Uranium Isotope Ratios Research Articles

Direct Uranium Isotopic Analysis of Swipe Surfaces by Microextraction-ICP-MS.

The ability to directly measure uranium isotope ratios on environmental swipes has been achieved through a solution-based microextraction process and represents a significant advancement toward the development of a rapid method to analyze international nuclear safeguard samples. Here, a microextraction probe is lowered and sealed onto the swipe surface, and analytes within the sampling site (∼8 mm2) are dissolved and extracted into a flowing solvent of 2% nitric acid (HNO3). The mobilized species are subsequently directed into an inductively coupled plasma-mass spectrometer (ICP-MS) for accurate and precise isotope ratio determination. This work highlights the novelty of the sampling mechanism, particularly with the direct coupling of the microextraction probe to the ICP-MS and measurement of uranium isotope ratios. The preliminary method detection limit for the microextraction-ICP-MS method, utilizing a quadrupole-based MS, was determined to be ∼50 pg of 238U. Additionally, precise and accurate isotope ratio measurements were achieved on uranium reference materials for both the major (235U/238U) and minor (234U/238U and 236U/238U) ratios. While the present work is focused on directly measuring uranium isotopic systems on swipe surfaces for nuclear safeguards and verification applications, the benefits would extend across many applications in which direct solid sampling is sought for elemental and isotopic analysis.

Reusable selective sensing-substrate for ultrasensitive and rapid detection of uranium radioisotopes

An analytical method based on a fabricated analytical disc was developed using a phosphonate-immobilized quartz substrate for the rapid analysis of uranium. Phosphonate groups selectively adsorb uranium dissolved in a solution through the formation of stable complexes. The uranium concentration and isotopic ratios in the sample can rapidly be determined by measuring the radioactivity of the adsorbed uranium on the analytical disc using alpha-particle spectrometry. The chemical structure and elemental composition of the fabricated disc were analyzed by XPS, and the adsorption properties were evaluated as functions of pH of a sample solution, reaction time, and adsorbate concentration, as well as reusability and selectivity, using alpha-particle spectrometry, ICP-OES, and ICP-MS. An analytical method was developed based on these properties and validated with prepared uranium solutions by assessing the chemical recovery yield, relative error, and relative standard deviation. The developed method is expected to be used for on-the-spot uranium analysis.

A multi-isotope baseline (O, H, C, S, Sr, B, Li, U) to assess leakage processes in the deep aquifers of the Paris basin (France)

Groundwaters from the deep Dogger and Albian aquifers from the Paris Basin in France have been analyzed for oxygen (H2O and SO4), hydrogen (H2O), carbon, boron, lithium, sulfur (SO4), strontium, and uranium isotopes. This study aims to establish a natural hydrogeochemical baseline against which any leak of saline fluids from deeper water masses could be evidenced in case of a hypothetic occurrence of non-conventional exploitation of the hydrocarbons that are present in the underlying Liassic shales. Waters from the Dogger and the Albian aquifers have respectively chloride-alkaline and calcium-bicarbonate geochemical facies, although some waters from the Albian aquifer tend to evolve towards the geochemical characteristics of the waters from the Dogger aquifer.Stable isotopes of the water molecule indicate that waters from the Albian aquifer have a meteoritic origin, whereas saline waters of the Dogger aquifer are mainly influenced by primary and secondary brine inflow from the Triassic evaporitic deposits, and also by diffusive exchanges with the porewaters of the Liassic shales (Bensenouci et al., 2010). Carbon isotopes display δ13C values that are much higher (>0‰) in waters from the Dogger aquifer waters than those from the Albian (≤- 9‰). Oxygen and sulfur isotopes of dissolved sulfates measured in the waters from the Dogger indicate that sulfur comes probably from the Triassic evaporites, whose signatures are overprinted by bacterial sulfate reduction. The water from the Pantin well near Paris displays isotopic characteristics that are comparable to the saline waters from the Dogger. On the other hand, dissolved sulfates of the other waters from the Albian indicate two different sources: sulfates derived from sulfides that have undergone abiotic oxidation processes, and atmospheric and/or crustal sources. Uranium activity ratios are very high in most groundwaters from the Albian, especially northwest of the Paris region where ratios as high as 20 have been measured. These activity ratios are in most cases higher than those of the saline waters from the Dogger, and suggest important water/rock interaction processes within the Albian aquifer in agreement with Li isotopes data. Boron and strontium isotopic data suggest that some waters from the Albian record the geochemical influence of saline waters comparable to those of underlying aquifers of the Paris Basin, especially Northeast of Paris, in agreement with recent geophysical studies.In the present work, we critically evaluate the information that can be derived from each of the tested isotope systematics in terms of leakage and mixing processes as might occur as the result of man-induced hydraulic shortcuts or changes in the pressure gradients between deep groundwater levels. Sulfur, oxygen, strontium and boron reveal the most sensitive indicators of mixing processes, whereas lithium and, in particular, uranium isotope ratios are strongly overprinted by water-rock interaction and redox processes.

