After 3 half-lives, if a cobalt source originally had an activity of 88 Ci, what is its current activity?

To determine the current activity of a cobalt source after three half-lives, it's crucial to understand how the concept of half-life works in radioactive decay. A half-life is the time required for half of the radioactive atoms in a sample to decay. Each half-life reduces the amount of the radioactive substance to half of its previous amount.

Starting with an initial activity of 88 curies (Ci), after one half-life, the activity would decrease to 44 Ci (half of 88). After two half-lives, the activity would reduce to 22 Ci (half of 44). Finally, after three half-lives, the activity would fall to 11 Ci (half of 22).

Thus, after three half-lives, the activity of the cobalt source would indeed be 11 Ci, which corresponds to the correct answer. Understanding the sequential halving of the activity is crucial in calculating the activity after multiple half-lives, confirming that the correct answer aligns with the principles of radioactive decay.