Two radioactive substances $X$ and $Y$ originally have $N _{1}$ and $N _{2}$ nuclei respectively. Half life of $X$ is half of the half life of $Y$. After three half lives of $Y$, number of nuclei of both are equal. The ratio $\frac{ N _{1}}{ N _{2}}$ will be equal to
$\frac{1}{8}$
$\frac{3}{1}$
$\frac{8}{1}$
$\frac{1}{3}$
The relation between $\lambda $ and $({T_{1/2}})$ is (${T_{1/2}}=$ half life, $\lambda=$ decay constant)
The half life of a radioactive nucleus is $50$ days. The time interval $\left( t _2-t_1\right)$ between the time $t _2$ when $\frac{2}{3}$ ot it has decayed and the time $t_1$, when $\frac{1}{3}$ of it had decayed is ......days
Two radioactive materials $X_1$ and $X_2$ contain same number of nuclei. If $6\,\lambda {s^{ - 1}}$ and $4\,\lambda {s^{ - 1}}$ are the decay constants of $X_1$ and $X_2$ respectively the ratio of number of nuclei, undecayed of $X_1$ to that of $X_2$ will be $\left( {\frac{1}{e}} \right)$ after a time
A sample of radioactive material $A$, that has an activity of $10\, mCi\, (1\, Ci = 3.7 \times 10^{10}\, decays/s)$, has twice the number of nuclei as another sample of different radioactive material $B$ which has an activity of $20\, mCi$. The correct choices for half-lives of $A$ and $B$ would then be respectively
A radioactive sample of $U^{238}$ decay to $Pb$ through a process for which half life is $4.5 × 10^9$ years. The ratio of number of nuclei of $Pb$ to $U^{238}$ after a time of $1.5 ×10^9$ years (given $2^{1/3} = 1.26$)