Most famously, uranium-238 decays into lead-206 with a half life of 4.5 billion years, though radioactive rubidium and samarium are also useful for dating things billions of years old.
最为有名的就是铀- 238衰变为铅- 206的半衰期为45亿年，当然放射性铷和钐也同样对测算几十亿年前的物体的年龄很有用。
Now, as you recall from the uranium 238 slide, I think the next slide will show it.
现在，正如你们从铀 238幻灯片中想起的，我想下一张幻灯片会展示它。
And if you keep these neutrons from escaping through leakage they then become available to become absorbed in uranium 238.
如果你阻止这些中子通过泄露逃跑，它们之后能够，变成在铀238里能吸收的。
Now as you recall from the uranium 238 slide, and I think the next slide will show it.
现在，如你们能在铀238的幻灯片中想起的，我想，下一张幻灯片就会展示它。
We can then look at uranium 238 which has a relatively low absorption thermal energy range and essentially has no fission cross section which is why we call uranium 238 a fertile atom.
我们能看看铀238，它有一个，相对低的吸收热能范围，基本上没有裂变横截面，那就是为什么我们称铀238为可转换核素。
The prime example is the element uranium (U), which occurs naturally as two isotopes-the lighter, fissionable U-235 and the heavier, non-fissionable U-238.
铀（U）元素就是一个很好的例子。天然铀有两种同位素；较轻的负235可以裂变，较重的铀238则不会裂变。
The prime example is the element uranium (U), which occurs naturally as two isotopes-the lighter, fissionable U-235 and the heavier, non-fissionable U-238.
铀（U）元素就是一个很好的例子。天然铀有两种同位素；较轻的负235可以裂变，较重的铀238则不会裂变。
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