Starting with a sample of pure ${}^{66}Cu$, $7/8$ of it decays into $Zn$ in $15\  minutes$ . The it decays into $Zn$ in $15\  minutes$ . The corresponding half-life is ................ $minutes$

Plutonium decays with a half-life of $24000 \,years$. If the plutonium is stored for $72000 \,years$, then the fraction of plutonium that remains is

The nucleus $_{10}^{23} Ne$ decays by $\beta^{-}$ emission. Write down the $\beta$ -decay equation and determine the maximum kinetic energy of the electrons emitted. Given that

$m\left(_{10}^{23} Ne \right)=22.994466 \;u$

$m\left(_{11}^{23} Na\right) =22.089770\; u$

Activities of three radioactive substances $A , B$ and $C$ are represented by the curves $A, B$ and $C,$ in the figure. Then their half-lives $T _{\frac{1}{2}}( A ): T _{\frac{1}{2}}( B ): T _{\frac{1}{2}}( C )$ are in the ratio

A freshly prepared sample of a radioisotope of half-life $1386 \ s$ has activity $10^3$ disintegrations per second. Given that In $2=0.693$, the fraction of the initial number of nuclei (expressed in nearest integer percentage) that will decay in the first $80 \ s$ after preparation of the sample is :

Half life of a radioactive substance is $T$. The time taken for all the nuclei to disintegrate will be