Starting with a sample of pure ${}^{66}Cu,\frac{7}{8}$ of it decays into $Zn$ in $15\, minutes$. The corresponding half life is..........$minutes$
$15$
$10$
$7\frac{1}{2}$
$5$
A radioactive substance is being produced at a constant rate of $10\, nuclei/s.$ The decay constant of the substance is $1/2\, sec^{-1}.$ After what time the number of radioactive nuclei will become $10$ $?$ Initially there are no nuclei present. Assume decay law holds for the sample.
After two hours, one- sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is
How much mass of uranium to be destroyed per minute to operate a nuclear reactor of $600\,MW$
At a given instant there are $25\%$ undecayed radioactive nuclei in a same. After $10 \,sec$ the number of undecayed nuclei reduces to $6.25\%$, the mean life of the nuclei is...........$ sec$
The $S.I.$ unit of radioactivity is