Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Experimental investigation of the flow in a bubble column
Zaruba, A.;
Computational Fluid Dynamics (CFD) models for two-phase flows always require closure relations representing the nature of the forces acting at the interface between the participating phases. This is vital for the modelling of momentum transfer term. In case of a gas-liquid flow, it is expressed in terms of forces acting on bubbles. The present study uses instantaneous high-speed video observations of the bubble motion to validate models for the interfacial forces.
The turbulent diffusion coefficient of the gaseous phase is obtained by a statistical evaluation of the movement of bubbles in a swarm, which is affected by the turbulence of the liquid phase. After the bubble trajectories were identified, the lateral displacement of bubbles was statistically analysed by constructing probability density functions. The dispersion coefficients of the standard distributions were found to grow proportionally to the square-root of the time. This supports the assumption of a diffusion model for the lateral displacement. Deviations from the linear dependency were identified to be the result of deterministic oscillatory motions of the rising bubbles.
Another objective is objective is to demonstrate the capabilities of the high-speed stereo-imaging technique to study the single (isolated) bubble dynamics in a vertical bubble column. The reconstruction algorithm of the 3D bubble trajectories from the stereo images of the bubble projection is presented. The bubble size, shape, orientation as well as bubble aspect ratio are investigated.
The first results of experiments on bubble motion in a vary narrow flat bubble column (width-100 mm, depth-8 mm, height – 600 mm) obtained for the validation of numerical predictions achieved using DNS-based analyses (Wörner et al. FZK) are presented. Results of high-speed video measurements of bubble parameters (bubble shape, size, rising velocity etc.) as well as PIV measurements of velocity of the liquid phase are discussed.
Keywords: Bubble column, CFD, interfacial forces, PIV
  • Invited lecture (Conferences)
    Seminar, 24.11.2005, Karlsruhe, Germany

Publ.-Id: 7970 - Permalink

Comparisons of DYN3D results with the reference solution of the AER-FCM-101 benchmark
Grundmann, U.;
The configuration of the reactor core used in the steady-state AER-FCM-101 benchmark is described. The results of different options of the DYN3D code are compared with the reference solution.
Keywords: reactor core benchmarks reference solution code validation nodal methods steady state
  • Invited lecture (Conferences)
    IAEA Workshop on “Neutronic Analyses of BNPP-1 Reactor Core. Task 7.8 of IRA4035”, 10.-14.10.2005, Wien, Austria

Publ.-Id: 7969 - Permalink

Molekulare Analysen von metallbindenden S-Layer-Proteinen
Pollmann, K.;
wird nachgereicht
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7966 - Permalink

Characterization of the Bacillus isolates from the uranium mining waste pile Haberlandhalde
Regenhardt, D.;
wird nachgereicht
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7965 - Permalink

Untersuchung des Einflusses von U(VI) auf die Struktur der natürlichen bakteriellen Gemeinschaft in einer Bodenprobe einer Uranabfallhalde
Geissler, A.;
wird nachgereicht
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7964 - Permalink

Optimum excitation conditions for the generation of high-electric-field THz radiation from an oscillator-driven photoconductive device
Dreyhaupt, A.; Winnerl, S.; Helm, M.; Dekorsy, T.;
We report on impulsive generation of terahertz (THz) radiation with more than 1.5 kV/cm field amplitude at MHz repetition rates, using an interdigitated photoconducting device. The approach provides an average THz power of 190 µW corresponding to an optical-to-THz conversion efficiency of 2.5 × 10-4. Optimum conditions are achieved when the excitation spot size is on the order of the THz wavelength.
  • Optics Letters 31(2006)10, 1546-1548

Publ.-Id: 7963 - Permalink

Jahresüberblick: Technische Entwicklungen, Nutzung, Erfolgsbilanz, ACTINET
Scheinost, A.; Claussner, J.; Dienel, S.; Funke, H.; Hennig, C.; Oehme, W.; Proehl, D.; Rossberg, A.; Strauch, U.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7961 - Permalink

XAS Characterization of metallic nanoparticles formed by cells and S-layer of Bacillus sphaericus JG-A12
Merroun, M.; Pollmann, K.; Raff, J.; Rossberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7960 - Permalink

Uranyl Minerals - special features of EXAFS spectra at 10-30 K
Funke, H.; Hennig, C.; Rossberg, A.; Scheinost, A.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7958 - Permalink

EXAFS-Untersuchungen am System U(VI)-Kaolinit-Huminsäure
Krepelova, A.; Sachs, S.; Reich, T.; Rossberg, A.; Bernhard, G.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7957 - Permalink

Müssen die Sorptionskomplexe von Uran(VI) an Ferrihydrit revidiert werden? II. Strukturaufklärung und spektroskopischer Nachweis mittels Monte Carlo Simulation und Faktoranalyse von EXAFS-Spektren
Rossberg, A.; Ulrich, K.-U.; Scheinost, A.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7956 - Permalink

Strukturanalyse von U(VI), U(IV) und Th(IV) Sulfato-Komplexen in wässriger Lösung
Hennig, C.; Schmeide, K.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7955 - Permalink

Size and structure of the Au nanoclusters formed on Cells and S-layer of Bacillus sphaericus JG-A12
Merroun, M.;
Cells and S-layer sheets of B. sphaericus JG-A12 were used as templates for the deposition of metallic gold nanoclusters using dimethyl amino borane (DMAB) as reducing agent . Gold LIII-edge XAS measurements confirmed the formation of Au(0) nanoclusters in both cases. In this Talk, the preliminary results on the size and the structure of the Au nanoclusters deposited on cells and S-layer protein of B. sphaericus JG-A12 will be presented.
  • Lecture (others)
    SMWK-Projekttreffen, 16.12.2005, Dresden, Germany

Publ.-Id: 7954 - Permalink

Microbial diversity in ground water at the deep-well monitoring site SI5 of the radioactive waste depository Tomske-7, Siberia, Russia
Nedelkova, M.;
Microbial diversity was studied in ground waters collected from a monitoring well at the radioactive waste depository Tomsk-7, Siberia, Russia, applying the 16S rDNA retrieval. The results demonstrated dominance of Betaproteobacteria, Bacteroidetes, and a novel “Cyanobacteria-like” group. The archaeal populations are represented by methanogens and three distinct clusters of Crenarchaeota. The autotrophic bacterial diversity was estimated via the RubisCO approach and the results confirm the dominance of Betaproteobacteria. Oligotrophic bacteria, from the groups of Alphaproteobacteria and Actinobacteria were isolated from the studied site. The strains tolerate relatively high concentration of different heavy metals and interact effectively with uranium. EXAFS analysis demonstrated that they immobilize U(VI) at pH 4.5 extracellularly in a form of meta-autunite. At pH 2 the U was bound by the organic phosphate residues of the cells. The environment around the radioactive waste repository site Tomsk-7 possesses microorganisms with a potential to bind and transport radionuclides.
  • Other report
    Bergakademie Freiberg: Doktorarbeit (Studiengang Chemie), 2005
    60 Seiten

Publ.-Id: 7953 - Permalink

Changing physical parameters to gain more information from EXAFS spectroscopy
Hennig, C.;
The contribution splits into three parts. (1) Theory and experiment of polarization dependent EXAFS at the U L1 and U L3 edge will be compared. (2) The effect of the temperature on the EXAFS Debye-Waller factor will be analyzed. (3) In-situ EXAFS experiments with changing electrochemical potential will be presented.
  • Lecture (others)
    CEA, 11.05.2005, Valduc, France

Publ.-Id: 7952 - Permalink

Speciation of uranium in environmental relevant compartments II
Bernhard, G.;
In the past, the chemistry of uranium was focused on its mining and milling for production of high pure uranium compounds as initial matter of reactor fuel elements for energy production and breeding of plutonium for weapons production. In this sense, the recovery of uranium and plutonium from the used reactor fuel elements was also technical realized. The increasing input into bio-sphere by uranium mining and milling and industrial processes like production of cement, fossil fuels, and fertilizers has led to the realization of the importance of environmental chemistry of uranium. Starting from uranium content in geo-and bio-systems, about the chemical behavior - the speciation of uranium - is reported in selected environmental compartments like seepage water, bacteria, and plants. The results obtained
by various spectroscopic methods show that the speciation of uranium is dominated in surface waters by uranyl carbonate complex in opposite to the speciation in bacteria and p! lants. In these compartments the speciation is dominated by binding of uranium on carboxylic and phosphorous containing functional groups.
  • Landbauforschung Volkenrode 55(2005), 139-148

Publ.-Id: 7951 - Permalink

Changes in microbial community structure induced by addition of U(VI) to uranium mining waste samples
Geissler, A.; Reitz, T.; Tschikov, J.; Selenska-Pobell, S.;
Microorganisms are involved in biogeochemical transformations and migration of uranium in the environment. In order to study the influence of U(VI) on natural bacterial and archaeal communities, a soil sample collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt was treated with different amounts of uranyl or sodium nitrate as a control. The samples were incubated for different periods of time and at different aeration conditions and their microbial communities were analyzed by the 16S rDNA retrieval using bacteria- and archaea-specific primers. Bacterial community of the untreated sample was predominated by Alphaproteobacteria and Acidobacteria. The increasing of the uranium content up to 100 mg U/kg with a subsequent incubation for four weeks under aerobic conditions stimulated a propagation of Pseudomonas spp., Arthrobacter spp. and Geobacter spp. Treatment of a parallel sample with sodium nitrate under the same conditions induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. After a longer incubation of fourteen weeks even in most contaminated samples containing 300 mg U/kg U-sensitive Bacteroidetes and alphaproteobacterial populations were stimulated. In parallel samples incubated under anaerobic conditions mainly Betaproteobacteria were identified. Archaeal diversity of the uranyl and sodium nitrate treated samples was significantly lower than in untreated samples and only sequences related to Crenarchaeotea were found. Our results demonstrate for the first time changes in the structure of a natural microbial community induced by incubation with uranyl nitrate for different periods of time and at different aeration conditions.
  • Contribution to proceedings
    VAAM-Jahrestagung, 19.-22.03.2006, Jena, Germany
  • Lecture (Conference)
    VAAM-Jahrestagung, 19.03.-22.06.2006, Jena, Germany

Publ.-Id: 7950 - Permalink

Spatial distribution and speciation of lead around corroding bullets in a shooting range soil studied by micro-X-ray fluorescence and absorption spectroscopy
Vantelon, D.; Lanzirotti, A.; Scheinost, A.; Kretzschmar, R.;
wird nachgereicht
  • Environmental Science & Technology 39(2005), 4808-4815

Publ.-Id: 7949 - Permalink

Chemical Heterogeneity of Organic Soil Colloids Investigated by Scanning Transmission X-ray Microscopy and C-1s NEXAFS Microspectroscopy
Schumacher, M.; Christl, I.; Scheinost, A.; Jacobsen, C.; Kretzschmar, R.;
Colloid release and deposition in soils and sorption of inorganic and organic pollutants to soil colloids are strongly influenced by the composition and chemical heterogeneity of colloidal soil particles. To investigate the chemical heterogeneity of organic soil colloids at the particle scale, we used synchrotron scanning transmission X-ray microscopy (STXM) and C-1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy on 49 individual particles isolated from the surface horizons of three forest soils. Stacks of 130 images of each particle were collected at different X-ray energies between 280 and 310 eV. From these image arrays, NEXAFS spectra were obtained for each pixel and analyzed by principle component analysis and cluster analysis (PCA-CA) to characterize the intraparticle heterogeneity of the organic components. The results demonstrate that the organic matter associated with water-dispersible soil colloids is chemically heterogeneous at the single-particle scale. PCA-CA identified at least two distinct regions within single particles. However, the spectral variations between these regions were much smaller than the variations of averaged NEXAFS spectra representing different particles from the same soil horizon, implying that interparticle heterogeneity is much larger than intraparticle heterogeneity. Especially the contents of aromatic and carboxyl carbon exhibited a large variability. Overall, the NEXAFS spectra of water-dispersible soil colloids were similar to the NEXAFS spectrum of the humic acid fraction, but differed clearly from the fulvic acid and dissolved organic matter fractions extracted from the same soil horizon using conventional techniques.
  • Environmental Science & Technology 39(2005), 9094-9100

Publ.-Id: 7948 - Permalink

Linking Monte-Carlo Simulation and Target Transformation Factor Analysis: A novel tool for the EXAFS analysis of mixtures
Rossberg, A.; Scheinost, A.;
wird nachgereicht
  • Physica Scripta T115(2005), 912-914

