Radon is one of a number of intermediate radioactive elements formed during the radioactive decay of uranium-238, uranium-235 or thorium-232 isotopes to form stable, non-radioactive isotopes of lead. Radon-222 is the radon isotope of most concern to public health because of its longer half-life (3.8 days).It is one of the decay products of uranium-238. It is formed by the radioactive decay of its immediate âparent isotopeâ radium-226 (1620-year half-life).adon-In its natural state radon is an odorless, colorless, tasteless, radioactive gas. It is the only naturally radioactive gas and is the heaviest of all of the elements that occur as gasses at room temperature and pressure conditions.