Specific features of reactions of Am(V) with reductants in weakly acidic solutions

In EDTA solutions with pH ??5 at 25°C, Am(V) in a concentration of 5 × 10^?4?3 × 10^?3 M slowly transforms into Am(III). The Am(V) reduction and Am(III) accumulation follow the zero-order rate law. In the range 60?C80°C, the reaction is faster. In some cases, an induction period is observed, disappearing in acetate buffer solutions. In the range pH 3?C7, the rate somewhat increases with pH. In an acetate buffer solution, an increase in [EDTA] accelerates the process. The activation energy is 47 kJ mol^?1. Zero reaction order with respect to [Am(V)] is observed in solutions of ascorbic and tartaric acids, of Li₂SO₃ (pH > 3), and of hydrazine. The process starts with the reaction of Am(V) with the reductant. The Am(III) ion formed in the reaction is in the excited state, *Am(III). On collision of *Am(III) with Am(V), the excitation is transferred to Am(V), and it reacts with the reductant: *Am(V) + reductant ?? Am(IV) + R₁ and then Am(IV) + reductant ?? *Am(III) + R₁, Am(V) + R₁ ?? Am(IV) + R₂. A branched chain reaction arises. The decay of radicals in side reactions keeps the system in the steady state; therefore, zero reaction order is observed.     

Upgrading the Design of Cruciform Fuel Elements to Increase their Heat-Engineering Characteristics

The change occurring in the heat-engineering characteristics of a cruciform fuel element in a SM reactor as a result of the change in the characteristic dimensions of the fuel element, such as the diameter of the circumscribing circle, the indentation radius, and the rounding radius of a lobe, and as a result of the presence of a central displacer in the element is examined. The optimal values of the indentation radius and rounding radius of a lobe are determined to be 0.5 mm. It is shown that the presence of a central displacer in a fuel element substantially decreases the maximum temperature of the kernel and decreases the coefficient of nonuniformity of the heat flux density. For the same maximum kernel temperature in a standard fuel element and a fuel element with a displacer, the maximum heat flux density in the latter element gives an additional margin up to the crisis of heat transfer.__________Translated from Atomnaya Energiya, Vol. 98, No. 4, pp. 274–280, April, 2005.     

Comparison of the results of summer and winter measurements of atomospheric water vapor absorption at wavelengths 1.5 ÷ 1.55 mm

Instrumental data on the water vapor absorption coefficient at air temperatures 255 ÷ 272 K, as well as the equipment and measurement procedure are briefly desribed. A comparison is performed with the summer measurement and the data reported by other authors.     

Method for estimating lineature by scanned samples of documents

The paper considers an algorithm for estimating lineature of scanned digital images based on the calculation of series lengths and local directional fields. The results of an experiment are given and the efficiency of the algorithm is investigated. Vitalii Anatol’evich Mitekin. Born in 1983. Graduated from Samara State Aerospace University (SSAU) in 2006. At present, he is a post-graduate student in the Department of Geoinformatics at SSAU. His scientific interests include image processing, stenography, and cryptography. He is the author of three publications, including three articles. Viktor Andreevich Fedoseev. Born in 1986. Defended a degree thesis at the Samara State Aerospace University in 2007. Continues teaching at the SSAU at present, and also works as a technician at the Institute of Image Processing Systems at the Russian Academy of Sciences. His scientific interests include computer graphics, image processing, stenography, and cryptography. He is the author of 11 publications, including six articles.     

Extraction of U(VI), Th(IV), Pu(IV), Am(III), and rare-earth elements from nitric acid solutions with diphenyl(dialkylcarbamoylmethyl)phosphine oxides substituted in the methylene bridge

The extractive power and selectivity of diphenyl(dialkylcarbamoylmethyl)phosphine oxides in extraction of U(VI), Th(IV), Pu(IV), Am(III), and rare-earth elements from nitric acid solutions was studied, as influenced by substitution of one or two hydrogen atoms in the methylene bridge with alkyl, cycloalkyl, CH₂P(O)Ph₂, and CH₂C(O)NBu₂ groups.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 427–432.Original Russian Text Copyright © 2004 by Turanov, Karandashev, Yarkevich, Safronova, Kharitonov, Radygina, Fedoseev.     

