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A radioactive substance is accidentally spread on the floor of a room. If its half-life is 30 days and the initial activity is 10 times the allowed safe level, after how many days will it become safe to enter the room?
- 100 days
- 1000 days
- 300 days
- 10 days
Correct answer: 100 days
Solution
Need activity to drop from 10x to 1x: 10 = 2^n, n = log10/log2 = 3.32 half-lives. Time = 3.32 x 30 = ~100 days.
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