A rock contains 18 mg of the radioactive isotope carbon-14.The half-life of carbon-14 is 5,600 years.How many half-lives and years will it take before the carbon-14 decays to less than 4 mg?

Question

Quizplus · Accepted Answer

After 3 half-lives (16,800 years), the amount of carbon-14 will be less than 4 mg. Starting with 18 mg, after one half-life, it becomes 9 mg, after two half-lives, it becomes 4.5 mg, and after three half-lives, it becomes 2.25 mg.

A Rock Contains 18 Mg of the Radioactive Isotope Carbon-14