Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34757 Publications

Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland - KTG-Fachtagung 2006

Grauf, E.; Stoll, U.; Teschendorff, V.; Weiß, F.-P.

Der Fachtag fand am 03. und 04. April 2006 im Forschungszentrum Rossendorf (FZR) e.V. bei Dresden statt.
Die Veranstaltung griff mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial zwei Themen der Reaktorsicherheit auf, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext beleuchteten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen und stellten die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb dar. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort.
Der Fachtag vermittelte den Teilnehmern aber insbesondere, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat.
In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb war eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden gewidmet. Dabei wurden u. a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.

  • atw - International Journal for Nuclear Power (2006)6, 405-409

Publ.-Id: 8625

Strong improvement of the electroluminescence stability of SiO2:Gd layers by potassium co-implantation.

Prucnal, S.; Sun, J. M.; Reuther, H.; Skorupa, W.; Buchal, C.

Metal-Oxide-Silicon-Based light emitting diodes with Gd implanted SiO2 layers exhibit strong ultraviolet electroluminescence at 316 nm coming from Gd3+ ions. Co-implantation of potassium ions into the SiO2:Gd layer leads to elimination of the luminescent peak from point defects in SiO2 layers. The electropositive potassium ions compensate the negative charge trapping in the gate oxide and thus improve the electrical stability of the ultraviolet emission from Gd3+ ions. The operating time of the devices was increased more than 30 times by using potassium co-implantation and millisecond flash lamp annealing.

Keywords: ion implantation; MOSLEDs; electroluminescence; silicon dioxide

  • Electrochemical and Solid State Letters 10(2007), 330

Publ.-Id: 8624

Dipole-strength distributions up to the particle-separation energies and photodissociation of Mo isotopes

Schwengner, R.; Benouaret, N.; Beyer, R.; Dönau, F.; Erhard, M.; Frauendorf, S.; Grosse, E.; Junghans, A. R.; Kosev, K.; Klug, J.; Nair, C.; Nankov, N.; Rusev, G.; Schilling, K. D.; Wagner, A.

Dipole-strength distributions in the nuclides 92$Mo, 98Mo and 100Mo have been investigated in photon-scattering experiments at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf.
A simulation of gamma cascades was performed in order to estimate the distribution of inelastic transitions to low-lying states and thus to deduce the correct dipole-strength distributions up to the neutron-separation energies. The obtained absorption cross sections connect smoothly to (gamma,n) cross sections and give novel information about the low-energy tail of the Giant Dipole Resonance below the neutron-separation energies. The experimental cross sections are compared with predictions of a Quasiparticle-Random-Phase Approximation in a deformed basis.

Photoactivation experiments were performed at various electron energies to study the 92Mo(gamma,n), 92Mo(gamma,p) and 92Mo(gamma,alpha) reactions. The deduced activation yields are compared with theoretical predictions.

Keywords: Photon scattering; photoabsorption cross section; dipole strength; Random-Phase-Approximation; photoactivation; p-nuclei; reaction yields

  • Contribution to proceedings
    International Conference on Collective Motion in Nuclei under Extreme Conditions, 20.-23.6. 2006, Sankt Goar, Deutschland
  • Nuclear Physics A 788(2007), 331c-336c

Publ.-Id: 8623

Excess vacancy generation in SiGe

Kögler, R.

The excess vacancy generation in SiGe by ion implantation was investigated. In contrast to theory the excess vacancy generation in SiGe was observed to be higher than in Si. The reason is the incomplete vacancy-interstitial recombination of defects in SiGe.

Keywords: Ion implantation; implantation defects; excess defects; vacancies; Si; SiGe

  • Lecture (Conference)
    Europien Materials Research Society Conference 2006 - E-MRS2006 -, 29.05.-02.06.2006, Nizza, France

Publ.-Id: 8622

Ion beam Engineering in the initial stage of SIMOX processing

Kögler, R.

Different modes of defect engineering were applied for synthesis of SiO2 nanoclusters in Si. In particular He ion pre-implantation and simultaneous dual-implantation of Si and O ions were performed. It was demonstrated that He pre-implantation is especially suitable for creation of a well defined narrow oxide layer.

Keywords: Silicon-on-insulator; SOI; SiO2 nanocluster; defect engineering; ion beam synthesis

  • Lecture (Conference)
    Ion Implantation - Jahrestagung, 16.-17.05.06, Berlin, Deutschland

Publ.-Id: 8621

Kinetics of precipitation in neutron irradiated steel

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

Gegenstand der Vortrags ist die ratentheoretische Modellierung der Entwicklung der Größenverteilung von Cu-reichen Defekt-Fremdatom-Clustern in Cu-angereicherten Fe-Basis-Modelllegierungen unter Neutronenbestrahlung. Die berechneten Clustergrößenverteilungen werden mit Ergebnissen von Neutronenkleinwinkelstreumessungen verglichen.

  • Lecture (Conference)
    Mathematical problems to describe the phase transformation of the 1-st kind, 02.-08.07.2006, Bugas, Ukraina

Publ.-Id: 8620

A novel needle probe based on high-speed complex permittivity measurements for investigation of dynamic fluid flows

Da Silva, M. J.; Schleicher, E.; Hampel, U.

For the investigation of multiphase or multicomponent flows, which are of interest, for instance, in oil extraction and processing or in chemical engineering, there are only few suitable measuring techniques. For this reason, we have developed a high-speed complex permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical permittivity at a high data rate (up to 20000 samples/s). The performance of the system, as well as its ability to differentiate organic substances, has been analyzed. A time-resolved experiment in an oil–water–gas flow, as well as a two-substance mixing experiment in a stirred tank, is presented.

Keywords: complex permittivity measurement; heterogeneous mixture; multiphase flow; multicomponent flow; needle probe


Publ.-Id: 8619

EXAFS investigation of U(VI), U(IV) and Th(IV) sulfato complexes in aqueous solution

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A.

The structures of U(VI), U(IV) and Th(IV) sulfato complexes were investigated by LIII edge EXAFS spectroscopy in aqueous solutions with total sulfate concentrations, [SO42-]total, ranged from 0.05 to 3 M in the pH range 1.0-2.7. In equimolar U(VI)/[SO42-]total solutions, the species distribution is dominated by monodentate sulfate coordination with a U-Smon distance of 3.57±0.02 Å. With increasing U(VI)/[SO42-]total ratio bidentate coordination becomes dominant with a U-Sbid distance of 3.11±0.02 Å. The aqueous Th(IV) sulfate comprises both, monodentate and bidentate coordination with Th-S distances of 3.14±0.02 and 3.81±0.02 Å, respectively. A similar coordination is obtained for U(IV) sulfato complexes at pH 1 with U-S distances of 3.08±0.02 Å and 3.67±0.02 Å. By increasing the pH value to 2, a U(IV) precipitate occurs, where sulfate act exclusively as bridging ligand with a U-S distance 3.67±0.02 Å.

Keywords: EXAFS; uranium; thorium; sulfate; coordination

  • Inorganic Chemistry 46(2007)15, 5882-5892
  • Poster
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
  • Contribution to proceedings
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, 978-92-64-99006-7, 219-224

Publ.-Id: 8618

Evidence for double-electron excitations in X-ray absorption spectra of actinides

Hennig, C.

