Word
Half-Life
The time over which half the nuclei in a large sample of a particular radioactive isotope are expected to decay
Examples
After two half-lives, about a quarter of the original radioactive nuclei remain.
An isotope's half-life describes a population pattern, not an appointment at which each atom must decay.
Origin
The term names a repeated halving under radioactive decay. Each interval removes about half of what remains, not another half of the original amount. That distinction makes the decline exponential rather than a straight-line countdown to zero.
How it connects
Half-life names the regular population pattern that makes decay measurable.
This word appeared in A clock made from disappearance, the Involves connection for October 5, 2026, which asked: How can unpredictable individual events produce a useful measure of time?
Check yourself
About what fraction remains after three half-lives?
One eighth. Exactly. Each interval halves the remaining amount: one half, one quarter, then one eighth.
What the sources establish
Half-life concerns expected decay in a population; repeated intervals halve what remains.
Sources
Half-life (U.S. Nuclear Regulatory Commission), Definition of radioactive half-life
Glossary: Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program (National Academies), Half-life: repeated expected halving of a radioactive population