If radon is collected and has an activity of 50 pCi/L, what will the approximate activity be after 8 days?

To determine the approximate activity of radon after 8 days when the initial concentration is 50 pCi/L, it's important to consider the half-life of radon-222, which is about 3.8 days. This means that after each half-life, the amount of radon will decrease by half.

Starting with 50 pCi/L, after one half-life (approximately 3.8 days), the concentration will reduce to 25 pCi/L. After the second half-life, which is another 3.8 days, the concentration will again be halved. Therefore, from 25 pCi/L, it will drop to approximately 12.5 pCi/L after an additional 3.8 days.

After 8 days, which encompasses two full half-lives (about 7.6 days), the activity becomes approximately 12.5 pCi/L. This reflects the exponential decay characteristic of radioactive substances. Thus, the answer is correct as it takes into account the nature of radioactive decay and the specific half-life of radon-222.