Natural Radionuclides In Soil Research Articles

Radioactivity concentrations and dose assessment for soil samples around nuclear powerplant IV in Taiwan

Activity concentrations and distributions of natural and man-made radionuclides insoil samples collected around nuclear power plant IV, Taiwan, were investigatedfor five years to assess the environmental radioactivity and characterisation ofradiological hazard prior to commercial operation. The activity concentrationsof radionuclides were determined via gamma-ray spectrometry using anHPGe detector. Data obtained show that the average concentrations of the238U and232Th series,and 40K, were within world median ranges in the UNSCEAR report. The137Cs rangedfrom 2.46 ± 0.55 to 12.13 ± 1.31 Bq kg−1. The terrestrial absorbed dose rate estimated by soil activity and directly measured with athermoluminescence dosemeter (excluding cosmic rays), and the annual effective doses, were 45.63,57.34 nGy h−1 and 57.19 µSv, respectively. Experimental results were compared with international recommended values.Since the soil in this area is an important building material, the mean radiumequivalent activity, external and inhalation hazard indices and the representativelevel index using various models given in the literature for the study area were98.18 Bq kg−1, 0.27, 0.34 and 0.73, respectively, which were below the recommended limits. Analyticalresults demonstrate that no radiological anomaly exists. The baseline data will prove usefuland important in estimating the collective dose near the new nuclear power plant underconstruction in Taiwan.

Comparative study of natural radioactivity concentrations in soil samples from the newly developed Tushki and Giza Regions in Egypt

Natural radioactive materials under certain conditions can reach hazardous radiological levels. So, it was felt necessary to study the natural radioactivity in soil to assess the dose to the population in order to know the health risks and to have a baseline for future changes in the environmental radioactivity due to human activities. The natural radionuclide (238U, 232Th, and 40K) contents were determined for 21 locations over the whole Giza area and Tushki area using gamma-spectrometric analysis. Estimates of the measured radionuclide content have been made for calculating the absorbed dose rate of gamma radiation. The absorbed dose rates resulting from those concentrations ranged from 5.35 ± 0.54 to 53.95 ± 1.61 nGy h−1 for major Giza and 34.21 ± 2.76 to 103355.69 ± 927.14 nGy h−1 for the Tushki area. The radium equivalent (R eq) and the external hazard index (H ex), which resulted from the natural radionuclides in soil, are also calculated and tabulated. The radium equivalent was from 11.47 ± 1.15 to 113.25 ± 3.53 Bq kg−1 and 73.38 ± 5.92 to 223331.64 ± 2008.2 Bq kg−1 for the major Giza and Tushki areas, respectively. The assessment of natural radioactivity reveals a high background radiation in the north Tushki region, which fortunately is distant from the habitant and cultivated regions. The results of this study can be used as a data baseline for preparing a radiological map of the Tushki area, especially at the chosen settlement sites.

Fractionation of natural radionuclides in soils from a uranium mineralized area in the south-west of Spain

A new version of a classical method was applied to study the distribution of natural radionuclides ( 238U, 230Th, and 226Ra) in the soil fractions obtained by a sequential extraction procedure. The potential significance of the fractions obtained with this method was tested on two very similar soils but with very different contents of the three radionuclides, collected in the proximity of a disused uranium mine located in the Extremadura region in the south-west of Spain. The results confirmed that, if only non-residual fractions are considered, the sequential method applied shows a characteristic speciation pattern of these natural radionuclides in this soil matrix, i.e., the distribution of each of the three radionuclides was very similar for the two soil samples.

Environmental radioactivity of the St. Martin's island of Bangladesh

The activity concentration of natural and anthropogenic radionuclides in soil and rock, and in benthic algae, corals and oysters across the St. Martin's island of Bangladesh were investigated together with physicochemical parameters and texture of soil with an aim of evaluating the radioecology of the island. Soil and rock samples from the twenty-two locations of the island, eleven species of benthic algae, six species of corals and two species of oysters were analyzed. The activity of 226 Ra in soil was found in the range of 7.22–103.8, in benthic algae 2.5–9.7, in coral 5.5–10 and in oyster 4.2–11.5 Bq kg-1 . The activity of 232 Th in soil was found in the range of 14.56–216, in benthic algae 1.3–12.6, in coral 4.4–15.6 and in oyster 3.2–8.4 Bq kg-1 ; and the activity of 40 K in soil was in the range of 322–732, in benthic algae 17.1–45.5, in coral 21–146 and in oyster 24–32 Bq kg-1 . The external radiation dose rate due to activity concentration of natural radionuclides in soil was assessed. The activity of anthropogenic 137 Cs was found below detection limit.

