Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35172 Publications

Cluster Core Controlled Reactions of Substitution of Terminal Bromide Ligands by Triphenylphosphine in Octahedral Rhenium Chalcobromide Complexes

Shestopalov, M. A.; Brylev, K. A.; Kozlova, S. G.; Fedorov, V. E.; Spies, H.; Pietzsch, H.-J.; Stephan, H.; Geipel, G.; Bernhard, G.

Reactions of rhenium chalcobromides Cs4[{Re63-S)8}Br6].2H2O, Cs3[{Re63-Se)8}Br6].2H2O, Cs3[{Re63-Q)73-Br)}Br6].H2O (Q) S, Se), and K2[{Re63-S)63-Br)2}Br6] with molten triphenylphosphine (PPh3) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh3 ligands with general formula [{Re63-Q)8-n3-Br)n}(PPh3)4-nBrn+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, 31P{1H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh3 ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re6Q8-nBrn}n+2. In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q8-nBrn] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re6Q8}(PPh3)4Br2] and fac-[{Re6Se7Br}(PPh3)3Br3] (Q ) S, Se) have been investigated in CH2Cl2 solution and the broad emission spectra in the range of 600-850 nm were observed.

  • Journal of the American Chemical Society 129(2007), 3714-3721

Publ.-Id: 9630

Beta decay of 101 Sn

Kavatsyuk, O.; Mazzocchi, C.; Janas, Z.; Banu, A.; Batist, L.; Becker, F.; Blazhev, A.; Brüchle, W.; Döring, J.; Faestermann, T.; Gorska, M.; Grawe, H.; Jungclaus, A.; Karny, M.; Kavatsyuk, M.; Klepper, O.; Kirchner, R.; La Commara, M.; Miernik, K.; Mukha, I.; Plettner, C.; Plochocki, A.; Roeckl, E.; Romoli, M.; Rykaczewski, K.; Schädel, M.; Schmidt, K.; Schwengner, R.; Zylicz, J.

The decay of the very neutron-deficient isotope 101 Sn was studied at the GSI on-line massseparator using silicon detectors for recording charged particles and germanium detectors for gamma-ray spectroscopy. Based on the beta-delayed proton data the production cross-section of 101 Sn in the 50 Cr+58 Ni fusion-evaporation reaction was determined to be about 60 nb. The half-life of 101 Sn was measured to be 1.9±0.3 s. For the first time beta-delayed gamma rays of 101 Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065 keV transitions in 101 In. The results are discussed by comparing them to predictions obtained from shell-model calculations employing a new interaction in the 88Sr to 132Sn model space.

Keywords: Nuclear energy levels; Beta decay; double beta decay; electron capture; Lifetimes

Publ.-Id: 9629

Cluster dynamics simulation of reactor pressure vessel steels under irradiation

Gokhman, A.; Bergner, F.; Ulbricht, A.; Birkenheuer, U.

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

Keywords: cluster dynamics; reactor pressure vessel steels; neutron irradaition

  • Lecture (Conference)
    4th International Workshop "Diffusion and Diffusional Phase Transformations in Alloys" DIFTRANS-2007, 16.-21.07.2007, Sofiyivka (Uman), Cherkasy region, Ukraine
  • Defect and Diffusion Forum 277(2008), 75-80
  • Contribution to proceedings
    4th International Workshop "Diffusion and Diffusional Phase Transformations in Alloys" DIFTRANS-2007, 16.-21.07.2007, Sofiyivka (Uman), Cherkasy region, Ukraine
    Proceedings of the 4th International Workshop "Diffusion and Diffusional Phase Transformations in Alloys", 75-76

Publ.-Id: 9628

Three-dimensional thermal-hydraulics analysis of ROCOM mixing experiment by RELAP5-3D© code

Frisani, A.; Del Nevo, A.; D’Auria, F.; Höhne, T.; Kliem, S.; Rohde, U.

The mixing phenomenon is relevant for the normal and off normal operation of the Nuclear Power Plant (NPP), because it influences the safety, mitigating the reactivity and structural consequences. The study of these issues was investigated performing experimental campaigns in large-scale test facilities and in real NPPs. In this framework ROCOM (Rossendorf Coolant Mixing Model) test facility was built with the purpose of investigating the coolant mixing phenomena occurring in the Reactor Pressure Vessel (RPV) of a Pressurizer Water Reactor (PWR). The experiments executed in this facility provide experimental data for code validation (CFD and TH-SYS codes). The purpose of this work is to address the capability of the RELAP5-3D© to reproduce ROCOM facility dynamic in simulating the mixing for a large range of operational and accident conditions. In particular, the attention is focused on the effects in the vessel downcomer, lower plenum and core inlet. Three experiments were selected for the analyses: two steady states and one transient. The ROCOM steady states are slug mixing experiments that analyze the mixing scalar trend inside the facility at different mass flow rates. The ROCOM transient represents the injection of a mixing scalar slug from one cold leg with an increasing mass flow rate in the same loop. A systematic comparison between ROCOM experimental data and the results of the simulations with the RELAP5-3D© is presented including a complete set of sensitivity analyses to find out the most relevant parameters which influence the results from nodalization and user effects points of view.

Keywords: Mixing; RELAP5-3D©; ROCOM facility; code assessment

  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
    CD-ROM, paper 159

Publ.-Id: 9626

Begleitende Untersuchungen zur Pilotierung eines Verfahrens zur elektrochemischen Aufbereitung saurer Wässer aus Tagebaurestseen (Zwischenbericht)

Kryk, H.; Schubert, M.; Hessel, G.

Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    86 Seiten
    ISSN: 1437-322X

Publ.-Id: 9623

Experimental determination of the boron concentration distribution in the primary circuit of a PWR after a postulated cold leg small break loss-of-coolant-accident with cold leg safety injection

Kliem, S.; Prasser, H.-M.; Sühnel, T.; Weiss, F.-P.; Hansen, A.

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

Publ.-Id: 9622

Investigation on thin films of new substituted quarterthiophene films of new substituted quarterthiophene

Zelenetskaya, K.; Jähne, E.; Adler, H.-J.; Loppacher, C.; Eng, L.; Grenzer, J.; Scholz, A.

alpha,beta-dicyano substituted beta, beta*-dibutylquarterthiophene (DCNDButQT) was synthesized and fully characterized by 1H-NMR and 13C-NMR, elemental analysis, UV-visible spectroscopy, DSC, TGA and cyclic voltammetry. The band gap energy (deltaEg) calculated from cyclic voltammetry data was found to be 1.97 eV, which is in the range of semiconductor materials (deltaEg < 3.0 eV). DCNDButQT was deposited on different substrates (Al2O3, SiO2, TiO2) by vacuum deposition and solution-cast methods. The structure of the thin films analysed by AFM and XRD showed different morphology depending on cast method. The spin-coating and drop-casting films showed amorphous structure, whereas the vacuum-deposition films exhibit a fine crystalline structure. AFM of vacuum-deposition film revealed the formation of well-ordered terrace structures, the step between adjacent terraces is about 1.5 nm.

Keywords: organic semiconductors

  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany

Publ.-Id: 9621

Ion-induced surface ripples in silicon

Biermanns, A.; Grenzer, J.; Facsko, S.; Grigorian, S.; Pietsch, U.

The morphological evolution of surfaces during ion-beam irradiation has attracted a significant interest due to possibility of the development and the controlling of selforganization in nanostructures. Pattering and texture on nanometer length scale at metal and semiconductor surfaces has become a topic of intense research. In particular the surface and subsurface ripple formation under 40Ar+ ion-beam irradiation of Si (100) crystal has been studied recently. Strong ripple formation has been found for an irradiation energy of 60keV and incident angles around 60degree. During implantation a corrugated surface layer is formed, consisting of a strongly damaged, amorphous near-surface layer followed by a nearly sinusoidal shaped interface towards the crystalline material. In the present work, we investigate the onset and evolution of ripple-formation as function of implantation energy and incidence angle of the ion beam.

Keywords: ion beam induced rippling

  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany

Publ.-Id: 9620

Glycoxidised LDL isolated from subjects with impaired glucose tolerance increases CD36 and peroxisome proliferator-activator receptor gamma gene expression in macrophages

Graessler, J.; Pietzsch, J.; Westendorf, T.; Julius, U.; Bornstein, S. R.; Kopprasch, S.

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

Publ.-Id: 9619

Forward and inverse problems in MHD: numerical and experimental results

Stefani, F.; Gailitis, A.; Gerbeth, G.; Gundrum, T.; Xu, M.

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

Publ.-Id: 9618

Mechanical and tribological properties of carbon and nitrogen consecutive ion implantation into aluminium

Szcancoski, J. C.; Foerster, C. E.; Serbena, F. C.; Fitz, T.; Kreissig, U.; Richter, E.; Möller, W.; Lepienski, C. M.; Soares, P. C.; Siqueira, C. J.

Mechanical and tribological properties of successive C and N ion implantation into Al were studied in the present work. Ion sequence, substrate temperature and subsequent thermal treatment were performed in order to understand the involved mechanisms on the surface hardening. The results showed that independent of the ion sequence, a higher surface hardness is obtained for room temperature ion implantation (≈ 10 GPa). At high substrate temperature the hardness decreases to 7 GPa. The hardening mechanisms are discussed in terms of: solid solution, hard embedded precipitates in the soft Al matrix and the damage produced by the ion implantation process. Adhesive and abrasive regimes are identified from the friction coefficient profiles and are function of the ion implantation parameters. Wear resistance is improved if subsequent thermal treatment at high temperature is performed. Wear improvement is correlated to the presence of a high concentration of carbon clusters in the Al matrix.

Keywords: Mechanical properties; Nanoindentation; Carburising; Nitriding; Aluminium; Wear

  • Surface & Coatings Technology 201(2006)3-4, 1488-1494

Publ.-Id: 9616

Investigation of K+ meson production in C+C collisions at 2A GEV with HADES

Sadovsky, A.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-464 2007
    ISSN: 1437-322X


Publ.-Id: 9615

Annual Report 2006 - Institute of Radiochemistry

Bernhard, G.; Foerstendorf, H.; Richter, A.; Viehweger, K.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-459 2007
    ISSN: 1437-322X


Publ.-Id: 9614

Effects of irradiation damage on the back-scattering of electrons: silicon-implanted silicon

Nasdala, L.; Kronz, A.; Grambole, D.; Trullenque, G.

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

Keywords: Back-scattered electron images; Raman spectroscopy; electron back-scatter diffraction; radiation damage; silicon

  • American Mineralogist 92(2007), 1768-1771

Publ.-Id: 9613

Gammatomographie zur Messung von Voidverteilungen im SWR-Bündel am KATHY-Versuchsstand in Karlstein Abschlussbericht 2007

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

Dieser Bericht beinhaltet insbesondere diejenigen durchgeführten Arbeiten und Untersuchungen, welche für die Planung zukünftiger Experimente am KATHY - Versuchsstand relevant sind. Der Bericht unterteilt sich in zwei voneinander weitgehend unabhängige Teile, zum einen die technische Weiterentwicklung des Tomographen (Abschnitt 2) und zum anderen methodisch orientierte Studien und Experimente (Abschnitt 3) betreffend. Konzeptionell basiert der Bericht auf Auswertungen der an KATHY im Oktober 2005 und Januar 2006 durchgeführten Experimente, wobei diese Auswertungen hier nicht noch einmal in ihrer Gesamtheit dargelegt werden, sondern nur auf ihre zukünftig relevanten Aspekte Bezug genommen wird.

Keywords: gamma tomography; determination of void distribution

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    45 Seiten
    ISSN: 1437-322X

Publ.-Id: 9612

Numerical simulation of coolant mixing in a pressurized water reactor with different CFD methods based on complex meshes

Höhne, T.

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

Keywords: Boron Dilution; CFD; Pressurized Water Reactor; Coolant Mixing

Publ.-Id: 9611

Complexation of uranium(VI) with aromatic acids such as hydroxamic and benzoic acid investigated by TRLFS

Glorius, M.; Moll, H.; Geipel, G.; Bernhard, G.

The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We observed in all three systems a decrease in the fluorescence intensity with increasing ligand concentration. All identified complexed uranyl species are of the type MpLqHr. In the uranium(VI)-salicylhydroxamate system a 1:1 complex with a stability constant of log β111 = 17.34 ± 0.06 and a 1:2 complex with a stability constant of log β122 = 35.0 ± 0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be log β110 = 7.92 ± 0.11 and log β120 = 16.88 ± 0.49. In the uranium(VI)-benzoate system only a 1:1 complex is existent with a stability constant of log β110 = 3.56 ± 0.05.

Keywords: Uranyl; Hydroxamic acid; Spectroscopy; TRLFS; Complexation

  • Journal of Radioanalytical and Nuclear Chemistry 277(2008)2, 371-377

Publ.-Id: 9610

Ferromagnetism in GaN induced by Fe ion implantation

Talut, G.; Reuther, H.; Stromberg, F.; Zhou, S.; Potzger, K.; Eichhorn, F.

We report about magnetic and structural studies on p-type GaN implanted with 57Fe with fuences from 1*10^16cm^-2 to 1.6*10^17cm^-2 at different temperatures and subsequently subjected to thermal treatment. X-ray diffraction, transmission electron microscopy, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometry were used for the crystallographic, electronic and magnetic characterization of the samples. Room temperature ferromagnetism was observed in GaN after implantation at 623 K with different fluences and is mainly ascribed to alpha-Fe precipitations. An additional contribution to ferromagnetic signal is observed in a Mössbauer spectrum and as a magnetization loop in SQUID in sample implanted with lowest fluence at 623 K which cannot be related to alpha-Fe. In samples implanted with low fluences at RT no ferromagnetism was observed by means of SQUID. However, in CEMS a 6.8 T magnetic hyperfine field was used to fit the experimental spectrum and is discussed in terms of possible origin. Samples implanted at 240 K do not exhibit ferromagnetic properties. Precipitation of alpha-Fe was successfully reduced by decreasing the implantation temperature, however this was accompanied by an enhanced crystal damage. Annealing between 973 K and 1123 K resulted in most cases predominantly in the formation of alpha-Fe-clusters. Thermal treatment brought no significant recover of the crystallinity as it was verified by RBS channeling measurements.

