Vertical Distribution Of Natural Radionuclides Research Articles

The application of 137 Cs and 210 Pb ex methods in soil erosion research of Titel loess plateau, Vojvodina, Northern Serbia

Abstract Soil erosion is one of the largest global problems of environmental protection and sustainable development, causing serious land degradation and environmental deterioration. The need for fast and accurate soil rate assessment of erosion and deposition favors the application of alternative methods based on the radionuclide measurement technique contrary to long-term conventional methods. In this paper, we used gamma spectrometry measurements of 137Cs and unsupported 210Pb ex in order to quantify the erosion on the Titel Loess Plateau near the Tisa (Tisza) River in the Vojvodina province of Serbia. Along the slope of the study area and in the immediate vicinity eight representative soil depth profiles were taken and the radioactivity content in 1 cm thick soil layers was analyzed. Soil erosion rates were estimated according to the profile distribution model and the diffusion and migration model for undisturbed soil. The net soil erosion rates, estimated by 137Cs method range from −2.3 t ha−1 yr−1 to −2.7 t ha−1 yr−1, related to the used conversion model which is comparable to published results of similar studies of soil erosion in the region. Vertical distribution of natural radionuclides in soil profiles was also discussed and compared with the profile distribution of unsupported 210Pb ex measurements. The use of diffusion and migration model to convert the results of 210Pb ex activities to soil redistribution rates indicates a slightly higher net erosion of −3.7 t ha−1 yr−1 with 98% of the sediment delivery ratio.

Vertical distribution and radiological risk assessment of 137Cs and natural radionuclides in soil samples

The aims of this study were to investigate the vertical distributions of natural radionuclides 232Th, 226Ra and 40K as well as anthropogenic radionuclide 137Cs in soil samples and to analyze the correlation among the radioactivity of these radionuclides and the physiochemical characteristics of soil samples namely pH, grain size, carbonate content and organic matter. Risk assessment of the radiological hazard has also been estimated. Forty-four soil samples were collected from eleven locations in Qatar at four depth levels from 0 to 16 cm. The average concentrations of 232Th, 226Ra, 40K and 137Cs in the soil depth of 16 cm were 10, 17, 201 and 4 Bq/kg, respectively, which were within the reported world mean. The external absorbed gamma dose rate, the annual effective dose, the mean radium equivalent activity, the external hazard index and the lifetime cancer risk were 22 nGy/h, 0.027 mSv/y, 47 Bq/kg, 0.125 and 0.096 × 10−3, respectively. These values were far below the minimum recommended international values. The level of radioactivity concentrations in the soil was affected by the physiochemical characteristics of the soil. The positive correlation with highest R2 value was found among the radioactivity concentrations of 232Th and 40K and the soil clay content. Total organic carbon was also positively correlated for 226Ra and 137Cs activity concentrations, whereas, carbonate content was negatively correlated with the radioactivity concentrations of 232Th and 40K. As far as soil moisture content is concerned, the positive correlation with highest R2 value was obtained for 226Ra activity concentrations.

Natural radionuclides in soil profiles surrounding the largest coal-fired power plant in Serbia

This study evaluates the influence of the largest Serbian coal-fired power plant on radionuclide concentrations in soil profiles up to 50 cm in depth. Thirty soil profiles were sampled from the plant surroundings (up to 10 km distance) and analyzed using standard methods for soil physicochemical properties and gamma ray spectrometry for specific activities of natural radionuclides (40K, 226Ra and 232Th). Spatial and vertical distribution of radionuclides was determined and analyzed to show the relations between the specific activities in the soil and soil properties and the most influential factors of natural radionuclide variability were identified. The radiological indices for surface soil were calculated and radiological risk assessment was performed. The measured specific activities were similar to values of background levels for Serbia. The sampling depth did not show any significant influence on specific activities of natural radionuclides. The strongest predictor of specific activities of the investigated radionuclides was soil granulometry. All parameters of radiological risk assessment were below the recommended values and adopted limits. It appears that the coal-fired power plant does not have a significant impact on the spatial and vertical distribution of natural radionuclides in the area of interest, but technologically enhanced natural radioactivity as a consequence of the plant operations was identified within the first 1.5 km from the power plant.

Estimates of tidal mixing in the Indonesian archipelago from multidisciplinary INDOMIX in-situ data

The Indonesian Mixing program (INDOMIX) was designed to quantify the very strong mixing that transforms Pacific waters into isohaline Indonesian Waters in the Indonesian archipelago. The turbulent dissipation rates and associated mixing were estimated and analyzed using a multidisciplinary approach that combines physical and geochemical in-situ observations: (1) direct measurements of the dissipation using a microstructure profiler, (2) use of density-based fine-scale methods applied to CTD and XCTD data, and (3) study of the vertical distribution of natural radionuclides (radium isotopes and actinium-227). Data were collected at five contrasting stations within the Indonesian archipelago, found above energetic straits or in relatively quiescent large basins.Strong instabilities, inversions of the density profiles and a very strong water mass transformation were observed. A wide range of dissipation values were obtained (between [10−10, 10−4]Wkg−1) with spots of higher dissipation in the ocean interior correlated with a strong internal tide signal. Both the fine-scale and micro-scale methods allow us to identify very strong energy dissipation levels above the straits, ranging between [10−7, 10−4]Wkg−1, in contrast to lower values at stations further away from the generation sites. The dissipation for the station located in the center of the Halmahera Sea ([10−9, 10−8]Wkg−1) is stronger than for the Banda station ([10−11, 10−10]Wkg−1), which is even further away from the generation sites. The three approaches agree relatively well and provide vertical eddy diffusivities values ranging between 5×10−4 and 5×10−1m2s−1, except in the Banda Sea where values are similar to the ones found in the open ocean (10−6m2s−1). CTD and XCTD profilers (deployed between stations) give estimates of dissipation all along the transit. It is found that enhanced mixing occurs preferentially above rough topography, such as in the Ombai Strait, the Halmahera Sea’s northern entrance, the Buru strait and Sumba strait.Finestructure parameters are very sensitive to depth and dissipation, which differs between stations. We recommend more systematic microstructure measurement in order to tune these parameters. Surface mixing, at the base of the mixed layer is found to be very strong with values between [10−4, 10−3m2s−1]. These results confirm the modeling studies that suggest the occurrence of intensified subsurface mixing which cools the sea surface temperatures and thus strongly affects the mean and variability of the tropical climate. We conclude, therefore, that climate models need to take into account this intensified ocean mixing to properly represent the mean state of the atmosphere and its climate variability.

