食品中的放射性碘直接引起人们的关注，但是它的半衰期相对较短并将在短时间内自然衰变。
Radioactive iodine in food is of immediate concern, but it has a relatively short half-life and will naturally decay over a short time frame.
半衰期实际上是,一半反应物消失的时间。
So, the half-life is just the time that it takes for half of the reactants to disappear.
但碘- 131则不同，它的半衰期是八天，意味着它需要数月时间才会完全消失。
However, iodine-131 has a short half-life of eight days, which means it will decay away completely in the environment in a matter of months.
该造影剂毒性低，生物相容性好，在血液中的半衰期达30 ~60分钟，时间窗口大，且饱和磁化强度大。
The contrast agent has low toxicity, good biocompatibility, large time window and high saturation magnetization, and the half-life period of the contrast agent in the blood reaches 30 to 60 minutes.
这里所指的半衰期是现存原子的一半发生衰变或爆炸所消耗的时间。
By that is meant the time which elapses before half of the existing atoms have disintegrated or exploded.
因半衰期短，为了延长药物作用时间和提高药效，本文合成了它的酯和硫醚类衍生物。
In order to search for new derivatives with longer duration of action and higher activity, captopril esters and thioethers were synthesized.
因半衰期短，为了延长药物作用时间和提高药效，本文合成了它的酯和硫醚类衍生物。
In order to search for new derivatives with longer duration of action and higher activity, captopril esters and thioethers were synthesized.
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