Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

THz sideband generation in GaAs/AlGaAs multi quantum wells

Wagner, M.; Schneider, H.; Helm, M.; Schartner, S.; Andrews, A. M.; Roch, T.; Strasser, G.

THz sideband generation is a nonlinear mixing process where a near-infrared (NIR) laser beam is mixed with a THz beam to generate new frequencies (sidebands) ω around the NIR frequency: ω = ω_NIR ± n × ω_THz (with integer n). This effect has been investigated in various semiconductor systems (e. g., in bulk GaAs [1] and in multi quantum wells [2]).
We report on third-order nonlinear mixing between a NIR laser and a free-electron laser (FEL) in an undoped AlGaAs/GaAs multi quantum well. Differently from the literature where electronic and heavy-hole intersubband transitions were used, we are covering different transitions by tuning the FEL wavelength. We directly compare the n=+2 sideband generation efficiency when the FEL pumps the heavy-hole light-hole transition with the efficiency when the intraexcitonic 1s-2p transition of the heavy-hole is pumped. In the latter case the efficiency increases up to 0.2%, which is comparable to the best values achieved for an even stronger n=+1 sideband process [2].

[1] M. A. Zudov et al., Phys. Rev. B 64, 121204, 2001
[2] S. G. Carter et al., Appl. Phys. Lett. 84, 840, 2004

Keywords: THz sidebands; free-electron laser

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12556

Measurements of an unsteady liquid metal flow during spin-up driven by a rotating magnetic field

Räbiger, D.; Eckert, S.; Gerbeth, G.

This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. A cylindrical cavity with an aspect ratio of unity is filled with liquid metal and suddenly exposed to an azimuthal body force generated by a rotating magnetic field (RMF). Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler velocimetry. The flow measurements confirm a theoretical study by Nikrityuk et al. (2005) who suggested the existence of two stages during the RMF-driven spin-up, in particular the so-called initial adjustment phase followed by an inertial phase which is dominated by inertial oscillations of the secondary flow. Evolving instabilities of the double-vortex structure of the secondary flow have been detected at a Taylor number of 1.24´105 confirming the predictions of Grants and Gerbeth (2002). Perturbations in form of Taylor-Görtler vortices have been observed just above the instability threshold.

Keywords: Liquid metal flow; Rotating magnetic field; Spin-up; Ultrasound Doppler velocimetry

  • Experiments in Fluids 48(2010), 233-244

Publ.-Id: 12555

Thermophysical properties of liquid tin-bismuth alloys

Plevachuk, Y.; Sklyarchuk, V.; Gerbeth, G.; Eckert, S.

Tin-bismuth alloys are under intense consideration as favourable lead-free solders for consumer electronics and telecommunications. The electrical and thermal conductivity, viscosity, surface tension and density were studied in a wide temperature range above the liquidus. The scaling relations have been proposed. A comparison with data available in the literature is given.

Keywords: lead-free alloys; liquid metal properties; tin-bismuth

  • International Journal of Materials Research 101(2010), 839-844

Publ.-Id: 12554

CONCAST – a liquid metal experimental facility for modeling the continuous casting process of steel

Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.

The pursuit of better product quality and higher productivity of the continuous casting of steel makes the flow control in tundish and mould and the initial solidification control in the mould to important issues. Numerous sophisticated numerical simulations concerned with the metal flow during the casting process need a fundamental experimental validation. The use of water models gives the advantage to save expense and to be able to apply a number of well-proofed measuring methods. However, a generalisation of these results to liquid metal flows has to be considered as questionable because the true values of flow parameters (Re, Pr, Gr, Ha, etc.) are difficult to meet. In many cases, for instance liquid metal flows with strong temperature gradients, two-phase flows or applications of electromagnetic fields, the flow phenomena cannot be modelled correctly by means of water experiments.
In this paper we present a new experimental facility CONCAST for modeling the continuous casting process by using the low melting point alloy BiSn. The facility operates at temperatures of 200°C-300°C. Main parameters of the facility and dimensions of the test sections will be shown. The resultant possibilities with respect to flow investigations in tundish, submerged entry nozzle and mould will be discussed. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic or electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range until 300°C.
First experimental results will be presented which have been obtained using a small-scale preliminary set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. The application of electromagnetic fields for flow and solidification control in steelmaking will be a crucial point of the future working program.

Keywords: Continuous casting of steel; Liquid metal model experiments; Flow measurements; Electromagnetic flow control

  • Lecture (Conference)
    3rd International Conference on Simulation and Modelling of Metallurgical Processes in Steelmaking, 08.-10.09.2009, Leoben, Austria
  • Contribution to proceedings
    3rd International Conference on Simulation and Modelling of Metallurgical Processes in Steelmaking, 08.-10.09.2009, Leoben, Austria

Publ.-Id: 12553

Solidification of a binary metal alloy in a turbulent melt flow driven by AC fields

Nikrityuk, P. A.; Eckert, K.; Eckert, S.

The application of an RMF during the solidification of a metal alloy may cause macrosegregations, which are the result of the secondary flow in the form of a double vortex structure appearing in a rotating flow due to the Ekman pumping effect. The aim of this work is to improve the understanding of the influence of turbulent RMF-driven flows on the final macrosegregation during unidirectional columnar and equiaxed solidification of a binary metal alloy. The weakly turbulent flow was modeled by means of direct numerical simulations in an axisymmetric approach, where the transient heat and mass transfer was simulated by means of a standard mixture model. Both types of solidification, columnar and equiaxed, were considered by the application of both a permeability and a hybrid model to treat the fluid flow in the mushy zone. Our analysis shows that the oscillations of the radial flow are damped by the rather high viscosity of the slurry region formed by the mixture of equiaxed dendrites and interdendritic liquid. The transport of the equiaxed dendrites towards the axis of the cylinder results in a faster cooling of the melt and a convex shape of the mushy zone. The final macrosegregation is significantly smaller in comparison with the columnar solidification. An increase of the Taylor number leads to a further decrease of the macrosegregation in the middle of the sample for two reasons. First, the enhancement of turbulent mixing of the rejected solute and floating dendrites with the bulk liquid mediated by the T-G vortices, and second, the transport of floating dendrites by the flow reduces the ‘washing’ effect, given by the convective transport of the rejected solute from the solid interface, in comparison with non-movable dendrites.

Keywords: solidification; melt flow; rotating magnetic field; turbulence; macrosegregation

  • Lecture (Conference)
    6th International Symposium on Turbulence, Heat and Mass Transfer, 14.-18.09.2009, Rome, Italy

Publ.-Id: 12552

High energy electron crystal spectrometer

Kudyakov, T.; Jochmann, A.; Zeil, K.; Kraft, S.; Finken, K. H.; Schramm, U.; Willi, O.

A spectrometer has been developed to measure relativistic electrons produced in di®erent types of plasmas, like: tokamak plasmas, laser produced plasmas. The spectrometer consists of 9 YSO (Y2SiO5 : Ce) crystals, which are shielded by stainless steel ¯lters. The absolute calibration of the spectrometer was performed at the superconducting electron linear accelerator ELBE. The spectrometer can provide information about energy distribution of electrons and their numbers for the energy range between 4 and 30 MeV. The spectrum is analyzed by means of the Monte Carlo 3D Geant4 code.

Keywords: electron spectrometer

  • Review of Scientific Instruments 80(2009)7, 076106

Publ.-Id: 12549

Kinematic dynamo simulations in cylindrical geometry

Giesecke, A.; Stefani, F.; Gerbeth, G.

In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.
A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data from water experiments, leads to dynamo action, and a strong influence of boundary conditions and additional (stagnant) fluid layers around the active domain is observed.
An additional source term for dynamo action exists in case of a spatially varying conductivity distribution. A very simple set-up -- serving as a proof of concept -- is given by a steady axial flow in an infinite cylinder with inhomogenous container walls. Such a configuration is sufficient for dynamo action, however, the critical Reynolds number might be too large for the realisation in a simple laboratory-sized experiment.
Similiar effects appear in case of permeability inhomogenities, where increased gradients might also lead to a significant reduction of the critical Reynolds number.

Keywords: Dynamo Experiment; MHD; Kinematic Simulations

  • Lecture (Conference)
    Astrophysical Magnetohydrodynamics, 06.-10.04.2009, Nurmijärvi, Finnland

Publ.-Id: 12548

4D in-beam PET Datenauswertung für bewegte Phantome bei Bestrahlung mit einem getrackten 12C6+-Strahl

Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.

In-beam PET has become a quality assurance tool providing valuable clinical feedback for static tumor entities and shall be extended to monitor the treatment of intra-fractional moving tumors like in the lung or
liver which are subjected to respiratory motion. The potential of 4D in-beam PET for the detection of possible malfunction of the motion compensated beam delivery has been investigated by means of systematic phantom experiments at the clinical in-beam PET installation at GSI Darmstadt. The new system for tracking moving targets with the scanned ion beam at GSI Darmstadt was used to adapt the Bragg peak positions laterally and in depth. The pencil beam has been rescanned on a horizontal line in a phantom placed at the central plane of the double head PET scanner with an energy corresponding to 60mm penetration depth while the target was performing a one dimensional periodic motion perpendicular to the beam direction. 4D PET data were compared with an appropriate 3D PET measurement which followed immediately after the dynamic acquisition. It is shown for different irradiation scenarios that in-beam PET is capable for detecting treatment errors for moving target irradiation.

Keywords: in-beam PET; moving targets; ion therapy

  • Lecture (Conference)
    DPG Frühjahrstagung 2009, 09.-13.03.2009, München, Deutschland

Publ.-Id: 12546

Performance of the new drift chambers for HADES @ FAIR

Göbel, K.; Kämpfer, B.; Kotte, R.; Naumann, L.; Palka, M.; Tarantola, T.; Traxler, M.; Wüstenfeld, J.

Seven new Multiwire Drift Chambers of plane 1 for the High - Acceptance Di - Elektron Spectrometer (HADES) are assembled in the Detector workshop of the Forschungszentrum Dresden - Rossendorf.
We present the results of test performed on the first chamber in comparison with the main design parameters .
End of 2008 one detector was completely equipped with the new generation of the readout system designed for the high multiplicity environment as provided in collisions of heavy systems at HADES @ FAIR.
The chamber was investigated with cosmic rays and β 90Sr source. The obtained results show that the new design fulfills the equirements with respect to efficiency, accuracy and rate capability.
These chambers will be installed in 2009 to be armed for the upcoming heavy ion program.

Keywords: HADES; FAIR; detector development

  • Lecture (Conference)
    Gemeinsame DPG Frühjahrstagung mit der European Physical Society (EuNPC) 2009, 16.-20.3.2009, Bochum, Deutschland

Publ.-Id: 12544

Fluorescence spectroscopic study on complexation of uranium(VI) by glucose - a comparison of room and low temperature measurements

Steudtner, R.; Arnold, T.; Geipel, G.; Bernhard, G.

The complexation of uranium(VI) with glucose was studied in the pH range from pH 2 to 6 by time resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature (RT) and for the first time under cryogenic conditions of 153 K (cryo-TRLFS). A uranyl(VI) glucose complex was spectroscopically identified by cryo-TRLFS measurements at pH 5. At lower pH values only the free uranyl(VI) ion was identified. The study revealed that quenching effects severely influenced the TRLFS measurements conducted at RT and significantly reduced the uranium(VI) fluorescence signal. This decrease in U(VI) fluorescence intensity is usually used to calculate complex formation constants of non-fluorescent uranyl(VI) organic complexes. However, our cryo-TRLFS results clearly showed that the observed decrease in U(VI) fluorescence intensity at RT for the samples at pH 2 to 4 is not attributed to the formation of such a non-fluorescent U(VI) glucose complex, i.e. to static quenching, but related to dynamic quenching of glucose on the uranyl(VI) fluorescence. At higher pH values the formation of uranyl(VI) glucose complexes were suppressed by the formation of uranyl(VI) carbonate species. The detected uranyl(VI) glucose complex was characterized by five emission bands at 499.0, 512.1, 525.2, 541.7, and 559.3 nm. The respective fluorescence lifetime determined at 153 K was 20.9 ± 2.9 µs. The uranyl(VI) glucose complex formation constant was calculated for the first time to be logßI = 0.1 M = 15.35 ± 0.91. Comparing this constant with formation constants of other important environmentally relevant inorganic ligands, in particular carbonate, it became evident that glucose only may influence the transport behaviour of uranium in a very small pH region of about 5. Our cryo-TRLFS investigation opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encounter at RT are suppressed by measurements at cryogenic conditions.

Keywords: uranyl; glucose; Laser fluorescence spectroscopy; TRLFS; cryogenic conditions

Publ.-Id: 12543

Complex Formation and Molecular Structure of Np(VI) and Np(V) Acetates

Takao, K.; Takao, S.; Scheinost, A. C.; Bernhard, G.; Hennig, C.

Neptunium is one of the most problematic actinides for long-term storage of the radioactive waste. Acetate (AcO-) is one of the important organic ligands occurring in natural environment. To study complexation reactions of Np(V) and Np(VI) with AcO-, we performed titration experiments based on UV-Vis-NIR spectroscopy. Furthermore, we used cyclic voltammetry to obtain information on the stability field of the individual solution species. However, it is difficult to extract structural information solely from these techniques. Therefore, we additionally adopted X-ray absorption fine structure (XAFS) spectroscopy to detect complexation reaction and molecular structure of Np(VI)- and Np(V)-AcO- complexes in aqueous solution.
The UV-Vis-NIR absorption spectra of the Np(VI)-AcO- system as a function of pH do not show any isosbestic points, indicating the presence of more than two equilibria. As a result of stability constant refinement, the spectral change is indicated as a 3-step complexation reaction of NpVIO2(AcO)n2-n (n = 1, 2, 3). The evaluated stability constants are log K1 = 2.98 ± 0.01, log b2 = 4.60 ± 0.01, and log b3 = 6.34 ± 0.01, which are comparable with the values reported previously. For comparison reasons the complex formation of Np(VI)-AcO- was investigated by XAFS spectroscopy (XANES and EXAFS). The refinement analysis of the XAFS spectra revealed similar stability constants (log K1 = 2.87 ± 0.03, log b2 = 4.20 ± 0.06, and log b3 = 6.00 ± 0.01). The k3-weighted EXAFS spectra of NpVIO2(AcO)n2-n (n = 0, 1, 3) provided structural data consistent with the complex stoichiometry, being well-explained by bidentate coordination of AcO- (Np-Oax: 1.76-1.77 Å, Np-Oeq: 2.43-2.47 Å, Np-Ccarbo: 2.87 Å, Np-Cterm: 4.38 Å) which are consistent with the crystal structure of NaNpVIO2(AcO)3.
Also in the UV-Vis-NIR spectrum of a pH series of the Np(V)-AcO- system, no isosbestic points were detected. The refinement analysis resulted also in 3-step complexation equilibrium of NpVO2(AcO)n1-n (n = 1, 2, 3) with the stability constants log K1 = 1.93 ± 0.01, log b2 = 3.11 ± 0.01, and log b3 = 3.56 ± 0.01. This result is corroborated by the structural data obtained from EXAFS (Np-Oax: 1.83-1.85 Å, Np-Oeq: 2.51 Å, Np-Ccarbo: 2.90-2.93 Å) which are comparable with the crystal structure of BaNpVO2(AcO)3.
The observed stability constants were used to calculate a Paurbaix diagram. The validity of the assumed complexation reactions was confirmed by comparing the boundary of the stability field between Np(V) and Np(VI) species with experimental Np(V/VI) redox potentials.

Keywords: Neptunyl; UV-Vis-NIR; XAFS; Stability Constant; Molecular Structure

Publ.-Id: 12542

Structural properties of MoS2 “mama”- tubes and related materials

Virsek, M.; Krause, M.; Kolitsch, A.; Mrzel, A.; Iskra, I.; Remskar, M.

MoS2 nanomaterials synthesized by sulphurization of Mo6S2I8 nanowires were studied by wavelength dependent Raman spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy (HRTEM). The transformation process leads to a variety of selective morphologies of the MoS2 product, like coaxial nanotubes, i.e. nanotubes with split walls, “mama”- tubes with encapsulated MoS2 fullerene-like particles, or other hybrid nanostructures. The temperature inside our horizontal fluidized-bed reactor directly determines the final morphology of the product. A temperature above 850°C leads to a formation of MoS2 “mama”– tubes, while below 850°C the growth of coaxial MoS2 nanotubes in which a number of multiwall nanotubes grow coaxially separated by gaps is favored. HRTEM was used to study how MoS2 layers form from outside of precursor nanowires toward inside and to observe the nucleation of fullerene-like particles. Results of a possible oxidation during the Raman experiments are correlated with partially or fully oxidized Mo6S2I8 nanowires of the composition MoO3-x, which can be afterwards also sulphurized resulting in MoS2 polycrystalline nanowires.
By the means of Raman and X-ray diffraction spectroscopies we have studied effect of temperature and duration of the sulphurization process. We followed the stages of the transformation to explore the chemical reaction kinetics.

  • Poster
    XXIIIrd International Winterschool on Electronic Properties of Novel Materials(IWEPNM 2009), 07.-14.03.2009, Kirchberg, Austria

Publ.-Id: 12541

Size and shape dependent Raman scattering of WS2 nanomaterials

Krause, M.; ViršEk, M.; Salacan, N.; Chen, L.; Abrasonis, G.; Kolitsch, A.; RemšKar, M.; Fleischer, N.; Hatto, P.; Möller, W.

Fullerene-like WS2 nanoparticles and WS2 nanotubes are studied by wavelength dependent Raman spectroscopy. The response from the nanomaterials is compared to that of 2H-WS2 crystals and microcrystalline 2H-WS2 powder. The Raman signatures point to a hexagonal 2H stacking of the WS2 layers in all nanostructures. While the wave numbers of 1st and 2nd order Raman scattering show only little dependence, the line widths and the intensity ratios exhibit a systematic evolution with respect to the specific WS2 nanostructure. The sulfur-sulfur stretching mode range is particularly sensitive to the different stages of disorder and is suitable for the diagnostic classification of the WS2 nanostructures. Raman mapping across the nanoparticles is used to distinguish between disorder and surface effects on the vibrational spectra. All the experiments were performed at low laser power, since the transformation into WO3 is induced already at moderate illumination due to the limited photo- and thermal stability of the materials.

