The half-life of a radioactive element is $6 \ months$. The time taken to reduce its original concentration to its $1/16$ value is ....... $years$.

The amount of $_{53}I^{128}$ $(t_{1/2} = 25 \ min)$ remaining after $75 \ min$ is:

An element has a half-life of $1600 \ years$. The fraction of the mass left after $6400 \ years$ will be:

$A$ radioactive isotope decays at such a rate that after $192 \ min$ only $1/16$ of the original amount remains. The half-life of the radioactive isotope is ....... $\min$

$A$ first-order nuclear reaction is half-completed in $45 \ minutes$. How long does it take for $99.9\%$ of the reaction to be completed in $hours$?

The ratio of $\frac{{}^{14}C}{{}^{12}C}$ in a piece of wood is $\frac{1}{8}$ part that of the atmosphere. If the half-life of ${}^{14}C$ is $5730 \text{ years}$,the age of the wood sample is $.....$ years.