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。

youdao

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。

youdao