Modern Physics 3 Question 10

10. 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

(2004, 2M)

(a) 6000

(b) 9000

(c) 3000

(d) 24000

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Solution:

  1. 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

$$ 4 \times 6000 dps=24000 dps $$



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