年久的弹头到了2008年将达到设计的30年使用期，这些旧弹头也就在没有危害国家的核屏蔽的情况下被淘汰。
The older warheads, the most elderly of which will reach the end of their 30-year design lifespan in 2008, could then be retired without compromising the country's nuclear shield.
所以我们来对屏蔽举两个例子，如果我们在讨论氦，举例来说一个氦原子核或者氦原子。
So let's take two cases of shielding if we're talking about, for example, the helium, a helium nucleus or a helium atom.
它们受到少的屏蔽,因为它们离原子核更近，它们感觉到一个更大的有效电荷量。
They're less shielded because they're closer to the nucleus, they feel a greater z effective.
应用推荐