radon -
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
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of radium. It is one of the densest substances that remains a gas under normal conditions and is considered to be a health hazard due to its radioactivity.
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radon A radioactive gaseous element emitted naturally from rocks and minerals where radioactive elements are present. It is released in non-coal mines, e.g. tin, iron, fluorspar, uranium. Radon is an alpha particle emitter as are its decay products and has been indicted as a cause of excessive occurrence of lung cancer in uranium miners. Concern has been expressed at radon levels in some housing usually adjacent to granite rocks or old tin mining regions.\n(Source: PORT)