Publ.-Id: 7947 - Permalink

Neptunium uptake by serum transferring
Llorens, I.; Den Auwer, C.; Moisy, P.; Ansoborlo, E.; Vidaud, C.; Funke, H.;
wird nachgereicht
  • FEBS journal 272(2005), 1739-1744

Publ.-Id: 7946 - Permalink

Structure and size of gold nanoparticles formed on cells and S-layers of Bacillus sphaericus JG-A12
Merroun, M.; Rossberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.;
The strain Bacillus sphaericus JG-A12, isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from uranium waste waters. The cells of this strain are enveloped by a surface layer protein (S-layer). The highly regular structure of this S-layer with many pores of identical size offers good binding sites for different kinds of molecules and provides nucleation sites for the formation of metal nanoclusters or minerals. In this study we demonstrate that B. sphaericus JG-A12 cells and their purified S-layer protein sheets were capable to reduce Au to metallic nanoclusters in the presence of reducing agents such as molecular H2. The gold nanoparticles were regularly distributed and sized according to the pores of the S-layer lattice. The metallic nature of the clusters was confirmed by different techniques such as extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge (XANES) spectroscopy, UV-vis spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopic (TEM) analysis. The size of the gold nanoparticles was estimated to be almost 1 nm. Our results demonstrate that B. sphaericus JG-A12 can be used to prepare gold nanoparticles for industrial applications.
  • Contribution to proceedings
    VAAM-Jahrestagung, 19.-22.03.2006, Jena, Germany
    Biospektrum Sonderausgabe, Tagungsband zur VAAM-Jahrestagung 2006, Heidelberg: Elsevier, 103

Publ.-Id: 7945 - Permalink

Actinide uptake by transferrin and ferritin metalloproteins
Den Auwer, C.; Llorens, I.; Moisy, P.; Vidaud, C.; Goudard, F.; Barbot, C.; Solari, P. L.; Funke, H.;
In order to better understand the mechanisms of actinide uptake by specific biomolecules, it is essential to explore the intramolecular interactions between the cation and the protein binding site. Although this has long been done for widely investigated transition metals, very few studies have been devoted to complexation mechanisms of actinides by active chelation sites of metalloproteins. In this field, X-ray absorption spectroscopy has been extensively used as a structural and electronic metal cation probe. The two examples that are presented here are related to two metalloproteins in charge of iron transport and storage in eukaryote cells: transferrin and ferritin. U(VI)O-2(2+),
Np(IV) and Pu(IV) have been selected because of their possible role as contaminant from the geosphere.
  • Radiochimica Acta 93(2005)11, 699-703

Publ.-Id: 7944 - Permalink

EXAFS spectra analysis for nanosystems studying
in Russian
Shabel'Nikova, S.; Funke, H.; Chukalina, M.;
wird nachgereicht
  • Poster
    Conference RSNE-NANO 2005, 14.-18.11.2005, Moscow, Russia
  • Contribution to proceedings
    Conference RSNE-NANO 2005, 14.-18.11.2005, Moscow, Russia
    Book of abstracts: Shubnikov Institute of Crystallography RAS, 328

Publ.-Id: 7943 - Permalink

Mathematical aspects of the scattering centers identification problem: mother wavelet choice
in Russian
Chukalina, M.; Funke, H.; Shabelnikova, S.;
wird nachgereicht
  • Lecture (Conference)
    Conference on Mathematical Methods of image recognition (MMRO-12), 02.-09.09.2005, Divnomorskoe, Russia
  • Contribution to proceedings
    Conference on Mathematical Methods of image recognition (MMRO-12), 02.-09.09.2005, Divnomorskoe, Russia
    Proceedings, 235-239

Publ.-Id: 7942 - Permalink

Uranium binding by cells and S-layers of Bacillus isolates recovered from uranium mining waste pile
Raff, J.; Berger, S.; Selenska-Pobell, S.;
Intensive studies of the surface-layer (S-layer) protein of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 demonstrated its capability to bind uranium with high affinity and selectivity. But there are still many open questions. Therefore several other S-layer carrying Bacillus isolates were investigated. The latter were recovered from the same uranium mining waste pile as JG-A12, but from a site 5 times more contaminated with uranium. First experiments included analyses of the uranium binding by intact cells and by purified S-layers, determination of posttranslational modifications of the S-layer proteins and comparisons with the S-layer protein of B. sphaericus JG-A12 by using immunoassay methods.
Altogether 21 isolates were investigated. 9 S-layer positive Bacillus sp. isolates were identified. Using modified standard protocols, the S-layers of all isolates were successfully extracted. None of the proteins were glycosylated but all were phosphorylated in different degree. Interestingly, the cells of the half of the investigated isolates possess lower uranium binding capacities than the cells of B. sphaericus JG-A12. In contrast to that all S-layer proteins of the investigated isolates have significantly higher uranium binding capacities. Further investigations of the mechanisms responsible for the extremely high uranium binding capacity of some S-layers are in progress.
  • Contribution to proceedings
    Annual Conference of the Association for General und Applied Micobiology, 19.-22.03.2006, Jena, Deutschland
    Abstract in Procceding: Biospektrum Sonderausgabe 2006 Elsevier, 153
  • Poster
    Annual Conference of the Association for General und Applied Micobiology, 19.-22.03.2006, Jena, Deutschland

Publ.-Id: 7941 - Permalink

Characterization of hydrous uranyl silicate by EXAFS
Reich, T.; Moll, H.; Denecke, M. A.; Geipel, G.; Bernhard, G.; Nitsche, H.; Allen, P. G.; Bucher, J. J.; Kaltsoyannis, N.; Edelstein, N. M.; Shuh, D. K.;
Extended X-ray absorption fine structure (EXAFS) analysis was performed on uranyl orthosilicate, (UO2)(2)SiO4 . 2H(2)O, and uranium(VI) sorbed onto silicic acid and silica gel. Uranyl orthosilicate was investigated as a reference for EXAFS studies of similar but non-crystalline uranium, oxygen, and silicon containing samples. Fitting the EXAFS spectrum yields the following distances for the first four coordination shells of uranium: U-O-ax = 1.79 Angstrom, U-O-eq = 2.38 Angstrom, U-Si = 3.16 Angstrom, and U-U = 3.88 Angstrom. These values agree well with results from single-crystal X-ray diffraction (XRD) measurements. Structural parameters of light elements such as oxygen and silicon at distances greater than 3.5 Angstrom could not he detected without a priori knowledge of their presence. The EXAFS spectra of uranyl species sorbed at pH 4 onto silicic acid and silica gel are identical indicating similar uranyl coordination. The main characteristic of the surface species are two well-separated oxygen coordination shells in the equatorial uranyl plane at 2.27 and 2.50 Angstrom. The results of the EXAFS analysis favor the interpretation of the uranyl surface species as an inner-sphere, mononuclear, bidentate complex.
  • Radiochimica Acta 74(1996), 219

Publ.-Id: 7939 - Permalink

Complexation in the System UO22+/PO43-/OH-(aq): potentiometric and spectroscopic investigations at very low ionic strenghts
Brendler, V.; Geipel, G.; Bernhard, G.; Nitsche, H.;
Sample analysis of seepage waters from old uranium mill tailings in Saxony and Thuringia shows both phosphate and uranium contents up to 10(-5) molar. Therefore the impact of phosphate on the speciation and transport behavior of uranium has to be investigated. At present, available complexation data are based only on few experiments and are not fully consistent. Therefore, the complex stability constants of the various uranyl(if) phosphate complexes were determined Over a pH range from 2 to 5 for uranyl and phosphate concentrations to 10(-6) molar, using potentiometric titrations and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Fluorescence lifetimes were obtained for the free uranyl cation and uranyl phosphate complexes. Stability constants were determined for the complexes UO2(H2PO4)(2)(aq), UO2(H2PO4)(+) and UO2HPO4(aq), using the software C-LETAGROP [1] and SQUAD [2]. The results are compared with the values recommended by NEA [3] and with some recent publications.
  • Radiochimica Acta 74(1996), 75-80

Publ.-Id: 7938 - Permalink

Speciation of uranium in seepage waters from a mine tailing pile studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)
Bernhard, G.; Geipel, G.; Brendler, V.; Nitsche, H.;
Chemical speciation of U(VI) in natural seepage water and corresponding model solutions was investigated by time-resolved laser-induced fluorescence spectroscopy. Calculations of uranium speciation in this medium show that UO2(CO3)(3)(4-) and UO2(CO3)(2)(2-) should be the major individual components. Due to the very low fluorescence intensity, the pure uranyl carbonate complexes could not be measured directly by TRLFS. However, a uranium fluorescence spectrum was recorded from seepage water samples. The TRLFS investigations show that the main component of uranium in this seepage water is a calcium uranium carbonate complex. The main fluorescence wavelengths of this complex are at 463.9, 483.6, 502.8, 524.3 and 555.4 nm. The fluorescence lifetime of the species is 64+/-17 ns. This study shows that the calcium content of the water has a great influence on the uranium speciation. For the first time, the existence of a calcium uranium carbonate complex - {Ca-2[UO2(CO3)3]}((ag.)) - is reported. The stability constant was determined to be log beta = 26.8+/-0.7. Existing thermodynamic data bases do not contain this species and modeling calculation must lead to erroneous results in the medium under investigation.
  • Radiochimica Acta 74(1996), 87-91

Publ.-Id: 7937 - Permalink

Plutonium. XAFS Measurements of Plutonium Hydrates
Reich, T.; Geipel, G.; Funke, H.; Hennig, C.; Rossberg, A.; Bernhard, G.;
wird nachgereicht
  • Contribution to external collection
    in: ESRF-Highlights, Grenoble: ESRF, 1999, 32

Publ.-Id: 7936 - Permalink

Influence of hydrothermal wood degradation products on the uranium adsorption onto metamorphic rocks and sediments
Baraniak, L.; Bernhard, G.; Nitsche, H.;
The influence of highly functionalized saccharic and phenolic polymers that are formed in the process of hydrothermal wood degradation on the uranium(VI) adsorption onto metamorphic rocks and sediments from the Saxon uranium mining sites Schlema-Alberoda and Konigstein was investigated in a laboratory study. Uranium(VI) adsorption from a simulated mine water takes place on the majority of rocks and sediments such as granite, gneiss, basalt, sandstone and clay marl. Exceptions are phyllite and clay stone that do not bind any uranium from the mine water. Polymeric wood degradation products such as fragments of celluloses and lignin increase the uranium(VI) adsorption whereas the presence of saccharic and phenolic monomers (vanillic acid and gluconic acid) leads to a lower adsorption.
  • Journal of Radioanalytical and Nuclear Chemistry 253(2002)2, 185-190

Publ.-Id: 7935 - Permalink

Study of uranyl(VI)malonate complexation by time-resolved laser-induced fluorescence spectroscopy (TRLFS)
Brachmann, A.; Geipel, G.; Bernhard, G.; Nitsche, H.;
The uranyl(VI) malonate complex formation was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 4 and an ionic strength of 0.1 M NaClO4. The uranium concentration was 5 × 10-6 M at ligand concentrations from 1 × 10-5 to 1 × -2 M.

