Half-life is measured by

If the half-life of a radioactive nucleus is $3$ days, nearly what fraction of the initial number of nuclei will decay on the third day? (Given, $\sqrt[3]{0.25} \approx 0.63$)

If a radioactive material remains $25 \%$ after $16$ days,then its half-life will be ......... days.

Obtain the amount of $_{27}^{60} Co$ necessary to provide a radioactive source of $8.0 \; mCi$ strength. The half-life of $_{27}^{60} Co$ is $5.3$ years.

Decay constants of two radioactive samples $A$ and $B$ are $15x$ and $3x$ respectively. They have an equal number of initial nuclei. The ratio of the number of nuclei left in $A$ and $B$ after a time $t = \frac{1}{6x}$ is

If the radioactive decay constant of radium is $1.07 \times 10^{-4}$ per year,then its half-life period is approximately equal to ......... $years$.