Radon is a naturally occurring radioactive gas that is created when the elements uranium, thorium, or radium decay. It is extremely toxic and can only be detected with specialized equipment because it is colorless and odorless.
Physical & chemical properties
Radon was discovered in 1900. It is a gas at room temperature and is one of the densest gases, about 8 times as dense as the Earth’s atmosphere. When it is cooled below -96° F, it becomes phosphorescent, giving off a yellow or orange-red glow. This glow is caused by radon’s radioactive properties.
Radon is a noble gas, which means that its outer electron shell is full. Because of this, it is considered inert and is not likely to be involved in chemical reactions. Very little chemical research has been done with radon because it is very radioactive and has a short half-life.
Where is it found?
Radon naturally occurs in several types of rock including uranium, phosphate, shale, granite, and limestone. On average, every square mile of surface soil (top 6 inches) contains approximately 1 gram of radium which releases small amounts of radon into the atmosphere. However, the specific amount of radon varies widely from place to place.
Radon is naturally released from the ground, particularly in soils containing granite or shale, which have a higher concentration of uranium. It can also be emitted by some building materials and can be present in some petroleum and natural gas products.
Uranium mines contain high levels of radon, particularly if they are not ventilated well. Some spring waters and hot springs have high levels of radon and have even been used as healing waters because of the effects of radon on certain health problems.
Radon can enter homes and other buildings by seeping through basement walls from the soil or entering through cracks in the walls or floors. It tends to accumulate in confined areas such as attics and basements and different rooms of the house can have significantly different levels of concentration.
Radon levels can also be affected by atmospheric conditions. For example, concentrations can rise during a time of inversion and little wind.
The highest indoor radon concentrations have been founding Iowa and southeastern Pennsylvania. This is in part due to glaciers breaking up granite rocks centuries ago and depositing the resulting soil in the plains which now make up farmland.