the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
half-life的用法和样例：
例句
用作名词 (n.)
The time it takes for half of its original amount to decay is called the half-life. 衰变至只剩下原来数目一半所需的时间称为该核素的半衰期。
It is not necessary to wait until half of a sample has decayed in order to measure the halflife. 不必一直等到样品衰变一半之后才测量它的半衰期。
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