The measured fluorescence lifetimes of the 1:1 and 1:2 uranyl(VI) malonate complexes are 1.24 ± 0.02 µs and 6.48 ± 0.02 µs, respectively. The fluorescence lifetime of the uranyl(VI) ion is 1.57 ± 0.06 µs in 0.1 M perchloric media. The main fluorescence bands of the malonate complexes show a bathochromic shift compared to the uranyl(VI) ion and are centered at 494 nm, 515 nm and 540 nm for the 1:1 complexes and at 496 nm, 517 nm and 542 nm for the 1:2 complex. The spectra of the individual uranyl(VI) malonate complexes were calculated using a multi exponential fluorescence decay function for each intensity value at each wavelength, covering the entire wavelength range. Stability constants were determined for the complexes UO2C3H2O4°(aq) and UO2(C3H2O4)22- from results of spectra deconvolution using a least square fit algorithm (logβ1° = 4.48 ± 0.06, logβ2° = 7.42 ± 0.06 or logK2° = 2.94 ± 0.04). The results are compared with literature values obtained by potentiometric measurements.
  • Radiochimica Acta 90(2002)3, 147-153

Publ.-Id: 7934 - Permalink

Radionuklidmigration und ökologische Konsequenzen für Mensch und Umwelt
Bernhard, G.;
wird nachgereicht
  • Acta Academiae Scientiarum (2002)6, 57-75

Publ.-Id: 7933 - Permalink

Chlorite dissolution in the acid pH-range: A combined microscopic and macroscopic approach
Brandt, F.; Bosbach, D.; Krawczyk-Bärsch, E.; Arnold, T.; Bernhard, G.;
The dissolution of chlorite with intermediate Fe-content was studied macroscopically via mixed flow experiments as well as microscopically via atomic force microscopy (AFM). BET surface area normalized steady state dissolution rates at 25 °C for pH 2 to 5 vary between 1012 and 1013 mol/m2.s. The order of the dissolution reaction with respect to protons was calculated to be about 0.29. For pH 2 to 4, chlorite was found to dissolve non-stoichiometrically, with a preferred release of the octahedrally coordinated cations. The additional release of octahedrally coordinated cations may be due to the transformation of chlorite to interstratified chlorite/vermiculite from the grain edges inward. In-situ atomic force microscopy performed on the basal surfaces of a chlorite sample, which has been preconditioned at pH 2 for several months, indicated a defect controlled dissolution mechanism. Molecular steps with height differences which correspond to the different subunits of chlorite, e.g. TOT sheet and brucite like layer, originated at surface defects such or compositional inhomogenities or cracks, which may be due to the deformation history of the chlorite sample. In contrast to other sheet silicates, at pH 2 nanoscale etch pits occur on the chlorite basal surfaces within flat terraces terminated by a TOT-sheet as well as within the brucite like layer. The chlorite basal surface dissolves layer by layer, because most of the surface defects are only expressed through single TOT or brucite-like layers. The defect controlled dissolution mechanism favours dissolution of molecular steps on the basal surfaces compared to dissolution of the grain edges. At pH 2 the dissolution of the chlorite basal surface is dominated by the retreat of 14 Å steps, representing one chlorite unit cell. The macroscopic and microscopic chlorite dissolution rates can be linked via the reactive surface area as identified by AFM. The reactive surface area with respect to dissolution consists of only 0.2% of the BET-surface area. A dissolution rate of 2.5 109 mol/m2s was calculated from macroscopic and microscopic dissolution experiments at pH 2, when normalized to the reactive surface area.

Publ.-Id: 7932 - Permalink

Pump-probe spectroscopy of interminiband relaxation and electron cooling in doped superlattices
Stehr, D.; Winnerl, S.; Helm, M.; Dekorsy, T.; Roch, T.; Strasser, G.;
The picosecond dynamics of electrons in a doped GaAs/AlGaAs superlattice have been investigated by pump-probe experiments using an infrared free-electron laser. We observe a fast bleaching of the interminiband absorption followed by thermalization and a slower cooling component. The latter can lead to a positive or negative transmission change, resulting from the temperature dependence of the linear absorption spectrum at the respective wavelength. We show that the superlattice in contrast to quantum wells provides a unique picosecond thermometer for the electron temperature based on the dependence of the absorption on the electron distribution function.
  • Applied Physics Letters 88(2006)15, 51108

Publ.-Id: 7931 - Permalink

Non-Destructive Investigation of Paintings with THz-Radiation
Panzner, M.; Köhler, W.; Winnerl, S.; Helm, M.; Rutz, F.; Koch, M.; Leitner, H.; Klotzbach, U.; Beyer, E.;
Nowadays the investigation of paintings is mainly done by means of X-ray radiography or ultra violet and infrared reflectometry. The latter is a non-invasive technique since the very low photon energies of the infrared radiation precludes damage to the paint by breaking molecular bonds as it is known to occur with UV-radiation.
Another advantage of infrared reflectometry appears when it is extended to picosecond pulses in the THz frequency band: X-ray radiography provides only an additive signal from absorption by all paint layers, which may be sufficient for revealing older painting hidden below the surface but does not provide information on the sequence of paint layers. However, THz time domain spectroscopy has the potential for providing depth information from the paint layers. In addition to this, the substances which the paint consist of can be identified by their absorption lines in the frequency spectrum of the reflected ps-THz-pulses.
Particularly evident is the potential of the THz technique for the investigation of wall paintings where X-ray radiography cannot be applied. Conventional infrared reflectometry is unsuitable for detecting hidden paintings when the cover layer is thick as it often is the case with wall paintings. THz-radiation is able to penetrate thicker layers and become partly reflected from them, thereby retrieving useful information from the depth.
The present contribution provides first results of transmission measurements on paintings in the frequency band up to 5 THz. It becomes evident that the different paints show a significantly different THz transmission. First THz transmission images of paintings give rise to the hope that hidden wall pictures can be made visible using a reflection geometry.
  • Poster
    9. Europäische Konferenz für zerstörungsfreie Werkstoffprüfung, 25.-29.09.2005, Berlin, Deutschland

Publ.-Id: 7930 - Permalink

High-Resolution THz Spectrometer with kHz scan rates
Bartels, A.; Thoma, A.; Janke, C.; Dekorsy, T.; Dreyhaupt, A.; Winnerl, S.; Helm, M.;
A high-resolution THz-spectrometer with 9kHz scan-rate is demonstrated for acquisition of THz-field-transients with 1ns duration without mechanical delay line. Spectra up to 3THz with a 40dB signal-to-noise ratio are acquired within 250 s.
  • Lecture (Conference)
    Conference on Lasers and Opto-Electronics, 21.-26.05.2006, Long Beach, USA
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics, 21.-26.05.2006, Long Beach, USA
    CLEO/QELS & PhAST Technical Digest CD-ROM 2006

Publ.-Id: 7929 - Permalink

Die Lichtrevolution durch Leuchtdioden
Winnerl, S.;
Die faszinierende Erfolgsgeschichte von Leuchtdioden (engl.: light emitting diode, LED) und Laserdioden wird vorgestellt. Es wird erklärt, wie Licht unterschiedlicher Farbe mit LEDs erzeugt wird und welche besondere Rolle blaue LEDs spielen. Neben weißen Leuchtdioden, die ein hohes Potential für zukünftige Alltagsbeleuchtung besitzen, werden auch aktuelle Forschungsergebnisse zu siliziumbasierenden LEDs diskutiert.
  • Lecture (others)
    Licht_Licht_Licht, Interdisziplinärer Studientag an der TU Dresden, 15.12.2005, Dresden, Deutschland

Publ.-Id: 7928 - Permalink

Die Lichtrevolution durch Leuchtdioden
Winnerl, S.;
Die faszinierende Erfolgsgeschichte von Leuchtdioden (engl.: light emitting diode, LED) und Laserdioden wird vorgestellt. Es wird erklärt, wie Licht unterschiedlicher Farbe mit LEDs erzeugt wird und welche besondere Rolle blaue LEDs spielen. Neben weißen Leuchtdioden, die ein hohes Potential für zukünftige Alltagsbeleuchtung besitzen, werden auch aktuelle Forschungsergebnisse zu siliziumbasierenden LEDs diskutiert.
  • Lecture (others)
    Lange Nacht der Wissenschaften, 01.07.2005, Dresden, Deutschland

Publ.-Id: 7927 - Permalink

High-resolution THz spectrometer with kHz scan rates
Bartels, A.; Thoma, A.; Janke, C.; Dekorsy, T.; Dreyhaupt, A.; Winnerl, S.; Helm, M.;
We demonstrate a rapid scanning high-resolution THz spectrometer capable of acquiring THz field transients with 1 ns duration without mechanical delay line. The THz spectrometer is based on two 1-GHz Ti:sapphire femtosecond lasers which are linked with a fixed repetition rate difference in order to perform high-speed asynchronous optical sampling. One laser drives a high-efficiency large-area GaAs based THz emitter, the other laser is used for electro-optic detection of the emitted THz-field. At a scan rate of 9 kHz a time resolution of 230 fs is accomplished. High-resolution spectra from 50 GHz up to 3 THz are obtained and water absorption lines with a width of 11 GHz are observed. The use of femtosecond lasers with 1 GHz repetition rate is essential to obtain rapid scanning and high time-resolution at the same time.
Keywords: terahertz, ultrafast spectroscopy, ultrafast laser
  • Open Access LogoOptics Express 14(2006), 430-437

Publ.-Id: 7925 - Permalink

Speciation of Uranyl Nitrato Complexes in Acetonitrile and in the Ionic Liquid 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide
Servaes, K.; Hennig, C.; Billard, I.; Gaillard, C.; Binnemans, K.; Görller-Walrand, C.; van Deun, R.;
Complex formation between the uranyl ion and nitrate ions in acetonitrile and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) has been studied by absorption, magnetic circular dichroism (MCD) and uranium LIII EXAFS spectroscopy. The experimental results point to the existence of a trinitrate species [UO2(NO3)3]– with D3h symmetry in both solvents. The atomic distances in the uranium(VI) coordination sphere for the trinitrato complex in acetonitrile are U–Oax = 1.770.01 Å and U–Oeq = 2.480.01 Å. EXAFS data show that the uranyl ion in the ionic liquid is surrounded by six oxygen atoms in the equatorial plane at a distance of 2.490.01 Å. The U–N distance of 2.920.01 Å indicates a bidentate coordination of the nitrate group in both solvents. A structural comparison is made between the uranyl trinitrato complex anion [UO2(NO3)3]– and the uranyl tricarbonato complex anion [UO2(CO3)3]4–. No evidence is found for the presence of uranyl nitrato complexes in aqueous solution. The optical absorption, MCD and EXAFS spectra resemble those of the hydrated free uranyl ion. There are two axial oxygen atoms at 1.770.01 Å and five equatorial oxygen atoms at 2.410.01 Å. These values agree well with structural parameters obtained for the uranyl aqua ion.
Keywords: Uranyl trinitrate, UV-Vis, EXAFS

Publ.-Id: 7924 - Permalink

Application of advanced Master Curve approaches on WWER-440 reactor pressure vessel steels
Viehrig, H.-W.; Scibetta, M.; Wallin, K.;
The Master Curve (MC) approach used to measure the transition temperature, T0, has been standardized in the ASTM Standard Test Method E 1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centered (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
The fracture toughness values measured on Charpy size SE(B) specimens of base metal from the Greifswald Unit 8 RPV show a large scatter. The basic MC evaluation following ASTM E1921 supplies a MC with many fracture toughness values which lie below the 1% fracture probability line. It is therefore suspected that this material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data.
Keywords: reactor pressure vessel steel, fracture toughness, Master Curve approach, inhomogeneous material, random inhomogeneity, maximum likelihood procedure, SINTAP procedure

Publ.-Id: 7923 - Permalink

Calculations of a steady state of the OECD/NRC PWR MOX/UO2 transient benchmark with DYN3D
Grundmann, U.;
Steady states and transients in thermal reactors with standard core loadings are simulated with the nodal codes based on the three-dimensional diffusion equation for two energy groups of neutrons. The assembly wise cross sections are generated with cell codes solving the transport equation for many energy groups in two-dimensions assuming reflecting boundary conditions. Loading cores with higher content of MOX fuel and the increase of the fuel cycle length is challenging for the standard methods. Different neutron spectra of UO2 and MOX fuel, inhomogeneities inside the fuel as-semblies arising during the exposure in the reactor lead to discrepancies which needs an improvement of the applied methods. The core model DYN3D which is ap-plied for three-dimensional analyses of thermal reactor cores with quadratic or hex-agonal fuel assemblies is based on standard methods. The first step of the code enhancement consists in the extension to multi energy groups. The OECD/NEA and U.S. NRC PWR MOX/UO2 Core Transient Benchmark which is a well defined problem with a complete set of data is used as a means for verification of the modifi-cations of DYN3D. The core chosen for the simulation is based on four-loop West-inghouse PWR power plant similar to the reactor used for Plutonium disposition in the U.S. Steady-state calculations with the non-consideration and consideration of the assembly discontinuity factors (ADF), with a different number of energy groups, and with different number of nodes per assembly are compared with a reference so-lution generated by the DeCart. A Two-group solutions is also compared with a published PARCS diffusion solution.
Keywords: nuclear reactor reactor physics benchmarks steady state three-dimensional diffusion theory nodal methods multi groups
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany

Publ.-Id: 7922 - Permalink

DYN3D/RELAP5 and RELAP5/PARCS calculations of the Kozloduy-6 pump trip test
Kozmenkov, Y.; Grundmann, U.; Kliem, S.; Rohde, U.; Bousbia Salah, A.;
The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate (BE) three-dimensional coupled code computational tools. Nowadays, this technique is extensively used since it allows decreasing conservatism in the calculation models by performing more realistic simulations based on a more precise consideration of multidimensional effects under complex transients in NPPs. This paper represents a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER-1000 pump trip test. The coupled REALP5/3.3-PARCS/2.6 and DYN3D/3-RELAP5/3.3 code systems are used in simulations. The obtained results are assessed against experimental data and also through the code-to-code comparison.

