a radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health.

 
  • 由镭裂变生成的放射性气体元素,惰性气体中最重的一种,天然生成(尤其在花岗岩上),被认为对健康有害。
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