Anomalous behaviour of uranium isotopes in backwater sediments of Zuari river

The surface leaching of the labile component of uranium has been carried out in estuarine sediments of Zuari river in Goa. The measurements of alpha activities of²³⁸U,²³⁵U and²³⁴U in the leachates indicated a remarkable anomaly between the activities of²³⁸U and²³⁴U. The activity ratios of²³⁴U/²³⁸U in these leachates have been found to be in the range of 1.10 to 1.14. However, the activity ratios of²³⁵U/²³⁸U have been found to be 0.045 which is close to that in natural uranium. It has also been observed that the anomaly between²³⁸U and²³⁴U exists only on the surface organic layers of the backwater sediments of the Zuari river.     

Studies on the geochemical behaviour of uranium isotopes in coastal environment of the east coast of india

Samples of coastal marine sediments of the East Coast of India were leached with a saturated solution of ammonium carbonate for the extraction of uranium from the sediment particle surface without attacking the mineral core of the particles. All the sediment samples were found to exhibit a²³⁴U/²³⁸U activity ratio in the range of 1.07 to 1.14. On removal of surface organic matter, the²³⁴U/²³⁸U activity ratio is close to 1.00, indicating that the anomaly between²³⁸U and²³⁴U exists only on the labile surface layer. However, no such variations are observed in²³⁵U/²³⁸U activity ratios. These ratios are close to 0.045 which is the same as that of natural uranium.     

The transfer of uranium from sediment to water along Jucar River, Spain

The effect of sediment size, pH, temperature and conductivity on the transfer of uranium from sediment to water has been studied. The uranium concentration and the²³⁴U/²³⁸U,²³⁵U/²³⁸U activity ratios were measured in water, sediments and suspended matter sampled from Jucar River, using low level alpha-spectrometry. Distribution factors were obtained from these measurements. A more detailed sampling was done in the neighbourhood of the Cofrentes Nuclear Plant (Valencia, Spain). Total uranium activity,²³⁴U/²³⁸U activity ratio and distribution factors for²³⁴U and²³⁸U were found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes.     

Determination of234U/238U and235U/238U ratios from commercially available uranium compounds by α-spectrometry

The²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios from uranium compounds by -spectrometry technique have been obtained. Ten commercially available uranium reagents were analyzed. The well-separated peaks corresponding to uranium isotopes are evident, providing an energy spectrum of the -particles of uranium isotopes. It was found that some commerical uranium salts were depleted in²³⁴U and²³⁵U.     

Determination of uranium isotopes in environmental samples

The determination of isotopes of uranium by alpha spectrometry in different environmental components (sediments, soil, water, plants and phosphogypsum) is presented and discussed in this paper. The alpha spectrometry is a very convenient and good technique for activity concentration of natural uranium isotopes (²³⁴U, ²³⁵U, ²³⁸U) in environmental samples and provides the most accurate determination of isotopic activity ratios between ²³⁴U and ²³⁸U. The analysis were provided information about possible sources of high concentrations of uranium in the examined sites determined by anthropogenic sources. The calculation of values ²³⁴U/²³⁸U in all analyzed samples was applied to identifying natural or anthropogenic uranium origin. Activity concentration of uranium isotopes in analyzed environmental samples shows that measurement of uranium levels is of great importance for environmental and safety assessment especially in contaminated areas (phosphogypsum waste heap).     

Anomalous behaviours of protactinium in the acid-leaching experiments on pitchblende

A series of leaching experiments with H₂O, HCl, HNO₂ and HF were carried out on a sample of pitchblende from Africa. Anomalously high²³¹Pa/²³⁵U ratios, which were not accompanied by similar enhancements of²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios, were observed in some uranium fractions. The observed²³¹Pa/²³⁵U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects.     