Keywords: Diluted magnetic semiconductor; GaN; ferromagnetism; Fe

  • Journal of Applied Physics 102(2007), 083909
  • Poster
    Nanospintronic Design and Realization 2007, 21.-25.05.2007, Dresden, Germany
  • Poster
    International Conference on the Applications of the Mössbauer Effect, 14.-19.10.2007, Kanpur, India

Publ.-Id: 9609

Charakterisierung des Opalinus-Tones und erste Ergebnisse zur U(VI)-Komplexierung mit Huminsäure-Modellliganden

Joseph, C.

Eine homogenisierte Probe Opalinus-Ton wurde charakterisiert. Die erhaltenen Ergebnisse (CEC, BET, TOC, XRD, IR) stimmen mit denen in der Literatur beschriebenen Ergebnissen überein. Erste Untersuchungen der U(VI)-Komplexierung mit HS-Modellliganden wurden durchgeführt.

Keywords: Opalinus clay; characterization; U(VI)-complexation; HA

  • Lecture (others)
    Workshop des Verbundprojektes Wechselwirkung und Transport von Actiniden im natuerlichen Tongestein unter Beruecksichtigung von Huminstoffen und Tonorganika, 02.-03.04.2007, Potsdam, Deutschland

Publ.-Id: 9608

Measurement of Mg-25(p, gamma)Al-26(g) resonance strengths via accelerator mass spectrometry

Arazi, A.; Faestermann, T.; Niello, J.; Knie, K.; Korschinek, G.; Poutivtsev, M.; Richter, E.; Rugel, G.; Wallner, A.

The strengths of resonances located at center-of-mass energies of E-c.m.=189, 304, 374, and 418 keV for the Mg-25(p,gamma) reaction have been measured for the first time with an off-line method: Mg targets were firstly activated with protons at the resonance energies and the produced Al-26(g) nuclei were counted by means of highly sensitive accelerator mass spectrometry (AMS). Thus, the production of Al-26 in its ground state is determined independently from the gamma-decay branching ratio. While the 304, 374, and 418 keV resonances show fair agreement with previous measurements, the 189 keV resonance yield a significantly less strength. In addition, an experimental upper limit for the E-c.m.=92 keV resonance was determined.

  • Physical Review C 7402(2006)2, 5802

Publ.-Id: 9607

Superconducting regions and Kondo effect of MgB2 formed by implantation of magnesium ions into boron substrate

Trybula, Z.; Kempinska, W.; Andrzejewski, B.; Piekara-Sady, L.; Kaszynski, J.; Trybula, M.; Piekoszewski, J.; Stanislawski, J.; Barlak, M.; Richter, E.

The results of investigation of the polycrystalline boron implanted by magnesium and argon plasma pulse treatment are presented. The four-probe electric conductivity measurements and magnetically modulated microwave absorption showed the presence of superconducting islands below the temperature of 25 K. Below T = 23 K we detected the Kondo effect, a logarithmic increase in the resistivity as the temperature is lowered, due to iron impurity.

  • Open Access Logo Acta Physica Polonica A 109(2006)4-5, 657-660

Publ.-Id: 9606

Einfluss von HS auf die U(VI)- und Am(III) Sorption an Kaolinit: TRLFS Untersuchungen

Krepelova, A.

We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.
Laser fluorescence spectroscopy measurements were carried out in the systems Am(III)-kaolinite and Am(III)-HA-kaolinite to study the surface complexes of Am(III) on kaolinite at different pH values (pH 5 - 8). HA decreases the fluorescence intensity of the samples. The shape of the measured fluorescence spectra in both systems, binary and ternary, differs from the spectrum observed in the solution. Further measurements are required to satisfactorily explain the obtained results.

Keywords: Sorption; kaolinite; HA; Am(III); U(VI); TRLFS

  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlilchen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 02.-03.04.07, Potsdam, Deutschland

Publ.-Id: 9605

Modeling of a Buoyancy-Driven Flow experiment in Pressurized Water Reactors using CFD-Methods

Höhne, T.; Kliem, S.

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

Keywords: Safety; Thermalhydraulics; Coolant Mixing; CFD

  • Open Access Logo Nuclear Engineering and Technology 39(2007)4, 327-336

Publ.-Id: 9604

P implantation into pre-amorphized germanium and subsequent annealing: solid phase epitaxial regrowth, P diffusion and activation

Posselt, M.; Schmidt, B.; Anwand, W.; Grötzschel, R.; Heera, V.; Wündisch, C.; Skorupa, W.; Hortenbach, H.; Gennaro, S.; Bersani, M.; Giubertoni, D.; Möller, A.; Bracht, H.

High fluence P implantation (30 keV, 3x1015 cm-2) into pre-amorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. In contrast to previous assumptions a significant P diffusion in amorphous Ge is not observed. However, during the fast solid phase epitaxial regrowth a rapid redistribution of P occurs. After completion of the regrowth and at temperatures above 500 0C, a concentration-dependent diffusion of P in crystalline Ge takes place. An appreciable influence of implantation defects on the diffusion coefficient of P cannot be found. For 60 s rapid thermal annealing at 600 0C and for 20 ms flash lamp annealing at 900 0C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ohm , respectively, and the maximum electrical activation of P is about 3 – 7x1019 cm-3.

Keywords: germanium implantation annealing doping

  • Contribution to proceedings
    International Workshop on INSIGHT in Semiconductor Device Fabrication, Metrology and Modeling (INSIGHT-2007), 06.-09.05.2007, Napa, United States
    Proceeding INSIGHT-2007 Workshop, 309-315
  • Lecture (Conference)
    International Workshop on INSIGHT in Semiconductor Device Fabrication, Metrology and Modeling (INSIGHT-2007), 06.-09.05.2007, Napa, United States

Publ.-Id: 9603

Experiments on the interface dynamics of stratified air/water flows

Vallee, C.

For the investigation of co-current two-phase flows, the Horizontal Air/Water Channel (HAWAC) was built at Forschungszentrum Dresden-Rossendorf. A special inlet device provides well-defined as well as variable boundary conditions for generic horizontal two-phase flow experiments. Optical measurements were performed with a high-speed video camera during slug flow. By an interface capture method, the water level can be measured in any observed cross-section. As a result, the water level history can be extracted from the image sequences. Furthermore, the profiles of the time-averaged water level bounded by the standard deviation were presented and show the evolution of the flow structure and of its dynamic component along the channel.

Keywords: horizontal two-phase flow; slug flow; image processing

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
    Jahrestagung Kerntechnik 2007 - Fachsitzung, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft, 23-26
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany

Publ.-Id: 9602

Synthesis report on work package 2.1: Pressurized Thermal Shock (PTS) - T0+24

Lucas, D.

This report summarizes the results of the first 24 months period of the NURESIM project for the work package 2.1 “Pressurized Thermal Shock (PTS)”. It mainly bases on the deliverables supplied by the partners involved in this work package. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the contributions are sorted according to these flow situations. The relation of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The present status PTS work package is in agreement with the planning of the NURESIM project, the expected results were met by the deliverables. The work done leads to an improvement of the simulation capabilities regarding a PTS flow situation, but caused by the complexity of the issue it will still be a long way to enable reliable predictions for the whole process from such simulations.

Keywords: PTS; CFD; Two-Phase Flow

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    27 Seiten
    ISSN: 1437-322X

Publ.-Id: 9601

On the simulation of two-phase flow pressurized thermal shock (PTS)

Lucas, D.; Bestion, D.; Bodèle, E.; Scheuerer, M.; F. D’Auria, D. M.; Smith, B.; Tiselj, I.; Martin, A.; Lakehal, D.; Seynhaeve, J.-M.; Kyrki-Rajamäki, R.; Ilvonen, M.; Macek, J.

This paper reports some activity about the Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. The PTS phenomenon is expected to take place in some water cooled nuclear reactors equipped with pressure vessels during selected accident scenarios. The PTS implies the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. Current generation Pressurized Water Reactors, PWR (including the Russian VVER types), are primarily affected by the phenomenon which is investigated within three broad areas: material damage originated by irradiation, thermal-hydraulics (including single and two-phase flow conditions in the region of the ‘shock’) and structural mechanics with main reference to fracture mechanics. The present paper, in the area of thermal-hydraulics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. Within the above context, the paper summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase mechanisms (or sub-phenomena) are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance (case of two phase flow) is presently not available.

Keywords: PTS; Two-Phase Flow; CFD

  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, paper [035], 30.09.-04.10.2007, Pittsburgh, Pennsylvania, United States
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, Pennsylvania, United States

Publ.-Id: 9600

CFD Modellierung in der Sicherheitstechnik - Möglichkeiten und Grenzen

Prasser, H.-M.; Frank, T.; Höhne, T.; Lucas, D.

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

Keywords: CFD; Leitfähigkeitsmesstechnik; MUSIG

  • Lecture (Conference)
    ProcessNet-Jahrestagung 2007, 16.-18.10.2007, Aachen, Deutschland

Publ.-Id: 9599

R&D on RPC with CBM

Dohrmann, F.; Kotte, R.; Naumann, L.; Stach, D.; Sytcheva, A.; Wüstenfeld, J.

The talk summarizes the latest tests and results w.r.t. MRPCs with silicate glass resistive plates. These
have been tested in a high flux environment with a continous electron beam at ELBE.

  • Lecture (Conference)
    9. Collaboration Meeting of the CBM Experiment at FAIR, 27.02.-02.03.2007, Darmstadt, Germany

Publ.-Id: 9598

Dielectron detection capabilities of HADES at SIS100/300

Bannier, B.

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

  • Lecture (Conference)
    Gießen 07 - DPG Frühjahrstagung, Hadronen und Kerne, 12.-16.03.2007, Giessen, Germany

Publ.-Id: 9597

Properties of Multigap RPC detectors tested with continuous electron beams at ELBE

Dohrmann, F.; Kotte, R.; Naumann, L.; Stach, D.; Sytcheva, A.; Wüstenfeld, J.

Multigap Resistive Plate Chambers (MRPC) provide the possibility for assembling high-granularity, large-area TOF sytems designed for modern nuclear and particle physics experiments. Currently, experiments like ALICE, STAR, FOPI, HADES prepare MRCP based TOF systems with time resolutions of less than 100 ps. The planned CBM experiment at the future FAIR facility at GSI/Darmstadt considers using an MRPC system provided sufficient time resolution and rate stability can be achieved. These properties of MRCP have been successfully demonstrated in prototype tests performed at the FZD electron linac ELBE, using continuous e− beams of 20-40 MeV. Typical time resolutions of 70 ps were achieved. The rate capabilities of MRCP using special low-resistive silicate glas were tested and stable efficiencies up to rates of 20 kHz/cm2 were observed.

  • Lecture (Conference)
    Gießen 07 - DPG Frühjahrstagung 2007, Hadronen und Kerne, 12.-16.03.2007, Giessen, Germany

Publ.-Id: 9596

Ion beam synthesis of 4H-(Si1-xC1-y)Gex+y solid solutions

Pezoldt, J.; Kups, T.; Voelskow, M.; Skorupa, W.

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

Keywords: silicon carbide; germanium implantation; rapid thermal annealing; RBS

Publ.-Id: 9595

DYN3D/ATHLET calculations of a boron dilution transient during natural circulation conditions

Kliem, S.; Rohde, U.

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

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

Keywords: boron dilution; natural circulation; neutron kinetics/thermal hydraulics coupling; coolant boiling

  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, United States
    Proceedings of the 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, CDROM, paper 053, 0894480588
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, United States

Publ.-Id: 9594

Dilepton production in pp and CC collisions with HADES

Fröhlich, I.; Agakichiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munziger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Duran, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hadjivasiliou, C.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kugler, A.; Kühn, W.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, S.; Lopez, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Palka, M.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Senger, P.; Shileev, K.; Simon, R. S.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniovski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

e+e- production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2 GeV kinetic energy, the exclusive η production and the Dalitz decay η -> γe+e- have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e+e- invariant-mass spectrum from the 12C +12C reaction at 2 AGeV is presented and compared with a simplified thermal model.

Publ.-Id: 9593

Nickel nanoparticle catalysed formation of fullerene like carbon nanostructures - a Raman analysis

Krause, M.; Abrasonis, G.; Kolitsch, A.; Mücklich, A.; Möller, W.

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

Keywords: Carbon films; Nanocomposites; Nickel catalysis; Raman

  • Poster
    XXIst International Winterschool Molecular Nanostructures, 10.-17.03.2007, Kirchberg, Österreich

Publ.-Id: 9591

Superposition of quantum and classical rotational motions in Sc2C2@C84 fullerite

Michel, K. H.; Verberck, B.; Hulman, M.; Kuzmany, H.; Krause, M.

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

Keywords: Fullerenes; Quantum Rotation

Publ.-Id: 9590

Hydrogen peroxide treatment induced rectifying behavior of Au/n-ZnO contact

Gu, Q. L.; Ling, C. C.; Chen, X. D.; Cheng, C. K.; Ng, A. M. C.; Beling, C. D.; S. Fung, S.; DjurišIć, A. B.; Brauer, G.; Ong, H. C.

Conversion of the Au/n-ZnO contact from Ohmic to rectifying with H2O2 pretreatment was studied systematically using I-V measurements, x-ray photoemission spectroscopy, positron annihilation spectroscopy, and deep level transient spectroscopy. H2O2 treatment did not affect the carbon surface contamination or the EC–0.31 eV deep level, but it resulted in a significant decrease of the surface OH contamination and the formation of vacancy-type defects (Zn vacancy or vacancy cluster) close to the surface. The formation of a rectifying contact can be attributed to the reduced conductivity of the surface region due to the removal of OH and the formation of vacancy-type defects.

