Half-Life received acclaim for its graphics, realistic gameplay, and seamless narrative. It won over fifty PC "Game of the Year" awards and is often considered one of the greatest games of all time. It influenced first-person shooters for years after its release; according to IGN, the history of the genre "breaks down pretty cleanly into pre-Half-Life and post-Half-Life eras."

Half-Life had sold eight million copies , and 9.3 million copies by December 2008. It was ported to the PlayStation 2 in 2001, and OS X and Linux in 2013. It was followed in 2004 by a sequel, Half-Life 2.

Half-Life (novel)

Half-Life is a debut novel by Aaron Krach. Published in 2004 by Alyson Books, the novel was nominated for a Violet Quill Award and was among the 2004 Lambda Literary Award finalists. It discusses young love, coping with death and the issues facing gay youth.

Half-life (disambiguation)

Half-life is a mathematical and scientific description of exponential or gradual decay.

Half-life may also refer to:

  • Biological half-life, the time it takes for a substance to lose half of its pharmacologic, physiologic, or radiologic activity
  • Effective half-life, the effective radioactive half-life in organisms after accounting for excretion
  • Half-Life (series), a video game series
    • Half-Life (video game), a 1998 game and the first title in the series
    • Half-Life 2, a 2004 sequel
  • Halflife (comics), the name of two different Marvel comic characters
  • Half-Life (novel), a 2004 novel by Aaron Krach
  • Half Life (novel), a 2006 novel by Shelley Jackson
  • Half Life (3 album), 2001
  • Halflife (EP), by Lacuna Coil
  • Half-Life E.P., by Local H
  • Half Life: A Parable for the Nuclear Age, a 1985 Australian documentary film
  • Half-Life (film), a 2008 independent film by Jennifer Phang
  • Halflife (Doctor Who), a 2004 BBC Books original novel written by Mark Michalowski
  • "Half Life" (Medical Investigation), episode 17 of the first season of Medical Investigation which had a crossover with an episode of Third Watch titled "In the Family Way"
  • "Half Life", a song by 10 Years from The Autumn Effect
Half-Life (series)

Half-Life (stylized HλLF-LIFE) is a series of first-person shooter video games that share a single science fiction alternate history. The games in the series all utilize either the GoldSrc or Source engines and are linear, narrative, single-player titles.

Valve Corporation is the developer, and partly the publisher and distributor, for their signature games of the series. The major titles in the series feature the player as the protagonist, Gordon Freeman, a theoretical physicist initially employed by the Black Mesa Research Facility. Two of these games, Half-Life and Half-Life 2 are full length titles, while two more, Half-Life 2: Episode One and Half-Life 2: Episode Two, are shorter, episodic titles. A final episode, Half-Life 2: Episode Three, was originally scheduled to appear around Christmas 2007, but now has no public release date.

A puzzle-based first-person series, set in the same fictional universe as the Half-Life games, was created with Portal in 2007, followed by a sequel, Portal 2, in 2011.

Half-Life (film)

Half-Life is a 2008 independent film directed by Jennifer Phang, starring Sanoe Lake, Julia Nickson-Soul, Leonardo Nam, Ben Redgrave, Lee Marks, James Eckhouse, Susan Ruttan and Alexander Agate. The film premiered in the 2008 Sundance Film Festival and has since been touring the American and international film festivals circuits. It premiered internationally in the Tokyo International Film Festival in competition, and then in Europe at the Mannheim-Heidelberg International Film Festival, also in competition. Half-Life was the opening night film for the International Women's Film Festival in Seoul, Korea. The film made a theatrical debut on December 1, 2009 in selected cities.

Usage examples of "half-life".

With a drug half-life of three to four hours, that would correspond to a blood level of forty-six nanograms in the first hour.

Its half-life in any other mammaloid creature was just as limited, so a constant supply was needed, for a constant demand.

Oh, to be as others were -- blind in that safest of all blindnesses, living only the hypnoidal half-life into which birth-shock precipitated most humans.

Oh, to be as others were — blind in that safest of all blindnesses, living only the hypnoidal half-life into which birth-shock precipitated most humans.

Unfortunately, it had a short half-life, because at three-thirty my phone rang, and a deep male voice identified himself as the commandant of the Fort Leavenworth Disciplinary Barracks.

The third will be handled only by uninterested people wearing full-body disposable rip-stop coveralls including 50-mil rubber gloves and boots and breathing through masks, who'll seal the kiddie porn in underground vaults where it can sit out its bazillion-year half-life.

It was quite a problem to calculate the exact detonation time, based on the half-life rate of radioactive decay.

I asked my co-worker, Martha, about it, and since she actually took physics in high school, she knows a bit more about quantum physics (if not quantum qats) than I do/did & after going on about isotopes, elements, electrons and protons in the neutral atom (the latter has matching numbers of electrons and protons), she moved on to half-lives, which amounts to time periods.

There are other radioactive nuclides that have half-lives a hundred times longer.

The half-life of the nuclides was less than ten years, but Horstmann would be too hot to touch for at least another century.

There was so much despair permeating the area the half-life would last for another thirty years.

Resurrection Day was just around the corner and the petite bourgeoisie, who flocked in great numbers to just such ceremonies, were lined up waiting to retrieve their half-lifer relatives.

The half-life of media-product grows shorter still, til it threatens to vanish altogether, everting into some weird quantum logic of its own, the Warholian Fifteen Minutes becoming a quark-like blink.

After eight half-lives, only 1/256 of the original radioactive carbon remains, which is too little to make a reliable measurement, so radiocarbon dating works only for objects up to forty thousand or so years old.