The half-life of a particular radioactive isotope of element X is 100 years. If you know that 400 years ago a fossil contained 10 mg of this isotope, you would expect to find about _______ in that fossil today.

Question

Quizplus · Accepted Answer

The half-life is 100 years, so in 400 years, the isotope would have gone through 4 half-lives (400/100). Each half-life reduces the amount by half: 10 mg → 5 mg → 2.5 mg → 1.25 mg → 0.625 mg, which is approximately 0.6 mg.

The Half-Life of a Particular Radioactive Isotope of Element X