The half-life of the radioactive isotope tritium $(_1^3H)$ is $12.3 \ years$. If the initial amount of tritium is $32 \ mg$,how many milligrams will remain after $49.2 \ years$ (in $mg$)?

The decay constant of $Ra^{226}$ is $1.37 \times 10^{-11} \ s^{-1}$. $A$ sample of $Ra^{226}$ having an activity of $1.5 \ mCi$ will contain ...... atoms.

Gadolinium-$153$,which is used to detect osteoporosis (porous bones),has a half-life of $242$ days. Which value is closest to the percentage of $Gd-153$ left in a patient's system after $2$ years? .......... $\%$

The disintegration constant of radium with a half-life of $1600 \ years$ is:

The decay constant of a radioactive sample is $\lambda$. The half-life and mean life of the sample are respectively

How many alpha particles are emitted per second by $1 \ \mu g$ of radium?