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31828 Publications
CFD-modelling of insulation debris transport phenomena in water flow
Krepper, E.; Cartland-Glover, G.; Grahn, A.; Weiss, F.-P.; Alt, S.; Hampel, R.; Kästner, W.; Seeliger, A.;
The investigation of insulation debris generation, transport and sedimentation becomes more important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core coolant systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are for example the particle load on strainers and corresponding pressure drop, the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow. A joint research project on such questions is being performed in cooperation with Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau. The project deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While the experiments are performed at the IPM-Zittau, the theoretical work is concentrated at Forschungszentrum Dresden-Rossendorf.
Whereas the paper Alt et al. is focused on the experiments in the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.
Keywords: CFD, two-fluid approach, fiber flows
  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.12.2007, Pittsburgh, USA

Publ.-Id: 9691 - Permalink

Review of available data for validation of nuresim two-phase CFD software applied to CHF investigations
Bestion, D.; Anglart, H.; Peturaud, P.; Smith, B.; Krepper, E.; Moretti, F.; Macek, J.;
The NURESIM Integrated Project of the 6th European Framework Program is envisaged to initiate the development of the next-generation common European Standard Software Platform for simulating nuclear reactors. The overall objective of NURESIM Thermalhydraulic sub-project is to improve the understanding and the predictive capabilities of the simulation tools for key two-phase flow thermal-hydraulic processes such as the Critical Heat Flux (CHF). A multi-scale analysis of reactor thermalhydraulics is envisaged and two-phase CFD is developed to allow some zoom on local processes when the resolution of system codes is not sufficient.
Current industrial methods for CHF mainly use the sub-channel analysis and empirical CHF correlations based on large scale experiments having the real geometry of the reactor assembly. The NURESIM-TH activities regarding CHF aim at using two-phase CFD as a tool for understanding boiling flow processes, in order to subsequently help new fuel assembly design and to develop better CHF predictions in both PWR and BWR. A “Local Predictive Approach” may be envisaged for the long term where CHF empirical correlations would be based on local T/H parameters provided by CFD.
This paper presents a review of existing experimental data bases which can be used for validation of the two-phase CFD application to Critical Heat Flux (CHF) investigations with respect to nuclear reactors. The phenomenology of DNB and Dry-Out are detailed identifying all basic flow processes which require a specific modeling in CFD tool. The resulting program of work is given and the current state of the art of the modeling is presented.
The resulting program of work is presented and the present state of the art in the modeling is detailed.
Keywords: Critical heat flux, experimenbtal data, CFD simulation
  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA

Publ.-Id: 9690 - Permalink

Application of the moment-density method in CFD code to model bubble size distribution
Ruyer, P.; Seiler, N.; Beyer, M.; Weiß, F.-P.;
This study, carried out at Institut de Radioprotection et de Sûreté Nucléaire, concerns the model of a polydispersed bubble population in the frame of an ensemble averaged two-phase flow formulation. We consider the ability of the moment density approach, e.g. Kamp et al. (2001), to represent bubble population size distribution within a multi-dimensional CFD code based on the two-fluid model. Special attention is given to the closure issue of the method. We consider in particular the influence of the polydispersion on (i) coalescence and break-up phenomena and on (ii) momentum inter-phase transfers related to drag and lift forces. A first approach formulation is developed allowing to represent a full spectrum of bubble size with a very reduced number of parameters. The latter property constitutes one of the main advantages of the moment density method with regard to alternative methods for polydispersion representation like population balance. The system of transport equations and corresponding main closure terms are derived in the case of adiabatic flows with spherical bubbles of an incompressible fluid that is immiscible in the continuous phase. Air-water polydispersed bubbly flows in a vertical pipe with obstacle of the TOPFLOW experiments series performed at FZD, e.g. Prasser et al. (2006), are then used as simulations test cases. The numerical results, obtained with NEPTUNE_CFD, e.g. Guelfi et al. (2005), allow to attest the validity of the approach. Perspectives concerning the improvement of the model, its validation, as well as the extension of its applicability range are discussed.
Keywords: two-phase flow, NEPTUNE_CFD, bubble size distribution, moment density
  • Lecture (Conference)
    European Two-Phase Flow Group Meeting 2007, 29.-31.05.2007, Toulouse, France

Publ.-Id: 9689 - Permalink

Numerical investigations of the transport of submerged insulation particle
Cartland-Glover, G.; Alt, S.; Kästner, W.; Krepper, E.;
A numerical investigation of insulation debris transport and sedimentation is being performed as part of a joint research project with the Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau. The study considers the impact of the transport of insulation wool debris on the long-term behaviour of emergency core coolant systems during all types of LOCA that occur in PWR and BWR. In order to implement models into computational fluid dynamic codes (CFD), the models that characterize insulation debris (particle buoyancy, drag, turbulent dispersion and the fluid-particle mixture viscosity) must be tested. Experimental investigations are being performed at the IPM-Zittau to provide detailed information with which the numerical models can be validated.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany

Publ.-Id: 9688 - Permalink

Application of multiphase flow modeling techniques to the transport of submerged mineral wool fibers
Cartland-Glover, G.; Alt, S.; Kästner, W.; Krepper, E.;
The transport of mineral wool insulation debris, which is generated during all types of loss of coolant accidents (LOCA) could impede the long-term operation of emergency core coolant systems (ECCS) in nuclear power plants. Therefore, a combined experimental and numerical investigation of mineral wool fibers is being pursued to improve the understanding of how ECCS can be undermined by the transport, sedimentation and resuspension of mineral wool fibers.
The application of the Eulerian-Eulerian multiphase flow model to the transport of the fibers is discussed here with regard to the transport of fibers in a racetrack type channel. The study examines the application of closure models such as the Favre-Averaged turbulence dispersion force and the mixture viscosity and the impact that they have on fiber transport. The intention of the study is to aid the experimental part of the study by determining which parameters influence the particle forces and which conditions can be used in analyzing the parameters for further model development and evaluation. The phenomena observed in the calculations correspond qualitatively to preliminary experimental observations.
Keywords: CFD, Eulerian-Eulerian Multiphase, Nuclear Reactor Containment Sump, Mineral Wool Fibers, Sedimentation and Resuspension
  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9687 - Permalink

Application of a population balance approach for polydispersed bubbly flows
Krepper, E.; Beyer, M.; Frank, T.; Lucas, D.; Prasser, H.-M.;
A population balance model was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10 (Frank et al. 2005, Krepper et al. 2007). The current paper presents the application of the model to upward flow in vertical pipes for air/water and for steam/water bubbly flow. Finally the application to a bubbly flow around a half moon shaped obstacle arranged in a 200 mm pipe is shown (see Frank et al. 2007).
Applying the inhomogeneous MUSIG approach a more deep understanding of the flow structure is possible. For upward two phase flow in vertical pipes the core peak in the cross sectional gas fraction distribution could be reproduced very well. For complex flows the general structure of the flow could be well reproduced in the simulations. This test case of the obstacle demonstrates the complicated relationship between size dependent bubble migration and bubble coalescence and break-up effects for real flows. While the closure models for bubble forces, which are responsible for the simulation of bubble migration are in agreement with the experimental observations, clear deviations occur for bubble coalescence and fragmentation. The presently applied models describing bubble fragmentation and coalescence could be proved as weak points in numerous CFD analyses of vertical upward two phase pipe flow. Further work on this topic is considered for future investigations.
Keywords: Bubbly flow, CFD, Non drag forces, bubble break up, bubble coalescence, population balance, validation
  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Poster No PS6_6
  • Poster
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9686 - Permalink

Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows
Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, P. J.;
A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. Simulating a poly-dispersed gaseous liquid two phase flow along with the mass exchanged between bubble size classes by bubble coalescence and bubble break-up and the momentum exchange of bubble size dependent bubble forces have to be considered. Particularly the lift force has been proved to play an important role establishing a certain flow regime. The paper describes the main concepts of the model approach and presents a model validation case. Further application test cases are presented by Krepper et al. 2007.
The inhomogeneous MUSIG model approach was shown to be able to describe of bubbly flow with higher gas content. Particularly the separation phenomenon of small and large bubbles which was proven to be a key phenomenon for the establishment of the corresponding flow regime is well described. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble break-up, which must be further investigated.
Keywords: Bubbly flow, CFD, Non drag forces, bubble break up, bubble coalescence, population balance, validation
  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Paper No S_6_Thu_B_51
  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9685 - Permalink

Compositional and structural changes in ZrOxNy films depending on growth condition
Carvalho, P.; Fernandes, A. C.; Rebouta, L.; Vaz, F.; Cunha, L.; Kreissig, U.; Barradas, N. P.; Ramos, A. R.; Alves, E.;
The present work focuses on the analysis of ZrOxNy thin films, the composition evolution with changing growth conditions and its relation with the structural and morphological properties of the films. The films were prepared by rf reactive magnetron sputtering, using different reactive gas flows. Composition and structure were measured combining ion beam analysis (IBA) and X-ray diffraction (XRD) techniques. The depth profiles of nitrogen and oxygen have been obtained by elastic recoil detection analysis (ERDA). Results showed that the oxygen fraction in the films increases with gas flow, reaching a value of x ~ 0.33 for a reactive gas flow mixture of 6.25 sccm. During growth mixed zirconium nitride and oxide phases form. Furthermore, the deposition rate correlates with the oxygen content variations, showing a continuous decrease with reactive gas flow.
Keywords: Decorative films; XRD; Nitrides; Oxides; Ion beams
  • Nuclear Instruments and Methods in Physics Research B 249(2006), 458-461

Publ.-Id: 9684 - Permalink

Study of anomalous behaviour of LiTaO3 during the annealed proton exchange process of optical waveguide´s formation - comparison with LiNbO3
Salavcova, L.; Spirkova, J.; Ondracek, F.; Mackova, A.; Vacik, J.; Kreissig, U.; Eichhorn, F.; Groetzschel, R.;
This paper deals with detailed study of changes that lithium tantalate (LT) and lithium niobate (LN) single crystals undergo during the APE (Annealed Proton Exchange) process of optical waveguides´ formation. It is a well-known fact that several cases of anomalous behaviour are connected to the APE:LT samples, bringing thus serious limitations for the practical utilization of the APE:LT waveguides. As the LT crystal posseses even better optical properties than the LN (e.g., it is less susceptible to optical damage), it is highly desirable to provide research focused on its behaviour during the APE in order to get a control over fabrication of the APE:LT devices.
Neutron Depth Profiling (NDP), Elastic Recoil Detection Analysis (ERDA) and High Ion Energy ERDA (HIERDA) were performed to study changes in the surface of the LT and LN Z-cut wafers caused by the APE treatment and to determine the concentration depth profiles of the exchanged ions (lithium and hydrogen). Information on modifications of the crystals during the APE were obtained using X-Ray Diffraction (XRD) analysis. Optical/waveguiding properties of the samples were obtained by means of the standard mode spectroscopy at 633 nm.
The experiments proved that the LT is significantly less affected by the APE process compared to the LN and that most characteristics of the APE:LT layers are relatively easily restored back towards that of the virgin crystal by the annealing process.
Keywords: APE; Ion exchange; Lithium niobate; Lithium tantalate
  • Optical Materials 29(2007), 913-918

Publ.-Id: 9683 - Permalink

Das Komplexbildungsverhalten von Uran(IV) mit Phosphat – Untersuchungen mittels Zeitaufgelöster Fluoreszenzspektroskopie
Lehmann, S.; Geipel, G.;
Die Zeitaufgelöste Fluoreszenzspektroskopie erlaubt die unmittelbare Untersuchung fester und flüssiger Systeme in mikro- und submikromolaren Stoffmengenkonzentrationen. Dies prädestiniert die Etablierung und den Einsatz der Fluoreszenzspektroskopie als analytische Methode für Untersuchungen von Festphasen- und aquatischen Umweltsystemen in ihren entsprechenden relevanten Konzentrationsbereichen. Die hier gezeigten Forschungsergebnisse repräsentieren die ersten Resultate zur Komplexbildung von Uran(IV) im Phosphatsystem, welche mit Hilfe der Zeitaufgelösten Fluoreszenzspektroskopie ermittelt wurden.
Zur Untersuchung der Komplexbildung zwischen Uran(IV) und Phosphat wurde die Konzentration des Uran(IV) im perchlorsauren Medium konstant gehalten und die Konzentration des zugegebenen Phosphat in einem Bereich zwischen einem 5fachen Unterschuss und einem 5fachen Überschuss variiert. Fluoreszenzspektroskopische Aufnahmen des Uran(IV) ohne Zusatz von Phosphat zeigen die Übereinstimmung der Peakpositionen mit [1] und [2]. Die Positionen der 5 Hauptpeaks wurden wie folgt ermittelt: 291, 320, 335, 394 and 409 nm. Die Auswertung der aufgenommenen zeitaufgelösten Spektren von Uran(IV) mit Phosphatzusatz zeigt insbesondere an den intensivsten Peaks bei 320 und 409nm, dass mit zunehmender Phosphatkonzentration die Fluoreszenzintensität abnimmt, freies Uran(IV) folglich im Komplex gebunden wird, bis freies Uran(IV) bei äquimolaren Stoffmengenkonzentrationen von Uran(IV) und Phosphat nicht mehr nachweisbar ist und somit vollständig mit Phosphat reagiert hat.
Die über die äquimolare Konzentration hinaus bis hin zum 5fachen Überschuss an Phosphat aufgenommenen Spektren sind gegenüber den zuvor beschriebenen gänzlich verändert und zeigen nur eine einzige breite Bande zwischen 290 und 400nm mit einem Peak schwacher Intensität bei 374nm. Die undefinierte Bande lässt sich möglicherweise auf die gelartigen Ausfällungen zurückführen, welche bei stöchiometrischen Konzentrationen und bei Phosphatüberschuss unter den hier gewählten Versuchsbe-dingungen zu beobachten sind.

Weitergehende Untersuchungen haben als Ziel, die Natur des Peaks bei 374nm zu klären und die gebildeten Uran(IV)-Phosphatspezies sowie die entsprechenden Komplexbildungskonstanten zu bestimmen.
Keywords: uranium(IV) phosphate, TRLFS, complex formation constant
  • Poster
    GDCh - Wissenschaftsforum Chemie 2007, 16.-19.09.2007, Ulm, Germany

Publ.-Id: 9682 - Permalink

Gas-liquid flow around an obstacle in a vertical pipe – CFD simulation & comparison to experimental data
Frank, T.; Prasser, H.-M.; Beyer, M.; Al Issa, S.;
A novel technique to study the two-phase flow field around an asymmetric diaphragm in a vertical pipe is presented, that allows to obtain detailed 3-dimensional data for CFD code validation in complex geometries. The investigated validation test case consists of an air-water two-phase bubbly flow around a half-moon shaped obstacle in a DN200 vertical pipe (TOPFLOW test facility), where the 3-dimensional flow field shows flow phenomena like curved stream lines, flow separation at sharp edges and
recirculation zones in the obstacle wake, like they are common to complex flow situations in bends, T-junctions, valves, safety valves and other components of power plant and other industrial equipment. Pre-test calculations with the commercial flow solver ANSYS CFX have been performed using an Eulerian two-phase flow model with a monodisperse bubble diameter assumption and by taking into account all significant drag and non-drag forces contributing to the interphase momentum transfer. Results of the CFD simulation have been compared to the 3-dimensional air volume fraction and water velocity fields, which were obtained from the wire-mesh sensor data, where the comparison showed a general very good agreement. Therefore CFD code validation on this type of complex 3-dimensional flow geometries permits the assessment of flow solver accuracy for other industrial type applications and contributes to further multiphase flow model development for ANSYS CFX.
Keywords: bubbly flows, CFD, wire-mesh sensor, 3-dimensional validation
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9681 - Permalink

[18F]FBAM and [18F]FBOM: Novel Thiol-reactive prosthetic groups derived from 4-[18F]fluorobenzaldehyde
Vogler, L.; Berndt, M.; Pietzsch, J.; Wüst, F.;
The incorporation of 18F into peptides and proteins usually takes advantage of prosthetic groups, also referred to as bifunctional labeling agents. This approach comprises 18F incorporation into a small organic molecule capable of being linked to peptides and proteins under mild conditions.
Two new prosthetic groups derived from 4-[18F]fluorobenzaldehyde for the mild and selective conjugation to thiol-group containing biomacromolecules are described: N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]-maleimide ([18F]FBAM) and 4-[18F]fluorobenzaldehyde-O-(2-{2-[2-(pyrol-2,5-dion-1-yl)ethoxy]ethoxy}ethyl)oxim ([18F]FBOM.
The aminooxy-functionalized labeling precursor for radiosynthesis of [18F]FBAM was prepared in a convenient three-step synthesis sequence in a total yield of 59%. The corresponding labeling precursor for the radiosynthesis of [18F]FBOM succeeded in a four-step reaction sequence in 14% total yield. Formation of the prosthetic groups [18F]FBAM and [18F]FBOM was achieved through condensation reaction with [18F]fluorobenzaldehyde to form the desired oximes in radiochemical yields of 20-30% ([18F]FBAM) and of 14-19% ([18F]FBOM), respectively. The syntheses were carried out in a remotely-controlled radiofluorination module allowing the convenient and reliable performance of the radiolabeling reactions. The radiochemical purity exceeded 95% and the specific activity ranged from 50 to 80 GBq/μmol. The total synthesis time was 70 to 80 min. The lipophilicity was determined to be logP=2.71 for [18F]FBAM and logP=0.84 for [18F]FBOM. Both prosthetic groups could successfully be used in the radiolabeling of thiol-group containing compounds such as glutathion, low density lipoproteins (LDL) and modified neurotensin derivatives.
  • Lecture (Conference)
    14th Workshop der International Isotope Society, 21.-22.06.2007, Bad Soden, Germany
  • Journal of Labelled Compounds and Radiopharmaceuticals 50(2007), 1276-1286

