Actinides and Lanthanides

The stopping power of protons through Hf foil has been studied both experimentally and theoretically. The measurements were performed at the Laboratory of Accelerators and X-Ray Diffraction in Lisbon by using the transmission method on self-supporting stopping material. The overall uncertainty of around 5% was established over the protons energy range (0.6-2.5) MeV. The theoretical developments involved fully relativistic atomic structure calculations for Hf, which required the solution of the Dirac equation. The shell-wise local plasma approximation was used to describe the energy transferred to the bound 1s-4 f electrons, and the outer four electrons were considered as a free electron gas. We found the relativistic description of the 4 f shell and the screening between 4 f and 5p electrons to be decisive around the stopping maximum. Present theoretical and experimental results are in very good agreement in the energy region of the new measurements. However, our theoretical stopping cross sections show substantial differences with the most used semiempirical models (SRIM2013 and ICRU-49) at intermediate to low energies. Our calculations suggest the stopping maximum to be higher and shifted to lower energies than these previous predictions. Future measurements around the maximum and below would be necessary for a better understanding of the stopping power of hafnium.

Three new actinide thiophosphates, SrU(PS 4) 2 , BaU(PS 4) 2 , and SrTh(PS 4) 2 , have been synthesized by high-temperature solid-state methods, and their crystal structures were determined from single-crystal X-ray diffraction studies. These three isostructural compounds crystallize in a new structure type in space group D 4h 13-P4 2 /mbc of the tetragonal system. Their structure features infinite one-dimensional chains of ∞ 1 [An(PS 4) 2 2− ] anions (An = U or Th). Each An atom is coordinated by eight S atoms in a bicapped trigonal prism, and each P atom is tetrahedrally bonded to four S atoms. The compounds are readily charge balanced as Ak 2+ An 4+ (P 5+ (S 2−) 4) 2. Optical studies on single crystals of SrU(PS 4) 2 and BaU(PS 4) 2 as well as ground single crystals of SrTh(PS 4) 2 revealed a direct band gap of 2.13(2) eV and an indirect band gap value of 1.99(2) eV for SrU(PS 4) 2 and a direct and indirect gap of about 2.28(2) eV for BaU(PS 4) 2. SrTh(PS 4) 2 has a relatively large band gap of 3.02(2) eV. DFT calculations for SrU(PS 4) 2 and BaU(PS 4) 2 using the HSE functional predict both compounds to be antiferromagnetic and have very similar electronic structures with band gaps of 2.7 eV. The band gap calculated for SrTh(PS 4) 2 is 3.2 eV.

A family of alkali uranium(IV) phosphates, AU 2 (PO 4) 3 (A = Li-Cs), was synthesized as single crystals by the reaction of US 2 and (NH 4) 2 HPO 4 in the respective ACl (A = Li-Cs) flux contained in a sealed quartz tube at 850 °C, and as phase pure powders from a similar reaction using UF 4 as the uranium source. AU 2 (PO 4) 3 (A = Li-Rb) crystallize in the NaTh 2 (PO 4) 3 (NTP) structure type with monoclinic space group C2/c and consist of a 3D structure that features a framework composed of edge-and corner-sharing polyhedra. The cesium analog, CsU 2 (PO 4) 3 , crystallizes in a different structure with space group P2 1 /n that is related to the NaZr 2 (PO 4) 3 (NZP) structure type and consists of a framework composed of corner sharing polyhedra. Two new alkali uranium phosphates, Li 2 U(PO 4) 2 and Cs 4 U 4 (P 2 O 7) 5 , were also grown at 700 °C. Li 2 U(PO 4) 2 was isolated in approximately 30% yield based on uranium. Li 2 U(PO 4) 2 crystallizes in space group P2 1 /c exhibiting a layered structure while Cs 4 U 4 (P 2 O 7) 5 , crystallizes in space group P2 1 /n in a new structure type featuring a 3D framework. The magnetic susceptibilities and the field dependent magnetizations were measured for AU 2 (PO 4) 3 (A = Li, Na, K and Cs); all compounds exhibit negative Weiss temperatures with no obvious antiferromagnetic transition. Optical properties were measured by UV-vis and IR spectroscopy.

