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. (Source: PORT)