Question

After 280 days, the activity of a radioactive sample is 6000 dps. The activity reduces to 3000 dps after another 140 days. The initial activity of the sample in dps is

• A. 6000
• B. 9000
• C. 3000
• D. 24000

Answer 1

Answer: (D)

24000

Answer 2

Activity reduces from 6000 dps to 3000 dps in 140 days. It implies that'half-life of the radioactive sample is 140 days. In 280 days (or two half-lives) activity will remain $\frac{1}{4}$ th of the initial activity. Hence, the initial activity of the sample is
$4\times6000 dps = 24000 dps$
Therefore, the correct option is (d).