Plutonium(III) oxidation under α-irradiation in nitric acid solutions

Plutonium(III) oxidation under high energy α-irradiation in nitric acid solutions has been studied relative to concentrations of both nitric acid (0.12–2.9 mol/l) and plutonium (1.4–10 mmol/l) using spectrophotometric techniques. Curium-244 has been used as the basic alpha-irradiation source. It has been stated that in solutions with nitric acid concentrations lower than 0.5 mol/l plutonium(III) does not oxidize completely. In the course of the process the formation of a plutonium(IV) peroxide complex is observed. Increase in the nitric acid concentration results in that in both the rate and degree of plutonium(III) oxidation. When c_{HNO 3} is higher than 0.5 mol/l the peroxide complex does not form and the process assumes an autocatalytic character. It has also been shown that plutonium(III) oxidation kinetics is significantly affected by nitrous acid, one of the nitrate ion radiolysis products. To describe plutonium chemical transformations under irradiation in nitric acid solutions, a kinetic scheme is proposed. The calculations have been carried out on a BESM-6 computer; a satisfactory agreement between the calculated and experimental data has been obtained.     

Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U-OAr2 and U-SAr2 bonding

A rigid NSN-donor proligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylthioxanthene (H(2)[TXA(2)], 1) was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylthioxanthene. Deprotonation of 1 using (n)BuLi provided Li(2)(DME)(2)[TXA(2)] (2), and subsequent reaction with UCl(4) afforded [Li(DME)(3)][(TXA(2))UCl(3)] (4). The analogous NON-donor ligated complex [(XA(2))UCl(3)K(DME)(3)] [3; XA(2) = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene] was prepared by the reaction of K(2)(DME)(x)[XA(2)] with UCl(4). A cyclic voltammogram (CV) of 3 in THF/[NBu(4)][B(C(6)F(5))(4)] at 200 mV s(-1) showed an irreversible reduction to uranium(III) at E(pc) = -2.46 V versus FeCp(2)(0/+1), followed by a product wave at E(1/2) = -1.83 V. Complex 4 also underwent irreversible reduction to uranium(iii) [E(pc) = -2.56 V], resulting in an irreversible product peak at E(pa) = -1.83 V. One-electron reduction of complexes 3 and 4 using K(naphthalenide) under an argon atmosphere in DME yielded 6-coordinate [(XA(2))UCl(DME)] (5) and the thermally unstable 7-coordinate [(TXA(2))U(DME)Cl(2)Li(DME)(2)] (6), respectively. The U-S distances in 4 and 6 are uncommonly short, the C-S-U angles are unusually acute, and the thioxanthene backbone of the TXA(2) ligand is significantly bent. By contrast, the xanthene backbone in XA(2) complexes 3 and 5 is planar. However, κ(3)-coordination and an approximately meridional arrangement of the ancillary ligand donor atoms is maintained in all complexes. DFT and Atoms in Molecules (AIM) calculations were carried out on 3, 4, 5, 6, [(XA(2))UCl(3)](-) (3B), [(TXA(2))UCl(2)(DME)](-) (6B) and [(TXA(2))UCl(DME)] (6C) to probe the extent of covalency in U-SAr(2) bonding relative to U-OAr(2) bonding.     

Kinetics of actinide valence transformation in alpha-radiolysis of nitrate and perchlorate solutions

This paper presents the results of systematic kinetic studies of valence transformation of U, Np, Pu, Am and Bk in nitrate- and perchlorate solutions under the effect of intensive internal alpha-radiation emitted by²⁴⁴Cm nuclides. The high dose rate of solutions (D=1–8 Gy/s) provides a sufficient yield of H₂O₂, HNO₂ and ClO₂ — the main products of alpharadiolysis of water, nitrate and perchlorate ions, respectively, which was determined by spectrophotometric methods immediately in the course of the process under study. To describe the results, a kinetic scheme considering the effect of dose rate and solution composition is proposed. The calculations have been carried out on a BESM-6 computer, a satisfactory agreement between the calculated and experimental data has been obtained.     

Stability of plutonium(IV) and plutonium(VI) in nitric acid solutions under strong α-irradiation

Plutonium(IV) oxidation has been studied in 1 to 20 mol/1 HNO₃ under 1 to 14 W/1 internal alpha-irradiation and at plutonium concentrations from 2 to 100 mmol/1. Curium isotopes have been used as the basic alpha-irradiation sources. It has been established that in the systems investigated both oxidation of plutonium(IV) and reduction of plutonium(VI) take place, resulting with time in reaching the equilibrium between plutonium(IV) and plutonium(VI). The presence of plutonium(IV) enhances the reduction of plutonium(VI). The rate constants for plutonium(IV) oxidation and plutonium(VI) reduction have been estimated and their dependences upon the concentrations of nitric acid, plutonium(IV) and plutonium(VI) as well as upon the dose rate investigated. An equation has been derived which permits to calculate the concentrations of plutonium(IV) and plutonium(VI) at any desired time.     

Steady vortical flow around a finite plate

An explicit solution for a layer of fluid with constant vorticitysurrounding a thin plate of finite length is obtained usingelementary conformal mapping methods. In the limit of largeplate length the behaviour of the solution near the ends ofthe plate tends to that of the previously known solution fora semi-infinite plate. Contour dynamics is used to investigatethe stability of the steady solutions.     

Study of the combined carbonization of poly(vinylidene fluoride) by X-Ray photoelectron spectroscopy

The surface composition of two samples synthesized by the combined carbonization of poly(vinylidene fluoride) (PVDF) films is studied by X-ray photoelectron spectroscopy. One of them is successively exposed only to chemical and radiation impacts, and the treatment of the other includes chemical, heat, and radiation exposure. The chemical preparation of both samples is the same. It is shown that the magnitude and direction of the gradient of the residual fluorine concentration in the surface layer of PVDF carbonization products can be controlled. Since dehydrofluorination decreases the surface electrical resistance of the material, a combination of chemical, heat, and radiation treatments can be used to create a predetermined sequence of heterolayers with different fluorine concentration on a flexible and transparent polymer base and, therefore, with different conductivities.