Radon is a natural radioactive gas that emanates from the ground into the air.

氡是一种放射性的自然气体，从地下散发到空气中。

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As a product from the uranium disintegration, radon is a natural radioactive idle gas.

氡是天然放射性惰性气体，是铀系衰变链中的一个衰变产物。

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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。

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But the indictment makes no mention of a plot to detonate a radioactive "dirty bomb" or blow up apartment buildings with natural gas -- allegations made previously in public statements and court arguments by Justice Department officials.

CNN: Specter launches probe of handling of case