This work is supported by the European Union sixth Framework Program (FOREMOST project under contract NMP3-CT-2005-515840).

  • Poster
    XXIIIrd International Winterschool on Electronic Properties of Novel Materials (IWEPNM 2009), 07.-14.03.2009, Kirchberg, Austria

Publ.-Id: 12540

Speciation of Rare-Earth Metal Complexes in Ionic Liquids: A Multiple-Technique Approach

Nockemann, P.; Thijs, B.; Lunstroot, K.; Parac-Vogt, T. N.; Görller-Walrand, C.; Binnemans, K.; van Hecke, K.; van Meervelt, L.; Nikitenko, S.; Daniels, J.; Hennig, C.; van Deun, R.

Abstract: The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species
of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl) imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu2(bet)8(H2O)4][Tf2N]6,
[Eu2(bet)8(H2O)2][Tf2N]6·2H2O, and [Y2(bet)6(H2O)4][Tf2N]6 were found to
consist of dimers. These rare-earth complexes are well soluble in the ionic
liquids [Hbet][Tf2N] and [C4mim]- [Tf2N] (C4mim=1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, 1H, 13C, and 89Y NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.


Publ.-Id: 12539

Neue Materialien zur Eliminierung von Arzneimittelreststoffen durch Nano-Biotechnologie

Pollmann, K.; Marquard, A.; Günther, T.; Lehmann, F.; Richter, L.; Raff, J.

  • wird nachgereicht
  • Poster
    4. Dresdner Symposium "Endokrin aktive Stoffe in Abwasser, Klärschlamm und Abfällen, 25.03.2009, Dresden, Deutschland

Publ.-Id: 12537

Fluorine-18-radiolabeled S100A12: a potential probe for functional characterization of inflammatory processes in vivo

Hoppmann, S.; Richter, S.; Steinbach, J.; Pietzsch, J.

S100A12 has been implicated in inflammation. However, the role of extracellular S100A12 in vivo is still unclear. We report a novel methodology using radiolabeling of human recombinant S100A12 with the positron-emitter fluorine-18 and the use of 18F-S100A12 in cell assays in vitro and in small animal positron emission tomography (PET) studies in rats in vivo. For S100A12 radiolabeling N-succinimidyl-4-(18F)fluorobenzoate was used. S100A12 was shown to stimulate secretion of cytokines by macrophages and endothelial cells. In vitro assays revealed specific binding of 18F-S100A12 to the soluble receptor for advanced glycation endproducts (sRAGE) and, furthermore, to membrane RAGE on both cell types. Cell interaction of 18F-S100A12 was inhibited by RAGE inhibitors like glycated LDL and, interestingly, also by scavenger receptor ligands, e.g., maleylated albumin, and by lectines. PET data showed sustained temporary association of 18F-S100A12 with tissues expressing RAGE, e.g., lung and endothelium in vivo. Moreover, specific accumulation of 18F-S100A12 in tissues enriched in cells expressing scavenger receptors, e.g., liver and spleen, was observed. Concluding, 18F-radiolabeling of S100A12 and the use of PET allow discrimination of the kinetics and the metabolic fate of S100A12 in vivo. The approach provides a novel probe for functional characterization of inflammation in rodent models of disease.

  • Poster
    9th World Congress on Inflammation, 06.-10.07.2009, Tokyo, Japan
  • Inflammation Research 58(2009)Suppl. 2, S145-S146
    ISSN: 1023-3830

Publ.-Id: 12536

Combined UV-vis and EXAFS study on the complex formation of uranium(VI) with several carboxylic acids

Lucks, C.; Roßberg, A.; Scheinost, A.

Natural organic matter (NOM) released by microorganisms and plants is ubiquitous in waters, soils and sediments. NOM can form relatively stable aqueous complexes with U(VI) and may interact like U(VI) with mineral surfaces. In systems containing U(VI), NOM and mineral surfaces binary and ternary sorption complexes have to be considered. These intricate interactions may profoundly influence the mobility of U(VI). However, the study of such a ternary system requires first its decomposition into simpler binary subsystems. Here we show the interaction of U(VI) with relatively simple carboxylic acids. Acetic, succinic and DL-tartaric acid were used as model compounds to simulate the different -COOH and -OH functionalities of the structurally more complicated, polyelectrolytic NOM.

Aqueous complexes of U(VI) with the model compounds were investigated by applying UV-VIS and EXAFS measurements. UV-VIS pH titration experiments were performed to identify the binary complexes formed in large excess of organic ligands and to derive their speciation. Uranium LIII-edge EXAFS spectra of pH series were then measured. Based on the speciation derived from UV-VIS spectroscopy, we were able to derive the EXAFS spectra of the pure U(VI) complexes from the EXAFS spectral mixtures by means of iterative target transform factor analysis [1]. Shell fit and an inversion method was then applied to validate their structures.
The uranium acetate and succinate complexes are characterized by a bidentate coordination of the carboxylic group. Furthermore, the formation of seven-membered rings can be rejected in the uranium succinate system. In contrast, the tartaric acid system is much more complicated because tartaric acid is able to form tridentate chelates with uranium using two carboxylic and one alcoholic groups. These chelates were identified to be dimeric at lower pH (3-5) and trimeric at higher pH (6-7). In addition, the structure of the trimer is also validated by the U-O radial pair distribution function (PDF) which is directly calculated from the EXAFS spectrum by an inversion method. The PDF of the oxygen atoms in the equatorial plane of U(VI) is asymmetric and gives evidence for one central oxygen atom linking the three uranyl ions of the trimer in a much shorter U-O distance than the remaining equatorial U-O distances.
In conclusion, we can provide structural models for the aqueous complexes of U(VI) with acetate, succinate and tartrate – the substances used as model compounds for NOM in this study.

[1] A. Rossberg, T. Reich, G. Bernhard, Anal. and Bioanal. Chem. 376, 631 (2003).

Keywords: uranium; complex formation; EXAFS

  • Poster
    PhD-Seminar 2009, 16.-18.09.2009, Krögis, Deutschland
  • Poster
    Migration Conference 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12534

Microbial communities in extreme environments and their interactions with uranium and other xenobiotics

Selenska-Pobell, S.; Merroun, M.; Satchanska, G.; Golovinski, E.

Bacteria are the most ubiquitous organisms in all terrestrial and aquatic environments. The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from different extreme habitats. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting oligotrophic environments such as deep subsurface layers or heavy metal and pesticides polluted industrial sites immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Some of the isolates demonstrated high capability to utilize phenol compounds as well. These properties of the studied extremophile bacterial isolates are promising for development of bioremediation approaches for heavy metal and phenol polluted environments

  • Invited lecture (Conferences)
    Ecology Seminar of the ECOLOGICAL ENGINERING AND ENVIRONMENTAL PROTECTION Society, 23.-24.04.2009, Sofia, Bulgaria

Publ.-Id: 12533

In-beam PET für die Therapie mit hochenergetischen Photonen

Kunath, D.; Kluge, T.; Pawelke, J.; Enghardt, W.

Poster über die Integration von PET in die Strahlentherapie mit hochenergetischen Photonen

  • Poster
    Strategie-Meeting des OncoRay, 14.-15.01.2009, Bautzen, Deutschland

Publ.-Id: 12532

Determining the radial pair distribution function from EXAFS spectra by use of the Landweber iteration method

Rossberg, A.; Funke, H.

The Landweber iteration method (1) is used to construct the radial pair distribution function (PDF) from an EXAFS spectrum. The PDF as solution of the fundamental EXAFS integral equation is determined in a stable way without additional supplementary conditions due to the semi-convergent behaviour of the Landweber iteration.
For the correct determination of the PDF it is important to know the energy shift dE0. If dE0 is unknown then usually it is determined by a shell fit of the spectrum before an inversion method is applied. If the shell fit model is incorrect then the determined dE0 is erroneous and an inverse method would give a wrong PDF. This leads in turn to the conclusion that the recent inversion procedures are only applicable if the structural model for the investigated system is already known; hence they are not “stand-alone” methods.

We developed an algorithm based on the Landweber iteration for deriving the appropriate dE0. The performance was tested by several theoretical and experimental EXAFS spectra of metal hydrates (U(IV), Np(IV), Th(IV), Cm(III)). For the estimation of the optimum number of iterations we adopted the L-curve concept which was recently used for the determination of the optimal regularization parameter in Tichonov’s method [2]. The examples show that the Landweber iteration in combination with the simultaneous determination of dE0 and the L-curve concept for the estimation of the optimum number of iterations is a robust way to calculate the PDF. The approach enables the calculation of the PDF even for strong overlapping shells like for Cm(III) hydrate.

(1) Landweber, L. Am. J. Math. 73, 615-624 (1951).
(2) Kunicke, M., et al. Physica Scripta T115, 237–239 (2005).

  • Lecture (Conference)
    The 14th International Conference on X-ray Absorption Fine Structure (XAFS14), 26.-31.07.2009, Camerino, Italy

Publ.-Id: 12531

The potential of in-beam positron emission tomography within image-guided radiation therapy

Kunath, D.; Fiedler, F.; Kluge, T.; Kormoll, T.; Laube, K.; Pawelke, J.; Priegnitz, M.; Shakirin, G.; Enghardt, W.

Abstract about the potential of in-beam PET within IGRT

  • Abstract in refereed journal
    Radiotherapy and Oncology 90(2009)Suppl. 3, S77-S78
    ISSN: 0167-8140

Publ.-Id: 12530

In-Beam and Off-Beam PET Measurements of Target Activation by Megavolt X-Ray Beams

Kunath, D.; Kluge, T.; Pawelke, J.; Priegnitz, M.; Enghardt, W.

In-beam positron emission tomography (in-beam PET) is a valuable in situ method for quality assurance in radiation therapy. It is well investigated for therapy with carbon ions and has been successfully implemented clinically at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. The extension of this efficient technique to other radiation treatment modalities may be worthwhile. For protons, 3-He, 7-Li, and 16-O the feasibility has already been experimentally shown. Furthermore, it seems to be feasible for the case of radiotherapy with high-energy photons, since positron emitters are generated by photons with energies above 20 MeV due to (gamma, n) photo-nuclear reactions (predominantly 11-C and 15-O in tissue). In this regard, promising conclusions have been obtained by Geant4 simulations as well as by off-beam PET experiments using a conventional PET scanner. The next step was the installation of a small double head positron camera consisting of two bismuth germanate (BGO) block detectors at the irradiation site to measure the generated beta+ activity distribution simultaneously to the irradiation. The relation between deposited dose and beta+ activity density was quantified. The obtained results are presented and compared to that of off-beam PET experiments. Higher activities as well as an improved contrast between materials of different stoichiometry are achieved by measuring in-beam, showing the advantage of in-beam PET over off-beam PET. Thus, the application of in-beam PET to radiation therapy with high-energy photons can be useful for quality assurance, comprising monitoring of dose delivery, patient positioning and tumor response.

Keywords: Dose monitoring; high-energy photon therapy; positron emission tomography

Publ.-Id: 12529

A two group analytical approximation solution for an external source problem without separation of space and time

Merk, B.; Weiß, F. P.

This work presents the development of analytical approximation solutions for a space-time dependent neutron transport problem in two energy groups for a one dimensional system consisting of a homogenized medium with a central external source. The approximation solutions are developed using Green's functions, the influence of the delayed neutrons is not considered. Qualitative results for a given system are analyzed. A detailed comparison of the developed analytical approximation solutions with solutions with one energy group and with results gained by the time dependent diffusion equation without separation of space and time is given.

Keywords: Time dependet neutron diffusion; Accelerator driven system; Experimental analysis; Green's funtion expansion

  • Annals of Nuclear Energy 37(2010), 942-952

Publ.-Id: 12528

Pu Bestimmung von 242Pu in Plutoniumnuklidgemischen mittels Flüssigszintillation

Nebelung, C.

Für Speziations- und Sorptionsuntersuchungen mit Plutonium steht am Institut für Radiochemie des FZ Dresden-Rossendorf 242Pu (T1/2 3,755*105 Jahre) zur Verfügung, das eine Reinheit von 99,93 Atom% hat. Da die übrigen enthaltenen Plutoniumisotope zum Teil wesentlich kürzere Halbwertszeiten haben (240Pu: T1/2 6563 Jahre, 238Pu: T1/2 87,7 Jahre, 241Pu: T1/2 14,35 Jahre), ist der Aktivitätsanteil dieser Isotope erheblich. Das Material wurde vor 29 Jahren hergestellt, so dass zusätzlich zu den Plutoniumisotopen die Tochter von 241Pu, das 241Am, zu beachten ist. Es besteht die Aufgabe, schnell für eine Vielzahl von Proben den Gehalt des 242Pu zu bestimmen. Das wird durch Flüssigszintillation erreicht, bei der zunächst eine alpha/beta Separation durchgeführt wird und anschließend durch Spektrenentfaltung [1] der Peak des 242Pu vom gemeinsamen 238Pu/241Am-Peak getrennt wird.

[1] Nebelung, C., Baraniak, L., 2007. Simultaneous Determination of 226Ra, 233U and 237Np by Liquid Scintillation Spectrometry. Applied Radiation and Isotopes, 65, 209-217.

Keywords: liquid scintillation; alpha/beta separation; Pu nuclide; spectra deconvolution

  • Lecture (Conference)
    5. LSC Anwendertreffen „Aktivitätsbestimmung mit Hilfe der Flüssigszintillationsmesstechnik“, 23.-24.04.2009, Karlsruhe, Deutschland

Publ.-Id: 12527

Flavonoids – natural phenolic complexing agents towards uranium

Geipel, G.; Viehweger, K.; Bernhard, G.

Flavonoids belong to a class of secondary plant metabolites. They are one of the largest classes of plant phenolics. All flavonoids consist of a 15 carbon skeleton. Flavonoids are most commonly known at least for four main properties: colored (to attract animals), absorbing ultraviolet light (to protect against damage), antimicrobial activity (to protect against bacterial or fungal infection) and antioxidant activity (which may be responsible for anticancer benefits) [1].
The structure of flavonoids is dominated by phenolic hydroxyl groups.

We studied the complex formation of the flavonoid kaempferol with uranium. Kaempferol is a 3,5,7-Trihydroxy-2- (4-hydroxyphenyl)-4H-1- benzopyran-4-on. As stated already flavonoids show strong absorption spectra in the UV-range. The change in their spectroscopic data was used to determine the stability constants. Spectra were evaluated with the factor analysis program Specfit [2]. All spectra of flavonoids show isosbestic points indicating a clear interaction between kaempferol and uranium(VI).
A strong interaction was found for kaempferol. The derived stability constant was assigned to be log β121 = 31.7 ± 0.4 at an ionic strength of 0.1 M for the reaction

UO22+ + C15H5O64- + 2 H+ → UO2C15H7O6 (1)

Data derived from studies with quercetin and hesperetin show an analogue stability constant for the non-charged complex.
We assume that the complex formation occur by a ring formation, whereas the flavonoids form rings between the phenolic group in position 3 or 5 respectively and the ketone oxygen in the benzopyran-4-one ring [3].

[1] Tiaz L, Zeiger E Plant Physiology 2006 4. Edition, Sinauer Associates Inc.
[2] Binstead R A, Jung B, Zuberbühler A D Specfit Global analysis system Spectrum Software Associates 2000-2003
[3] Malesev D, Kuntic V 2007 J. Serb. Chem. Soc. 72 921

Keywords: flavonoids; actinides; uranium; complex formation

  • Contribution to proceedings
    Migration Conference 2009, 20.-25.09.2009, Kennewick, Washington,, USA
  • Poster
    Migration 2009, 20.-25.09.2009, Kennewick, Washington,, USA

Publ.-Id: 12526

Double-electron excitation in absorption spectra of actinides

Hennig, C.; Le Naour, C.; Den Auer, C.

The photoexcitation of a inner-shell photoelectron is is usually accompanied by the excitation of outher-shell electrons. Early systematic studies were performed with noble gases because their absorption signal is not affected by photoelectron backscattering from neighbored atoms. Up to now, most of the elements until Bi were investigated for multieletron excitations even in the presence of photoelectron backscattering effects from extended X-ray absortion fine structure. All elemets with Z > Bi comprise only radioactive isotopes and their mutielectron features are more difficult accesible. Recently we found evidence for multielectron excitations even in the L-absorption edges of actinide hydrates [1,2]. The actinides investigated up to now are Th, Pa, U, Np, Pu and Am. The strongest resonances result from [2p4f] double electron excitations, but there is also evidence for [2p5d] excitations. The [2p4f] resonance energies follow systematically the trend observed by Di Cicco and Filipponi for Hg, Pb and Bi [3]. The actinide elements show numerous oxidation states in particular for Np and Pu, where they range from III to VII. The electronic configuration involves besides 6d states partly filled 5f shells. The 5f states are less strictly located than the 4f states of the lanthanides, and can therefore participate in the chemical bond. This electronic configuration influences the physical and chemical properties and posses a large variation in the coordination geometry including transdioxo cations, AnO2n+ (n = 1 and 2). There is a clear correlation of the oxidation state, coordination geometry and the spectral feature of the multielectron resonance, resulting from final state density. The change in the resonance intensity of the single electron 2p6d transition as function of the electron configuration correspond well with the double-electron [2p4f] resonance intensity.

  • Lecture (Conference)
    14th International Conference on X-ray Absorption Fine Structure (XAFS14), 26.-31.07.2009, Camerino, Italy

Publ.-Id: 12525

Redox behaviour and coordination of neptunium in presence of inorganic oxoanions

Hennig, C.; Ikeda-Ohno, A.; Tsushima, S.; Takao, K.; Takao, S.; Scheinost, A. C.; Bernhard, G.

