half-life
n.（名词）Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.【物理学】 半衰期：放射性样品的原子核经历一半放射性衰变所需要的时间Biology 【生物学】 The time required for half the quantity of a drug or other substance deposited in a living organism to be metabolized or eliminated by normal biological processes.Also called biological half-life 生物半衰期： 存储在活的有机体内的药物或其它物质经新陈代谢或被正常的生理活动消失一半所需要的时间也作 biological half-lifeThe time required for the radioactivity of material taken in by a living organism to be reduced to half its initial value by a combination of biological elimination processes and radioactive decay.半减期： 被活的有机体摄入的放射性元素经过生物衰减及放射性衰变过程综合，其剂量减至一半所需要的时间