Precise measurement of uranium isotope ratios in Fukushima soils using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

Precise measurement of 234U/238U and 235U/238U isotope ratios was performed using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in this study. The 234U ions were measured using a Daly detector, the 235U ions were measured using a Faraday cup with a 1012 Ω resistor, and the 238U ions were measured using a Faraday cup with the usual 1011 Ω resistor. Chemical separation of uranium was carried out by three different methods using either combinations of anion exchange and UTEVA resins or UTEVA resin three times. Chromatography combining three UTEVA resin columns provided the highest recovery (%) of uranium and biggest improvement in precise measurements of uranium isotope ratios. The certificate reference material (CRM) JLk-1 was used as an in-house standard for the uranium isotope ratio measurements. The long-term reproducibility of the in-house standard was 0.60% for 234U/238U and 0.05% for 235U/238U. The measured ratios were compared with the natural ratios, and the relative deviation obtained for uranium isotope ratios was less than 0.005% for 234U/238U and 235U/238U. Finally, the present method was applied to measure uranium isotope ratios in Fukushima microwave-digested soil samples.

Determination of minor isotope ratios of individual uranium particles by accelerator mass spectrometry.

The determination of uranium isotope ratios in uranium particle is an essential technique in the analysis of environmental samples for nuclear safeguards. At present, mass spectrometry has been widely used to measure isotope ratios of uranium particles. We developed a new analytical method for measuring minor isotope ratios of individual uranium particles directly. The technique includes single particle identification by energy dispersive X-ray spectrometer (EDX), transfer by scanning electron microscope (SEM) combined with micromanipulator and isotope ratios analysis with accelerator mass spectrometry (AMS). The minor isotope ratios of individual uranium particles with four isotopic abundances and different sizes from certified reference materials were measured by AMS. The results show that the relative error (RE, i.e., the deviation of measured value from the certified value) of 234 U/235 U and 234 U/236 U isotope ratios was 9.0% and 19.3%, respectively, and the relative standard deviation (RSD) was within 9.9% and 16%, respectively. The minimum particle determined was about 2 μm. The method was found to be an alternative analytical means for nuclear safeguards.

Behavior of the Mo, Tl, and U isotope systems during differentiation in the Kilauea Iki lava lake

Stable molybdenum (Mo), thallium (Tl), and uranium (U) isotope ratios were determined in a suite of samples from the 1959 Kilauea eruption and from Kilauea Iki lava lake with the aim of understanding the effects of igneous differentiation on these isotope systems. The samples range from olivine cumulate with MgO up to 27% to internal differentiates with MgO less than 3%, representing a tholeiitic differentiation series. Molybdenum, Tl, and U behave incompatibly during differentiation, and Mo and U isotope ratios do not systematically vary amongst the different samples. δ98Mo values range from −0.17 to −0.31‰ and δ238U values range from −0.20 to −0.38‰. Most individual analyses for both isotope systems overlap within measurement uncertainty (± ~0.7 and ~ 0.6, respectively). Mean δ98Mo and δ238U values are −0.22 ± 0.08‰ (2σ) and − 0.29 ± 0.09‰ (2σ), respectively, which overlap with Pacific mid ocean ridge basalt (MORB). In contrast, Tl isotopes show small but resolvable variations, with ε205Tl ranging from +1.20 to −1.38. The most negative ε205Tl values are confined to some of the lowest [Tl] samples, but the ε205Tl values do not otherwise vary smoothly with MgO or [Tl]. Possible mechanisms for thallium isotope fractionation are considered (e.g., degassing, water leaching, sulfide fractionation) but none are found to be satisfactory. Overall, the lack of resolvable variation in the Mo and U isotope systems and the small magnitude of heterogeneity in the Tl isotope system indicate that differentiation in tholeiitic systems is unlikely to be a major contributor to global variation in these isotope systems.

