SAT Subject Physics Practice Question 453: Answer and Explanation
14. A radioactive isotope of iodine has a halflife of 8 hours and causes a counter to register 180 counts/min. Find the count rate for this sample of iodine two days later.
Correct Answer: B
The correct answer is (B). Half-life means that half of the substance decays away during that time. Over 48 hours there are 6 half-lives.