  • Applied Physics Letters 90(2007), 122101

Publ.-Id: 9589

Dresden pulsed magnetic field facility

Wosnitza, J.; Bianchi, A. D.; Freudenberger, J.; Haase, J.; Herrmannsdörfer, T.; Kozlova, N.; Schultz, L.; Skourski, Y.; Zherlitsyn, S.; Zvyagin, S. A.

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71T with a pulse duration of about 100 ms have been designed, constructed, and tested. A two-coil 100 T magnet and a long-pulse (1000 ms) 60T magnet are under construction. Electrical transport and magnetization experiments are running routinely in the pilot laboratory at the IFW Dresden. The feasibility of NMR experiments in pulsed-field environments has been proven.

  • Journal of Magnetism and Magnetic Materials 310(2007), 2728-2730

Publ.-Id: 9588

Magnetism of the single molecule magnet system [(MnIIL2)3MnII](BF4)2

Prinz, M.; Voget, S.; Damnik, N.; Raekers, M.; Kuepper, K.; Chaudhuri, P.; George, S.; Coldea, M.; Neumann, M.

The single molecule magnet system [(MnIIL2)3MnII](BF4)2 containing four Mn2+ ions has been studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XMCD). The XPS Mn 2p and Mn 3s spectra confirm the manganese 2+ valency. From XMCD measurements at a temperature of T = 2 K and a magnetic field of B = 5 T we obtained a high magnetic moment of 12 μB/f.u. This spin moment agrees in an excellent way with magnetic measurements which show a magnetization saturation of 10 μB/f.u. at 7 T and 2 K. From XMCD a quenching of the Mn orbital moments was observed (morb = 0.4 μB/f.u.).

Keywords: Molecular magnetism; Mn2+ complex; x-ray magnetic circular dischroism

  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des AKF, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9587

Investigation of high-k materials RScO3 (R=Sm,Gd,Dy) by XPS and band structure calculations

Raekers, M.; Bartkowski, S.; Kuepper, K.; Zhou, S.; Potzger, K.; Postnikov, A.; Uecker, R.; Neumann, M.

There has been considerable interest in high-k-dielectrics rare earth oxides as replacement for SiO2 in advanced field-effect transistors (FETs). Promising candidates are the perovskites SmScO3, GdScO3 and DyScO3. A tendency towards antiferromagnetic ordering at low temperatures is observed for the high magnetic moments at rare earth atoms. We analyse the electronic structure of the single crystalline samlpes by means of X-ray photoelectron spectroscopy and firstprinciples theory. The electronic structure calculations are performed with the augmented plane waves method (WIEN2k code) of the density functional theory, taking into account the spin-orbit interaction and orbital-dependent potential (LDA+U). The calculated positions of the main features in the valence band agree with the XPS data, the underlying chemical bonding can be analysed in detail. Small differences in the electronic structure, resulting in different stability of ferroand antiferromagnetic configurations, are discussed.

Keywords: high-k dielectrics; wide band gap insulators; perovskites; electronic structure calculations; x-ray photoelectron spectroscopy

  • Poster
    DPG Jahrestagung und DPG Frühjahrstagung des AKF, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9586

Magnetization dynamics of a single cross-tie wall

Kuepper, K.; Marko, D.; Buess, M.; Raabe, J.; Quitmann, C.; Fassbender, J.

We report the imaging of the magnetic excitation spectrum of a single cross-tie wall by means of x-ray magnetic circular dichroism - photoemission electron microscopy (XMCD-PEEM). The permalloy rectangle was excited by a short magnetic in plane pulse with a maximum field value of about 20 Oe. The high temporal and lateral resolution allows a detailed quantitative analysis of the magnetodynamic excitations. We find new eigenmodes in the frequency domain which are characteristic for the vortex-antivortex interaction in a single cross-tie wall. We discuss our experiment along micromagnetic simulations.

Keywords: vortex; antivortex; cross-tie wall; magnetization dynamics

  • Lecture (Conference)
    DPG Jahrestagung und DPG Frühjahrstagung des AKF, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9585

Nanomagnetism at the Forschungszentrum Dresden-Rossendorf

Kuepper, K.

The activities of the nanomagnetism group at the Forschungszentrum Dresden-Rossendorf will be briefly presented.
Special emphasis will be given to lateral and time resolved x-ray microscopies in order to study the magnetization
dynamics of micromagnetic elements in detail.

Keywords: Nanomagnetism; vortex; antivortex; dynamics

  • Lecture (others)
    MSD Seminar, Argonne National Lab., Argonne, USA, 17.01.2007, Argonne, USA

Publ.-Id: 9584

Operational Experiences with Megawatt PV Plants in Central Germany

Rindelhardt, U.; Bodach, M.

Stimulated by the German Feed-in-Law, a number of grid-connected Megawatt PV plants have been put into operation during the last 5 years. Because of the higher irradiance these plants were originally concentrated in the southern part of Germany (Bavaria and Baden-Wuerttemberg). Starting in 2004 some plants have been also installed in Central Germany. The paper describes design and operation results of seven plants operating in the region of Saxony and Thuringia.

Locations and design
The most plants are concentrated in a region earlier defined by the DWD as "solar island" around Leipzig and Chemnitz. One plant is located in north-west Thuringia.
All plants were built on heavily used or loaded areas (former industrial sites or waste sites). Different types of fundaments and rack support constructions (desks) were used for the module mounting. The connection with the grid was done in the 10 to 20 kV voltage level, the distance between the plants and the grid was several thousands meters in some cases. All plants started their operation before 2006. The operation of the plants is monitored by the owners or by professional service providers.

Results and conclusions
The operation results of the year 2006 are exemplarily presented. The solar irradiance in 2006 was higher than the long year average, similar to the years before. The final yield of the plants ranges between 950 and 1050 kWh/kW. These surprisingly high values are near the values which were only found in Germany south of 50° latitude so far. The final yield of the tracked plant in Borna surpasses the yield of the other plants by 25%.
The performance ratios were determined to be between 0.77 and 0.84. The sources of energy losses are analysed and discussed. Beside component failures in the plants also grid disconnections reduced the feed-in energy in some cases.
Finally a long term estimation of the yield for the different plants will be given. Based on the data of the year 2006 a mean yield between 900 and 1000 kWh/kW can be expected.

Keywords: photovoltaics; PV plants; performance

  • Contribution to proceedings
    22. European Photovoltaic Solar Energy Conference, 03.-07.09.2007, Milano, Italy
    Operational Experiences with Megawatt PV Plants in Central Germany, 3-936338-22-1, 2952-2955
  • Lecture (Conference)
    22. European Photovoltaic Solar Energy Conference, 03.-07.09.2007, Milano, Italy

Publ.-Id: 9581

Kernenergie im 21. Jahrhundert - Herausforderungen und Möglichkeiten

Rindelhardt, U.

Im Beitrag werden die Optionen und die Herausforderung für die Nutzung der Kernenergie im 21. Jahrhundert aufgezeigt. Ausgangspunkt sind die vorhandenen Vorräte an Kernbrennstoff und die Darstellung seiner derzeitigen Nutzung. Die Entwicklung der Kernkraftwerkstechnik seit 1960 wird beispielhaft dargestellt. Die Optionen und Entwicklungsziele der Kernreaktoren der 4. Generation (EInsatz etwa ab 2040) werden exemplarisch vorgestellt. Dabei wird besonders auf die zentrale Rolle der schnellen Brutreaktoren eingegangen.Ein besonderer Abschnitt ist der Wiederaufarbeitung und Endlagerung von Kernbrennstoff gewidmet.

Keywords: Kernenergie; Kernkraftwerke; Kernbrennstoff

  • Lecture (others)
    Informationsveranstaltung, 18.04.2007, Chemnitz, Deutschland

Publ.-Id: 9580

Laserinduzierte Breakdown-Detektion (LIBD)

Zänker, H.; Weiß, S.

Die LIBD ist eine Methode, die Kolloidpartikel in sehr niedrigen Konzentrationen zu vermessen vermag. Sie wurde bisher vorwiegend zur Untersuchung von Kolloidproblemen in der Umweltforschung eingesetzt. Wegen ihrer hohen Empfindlichkeit könnte die LIBD potentiell aber auch für die Überwachung von Reinst- und Prozesswässern in der Halbleiterindustrie interessant sein. Hier ist die etablierte Methode zur Überwachung der Partikelfreiheit von Wässern das Single Particle Counting (SPC), vor allem mit den kommerziellen Geräten von PMS und Horiba. Es wird gezeigt, dass (i) für Kolloidpartikel > 50 nm das SPC der LIBD bezüglich der Konzentrationsempfindlichkeit deutlich überlegen ist, (ii) für Kolloidpartikel < 50 nm die Konzentrationsempfindlichkeit der LIBD heute unbefriedigend ist (sie liegt über den zu vermutenden typischen Konzentrationen der Partikel < 50 nm in den Reinstwässern der Halbleiterindustrie), (iii) die LIBD die einzige Methode ist, die überhaupt eine Information über Partikel < 50 nm liefern kann und (iv) durch technische Weiterentwicklung die LIBD wahrscheinlich in den erforderlichen Bereich der Partikelkonzentrationsempfindlichkeit gebracht werden könnte. Die Methode würde (nach Weiterentwicklung) für die Halbleiterindustrie interessant, wenn Partikel der Größe < 50 nm als Verunreinigungen interessant werden.

Keywords: Particle-free waters; semiconductor industries; colloids; laser-induced breakdown detection (LIBD); single particle counting (SPC)

  • Invited lecture (Conferences)
    Seminar über Partikelmessung an Reinstwässern der Halbeiterindustrie, 20.03.2007, Dresden, Deutschland

Publ.-Id: 9579

K0 and Λ production in Ni+Ni collisions near threshold

Merschmeyer, M.; Lopez, X.; Bastid, N.; Crochet, P.; Herrmann, N.; Andronic, A.; Barret, V.; Basrak, Z.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kis, M.; Matulewicz, T.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Mangiarotti, A.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Ryu, M. S.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Xiao, Z.; Xu, H. S.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.

New results concerning the production of neutral strange particles, K0 and Λ in Ni+Ni collisions at 1.93 AGeV, measured with the FOPI detector at GSI Darmstadt, are presented. Rapidity density distributions and Boltzmann slope parameter distributions are measured in nearly the full phase space of the reaction. The observables are compared to existing K+ and proton data. While the K0 data agree with previously reported K+ measurements, the Λ distributions show a different behavior relative to that of protons. The strangeness balance and the production yield per participating nucleon as a function of the centrality of the reaction are discussed, for the first time at SIS energies.

Publ.-Id: 9578

Confinement of strongly anisotropic hot-ion plasma in a compact mirror

Anikeev, A. V.; Bagryansky, P. A.; Ivanov, A. A.; Lizunov, A. A.; Murakhtin, S. V.; Prikhodko, V. V.; Solomakhin, A. L.; Noack, K.

The paper presents the results of recent study of anisotropic plasma with thermonuclear ions confined in the axially symmetric Gas Dynamic Trap (GDT) mirror. Anisotropic ions are produced by the perpendicular injection of two focused 18 keV neutral beams in the small mirror section attached to the GDT central cell. We observed build-up of density of anisotropic ions up to approximately 10^13cm^−3 with the localized spatial profile and the mean energy of 7 keV. The average fast ion density three times exceeded the background plasma density. Fast ion accumulation is accompanied by the decrease of the plasma flux from the central cell recorded outside the mirror, that was qualified as a potential barrier development causing confinement improvement. Analysis of measurement results compared with estimates of plasma parameters in the compact mirror allows to scale to the experiments with next generation neutral beams with increased power and pulse duration.

Keywords: Compact mirror; Anisotropic ions

Publ.-Id: 9577

Practical experiences with the synthesis of [11C]CH3 trough gas phase iodination reaction using a TRACERlabFXC synthesis module

Knieß, T.; Rode, K.; Wüst, F.

The results of [11C]CH3I synthesis through hydrogen gas reduction of [11C]CO2 on different nickel catalysts (HARSHAW-nickel, SHIMALITE-nickel, nickel on silica/alumina, nickel nanosize 99.99%) followed by gas phase iodination using a TRACERlab FXC synthesis unit are reported. Further reaction parameters such as furnace temperatures, flow rate of hydrogen gas and reduction time were optimized. It was found that reduction of [11C]CO2 proceeded in 28-83% yield depending on the nickel catalyst and temperature. The gas phase iodination (methane conversion) gave 31-62% of [11C]CH3I depending on temperature and amount of iodine in the iodine furnace. [11C]CH3I was used for heteroatom methylation reactions exemplified by a piperazine and a phenol (1 and 3). The specific activity of the 11C-labelled products 2 and 4 was determined after HPLC purification and solid-phase extraction. Compounds 2 and 4 were obtained in 8-14% radiochemical yield (decay-corrected, based upon trapped [11C]CH4) within 30 minutes. The specific activity was determined to be in the range of 20-30 GBq/µmol at the end-of-synthesis. Nickel catalyst nanosize was found to be superior compared with other Ni catalysts tested. The relatively low specific activity may be mainly due to carbon contaminations originating from the long copper tubing (500m) between the cyclotron and the radiochemistry facility.

Keywords: [11C]CH4; [11C]CH3I; gas phase iodination; TRACERlabFXC

Publ.-Id: 9576

Dielectron production in C+C and p+p collisions with HADES

Pietraszko, J.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Durán, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P. J. R.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Hadjivasiliou, C.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kugler, A.; Kühn, W.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, S.; Lopez, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Pechenov, V.; Pérez, T.; Pleskac, R.; Pospísil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Senger, P.; Shileev, K.; Simon, R.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wiśniowski, M.; Wójcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

The High Acceptance Di-Electron Spectrometer HADES has been constructed at the SIS accelerator (GSI Darmstadt) to investigate electron-positron pairs produced in proton, pion and heavy ion induced reactions. The main goal of these studies is to explore properties of hadrons in nuclear matter. The apparatus and the experimental results from C+C at 2.0 AGeV and 1.0 AGeV and p+p at 2.2 GeV compared with Monte-Carlo events from a generator based on known cross-sections and branching ratios are presented.

