If a source has a half-life of 20 years, how old would it be after 3 half-lives?

The age of a radioactive source after a certain number of half-lives can be determined by multiplying the half-life duration by the number of half-lives that have passed. In this case, the half-life of the source is 20 years, and the question asks what the age would be after 3 half-lives.

To find the age, you can use the following calculation:

Number of half-lives (3) multiplied by the duration of one half-life (20 years) gives:

3 half-lives × 20 years/half-life = 60 years.

Therefore, after 3 half-lives, the source would be 60 years old. This method illustrates how radioactive decay works over time, with each half-life representing an interval where half of the original quantity has decayed. This understanding is crucial in radiation safety, where knowledge of the behavior of radioactive materials over time impacts safety protocols and risk assessment.