Neptunium shows a complex redox chemistry comprising reversible redox couples like Np(VI)/Np(V) and Np(IV)/Np(III), as well as irreversible couples like Np(V)/Np(IV). The reversibility of Np(VI)/Np(V) is rather unique among the actinides, because other actinide redox couples like U(VI)/U(V) and Pu(VI)/Pu(V) are prone to disproportionation effects in weakly complexing media [1,2]. The basics of reversible redox behavior is well explained by electron transfer without changes of the ligand arrangement, whereas the irreversibility of the transition Np(V)/Np(IV) is due to the formation or release of the NpO2+ oxygen atoms of the trans-dioxo moiety. However, also the reversible transitions may become quasi-reversible and irreversible for several reasons, e.g. as function of ligand exchange and electron transfer kinetics. Structural information on the neptunium redox species in aqueous solution is currently rather scarce. Therefore we performed a systematic study based on cyclic voltammetry, electrolysis, UV-Vis-NIR and EXAFS spectroscopy of the Np redox species in presence of the oxoanions ClO4, SO42, NO3 and CO32. The redox couple Np(V)/Np(IV) remains reversible in non-complexing ClO4 by retaining associated H2O molecules, but becomes irreversible already in weakly coordinating NO3 media [2]. The Np(V)/Np(IV) couple becomes more irreversible in presence of stronger ligands like SO42 and CO32. The slow kinetics of the Np(V)/Np(IV) couple in cyclic voltammetry results in a superposition with the reversible Np(IV)/Np(III) couple. The related species were partly separated by electrolysis and their coordination was analyzed independently. The redox couple Np(VI)/Np(VII) could be observed only in CO32 media at high pH. It is also irreversible as result of a rearrangement of the inner-sphere coordination. The neptunium sulfate system comprises a larger variety of isomers due to similar Gibbs free energies for monodentate and bidentate coordination. A comparison along the series Th(IV) - U(IV) - Np(IV) reveals that the monodentate sulfate coordination decreases whereas the bidentate coordination increases. This trend was studied by DFT calculations and will be discussed in terms of solvation energy and covalency of the molecular bonds.

  • Lecture (Conference)
    Migration 2009; 12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12523

Establishment of technical prerequisites for cell irradiation experiments with laser-accelerated electrons

Beyreuther, E.; Enghardt, W.; Kaluza, M.; Karsch, L.; Laschinsky, L.; Lessmann, E.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.

Purpose: In recent years, laser-based acceleration of charged particles has rapidly progressed and medical applications, e.g., in radiotherapy, might become feasible in the coming decade. Requirements are monoenergetic particle beams with long-term stable and reproducible properties as well as sufficient particle intensities and a controlled delivery of prescribed doses at the treatment site. Although conventional and laser-based particle accelerators will administer the same dose to the patient, their different time structures could result in different radiobiological properties. Therefore, the biological response to the ultrashort pulse durations and the resulting high peak dose rates ofthese particle beams have to be investigated. The technical prerequisites, i.e., a suitable cell irradiation setup and the precise dosimetric characterization of a laser-based particle accelerator, have to be realized in order to prepare systematic cell irradiation experiments.

Methods: The Jena titanium:sapphire laser system (JETI) was customized in preparation for cell irradiation experiments with laser-accelerated electrons. The delivered electron beam was optimized with regard to its spectrum, diameter, dose rate, and dose homogeneity. A custom-designed beam and dose monitoring system, consisting of a Roos ionization chamber, a Faraday cup, and EBT-1 dosimetry films, enables real-time monitoring of irradiation experiments and precise determination of the dose delivered to the cells. Finally, as proof-of-principle experiment cell samples were irradiated using this setup.

Results: Laser-accelerated electron beams, appropriate for in vitro radiobiological experiments, were generated with a laser shot frequency of 2.5 Hz and a pulse length of 80 fs. After laser acceleration in the helium gas jet, the electrons were filtered by a magnet, released from the vacuum target chamber, and propagated in air for a distance of 220 mm. Within this distance a lead collimator (aperture of 35 mm) was introduced, leading, along with the optimized setup, to a beam diameter of 35 mm, sufficient for the irradiation of common cell culture vessels. The corresponding maximum dose inhomogeneity over the beam spot was less than 10% for all irradiated samples. At cell position, the electrons posses a mean kinetic energy of 13.6 MeV, a bunch length of about 5 ps (FWHM), and a mean pulse dose of 1.6 mGy/bunch. Cross correlations show clear linear dependencies for the online recorded accumulated bunch charges, pulse doses, and pulse numbers on absolute doses determined with EBT-1 films. Hence, the established monitoring system is suitable for beam control and a dedicated dose delivery. Additionally, reasonable day-to-day stable and reproducible properties of the electron beam were achieved. Conclusions: Basic technical prerequisites for future cell irradiation experiments with ultrashort pulsed laser-accelerated electrons were established at the JETI laser system. The implemented online control system is suitable to compensate beam intensity fluctuations and the achieved accuracy of dose delivery to the cells is sufficient for radiobiological cell experiments. Hence, systematic in vitro cell irradiation experiments can be performed, being the first step toward clinical application of laser-accelerated particles. Further steps, including the transfer of the established methods to experiments on higher biological systems or to other laser-based particle accelerators, will be prepared.

Keywords: laser electron acceleration (SM-LWFA); laser radiotherapy; cell irradiations

Publ.-Id: 12522

XAS-based characterization of thioarsenates and their transformation to thioarsenites in acidic synthetic solutions

Suess, E.; Scheinost, A. C.; Merkel, B. J.; Bostick, B.; Wallschlaeger, D.; Planer-Friedrich, B.

Recent ab initio calculations predict that As(III)- and As(V)-thioanions can occur simultaneously in sulfidic environments under commonly encountered pH conditions. However, unambiguous structural characterizations for the two homologue series of thioarsenites or thioarsenates are still missing. In the present study, the molecular structures of synthesized mono-, di-, and tetrathioarsenate were characterized by XRD and XAS in their solid state and dissolved at alkaline or near-neutral pH-conditions. The determined As(V)-S and As(V)-O bond distances of 2.13-2.18 Å and 1.70 Å, respectively, are consistent with the theoretical expectations for thioarsenates and can be clearly differentiated from the respective As(III)-bondings, with 2.24-2.34 Å and 1.78 Å. The XANES edge positions of the individual thioarsenates (mono- 11871 eV, di- 11870, and tetrathioarsenate 11869.5) lie between those of As2O5 (11872.3 eV) and As2O3 (11868.2 eV) and reveal the influence of increasing sulfur substitution by decreasing bond energies and hence absorption edge energy. These thioarsenates can be clearly distinguished from the species formed upon acidification of tetrathioarsenate below pH 6.3. These species were identified as thioarsenites. Their XANES edge energy of ca. 1 eV below that of As2O3 indicates the redox-state change from As(V) to As(III), which is further confirmed by the increased As-S distance of 2.23-2.28 Å corresponding to As(III)-S species. At pH 3, the detection of As-As-bonds indicates the beginning formation of colloids, most likely amorphous As2S3. Our results indicate that in synthetic solutions, thioarsenites can form as transitory species between dissolved thioarsenates at near-neutral pH and AsS-precipitates formed under acidic conditions.

Keywords: thioarsenites; thioarsenates; EXAFS; XANES

  • Lecture (Conference)
    Goldschmidt Conference 2009; Challenges to our Volatile Planet, 21.-26.06.2009, Davos, Switzerland
  • Geochimica et Cosmochimica Acta 73(2009)13, A1288-A1288

Publ.-Id: 12521

Homogeneity at molecular scale of (U,Pu)O2 solid solutions probed by XAS

Martin, P. M.; Robisson, A. C.; Grandjean, S.; Arab-Chapelet, B.; Leturcq, G.; Scheinost, A. C.; Rossberg, A.

Main objectives of new fuel developed for Generation III/IV systems are economy of resources, minimized volume and lower long-term potential radiotoxicity of ultimate wastes and proliferation risk reduction. To achieve these goals, one major fuel cycle option under evaluation is co-management of the actinides (An) in an integrated closed fuel cycle.1 Co-management of two (or more) actinides implies separating these actinides from the fission products, most often by hydrometallurgical processes, and then converting them to solid forms to re-fabricate fresh fuel or dedicated fuels or targets. Considering the significant amount of minor actinides and the different designs of future nuclear fuels, including mixed actinide pellets, composite materials or spherical particles, various uranium-actinide(s) wet co-conversion routes are currently investigated at the CEA-ATALANTE facility. Once the precipitation is achieved, the resulting mixed-actinide compound is calcined into a mixed oxide. As this compound will be the solid precursor of fuel or a dedicated transmutation target, controlling its composition at the molecular scale is of major importance. Usually, solid solution structures are studied using diffraction methods. But, as demonstrated in a previous study2, in order to fully investigate the ideality of a solid solution, X-ray absorption spectroscopy (XAS) using synchrotron radiation is an extremely suitable technique.
The subject of this paper is the study of (U1-x,Pux)O2 (with x=0.15, 0.28, 0.45 and 0.50) solid solutions synthesized by two co-conversion routes: the first one based on the oxalic co-precipitation of U(IV) and Pu(III) complex3 and the second on the internal gelation of a U(VI)-Pu(IV) or U(IV)-Pu(III) solution4. Before XAS experiments, samples were characterized by X-Ray diffraction and exhibit the expected cubic face centered structure with lattice parameters in agreement with Vegard Law.
XAS experiments were performed at the Rossendorf Beamline (BM20) located at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). For each sample, plutonium LII and U LIII-edge were collected at 15K using a helium cryostat.

Keywords: Uranium; Plutonium; MOX; EXAFS

  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Francisco, USA

Publ.-Id: 12520

Existence of uranyl aluminate at the nanoscale

Chave, T.; Nikitenko, S. I.; Scheinost, A. C.; Berthon, C.; Moisy, P.

The aluminate complexes of uranyl ion cannot be obtained in aqueous solutions due to the hydrolysis of U(VI). However, U(VI) is known to be readily adsorbed with alumina from aqueous near-neutral solutions owing to the formation of inner-sphere, bidentate complexes at the surface [1]. Herein, for the first time we present the data indicating possibility of uranyl aluminate (UrAl) formation as nanoparticles dispersed in alumina matrix.
The precursor for UrAl was prepared by U(VI) precipitation with ammonia (pH=11) in the presence of mesoporous alumina MSU-X under the effect of power ultrasound (f = 20 kHz, Pac = 0.6 Wcm-2, Ar, T = 37°C). Finally, solids were centrifuged, washed until neutral pH with pure water, dried at 70°C and annealed at 800°C prior to low resolution TEM, U LIII XAFS and 27Al MAS NMR analysis.
The sample with 5 weight % of uranium yields an orange air-stable product after annealing. TEM images show uranium nanoparticles with an average size of about 5 nm dispersed in alumina matrix. XAFS spectrum of this sample reveals the presence of uranyl group with a U=O trans-dioxo distance equal to 1.80 (0.01) Å. Both XANES and EXAFS spectra are quite similar to the spectra obtained with uranyl ions adsorbed onto alumina at pH 6.
27Al MAS NMR spectra of initial MSU-X alumina exhibits three peaks assigned to octahedral, tetrahedral, and pentagonal local environment of aluminum. According to literature, pentagonal coordination of aluminum is typical for protonated boehmite-like forms of alumina, AlO(OH) [2]. Heating of MSU-X without uranium causes sharp decrease in pentagonal aluminum occupancy. By contrast, with 5% of uranium NMR spectra after annealing at 800°C clearly indicate the presence of aluminum ions coordinated by five oxygen atoms, which could be assigned to uranyl coordination with AlO2- anions.
The increase of uranium concentration to 30 weight % causes formation of green-black solids after annealing at 800°C. TEM measurements demonstrate formation of 50 nm uranium crystallites embedded into alumina matrix. EXAFS spectrum of this sample exhibits the absence of UO22+ groups and a strong U-U interaction with a characteristic distance of 4.39 (0.01) Å comparable with U3O8 reference sample.
Presumably UrAl is formed during the calcination of precursor only at low content of uranium hydrolyzed species finely dispersed or adsorbed at alumina surface. Otherwise, annealing leads to predominated formation of uranium oxides, probably, due to the favorable kinetics of solid state reaction. Thus, interaction of uranyl ions with alumina matrix represents a relatively rare example of real nanochemistry, when the chemical composition of species is a strong function of the particle size. In conclusion, it should be emphasized that a further structural study is necessary to refine the UrAl structure.
Acknowledgements This work was supported by European ACTINET and French PARIS Research Programs.
1. Sylwester E.R., Hudson E.A., Allen P.G. Geochim. Cosmochim. Acta, 64 (2000) 2431-2438.
2. Wang J.A., Bokhimi X., Morales A., Novaro O., Lopez T., Gomez R. J. Phys. Chem. B, 103 (1999) 299-303.

Keywords: nanoparticles; uranate; aluminate; EXAFS

  • Lecture (Conference)
    39èmes Journées des Actinides, 28.-31.03.2009, La Grande Motte, France

Publ.-Id: 12519

Free and silica-gel bound tetraazamacrocycles as complexing agents of actinide cations: a XAFS investigation of the solid-state coordination scheme

Giachini, L.; Faure, S.; Meyer, M.; Vi Nguyen, L.; Batifol, B.; Chollet, H.; Guilard, R.; Hennig, C.; Scheinost, A. C.

There is a continuous need for processes aimed at the selective uptake of toxic metal ions from dilute wastewaters and industrial process streams. Insofar, solid-liquid extraction processes using chelating agents grafted onto hydrophilic supports are appealing. The Institut de Chimie Moléculaire de l'Université de Bourgogne has designed a series of hybrid organic-inorganic materials for the selective uptake of toxic metal ions, including actinides [1]. These extracting agents are obtained by grafting functionalized tetraazamacrocyclic ligands (cyclen and cyclam derivatives) on the surface of silica-gel beads. In collaboration with the Commissariat à l'Energie Atomique (CEA Center of Valduc), one of these modified gel has been prepared on a semi-industrial scale and used in the final decontamination step of real effluents for removing the residual -emitters (U, Pu, Am) contained at the sub-g/L level. This process allowed the successful decontamination of more than 50 m3 wastewaters, with a residual radioactivity level of less than 5 Bq/m3.
We have used XAFS to investigate the coordination scheme of UO22+ and Pu4+ cations at the surface of the organic-inorganic hybrid materials. The results show that surface complexes are formed through a combined action between the reactive solid support, namely amorphous silica, and the chelating groups appended on the immobilized ligands [2].

[1] F. Barbette, F. Rascalou, H. Chollet, J. L. Babouhot, F. Denat, R. Guilard, Anal. Chim. Acta, 502, 179-187, 2004.
[2] L. Giachini, S. Faure, M. Meyer, L.V. Nguyen, B. Batifol, H. Chollet, R. Guilard, A.C. Scheinost, C. Hennig, Proceedings of the 5th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources (Actinide XAS 2008), in press.

Keywords: macrocycles; actinides; cyclen; cyclam; nuclear waste; EXAFS

  • Lecture (Conference)
    The 14th International Conference on X-ray Absorption Fine Structure (XAFS14), 26.-31.07.2009, Camerino, Italy

Publ.-Id: 12518

THEREDA – A thermodynamic reference database for nuclear waste disposal in Germany

Gester, S.; Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Marquardt, C.; Moog, H. C.; Neck, V.; Richter, A.; Scharge, T.; Voigt, W.; Wilhelm, S.; Willms, T.; Wollmann, G.

The long-term safety of radioactive waste disposal in deep geological repositories with respective reliable predictions is an important fact in the disposal site selection process. To ensure the safety geochemical modeling calculations using comprehensive and consistent thermodynamic data are required.
The relational databank THEREDA will provide such thermodynamic datasets. It takes into account specific German requirements (high ionic strengths in salt host rocks) and temperatures up to 100°C. Available databases do not suffice these needs because of very restrictive data selection procedures or heterogeneous and inconsistent data. THEREDA mainly builds on data derived from solution experiments with a focus on ternary and higher systems.
The application of referential integrity, thermodynamic dependencies, alternative datasets and uncertainty estimates allows THEREDA to deliver tailor-made parameter files for use in geochemical modeling software like EQ3/6, GWB and ChemApp.
To enhance public use THEREDA is accessible via internet.

Keywords: THEREDA; database; nuclear waste disposal; long-term safety; reliable predictions; thermodynamic data; high ionic strength; Pitzer; SIT; solution experiments; alternative datasets; referential integrity; uncertainty estimates; geochemical modelling; EQ3/6; GWB; ChemApp

  • Lecture (Conference)
    238th ACS National Meeting & Exposition (Fall 2009), 16.-20.08.2009, Washington DC, United States
  • Abstract in refereed journal
    American Chemical society: Abstracts of scientific papers 238(2009), 58-NUCL
    ISSN: 978-0-8412-0005-0

Publ.-Id: 12516

THEREDA – A thermodynamic reference database for nuclear waste disposal in Germany

Gester, S.; Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Marquardt, C.; Moog, H. C.; Neck, V.; Richter, A.; Scharge, T.; Voigt, W.; Wilhelm, S.; Willms, T.; Wollmann, G.

THEREDA provides consistent thermodynamic datasets to assist the long-term safety assessment of nuclear waste repositories. It meets specific German requirements (high salinities and temperatures). THEREDA is build on a relational SQL-database. The application of referential integrity, thermodynamic dependencies, alternative datasets and uncertainty estimates allows to deliver tailor-made parameter files for use in geochemical modelling software like EQ3/6, GWB and ChemApp covering law-of-mass-action and Gibbs-energy-minimization codes.

