Dictionary

half–life

noun \-ˌlīf\

: the time it takes for a radioactive substance to lose half its radioactivity

Full Definition of HALF-LIFE

1
:  the time required for half of something to undergo a process: as
a :  the time required for half of the atoms of a radioactive substance to become disintegrated
b :  the time required for half the amount of a substance (as a drug, radioactive tracer, or pesticide) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
2
:  a period of usefulness or popularity preceding decline or obsolescence <slang usually has a short half–life>

First Known Use of HALF-LIFE

1907

half–life

noun \-ˌlīf\   (Medical Dictionary)

Medical Definition of HALF–LIFE

:  the time required for half of something to undergo a process: as a :  the time required for half of the atoms of a radioactive substance to become disintegrated b :  the time required for half the amount of a substance (as a drug or radioactive tracer) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes <the serum half–life is about 2 days—Journal of the American Medical Association>

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