- The time interval that elapses for a given radioactive substance to lose half of its radioactive intensity. That is, it is the time required for half the atoms of a given sample of identical nuclides to undergo decay. The half-life of V (an isotope of vanadium), for instance, is approximately 1.4 × 1017 years, while that for 6Be (an isotope of beryllium) is approximately 5.9 × 10-21 seconds. Also called half-life.
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