Publ.-Id: 9680 - Permalink

Mobilisation and speciation of depleted uranium in water and soils
Geipel, G.; Baumann, N.; Arnold, T.; Bernhard, G.; Gerstmann, U.; Schimmack, K.; Read, D.;
Depleted uranium (DU) from penetrating ammunition was exposed to several environmental conditions in order to determine the binding forms of uranium as well as in its dissolved and solid forms.
In a first series fresh disks of DU were treated with a calcium phosphate solution. The results from time-resolved laser-induced fluorescence spectroscopy clearly show that metaautunite Ca(UO2)2(PO4)2 x 2-6(H2O) has formed during alteration [1].
In a second experiment the corrosion and leaching of used up DU was investigated for three years in a column with a soil core. The columns were irrigated with synthetic rainwater.
The luminescence spectrum of a yellow material, which was crystallized at the soil surface was assigned clearly to be the mineral sabugalite AlH(UO2)(PO4)4 x 16(H2O).
In contrast to the luminescence spectra of the solid material the spectra of the uranium species in the dissolved samples could only obtained at temperatures below 220 K. From the shape of the spectrum and the emission maxima of the luminescence of seepage water samples it could be clearly concluded that the solution species are mostly uranyl carbonate species UO2(CO3)34- [2].
Keywords: Depleted uranium, TRLFS, Binding form
  • Contribution to proceedings
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany

Publ.-Id: 9679 - Permalink

Model studies with DU to assess the mobilisation and speciation of U in soils
Geipel, G.; Baumann, N.; Arnold, T.; Bernhard, G.; Gerstmann, U.; Schimmack, K.; Read, D.;
Since the 1990th, depleted uranium (DU) was used in several conflict regions as 'penetrator' in munition rounds designed to pierce battle tanks. Lots of this amunition undergo wheatering processes under environmental conditions. One goal of our studies was the determination of the binding forms of uranium, if the DU is exposed to several environmental conditions.
The formed uranium species were detected by time-resolved laser-induced fluorescence spectroscopy (Geipel 2005). By use of spectroscopic databases including U(VI)-oxides, U(VI)-hydroxides, U(VI)-sulphates and U(VI)-phosphates the different formed uranium species in solution as well as solid species can be clearly assigned.
In a first series disks of DU were treated with a calcium phosphate solution at ambient temperature for 182 days. The weathering solution contained 2.49 mM calcium and 1.05 mM phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that metaautunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. The TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50±5 ns and 700±25 ns (Baumann, 2006).
In a second experiment the corrosion and leaching of depleted uranium (DU) was investigated for three years in a column with a soil core. The columns were installed in a laboratory with controlled temperature of (21 ± 1) °C and a relative humidity of (55 ± 10) %. The columns were irrigated weekly with 16 mm synthetic rainwater of pH 6 consisting mainly of 0.09 mM NH4NO3, 0.08 mM (NH4)2SO4 and 0.05 mM CaSO4.
The luminescence spectrum of a yellow material, which was crystallized at the soil surface was measured and the comparison with the TRLFS database assigned this luminescence spectrum clearly to be the mineral sabugalite AlH(UO2)(PO4)4 x 16(H2O).
In contrast to the luminescence spectra of the solid material the spectra of the uranium species in the dissolved samples could only obtained at temperatures below 220 K. From the shape of the spectrum and the emission maxima of the luminescence of seepage water samples it could be clearly concluded that the solution species are mostly uranyl carbonate species UO2(CO3)34- (Schimmack, Schimmack 2007).
Keywords: Depleted uranium, binding form
  • Invited lecture (Conferences)
    International Symposium Protecting Water Bodies from Negative Impacts of Agriculture, 04.-06.06.2007, Braunschweig, Germany

Publ.-Id: 9678 - Permalink

FT-IR investigation of the uranium S-layer interaction in aqueous solutions
Li, B.; Foerstendorf, H.; Raff, J.; Bernhard, G.;
Many bacteria possess so-called surface layer (S-layer) proteins, forming paracrystalline lattice structures on the cell wall (1). Beside its ecological relevance for the retention of toxic metals, they are a good model system for investigations of the interaction of bio-ligands, e.g. proteins, with uranium in aqueous solutions. Several S-layers from different Bacillus strains were proved to have high binding capacity to uranium. But there is still little knowledge of the interactions between the functional groups of the protein with the actinyl ions at a molecular level (2).
In this work we present results of batch experiments where the uranium binding capacities of different S-layer protein from different Bacilllus strains were determined. The experiments were carried out at different pH values (pH 4, 6, and 8) for each isolated S-layer protein. It was found that the uranium binding capacities of each gram S-layer range from 5.0 mg and 63.9 mg, from 11.1 mg and 561.1 mg, and from 14.2 mg and 33.5 mg at pH 4, 6, and 8, respectively, depending on the respective S-layer.
For a deeper understanding of the molecular binding of the uranyl ion to the protein we used Attenuated Total Reflectance Fourier-transform Infrared spectroscopy (ATR-FTIR) which allows vibrational spectroscopic investigations of aqueous solutions containing actinide ions and disolved proteins as well (3, 4). The spectra clearly demonstrate carboxyl groups are the major functional groups which interact with the uranyl ions at pH 4. Additionally, the infrared spectra suggest the formation of different uranium-protein complexes depending on the incubation period (1 h vs. 48 h) which can be observed by a peak shift of the absorption band representing the antisymetric uranyl stretch to lower wavenumbers.
This spectroscopic approach constitutes the foundation of more detailed investigations on the impact of the pH value and of other functional groups (e.g. phosphate or amino groups) on the uranium complexation by bio-systems.

(1) Sleytr, U.B., Beveridge T.J., Trends Microbiol. 1999 7(6), 253-260
(2) Merroun, M.L., et al. Appl. Environ. Microbiol. 2005, 71(9), 5532–5543
(3) Quilès, F.; Burneau, A. Vib. Spec. 2000, 23, 231-241.
(4) Fahmy, K. et al. Biophys. J. 2006, 91(3), 996-1007
  • Contribution to proceedings
    17th Annual Goldschmidt Conference, Cologne, Germany, 19.-24.08.2007, Köln, Germany
    FT-IR investigation of the uranium S-layer interaction in aqueous solutions

Publ.-Id: 9677 - Permalink

Complexation of Uranium(VI) with Nitrate in Nonaqueous and Aqueous solutions: Speciation and Structural Studies
Ikeda, A.; Hennig, C.; Rossberg, A.; Tsushima, S.; Scheinost, A. C.; Bernhard, G.;
Understanding the complexation behavior of uranium(VI) with nitrate ions in solution is important for the assessment of environmental impact on the geological disposal of radioactive wastes or for the development of nuclear fuel reprocessing since the present reprocessing plants employ PUREX process, that separates uranium and plutonium from other actinides and fission products in nitric acid solution and, as a result, produces radioactive liquid wastes in nitrate solution. In this study, the chemical speciation and the structure of uranium(VI) nitrate complexes have been investigated in nonaqueous (acetonitrile) and aqueous (nitric acid) solutions by UV-visible absorption spectroscopy, U LIII-edge x-ray absorption spectroscopy, and quantum chemical calculations.

In acetonitrile, the complexation between uranium(VI) and nitrate ions is very strong and the trinitrato complex, [UO2(NO3)3]-, becomes the dominant species when [NO3]/[U] is above 3. The extended x-ray absorption fine structure (EXAFS) spectrum of this trinitrato species indicates that the nitrate ions coordinate to the uranyl ion in a bidentate mode and the average U-Oax, U-Oeq, and U-N distances are 1.77, 2.50, and 2.95 Å, respectively. These values are in good agreement with the results of DFT calculations in acetonitrile (i.e. 1.76, 2.50, and 2.96 Å for U-Oax, U-Oeq, and U-N distances, respectively). By varying the [NO3]/[U] ratio from 0 to 3, we observe a complex speciation diagram composed of four species (UO22+, [UO2NO3(H2O)n]+, [UO2(NO3)2(H2O)m]0, and [UO2(NO3)3]-). However, it is impossible to determine the complex structures of these species directly by EXAFS. In order to estimate their structure, we have isolated their individual EXAFS spectra from the spectra of the mixtures by performing factor analysis [1] on the basis of the speciation diagram obtained from the UV-visible spectral titration. The data analysis of the isolated EXAFS spectra demonstrates that the dinitrato complex has a coordination number of 6 in the equatorial plane of the uranyl ion and forms the complex [UO2(NO3)2(H2O)2]0. On the other hand, the estimated EXAFS spectrum for the mononitrato complex indicates that it has a coordination number of 5 and forms the complex [UO2NO3(H2O)3]+. These results are supported by DFT calculations. The same data treatment (i.e. factor analysis combined with the speciation diagram from spectral titration) has also applied to the EXAFS spectra in aqueous solutions of nitric acid. The results suggest that the nitrate complexation of uranium(VI) is far weaker in aqueous solution than that in acetonitrile and almost no trinitrato complex is formed even when the [NO3]/[U] ratio exceeds 360.
Keywords: uranium(VI), nitrate, solution, acetonitrile, nitric acid, XAFS, UV-visible absorption, DFT, factor alanysis, speciation
  • Poster
    Migration 2007, 26.-31.08.2007, Arabella Sheraton Grand Hotel, Munich, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 178

Publ.-Id: 9676 - Permalink

Infrared spectroscopic identification of aqueous uranium(VI) species
Müller, K.; Foerstendorf, H.; Bernhard, G.;
Migration of uranium(VI), the most stable form of uranium in environmental waters, is largely controlled by its geochemical reactions, both in solution and at the mineral-water interface. Current knowledge about U(VI) speciation is mainly based on thermodynamic calculations using data obtained by non-structural experiments, i.e. potentiometric titration [1]. A spectroscopic verification of the speciation of aqueous U(VI) is still insufficient. For the identification of different molecular species previous studies applied primarily EXAFS and Raman spectroscopy at very high uranyl concentrations (>100 mM) unreasonably in an environmental context [2-4].
In this study we used Attenuated Total Reflectance Fourier-transform Infrared (ATR-FTIR) spectroscopy, that allows the direct measurement of liquid samples. Our aim was to obtain additional vibrational spectroscopic information on the U(VI) species and especially to verify the U(VI) speciation throughout a wide pH range (pH 2-10) at a micromolar concentration level. The obtained spectral information was compared to previously reported thermodynamic data [1].
ATR-FTIR spectra were recorded at UO22+ concentrations ranging from 5 to 0.005 mM at pH 4. The spectroscopic results indicate distinctly that dimer and trimer hydroxo complexes become dominant upon lowering the uranyl concentration at pH 4. The thermodynamic data predict an absolute predominance of the free uranyl species UO22+ until pH 5 at these conditions.
At the micromolar concentration level the calculations predict the dominance of the uncomplexed uranyl ion until pH 5 and the formation of uranyl hydroxo complexes at neutral pH. Uranyl complexes with atmospheric carbonate in alkaline solutions are proposed above pH 6.5. However, the obtained ATR-FTIR spectra of low concentrated 0.02 mM uranyl solutions already show the coexistence of free and hydroxo complexed uranyl at pH 2.5. The appearance of carbonate complexes in solution becomes noticeable at the spectra of solutions at pH 7. Since the results are partially contradictionary to previous predictions of U(VI) speciation a critical review of the present knowledge of uranium migration in the environment is required.

[1] Guillaumont, R. et al. (2003) Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc. (Elsevier, Amsterdam)
[2] Moll, H. et al. (2000) Radiochim. Acta 88, 411-415.
[3] Nguyen-Trung, C. et al. (1992) Inorg. Chem. 31, 5280-5287.
[4] Quiles, F. et al. (2000) Vib. Spec. 23, 231-241.
  • Lecture (Conference)
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 71(2007)15S, A694

Publ.-Id: 9675 - Permalink

Additional FDG PET-CT in week 5-6 of radiotherapy for patients with NSCLC as a means of dose escalation planning
Gillham, C.; Zips, D.; Pönisch, F.; Evers, C.; Enghardt, W.; Abolmaali, N.; Zöphel, K.; Appold, S.; Hölscher, T.; Steinbach, J.; Kotzerke, J.; Herrmann, T.; Baumann, M.;
To detect a reduction in disease volume during radical radiotherapy for non-small cell lung cancer (NSCLC) using PET-CT and to determine whether this would facilitate dose escalation.

Ten patients with localised inoperable NSCLC were prospectively enrolled. Each received conformally planned radiotherapy to a dose of 66Gy/33# over 6.5 weeks using 6-15MV photons and prescribed to the 100% isodose. PET-CT imaging was performed just prior to and following 50 or 60Gy. Target volume definition was performed by one senior radiation oncologist with the help of a senior radiologist and nuclear medicine physician. For all patients and at both time points CT and PET-delineated gross tumour volumes were generated (GTVCT, GTVPET). A composite GTV was then created (GTVCT+PET) and 15mm added in all planes to form the planning target volume (PTV). No correction for organ movement was incorporated and no elective nodal irradiation performed. Each of the different volumes were compared before and after 50-60 Gray. Two plans were then created and compared: 78Gy delivered to the initial PTV and 66Gy to the initial PTV with a 12Gy boost to the post 50/60Gy PTV.

All patients (mean age 64 years) had stage III disease (4 IIIA and 6 IIIB). There were 4 squamous cell and 6 adeno-carcinomas. After 50/60 Gray the GTVCT, GTVPET, GTVCT+PET and PTV reduced by a mean of 22%, 43%, 30% and 22% respectively. The delivery of 78 Gray to the initial PTV could have been safely achieved in 4/10 patients. Of these delivering treatment in two phases would have substantially spared normal tissue in 2 patients. In the remaining 6 patients, delivering 78 Gray to the initial PTV would have exceeded normal tissue constraints
and no benefit was seen when planned in 2 phases.

The PTV, consequent on changes seen on PET-CT, reduces during a course of radical radiotherapy for NSCLC. Such a reduction permits dose escalation in a subset of patients and may lead to improved therapeutic outcomes.
  • Lecture (Conference)
    14th European Cancer Conference, 23.-27.09.2007, Barcelona, Spanien

Publ.-Id: 9674 - Permalink

Rising gas bubbles in a liquid metal under the influence of external magnetic fields
Zhang, C.; Eckert, S.; Gerbeth, G.;
In the present paper we consider the impact of various external DC magnetic fields on the motion of a single bubble rising in a cylindrical column of stagnant liquid metal and the flow structure of a bubble plume, respectively. The ultrasound Doppler method (UDV) has been used to measure the velocity non-intrusively. The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC vertical magnetic field was examined. The bubble terminal velocity showed oscillations indicating a zizag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. A global damping of the flow field was also observed if a vertical magnetic field has been imposed on a bubble plume. By contrast, a restructuring of the flow pattern being typical for a bubble plume was observed in the case of a horizontal magnetic field. The DC field gave rise to non-steady, non-isotropic and large-scale flow structures which was rather unknown until now and therefore not sufficiently considered for electromagnetic processing of materials.
Keywords: single bubble, bubble plume, liquid metal, magnetic field, ultrasound Doppler velocity measurements
  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF2007, 09.-13.07.2007, Leipzig, Germany, No. 279

Publ.-Id: 9673 - Permalink

Diagnostic impact of PET with 18F-FDG, 18F-DOPA and 3-O-methyl-6-[18F]fluoro-DOPA in recurrent or metastatic medullary thyroid carcinoma
Beuthien-Baumann, B.; Strumpf, A.; Zessin, J.; Bredow, J.; Kotzerke, J.;
In patients with medullary thyroid carcinoma (MTC), rising levels of the tumour markers calcitonin and CEA after primary surgery indicate tumour recurrence or metastases. The only chance of cure is the resection of localised tumour tissue. For positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) and 18F-dihydroxyphenylalanine (18F-DOPA), sensitivities of 78% and 63% have been reported, but in a considerable percentage of MTC patients the source of tumour marker elevation is not detected. The aim of this retrospective data evaluation was to compare the value of PET with 18F-FDG, 18F-DOPA and the amino acid tracer 3-O-methyl-6-[18F] fluoro-DOPA (18F-OMFD) in the detection of MTC recurrence.

Fifteen patients with elevated calcitonin were investigated with PET as part of their individual clinical work-up. All patients underwent 18F-FDG PET and 18FDOPA PET, and ten patients underwent 18F-OMFD PET.

With 18F-FDG, seven patients showed foci in the neck, mediastinum, upper abdomen or bone. In seven patients, 18F-DOPA revealed suspicious foci; five of these seven patients showed partially corresponding uptake of 18F-FDG in the neck and mediastinum. Two of these patients underwent surgery and metastases were verified. With 18F-OMFD, a small focus in the liver was suspected in one patient without a correlate on 18F-FDG PET, 18FDOPA PET or conventional imaging.