Keywords: THEREDA; database; nuclear waste disposal; long-term safety; thermodynamic data; high saline systems; Pitzer; SIT; alternative datasets; referential integrity; uncertainty estimates; geochemical modelling; EQ3/6; GWB; ChemApp

  • Lecture (Conference)
    SIAM Conference on Mathematical & Computational Issues in the Geosciences (GS 09), 15.-18.06.2009, Leipzig, Deutschland

Publ.-Id: 12515

The role of colloids in uranium transport: Facilitating and impeding effects

Zänker, H.; Brendler, V.

Tetravalent uranium is generally regarded as sparingly soluble and hence immobile in the aquatic environment. The solubility product of UO2·xH2O was determined by laser-induced breakdown detection (LIBD). For the given reaction, UO2·xH2O + 4 H+ = U4+ + (2+x) H2O, a value of log Ksp0 = -54.30 ± 1.0 was found (cf. [1]). It results in U(IV) solubilities of about 10-8 M in the near-neutral pH region. On the other hand, hexavalent uranium is much more soluble, in particular if carbonate is present in a water. Calculations with the EQ3/6 geochemical speciation software (thermodynamic data from the NEA data base) were performed for a typical oxic groundwater in equilibrium with air CO2 and varying pH. They yielded uranium solubilities of as much as 10-5 M in the near-neutral pH region. Normally, uranium is regarded as mobile under typical groundwater conditions in geochemistry.
However, this apparently clear picture can be counteracted if colloids come into the play. By our laboratory experiments (cf. [2]) the formation of intrinsic U(IV) colloids in the presence of silicate was demonstrated. The possibility that U(IV) forms colloids can not be ruled out also in the aquatic environment. In the colloidal form U(IV) is “undissolved” in the thermodynamic sense of the word but nevertheless mobile. Second, the high mobility of U(VI) in groundwaters or mine waters can be significantly reduced by scavenging and co-precipitation of U(VI) due to the formation of pseudocolloids with unstable (coagulating) ferrihydrite colloids. Laboratory mine flooding simulation experiments were carried out and it was found that more than 98 % of the U(VI) present was scavenged by such colloids ([3, 4]). It follows that both transport-facilitating effects of colloids on “immobile” contaminants such as U(IV) and transport-impeding effects on “mobile” contaminants such as U(VI) may play a part. It is the geochemical ambiance that decides which effect prevails. A comparison of geochemical cases (uranium mine / nuclear waste depository, oxidizing/reducing, acidic/near-neutral) is given.

[1] Opel K., Weiß S., Hübener S., Zänker H., Bernhard G., Radiochim. Acta 95 (2007) 143-149.
[2] Zänker, H., Opel, K., Weiß, S., Hübener, S., Bernhard, G., 2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm.
[3] Zänker, H., Richter, W., Hüttig, G., Coll. Surf. A: Physicochem. Eng. Aspects 217 (2003) 21-31.
[4] Ulrich, K.-U., Rossberg, A., Foerstendorf, H., Zänker, H., Scheinost, A., Geochim. Cosmochim. Acta 70 (2006) 5469-5487.

Keywords: uranium(IV); uranium(VI); intrinsic colloids; pseudocolloids

  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, USA

Publ.-Id: 12514

Sorption of uranium(VI) on clay in absence and presence of humic acid

Joseph, C.; Schmeide, K.; Sachs, S.; Bernhard, G.

In Germany, the investigated host rocks for nuclear waste disposal in deep geological formations are salt, crystalline rock and argillaceous rock. Natural clay contains organic matter, such as humic acid (HA), which has an influence on the sorption of metal ions. In this work, we studied the uranium(VI) sorption onto the reference clay mineral kaolinite and the natural opalinus clay in absence and presence of HA. The results are compared with our previous studies focused on kaolinite [1].
The influence of the background electrolyte on uranium(VI) sorption onto kaolinite was investigated. The NaClO4 electrolyte previously used [1] was compared with synthetic opalinus clay pore water (I = 0.42 M, pH 7.6) [2]. The experiments show that a lower amount of uranium(VI) is adsorbed onto the clay when the opalinus clay pore water is used. This behavior can be explained with the uranium(VI) speciation. At pH 7.6, the speciation in opalinus clay pore water is dominated by the neutral aquatic Ca2UO2(CO3)3 complex, which has a lower sorption affinity towards kaolinite than the charged UO2(CO3)34-, (UO2)2CO3(OH)3- and UO2(CO3)22- species formed in the NaClO4 system (I = 0.42 M) at pH 7.6.
In the presence of HA (10 mg/L, 50 mg/L), in opalinus clay pore water a lower percental amount of uranium(VI) is adsorbed onto kaolinite. But the concentration of HA has no influence on the amount of sorbed uranium(VI). The reason is that HA has no influence on the uranium(VI) speciation in opalinus clay pore water at pH 7.6, thus, no uranium(VI) humate complexes are formed. The decrease of sorbed uranium(VI) in presence of HA is only due to the competition for surface binding sites between uranium(VI) and HA. These results are in contrast to the results obtained in the NaClO4 system (I = 0.1 M) [1]. There, the speciation of uranium(VI) in NaClO4 changes because aqueous uranium(VI) humate complexes are formed. Due to this and due to a competition for surface binding sites, the percental amount of sorbed uranium(VI) decreases. This effect is increased with increasing HA concentration.
Furhermore, the uranium(VI) sorption onto kaolinite and opalinus clay in opalinus clay pore water was compared. Results show a stronger sorption of uranium(VI) onto kaolinite (2.8 ± 0.2 µg/m2) than onto opalinus clay (0.049 ± 0.002 µg/m2). Since opalinus clay has a higher specific surface area than kaolinite (opalinus clay: Asp = 42 m2/g; kaolinite: Asp = 11.7 m2/g [1]), and contains a higher amount of iron-containing minerals (opalinus clay: 5 wt.% Fe; kaolinite: 0.27 wt.% Fe [1]), which are able to sorb uranium(VI) very well [3], this result is unexpected. To clarify this observation, leaching experiments with opalinus clay applying the two background electrolytes are performed in order to determine the release of ions into the solution in dependence on time and pH and to investigate their influence on the uranium(VI) sorption. We studied the pH dependence of the uranium(VI) sorption onto opalinus clay in absence and presence of HA, and compared this with previous results obtained for kaolinite [1].

[1] A. Křepelová et al., Radiochim. Acta 2007, 94, 825.
[2] F.J. Pearson, PSI Internal Report TM-44-98-07 1998, Paul Scherrer Institute, Villigen, Switzerland.
[3] K. Schmeide et al., Radiochim. Acta 2000, 88, 723.

Keywords: sorption; uranium(VI); humic acid; clay; kaolinite; opalinus clay; speciation; opalinus clay pore water

  • Contribution to proceedings
    12th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
  • Poster
    12th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12513

Ion Bombardment induced self-organization of nanopattern studied by 3D lattice kinetic MC simulation

Numazawa, S.; Heinig, K.-H.

The surface damage (sputtered atoms, adatoms, surface vacancies) produced by ion impact is determined by random displacement of the atom at impact point. Using the statistics of this damage for multiple ion impacts in 3D kinetic lattice Monte Carlo simulations, the self-organization of nano-scale surface pattern by the competition between damage creation and damage diffusion/annealing is studied. Especially, anisotropic displacement of surface atoms creates ripple formation even sputtering is suppressed. The ripple wavelength follows a power low of fluence and temperature of substrate. Local temperature enhancement of impact points refers also Frenkel-pair and ripples on f.c.c.(110) surface. The direction of ripples depends on the temperature of migration atoms which is corresponding to the experimental result of Ag(110) ion bombardment.

  • Poster
    The CCP5 Molecular Simulation Summer School 2008, 07.-15.7.2008, Sheffield, UK
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Poster
    IUMRS-ICA 2008, 09.-13.12.2008, Nagoya, Japan

Publ.-Id: 12512

Sorption of U(VI) onto TiO2. A vibrational spectroscopic analysis of the sorption processes

Foerstendorf, H.; Müller, K.; Meusel, T.; Brendler, V.; Comarmond, J.; Payne, T.; Lefèvre, G.

A detailed knowledge of the sorption processes of uranium(VI) onto titanium(IV) dioxide (TiO2) can serve as a model for the elucidation of molecular processes on more complex mineral surfaces. Because of the high stability, low solubility over a wide pH range and the well-known structure of TiO2, sorption studies with U(VI) can be carried out throughout a large range of experimental parameters [1-3].

In this work, we used attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy in an in situ investigation of the sorption processes of U(VI) onto TiO2. A set of highly purified and well characterized TiO2 phases from different origins differing in the ratio of the most stable polymorphs, i.e. anatase and rutile, in specific surface area and in particle size distribution was investigated. Irrespective of the composition of the mineral phase, it was shown that U(VI) mainly forms a similar inner sphere complex, showing an absorption maximum shifted of about 20 cm−1 to lower wavenumbers compared to the aqueous species.

The influence of the aqueous speciation on the sorption process was studied using different concentrations of the actinide ions and at different pH values. The high sensitivity of the in situ ATR FT-IR technique allows the study of U(VI) concentrations down to the lower micromolar range. From these results, it is concluded that only one significant surface U(VI) complex forms in the pH range between 4 and 7, and across a range of aqueous uranyl concentrations. The surface speciation of uranyl therefore involves fewer species than the aqueous speciation in these experimental systems, as is consistent with the findings of a previous study [4].

Furthermore, the capability of a fast scanning of IR spectra makes it feasible to carry out time-resolved experiments of the sorption processes with a time resolution in the sub-minute time range. It is shown that in the early steps of the U(VI) sorption a transient species is formed on the mineral phase showing a clearly red-shifted absorption maximum. After prolonged sorption the IR spectra indicate the formation of a stable surface species which is commonly found on TiO2 phases. These findings give new insights into the surface complex formation of U(VI) on titanium dioxide at a molecular level.

[1] Den Auwer, C., Drot, R., Simoni, E., Conradson, S. D., Gailhanou, M. and de Leon, J. M. (2003) "Grazing incidence XAFS spectroscopy of uranyl sorbed onto TiO2 rutile surfaces." New J. Chem. 27, 648-655.
[2] Wazne, M., Meng, X. G., Korfiatis, G. P. and Christodoulatos, C. (2006) "Carbonate effects on hexavalent uranium removal from water by nanocrystalline titanium dioxide." J. Hazard. Mater. 136, 47-52.
[3] Vandenborre, J., Drot, R. and Simoni, E. (2007) "Interaction mechanisms between uranium(VI) and rutile titanium dioxide: From single crystal to powder." Inorg. Chem. 46, 1291-1296.
[4] Lefèvre, G., Kneppers, J. and Fédoroff, M. (2008) "Sorption of uranyl ions on titanium oxide studied by ATR-IR spectroscopy." J. Colloid Interface Sci. 327, 15-20.

  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, U.S.A.

Publ.-Id: 12511

J-self-adjointness, Krein spaces and related physics

Günther, U.

As brief introduction, a few basic aspects of the theory of J-self-adjoint operators and matrices are sketched as well as their natural relation to Krein spaces --- Hilbert spaces with indefinite metric structures. The mathematical facts are then illustrated by some recent results from PT quantum mechanics:
  • the highly nontrivial spectral behavior of a quantum mechanical Hamiltonian with x2(ix)ν potential in the sector of spontaneously broken PT-symmetry, the form invariant resolution of the spectral singularity in the limit ν → -1 and a hidden UV-IR duality
  • the unfolding of higher-order branch-points (exceptional points) in PT-symmetric Bose-Hubbard models and the relevance of the underlying Hessenberg type of perturbation matrices
  • the Naimark dilation of the PT-symmetric quantum brachistochrone solution with the unexpected physical result of inducing ultra-fast (wormhole-like) evolution regimes via fine-tuned entanglement
The talk concludes with briefly indicating further applications and possible future developments.

Keywords: J-self-adjoint operators; Krein space; PT quantum mechanics; spontaneously broken symmetry; UV-IR duality; Bose-Hubbard model; Bose-Einstein condensate; exceptional point; branch point; brachistochrone; entangled states; ultra-fast evolution; wormhole-like behavior

  • Invited lecture (Conferences)
    Editorial Board Meeting; Journal of Physics A: Mathematical and Theoretical, 23.-24.04.2009, London, UK

Publ.-Id: 12510

Radiation-induced defect centers: Luminescence and optical absorption study of helium-irradiated diamond and zircon

Nasdala, L.; Grambole, D.; Wildner, M.; Zaitsev, A. M.; Götze, J.; Kempe, U.; Hanchar, J. M.; Harris, J. W.

The impact of radioactivity can generate optically active defect centers in minerals. These defects may first affect light absorption, i.e., they may cause radio-coloration or -de-coloration. Second, radio-induced defects may enhance or suppress luminescence emissions of their host minerals. The action of such centers is, for instance, seen in spotted diamond specimens showing green or brown radio-coloration (the latter is typically associated with yellowish-green photoluminescence). Another example is the yellow broad-band luminescence emission of zircon, which is commonly observed in cathodo- and photoluminescence spectra of this mineral. So study whether, and how, natural alpha radiation generates and affects such centers, flat polished diamond and zircon samples were irradiated in a tandem accelerator facility with 8.8 MeV He2+ ions, which are the analog of alpha particles generated in the 212Po α-decay (Th decay chain).
Helium ions were found to penetrate 29 μm into diamond and 32 μm into zircon, respectively, which corresponds very well to ranges predicted by Monte Carlo simulations using the SRIM code. Notable pale green coloration of diamond was observed to start at 1014 to 1015 He/cm². Spots irradiated with 1017 He/cm² appeared dark green and were found to show initial amorphization. Green colors transformed to orange-brown through heat-treatment at about 550 °C, which is mainly due to the disappearance of the ∼16,000 cm-1 GR1 band. The latter process was found to be associated with the appearance of intense green UV-induced photoluminescence. Associated observations include strong volume expansion due to the accumulated radiation-damage, which may result in notable up-doming of radiohaloes. First studies of He-implanted zircon indicated a similar luminescence behavior, with an irradiation-induced broad-band yellow emission at 575 nm. This emission band decreases in intensity in samples that were affected by natural radiation damage prior to the He irradiation experiment.
The observed depth profiles of the luminescence emission intensity in the two minerals correspond to the calculated defect distribution profiles but not to the ionization distribution profiles. This suggests that ionization alone is insufficient to create optically active centers. Additional carbon- (diamond) and oxygen-irradiation experiments (zircon) were done to generate similar structural damage with an elemental species which is already present in the respective host mineral. Observations on these samples are largely similar to those on He-irradiated samples. Consequently, optically active centers are related to structural point defects that are created by atomic knock-ons whereas our observations did not yield independent evidence which suggests that He ions themselves might be optically active species.

  • Lecture (Conference)
    AGU Joint Assembly 2009 - The Meeting of the Americas, 24.-27.05.2009, Toronto, Canada

Publ.-Id: 12509

DYN3D - Advanced Reactor Simulations in 3D

Rohde, U.; Grundmann, U.; Kliem, S.

DYN3D is a three-dimensional core model for dynamic and depletion calculations in light water reactor cores with quadratic or hexagonal fuel assembly geometry. The neutron kinetic model is based on the solution of the three dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal hydraulic model of the reactor core and the fuel rod model are implemented in the module FLOCAL, which is a part of DYN3D.
The paper gaves an overview on the application possibilities of DYN3D.

  • Nuclear Energy Review 2(2007), 28-30
    ISSN: 1753-3910

Publ.-Id: 12508

Phi decay: A relevant source for K- production at energies available at the GSI Schwerionen-Synchrotron (SIS)?

Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Bielcik, J.; Blanco, A.; Bortolotti, A.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Duran, I.; Dybczak, A.; Eberl, T.; Fabietti, L.; Fateev, O.; Ferreira-Marques, R.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Lorenz, M.; Maier, L.; Maiolino, C.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez Cavalcanti, T.; Piatelli, P.; Pietraszko, J.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sapienza, P.; Schmah, A.; Schröder, C.; Schwab, E.; Simon, R.; Smolyankin, V.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.

We present phase space distributions and multiplicities of K+, K- and phi mesons produced in Ar+KCl reactions at a kinetic beam energy of 1.756 AGeV and measured with the HADES spectrometer. The inverse slope parameters and yields of kaons supplement the systematics of previous measurements. The percentage of K- mesons coming fromphi decay is found to be 18+- 7%.

  • Physical Review C 80(2009)2, 025209

Publ.-Id: 12507

The High-Acceptance Dielectron Spectrometer HADES

Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Bielcik, J.; Blanco, A.; Bortolotti, A.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Duran, I.; Dybczak, A.; Eberl, T.; Fabietti, L.; Fateev, O.; Ferreira-Marques, R.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Lorenz, M.; Maier, L.; Maiolino, C.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez Cavalcanti, T.; Piatelli, P.; Pietraszko, J.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sapienza, P.; Schmah, A.; Schröder, C.; Schwab, E.; Simon, R.; Smolyankin, V.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.

HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85% azimuthal coverage over a polar angle interval from 18 to 85 degree, a single electron efficiency of 50% and a vector meson mass resolution of 2.5%. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range. This paper describes the main features and the performance of the detector system.

Publ.-Id: 12506

Measurement of charged pions in 12C + 12C collisions at 1A GeV and 2A GeV with HADES

Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Bielcik, J.; Blanco, A.; Bortolotti, A.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Duran, I.; Dybczak, A.; Eberl, T.; Fabietti, L.; Fateev, O.; Ferreira-Marques, R.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Lorenz, M.; Maier, L.; Maiolino, C.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez Cavalcanti, T.; Piatelli, P.; Pietraszko, J.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sapienza, P.; Schmah, A.; Schröder, C.; Schwab, E.; Simon, R.; Smolyankin, V.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.

We present the results of a study of charged pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect to the emission of charged hadrons, specifically the production of pi+- mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed the first large-angular range measurement of the distribution of pi+- mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy of pion production is systematically analyzed.

  • European Physical Journal A 40(2009), 45-59


Publ.-Id: 12504

Study of the role of sulfur functionalities in humic acids for uranium(VI) complexation

Sachs, S.; Reich, T.; Bernhard, G.