A systematic investigation of double-electron resonances in L3 edge X-ray absorption spectra of actinides in aqueous solution is presented. Actinide species in valence states IV and III were investigated by using experimental data of Th4+, U4+, Np4+, Pu3+, and Am3+ hydrates. The double-electron excitation was identified as a L3N6,7 shake-up effect. Energy positions of the double-electron features were found in good agreement with the Z+1 approximation. The double-electron resonances undergo a larger chemical shift as the L3 edge.

Keywords: double-electron excitation; shake-up; Z+1 approximation; actinides

Publ.-Id: 8617

Enhanced local void and temperature measurements for highly transient two-phase flows

Schleicher, E.; Da Silva, M. J.; Hampel, U.

Abstract: Local void fractions measurements in two-phase flow phenomena are commonly carried out by the use of needle probes. The measuring principle of these probes is based on conductivity or optical measurements. In the past advanced needle probes with integrated micro-thermocouples have been introduced by Prasser et al., making possible to measure local temperatures at the same position where the void fractions are determined because the sheath of the micro-thermocouple serves as the measuring electrode for the conductivity measurement. Thereby - in principle - the temperatures of the two different phases (e. g. steam and water) can be distinguished. The big disadvantage of this technique is the relative long time constant (~20 ms) of mineral-insulated sheathed thermocouples. The usage of this type of thermocouples was necessary because the electronic was not able to separate the two signals (temperature and conductivity) from each other. Measuring of high-transient two phase flows were impossible due to the slow time response. Additionally the two signals had to be sampled sequentially because of influence of the rectangular excitation signal into the small temperature voltage. Investigations of temperature changing in the interfacial area between gas and liquid were therefore very difficult. To solve this problem we have developed a new combined temperature and conductivity needle probe measuring system, which is able to handle grounded or direct sheathed thermocouples (where the thermocouple wires are electrically-joined to the protective sheath) as well as open thermocouples (exposed junction).

Keywords: needle probe; temperature measurement; two-phase flows; micro-thermocouple

Publ.-Id: 8614

Improving Resolution in k and r Space: A FEFF-based Wavelet for EXAFS Data Analysis

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

Applying the wavelet analysis of Extended X-Ray Absorption Fine Structure (EXAFS) spectra to a Zn-Al layered double hydroxide, we could unequivocally identify the presence of Al and Zn atoms at the same distance of r ≈ 3 Å from the central Zn atom. The focused paths (including MS) at r ≈ 5 - 6 Å (2nd and 3th metal shell) show also both Al and Zn for all LDH spectra. With the newly developed FEFF-Morlet wavelet it is possible to resolve the two shells individually. The result is, that the 2nd shell not contains Al. This confirms directly the homogeneity of the Al - Zn distribution. No significant differences were found by shell fit- and wavelet analysis between the EXAFS spectra of pure Zn-,Co- or Ni LDH on the one hand and the mixed Zn/Co and Zn/Ni LDH on the other hand.

Keywords: EXAFS; wavelet analysis; layered double hydroxides

  • Lecture (Conference)
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.-14.07.2006, Stanford, United States
  • Contribution to proceedings
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.02.-14.07.2006, Stanford, United States
    AIP Conference Proceedings, Vol. 882, Melville, N.Y., 72-74

Publ.-Id: 8613

Influence of carbonate on U(VI) aqueous speciation and adsorption to ferrihydrite investigated by advanced EXAFS data analysis methods

Rossberg, A.; Ulrich, K.-U.; Brendler, V.; Scheinost, A.

At alkaline pH conditions, formation of soluble uranyl carbonato complexes commonly prevents U(VI) sorption to mineral surfaces, thereby promoting uranium migration in the liquid phase. Microbial activity may increase the partial CO2 pressure by several orders of magnitude in relation to the atmosphere, hence negatively charged carbonato complexes may play a significant role even at acidic pH values, where sorption to positively charged surfaces may compete with formation of binary inner-sphere sorption complexes. Therefore, we studied by EXAFS the sorption of UO22+ on ferrihydrite in aqueous solution as a function of pH and at elevated carbonate concentrations. We used iterative target transformation factor analysis (ITFA) [1] to derive the spectra of the pure species from the EXAFS spectral mixtures. Then we applied Monte Carlo simulations (MCTFA) [2] to determine the three-dimensional structure of the pure species and the radial pair distribution functions of the single and multiple scattering paths. The spectra of the mixtures can be described by a linear combination of two species. Species 1 is an inner-sphere binary U(VI)-ferrihydrite complex, with U(VI) coordinating to the edge of an Fe octahedron. In species 2, U(VI) is coordinated to two or three carbonato ligands, suggesting formation of [(UO2)(CO2)2]2- or [(UO2)(CO2)3]4- complexes associated with the ferrihydrite solid.

[1] Rossberg, A., Reich, T. & Bernhard, G. Complexation of uranium(VI) with protocatechuic acid - application of iterative transformation factor analysis to EXAFS spectroscopy. Analytical and Bioanalytical Chemistry 376, 631-638 (2003).
[2] Rossberg, A. & Scheinost, A. C. Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo Simulations and Target Transformation Factor Analysis. Analytical and Bioanalytical Chemistry 383(1), 56-66 (2005).

  • Poster
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.-14.07.2006, Stanford, United States

Publ.-Id: 8612

Modified spectro-electrochemical cell for experiments with ionic liquids

Hennig, C.

The presentation concludes the technical development of a spectro-electrochemical cell for actinide research. Electrolysis can be applied with an electrode of second order or by using a diaphragm to seperate catodic and anodic space. The results of chloro and sulfato coordination in presence of U(VI) and U(IV) will be discussed.

Keywords: EXAFS; spectro-electrochemistry; uranium

  • Invited lecture (Conferences)
    Actinet Meeting "Actinides and lanthanides solution chemistry in water stable Room Temperature Ionic Liquids", 08.-09.06.2006, Strasbourg, France

Publ.-Id: 8611

The Structure Of Uranyl Sulfate In Aqueous Solution - Monodentate versus Bidentate Coordination

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A. C.

The structure of U(VI) aquo sulfato complexes has been investigated by LIII edge EXAFS spectroscopy. A monodentate coordination with a U-Smon distance of 3.57±0.02 Å prevail in equimolar [SO42-]total/U(VI) solutions. With increasing [SO42-]total/U(VI) ratio, bidentate coordination with a U-Sbid distance of 3.11±0.02 Å becomes dominant.

Keywords: EXAFS; U(VI); aquo sulfato complex

  • Contribution to proceedings
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.-14.07.2006, Stanford, United States
    API - Special Edition

Publ.-Id: 8610

Coordination of uranium aquo chloro and sulfato complexes under different redox conditions

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A. C.

Natural aquatic systems may exert large variations in actinide oxidation states because of limited oxygen diffusion, and microbially and inorganic (surface catalyzed) redox processes. Redox state and coordination hence is a key variable controlling uranium mobility at former uranium mining areas. We have developed a spectro-electrochemical cell, which allows to study the structure speciation of aqueous U(VI) and U(IV) complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential [1]. Here we present data on the influence of redox state on the uranium coordination by chloride and sulfate. The reduction of U(VI) to U(IV) involves an electron transfer and a chemical reaction transforming the trans-dioxo cation to the spherically coordinated U4+ cation. With [Cl] increasing from 0 to 9 M, we observed for U(VI) the complexes UO2(H2O)52+, UO2(H2O)4Cl+, UO2(H2O)3Cl20 and UO2(H2O)2Cl3, and for U(IV) the complexes U(H2O)94+, U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+ [1]. Elevated sulfate concentrations have been monitored at the former uranium mine Königstein/Germany, where uranium was leached by sulfuric acid. We observed that tetra- and hexavalent uranium forms both monodentate and bidentate complexes with sulfate. However, with increasing [SO42-] concentration the bidentate coordination prevails. The observed formation of soluble U(IV) sulfato complexes may prevent uraninite precipitation even at low pH, thus increasing the mobility of uranium even under reducing conditions.

