half-life

2 definitions found

half-life - Collaborative International Dictionary of English v.0.48 :

  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.
     [PJC]

half-life - WordNet (r) 2.1 (2005) :

  half-life
      n 1: 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]