The half-life of polonium is $140 \, days$. After how many days will $16 \, g$ of polonium be reduced to $1 \, g$ (or $15 \, g$ will decay)?

${ }^{131} I$ is an isotope of Iodine that $\beta$ decays to an isotope of Xenon with a half-life of $8$ days. $A$ small amount of a serum labelled with ${ }^{131} I$ is injected into the blood of a person. The activity of the amount of ${ }^{131} I$ injected was $2.4 \times 10^5 \text{ Bq}$. It is known that the injected serum will get distributed uniformly in the blood stream in less than half an hour. After $11.5$ hours,$2.5 \text{ ml}$ of blood is drawn from the person's body,and gives an activity of $115 \text{ Bq}$. The total volume of blood in the person's body,in liters,is approximately (you may use $e^{x} \approx 1+x$ for $|x| \ll 1$ and $\ln 2 \approx 0.7$):

In a radioactive disintegration,the ratio of the initial number of atoms to the number of atoms present at an instant of time equal to its mean life is:

The ratio of the number of active nuclei of two different radioactive samples is $2:3$. Their half-lives are $1 \ h$ and $2 \ h$ respectively. The ratio of the number of active nuclei after $6 \ h$ will be:

The half-life of a radioactive substance against $\alpha$-decay is $1.2 \times 10^7 \, s$. What is the decay rate for $4.0 \times 10^{15}$ atoms of the substance?

The number of half-lives elapsed before $93.75 \%$ of a radioactive sample has decayed is