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  4. The decay constant of a radio isotope is λ. If A1 and A2 are its activities at times t1 and t2 respectively, the number of nuclei which have decayed during the time (t1-t2)

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Q. The decay constant of a radio isotope is $\lambda$. If $A_1$ and $A_2$ are its activities at times $t_1 $ and $t_2$ respectively, the number of nuclei which have decayed during the time $(t_1-t_2)$

AIPMTAIPMT 2010Nuclei

Solution:

$A_1=\lambda N_1 \, at \, time \, t_1$
$A_2=\lambda N_2$ at time $t_2$
Therefore, number of nuclei decayed during time interval $(t_1-t_2)$ is
$N_1-N_2 =\frac{[A_1-A_2]}{\lambda}$