Aerial measurements of artificial radionuclides in Germany in case of a nuclear accident

Gamma-ray spectrometric systems carried by helicopters prove to be indispensable for the surveillance of environmental radioactivity. The aerial measurements are an important tool for rapid and large-scale nuclide specific determination of soil contamination after an accidental release of radionuclides from a nuclear facility. Furthermore this technique is also applied for the determination of anomalies of elevated radioactivity of natural radionuclides, the detection of lost radioactive sources and geological mapping. For the measurements the helicopters are equipped with a NaI(Tl)-detector array and a high purity germanium-semiconductor (HPGe) detector. Especially with the HPGe-detector it is possible to clearly identify individual radionuclides. To improve and to guarantee the quality of this method several exercises with different fields of interest have been carried out during the last years. Thereby the main focus is on the improvement of the instrumentation, data handling and data analysis. The results of the airborne radionuclide measurements from the Black Forest which was performed in co-operation with the Swiss National Emergency Operation Centre, are presented here. During this exercise the gamma dose rate, soil contamination due to 137Cs and the specific activities of natural radionuclides in soil were determined.

Conversion factors for external gamma dose derived from natural radionuclides in soils

Field in situ gamma radiation exposure rates and laboratory measured radioactivity contents of 1500 Spanish soils were compared. The main objective was to determine if published theoretically derived conversion factors would yield accurate quantitative activity concentration (Bq kg −1) for the data carried out in different surveys developed by our laboratory during the last ten years. The in situ external gamma dose rate results were compared to laboratory gamma analysis of soils samples gathered from each site, considering the concentrations of seven radionuclides: 40K, 214Pb, 214Bi, 212Bi, 212Pb, 208Tl and 228Ac. The coefficient of correlation found between these variables indicate a good relationship. A discussion of the factors contributing to the uncertainties as well as measurement procedure are also given in this paper.

Environmental pollutant isotope measurements and natural radioactivity assessment for North Tushki area, south western desert, Egypt

Natural radioactive materials under certain conditions can reach hazardous radiological levels. The natural radionuclide ( 238U, 232Th, 40K) contents of rock samples at various locations in the North Tushki area were investigated using gamma-spectrometric analysis. Estimates of the measured radionuclide content have been made for the absorbed dose rate of gamma radiation. The equivalent radium ( R eq) and the external hazard index ( H ex) which resulted from the natural radionuclides in soil are also calculated and tabulated. The studied samples have been collected from various rock exposures in the North Tushki area. The distribution of major oxides, U and Th were studied. It is found that the enrichment and depletion of the major oxides are mainly due to the effect of hydrothermal alteration, which caused mobility of some major oxides, which increases some elements and decreases others. It is important to mention that the study area is far from the development region of the Tushki project and is only a local hazard. Therefore, additional regional studies of the Tushki Project area should be under taken to explore any unexpected environmental hazard due to the high concentration of the radioactive elements, which have been observed at its north boundary.

Distribution of natural and anthropogenic radionuclides in soil and beach sand samples of Kalpakkam (India) using hyper pure germanium (HPGe) gamma ray spectrometry

Pre-operational survey at Kalpakkam coast, indicated elevated gamma background radiation levels in the range of 100–4000 nGy h −1 over the large tracts of the coastal sands due to the presence of pockets of monazite mineral in beach sands. In view of the prevalence of monazite, a systematic gamma spectrometric study of distribution of natural radionuclides in soil and beach sand samples collected from the terrestrial and coastal environment of Kalpakkam was performed and concentrations of primordial radionuclides such as 238U, 232Th and 40K and anthropogenic radionuclide 137Cs were determined. The concentrations of 238U, 232Th and 40K in soil samples were 5–71, 15–776 and 200–854 Bq kg −1 dry, respectively. In beach sand samples, 238U, 232Th and 40K contents varied in the range of 36–258, 352–3872 and 324–405 Bq kg −1 dry, respectively. The total absorbed gamma dose rate in air due to the presence of 238U, 232Th and 40K in Kalpakkam soil samples varied between 24 and 556 nGy h −1 with a mean of 103 nGy h −1. The contribution to the total absorbed gamma dose rate in air in the decreasing order was due to the presence of 232Th (76.4%), followed by 40K (16.9%) and 238U (6.7%) in Kalpakkam soils. However, in beach areas of Kalpakkam, the presence of 232Th in beach sand contributed maximum (94.0%) to the total absorbed gamma dose rate in air followed by 238U (4.7%) and minimum contribution was by 40K (1.3%). 137Cs in Kalpakkam soils ranged from ⩽1.0 to 2.8 Bq kg −1 dry, which was 1–3 order of magnitude less than the concentration of primordial radionuclides in soil.

