What is radon?

Radon: The Health Hazard with a Simple Solution
Radon is a cancer-causing natural radioactive gas that you can’t see, smell or taste. Its presence in your home can pose a danger to your family's health.

Radon is the leading cause of lung cancer among non-smokers. Radon is the second leading cause of lung cancer in America and claims about 20,000 lives annually.

Testing your home for radon can be easy and inexpensive, and if your levels are elevated, they can be lowered.


Radon is a chemical element that has the symbol Rn and atomic number 86. Radon is a radioactive noble gas that is formed by the decay of radium. It is one of the heaviest gases and is considered to be a health hazard. The most stable isotope is 222Rn which has a half-life of 3.8 days and is used in radiotherapy. Radon is a significant contaminant that affects indoor air quality worldwide. Radon gas from natural sources can accumulate in buildings and reportedly causes 21,000 lung cancer deaths per year in the United States alone.[1]

Notable characteristics

Essentially chemically inert but radioactive, radon is the heaviest noble gas and one of the heaviest gases at room temperature. At standard temperature and pressure radon is a colorless gas, but when it is cooled below its freezing point (202 K ; −71 °C ; −96 °F) it has a brilliant phosphorescence which turns yellow as the temperature is lowered, and becomes orange-red as the temperature is lowered further (below 93 K ; −180 °C).

Natural radon concentrations in Earth's atmosphere are so low that radon-rich water in contact with the atmosphere will continually lose radon by volatilization. Hence, ground water has a higher concentration of 222Rn than surface water, because it is continuously produced by radioactive decay of 226Ra present in rocks. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone because of diffusional losses to the atmosphere.


Radon (named after radium) was discovered in 1900 by Friedrich Ernst Dorn, who called it radium emanation. In 1908 William Ramsay and Robert Whytlaw-Gray, named it niton (Latin nitens meaning "shining"; symbol Nt) and isolated it, determined its density, and determined that it was the heaviest known gas. It has been called "radon" since 1923.

The first major studies of the health concern occurred in the context of uranium mining, first in the Joachimsthal region of Bohemia and then in the Southwestern United States during the early Cold War. Because radon is a product of uranium, uranium mines have high concentrations of radon and its highly radioactive daughter products. Many Native Americans, Mormons, and other miners in the Four Corners region contracted lung cancer and other pathologies as a result of high levels of exposure to radon gas while mining uranium for the Atomic Energy Commission in the mid-1950s. Safety standards instituted required expensive ventilation and as such were not widely implemented or policed.

The danger of radon exposure in dwellings was discovered in 1984 with the case of Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Watras set off the radiation alarms on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of radon, around 100,000 Bq/m3 (2,700 pCi/L), in his house's basement and it was not related to the nuclear plant. The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day. Following this event, which was highly publicized, national radon safety standards were set, and radon detection and ventilation became a standard homeowner concern.

Health Effects

Radon is the leading cause of lung cancer among non-smokers.