The DYN3D/RELAP5 computational model of VVER-1000 has been developed and adjusted for simulations with the parallel running scheme (PVM) of RELAP5/PARCS. Also, the macroscopic cross-section library used in the DYN3D/RELAP5 calculations has been adapted to meet the input requirements of PARCS. Prior to the test simulations, the RELAP5/PARCS model of the plant has been assessed in the standalone PARCS and RELAP5 test calculations.

A reasonably good agreement between the experimental data and the calculated results is obtained. For the initial state, the observed discrepancies are mainly due to the absence of ADF correction and the evaluation of the Doppler feedback effect. During the transient, the deviations are mainly due to the combined effect of the measurement uncertainty in the control rod axial position and the estimation of the Doppler effect.
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany
    Proceedings, Berlin: Inforum GmbH, 54-59
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany

Publ.-Id: 7921 - Permalink

Evaluation of homogenisation error in two-group nodal diffusion calculation for VVER-1000 core
Petkov, P. T.; Mittag, S.;
A two-dimensional benchmark problem for a VVER-1000 hot zero-power state with fresh fuel loading is presented. The reference solution has been obtained by many-group heterogeneous transport-theory calculations with the code Mariko, applying the method of characteristics. An equivalent two-group diffusion problem has been defined by homogenized two-group diffusion parameters and discontinuity factors for the fuel assemblies and the radial reflector nodes. The two-group nodal neutron diffusion model DYN3D has been verified against this benchmark. The DYN3D errors in the relative assembly-wise power distribution vary between -1.6 % and +1.1 %, the deviation in k-eff is –50 pcm.
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, 16.-18.05.2006, Aachen, Germany

Publ.-Id: 7920 - Permalink

Experimental and CFD analysis of a stirred tank reaction mechanically agitated by gas-inducing turbine
Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.;
A non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine, was experimentally and numerically studied. The system under investigation comprises air as gas phase and isopropanol as liquid phase at room temperature. The initially stationary isopropanol and air were brought into motion by the rotating impeller. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions. The final stirrer speed was 1200 rpm at which the central vortex virtually reaches the impeller. Additionally, video observations, performed with a digital camcorder, were taken to study the unsteady behaviour of the central vortex.
CFX 10.0 numerical software was used to carry out the computational fluid dynamics analyses of the stirred tank reactor. A full three dimensional approach was adopted in order to capture the unsteady behaviour of the central vortex. Transient and steady state numerical calculations were performed. Four steady state simulations, at stirrer speed from 200 to 800 rpm, were conducted to obtain an initial guess of the flow field and the phase distribution for the steady state and the transient simulations at 1000 rpm. The numerical predictions above 1000 rpm used the previous simulation results as an initial guess. Starting from 1000rpm, five steady state simulations were performed at stirrer speed thresholds of 50 rpm to be compared with the experimental observations. The transient numerical predictions were compared with visual observations, since the X-Ray cone beam tomography provides an average phase distributions more suitable for comparison with the steady state predictions. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid with a mean diameter of 1 mm and the liquid phase as continuous fluid. Different turbulence models were considered for the liquid phase but the k-ε turbulence model was found to be the most computationally stable and was used in the simulations. The gas phase turbulence was modelled using the dispersed phase zero equation. The flow was regarded as buoyant and implemented using the density difference model.
The CFD predictions closely mimic the experimental observations for the central vortex depth as well as for its spread out. The results demonstrate the X-Ray cone beam tomography and the CFD capabilities to capture the two-phase flow in detail, which can provide valuable information for the industry. In particular the special gas phase distribution, which can also have time-dependent behaviour, can have a crucial impact on the reactor performance. This can be in detail predicted by the computational fluid dynamic software, which can prove to be an essential tool for the reactor optimisation and scale-up.
  • Lecture (Conference)
    17th International Congress of Chemical and Process Engineering, 27.-31.08.2006, Praha, Czech Republic
  • Contribution to proceedings
    17th International Congress of Chemical and Process Engineering, 27.-31.08.2006, Praha, Czech Republic
    Materials of the 17th International Congress of Chemical and Process Engineering, Praha: Process Engineering Publisher, 80-86059-45-6, 760-761

Publ.-Id: 7919 - Permalink

The interaction of Desulfovibrio äspöensis DSM 10631T with plutonium
Moll, H.; Merroun, M. L.; Hennig, C.; Rossberg, A.; Selenska-Pobell, S.; Bernhard, G.;
Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. This investigation describes the interaction of plutonium in mixed oxidation states (Pu(VI) and Pu(IV)-polymers) with cells of the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis DSM 10631T, which frequently occurs in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. In this study, accumulation experiments were performed in order to obtain information about the amount of Pu bound by the bacteria in dependence on the contact time and the initial plutonium concentration. We used solvent extractions, UV-vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy to determine the speciation of Pu oxidation states. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to study the coordination of the Pu bound by the bacteria. In the first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. Solvent extractions showed that 97 % of the initially present Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves from the cell envelope back to the aqueous solution due to the weak complexing properties of this plutonium oxidation state. Indications were found for a penetration of Pu species inside the bacterial cells.
Keywords: Plutonium, Bacteria, Desulfovibrio äspöensis, Biosorption, Bioreduction, Absorption spectroscopy, XAS
  • Radiochimica Acta 94(2006), 815-824

Publ.-Id: 7918 - Permalink

High-resolution measurements of the coolant mixing in the downcomer of the ROCOM test facility
Kliem, S.; Prasser, H.-M.; Sühnel, T.;
A new sensor was developed for an improved visualisation and quantification of the coolant mixing in the downcomer of the ROCOM test facility. This sensor spans a measuring grid of 64 azimuthal and 32 positions over the height of the downcomer On behalf of an experiment with the start-up of the main coolant pump the possibilities of the new sensor are demonstrated.
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany
    Proceedings, Berlin: Inforum GmbH, 78-84
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany

Publ.-Id: 7917 - Permalink

Understanding low-energy magnetic excitations and hydrogen bonding in VOHP O4 * 1 / 2 H2O
Cao, J.; Haraldsen, J. T.; Brown, S.; Musfeldt, J. L.; Thompson, J. R.; Zvyagin, S. A.; Krzystek, J.; Whangbo, M.-H.; Nagler, S. E.; Torardi, C. C.;
We report the variable temperature vibrational properties of single crystals of the S=1/2 Heisenberg antiferromagnet VOHP O4 *1/2 H2O. A pair of peaks in the far infrared spectral response may be due to magnetic excitations. We invoke a dynamic Dzyaloshinskii-Moriya mechanism to explain the activation and polarization dependence of the singlet-to-triplet gap in the far infrared, and we identify the low-energy phonons that likely facilitate this coupling. The spin-gap values are compared to those obtained via magnetic susceptibility, electron spin resonance, and neutron scattering. Vibrational mode splitting in VOHP O4 * 1 / 2 H2 O indicates a weak local symmetry breaking near 180 K , and the low-temperature redshift of V-O and H-O related modes demonstrates enhanced low-temperature hydrogen bonding. The low lattice symmetry is important for the proposed magnetoelastic interactions.

Publ.-Id: 7916 - Permalink

1D-modelling of differential pressure buildup at clogged containment sump strainers after LOCA
Grahn, A.; Krepper, E.; Alt, S.; Kästner, W.;
The present paper reports on our efforts in modelling the pressure drop buildup at sump strainers obstructed by mineral fibrous insulation material after a Loss of Coolant Accident (LOCA). Special attention is drawn to the compressibility of the fibrous filter cake. Comparison of numerical results with pressure drop measurements has been provided.
Keywords: reactor safety, pressure drop, sump strainer blockage, Loss of Coolant Accident
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2006, 16.-18.5.2006, Aachen, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 15.-18.05.2006, Aachen, Germany

Publ.-Id: 7915 - Permalink

Using CFD to simulate turbulent mixing in nuclear reactor pressure vessels
Rohde, U.; Höhne, T.; Kliem, S.;
FZR has 10 years of experience using ANSYS CFX software for CFD applications focused on nuclear reactor applications and more recently also chemical process simulations. These CFD activities are very closely connected to experimental investigations at facilities in the institute. Using advanced two-phase flow measurement techniques, a comprehensive data base for CFD code verification is being created. So in addition to single-phase flow nuclear reactor engineering applications, development and verification of physical models for two-phase flows can be performed. FZR is participating in the German initiative on CFD applications in nuclear reactor safety research in close co-operation with the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS, the German nuclear safety authority) and ANSYS. The group of young and highly motivated CFD scientists that has been established at the institute also has a significant portion of the 100 processor Linux cluster of the FZR at its disposal. The FZR coordinated the experimental and analytical investigations of turbulent mixing inside pressurized water reactors (PWRs) performed within the EC project FLOMIX-R (Fluid mixing and flow distribution in the reactor circuit). The purpose of this project was to describe coolant mixing phenomena, particularly for severe accident scenarios. Such scenarios include steam line breaks and boron dilution, where mixing of coolant from different loops moderates the inflow of water with insufficient boron content or temperature into the reactor core. These changes can lead to reactor power excursions (rapid increase in reactor power) due to positive reactivity effects. An example of a typical boron dilution scenario is during start-up of the first main coolant pump after a slug of low borated water has formed in one of the cooling loops, where mixing is largely forced by the momentum introduced by the pump starting. Another safety issue arises during emergency core cooling (ECC) situations, when cold water is injected into a hot cooling loop. In this case, buoyancy-driven mixing is influenced by density differences in the fluid and is typical for so-called pressurized thermal shock (PTS) scenarios. When a streak of cold ECC water touches the reactor pressure vessel (RPV) wall, unacceptable thermal stresses can occur. Measurement data from several sets of mixing experiments, using advanced measurement techniques with enhanced temporal and spatial resolution, improved the basic understanding of turbulent mixing and provided data for CFD code verification.
Selected experiments were then simulated using ANSYS CFX and applying best practice guidelines (BPGs), a set of systematic procedures for quantifying and reducing numerical errors. BPGs were applied when considering computational grid resolution and time step, turbulence models, internal geometry modelling, boundary conditions, numerical schemes, and convergence criteria. These investigations highlighted the importance of grid quality, and also the need to minimize numerical diffusion by using second order discretization. In fact, first order schemes were found
to sometimes even provide physically incorrect results. ANSYS CFX was well able to predict the experimental flow patterns and mixing phenomena for both buoyancy-driven and momentum-driven flows. Two-equation turbulence models like k-ω or SST were found to be suitable for momentum-driven slug mixing, while Reynolds stress models provided better results for buoyancy driven mixing.
Comprehensive multiphase flow models, advanced turbulence models, second order discretization, and scalable parallel performance all combine to make ANSYS CFX a valuable tool at FZR. ANSYS CFX software has been instrumental in the development and verification of best practices guidelines for the use of CFD in nuclear safety analyses.
Keywords: Boron Dilution, CFD, ROCOM
  • ANSYS Solutions 7(2006)2, 27-28

Publ.-Id: 7914 - Permalink

Spectroscopic evidence of adsorbed U(VI) surface species onto gibbsite and quartz obtained by TRLFS
Baumann, N.; Brendler, V.; Arnold, T.; Geipel, G.; Bernhard, G.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite (γ-Al(OH)3).
Two uranyl surface species with fluorescence lifetimes of 330 ± 115 ns and 5600 ± 1640 ns, respectively, were identified.
The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1, 497.4 ± 0.8, 518.7 ± 1.0, 541.6 ± 0.7, 563.9 ± 1.2, and 585.8 ± 2.1 nm. The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH- groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.
Spectroscopic evidence of sorbed U(VI) surface species on quartz and kaolinite, also obtained by TRLFS were presented and compared with the U(VI) gibbsite system.
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2005, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University, 80-01-03474-7, 44-44
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7913 - Permalink

