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A 280 day old radioactive substances sho...

A 280 day old radioactive substances shows an activity of 6000 dps, 140 days later its activity becomes 3000 dps. What was its initial activity ?

A

9000

B

24000

C

12000

D

18000

Text Solution

Verified by Experts

The correct Answer is:
B
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 `1//4^(th)` of the initial activity. Hence the initial activity of the sample is `4 xx 6000` dps = 24000 dps.
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