Releases of natural radionuclides from oil-shale-fired power plants in Estonia

In the vicinity of two large oil-shale-fired power plants in northeast Estonia, depth-dependent activity concentrations of natural radionuclides in soil were determined by gamma spectrometry. In the surface soil considerably higher (or lower) concentrations of 40K, 226Ra and 232Th were found than in deeper soil layers. The observed increase or decrease of the enrichment of radionuclides for different sampling sites was dependent on the relative concentrations of radionuclides in fly-ash and in deep soil layers. The fraction of the radionuclides deposited onto the ground was characterized by a mean 226Ra 232Th activity concentration ratio of 2.2, approximately equal to the one (2.1) found for oil-shale filter ash. The atmospheric deposition rates of fly-ash radionuclides onto the ground were estimated and compared to other relevant published data. The migration of the deposited fly-ash radionuclides into soil was satisfactorily described assuming an exponential depth distribution with the relaxation length value, α −1 = 2.9 ± 0.6 cm, for both 226Ra and 232Th.

Activity variations and concentration factors for natural radionuclides in a “soil-plant-honey” system

The activity of natural radionuclides ( 226Ra, 238U, 235U, 232Th, and 40K) was measured in soils, meadow flowers, and honey from a mountain region in West Serbia. No statistically significant differences in the contents of natural radionuclides in soil or meadow flora from different soils (shale or limestone) were obtained, although concentrations were generally higher in shale soils than in soils mainly composed of limestone rocks. Activity of 226Ra, 238U, and 235U in plants was below minimal detectable concentrations (0.4 - 0.1 Bq/kg). The content of 232Th was higher in meadow flora from shale soils. For 40K, there were no significant differences in its concentrations in plants from different soils. The activity of natural radionuclides in honey did not depend on the type of soil or meadow flora, but the variations for 238U and 235U concentrations were high. Concentration factors for “soil-honey” phase were in the range 0.01-0.07, while for “soil-plant” and “plant-honey” phase they could be calculated only for 232Th and 40K and were in the range 0.1–3.0 and 0.09-0.02, respectively.

Distribution of gamma-emitting natural radionuclides in soils and water around nuclear research establishments, Ile-Ife, Nigeria

The average concentrations of gamma-emitting natural radionuclides 238U, 232Th and 40K in soils from 13 sampling locations around the nuclear research facilities at the Obafemi Awolowo University (OAU), Ile-Ife, have been measured by means of a well-calibrated high resolution gamma-ray spectrometer. Average data on 0–150 mm and 150–300 mm depth distributions in soils have been obtained. The average total specific activity values of 29.1 ± 4.0, 26.5 ± 3.8 and 131.8 ± 32.8 Bq kg −1 for 238U, 232Th and 40K respectively were obtained. The 137Cs concentration in soil samples was below the limit of detection. Average total specific-activity values of 4.2 ± 1.9 and 3.6 ± 2.1 Bq 1 −1 were recorded for 238U and 232Th, respectively, in surface and drinking water.

Natural Radioactivity in Spanish Soils

The program of studies and surveys of natural radiation and radioactivity in Spain organized by our research group at the end of the 1980s included a 4-y national survey to determine the concentrations of natural radionuclides in soil. Results obtained from measurements of soil samples collected nationwide at > 900 sampling sites are reported and discussed in this paper. Correlations between absorbed dose rates in air calculated from natural radionuclide concentrations in soil and terrestrial gamma dose rates measured experimentally outdoors are shown for the different autonomous regions of Spain. Assessment is also made of the dose to the Spanish population from outdoor exposure to terrestrial gamma rays.

Radon Concentration, Absorbed Dose Rate in Air and Concentration of Natural Radionuclides in Soil in the Osaka District of Japan

Radon concentrations in outdoor air at 18 sites in the Osaka district, in the central part of Japan's main island, were measured with electrostatic integrating radon monitors which were developed by Y. Ikebe et al of the Osaka survey centre as part of a nationwide survey of radon indoors and outdoors in Japan conducted by the National Institute of Radiological Science (S. and M. Abe and K. Fujitaka). The mean radon concentration in outdoor air during 2-month periods was measured over a period of a year and a half. In addition, the absorbed dose rate in air and the concentration of natural radionuclides in soil were measured at 40 sites in Osaka Prefecture which is located in the central part of the Osaka district using thermoluminescence dosemeters and with gamma ray spectrometry, respectively. Radon concentration in outdoor air showed a seasonal pattern, reaching its maximum during the winter and its minimum during the summer, but this variation was not significant at the coastal sites. It was concluded that this variation is correlated with a seasonal wind which blows from the continental interior to the ocean in winter and in the opposite direction in summer, as well as the geographical factors. Radon concentration in outdoor air in the Osaka district ranged from 0.6 to 17.9 Bq.m-3 and mean annual radon concentration in outdoor air at the 18 sites ranged from 2.7 to 6.9 Bq.m-3. It was discovered that radon concentration in outdoor air decreased with wind speed in both winter and summer. The absorbed dose rate in air ranged from 66 to 114 nGy.h-1, and the concentration of 226Ra in soil ranged from 20 to 60 Bq.kg-1 respectively.