MHD research activities at the Research Center Rossendorf
Gerbeth, G.;
An overview on applied MHD projects of the Rossendorf MHD department will be given.
  • Lecture (others)
    Meeting of COST Action P17, Working Group VI, 07.-08.12.2005, Hannover, Germany

Publ.-Id: 7911 - Permalink

Neue Möglichkeiten zur kontaktlosen Beeinflussung von Metallschmelzen
Eckert, S.; Galindo, V.; Gerbeth, G.; Willers, B.;
Es wird eine Übersicht zur kontaktlosen Kontrolle von Metallschmelzen und zur Messung von Strömungsgeschwindigkeiten gegeben.
  • Poster
    Weltmesse EuroMold, 30.11.-03.12.2005, Frankfurt / Main, Deutschland

Publ.-Id: 7910 - Permalink

NURESIM-TH Deliverable D2.1.2: Review of the existing data basis for the validation of models for PTS
Lucas, D.; Beghini, M.; Bestion, D.; Bichet, T.; Ézsöl, G.; Höhne, T.; Martin, A.; Mazzine, D.; Peturaud, P.; Prasser, H.-M.; Puustinen, M.; Schäfer, F.; Scheuerer, M.; Smith, B.; Sühnel, T.; Tiselj, I.; Vallée, C.; Vihavainen, J.;
This report gives a review on existing experimental data for the development, verification and valida-tion of models for the simulation of a two-phase PTS situation. This includes single effect data, which are useful for the development and validation of closure models for CFD codes as well as integral test data for the validation of the applicability of the code for PTS situations. For the development and validation of closure models for CFD codes, data are required with a high resolution in space and time. There is a need of additional data. Information on the planned TOPFLOW PTS experimental programme is also included in the report.
Keywords: Pressurized Thermal Shock, Experiment
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2005
    113 Seiten

Publ.-Id: 7909 - Permalink

NURESIM-TH Deliverable D2.1.1: Identification of relevant PTS-scenarios, state of the art of modelling and needs for model improvements
Lucas, D.; Bestion, D.; Bodele, E.; Bousbia Salah, A.; D’Auria, F.; Ilvonen, M.; Kral, P.; Lakehal, D.; Macek, J.; Manera, A.; Martin, A.; Moretti, F.; Riikonen, V.; Scheuerer, M.; Seynhaeve, J.-M.; Strubelj, L.; Tiselj, I.;
This report identifies PTS-scenarios for the French 900 MW CPY PWR, the German 1300 MW Kon-voi reactor, the Loviisa 400 MW VVER, the Russian VVER-1000 and the Czech VVER-100. Accord-ing to the resulting basic flow conditions relevant physical phenomena for the simulation of the scenes during Emergency Core Cooling (ECC) injection into the cold leg are identified. The main focus is on two-phase flow phenomena. The state of the art of modelling these phenomena and needs for models improvement are discussed. Thus the report is a suitable basis for the specification of the main topics to be provided in Task T2.1.4 of the NURESIM project.
Keywords: Pressurized Thermal Shock, CFD
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2005
    123 Seiten

Publ.-Id: 7908 - Permalink

Spektrochemische Zelle zur Strukturanalyse von Aktinidenspezies in wässriger Lösung - gegenwärtiger Stand und künftige Entwicklungen
Hennig, C.;
wird nachgereicht
  • Lecture (others)
    Kolloquium im Kurt-Schwabe-Institut Meinsberg, 09.12.2005, Meinsberg, Germany

Publ.-Id: 7907 - Permalink

The feasibility of in-beam PET for therapeutic beams of 3 He
Fiedler, F.; Crespo, P.; Sellesk, M.; Parodi, K.; Enghardt, W.;
At present in-beam PET is the only possibility for an in-situ monitoring of the particle delivery in hadron tumor therapy and there is a unique clinical implementation at the Gesellschaft fuer Schwerionenforschung (GSI) Darmstadt.
Several heavy ion treatment facilities are under construction, which will provide a large variety of ions from protons to oxygen. This requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. For the 3He-case experiments at GSI with three mono-energetic 3He-beams of 130.03 AMeV to 207.92 AMeV have been carried out. The beams were stopped in homogeneous thick targets consisting of PMMA, graphite and water. Results on the production rate and the spatial distribution of 3He ion induced beta+-activity will be presented and compared with data from 12C-irradiation. From these, the accuracy and resolution for determining the range of the 3He primary beams is deduced. Furthermore, energy dependent thick target cross sections for different reaction channels leading to positron emitters will be estimated from the experimental data.
Keywords: in-beam PET, heavy ion therapy, 3He
  • Lecture (Conference)
    PTCOG 43, 10.-14.12.2005, München, Deutschland

Publ.-Id: 7906 - Permalink

Resonant impurity bands in semiconductor superlattices
Stehr, D.; Metzner, C.; Helm, M.; Roch, T.; Strasser, G.;
It is shown that the 2pz confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three dimensional Hamiltonian for a quantum well system with random impurities. Intersubband
absorption experiments, which can be nearly perfectly reproduced by the theory, corroborate this interpretation, which also requires re-interpretation of previous data.
Keywords: superlattice, impurity band, infrared, intersubbadn transition

Publ.-Id: 7905 - Permalink

Tunable-frequency electron paramagnetic resonance - a novel tool to investigate high-spin transition metal coordination complexes
Krzystek, J.; Ozarowski, A.; Trofimenko, S.; Zvyagin, S. A.; Telser, S. A.;
Although Electron Paramagnetic Resonance (EPR) has been a very successful method to investigate transition metal ions in coordination complexes and biomolecules, not all such ions can be subject to conventional EPR investigations even if they are paramagnetic. In particular, high-spin (S > 1/2) species pose serious challenges to spectroscopists, and of these, the non-Kramers (integer-spin) ions have been long considered ‘EPR-silent’ at conventional frequencies and fields.
We propose a novel EPR-related technique that takes an advantage of tunable sources operating in the sub-THz range of frequencies in conjunction with very high magnetic fields (up to 25 Tesla) to determine accurate intrinsic spin Hamiltonian parameters not only for a variety of non-Kramers transition metal ions (such as Ni2+, Mn3+, and Fe2+) that have traditionally been termed ‘EPR-silent’, but also for those Kramers (half-integer) species that are poorly characterized in their high-spin states, such as Co2+.
The obtained parameters can serve to better characterize the electronic structure of the ions in question, in combination with other experimental methods.
  • Contribution to external collection
    M. Melník, J. Šima, and M. Tatarko: Advances in Coordination, Bioinorganic and Inorganic Chemistry, Bratislava: Slovak Technical University Press, 2005, 1-15

Publ.-Id: 7900 - Permalink

Conditions for the manifestation of transient effects in fission
Jurado, B.; Schmitt, C.; Schmidt, K.; Benlliure, J.; Junghans, A.;
The conditions for the manifestation of transient effects in fission are carefully examined by analysing experimental data where fission is induced by peripheral heavy-ion collisions at relativistic energies. Experimental total nuclear fission cross sections of U-238 at 1 A GeV on gold and uranium targets are compared with the predictions of a nuclear-reaction code, where transient effects in fission are modeled using different approximations to the numerical time-dependent fission-decay width: a new analytical description based on the solution of the Fokker-Planck equation and two widely used but less realistic descriptions, a step function and an exponential-like function. The experimental data are only reproduced when dissipation is considered. The influence of transient effects on the fission process, as well as the deduced value of the dissipation strength P, depends strongly on the approximation applied for the time-dependent fission-decay width. In particular, a metic! ulous analysis sheds severe doubts on the use of the exponential-like in-growth function. Finally, we investigate which should be the characteristics of experimental observables to be most sensitive to transient effects in fission. The pertinence of observables related to the excitation energy at saddle is discussed.
Keywords: Nuclear Fission; Transient effects; Dynamical nuclear deexcitation code; Time-dependent fission-decay width; Relativistic nucleus-nucleus collisions; Comparison with experimental total nuclear fission-cross sections

Publ.-Id: 7898 - Permalink

Untersuchungen zur Löslichkeit verschiedener Urandioxidmodifikationen mittels LIBD und anderer spektroskopischer Methoden
Opel, K.; Hübener, S.; Weiß, S.; Zänker, H.; Bernhard, G.;
Die Löslichkeitsprodukte kristallinen und amorphen Urandioxids werden durch die Kombination von coulometrischer Titration einer U(IV)-Lösung und der Detektion der bei Überschreitung der Löslichkeit entstehenden Kolloide mittels laserinduzierter Breakdown-Detektion (LIBD) bestimmt. Die Quantifizierung von U(VI)-Spuren erfolgt mittels laserinduzierter Fluoreszenzspektroskopie.
Die Partikelgröße der entstehenden Kolloide und die Ionenstärke wird in den thermodynamischen Berechnungen berücksichtigt. Für die kristalline Modifikation resultiert log Ksp = -59,6, für die amorphe Modifikation log Ksp = -54,4.
Ergänzende Untersuchungen mittels EXAFS-Spektroskopie bestätigen das Vorliegen der kristallinen Modifikation.
Keywords: colloids, uranium, LIBD, solubility product, particle size
  • Contribution to proceedings
    Jahrestagung der Wasserchemischen Gesellschaft der GDCh, 22.-24.05.2006, Celle, Germany
    Wasserchemischen Gesellschaft, Fachgruppe der Gesellschaft Deutscher Chemiker, 72. Jahrestagung 2006: Wächtersbach: PM-GraphikDesign, 3-936028-39-7, 108-112
  • Lecture (Conference)
    Jahrestagung der Wasserchemischen Gesellschaft der GDCh, 22.-24.05.2006, Celle, Germany

Publ.-Id: 7897 - Permalink

Fluorine-18 Labelling of Small Molecules: The Use of 18F-Labelled Aryl Fluorides Derived from No-Carrier-Added [18F]Fluoride as Labelling Precursors
Wüst, F.;
The favourable long-half life, the ease of production and the low enery of the emitted positron make 18F an ideal radionuclide for PET imaging. Radiochemistry of 18F basically relies of two distinctive types of reactions: nucleophilic and electrophilic reactions. All syntheses of 18F-labelled radiotracers are based on either [18F]fluoride ion or [18F]fluorine gas as simple the primary labelling precursors which are obtained directly from the cyclotron. They can be applied either directly to the radiosynthesis or they can be transformed into more complex labelling precursors enabling the multi-step built up of organic tracer molecules. The topic of this review is a survey on the application of several 18F-labelled aryl fluorides as building blocks derived from no-carrier-added (n.c.a.) [18F]fluoride to built up small mono-molecular PET radiotracers at high specific radioactivity by multi-step synthesis procedures.
  • Contribution to external collection
    P.A. Schubiger, L. Lehmann, M. Friebe: E.Schering Research Foundation Workshop, Vol. 62, PET Chemistry, The Driving Force in Molecular Imaging, Berlin Heidelberg: Springer Verlag, 2006, 10-3-540 326 23-5, 51-78

Publ.-Id: 7896 - Permalink

Fluorine-18 Labelling of Small Molecules
Wüst, F.;
kein Abstract verfügbar
  • Lecture (Conference)
    Ernst Schering Research Foundation Workshop 62 PET chemistry: The driving force in molecular imaging, 05.-07.12.2005, Berlin, Germany

Publ.-Id: 7895 - Permalink

Buoyancy driven mixing studies of natural circulation flows at the ROCOM facility using ANSYS CFX
Höhne, T.; Kliem, S.; Weiß, F.-P.;
Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied.

From the test matrix an experiment with 2% density difference between the de-borated slugs and the ambient coolant was used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used.

