The activity of a sample is $ 64 \times 10^{-5}\ Ci$ . Its half-life $3$ days. The activity will become$5 \times {10^{ - 6}}\ Ci$ after ........... $days$
$12$
$ 7$
$18 $
$21$
A sample of radioactive element has a mass of $10\, gm$ at an instant $t = 0$.The approximate mass of this element in the sample after two mean lives is ..........$gm$
A sample contains $16\, gm$ of a radioactive material, the half life of which is two days. After $32\, days,$ the amount of radioactive material left in the sample is
If half life of radium is $77$ days. Its decay constant in day will be
$99\%$ of a radioactive element will decay between
Define the disintegration rate or radioactivity of a sample and obtain the relation $R = \lambda N$ and define its different units.