Size-fractionated uranium isotopes in surface waters in the Jiulong Estuary in China

Surface water was collected from the Jiulong Estuary for determination of activity concentrations of uranium isotopes in different size fractions, namely, greater than 53, 10 -53, 2 - 10, 0.4 -2 μm, 10 000 u -0.4 μm and less than 10 000 u fractions by microfihration and cross-flow uhrafiltration technologies. Results indicated that most of the dissolved uranium （ 〈 0.4 μm） exis- ted in the low molecular mass fraction （ 〈 10 000 u）, and the colloidal uranium-238 （10 000 u -0.4 μm） only contributed less than 1% of the dissolved uranium-238. The fractions of colloidal uranium in the dissolved phases decreased with the increasing sa- linity. A positive linear relationship between uranium-238 activities and salinities was observed for the dissolved, colloidal and low molecular mass fractions, indicating a conservative behavior of uranium in the Jiulong Estuary. In the particulate phases （ 〉 0.4 μm）, the partitioning of uranium isotopes among different size fractions was controlled by the partitioning of particle concentrations. In the regions with salinities below 20, the partitioning of uranium-238 among different size fractions was as follows： 10 - 53 μm 〉 2 - 10 μm 〉 0.4 - 2 μm greater than above 53 μm. However, the order at the offshore station with salinities above 30 changed as follows ： 0.4 - 2 μm 〉 10 - 53 μm 〉 2 - 10 μm greater than above 53 μm. The fraction of the 0.4 - 2 μm particles increased at the offshore station, suggesting the increased contribution of the authigenic uranium. The activity ratio of uranium-234 to uranium-238 in the dissolved phases, including the low molecular mass fraction and the colloidal fraction, was larger than unity, showing the occurrence of excess uranium-234. In contrast, the activity ratio of uranium-234 to uranium-238 in all size fractions of the particulate phase was close to the equilibrium value （1.0）. The observed different values of the activity ratio of uranium-234 to uranium-238 in the dissolved phase and the particulate phase were ascribed to the preferential leaching of uranium-234 and the small amount of the leaching particulate uranium. The mass ratio of thorium-232 to uranium-238 also showed different values between the dissolved phase and the particulate phase. Mass ratio of thorium-232 to uranium-238 in the dissolved, colloidal and low molecular mass fractions was less than unity, while those in the different size fractions of particulate phases were larger than unity, reflecting a different behavior between uranium and thorium during their transport into the ocean.

Limited Contribution of Preferential Dissolution to Radiogenic Uranium Isotope Disequilibrium Observed in Weathered Moraines

Radiogenic uranium isotope disequilibrium(^(234)U/^(238)U) has been used to trace a variety of Earth surface processes,and is usually attributed to direct recoil of ^(234)Th and preferential dissolution of radioactively damaged lattices at the mineral surface.However,the relative contribution of these two mechanisms in the natural environment remains unresolved,making it hard to use the extent of disequilibrium to quantify processes such as weathering.This study tests the contribution of preferential dissolution using well-characterized weathered moraines and river sediments from the southeastern Tibetan Plateau.The observations show that weathering of recent moraines where the contribution from direct recoil is negligible and is not associated with depletion of ^(234)U at the mineral surface.It suggests a limited role for preferential dissolution in this setting.We attribute this lack of preferential dissolution to a near-to-equilibrium dissolution at the weathering interfaces,with little development of etch pits associated with radioactively damaged energetic sites.

Uranium Isotope Variations(234U/238U and 238U/235U)and Behavior of U-Pb Isotope System in the Vershinnoe Sandstone-Type Uranium Deposit,Vitim Uranium Ore District,Russia

The U-Pb isotope system and uranium isotope composition(235U/238U and 234U/238U)were studied in a number of samples from the vertical section of the uranium ore body at the Vershinnoe sandstone-type deposit,Vitim uranium ore district,Russia.These parameters were determined to broadly vary.Deviations of the 234U/238U ratio from the equilibrium value indicate that the uranium ore was not completely conserved during the postore stage,and uranium was determined to continue migrating at the deposit.Comparison of the U-Pb isotope age value and 234U/238U isotope ratio provides an insight into the migrate direction of uranium in the ore body.The broad variations(137.377–137.772)in the 238U/235U ratio over the vertical section of the ore body can be explained by the different settings of the samples relative to the ore deposition front and changes in the redox conditions when this front shifted.The fact that theδ238U and K234/238 values are correlated indicates that the transfer of the 234U isotope into the aqueous phase may have been coupled with isotope fractionation in the 238U-235U system during the postformation uranium migration within the orebody.

