The half-life of $_{38}^{90}Sr$ is $20 \text{ years}$. If a sample having an initial activity of $8000 \text{ dis/min}$ is taken,what would be its activity after $80 \text{ years}$?

The unit for the radioactive decay constant is:

$\frac{15}{16}$-th of a radioactive sample decays in $40$ days. The half-life of the sample is ...... days.

During a nuclear explosion,one of the products is $^{90}Sr$ with a half-life of $6.93 \; \text{years}$. If $1 \; \mu g$ of $^{90}Sr$ was absorbed in the bones of a newly born baby in place of $Ca$,how much time,in years,is required to reduce it by $90 \%$ if it is not lost metabolically?

The half-life period of a radioactive element is $30 \ min$. One sixteenth of the original quantity of the element will remain unchanged after ........... $min$.

The half-life of $C^{14}$ is $5760 \ years$. For a $200 \ mg$ sample of $C^{14}$, the time taken to change to $25 \ mg$ is (in $years$)