After chemical analysis, a radioactive sample is found to contain 2 g of uranium to every 5 g of thorium, its daughter isotope. If the half-life of uranium is 68.9 y, approximately how old is the sample?

Question

Quizplus · Accepted Answer

The ratio of uranium to thorium is 2:5, meaning that for every 7 parts of the mixture, 2 parts are uranium. This indicates that the uranium has gone through more than one half-life but less than two, as it has decayed to less than its original amount but more than a quarter of the mixture. Since the half-life of uranium is 68.9 years, and the sample has gone through more than one but less than two half-lives, the closest estimate to the age of the sample given the options is 125 years.

After Chemical Analysis, a Radioactive Sample Is Found to Contain