Improved Uranium Isotope Ratio Analysis in Liquid Sampling-Atmospheric Pressure Glow Discharge/Orbitrap FTMS Coupling through the Use of an External Data Acquisition System.

Isotope ratio (IR) analysis of natural abundance uranium presents a formidable challenge for mass spectrometry (MS): the required spectral dynamic range needs to enable the quantitatively accurate measurement of the 234UO2 species present at ∼0.0053% isotopic abundance. We address this by empowering a benchtop Orbitrap Fourier transform mass spectrometer (FTMS) coupled with the liquid sampling-atmospheric pressure glow discharge (LS-APGD) ion source and an external high-performance data acquisition system, FTMS Booster X2. The LS-APGD microplasma has demonstrated impressive capabilities regarding elemental and IR analysis when coupled with Orbitrap FTMS. Despite successes, there are limitations regarding the dynamic range and mass resolution that stem from space charge effects and data acquisition and processing restrictions. To overcome these limitations, the FTMS Booster was externally interfaced to an LS-APGD Q Exactive Focus Orbitrap FTMS to obtain time-domain signals (transients) and to process unreduced data. The unreduced time-domain data acquisition with user-controlled processing permit the evaluation of the effects of in-hardware transient phasing, increased transient lengths, advanced transient coadding, varying the length of a transient to be processed with a user-defined time increment, and the use of absorption-mode FT (aFT) processing methods on IR analysis. The added capabilities extend the spectral dynamic range of the instrument to at least 4-5 orders of magnitude and provide a resolution improvement from ∼70k to 900k m/Δm at 200 m/z. The empowered LS-APGD Orbitrap platform allows for the simultaneous measurement of 234UO2 and the prominent 235UO2 and 238UO2 isotopic species at their natural abundances, ultimately yielding improvements in performance when compared to previous uranium IR results on this same Q Exactive Focus instrument.

Determination of Uranium Isotopic Ratio by ICP-OES Using Optimal Sensitivity Position Analysis.

Isotopic composition analysis of natural and depleted uranium by inductively coupled plasma optical emission spectrometry (ICP-OES) requires the use of a high-resolution instrument due to the very slight isotopic shifts between the atomic emission spectra of the 238U and 235U isotopes. In this work, we show that conventional ICP-OES (without high-resolution optics) can be used for highly accurate uranium isotopic analysis, on par with the results obtained by ICP-MS. Such accurate measurements are achieved by applying a preparatory mathematical procedure termed the optimal sensitivity position (OSP) procedure. In the OSP procedure, a theoretical spectrum for 238U is constructed and subtracted from the measured spectra of calibration solutions encompassing various isotopic ratios. The resultant spectra are used to locate the optimal measurement positions for both major uranium isotopes (238U and 235U) and the background measurement position. Herein, the optimal measurement positions are revealed to be located not at each isotope's peak maximum but at 424.427, 424.409, and 424.390 nm for 238U, 235U, and the background position, respectively. These locations remained stationary during the period of this work, implying that the use of a routine mathematical procedure is not required before every analysis. The OSP procedure offers a direct and highly accurate approach for determining the isotopic ratio of uranium in a relatively cheap and simple fashion. Furthermore, this work also demonstrates the possibility of greatly enhancing ICP-OES capabilities using mathematical analysis of spectra.

Measurement of uranium isotope ratios in Fukushima-accident contaminated soil samples using multi collector inductively coupled plasma mass spectrometry

In the present study, 137Cs and 238U activity concentrations, 234U/238U activity ratio, and 235U/238U isotope ratio were measured in fifteen soil samples collected from the exclusion zone around the Fukushima Daiichi Nuclear Power Station (FDNPS). The 137Cs activity concentrations of Fukushima-accident contaminated soil samples ranged from 29.9 to 4780 kBq kg−1 with a mean of 2007 kBq kg−1. On the other hand, the 238U activity concentrations of these soil samples ranged from 5.2 to 22.4 Bq kg−1 with a mean of 13.2 Bq kg−1. The activity ratios of 234U/238U ranged from 0.973 to 1.023. The 235U/238U isotope ratios of these exclusion zone soil samples varied from 0.007246 to 0.007260, and they were similar to the natural terrestrial ratio confirming the natural origin. Using isotope dilution technique, the 235U/137Cs activity ratio was theoretically estimated for highly 137Cs contaminated soil samples from Fukushima exclusion zone ranged from 5.01 × 10−8 - 6.16 × 10−7 with a mean value of 2.51 × 10−7.

