Radon was discovered in 1900 by a German chemist Friedrich E. Dorn. He called it radium emanation. What he discovered was radon-222, while a scarcer isotope, radon-220, was actually observed first, in 1899, by the British scientist, R.B. Owens, and the New Zealand scientist, Ernest Rutherford. In 1984 a nuclear plant worker in Pennsylvania discovered radioactivity on his clothing while exiting his place of work through a radiation detector. The source of the radiation was determined to be radon decay products on his clothing originating from his home. It wasn’t until then that the medical community became aware of the possible extent of radon related problems.