Iodine-131 has a half-life of 8 days. A sample of iodine-131 has an activity of 800 counts per minute. What is its activity after 24 days?
Answer and explanation
Correct answer: D. 100 counts per minute
- Step 1: 24 days is half-lives. Step 2. counts per minute. Answer: 100 counts per minute. Why not the others: '400 counts per minute' is the activity after one half-life, '200 counts per minute' after two, and '50 counts per minute' after four, which would take 32 days.
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