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