Concentration, distribution and characteristics of depleted uranium (DU) in the Kosovo ecosystem: A comparison with the uranium behavior in the environment uncontaminated by DU

The smear samples of the penetrator were analyzed for the determination of the uranium composition. The obtained relative composition (m/m) of uranium isotopes in all the smear samples is in the range of 99.76-99.78% for ²³⁸U, 0.000659-0.000696% for ²³⁴U, 0.213-0.234% for ²³⁵U, and 0.00274-0.00328% for ²³⁶U, showing characteristics of depleted uranium (DU). The uranium concentrations in Kosovo soil and water samples as well as biological samples were investigated. It was found that the uranium concentrations in the Kosovo soil samples are in the range of 11.3-2.26·10⁵ Bq·kg^-1 for ²³⁸U, 10.3-3.01·10⁴ Bq·kg^-1 for ²³⁴U, 0.60-3251 Bq·kg^-1 for ²³⁵U, and ￡0.019-1309 Bq·kg^-1 for ²³⁶U. The obtained activity ratios are in the range of 0.112-1.086 for ²³⁴U/²³⁸U, 0.0123-0.1144 for ²³⁵U/²³⁸U, and 0-0.0078 for ²³⁶U/²³⁸U, indicating the presence of DU in about 77% of the surface soil samples. At a specific site, the DU inventory in the surface soil is about 140 mg·cm^-2, which is 1.68·10⁶ times higher as the estimated mean DU dispersion rate in the region. The uranium concentrations in Kosovo lichen, mushroom, bark, etc., are in the range of 1.97-4.06·10⁴ Bq·kg^-1 for ²³⁸U, 0.48-5158 Bq·kg^-1 for ²³⁴U, 0.032-617 Bq·kg^-1 for ²³⁵U, and ￡0.019-235 Bq·kg^-1 for ²³⁶U with mean activity ratios of 0.325±0.0223 for ²³⁴U/²³⁸U, of 0.0238±0.0122 for ²³⁵U/²³⁸U, and 0.0034±0.0028 for +U/²³⁸U, indicating the presence of DU in the entire sample. On the contrary, the uranium concentrations in Kosovo water samples are low, compared with the water samples collected in central Italy, indicating the presence of negligible amount of DU. The uranium isotopes in Kosovo waters do not constitute a risk of health at the present time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the geochemical behaviour of uranium isotopes in Tuwa springs and Khari river sediments

High activities of radium were observed in the spring waters of Tuwa in Panchamahal district of Gujarat state. These determinations have led to further studies on geochemical behaviour of uranium in the surface sediments of this region. Labile uranium from the surface of the sediment particles is leached with saturated solution of ammonium carbonate. Uranium is chemically separated from the leachates by cellulose column chromatography. Unusually high activity ratios of²³⁴U/²³⁸U in the range of 2.3 to 2.77 were observed on the surface of the particles. The core of the particles exhibited a ratio of 1.00 indicating soluble²³⁴U fraction has migrated.     

Determination of U isotope ratios in sediments using ICP-QMS after sample cleanup with anion-exchange and extraction chromatography

The determination of uranium is important for environmental radioactivity monitoring, which investigates the releases of uranium from nuclear facilities and of naturally occurring radioactive materials by the coal, oil, natural gas, mineral, ore refining and phosphate fertilizer industries, and it is also important for studies on the biogeochemical behavior of uranium in the environment. In this paper, we describe a quadrupole ICP-MS (ICP-QMS)-based analytical procedure for the accurate determination of U isotope ratios (²³⁵U/²³⁸U atom ratio and ²³⁴U/²³⁸U activity ratio) in sediment samples. A two-stage sample cleanup using anion-exchange and TEVA extraction chromatography was employed in order to obtain accurate and precise ²³⁴U/²³⁸U activity ratios. The factors that affect the accuracy and precision of U isotope ratio analysis, such as detector dead time, abundance sensitivity, dwell time and mass bias were carefully evaluated and corrected. With natural U, a precision lower than 0.5% R.S.D. for ²³⁵U/²³⁸U atom ratio and lower than 2.0% R.S.D. for ²³⁴U/²³⁸U activity ratio was obtained with less than 90 ng uranium. The developed analytical method was validated using an ocean sediment reference material and applied to an investigation into the uranium isotopic compositions in a sediment core in a brackish lake in the vicinity of U-related nuclear facilities in Japan.     

