Problem

Two radioactive samples of different elements (half-lives

t_1

and

t_2

respectively) have same number of nuclei at

t = 0

. The time after which their activities are same is a.

\frac{t_1 t_2}{0.693(t_2 - t_1)} \ln \frac{t_2}{t_1}

\frac{t_1 t_2}{0.693} \ln \frac{t_2}{t_1}

\frac{t_1 t_2}{0.693(t_1 + t_2)} \ln \frac{t_2}{t_1}

d. None of these