The decay constant of a radioactive substance is $0.173 \, (years)^{-1}.$ Therefore:

The fraction of the initial number of radioactive nuclei which remain undecayed after half of a half-life of the radioactive sample is

$A$ radioactive isotope $X$ with a half-life of $1.37 \times 10^9$ years decays to $Y$,which is stable. $A$ sample of rock from the moon was found to contain both the elements $X$ and $Y$ in the ratio of $1 : 7$. The age of the rock is

The half-life of a stream of radioactive particles moving along a straight path with a constant kinetic energy of $4 \text{ eV}$ is $1 \text{ minute}$. The percentage of particles which decay before travelling a distance of $3.6 \text{ km}$ is (Mass of the radioactive particles $= 3.2 \times 10^{-21} \text{ kg}$ and charge of the electron $= 1.6 \times 10^{-19} \text{ C}$).

The half-life period of a radioactive sample is $3.8 \ days$. After how many days will the sample become $\frac{1}{8}$ of the original substance?

If a radioactive substance reduces to $\frac{1}{16}$ of its original mass in $40$ days,what is its half-life in days?