Half-life
The key idea
Half-life is the time required for the expected number of undecayed nuclei, or equivalently the activity of a large sample, to fall to one half of its initial value.
Why it matters
Successive half-lives produce halves, quarters, eighths and so on; the process is exponential rather than linear.
A picture to remember
Successive half-lives produce halves, quarters, eighths and so on; the process is exponential rather than linear.