Radon gas (Rn-222) is a naturally occuring, colorless, odorless, chemically inert noble gas produced by the natural decay of uranium in soil, rock and groundwater. As an inert gas, radon moves freely through pore spaces and fractures, it can travel significant distances from where it is formed. Because it neither emits color nor odor and reacts little with surrounding materials, radon can accumulate undetected in enclosed structures.
When radon gas decays, it emits a series of short lived isotopes - polonium-218, lead-214, bismuth-214, and polonium-214. Unlike radon gas, these decay products are chemically active particulates that tend to cling to airborne dust and aerosols. Although you cannot see or smell them, if inhaled they can lodge in your lung tissue and deliver concentrated burst of alpha radiation.
Uranium is ubiquitously found in the earth's crust, when it decays it emits radium. Radium then emits radon gas as its decay products. These isotopes are found worldwide, however concentrations vary by geology and soil permeability.
Most radon emanates upward through soil and rock into buildings via foundation cracks, gaps around pipes, crawlspaces and other openings in the building envelope. Once indoors, radon can accumulate to concentrations many times higher than outdoor levels. It’s measured in picocuries per liter (pCi/L) or becquerels per cubic meter (Bq/m³) and, because it’s invisible and odorless, testing is the only way to know your home’s radon concentration.
