What Is Radon?
QUICK ANSWER
Radon is a radioactive chemical element with atomic number 86 and the symbol Rn. It's a colorless, odorless, tasteless noble gas formed from the natural radioactive decay of uranium in rocks and soil. Radon is the second-leading cause of lung cancer in the US after smoking, primarily through accumulation in poorly ventilated buildings.
Radon is the element most homeowners discover they should worry about only after a home inspection. It's invisible, has no smell, and seeps silently from soil into basements and crawlspaces, where it can build to dangerous levels. Long-term exposure significantly raises lung cancer risk, but testing is cheap and mitigation systems are straightforward, which is why radon awareness has become standard in many places.
Where does radon come from?
Radon forms naturally from the radioactive decay of uranium and thorium in rocks and soil. Uranium-238, present in trace amounts in most rocks, slowly decays through a long chain of intermediate elements, eventually producing radon-222 as one step. Because radon is a noble gas, it doesn't bond with other elements and can escape from rock and soil into the air. Outdoors, it disperses harmlessly. Indoors, it can accumulate to dangerous levels if buildings have cracks in foundations or poor ventilation. Granite-rich areas tend to have higher radon levels.
What are the properties of radon?
Radon has atomic number 86 and sits in group 18 of the periodic table among the noble gases, with neon, argon, krypton, and xenon. It's the densest gas at room temperature, about eight times denser than air, which is why it sinks into low-lying areas like basements. Radon is colorless, odorless, and tasteless, making it impossible to detect without instruments. All radon isotopes are radioactive, with Rn-222 being the most common and having a half-life of about 3.8 days. It decays into polonium, lead, and other radioactive elements.
Why is radon dangerous?
When radon decays, it produces solid radioactive particles called radon progeny that can lodge in the lungs when inhaled. These particles emit alpha radiation that damages lung tissue, dramatically increasing cancer risk. The EPA estimates radon causes about 21,000 lung cancer deaths annually in the US, second only to smoking. Smokers exposed to high radon have especially elevated risk because the effects compound. The danger is highest in homes with foundations cracked or built on radon-rich soil, with prolonged exposure being the key risk factor rather than short visits to affected buildings.
How is radon tested and removed?
Radon testing uses simple detectors that homeowners can buy for under $30 or that professionals can install. Short-term tests run 2-7 days; long-term tests run 90 days to a year. The EPA action level is 4 picocuries per liter (pCi/L), though they recommend considering mitigation even at 2 pCi/L. Mitigation systems use pipes and fans to vent radon from beneath the foundation to the outdoors, where it disperses safely. A typical mitigation system costs $800-$2,500 and can reduce indoor radon by 95% or more. Many regions now require radon disclosure when homes are sold.
Radon is the invisible threat hiding in roughly 1 in 15 American homes at elevated levels. The element itself is just a natural noble gas, but its radioactive decay products make long-term exposure a real cancer risk. Testing is cheap and mitigation works, which is why radon awareness has become a standard part of home ownership.
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