Curie is a unit of

$'Rn$' decays into $'Po'$ by emitting $a -$ particle with half life of $4\, days$. A sample contains $6.4 \times 10^{10}$ atoms of $Rn$. After $12\, days$, the number of atoms of $'Rn'$ left in the sample will be

After $3$ hours, only $0.25 \,mg$ of a pure radioactive material is left. If initial mass was $2 \,mg$ then the half life of the substance is ...... $hr$

A radioactive sample decays $\frac{7}{4}$ times its original quantity in $15$ minutes. The half-life of the sample is $......min$

$10\, gm$ of radioactive material of half-life $15$ year is kept in store for $20$ years. The disintegrated material is ............$gm$

Half lives for $\alpha$ and $\beta$ emission of a radioactive material are $16$ years and $48$ years respectively. When material decays giving $\alpha$ and $\beta$ emission simultaneously then time in which $\frac{3}{4}$ th of the material decays is ....... years