Background: Radon, an invisible, odorless, heaviest (nine times heavier than air) and radioactive gas is an aberration (the only gas in the long decay chain of heavy metal elements). It is ubiquitously present in dwellings and in the environment. Humans receive the greatest radiation dose in their homes. That's where they spend most time - typically 70%, more for small children. Recent worldwide surveys reveal that an average person receives each year more radiation from radon than from all other natural or man-made sources combined. Over the years, the radiation exposure accumulated at home may exceed the exposure of uranium miners and lead to lung disorders. Therefore it is fundamental and justified to make a quantitative assessment of the radon in dwellings and the environment of work place. In this study, measurement of radon and its progeny levels was carried out in the environment of an oil refinery. Besides, radon and its progeny levels were also measured in the dwellings situated on the refinery premises and the dwellings in the city for comparison.

Materials and Methods: LR-115, Type- II (Kodak Pathe, France), plastic track detectors commonly known as solid state nuclear track detectors (SSNTDs) were used to measure the radon concentration over long integrated times. Alpha particles emitted from radon cause radiation damage tracks, which were subsequently revealed by chemical etching in NaOH. These alpha tracks registered were counted by optical microscope at suitable magnification and converted into radon concentration.

Results: The geometric means (GM) of potential alpha energy concentration (PAEC), Equilibrium Equivalent Concentration of radon (EEC value), annual exposure and annual effective dose in the environment of refinery premises was 10.09 mWL, 93.43 Bq m^-3, 0.41 WLM and 1.61 mSv, in refinery dwellings 12.21 mWL, 112.96 Bq m^-3, 0.50 WLM and 1.94 mSv and in city dwellings 8.24 mWL, 76.23 Bq m^-3, 0.34 WLM and 1.31 mSv respectively.

Conclusion: The dose levels in the refinery premises were found to be marginally below the ICRP recommendations. The radon and its progeny levels were higher in the dwellings of refinery township as compared to the city dwellings. While studying seasonal variation, it was found that the measured values of radon and its progeny levels were higher in winter (November to February) than in summer (May to August). This study showed that the presence of fossil fuels like natural gas, LPG etc. in the environment had resulted into higher levels of radon and its progeny in the refinery dwellings. Iran . J. Radiat. Res., 2004 1(4): 181-186