CoachThe half-life of a nuclide is the time after which half of any large sample has decayed. Each further half-life halves what remains: of nuclei, are left at , at , at , after half-lives.
Examples
Example 19.17 (Carbon-14 dating)
Living matter exchanges carbon with the atmosphere, so it holds the atmospheric proportion of carbon-14; at death the intake stops and the proportion halves every years. Charcoal from a painted cave shows one quarter of the living proportion: a quarter is half of a half, so the fire burned two half-lives, years, ago.