The decay constant of a radio isotope is λ. If A_1 and A_2 are its activities at times t_1 and t_2 respectively, the number of nuclei which have…

The decay constant of a radio isotope is $\displaystyle \lambda$. If $\displaystyle \mathrm{A}_1$ and $\displaystyle A_2$ are its activities at times $\displaystyle t_1$ and $\displaystyle t_2$ respectively, the number of nuclei which have decayed during the time $\displaystyle \left(t_1-t_2\right)$