Keywords: EXAFS; U(VI); U(IV); electrochemistry

  • Poster
    XAFS-13 Conference, 09.-14.07.2006, Stanford, USA

Publ.-Id: 8609

The problem to account for processes on different time scales in the investigation of neutron embrittlement

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

Neutrons with energy of about 1 МeV or higher, to which reactor pressure vessel steels are exposed under service conditions of nuclear power plants, can stimulate the phenomenon of so-called neutron embrittlement. The reason is the irradiation-induced formation and evolution of precipitates and solute/defect clusters. The set of experimental methods to investigate the nanostructure, including X- ray and neutron small angle scattering, atom probe field ion microscopy method, TEM as well as direct determination of the mechanical properties of the reactor vessel is usually carried out after irradiation intervals of the order of one year.
Therefore a project called virtual test reactor has been started recently within the framework of the European program “PERFECT”. Experimental data obtained for neutron irradiated pressure vessel steels are used as the reference for working out and study theoretical models of the kinetics of neutron embrittlement.
In the cascade stage, following the interaction of a neutron with a so-called primary knock-on atom, the recoil energy transferred to the crystal lattice causes a local increase of the temperature to beyond the melting temperature and the formation of defects. A typical time scale for these processes is picoseconds. Such processes are studied by the molecular dynamics and Monte-Carlo methods.
Unlike the case of electron irradiation, where only Frenkel pairs are formed, point defect clusters and Cu-precipitates are produced in the case of neutron irradiation. The evolution of these clusters can be studied in the rate theory approach, in particular by cluster dynamics method. This method allows for the determination of the time dependence of the number density of clusters (precipitates) via integration of the system of ordinary differential equations with the initial data as the final data of the cluster number density after cascade stage. The characteristic relaxation time depends on the kind of the irradiated feature. For example for point defect clusters this time is about 1 day but for Cu-precipitates the relaxation time is about one month. Hence the problem to integrate the master equation of cluster dynamics is the problem of integration of so-called stiff ordinary differential equations.
The objective of our present investigation is the comparative analysis of software tools applied to the cluster dynamics modeling. The most effective one, namely the code D02EJF from the licensed Fortran NAG Library has been used to investigate the kinetics of the following three kinds of neutron irradiated features in reactor pressure vessel steels:

  • The system of free and clustering vacancies (V) and interstitials (I), denoted (V+I)-system,
  • The system of the Cu-precipitates favoured because of irradiation-enhanced Cu diffusivity, denoted (V+I)=>Cu system,
  • The (V+I)óCu system, when the effect of Cu-precipitates on the sink strength in the first and second model is additionally considered.
The comparison of the experimental and cluster dynamics data has been carried out on the basis of low-Cu and Cu-enriched mock-up alloys after neutron irradiation.
  • Lecture (Conference)
    4-th Russian Symposium "Physics Problems of Ultrashort Phenomena in Strongly Non-Equilibrium Media", 22.07.-01.08.2006, New Athos, Russia

Publ.-Id: 8608

CFD-simulation of OECD V1000CT2 with advanced turbulence models

Höhne, T.

CFD calculations have been performed for the themalhydraulic benchmark V1000CT-2.
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor ANSYS CFX and contains 4.7 Mio. tetrahedral elements Different advanced turbulence models were used in the numerical simulation The best agreement with the Kozloduy experiment at the core inlet shows the DES simulation. Strong fluctuations occur in the downcomer of the RPV.
The results show a clear sector formation of the affected loop at 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%
Deficits: Estimation of experimental values at the core outlet to the core inlet, interpolation

Keywords: OECD; VVER-1000; CFD

  • Lecture (Conference)
    Annual meeting of Working Group C and G of AER, 22.-23.05.2006, Balatonfüred, Hungary

Publ.-Id: 8607

Fluid mixing and flow distribution ín a primary circuit of a nuclear pressurized water reactor – Validation of CFD codes

Rohde, U.; Höhne, T.; Kliem, S.; Hemström, B.; Scheuerer, M.; Toppila, T.; Aszodi, A.; Boros, I.; Farkas, I.; Muehlbauer, P.; Vyskocil, V.; Klepac, J.; Remis, J.; Dury, T.

The EU project FLOMIX-R was aimed at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity.
This report will focus on the Computational Fluid Dynamics (CFD) code validation. Slug mixing tests simulating the start-up of the first main circulation pump have been performed with two 1:5 scaled facilities: The Rossendorf coolant mixing model ROCOM and the VATTENFALL test facility. Additional data on slug mixing in a VVER-1000 type reactor gained at a 1:5 scaled metal mock-up at EDO Gidropress are provided. Experimental results on mixing of fluids with density differences obtained at ROCOM and the FORTUM PTS test facility were made available. Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests have been used together with the data from the ROCOM facility as a basis for the flow distribution studies. CFD calculations have been accomplished for selected experiments with two different CFD codes (CFX-5, FLUENT). Best practice guidelines (BPG) were applied in all CFD work when choosing computational grid, time step, turbulence models, modelling of internal geometry, boundary conditions, numerical schemes and convergence criteria. The strategy of code validation based on the BPG and a matrix of CFD code validation calculations have been elaborated. Based on the “best practice solutions”, conclusions on the applicability of CFD for turbulent mixing problems in PWR were drawn and recommendations on CFD modelling were given.


Publ.-Id: 8606

Surface speciation of uranyl(VI) on gibbsite: A combined spectroscopic approach

Arnold, T.; Scheinost, A.; Baumann, N.; Brendler, V.

Sorption phenomena are important immobilization processes to be considered in the design of nuclear waste repositories. Confidence in respective performance assessments requires a mechanistic understanding of the dominant surface reactions. Highly sensitive and non-invasive techniques such as Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) and Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy are valuable tools to reveal the true surface speciation.
Here TRLFS and EXAFS were applied to study the species of uranyl(VI) adsorbed onto gibbsite particles. This system is important as a model for the characterization of the edge sites of aluminosilicates, relevant as potential host rock and as part of engineered barrier systems.
The experiments were performed with both normal and CO2-free atmosphere, in the pH range 4 to 9, with a total uranium concentration of 10 µM, an ionic strength of 0.01 M (NaClO4), a solid concentration of 4.15 and 12.5 g/L, and using a grain size of 0.2 – 12 µm.
TRLFS at room temperature provided evidence for two adsorbed uranium(VI) surface species. The two species showed similar positions of the fluorescence emission bands and different fluorescence lifetimes indicating a different coordination environment for the two species. The first surface species with the shorter fluorescence lifetimes was assigned to a mononuclear surface complex, where EXAFS indicated (AlO)2UO2 distance of 3.6 Å. The second species with the longer fluorescence lifetimes was attributed to polynuclear surface species supported by a U – U distance of 4.2 Å obtained by EXAFS at cryogenic temperature. Cryogenic TRLFS experiments at 10 K implied the presence of a third surface species. The significant shift of the fluorescence emission bands to shorter wavelength (approximately 16 nm) points to a ternary uranyl carbonato surface species, supported by an EXAFS-derived U – C distance of 2.9 Å. These results will help to formulate more realistic surface reactions on aluminosilicates.