Resolving whether inhalation of depleted uranium contributed to Gulf War Illness using high-sensitivity mass spectrometry

Of the hypothesized causes of Gulf War Illness (GWI), a chronic multi-symptom illness afflicting approximately 25% of military personnel deployed to the 1991 Gulf War, exposure to depleted uranium (DU) munitions has attracted international concern. Past research has not tested the potential association of GWI with inhaled DU nor used isotope mass spectrometry of sufficient sensitivity to rigorously assess prior DU exposure. We applied a standard biokinetic model to predict the urinary concentration and uranium isotopic ratios for a range of inhalation exposures. We then applied sensitive mass spectrometry capable of detecting the predicted urinary DU to 154 individuals of a population-representative sample of U.S. veterans in whom GWI had been determined by standard case definitions and DU inhalation exposures obtained by medical history. We found no difference in the 238U/235U ratio in veterans meeting the standard case definitions of GWI versus control veterans, no differences by levels of DU inhalation exposure, and no 236U associated with DU was detected. These findings show that even the highest likely levels of DU inhalation played no role in the development of GWI, leaving exposure to aerosolized organophosphate compounds (pesticides and sarin nerve agent) as the most likely cause(s) of GWI.

Combining Uranium, Boron, and Strontium Isotope Ratios (234U/238U, δ11B, 87Sr/86Sr) to Trace and Quantify Salinity Contributions to Rio Grande River in Southwestern United States

In semi-arid to arid regions, both anthropogenic sources (urban and agriculture) and deeper Critical Zone (groundwater with long flow paths and water residence times) may play an important role in controlling chemical exports to rivers. Here, we combined two anthropogenic isotope tracers: uranium isotope ratios (234U/238U) and boron isotope ratios (δ11B), with the 87Sr/86Sr ratios to identify and quantify multiple solute (salinity) sources in the Rio Grande river in southern New Mexico and western Texas. The Rio Grande river is a major source of freshwater for irrigation and municipal uses in southwestern United States. There has been a large disagreement about the dominant salinity sources to the Rio Grande and particularly significant sources are of anthropogenic (agriculture practices and shallow groundwater flows, groundwater pumping, and urban developments) and/or geological (natural groundwater upwelling) origins. Between 2014 and 2016, we collected monthly river samples at 15 locations along a 200-km stretch of the Rio Grande river from Elephant Butte Reservoir, New Mexico to El Paso, Texas, as well as water samples from agricultural canals and drains, urban effluents and drains, and groundwater wells. Our study shows that due to the presence of localized and multiple salinity inputs, total dissolved solids (TDS) and isotope ratios of U, B, and Sr in the Rio Grande river show high spatial and temporal variability. Several agricultural, urban, and geological sources of salinity in the Rio Grande watershed have characteristic and distinguishable U, Sr, and B isotope signatures. However, due to the common issue of overlapping signatures as identified by previous tracer studies (such as δ18O, δD, δ34S), no single isotope tracer of U, Sr, or B isotopes was powerful enough to distinguish multiple salinity sources. Here, combining the multiple U, Sr, and B isotope and elemental signatures, we applied a multi-tracer mass balance approach to quantify the relative contributions of water mass from the identified various salinity end members along the 200-km stretch of the Rio Grande during different river flow seasons. Our results show that during irrigation (high river flow) seasons, the Rio Grande had uniform chemical and isotopic compositions, similar to the Elephant Butte reservoir where water is stored and well-mixed, reflecting the dominant contribution from shallow Critical Zone in headwater regions in temperate southern Colorado and northern New Mexico. In non-irrigation (low flow) seasons when the river water is stored at Elephant Butte reservoir, the Rio Grande river at many downstream locations showed heterogeneous chemical and isotopic compositions, reflecting variable inputs from upwelling of groundwater (deeper CZ), displacement of shallow groundwater, agricultural return flows, and urban effluents. Our study highlights the needs of using multi-tracer approach to investigate multiple solutes and salinity sources in rivers with complex geology and human impacts.