Study of uranium isotopic composition in groundwater and deviation from secular equilibrium condition

Uranium concentration in groundwater reflect both redox conditions and uranium content in host rock. In the present study an attempt has been made to study the uranium concentration and activity ratios of uranium isotopes to present the geochemical conditions of the groundwater in Malwa region of Punjab state, India and the reason for high uranium levels and variation of activity ratios from secular equilibrium conditions. Uranium concentration in groundwater samples was found to be in the range of 13.9 ± 1.2 to 172.8 ± 12.3 μg/l with an average value of 72.9 μg/l which is higher than the national and international guideline values. On the basis of uranium concentration, the groundwater of the study region may be classified as oxidized aquifer on normal uranium content strata (20 %) or oxidized aquifer on enhanced uranium content strata (80 %). The ²³⁸U, ²³⁵U and ²³⁴U isotopic concentration in groundwater samples was found to be in the range of 89.2–1534.5, 4.4–68.5, and 76.4–1386.2 mBq/l, respectively. Activity ratios of ²³⁴U/²³⁸U varies from 0.94 to 1.85 with a mean value of 1.11 which is close to unity that shows secular equilibrium condition. High value of ²³⁴U isotope than ²³⁸U may be due to alpha recoil phenomenon. The plot of AR of ²³⁴U/²³⁸U against the total uranium content in log scale reveals that the groundwaters of the study region either belongs to stable accumulation or normal oxidized aquifer.     

222Rn content and234U/238U activity ratio in groundwaters

Geochemical radioanalytical studies of groundwater were performed in the valleys of Villa de Reyes and San Luis Potosi (Mexico). The experiments were designed to measure radon and uranium content and²³⁴U/²³⁸U activity ratio in groundwater samples taken from wells in these sites and at the Nuclear Center of Salazar, Mexico.²²²Rn content varied depending on the sample source, reaching a maximum value of 235 pCi/l; uranium concentration results were less than 1 g/1 and²³⁴U/²³⁸U activity ratios were close to equilibrium.     

Alpha-emitting radionuclide contents in food samples as related to the Chernobyl accident

As a preliminary survey to establish intake of -emitting nuclides, in particular^239,240Pu, from a daily diet for inhabitants living near the Chernobyl reactor site, some kinds of food samples including total diet samples were collected in the Chernobyl (Ukraine) area and in the Ibaraki prefecture (Japan). Plutonium-239 and 240 were determined together with naturally occurring -emitters²²⁶Ra and U isotopes (²³⁴U,²³⁵U and²³⁸U) by -spectrometry after chemical separation. In most of the samples studied,^239,240Pu was less than the detectable amount, but in some mushrooms from the Ukraine it was found to be 41.6 mBq kg^–1 (wet mass) with a high activity ratio(0.58±0.08) of²³⁸Pu/^239,240Pu, indicating that nearly 100% of the^239,240Pu was attributable to the accident. Concentrations of²²⁶Ra and²³⁸U varied largely, depending on the samples. The measured activity ratios of²³⁵U/²³⁸U for some samples showed the isotopic composition of natural uranium.     

