engleski

137Cs And Naturally Occurring Radionuclides In Soil In Croatia

Soil contributes significantly to both external and internal exposure to ionising radiation, via direct emission of gamma radiation and soil-to-plant radionuclide transfer, respectively. Next to primordial radionuclides, soil contains radionuclides dispersed during nuclear weapon testing and Chernobyl and Fukushima accidents, especially 137Cs. This motivated us to carry out a systematic research on the radioactivity of soil in Croatia, with a goal to obtain relevant data about the spread of 137Cs in Croatia, as well as about the primordial radionuclides. We had collected samples of the surface layer of uncultivated soil (0-10 cm) at 138 sites from all over the country and measured them for radionuclide activity concentrations by means of high-resolution gamma-ray spectrometry. This resulted in maps of the radioactivity of Croatian soil, containing data on activity concentrations of representative radionuclides in the environment. We focused on 137Cs, and also mapped 40K and radionuclides from 232Th and 238U decay chains. We found that the concentrations of 137Cs tended to increase with altitude, annual precipitation, and vegetation density. Activity concentrations of 40K were the highest in the Pannonian region. The ratio of the concentrations of 137Cs and K in soil, representing the potential for 137Cs entering food chains via uptake by plants, was the lowest in agriculturally important areas in the east of the Pannonian region. For both 232Th and 238U decay chains, activity concentrations were the highest in the Dinaric region, the lowest in the Pannonian region, and intermediate in the Adriatic region. In particular, relatively high concentrations of 226Ra in the soil of the Dinaric region implied a possibility of an enhanced emanation of its progeny 222Rn into the air. Activity concentrations of 210Pb were additionally elevated in areas with dense vegetation, most probably due to an atmospheric deposition of airborne 210Pb onto the surface of plants and their eventual decomposition on the ground. We used the obtained results on activity concentrations to calculate the related absorbed dose rate as a measure of external exposure to ionising radiation from soil. The sum of the absorbed dose rates for naturally occurring radionuclides and 137Cs showed that the external exposure was generally the highest in the Dinaric region and the Istrian Peninsula.

gamma radiation, high-resolution gamma-ray spectrometry, radioecology, representative radionuclides, 137Cs 40K 210Pb 222Rn 226Ra 232Th 238U

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