  • Lecture (Conference)
    2006 Fall Meeting, 27.11.-01.12.2006, Boston, United States
  • Contribution to proceedings
    2006 Fall Meeting, 27.11.-01.12.2006, Boston, United States

Publ.-Id: 8605

Analytische und experimentelle Untersuchungen zur Modellierung der Fluid-Struktur-Wechselwirkung in einem 2D-Ringspalt

Grunwald, G.; Altstadt, E.

  • Open Access Logo Forschungszentrum Rossendorf; FZR 1 1993
    ISSN: 1436-3976


Publ.-Id: 8604

Complexation of uranium(VI) with aromatic acids in aqueous solution – A comparison of hydroxamic acids and benzoic acid

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

The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid in 0.1 M NaClO4 was studied by UV-vis spectroscopy at pH 3 and 4. Uranium(VI) species of the type MpLqHr were identified from the UV-vis spectra in all three systems. An increase in the absorption combined with a blue shift of the absorption maxima in comparison to the bands of the free uranyl ion of 22.5 ± 2 nm was observed in the uranium (VI)-salicylhydroxamic acid-system. Besides indications for a 1:2 complex, the formation of a 1:1 complex with a stability constant of log β111= 17.12 ± 0.10 could be demonstrated by its individual absorption spectrum and molar absorption coefficient. Also in the uranium(VI)-benzohydroxamic acid-system a blue shift of the absorption maxima in comparison to the bands of the free uranyl ion of 27 ± 1.4 nm indicate the complex formation. The stability constants are log β110 = 7.96 ± 0.05 for UO2[C6H4CONHO]+ and log β120 = 15.25 ± 0.11 for UO2[C6H4CONHO]2. In contrast to the hydroxamic acids, benzoic acid shows a red shift of the absorption maxima of 2.5 ± 2 nm. Only the 1:1 complex UO2[C6H4COO]+ with a stability constant of log β110 = 3.37 ± 0.14 is existent. An estimate is made in order to discuss the dependencies observed in the absorption spectra in relation to possible coordination modes of uranium(VI). The strength of the complex formation between uranyl and the three aromatic acids is discussed.

Keywords: Uranyl; Hydroxamic acid; Spectroscopy; UV-vis spectra; Complexation

Publ.-Id: 8603

ROSY - Rossendorfer Synchrotronstrahlungsquelle, Vorschlag für die Errichtung einer Synchrotronstrahlungsquelle für die Materialforschung im Forschungszentrum Rossendorf

Einfeld, D.; Matz, W.

Der Projektvorschlag für eine kompakte Synchrotronstrahlungsquelle der 3. Generation ROSY wird beschrieben. Die Quelle sol1 für die Materialforschung dediziert sein, die für die Forschung im regionalen Umfeld von Rossendorf prägend ist.
Bei einer Speicherringenergie von 3 GeV wird Synchrotronstrahlung im harten Röntgenbereich mit einer kritischen Energie des Spektrums von Ec = 8,4 keV (hc=0,14 nm) emittiert. Mit einer naturlichen Emittanz von 28 n nm rad wird eine sehr brillante Strahlung zur Verfügung gestellt. Neben der Strahlung aus Ablenkmagneten kann Strahlung aus Wigglern und Undulatoren genutzt werden. Für diese insertion devices sind 8 Einbaumöglichkeiten vorhanden, von denen 4 in nichtdispersionsfreien geraden Strecken liegen. Der Speicherring hat eine vierfache Symmmetrie, einen Umfang von 148 m und ist als modifizierte FODO-Struktur konzipiert. Ein nachträglicher Einbau von supraleitenden Ablenkmagneten zur Erzeugung eines harteren Spektrums und
damit zur Ausweitung des Anwendungsbereiches ist möglich.
Der Teil I enthält die wissenschaftliche Begründung fur ROSY und eine Darstellung der Nutzungsmöglichkeiten. Im Teil II werden das Speicherringkonzept und die technischen Details der einzelnen Komponenten beschrieben.

  • Open Access Logo Forschungszentrum Rossendorf; FZR 10 1992
    ISSN: 1436-3976


Publ.-Id: 8602

Electronegativity and point defect formation in ion implanted SiO2 layers

Prucnal, S.; Sun, J.; Reuther, H.; Skorupa, W.; Buchal, C.

The Metal-Oxide-Silicon (MOS) diode structure containing ion implanted electropositive (M+) and electronegative (M-) ions is one of the most promising candidates for a new type of high-efficiency electroluminescence (EL) devices which can be integrated with standard silicon CMOS technology. The implantation process creates defects in the SiO2 layer. After implantation an annealing process leads to the diffusion of the implanted elements and a broadening of the SiO2/Si interface. The influence of the different implanted ions (Gd, F, K) was investigated by electroluminescence measurements and correlated to different defects in the oxide layer. Implanted electronegative ions (such as F) lead defects comprising O2 molecules and peroxy radicals (POR). On the other hand, the electropositive ions (Gd and K) increase the number of the oxygen vacancy defects.

Keywords: ion implantation; electronegativity; electroluminescence

  • Vacuum 81(2007)10, 1296-1300

Publ.-Id: 8601

Annual Report 1992, Institute of Nuclear and Hadronic Physics

Dönau, F.; Prade, H.; (Editors)

  • Open Access Logo Forschungszentrum Rossendorf; FZR 10 1993
    ISSN: 1436-3976


Publ.-Id: 8600

Evolution of interfacial area concentration in a vertical air-water flow measured by wire-mesh sensors

Prasser, H.-M.

An application of wire-mesh sensors to obtain the interfacial area concentration in vertical pipes is presented as an alternative to widely used multiple-tip electrical or optical fibre probes. The measuring data of a mesh sensor consists in a three-dimensional matrix of local instantaneous gas fractions measured at each crossing point of the wires and recorded as a time sequence. Bubbles are clearly reflected in this data matrix, since they represent regions of interconnected elements containing the gaseous phase. The method to deduce the interfacial area concentration from this data is based on a full reconstruction of the gas-liquid interface, where the interfacial area of each bubble is recovered as the sum of the surface area of all surface elements belonging to the given bubble. The new method can be applied to large bubbles with an arbitrary shape. To study the change of the interfacial area concentration along the pipe the distance between sensor and gas injection was varied. Obtained results were compared to the findings reported in literature.

Keywords: two-phase flow; flow pattern; interfacial area concentration; vertical upwards flow; wire-mesh sensors

  • Nuclear Engineering and Design 237(2007), 1608-1617

Publ.-Id: 8599

CFD modelling of subcooled boiling – concept, validation and application to fuel assembly design

Krepper, E.; Koncar, B.; Egorov, Y.