Simultaneous determination of uranium and plutonium isotopes in soils by means of single alpha-spectrometry

A simple, rapid and reliable method was developed for the simultaneous determination of uranium and plutonium isotopes by alpha-spectrometry using a single source. A new uranium tracer²³⁰U was applied as well as the²³⁶Pu tracer to determine overall yields of uranium and plutonium isotopes throughout the entire procedure employed. The analytical procedure consists of sample leaching with 8N HNO₃ solution, purification by solvent extraction, simultaneous electrodeposition of U and Pu, and subsequent alpha-spectrometry with a silicon detector. In the solvent extraction using TOA/xylene from 8N HNO₃ solution, the preferential extractability of Pu rather than U permits to purify simultaneously the trace amounts of Pu and the macro amounts of U, as in the case of ordinary soil samples, resulting in favourable peak heights for both isotopes. From a single alpha-spectrum, the determinations of²³⁸U,²³⁴U (and their ratio of²³⁴U/²³⁸U),^239+240Pu, and²³⁸Pu contents were conveniently carried out after correcting the overall yields obtained from²³⁰U and²³⁶Pu activities in the same spectrum. This analytical method was satisfactorily applied to the determination of U and Pu isotope contents in some soils.     

<Superscript>234</Superscript>U/<Superscript>238</Superscript>U and <Superscript>235</Superscript>U/<Superscript>238</Superscript>U ratios in domestic water from the environs of Obuasi mine in Ghana

Activity concentrations of ²³⁸U, ²³⁵U and ²³⁴U were determined in different sources of drinking water at the Obuasi gold mines and its surrounding areas in Ghana. Water samples collected from the mines and its surrounding areas were analyzed using direct gamma-ray spectrometry and neutron activation analysis. The ²³⁴U/²³⁸U and ²³⁵U/²³⁸U ratios were calculated and the mean values range from 1.27 to 1.38 and from 0.044 to 0.045 respectively. The average ²³⁴U/²³⁸U ratio was from 1.27 for groundwater to 1.38 for treated water, demonstrating the lack of equilibrium. The average ²³⁵U/²³⁸U activity ratio is 0.045, indicating that only natural uranium was detected in the samples investigated.     

Natural radionuclides and 137Cs activity concentration in the bottom sediment cores from Kuwait Bay

Summary The activity concentration of natural radionuclides and ¹³⁷Cs in the bottom sediments cores from Kuwait Bay have been determined by γ-ray spectrometry. Particular attention was devoted to the exact determination of two uranium isotopes: ²³⁵U and ²³⁸U in order to find any presence of depleted uranium dispersed during the 1991 Gulf War. The calculated ²³⁸U/²³⁵U activity ratios for all the surface (15 cm) as well as the core profile (up to 70 cm in depth) samples were within the limit of one standard deviation close to the value of 21.5 for natural uranium. Simultaneous instrumental determination of the unsupported ²¹⁰Pb and ²²⁶Ra in a few sediment core profiles was used for quantification of sediment accumulation rates. The calculated sedimentation rates (for the constant atmospheric ²¹⁰Pb flux rate - CRS model) ranged from 0.2 to 0.6 cm ^. y^-1 and were close to the data calculated by the Weibull distribution of ¹³⁷Cs in undisturbed sediment cores.     

A comparative study of234U/238U alpha-activity ratios determined by alpha-spectrometry and calculated from mass spectrometric data

²³⁴U/²³⁸U α-activity ratios determined by α-spectrometry (AS) and those calculated from the atom ratio data using the half-life values are compared in some of the isotopic reference materials of uranium and a few other uranium samples. For α-spectrometry, electrodeposited sources were prepared and a large area passivated ion implanted (IPE) detector (450 mm²) was used for recording the α-spectra. The isotopic composition of U was determined by thermal ionisation mass spectrometry (TIMS) and the recommended half-life values of²³⁴U and²³⁸U were used to calculate the α-activity ratio. It is observed that²³⁴U/²³⁸U α-activity ratios calculated from the atom ratio data are consistently high, with a mean difference of about 5%, when compared to the α-spectrometry results. This discrepancy warrants confirmation by a few more laboratories and suggests redetermination of the half-life values of²³⁴U and²³⁸U.     