Uranium isotopes of aeolian dust deposited in northern Tibetan Plateau glaciers:Implications for tracing aeolian dust provenance

Asian dust comprises a large portion of the northern hemisphere atmospheric dust load,thereby exerting substantial influence on the Earth’s climate,global biogeochemistry and hydrological cycle through accelerated snow and ice melt.Dust deposited on alpine glaciers encodes information on broad scale atmospheric-environmental processes.The(^(234)U/^(238)U)values of dust fine particulates can reflect the comminuting time and intermediate processes;thus,it provides a new method for the provenance of aeolian dust in the glacial snowpack/cryoconite.Here we present results from a comprehensive survey of uranium isotopic concentrations in dust collected from cryoconites on the glaciers of the northern Tibetan Plateau(TP).These results indicate significant spatial heterogeneity in the(^(234)U/^(238)U)values associated with snowpack/cryoconite dust over a broad range of glaciers in the northern TP.The values of the(^(234)U/^(238)U)ratio in the glaciers of western Qilian Mountains(Qiyi Glacier,Shiyi Glacier,Laohugou Glacier No.12)were the highest,followed by the Tanggula(Dunkemadi Glacier)and Kunlun Mountains(Yuzhufeng Glacier),whereas these values were the lowest in the eastern Qilian Mountains(Jingyangling Snowpack,Dabanshan Snowpack,Lenglongling Glacier).By including the analysis of Sr-Nd isotopic compositions,we find the spatial isotopic distribution reflects a combination of local dust,which is associated with short comminuting times,and dust transported over long ranges.Meteorological data indicate that the dust production in the west and north TP,Alxa arid lands and Gobi Deserts,may have a significant impact on the TP glaciers.Moreover,U-Sr-Nd isotopic composition and end-member mixing models(EMMA)were used in our study to find out the relative contribution of distinct Asian dust sources to the dust budget in the TP glaciers.The results reveal that snowpack/cryoconite dust is derived from both local sources(low comminution signatures)as well as other dust sources in the Asian region.Our study demonstrates the potential of U isotope composition as a dust tracing method.In particular,by investigating this composition on dust collected from glacier snowpack and cryoconite holes,we arrive at a map of the distribution characteristics of(^(234)U/^(238)U)values in different regions of the TP.Our study is the first to deploy uranium comminution age for Tibetan dust source tracing,and the results are important to elucidate the multiple origins and dynamics of dust in the Tibetan Plateau.

Uranium comminution age responds to erosion rate semiquantitatively

Here we present(^(234)U/^(238)U)data from river sediments collected on the Tibetan Plateau.The(^(234)U/^(238)U)ratios of a specific grain size fraction show good correlation with erosion rates,which were determined by in-situ–produced cosmogenic nuclides.This correlation has previously been observed in a wide range of geomorphic settings,suggesting that(^(234)U/^(238)U)ratios of fluvial sediments have great potential to quantify erosion rates.

Study of Even ^(230-238)U Isotopes by Using Cranked Nilsson Model,Single Particle Schrodinger Fluid and Collective Model

The Cranking Nilsson model is applied to calculate the single-particle energy eigenvalues and eigenfunctions of nuclei in a strongly deformed potential. Accordingly, The L. D. Energy, the Strutinsky inertia, the L. D. inertia, the volume conservation factor , the smoothed energy, the BCS energy, the G-value and the electric quadrupole moment of the five uranium isotopes: 230U, 232U, 234U, 236U and 238U are calculated as functions of the deformation parameter. Furthermore, the single-particle Schrodinger fluid is applied to calculate the rigid-body model, the cranking-model and the equilibrium-model moments of inertia of the five uranium isotopes. Moreover, the collective model is applied to calculate the rotational energies of these isotopes. The best potential and deformation parameters are also given.

Identification of Pu and U isotopic composition and its applications in environmental and CBRN research

This paper describes the most common presently used methods for detecting uranium and plutonium isotopes after their introduction to environment. Known isotope ratios of U and Pu in different nuclear events are important tool for characterizing the sources of nuclear material. Detection techniques both in field and in laboratory are presented, as well as different models that can be used for identifying the origin and age of the nuclear material. Identification of the source of nuclear material in environmental samples is needed for estimating the quality and quantity of the nuclear hazard. This information is essential in risk assessment and crisis management, in chemical, biological, radiological and nuclear(CBRN) research after e.g. a terrorist attack, in radioecology and environmental radioactivity research.

Alpha Decay of the Neutron-deficient Isotopes 215,216U

The most neutron-deficient isotopes215,216 U were produced in the complete-fusion reaction ^(180)W(^(40)Ar, 4-5n)^(215,216) U. Evaporation residues recoiled from the target were separated in-flight from the primary beam by the gas-filled recoil separator SHANS and subsequently identified on the basis of correlated α-decay chains. Two α-decaying states were identified in ^(216)U, one for the ground state and the other for the isomeric state with 8+(πh_(9/2)πf_(7/2)) configuration. The α-decay properties for ^(215,216)U and the systematics of 8+isomeric state in N = 124, 126 isotones were investigated.