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The mean lives of an unstable nucleus in two different decay processes are 1620 yr and 405 yr, respectively. Find out the time during which three-fourth of a sample will decay. |
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Answer» Correct Answer - D Let at some instant of time t, number of nuclei are N. Then, `((-dN)/(dt))_(net)=((-dN)/(dt))_1+((-dN)/(dt))_2` If the effective decay constant is `lambda`, then `lambdaN=Lambda_1N+lambda_2N` or `lambda=lamba_1+lambda_2=1/1620+1/405=1/324year^-1` Now, `N_0/4=N_0e^(-lambdat)` :. `-lambdat=1n(1/4)=-1.386` or `(1/324)t=1.386` :. `t=449 yr` |
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