  • International Journal of Modern Physics A 22(2007), 388-396

Publ.-Id: 9575

Experimental investigation of a flow driven by a combination of a rotating and a traveling magnetic field

Cramer, A.; Pal, J.; Gerbeth, G.

Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a traveling magnetic field (TMF). In a cylindrical container, an RMF as well as a TMF alone cause axisymmetric volume forces, which drive according axisymmetric base flows. The combination of both fields gives rise to an inherent three-dimensional part of the electromagnetic force distribution. In case of equal frequencies, this drives a three-dimensional flow consisting of a single large-scale helical motion, which implicates an intense mixing of the melt. The necessary admixture of a TMF to accomplish a qualitative change of the flow structure in a given RMF is shown to be two orders of magnitude smaller in case of equal field frequencies compared to the case of differing frequencies.

  • Physics of Fluids 19(2007)11, 118109

Publ.-Id: 9574

The spherically symmetric α2-dynamo and some of its spectral peculiarities

Günther, U.; Kirillov, O.; Samsonov, B.; Stefani, F.

A brief overview is given over recent results on the spectral properties of spherically symmetric MHD α2-dynamos. In particular, the spectra of sphere-confined fluid or plasma configurations with physically realistic boundary conditions (BCs) (surrounding vacuum) and with idealized BCs (super-conducting surrounding) are discussed. The subjects comprise third-order branch points of the spectrum, self-adjointness of the dynamo operator in a Krein space as well as the resonant unfolding of diabolical points. It is sketched how certain classes of dynamos with a strongly localized α-profile embedded in a conducting surrounding can be mode decoupled by a diagonalization of the dynamo operator matrix. A mapping of the dynamo eigenvalue problem to that of a quantum mechanical Hamiltonian with energy dependent potential is used to obtain qualitative information about the spectral behavior. Links to supersymmetric Quantum Mechanics and to the Dirac equation are indicated.

Keywords: MHD dynamo; operator theory; spectrum; Krein space; boundary conditions; third-order branch points; Jordan structures; diabolical points; resonance; Korteveg-de Vries equation; supersymmetry; Quantum Mechanics; Dirac equation

  • Open Access Logo Acta Polytechnica 47(2007)2-3, 75-81

Publ.-Id: 9573

High Performance Thermal Imaging Using Quantum Well Infrared Photodetector Arrays

Schneider, H.

Quantum well infrared photodetector (QWIP) technology has opened up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging [1]. High thermal and spatial resolution, low 1/f noise, low fixed-pattern noise, and high pixel operability makes QWIP FPAs appropriate for many applications. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. For dual-band/dual-color FPAs, QWIP technology has the unique property that the active region for the long-wavelength band is transparent for the short-wavelength band. In this talk, I will report on typical QWIP structures optimized for thermal imaging applications and on the performance of some state-of-the-art QWIP cameras which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). Besides imagers for the 8 – 12 µm long-wavelength infrared (LWIR) and 3 – 5 µm mid-wavelength infrared (MWIR) regimes these include a LWIR/MWIR dual-band QWIP FPA with 384x288 pixels which, at 6.8 ms integration time, exhibits a noise-equivalent temperature difference as low as 20.6 mK in the LWIR and 26.7 mK in the MWIR spectral bands. A specially designed diffraction grating is used for optical coupling of both spectral regimes. The array, which is based on a photoconductive QWIP for the MWIR and a photovoltaic "low-noise" QWIP for the LWIR, allows for synchronous and pixel-registered image acquisition in both bands. This functionality yields several advantages, including better distinction between target and background clutter, operation in a much wider range of ambient conditions, and the ability of remote absolute temperature measurement.
[1] H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors: Physics and Applications, ISBN 3540363238, Springer Series in Optical Sciences Vol. 126, 2006.

Keywords: quantum well infrared photodetector; QWIP; focal plane array; thermal imaging; noise-equivalent temperature difference; GaAs/AlGaAs

  • Invited lecture (Conferences)
    March Meeting of the American Physical Society, 05.-09.03.2007, Denver, CO, USA

Publ.-Id: 9572

Four-Quark Condensates in Nucleon QCD Sum Rules

Thomas, R.; Hilger, T.; Kämpfer, B.

The in-medium behaviour of the nucleon spectral density including self-energies is revisited within the framework of QCD sum rules. Special emphasis is given to the density dependence of four-quark condensates. A complete catalog of four-quark condensates is presented and relations among them are derived. Generic differences of such four-quark condensates occuring in QCD sum rules for light baryons and light vector mesons are discussed.

Publ.-Id: 9571

An analytical solution for a simple time dependent neutron transport problem with external source

Merk, B.

An analytical solution for the startup of an external source in a homogeneous subcritical reactor problem is developed. The problem is described through an approximation of the Boltzmann Transport equation, the Telegrapher's or time dependent P1 equation. The analytical solution to the problem is expressed in terms of a Green's function.

Keywords: Telegrapher's equation; Neutron Transport; Space-Time Dependent Transport

  • Contribution to proceedings
    20th International Conference on Transport Theory, 22.-28.07.07, Obninsk, Russia
    Book of Abstracts
  • Lecture (Conference)
    20th International Conference on Transport Theory, 22.-28.07.07, Obninsk, Russia

Publ.-Id: 9570

High resolution gamma ray tomography scanner for flow measurement and non-destructive testing applications

Hampel, U.; Bieberle, A.; Hoppe, D.; Kronenberg, J.; Schleicher, E.; Sühnel, T.; Zimmermann, F.; Zippe, C.

We report on the development of a high resolution gamma ray tomography scanner that is operated with a Cs-137 isotopic source at 662 keV gamma photon energy and achieves a spatial image resolution of 0.2 lp/mm at 10% MTF for non-collimated detectors. It is primarily intended for the scientific study of flow regimes and phase fraction distributions in fuel element assemblies, chemical reactors, pipelines and hydrodynamic machines. Furthermore, it is applicable to non-destructive testing of larger radiologically dense objects. The radiation detector is based on advanced avalanche photo diode technology in conjunction with LYSO scintillation crystals. The detector arc comprises 320 single detector elements which are operated in pulse counting mode. For measurements at fixed vessels or plant components we built a CT scanner gantry that comprises rotational and translational stages, power supply via slip rings and data communication to the measurement PC via wireless LAN.

Keywords: Gamma ray tomography; gamma ray detector

Publ.-Id: 9567

The suppression of temperature fluctuations by a rotating magnetic field in a high aspect ratio Czochralski configuration

Grants, I.; Gerbeth, G.

We demonstrate experimentally in a low temperature model that a rotating magnetic field (RMF) has the potential to stabilize the inverse temperature gradient in a medium scale Czochralski facility with a high initial melt level. This stabilization occurs as a result of a flow transition from large scale buoyancy driven to small scale magnetically driven turbulence. The dependency of the required field strength is found vs.\ the imposed temperature drop for an at least 10 times higher Grashof number than in earlier experiments. The observed scaling agrees well with previous results. It is observed that the flow transition becomes even more pronounced, i.e. occurs in a more narrow range of the magnetic forcing, as the Grashof number is increased. The influence of the RMF frequency is investigated. It is found that an increasing frequency of the RMF gradually eliminates the stabilizing effect. The optimum dimensionless frequency is found minimizing the required strength of the RMF. The characteristic azimuthal velocity of the flow is measured by the temperature correlation technique.

  • Journal of Crystal Growth 308(2007)2, 290-296

Publ.-Id: 9566

Thermophysical properties of Nd-, Er-, YNi- alloys

Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.

Nd-Fe-B alloys are widely used in many technical applications due to their excellent permanent magnetic properties. YNi2B2C intermetallic compounds own much attention because of the coexistence of superconductivity and magnetic ordering phenomena. Er2PdSi3 alloys with hexagonal AlB2-type crystallographic structure are of special interest because of their complex magnetic ordering, Kondo and heavy fermion behaviour. The thermophysical properties (electrical conductivity, thermoelectric power, thermal conductivity and viscosity) of these liquid multicomponent intermetallic alloys have been measured in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.

  • International Journal of Materials Research 99(2008), 261-264

Publ.-Id: 9565

Thermal expansion of single-crystalline HoNi2B2C

Schneider, M.; Gladun, A.; Kreyssig, A.; Wosnitza, J.; Souptel, D.; Behr, G.

The thermal expansion a has been measured for single-crystalline HoNi2B2C in the range between 2 and 200 K. At low temperatures, a is dominated by magnetic contributions leading to a strongly anisotropic behaviour with different signs for the expansion coefficients near the antiferromagnetic phase transition. Analysing the magnetic and lattice contributions of a well above this temperature, a nearly isotropic behaviour of the latter one can be deduced. Using the Ehrenfest relation, a relatively weak pressure dependence of the superconducting transition temperature of dTc=dp ¼ 0:1K=GPa was determined for pressure applied along the c direction which points to a rather small pressure-induced lattice stiffening. The ratio between expansion coefficient and specific-heat features large values at the onset of magnetic order.

  • Journal of Magnetism and Magnetic Materials 311(2007), 489-493

Publ.-Id: 9564

Structure and dielectric function of two- and single-domain ZnO epitaxial films

Vinnichenko, M.; Shevchenko, N.; Rogozin, A.; Grötzschel, R.; Mücklich, A.; Kolitsch, A.; Möller, W.

The differences between two- and single-domain ZnO epitaxial films, grown by reactive pulsed magnetron sputtering, have been studied with respect to their texture development and x-ray coherence length behavior at various substrate temperatures and oxygen partial pressures. The film in-plane ordering depends on the surface pretreatment of the sapphire substrate. After pretreatment in an oxygen radio-frequency plasma, single-domain films form even at a substrate temperature of 100 degrees C in a wide range of oxygen pressures, and at a growth rate up to 1.2 nm/s. The single-domain films show a linear dependence of the x-ray coherence length on the substrate temperature, while a steplike dependence is characteristic of the two-domain films. The ZnO complex dielectric function was obtained using a parametrized semiconductor oscillator model for spectroscopic ellipsometry data analysis. For the films grown at 550 degrees C, the band gap of 3.29 +/- 0.01 eV is independent of the type of in-plane ordering and variation of the texture. The oscillator broadening correlates with the width of (0002) diffraction peak rocking curve. Both parameters increase at high oxygen pressure and low substrate temperature, which is attributed to a higher defect (dislocation) density.

Keywords: ZnO; reactive pulsed magnetron sputtering; epitaxial growth; in-plane ordering; texture; spectroscopic ellipsometry; dielectric function

Publ.-Id: 9563

Novel supported Pd hydrogenation bionanocatalyst for hybrid homogeneous/heterogeneous catalysis

Creamer, N.; Mikheenko, I.; Yong, P.; Deplanche, K.; Sanyahumbi, D.; Wood, J.; Pollmann, K.; Merroun, M.; Selenska-Pobell, S.; Macaskie, L.

Homogeneous and heterogeneous catalysis approaches to hydrogenation have different advantages and disadvantages and hybrid approaches are sought to maximise the advantages of both. Bacterial cells, of length 1-2 microns, present an economical alternative to conventional micro-scale supports such as graphite and alumina. Certain strains of bacteria can reduce soluble Pd(II), from stock solutions or acid extracts of spent catalysts, forming nanocrystals of Pd which are supported within the bacterial cell surface layers. The biologically-supported nano-Pd contains particles of size ~ 5nm and below, as determined using magnetic measurements (SQUID) and EXAFS. Bio-nano-Pd supported on exemplar Gram negative and Gram positive bacterial types catalysed the hydrogenation of itaconic acid (initial rates 1.1 and 1.2 × 10-4 mol gPd-1 s-1 ) comparing well with commercial 5% Pd-graphite (1.3 × 10-4 mol gPd-1 s-1).

Keywords: Bacillus sphaericus Desulfovibrio desulfuricans; heterogeneous catalyst; hydrogenation; itaconic acid; palladium

Publ.-Id: 9562

A new FEFF-based wavelet for EXAFS data analysis

Funke, H.; Chukalina, M.; Scheinost, A.

A new mother wavelet function for extended X-ray absorption fine-structure (EXAFS) data analysis has been designed, combining a model EXAFS function derived from the ab initio EXAFS code FEFF8.20 and the complex Morlet wavelet. This new FEFF–Morlet mother wavelet routine allows the generation of wavelets well adapted to specific EXAFS problems. A substantial gain in resolution of the wavelet ridges in k and r space is achieved. The method is applied to a structural problem of Zn–Al double-layer hydroxides, demonstrating unequivocally the homogeneity of the metal cation distribution in the hydroxide layers.

Keywords: EXAFS; wavelet transform; data evaluation; layered double hydroxides

Publ.-Id: 9561

Interactions of U(VI) with members of a microbial consortium recovered from a uranium mining waste pile

Reitz, T.; Geissler, A.; Merroun, M.; Selenska-Pobell, S.

Treatments of a soil sample from a uranium mining waste pile with uranyl nitrate led to a shifting in the crenarchaeal populations from subgroup 1.1a to 1.1b. Efforts to culture members of these Crenarchaeota resulted in an enrichment of a mixed microbial consortium consisting of representatives of 1.1b Crenarchaeota and Firmicutes.
In this study interactions of U(VI) with a pure culture of Paenibacillus sp. JG35+U4-B1 isolated from the mentioned consortium were studied by using a combination of wet chemistry and microscopic methods. Preliminary analyses on U sorption showed that the Paenibacillus strain studied accumulated up to 85 mg U/g dry biomass from a solution with an initial uranium concentration of 120 mg U/l. Live/Dead cell staining indicated that less than 10% of the U-treated cells were viable. Transmission electron microscope (TEM) analyses showed that the cells of the isolated strain accumulated uranium intracellularly as needle-like fibrils (Fig. 1A), and also at the cell surface (Fig. 2A). Energy dispersive X-ray (EDX) analysis of these U accumulates demonstrated the presence of U and P peaks (Figs. 1B and 2B) indicating that in both cases the phosphate groups are, probably, the main functional binding sites for U(VI).

