Question

After 280 days, the activity of radioactive sample is 6000 disintegration per second. The
activity reduces to 3000 disintegration per second after an-other 140 days. The initial
activity of the sample in disintegration per second is
A) 6000
C) 3000
B) 9000
(D) 24000
nctive substance during their decay?
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Answer 1

Here, the activity of the radioactive sample reduces to half in 140 days. Therefore, the half life of the sample is 140 days. 280 days is it's two half lives. So before two half lives it's activity was

2

6

×6000=24000dps.

Hence, the option D is the correct answer.

Answer 2

Answer:

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  th of the initial activity. Hence, the initial activity of the sample is  Therefore, the correct option is (d).

Explanation:

hope it help you!