The metallicity of a star measures the amount of " metals" it has — that is, any element heavier than helium.
恒星的金属度用于表征它含有的“金属”的量——其实是所有比氦重的元素的量。
The metallicity of a star measures the amount of "metals" it has —that is, any element heavier than helium.
恒星的金属度用于表征它含有的“金属”的量——其实是所有比氦重的元素的量。
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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