The count rate of a Geiger- Muller counter for the radiation of a radioactive material of half life of $30\, minutes$ decreases to $5\,{s^{ - 1}}$ after $2\, hours.$ The initial count rate was..........${s^{ - 1}}$

A radio nuclide $A_1$ with decay constant $\lambda_1$  transforms into a radio nuclide $A_2$ with decay constant $\lambda_2$ . If at the initial moment the preparation contained only the radio nuclide $A_1$, then the time interval after which the activity of the radio nuclide $A_2$ reaches its maximum value is :-

A radioactive element emits $200$ particles per second. After three hours $25$ particles per second are emitted. The half life period of element will be ..........$minntes$

For a substance the average life for $\alpha $ -emission is $1620\ years$ and for $\beta $ emission is $405\ years$ . After how much time the $\frac {1}{4}$ of the material remains by simultaneous emission ............ $years$

The half-life of $^{238} _{92} U$ undergoing $\alpha$ -decay is $4.5 \times 10^{9}$ $years$. What is the activity of $1\; g$ sample of $^{238} _{92} U$?

Radioacitive nuclei $A$ and $B$ disintegrate into $C$ with half lives $T$ and $2T$. At $t = 0$, pumber of nuclei of each $A$ and $B$ is $x$. The number of nuclei of $C$ when rate of disintegration of $A$ and $B$ are equal is