18F-FDG and 18F-DOPA showed foci that were highly suspicious for local recurrence or metastasis of MTC, although histological verification in these patients with numerous previous surgical interventions was performed in only two patients. The amino acid tracer 18FOMFD had no diagnostic impact in these patients.
Keywords: Medullary thyroid carcinoma . Positron emission tomography . 18F-fluorodeoxyglucose . 18F-DOPA. 3-O-methyl-6-[18F]fluoro-DOPA

Publ.-Id: 9672 - Permalink

Data acquisition system for angle synchronized gamma-ray tomography of rapidly rotating objects
Bieberle, A.; Schleicher, E.; Hampel, U.;
We developed a fast read-out electronics which is used in conjunction with a radiation detector for gamma ray computed tomography. The detector comprises 320 single scintillation detector elements and is operated in pulse counting mode. Digital pulses corresponding to gamma or x-ray absorption events in the scintillation crystals are counted by a counter bank implemented fully parallel in FPGA electronics. The counter data may be read-out at a maximum rate of 5 MHz via micro controller and USB 2.0 interface. This enables to take full projection data within intervals of down to 23 µs which in turn gives the opportunity to produce sharp tomographic slice images of objects rotating with more than 1000 rotations per minute. As an example we demonstrate the reconstruction of the gas distribution in the turbine region of a stirred tank reactor.
Keywords: high-resolution gamma ray tomography, multi-phase flow
  • Measurement Science and Technology 18(2007), MST/248418/PAP/167103

Publ.-Id: 9671 - Permalink

Uranium(VI) complexation studies with selected aromatic acids - a comparison of different spectroscopic techniques
Glorius, M.; Moll, H.; Geipel, G.; Bernhard, G.;
To understand the actinide interaction processes in biological systems on a molecular level it is necessary to explore the complexation behaviour of actinides with selected bioligands of relevant functionalities as model compounds. We used salicylhydroxamic acid (SHA), benzohydroxamic acid (BHA) and benzoic acid (BA) as model compounds for pyoverdins, which are natural bioligands secreted from Pseudomonas ssp. possessing a high potential to bind actinides [1]. The different U(VI) species, MpLqHr, were characterized by UV-vis spectroscopy and laser-induced spectroscopic techniques (TRLFS, fs-TRLFS).
From the UV-vis measurements different coordination modes of uranyl can be postulated [2]. If uranyl is coordinated to hydroxamic acids this results in a blue shift of the absorption maxima in comparison to the bands of the free uranyl ion of app. 25 nm. Whereas in the case of coordination to the carboxylic acid group of benzoic acid, a red shift of the absorption maxima of app. 2.5 nm was observed.
The U(VI)-TRLFS measurements show, that all uranyl ligand species emit no fluorescence light. In all three systems a static quench process of the uranyl fluorescence due to the complex formation was observed.
In the U(VI)-SHA system the stability constant for the 1:1 complex, UO2[HOC6H4CONHO]+, is log β 0111 = 16.33 0.16 and for the 1:2 complex, UO2[HOC6H4CONHO]2, log β 0122 = 33.43 0.11. In the U(VI)-BHA system the stability constants results to log β 0110 = 7.49 0.03 for UO2C6H4CONHO+ and log β 0120 = 15.40 1.15 for UO2[C6H4CONHO]2. In the U(VI)-BA system the stability constant for the 1:1 complex, UO2C6H4COO+, was determined to log β 0110 = 3.02 0.13. All stability constants were averaged from the measurements by UV-vis and TRLFS.
The higher formation constants of uranyl with the aromatic hydroxamate compounds compared to benzoic acid points to the high potential of the pyoverdins to bind and mobilize uranium(VI) in the environment.

[1] M. Bouby, I. Billard, H. J. Maccordick, Czechoslovak. J. Phys. 49, 769-772 (1999).
[2] M. Glorius, H. Moll, G. Bernhard, Complexation of uranium(VI) with aromatic acids in aqueous solution – A comparison of hydroxamic acids and benzoic acid, Radiochimica Acta, in press (2007).

This work was funded by the BMWi under contract number 02E9985.
Keywords: Uranium; aromatic acids; spectroscopy; TRLFS; complexation
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 175-176

Publ.-Id: 9670 - Permalink

3He(alpha,gamma)7Be cross section at low energies
Gyürky, G.; Confortola, F.; Costantini, H.; Formicola, A.; Bemmerer, D.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Laubenstein, M.; Lemut, A.; Limata, B.; Lozza, V.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.;
The flux of 7Be and 8B neutrinos from the Sun and the production of 7Li via primordial nucleosynthesis depend on the rate of the 3He(alpha,gamma)7Be reaction. In extension of a previous study showing cross section data at 127 - 167 keV center of mass energy, the present work reports on a measurement of the 3He(alpha,gamma)7Be cross section at 106 keV performed at Italy's Gran Sasso underground laboratory by the activation method. This energy is closer to the solar Gamow energy than ever reached before. The result is sigma = 0.567 +- 0.029(stat) +- 0.016(syst) nbarn. The data are compared with previous activation studies at high energy, and a recommended S(0) value for all 3He(alpha,gamma)7Be activation studies, including the present work, is given.

Publ.-Id: 9669 - Permalink

g-factor measurements on relativistic isomeric beams produced by fragmentation and U-fission: the g-Rising project at GSI
Neyens, G.; Atanasova, L.; Balabanski, D. L.; Becker, F.; Bednarczyk, P.; Caceres, L.; Doornenbal, P.; Gerl, J.; Gorska, M.; Grebosz, J.; Hass, M.; Ilie, G.; Kurz, N.; Kojouharov, I.; Lozeva, R.; Maj, A.; Pfutzner, M.; Pietri, S.; Podolyak, Z.; Prokopowicz, W.; Saitoh, T. R.; Schaffner, H.; Simpson, G.; Vermeulen, N.; Werner-Malento, E.; Walker, J.; Wollersheim, H. J.; Bazzacco, D.; Benzoni, G.; Blazhev, A.; Blasi, N.; Bracco, A.; Brandau, C.; Camera, F.; Chamoli, S. K.; Chmel, S.; Crespi, F. C. L.; Daugas, J. M.; de Rydt, M.; Detistov, P.; Fahlander, C.; Farnea, E.; Georgiev, G.; Gladnishki, K.; Hoischen, R.; Ionescu-Bujor, M.; Iordachescu, A.; Jolie, J.; Jungclaus, A.; Kmiecik, M.; Krasznahorkay, A.; Kulessa, R.; Lakshmi, S.; Lo Bianco, G.; Mallion, S.; Mazurek, K.; Meczynski, W.; Montanari, D.; Myalsky, S.; Perru, O.; Rudolph, D.; Rusev, G.; Saltarelli, A.; Schwengner, R.; Styczen, J.; Turzo, K.; Valiente-Dobon, J. J.; Wieland, O.; Zieblinski, M.;
Within the RISING (Rare ISotope INvestigations @ GSI) Collabora-tion at GSI, g factor measurements have been performed on isomeric states in neutron-rich isotopes approaching 132 Sn and in the neutron deficient Pb-region (the g-RISING campaign). We present the experimental technique and some typical aspects related to such studies on relativistic beams selected with the FRS fragment separator. First results are presented for the (19/2+ ) 4.5 µs isomeric state in 127 Sn, which has been produced by means of fission of a relativistic 238 U beam on the one hand, and by the fragmentation of a relativistic 136 Xe beam on the other hand. Spin-alignment has been observed in both reactions. It was the first time that spin-alignment has been established in a relativistic fission reaction.
Keywords: Nuclear structure, radioactive beams, g-factor measurements
  • Contribution to proceedings
    Zakopane Conference on Nuclear Physics, 04.-10.10.2006, Zakopane, Poland
    Acta Physica Polonica B 38, 1237-1245

Publ.-Id: 9668 - Permalink

U(VI) sorption on sandstone: Experiments and modeling
Richter, A.; Nebelung, C.; Brendler, V.;
The sorption of U(VI) on natural and synthetic sandstone was investigated in batch sorption experiments (air atmosphere, 0.1M NaClO4, pH 3-11, [U(VI)] 10-9-10-4M. The synthetic sandstone was a mixture of quartz with muscovite and hematite. The surface area (N2-BET) of quartz was 0.047 m2/g, of muscovite 0.88 m2/g, of hematite 0.89 m2/g and of natural sandstone (mainly quartz) 0.69 m2/g.
The pH dependence shows a maximal sorption between pH 5.5-7.5. The U(VI) sorption varied between 95% (10-9M) and 7% (10-4) on natural sandstone, and between 80% (10-9M) and 2% (10-4M) on synthetic sandstone. Fig. 1 shows the comparison of sandstone with pure components (at similar conditions) quartz, muscovite, and hematite. More U(VI) was adsorbed on natural and on synthetic sandstone, than on quartz. The higher sorption are caused by the other components muscovite and hematite, and by the higher surface area.
The linear Freundlich sorption isotherms indicate one binding type. Sorption predicted by the Diffuse Double Layer Model (using the code FITEQL) agreed with the experimental sorption values within their uncertainty.
Keywords: sorption, uranium, sandstone, surface complexation, diffuse double layer model
  • Lecture (Conference)
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 71(2007), A838

Publ.-Id: 9667 - Permalink

Ultra fast electron beam X-ray CT for two-phase flow measurements
Bieberle, M.; Schleicher, E.; Fischer, F.; Hampel, U.; Do Couto Aktay, K. S.; Koch, D.; Menz, H.-J.; Mayer, H.-G.;
Nuclear reactor safety concerns for todays operated light water reactors are closely linked to thermal hydraulic phenomena in the primary and secondary coolant circuits of nuclear systems. To gain an improved understanding of phenomena associated with certain types of accidents as well as for the optimisation of fuel elements regarding the heat transfer in the reactor core simulation tools, such as system codes and more recently CFD codes are frequently applied. However, both types of tools today still exhibit some problems when treating two-phase flow scenarios. Therefore, in recent years much effort has been spent on further code development as well as on validation. This, however, was and is always accompanied by the requirement for reliable measurement data from two-phase flows under typical nuclear thermal hydraulic conditions. Experimental thermal hydraulic facilities, such as the TOPFLOW facility at FZD [1], may provide such data if they are equipped with sophisticated two-phase flow measurement sensors. One example is the wire-mesh sensor [2] that can provide phase and velocity data from steam-water two-phase flows at frame rates of up to 10 kHz and spatial resolution down to 2 mm. Since the wire mesh sensor is intrusive it has some influence on the flow. More appropriate would be tomographic imaging techniques based on either X-ray or gamma rays. However, classical CT systems, though being non-intrusive and sufficiently penetrative even for thicker metallic vessel walls, suffer from low temporal resolution, which is due to the requirement for taking different angular views of an object prior to reconstruction. So far this problem has been considered as intractable and unavoidable and tomographic techniques have almost exclusively been used to measure time averaged quantities, such as the gas hold-up.
We recently suggested [1] a computed tomography (CT) system which uses a fast moving electron beam X-ray source for the application in two-phase flow measurements. We have experimentally shown that frame rates of 10000 images per second can be reached. The static installation of the detector, however, limits the angular range of the source path which leads to so called limited-angle artefacts in the reconstructed images. Although these artefacts cannot be completely eliminated, because they are due to missing data, they can be reduced by maximizing the angular viewing range and by adequate image reconstruction algorithms [4].
Keywords: electron beam x-ray CT, two-phase flow
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
    Proc. Jahrestagung Kerntechnik 2007, CD-ROM plus, 27-30

Publ.-Id: 9666 - Permalink

Gründungsidee und Geschäftskonzept - BIOREM
Raff, J.;
Im Rahmen der zweiten Phase des Businessplan-Wettbewerbs FutureSAX hat es die Geschäftsidee "BIOREM" erneut unter die besten Teams geschafft.
Vor der eigentlichen Prämierung muss die Geschäftsidee und die Marketingstrategie vor der Expertenjury der Branche Bio-/ Nanotechnologie verteidigt werden. Erst nach Prüfung aller Anträge werden die eigentlichen Gewinner gekürt.
  • Lecture (others)
    2. Phase FutureSAX-Businessplan-Wettbewerb, 19.04.2007, Leipzig, Deutschland

Publ.-Id: 9665 - Permalink

Direct Time-of-Flight for Quantitative, Real-Time In-Beam PET: Concept and Feasibility Study
Crespo, P.; Shakirin, G.; Fiedler, F.; Enghardt, W.; Wagner, A.;
We extrapolate the impact of recent detector and scintillator developments, enabling sub-nanosecond coincidence timing resolution t, onto in-beam positron emission tomography (in-beam PET) for monitoring charged-hadron radiation therapy. For t <= 200 ps full width at half maximum, the information given by the time-of-flight (TOF) difference between the two opposing gamma-rays enables shift-variant (fixed dual-head), artifact-free tomograms to be utilized for in-beam PET. We present the corresponding fast, TOF-based and backprojection-free, 3D reconstruction algorithm that, coupled with a real-time data acquisition and a fast detector encoding scheme, allows the sampled beta-plus-activity to be visualized in the object during the course of the irradiation. Despite the very low statistics scenario typical of in-beam PET, real-treatment simulations show that in-beam TOF-PET enables high-precision, quantified images to be obtained in real-time, either with closed-ring or with fixed, dual-head in-beam TOF-PET systems. The latter alleviates greatly the installation of in-beam PET at radiotherapeutic sites.
Keywords: TOF-PET, radiotherapy, proton therapy, ion therapy

Publ.-Id: 9664 - Permalink

On projective Hilbert space structures at exceptional points
Günther, U.; Rotter, I.; Samsonov, B.;
We consider a non-Hermitian complex symmetric 2×2 matrix toy model to study projective Hilbert space structures in the vicinity of exceptional points (EPs). After Puiseux-expanding the bi-orthogonal eigenvectors of a diagonalizable matrix in terms of the root vectors at the EP we resolve the apparent contradiction between the two incompatible normalization conditions with finite and singular behavior in the EP-limit by projectively extending the original Hilbert space. The complementary normalization conditions correspond then to two different affine charts of this enlarged projective Hilbert space. Geometric phase and phase jump behavior are analyzed and the usefulness of the phase rigidity as measure for the distance to EP configurations is demonstrated. Finally, EP-related aspects of PT-symmetrically extended Quantum Mechanics are discussed and the zero limit of the optimal passage time in non-Hermitian quantum brachistochrone problems is identified as an EP-related artifact.
Keywords: exceptional points, branch points, projective Hilbert space, geometric phase, singularities, PT-symmetric Quantum Mechanics, quantum brachistochrone problem
  • Invited lecture (Conferences)
    Many-body open quantum systems: From atomic nuclei to quantum dots, 14.-18.05.2007, Trento, Italy

Publ.-Id: 9663 - Permalink

Projective Hilbert space structures at exceptional points
Günther, U.; Rotter, I.; Samsonov, B.;
A non-Hermitian complex symmetric 2×2 matrix toy model is used to study projective Hilbert space structures in the vicinity of exceptional points (EPs). The bi-orthogonal eigenvectors of a diagonalizable matrix are Puiseux-expanded in terms of the root vectors at the EP. It is shown that the apparent contradiction between the two incompatible normalization conditions with finite and singular behavior in the EP-limit can be resolved by projectively extending the original Hilbert space. The complementary normalization conditions correspond then to two different affine charts of this enlarged projective Hilbert space. Geometric phase and phase jump behavior are analyzed and the usefulness of the phase rigidity as measure for the distance to EP configurations is demonstrated. Finally, EP-related aspects of PT-symmetrically extended Quantum Mechanics are discussed.
Keywords: exceptional points, branch points, projective Hilbert space, geometric phase, singularities, PT-symmetric Quantum Mechanics, quantum brachistochrone problem

Publ.-Id: 9662 - Permalink

L-Type Amino Acid Transporters LAT1 and LAT4 in Cancer: Uptake of 3-O- Methyl-6-18F-Fluoro-L-Dopa (18F-OMFD) in Human Adenocarcinoma and Squamous Cell Carcinoma in vitro and in vivo
Haase, C.; Bergmann, R.; Füchtner, F.; Hoepping, A.; Pietzsch, J.;
Expression of system L amino acid transporters (LAT) is strongly increased in many types of tumor cells. The purpose of this study was to demonstrate that 18F-labeled amino acids, e.g., 3-O-Methyl-6-18F-Fluoro-L-Dopa (18F-OMFD), that were accumulated in tumors via LAT, represent an important class of imaging agents for visualization of tumors in vivo by positron emission tomography (PET).
In the present study 18F-OMFD uptake kinetics, transport inhibition, and the system L mRNA expression were studied in vitro in human adenocarcinoma (HT-29), squamous cell carcinoma (FaDu) cells, macrophages (THP-1) and primary aortic endothelial cells (HAEC), and in vivo in the corresponding mouse tumor xenograft models. Results: It was demonstrated that uptake of 18F-OMFD in all cell lines tested was mediated mainly by the sodium-independent high-capacity LAT. We found an increased uptake in FaDu cells (Vmax 10.6±1.1 nmol/min ´ mg cell protein) and in the corresponding FaDu tumor xenografts in comparison to the other cells and corresponding xenograft models studied. Quantitative mRNA analysis revealed that tumor cells and xenografts have a higher expression of LAT1 compared to HAEC and THP-1 macrophages. However, only in the FaDu tumor model an increased OMFD uptake seems to be explained by increased LAT expression. Furthermore, we demonstrated a high expression for LAT4, a recently new identified system L amino acid transporter.
Our findings support the hypothesis that 18F-OMFD is a tracer for visualization of tumor cells, and, in particular, seems to be a suitable tracer for diagnostic imaging of amino acid transport in poorly differentiated squamous cell head and neck carcinoma with increased LAT1 and LAT4 expression.

