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half-hour |
half-hourly |
half-intensity |
half-learned |
half-length |
half-life
| half-light
| half-mast
| half-moon
| half-pay
| half-penny
half-life
WORDNET DICTIONARY
Noun half-life has 1 sense
- half-life(n = noun.time) half life - 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); Array is a kind of period, period of time, time period
CIDE DICTIONARY
half-life, n.
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]
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