Question

The activity of a radioactive sample is measured as N○ counts per minute at t=0 and N○/e counts per minute at t= 5 minutes. The time ( in minutes) at which the activity reduces to half its value is

Answer 1

A is activity.
Ao = No/min
$$\begin{gathered} A_t=Ao{e}^{-\lambda t} \\ Aoisinitialactivity. \\ {A}_{t}isatanttimet. \\ No/e=No{e}^{-\lambda t} \\ so\lambda comestobe1/5 \\ {t}_{1/2}=\ln 2/\lambda =3.466\; min \end{gathered}$$