Measurement of uranium isotope ratio by laser ablation absorption spectroscopy

<sec>High precision measurement of uranium isotope ratio (<sup>235</sup>U/<sup>238</sup>U) has important application in the field of nuclear energy safety. In this paper, based on high sensitivity tunable absorption spectroscopy technology, combined with the sample processing method of pulsed laser ablation plasma, high-precision measurement of uranium <sup>235</sup>U/<sup>238</sup>U isotope ratio in solid material is realized. In the experimental measurement, transitions near 394.4884 nm/394.4930 nm (vacuum) are selected as the <sup>235</sup>U/<sup>238</sup>U analytical lines. The influence of buffer gas and its pressure on the persistence time of uranium atom in laser ablated plasma are studied in detail. </sec><sec> The experimental results show that different buffer gases have different ability to restrict the movement of particles in the plasma, which leads to different longitudinal expansion velocity of the plasma (perpendicular to the surface of the sample), and increases the persistence time of uranium atoms in the laser beam. The effect of pressure change on plasma evolution can be reduced by adding buffer gas. When helium is used as the buffer gas, the persistence time of uranium atoms in the plasma is longer, which can improve the selection space of data acquisition delay. In the ablation environment with helium, the electron number density of laser ablated plasma is relatively low, which can reduce the influence of Stark broadening effect and obtain narrower absorption lines, which is more conducive to the measurement of uranium atomic absorption spectrum. In order to reduce the influence of Doppler shift effect on absorption spectrum measurement and avoid misjudgment in spectrum analysis, it is more appropriate to carry out experimental measurement after 3μs sampling delay. Through experiments, the optimal conditions for measuring atomic absorption spectrum of uranium are obtained. Under these conditions, five different samples with <sup>235</sup>U content of 4.95%, 4.10%, 3.00%, 1.10% and 0.25% respectively are measured, and the high-resolution absorption spectrum signals of <sup>235</sup>U and <sup>238</sup>U are obtained. The absorption spectra of samples with different content are measured and statistically analyzed, the <sup>235</sup>U absorption signal has high linearity, the fitting correlation coefficient can reach 0.989, and the limit of detection is 0.033% (3σ). The stability test of absorption spectrum signal shows that the relative standard deviation of <sup>238</sup>U, <sup>235</sup>U and <sup>235</sup>U / <sup>238</sup>U signals are 2.054%, 2.152% and 0.524% respectively. The wavelength scanning mode is superior to the fixed wavelength spectrum measurement, and the influence of the energy fluctuation between different ablation pulses on the spectrum measurement is weakened by the wavelength scanning mode to a certain extent. The results show that laser ablation combined with absorption spectroscopy technology is suitable for uranium isotope ratio analysis and has great potential applications in rapid isotope analysis of nuclear fuel.</sec>

Performance and optimisation of triple quadrupole ICP-MS for accurate measurement of uranium isotopic ratios

This study presents improved accuracy and precision in ICP-MS/MS analyses of uranium isotopic ratios by correcting for the instrumental drift in the mass calibration of the first and second mass filters.

Radiochemical technique as a tool for determination and characterisation of El Sela ore grade uranium deposits

ABSTRACT The present study is an application of a radiochemical procedure for the determination of 238U, 235U and 234U as well as uranium isotopic ratios in El Sela ore grade samples that located at the Southeastern Desert of Egypt. This procedure is consisting of several steps include sample preparation, chemical separation and source preparation followed by counting using alpha-particle spectrometry technique. Radiochemical determination of various uranium isotopes contents indicated that El Sela uranium deposits are considered as a recent deposit where there was a large difference between radiochemically and radiometrically determined uranium. The measured 234U/238U activity ratios for most samples were approximately unity, indicating that secular radioactive equilibrium was established between 238U and 234U in the El Sela mineralised rocks. On the other hand, 238U and 234U might be equally leached due to the effect of rock-water interactions during the pluvial time by the action of surficial or underground water. The 238U/235U activity ratios of the studied mineralised granites were significantly shifted from the natural ratio 21.7, indicating that the redox conditions and alteration processes played an important role in the fractionation of 238U from 235U. The values of 234U/235U ratios in the studied granites varied between 23.08 and 34.70 in different samples, suggesting 235U migration out due to the prevailing conditions.