Humic substances influence the speciation and migration behavior of toxic and radiotoxic metal ions, such as actinides, in the environment. Depending on their origin, humic substances contain different amounts of sulfur ranging from 0.1 to 3.6% and 0.5 to 1.43% in soil and aquatic humic substances, respectively [1]. Reduced, intermediately oxidized and highly oxidized sulfur functionalities occur in humic substances [1]. Although sulfur functionalities occur in small concentrations, they can play an important role in the complexation of selected metal ions. Knowledge about the impact of sulfur functionalities on the metal ion complexation by humic substances and their significance compared to oxygen- and nitrogen-containing functional groups helps to improve complexation models for humic substances. Consequently, this contributes to a more reliable geochemical modeling of the interaction processes between humic matter and metal ions in the environment.
In the present work sulfur-containing humic acid (HA) model substances have been synthesized to study the influence of sulfur functionalities on the metal ion complexation by HA. HA type M1-S with different sulfur contents was synthesized from xylose, phenylalanine, glycine, and cysteine and the resulting products were characterized. The identity of the sulfur species was determined by X-ray photoelectron spectroscopy (XPS). XPS results of HA M1-S with 1.94 wt-% sulfur indicate the occurrence of at least two different sulfur species. About 82% of sulfur occurs in form of reduced sulfur species (e.g., thiols, dialkylsulfide and/or disulfides) and about 18% of sulfur is attributed to sulfoxides.
The uranium(VI) complexation of HA with different sulfur contents (0, 1.94 and 3.94 wt-%) has been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses. Applying the metal ion charge neutralization model [2] comparable complexation constants with a mean value of logβ0.1M = 6.3 ± 0.1 were determined by TRLFS. However, with increasing sulfur content of the HA an increase in the uranium(VI) loading capacities from 26 ± 4 to 37 ± 2% (pH 3.8) was observed. This indicates that with increasing amounts of sulfur functionalities more sites become available for the complexation of uranium(VI) by HA.

Keywords: Humic substances; humic acids; complexation; functional groups; sulfur; uranium(VI); XPS; TRLFS; fs-TRLFS

  • Contribution to proceedings
    12th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
  • Lecture (Conference)
    12th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12503

Complexation of low-valent actinides (uranium(IV), plutonium(III)) by organic model ligands and humic acid in aqueous solution

Schmeide, K.; Sachs, S.; Bernhard, G.

Risk assessments predicting the transport of actinides under environmentally relevant conditions require basic knowledge of their solubility, their interaction with complexing ligands, their sorption and redox behavior as well as their ability to form colloids. Under reducing conditions as prevalent in deep underground nuclear waste repositories and in the depth of flooded uranium mines, actinide species occur in lower oxidation states. Both the speciation and the mobility of actinides in aquatic systems strongly depend on their oxidation state. For instance, in contrast to the soluble and mobile uranium(VI), uranium(IV) is much less mobile due to the low solubility of uranium(IV) hydrous oxide (UO2•xH2O(am)). However, in the presence of inorganic and organic ligands also uranium(IV) may become mobile due to formation of soluble complexes. Also the mobility of plutonium depends strongly on the existing oxidation states and the chemical species formed. Thus, the speciation of low-valent actinides in aqueous solution has to be studied to predict their migration behavior in natural environments.
Data for the complexation of uranium(IV) and plutonium(III) with inorganic and organic ligands are scarce or vary strongly. In the present study, the complexation behavior of the model ligands citric acid, succinic acid, mandelic acid and glycolic acid is studied and compared to that of humic acid. These model ligands stand for a variety of organic ligands in aqueous systems. The actinide complexation by model ligands and humic acid is studied applying UV-vis absorption spectroscopy and ultrafiltration, respectively.
The stability constants for 1:1 and 1:2 uranium(IV) citrate complexes of the type MpHqLr were determined with log ß101 = 13.5 ± 0.2 and log ß102 = 25.1 ± 0.2 [1]. This shows a strong interaction between uranium(IV) and the ligand. The uranium(IV) complexation with mandelic and glycolic acid is weaker. Stability constants for 1:1 and 1:2 uranium(IV) ligand complexes of the type MpHqLr were determined with log ß101 = 4.53 ± 0.09 and log ß102 = 8.02 ± 0.13 for mandelate and with log ß101 = 4.71 ± 0.08 and log ß102 = 8.25 ± 0.15 for glycolate (I = 1.0 M). Speciation calculations show that due to complexation with organic ligands the solubility and thus, the mobility of uranium(IV) in aquatic systems is increased.
Also plutonium(III) is strongly complexed by organic ligands and humic acid under environmentally relevant conditions which shows the need for speciation studies of plutonium in aqueous solutions containing various complexing agents.

[1] Schmeide, K., Bernhard, G.: Spectroscopic Study of the Uranium(IV) Complexation by Organic Model Ligands in Aqueous Solution. In: Uranium, Mining and Hydrogeology (Merkel, B.J.; Hasche-Berger, A. eds.), Springer Verlag, Berlin, 591-598 (2008).

Keywords: uranium; tetravalent; citric acid; succinic acid; mandelic acid; glycolic acid; plutonium; humic acid; stability constants; speciation

  • Contribution to proceedings
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12502

Terahertz two-photon quantum well infrared photodetector

Schneider, H.; Liu, H. C.; Winnerl, S.; Song, C. Y.; Walther, M.; Helm, M.

A two-photon detector based on intersubband transitions in GaAs/AlGaAs quantum wells operating in the Terahertz regime below the Reststrahlenband is reported. Resonantly enhanced optical nonlinearities enables sensitive quadratic detection at pJ pulse energies. We demonstrate its use in a quadratic autocorrelator for far-infrared picosecond pulses at around 7 THz.

Keywords: Quantum well infrared photodetector; two-photon intersubband transition; GaAs/AlGaAs quantum well; quadratic autocorrelation

Publ.-Id: 12501

UV-vis spectroscopy of Eu(III) and Am(III) complexation with small organic acids at low concentrations and variable temperatures

Müller, M.; Acker, M.; Barkleit, A.; Taut, S.; Bernhard, G.

The long-term safety analysis of nuclear waste disposals in clay formations requires detailed knowledge of the interaction of actinides at relevant temperatures (up to 100 °C). It is well known that the migration behaviour of the actinides is strongly influenced by natural organic matter (NOM) from the clay. However, the current thermodynamic database is lacking fundamental data about the temperature-dependent complexation of americium (and its analogue europium) with small organic acids, which are structural similar components of natural organic matter in the clay.

We present our results for the complexation of both Am(III) and Eu(III) with 2-hydroxybenzoic acid (salicylic acid), 1,2,4,5-benzentetracarboxylic acid (pyromellitic acid) and 2,3-dihydroxbutanedioic acid (L-tartaric acid) in the temperature range from 20 to 50°C, at ionic strength of 0.1 mol/l NaClO4 and pH below 6.

For the first time, temperature-dependent UV-Vis spectroscopic measurements with a Liquid Waveguide Capillary Cell were used for complexation investigations. Due to the long optical path length of the capillary cell (up to 2 m) very low americium and europium concentrations can be measured. Thus, the presented absorption measurements were carried out at Am(III) concentrations below 5e-7 mol/l and Eu(III) concentration below 5e-4 mol/l. For all investigated model ligands we observed a slight shift of the absorption maxima of Eu(III) (394 nm) and Am(III) (504 nm) spectra of 0.5 to 2 nm to higher wavelengths due to the complexation.
We first validated the method with europium: at 25°C the determined constants for the 1:1 complexes of europium salicylate, europium pyromellitate and europium L tartrate with logß111=15.4+/-0.06, logß112 = 14.3 +/-0.2, logß111=7.9+/-0.3 respectively, are in good agreement with the literature values [1], [2].
For the americium salicylate system, both a 1:1 complex and a 1:2 complex were observed at pH 4. The stability constants of these complexes are logß111= 15.42+/-0.06 and logß122=30.98+/-0.05 and comparable to the reported ones for the analogous complexes with europium [1]. With increasing temperature, the stability constants for both complex systems increase, indicating an endothermic complexation reaction. The same behaviour is expected for the americium pyromellitate system, where just a 1:1 complex with log ß112=15.03+/-0.1 can be reported until now.

The temperature dependence and the interaction of americium with L-tartrate is presently under investigation. The stability constants and thermodynamic parameters (enthalpy, entropy, Gibbs energy) of all above investigated systems are reported.

[1] Aoyagi, N. et al. Radiochemica Acta, Vol. 92, 2004, 589-593
[2] R. Kulshrestha, S. Sengar, M. Singh, Indian J. of Chemistry 26A, 1987, 940-943

  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12500

Optimized Detector Configurations for Particle Therapy Positron Emission Tomography

Fiedler, F.; Braess, H.; Kunath, D.; Laube, K.; Parodi, K.; Priegnitz, M.; Shakirin, G.; Enghardt, W.

no abstract available

Keywords: PT PET; ion therapy

  • Lecture (Conference)
    Heavy Ions in Therapy and Space Symposium 2009, 06.-10.07.2009, Köln, Deutschland

Publ.-Id: 12499

Atomistic simulation of ion-erosion-induced surface patterning

Numazawa, S.; Posselt, M.; Heinig, K.-H.

Kinetic 3D lattice Monte-Carlo simulation of ion beam induced surface modification was performed for f.c.c. (100) surface and preliminary Crystal-TCAS calculations of 5keV As+ on Si(001) have been simulated. By KMC, the observed surface patterning was depending on the incidence angle even the direction of ion-induced surface atom displacement is arbitrary next lattice position. Angular dependency of the sputtering yield by the Crystal-TCAS calculation has been studied.

Keywords: TRIM; Kinetic Monte-Carlo; nanopatterninig

  • Lecture (others)
    Seminar of DFG project FOR845, 06.-07.05.08, Münster, Germany

Publ.-Id: 12498

Polyhedral Surface Approximation of Non-Convex Voxel Sets and Improvements to the Convex Hull Computing Method

Schulz, H.

In this paper we introduce an algorithm for the creation of polyhedral approximations for objects represented as strongly connected sets of voxels in three-dimensional binary images. The algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0. The second aim of this paper is to present some improvements to our convex hull algorithm to reduce computation time.

Keywords: digital geometry; surface approximation; abstract cell complex; polyhedron; voxel

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-514 2009
    ISSN: 1437-322X


Publ.-Id: 12497

Photoeffects on U(VI) sorption onto TiO2 studied by in situ ATR FT-IR spectroscopy.

Müller, K.; Meusel, T.; Steudtner, R.; Foerstendorf, H.; Brendler, V.; Bernhard, G.

Uranium(VI), is known to be the most stable oxidation state of uranium in oxygenated waters, with the uranyl ion UO22+ forming soluble hydroxo and carbonate complexes [1, 2]. Thermodynamic unstable U(IV) complexes might be formed in oxygenated waters by photoreduction of U(VI) supplied by solar radiation. Although U(VI) photoinduced reduction is reported to occur in acidic solutions, it is prevented at neutral conditions because of structural arrangements resulting from hydrolysis reactions. However, sorbed U(VI) species at the water-mineral interface on particles with semiconducting properties, e.g. TiO2 have shown different redox behavior than solution species [3-5].

TiO2 is the material mostly applied for the investigation of photocatalysis, due to its exceptional optical and electronic properties, chemical stability and low cost. Anatase was found photocatalytically more active than rutile [6]. The mixed sample of 80% antase and 20% rutile Degussa P-25 was investigated for U(VI) photoreduction using laser fluorescence spectroscopy [3, 4]. ATR FT-IR spectroscopy, which was applied to photoreactions of oxalic acid, has not been applied for U(VI), yet.

We investigated the effects of UV-visible light on the sorption processes of U(VI) onto TiO2 by application of in situ ATR FT-IR spectroscopy. Thus, changes of the excitation wavelength and the TiO2 phase, namely anatase, rutile, and a mixture of both (P-25), were considered. Furthermore, the results were compared to photoeffects observed for U(VI) sorption onto ZnO.

From the obtained spectra different photoinduced effects on U(VI) sorption onto different TiO2 phases are derived. Photocatalysis is clearly suggested for the P-25 sample. In contrast, pure anatase and rutile did not show spectral differences for the sorption mechanisms under dark and light conditions. Furthermore, the photoreaction was found to be limited to incident light with wavelengths below 580 nm. The comparison between TiO2 and ZnO evidence a higher photoactivity for TiO2.

1.Guillaumont, R.; Fanghänel, T.; Fuger, J.; Grenthe, I.; Neck, V.; Palmer, D. A.; Rand, M. H., Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc. Elsevier: Amsterdam, 2003.
2.Müller, K.; Brendler, V.; Foerstendorf, H., Inorganic Chemistry 2008, 47, (21), 10127-10134.
3.Eliet, V.; Bidoglio, G., Environmental Science & Technology 1998, 32, (20), 3155-3161.
4.Selli, E.; Eliet, V.; Spini, M. R.; Bidoglio, G., Environmental Science & Technology 2000, 34, (17), 3742-3748.
5.Amadelli, R.; Maldotti, A.; Sostero, S.; Carassiti, V., Journal of the Chemical Society-Faraday Transactions 1991, 87, (19), 3267-3273.
6.Litter, M. I., Applied Catalysis B-Environmental 1999, 23, (2-3), 89-114.

  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
  • Contribution to proceedings
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 169-170

Publ.-Id: 12496

Sorption of Np(V) onto metal oxide surfaces: An in situ ATR FT-IR spectroscopic study.

Müller, K.; Foerstendorf, H.; Brendler, V.; Bernhard, G.

Neptunium (Np) is one of the most important components of nuclear waste to consider for the long-term safety assessment of nuclear waste repositories and hence, great attention is paid to its geochemistry and migration behavior [1]. Among the various geochemical processes, the migration of actinides in the environment is strongly affected by molecular reactions at the solid-water interface, e.g. sorption onto mineral phases, surface precipitation, and colloid formation [2]. In aqueous solution the pentavalent form dominates the neptunium speciation under a wide range of environmental conditions [1]. Thus, reliable results of Np(V) sorption data and its molecular speciation at the water-mineral interface are crucial to allow an improved modeling of Np migration in the environment. Vibrational spectroscopy is a useful tool for the in situ identification of molecular species in aqueous solution and sorbed onto mineral surfaces [3, 4]. Using attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, the type of the sorbed species, e.g. inner- and outer-sphere complex, can be elucidated by shifts of the antisymmetric stretching vibration ν3 of the Np=O bond compared to the aqueous species.

In this study, we investigated the Np(V) speciation in aqueous solution and upon sorption onto oxides of titanium, silicon, and zinc at a micromolar concentration level by application of NIR and ATR FT-IR spectroscopy.

The obtained spectra of aqueous 50 µM Np(V) solution confirmed the predominance of the fully hydrated neptunyl(V) species NpO2+ up to pH 7.7 at inert gas atmosphere, excluding atmospheric CO2, as was predicted by the updated NEA thermodynamic database [5]. Upon sorption of 50 µM Np(V) on TiO2 at pH 7.6 at inert gas atmosphere, NpO2+ forms stable surface species. The formation of an inner-sphere complex can be derived from the significant shift of the band representing the antisymmetric stretching vibration ν3 of the NpO2+ ion. Furthermore, since the spectra of the sorption processes show no significant deviations within the pH range from 4 to 7.6, and no indications of aqueous NpO2+ species are obtained, the formation of outer-sphere complexes can be neglected. Additionally, from the on-line monitored measurements it is obvious that only one Np(V) surface species is formed during the sorption experiments.

A comparative in situ ATR FT-IR investigation of Np(V) sorption onto TiO2, SiO2 and ZnO indicates the formation of structurally similar inner-sphere surface complexation. From minor spectral deviations of the ν3 band representing the Np(V) surface species bidentate complexes can be suggested.

For future spectroscopic investigations of neptunyl sorption at the water-mineral interface the present work may provide vibrational reference data for the interpretation of more complex systems relevant for environment.

1.Kaszuba, J. P.; Runde, W. H., Environmental Science & Technology 1999, 33, (24), 4427-4433.
2.O'Day, P. A., Reviews of Geophysics 1999, 37, (2), 249-274.
3.Lefevre, G., Advances in Colloid and Interface Science 2004, 107, (2-3), 109-123.
4.Müller, K.; Brendler, V.; Foerstendorf, H., Inorganic Chemistry 2008, 47, (21), 10127-10134.
5.Guillaumont, R.; Fanghänel, T.; Fuger, J.; Grenthe, I.; Neck, V.; Palmer, D. A.; Rand, M. H., Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc. Elsevier: Amsterdam, 2003.

  • Contribution to proceedings
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 170-171
  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12495

Time resolved fluorescence spectroscopy of Eu(III) complexes with benzoic acid derivatives at different temperatures

Barkleit, A.; Acker, M.; Taut, S.; Bernhard, G.

Humic acids have a great influence on the migration of actinides and heavy metals. To get a quantitative understanding of the humic acid / actinide interaction on a molecular level, we investigate the complexation behavior of trivalent lanthanides and actinides with different functionalized benzoic acids as model compounds for humic acids. Our primary objective is to determine the temperature dependence of the complexation behavior, because in radioactive waste repositories one can observe elevated temperatures and concerning this matter only few investigations are known.

In this study, we present the reaction of Eu(III) with 2-hydroxybenzoate (salicylate), 2,5-dihydroxybenzoate and 1,2,4,5-benzenetetracarboxylate (pyromellitate), investigated with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at different temperatures (10-50°C).

