If a Cobalt-60 source has an initial activity of 80 GBq and its half-life is approximately 5.3 years, what will its activity be after 10.6 years (two half-lives)?
Answer: A — 20 GBq (halved twice: 80 -> 40 -> 20 GBq)
The correct answer is shown above. Try the full quiz for additional practice.