The paper describes actual CFD (Computational Fluid Dynamics) approaches to subcooled boiling and investigates their capability to contribute to fuel assembly design. In a prototype version of the CFD code CFX a wall boiling model is implemented based on a wall heat flux partition algorithm. It can be shown, that the wall boiling model is able to calculate the cross sectional averaged vapour volume fraction of vertical heated tubes tests with good agreement to published experimental data. The most sensitive parameters of the model are identified. Needs for more detailed experiments are established which are necessary to support further model development. The model is applied for investigation of the phenomena inside a hot channel of a fuel assembly. Here the essential phenomenon is the critical heat flux. Although subcooled boiling represents only a preliminary state towards the critical heat flux occurrence, essential parameters like swirl, cross flow between adjacent channels and concentration regions of bubbles can be determined. By calculating the temperature of the rod surface the critical regions can be identified which may later on lead to departure from nucleate boiling and possible damage of the fuel pin. The application of up-to-date CFD with a subcooled boiling model for the simulation of a hot channel enables the comparison and the evaluation of different geometrical designs of the spacer grids of a fuel rod bundle.

Keywords: CFD; bubbly flow; boiling; code validation; fuel rod bundle

Publ.-Id: 8597

Picosecond dynamics of interminiband transitions in doped GaAs/AlGaAs superlattices

Stehr, D.; Winnerl, S.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.

Semiconductor superlattices are an essential component of novel infrared devices such as detectors and quantum cascade lasers and their optical and transport properties have been investigated extensively during the past two decades. However, unlike for quantum well structures where considerable knowledge on the intersubband relaxation dynamics has been obtained, so far no experimental work has been published on the interminiband relaxation dynamics in superlattices.

In this work we have studied the transient transmission of a doped GaAs/Al0.3Ga0.7As superlattice in pump-probe experiments [1]. The superlattice with thickness of 9.0 nm and 2.5 nm of the wells and barriers, respectively, was n-doped in the center of the wells, resulting in a doping density of 1.51016 cm-3 averaged over one superlattice period. Picosecond infrared pulses with energies up to 100 nJ in the range from 4 µm to 22 µm were generated at 13 MHz repetition rate by the free-electron laser FELBE at the Forschungszentrum Rossendorf. In particular, the experiments were performed at the absorption maxima of the superlattice at 9.0 µm and 15.8 µm (compare Fig. 1). These wavelengths are the spectral positions of the van Hove singularities of the joint density of states in the center and at the edge of the mini-Brillouin zone, respectively.

The measured pump-probe signals shown in Fig 2 consist of a fast component due to the bleaching of the interminiband transition and subsequent relaxation and thermalization, and a slower component due to cooling of the heated electron system. The fast component decays typically around 2-2.5 ps, in reasonable agreement with published theoretical values [2]. The slower component due to cooling is positive for excitation at 9.0 µm and negative at 15.8 µm and shows a strong temperature and excitation density dependence with cooling times ranging from 5 to 50 ps. This behavior is consistent with the temperature dependence of the linear absorption spectrum, i.e. yielding higher or lower transmission for increasing electron temperature. The effect provides an internal thermometer for the miniband electrons on a picosecond timescale.

[1] D. Stehr et al., Appl. Phys. Lett. (in print)
[2] F. Compagnone, A. Di Carlo, and P. Lugli, Appl. Phys. Lett. 80, 920 (2002)

  • Lecture (Conference)
    POISE Summer School, 25.-30.06.2006, Cortona, Italia

Publ.-Id: 8596

Nanocluster formation in Fe implanted GaN

Talut, G.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Potzger, K.

The formation of Fe-clusters in wurtzite GaN implanted with 200 keV 57Fe ions at 350 ±C was investigated. Cluster sizes from few nanometers up to several 100 nm depending on ion fluence, implantation and annealing temperature have been observed for ion fluences between 4·1016 cm−2 and 1.6·1017 cm−2. A clear epitaxial relation between Fe and GaN was determined. X-ray diffraction, conversion electron Mössbauer spectroscopy, transmission electron microscopy and Auger electron spectroscopy were used for the characterization of the implanted samples. Mössbauer spectroscopy shows that precipitation of Fe occurs already during implantation.

Keywords: Fe; clusters; GaN; DMS; Mössbauer

Publ.-Id: 8595

Magnetohydrodynamic drag reduction and its efficiency

Shatrov, V.; Gerbeth, G.

We present results of direct numerical simulations of a turbulent channel flow influenced by electromagnetic forces. The magnetohydrodynamic Lorentz force is created by the interaction of a steady magnetic field and electric currents fed to the fluid via electrodes placed at the wall surface. Two different cases are considered. At first, a time-oscillating electric current and a steady magnetic field create a spanwise time-oscillating Lorentz force. In the second case, a stationary electric current and a steady magnetic field create a steady, mainly streamwise Lorentz force. Besides the viscous drag, the importance of the electromagnetic force acting on the wall is figured out. Regarding the energetic efficiency it is demonstrated that in all cases a balance between applied and flow induced electric currents improves the efficiency significantly. But even then, the case of a spanwise oscillating Lorentz force remains with a very low efficiency, whereas for the self-moved regime in case of a steady streamwise force much higher efficiencies are found. Still, no set of parameters has yet been found for which an

energetic breakthrough, i.e. a saved power exceeding the used power, is reached.

  • Physics of Fluids 19, 035109(2007)

Publ.-Id: 8594

Low-energy cross section of the 7Be(p , γ)8B solar fusion reaction from the Coulomb dissociation of 8B

Schümann, F.; Typel, S.; Hammache, F.; Sümmerer, K.; Uhlig, F.; Böttcher, I.; Cortina, D.; Förster, A.; Gai, M.; Geissel, H.; Greife, U.; Grosse, E.; Iwasa, N.; Koczon, P.; Kohlmeyer, B.; Kulessa, R.; Kumagai, H.; Kurz, N.; Menzel, M.; Motobayashi, T.; Oeschler, H.; Ozawa, A.; Ploskon, M.; Prokopowicz, W.; Schwab, E.; Senger, P.; Strieder, F.; Sturm, C.; Zhi-Yu, S.; Surowka, G.; Wagner, A.; Walus, W.

An exclusive measurement of the Coulomb breakup of 8B into 7Be + p at 254A MeV was used to infer the low-energy 7Be(p , γ)8B cross section. The radioactive 8B beam was produced by projectile fragmentation of 350A MeV 12C and separated with the FRagment Separator (FRS) at Gesellschaft für Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S 17 factors exhibit good agreement with the most recent direct 7Be(p , γ)8B measurements. By using the energy dependence of S 17 according to the recently refined cluster model for 8B of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S 17(0)= 20.6 ± 0.8(stat) ± 1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%.

  • Physical Review C 73(2006), 15806-1-15806-13
    DOI: 10.1103

Publ.-Id: 8593

Study of crystal damage by ion implantation using micro RBS/Channeling

Grambole, D.; Herrmann, F.; Heera, V.; Meijer, J.

The combination of microbeam implantation and in-situ micro RBS/Channeling analysis in the Rossendorf nuclear microprobe facility enables crystal damage studies with high current densities not achievable in standard ion implantation experiments. Si(100) samples were implanted with 600 keV Si+ ions and a fluence of 1 x 1016 Si/cm². Using a beam spot of 200 µm x 200 µm current densities from 4 to 120 µA/cm² were obtained. The substrate temperature was varied between RT and 265 °C. The implanted regions were subsequently analysed by micro RBS/Channeling with a 3 MeV He+ beam having a spot size of 50 µm x 50 µm.
Crystal damage up to amorphisation was obtained in dependence on the substrate temperature. Above a critical temperature TC no amorphisation occurs. TC was determined for each series of samples implanted with the same ion current density j. It was found that the empirical Arrhenius relation j ~ exp(- Em/ kTC), known from standard implantation experiments, is also valid at high current densities. The observed Arrhenius law can be derived from a model of epitaxial crystallisation stimulated by defect diffusion.

