Radon - Chapter 5

Abstract

Radon isotopes (222Rn, 220Rn) are noble, naturally occurring radioactive gases. They originate from the alpha decay of radium isotopes (226Ra, 224Ra), which occur in most materials in the environment, i.e. soil, rocks, raw and building materials. Radon is also found in ground and tap water. The two radon isotopes are chemically identical, but they have very different halflives: 3.82 days for radon (222Rn) and 56 seconds for thoron (220Rn). Thus, they behave very differently in the environment. Both isotopes are alpha-emitters; their decay products are polonium, bismuth and lead isotopes. The main source of radon in air (indoor or outdoor) is soil, where radon concentrations are very high and reach tens of Bq/m3. Radon release from soil into the atmosphere depends on radium (226Ra) concentration in soil, soil parameters (porosity, density, humidity) and weather conditions (e.g. air temperature and pressure, wind, precipitation). Outdoor radon concentrations are relatively low and change daily and seasonally. These changes may be used to study the movement of air masses and other climatic conditions. Radon gas enters buildings (homes, workplaces) through cracks, crevices and leaks that occur in foundations and connections between different materials in the building. This is due to temperature and pressure differences between indoors and outdoors. Indoor radon is the most important source of radiation exposure to the public, especially on ground floor. Radon and its decay products represent the main contributor to the effective dose of ionising radiation that people receive. Radon is generally considered as the second cause of increased risk of lung cancer (after smoking). The only way to assess indoor radon concentration is to make measurements. Different methods exist, but the most common one is to use track-etched detectors. Such detectors may be used to perform longterm (e.g. annual) measurements in buildings. The exposure time is important because indoor radon levels change daily and seasonally. Moreover, radon concentration shows a high spatial variation on a local scale, and is strongly connected with geological structure, building characteristics and ventilation habits of occupants. A European map of indoor radon concentration has been prepared and is displayed. It is derived from survey data received from 35 countries participating on a voluntary basis.