Half-life, denoted t½, is a useful concept by which to express the rate of radioactive decay. After one half-life, half of the original number of atoms of a radioactive element will remain. After two half-lives, one-quarter (= ½ × ½) will remain. After three half-lives, 1/8 (= ½ × ½ × ½) will remain, and so on.
The mathematical relationship is exponential and at any time t the number remaining n is given by
where n0 is the original number and λ is the decay constant, which is equal to 0.693t½.
The following relationships also exist between the half-life (t½), decay constant (λ), and average lifetime (τ):
t½ = λ-1 · ln 2 = 0.693/λThere are extreme variations in the half-lives of the various radionuclides, e.g. from 7.2 × 1024 years for tellurium-128 down to 2 × 10-16 seconds for beryllium-8.
Related categories• ATOMIC AND NUCLEAR PHYSICS
• PARTICLE PHYSICS
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