Publ.-Id: 9661 - Permalink

Aspects of 6-[18F]fluoro-L-DOPA preparation: Deuterochloroform as a substitute solvent for Freon 11
Füchtner, F.; Zessin, J.; Mäding, P.; Wüst, F.;
Replacement of the ecologically harmful solvent Freon 11 (CFCl3) by chloroform for the module-assisted preparation of 6-[18F]fluoro-L-DOPA based on the electrophilic radiofluorodestannylation of the precursor N-formyl-3,4-di-tert-butoxycarbonyloxy-6-(trimethylstannyl)-L-phenylalanine ethyl ester.

Materials and methods:
The TRACERlab Fx FDOPA module (GE Medical Systems) was used for the preparation of 6-[18F]fluoro-L-DOPA. Cyclotron-produced [18F]F2 gas (5 GBq) was passed through a cooled solution (5°C) of the stannyl precursor (45 mg) in CDCl3 (10 ml). After the [18F]fluorination step, HCl (2 ml, 6 M) was added to the solution. Then the reaction mixture was heated at 80°C for 5 min under vacuum to evaporate the chloroform. The hydrolysis to remove the protecting groups was completed by heating the closed reactor at 130°C for 8 min. After cooling to 20°C the reaction mixture was purified by HPLC with two polymer-based RP columns (PRP 1, 7 μm, 10×250 mm, Hamilton) using a solution of AcOH/AcONa (pH 4.7) as eluent. The [18F]fluoro-L-DOPA fraction was collected and sterile filtrated.

Three types of stabilised chloroform were tested for the radiofluorination of the precursor. Only by use of deuterochloroform stabilised with silver no significant losses of radioactivity were observed. Thus, 6 [18F]fluoro-L-DOPA purified by HPLC was obtained in decay-corrected radiochemical yields of 25±3%, ready for human use.

CDCl3 has proved to be a convenient solvent for the module-assisted preparation of 6-[18F]fluoro-L-DOPA. In this way the use of the polluting Freon 11 can be avoided.
Keywords: 6-[18F]fluoro-L-DOPA, electrophilic radiofluorodestannylation, Freon 11 substitution, deuterochloroform

Publ.-Id: 9660 - Permalink

Multimodal electronic–vibronic spectra of luminescence in ion-implanted silica layers
Fitting, H.-J.; Salh, R.; Schmidt, B.;
Thermally oxidized SiO2 layers of 100 and 500 nm thickness have been implanted by oxygen and sulfur ions with a dose of 3x1016 and 5x1016 ions/cm2, respectively, leading to an atomic dopant fraction of about 4 at.% at the half depth of the SiO2 layers. The cathodoluminescence spectra of oxygen and sulfur implanted SiO2 layers show besides characteristic bands a sharp and intensive multimodal structure beginning in the green region at 500nm over the yellow-red region extending to the near IR measured up to 820 nm. The energy step differences of the sublevels amount on average 120meV and indicate vibration associated electronic states, probably of O2- interstitial molecules, as we could demonstrate by a respective configuration coordinate model.
Keywords: Cathodoluminescence; defect luminescence; vibronic spectra; photonic crystals

Publ.-Id: 9659 - Permalink

Multimodal Luminescence Spectra of Ion-Implanted Silica
Fitting, H.-J.; Salh, R.; Schmidt, B.;
The main luminescence bands in silica SiO2 are the red luminescence R (650 nm, 1.9 eV) of the non-bridging oxygen hole center, and the blue band B (460 nm, 2.7 eV) and ultraviolet luminescence UV (290 nm, 4.3 eV), both commonly related to oxygen-deficient centers. In the present work, we will enhance or replace either the first or second constituent of SiO2, i.e., silicon or oxygen, isoelectronically by additional implantation of the respective ions. Thus, thermally oxidized SiO2 layers have been implanted by different ions of the IV group (C, Si, Ge, Sn, Pb) and of the VI group (O, S, Se) with doses up to 5x1016 cm-2, leading to an atomic dopant fraction of about 4 at % at the half depth of the SiO2 layers. Very surprisingly, the cathodoluminescence spectra of oxygen- and sulfur-implanted SiO 2 layers show, besides the characteristic bands, a sharp and intensive multimodal structure beginning at the green region at 500 nm up to the near infrared. The energy step differences of the sublevels equal on average 120 meV, and indicate vibration associated electronic states, probably of O2- interstitial molecules.
Keywords: Cathodoluminesence, silicon dioxide, ion implantation

Publ.-Id: 9658 - Permalink

Nanosized allotropes of molybdenum disulfide
Enyashin, A. N.; Gemming, S.; Seifert, G.;
The present review provides an overview of the rich polymorphism encountered on different length scales within the very versatile material class of transition metal chalcogenides. On the mesoscopic to nanoscopic scale such compounds exhibit a wide variety of nanostructured allotropes with varying dimensionality and competing internal structure, such as nanorods, nanostripes, nanotubes, fullerene-like particles and fullerenes. On the atomistic scale, competing local atomic arrangements within one type of allotrope determine crucially the stability, the chemical potential, and the electronic properties. Thus, any modeling of such structures can not be restricted to purely classical or quantum-mechanical approaches, but rather the development of classical models on the basis of electronic-structure calculations is required to fully account for all relevant nano- and meso-scale effects. The main part of this review is dedicated to the stability of such nanosystems in relation with the stable size regimes, with their electronic structure, and the derived analysis of the reactivity and application potential.
The calculations explain, why the nano-scale properties of the MoS allotropes can be quite different from the bulk ones, and predict novel effects both within and in addition to the established applications of MoS2 compounds in catalysis, tribology, electronics and electrochemistry.
Keywords: MoS2, nanostructures

Publ.-Id: 9657 - Permalink

Finding polymorphic structures during vicinal surface growth
Radke De Cuba, M.; Emmerich, H.; Gemming, S.;
A hybrid scheme is developed to describe vicinal surface growth during epitaxy on two different time and length scales. For this purpose this algorithm combines two modules based on a continuum and an atomistic approach. The continuum module is realized by a phase-field-model which traces back to the Burton-Cabrera-Frank theory, the atomistic module is based on the anisotropic Ising model which is mapped onto a lattice-gas model. The latter provides thermal density fluctuations resulting in adatom clustering. With increasing temperature the probability for island nucleation on the terraces decreases according to1-p where p is an Arrhenius-type activation probability which prevents clusters from becoming islands. Within this framework it is possible to find the transition from a rough surface at low temperatures to an evenly stepped surface at high temperatures where slight step meandering is observed. Furthermore two competing mechanisms of step bunching are investigated within this algorithm: alternating anisotropic diffusion and different Ehrlich-Schwoebel barriers at the step edges. Step bunching is found on two different time and length scales.
Keywords: self-assembly, patterning, phase-field, Ising, roughening, multi-scale modelling

Publ.-Id: 9656 - Permalink

Modelling Ferroic Functional Elements
Gemming, S.; Luschtinetz, R.; Alsheimer, W.; Seifert, G.; Loppacher, C.; Eng, L. M.;
The present study aims at the modelling of an organic field-effect transistor generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods for the microscopic properties of the surface, the molecules, and the respective interactions are combined with classical modelling on the self-assembly of larger adsorbate arrays on a scale-hopping basis. The structural and electronic characteristics of a realistic, stepped titanate surface as well as the electric field strength above such a surface are modelled quantum-mechanically by a combination of density-functional theory (DFT) and density-functional-based tight-binding (DF-TB). The effect of such fields on the electronic and optical properties of polarizable organic molecules is investigated by the time-dependent analogues of the DFT and DF-TB methods. For the integration of organic components via self-assembly a classical Ising Hamiltonian is developped for the coverage of stepped surfaces with molecules and parametrized on the basis of ab-initio and first-principles data.
Keywords: functional materials, ferroelectric, multi-scale modelling

Publ.-Id: 9655 - Permalink

Simulation and AFM-Measurement Of PTCDA On Ag-supported KBr Films
Loppacher, C.; Zerweck, U.; Eng, L. M.; Gemming, S.; Seifert, G.; Olbrich, C.; Morawetz, K.; Schreiber, M.;
Ordered growth of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on Ag(111) partially covered by one or two monolayers of KBr was investigated by non-contact AFM and Monte-Carlo simulation. PTCDA grows partially ordered on pure Ag(111), smaller PTCDA aggregates occur on the first ML KBr, and large clusters and ordered planar growth are observed on the typical quadratic islands of the second KBr ML. In analogy to KBr covered Cu(111) we conclude that weak silver-bromine bonds are formed. In contrast, for a more weakly interacting substrate such as KBr|Au(111) PTCDA forms single crystals along step edges [1]. The delicate balance of vertical, adsorbate-substrate interactions and lateral, intermolecular ones was investigated by Metropolis-Monte-Carlo (MC) simulations with an extended Ising Hamiltonian on a periodically repeated 2D square lattice [2]. At fixed lateral interactions J12 = J13 the simulation reproduces the experimentally observed cluster formation by varying the adsorbate-substrate interaction H as the substrate changes from Ag(111) to 2 ML KBr|Ag(111): (i) on Ag(111) H dominantes (H >> J) (ii) on 2 ML KBr|Ag(111) J12 and J13 are dominant (J >> H) (iii) on 1 ML KBr|Ag(111) J12, J13, and H are competing (H ~ J) In the simulation the cases (i) and (ii) lead to the observed large and regular clusters, for case (iii) the competition of the different cluster stabilization mechanisms leads to the pinning of many smaller clusters. [1] Kunstmann T., Schlarb A., Fendrich M. et al., Phys. Rev. B, 71 (2005) 121403(R). [2] Loppacher C., Zerweck U., Eng L. M., Gemming S., et al., Nanotechnol., 17 (2006) 1-6.
Keywords: self-assembly, patterning, PTCDA, OLED
  • Poster
    E-MRS 2007 Spring Meeting, 27.05.-01.06.2007, Strasbourg, Frankreich

Publ.-Id: 9654 - Permalink

Theory of DNA-wrapped Carbon Nanotubes
Enyashin, A. N.; Gemming, S.; Seifert, G.;
Carbon nanotubes embedded in single-stranded DNA (CNT@DNA) were investigated by self-consistent density-functional-based tight-binding calculations (DFTB). A phenomenological model for the stability was derived, which gives the CNT-DNA interaction energy as a function of the nanotube radii and the number of DNA chains. Single CNTs are readily complexed by the DNA, but for CNT bundles an essential energy gain is only obtained, if multiple chains wrap around the tubes. Hence, the destruction of the CNT bundles, e.g. by sonication, can promote the CNT@DNA complex formation. Pyrimidine-based homopolymeric DNA more effectively wraps the DNA, whereas purine-based DNA exhibits the larger radius selectivity. The CNT-DNA interaction is not a genuine Van-der-Waals’ interaction. In general, the electronic structure is close to the superposition of the DOS curves of the “free” DNA and CNT fragments, but the most strongly bonding systems are characterized by a number of the mixed electronic states below Fermi level. Hence, magic matching occurs in conjunction with remarkable charge transfer.
Keywords: DNA, carbon nanotubes, nanoelectronics, functional materials
  • Lecture (Conference)
    E-MRS 2007 Spring Meeting, 27.05.-01.06.2007, Strasbourg, France

Publ.-Id: 9653 - Permalink

Molecular scale characterization of speciation of uranium(VI) associated with bacterial strains isolated form extreme habitats
Merroun, M.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.;
This paper deals with the speciation of U(VI) associated with the cells of bacterial strains isolated from extreme habitats. For this propose, a combination of synchrotron-based X-ray absorption spectroscopy (XAS), time-resolved laser-induced fluorescence spectroscopy (TRLFS), transmission electron microscope (TEM) coupled with energy dispersive-X ray (EDX) analysis and electron diffraction were used. XAS analysis indicated that the effect of pH on the local coordination of U in the U-complexes formed by the different bacterial strains is species specific. No structural differences were found between the U complexes formed by three different eco-types of Acidothiobacillus ferrooxidans at pH 2, 3 and 4.5. In contrast, the cells of Bacillus sphaericus JG-B7, Microbacterium oxydans M2, and Sphingomonas sp. S15-S1 precipitate U(VI) as a meta-autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells. At pH 2, the U is coordinated to the organic phosphate groups of the cells of the listed bacteria. Both organic and inorganic uranyl/bacterial complexes were formed at pH 3. TEM/EDX analysis confirms these results and showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees. We applied Iterative Target Test Factor Analysis to determine the uranium speciation at different pH values quantitatively from the EXAFS spectra. Different hypothesis explaining the different coordination chemistry of uranium to bacteria as a function of pH of uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.
  • Lecture (Conference)
    9th Symposium on Bacterial Genetics and Ecology (Bageco 9), 23.-27.06.2007, Wernigerode, Germany

Publ.-Id: 9652 - Permalink

Characterization of a novel Idiomarina loihiensis strain isolated from the westernmost Mediterranean: heavy-metal resistance and biomineralization capability
Gonzalez-Munoz, M.; de Linares, C.; Martinez-Ruiz, F.; Morcillo, F.; Merroun, M.; Arias, J.;
This communication presents the identification of a bacterial strain, MAH1, isolated from a seawater sample collected from the westernmost Mediterranean surface waters. This strain was characterized using polyphasic taxonomy. It is Gram-negative, growing between 2--43 ºC (optimum 28-37 ºC), heterotrophic, aerobic and required NaCl for growth (0.7-20.0%, optimum being 2%). This strain is rod-shaped slightly curved with a single polar flagellum. Results of phylogenetic analyses evidenced that the strain belongs to Idiomarina loihiensis species (Donachie et al., 2003). The strain MAH1 displays a DNA base composition in G+C of the 48.2 mol%. The similarity of the 16S rDNA sequence and of the DNA-DNA hybridization to I. loihiensis (AF288370) is 100% and 96.1% respectively. Polar lipids were predominantly odd-numbered and iso-branched (15 and 17). According to these data we propose that the isolated MAH1 is a strain of the I. loihiensis species.
A preliminary study of the MAH1 strain mineralization capability and heavy metal resistance has also been performed. When the MAH1 strain is cultivated in a sea water solid medium (yeast extract 0.5%, triptone 1%, purified agar-agar 2% in seawater, pH 7.6) produces carbonates and phosphates. On the other hand, the minimal inhibitory concentrations of Ag, Cd, Pb, U, Ni, Cu, Cr, Mn and Zn for the growth of this bacterial strain are (concentration expressed as mM) 0.125, 0.125, 8.00, 8.00, 4.00, 4.00, 1.00, 8.00 and 2.00, respectively.
The obtained results are especially interesting in relation to the Idiomarina genus (Ivanova et al 2000), a member of the family Alteromonadaceae (Ivanova and Mikhailov, 2001) belonging to the subclases of the Proteobacteria.

