Modern Physics 3 Question 10

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

(2004, 2M)

(a) 6000

(b) 9000

(c) 3000

(d) 24000

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Solution:

  1. Activity reduces from 6000dps to 3000dps 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 14 th of the initial activity. Hence, the initial activity of the sample is

4×6000dps=24000dps



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