Radon is a natural radioactivegas 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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For most people more than half of their natural background radiation dose comes from radon, a radioactivegas that can accumulate in homes, schools and workplaces.
What little relief Thornburgh felt at hearing Scranton's report, dissolved the next day when it was reported that a large burst of radioactivegas had escaped from Three Mile Island.