Donachie, S. P., S. Hou, T. S. Gregory, A. Malahoff, and M. Alam. 2003. Int. J. Syst. Evol. Microbiol. 53:1873-1879
Ivanova, E. P., and V. V. Mikhailov. 2001. Mikrobiologia 70:15-23
Ivanova, E. P., L. A. Romanenko, J. Chun, M. H. Matte, G. R. Matte, V. V. Mikhailov, V. I. Svetashev, A. Huq, T. Maugel, and R. R. Colwell. 2000. Int. J. Syst. Evol. Microbiol. 50:901–907
  • Poster
    9th Symposium on Bacterial Genetics and Ecology (Bageco 9), 23.-27.06.2007, Wernigerode, Germany

Publ.-Id: 9651 - Permalink

Development of a high-speed capacitive surface sensor for fluid distribution imaging
Thiele, S.; Da Silva, M. J.; Hampel, U.;
Experimental investigation of multiphase flows plays an important role in many research and industrial application areas. We introduce a novel surface sensor based on electrical capacitance (permittivity) measurements to imaging near-wall fluid distributions of multiphase flows. The sensor is formed by 32 x 32 interdigitated sensing structures and can be mounted on the edges of a pipe or vessel and thus has a minimal influence on the flow. An associated electronics measures the capacitance of the fluid overlaying each sensing structure in a multiplexed manner. This way, images of the fluid distribution can be achieved directly without the need for any reconstruction procedure. Images at up to 10,000 frames per second can be obtained. The system was evaluated showing good reproducibility and adequate accuracy. The system is able to well distinguish permittivity differences of up to one, which corresponds, for instance, to a two-phase flow of air and oil (rel. permittivity about 2).
Keywords: capacitance measurements, relative permittivity, multiphase flow
  • Contribution to proceedings
    IEEE SENSORS 2007 Conference, 28.-31.10.2007, Atlanta, USA
    Proceedings of the 6th Annual IEEE Conference on Sensors 2007 Atlanta, Stoughton, Wisconsin, USA: The Printing House, Inc., 1-4244-1262-5, 236-239
  • Poster
    IEEE SENSORS 2007 Conference, 28.-31.10.2007, Atlanta, USA

Publ.-Id: 9650 - Permalink

A new wire-mesh tomograph for multiphase flow measurement
Da Silva, M. J.; Schleicher, E.; Hampel, U.;
We have developed and tested a new wire-mesh tomograph based on capacitance measurements, which may now be used for the investigation of non-conducting fluids. It can at the moment acquire up to 625 frames per second. For the experimental measurements we have employed a 16 x 16 laboratory wire-mesh sensor. The evaluation of the wire-mesh tomograph prototype has shown good reproducibility and accuracy in capacitance measurements, thus allowing the system to be employed in the investigation of a wide range of substances even with close relative permittivity values, such as for air and oil. Furthermore, time resolved measurements of different flow patterns for oil-air mixtures have been performed.
Keywords: capacitance measurement, multiphase flow, relative permittivity
  • Contribution to proceedings
    Multi-Phase Flow: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Germany
    Proceedings of FZR & ANSYS Multiphase Flow Workshop
  • Lecture (Conference)
    Multi-Phase Flow: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Germany

Publ.-Id: 9649 - Permalink

TRLFS: Analysing Spectra with an Expectation-Maximization (EM) Algorithm
Steinborn, A.; Taut, S.; Brendler, V.; Geipel, G.; Flach, B.;
A new approach for fitting statistical models to time-resolved laser-induced fluorescence spectroscopy (TRLFS) spectra is presented. Such spectra result from counting emitted photons in defined intervals. Any photon can be described by emission time and wavelength as observable attributes and by component and peak affiliation as hidden ones. Understanding the attribute values of the emitted photons as drawn from a probability density distribution, the model estimation problem can be described as a statistical problem with incomplete data. To solve the maximum likelihood task, an expectation maximization (EM) algorithm is derived and tested. In contrast to the well known least squares method, the advantage of the new approach is the ability to decompose the spectrum into its components and peaks using the revealed hidden attributes of the photons. The simultaneous detection of temporal and spectral model parameters provides a mutually consistent description of TRLFS spectra. Theoretical aspects were investigated using simulated spectra and the applicability in practice is illustrated by spectra originating from uranyl species.
Keywords: Time-resolved laser-induced fluorescence spectroscopy, expectation maximization
  • Spectrochimica Acta Part A 71(2008)4, 1425-1432

Publ.-Id: 9648 - Permalink

95 MeV neutron scattering on hydrogen, deuterium, carbon, and oxygen
Mermod, P.; Blomgren, J.; Johansson, C.; Ohrn, A.; Osterlund, M.; Pomp, S.; Bergenwall, B.; Klug, J.; Nilsson, L.; Olsson, N.; Tippawan, U.; Nadel-Turonski, P.; Jonsson, O.; Prokofiev, A.; Renberg, P.; Maeda, Y.; Sakai, H.; Tamii, A.; Amos, K.; Crespo, R.; Moro, A.;
Three neutron-deuteron scattering experiments at 95 MeV have been performed recently at The Svedberg Laboratory in Uppsala. Subsets of the results of these experiments have been reported in two short articles, showing clear evidence for three-nucleon force effects. In this paper, we present a more detailed description of the experimental methods as well as further discussion of the results. In addition to neutron-deuteron scattering data, neutron-proton and C-12(n,n) elastic scattering data have been measured for normalization purposes, and O-16(n,n) data have been obtained for the first time at this energy.
It was possible to extract C-12(n,n(')) and O-16(n,n(')) inelastic scattering cross sections to excited states below 12 MeV excitation energy. The inelastic scattering data (for both carbon and oxygen) are shown to have a significant impact on the determination of nuclear recoil kerma coefficients.

Publ.-Id: 9647 - Permalink

Dynamics of Molten Salt Reactors
Krepel, J.; Grundmann, U.; Rohde, U.; Weiss, F.-P.;
Dynamics of the Molten Salt Reactor, one of the 'Generation IV International Forum' concepts, was studied in this paper. The graphite-moderated channel type MSR was selected for the numerical simulation. The MSR represents a liquid fueled reactor with very specific dynamics because of two physical peculiarities: the delayed neutrons precursors are drifted by the fuel flow and the fission energy is immediately released directly into the coolant. Presently, there are not many accessible numerical codes appropriate for the MSR simulation, therefore the DYN1D-MSR and DYN3D-MSR codes were developed based on the Light Water Reactor dynamics code DYN3D. It allows calculating of full 3D transient neutronics in combination with parallel channel type thermal-hydraulics. The codes were validated on experimental results of Molten Salt Reactor Experiment from Oak Ridge National Laboratory and applied to several transients typical for the liquid fuel system. Those transients were initiated by reactivity insertion, by overcooled or overfueled fuel slug, by the fuel pump start-up or coast-down, or by the blockage of single fuel channels. In these considered transients, the response of the MSR is characterized by the immediate change of the fuel temperature according to the power level. This causes fast feedback reactivity insertion, which is negative in the case of power increase. On the other hand, the graphite response is slower and its feedback coefficient is in some cases positive. The addition of erbium to the graphite can ensure the negative feedback and inherent safety features. The DYN1D-MSR and DYN3D-MSR codes have been shown as an effective tools for MSR dynamics studies.
Keywords: Molten Salt, Reactor, Dynamics, MSR, MSRE, MSBR.
  • Nuclear Technology 164(2008), 34-44

Publ.-Id: 9645 - Permalink

Switchable two-color electroluminescence based on a Si metal-oxide-semiconductor structure doped with Eu
Prucnal, S.; Sun, J. M.; Skorupa, W.; Helm, M.;
A Si metal-oxide-semiconductor (MOS) electroluminescent device structure is reported which emits two colors, while being doped with a single rare-earth element. Thermally grown SiO2 oxide layers were implanted with Eu and subseqently annealed. Depending on the electrical excitation current, the luminescence is red or blue, which can be ascribed to electronic transitions in tri- and di-valent europium (Eu3+ and Eu2+), respectively.
Keywords: electroluminescence, rare earth, Si MOS, light emitter

Publ.-Id: 9644 - Permalink

Coherent structure eduction from PIV data of an electromagnetically forced separated flow
Weier, T.; Cierpka, C.; Gerbeth, G.;
Periodic addition of momentum by wall–parallel electromagnetic forces has a strong influence on the separated region of a stalled airfoil. As in the case of periodic blowing and suction, actuation frequency and momentum input are the main factors of influence. However, the control authority depends as well on the actuation wave form. This latter aspect is investigated in the present paper by means of time resolved particle image velocimetry data from the suction side of an inclined flat plate. The control effect is rated by the size of the remaining recirculation region in the time averaged flow fields. The controlled flow possesses typically a small number of relatively large vortices, which are believed to be related to the control mechanism. Consequently, the time resolved flow fields have been analyzed by proper orthogonal decomposition and continuous wavelet transform to extract dominant features of the flow.
Keywords: active flow control, proper orthogonal decomposition, continuous wavelet transform, waveform, coherent structures
  • Lecture (Conference)
    IUTAM Symposium on Unsteady Separated Flows and Their Control, 18.-22.06.2007, Korfu, Greece
  • Contribution to proceedings
    IUTAM Symposium on Unsteady Separated Flows and Their Control, 18.-22.06.2007, Korfu, Greece
    IUTAM Symposium on Unsteady Separated Flows and their Control
  • Journal of Fluids and Structure 24(2008), 1339-1348
    DOI: 10.1016/j.jfluidstructs.2008.06.005

Publ.-Id: 9643 - Permalink

Complex formation between UO2+2 and CO2-3: Studied by laser-inducted photoacoustic spectroscopy (LIPAS)
Geipel, G.; Bernhard, G.; Brendler, V.; Nitsche, H.;
wird nachgereicht
  • Radiochimica Acta 82(1998), 59-62

Publ.-Id: 9642 - Permalink

PT-symmetric Quantum Mechanics, the hydrodynamic Squire equation and UV-IR-duality
Günther, U.; Stefani, F.; Znojil, M.;
Some facts about the spectrum of a PT-symmetric quantum mechanical (PTSQM) toy model with potential V(x)=Gx2(ix)ν in a box x∈[-L,L] are presented for the parameter region ν∈[-2,0]. The corresponding Hamiltonian is selfadjoint in an appropriately chosen Krein space and for ν=-1 the spectral problem maps into that of the hydrodynamic Squire equation. It is shown that in the limit L→∞ a spectral singularity occurs and that the PTSQM ⇄ Squire mapping can be interpreted as a special type of strong-coupling ⇄ weak-coupling (UV-IR) duality. Finally, the system behavior in the vicinity of a spectral triple point is sketched.
partially based on:
J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.
Keywords: PT-symmetric Quantum Mechanics, Krein space, spectral analysis, spectral triple point, UV-IR duality
  • Lecture (Conference)
    International conference "Modern Analysis and Applications (MAA 2007)" dedicated to the centenary of Mark Krein, 09.-14.04.2007, Odessa, Ukraine

Publ.-Id: 9641 - Permalink

On the observation of vacuum birefringence
Heinzl, T.; Liesfeld, B.; Amthor, K.; Schwoerer, H.; Sauerbrey, R.; Wipf, A.;
We suggest an experiment to observe vacuum birefringence induced by intense laser fields. A high-intensity laser pulse is focused to ultra-relativistic intensity and polarizes the vacuum which then acts like a birefringent medium. The latter is probed by a linearly polarized X-ray pulse. We calculate the resulting ellipticity signal within strong-field QED assuming Gaussian beams. The laser technology required for detecting the signal will be available within the next three years.
  • Optics Communications 267(2006)2, 318-321

Publ.-Id: 9640 - Permalink

Self-induced transparency assisted by electromagnetically induced transparency
Nazarkin, A.; Netz, R.; Sauerbrey, R.;
We show the possibility of transparency and soliton effects for an intense pulse propagating in a V-type medium in which two upper resonant sublevels experience fast field-induced decay due to incoherent coupling to an upper lying state or continuum. The transparency arises as a result of the combined action of population trapping on the sublevels leading to interference suppression of the relaxation channel, and coherent Rabi cycling induced by the laser field.
  • Physical Review A 7404(2006)4, 1806

Publ.-Id: 9639 - Permalink

Fingerprinting of a thin secondary mineral film on DU
Baumann, N.; Arnold, T.; Foerstendorf, H.; Read, D.; Black, S.; Massanek, A.;
Discs of depleted uranium (DU), obtained from a British pristine military tank shell were used in our experiments. One sample was placed in a solution containing 2.5 • 10−3 M Ca(NO3)2 and 1.05 • 10−3 M (NH4)3PO4. After a contact time of 360 days the sample was taken out of the solution. IR- and TRLFS measurements were made on the surface of the sample. The spectra obtained were compared with those of natural uranium minerals, formed under oxidising weathering conditions. Comparison of the IR-spectra from the DU surface with those of the reference minerals revealed that the newly formed secondary mineral on DU is a uranium (VI) phosphate. Further identification of the respective uranium phosphate mineral was not possible with IR. However, a comparison between the TRLFS spectra of the newly formed unknown uranium phase on the DU disc with well-known TRLFS spectra of uranium reference compounds clearly showed the presence of meta-autunite.
Keywords: depleted uranium, IR, TRLFS, uranium minerals
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 71(2007)15S, A66-A66
  • Poster
    Goldschmidt 2007, 20.-24.08.2007, Köln, Germany

Publ.-Id: 9638 - Permalink

Influence of humic colloids on the migration of U(VI) in compacted clay
Mibus, J.; Sachs, S.;
Clay minerals and organic substances are widespread components of many soils, sediments, and rocks. As humic acids (HA) possess a strong ability for metal complexation, they can influence the migration of radioactive and toxic metal ions in clayey environments. However, the migration behavior of humic colloids and its impact on the actinide migration in clay formations is poorly understood.
Former studies discuss the influence of HA on the radionuclide migration in clays controversially. Wold and Eriksen [1] reported the diffusion of humic colloids through compacted bentonite without strong physical hindrance mobilizing metal ions. In contrast, Wang et al. [2] found a significant immobilization of Eu(III) by humic substances. Maes et al. [3] stressed the reversibility of the interaction between radionuclide, organic matter, and clay. The competition of the adsorbents for radionuclides is kinetic and determines their distribution between mobile and immobile phase.
In the present study we investigated the diffusion behavior of humic colloids in compacted clay as a function of compaction and pH. The impact on the uranium transport was studied by comparing the uranium diffusion in absence and presence of HA.
The migration of HA in clay is governed by diffusion. It is influenced by the colloidal behavior of HA. At higher clay bulk densities, size fractionation affects the diffusion parameters. In presence of HA colloids U(VI) is immobilized in association with HA near the high concentration boundary.
The German Federal Ministry of Economics and Technology funded this study under contract 02E9673. The technical assistance of Ch. Müller is gratefully acknowledged.
[1] Wold, S., Eriksen, T.E. (2005) Proceedings of the 2nd International Symposium Clays in natural and engineered barriers for radioactive waste confinement. Tours, France, 14-18 March 2005, 547.
[2] Wang, X. et al. (2005) Adsorption Science and Technology, 23, 801-811.
[3] Maes, N. et al. (2004) Report SCK•CEN-BLG-988. SCK•CEN, Mol, Belgium.
[4] Sachs, S. et al. (2004) Report FZR-399, FZ Rossendorf, Dresden, Germany.
[5] Lead, et al. (2000) Environ. Sci. Technol. 34, 1365-1369.
  • Contribution to proceedings
    3rd International Meeting "Clays in natural and engineered barriers for radioactive waste confinement", 17.-20.09.2007, Lille, France
    Clays in Natural & Engineered Barriers for Radioactive Waste Confinement, 467-468
  • Poster
    3rd International Meeting "Clays in natural and engineered barriers for radioactive waste confinement", 17.-20.09.2007, Lille, France

Publ.-Id: 9637 - Permalink

CFD application in nuclear engineering/industy
Höhne, T.; Krepper, E.; Weiss, F. P.; Stosic, Z.; Salnikova, T.;
The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors. The reason for the increased use of multidimensional CFD methods is that a number of important phenomena such as pressurized thermal shocks, boron mixing, and thermal striping cannot be predicted by traditional one dimensional system codes with the required accuracy and spatial resolution.

CFD codes contain empirical models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in NRS applications. The necessary validation is performed by comparing model results against trustworthy data. However, in order to obtain a reliable model assessment, CFD simulations for validation purposes must satisfy strict quality criteria. For instance, numerical errors caused by too coarse numerical grids should be separated from shortcomings of the physical models to avoid wrong conclusions about model performance.

CFD simulations are shown with an emphasis on validation in areas such as: heat transfer, buoyancy, multi-phase flows, natural circulation, free-surface flows, turbulent mixing, and complex geometries. These topics are related to NRS-relevant issues such as: pressurized thermal shocks, boron dilution, hydrogen distribution, induced breaks, subcooled boiling, thermal striping, etc.
Keywords: Nuclear Engineering, CFD, Coolant Mixing, pressurized thermal shocks, boron dilution, hydrogen distribution, induced breaks, subcooled boiling
  • Invited lecture (Conferences)
    15th International Conference on Nuclear Engineering, 22.-26.04.2007, Nagoya, Japan

Publ.-Id: 9636 - Permalink

Density Functional Theory - Investigations of Vanadium Silicides
Thieme, M.; Gemming, S.;
Vanadium and silicon form several binary compounds; the most well characterized structures have the compositions V:Si= 3:1, 6:5, 5:3, 1:2. Density-functional band-structure calculations with a plane-wave basis for the valence electrons and norm-conserving pseudopotentials for the core-valence interaction have been carried out to investigate the structural properties and the phase stability for the experimentally known binary crystals. As the early transition metal silicides belong to the class of refractory materials, also the elastic properties were determined. It is furthermore shown that the electronic properties of the compounds depend strongly on the composition.
  • Poster
    DPG-Frühjahrstagung Regensburg, 27.03.2007, Regensburg, Deutschland

Publ.-Id: 9635 - Permalink

Tripodal polyamines as anion receptors: Extraction and structural studies
Wenzel, M.; Antonioli, B.; Gloe, K.; Gloe, K.; Sanchez, M. G.; Bernhard, G.; Bray, D. J.; Clegg, J. K.; Lindoy, L. F.;
Tripodal polyamines based on the tris(2-aminoethyl)amine (tren) platform are useful complexing agents for cations or anions depending on the pH of the solution.[1,2] The binding properties of such compounds can be tuned by the addition of aromatic binding groups to the molecule.
A series of different substituted tren (1-4) derivatives were synthesised and characterised.
Here we present some recent solvent extraction and liquid membrane transport results that show a gradation in anion binding behaviour along I-, Cl-, Br-, CrO4
2-, SO4
2- and PO4
Finally, structural aspects of the anion complexes formed will be discussed, with the X-ray structure of the bromide complex of ligand 3 being presented.
[1] A.G. Blackman, Polyhedron, 2005, 24, 1-39
[2] K. Wichmann, B. Antonioli, T. Söhnel, M. Wenzel, K. Gloe, K. Gloe, J.R. Price, L. F.
Lindoy, A.J. Blake, M. Schröder, Coord. Chem. Rev., 2006, 250, 2987-3003
  • Contribution to proceedings
    ISMSC 2007, 2nd International Symposium on Macrocyclic and Supramolecular Chemistry, 24.-28.06.2007, Salice Therme (Pavia), Italy