Determination of Uranium Isotopic Ratios by Alpha Spectrometry for Nuclear Materials Control Purposes

Uranium is the most common element in the nuclear fuel cycle. Different techniques have been used for analyzing the isotopic composition of uranium. Precise determination of uranium isotopic ratios for an efficient control of nuclear material was carried out through the modification of the used chromatographic method of uranium. Alpha spectrometry was utilized to identify different types of natural, depleted and enriched samples for safeguard purposes. Uranium element was extracted from other interfering radionuclides, purified, electrodeposited on a stainless-steel disc, and measured using alpha-spectrometer, then isotopic ratios were calculated. For comparison purposes, the samples were also measured using a hyper pure germanium (HPGe) spectrometer and the uranium isotopic ratios were obtained. The results obtained by both techniques were in agreement within difference ranged from -8.7 to 12%. It was concluded that alpha spectrometric measurements of uranium isotopes preceded by efficient radiochemical separation using extraction chromatography is a fast and reliable technique for safeguard purposes.

Pushing Limits of ICP–MS/MS for the Determination of Ultralow 236U/238U Isotope Ratios

Determination of uranium isotope ratios is of great expedience for assessing its origin in environmental samples. In particular, the 236U/238U isotope ratio provides a powerful tool to discriminate between the different sources of uranium (uranium ore, geochemical background, and uranium from anthropogenic activities). However, in the environment, this ratio is typically below 10-8. This low abundance of 236U and the presence in large excess of major isotopes (mainly 238U and 235U) complicates the accurate detection of 236U signal by mass spectrometry and thus highly sensitive analytical instruments providing high abundance sensitivity are required. This work pushes the limits of triple quadrupole-based ICP-MS technology for accurate detection of 236U/238U isotope ratios down to 10-10, which is so far mainly achievable by AMS. Coupled with an efficient desolvating module, N2O was used as the reaction gas in the collision reaction cell of the ICP-MS/MS. This configuration allows a significant decrease of the uranium polyatomic interferences (235UH+ ions) and an accurate determination of low 236U/238U isotope ratios. This new methodology was successfully validated through measurements of certified reference material from 10-7 to 10-9 and then through comparisons with AMS measurement results for ratios down to 10-10. This is the first time that 236U/238U isotope ratios as low as 10-10 were determined by ICP-MS/MS. The possibility of measuring low 236U/238U isotope ratios can offer a large variety of geochemical applications in particular for the determination of uranium sources in the environment.

The use of major, trace elements and uranium isotopic ratio (234U/238U) for tracing of hydrogeochemical evolution of surface waters in the Andarax River catchment (SE Spain)

Chemical and isotopic tracers are used to identify and discriminate the factors controlling the chemical characteristics of surface water in the Andarax River. Along the river, two areas are found to have distinct processes. In the Upper Andarax zone, the surface water (163–645 μS cm−1) is influenced by the direct infiltration associated with precipitations and groundwater discharge from the carbonate aquifer of Sierra de Gádor. This is responsible for the increase in the Sr/Ca and Mg/HCO3 ratio in the surface flow direction. The influence of groundwater on the surface waters contributes to the maintenance of the channel and affects the hydrochemical and isotopic characteristics of the surface water in the area. All of this has been characterized through the combined use of the 234U/238U isotopic ratio (1.59–1.92) and the uranium content (<0.009 μmol/L). In the Middle Andarax, the surface water has an increased salinity (724–1850 μS cm−1) and the values of the Ca/SO4 (0.73–1.38) and Sr/SO4 (0.005–0.008) molar ratios are lower than those of the Upper Andarax zone (1.49–4.17) and (0.009–0.011). This middle zone has an area of temporary water having low B/Li molar ratio (0.31–0.93) values, and another area of permanent flow having similar values (1.07–1.26) to those of the nearby groundwater (1.22–1.26). The groundwater-surface water interaction and the lithological influence notably condition these differences in hydrochemistry. Therefore, the use of hydrochemical and isotopic tracers assists in the understanding of the processes affecting the evolution of the surface waters, considering the interaction with groundwater, the lithology of the aquifers and rocks of the basin, and other relevant environmental factors. This knowledge is useful for the management of water resources in semiarid zones having problems with quality and quantity of surface waters.

