Topological (Sliced) Doping of a 3D Peierls System: Predicted Structure of Doped BaBiO3

At hole concentrations below x=0.4, Ba_(1-x)K_xBiO_3 is non-metallic. At x=0, pure BaBiO3 is a Peierls insulator. Very dilute holes create bipolaronic point defects in the Peierls order parameter. Here we find that the Rice-Sneddon version of Peierls theory predicts that more concentrated holes should form stacking faults (two-dimensional topological defects, called slices) in the Peierls order parameter. However, the long-range Coulomb interaction, left out of the Rice-Sneddon model, destabilizes slices in favor of point bipolarons at low concentrations, leaving a window near 30% doping where the sliced state is marginally stable.Comment: 6 pages with 5 embedded postscript figure

Solvent Optimization Studies for a New EURO-GANEX Process with 2,2’-Oxybis( N,N -di- n -decylpropanamide) (mTDDGA) and Its Radiolysis Products

The diglycolamide 2,2’-oxybis(N,N-di-n-decylpropanamide) (mTDDGA) is being studied as an extractant for actinides and lanthanides in the European Grouped Actinide Extraction (EURO-GANEX) process. The aim is the development of a more simplified process using a single extractant instead of a mixture of extractants used in the current EURO-GANEX process. This work presents solvent optimization studies of mTDDGA, with regards to the extraction characteristics of the different diastereomers of mTDGA and of mixed diastereomer solutions. Also radiolysis behavior has been studied by irradiation of solvent extraction systems in a gamma irradiation facility using $^{60}$Co. The availability of irradiated organic solutions made it possible to gain valuable insights into the plutonium loading capacity after gamma-irradiation of the solvent up to 445 kGy and to quantify degradation compounds. Solvent extraction characteristic of the major degradation compounds themselves were determined. Like other methylated diglycolamides, we found a remarkable difference in extraction of up to two orders of magnitude between the two diastereomers. High plutonium loading (36 g L$^{−1}$) is feasible using this single extractant, even after absorbing a dose of 445 kGy. This remarkable observation is possibly promoted by the presence of the main degradation compound which extracts plutonium verywell

An absolute measurement of the neutron production rate of a spent nuclear fuel sample used for depletion code validation

A method to determine the neutron production rate of a spent nuclear fuel segment sample by means of non-destructive assay conducted under standard controlled-area conditions is described and demonstrated. A neutron well counter designed for routine nuclear safeguards applications is applied. The method relies on a transfer procedure that is adapted to the hot cell facilities at the Laboratory for High and Medium level Activity of SCK CEN in Belgium. Experiments with 252Cf(sf) sources, certified for their neutron emission rate, were carried out at the Joint Research Centre to determine the characteristics of the detection device. Measurements of a segment of a spent nuclear fuel rod were carried out at SCK CEN resulting in an absolute and non-destructive measurement of the neutron production rate avoiding any reference to a representative spent nuclear fuel sample to calibrate the device. Results of these measurements were used to study the performance of depletion codes, i.e., ALEPH2, SCALE, and Serpent2. The study includes a code-to-code and code-to-experiment comparison using different nuclear data libraries

Depth-Sensing Indentation on REBa2Cu3O(7-\delta) Single Crystals obtained from Xenotime Mineral

A natural mixture of heavy rare earths oxides extracted from xenotime mineral have been used to prepare large single crystals of high-temperature REBa2Cu3O(7-\delta) superconductor grown using the CuO-BaO self-flux method. Its mechanical properties along the ab-plane were characterized using instrumented indentation. Hardness and elastic modulus were obtained by the Oliver and Pharr method and corresponds to 7.4 \pm 0.2 GPa and in range 135-175 GPa at small depths, respectively. Increasing the load promotes the nucleation of lateral cracks that causes a decrease in hardness and the measured elastic modulus by instrumented indentation at higher loads. The indentation fracture toughness was estimated by measuring the radial crack length from cube-corner indentations at various loads and was 0.8 \pm 0.2 MPa.m1/2. The observed slip systems of REBa2Cu3O(7-\delta) single crystals were [100](001) and [010](001), the same as for YBa2Cu3O(7-\delta) single crystals. The initial stages of deformation and fracture in the indentation process were investigated. The hardness and elastic modulus were not strongly modified by the crystallographic orientation in the ab-plane. This was interpreted in terms of the resolved shear stresses in the active slip systems. Evidence of cracking along the {100} and {110} planes on the ab-plane was observed. As a conclusion, the mechanical properties of REBa2Cu3O(7-\delta) single crystals prepared from xenotime are equivalent to those of YBa2Cu3O(7-\delta) single crystals produced by conventional rare earths oxides.Comment: The paper will appear in Volume 42 (2012) of the Brazilian Journal of Physic

