The half life of radium is $1620$ years and its atomic weight is $226\, k\,gm$ per kilomol. The number of atoms that will decay from its $1\, gm$ sample per second will be

(Avogadro's number $N = 6.02 \times {10^{26}}$atom/kilomol)

Consider two nuclei of the same radioactive nuclide. One of the nuclei was created in a supernova explosion $5$ billion years ago. The other was created in a nuclear reactor $5$ minutes ago. The probability of decay during the next time is

If one starts with one curie of radioactive substance ($T_{1/2}  = 12\,hrs$) the activity left after a period of $1$ week will be about

Curie is a unit of

A radioactive substance decays to $\left(\frac{1}{16}\right)^{t h}$ of its initial activity in $80\, days.$ The half life of the radioactive substance expressed in days is … .