Keywords: Nuclear microprobe; Micro RBS/Channeling; Experimental setup; Ion implantation; Si ions; Silicon; Ion current density; Radiation damage; Amorphisation; Critical temperature

  • Invited lecture (Conferences)
    10th International Conference on Nuclear Microprobe Technology and Applications, 10.-14.07.2006, Singapore, Singapore
  • Nuclear Instruments and Methods in Physics Research B 260(2007), 276-280

Publ.-Id: 8592

Ion beam analysis by nuclear microprobes

Grambole, D.; Herrmann, F.

The nuclear microprobe is extensively applied to a wide research field, due to the combination of the good ability of the ion beam analysis and the spatial resolution in the range of a few micrometer.
The nuclear microprobe at the 3MV Tandetron accelerator of the Forschungs-zentrum Rossendorf is one of very few probes about the world, at which all ion beam analytical methods are availably:

  • micro Rutherford Backscattering Spectrometry (µRBS) for detection of mainly heavier elements,
  • micro RBS – Channeling (µRBS/Channeling) to investigate the crystal structure and damage in small regions,
  • micro Elastic Recoil Detection Analysis (µERDA) for profiling of light elements,
  • micro Particle Induced X-ray Emission (µPIXE) for mapping of especially trace elements and
  • micro Nuclear Reaction Analysis (µNRA) for detection of special light isotopes.
In order to demonstrate the generally analytical performance of nuclear microprobes a selection of various uses of the Rossendorf microprobe for ion beam analysis will be presented and discussed.
  • Invited lecture (Conferences)
    6th International Conference "Ion Implantation and other Applications of Ions and Electrons" ION 2006, 26.-29.06.2006, Kazimierz Dolny, Poland

Publ.-Id: 8591

Steam bubble condensation in sub-cooled vertical pipe flow

Lucas, D.; Prasser, H.-M.

Detailed experimental data on the evolution of a two-phase flow along a vertical pipe with an inner diameter of 195 mm and a length of 8 m were obtained for adiabatic air-water mixture as well as for steam-water mixture under adiabatic and non-adiabatic conditions at different pressure. The experiments were performed at the TOPFLOW facility of our institute. The measurements were carried out using the wire-mesh sensor technology. The data include local gas volume fraction values (lateral resolution: 3 mm) as well as bubble size distributions and local volume fraction distributions decomposed according to bubble size classes. A slight sub-cooling of the water (max. 4 K) was achieved by throttling the globe valve at the upper end of the vertical test section.

Since the wire-mesh sensor disturbs the flow in downflow direction (but still measures the undisturbed flow!) it doesn’t make sense to place a number of wire-mesh sensors behind each other in order to investigate the evolution of the flow along the pipe. Because of the large dimensions of the facility it is also not applicably to shift a single sensor to different height positions by dismantling the facility each time. For this reason the measuring plane was fixed at the upper end of the test section and a variable gas injection was used. The gas was injected by rings of holes at the pipe wall, which are placed at different height positions 1 mm and 4 mm holes can be used for the injection.

The previously developed Multi-Bubble-Size-Group Test Solver was extended to consider the phase transfer. The large number of bubble classes (50) in the simulation allows the investigation of the influence of the bubble size distribution. The interfacial area density is calculated according to the bubble size distributions and the assumption of ellipsoidal bubbles with a deformation according to the well-known Wellek-correlation. Simulations show, that there are clear differences in the condensation process along the pipe for poly-dispersed flow in comparison with the assumption of mono-dispersed flow is discussed.

The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.

Keywords: Condensation; Bubbly Flow; Phase Transfer

  • Lecture (others)
    44rd European Two-Phase Flow Group Meeting, 07.-09.06.2006, Lausanne, Schwizerland

Publ.-Id: 8590

The traveling wave MRI in cylindrical Taylor-Couette flow: comparing wavelengths and speeds in theory and experiment

Rüdiger, G.; Hollerbach, R.; Stefani, F.; Gundrum, T.; Gerbeth, G.; Rosner, R.

We study experimentally the flow of a liquid metal confined between differentially rotating cylinders, in the presence of externally imposed axial and azimuthal magnetic fields. For increasingly large azimuthal fields a wave-like disturbance arises, traveling along the axis of the cylinders. The wavelengths and speeds of these structures, as well as the field strengths and rotation rates at which they arise, are broadly consistent with theoretical predictions of such a traveling wave magnetorotational instability.

  • The Astrophysical Journal Letters 649(2006)2, L145-L147
    DOI: 10.1086/508422

Publ.-Id: 8589

QWIP Camera Development and Applications

Schneider, H.

Quantum well infrared photodetector (QWIP) technology opens up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging. Large infrared detector arrays with excellent thermal and spatial resolution, low fixed-pattern noise, low 1/f noise, and high pixel yield can thus be realized at moderate cost.
In this tutorial, I will report on typical QWIP structures optimized for thermal imaging applications, the development of focal plane arrays, and the performance of state-of-the-art QWIP cameras. Dual-band QWIP FPAs detecting simultaneously in different spectral bands will also be addressed.
In most cases, a successful novel technology is not only suitable for existing applications; it will also create its new applications. Talking about applications of QWIP FPAs, I will show that QWIP technology has in fact lead to new and interesting opportunities, in particular in the medical market.

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

  • Invited lecture (Conferences)
    International Workshop on Quantum Well Infrared Photodetectors (QWIP2006), 18.-24.06.2006, Kandy, Sri Lanka

Publ.-Id: 8588

Autocorrelation measurements of free-electron laser radiation using a two-photon QWIP

Schneider, H.; Drachenko, O.; Winnerl, S.; Helm, M.; Maier, T.; Walther, M.

The two-photon QWIP approach involves three equidistant subbands, namely two bound states localized in the quantum well and an extended state in the continuum. Here the intermediate state generates a huge optical nonlinearity, six orders of magnitude larger than in usual bulk semiconductors, which makes this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared lasers. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization [1]. We will report here on autocorrelation measurements of ps optical pulses from a free-electron laser (FEL). Due to the intense nonlinear signal, two-photon QWIP operation is possible at room temperature. The device is thus ideally suited for standard diagnostics of the FEL pulse shape.
[1] H. Schneider, T. Maier, H. C. Liu, M. Walther, P. Koidl, Ultra-sensitive femtosecond two-photon detector with resonantly enhanced nonlinear absorption, Optics Letters 30, 287 (2005).

Keywords: quantum-well infrared photodetector; QWIP; quadratic autocorrelation; GaAs/AlGaAs; free-electron laser

  • Lecture (Conference)
    International Workshop on Quantum Well Infrared Photodetectors (QWIP2006), 18.-24.06.2006, Kandy, Sri Lanka
  • Infrared Physics and Technology 50(2007), 95-99
    DOI: 10.1016/j.infrared.2006.10.028

Publ.-Id: 8587

Consideration of steel corrosion rates from the MASCA / METCOR-tests to the RPV strength under IVR conditions

Willschuetz, H.-G.; Altstadt, E.