  • Lecture (Conference)
    Journées des Actinides 2007, 24.-27.03.2007, Sesimbra, Portugal
  • Contribution to proceedings
    37ièmes Journées des Actinides, 24.-27.03.2007, Sesimbra, Portugal
    Programme and Abstracts, 56

Publ.-Id: 9560

Deviations from Vegard's rule in Al1-xInxN (0001) alloy thin films grown by magnetron sputter epitaxy

Seppänen, T.; Hultman, L.; Birch, J.; Beckers, M.; Kreißig, U.

Al1−xInxN (0001) thin films of the pseudobinary AlN–InN system were grown epitaxially onto (111)-oriented MgO wafers with seed layers of Ti1−yZryN by dual direct current magnetron
sputtering under ultrahigh vacuum conditions. The relaxed film c-axis lattice parameters determined
by x-ray diffraction were studied as a function of composition in the range of 0.07 < x < 0.82 measured by Rutherford backscattering spectrometry. We find a relative deviation by as much as
37% from the linear dependency described by Vegard’s rule for the lattice parameter versus film
composition. The highest relative deviations were found at low InN mole fractions, while the largest
absolute deviation was found at x=0.63. This shows that Vegard’s rule is not directly applicable to
determine the compositions in the wurtzite Al1−xInxN system. © 2007 American Institute of Physics.
[DOI: 10.1063/1.2450675 ]

  • Journal of Applied Physics 101(2007), 043519

Publ.-Id: 9559

Use of metal plasma immersion ion implantation and deposition for preparation of hemocompatible titanium-based coatings

Tsyganov, I. A.; Mashina, A. I.; Richter, E.; Maitz, M. F.; Rustichelli, F.

Metal plasma immersion ion implantation and deposition (MePIIID) provides a useful technique to control composition and structure of metal-based thin films. By this method Ti-based coatings such as Ti nitrides, oxides or oxynitrides are formed on the objects with an irregular shape from a plasma produced by cathodic arc evaporation of Ti under addition of nitrogen and/or oxygen to the ambient near the substrate. Coating with Ti oxide or Ti-nitride-oxide (TiNOX) is a promising method to improve the blood compatibility of materials for use as medical implants.

Keywords: Metal plasma immersion ion implantation and deposition (MePIIID); Titanium oxynitride; Phase composition; Hemocompatibility

  • Contribution to proceedings
    International Conference on Advanced Technologies and Equipment in Mechanical Engineering and Metallurgy, 11.-12.05.2006, Lipetsk, Russia

Publ.-Id: 9558

Correlation between physical surface properties and blood compatibility of titanium-based coatings prepared by metal plasma immersion ion implantation and deposition

Tsyganov, I. A.; Maitz, M. F.; Richter, E.; Reuther, H.; Mashina, A. I.

In this work layers of the ternary system Ti-N-O were produced in a wide range of composition by MePIIID and their structure, physicochemical properties and blood compatibility were investigated. In the dependence on the relation of the reactive gases partial pressure Ti nitride and oxide have been produced as crystalline phases. For pure N2 flow and for the relationship p(O2)/p(N2) = 1/3 XRD patterns are typical for the fcc structure of TiN. For p(N2) = p(O2) a two-phase system of fcc TiN and fcc TiO has been found. Further enhancing O2 flow leads to the beginning formation of rutile and anatase modifications of TiO2. For p(O2)/p(N2) = 1/3 up to p(N2) = p(O2) in addition to the phases detected by the XRD the amorphous TiO2 phase with nitrogen substitution has been found.
The polar component of the surface energy and the hydrophobicity of the surface show a dependence on the composition of the coating. The crystalline TiO2 surface was the most hydrophobic, but also the crystalline TiN phase showed a slightly higher hydrophobicity than the mainly amorphous mixed phases.
The clotting time of blood plasma, the thrombocyte adhesion and activation as well as the fibrinogen adsorption on the surface were investigated to study the correlation between structure of the coating and blood compatibility. The blood compatibility of Ti oxide can be improved by the addition of N into the layer. TiN and oxynitrides show the longest clotting time in comparison with TiO2 (rutile). The lowest platelet activation was found on TiN and oxynitrides in comparison with rutile. The thrombocyte adhesion and fibrinogen adsorption were lower for TiNxOy than for TiO2. This behavior is correlated with the decreasing of contact angle and is inversely correlated with the increasing of surface energy (especially with its polar component).
In this study the blood platelet adhesion on the surfaces in general was very low, usually below 3% of the whole amount of blood platelets present in the plasma sample. It renders this class of surfaces a promising candidate for good blood compatibility and low clotting activation.

Keywords: Titanium oxynitride; Metal plasma immersion ion implantation and deposition (MePIIID); Filtered arc; Phase formation; Hemocompatibility

  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Publ.-Id: 9557

Photon scattering experiments on the quasistable, odd-odd mass nucleus 176Lu

Walter, S.; Stedile, F.; Carroll, J. J.; Fransen, C.; Friessner, G.; Hollmann, N.; von Garrel, H.; Jolie, J.; Karg, O.; Käppeler, F.; Kneissl, U.; Kohstall, C.; von Neumann-Cosel, P.; Linnemann, A.; Mücher, D.; Pietralla, N.; Pitz, H. H.; Rusev, G.; Scheck, M.; Scholl, C.; Schwengner, R.; Werner, V.; Wisshak, K.

The quasistable odd-odd-mass nucleus 176 Lu is of special interest in nuclear structure physics and, above all, in nuclear astrophysics. Systematic photon scattering experiments have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator with bremsstrahlung end-point energies of 2.3 and 3.1 MeV to determine the low-energy dipole strength distribution in the s-only isotope 176 Lu. The main goal was to pin down possible intermediate states (IS) for the photoactivation of the short-lived 123-keV isomer, which is the key process determining the effective lifetime of 176 Lu in a stellar photon bath and hence for the use of this isotope as a stellar chronometer. Using an enriched sample, 29 transitions ascribed to 176 Lu were detected below 2.9-MeV excitation energy. The corresponding excitation strengths were determined. For the previously proposed lowest IS at 839 keV, an upper limit for the excitation strength corresponding to a lifetime of 1.5 ps can be given. Astrophysical consequences, also in view of new Stuttgart photoactivation experiments, are discussed. The fragmentation of the dipole strength is compared to those in neighboring even-even and odd-even nuclei.

Keywords: Nuclear Structure; Nuclear Astrophysics; Photon scattering; Photoactivation

Publ.-Id: 9556

DYN3D/ATHLET and ANSYS CFX calculations of the OECD VVER-1000 coolant transient benchmark

Kliem, S.; Höhne, T.; Rohde, U.; Kozmenkov, Y.

Plant-measured data provided within the specification of the OECD/NEA VVER-1000 coolant transient benchmark (V1000CT) were used to validate the DYN3D/ATHLET coupled code system. Phase 1 of the benchmark (V1000CT-1) refers to the main coolant pump (MCP) switching-on experiment conducted in the frame of the plant-commissioning activities at the NPP Kozloduy-6 in Bulgaria.
The transient is characterized by a rapid increase in the primary coolant flow through the core and, as a consequence, a decrease of the space-dependent core inlet temperature. A DYN3D/ATHLET model of the primary and secondary circuit of the plant including MCP characteristics, boundary conditions and benchmark-specified nuclear data library was created. For an adequate modeling of the redistribution of the coolant flow in the reactor pressure vessel (RPV) during the transient a simplified mixing model for the DYN3D/ATHLET code was developed and validated against a computational fluid dynamics (CFD) calculation with the code ANSYS CFX. The results of the coupled code calculation are in good agreement with the available experimental data. The discrepancies between experimental data and the results of the calculation do not exceed the accuracy of the measurement data. This concerns the initial steady state data as well as the time histories during the transient.
The above mentioned CFD model was used also in the second phase of the benchmark (V1000CT-2). In this part of the benchmark, post-test calculations of coolant mixing experiments at the same NPP are carried out. The comparison is made with assembly-wise mixing coefficients being the results of the experiments. The numerical grid model contains 4.7*106 tetrahedral elements. Different advanced turbulence models were used in the numerical simulations. The best agreement with the experimental data at the core inlet shows the Detached-Eddy-Simulation. Strong fluctuations occur in the downcomer of the RPV. The results show a clear sector formation of the affected loop in the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%.

  • Contribution to proceedings
    5th International conference on safety assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia
    Proceedings of the 5th International conference on safety assurance of NPP with WWER
  • Lecture (Conference)
    5th International conference on safety assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia

Publ.-Id: 9555

A Comparative Study of U(VI) and U(V) Carbonato Complexes in Aqueous Solution

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

Electrochemical, complexation, and electronic properties of uranyl(VI)- and uranyl(V) carbonato complexes in aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry (CV) using three different working electrodes of Pt, Au, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasireversibly. Electrolysis of UO22+ has been performed in the Na2CO3 solutions more than 0.8 M with the limited pH range of 11.7 < pH < 12.0 using a Pt mesh electrode. It produces high purity of uranyl(V) carbonate solution that has been confirmed to be stable at least for two weeks in a sealed glass cuvette. EXAFS measurements revealed the structural arrangement of uranyl(VI)- and uranyl(V) tricarbonato complexes, [UO2(CO3)3]n- (n = 4 for uranyl(VI), 5 for uranyl(V)). The bond distances of U-Oax, U-Oeq, U-C, and U-Odist are determined to be 1.81, 2.44, 2.92, and 4.17 Å for the uranyl(VI) complex, and 1.91, 2.50, 2.93, and 4.23 Å for the uranyl(V) complex, respectively. The validity of the structural parameters obtained from EXAFS has been supported by quantum chemical calculations for the uranyl(VI) complex. The uranium LI- and LIII-edge XANES spectra have been interpreted in terms of electron transitions and multiple scattering features.

Keywords: uranium; uranyl; carbonate; solution; U(VI); U(V); electrochemistry; cyclic voltammetry; UV-visible absorption; XAFS; EXAFS; XANES; complex; coordination


Publ.-Id: 9553

Selbstorganisierende bakterielle Hüllproteine als Grundlage für die Entwicklung neuartiger Nanomaterialien

Pollmann, K.; Raff, J.; Merroun, M.; Selenska-Pobell, S.; Herrmannsdörfer, T.

Die Kombination von Bio- und Nanotechnologie eröffnet ein großes Potential für die Entwicklung neuer Materialien. Da sich Nanopartikel in ihren chemischen und physikalischen Eigenschaften oft grundlegend von ihren Ausgangsmaterialien unterscheiden, sind sie von großem Interesse für die Entwicklung neuer Materialien und Werkstoffe wie Katalysatoren oder Biosensoren, in der Nanoelektronik, in der optischen Industrie, Halbleiterindustrie, aber auch für biomedizinische Anwendungen.
Eine aussichtsreiche, unkomplizierte Alternative zu konventionellen Methoden bei der Herstellung regelmäßig angeordneter Nanopartikel ist die Verwendung von selbstorganisierenden biologischen Trägermaterialien als Matrix. Besonders aussichtsreiche Biomoleküle sind hierbei die selbstorganisierenden Hüllproteine (S-Layer) von Bakterien.

In einem interdisziplinären Ansatz werden neuartige Materialien auf der Basis von Nanopartikeln aus metallischen, magnetischen und halbleitenden Materialien entwickelt. Für ihre Synthese werden verschiedene bakterielle Hüllproteine (S-Layer) als biologische Trägermaterialien (sogen. Template) verwendet. Diese bestehen meist aus Proteinmonomeren, welche nach ihrer Sekretion an der Zelloberfläche regelmäßige Gitterstrukturen unterschiedlicher Symmetrie ausbilden. Für ihre technische Nutzung ist es bemerkenswert, dass die isolierten Monomere ihre Eigenschaft der Selbstorganisation beibehalten und an Grenzflächen parakristalline Monolagen bilden. Die regelmäßig angeordneten Poren dieser Proteine bieten ideale Strukturen für die Bindung von Metallkomplexen und die Synthese von hochgeordneten Nanopartikeln definierter Größe. Die Synthese erfolgt dabei zweistufig: Nach der Anbindung der Metallkomplexe aus einer wässerigen Metallsalzlösung und anschließender Dialyse erfolgt eine Reduktion der Komplexe durch die Zugabe eines Reduktionsmittels. Auf diese Weise konnten bislang erfolgreich Pd-, Pt-, Au- und Pb-Nanopartikel einer einheitlichen Größe hergestellt werden, deren chemische und magnetische Eigenschaften sich z.T. erheblich von denen der jeweiligen makroskopischen Materialien unterscheiden. Durch die Beschichtung verschiedener technisch relevanter Materialien wie Keramiken, Zeolithe, Aluminiumoxid, Siliziumdioxid und Kohlenstoff mit den Proteinen sollen neuartige Materialien entwickelt werden, die in der Industrie Verwendung finden können.

  • Poster
    6. Präsentation BMBF BioFuture, 29.-30.01.2007, Berlin, Deutschland

Publ.-Id: 9551

DNA-wrapped Carbon Nanotubes

Enyashin, A. N.; Gemming, S.; Seifert, G.

The stability and electronic properties of the associates of the single-walled carbon nanotubes wrapped by homopolymeric single-stranded DNA molecules (CNT@DNA) are considered using a quantum mechanical density-functional tight-binding method (DFTB). A phenomenological model of the CNT@DNA formation energy depending on the nanotube radii is developed, which shows that the decoration of a CNT by a few DNA chains leads to a high water solubility of CNT@DNA. Pyrimidine-based DNAs are found to be more effective to wrap the CNTs than other DNAs. The densities-of-states of the CNT@DNA complexes are close to the superposition of those of the “free” components with some additional states below Fermi level. The band gap in a hybrid CNT@DNA system is determined by the competition between the Fermi levels of the “free” DNA and CNT. In a few specific cases a considerable charge transfer from the DNA to the CNT was observed, combined with an additional gain in the CNT@DNA formation energy.

