The radioactivity of a sample of air obtained from a basement containing radon-222 was found to be 8 pCi/L.This isotope has a half-life of 3.8 days.If no additional radon-222 entered the basement, how long would it take for the activity to decline to 1 pCi/L?

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Quizplus · Accepted Answer

The half-life of radon-222 is 3.8 days. To decrease from 8 pCi/L to 1 pCi/L, the activity must go through three half-lives (8 to 4, 4 to 2, 2 to 1), which is 3 x 3.8 = 11.4 days, a bit more than 10 days.

The Radioactivity of a Sample of Air Obtained from a Basement