Physico-chemical conditions controlling the radionuclides mobilisation in various granitic environments

ABSTRACT Nine samples were chemically characterized and radiometrically analyzed for determination of 234U, 238U, 235U, 230Th, 232Th, 226Ra and 40K by γ-ray spectrometer Hyper Purity Germanium (HPGe detector). 238U activity concentrations reach up to 79.78 Bq Kg-1in the altered granites, 1714.11 and 2223.48 Bq Kg-1in the episyenite and pegmatite. Average 234U activity concentrations in the altered granite is 59.26 Bq Kg-1, between 175.88-543.47 Bq Kg-1and 48.19-1102.88 Bq Kg-1in the episyenite and pegmatite, respectively. 232Th activity concentrations vary between 14.16-1024.8 Bq Kg-1in the episyenite, 11.46-240.27 in the pegmatite and reach up to 201.45 Bq Kg-1in the altered granites. 40K activity concentrations range between 4.42-9.15, 2.76-7.34 and 2.68-9.94 Bq Kg-1in the altered granite, episyenite and pegmatite, respectively. 235U activity concentration ranges between 3.74–2.56, 12.45-78.86 and 0.58-102.34 Bq Kg-1 in the altered granite, episyenite and pegmatite, respectively. The studied altered granite, episyenite and pegmatite samples have relatively higher values than recorded in the international standards with the exception of potassium which has lesser amounts. It is demonstrated that pH changes, oxidation-reduction conditions, mineralogical constituents, in addition to alteration processes in these variable granitic environments were the main factors controlling uranium mobilization according to valid processes. The difference in alteration processes and La/Y ratio clarified the presence of more than one event of uranium accumulation and/or leaching in these rocks as confirmed by the presence of uranium accumulation and uranium vacant occurrences. Also, the isotopic ratios of uranium as 238U/235U,234U/235U, 234U/ 238U, 226Ra/ 238U,226Ra/ 230Th, 210Pb/ 226Ra, 230Th/ 238U, 230Th/ 234U with major, trace and rare earth elements were also affected by physico-chemical conditions changes. The present study shows that the samples of episyenite and pegmatite have been affected by leaching-accumulation events in the period from (1 × 105 to ˃2 × 105years).

Isotopic ratios of uranium and caesium in spherical radioactive caesium-bearing microparticles derived from the Fukushima Dai-ichi Nuclear Power Plant

Spherical radioactive caesium (Cs)-bearing microparticles (CsMPs) were emitted during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March, 2011. The emission source (timing) and formation process of these particles remain unclear. In this study, the isotopic ratios of uranium (235U and 238U) and caesium (133Cs, 134Cs, 135Cs, and 137Cs) isotopes in the five spherical CsMPs (ca. 2 μm in size) sampled at 50 km west of the FDNPP were determined using secondary ion mass spectrometry and laser ablation-ICPMS, respectively. Results showed that the 235U/238U ratios of CsMPs were homogeneous (1.93 ± 0.03, N = 4) and close to those estimated for the fuel cores in units 2 and 3, and that the Cs isotopic ratios of CsMP were identical to those of units 2 and 3. These results indicated that U and Cs in the spherical CsMPs originated exclusively from the fuel melt in the reactors. Based on a thorough review of literatures related to the detailed atmospheric releases of radionuclides, the flow of plumes from the FDNPP reactor units during the accident and the U and Cs isotopic ratio results in this study, we hereby suggest that the spherical CsMPs originate only from the fuel in unit 2 on the night of 14 March to the morning of 15 March. The variation range of the analysed 235U/238U isotopic ratios for the four spherical particles was extremely narrow. Thus, U may have been homogenised in the source through the formation of fuel melt, which ultimately evaporating and taken into CsMPs in the reactor and was released from the unit 2.

Uranium isotopic ratios and their implication for uranium–uranium dating and groundwater circulation studies: A case study from speleothems of the Demänová caves, Nízke Tatry Mts., Slovakia

Uranium isotopic ratios and their implication for uranium–uranium dating and groundwater circulation studies: A case study from speleothems of the Demänová caves, Nízke Tatry Mts., Slovakia