Radon, << RAY don, >> is a radioactive chemical element that occurs naturally as a gas. The gas is produced by the radioactive decay (breakdown) of radium, a metallic element found in nearly all soil and rocks. Radon gas is colorless and odorless. It is classified as a noble gas or an inert gas, because its atoms do not combine readily with other atoms. For information on the position of radon on the periodic table, see the article Periodic table .
Radon gas may become a health hazard in certain buildings. The gas seeps from soil and rocks into water and air. Radon may enter a basement through cracks or other openings. If the building is in a high-radon area, the gas may build up inside to an unhealthy level.
The main sources of radon in buildings are the soil and rocks beneath basements. Minor sources include water that comes from wells and building materials such as granite and gypsum that come from the ground. Some areas have a high concentration in the ground.
Radon decay.
Radon atoms decay by giving off a form of radiation called an alpha particle. When a radon atom decays, it becomes an atom of the radioactive element polonium. Further decay produces atoms of other elements. Atoms produced by one or more decays of what were originally radon atoms are called radon daughters, also known as radon progeny (children).
How radon affects health.
Radon daughters cling to airborne dust particles and can catch in the lungs when people breathe them. When well water contains high levels, turning on faucets or showers may release radon and its daughters into the air. Some radon may also enter the body when people drink water containing the gas.
Alpha particles released by radon and its daughters in the body disrupt the normal genetic or chemical processes of living cells, causing cells to grow abnormally or to die. Over time, such cell damage may lead to cancer.
During the 1960’s and 1970’s, studies of uranium miners, who breathed large amounts of radon in the air of mines, showed unusually high rates of lung cancer. Smokers who are exposed to high radon levels are also at increased risk. The United States Environmental Protection Agency (EPA) estimates that radon may cause as many as 10 percent of cancer deaths in the country.
Protection against radon.
Test kits that people can use to check the radon levels in their homes are available from stores and mail-order sources. The EPA recommends corrective action if the radioactivity due to radon exceeds 4 picocuries per liter of air (4 pCi/L). A picocurie is one-trillionth of a curie, a unit of radioactivity. The EPA estimates that 6 percent of U.S. homes exceed 4 pCi/L. Some experts believe that the EPA threshold is too low, and that 4 pCi/L of radon does not threaten health significantly.
Contractors use several methods to lower radon levels in houses. Some of these techniques prevent radon from entering the home. Others reduce the level of the radon after it has entered. The EPA generally recommends methods that prevent the entry of radon. For example, a technique known as soil suction draws radon from below the house. The radon is then vented through a pipe or pipes to the air above the house.
In 1988, Congress passed the Indoor Radon Abatement Act to help reduce the threat from radon. The act set a goal of reducing radon until all home air was as pure as outdoor air. In outdoor air, the radioactivity due to radon is usually less than 1/2 pCi/L.
Chemical properties.
Radon’s chemical symbol is Rn. Its atomic number (number of protons in its nucleus) is 86. The atomic mass number (total number of protons and neutrons) of its most stable isotope (form) is 222. Radon freezes at –71 °C and boils at –61.7 °C. Friedrich E. Dorn, a German chemist, discovered radon in 1900.