Physicochemical interaction of prototypic UO2-ZrO2-Zr corium melt and VVER vessel steel was examined during the 2nd Phase of the ISTC METCOR Project. Rasplav-3 test facility was used for conducting four tests, in which the Zr oxidation degree and interaction front temperature were varied; in one of the tests, stainless steel was added to the melt.
Direct experimental measurements and posttest analyses were used for determining corrosion kinetics and maximum corrosion depth, as well as the steel temperature conditions during the interaction, and finally the structure and composition of crystallized ingots, including the interaction zone. The minimum temperature on the interaction front boundary, which determined its final position and maximum corrosion depth was ~1090°С. An empirical correlation for calculation of corrosion kinetics has been derived.
In this presentation the impact of the so called "corrosion" is compared to calculations without a consideration of the corrosion. The evaluated scenario considers the In-Vessel-Retention for a VVER-1000 with a stratified melt pool and with a homogeneous melt pool.

Keywords: In-Vessel-Retention; VVER-1000; vessel wall corrosion; homogeneous and stratified melt pool

  • Invited lecture (Conferences)
    Seminar at the Division of Nuclear Power Safety, 26.06.2006, Stockholm, Sveden

Publ.-Id: 8586

Innovationspool Natur: Bakterien und Bionik

Raff, J.

Ein Ziel der heutigen Forschung ist es, neue und innovative Wege zur Lösung technischer Fragestellungen zu erschließen. In der Bionik wird dazu versucht, von der Natur zu lernen. Höchst erfolgreiche Beispiele dafür sind der Lotuseffekt, der Klettverschluss oder die Nutzung der Struktur der Haifischschuppe zur Reduktion des Luftwiderstandes bei Flugzeugen. Aber nur wenige wissen, dass auch die kleinsten Lebewesen unseres Planten, die Bakterien, hier einen großen Beitrag leisten können.

  • Lecture (others)
    Vortrag anlässlich des Besuch der Berufschulzentrum Technik, Bautzen, 26.01.2006, Dresden, Germany
  • Lecture (others)
    Vortrag anlässlich des Besuch des Leistungskurses Physik des Vizthum-Gymnasiums Dresden, 19.06.2006, Dresden, Germany

Publ.-Id: 8585

Measurement of porosity in polyolefin particles using X-ray microtomography

Boden, S.; Bieberle, M.; Hampel, U.

The morphology of polymer macroparticles is directly linked to the various parameters of the polymerisation process. X-ray cone beam microtomography is a tool to provide key information on internal structure like morphology, porosity and interfacial area of such particles to the process engineers. By further application of image processing tools to the reconstructed tomograms, we were able to identify different characteristic morphologies within different polyolefin samples and to detect enclosed voids, which will ultimately not contribute to the active surface area.

Keywords: microstructure; polymer; polyolefin; macroparticle; microtomography; X-ray

  • Contribution to proceedings
    4th International Symposium on Process Tomography in Poland, 14.-15.09.2006, Warsaw, Poland
    Proceedings, 83-60660-01-8, 102-105

Publ.-Id: 8584

Isospin dependence of relative yields of K+ and K0 mesons at 1.528 AGeV

Lopez, X.; Kim, Y. J.; Herrmann, N.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Gobbi, A.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kirejczyk, M.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Merschmeyer, M.; Neubert, W.; 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.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Yushmanov, I.; Zhilin, A.; Ferini, G.; Gaitanos, T.

New results of K+ and K0 meson production in Ru+Ru and Zr+Zr collisions at beam energy of 1.528 AGeV, measured with the FOPI detector at GSI Darmstadt, are presented as a possible probe of isospin effects in high density nuclear matter. The measured double ratio (K+/K0)Ru/K+/K0)Zr is compared with a thermal model and a Relativistic Mean Field transport model using two different collision scenarios and under different assumptions on the stiffness of the symmetry energy. We found a good agreement with the thermal model predictions and the assumption of a soft symmetry energy for infinite nuclear matter.

Publ.-Id: 8583

Si Nanocrystals for nanoelectronic applications

Zacharias, M.; Gösele, U.

First experimental results more than one decade ago demonstrated the visible room temperature luminescence of Si nanocrystals in implanted SiO2 or porous Si which triggered the strong interest in Si nanocrystal based systems and their properties. Basic fundamental questions concerning quantum confinement effects in indirect semiconductors as well as potential applications such as light emission from electrically excited Si nanocrystals, energy transfer to Er 3+ ions, and non volatile Si NC based memories also stimulated the broad scientific interest in this material system. For clarifying the origin of the observed luminescence signal as well as for applications, tight control over the size of the nanocrystals is essential. The talk will give an overview about ways for size controlled Si nanocrystals. Basic properties as well as various applications including memory applications will be discussed in details.

Keywords: Si nanocrystals; optical properties; electronic properties

  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2006, Symposium C, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8582

Ordered Arrays of ZnO Nanowires: Piezoelectric properties and stimulated emission from single wires

Fan, H. J.; Alexe, M.; Hauschild, R.; Kalt, H.; Zacharias, M.

The current interest in ZnO nanostructures is based on its possible applications in UV optoelectronics. In particular, ZnO nanowires (NWs) appear to be promising candidates for the realization of dense arrays of nanosized lasers.
ZnO NW arrays were grown by a modified vapor liquid solid process which results in the Au catalyst remaining at the base of the nanowires. The fabrication process is template assisted involving a gold nanodisk array. This allows a site-specific growth of the ZnO NWs in an ordered hexagonal arrangement. The typical separation of the wires is around 500 nm, the NWs have a narrow size distribution centered at 300 nm and a typical height of 1.5 mm. The effective piezoelectric coefficient of individual ZnO NWs will be shown for various sizes and length. High-excitation phenomena, in particular excitonic nonlinearities and lasing will be reported. Under low excitation the NWs show bulk-like PL spectra. However, there is still a one-dimensional confinement of exciton-polaritons resulting in the absence of the P-band emission resulting from polariton-polariton scattering in thin wires. Stimulated emission is observed in single NWs up to 150 K. Upon raising the excitation fluency a spectrally and temporally narrow emission peak shows up while the P-band emission is quenched. We will show that free carriers are involved in the laser emission. We observe, that the lasing is influenced by details of the wire geometry. Calculations show the increasing leakage of the guided modes into the vacuum when decreasing the wire diameter. There is also a significant leakage of the resonator modes into the substrate. This loss can be reduced significantly by introducing thin layers of gold at the resonator facets as done here.

Keywords: nanowire; stimulated emission; piezoelectric effect

  • Lecture (Conference)
    E-MRS, Symposium E, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8581

Computer Simulations of Epitaxial Recrystallization and Amorphous-to-Crystalline Transition in 4H-SiC

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

Molecular dynamics (MD) methods have been employed to study the epitaxail recrystallization and amorphous-to-crystalline (a-c) transition in 4H-SiC, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Three nano-sized amorphous layers with the normal of a-c interfaces along the [-12-10], [-1010] and [0001] directions, respectively, were created within a crystalline cell to investigate the anisotropies of recrystallization processes. The amorphous structures were analyzed using a topological method, which indicates the complete loss of long-rang order, and the existing short-range disorder is quantified by the fraction of homonuclear bonds. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interfaces normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. The temperatures required for complete recrystallization are in good agreement with those observed at experiments. On the other hand, the recrystallization processes for the a-c interfaces normal along [-1010] and [0001] directions are hindered by the nucleation of polycrystalline phases. These secondary ordered phases have been identified as 4H- and 3C-SiC with different crystallographic orientations to the original 4H-SiC. The bond mismatches at the interfaces between different microcrystals result in the formation of number stacking faults. The temperature is an important parameter to control the nucleation of secondary ordered phase, whereas the size of amorphous region has a significant effect on their growth. These results are in good agreement with the previous experimental observations. One of the most important results is that the epitaxial recrystallization of amorphous layer with a-c interface along the c axis is much slower than those long the basal plane, which provides atomic-level insights into the anisotropies in the different activation energies for recrystallization.
Based on a model developed in the previous annealing simulations of 3C-SiC, the activation energy spectra for recrystallization along the three directions have been determined. In general, the activation spectra show that there is a number of activation energy peaks associated with different recrystallization processes. These activation energy values for full recrystallization are in the range of from 1.2 to 1.7 eV for the amorphous layers with the a-c interfaces along [-12-10] and [-1010] directions, and 1.1 to 2.3 eV for the amorphous layer with the a-c interfaces along [0001] direction. However, the highest activation energy of 2.3 eV is consistent with the experimental value of 2.1±0.5 eV reported for 6H-SiC. The internal energy distribution provides a detailed analysis of energy paths to recrystallization, and the nucleation and growth of the secondary ordered phases.

