Radon

 Atomic Number:

86

 Melting Point: -71 ºC
Atomic Symbol: Rn Boiling Point:  -61.7 ºC
Atomic Weight: 222 amu Density: 9.73 kg/m 3
Atomic Radius:

--

 Oxidation States: --
Covalent Radius: 145 pm Electron Configuration: [Xe]6s24f145d106p6
van der Waals Radius:

--

 State of Matter: gas (nonmagnetic)

History

(From radium; called niton at first, L. nitens: shining) The element was discovered in 1900 by Dorn, who called it radium emanation. In 1908 Ramsay and Gray, who named it niton, isolated the element and determined its density, finding it to be the heaviest known gas. It is essentially inert and occupies the last place in the zero group of gases in the Periodic Table. Since 1923, it has been called radon.

Properties

On the average, one part of radon is present at 1 x 1021 part of air. At ordinary temperatures radon is a colorless gas; when cooled below the freezing point, radon exhibits a brilliant phosphorescence which becomes yellow as the temperature is lowered and orange-red at the temperature of liquid air. It has been reported that fluorine reacts with radon, forming a fluoride. Radon clathrates have also been reported.

Sources

Soil down to depth of 6 inches (150 mm) has about 1 gram of radium, which decays to radon and releases tiny amounts of this deadly gas into the atmosphere. Radon can be found in some spring waters and hot springs. The town of Misasa, Japan, boasts its radium-rich springs exhausting radon.

Radon exhausts naturally from the ground, particularly in certain regions, especially but not only regions with granitic soils. Not all granitic regions are prone to high exhausts of radon. Depending on how houses are built and ventilated, radon may accumulate in basements and dwellings.

Uses

Radon is still produced for therapeutic use by a few hospitals by pumping it from a radium source and sealing it in minute tubes, called seeds or needles, for application to patient. This practice has been largely discontinued as hospitals can get the seeds directly from suppliers, who make up the seeds with the desired activity for the day of use. Such seeds - often using radioactive forms of cobalt and cesium - also last for several years, which is a logistical advantage.

Because of its rapid loss to air, radon is used in hydrologic research that studies the interaction between ground water, streams and rivers. Any significant concentration of radon in a stream or river is a good indicator that there are local inputs of ground water.

Isotopes

Twenty isotopes are known. Radon-22, from radium, has a half-life of 3.823 days and is an alpha emitter; Radon-220, emanating naturally from thorium and called thoron, has a half-life of 55.6 s and is also an alpha emitter. Radon-219 emanates from actinium and is called actinon. It has a half-life of 3.96 s and is also an alpha emitter. It is estimated that every square mile of soil to a depth of 6 inches contains about 1 g of radium, which releases radon in tiny amounts into the atmosphere. Radon is present in some spring waters, such as those at Hot Springs, Arkansas.

Hazards

Radon is a carcinogenic gas. Radon is a radioactive material and must be handled with care at all times. It is hazardous to inhale this element since it emits alpha particles.

Also, its solid decay products, and their respective products, tend to form a fine dust which can easily enter the airways and become permanently stuck in lung tissue, producing heavy localized exposure. Rooms where radium, actinium, or thorium are stored should be well-ventilated in order to prevent build-up in the air. The build-up of radon is a potential health hazard in uranium and some lead mines. Build-up of radon in homes has also been a more recent health concern and many lung cancer cases are attributed to radon exposure each year.

Radon is of greatly increased danger to smokers. The solid decay products of radon staying in the atmosphere in dust form can fix themselves on the micro particles in tobacco smoke, which then enter the lungs.

Radon can cause lung cancer. Many deaths from lung cancer are caused by radon exposure. In the U.S. it is recommended that remedial action be taken if the air in homes exceeds 4 pCi/l.