The accumulation of long-lived americium-241 radionuclide in spent nuclear fuel reprocessing products necessitates the search for methods to minimize or stabilize its amount. One of the possible solutions to this problem is the involvement of americium in fuel compositions based on mixed uranium and plutonium nitrides. The technology of carbothermic synthesis and sintering of tablets of mixed uranium and plutonium nitrides is the most studied, experimentally justified for implementation on an industrial scale. The aim of the work is to manufacture and study tablets of mixed nitrides of uranium, plutonium, americium and neptunium. As a result of the work, data were obtained on the content of americium in MNUP fuel at various process parameters; batches of tablets with an initial content of americium of 0.4, 0.7 and 1.1% by weight were manufactured and tested, samples with a density of up to 12.6 g/cm3 were made. Metallographic studies have shown that Np and Am, in general, are evenly distributed over the cross-section of the tablets. The mass fraction of Np in the sum of U, Pu and Np isotopes does not change under the selected technological modes of manufacturing experimental batches. There are conditions under which the mass fraction of Am in tablets does not decrease both relative to the content of Am in actinide oxides before synthesis, and relative to its content in tablets after carbothermic synthesis before sintering. Also, with certain Am contents, there is a decrease in its concentration on the periphery relative to the center of the tablet after sintering. The work was carried out within the framework of the project direction "PRORYV".

Fully relativistic atomic structure calculations for Zr, Nb, Pd, Gd, Er, Hf, Ta, Os, and Pt are presented here. The description of these atoms requires the solution of the Dirac equation. The electron binding energies attained are compared with experimental values, achieving excellent overall agreement for the inner shells. Discrepancies in the outer shell binding energies between the isolated atom and the solid are discussed, giving special attention to the open f 4-subshell. Based on the present calculations, we analyzed the valence shell of the nine elements studied here and propose theoretical values for the Wigner-Seitz radio.

Two new monomers of N-4-antipyrinyl methyl nadamic acid M1 and N-Procaienyl methyl nadamic acid M2 were synthesized from reaction of 4-Aminoantipyrine or procaine with methyl nadic anhydride at room temperature with dioxane as a solvent. The prepared monomers M1 and M2 were polymerized free radically with AIBN as initiator to corresponding polyamic acids P1 and P2, Which were converted to their sodium salt polymers P3 and P4 to enhanced their solubility's in water. The physical and chemical properties were studied for monomers and polymers, also FT-IR ,1H-NMR  and UV. Spectroscopy was characterized of M1or M2. The intrinsic viscosity was measured by  Ostwald viscometer at 30 0C  .The swelling %was measured and the controlled release rates of drug polymers were studied in different pH values at 37 0C.

The method of carbothermic synthesis produced 260 g tablets of mixed nitrides of uranium, plutonium, americium and neptunium with a mass fraction of americium 0.61%. For the production of tablets were used uranium oxide manufactured by the water method, as well as plutonium dioxide containing impurities of uranium and americium oxides with a mass of 0.9 g americium, obtained by volumetric crystallization method in a NaCl — 2CsCl melt. Neptunium dioxide and americium oxide were added to the mixture of uranium and plutonium oxides before carbothermic synthesis. The resulting tablets had a density of 11.6-11.9 g / cm3. By methods of gamma-spectrometry, scanning electron microscopy and x-ray microanalysis is showed that the heat treatment of the mixture of the source chemicals - oxides of uranium, plutonium, americium, neptunium with carbon black at a temperature 1600-1500 °C for 72 h (24 h in nitrogen and 48 h in nitrogen-hydrogen atmospheres), and also the subsequent sintering synthesized by the press powders for 48 h at a temperature of 1800°C in nitrogen-hydrogen atmosphere doesn't leads in average to the significant losses of americium.

