The halflife of oxygen15 is 124 s If a sample of oxygen15 ha

The half-life of oxygen-15 is 124 s. If a sample of oxygen-15 has an activity of 4000. Bq, how many minutes will elapse before it reaches an activity of 500. Bq? 2.07 min 6.20 min 8.27 min 372 min 22 320 min

Solution

The correct answer is: 6.20 min

CALCULATION:

We will start with 4000. Bq

After one half life,it will decay to 2000. Bq

Again after second half-live,it will decay to 1000. Bq

Again after a third half-life, it will decay to 500. Bq

Total number of half-lives = 3

Each half life = 124 s

So, three half-lives will be :3 *124 s = 372 s = 6.20 min. ( ans)