SAT Subject Physics Practice Question 453: Answer and Explanation

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Question: 453

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.

A. 1.4/min
B. 2.8/min
C. 5.6/min
D. 11.2/min
E. 22.4/min

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.

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