36
Radon [Rn, 88]
36.1 INTRODUCTION
Radon (Rn) is a radioactive, colorless, and odorless noble gas of group 18 in the periodic table of elements, occurring naturally, as an indirect decay product of the U and
Th chains. Its concentration in surface layer of the Earth’s crust is about 2 mg/kg.
The gamma rays are produced by radon and the first short-lived elements of its decay
chain are isotopes of Po, Pb, and Bi. It may form some compounds, such as RnF 2 and
RnCl 4 . It is associated with a few minerals, mainly uranite, UO 2 , and zircon, ZrSiO 4 .
It has about 30 isotopes and the most stable is 222 Rn, with a half-life of 3.8 days. It is
often the important contributor to an individual’s local background radiations.
36.2 ENVIRONMENT
Radon is one of the densest substances that remain as gas under normal conditions, and as easily inhaled, it is considered a health hazard due to its radioactivity.
It exhausts naturally from the ground, particularly in certain regions, especially, but
not only, in regions with granitic soils. It may also be emitted directly from granites.
Also soils derived from gneisses, schists, and limestones may contain its elevated
amounts. Radon is easily released from these soils to the atmosphere, which is estimated, on a global scale, to be 2400 mCi (90 TBq) annually.
Despite short lifetime of 222 Rn, its gas from natural sources can accumulate to
far higher than normal concentrations in buildings, especially in low areas, such as
basements. In some locations, U tailing materials have been used for landfills and
were subsequently built on, resulting in possible increased exposure to Rn. In some
buildings, Rn concentration may be >200 Bq/m 3 (Talbot et al. vide Kabata-Pendias
and Pendias 1999).
Owing to its very short half-life (4 days for 222 Rn), its concentration in air de creases
very quickly, when the distance from its production areas increases. Its concentration ranges from <10  Bq/m 3 to over 100  Bq/m 3 in some European countries and
varies greatly with seasons and atmospheric conditions.
Radon may migrate freely through faults and fragmented soils, and may accumulate in caves or water. Thus, its higher concentrations can be found in some springwaters and hot springs. Water of hot springs in health spa of Poland contains 222 Rn
within the range of 0.9–193.1 Bq/L, at an average of 14.5 Bq/L (Pachocki et al. 2009).
The major Rn exposure is through inhalation, with background levels in ambient
air of approximately 0.1–0.4 pCi/L. Its higher levels are in indoor locations, where
its mean level is estimated to be 1.6 pCi/L. In some family homes, it may exceed
8 pCi/L. It is a known pollutant emitted from geothermal power stations, because
it is present in the material pumped from deep underground. Its content may also
be elevated in the air of coal mines. However, its environmental impact is minimal.
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