Ground level 222Rn measurements indicate average concentrations of about 5–10 Bq/m 3. Diurnal variation in concentration is typically within a range of factor of three to five, but variations of >10 have been reported at some locations. Toward sunset, concentrations increase as the earth cools and atmospheric stability increases. Radon concentrations are usually low in the afternoon. After sunrise, heating causes inversion to burn off, allowing radon to rise by occupying larger volumes. Diurnally, radon concentrations are usually greatest during early morning because atmospheric temperature inversions are more likely to occur. Globally, ground level concentrations are maximal during autumn and early winter, and minimal during spring ( 5). Seasonal and diurnal variations in atmospheric radon concentrations vary with geographic location. Various factors affect 222Rn concentrations in air: (1) ground cover (e.g., paving, buildings, and vegetation) (2) altitude or height above ground (3) soil porosity and grain size (4) temperature (5) atmospheric pressure (6) soil moisture, rainfall, and snow cover (7) atmospheric conditions and (8) season. The corresponding concentrations are lower over oceans and large water tanks because of lower concentrations of 226Ra. Atmospheric concentrations are greater over areas in which soil is rich in 226Ra and 232Th. Some attached particles plate-out on surfaces ( 3).Ĭoncentration of radon and progeny vary considerably due to concentration variations of 226Ra and 232Th present in soil. Attached radon progeny in the air settle to earth by gravity and other processes ( 3). Generally, dustier atmospheres are associated with smaller values of unattached fraction and higher concentrations of radon due to additional radiation emission from dust. A small fraction of radon progeny, typically 0.1 or less, remains unattached and in dynamic equilibrium with attached particles. Most of the activity of radon progeny is associated with particles of small diameter between 0.006 and 0.2 mm, with mean diameter of about 0.025 mm. Radon progeny appears in two forms attached on aerosol particles and unattached. These produce an inhalable radioactive mixture indoors. Radon and progeny interact indoors with aerosol particles via complex physical phenomena. Radon ( 222Rn) is released primarily from soil and approximately 10% of it is released into the atmosphere ( 3, 4).Ģ18Po, 214Pb, and 214Bi are radon’s most significant progeny in terms of radiation dose. For that reason, the term “radon” identifies mainly the 222Rn and this is the convention followed thereafter. 222Rn importance is due to its high abundance of weight (99.27%) compared to the total natural mixture of all radon isotopes. However, most of the radioactivity in the atmosphere at sea level is attributable to 220Rn and, mostly, 222Rn. 220Rn is also known as thoron (Tn) because it is a member of the thorium (4n) series. Both of them are members of the uranium (4n + 2) series. Three are the main naturally occurring isotopes of radon, 222Rn, 220Rn, and 219Rn. In recent years, considerable attention has been paid to radon, which is a natural, colorless, odorless, and tasteless radioactive noble gas. Naturally occurring radioactive materials (NORMs) are present in human radiation environment. Furthermore, radon risk assessment and relevant legislation for the dose delivered by man from radon and its progeny has been also reviewed. Special mention was made to the case of water workers due to inadequate data. Prior research at that topic focused on the exposure on PAEC and the dose delivered by the human body or tissues. Indoor radon and its short-lived progeny either attached on aerosol particles or free, compose an air mixture that carries a significant energy amount. These pathways can be controlled by preventive and corrective actions ( 2). Human activities may create or modify pathways increasing indoor radon concentration compared to outdoor background. Nowadays, there is a concrete evidence that radon and its progeny can cause lung cancer ( 1). Miners in Europe and later in the U.S were the primary target groups surveyed. The initial brilliant period of its use as medicine was followed by a period of intense concern for its health effects. Radon concerns the international scientific community from the early twentieth century, initially as radium emanation and nearly the second half of the century as a significant hazard to human health.
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