It has a half-life of approximately three years at which time it stops decaying.

它生命的一半是三年,在三年的时候，它就停止衰亡。

麻省理工公开课 - 固态化学导论课程节选

How do we know this always stops? I mean, I ran three trials here, and it did. But how would I reason about, does this always stop?

我指的是我在这儿试了三次，它都停了，那这是为什么呢？,它总是会停下么？

麻省理工公开课 - 计算机科学及编程导论课程节选