Keywords: Nanotube; CNT; DNA; DFT; tight-binding

Publ.-Id: 9550

Self-assembly of Mo6S8 Clusters on the Au(111) Surface

Popov, I.; Kunze, T.; Gemming, S.; Seifert, G.

The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact. It experiences a strong, mostly non-ionic attraction to the surface at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room temperature. The analysis of the electronic structure reveals a negligible electron transfer and S-Au hybridised states, which indicate that the luster-surface interaction is dominated by S-Au bonds, with minor contributions from the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within nano-devices. Therefore, a classical potential model was developed on the basis of the DFT data, which allows to study larger cluster assemblies on the Au(111).

Keywords: adsorption; self-assembly; metal surface; chalcogenide cluster

Publ.-Id: 9549

High Temperature Plasma Immersion Ion Implantation

Ueda, M.; Silva, M. M.; Lepienski, C. M.; Soares, P. C. J.; Gonçalves, J. A. N.; Reuther, H.

We have performed high temperature nitrogen plasma immersion ion implantation (PIII) of Ti6Al4V by heating the samples for up to 800 °C, using tungsten filaments inside the sample holder. Ion implantation was done with the high voltage pulser at 5 kV, 40 μs duration and 400 Hz frequency, and a nitrogen glow discharge as the plasma source. Nanoindentation analysis of the treated surface indicated an improvement of 5 times in hardness for PIII treatment of 120 min. X-ray diffraction indicated the formation of Ti2N. Auger Electron Spectroscopy (AES) showed that the peak concentration is greater than 30% in the implanted nitrogen with the maximum penetration of 150 nm for the sample treated during 120 min.

  • Surface & Coatings Technology 201(2007), 4953-4956

Publ.-Id: 9548

Plasma Immersion Ion Implantation in Arc and Glow Discharge Plasmas Submitted to Low Magnetic Fields

Tan, I. H.; Ueda, M.; Oliveira, R. M.; Dallaqua, R. S.; Reuther, H.

The influence of low magnetic fields (B≤130 G) on the plasma parameters of a DC nitrogen glow discharge is investigated with a double Langmuir probe. The discharge was optimized for maximum plasma density for different values of a magnetic field, and a condition was found in which density was enhanced by an order of magnitude. In this condition partial suppression of secondary electron emission was obtained during ion implantation experiments. Silicon samples implanted in this optimum density condition showed larger retained dose and penetration depth compared with samples treated in non-magnetized plasmas as shown by Auger electron spectroscopy depth profile analysis. These results were compared with previous similar experiments in much denser magnetized vacuum arc plasmas, in which total suppression of secondary electrons (SE) was obtained, corroborating the theory that the maintenance of a virtual cathode for SE suppression is favored by higher plasma density. Silicon samples implanted in magnetized magnesium plasmas exhibited much larger doses (as expected) and penetration depths (not so obvious) than the ones treated in non-magnetized plasmas. The deeper ion penetration obtained in magnetized gaseous and vacuum arc plasmas indicates that an enhanced diffusion may be taking place induced by the large ion bombardment in dense plasmas.

  • Surface & Coatings Technology 201(2007), 4826-4831

Publ.-Id: 9547

Structure and Speciation of U(VI) sulfate in aqueous solution

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Ikeda, A.; Scheinost, A. C.; Skanthakumar, S.; Wilson, R.; Soderholm, L.; Servaes, K.; van Deun, R.; Görller-Walrand, C.

The local structure of U(VI) sulfato complexes in aqueous solution has been investigated by U L3-edge EXAFS, high energy x-ray scattering (HEXS), x-ray diffraction (XRD) and UV-Vis spectroscopy using samples of 50 mM U(VI) and total sulfate concentrations, 0.05 ≤ [SO42-] ≤ 3 M at pH 1 and 2. At low [SO42-]/[UO22+] ratio (~1), where the UO2SO4(aq) species prevails, the sulfate coordinates in a monodentate fashion. At high [SO42-]/[UO22+] ratio, where UO2(SO4)22- species prevails, bidentate sulfate coordination becomes dominant. In all cases, the equatorial coordination number NOeq, remains 5. According to the bond-valence rule this is in line with the average bond distance between U(VI) and oxygen of ~2.42 Å observed by EXAFS and HEXS. The bidentate sulfate reaches a maximal coordination number NSbid of 2 for a [SO42-]/[UO22+] ratio of 60, hence, related with the structure of [UO2(SO4)2bidH2O]2-. The upper limit of NSbid allows to rule out the existence of a species with three monodentate coordinated sulfate groups, [UO2(SO4)3bid]4-. This observation has been confirmed by MCD measurements. Therefore, the species UO2(SO4)34- might be related with the structure [UO2(SO4)2bid(SO4)mon]4-. The existence of two bidentate coordinated sulfate groups has up to now never been observed in crystal structures. The evaporation of the above mentioned solutions with several [SO42-]/[UO22+] ratios resulted always in crystal structures where the sulfate group acts monodentate-bridging. The coordination of U(VI) by two bidentate coordinated sulfate groups might be restricted to solution species. This observation indicates a structural re-arrangement of SO42- during the crystallization. The potential structures in solution were modeled by DFT calculation and compared with the experimental data from EXAFS and HEXS.

Keywords: Uranyl sulfate; U(VI); solution; speciation; structure; EXAFS; XRD; HEXS; MCD; UV-vis

  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 36
  • Lecture (Conference)
    Migration 2007, 26.-31.08.2007, München, Germany

Publ.-Id: 9546

Hydrolysis of U(VI). An infrared spectroscopic verification of uranyl species

Müller, K.; Foerstendorf, H.

Detailed information about aqueous species of uranium(VI) is an indispensable prerequisite for a reliable assessment of its migration in the environment. Up to now the identification of distinct U(VI) species in aqueous solution was mostly accomplished by thermodynamical calculations based on non-structural experiments such as potentiometric titration [1] and by spectroscopic investigations of UO22+ solutions in the upper millimolar range at low pH values [2,3].
Attenuated total reflectance (ATR)-FT-IR spectroscopy has shown to be a useful tool for investigations of molecule complexes formed during sorption processes in aqueous solutions [4]. In this study we focus on the hydrolysis reactions of U(VI) under atmospheric conditions throughout a wide pH range (pH 2 – 9).
First, we investigated diluted uranyl(VI) solutions. Due to the low concentration ([UO22+] = 20 µM) the acquisition of infrared spectra of UO22+ solutions have become feasible even at high pH values avoiding the precipitation of solid uranyl phases. Our results clearly demonstrate that already at pH values < 4 not yet identified hydroxo uranyl complexes considerably contribute to the infrared spectra which is in contrast to recent thermodynamical calculations. It is also quite conceivable that we identified new U(VI) species in aqueous solutions. At higher pH values (> 7) the spectra indicate the formation of another uranyl species possibly with contributions of atmospheric carbonate anions which can be derived from model spectra of the pure UO2(CO3)34− complex.
In a second series of experiments we studied the hydroxo species of uranium(VI) at different concentrations (5 mM – 5 µM UO22+) at a constant pH value (pH 4). Upon lowering the concentration below 500 µM the fraction of the uncomplexed uranyl species is significantly reduced and can not be detected at a concentration of 50 µM any longer. Simultaneously two other hydroxo complexes are obviously formed at these lower concentrations.
A critical evaluation of literature data and the obtained spectral data constitute a reference to a modified speciation of U(VI) in particular at lower pH values and at concentrations in the micromolar range.

[1] R. Guillaumont et al. (OECD-NEA TDB), Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, 2003.
[2] H. Moll et al., Radiochim. Acta 88, 411 (2000).
[3] F. Quilès and A. Burneau, Vib. Spec. 23, 231 (2000).
[4] G. Lefèvre, Adv. Colloid Interface Sci. 107, 109 (2004).

  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 187-188
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany

Publ.-Id: 9545

A bis(2-pyridylmethyl) derivative of 1,4,7-triazacyclononane as highly hydrophilic chelation agent for copper

Gasser, G.; Tijoe, L.; Belousoff, M. J.; Spiccia, L.; Graham, B.; Juran, S.; Walther, M.; Künstler, J.-U.; Bergmann, R.; Stephan, H.

Highly thermodynamically stable Cu(II) complexes are required for the development of new copper(II) target-specific radiopharmaceuticals. In this perspective, azamacrocycle derivatives [1], and in particular a 1,4,7-triazacyclononane derivative containing two pyridine pendant arms [2] is a potentially promising ligand candidate. The further addition of a carboxylic group to this chelating agent could provide an attractive lead for the labelling of biomolecules with copper radionuclides.

A new ligand, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (1), has been synthesised, and the X-ray structure of a corresponding copper(II)-complex determined. A bioconjugate (2) was obtained by coupling a modified bombesin derivative [3] to 1 (HBTU, DIPEA, DMF, r.t.). 2 was purified by semi-preparative HPLC. The free ligand 1 and the bioconjugate 2 were labelled with 64Cu. To 100 µl of ligand solution (0.0001 M ligand dissolved in 0.05 M NH4OAc), 200 kBq of 64CuCl2 was added. Labelling yields were studied by TLC.

Results and Discussion:
The structure of [1-Cu-complex]2+ was solved by X-ray single-crystal diffraction and indicates that the ligand is able to bind Cu2+ in a hexacoordinate manner. A high complex stability (logK1 > 20) was determined. The bioconjugation of 1 to a bombesin derivative was successfully achieved via amide coupling to give 2. The free ligand 1 and the bioconjugate 2 were labelled with 64Cu and the resulting complexes were found to be stable in the presence of a large excess of competing ligands such as cyclam and glutathione as well as in rat plasma. These 64Cu complexes are highly hydrophilic (logDo/w < -2.3).

A bis(2-pyridylmethyl) derivative of 1,4,7-triazacyclononane 1 and its bombesin bioconjugate 2 can readily form 64Cu complexes with high stability. The bifunctional chelating agent 1 may be an attractive candidate for developing new copper radiopharmaceuticals. Preliminary biodistribution studies of 64Cu complexes of 2 are currently underway.

[1] K. P. Guerra et al., Dalton Trans., 2006, 4124-4133.
[2] G. A. McLachlan et al., Inorg. Chem. 1994, 33, 4663-4668.
[3] E. Garcia Garayoa et al., Quart. J. Nucl. Med. Molec. Imaging, 2006, 50, 15-16.

  • Poster
    17th International Symposium on Radiopharmaceutical Sciences, 30.04.-04.05.2007, Aachen, Deutschland
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 50(2007)Suppl. 1, S230

Publ.-Id: 9544

Binding properties of a phosphonate substituted clip towards nucleosides

Raditzky, B.; Stephan, H.; Weiß, S.; Geipel, G.; Polkowska, J.; Klärner, F.-G.

Molecular recognition and self-assembly, based on weak non-covalent interactions, are significant processes in chemical and biological systems [1], e.g. in enzyme-substrate binding or formation of protein complexes. So, the development of efficient synthetic receptors with the ability to bind substrates selectively is important. The water-soluble naphthalene clip with substituted phosphonate groups (Fig. 1) offers electron-rich side walls, which are suitable to bind electron-poor guests [2]. The complexation behavior of this clip toward nucleosides has been studied by time resolved laser fluorescence spectroscopy with ultrafast pulses (fs-TRLFS).

[1] Vögtle, F. (1997) Supramolekulare Chemie, Teubner Verlag, Stuttgart.
[2] Jasper, C. et al. (2002) Angew. Chem. 114, 1411-1415.

  • Poster
    COST D31 3nd Workshop, 28.-31.03.2007, Athens, Greece

Publ.-Id: 9543

Toward Bio-Inspired Photoadressable Supramolecular Systems. Synthesis, Light-Emission, Dynamics, Biomedical Application

Stephan, H.

Noncovalent intermolecular forces play a fundamental, ubiquitous role in living systems particularly in view of molecular recognition and self-organization / self-assembly. In an increasing extent the principles found in organized biological systems are utilized for the development of artificial structures which are able to mimic certain properties of the naturally occurring systems. In this context, some novel supramolecular receptors such as dendritic hosts, molecular tweezers, helical systems, and synthetic flavylium salts gain more and more importance. Fine-tuning of photochemical, photophysical and electrochemical properties of host-guest systems provide the possibility of tailoring the supramolecular reactivity opening fascinating and important development in biomedical application such as the design of novel diagnostic and therapeutic agents. This field is in its infancy, and in particular a deep understanding about binding and transport behaviour in both aqueous and mixed organic-aqueous systems must be achieved. The study of molecular recognition and self-assembly processes in the most competitive environment - the aqueous media - is still a challenge and a stimulus for the creation of novel supramolecular ensembles which possess more simple structures but similar functions as the complex biological systems.

  • Lecture (Conference)
    COST D31 3nd Workshop, 28.-31.03.2007, Athens, Greece

Publ.-Id: 9542

Development of a neutron time-of-flight source at the ELBE accelerator

Klug, J.; Altstadt, E.; Beckert, C.; Beyer, R.; Freiesleben, H.; Galindo, V.; Grosse, E.; Junghans, A. R.; Legrady, D.; Naumann, B.; Noack, K.; Rusev, G.; Schilling, K. D.; Schlenk, R.; Schneider, S.; Wagner, A.; Weiß, F.-P.

The radiation source ELBE at Forschungszentrum Dresden-Rossendorf (FZD) has a superconducting linear accelerator with electron energies up to 40 MeV as a central instrument, and it will be used to produce intense neutron beams. The neutron radiator consists of a liquid lead circuit where bremsstrahlung photons generated from the electron beam produce neutrons in (gamma,n) reactions. Monte Carlo simulations with MCNP4C3/MCNP5 were performed to characterise neutron and photon intensities as well as time and energy distributions, and to optimise the neutron transport.

