Search results for "uranium"

The impact of a disused mine on uranium transport in the River Fal, South West England.

2004

Unfiltered and filtered (0.45 and 0.2 microm) water samples and sediment samples (sieved to180 microm and 180-1000 microm) were collected along an approximately 15 km transect of the River Fal, Cornwall, UK, to examine the impact of the disused South Terras uranium mine on the uranium concentrations of the river water and underlying sediments. The uranium concentration of the water samples fluctuated along the river, with the 0.45 microm filtered water showing the largest, seven-fold, difference between minimum (0.19 microg L(-1)) and maximum (1.34 microg L(-1)) concentrations. The historical uranium mine and spoil heaps were not a significant source of uranium to the river water, as water …

Beta-Decay Half-Lives and Neutron-Emission Probabilities of Very Neutron-Rich Y to Tc Isotopes

1996

Neutron-rich {sub 39}Y to {sub 43}Tc isotopes have been produced by fission of uranium with a 50MeV H{sub 2}{sup +} beam. Beta-decay half-lives, delayed neutron-emission probabilities, and production yields have been measured and compared with theory. Beta decay of 4 new isotopes is reported, and the {beta}-delayed neutron-emission mode has been discovered for 12 isotopes of the elements niobium and technetium. The results compared to quasiparticle random phase approximation predictions indicate the increasing importance of fast {beta} transitions to high-lying states of nuclei with large neutron excess. {copyright} {ital 1996 The American Physical Society.}

UraniumIV and uranyle salts, efficient and reusable catalysts for acylation of aromatic compounds

2000

Abstract Uranium tetrachloride, uranyle chloride, fluoride and also nitrate or acetate are very efficient homogeneous catalysts for the Friedel–Crafts acylation of aromatic compounds. With uranyle salts, the reaction, carried under dry air, is highly specific and the mono- or bisacylation products are obtained in high yield. Uranyle catalyst can be quantitatively recovered and reused and the organic products are obtained free of uranium.

Sorption of uranium(VI) onto ferric oxides in sulfate-rich acid waters.

2003

The mechanisms of the uranium(VI) sorption on schwertmannite and goethite in acid sulfate-rich solutions were studied by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The samples were prepared under N2 atmosphere and initial uranium(VI) concentrations of 1 x 10(-5) (pH 6.5) to 5 x 10(-5) M (pH 4.2). The ionic strength was adjusted using 0.01 M Na2SO4 or 0.01 M NaClO4, respectively. The EXAFS structural parameters for uranium(VI) sorbed on goethite in sulfate-rich, acid and near-neutral solutions indicate that uranium(VI) forms an inner-sphere, mononuclear, bidentate surface complex. This complex is characterized by a uranium-ferric-iron distance of approximately 3.45 A. Ura…

Study of the role of sulfur functionalities in humic acids for uranium(VI) complexation

2009

Humic substances influence the speciation and migration behavior of toxic and radiotoxic metal ions, such as actinides, in the environment. Depending on their origin, humic substances contain different amounts of sulfur ranging from 0.1 to 3.6% and 0.5 to 1.43% in soil and aquatic humic substances, respectively [1]. Reduced, intermediately oxidized and highly oxidized sulfur functionalities occur in humic substances [1]. Although sulfur functionalities occur in small concentrations, they can play an important role in the complexation of selected metal ions. Knowledge about the impact of sulfur functionalities on the metal ion complexation by humic substances and their significance compared …

A new resonant Laser-SNMS system for environmental ultra-trace analysis: Installation and optimization

2017

Abstract Localization, analysis and mobility of radioactive contaminated particles is of major concern for assessment of contamination threads and nuclear forensics. For this purpose, a new resonant Laser-SNMS system was developed and set up at the Institute for Radioecology and Radiation Protection for spatially resolved ultra-trace analysis of low concentrated radionuclides directly on environmental samples. This paper describes the adaption and combination of a dedicated Ti:sapphire laser system with a commercial TOF-SIMS instrument for resonant Laser-SNMS. The project includes computer simulations for optimization of the TOF analyzer. Results on synthetic uranium and technetium samples …

Preparation of tungstophosphoric acid/cerium-doped NH2-UiO-66 Z-scheme photocatalyst: a new candidate for green photo-oxidation of dibenzothiophene a…

2021

International audience; The goal of this study was to introduce an effective visible-light induced photocatalytic system with a good ability for photocatalytic oxidative desulfurization (PODS) and denitrogenation (PODN) using molecular oxygen (O2) as an oxidant. In this regard, tungestophosphoric acid (PW12) was supported onto cerium-doped NH2-UiO-66 (PW12/Ce-NUiO-66) and employed for the photo-oxidation of dibenzothiophene (DBT) and quinoline (Qu). Herein, using cerium (Ce) as a “mediator” facilitated the separation of charge carriers, while NH2-UiO-66 remarkably enhanced the surface area with plentiful adsorption sites and shifted the adsorption edge of PW12to the visible region. The sum …

The formal redox potential of the U(IV-III) couple at 25°C in the aqueous 3 M (Na+, H+) Cl- medium

1998

Interaction of Dioxouranium(VI) ion with aspartate and glutamate in NaClaq at different ionic strengths

2005

The formation of complexes species of the dioxouranium(VI) ion with aspartic and glutamic acids was studied in the pH range of 3 to 6 at 25 °C by potentiometric measurements (H+-glass electrode). Results gave evidence for the formation of the following species: (UO2)A0, (UO2)AH+, and (UO2)2A(OH)2 0 (A2- ) a glutamic or aspartic ligand). Investigations were carried out in a NaCl ionic medium at I (0.1, 0.25, 0.5, and 1.0) mol L-1. The dependence on ionic strength of the formation constants was analyzed by the specific ion interaction theory (SIT) model. The formation constants at infinite dilution, obtained using this model, are log â110 ) 8.53 ( 0.03, 8.37 ( 0.05; log â111 ) 13.60 ( 0.05, 1…

Spectroscopic characterization of alkaline earth uranyl carbonates

2005

A series of alkaline uranyl carbonates, M[UO{sub 2}(CO{sub 3}){sub 3}].nH{sub 2}O (M=Mg{sub 2}, Ca{sub 2}, Sr{sub 2}, Ba{sub 2}, Na{sub 2}Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). The molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba{sub 2}[UO{sub 2}(CO{sub 3}){sub 3}].6H{sub 2}O was obtained for the first time. The EXAFS analysis showed that this compound consists of …