Assessment of the vertical distribution of natural radionuclides in a mineralized uranium area in south-west Spain

Low-level alpha spectrometry techniques using semiconductor detectors (PIPS) and liquid scintillation (LKB Quantulus 1220™) were used to determine the activity concentration of 238U, 234U, 230Th, 226Ra, 232Th, and 210Pb in soil samples. The soils were collected from an old disused uranium mine located in southwest Spain. The soils were sampled from areas with different levels of influence from the installation and hence had different levels of contamination. The vertical profiles of the soils (down to 40cm depth) were studied in order to evaluate the vertical distribution of the natural radionuclides. To determine the origin of these natural radionuclides the Enrichment Factor was used. Also, study of the activity ratios between radionuclides belonging to the same radioactive series allowed us to assess the different types of behaviors of the radionuclides involved. The vertical profiles for the radionuclide members of the 238U series were different at each sampling point, depending on the level of influence of the installation. However, the profiles of each point were similar for the long-lived radionuclides of the 238U series (238U, 234U, 230Th, and 226Ra). Moreover, a major imbalance was observed between 210Pb and 226Ra in the surface layer, due to 222Rn exhalation and the subsequent surface deposition of 210Pb.

Vertical distribution of natural radionuclides in soil: Assessment of external exposure of population in cultivated and undisturbed areas

In the present work, naturally occurring radionuclides 238U, 232Th and 40K were measured in soil samples from the cultivated and undisturbed areas in Rudovci, municipality of Lazarevac, Serbia. There were three profiles, each profile divided into four horizons, giving the twelve soil samples. The specific activity of 238U, 232Th and 40K in soil and sediment samples was determined by gamma spectrometry using the HPGe semiconductor detector. Obtained activity concentrations ranged from 28.0 to 44.0Bq/kg for 238U, from 59.4 to 71.4Bq/kg for 232Th and from 335.0 to 517.0Bq/kg for 40K. The evaluation of the radiological hazards originated from 238U, 232Th and 40K in the samples, the absorbed dose rate (D) and the annual effective dose rate (E), calculated in accordance with the UNSCEAR 2000 report, are presented in this paper.

Vertical distribution of natural radionuclides in soils

Low-level alpha spectrometry techniques using semiconductor detectors (PIPS) and liquid scintillation counters (LKB Quantulus 1220™) were used in order to determine the activity concentration of 238U, 232Th, 234U, 230Th, 226Ra, and 210Pb in soil samples. The soils were collected from an old disused uranium mine located in southwest Spain. The soils were selected with different levels of influence from the installation, in such a way that they had different levels of radioactive contamination. The vertical profiles in the soils (down to 40 cm depth) were studied in order to evaluate the vertical distribution of the natural radionuclides. The possible contamination of subsurface waters depends strongly on vertical migration, and the transfer to plants (herbs, shrubs, and trees) also will depend on the distribution of the radionuclides in the root zone. The study of the activity ratios between radionuclides belonging to the same series allowed us to assess the differing behaviour of the radionuclides involved. The vertical profiles for these radionuclides were different at each sampling point, showing the local impact of the installation. However, the profiles per point were similar for the long-lived radionuclides of the 238TJ series (238U, 234U, 230Th, and 226Ra). Also, a major disequilibrium was observed between 210Pb and 226Ra in the surface layer, due to 222Rn emanation and subsequent surface deposition of 210Pb.

Distribution of natural radioactivity in sediment cores from Amvrakikos Gulf (Western Greece) as a part of IAEA's campaign in the Adriatic and Ionian Seas

The vertical distribution of natural radionuclides ((232)Th decay, (238)U decay, (40)K and (210)Pb) was assessed in sediment cores collected from the Amvrakikos Gulf, (Ionian Sea, Western Greece). Two collection stations were selected, the first at the western part of the Gulf near Preveza Strait (13A station) and the other near the centre of the Gulf (13B station). Activity concentrations were measured by means of gamma-ray spectrometry using high-purity germanium (HPGe) detectors installed at two national laboratories. The activity concentration of (226)Ra was found in a range from 10 to 20 Bq kg(-1), while the activity concentration of (222)Rn daughters ((214)Pb, (214)Bi) ranged from 6 to 20 Bq kg(-1). The activity concentration of (228)Ac varied from 20 to 28 Bq kg(-1), while (220)Rn daughters ((212)Pb, (208)Tl) from 7 to 35 Bq kg(-1). As concerns (40)K and (210)Pb, their activities varied from 400 to 830 Bq kg(-1) and from 11 to 360 Bq kg(-1), respectively. Also, the data of (210)Pb were utilised in the calculations of the sedimentation rate along the sediment cores. Both locations were characterised by a consistent pattern with the average rates of 0.55 ± 0.02 and 0.32 ± 0.02 cm y(-1), corresponding to 13A and 13B stations, respectively. Finally, the measurements constituted the basis of the first reported database concerning the radiological condition of the Gulf and which can be reclaimed as reference values in future monitoring studies.