The short beam pulses (5 ps at FWHM) provide the basis for an excellent time resolution for neutron time-of-flight experiments, allowing an energy resolution of about 1 % with a flight path of 4 m when using a fast detector stop signal (e. g., 1 ns for 5 MeV neutrons). The neutron beam is shaped by a 2.4 m long collimator made from borated polyethylene and lead, reducing the background of scattered neutrons and of photons at the sample position. About 96 % of the neutrons at the experiment site retain their correct energy to time-of-flight correlation. The neutron flux at the sample position is calculated to be 10^7 cm^−2 s^−1. As ELBE will be able to deliver a full intensity beam with a repetition rate of 0.5 MHz, the usable neutron energy range goes from 50 keV up to 10 MeV. In this energy interval, there is a need for neutron cross section measurements relevant for the transmutation of minor actinides in nuclear waste, as well as for applications to fission and fusion reactors.

A BaF2 scintillation detector array of 42 crystals is being constructed for neutron-capture gamma-rays. The setup covers up to 96 % of the total solid angle. Simulations of gamma-ray cascades from 56Fe(n,gamma)57Fe reactions have been combined with detector simulations to characterise the response of the detector setup.

Keywords: superconducting electron accelerator; liquid-lead radiator; neutron beam; neutron time-of-flight; nToF; neutron scattering; neutron detector

Publ.-Id: 9541

Polarization of Human Hematopoietic Progenitors During Contact with Multipotent Mesenchymal Stromal Cells: Effects on Proliferation and Clonogenicity

Freund, D.; Bauer, N.; Boxberger, S.; Feldmann, S.; Streller, U.; Ehninger, G.; Werner, C.; Bornhäuser, M.; Oswald, J.; Corbeil, D.

Establishment of a defined cell culture system that facilitates ex vivo expansion of isolated hematopoietic stem and progenitor cells (HSPCs) is a crucial issue in hematology and stem cell transplantation. Here we have evaluated the capacity of primary human multipotent mesenchymal stromal cells (MSCs) to support the ex vivo expansion of peripheral CD34+-enriched HSPCs. We observed that HSPCs co-cultured on MSCs showed a substantially higher total expansion rate compared to those growing without. Moreover, in addition to the expansion of
CD34+CD3133+ and CD34+CD133-cells, a third population of CD133+CD34- stem cells became detectable after expansion. Direct contact between HSPCs and the feeder layer appears beneficial for the expansion of HSPCs harboring
CD133+phenotype, i.e., CD34+CD133+ and CD3133SUP>+CD34- contrast to CD34+CD133- cells.
Interestingly, electron microscopy and immunofluorescence analyses revealed that adherent HSPCs display various morphologies; they are either round with, in some cases, the appearance of a microvillar pole or exhibit several distinct types of plasma membrane protrusions such as lamellipodium and magnupodium. CD133 is selectively concentrated therein, whereas CD34 is randomly distributed over the entire surface of HSPCs. Together, this co-culture offers a unique experimental system to further characterize the biology and role of markers of rare stem cell populations.

  • Stem Cells and Development 15(2006), 815-829

Publ.-Id: 9540

Development of novel nanomaterials based on self-organising bacterial S-layer proteins

Pollmann, K.; Raff, J.; Merroun, M.; Selenska-Pobell, S.; Herrmannsdörfer, T.

Nanoparticles attract great attention for the development of new materials since their properties usually differ significantly from those of the bulk material. They play a key role in future technologies and are used for the manufacturing of novel nanocatalysts, biosensors, for biomedical applications and nanoelectronic devices. The development of cluster-assembled materials with discrete, size-selected nanoparticles is of great interest to enable the fine-tuning of the properties of the nanoparticles. The use of self-assembling biological templates which allow the synthesis of a wide range of inorganic nanocrystals is a promising approach to produce arrays of nanoparticles in a simple way.
We present a unique interdisciplinary approach to produce arrays of nanoparticles of a defined size which posses magnetic, semiconducting, or catalytic properties. In this approach the proteinaceous self-assembling bacterial surface layers (S-layers) are used as biological templates. Most of the S-layers are composed of protein monomers with the ability to self-assemble into two-dimensional arrays. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals such as Pt, Pd, Au, Fe, and offer ideal structures for the formation of regular distributed nanoclusters of a defined size [1]. Such arrays of inorganic nanoparticles as hybrids with self-assembling biological molecules, which possess a high stability [2], are very attractive for technical applications such as the development of novel catalysts, biomedical applications, the programmed assembly of nanometer scale electronic devices, and optical industry.

[1] Pollmann, K., J. Raff, M. Merroun, K. Fahmy, S. Selenska-Pobell. 2006. Metal binding by bacteria from uranium mining waste piles and its technological applications. Biotechnol. Adv. 24: 58-68.
[2] Fahmy, K., M. Merroun, K. Pollmann, J. Raff, O. Savchuk, C. Hennig, S. Selenska-Pobell. 2006. Secondary structure and Pd(II) coordination in S-layer proteins from Bacillus sphaericus studied by infrared and X-ray absorption spectroscopy. Biophys. J. 91: 996-1007.

  • Lecture (Conference)
    NanoBio-Europe 2007, 13.-15.06.2007, Münster, Germany

Publ.-Id: 9539

Speciation of Np(V) in aqueous solution investigated by FT-IR spectroscopy.

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

The distribution of aqueous species of neptunium, one of the most relevant radionuclides for long-term emplacement of nuclear waste, primarily defines its geochemical reactions and migration behavior. Current knowledge about Np(V) species is mainly based on thermodynamical calculations relying on data obtained by non-structural experiments such as potentiometric titration [1]. A spectroscopic verification of these Np(V) speciations is still lacking. Furthermore, there is still considerable uncertainty about the predominating neptunyl species, whether they arise from hydrolysis or carbonate complexation.
Vibrational spectroscopy is a useful tool for the identification of different molecular species. Due to the difficulty to obtain IR spectra from aqueous solutions mainly Raman studies of high concentrated Np(V) solutions were carried out [2-4]. Attenuated Total Reflectance Fourier-transform Infrared (ATR-FTIR) spectroscopy allows the direct measurement of liquid samples and provides additional important spectral information even at low neptunyl concentrations.
In this study we investigate Np(V) hydrolysis and neptunyl carbonate complexation using ATR-FTIR spectroscopy. We focus on micromolar neptunyl concentrations and present infrared spectra recorded over a wide pH range (pH 2-10). The speciation of Np(V), i.e. its hydrolysis at lower pH (< 6) and its complexation with atmospheric carbonate at higher pH values is compared to previous thermodynamic data.

[1] R. Guillaumont et al. (OECD-NEA TDB), Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, 2003.
[2] Gregoire-Kappenstein, A. C. et al., Radiochim. Acta 91, 665 (2003).
[3] Jones, L. H. et al., J. Chem. Phys. 21, 542 (1953).
[4] Madic, C. et al., Inorg. Chem. 22, 1494 (1983).

  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 180

Publ.-Id: 9538

Carbonate effects on surface speciation of uranyl at the ferrihydrite-water interface: New insights from advanced EXAFS data analysis

Rossberg, A.; Tsushima, S.; Ulrich, K.-U.; Scheinost, A. C.

The assessment of uranium migration requires the proper use of geochemical specition and reactive transport models due to the complexity of reactions and phase interactions. In the past decades the main focus has shifted from improving the modelling algorithms to a proper formulation of reaction mechanisms and the validation of thermodynamic data [1]. Thermodynamic constants should only be used if the corresponding reaction mechanism is supported by structural data (spectroscopic data, or theoretical calculations) [1]. This recommendation assumes that the spectroscopic studies provide reliable structural models. However, a comparison of recent literature on U(VI)-iron(hydr)oxide sorption complexes showed that XAS data enable a variety of interpretations and structural assemblies. Most data analysis routines do not address the multivariate character of such systems. The EXAFS spectra of the aqueous system U(VI)/ferrihydrite(Fh)/carbonate show a strong dependence on pH and CO2 partial pressure (pCO2). We used advanced multi-factorial analysis such as ITFA (Iterative Target Transformation Factor Analysis) [2] for the extraction of end-member spectra from the EXAFS spectral mixtures; and MCTFA (Monte Carlo Target Transformation Factor Analysis) [3] for the 3-dimensional structure analysis of the sorption complexes. We found that the whole set of EXAFS spectra derived from the experimental system U(VI)/Fh/pH/pCO2 supports only two structurally different sorption complexes. The two isolated species are: (i) a binary inner-sphere U(VI)-Fh sorption complex in which U(VI) shares the edge of an FeO6 octahedron, and (ii) an outer-sphere U(VI)-carbonato complex. The structure of the outer-sphere complex matches the structure of the aqueous UO2(CO3)34- complex. For the 3-dimensional analysis of the UO2(CO3)34- complex we included multiple scattering calculations in the MCTFA algorithm. By this combination the radial pair distribution functions and the spatial disorder of the backscattering atoms were determined at the first time for an isolated aqueous metal complex. We compare the structure of the UO2(CO3)34- complex and the spatial atomic disorder with quantum chemical calculations. The EXAFS spectra of the binary inner-sphere complex are more difficult to interprete. A Fourier Transform (FT) peak at 2.4 Å seems to be present in many U(VI) systems and may disturb the analysis of the EXAFS data. Up to now, this feature was either neglected, or attributed to C-atoms at a radial distance of 2.9 Å. Based on this latter interpretation, ternary U(VI)-iron(hydr)oxide carbonato complexes have been proposed even at pH as low as 4.6, where carbonato complexes are highly unlikely according to thermodynamic considerations [4]. Implications for the modelling of sorption data are manyfold. For example, Lenhart et al. (1999) [5] modelled the sorption of U(VI) onto hematite under atmospheric conditions and found that their sorption edges can be explained without the inclusion of inner-sphere ternary carbonato complexes as proposed by Bargar et al. (2000) [4]. However, Lenhart et al. (1999) [5] followed the general recommendation that the reaction mechanism should be supported by structural data [1], hence included a ternary U(VI)-iron(hydr)oxide carbonato complex into their sorption model. We present a tentative structural model for the binary inner-sphere complex and discuss the origin of the FT peak at 2.4 Å.

[1] J. van der Lee, C. Lomenech, Radiochimica Acta 92, 811 (2004).
[2] A. Rossberg, T. Reich, G. Bernhard, Anal. and Bioanal. Chem. 376, 631 (2003).
[3] A. Rossberg, A. C. Scheinost, Anal. and Bioanal. Chem. 383(1), 56 (2005).
[4] J. R. Bargar, R. Reitmeyer, J. J. Lenhart, J. A. Davis, Geochim. Et Cosmochim. Acta 64, 2749
[5] J. J., Lenhart, B. D. Honeyman, Geochim. Et Cosmochim. Acta 63, 2891 (1999).

Keywords: Monte Carlo Simulation; EXAFS; factor analyis

  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 85

Publ.-Id: 9537

Microbacterium isolates fromthe vicinityofa radioactivewaste depositoryand their interactionswith uranium

Nedelkova, M.; Merroun, M.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.

Three oligotrophic bacterial strains were cultured from the ground water of the deep-well monitoring site S15 of the Siberian radioactive waste depository Tomsk-7, Russia. They were affiliated with Actinobacteria from the genus Microbacterium. The almost fully sequenced 16S rRNA genes of two of the isolates, S15-M2 and S15-M5, were identical to those of cultured representatives of the species Microbacterium oxydans. The third isolate, S15-M4, shared 99.8% of 16S rRNA gene identity with them. The latter isolate possessed a distinct cell morphology as well as carbon source utilization pattern from the M. oxydans strains S15-M2 and S15-M5. The three isolates tolerated equal amounts of uranium, lead, copper, silver and chromium but they differed in their tolerance of cadmium and nickel. The cells of all three strains accumulated high amounts of uranium, i.e. up to 240 mgU (g dry biomass)1 in the case of M. oxydans S15-M2. X-ray absorption spectroscopy (XAS) analysis showed that this strain precipitated U(VI) at pH 4.5 as a meta-autunite-like phase. At pH 2, the uranium formed complexes with organically bound phosphate groups on the cell surface. The results of the XAS studies were consistent with those obtained by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX).

Publ.-Id: 9536

Atomistic simulations of epitaxial recrystallization in 4H-SiC along the [0001] direction

Gao, F.; Zhang, Y.; Devanathan, R.; Posselt, M.; Weber, W. J.

Molecular dynamics methods have been employed to study epitaxial recrystallization and the amorphous-to-crystalline (a–c) transition in 4H-SiC along the [0001] direction, with simulation times of up to a few hundred nanoseconds and at temperatures of 1500 and 2000 K. The results are compared with those simulated previously along the [-12-10] and [-1010] directions to investigate the anisotropies of recrystallization processes. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layers. The amorphous layers with the a–c interface normal along the [0001] direction can be completely recrystallized at 2000 K, but the recrystallized region contains dislocation loops. The temperature required for complete recrystallization is in good agreement with those observed experimentally.

Keywords: Defects; Epitaxial recrystallization; Computer simulations; Silicon carbide

  • Nuclear Instruments and Methods in Physics Research B 255(2007), 136-140

Publ.-Id: 9535

Imaging and functional characterization of metabolic pathways of modified lipoproteins and proteins in vivo using small animal positron emission tomography (PET)

Pietzsch, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Gastvortrag am Department of Pediatrics, Division of Clinical Chemistry & Biochemistry, University of Zurich, 21.02.2007, Zürich, Schweiz

Publ.-Id: 9534

Rhenium cluster complexes as promising metal drugs for cancer therapeutics and diagnostics

Fedorov, V. E.; Mironov, Y.; Brylev, K.; Shestopalov, M.; Efremova, O.; Kim, S.; Spies, H.; Pietzsch, H.-J.; Stephan, H.; Röhrich, A.