The experiment and CFD calculation show a stratification in the downcomer. The less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core.The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.
Keywords: CFD, ROCOM, boron dilution, PWR
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 16.05.-18.06.2006, Aachen, Germany
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2006, 16.05.2006, Aachen, Germany

Publ.-Id: 7894 - Permalink

Mercaptoimidazole Derivatives Labelled with 11C/99mTc for the Targeting of 5-HT1A Receptors
Paulo, A.; Garcia, R.; Maria, L.; Xavier, C.; Santos, I.; Knieß, T.; Wüst, F.; Bergmann, R.;
Our research group has focused on mercaptoimidazole derivatives as the lead structure to design radioactive probes for in vivo imaging of 5-HT1A receptors. This type of compounds can be labelled directly with 11C or can be used to prepare tripodal ligands suitable to stabilize the fac-[M(CO)3]+ (M = Re, 99mTc) moieties.1,2 Interestingly, this versatility allows an easy assessment of the influence of the bulkier metallic fragment on the biological properties of PET (11C) or SPECT (99mTc) radioligands bearing a common pharmacophore.
Scheme 1
In this communication, we report on the radiosynthesis, characterization and biological evaluation of mercaptoimidazole piperazinyl derivatives labelled with 11C (1) and with 99mTc (2 and 3) (Scheme 1). It will be discussed their interest as radioactive probes for imaging 5-HT1A receptors by means of PET or SPECT, as well as the effect of the presence of the organometallic moiety on the affinity and biodistribution profile of the compounds.
Acknowledgments: R. Garcia and L. Maria thank FCT for PhD and Post-Doc grants, respectively. This work has been partially supported by the FCT (POCTI/2001/QUI/42939).
[1] Garcia, R; Xavier, C.; Paulo, A.; Santos, I.; Kniess, T.; Bergmann, R.; Wüst, F. J. Labelled Cpd. Radiopharm. 2005, 48, 301.
[2] Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Ortner, K.; Alberto, R. J.Am Chem. Soc. 2000, 122, 11240.
  • Poster
    Fourth Annual Meeting of the Society for Molecular Imaging, 07.-10.09.2005, Köln, Deutschland
  • Abstract in refereed journal
    Molecular Imaging 4(2005)3, 337

Publ.-Id: 7893 - Permalink

A solid-state compact pulser of 5kV/2A/5kHz for surface treatment by plasma immersion ion implantation
Rossi, J. O.; Ueda, M.; Silva, G.; Reuther, H.;
A solid-state compact pulser of 5kV/2A/5kHz for surface treatment by plasma immersion ion implantation
  • Lecture (Conference)
    8th Brazilian Meeting of Plasma Physics, 27.-30.11.2005, Niteroi, Rio de Janeiro, Brazil

Publ.-Id: 7892 - Permalink

Effects of low magnetic fields on nitrogen implantation in silicon by plasma immersion
Tan, I. H.; Ueda, M.; Dallaqua, R. S.; Abramof, E.; Reuther, H.;
Effects of low magnetic fields on nitrogen implantation in silicon by plasma immersion
  • Lecture (Conference)
    8th Brazilian Meeting of Plasma Physics, 27.-30.11.2005, Niteroi, Rio de Janeiro, Brazil

Publ.-Id: 7891 - Permalink

Influence of the plasma density on the performance of plasma immersion íon implantation of silicon surface
Castro, R. M.; Ueda, M.; Oliveira, R. M.; Reuther, H.; Morena, B. L. D.;
Influence of the plasma density on the performance of plasma immersion íon implantation of silicon surface
  • Lecture (Conference)
    8th Brazilian Meeting of Plasma Physics, 27.-30.11.2005, Niteroi, Rio de Janeiro, Brazil

Publ.-Id: 7890 - Permalink

Plasma immersion íon implantation with high-energy íons for use in surface treatments
Rossi, J. O.; Ueda, M.; Reuther, H.;
Plasma immersion íon implantation with high-energy íons for use in surface treatments
  • Lecture (Conference)
    8th Brazilian Meeting of Plasma Physics, 27.-30.11.2005, Niteroi, Rio de Janeiro, Brazil

Publ.-Id: 7889 - Permalink

Surface modification of Ti6Al4V alloy by duplex plasma processing
Silva, M. M.; Ueda, M.; Otani, C.; Reuther, H.; Lepienski, C. M.; Soares Jr, P. C.;
Surface modification of Ti6Al4V alloy by duplex plasma processing
  • Lecture (Conference)
    Cobem 2005 - 18th International Congress of Mechanical Engineering, 06.-11.11.2005, Ouro Preto, Minas Gerais, Brazil

Publ.-Id: 7888 - Permalink

High Temperature Plasma Immersion Ion Implantation of Ti6Al4V
Ueda, M.; Silva, M. M.; Lepienski, C. M.; Soares, P. C. J.; Gonçalves, J. A.; Reuther, H.;
High Temperature Plasma Immersion Ion Implantation of Ti6Al4V
  • Lecture (Conference)
    8th International Workshop on Plasma-Based Ion Implantation and Deposition, 18.-22.09.2005, Chengdu, China

Publ.-Id: 7887 - Permalink

Nitrogen Plasma Immersion Ion Implantation in Ti6Al4V with treatment temperatures ranging from 400 to 800°C
Silva, M. M.; Ueda, M.; Lepienski, C. M.; Soares, P. C. J.; Gonçalves, J. A. N.; Reuther, H.;
Nitrogen Plasma Immersion Ion Implantation in Ti6Al4V with treatment temperatures ranging from 400 to 800°C
  • Lecture (Conference)
    Fifth Asian_European International Conference on Plasma Surface Engineering, 12.-16.09.2005, Qingdao City, China

Publ.-Id: 7886 - Permalink

Interaction of Desulfovibrio äspöensis Bacteria with Plutonium - A Solvent Extraction and X-ray Absorption Spectroscopy (XAS) Study
Moll, H.; Merroun, M.; Hennig, C.; Rossberg, A.; Selenska-Pobell, S.; Bernhard, G.;
Presentation of recent results describing the interaction of plutonium with cells of Desulfovibrio aespoeensis. Application of solvent extraction and X-ray absorption spectroscopy.
Keywords: Plutonium, Bacteria, Desulfovibrio aespoeensis, Biosorption, Bioreduction, XAS
  • Lecture (others)
    ROBL-RC-Workshop 2005 (Rossendorf Beamline: Radiochemie-Workshop), 07.12.2005, Dresden (Rossendorf), Germany

Publ.-Id: 7885 - Permalink

Epitaxial recrystallization of nano-sized amorphous layers, phase nucleation and growth in 4H-SiC
Gao, F.; Zhang, Y.; Posselt, M.; Devanathan, R.; Weber, W. J.;
Two nano-sized amorphous layers embedded in perfect crystals have been modeled to study the amorphous-to-crystalline (a-c) transition in the temperature range from 1000 to 2000 K in 4H-SiC by means of classical molecular dynamics methods. The results show that the epitaxial recrystallization of amorphous layers with a-c interface along the c-axis is much faster than that along the basal plane, which suggest the anisotropies in the different activation energies for recrystallization. The recovery of bond defects and the rearrangement of atoms at the interface are important processes driving the epitaxial recrystallization of the amorphous layers. The nano-sized amorphous layer with the a-c interface oriented along the c-axis can be fully recrystallized at all temperatures considered. However, it is observed that second ordered phases, crystalline 3C-SiC, nucleate and grow during the recrystallization process inside the amorphous layer with the a-c interface along the basal plane, and these new phases are stable for long simulation times. Based on a model developed in the previous annealing simulations of 3C-SiC, the range of activation energies are determined to be about 0.35 eV to 2.4 eV, which suggests that the recrystallization consists of multiple recovery processes, rather than a single process proposed previously. The present results are discussed and compared with the annealing simulations of 3C-SiC and experimental observations. The simulation results are in good agreement with previous experimental results in SiC, and thus, provide atomic-level insights into the interpretation of experimentally observed phenomena.
Keywords: computer simulation, recrystallization, SiC
  • Invited lecture (Conferences)
    MRS 2005 Fall Meeting, 27.11.-01.12.2005, Boston, MA, USA

Publ.-Id: 7884 - Permalink

Effect of Molecular Weight on the Structure and Crystallinity of Poly(3-hexylthiophene)
Zen, A.; Saphiannikova, M.; Neher, D.; Grenzer, J.; Grigorian, S.; Pietsch, U.; Asawapirom, U.; Janietz, S.; Scherf, U.; Lieberwirth, I.; Wegner, G.;
Recently, two different groups have reported independently, that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented, one proposing carrier trapping at grain boundaries and the second putting emphasis on different conformation and packing of the polymer chains in the thin layers.
Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to investigate the structure and crystallization behaviors of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements revealed a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. In order to study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in disordered matrix. In contrast, films of the high molecular weight fraction exhibit partially-ordered domains throughout the whole sample area. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight is largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites.
Keywords: organic field-effect transistors, regioregular poly(3-hexylthiophene) (P3HT)
  • Macromolecules 39(2006)6, 2162-2171

Publ.-Id: 7883 - Permalink

Structure, energetics and migration of V and I in Ge: an atomistic study
Geßner, H.; Posselt, M.;
For details of this talk, please contact the authors.
Keywords: defects, Ge, computer simulations
  • Lecture (Conference)
    2nd CADRES Germanium Workshop, 01.12.2005, Brussels, Belgium

Publ.-Id: 7881 - Permalink

Identification of ductile damage and fracture parameters from the small punch test using neural networks
Abendroth, M.; Kuna, M.;
This paper presents a method for the identification of deformation, damage and fracture properties of ductile materials.
The small punch test is used to obtain the material response under loading. The resulting load displacement curve contains information about the deformation and failure behavior of the tested material. The finite element method is used to compute the load displacement curve depending on the parameters of the Gurson-Tvergaard-Needleman damage law. Via a systematic variation of the material parameters a data base is built up, which is used to train neural networks. This neural network can be used to predict the load displacement curve of the SPT for a given material parameter set. The identification of the material parameters is done by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one predicted by the network function. The identified material parameters are validated by independent tests on notched tensile specimens. Furthermore, these parameters can be used to compute the crack growth in fracture specimens, which finally leads to a prediction of classical fracture toughness parameters.

Publ.-Id: 7879 - Permalink

Einfluss von eisenreichen Kolloiden auf das Uran(VI) in Bergwerkshalden
Zänker, H.; Weiß, S.;
Die Ausfällung von Sekundärmineralien im Bulk von Umweltwässern durch chemische Reaktionen nach der Mischung von Wässern unterschiedlicher Zusammensetzung oder nach dem Zutritt von Luft zu vorher isolierten Wässern stellt nicht den einzigen Weg zur Bildung von eisenreichen Umweltkolloiden dar. In einer früheren Arbeit zeigten wir, dass ein alternativer Mechanismus die direkte Produktion von Sekundärmineralkolloiden an der Gestein-Wasser-Grenzfläche bei der Verwitterung ist. Er besitzt vor allem für die Kolloidentstehung bei der Verwitterung von frisch zerkleinertem Gestein in der ungesättigten Zone wie z. B. Gestein in Bergwerkshalden Bedeutung. Hier wird demonstriert, dass auch die auf diesem Wege entstehenden Kolloide Einfluss auf das Schadstoffverhalten nehmen können. Als Beispiel dient das Uran(VI)-Verhalten.
Keywords: Colloids, phyllite, uranium(VI), weathering, mine waste rock piles
  • Contribution to proceedings
    72. Jahrestagung der Wasserchemischen Gesellschaft, 22.-24.05.2006, Celle, Deutschland
    Wasserchemischen Gesellschaft, Fachgruppe der Gesellschaft Deutscher Chemiker, 72. Jahrestagung 2006, Wächtersbach: PM-GraphikDesign, ISBN 3-936028-39-7, 250-254
  • Poster
    72. Jahrestagung der Wasserchemischen Gesellschaft, 22.-24.05.2006, Celle, Deutschland

Publ.-Id: 7878 - Permalink

Application of recursively coupled FE-models to a PWR In-Vessel-Retention analysis
Willschuetz, H.-G.; Altstadt, E.; Weiss, F.-P.;
The improbable scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a Light Water Reactor (LWR) Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the containment. One accident management strategy could be to stabilize the in-vessel debris or melt pool configuration in the RPV as one major barrier against uncontrolled release of heat and radionuclides into the containment of the plant.
Based on the successful simulation and analysis work of the FOREVER-experiments the models have been developed further to simulate the prototypical scenario of an In-Vessel-Retention in a large German PWR (KONVOI). As shown in an earlier publication a recursively coupled simulation between the thermal and the mechanical model has to be performed to consider the mutual influence of the heat fluxes respectively the temperatures and the mechanical vessel behaviour.
After the validation of the recursively coupled thermal and mechanical FE-models against the scaled FOREVER-tests the models were improved to simulate a prototypic scenario under certain assumptions. The calculations show that an In-Vessel-Retention might be possible for large PWRs like KONVOI, if the RPV is flooded externally. The remaining vessel wall thickness seems to be sufficient to prevail even higher pressure loads. But in any case a support of the lower head would increase the margin to failure and therefore ensure the integrity of the last barrier within the containment of the plant.
Keywords: core melt down, coupled FEM-analysis, experimental and prototypical scenario
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany
    CD-ROM, Paper 317, 229-234
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2006, 16.-18.05.2006, Aachen, Germany