Radon Concentration, Absorbed Dose Rate in Air and Concentration of Natural Radionuclides in Soil in the Osaka District of Japan

Radon Concentration, Absorbed Dose Rate in Air and Concentration of Natural Radionuclides in Soil in the Osaka District of Japan

Radioactive contamination of soils in lower Saxony, Germany, after the Chernobyl accident.

The horizontal and spatial distribution of artificial and natural radionuclides in soils, and the vertical migration velocity of 0.8-2.0 cm per annum for caesium were examined in order to determine whether caesium is still in the root zone of major plants and, therefore, part of the food-chain. The vertical distribution patterns of caesium are dependent on the different physico-chemical soil properties. The soil samples were analysed with a pure Ge detector. In south-eastern Lower Saxony, the maximum gamma-activity for 137Cs of 33.3 kBq m-2 was found in a depth range of 0-20 cm (January 1, 1989). This was correlated with areas that had received heavy rainfall on May 4, 1986. On January 1, 1989 approximately 60% of the Chernobyl caesium was still in the top 0-2 cm of the topsoil.

A Study on Natural Absorbed Dose Rate in Air(Using TLDs) and Concentration of Natural Radionuclides in Soil in All Area of the Osaka Pref.

Absorbed dose rates in air at 40 sites throughout Osaka Pref. were measured by TLDs and a relationship between the dose rates and the rates estimated from concentrations of natural radionuclides in the surface soils collected at the sites was studied. The highest and lowest values of air absorbed dose rates obtained in Osaka Pref. were 114.1±1.0, 66.3±2.3nGy/h, respectively, and the former value was obtained at granite zone and the latter at andesite zone. It was found that soil particles smaller than 10 mesh contribute to the dose rates more significantly than those larger than 10 mesh. We found a fairly good correlation between the dose rates and the concentrations of 40K in the surface soils at the sites.

Natural radionuclides in the soils of a small agricultural basin in the Canadian prairies and their association with topography, soil properties and erosion

Summary Samples taken from the A and B horizons of the soil at 160 sites in a small (178 ha) cultivated drainage basin in central Saskatchewan were analysed by gamma spectroscopy to determine the concentration of a number of natural radionuclides in the soil. The concentration of 40K, the 238U daughters 226Ra,214Pb, and 214Bi, and the 232Th daughters228Ac, 212Bi, and 208Tl was determined. A variety of soil properties and topographic variables were measured at each sampling site. Earlier studies in the basin provided net soil erosion estimates (i.e. net loss or gain) for each site. The association of isotope activities with topography, soil properties and net erosion was evaluated. Mean isotope activities for the basin were very close to mean values reported earlier for native soils in southern Saskatchewan. Differences in isotope concentrations between the A and B horizons of the soils were related to differences in the degree to which the different isotopes are taken up by plants. Isotope concentrations in the surface soil were inversely correlated with soil particle size. Variation in isotope activities within the basin appeared to be linked to soil redistribution by erosion, but in a complex manner which reflects size sorting of soil particles by erosion processes. Erosion processes seem to be at least as important as leaching processes in determining the spatial distribution of natural radionuclides in the surface soils of the study area.

Root absorption of 222Rn and its transfer into above-ground plant organs.

Experimental data are given on the content of genetically related pairs of radionuclides (226Ra and 222Rn; 224Ra and 220Rn) in soils and the above-ground phytomass of plants growing on plots with differing genesis of the higher concentrations of natural radionuclides in soils. Methods for determining gaseous radionuclides in the above-ground phytomass are described. Different transport routes of 222Rn and 220Rn into above-ground plant organs are considered. The noted absence of balance between 222Rn and 226Ra in plants as well as higher 222Rn/226Ra ratios in the above-ground phytomass as compared to that of the root-containing soil layer (25- to 185-fold) appears to be accounted for by the root pathway of 222Rn uptake and transport of this radionuclide to above-ground plants organs. The existence of the root pathway for 222Rn uptake is proved by direct observations of daily radionuclide movement with bleeding sap in experiments on pumpkins. For the short-lived Rn isotopes, 220Rn and 219Rn, the root pathway of uptake and transport to the above-ground phytomass is less probable, and this causes a notable redistribution of gaseous radionuclides during their movement along the soil-plant route.