Publ.-Id: 9634 - Permalink

Cation and anion binding studies of a large N,O-donor macrocycle: Single ion extraction and synergistic enhancement
Wenzel, M.; Gloe, K.; Gloe, K.; Bernhard, G.; Clegg, J. K.; Ji, X.-K.; Lindoy, L. F.;
Mixed N,O-donor macrocycles have been shown to result in interesting complexation properties towards both cations and anions (the latter on protonation of the macrocycle's nitrogen functions).[1-3]
In the present study the phase transfer properties of 1 toward selected transition metal ions and anions have been evaluated by liquid-liquid extraction studies under different pH conditions. The order of increasing extraction follows the Irving-Williams series Co(II) < Ni(II) < Cu(II) > Zn(II), while the anion extraction is contolled by the Hofmeister series. A synergistic enhancement of metal extraction was obtained on exploiting a dual host strategy [4] in which the tripodal thiourea host 2 was incorporated in the system. In this case atypical anti-Hofmeister behaviour was obtained in which significant metal extraction of chloride or sulfate was observed from solution.
[1] N.A. Bailey, D. E. Fenton, S.J. Kitchen, T.H. Lilley, M.G. Williams, P.A. Tasker, A.J.
Leong and L.F. Lindoy, J. Chem. Soc. Dalton Trans., 1991, 627-637.
[2] H. Adams, N.A. Bailey, D.E. Fenton, I.G. Ford, S.J. Kitchen, M.G. Williams, P.A.
Tasker, A.J. Leong and L.F. Lindoy, J. Chem. Soc. Dalton Trans., 1991,1665-1674.
[3] L. Tušek-Božić, A. Višnjevac, E. Marotta, B. Kojić-Prodic, Polyhedron 24, 2005, 97–
[4] K. Kavallieratos, R.A. Sachleben, G.J. Van Berkel and B.A. Moyer, Chem. Commun.,
2000, 187-188.
  • Contribution to proceedings
    ISMSC 2007, 2nd International Symposium on Macrocyclic and Supramolecular Chemistry, 24.-28.06.2007, Salice Therme (Pavia), Italy

Publ.-Id: 9633 - Permalink

Bacterial responses to uranyl and sodium nitrate treatments and fate of the added U(VI) in uranium mining waste piles
Geissler, A.; Merroun, M.; Geipel, G.; Reuther, H.; Selenska-Pobell, S.;
The responses of the bacterial community of a uranium mining waste pile to increased concentrations of uranyl or sodium nitrate were studied in microcosm experiments under conditions corresponding to the natural. For this study, the 16S rRNA (Fig. 1) and the narG-gene retrievals were applied. Both retrievals demonstrated that at the early stages of the treatments with sodium nitrate a strong activation of nitrate reducing and denitrifying populations, mainly of Firmicutes and Betaproteobacteria, occurred; they had overgrown the Acidobacteria, Alpha-, and Deltaproteobacteria which originally predominated in the untreated samples. Due to the U(VI) toxicity only a few populations of the mentioned Firmicutes and betaproteobacterial nitrate reducers proliferated in the samples treated with uranyl nitrate. More significant for these samples was the stimulation of the gammaproteobacterial denitrifyers, able to effectively interact with the added uranium. After longer incubations both treatments resulted in an establishment of betaproteobacterial populations and also of populations characteristic for the original, non-treated sample. As measured by using Mössbauer spectroscopy, at these stages a strong reduction of Fe(III) to Fe(II) occurred in the samples. Time-resolved laser fluorescence spectroscopic analyses demonstrated that most of the added U(VI) was bound in uranyl-hydro-phosphate phases or was complexed by organic phosphate groups (Fig. 2). The phosphate groups were liberated by different kinds of bacteria due to the activity of their intrinsic acidic phosphatases or were supplied by the lysed cells of the dead parts of the numerically reduced populations. The latter was confirmed by X-ray structural analyses of the formed bacteria - uranium complexes in the studied samples. Our results demonstrate that bacteria in uranium mining waste piles possess a high potential to deal with increased, toxic concentrations of U(VI) and nitrate, which usually co-contaminate these environments.
  • Lecture (Conference)
    9th Symposium on Bacterial Genetics and Ecology (BAGECO 9), 23.-27.06.2007, Wernigerode, Germany

Publ.-Id: 9632 - Permalink

Bestimmung der Eigenfrequenzen von Brennelementen
Altstadt, E.;
Mit Hilfe eines Finite Elemente Modells werden Eigenfrequenzen und Schwingungsformen eines DWR- Brennelements berechnet. Der Einfluss von Kontakt mit benachbarten Brennelementen wird untersucht. Der Bericht ist nicht öffentlich verfügbar (Industrieauftrag).
Keywords: Finite Element Model, Modal Analysis, Pressurized Water Reactor, Fuel Element Vibrations
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    14 Seiten

Publ.-Id: 9631 - Permalink

Cluster Core Controlled Reactions of Substitution of Terminal Bromide Ligands by Triphenylphosphine in Octahedral Rhenium Chalcobromide Complexes
Shestopalov, M. A.; Brylev, K. A.; Kozlova, S. G.; Fedorov, V. E.; Spies, H.; Pietzsch, H.-J.; Stephan, H.; Geipel, G.; Bernhard, G.;
Reactions of rhenium chalcobromides Cs4[{Re63-S)8}Br6].2H2O, Cs3[{Re63-Se)8}Br6].2H2O, Cs3[{Re63-Q)73-Br)}Br6].H2O (Q) S, Se), and K2[{Re63-S)63-Br)2}Br6] with molten triphenylphosphine (PPh3) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh3 ligands with general formula [{Re63-Q)8-n3-Br)n}(PPh3)4-nBrn+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, 31P{1H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh3 ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re6Q8-nBrn}n+2. In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q8-nBrn] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re6Q8}(PPh3)4Br2] and fac-[{Re6Se7Br}(PPh3)3Br3] (Q ) S, Se) have been investigated in CH2Cl2 solution and the broad emission spectra in the range of 600-850 nm were observed.
  • Journal of the American Chemical Society 129(2007), 3714-3721

Publ.-Id: 9630 - Permalink

Beta decay of 101 Sn
Kavatsyuk, O.; Mazzocchi, C.; Janas, Z.; Banu, A.; Batist, L.; Becker, F.; Blazhev, A.; Brüchle, W.; Döring, J.; Faestermann, T.; Gorska, M.; Grawe, H.; Jungclaus, A.; Karny, M.; Kavatsyuk, M.; Klepper, O.; Kirchner, R.; La Commara, M.; Miernik, K.; Mukha, I.; Plettner, C.; Plochocki, A.; Roeckl, E.; Romoli, M.; Rykaczewski, K.; Schädel, M.; Schmidt, K.; Schwengner, R.; Zylicz, J.;
The decay of the very neutron-deficient isotope 101 Sn was studied at the GSI on-line massseparator using silicon detectors for recording charged particles and germanium detectors for gamma-ray spectroscopy. Based on the beta-delayed proton data the production cross-section of 101 Sn in the 50 Cr+58 Ni fusion-evaporation reaction was determined to be about 60 nb. The half-life of 101 Sn was measured to be 1.9±0.3 s. For the first time beta-delayed gamma rays of 101 Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065 keV transitions in 101 In. The results are discussed by comparing them to predictions obtained from shell-model calculations employing a new interaction in the 88Sr to 132Sn model space.
Keywords: Nuclear energy levels, Beta decay, double beta decay, electron capture, Lifetimes

Publ.-Id: 9629 - Permalink

Cluster dynamics simulation of reactor pressure vessel steels under irradiation
Gokhman, A.; Bergner, F.; Ulbricht, A.; Birkenheuer, U.;
The distance between irradiated features (precipitates, clusters and atmospheres) exceeds significantly the size of them in neutron irradiated reactor pressure vessel (RPV) steels. Therefore, cluster dynamics (CD) that originally has been suggested for small clusters and that can be applied to any ideal gas of clusters is found to be very effective to investigate the long-term behavior of the neutron stimulated changes of the microstructure of RPV steels.
In the present paper CD simulation have been carried out for model iron alloys with small and high copper content as well as for VVER 1000 steels R16, R17 and D under neutron irradiation. For this case CD simulations are needed for two sets of input parameters. The first one relates to the description of the local material damage at the cascade stage when the local temperature increases to the melting point and then decreases to a temperature of about 300°C over a time of some ps and CD is not applicable. The cascade stage is investigated by molecular dynamics (MD) and kinetic lattice Monte-Carlo (KLMC) methods that provide the data on the neutron cascade efficiency, rate of the vacancies (interstitials) that form the clusters, the planar or spherical or another shape of clusters, content and distribution of them by size at the end of cascade stage. The second set of input parameters contains the energy of formation and energy of migration, pre-exponential factor of diffusivity for vacancy and interstitial, copper, manganese, silicon and other alloying elements in iron; recombination radius for pair vacancy-interstitial; dislocation density, capture efficiency of vacancies (interstitials) by dislocations, surface tension for boundary between cluster and iron matrix; binding energy dependence on cluster size; lattice parameters of iron and precipitates. Some of these characteristics are well-known with some accuracy from the experiment and can be considered as materials constants for RPV steels.
It was found that the coupling between copper rich precipitates (CRP) and point defects in neutron irradiated iron alloys and VVER steels can be investigated by CD simulations using LSODA code as a solver of the stiff ordinary differential equations system. The additional consideration of the strain energy effect on CRP kinetics as well as the application of the regular solution model for the case of different fixed copper contents of CRP improves quantitatively the simulation results for considered model alloys. The additional accounting of the Ni effect in CD simulation is needed to study the kinetics in the investigated VVER steels under irradiation.
Keywords: cluster dynamics, reactor pressure vessel steels, neutron irradaition
  • Lecture (Conference)
    4th International Workshop "Diffusion and Diffusional Phase Transformations in Alloys" DIFTRANS-2007, 16.-21.07.2007, Sofiyivka (Uman), Cherkasy region, Ukraine
  • Defect and Diffusion Forum 277(2008), 75-80
  • Contribution to proceedings
    4th International Workshop "Diffusion and Diffusional Phase Transformations in Alloys" DIFTRANS-2007, 16.-21.07.2007, Sofiyivka (Uman), Cherkasy region, Ukraine
    Proceedings of the 4th International Workshop "Diffusion and Diffusional Phase Transformations in Alloys", 75-76

Publ.-Id: 9628 - Permalink

Three-dimensional thermal-hydraulics analysis of ROCOM mixing experiment by RELAP5-3D© code
Frisani, A.; Del Nevo, A.; D’Auria, F.; Höhne, T.; Kliem, S.; Rohde, U.;
The mixing phenomenon is relevant for the normal and off normal operation of the Nuclear Power Plant (NPP), because it influences the safety, mitigating the reactivity and structural consequences. The study of these issues was investigated performing experimental campaigns in large-scale test facilities and in real NPPs. In this framework ROCOM (Rossendorf Coolant Mixing Model) test facility was built with the purpose of investigating the coolant mixing phenomena occurring in the Reactor Pressure Vessel (RPV) of a Pressurizer Water Reactor (PWR). The experiments executed in this facility provide experimental data for code validation (CFD and TH-SYS codes). The purpose of this work is to address the capability of the RELAP5-3D© to reproduce ROCOM facility dynamic in simulating the mixing for a large range of operational and accident conditions. In particular, the attention is focused on the effects in the vessel downcomer, lower plenum and core inlet. Three experiments were selected for the analyses: two steady states and one transient. The ROCOM steady states are slug mixing experiments that analyze the mixing scalar trend inside the facility at different mass flow rates. The ROCOM transient represents the injection of a mixing scalar slug from one cold leg with an increasing mass flow rate in the same loop. A systematic comparison between ROCOM experimental data and the results of the simulations with the RELAP5-3D© is presented including a complete set of sensitivity analyses to find out the most relevant parameters which influence the results from nodalization and user effects points of view.
Keywords: Mixing, RELAP5-3D©, ROCOM facility, code assessment
  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
    CD-ROM, paper 159

Publ.-Id: 9626 - Permalink

Begleitende Untersuchungen zur Pilotierung eines Verfahrens zur elektrochemischen Aufbereitung saurer Wässer aus Tagebaurestseen (Zwischenbericht)
Kryk, H.; Schubert, M.; Hessel, G.;
Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    86 Seiten

Publ.-Id: 9623 - Permalink

Experimental determination of the boron concentration distribution in the primary circuit of a PWR after a postulated cold leg small break loss-of-coolant-accident with cold leg safety injection
Kliem, S.; Prasser, H.-M.; Sühnel, T.; Weiss, F.-P.; Hansen, A.;
It is known that under-borated coolant can accumulate in the loops and that it can be transported towards the reactor core during a loss of coolant accident. Therefore, the mixing of weakly borated water inside the reactor pressure vessel was investigated using the ROCOM test facility. Wire mesh sensors based on electrical conductivity measurement are used to measure in detail the spreading of a tracer solution in the facility. The mixing in the downcomer was observed with a measuring grid of 64 azimuthal and 32 vertical positions. The resulting distribution of the boron concentration at the core inlet was measured with a sensor integrated into the lower core support plate providing one measurement position at the entry into each fuel assembly.
The boundary conditions for this mixing experiment are taken from an experiment at the thermal hydraulic test facility PKL operated by AREVA Germany. The slugs, which have a lower density, accumulate in the upper part of the downcomer after entering the vessel. The ECC water injected into the reactor pressure vessel falls almost straight down through this weakly borated water layer and accelerates as it drops over the height of the downcomer. On the outer sides of the ECC streak, lower borated coolant admixes and flows together with the ECC water downwards. This has been found to be the only mechanism of transporting the lower borated water into the lower plenum. In the core inlet plane, a reduced boron concentration is detected only in the outer reaches of the core inlet. The minimum instantaneous boron concentration that was measured at a single fuel element inlet was found to be 66.3 % of the initial 2500 ppm.

Publ.-Id: 9622 - Permalink

Investigation on thin films of new substituted quarterthiophene films of new substituted quarterthiophene
Zelenetskaya, K.; Jähne, E.; Adler, H.-J.; Loppacher, C.; Eng, L.; Grenzer, J.; Scholz, A.;
alpha,beta-dicyano substituted beta, beta*-dibutylquarterthiophene (DCNDButQT) was synthesized and fully characterized by 1H-NMR and 13C-NMR, elemental analysis, UV-visible spectroscopy, DSC, TGA and cyclic voltammetry. The band gap energy (deltaEg) calculated from cyclic voltammetry data was found to be 1.97 eV, which is in the range of semiconductor materials (deltaEg < 3.0 eV). DCNDButQT was deposited on different substrates (Al2O3, SiO2, TiO2) by vacuum deposition and solution-cast methods. The structure of the thin films analysed by AFM and XRD showed different morphology depending on cast method. The spin-coating and drop-casting films showed amorphous structure, whereas the vacuum-deposition films exhibit a fine crystalline structure. AFM of vacuum-deposition film revealed the formation of well-ordered terrace structures, the step between adjacent terraces is about 1.5 nm.
Keywords: organic semiconductors
  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany

Publ.-Id: 9621 - Permalink

Ion-induced surface ripples in silicon
Biermanns, A.; Grenzer, J.; Facsko, S.; Grigorian, S.; Pietsch, U.;
The morphological evolution of surfaces during ion-beam irradiation has attracted a significant interest due to possibility of the development and the controlling of selforganization in nanostructures. Pattering and texture on nanometer length scale at metal and semiconductor surfaces has become a topic of intense research. In particular the surface and subsurface ripple formation under 40Ar+ ion-beam irradiation of Si (100) crystal has been studied recently. Strong ripple formation has been found for an irradiation energy of 60keV and incident angles around 60degree. During implantation a corrugated surface layer is formed, consisting of a strongly damaged, amorphous near-surface layer followed by a nearly sinusoidal shaped interface towards the crystalline material. In the present work, we investigate the onset and evolution of ripple-formation as function of implantation energy and incidence angle of the ion beam.
Keywords: ion beam induced rippling
  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany

Publ.-Id: 9620 - Permalink

Glycoxidised LDL isolated from subjects with impaired glucose tolerance increases CD36 and peroxisome proliferator-activator receptor gamma gene expression in macrophages
Graessler, J.; Pietzsch, J.; Westendorf, T.; Julius, U.; Bornstein, S. R.; Kopprasch, S.;
Aims/hypothesis: Glycoxidized low density lipoprotein (LDL) has been implicated in the pathogenesis of atherosclerosis, one of the major diabetic complications. Since atherogenesis may occur early at the onset of diabetes, we investigated whether circulating LDL isolated from subjects with impaired glucose tolerance (n=20, IGT-LDL) showed an increased glycoxidation status and explored their proatherogenic effects on macrophages.
Methods/Results: Using gas chromatography/mass spectrometry we could demonstrate a 3- to 5-fold higher oxidative apolipoprotein B-100 proline, arginine, lysine, and tyrosine modification as compared to LDL obtained from subjects with normal glucose tolerance (n=20, NGT-LDL). Moreover, LDL glycoxidation estimated by both N Epsilon-(carboxymethyl)lysine (CML) and N Epsilon-(carboxyethyl)lysine (CEL) residues was increased more than 9-fold in IGT-LDL when compared to NGT-LDL. After one hour incubation of murine macrophages with LDL mRNA expression rates of the scavenger receptors CD36 and SR-BI and transcription factor PPAR Gamma were quantified by reverse-transcription real-time PCR. In comparison to NGT-LDL, IGT-LDL elicited a significantly higher CD36 (p<0.05) and PPAR Gamma (p<0.05) gene expression, whereas SR-BI mRNA expression was not affected.
Conclusion: These data suggest that impaired glucose tolerance is associated with increased glycoxidation of circulating LDL that might contribute to conversion of macrophages into a proatherogenic phenotype.

