Radon-222 has a half-life of 3.8 days. A sample from a basement in Colorado was analyzed 5.0 days after it was collected and found to have an activity of 0.17 Bq. What was the original activity of this sample?

Question

Quizplus · Accepted Answer

Using the formula for radioactive decay
A = A0 * (1/2)^(t/T)
where A is the activity of the sample at the time of measurement,
A0 is the original activity of the sample,
t is the time elapsed between collection and measurement, and
T is the half-life of the radionuclide.

Substituting the given values, we get
0.17 Bq = A0 * (1/2)^(5/3.8)
Solving for A0, we get A0 = 0.42 Bq (rounded to two significant figures). Therefore, the correct answer is C.

Radon-222 Has a Half-Life of 3