The Eu pyromellitate complex system shows strong luminescence behavior. The intensity of the 5D0 7F2 transition band increases with increasing ligand concentration. With increasing temperature, the total emission intensity decreases slightly. At lower pH (around 3) a MHL complex species with a stability constant of logK = 3.92 (25°C) could be determined. The lifetime of about 125 µs indicates, according to the equation of Kimura et al. (n(H2O) = 1.07 x (1/t -0.62) [1]), the exclusion of 1 water molecule from the first shell, implying an inner sphere complex with monodentate coordination. At pH around 5, a ML complex species (logK = 4.74, 25°C) was identified. The lifetime of about 135 µs stands for the substitution of 2 water molecules, according to an inner sphere complex with bidentate coordination. The lifetimes remain constant over the determined temperature range, as well as the lifetime of the free Eu3+(aq) ion. With increasing temperature, the stability constants increase, indicating an endothermic complexation reaction. The thermodynamic parameters of the Eu pyromellitate complexes were calculated to be ΔH = 9.4 kJ mol-1, ΔG = 22.3 kJ mol-1, ΔS = 106 J mol-1 K-1 (MHL; 25 °C) and ΔH = 15.2 kJ mol-1, ΔG = 28.1 kJ mol-1, ΔS = 145 J mol-1 K-1 (ML; 25 °C); these values are in good agreement with the literature [2]. The Eu complexes with salicylate and 2,5-dihydroxybenzoate show no luminescence behavior; only static and dynamic quenching is observable. For both ligands, the complex stability constants for a 1 : 1 complex species each could be determined. With increasing temperature, the stability constant also increases in both cases, indicating again an endothermic complexation reaction. The stability constants and thermodynamic parameters of these complexes are reported and compared with those determined by UV-vis spectroscopy with a liquid waveguide capillary cell (LWCC).

[1] T. Kimura, G.R. Choppin, Y. Kato, Z. Yoshida, Radiochim. Acta 72 (1996) 61-64.
[2] G.R. Choppin, E.N. Rizkalla, T.A. El-Ansi, A. Dadgar, J. Coord. Chem. 31 (1994) 297-304.

  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12494

Interaction of uranium(VI) and europium(III) with alpha-amylase

Barkleit, A.; Jähnigen, P.; Hennig, C.; Rossberg, A.

The calcium-binding protein α-amylase (α-1,4 glucan-4-glucanhydrolase) catalyzes the degradation of starch and glycogen. It is widely distributed in plants, animals, and microorganisms. In saliva and pancreas it is a main enzyme which is built in high amounts. Incorporated heavy metals like actinides firstly come into contact with saliva. In order to explore the origin of the well known toxic effect of these metals we investigate the interaction between UO22+ and Eu3+ (as an inactive analogue for threefold actinides) with the main constituents of saliva like α-amylase.

The influence of UO22+ and Eu3+ on the enzyme activity was tested with the α-amylase assay method by Bernfeld [1]. Both metal ions have a strong inhibition effect even at very low metal to α-amylase ratios. Sorption experiments showed a high binding capacity of α-amylase and that in the sorption maximum (pH 6-7) the protein can bind up to a tenfold molar excess of the metal ions. Both metal ions displace the Ca2+ ion, which is the central metal ion in the protein, even at equimolar amounts. UO22+ and Eu3+ seem to occupy first the Ca2+ binding place and then other potential metal binding sites in the protein. The binding process occurs in a short time, so that after 5 minutes the main metal amount is accumulated by α-amylase.

The UO22+ and Eu3+ α-amylase complexes were investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS) and extended x-ray absorption fine structure (EXAFS) spectroscopy. In case of UO22+ and TRLFS, we observed in the pH range 3-7 a red shift of the peak maxima and two different luminescence lifetimes, indicating the formation of two different UO22+ protein complex types. With EXAFS spectroscopy two different binding types were identified. At equimolar metal to ligand ratio we identified a fourfold coordination of UO22+ with only monodentate binding carbonyl groups. With excess of UO22+ the binding properties changes and higher coordination numbers are observed with indication of monodentate and bidentate binding carbonyl and carboxylate groups. For the Eu3+ α-amylase complex, the luminescence lifetimes show that 2 or 3 water molecules remain in the first coordination sphere. EXAFS measurements points at the presence of monodentate and bidentate coordinated carbonyl or carboxylate groups.

[1] P. Bernfeld, Methods in Enzymology 1(1955) S. 149-158

  • Poster
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12493

EXAFS study of the structural phase transition in the americium zirconate pyrochlore

Martin, P. M.; Belin, R. C.; Valenza, P. J.; Scheinost, A. C.

The 241Am2Zr2O7 phase undergoes a structural transition from pyrochlore to defect fluorite driven by alpha self-irradiation. In an effort to better understand the underlying phenomena of this order-disorder transition, powder X-ray diffraction (PXRD) and X-ray absorption fine-structure (XAFS) spectroscopy experiments were conducted on two samples aged for 40 days (0.02 dpa) and 370 days (0.21 dpa), respectively. While the XAFS data support the phase transition observed by XRD, they reveal different local coordinations of americium and zirconium. The transition occurs through oxygen Frenkel and cation antisite formation. The XAFS, clearly showed that the ZrO polyhedron is stable against irradiation, probably a main factor explaining the excellent resistance to amorphization observed for americium zirconia defect fluorite structures.

Keywords: Rietveld; XRD; EXAFS; americium; zirconia; transmutation; nuclear waste

  • Journal of Nuclear Materials 385(2009), 126-130

Publ.-Id: 12492

Implementation of a pressure drop model for the CFD simulation of clogged containment sump strainers

Grahn, A.; Krepper, E.; Weiß, F.-P.; Alt, S.; Kästner, W.; Kratzsch, A.; Hampel, R.

The present study aims at modelling the pressure drop of flows across growing cakes of compressible, fibrous materials which may form on the upstream side of containment sump strainers after a loss-of-coolant accident (LOCA). The model developed is based on the coupled solution of a differential equation for the change of the pressure drop in terms of superficial liquid velocity and local porosity of the fibre cake and a material equation that accounts for the compaction pressure dependent cake porosity. Details of its implementation into a general-purpose three-dimensional computational fluid dynamics code (CFD) are given. An extension to this basic model is presented, which simulates the time dependent clogging of the fibre cake due to capturing of suspended particles as they pass trough the cake. The extended model relies on empirical relations which model the change of pressure drop and removal efficiency in terms of particle deposit in the fibre cake.

Keywords: CFD; pressure drop; strainer clogging; LOCA; containment sump

  • Contribution to proceedings
    17th International Conference On Nuclear Engineering ICONE 17, 12.-16.07.2009, Brussels, Belgium
    Implementation of a pressure drop model for the CFD simulation of clogged containment sump strainers
  • Lecture (Conference)
    17th International Conference On Nuclear Engineering ICONE 17, 12.-16.07.2009, Brussels, Belgium
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 132(2010), 082902
    DOI: 10.1115/1.4000365
    Cited 7 times in Scopus


Publ.-Id: 12491

P0713 - Anordnung zur Röntgen-Computertomographie mit elektromagnetisch abgelenktem Elektronenstrahl

Bieberle, M.; Hampel, U.; Schleicher, E.

Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur Röntgen-Computertomographie anzugeben, die ohne einen axialen Versatz zwischen Brennfleckbahn und Röntgendetektorbogen auskommt und dennoch einen im Sinne der tomographischen Bildrekonstruktion vollständigen Projektionsdatensatz liefert. Gelöst wurde die Aufgabe durch die Kombination zweier Target-Detektor-Einheiten, die mit einem geringen axialen Versatz in zwei Ebenen angeordnet sind.
Der hauptsächliche Vorteil der beschriebenen Anordnung zur Röntgen-Computertomographie mit zwei Tomographieebenen besteht darin, dass Target- und Röntgendetektorbogen jeder Einheit vollständig innerhalb einer axialen Ebene angeordnet werden können und durch die Kombination beider Datensätze eine vollständige tomographische Datenaufnahme von einer axialen Ebene des Untersuchungsobjektes möglich ist. Damit wird eine höchstmögliche Bildqualität und axiale Ortsauflösung erreicht. Die Anordnung kann insbesondere für Elektronenstrahltomographen oder andere Computertomographie-Scanner mit feststehendem Quell-Detektorverbund angewendet werden. Besonders vorteilhaft ist sie für sich axial bewegende Objekte, zum Beispiel Rohrströmungen, da dort die Bewegung zwischen den Ebenen dem Untersuchungsobjekt inhärent ist und somit ohne zusätzlichen Aufwand sehr schnelle Prozesse mit hoher lateraler und axialer Ortsauflösung sowie hoher zeitlicher Auflösung abgebildet werden können.

  • Patent
    DE 10 2007 040 778 A1 - 2009.03.05

Publ.-Id: 12490

The Potential of In-beam Positron Emission Tomography within Image-Guided Radiation Therapy

Kunath, D.

Presentation about in-beam PET in the context of IGRT

  • Lecture (Conference)
    4th International Conference on Translational Research and Pre-Clinical Strategies in Radiation Oncology, 11.-13.03.2009, Genf, Schweiz

Publ.-Id: 12489

Xenobiotics tolerant bacteria in soils near a Pb-Zn smelter in Bulgaria as estimated via the 16S rRNA gene approach

Satchanska, G.; Golovinski, E.; Selenska-Pobell, S.

Microbial diversity in xenobiotics polluted soils was investigated by the 16S rRNA gene approach. The samples studied were collected from the vicinity of a Pb-Zn (KCM) smelter and pesticides manufacturing plant situated in South Bulgaria. ICP-MS analyses showed that some metals such as Zn, Pb, Cu, Cd, As, Ni and Hg exceeded in high extent the maximum permission standard. Two 16S rRNA gene clone banks were constructed – KCM-B and KCM-C. The main part of the studied microbial communities consisted of members of Proteobacteria (and ) - 42 % for KCM-B and 72 % for the KCM-C sample. In both soils Proteobacteria were registered in equal content of 28 %. Acidobacteria, Holophaga, Cytophaga/Flavo-bacterium/Bacteroides, AD1 and other novel divisions were represented as well.
Most of the identified bacterial groups were closely related to bacteria inhabiting other extreme environments such as uranium mill-tailings, sulphide mines, mine drainages and dumps, metal-rich sediments, soils contaminated with polychlorinated hydrocarbons, deserts, and Antarctic permafrost. Some of the closest relatives of several identified groups were xenobiotics-degrading bacteria inhabiting a hexane-degrading biofilm, 1,2-dichloropropan transforming bacteria and phosphorous eliminating bacteria.

  • Contribution to proceedings
    Ecology Seminar of the "Ecological Engineering and Environmental protection", 23.-24.04.2009, Sofia, Bulgaria

Publ.-Id: 12488

Deposition of functional coatings on polyethylene terephthalate films by magnetronplasma-enhanced chemical vapour deposition

Fahland, M.; Vogt, T.; Meyer, B.; Fahlteich, J.; Schiller, N.; Vinnichenko, M.; Munnik, F.

Magnetron-plasma enhanced chemical vapour deposition (PECVD) is a process tool which allows the deposition of plasma polymer coatings at process pressures below 1 Pa. The striking features of this technology are the relatively easy realisation of large area deposition as well as the possibility of the combination with sputtering processes for multilayer coating designs. SiOxCy coatings were deposited on polymer film in a roll-to-roll deposition machine. Dynamic deposition rates as high as 120 nm*m/min were achieved. The process was set up with both the monomer hexamethyldisiloxane and the monomer tetraethylorthosilicate (TEOS) and with mixtures thereof. The coatings were analysed by Fourier transform infrared spectroscopy. This method identifies the existence of different types of Si–O bonding in the layer. The results show how the layer properties are linked to the plasma parameters of the deposition process. The properties were compared to sputtered SiO2 and to layers obtained by other PECVD processes. Elastic recoil detection analysis (ERDA) was used in order to determine the composition of the samples. Both IR spectroscopy and ERDA revealed that the usage of TEOS provided more SiO2-like layers. The process was applied to the deposition of optical multilayer coating in a roll-to-roll coating system.

Keywords: Sputtering; Web coating; Plasma-enhanced chemical vapour deposition; Magnetron

Publ.-Id: 12487

Study of photo-proton reactions driven by bremsstrahlung radiation of high-intensity laser generated electrons

Spohr, K. M.; Shaw, M.; Galster, W.; Ledingham, K. W. D.; Robson, L.; Yang, J. M.; Mc Kenna, P.; Mc Canny, T.; Melone, J.; Amthor, K.-U.; Ewald, F.; Liesfeld, B.; Schwoerer, H.; Sauerbrey, R.

Photo-nuclear reactions were investigated using a high power table-top laser. The laser system at the University of Jena (I ~ 3-5×1019 W cm-2) produced hard bremsstrahlung photons (kT~2.9 MeV) via a laser-gas interaction which served to induce (γ, p) and (γ, n) reactions in Mg, Ti, Zn and Mo isotopes. Several (γ, p) decay channels were identified using nuclear activation analysis to determine their integral reaction yields. As the laser-generated bremsstrahlung spectra stretches over the energy regime dominated by the giant dipole resonance (GDR), these yield measurements were used in conjunction with theoretical estimates of the resonance energies Eres and their widths Γres to derive the integral reaction cross-section σint(γ,p) for 25Mn, 48, 49Ti, 68Zn and 97, 98Mo isotopes for the first time. This study enabled the determination of the previously unknown cross-section ratios for these isotopes. The experiments were supported by extensive model calculations (Empire) and the results were compared to the Thomas-Reiche-Kuhn (TRK) dipole sum rule as well as to the experimental data in neighboring isotopes and good agreement was observed. The Coulomb barrier and the neutron excess strongly influence the ratios for increasing target proton and neutron numbers.

Publ.-Id: 12486

Electric events synchronized with laser filaments in thunderclouds

Kasparian, J.; Ackermann, R.; André, Y.; Méchain, G.; Méjean, G.; Prade, B.; Rohwetter, P.; Salmon, E.; Stelmaszczyk, K.; Yu, J.; Mysyrowicz, A.; Sauerbrey, R.; Woeste, L.; Wolf, J.

We investigated the possibility to trigger real-scale lightning using ionized filaments generated by ultrashort laser pulses in the atmosphere. Under conditions of high electric field during two thunderstorms, we observed a statistically significant number of electric events synchronized with the laser pulses, at the location of the filaments. This observation suggests that corona discharges may have been triggered by filaments.

  • Optics Express 16(2008)8, 5757-5763
    ISSN: 1094-4087

Publ.-Id: 12485

Void measurement using high-resolution gamma-ray computed tomography

Bieberle, A.; Hoppe, D.; Schleicher, E.; Hampel, U.

We present a high-resolution gamma-ray computed tomography (CT) system for the measurement of cross-sectional time-averaged void distributions in thermo hydraulic facilities. The system has been carefully designed for harsh operating conditions, such as varying temperature fields and strong magnetic fields, typically produced by thermal hydraulic test loops with direct electric bundle heating. Measurements are non invasive, thus the two-phase flow in the test section is not influenced. The gamma-ray CT system consists of a collimated 137Cs isotopic source, a gamma radiation detector arc including 320 single elements, a pulse processing unit and a thermal stabilisation unit. The spatial resolution of the CT system is about 2 mm in plane. Recently, the thermal design of the detector arc is improved to secure maintenance of constant temperature of thermally sensitive components under changing environmental conditions. This turned out to be a key issue for achieving accurate quantitative measurements. First results of laboratory measurements on a bundle mock-up with this improved system are presented.

Keywords: Gamma-ray computed tomography

Publ.-Id: 12484

Ultra-fast evolution via PT-symmetry and entanglement: extending the BBJM brachistochrone

Günther, U.; Samsonov, B.

The basics of quantum mechanical brachistochrones are briefly sketched for Hermitian systems as well as for PT-symmetric systems --- as the latter have been recently proposed by Bender, Brody, Jones and Meister (BBJM) in [C. M. Bender et al, Phys. Rev. Lett. 98, 040403 (2007)]. Using a mainly geometric approach, the hidden new features of this PT-symmetric brachsistochrone with its close relation to non-diagonalizable operator realizations with non-trivial Jordan block structures and spectral singularities (spectral exceptional points) are discussed. Furthermore the Naimark dilation technique as basic tool for an extension toward possible experimental implementations is explained. The remarkable links to wormhole-type setups and entangled states (Einstein's 'spooky action') are highlighted and sketched geometrically. The talk is mainly based on [Phys. Rev. Lett. 101, 230404 (2008)].

Keywords: quantum brachistochrone; quantum computing; PT quantum mechanics; strongly non-Hermitian regime; exceptional point; Anandan-Aharonov lower bound; ultra-fast evolution; POVM; Naimark dilation; Naimark extension; entangled state; two-qubit system; wormhole; Einstein's spooky action

  • Invited lecture (Conferences)
    Quantum Mechanics in the Complex Domain (QMCD09), 27.-28.03.2009, St. Louis, USA

Publ.-Id: 12483

Be-10 and Cl-36 interlaboratory comparisons: Implications for terrestrial production rates?

Merchel, S.; Bremser, W.; Alfimov, V.; Arnold, M.; Aumaître, G.; Benedetti, L.; Bourlès, D. L.; Braucher, R.; Caffee, M.; Christl, M.; Fifield, L. K.; Finkel, R. C.; Freeman, S. P. H. T.; Ruiz-Gómez, A.; Kubik, P. W.; Rood, D. H.; Sasa, K.; Steier, P.; Tims, S. G.; Wallner, A.; Wilcken, K. M.; Xu, S.

Driven by the progress in accelerator mass spectrometry (AMS) and its spreading application within geosciences, the number of samples with low isotopic ratios will increase. Therefore, we have examined the linearity of 10Be/9Be as a function of isotope ratio by distributing three secondary standards (dilutions of NIST4325: 10-12-10-14) to nine AMS labs. The problem of low ratio samples is even more crucial for 36Cl. Thus, we have prepared large quantities of three 36Cl/Cl solutions from a certified 36Cl activity (NIST4943) by dilution with NaCl. AgCl precipitated from these solutions (10-11-10-13) has been distributed to nine AMS labs. We are still awaiting some final results, but first results from eight labs for each nuclide show that these interlaboratory exercises are very valuable, as they show maximum differences between individual AMS labs up to 35% for 10Be, and 25% for 36Cl, respectively.
Our data indicate that actual 36Cl measurements at LLNL, PRIME Lab and ANU can differ by more than 10%. The implications of this for 36Cl in-situ production rates, determined earlier at these facilities, cannot be ignored. Some, although not all, of the current disagreement concerning 36Cl production rates may result from these discrepancies. However, we are assuming that our new data at the 10-12-10-13 level are still representative for earlier measurements of in-situ samples at that level.
This work was partially funded by CRONUS-EU (Marie-Curie Action, 6th FP #511927).

