The half-life of a radioactive isotope is $4 \ hours$. If the initial mass of the isotope is $200 \ g$,then what will be the disintegrated amount of it after $16 \ hours$?

The decay constant of a radioactive element is $3 \times 10^{-6} \ min^{-1}$. Its half-life is

If $n_t$ number of radioatoms are present at time $t$, the following expression will be a constant:

$A$ freshly prepared radioactive source of half-life $2 \ hours$ emits radiations of intensity which is $64$ times the permissible safe level. The minimum time after which it would be possible to work safely with this source is ......... $hours$.

The radium and uranium atoms in a sample of uranium mineral are in the ratio of $1 : 2.8 \times 10^6$. If the half-life period of radium is $1620$ years,the half-life period of uranium will be:

$A$ radioactive substance has a half-life $(t_{1/2})$ of $60 \ minutes$. After $3 \ hours$,what percentage of the radioactive substance will remain?