How regressive are indirect taxes. A microsimulation analysis for five European countries

Shifting the tax burden from labor to consumption is proposed in many developed countries as a way to make the tax system more incentive compatible. This article deals with the simulation of such a policy change to sharpen the distributional picture. Expenditures are imputed into the EUROMOD microsimulation program. Then social security contributions are lowered and the standard VAT rate is increased to maintain government revenue neutrality. The main conclusions are that (1) indirect taxes are regressive with respect to disposable income but proportional or progressive with respect to total expenditures, and (2) indirect taxes are in any case less progressive than other components of the tax system, making the proposed measure a regressive one. A possible solution exists in increasing the progressivity of the remaining income tax.status: publishe

Electron microscopic study of the phase transformations in silver niobate (AgNbO3)

Results of an investigation by means of electron diffraction and imaging of the phase transitions occurring in the perovskite material Agnbo3 are presented. The schemes of the tilt modes of the Nb06 octahedra are derived for the different phases. An interpretation of the diffuse electron scattering occurring at higher temperatures is presented in terms of the cluster method. Es werden experimentelle Ergebnisse zur Elektronenbeugung und zur Gitterabbildung für die Phasenübergange berichtet, die in Agnb03, einem Material mit Perovskit-Struktur, auftreten. Für die verschiedenen Phasen werden schematische Darstellungen für die Neigungsmoden der Nbo6-Oktaeder hergeleitet. Die diffuse Elektronenstreuung, die bei hohen Temperaturen auftritt, wird mit Hilfe der Ciuster-Methode interpretiert

Morphology dependent sintering path of nanocrystalline ThO2

status: publishe

Dopant solubility and lattice contraction in gadolinia and gadolinia-chromia doped UO2 fuels

Gadolinia doped UO 2 fuel is widely used as burnable neutron absorber in Light Water Reactors to reduce power peaking and excess reactivity during the first reactor cycle of fresh fuel assemblies. The thermal conductivity of gadolinia doped fuel is substantially lower than that of standard UO 2. To maintain safety margins later in life, some design or operating restrictions can be defined, for example to compensate higher fission gas release levels. Development of large grain U/Gd fuel by suitable doping, e.g. Cr 2O 3, could offer a solution to such restrictions, but solid state information about the double doped (U 1-x-yGd xCr y)O 2 system is very scarce. In the present paper, we present X-ray diffraction and microstructure results of standard U/Gd fuel and chromia doped U/Gd fuel manufactured by powder metallurgy. The dissolution of chromium in (U 1-xGd x)O 2 as a function of Gd content, the role of free UO 2 and the lattice contraction at different Gd and Cr doping levels of (U 1-x-yGd xCr y)O 2 is studied both for the single doped and double doped system. On the basis of lattice contraction and precise measurements of the composition of the solid solution phases, the evolution of theoretical density with dopant concentration is derived. © 2012 Elsevier B.V. All rights reserved.status: publishe

Highly pressurized Kr agglomerates in sputtered Si films

High resolution electron microscopy experiments are presented for a plasma-sputter-deposited Si film with a high Kr concentration. The amorphous layer deposited shows an oscillating Kr concentration. The Kr resides in very small agglomerates of size <1 nm. Bending measurements show that the pressure in the Kr agglomerates is very high, 3.9 GPa. Hardness measurements show that this pressure is limited by the fracture stress of the deposited film

The Local Uranium Environment in Cesium Uranates: A Combined XPS, XAS, XRD, and Neutron Diffraction Analysis

International audienc