Q.The decay constant of a radioactive substance is $4.33\times10^{-4}$ per year. Calculate its half life period.

Two related time-scales characterise how quickly a radioactive species decays. The half-life $T_{1/2}$ is the time for the parent population to fall to exactly half its value; from the exponential decay law, $T_{1/2}=\frac{\ln2}{\lambda}=\frac{0.693}{\lambda}$. A subtle but important point: the SAME fractional (halving) reduction applies to every successive interval of length $T_{1/2}$, regardless of how much time has already elapsed -- after two half-lives the population is a QUARTER of the original, not zero, and after n half-lives it is $(1/2)^n$ of the original, however large n is. …