[en] The first high-nuclearity uranium complex contains an octahedral array of metal centers that is coordinated by twelve diphenylphosphate as well as eight oxo or hydroxo ligands. Although the degree of protonation of the capping centers could not be determined unambiguously, many of the findings point to OH ligands. The picture on the right shows the U₆O₈ framework of the complex. (orig.)

[en] Current literature suggests uncertainty about the numerical values of the hydrolysis constants for tetravalent plutonium. This letter uses recent data to propose that newer methods for estimating the hydrolysis constants are not necessarily more accurate than the traditional methods. (author)

[en] The state of the art of fast scintillator development is considered. Decay curves of some scintillators measured at pulsed (0.5 ns) X-ray excitation are presented. Literature results are analyzed and summarized. It is shown that radiative core-valence transitions are best suited for subnanosecond and nanosecond scintillations, while rare earth ions show efficient scintillation with decay constants of tens of nanoseconds in oxygen-based crystals. Emissions from both Ce³⁺ ions and core-valence transitions in a crystal are particularly useful for neutron/gamma discrimination. Promising emission mechanisms are proposed to be used in fast scintillators

[en] Pulsed-laser photoacoustic spectroscopy (PAS) and Fourier-transform nuclear magnetic resonance (NMR) spectroscopy were used to study speciation of actinide(IV) and actinide(VI) ions (Np, Pu, Am) in aqueous carbonate solutions vs of pH, carbonate concentration, actinide content, and temperature. PAS focused on Pu(IV) speciation. Stability fields on a pH (8.4 to 12.0) versus total carbonate content (0.003 to 1.0 M) plot for dilute Pu(IV) carbonate species ([Pu]_tot = 1 mM) were mapped. Four plutonium species, with absorption peaks at 486, 492, 500, and 512 nm were found. Loss of a single carbonate ligand does not account for the difference in speciation for the 486 and 492 nm absorption peaks, nor can any of the observed species be identified as colloidal Pu(IV). NMR data have been obtained for UO₂²⁺, PuO₂²⁺ and AmO₂²⁺. This report focuses on results for PuO₂²⁺. The ligand exchange reaction between free and coordinated carbonate on the PuO₂(CO₃)₃^4- systems has been examined by variable temperature ¹³C NMR spectroscopy. In each of the six different PuO₂(CO₃)₃^4- samples, two NMR signals are present, one for the free carbonate ligand and one for the carbonate ligand coordinated to a paramagnetic plutonium metal center. The single¹³C resonance line for coordinated carbonate is consistent with expectations of a monomeric PuO₂(CO₃)₃^4- species in solution. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was used for determining of ligand exchange parameters for paramagnetic actinide complexes. Eyring analysis at standard conditions provided activation parameters of ΔH = 38 KJ/M and ΔS = -60 J/K for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl(VI) carbonate complex self-exc

[en] We present a systematic study on the coordination chemistry of U(IV) and -(VI) with bipy and phen under different chemical conditions, such as different solvents and changing the metal / ligand ratio. We succeeded to obtain a series of U(IV) complexes with U:ligand ratios of 1:1 and 1:2, all of which show an eight-fold coordinated uranium centre. In addition to the ligand, chloro and methanolato ligands are coordinating to the metal centre for charge compensation. Interestingly, the complexation between U(IV) and the ligand does occur even in protic solvents, in which the ligand is expected to be protonated. We also obtained another series of U(VI) complexes with both bipy and phen, underlining the versatile coordination chemistry of uranyl (UO₂²⁺). That is, the coordination between uranyl and the ligand depends strongly on the pH of the solvent used. For instance, in media with lower pH mononuclear complexes are formed, showing the uranyl unit in an unusually bent geometry. On the other hand, dinuclear uranyl arrangements with hydroxo-bridging are dominated in the media with higher pH.

[en] Published in summary form only

[en] From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M⁺(aq) + Cs⁺(org) ↔ M⁺(org) + Cs⁺(aq) taking place in the two-phase water-phenyltrifluoromethyl sulfone (abbrev. FS 13) system (M⁺ Li⁺, H₃O⁺, Na⁺, NH₄⁺, Ag⁺, Tl⁺, K⁺, Rb⁺; aq = aqueous phase, org FS 13 phase) were evaluated. Furthermore, the individual extraction constants of the M⁺ cations in the mentioned two-phase system were calculated; they were found to increase in the series of Li⁺ < H₃O⁺ < Na⁺< NH₄⁺ < Ag⁺ < Tl⁺ < K⁺ < Rb⁺ < Cs⁺. (author)

[en] We investigate how coupling of valence q qbar to meson pairs can modify the properties of conventional q qbar and hybrid mesons. In a symmetry limit the mixing between hybrids and conventional q qbar with the same J^PC is shown to vanish. Flavor mixing between heavy and light q qbar due to meson loops is shown to be dual to the

[en] We give a theoretical approach to the valence change in small Pr_n aggregates [transition: 4f³(5d6s)²→4f²(5d6s)³], our study limited to n≤4. The quantum-mechanics problem (Anderson Hamiltonian) exhibits various difficulties: f-valence mixing and strong intra-atomic f correlations. For dealing with this problem we use an extension to the mixed-band systems of the Gutzwiller method. The extension is detailed and controlled by an application to the Hubbard s chain, for which the exact solution is known. As the number of f electrons and sites of our Pr_n system is relatively small, we take into account the full f degeneracy. We find the transition for n=3, which is close to the experimental result, n=5. A physical explanation of the phenomenon is proposed

[en] A new method for estimating the numerical value of the first hydrolysis constant of tetravalent plutonium is illustrated by examples. It uses the pH and the equilibrium fractions of two of the Pu oxidation states. They are substituted into one or more of a choice of formulas that render explicit estimates of the hydrolysis constant. (author)