Publ.-Id: 9619 - Permalink

Forward and inverse problems in MHD: numerical and experimental results
Stefani, F.; Gailitis, A.; Gerbeth, G.; Gundrum, T.; Xu, M.;
When a conducting fluid comes under the influence of a magnetic field, electrical currents are induced that give rise to a modification of this magnetic field. The ratio of induced magnetic field to applied magnetic field is characterized by the magnetic Reynolds number Rm of the flow. For large Rm, even self-excitation of a magnetic field can occur. This hydromagnetic dynamo effect is responsible for the maintenance of the magnetic fields of planets, stars and galaxies. In the present paper, we delineate some recent developments in the numerical treatment of induction effects in arbitrary geometry, and their application for dynamo experiments as well as for a Contactless Inductive Flow Tomography (CIFT).

Publ.-Id: 9618 - Permalink

Mechanical and tribological properties of carbon and nitrogen consecutive ion implantation into aluminium
Szcancoski, J. C.; Foerster, C. E.; Serbena, F. C.; Fitz, T.; Kreissig, U.; Richter, E.; Möller, W.; Lepienski, C. M.; Soares, P. C.; Siqueira, C. J.;
Mechanical and tribological properties of successive C and N ion implantation into Al were studied in the present work. Ion sequence, substrate temperature and subsequent thermal treatment were performed in order to understand the involved mechanisms on the surface hardening. The results showed that independent of the ion sequence, a higher surface hardness is obtained for room temperature ion implantation (≈ 10 GPa). At high substrate temperature the hardness decreases to 7 GPa. The hardening mechanisms are discussed in terms of: solid solution, hard embedded precipitates in the soft Al matrix and the damage produced by the ion implantation process. Adhesive and abrasive regimes are identified from the friction coefficient profiles and are function of the ion implantation parameters. Wear resistance is improved if subsequent thermal treatment at high temperature is performed. Wear improvement is correlated to the presence of a high concentration of carbon clusters in the Al matrix.
Keywords: Mechanical properties; Nanoindentation; Carburising; Nitriding; Aluminium; Wear
  • Surface & Coatings Technology 201(2006)3-4, 1488-1494

Publ.-Id: 9616 - Permalink

Investigation of K+ meson production in C+C collisions at 2A GEV with HADES
Sadovsky, A.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-464 2007


Publ.-Id: 9615 - Permalink

Annual Report 2006 - Institute of Radiochemistry
Bernhard, G.; Foerstendorf, H.; Richter, A.; Viehweger, K.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-459 2007


Publ.-Id: 9614 - Permalink

Effects of irradiation damage on the back-scattering of electrons: silicon-implanted silicon
Nasdala, L.; Kronz, A.; Grambole, D.; Trullenque, G.;
Radiation damage in an (initially crystalline) silicon wafer was generated by microbeam implantation with 600 keV Si+ ions (fluence 5 x 1014 ions/cm²). To produce micro-areas with different degrees of damage, 14 implantations at different temperatures (between 23 and 225 °C) were done. The structural state of irradiated areas was characterized using Raman spectroscopy and electron back-scatter diffraction. All irradiated areas showed strong structural damage in surficial regions (estimated depth <1 μm), and at implant substrate temperatures of below 130 °C, the treatment has caused complete amorphization. Back-scattered electron (BSE) images exhibited that observed BSE intensities correlate with the degree of irradiation damage; all irradiated areas were higher in BSE than the surrounding host. Because there were no variations in the chemical composition and, with that, no Z contrast in our sample, this observation again supports the hypothesis that structural radiation damage may strongly affect BSE images of solids.
Keywords: Back-scattered electron images, Raman spectroscopy, electron back-scatter diffraction, radiation damage, silicon
  • American Mineralogist 92(2007), 1768-1771

Publ.-Id: 9613 - Permalink

Gammatomographie zur Messung von Voidverteilungen im SWR-Bündel am KATHY-Versuchsstand in Karlstein Abschlussbericht 2007
Bieberle, A.; Hampel, U.; Hoppe, D.;
Dieser Bericht beinhaltet insbesondere diejenigen durchgeführten Arbeiten und Untersuchungen, welche für die Planung zukünftiger Experimente am KATHY - Versuchsstand relevant sind. Der Bericht unterteilt sich in zwei voneinander weitgehend unabhängige Teile, zum einen die technische Weiterentwicklung des Tomographen (Abschnitt 2) und zum anderen methodisch orientierte Studien und Experimente (Abschnitt 3) betreffend. Konzeptionell basiert der Bericht auf Auswertungen der an KATHY im Oktober 2005 und Januar 2006 durchgeführten Experimente, wobei diese Auswertungen hier nicht noch einmal in ihrer Gesamtheit dargelegt werden, sondern nur auf ihre zukünftig relevanten Aspekte Bezug genommen wird.
Keywords: gamma tomography, determination of void distribution
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    45 Seiten

Publ.-Id: 9612 - Permalink

Numerical simulation of coolant mixing in a pressurized water reactor with different CFD methods based on complex meshes
Höhne, T.;
The work was aimed at the numerical simulation of coolant mixing in the downcomer and the lower plenum of the Rossendorf test facility ROCOM. ROCOM is a 1:5 scaled Plexiglas model of a German pressurized water reactor allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-codes CFX-4 and CFX-5. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. The comparison of a very detailed mesh (CFX-5) and a mesh with simplifications and additional physical models (CFX-4) showed, that in the referred case the use of these models are allowed. For turbulent flows CFX-4 and CFX-5 were validated in accordance with the Best Practice Guidelines and can be used in the reactor safety analysis. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.
Keywords: Boron Dilution, CFD, Pressurized Water Reactor, Coolant Mixing

Publ.-Id: 9611 - Permalink

Complexation of uranium(VI) with aromatic acids such as hydroxamic and benzoic acid investigated by TRLFS
Glorius, M.; Moll, H.; Geipel, G.; Bernhard, G.;
The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We observed in all three systems a decrease in the fluorescence intensity with increasing ligand concentration. All identified complexed uranyl species are of the type MpLqHr. In the uranium(VI)-salicylhydroxamate system a 1:1 complex with a stability constant of log β111 = 17.34 ± 0.06 and a 1:2 complex with a stability constant of log β122 = 35.0 ± 0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be log β110 = 7.92 ± 0.11 and log β120 = 16.88 ± 0.49. In the uranium(VI)-benzoate system only a 1:1 complex is existent with a stability constant of log β110 = 3.56 ± 0.05.
Keywords: Uranyl; Hydroxamic acid; Spectroscopy; TRLFS; Complexation
  • Journal of Radioanalytical and Nuclear Chemistry 277(2008)2, 371-377

Publ.-Id: 9610 - Permalink

Ferromagnetism in GaN induced by Fe ion implantation
Talut, G.; Reuther, H.; Stromberg, F.; Zhou, S.; Potzger, K.; Eichhorn, F.;
We report about magnetic and structural studies on p-type GaN implanted with 57Fe with fuences from 1*10^16cm^-2 to 1.6*10^17cm^-2 at different temperatures and subsequently subjected to thermal treatment. X-ray diffraction, transmission electron microscopy, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometry were used for the crystallographic, electronic and magnetic characterization of the samples. Room temperature ferromagnetism was observed in GaN after implantation at 623 K with different fluences and is mainly ascribed to alpha-Fe precipitations. An additional contribution to ferromagnetic signal is observed in a Mössbauer spectrum and as a magnetization loop in SQUID in sample implanted with lowest fluence at 623 K which cannot be related to alpha-Fe. In samples implanted with low fluences at RT no ferromagnetism was observed by means of SQUID. However, in CEMS a 6.8 T magnetic hyperfine field was used to fit the experimental spectrum and is discussed in terms of possible origin. Samples implanted at 240 K do not exhibit ferromagnetic properties. Precipitation of alpha-Fe was successfully reduced by decreasing the implantation temperature, however this was accompanied by an enhanced crystal damage. Annealing between 973 K and 1123 K resulted in most cases predominantly in the formation of alpha-Fe-clusters. Thermal treatment brought no significant recover of the crystallinity as it was verified by RBS channeling measurements.
Keywords: Diluted magnetic semiconductor, GaN, ferromagnetism, Fe
  • Journal of Applied Physics 102(2007), 083909
  • Poster
    Nanospintronic Design and Realization 2007, 21.-25.05.2007, Dresden, Germany
  • Poster
    International Conference on the Applications of the Mössbauer Effect, 14.-19.10.2007, Kanpur, India

Publ.-Id: 9609 - Permalink

Charakterisierung des Opalinus-Tones und erste Ergebnisse zur U(VI)-Komplexierung mit Huminsäure-Modellliganden
Joseph, C.;
Eine homogenisierte Probe Opalinus-Ton wurde charakterisiert. Die erhaltenen Ergebnisse (CEC, BET, TOC, XRD, IR) stimmen mit denen in der Literatur beschriebenen Ergebnissen überein. Erste Untersuchungen der U(VI)-Komplexierung mit HS-Modellliganden wurden durchgeführt.
Keywords: Opalinus clay, characterization, U(VI)-complexation, HA
  • Lecture (others)
    Workshop des Verbundprojektes Wechselwirkung und Transport von Actiniden im natuerlichen Tongestein unter Beruecksichtigung von Huminstoffen und Tonorganika, 02.-03.04.2007, Potsdam, Deutschland

Publ.-Id: 9608 - Permalink

Measurement of Mg-25(p, gamma)Al-26(g) resonance strengths via accelerator mass spectrometry
Arazi, A.; Faestermann, T.; Niello, J.; Knie, K.; Korschinek, G.; Poutivtsev, M.; Richter, E.; Rugel, G.; Wallner, A.;
The strengths of resonances located at center-of-mass energies of E-c.m.=189, 304, 374, and 418 keV for the Mg-25(p,gamma) reaction have been measured for the first time with an off-line method: Mg targets were firstly activated with protons at the resonance energies and the produced Al-26(g) nuclei were counted by means of highly sensitive accelerator mass spectrometry (AMS). Thus, the production of Al-26 in its ground state is determined independently from the gamma-decay branching ratio. While the 304, 374, and 418 keV resonances show fair agreement with previous measurements, the 189 keV resonance yield a significantly less strength. In addition, an experimental upper limit for the E-c.m.=92 keV resonance was determined.
  • Physical Review C 7402(2006)2, 5802

Publ.-Id: 9607 - Permalink

Superconducting regions and Kondo effect of MgB2 formed by implantation of magnesium ions into boron substrate
Trybula, Z.; Kempinska, W.; Andrzejewski, B.; Piekara-Sady, L.; Kaszynski, J.; Trybula, M.; Piekoszewski, J.; Stanislawski, J.; Barlak, M.; Richter, E.;
The results of investigation of the polycrystalline boron implanted by magnesium and argon plasma pulse treatment are presented. The four-probe electric conductivity measurements and magnetically modulated microwave absorption showed the presence of superconducting islands below the temperature of 25 K. Below T = 23 K we detected the Kondo effect, a logarithmic increase in the resistivity as the temperature is lowered, due to iron impurity.
  • Open Access LogoActa Physica Polonica A 109(2006)4-5, 657-660

Publ.-Id: 9606 - Permalink

Einfluss von HS auf die U(VI)- und Am(III) Sorption an Kaolinit: TRLFS Untersuchungen
Krepelova, A.;
We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.
Laser fluorescence spectroscopy measurements were carried out in the systems Am(III)-kaolinite and Am(III)-HA-kaolinite to study the surface complexes of Am(III) on kaolinite at different pH values (pH 5 - 8). HA decreases the fluorescence intensity of the samples. The shape of the measured fluorescence spectra in both systems, binary and ternary, differs from the spectrum observed in the solution. Further measurements are required to satisfactorily explain the obtained results.
Keywords: Sorption, kaolinite, HA, Am(III), U(VI), TRLFS
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlilchen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 02.-03.04.07, Potsdam, Deutschland

Publ.-Id: 9605 - Permalink

Modeling of a Buoyancy-Driven Flow experiment in Pressurized Water Reactors using CFD-Methods
Höhne, T.; Kliem, S.;
The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the downcomer of a Pressurised Water Reactor (PWR) was analyzed at the ROssendorf COolant Mixing (ROCOM) test facility. ROCOM is a 1:5 scaled model of a German PWR, and has been designed for coolant mixing studies. It is equipped with advanced instrumentation, which delivers high-resolution information for temperature or Boron concentration fields. This paper presents ROCOM experiments in which water with higher density was injected into a cold leg of the reactor model. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the upper and lower part of the downcomer. An experiment with 5 % of the design flow rate in one loop and 10 % density difference between the ECC and loop water was selected for validation of the CFD software ANSYS CFX. A mesh with two million control volumes was used for the calculations. The effects of turbulence on the mean flow were modelled with a Reynolds stress turbulence model. The results of the experiment and of the numerical calculations show that mixing is dominated by buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation. The ECC water falls in an almost vertical path and reaches the lower down¬comer sen¬sor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWRs. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.
Keywords: Safety, Thermalhydraulics, Coolant Mixing, CFD
  • Open Access LogoNuclear Engineering and Technology 39(2007)4, 327-336

Publ.-Id: 9604 - Permalink

P implantation into pre-amorphized germanium and subsequent annealing: solid phase epitaxial regrowth, P diffusion and activation
Posselt, M.; Schmidt, B.; Anwand, W.; Grötzschel, R.; Heera, V.; Wündisch, C.; Skorupa, W.; Hortenbach, H.; Gennaro, S.; Bersani, M.; Giubertoni, D.; Möller, A.; Bracht, H.;
High fluence P implantation (30 keV, 3x1015 cm-2) into pre-amorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. In contrast to previous assumptions a significant P diffusion in amorphous Ge is not observed. However, during the fast solid phase epitaxial regrowth a rapid redistribution of P occurs. After completion of the regrowth and at temperatures above 500 0C, a concentration-dependent diffusion of P in crystalline Ge takes place. An appreciable influence of implantation defects on the diffusion coefficient of P cannot be found. For 60 s rapid thermal annealing at 600 0C and for 20 ms flash lamp annealing at 900 0C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ohm , respectively, and the maximum electrical activation of P is about 3 – 7x1019 cm-3.
Keywords: germanium implantation annealing doping
  • Contribution to proceedings
    International Workshop on INSIGHT in Semiconductor Device Fabrication, Metrology and Modeling (INSIGHT-2007), 06.-09.05.2007, Napa, United States
    Proceeding INSIGHT-2007 Workshop, 309-315
  • Lecture (Conference)
    International Workshop on INSIGHT in Semiconductor Device Fabrication, Metrology and Modeling (INSIGHT-2007), 06.-09.05.2007, Napa, United States

Publ.-Id: 9603 - Permalink

Experiments on the interface dynamics of stratified air/water flows
Vallee, C.;
For the investigation of co-current two-phase flows, the Horizontal Air/Water Channel (HAWAC) was built at Forschungszentrum Dresden-Rossendorf. A special inlet device provides well-defined as well as variable boundary conditions for generic horizontal two-phase flow experiments. Optical measurements were performed with a high-speed video camera during slug flow. By an interface capture method, the water level can be measured in any observed cross-section. As a result, the water level history can be extracted from the image sequences. Furthermore, the profiles of the time-averaged water level bounded by the standard deviation were presented and show the evolution of the flow structure and of its dynamic component along the channel.
Keywords: horizontal two-phase flow, slug flow, image processing
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
    Jahrestagung Kerntechnik 2007 - Fachsitzung, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft, 23-26
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany

Publ.-Id: 9602 - Permalink

Synthesis report on work package 2.1: Pressurized Thermal Shock (PTS) - T0+24
Lucas, D.;
This report summarizes the results of the first 24 months period of the NURESIM project for the work package 2.1 “Pressurized Thermal Shock (PTS)”. It mainly bases on the deliverables supplied by the partners involved in this work package. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the contributions are sorted according to these flow situations. The relation of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The present status PTS work package is in agreement with the planning of the NURESIM project, the expected results were met by the deliverables. The work done leads to an improvement of the simulation capabilities regarding a PTS flow situation, but caused by the complexity of the issue it will still be a long way to enable reliable predictions for the whole process from such simulations.
Keywords: PTS, CFD, Two-Phase Flow
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    27 Seiten

