Radon is a noble gas element denoted by the atomic symbol, Rn. It has an atomic number of 86 and the atomic weight of its most stable isotope is 222. It is a colorless, odorless gas that emits radioactivity.

Radon is the heaviest element in the family of inert, or noble, gases. The term radon refers loosely to the gas itself, which is emitted from the decay of the element radium, and to its twenty-five isotopes, all of which are also highly radioactive. Normally a colorless gas, radon can be condensed into a fluorescent liquid. Although radon's parent radium is extremely rare (it decays very rapidly), radon and its natural isotopes are also produced from uranium and thorium, which are much more prevalent in minerals, ores, and rocks. Uranium miners must take special precautions to avoid radioactive poisoning by radon. The gas can also migrate upward into the soil--the mechanism...