Publ.-Id: 7877 - Permalink

Control of saturation magnetization, anisotropy and damping due to Ni implantation in thin Ni81Fe19 layers
Fassbender, J.ORC; McCord, J.
The static and dynamic magnetic properties of 20 nm thick Ni81Fe19 films have been investigated as a function of Ni ion fluence up to 1x1016 Ni/cm2 (~ 5 atom-%). The implantation has been performed at 30 keV in order to implant the Ni ions in the center of the ferromagnetic layer and to achieve a rather homogeneous energy distribution throughout the film. With increasing ion fluence the saturation magnetization and the effective magnetic anisotropies (static and dynamic) are reduced. However, the effective magnetic damping is drastically enhanced for higher ion fluences. This increase can be explained mainly by the drop in saturation magnetization in connection with structural changes. In addition ion implantation in an applied magnetic field allows the setting of the uniaxial anisotropy direction irrespective of the initial orientation.
Keywords: magnetism, ion implantation, magnetic properties, anisotropy, damping, magnetization
  • Applied Physics Letters 88(2006), 252501
    DOI: 10.1063/1.2213948
  • Lecture (Conference)
    International Colloquium on Magnetic Films and Surfaces, 14.-18.08.2006, Sendai, Japan

Publ.-Id: 7876 - Permalink

Low temperature L10 ordering of FePt films fabricated on SiO2/Si substrates
von Borany, J.; Cantelli, V.; Beckers, M.; Mücklich, A.; Potzger, K.; Fassbender, J.ORC
The transition temperature for the A1 to L10 phase transition of magnetron sputter deposited FePt films in the thickness range between 35 and 130 nm is investigated. Large ordering factors up to S = 0.93 are observed either for a deposition at T = 350°C or a post-deposition annealing at 400°C. These low ordering temperatures are explained by a defect enhanced atomic site exchanges induced by the impact of energetic ions. Due to the use of amorphous substrates no preferential grain orientation and thus only a weak magnetic anisotropy could be achieved.
Keywords: FePt, L10-ordering, structural phase transition, hard magnetic properties
  • Applied Physics Letters (2007)

Publ.-Id: 7875 - Permalink

Matched asymptotic solution for the solute boundary layer in a converging axisymmetric stagnation point flow
Priede, J.; Gerbeth, G.;
A novel boundary-layer solution is obtained by the method of matched asymptotic expansions for the solute distribution at a solidification front represented by a disk of finite radius R0 immersed in an axisymmetric converging stagnation point flow. The detailed analysis reveals a complex internal structure of the boundary layer consisting of eight subregions. The development of the boundary layer starts from the rim region where the concentration, according to the obtained similarity solution, varies with the radius r along the solidification front as ~ ln1/3(R0/r). At intermediate radii, where the corresponding concentration is found to vary as ~ln(R0/r), the boundary layer has an inner diffusion sublayer adjacent to the solidification front, an inner core region, and an outer diffusion sublayer which separates the former from the outer uniformly mixed region. The inner core, where the solute transport is dominated by convection, is characterized by a logarithmically decreasing axial concentration distribution. The logarithmic increase of concentration along the radius is limited by the radial diffusion becoming effective in the vicinity of the symmetry axis at distances comparable to the characteristic thickness of the solute boundary layer.
  • International Journal of Heat and Mass Transfer 50(2007), 216-225

Publ.-Id: 7874 - Permalink

Detection of U(V) in Pseudomonas stutzeri biofilms by confocal laser scanning microscopy
Großmann, K.; Arnold, T.; Krawczyk-Bärsch, E.;
A biofilm of Pseudomonas stutzeri was cultured in a annular rotating reactor /1/ at near-neutral pH conditions on glass slides. After reaching a mature confluent biofilm uranium(VI) was added to the nutrient solution to obtain a final uranium(VI) concentration of 5 ´ 10-6 M. The resulting biofilm was studied by Confocal Laser Scanning Microscopy (CLSM) and a biofilm thickness of 43 µm was recorded. Particles of approximately 5 µm were detected in the biofilm. These particles were excited by an diode laser with an excitation wavelength of 405 nm and the resulting fluorescence signal was recorded. Two kinds of flourescence signals were detected. One with a characteristic fluorecence signal in the range of 490 to 560 nm which is indicative for U(VI) /2/ and a second one with a fluorescence signal from 420 to 470 nm. Since U(IV) requires an excitation wavelength of 245 nm and shows a completely different fluorescence spectrum the formation of uranium(IV) particles was ruled out. However, based on UV-vis measurements of U(V) containing standard solutions these signals were interpreted as U(V) species, indicating that redox processes must have occured within the biofilm.
Keywords: biofilm, uranium, CLSM
  • Poster
    Biofilm II, 23.-24.03.2006, Leipzig, Deutschland
  • Contribution to proceedings
    Biofilm II, UFZ Centre for Environmental Research Leipzig-Halle, 23.-24.03.2006, Leipzig, Germany, 14

Publ.-Id: 7873 - Permalink

Adsorbed U(VI) surface species on muscovite identified by laser fluorescence spectroscopy and transmission electron microscopy
Arnold, T.; Utsunomiya, S.; Geipel, G.; Ewing, T. C.; Baumann, N.; Brendler, V.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) were applied to investigate the species of uranyl(VI) adsorbed onto muscovite platelets and muscovite suspensions ( grain size: 63-200 mu m). TRLFS provided evidence for the presence of two adsorbed uranium( VI) surface species on edge-surfaces of muscovite. The two species showed different positions of the fluorescence emission bands and different fluorescence lifetimes indicating a different coordination environment for the two species. HAADF-STEM revealed that nanoclusters of an amorphous uranium phase were attached to the edge-surfaces of muscovite powder during batch sorption experiments. These U-nanoclusters were not observed on {001} cleavage planes of the muscovite. The surface species with the shorter fluorescence lifetimes are interpreted as truly adsorbed bidentate surface complexes, in which the U(VI) binds to alum!
inol groups of edge-surfaces. The surface species with the longer fluorescence lifetimes are interpreted to be an amorphous U(VI) condensate or nanosized clusters of polynuclear uranyl(VI) surface species with a particle diameter of 1 to 2 nm. Depending on the size of these clusters the fluorescence lifetimes vary; i.e., the larger the nanosized clusters, the longer is the fluorescence lifetime.
Keywords: U(VI), muscovite, U(VI)nanoparticles, TRLFS, HAADF-STEM, sorption
  • Environmental Science & Technology 40(2006)15, 4646-4652

Publ.-Id: 7872 - Permalink

Evidence for Nontermination of Rotational Bands in 74Kr
Valiente-Dobon, J. J.; Steinhardt, T.; Svensson, C. E.; Afanasjev, A. V.; Ragnarsson, I.; Andreoiu, C.; Austin, R. A. E.; Carpenter, M. P.; Dashdorj, D.; de Angelis, G.; Dönau, F.; Eberth, J.; Farnea, E.; Freeman, S. J.; Gadea, A.; Garrett, P. E.; Görgen, A.; Grinyer, G. F.; Hyland, B.; Jenkins, D.; Johnston-Theasby, F.; Joshi, P.; Jungclaus, A.; Lieb, K. P.; Macchiavelli, A. O.; Moore, E. F.; Mukherjee, G.; Napoli, D. R.; Phillips, A. A.; Plettner, C.; Reviol, W.; Sarantites, D.; Schnare, H.; Schumaker, M. A.; Schwengner, R.; Seweryniak, D.; Smith, M. B.; Stefanescu, I.; Thelen, O.; Wadsworth, R.;
Three rotational bands in 74 Kr were studied up to (in one case one transition short of ) the maximum spin Imax of their respective single-particle configuratio ns. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin Imax . This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I=Imax .
Keywords: Nuclear structure, gamma-ray spectroscopy, mean-field calculations.

Publ.-Id: 7870 - Permalink

First 99mTc(l)- and 188Re(l)-carbonyl labeled aptamers
Hecht, M.; Friebe, M.; Borkowski, S.; Hilger, C.; Stephens, A.; Johannsen, B.; Dinkelborg, L. M.;
Aim: Aptamers (synthetic oligonucleotides), can be generated by a combinatorial approach (SELEX1) and are promising probes for radiodiagnostic imaging and therapy due to their high affinity and target specificity. The aptamer, TTA1 is characterized by a low nanomolar affinity and a high selectivity for the human matrix protein tenascin-C. Tenascin-C concentration in normal adult matrix tissue is rather low, whereas it is overexpressed in the stroma of a variety of malignant tumors2, making this target potentially suitable as a multi tumor imaging agent. The aim of this study was to evaluate the pharmacokinetic properties of 99mTc(I) and 188Re(I) carbonyl radiometal chelates attached to TTA1 in tumor animal models in vivo. Material and Methods: [Carboxymethyl-(2-ethylsulfanyl-ethyl)-amino]-acetic acid, an appropriate chelating unit for coordination of 99mTc(I) or 188Re(I), was conjugated to the aptamer and a 99mTc(I) carbonyl precursor was synthesized3. Labeling of the aptamer with the 99mTc(I) carbonyl precursor was achieved in 15 min at 100°C. Synthesis of the 188Re(I) carbonyl labeled aptamer was performed in a one pot reaction at 60°C for 30 min. Both, binding affinity for human tenascin-C and in vitro stability in human plasma were measured. The biodistribution and elimination of the 99mTc-tracer was evaluated in a human U251 xenograft NMRI nude mouse model. Results: The radiochemical purity of the products was >95 % after purification by spin dialysis. Reaction yields ranged from 65 % to 72 % for the 99mTc(I) carbonyl labeled aptamer and from 25 % to 35 % for the 188Re(I) carbonyl labeled aptamer. The specific activity of the Tc(I) carbonyl labeled aptamer was 37 MBq/nmol and the stability in human blood plasma proved to be 65 % after incubation at 37°C for 24h. The binding affinity of the compound against human tenascin-C lies in the low nanomolar range. Significant tumor uptake was observed in the U251 tumor xenograft model after i.v. injection of the 99mTc(I) carbonyl complex. Conclusion: Aptamers can be labeled with both 99mTc(I) and 188Re(I) carbonyls in acceptable yields and good purity. Further investigations are ongoing to fully characterize the potential of the compounds for their use as diagnostic and therapeutic agents. Lit: 1. C. Tuerk, L. Gold, Science, 249, 505-510, 1990; 2. H. P. Erickson, M. A. Bourdon, Annu. Rev. Cell Biol., 5, 71-92, 1989; 3. R. Alberto, R. Schibli, A. P. Schubiger, J. Am. Chem. Soc. 121,6076 - 6077, 1999
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 32(2005)Suppl. 1
  • Lecture (Conference)
    Annual Congress of the EANM, 15.-19.10.2005, Istanbul, Turkey

Publ.-Id: 7869 - Permalink

Influence of Humic Acid on U(VI) Sorption onto Kaolinte: Studies Using Extended X-ray Absorption Fine Structure Measurements and Time-Resolved Laser-Induced Fluorescence Spectroscopy.
Krepelova, A.; Sachs, S.; Reich, T.; Roßberg, A.; Brendler, V.; Baumann, N.; Bernhard, G.;
Understanding the migration behavior of actinides is important for the reliable long-term risk assessment of potential nuclear waste repositories. Depending on geochemical conditions different materials and processes can influence the behavior of such pollutants in natural aquifer systems. Humic acids (HA) comprise an important part of natural organic materials. HA are soluble in the pH range of natural waters and have the ability for complex and colloid formation. Due to these properties HA can affect the speciation of actinide ions, and therefore, their migration in the environment.
In the present study results from our previous batch experiments (1) were combined with spectroscopic measurements to obtain molecular-level information on the interaction of U(VI) with HA and kaolinite in natural systems.
Keywords: U(VI), humic acid, sorption, kaolinite, EXAFS, TRLFS
  • Contribution to proceedings
    13th Meeting of the International Humic Substances Society, 30.07.-04.08.2006, Karlsruhe, Germany
    Humic Substances - Linking Structure to Functions (F.H.Frimmel, G. Abbt-Braun), Karlsruhe, ISSN 1612-118x, 733-736
  • Poster
    13th Meeting of the International Humic Substances Society, 30.07.-04.08.2006, Karlsruhe, Deutschland

