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halflife
Columbia Encyclopedia entry: half-life
Half-life, measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay. For example, the half-life of a particular radioactive isotope of thorium is 8 minutes. If 100 grams of the isotope are originally present, then only 50 grams will remain after 8 minutes, 25 grams after 16 minutes (2 half-lives), 12.5 grams after 24 minutes (3 half-lives), and so on. Of course the 87.5 grams that are no longer present as the original substance after 24 minutes have not disappeared but remain in the form of one or more other substances in the isotope's radioactive decay series. Individual decays are random and cannot be predicted, but this statistical measure of the great number of atoms in the sample is very accurate. The half-life of a radioactive isotope is a characteristic of that isotope and is not affected by any change in physical or chemical conditions.

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Wikipedia search results for: Half-life
From Wikipedia, the free encyclopedia
Half-life (redirected from halflife) is the period of time it takes for a substance undergoing decay to decrease by half. The name originally was used to describe a characteristic of unstable atoms, but may apply to any quantity which follows a set-rate decay. The original term, dating to 1907, was "half-life period", which was later shortened to "half-life" sometime in the early 1950s. Half-lives are very often used to describe quantities undergoing exponential decay—for example radioactive decay—where the half-life is constant over the whole life of the decay, and is a characteristic unit for the exponential decay equation. However, a half-life can also be defined for...more »
Columbia Encyclopedia search results: halflife
Results 1 - 10  of 49
  • tritium

    Tritium, radioactive isotope of hydrogen with mass number 3. The tritium nucleus, called a triton, contains one proton and two neutrons. It has a half-life of 12.5 years and decays by beta-par...

  • fermium

    Fermium [for Enrico Fermi], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no. of most stable isotope 257; m.p. 1,527°C; b.p. and sp. gr. unknown; valence +2,...

  • polonium

    Polonium, radioactive chemical element; symbol Po; at. no. 84; mass no. of most stable isotope 209; m.p. 254°C; b.p. 962°C; sp. gr. about 9.4; valence +2 or +4. Polonium is an extremely rare e...

  • radon

    Radon, gaseous radioactive chemical element; symbol Rn; at. no. 86; mass no. of most stable isotope 222; m.p. about -71°C; b.p. -61.8°C; density 9.73 grams per liter at STP; valence usually 0....

  • astatine

    Astatine [Gr.,=unstable], semimetallic radioactive chemical element; symbol At; at. no. 85; at. wt. of most stable isotope 210; m.p. 302°C (estimated); b.p. 337°C (estimated); density unknown;...

  • berkelium

    Berkelium [from Berkeley], artificially produced radioactive chemical element; symbol Bk; at. no. 97; mass no. of most stable isotope 247; m.p. about 1,050°C; b.p. about 2,590°C; sp. gr. 14 (e...

  • darmstadtium

    Darmstadtium, artificially produced radioactive chemical element; symbol Ds; at. no. 110; mass number of most stable isotope 271; m.p., b.p., sp. gr., and valence unknown. Situated in Group 10...

  • einsteinium

    Einsteinium [for Albert Einstein], artificially produced radioactive chemical element; symbol Es; at. no. 99; mass no. of most stable isotope 252; m.p. about 860°C; b.p. and sp. gr. unknown; v...

  • lawrencium

    Lawrencium, artificially produced radioactive chemical element; symbol Lr; at. no. 103; mass number of most stable isotope 262; m.p. about 1,627°C; b.p. and sp. gr. unknown; valence +3. Lawren...

  • mendelevium

    Mendelevium, artificially produced radioactive chemical element; symbol Md; at. no. 101; mass no. of most stable isotope 258; m.p. 827°C; b.p. and sp. gr. unknown; valence +1, +2, +3. Mendelev...

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