Two radioactive materials $X_1$ and $X_2$ have decay constant $5\lambda$ and $\lambda$ respectively intially they have the saame number of nuclei, then the ratio of the number of nuclei of $X_1$ to that $X_2$ will be $\frac{1}{e}$ after a time
$4λ$
$2λ$
$\frac{1}{{2\lambda }}$
$\;\frac{1}{{4\lambda }}$
Define the average life of a radioactive substance.
Half life of radioactive element depends upon
The half life period of a radioactive substance is 60 days. The time taken for $\frac{7}{8}$ th of its original mass to disintegrate will be $......days$
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
A heavy nucleus $Q$ of half-life $20$ minutes undergoes alpha-decay with probability of $60 \%$ and beta-decay with probability of $40 \%$. Initially, the number of Q nuclei is $1000$ . The number of alphadecays of $Q$ in the first one hour is