Publ.-Id: 7868 - Permalink

Migration Behavior of Humic Acids in Compacted Clay and its Influence on the Uranium Transport
Sachs, S.; Mibus, J.;
Clay minerals and organic substances are common components of many soils, sediments, and rocks. However, little is known on the migration behavior of humic substances in clay formations which is supposed to be governed by diffusion processes. Since humic acids (HA) show a strong ability for complex formation they can influence the migration of radioactive and non-radioactive toxic metal ions in clayey environments.
In the present study we investigated the diffusion behavior of humic colloids in compacted clay and its impact on the uranium transport. These studies are of high importance for the reliable risk-assessment of future nuclear waste repositories which requires knowledge on the actinide migration behavior in potential host rock formations. Clay formations as possible host rocks are closely associated with natural organic matter.
Keywords: Humic acids, Migration, Uranium, Clay, Diffusion
  • Contribution to proceedings
    13th Meeting of the International Humic Substances Society, 30.07.-04.08.2006, Karlsruhe, Germany
    Humic Substances-Linking Structure to Functions (Frimmel, F.H., Abbt-Braun, G., Eds.), Karlsruhe, ISSN: 1612-118X, 713-716
  • Poster
    13th Meeting of the International Humic Substances Society, 30.07.-04.08.2006, Karlsruhe, Germany

Publ.-Id: 7867 - Permalink

Ion induced modifications of magnetic thin films and multilayers
Fassbender, J.ORC
A review of ion induced modification of magnetic thin films and multilayers is given.
Keywords: ion irradiation, ion implantation, magnetism
  • Lecture (others)
    Seminarvortrag, 02.12.2005, Konstanz, Deutschland

Publ.-Id: 7866 - Permalink

Nucleation and growth of Ti2AlN thin films deposited by reactive magnetron sputtering onto MgO(111)
Beckers, M.; Schell, N.; Martins, R. M. S.; Mücklich, A.; Möller, W.; Hultman, L.;
The nucleation and growth of Ti2AlN thin films on MgO(111) substrates during dual DC reactive magnetron cosputtering from Ti and Al targets in an Ar/N2 atmosphere at a substrate temperature of 690°C have been investigated . Time and thickness dependent in situ specular x-ray reflectivity and x-ray diffraction (XRD) in coplanar scattering geometry in combination with cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy revealed the formation of competing phases. It is found that initially an ~380-Åthick epitaxial cubic (Ti1-xAlx)Ny layer of substoichiometric composition forms with a layer-by-layer growth mode. Nitrogen-vacancy driven diffusion of Ti and Al leads to spinodal decomposition of this metastable solid solution into nano-sized cubic TiNy and AlNy domains as well as to a solid-state reaction where Mg2(Al:Ti)O4 spinel forming below the interface to the MgO(111). Spatial and temporal fluctuations of the nitrogen activity on the (Ti1-xAlx)Ny surface at higher thicknesses yield thermodynamically favored Ti2AlN nucleation and polycrystalline growth. Concurrent Ti2AlN inward grain growth by diffusion of weakly bonded Al atoms along the Ti2AlN basal planes reduces the thickness of the phase-separated (Ti1-xAlx)Ny layer to ~60 Å. Individual Ti2AlN grains retain local epitaxy to the substrate with vertical grain sizes in the range of the final film thickness.
Keywords: Nucleation and growth, Ti-Al-N MAX-phase, sputter deposition, in-situ x-ray diffraction

Publ.-Id: 7865 - Permalink

Atomistic simulations on the thermal stability of the antisite pair in 3C- and 4H-SiC
Posselt, M.; Gao, F.; Weber, W. J.;
The thermal stability of the first-neighbor antisite pair configurations in 3C- and 4H-SiC is investigated by atomic-level computer simulations. At first the structure and energetics of these defects are determined in order to check the accuracy of the interatomic potential employed. The results are comparable with literature data obtained by the density-functional theory. Then, the lifetime of the antisite pair configurations is calculated for temperatures between 800 and 2500 K. Both in 3C- and 4H-SiC the thermal stability of the antisite pairs is rather low. In contrast to previous theoretical interpretations, the antisite pair cannot be therefore correlated with the DI photoluminescence center that is stable to above 2000 K. The atomic mechanism of the recombination of the antisite pair in 3C-SiC and of three antisite pair configurations in 4H-SiC is a modified concerted exchange. Due to the different sizes of the silicon and the carbon atoms, this process is not identical to the concerted exchange in Si. Two intermediate metastable configurations found during the recombination are similar to the bond defect in Si. Since the SiC lattice contains two types of atoms, there are also two different types of bond defects. The two bond defects can be considered as the result of he incomplete recombination of a carbon vacancy and a neighboring mixed dumbbell interstitial. The antisite pair in 4H-SiC with the two atoms on hexagonal sites has a slightly higher formation energy than the other three antisite pair configurations in 4H-SiC. Its lifetime shows another dependence on the temperature, and its recombination is characterized by a separate motion of atoms. The comparison with results obtained by molecular dynamics simulations that are based on the density-functional theory demonstrates that the atomistic simulations describe the antisite pair and its recombination reasonably well.
Keywords: computer simulations, defects, SiC
  • Physical Review B 73(2006), 125206

Publ.-Id: 7864 - Permalink

Quantitative measurement of gas hold-up distribution in a stirred chemical reactor using X-ray cone-beam computed tomography
Boden, S.; Hampel, U.; Bieberle, M.;
Cone-beam type X-ray computed tomography (CBCT) is a potential method to measure three-dimensional phase-distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data is highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transfer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effects of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate measurement of void fraction profiles with CBCT.
Keywords: cone-beam computed tomography, gas hold-up measurement, chemical reactor

Publ.-Id: 7863 - Permalink

Mean electromotive force for a ring of helical vortices
Avalos-Zuniga, R.; Plunian, F.; Xu, M.; Stefani, F.; Rädler, K.-H.;
A ring of helical vortices is a common feature of the onset of thermal convective instability in a rapidly rotating spherical shell as expected in the Earth's core. In fact, there are good reasons that this kind of fluid motion plays an important role in the generation of earth's magnetic field. On the other hand, this ring of rolls can also result from a spherical Taylor-Couette instability as expected to be reproduced in a sodium experiment in Grenoble, France. In this work, the mean electromotive force (e.m.f) for such kind of flow structure is derived analytically following the lines of the mean field concept. The main idea is to split the basic mechanisms that could generate the dynamo action at large scale. Some numerical examples are also calculated.
  • Poster
    8th MHD-Days 2005, 28.-29.11.2005, Potsdam, Deutschland

Publ.-Id: 7862 - Permalink

Contactless inductive flow tomography experiments with liquid metals
Gundrum, T.; Gerbeth, G.; Kunadt, H.; Stefani, F.; Xu, M.;
The three-dimensional velocity field of a propeller driven liquid metal flow in a cylindrical vessel is reconstructed by a contactless inductive flow tomography (CIFT). A reliable online monitoring of the flow can already be achieved by applying the external magnetic field alternately in two orthogonal directions and by measuring the corresponding sets of induced magnetic fields. The results of the new technique are shown to be in satisfactory agreement with ultrasonic measurements.
  • Lecture (Conference)
    8th MHD-Days 2005, 28.-29.11.2005, Potsdam, Germany

Publ.-Id: 7861 - Permalink

Simulations of cylindrical dynamos with an integral equation solver: Application to the VKS experiment
Xu, M.; Stefani, F.; Gerbeth, G.; Ravelet, F.; Chiffaudel, A.; Daviaud, F.; Leorat, J.;
The von Karmann sodium (VKS) experiment in Cadarache, France, is intended to study the hydromagnetic dynamo effect in a highly turbulent flow. Up to present, no dynamo effect was measured in this facility, despite the fact that the sodium flow has been carefully optimized. We show that lid layers, i.e. layers of liquid sodium between the impellers and the end walls of the cylinder, and the flow therein are responsible for a dramatic increase of the critical magnetic Reynolds number for cylindrical dynamos of this kind. Possible solutions of this problem are discussed for the real dynamo facility.
  • Poster
    8th MHD-Days 2005, 28.-29.11.2005, Potsdam, Deutschland

Publ.-Id: 7860 - Permalink

Reversals made simple
Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.;
It was shown recently that a simple mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha can show a number of features of Earth's magnetic field reversals. This model relies basically on the existence of an exceptional point of the spectrum of the non-selfadjoint dynamo operator. It is shown that highly supercritical dynamos undergo a self-tuning process into a reversal prone state. As a consequence, reversing dynamos might be much more typical and may occur much more frequently in nature than what could be expected from a purely kinematic perspective.
  • Lecture (Conference)
    8th MHD - Days 2005, 28.-29.11.2005, Potsdam, Germany

Publ.-Id: 7859 - Permalink

Plasma immersion ion implantation of nitrogen into H13 steel under moderate temperatures
Ueda, M.; Leandro, C.; Reuther, H.; Lepienski, C. M.;
Ion implantation of nitrogen into samples of tempered and quenched H13 steel was carried out by plasma immersion technique. A glow discharge plasma of nitrogen species was the ion source and the negative high voltage pulser provided 10-12 kV, 60 mu s duration and 1.0-2.0 kHz frequency, flat voltage pulses. The temperatures of the samples remained between 300 and 450 degrees C, sustained solely by the ion bombardment. In some of the discharges, we used a N-2 + H-2 gas mixture with 1:1 ratio. PIII treatments as long as 3, 6, 9 and up to 12 h were carried out to achieve as thickest treated layer as possible, and we were able to reach over 20 mu m treated layers, as a result of ion implantation and thermal (and possibly radiation enhanced) diffusion. The nitrogen depth profiles were obtained by GDOS (Glow Discharge Optical Spectroscopy) and the exact composition profiles by AES (Auger Electron Spectroscopy). The hardness of the treated surface was increased by more than 250%, re! aching 18.8 GPa. No white layer was seen in this case. A hardness profile was obtained which corroborated a deep hardened layer, confirming the high efficacy of the moderate temperature PIII treatment of steels.
  • Nuclear Instruments and Methods in Physics Research B 240(2005), 204-207

Publ.-Id: 7858 - Permalink

Comparison of nitrogen ion beam and plasma immersion implantation in A15052 alloy
Ueda, M.; Reuther, H.; Lepienski, C. M.;
Experiments comparing nitrogen ion implantations in Al5052 by beam and plasma immersion were carried out. Beam implantation (BI) was carried out using a 100 keV, high current beam implanter while the plasma immersion ion implantation (PIII) was obtained using a glow discharge plasma source coupled to a pulsed high voltage supply. A nitrogen BI dose of 5 x 10(17) cm(-2) at 100 keV was attained with near Gaussian implantation profile while the PIII was performed until we reached similar doses with a maximum energy of 15 keV. Implantation profiles were obtained by Auger electron spectroscopy (AES). X-ray diffraction (XRD) indicated the formation of AlN in both cases but it was more clearly demonstrated by high resolution AES. For BI treatment, a buried AlN layer was achieved while for PIII, a layer of AlNxOy close to the surface was seen. Due to the high temperature reached in the PIII processing (400 degrees C), a softening of the Al5052 bulk resulted while for BI processed sa! mples with < 200 'C an increase in hardness was observed.
  • Nuclear Instruments and Methods in Physics Research B 240(2005), 199-203

Publ.-Id: 7857 - Permalink

Chromium enrichment of AISI 304 stainless steel surface after nitrogen ion recoil bombardment of chromium film
Gomes, G. F.; Ueda, M.; Beloto, A.; Reuther, H.; Richter, E.;
When performing nitriding of stainless steels, there is a decrease or even complete depletion of chromium in the nitrogen rich region just beneath the surface, inhibiting the formation of passivated Cr oxide layer, beneficial to withstand corrosive attacks and Cr/Fe nitrides, responsible for hardness enhancement. To overcome this problem, a hybrid technique was used, consisting of depositing a thin chromium film on steel surface and then bombarding it with nitrogen ions. By a complex recoil process, chromium atoms are implanted into the steel matrix. Plasma immersion ion implantation (PIII) was used in this bombardment. The new Cr-rich layer allows the formation of Cr oxides and nitrides. Treated surfaces were characterized by Auger electron spectroscopy (AES) and conversion electron Mossbauer spectroscopy (CEMS), showing formation of a new Cr-rich layer. (c) 2005 Elsevier B.V. All rights reserved.
  • Nuclear Instruments and Methods in Physics Research B 240(2005)1-2, 194-198

Publ.-Id: 7856 - Permalink

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