Influence of the Redox Potential and Charge of <Emphasis Type="Italic">f</Emphasis> Element Ions on the Kinetics of Reactions Involving Them

Experimental data on the kinetics of reactions of lanthanide and actinide ions with ОН radicals, e _aq ^– , each other, and d element ions are analyzed. The reactions with ОН radicals are kinetically controlled, with the rate constants being independent of the redox potential of the ion. This is due to the fact that the ОН radical abstracts the H atom from Н₂О in the hydration shell, which is followed by the charge transfer. The An⁴⁺ ions are oxidized with the formation of the An⁵⁺ ions, followed by their hydrolysis. The hydrated electrons e _aq ^– react with f element ions whose potential is less negative than–2.0 V, with the reaction being diffusion-controlled. The reactions of e_aq^– with An⁴⁺ and AnO ₂ ²⁺ occur by the tunneling mechanism. The reactions of the ions with each other are kinetically controlled, with the rate constants depending on ΔЕ of the reaction. The correlation is broken in the case of formation of AnO ₂ ⁺ –An⁴⁺ cation–cation complexes or of reactions involving the structure rearrangement. The stability of heptavalent ions in an alkaline solution decreases with an increase in the oxidation potential and with a decrease in the ion charge.     

Synthesis and crystal structure of cesium actinide(VI) tricarbonate complexes Cs4AnO<Subscript>2</Subscript>(CO<Subscript>3</Subscript>)<Subscript>3</Subscript>·6H<Subscript>2</Subscript>O,An(VI) = U,Np, Pu

Tricarbonate complexes of hexavalent U, Np, and Pu with outer-sphere cesium cations, Cs₄AnO₂·(CO₃)₃·6H₂O, were synthesized and studied by single crystal X-ray diffraction analysis. Crystals of Cs₄AnO₂·(CO₃)₃·6H₂O consist of [AnO₂(CO₃)₃]^4– complex anions and hydrated Cs⁺ cations. The coordination polyhedron (CP) of An(VI) atoms is a distorted hexagonal bipyramid with three CO ₃ ^2– anions arranged in the equatorial plane. Four independent Cs+ cations have the coordination surrounding in the form of 11-, 10-, and 9-vertex polyhedra formed by the O atoms of CO ₃ ^2– anions, AnO ₂ ²⁺ cations, and water molecules. Six crystallographically independent water molecules in the structure of Cs₄AnO₂(CO₃)₃·6H₂O form a three-dimensional system of hydrogen bonds in which the O atoms of carbonate ions and water molecules act as proton acceptors. The “yl” oxygen atoms of AnO ₂ ²⁺ cations are not involved in hydrogen bonding. The lengths of the An–O_carb bonds in the equator of the U, Np, and Pu hexagonal bipyramids are noticeably influenced by incorporation of the O atoms of the CO ₃ ^2– anions in the coordination polyhedra of Cs⁺ ions and by involvement of these atoms in hydrogen bonding.     

Mechanism of transformation of Np(V) into Np(IV) in sodium 1,2-cyclohexanediaminetetraacetate solutions

The kinetics of the transformation of Np(V) into Np(IV) in 0.1 M potassium biphthalate solutions containing 5–74 mM sodium 1,2-cyclohexanediaminetetraacetate (Na₂CHDTA) or in a 96–97 mM Na₂CHDTA solution at 25–45°С was studied. The reaction rate at Na₂CHDTA concentrations in the range 5–60 mM and pH 3.5–5.9 is described by the equation V = k[Np(V)]^1.4[CHDTA], and at Na₂CHDTA concentrations in the range 70–100 mM and pH 4.1–5.2, by the equation V = k _A[Np(V)]^1.4. Neptunium(V) forms with the CHDTA ion an activated complex in which Np(V) is reduced to Np(IV). The dimer {Np(V)}₂ forming another activated complex with the CHDTA ion is formed concurrently. The latter complex decomposes along the disproportionation pathway to give Np(IV) and Np(VI). Np(VI) is reduced with the CHDTA ion to Np(V).