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.
自然伽马测井是套管井测井中一种最基本的方法。它以地层自然放射性为基础，测井时用伽马射线探测器沿井眼进行测量。地层中的自然伽马放射性不是一成不变的。
Natural gamma logging is a kind of most basic methods of well logging in cased Wells which measure with gamma ray detector along well during logging.
氡是一种放射性的自然气体，从地下散发到空气中。
Radon is a natural radioactive gas that emanates from the ground into the air.
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