Keywords: accelerator mass spectrometry

  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 73(2009)13, A871
    DOI: 10.1016/j.gca.2009.05.011
    ISSN: 0016-7037
  • Poster
    19th V.M. Goldschmidt™ conference, 21.-26.06.2009, Davos, Schweiz

Publ.-Id: 12482

X-ray Spectromicroscopy of Carbon Nanotubes

Sedlmair, J.; Gleber, S.-C.; Zänker, H.; Thieme, J.

The analysis of pristine and functionalized carbon nanotubes by X-ray spectromicroscopy was demonstrated. It was shown that both the generation of COOH groups due to functionalization and the reaction of these groups with hexavalent uranium (surface complexation) influenses the NEXAFS spectra. The method may become a promising tool for "mapping" chemical properties such as the presence or absence of chemical elements or the type of binding between these elements on the surface of carbon nanotubes.

Keywords: Carbon nanotubes; X-ray spectromicroscopy; carboxylic groups; uranium; sorption

  • Poster
    Wasser 2009 - Jahrestagung der Wasserchemischen Gesellschaft, 18.-20.05.2009, Stralsund, Deutschland
  • Contribution to proceedings
    Wasser 2009 - Jahrestagung der Wasserchemischen Gesellschaft, 18.-20.05.2009, Stralsund, Deutschland
    Wasser2009, ISBN 978-3-936028-56-0, 345-346

Publ.-Id: 12481

Influence of specimen type, crack length and evaluation method on quasi-static and dynamic fracture toughness properties

Zurbuchen, C.

For up-to-date safety analyses and lifetime assessments of nuclear power plants (NPPs) fracture mechanical based methods are indispensable. When two Swiss NPPs were planned in the 1970s, no standards existed concerning the geometry or testing of pre-cracked Charpy-V-size surveillance specimens. Therefore, the guideline HSK-AN-425 was drafted for fracture toughness evaluation by dynamic testing. Before becoming a Swiss standard it is to be thoroughly checked for potential pitfalls. Furthermore, it has to be verified that surveillance specimens of those NPPs with shorter cracks than recommended in present standards are eligible for fracture mechanics assessment.

Experiments were performed on unirradiated commercial NPP steel 22NiMoCr3-7.
Quasi-static Master Curve (MC) reference temperature T0 were evaluated according to ASTM E1921 on Charpy-size (width B=0.4T, 1T=1 inch=25.4mm) single edge bend (SE(B)) specimens with crack lengths of 3 mm and 5 mm as well as 1T-C(T) specimens. Furthermore, transferability of surveillance specimen results to heavy-walled structures was checked with SE(B) specimens of B=0.4T, 0.8T, 1.6T and 3.2T. Dynamic MC results were retrieved from instrumented impact tests performed at 1.2 to 2.4 m/s in which T0 was calculated according to HSK-AN-425 and also by a modified ASTM 1921 method. Quasi-static J resistance curves were obtained according to standards ASTM E1820, ISO12135 and ESIS-P2.

In quasi-static MC tests it could be demonstrated that SE(B) specimens with 3 mm and 5 mm fatigue cracks yield the same T0 of ca. -80°C. Thus, surveillance 0.4T-SE(B) specimens with 3 mm crack length may be used for safety assessment without further modifications. The transferability of small-scale results to structural behaviour was proven. T0 obtained from 1T-C(T) specimens is 15K above T0 from 0.4T-SE(B) specimens.

The dynamic MC T0 (v=2.4m/s) is nearly equal for 0.4T-SE(B) specimens of both crack lengths but is ca. 80K above the quasi-static T0.

Small surveillance specimens do not yield valid quasi-static J resistance curve crack initiation values as requirements based on size unnecessarily invalidate all of the results. The idea of using a size criterion to limit J values should be re-evaluated. Ductile crack initiation values are highly dependent on the evaluation standard used. Ordered from highest to lowest, JIc(E1820) > J0.2BL(ISO 12135) > J0.2(ESIS-P2) > Ji(stretch zone width, ISO 12135). Ji is said to be a physically sound crack initiation value but numerous problems arise in stretch zone width determination. It is often not traceable throughout the whole crack front, affected by subjectivity and intricate for irradiated material.

Keywords: fracture mechanics; Master Curve; JR curve; constraint; E1921; E1820; ISO12135; HSK-AN-425

  • Lecture (Conference)
    2009 ASME Pressure Vessels and Piping Division Conference, 26.-30.07.2009, Prag, Czech Republic
  • Contribution to proceedings
    2009 ASME Pressure Vessels and Piping Division Conference, 26.-30.07.2009, Prag, Czech Republic
    2009 Proceedings of the ASME Pressure Vessels and Piping, West Conshohocken: ASME, 9780791838549

Publ.-Id: 12480

Infrared solid state spectroscopy using a free-electron laser

Helm, M.

I will introduce the free electron laser at the Forschungszentrum Dresden-Rossendorf, which covers a wavelength range between 3 and 200 micrometers with picosecond pulses. Then I will discuss a few experiments which focus on temporal and spatial resolution, respectively. The former refers to pump-probe experiments on semiconductor quantum structures and the latter to near-field spectro-microscopy on ferroelectrics.

Keywords: free electron alser; semiconductor quantum structures; pump-probe; near-field; infrared

  • Lecture (others)
    Seminarvortrag bei ANKA, 02.03.2009, Karlsruhe, Deutschland

Publ.-Id: 12479

Enhanced blue-violet emission by inverse energy transfer to the Ge-related oxygen deficiency centers via Er3+ ions in metal-oxide semiconductor structures

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

It is generally believed that the 1.5 um Er luminescence is enhanced by transferring energy from Si nanocrystals to the nearest Er3+ ions in Er-doped Si-rich SiO2 layers during optical pumping. Here, the influence of Ge nanocrystals instead of excess Si in the same environment is studied using electroluminescence technique on metal-oxide-semiconductor structures. An increase of the 400 nm electroluminescence intensity with a concomitant reduction of the Er-related emission is observed. This is explained in the light of an inverse energy transfer process from Er3+ to the Ge-related oxygen-deficiency centers.

Keywords: EL; Er; Ge; Nanocrystals; MOS

Publ.-Id: 12478

Buckling Stabilization and Stress Reduction in SiC on Si by i-FLASiC Processing

Andreadou, A.; Pezoldt, J.; Förster, C.; Polychroniadis, E. K.; Voelskow, M.; Skorupa, W.

One of the main challenging tasks in the prospective technology is the buckling suppression of the 3C-SiC film due to the melting and solidification process and the stress relief as a consequence of the short time Si melting during the Flash Lamp Annealing. To overcome this effect and to stabilize a flat surface morphology an alternative i-FlASiC process was developed. This work refers to the influence of the layer stack modifications by doping and meltstop formation by ion implantation on the wafer buckling. The samples were studied by transmission electron microscopy, high resolution x-ray diffraction and infrared ellipsometry. The aim was to optimize the doping and flash lamp annealing conditions in relation to the i-FLASiC layer stack modification.

Keywords: Characterization; 3C-SiC; Flash Lamp Annealing; Buckling

  • Materials Science Forum 600-603(2009), 239-242

Publ.-Id: 12477

Redox stability of neptunium(V) and neptunium(IV) in the presence of humic substances of varying functionality

Schmeide, K.; Bernhard, G.

The reducing properties of humic substances (humic acid (HA) and fulvic acid (FA)) of varying functionality towards Np(V) have been studied under anaerobic conditions between pH 3.5 and pH 9.0 in batch experiments. For Np redox speciation in solution solvent extraction, NIR absorption spectroscopy and ultrafiltration were applied. The reduction rate varied with type of humic substances, solution pH, HA to Np concentration ratio, and equilibration time. In comparison to natural humic substances, synthetic HA with designed redox properties lead to a stronger reduction of Np(V) to Np(IV). The reducing capacities of humic substances towards Np(V) could be correlated to their phenolic/acidic OH group content, which includes both hydroquinone-like moieties and non-quinonoid phenols. By applying a synthetic HA with blocked phenolic/acidic OH groups, the dominance of phenolic/acidic OH groups as the redox-active moieties of humic substances was verified.
The Np(IV) formed in the course of the experiments is predominantly humic colloid-bound. Np(IV) oxo/hydroxide colloids, that might be formed in addition, are stabilized by adsorbed humic substances. The remaining Np(V) occurs as NpO2 + ion or Np(V) humate depending on pH. The ability of synthetic HA to effectively maintain Np in the tetravalent state during complexation experiments could be shown.

Keywords: Neptunium; Tetravalent; Humic acid; Reduction; Reducing capacity; Redox speciation; Redox process; Np(V); Np(IV)

Publ.-Id: 12476

SANS investigation of a neutron-irradiated Fe-9at%Cr alloy

Ulbricht, A.; Heintze, C.; Bergner, F.; Eckerlebe, H.

Available experimental results indicate that the addition of Cr to Fe and steels significantly influences the response of Fe-Cr alloys and ferritic/martensitic high-Cr steels to neutron irradiation. A level of 9 at% Cr is of particular interest because this composition is close to the boundary of the Fe-Cr miscibility gap. Furthermore, it corresponds to the composition of several candidate steels for application in nuclear technology. However, experimental evidence has been incomplete so far. The reported study by means of small-angle neutron scattering is devoted to the effect of neutron irradiation at 300°C up to fluences of 0.6 and 1.5 dpa on the microstructure of an Fe-9at%Cr alloy. We have observed a pronounced irradiation-induced increase of scattering cross-sections for both magnetic and nuclear scattering. Bimodal size distributions of irradiation-induced defect-solute clusters have been reconstructed. The restrictions on the composition of these clusters have been discussed in terms of the scattering contrast. We have found that vacancy clusters and alpha’-particles alone cannot explain the full set of experimental findings. The remaining inconsistency can be solved by taking into account a contribution of impurity carbon.

Keywords: SANS; Fe-Cr alloy; irradiation-induced defect-solute cluster

Publ.-Id: 12475

SANS investigation of irradiation-induced phase separation in a binary Fe-Cr alloy

Ulbricht, A.; Bergner, F.; Heintze, C.

Ferritic-martensitic chromium steels are candidate materials for future applications in both Gen-IV fi ssion and fusion technology. Investigations of binary Fe-Cr alloys will contribute to the understanding of the behaviour of more complex alloys. The presented SANS results are focused on a Fe-9at%Cr alloy neutron-irradiated up to neutron doses of 0.6 and 1.5 dpa. We have observed a pronounced increase of scattering cross-sections for both magnetic and nuclear scattering. The A-ratio is about 2.8 for both irradiation conditions. This value is far from a value of 1.45 corresponding to nanovoids as scattering objects. This indicates that the irradiation-induced clusters are different from pure nanovoids and must contain Cr-atoms with the same or very similar average composition for both irradiation conditions. The composition of the clusters will be discussed in more detail. The size distributions of irradiation-induced defects have been calculated. The volume fraction of clusters increases slightly with neutron dose.

Keywords: SANS; Fe-Cr alloy; irradiation-induced defect-solute cluster

  • Poster
    TMS 2009, Symposium Material Characterization: Microstructural Processes in Irradiated Materials, 15.-19.02.2009, San Francisco, USA

Publ.-Id: 12474

QCD sum rules for D and B mesons in nuclear matter

Hilger, T.; Thomas, R.; Kämpfer, B.

QCD sum rules for D and B mesons embedded in cold nuclear matter are evaluated. We quantify the mass splitting of D - D-bar and B - B-bar mesons as a function of the nuclear matter density; extrapolated to saturation density it is in the order of 60 and 130 MeV driven essentially by the condensates , and . The genuine chiral condensate , amplified by heavy-quark masses, enters the Borel transformed sum rules for the mass splitting beyond linear density dependence. Including strange quark condensates reveals a umerically smaller and opposite effect for the Ds - Ds-bar mass splitting.

  • Physical Review C 79(2009), 025202
  • Lecture (Conference)
    XLVII International Winter Meeting on Nuclear Physics, 26.-30.01.2009, Bormio, Italien
  • Lecture (Conference)
    40. Arbeitstreffen Kernphysik in Schleching, 02.-06.03.2009, Schleching, Deutschland
  • Lecture (Conference)
    DPG Spring Meeting 2009 (Hadronic and Nuclear Physics) in conjunction with the European Nuclear Physics Conference (EuNPC) (Nuclear Physics Board of the European Physical Society (EPS)), 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12468

Bioaktive Oberflächen

Raff, J.

Bioaktive Oberflächen lassen sich auf ganz unterschiedliche Art und Weise herstellen. Am Institut für Radiochemie werden insbesondere S-Layer-Proteine verschiedener Naturisolate zur Beschichtung und Funktionalisierung verschiedenere Trägermaterialien genutzt. Durch die Verwendung dieser monolagigen Proteinschicht können nicht nur vielfältige Biomoleküle sehr regelmäßig, in großer Dichte und mit unterschiedlichen Funktionen auf den Trägern immobilisiert werden, sondern auch mit anorganischen Nanopartikeln, z. B. mit (foto)katalytischen Eigenschaften, kombiniert werden. Auf diese Weise können neuartige intelligente Materialien für technische Anwendungen entwickelt werden. Beispielhaft werden diesbezüglich Arbeiten zur Entwicklung von Filtermaterialien, (Foto)kalysatoren und Sensoren vorgestellt.

  • Lecture (others)
    Vortrag bei GMBU e.V., Arbeitsgruppe "Funktionelle Schichten", 04.03.2009, Dresden, Deutschland

Publ.-Id: 12456

Methodik, Zielstellung und Möglichkeiten der PET/CT bei kongenitalem Hyperinsulinismus

Blankenstein, O.; Mohnike, K.; Barthlen, W.; Füchtner, F.

kein Abstract verfügbar

  • Lecture (Conference)
    6. Berliner PET/CT Symposium, 07.05.2008, Berlin, Deutschland

Publ.-Id: 12455

Micro-elemental Analysis of some Transylvanian Meteorites and Lunar Samples

Vasilescu, A.; Constantinescu, B.; Bugoi, R.; Ceccato, D.; Grambole, D.; Herrmann, F.

Micro-PIXE investigations on some Transylvanian chondritic meteorite fragments and on small Moon soil pieces from the LUNA-16 mission were performed at the Legnaro and Rossendorf proton microprobes. The most exciting finding of the study was the presence of Pt grains in the Moci meteorite. The results are compared to previously published data.

Keywords: micro-PIXE; elemental analysis; meteorites; lunar soil

  • Lecture (Conference)
    ICNMTA2008 - 11th International Conference on Nuclear Microprobe Technology and Applications, 20.-25.07.2008, Debrecen, Hungary
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 2233-2235
    DOI: 10.1016/j.nimb.2009.03.017
    Cited 2 times in Scopus

Publ.-Id: 12454

Ergebnisse der multzentrischen Gruppe im internationalen Vergleich

Mohnike, K.; Blankenstein, O.; Barthlen, W.; Füchtner, F.

kein Abstract verfügbar

  • Lecture (Conference)
    6. Berliner PET/CT Symposium, 07.05.2008, Berlin, Deutschland

Publ.-Id: 12453

The First Octahedral Cluster Complexes With Terminal Formate Ligands: Synthesis, Structure, and Properties of K4[Re6S8(HCOO)6] and Cs4[Re6S8(HCOO)6]

Brylev, K. A.; Mironov, Y. V.; Kozlova, S. G.; Fedorov, V. E.; Kim, S.-J.; Pietzsch, H.-J.; Stephan, H.; Ito, A.; Ishizaka, S.; Kitamura, N.

The hexarhenium anionic cluster complex with terminal formate ligands [Re6S8(HCOO)6]4- was obtained by the room-temperature reaction between [Re6S8(OH)6]4- and formic acid in an aqueous solution. The cluster was crystallized as a potassium or cesium salt and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1H NMR, UV/vis, and luminescence spectroscopies. In particular, the emission quantum yield of the potassium salt of the Re6 cluster anion in the solid phase was determined for the first time. The electronic structures of [Re6S8(HCOO)6]4- and [Re6S8(OH)6]4- were also elucidated by DFT calculations.

Publ.-Id: 12452

Hexadentate Bispidine Derivatives as Versatile Bifunctional Chelate Agents for Copper(II) Radioisotopes

Juran, S.; Walther, M.; Stephan, H.; Bergmann, R.; Steinbach, J.; Kraus, W.; Emmerling, F.; Comba, P.

The preparation and use of bispidine derivatives (3,7-diazabicyclo[3.3.1]nonane) as chelate ligands for radioactive copper isotopes for diagnosis (64Cu) or therapy (67Cu) are reported. Starting from the hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand 1 with a keto and two ester substituents, the corresponding mono-ol 2 and two dicarboxylic acid derivatives 3 and 5 have been synthesized. A range of techniques, including single-crystal X-ray structure analysis, UV/vis spectroscopy, cyclic voltammetry, thin-layer- (TLC), and high-performance liquid chromatography (HPLC), have been used to characterize the structure and stability of the copper(II)-bispidine complexes. A rapid formation (within 1 min) of stable copper(II)-bispidine complexes under mild conditions (ambient temperature, aqueous solution) has been observed. Challenge experiments of these complexes in the presence of a high excess of competing ligands, such as glutathione, cyclam, or superoxide dismutase (SOD), as well as in rat plasma, gave no evidence of demetalation or transchelation. The bifunctional bispidine derivative 5 can be readily functionalized with biologically active molecules at the pendant carboxylate groups. The coupling of a bombesin analogue ßhomo-Glu-ßAla-ßAla-[Cha13,Nle14]BBN(7-14), by condensation of a carboxylate of the bispidine backbone with the N-terminus of the peptide produced the bifunctional ligand 6. The radiocopper(II) complex of this bombesin-bispidine conjugate has a considerable hydrophilicity (log Do/w < -2.4), and this leads to a very fast blood clearance (blood: 0.28 +/- 0.02 SUV, 1 h p.i.), low liver tissue accumulation (liver: 1.20 +/- 0.27 SUV, 1 h p.i.), and rapid renal-urinary excretion (kidneys: 6.06 +/- 2.96 SUV, 1 h p.i.) as shown by biodistribution studies of 64Cu-6 in Wistar rats. Preliminary in vivo studies of 64Cu-6 in NMRI nu/nu mice, bearing the human prostate tumor PC-3 showed an accumulation of the conjugate in the tumor (2.25 +/- 0.13 SUV, 12.5 min p.i.; 0.94 +/- 0.05 SUV, 55 min p.i.) and allowed a clear visualization of the gastrin-releasing peptide receptor distribution by positron emission tomography (PET).

