Many U.S. homes accumulate radon. Radon is a poisonous gas and a by-product of radioactive decay of the uranium decay series. A heavy gas, radon is a serious indoor hazard in every part of the country. It tends to accumulate in poorly ventilated basements and well-insulated homes built on specific types of soil or bedrock rich in uranium minerals. Radon is known to cause lung cancer; since it is odorless and colorless, it can go unnoticed in homes for years. But the radon hazard is easily mitigated and homes can be made safe once the hazard is identified.
Uranium is a radioactive mineral that spontaneously decays to lighter daughter elements by losing high-energy particles at a predictable rate known as a half-life. The half-life specifically measures how long it takes for half of the original or parent element to decay to the daughter element. Uranium decays to radium through a long series of steps with a cumula tive half-life of 4.4 billion years. During these steps intermediate daughter products are produced, and high-energy particles including alpha particles, consisting of two protons and two neutrons, are released. This produces heat. The daughter mineral radium is itself radioactive, and it decays with a half-life of 1,620 years by losing an alpha particle, thus forming the heavy gas radon. Radon escapes from the minerals and ground and makes its way to the atmosphere, where it is dispersed unless it gets trapped in homes. If it gets trapped, it can be inhaled and do damage. Radon is a radioactive gas that decays with a half-life of 3.8 days, producing daughter products of polonium, bismuth, and lead. If this decay occurs while the gas is in someone's lungs, then the solid daughter products become lodged in the lungs. This is how radon damage is initiated. Most of the health risks from radon are associated with the daughter product polonium, which is easily lodged in lung tissue. Polonium is radioactive, and its decay and emission of high-energy particles in the lungs can damage lung tissue, eventually causing lung cancer.
The concentration of radon among geographic regions and in specific places in those regions varies tremendously. There is also a great variation in the concentration of the gas at different levels in the soil, home, and atmosphere. This variation is related to the concentration and type of radioactive elements present at a location. Radioactivity is measured by the picocurie (pCi), which is approximately equal to the amount of radiation produced by the decay of two atoms per minute.
Soils have gases trapped between the individual grains that make up the soil, and these soil gases have typical radon levels of 20 pCi per liter to 100,000 pCi per liter, with most soils in the United States falling in the range of 200-2,000 pCi/L. Radon can also be dissolved in groundwater with typical levels falling between 100-2 million pCi/Liter. Outdoor air typically has 0.1-20 pCi/Liter, and radon inside homes ranges from 1-3,000 pCi/Liter, with 0.2 pCi/ Liter being typical.
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