The activity of a sample of gas 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 decay of radon-222 follows an exponential decay model, where the time to decay to a certain fraction of the original amount can be calculated using the half-life formula. To go from 8 pCi/L to 1 pCi/L, the activity needs to be reduced to 1/8 of its original value. This requires three half-lives (since 2^3 = 8), and with each half-life being 3.8 days, the total time is approximately 3 * 3.8 = 11.4 days, which is a bit more than 10 days.

The Activity of a Sample of Gas Obtained from a Basement