Alpha particles are positively charged helium nuclei obtained from naturalradioactivedecay.
粒子是从天然放射性蜕变得到的带正电的氦核。
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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 naturalradioactivedecay of the elements uranium and thorium.
Two test methods, naturalradioactive background method and decay method, used to verify the detection limit of radioactive aerosol monitors are studied.