It is part of the natural radioactive decay series starting with uranium-238. It is radioactive with a half-life of 3.8 days, decaying by the emission of alpha particles to polonium, bismuth, and lead in successive steps. Radon is a colorless, odorless gas, a radioactive byproduct of radium.o Back. The decay of radon-222 with emission of an alpha particle is followed within about an hour by a series of four further decays, two of them accompanied by emission of alpha particles and the other two accompanied by other types of radiation.