Question

A 24-gram sample of a radioactive nuclide decayed to 3.0 grams of the nuclide in 36 minutes. How much of the original nuclide sample remained after the first 12 minutes?

Answer 1

The sample decreased to
`(1)/(8)` of its original size, so it underwent
`\log_(2) 8=3` half-lives.

One half life is then

`(36\ min)/(3)=12\ min`

One-half of 24 grams is 12 grams, so 12 grams remained after the first 12 minutes.