Publ.-Id: 9601 - Permalink

On the simulation of two-phase flow pressurized thermal shock (PTS)
Lucas, D.; Bestion, D.; Bodèle, E.; Scheuerer, M.; F. D’Auria, D. M.; Smith, B.; Tiselj, I.; Martin, A.; Lakehal, D.; Seynhaeve, J.-M.; Kyrki-Rajamäki, R.; Ilvonen, M.; Macek, J.;
This paper reports some activity about the Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. The PTS phenomenon is expected to take place in some water cooled nuclear reactors equipped with pressure vessels during selected accident scenarios. The PTS implies the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. Current generation Pressurized Water Reactors, PWR (including the Russian VVER types), are primarily affected by the phenomenon which is investigated within three broad areas: material damage originated by irradiation, thermal-hydraulics (including single and two-phase flow conditions in the region of the ‘shock’) and structural mechanics with main reference to fracture mechanics. The present paper, in the area of thermal-hydraulics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. Within the above context, the paper summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase mechanisms (or sub-phenomena) are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance (case of two phase flow) is presently not available.
Keywords: PTS, Two-Phase Flow, CFD
  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, paper [035], 30.09.-04.10.2007, Pittsburgh, Pennsylvania, United States
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, Pennsylvania, United States

Publ.-Id: 9600 - Permalink

CFD Modellierung in der Sicherheitstechnik - Möglichkeiten und Grenzen
Prasser, H.-M.; Frank, T.; Höhne, T.; Lucas, D.;
Die CFD Modellierung hat Einzug gehalten in die nukleare Sicherheit. CFD-Codes werden erfolgreich eingesetzt, um komplexe Strömungsfelder in ganzen Druckwasserreaktoren zu berechnen. Dabei geht es vornehmlich um die Vermischung von Borsäure bei mit unboriertem Wasser und von kalten Notkühlwasser mit heißem Reaktorkühlmittel. Die Validierung anhand von Versuchen an verhätnismässig grossskaligen Testständen, die mit hochauflösender Leitfähigkeitsmesstechnik ausgestattet sind, zeigt die bereits erreichte hohe Zuverlässigkeit der Vorhersagen im Einphasenbereich. Diese Erkenntnisse können auf chemisch-verfahrenstechnische Anlagen übertragen werden. Beim Übergang zur Zweiphasenströmung treten zusätzliche Schwierigkeiten auf, die mit der Beschreibung der Prozesse an der Phasengrenze und der Modellierung der Topologie und Ausdehnung derselben zusammenhängen. Hierzu werden neuere Entwicklungen auf dem Gebiet der Zweifluidmodelle für Gas-Flüssigkeitsströmungen vorgestellt. Speziell handelt es sich um das Inhomogeneous MUSIG Model, das Bestandteil des Codes ANSYS CFX ist. Dieser Ansatz erlaubt die Beschreibung der Wechselwirkung mehrerer Blasenklassen unter Berücksichtigung der auf die Blasen wirkenden Kräfte und von Koaleszenz und Zerfall. Das Modell wurde ausgehend von Experimenten an vertikalen Rohrleitungen vorgeschlagen und dann anhand von Messergebnissen validiert. Auch hier kommen Leitfähigkeitssensoren zum Einsatz, die die Struktur der Phasengrenzfläche im gesamten Strömungsquerschnitt hochaufgelöst erfassen. Dabei wurden u.a. Strömungen mit Phasenübergang infolge Kondensation von Dampf an einer unterkühlten Flüssigphase untersucht. Mit solchen Gittersensoren wurden auch komplexe dreidimensionale Gas-Flüssigkeitsströmungen, z.T. bei Drücken bis zu 70 bar und Temperaturen bis 286 °C (Wasser-Dampf) vermessen, die charakteristische Merkmale von Strömungen in technisch relevanten Anlagenteilen aufweisen, wie Strömungsabriss, Staupunkte, Strahlausbildung, Rezirkulationsgebiete u.ä.. Der Vergleich zwischen Rechnungen und Experiment dokumentiert den erreichten Stand bei der dreidimensionalen Modellierung. Durch die Diskretisierung der zu untersuchenden Geometrie ist der CFD-Code in der Lage, die Einzelmodelle auch Geometrien zu übertragen, die bei der Validierung nicht betrachtetet wurden. Dies wird anhand von Rechenergebnissen für Sicherheitsventile demonstriert.
Keywords: CFD, Leitfähigkeitsmesstechnik, MUSIG
  • Lecture (Conference)
    ProcessNet-Jahrestagung 2007, 16.-18.10.2007, Aachen, Deutschland

Publ.-Id: 9599 - Permalink

R&D on RPC with CBM
Dohrmann, F.; Kotte, R.; Naumann, L.; Stach, D.; Sytcheva, A.; Wüstenfeld, J.;
The talk summarizes the latest tests and results w.r.t. MRPCs with silicate glass resistive plates. These
have been tested in a high flux environment with a continous electron beam at ELBE.
  • Lecture (Conference)
    9. Collaboration Meeting of the CBM Experiment at FAIR, 27.02.-02.03.2007, Darmstadt, Germany

Publ.-Id: 9598 - Permalink

Dielectron detection capabilities of HADES at SIS100/300
Bannier, B.;
The HADES experiment at SIS18 at GSI/Darmstadt is a dedicated experiment for studying medium modifications of hadrons, i.e. the light vector mesons rho, omega and phi, in pA, piA and AA collisions. Specifically, dileptonic decays of these vector mesons provide an direct probe for the properties of hadronic matter at high nuclear densities. The future FAIR facility at GSI/Darmstadt with SIS100/300 will provide heavy-ion beams with energies of up to 45 AGeV. It is planned to operate the HADES detector at these higher energies. In this work the principle possibilities of detecting dielectrons with an unmodified HADES detector are studied. Simulations of dielectron production for several beam energies have been performed using the UrQMDv1.3p1 transport code together with the PLUTO++ phase space generator. Future measurements of dileptons with HADES at FAIR are shown to be within reach of the current setup.
  • Lecture (Conference)
    Gießen 07 - DPG Frühjahrstagung, Hadronen und Kerne, 12.-16.03.2007, Giessen, Germany

Publ.-Id: 9597 - Permalink

Properties of Multigap RPC detectors tested with continuous electron beams at ELBE
Dohrmann, F.; Kotte, R.; Naumann, L.; Stach, D.; Sytcheva, A.; Wüstenfeld, J.;
Multigap Resistive Plate Chambers (MRPC) provide the possibility for assembling high-granularity, large-area TOF sytems designed for modern nuclear and particle physics experiments. Currently, experiments like ALICE, STAR, FOPI, HADES prepare MRCP based TOF systems with time resolutions of less than 100 ps. The planned CBM experiment at the future FAIR facility at GSI/Darmstadt considers using an MRPC system provided sufficient time resolution and rate stability can be achieved. These properties of MRCP have been successfully demonstrated in prototype tests performed at the FZD electron linac ELBE, using continuous e− beams of 20-40 MeV. Typical time resolutions of 70 ps were achieved. The rate capabilities of MRCP using special low-resistive silicate glas were tested and stable efficiencies up to rates of 20 kHz/cm2 were observed.
  • Lecture (Conference)
    Gießen 07 - DPG Frühjahrstagung 2007, Hadronen und Kerne, 12.-16.03.2007, Giessen, Germany

Publ.-Id: 9596 - Permalink

Ion beam synthesis of 4H-(Si1-xC1-y)Gex+y solid solutions
Pezoldt, J.; Kups, T.; Voelskow, M.; Skorupa, W.;
4H silicon carbide (Si1-xC1-y)Gex+y solid solutions with an average Ge incorporation on lattice sites ranging from 0.7 to 2.5 percent were formed by ion beam synthesis. RBS and RBS/C investigations revealed a decreasing Ge lattice incorporation with increasing implantation dose above 10%. The carried out rapid thermal annealing at 1300 °C reduces the residual damage, increases the lattice site occupation and led to negligible change in the concentration profiles.
Keywords: silicon carbide, germanium implantation, rapid thermal annealing, RBS

Publ.-Id: 9595 - Permalink

DYN3D/ATHLET calculations of a boron dilution transient during natural circulation conditions
Kliem, S.; Rohde, U.;
Slugs of under-borated, or even boron-free, coolant can be formed in the primary circuit during different accident scenarios, e. g. due to a malfunction of the chemical and volume control system, or due to an SBLOCA with partial failure of the safety injection system. An unintentional, or even unavoidable, decrease of boron concentration in the reactor core leads to a reactivity increase and may result in a power excursion, a so-called boron dilution transient. Whether re-criticality of the scrammed reactor occurs, and how high the power peak is, depends among other factors, in a sensitive manner, on the mixing of the too weakly borated water with the ambient coolant in the downcomer and the lower plenum on its way to the core. For an adequate simulation of such boron dilution transients, 3D neutron kinetic core models coupled with advanced thermal hydraulic system codes are necessary. Such analyses should be completed by a simulation of the above mentioned coolant mixing processes inside the reactor pressure vessel.

An earlier developed fast running semi-analytical coolant mixing model has been recently extended to natural circulation conditions. A parameter study, incorporating stationary and transient core calculations, was carried out for a hypothetical boron dilution event in a pressurized water reactor during the operation of the residual heat removal system, using the coupled 3D neutron kinetics/thermal hydraulics code system DYN3D/ATHLET in combination with this coolant mixing model. According to the boundary conditions, this analysis is carried out at atmospheric pressure conditions and a coolant temperature of 25 °C. By varying the initial slug volume, it was found in stationary calculations that, for the given core configuration, slugs of less than 6 m³ do not lead to re-criticality. Transient core calculations from 8 to the maximum initial slug volume of 15 m3 show a significant reactivity insertion and over-criticality. The resulting power excursion is mitigated and stopped by Doppler and moderator density feedback. The power increase in all calculations is accompanied by significant coolant boiling in single channels. It should be pointed out, that the thermal hydraulics simulations at low pressure are quite challenging because of the high density difference between water and steam and therefore, high sensitivity of void fraction versus coolant enthalpy. Although in all calculations local coolant boiling occurs over several tenths of seconds, the integrity of the fuel is always ensured according to the calculation results.
Keywords: boron dilution, natural circulation, neutron kinetics/thermal hydraulics coupling, coolant boiling
  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, United States
    Proceedings of the 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, CDROM, paper 053, 0894480588
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, United States

Publ.-Id: 9594 - Permalink

Dilepton production in pp and CC collisions with HADES
Fröhlich, I.; Agakichiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munziger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Duran, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hadjivasiliou, C.; Heilmann, M.; 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.; Krizek, F.; Krücken, R.; Kugler, A.; Kühn, W.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, S.; Lopez, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Palka, M.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Senger, P.; Shileev, K.; Simon, R. S.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniovski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.;
e+e- production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2 GeV kinetic energy, the exclusive η production and the Dalitz decay η -> γe+e- have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e+e- invariant-mass spectrum from the 12C +12C reaction at 2 AGeV is presented and compared with a simplified thermal model.

Publ.-Id: 9593 - Permalink

Nickel nanoparticle catalysed formation of fullerene like carbon nanostructures - a Raman analysis
Krause, M.; Abrasonis, G.; Kolitsch, A.; Mücklich, A.; Möller, W.;
The catalytic effect of nickel nanoparticles on the formation and on the structure of fullerene-like carbon nanostructures prepared by ion beam sputtering at different temperatures was studied by wavelength dependent Raman spectroscopy. Compared to nickel-free reference films the formation of carbon nanostructures is enhanced in the whole range of deposition temperatures from 25°C =< T (°C) <= 500°C. Several phases characterized by different ratios of amorphous and graphite-like carbon, a different film transparency, and a different elastic Raman background intensity, were observed. Amorphous carbon structures are preferentially formed at lower deposition temperatures, whereas graphitic structures are dominant for higher growth temperatures. Based on data for different excitation wavelengths and using difference spectroscopy, a quantitative model for the composition of these nanostructured carbon materials is developed. The results are in full agreement with those obtained by TEM, XANES and XRD analysis.[1] The model might be used as well for the analysis of other pure carbon or carbon based composite materials like CN and BCN films.
[1] G. Abrasonis, A. Mücklich, K. Küpper, M. Krause, U. Kreissig, A. Kolitsch, W. Möller, K. Sedlackova, G. Radnoczi, R. Torres, and I. Jimenez, "Morphology and bonding structure of fullerene-like nanocomposite C:Ni (~30 at%.) thin films grown by ion beam sputtering", to be presented on XXI. IWEPNM, Kirchberg, 2007
Keywords: Carbon films, Nanocomposites, Nickel catalysis, Raman
  • Poster
    XXIst International Winterschool Molecular Nanostructures, 10.-17.03.2007, Kirchberg, Österreich

Publ.-Id: 9591 - Permalink

Superposition of quantum and classical rotational motions in Sc2C2@C84 fullerite
Michel, K. H.; Verberck, B.; Hulman, M.; Kuzmany, H.; Krause, M.;
The superposition of the quantum rotational motion (tunneling) of the encapsulated Sc2C2 complex with the classical rotational motion of the surrounding C84 molecule in a powder crystal of Sc2C2@C84 fullerite is investigated by theory. Since the quantum rotor is dragged along by the C84 molecule, any detection method which couples to the quantum rotor (in casu the C2 bond of the Sc2C2 complex) also probes the thermally excited classical motion (uniaxial rotational diffusion and stochastic meroaxial jumps) of the surrounding fullerene. The dynamic rotation-rotation response functions in frequency space are obtained as convolutions of quantum and classical dynamic correlation functions. The corresponding Raman scattering laws are derived, and the overall shape of the spectra and the width of the resonance lines are studied as functions of temperature. The results of the theory are confronted with experimental low-frequency Raman spectra on powder crystals of Sc2C2@C84 [M. Krause et al., Phys. Rev. Lett. 93, 137403 (2004)]. The agreement of theory with experiment is very satisfactory in a broad temperature range.
Keywords: Fullerenes, Quantum Rotation

Publ.-Id: 9590 - Permalink

Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact
Gu, Q. L.; Ling, C. C.; Chen, X. D.; Cheng, C. K.; Ng, A. M. C.; Beling, C. D.; S. Fung, S.; DjurišIć, A. B.; Brauer, G.; Ong, H. C.;
Conversion of the Au/n-ZnO contact from Ohmic to rectifying with H2O2 pretreatment was studied systematically using I-V measurements, x-ray photoemission spectroscopy, positron annihilation spectroscopy, and deep level transient spectroscopy. H2O2 treatment did not affect the carbon surface contamination or the EC–0.31 eV deep level, but it resulted in a significant decrease of the surface OH contamination and the formation of vacancy-type defects (Zn vacancy or vacancy cluster) close to the surface. The formation of a rectifying contact can be attributed to the reduced conductivity of the surface region due to the removal of OH and the formation of vacancy-type defects.
  • Applied Physics Letters 90(2007), 122101

Publ.-Id: 9589 - Permalink

Dresden pulsed magnetic field facility
Wosnitza, J.; Bianchi, A. D.; Freudenberger, J.; Haase, J.; Herrmannsdörfer, T.; Kozlova, N.; Schultz, L.; Skourski, Y.; Zherlitsyn, S.; Zvyagin, S. A.;
We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71T with a pulse duration of about 100 ms have been designed, constructed, and tested. A two-coil 100 T magnet and a long-pulse (1000 ms) 60T magnet are under construction. Electrical transport and magnetization experiments are running routinely in the pilot laboratory at the IFW Dresden. The feasibility of NMR experiments in pulsed-field environments has been proven.
  • Journal of Magnetism and Magnetic Materials 310(2007), 2728-2730

Publ.-Id: 9588 - Permalink

Magnetism of the single molecule magnet system [(MnIIL2)3MnII](BF4)2
Prinz, M.; Voget, S.; Damnik, N.; Raekers, M.; Kuepper, K.; Chaudhuri, P.; George, S.; Coldea, M.; Neumann, M.;
The single molecule magnet system [(MnIIL2)3MnII](BF4)2 containing four Mn2+ ions has been studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XMCD). The XPS Mn 2p and Mn 3s spectra confirm the manganese 2+ valency. From XMCD measurements at a temperature of T = 2 K and a magnetic field of B = 5 T we obtained a high magnetic moment of 12 μB/f.u. This spin moment agrees in an excellent way with magnetic measurements which show a magnetization saturation of 10 μB/f.u. at 7 T and 2 K. From XMCD a quenching of the Mn orbital moments was observed (morb = 0.4 μB/f.u.).
Keywords: Molecular magnetism, Mn2+ complex, x-ray magnetic circular dischroism
  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des AKF, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9587 - Permalink

Investigation of high-k materials RScO3 (R=Sm,Gd,Dy) by XPS and band structure calculations
Raekers, M.; Bartkowski, S.; Kuepper, K.; Zhou, S.; Potzger, K.; Postnikov, A.; Uecker, R.; Neumann, M.;
There has been considerable interest in high-k-dielectrics rare earth oxides as replacement for SiO2 in advanced field-effect transistors (FETs). Promising candidates are the perovskites SmScO3, GdScO3 and DyScO3. A tendency towards antiferromagnetic ordering at low temperatures is observed for the high magnetic moments at rare earth atoms. We analyse the electronic structure of the single crystalline samlpes by means of X-ray photoelectron spectroscopy and firstprinciples theory. The electronic structure calculations are performed with the augmented plane waves method (WIEN2k code) of the density functional theory, taking into account the spin-orbit interaction and orbital-dependent potential (LDA+U). The calculated positions of the main features in the valence band agree with the XPS data, the underlying chemical bonding can be analysed in detail. Small differences in the electronic structure, resulting in different stability of ferroand antiferromagnetic configurations, are discussed.
Keywords: high-k dielectrics, wide band gap insulators, perovskites, electronic structure calculations, x-ray photoelectron spectroscopy
  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des AKF, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9586 - Permalink

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