The radioisotope,tritium $({}_1^3H)$ has a half-life of $12.3 \ years$. If the initial amount of tritium is $32 \ mg$,how many milligrams of it would remain after $49.2 \ years$?

$A$ radioactive sample is emitting $64$ times more radiation than the non-hazardous limit. If its half-life is $2 \ hr$,after what time will it become non-hazardous? $(hr)$

$A$ radioactive isotope has a half-life of $10 \ days$. If today $125 \ mg$ is left over,what was its original weight $40 \ days$ earlier?

The decay constant of a radioactive element is $3 \times 10^{-6} \ min^{-1}$. Its half-life is

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

In a radioactive decay,a uranium atom transforms into a lead atom. If a rock sample from the moon contains an equal number of uranium and lead atoms,and the half-life $(t_{1/2})$ for uranium is $4.5 \times 10^9$ years,then the age of the rock will be: