Inside the lung, radon daughters emit alpha particles that are absorbed in the nearby lung tissues. Since alpha particles cannot penetrate more than a fraction of a millimeter into the tissue, the damage is confined to the lung tissue in the immediate area. Radon daughters also emit some low intensity beta particles and gamma rays that travel farther through the lung tissue. People exposed to high radon levels have an increased risk of developing lung cancer. The extent of risk depends on the radon concentration in the air and the duration of exposure.
Smoking increases the risk of lung cancer.
Smokers exposed to radon daughters are at greater risk of developing lung cancer. The following figure illustrates the radioactive decay chain that produces radon and radon daughters. Each radioactive isotope decays at a unique rate described as the half-life of that isotope. This is the time required for half the atoms of a radioactive substance to disintegrate. Radon's half-life is 3.8 days.