Half-life 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.
... he is weak—one quarter where temptations are either not irresistible, or else are not recognised as alluring to what is wrong. But we all know that training, though never perfect, can make the difference between a decently right and happy life and a bad, corrupt half-life or no life. What does training do for the nimble-footed young beauties of the London ball-room? It makes them nimble-footed, we admit. ... — Modern Women and What is Said of Them - A Reprint of A Series of Articles in the Saturday Review (1868) • Anonymous Read full book for free!
... returned the little prophet. "I think rather we have done with it for ever. The man with life so in himself, will not dream of asking whether he shall live. It is only in the twilight of a half-life, holding in it at once much wherefore it should desire its own continuance, and much that renders it unworthy of continuance, that the doubtful desire of immortality can arise.—Do you remember"—here Polwarth turned to Wingfold—"my mentioning to you once a ... — Thomas Wingfold, Curate • George MacDonald Read full book for free!
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