The first entirely pentavalent uranium borate, Na 2 (UO 2)(BO 3), was synthesized under mild hydrothermal conditions. The single-crystal structure was solved in the orthorhombic space group Cmcm with a = 10.0472(3) Å, b = 6.5942(2) Å, and c = 6.9569(2) Å. Magnetic susceptibility measurements revealed an anti-ferromagnetic transition at 12 K and an effective magnetic moment of 2.33 μ B. Density functional theory calculations indicated dynamic stability of the structure above 0 K. H istorically, almost all research in uranium chemistry was motivated by weapons and energy applications. More recently, however, the remediation and sequestration of legacy waste has become more pressing and is one reason for the current more comprehensive research efforts. 1 As part of our program to prepare different classes of materials for potential use in future nuclear waste forms, 2 we have focused on uranium borates as one class of materials that can lead to structure types practical for nuclear waste forms because uranium borates have been investigated in the past and numerous structures have been observed. 3−6 As part of this effort, there exists the need to understand uranium cation stability and mobility in the environment and uranium complexation, crystal, and redox chemistry. In aqueous conditions, uranium(VI) and-(IV) are the most stable among the four accessible oxidation states of uranium and, thus, the most prevalent in both synthetically derived compounds and reported minerals; comparatively, uranium(V) and-(III) are considerably less stable. 7 Reaction conditions that promote uranium(V) formation are limited, and the stability of the aqueous pentavalent [UO 2 ] + species is inhibited by its tendency to either oxidize to uranium(VI) or undergo rapid disproportionation into hexavalent [UO 2 ] 2+ and tetravalent UO 2 species. 8,9 As a result of this limited stability, there are very few examples of exclusively pentavalent uranium oxides in the literature. A primary challenge in the preparation of uranium(V) oxides lies in achieving conditions that favor the formation of exclusively uranium(V) phases over those that are mixed-valent, such as the common U 3 O 8 phase. Solid-state methods have yielded ternary uranium(V) oxides, including AUO 3 (A = Na, K) 10,11 and MU 2 O 6 (M = Co, Ni); 12 however, this method has, to date, resulted in only a handful of compositions.

Emerald-green single crystals of U(PO 4)Cl were grown by chemical vapor transport in a temperature gradient (1000 → 900 °C). The crystal structure of U(PO 4)Cl (Cmcm, Z = 4, a = 5.2289(7) Å, b = 11.709(2) Å, c = 6.9991(8) Å) consists of a three-dimensional network of [PO 4 ] tetrahedra and bicapped octahedral [U IV O 6 Cl 2 ] groups. Polarized absorption spectra measured for two perpendicular polarization directions show a large number of well-resolved electronic transitions. These transitions can be fully assigned on the basis of a detailed ligand-field treatment within the framework of the angular overlap model. The magnetic behavior predicted on the basis of the spectroscopic data is in agreement with an f 2 system and perfectly matched by the results of temperature-dependent susceptibility measurements.

Endohedral actinide fullerenes are rare and a little is known about their molecular properties.
Here we characterize U2@C80 system, which was recently detected experimentally by means
of mass spectrometry (Akiyama et al., JACS 2001, 123, 181). Theoretical calculations predict
a stable endohedral system, 7U2@C80 derived from the C80:7 IPR fullerene cage, with six
unpaired electrons. Bonding analysis reveals a double ferromagnetic (one-electron-twocenter)
U‒U bond at rU‒U distance of 3.9 Å. This bonding is realized mainly via U(5f) orbitals.
The U-U interaction inside the cage is estimated to be about -18 kcal/mol. The U‒U bonding
is further studied along the U2@Cn (n = 60, 70, 80, 84, 90) series and the U‒U bonds are also
identified in U2@C70 and U2@C84 systems at rU‒U ~4 Å. It is found that the character of U‒U
bonding depends on the U‒U distance, which is dictated by the cage type. A concept of
unwilling metal-metal bonding is suggested: Uranium atoms are strongly bound to the cage
and carry a positive charge. Pushing the U(5f) electron density into U-U bonding region
reduces electrostatic repulsion between enclosed atoms, thus forcing U‒U bonds.