A radioactive sample has ${N_0}$ active atoms at $t = 0$. If the rate of disintegration at any time is $R$ and the number of atoms is $N$, then the ratio $ R/N$ varies with time as
The half-life of a radioactive substance is $30$ minutes. The times (in minutes ) taken between $40\%$ decay and $85\%$ decay of the same radioactive substance is
In a radioactive decay process , the negatively charged emitted $\beta -$ particles are
A radioactive sample decays by $\beta$ -emission. In first two seconds $‘n’$ $\beta$ -particles are emitted and in next $2\ seconds$ , $‘0.25n’$ $\beta$ -particles are emitted. The half life of radioactive nuclei is ...... $sec$
If ${N_0}$ is the original mass of the substance of half life period ${T_{1/2}} = 5$ years, then the amount of substance left after $15$ years is
Starting with a sample of pure ${}^{66}Cu,\frac{7}{8}$ of it decays into $Zn$ in $15\, minutes$. The corresponding half life is..........$minutes$