Radiation Protection

Radionuclide Basics: Radon

Radon Radon (chemical symbol Rn) is an odorless, colorless, radioactive gas. It comes from the natural decay of uranium and radium found in nearly all rocks and soils. Radon can move up from the ground into buildings through openings in floors or walls that are in contact with the ground.

Radon can accumulate in buildings and, over time, can pose a serious health hazard. For more information about indoor air quality and the health risk of radon, visit the Health Risk of Radon page on EPA.gov.

Type of Radiation Emitted:  Half-lifeHelpHalf-lifeThe time required for half of the radioactive atoms present to decay or transform. Some radionuclides have half-lives of mere seconds, but others have half-lives of hundreds or millions of years.
Alpha Half-Life
Alpha ParticlesHelpAlpha ParticleA form of particulate ionizing radiation made up of two neutrons and two protons. Alpha particles pose no direct or external radiation threat; however, they can pose a serious health threat if ingested or inhaled. 3.8 days
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Radon in the Environment

Radon is a radioactive gas that results from the natural decay of uranium and radium found in nearly all rocks and soils. Elevated radon levels have been found in every state. Radon is in the atmosphere and can also be found in ground water. The national average for radon in outdoor air is 0.4 picocuries per liter (pCi/L), while the average for indoor air is 1.3 pCi/L.

Radon can move up from the ground into buildings through openings in floors or walls that are in contact with the ground. Radon can accumulate in buildings and, over time, can pose a serious health hazard. Learn more about radon.

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Radon Sources

Any building can have high levels of radon, including new and old homes, well-sealed and drafty homes, office buildings and schools, and homes with or without basements. Testing is the only way to know if your home has elevated radon levels.

Radon gas can get into buildings through:Radon House

  • Cracks in solid floors and walls
  • Construction joints
  • Gaps in suspended floors
  • Gaps around service pipes
  • Cavities inside walls
  • The water supply
  • Building materials

EPA recommends fixing your home when the radon level is at or above 4 pCi/L. Additionally, having your school tested for radon is something you may want to discuss with school officials.

Testing is inexpensive and easy — it should only take a few minutes of your time. Millions of Americans have already tested their homes for radon. If elevated levels are found, radon reduction systems work and they are cost effective. Even very high levels can be reduced to acceptable levels. Learn more about testing your home for radon.

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Radon and Health

EPA estimates that about 21,000 lung cancer deaths each year in the U.S. are radon-related. Exposure to radon is the second leading cause of lung cancer after smoking. For never-smokers, it is the leading cause of lung cancer. 

For most people, radon is the single greatest environmental source of radiation exposure. Learn more about radiation sources and doses, including radon. EPA recommends that all homes and schools be tested for radon. For smokers, the risk of lung cancer is heightened due to the combined effects of radon and smoking.

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