After 10 years, what is the approximate activity of a cobalt-60 source that originally had an activity of 10 Ci?

To determine the approximate activity of a cobalt-60 source after 10 years when it originally had an activity of 10 Ci, it is important to consider the half-life of cobalt-60. The half-life of cobalt-60 is approximately 5.27 years.

In the context of this scenario, after one half-life (about 5.27 years), the activity of the cobalt-60 source would decrease to half of the original activity. Starting from 10 Ci, the activity would drop to approximately 5 Ci after the first half-life. After another half-life (approximately another 5.27 years, totaling around 10.54 years), the activity would again be halved, resulting in an activity of about 2.5 Ci.

Therefore, after a complete cycle of two half-lives (which covers just over 10 years), the activity of the cobalt-60 source is approximately 2.5 Ci. This analysis confirms that the correct answer is indeed that the activity would be around 2.5 Ci after 10 years. Understanding the concept of half-lives is crucial in radiological science, as it allows anticipating the remaining activity of radioactive materials as they decay over time.