食品中的放射性碘直接引起人们的关注，但是它的半衰期相对较短并将在短时间内自然衰变。
Radioactive iodine in food is of immediate concern, but it has a relatively short half-life and will naturally decay over a short time frame.
放射性碘的半衰期为八天，几周内自然衰变。
Radioactive iodine has a half-life of eight days and decays naturally within weeks.
当氦衰变成为氦-3相对于我们在太阳里看到的那它就可用了，因为地球上多数的氦-4是通过元素铀和钍自然放射性衰变而造成的。
What helium is available is depleted in helium-3 relative to what we see in the sun, because most of Earth's helium-4 is freshly made via natural radioactive decay of the elements uranium and thorium.
如同伽利略号，卡西尼号的能源来自放射性元素钸的自然衰变，产生热后再转换成电。
Like Galileo, Cassini is powered by the natural decay of the radioactive element plutonium, which generates heat that is then converted to electricity.
如同伽利略号，卡西尼号的能源来自放射性元素钸的自然衰变，产生热后再转换成电。
Like Galileo, Cassini is powered by the natural decay of the radioactive element plutonium, which generates heat that is then converted to electricity.
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