Alpha particles are positively charged helium nuclei obtained from natural radioactive decay.
粒子是从天然放射性蜕变得到的带正电的氦核。
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.
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。
Two test methods, natural radioactive background method and decay method, used to verify the detection limit of radioactive aerosol monitors are studied.
研究了放射性气溶胶监测仪的检测方法，即天然本底检测法和衰变检测法。
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