TRANSECT SURVEY OF U-238, RA-228, RA-226, PB-210, CS-137 AND K-40 IN AN AGRICULTURAL SOIL NEAR AN EXHAUST VENTILATING SHAFT OF A URANIUM-MINE

To study the effect of exhaust air from a ventilating shaft of a uranium mine on an adjacent field, we determined, along a 200-m transect in 4-m intervals, the activity concentrations of the natural radionuclides U-238, Ra-228, Ra-226, Pb-210, and K-40 as well as the artificial fallout radionuclide Cs-137 in the soil. Data showed that increased activity concentrations, due to the emissions from the mine, are observable for all radionuclides with the exception of K-40 at up to a distance of about 40 m in the field (i.e. 50 m from the air outlet). The largest effect was observed for Pb-210 (an increase by one order of magnitude) and the smallest was for Ra-228. The increased levels of Cs-137 in the soil near the ventilating shaft were not the result of Cs-137 in the rock material of the mine, but this radionuclide arrived in the air of the mine via the main fresh airways and was consequently also found in the exhausted air. The semivariograms of the activity concentrations of the radionuclides at distances where the effect of the emissions from the mine was no longer detectable indicated, for Ra-226, the presence of a range (about 30 m) within which the variance attained its maximum value (approximately the sample variance).