Publ.-Id: 12451

Multiple condensed phases in attractively interacting Bose systems

Männel, M.; Morawetz, K.; Lipavsky, P.

We investigate a Bose gas with finite-range interaction using a scheme to eliminate unphysical repeated collisions in the T-matrix approximation. In this way the corrected T-matrix becomes suitable to calculate properties below the critical temperature. For attractive interaction, the Evans-Rashid transition occurs from the quasi-ideal Bose gas to the BCS-like phase with a gaped dispersion. The gap decreases with increasing density and vanishes at a critical density where the single-particle dispersion becomes linear for small momenta indicating Bose-Einstein condensation.

  • Open Access Logo New Journal of Physics 12(2010), 033013

Publ.-Id: 12450

Ion beam-induced hydrogen migration in a SiO2/a-Si:H/SiO2 layer stack

Pantchev, B.; Danesh, P.; Schmidt, B.; Grambole, D.; Möller, W.

The phenomenon of radiation-induced hydrogen migration has been studied in hydrogenated amorphous silicon (a-Si:H) using layer stacks of SiO2/a-Si:H/SiO2. The top and bottom SiO2 layers were deposited by magnetron sputtering at room temperature. The intermediate a-Si:H layers were deposited using plasma-enhanced chemical vapor deposition at three temperatures - room temperature, 150 ◦C and 270 ◦C. The samples were irradiated with MeV 15N+ ions during nuclear reaction analysis of hydrogen concentration. It has been established that the irradiation leads to hydrogen migration and redistribution, which depend on the a-Si:H deposition temperature. The symmetric hydrogen concentration profile in the as-prepared layer stack becomes asymmetric after the irradiation due to increase in the hydrogen concentration in the bottom SiO2 layer. Hydrogen concentration in the layer stacks decreases during the initial irradiation stage and then remains constant. In contrast, hydrogen loss from the a-Si:H layer proceeds gradually and continuously with increasing radiation fluence. It has been suggested that the hydrogen atoms liberated by the MeV ion irradiation do not recombine in molecules and that the hydrogen migration in a-Si:H is related to the diffusion of the hydrogen atoms. The radiation-induced asymmetry of the hydrogen profiles in the layer stack implies that there is a difference in the diffusion parameters at the inner and outer interface.

Keywords: hydrogenated amorphous silicon (a-Si:H); nuclear reaction analysis of hydrogen (NRA); radiation-induced hydrogen migration

Publ.-Id: 12449

Simulation studies for the positron source EPOS

Butterling, M.; Jungmann, M.; Krille, A.; Anwand, W.; Krause-Rehberg, R.

  • Poster
    XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India

Publ.-Id: 12448

Hydrogen-induced defects in Pd films

Melikhova, O.; Cizek, J.; Kuriplach, J.; Prochazka, I.; Cieslar, M.; Brauer, G.; Anwand, W.

  • Poster
    XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India

Publ.-Id: 12447

Quenched-in vacancies in Fe-Al alloys

Melikhova, O.; Cizek, J.; Kuriplach, J.; Prochazka, I.; Cieslar, M.; Brauer, G.; Anwand, W.

  • Poster
    XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India

Publ.-Id: 12446

Defects in nanostructured Yttria-stabilized zirconia studied by positron annihilation spectroscopy

Prochazka, I.; Cizek, J.; Melikhova, O.; Kuriplach, J.; Kuzel, R.; Brauer, G.; Anwand, W.; Konstantinova, T. E.; Danilenko, I. A.

  • Lecture (Conference)
    XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India

Publ.-Id: 12445

Positron Annihilation Spectroscopy in connection with activities towards p-type doping of ZnO

Brauer, G.

  • Lecture (Conference)
    Seminar an der University of Orissa (Institute of Physics), 16.01.2009, Bhubaneswar, India

Publ.-Id: 12443

Analytische HPLC synthetischer Sparteinabkömmlinge

Fähnemann, S.; Matterna, M.

kein Abstract verfügbar

  • Lecture (others)
    2. Workshop "Möglichkeiten und Grenzen der HPLC in den Lebenswissenschaften", 20.02.2009, Dresden-Rossendorf, Deutschland

Publ.-Id: 12442

From experiment to clinical application: particle therapy PET solution

Shakirin, G.

A knowledge transfer of particle therapy PET applications to industry is discussed

Keywords: PET; particle therpay

  • Invited lecture (Conferences)
    4th Meeting of the Scientific Advisory Board of OncoRay, 26.02.2009, Dresden, Germany

Publ.-Id: 12441

Spectroscopic identification of ternary carbonate complexes upon U(VI) sorption onto ferrihydrite

Foerstendorf, H.; Heim, K.

The sorption processes of uranium(VI) onto ferrihydrite (Fh) were investigated by in situ Attenuated Total Reflection Fourier-transform Infrared (ATR FT-IR) spectroscopy. This technique provides structural information of the molecular complexes occurring during the sorption processes of actinide ions on mineral phases in aqueous solution [1].
The influence of the presence of atmospheric carbon dioxide during the sorption processes of the actinide ions was studied by sorption experiments which were carried out under inert gas conditions and in an ambient atmosphere.
The spectra demonstrate that the uranyl ion recovers in a similar molecular environment irrespective to the prevailing atmospheric conditions. However, the carbonate ions sorbed to the mineral phase in ambient atmosphere undergo significant structural changes upon the sorption of the actinide ions. While carbonate binds monodentately to the pristine Fh-surface, it forms bidendate surface complexes upon the sorption of U(VI). Moreover, the formation of ternary inner-sphere complexes can be derived from spectra recorded during the sorption processes of atmospheric carbonate onto a Fh-film which was preloaded with U(VI) under inert gas conditions. With respect to the absorption frequency of the uranyl ion sorbed onto Fh under different conditions, we suggest the formation of [Fh•••UO2•••O2CO] complexes. Surface complexes with carbonate serving as a bridging ligand between Fh and UO22+ ions were not found in our experiments. These findings are in good agreement with recent EXAFS results [2].
Furthermore, we investigated the sorption processes at acidic (5.5) and at ambient (7.8) pH values. No significant differences were observed in the spectra. However, the sorption processes obviously occur with reduced velocity at higher pH values which might be due to the dominating aqueous U(VI) species at different pH values [3].

[1] Lefèvre (2004) Adv. Colloid Interface Sci. 107, 109-123. [2] Rossberg et al. (2009) Environ. Sci. Technol. (in press). [3] Müller et al. (2008) Inorg. Chem. 47, 10127-10134.

  • Poster
    Goldschmidt™2009 - "Challenges to Our Volatile Planet", 21.-26.06.2009, Davos, Switzerland
  • Geochimica et Cosmochimica Acta 73(2009)13, A386-A386
    ISSN: 0016-7037

Publ.-Id: 12440

Investigation of fuel assembly design options for high conversion thorium fuel cycle in PWRs

Fridman, E.; Shwageraus, E.; Volaski, D.

This study explores the basic possibility of achieving a self-sustainable Th-U233 fuel cycle that can be adopted in the current generation of Pressurized Water Reactors. This study outlines some fuel design strategies to achieve (or to approach as closely as possible) a sustainable fuel cycle. Major design tradeoffs in the core design are discussed. Preliminary neutronic analysis performed on the fuel assembly level with BOXER computer code suggests that net breeding of U233 is feasible in principle within a typical PWR operating envelope. However, some reduction in the core power density and/or shorter than typical fuel cycle length would most likely be required in order to achieve such performance.

Keywords: thorium fuel cycle; high conversion reactor

  • Contribution to proceedings
    Advances in Nuclear Fuel Management IV, 12.-15.04.2009, Hilton Head Island, South Carolina, USA

Publ.-Id: 12439

Growth Aspects of Iron-Filled Carbon Nanotubes Obtained by Catalytic Chemical Vapor Deposition of Ferrocene

Müller, C.; Leonhardt, A.; Kutz, M. C.; Büchner, B.; Reuther, H.

The thermal decomposition of ferrocene combined with an Fe-catalyst nanostructuring on an oxidized Si
substrate is investigated in the temperature range of 1015-1200 K. The optimal growth conditions for aligned
and homogeneous Fe-filled carbon nanotubes are found at 1100 K. From the nanostructures the corresponding
growth rates are determined, and the activation energy of carbon diffusion is calculated to be ∼0.4-0.5
eV/atom. Further, the Fe particle size on the substrate after pretreatment in different gas atmospheres is studied
and compared with the nanotube dimensions. With these data the diffusion coefficient of carbon in the catalyst
particle amounts to 0.5-1.5 × 10-9 m2/s. Such values prove the formation of liquid catalyst particles during
the nanotube growth. Mo¨ssbauer spectroscopy was utilized to analyze and quantify the different Fe phases.
In conclusion we propose a simple base-growth model from the experimental results.

  • Journal of Physical Chemistry C 113(2009)7, 2736-2740

Publ.-Id: 12438

Experimental Conditions in Underground Measurements

Bemmerer, D.

I will summarize technical aspects relevant to the measurement of extremely small cross sections at accelerator facilities deep underground, with a focus on the laboratory background observed in gamma-ray detectors.

Keywords: underground nuclear astrophysics

  • Invited lecture (Conferences)
    Nuclear Astrophysics Opportunities at the Underground Laboratory in Canfranc, 19.-20.02.2009, Barcelona, Spain

Publ.-Id: 12437

Study of high temperature and high density plasmoids in axially symmetrical magnetic fields

Anikeev, A. V.; Bagryansky, P. A.; Prikhodko, V. V.; Soldatkina, E. I.; Tsidulko, Y. A.; Kolesnikov, E. Y.; Lizunov, A. A.; Noack, K.; Konheiser, J.; Berger, T.

Within the framework of an Institutional Partnership of the Alexander von Humboldt Foundation, the Budker Institute of Nuclear Physics Novisibirsk (BINP) and Forschungszentrum Dresden-Rossendorf worked together in a joint project devoted to the research at the coupled GDT-SHIP facility of the BINP with the focus on the study of plasma phenomena within the SHIP mirror section. The project began at July 1st, 2005 and ended on August 30th, 2008. It included work packages of significant theoretical, computational and analyzing investigations.
The focus of this final report is on the presentation of results achieved whereas the work that was done is described briefly only. Chapter 2 illustrates the GDT-SHIP facility and describes shortly the planned topics of the SHIP plasma research. Chapter 3 explains the main extensions and modifications of the Integrated Transport Code System (ITCS) which were necessary for the calculations of the fast ion and neutral gas particle fields in SHIP, describes briefly the scheme of computations and presents significant results of pre-calculations from which conclusions were drawn regarding the experimental program of SHIP. In chapter 4, the theoretical and computational investigations of self-organizing processes in two-component plasmas of the GDT-SHIP device are explained and the results hitherto achieved are presented. In chapter 5, significant results of several experiments with moderate and with enhanced plasma parameters are presented and compared with computational results obtained with the ITCS. Preparing neutron measurements which are planned for neutron producing experiments with deuterium injection, Monte Carlo neutron transport calculations with the MCNP code were also carried out. The results are presented. Finally, from the results obtained within the joint research project important conclusions are drawn in chapter 6.

Keywords: fusion neutron source; gas dynamic trap; synthesized hot ion plasmoid

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-513 2009
    ISSN: 1437-322X


Publ.-Id: 12436

Aktivitäten des FZD für die (Dünnschicht) Photovoltaik

von Borany, J.

Kurze Übersicht der PV-Aktivitäten im FZD.

Keywords: Photovoltaik; Ionentechniken; dünne Schichten; Magnetohydrodynamik

  • Lecture (others)
    EFDS Fachausschuss "Großflächenbeschichtung für solar- und lichttechnische Anwendungen", 10.07.2008, Dresden, Germany

Publ.-Id: 12435

In-situ study of film growth by synchrotron radiation scattering

Martins, R.M.S; Schell, N.; von Borany, J.; Bähtz, C.

The possibilities of in-situ X-ray investigations at ROBL for the study of thin films growth are summarized.

Keywords: ROBL; X-ray studies; thin films; microstructure

  • Poster
    2008 International Conference for Shape Memory and Superelatic Technologies (R&D Exhibition Event), 21.-25.09.2008, Stresa, Italy

Publ.-Id: 12434

Texture development and phase transformation behaviour of sputtered Ni-Ti films

Martins, R. M. S.; Schell, N.; Silva, R.; Pereira, L.; Mahesh, K. K.; Braz Fernandes, F. M.

The technological importance of thin films has led to an unabated interest in the detailed characterization of their structure, morphology, and their interfaces. A real understanding of the underlying growth mechanisms and their microstructural development requires sophisticated in situ techniques. X-ray diffraction with high-brilliance beams is such a powerful technique, as it is demonstrated here for the study of Ni-Ti films.
Numerous examples of investigations on Ni-Ti films can be found in the literature but it has been reported that the deposition of Ni-Ti films with definite stoichiometry and high purity remains a challenge, and important issues like formation of film texture and its control are still unresolved.
It is essential to identify and control their preferential orientation since it is a crucial factor in determining the shape memory behaviour. Widening the scope of our previous experiments concerning the influence of the deposition parameters on the structure of the Ni-Ti films, the incorporation of a TiN buffer layer has been tested.
Here, it is established a clear relationship between the TiN substrates and Ni-Ti texture development (B2 phase) and it is shown that the distinct crystallographic orientations of the Ni-Ti films influence their phase transformation behaviour. The influence of a substrate bias voltage on the preferential orientation of the B2 phase and transformation temperatures is as well revealed. A lower biaxial stress state and lower phase transformation temperatures have been observed for the films deposited with bias (-45 and -90V). Therefore, the control of the energy of the bombarding ions could be used as a tool for the manipulation of the transformation temperatures.

Keywords: NiTi; shape memory alloys; texture; X-ray diffraction

  • Lecture (Conference)
    2008 International Conference for Shape Memory and Superelastic Technologies, 21.-25.09.2008, Stresa, Italy
  • Journal of Materials Engineering and Performance 18(2009), 543-547
    ISSN: 1059-9495

Publ.-Id: 12433

Texture development and phase transformation behaviour of sputtered Shape Memory Alloy Ni-Ti films

Martins, R. M. S.; Schell, N.; Silva, R.; Pereira, L.; Mahesh, K. K.; Braz Fernandes, F. M.

Ni-Ti SMA films are attractive materials for microfabrication and integration in micro-miniature systems composed of mechanical elements, actuators, sensors and electronics made on one chip. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. It is essential to identify and control their preferential orientation since it is a crucial factor in determining the shape memory behaviour. Widening the scope of previous experiments concerning the influence of the deposition parameters on the Ni-Ti films structure, the incorporation of a TiN intermediate layer was tested.
Here, it is established a clear relationship between the TiN substrates and Ni-Ti texture development (B2 phase) and it is shown that the distinct crystallographic orientations of the Ni-Ti films influence their phase transformation behaviour. The influence of a substrate bias voltage on the preferential orientation of the B2 phase and transformation temperatures is as well revealed.

Keywords: NiTi; shape memory alloys; texture; x-ray diffraction

  • Poster
    ESRF User Meeting 2008, 05.-07.02.2008, Grenoble, France

Publ.-Id: 12432

Speciation and Structural Study of U(IV) and -(VI) in Perchloric and Nitric Acid Solutions

Ikeda-Ohno, A.; Hennig, C.; Tsushima, S.; Scheinost, A. C.; Bernhard, G.; Yaita, T.

In order to elucidate the uranium solution chemistry at the high HNO3 concentrations typically employed for the reprocessing of spent nuclear fuels, speciation and complex structures of UIV and UVI are studied in aqueous HNO3 solutions, as well as in HClO4 solutions, by means of UV-visible-near-infrared and X-ray absorption spectroscopies and density functional theory calculations. In 1.0 M HClO4, UIV exists as a spherical cation of U4+, which is surrounded by 9-10 water molecules in the primary coordination sphere, while it forms a colloidal hydrous oxide, UIVO2 nH2O, at a lower acidic concentration of 0.1 M HClO4. UVI exists as a transdioxo uranyl cation, UO2 2+, and forms a 5-fold pure hydrate complex of [UVIO2(H2O)5]2+ in 1.0M HClO4. With increasing HNO3concentration, the water molecules of the UIV and UVI hydrate complexes are successively replaced by planar bidentate coordinating nitrate ions (NO3 -), forming dominant species of [UIV(H2O)x(NO3)5]- in 9.0 M HNO3 and [UVIO2(NO3)3]- in 14.5 M HNO3, respectively. The present multitechnique approach also suggests the formation of two intermediate UVI species, a 5-fold mononitrato complex ([UVIO2(H2O)32-NO3)]+) and a 6-fold dinitrato complex ([UVIO2(H2O)22-NO3)2]0), involving an increase in the total coordination number on the uranyl(VI) equatorial plane from 5 to 6 with increasing HNO3 concentration. The presence of unidentate coordinate nitrato complexes or tetranitrato UVI complexes is less probable in the present HNO3 system.

Publ.-Id: 12431

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