Determination of231Pa in coastal sediments and sea water and disequilibrium studies in231Pa/235U activity ratios

Coastal sediment samples are collected from the top surface layers of the sediments from Bombay to Kottilppad along the West coast of India in order to understand the geochemical behaviour of²³¹Pa and the activity ratios of²³¹Pa/²³⁵U in this region of the Indian sub-continent. These coastal regions offer a unique advantage for studying the geochemistry and transport of natural radioactivity due to the placer deposits of monazite in the southern part of India. The top layers of the surface sediments are leached with 1.0M oxalic acid for the extraction of protactinium activities without attacking the mineral core of the particles.²³³Pa tracer is added to the samples. The chemical recovery obtained by counting²³³Pa is found to vary from 40 to 90%. Total uranium leached from the sediment surface is determined by fluorimetric method and the concentrations of²³⁵U in the leachates are calculated. Using these data, the activity ratios of²³¹Pa/²³⁵U have been calculated. These ratios lie in the range of 11.0 to 21.0 for sediments from Bombay to Kottilppad. The data of²³¹Pa activity indicates that there is a deficiency of²³¹Pa in coastal waters of the ocean and that²³¹Pa is removed by precipitation as soon as it is formed by radioactive decay of²³⁵U.²³¹Pa is observed to be bound mostly to organic humous material on the surface of the sediment.     

Seasonal variation of activity ratios for natural uranium in surface waters

The uranium concentration, and²³⁴U/²³⁸U and²³⁵U/²³⁸U activity ratios were measured by alpha spectrometry of surface water from the neighbourhood of the uranium mines El Lobo and El Pedregal (Badajoz, Spain) before and after the rainy season. Changes were observed in all the three parameters studied. Leaching and dilution are the probable mechanisms for the seasonal changes in the concentration and in the²³⁴U/²³⁸U activity ratio as measured in open and dynamic systems (rivers).     

Radioanalytical investigations of uranium concentrations in natural spring, mineral, spa and drinking waters in Hungary

Within this work, the activity concentrations of uranium isotopes (²³⁴U, ²³⁵U, and ²³⁸U) were analyzed in some of the popular and regularly consumed Hungarian mineral-, spring-, therapeutic waters and tap waters. Samples were selected randomly and were taken from different regions of Hungary (Balaton Upland, Bükk Mountain, Somogy Hills, Mez?föld, and Lake Hévíz). Concentration (mBq L^?1) of ²³⁴U, ²³⁵U, and ²³⁸U in the waters varied from 1.1 to 685.2, from <0.3 to 7.9, and from 0.8 to 231.6 respectively. In general, the highest uranium concentrations were measured in spring waters, while the lowest were found in tap waters. In most cases radioactive disequilibrium was observed between uranium isotopes (²³⁴U and ²³⁸U). The activity ratio between ²³⁴U and ²³⁸U varies from 0.57 to 4.97. The calculated doses for the analyzed samples of spring water are in the range 0.07–32.39 μSv year^?1 with an average 4.32 μSv year^?1. This is well below the 100 μSv year^?1 reference level of the committed effective dose recommended by WHO and the EU Council. The other naturally occurring alpha emitting radionuclides (²²⁶Ra and ²¹⁰Po) will be analyzed later to complete the dose assessment. This study provides preliminary information for consumers and authorities about their internal radiological exposure risk due to annual intake of uranium isotopes via water consumption.     

Behavior of uranium along Jucar River (Eastern Spain): Determination of234U/238U and235U/238U ratios

The uranium concentration and the²³⁴U/²³⁸U,²³⁵U/²³⁸U activity ratios were studied in water samples from Jucar River, using low-level -spectrometry. The effects of pH, temperature and salinity were considered and more detailed sampling was done in the neighbourhood of Cofrentes Nuclear Plant (Valencia, Spain). Changes were observed in the uranium concentration with the salinity and the²³⁴U/²³⁸U activity ratio was found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes in the concentration of uranium and the activity ratios.