Background:
Half-life is the period of time it takes one half of a sample of radioactive isotope to decay into another isotope, assuming decay is a random event.
\[ \newcommand\T{\Rule{0pt}{1em}{.3em}} \begin{array}{|l|l|l|l|l|l|l|l|} \hline \mbox{Half-lives elapsed} \T & 1 \T & 2 \T & 3 \T & 4 \T & 5 \T & \cdots \T & N \\ \\\hline \mbox{Mass of sample remaining} \T & \frac{1}{2} \T & \frac{1}{4} \T & \frac{1}{8} \T & \frac{1}{16} \T & \frac{1}{32} \T & \cdots \T & \frac{1}{2^N} \\\hline \end{array} \]Key Concept:
As the number of half-lives increase, the mass and activity level of a radioactive substance decrease.