During the last years the mononuclear rhenium complexes have been studied intensively in radiopharmaceutical chemistry because of the favorable properties of 186Re and 188Re radioactive isotopes for cancer therapeutics and diagnostics. Considering that the acting element of such preparations is metal atoms, the rhenium cluster complexes may be promising metal drugs. On the other hand, many rhenium cluster complexes possessing bright red luminescence have considerable potential to be used in photodynamic therapy. Having used these two remarkable properties for medical treatment, it seems, the rhenium cluster complexes can provide synergetic therapeutic efficacy. Thus, the development of cluster rhenium chemistry and design of hybrid cluster complexes by introducing appropriate organic molecules (e.g. sugars, PEG, small peptides) into the cluster moiety to make them water-soluble and acceptable for living cells is very interesting and important task.
Here we report our recent results on synthesis of novel hybrid chalcogenide (Q=S, Se, Te) rhenium tetranuclear Re4Q4L12, hexanuclear Re6Q8L6 and dodecanuclear Re12CS17L6 cluster complexes with inorganic and organic ligands L, study of their crystal and electronic structures, physico-chemical properties and biomedical behavior.

  • Lecture (Conference)
    ICBIC XIII, 13th International Conference on Biological Inorganic Chemistry, 15.-20.07.2007, Wien, Austria
  • Abstract in refereed journal
    Journal of Biological Inorganic Chemistry 12(2007)Suppl. 1, S18

Publ.-Id: 9533

Competences and perception of the management in slovak companies

KožÍková, O.; Joehnk, P.

Vortrag auf CO-MAT-TECH 2006

  • Invited lecture (Conferences)
    CO-MAT-TECH 2006,14. International Scientific Conference, 19.-20.10.2006, Trnava, Slovakia

Publ.-Id: 9532

Aqueous uranium(IV) fluoride complexes: determination of fluorescence properties by means of TRLFS

Lehmann, S.; Geipel, G.; Bernhard, G.

Fluorescence properties of uranium(IV) complexes have only been little investigated up to now. Our research contributes first data on uranium(IV) fluoride complexes in an aqueous environment. Investigations were carried out using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The excitation wavelength for all samples applied was 245 nm. Samples investigated comprised a constant uranium(IV) concentration. Fluoride was added with varying concentrations (stoichiometrical deficiency up to an excess with respect to uranium).
The fluorescence spectrum of a pure uranium(IV) solution without the addition of fluoride is in accordance with the ones described by [1] and [2]. Positions of 5 main peaks were determined: 291, 320, 335, 394 and 409 nm. Addition of a stoichiometrically deficient proportion of fluoride of one tenth the uranium concentration does not a result in a change of the fluorescence spectrum. There is no shift of peaks or increase or decrease of fluorescence intensity observable. However, raising the fluoride concentration up to one third the concentration of uranium(IV) affects the spectra in a way that all the peaks commence to diminish, best observable via the main peaks at 319 and 409 nm.
At the same time, a new peak in the region around 400 nm occurs. This peak broadens with increasing fluoride concentration. In addition, a peak around 320 nm starts to build up and superimpose the original uranium(IV) peak at 320 nm. Enhancing the fluoride concentration further on up to half the uranium(IV) concentration results in an increase of the fluorescence spectrum of the complex formed. A further increase of the fluoride concentration does not affect the spectrum. The position of the new formed peaks as well as the fluorescence intensity remain stable. Hence, the formation of the uranium(IV)-fluoride complex has been complete.
Future investigations aim at the determination of the complex formation constants of the uranium(IV) fluoride complexes.

Keywords: uranium(IV) fluoride; TRLFS; formation constant

  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 180-181

Publ.-Id: 9531

Exact propagators for SUSY partners

Pupasov, A.; Samsonov, B.; Günther, U.

Pairs of SUSY partner Hamiltonians are studied which are interrelated by usual (linear) or polynomial supersymmetry. Assuming the model of one of the Hamiltonians as exactly solvable with known propagator, expressions for propagators of partner models are derived. The corresponding general results are applied to "a particle in a box", the Harmonic oscillator and a free particle (i.e. to transparent potentials).

Keywords: linear supersymmetry; polynomial supersymmetry; quantum mechanics; propagator; Green function; harmonic oscillator; transparent potential

Publ.-Id: 9530

Investigations into the formation of real colloids and pseudocolloids of uranium(IV)

Zänker, H.; Opel, K.; Weiß, S.; Hübener, S.; Bernhard, G.

The formation of real colloids and pseudocolloids of uranium(IV) was investigated. Coulometric titrations of strongly acidic U(IV) solutions in HClO4/NaClO4 medium were carried out in order to find the pH of first colloid formation. Laser-induced breakdown detection (LIBD) was applied for the detection of traces of uranium colloids as the pH was increased. The pH values at the onset of colloid formation were used for thermodynamic calculations aimed at determining the solubility products of crystalline and amorphous uranium dioxide. For uranium(IV) this novel approach was applied for the first time. Published solubility products for UO2 obtained by classic techniques vary by several orders of magnitude. Our experiments provided solubility products of log Ksp0 = 59.6 ± 1.0 for UO2(cr) and log Ksp0 = -54.1 ± 1.0 for UO2·xH2O(am) for the given reaction UO2·xH2O + 4 H+ ↔ U4+ + (2+x) H2O. Furthermore, the UO2·xH2O(am) colloids were investigated for their colloidal stability. Zeta potentials of ≥ 30 mV were found for pH values of less than 4. The point of zero charge was at pH ~ 6.9. Colloidal suspensions of 1 mMol/L UO2·xH2O(am) at a pH value of 2.5 proved to be stable over > 1.5 years. The interaction of the forming UO2·xH2O(am) colloids with other colloid-forming species was tested. Therefore, coulometric titrations of U(IV) solutions in the presence of (a) dissolved Al(III) and (b) dissolved silicate were carried out. The presence of Al(III) does not significantly influence the formation of the UO2·xH2O(am) colloids, and the presence of U(IV) does not significantly influence the behaviour of Al(III). There is more interaction of the U(IV) with silicate. Silicate, on the one hand, does not significantly influence the pH value of first UO2·xH2O(am) colloid formation, i.e. it does not significantly influence UO2·xH2O(am) solubility. However, the presence of U(IV) significantly influences the precipitation behaviour of the silicate (formation of U(IV) pseudocolloids due to coprecipitation). The nature of the interaction between the silicate and the U(IV) is not yet known. Adsorption of the silicate onto the UO2·xH2O(am) colloids and/or formation of a coffinite precursor come into question. EXAFS experiments to elucidate the local structure around the U(IV) atoms in the pseudocolloids are underway.

Keywords: colloids; uranium dioxide; laser-induced breakdown detection; coprecipitation

  • Lecture (Conference)
    Migration 2007, 26.-31.8.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 161-162

Publ.-Id: 9529

Vibrational excitations and tilted rotation in Lu-163

Almehed, D.; Nazmitdinov, R. G.; Doenau, F.

Using a microscopic self-consistent model, we analyse the excitation built upon the rotational band in Lu-163, which has been identified as a wobbling excitation on top of the rotation of a triaxial, trongly deformed shape. We find that the presence of pairing correlations substantially affects the energy of the excitation. Our calculations predict the onset of tilted rotation at a critical rotational requency where the energy of the excitation approaches zero.

  • Physica Scripta T 125(2006), 139-141

Publ.-Id: 9528

Orbits, shapes and currents

Frauendorf, S.

Shapes and current distributions of nuclei and alkali clusters are discussed in terms of the single particle motion of fermions in the average potential. For small particle number, an interpretation in terms of the lowest spherical harmonics is presented. For large particle number, an interpretation in terms of classical periodic orbits is presented.

  • Physica Scripta T125(2006)
  • Lecture (Conference)
    Int. Conf. on Finite Fermionic Systems, Nilsson Model 50 Years, 14.06.2005, Lund, Sweden

Publ.-Id: 9527

Scanning capacitance microscopy and the role of localized charges in dielectric films: Infering or challenging?

Beyer, R.; Schmidt, B.

Scanning capacitance microscopy (SCM) is considered a suitable technique to examine dopant profiles and to provide images of the charge carrier distribution in real device structures. A drawback of the application is the sensitivity of the method to different kinds of charges in the surface passivation layer. For a systematic study silicon structures with stripe patterns of different doping concentrations, covered either by a native oxide or by a thermally grown silicondioxide layer, were examined. The dependence of the dC/dV characteristic
on the sweep rate of the tip bias and on the bias sweep direction was analyzed. Local charge trapping in the passivation layer was estimated from shifts of the peak position of the dC/dV versus V curves. It is demonstrated as to how features related to the charge trapping in the passivation layer and induced by a certain dc bias at the tip superimpose the dopant related features in the SCM image.

Keywords: Scanning capacitance microscopy; Dopant profiling; Oxide layer; Charge trapping

Publ.-Id: 9526

Comparison between wire-mesh sensors and conductive needle-probes for measurements of two-phase flow parameters

Manera, A.; Ozar, B.; Paranjape, S.; Ishii, M.; Prasser, H.-M.

Measurements of two-phase flow parameters such as void-fraction, bubble velocities, and interfacial area densities have been performed in an upwards air-water flow at atmospheric pressure by means of a four-tip needle-probe and a wire-mesh sensor. For the first time, a direct comparison between the two measuring techniques has been carried out. Both techniques are based on the measurement of the fluid conductivity. For void fraction and velocity measurements, similarity exists between the two methodologies for signal analysis. A significantly different approach is followed, instead, for the estimation of the interfacial area concentration: while the evaluation based on the needle-probe signal is carried out by using projections of the gas-liquid interface velocity, the evaluation based on the wire-mesh signals consist in a full reconstruction of the bubbles interfaces. The comparison between the two techniques shows a good agreement.

Keywords: two-phase flow; interfacial area; needle-probe; wire-mesh sensor

  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
    paper ICONE15-10312
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
  • Nuclear Engineering and Design 239(2009)9, 1718-1724
    DOI: doi:10.1016/j.nucengdes.2008.06.015

Publ.-Id: 9525

Observation of two-magnon bound states in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl2-4SC(NH2)2

Zvyagin, S.

NiCl2-4SC(NH2)2 (DTN) is a quantum S = 1 chain system with strong easy-pane anisotropy and a new candidate for the field-induced Bose-Einstein condensation of the spin degrees of freedom. ESR studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode in the high- field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8:9 K, Jc = 2:2 K, and Ja;b = 0:18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement between the theory and experimental data is obtained.

  • Lecture (others)
    The International Conference on Strongly Correlated Electron Systems (SCES07), 13.-18.05.2007, Houston, United States

Publ.-Id: 9524

Spin Dynamics in the Spin-1 Large-D Antiferromagnetic Chain System NiCl2-4SC(NH2)2 in high magnetic fields

Zvyagin, S.

NiCl2-4SC(NH2)2 (DTN) is a quantum S = 1 chain system with strong easy-pane anisotropy and a new candidate for the field-induced Bose-Einstein condensation of the spin degrees of freedom. ESR studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode in the high- field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8:9 K, Jc = 2:2 K, and Ja;b = 0:18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement between the theory and experimental data is obtained.

  • Invited lecture (Conferences)
    Kolloquium an der Clemson University, Greenville, 02.03.2007, Greenville, USA

Publ.-Id: 9523

Hydrogen 3D-distribution and the kinetics in a Ti/H system studied by micro-ERDA, NRA and XRD

Wang, T. S.; Grambole, D.; Herrmann, F.; Peng, H. B.; Wang, S. W.

The micro kinetics of titanium hydrogenation is studied by measuring the three-dimensional hydrogen distribution in titanium subsurfaces by elastic recoil detection analysis with a heavy ion micro-beam, H-1(N-15, alpha gamma) C-12 resonant nuclear reaction analysis and X-ray diffraction. The hydrogen rich layers in the titanium subsurface region are formed by mechanical polishing and hydrogen ion implantation. An inhomogeneous hydrogen distribution is found in the subsurface region. The inhomogeneity varies with hydrogen concentration and depth. The hydrogen loaded by surface polishing distributes roughly homogeneously in the near surface with a high concentration up by 60 at.%, whereas the implanted hydrogen distributes inhomogeneously inside the sample with a lower concentration. Nevertheless, the inhomogeneity changes with the implantation fluence; the higher the fluence, the better the homogeneity. This phenomenon is considered to be affected by complications such as the hydrogen ingression process, hydrogen states, titanium grain size and orientation, etc.

Keywords: hydrogen ingression process; hydrogen states; titanium grain size and orientation

  • Surface and Interface Analysis 39(2007), 52-57

Publ.-Id: 9522

The Relative Biological Effectiveness of X-rays

Beyreuther, E.

The Relative biological effectiveness of X-rays

  • Lecture (others)
    Seminar der AG Mikrobiologie, 05.10.2006, Freiberg, Deutschland

Publ.-Id: 9521

Adhesion Issues in PBO/Epoxy Composites

Liu, J.; Gao, S. L.; Mäder, E.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S. A.; Wosnitza, J.

The high performance of poly p-phenylene-2,6-benzobisoxazole (PBO) fibre in mechanical properties and environmental resistance provides great potential applications as reinforcement fibres for composites. However, poor adhesion between PBO fibre and matrix is found because of the chemically inactive and/or relatively smooth surface of the reinforcement fibre. Here, we report the surface modification of PBO fibres by O2 and NH3 plasma treatments. The surface energy and roughness are increased for both sized and extracted fibres after plasma treatments. The sized fibre shows marginal improvement in interfacial adhesion and no change in fibre tensile strength because of the barrier effect of the sizing layer. For the extracted fibre, the plasma treatments cause reduction in both interfacial adhesion and the tensile strength, which is sensitive to plasma treatment conditions as revealed by a bimodal Weibull statistical distribution analysis. The fibre surface roughness is increased and more surface flaws are induced, which could result in coarse interface structures when the treated fibre surface has no adequate wetting and functional groups.

  • Key Engineering Materials 334-335(2007), 233-236

Publ.-Id: 9519

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