Keywords: SiC; atomistic simulation; recrystallization

  • Poster
    8th Int. Conf. on Computer Simulation of Radiation Effects in Solids (COSIRES 2006), 18.-23.06.2006, Richland, WA, USA

Publ.-Id: 8580

An improved interatomic potential for Ge

Geßner, H.; Posselt, M.

Two classes of interatomic potentials for germanium are presently available: (i) a Stillinger-Weber-type potential with different parametrizations, and (ii) a Tersoff-type potential. The evaluation shows that one group of potentials overestimates the melting temperature considerably, whereas the other group does not give the correct values for the lattice parameter and the cohesive energy. In the present work an improved Stillinger-Weber-type potential is developed by adjusting the two three-body parameters in such a manner, that the potential yields the correct lattice constant and the correct cohesive energy, and the melting point and other properties are reproduced satisfactorily. The influence of the three-body parameters on the structural and thermal properties is investigated in detail. Besides the lattice constant, the cohesive energy, and the melting point, the elastic constants and the thermal expansion coefficient of the diamond structure are considered. Furthermore, the properties of the liquid and the amorphous state as well as different crystalline structures of Ge are studied. Particular attention is paid to point defects and self-diffusion in the diamond structure. The influence of the three-body parameters on the formation and migration energies of vacancies and self-interstitials is investigated.

Keywords: Ge; atomistic simulations; interatomic potential

  • Lecture (Conference)
    8th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2006), 18.-23.06.2006, Richland, WA, USA

Publ.-Id: 8579

Interstitial contribution to self-diffusion in Si: Dependence of the correlation factor on the migration mechanism

Posselt, M.

Self-diffusion in Si is determined by the concentration and the mobility of both vacancies and self-interstitials. The self-diffusion coefficient is usually given by Dsd = fV CV DV + fI CI DI, where CV and CI are the relative concentrations of vacancies and self-interstitials, respectively; DV and DI denote the diffusivities. The quantities fV and fI describe the correlation between the migration of Si atoms and the migration of vacancies and self-interstitials; fV and fI are therefore called correlation factors. The statistical theory of diffusion allows the determination of these factors if certain atomic mechanisms for vacancy and self-interstitial migration are assumed. On the other hand, the self-diffusion coefficient per point defect as well as the point defect diffusivity can be calculated by molecular dynamics (MD) simulations. The ratio of both quantities yields the correlation factors fV and fI. In this manner, they can be determined without any assumption about the atomic migration mechanisms. In the present work, point defect migration and the related atomic mobility are investigated by MD simulations using the interatomic potentials of Stillinger-Weber and Tersoff. It is shown that the value for fV obtained by MD simulations is identical with that determined by the statistical diffusion theory, since the simple atomic mechanism assumed in the theory is also found by the simulations. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. MD simulations with the Stillinger-Weber potential show, that the self-interstitial migration is dominated by the dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor fI are different.

Keywords: diffusion Si defects atomistic simulations

  • Lecture (Conference)
    8th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2006), 18.-23.06.2006, Richland, WA, USA

Publ.-Id: 8578

Effect of electron-Beam Treatment on Subsequent Titanium Alloy Nitriding

Markov, A. B.; Gunzel, R.; Reuther, H.; Shevchenko, N.; Rotshtein, V. P.; Akhmadeev, Y. K.; Schanin, P. M.

  • Electrotehnica, Elektronica 5-6(2006), 230-233
  • Lecture (Conference)
    8th International conference on Electron Beam Technologies, 05.-10.06.2006, Varna, Bulgaria

Publ.-Id: 8577

Atomic-level simulation of epitaxial recrystallization and phase transformation in SiC

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

A nano-sized amorphous layer embedded in an atomic simulation cell was used to study the amorphous-to-crystalline (a-c) transition and subsequent phase transformation by molecular-dynamics computer simulations in 3C–SiC. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layer, which is hindered by the nucleation of a polycrystalline 2H–SiC phase. The kink sites and triple junctions formed at the interfaces between 2H– and 3C–SiC provide low-energy paths for 2H–SiC atoms to transform to 3C–SiC atoms. The spectrum of activation energies associated with these processes ranges from below 0.8 eV to about 1.9 eV.

Keywords: SiC; atomistic simulation; recrystallization

Publ.-Id: 8576

Thermohydraulische Modellierung der Kondensation von Dampf in einer unterkühlten Flüssigkeitsströmung

Gregor, S.; Prasser, H.-M.; Beyer, M.

Nach einer kurzen technischen Beschreibung der Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW und der verwendeten Messtechnik werden die theoretischen Grundlagen zur Modellierung der Kondensation von Dampf in einer Wasserströmung erläutert. Dabei gehen die Autoren besonders auf die Auswahl geeigneter Modelle zur Beschreibung des Wärmeübergangs und der Zwischenphasengrenzfläche im Druckbereich zwischen 10 und 65 bar detailliert ein. Außerdem werden verschiedene Drift-Flux-Modelle auf ihre Tauglichkeit anhand von experimentellen Daten geprüft.
Da Veränderungen thermodynamischer und strömungstechnischer Parameter hauptsächlich in axialer Richtung stattfinden, wurden diese Modelle in einen eindimensionalen Code eingebettet, mit dem der Strömungsverlauf entlang einer vertikalen Rohrleitung mit einer Länge von 8 m und einem Nenndurchmesser von 200 mm berechnet werden kann. Anschließend werden Aufbau und Funktion dieses Programms vorgestellt.
Nachfolgend vergleichen die Autoren experimentelle und berechnete Strömungsverläufe bei der Kondensation von Dampf sowohl in einer unterkühlten Wasserströmung als auch nahe der Siedetemperatur. Dabei wird der Einfluss wichtiger Randbedingungen, wie z.B. Druck oder Primärblasengröße, auf die Kondensationsintensität analysiert.
Eine Einschätzung der Fehlerbanden für die experimentellen Daten, die verwendeten Gittersensoren und die numerische Simulation schließen den Bericht ab.

Keywords: multi-phase flow; condensation; wire-mesh sensor; interfacial area; heat transfer; TOPFLOW

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-440 2006
    ISSN: 1437-322X


Publ.-Id: 8575

Melt extraction of short metallic filaments: fibre formation process revisited

Cramer, A.; Gerbeth, G.

This article presents experimental results of the extraction of metallic fibres from the surface of a melt pool. A low-melting alloy was used in a model facility to produce filaments of equal length. Operational parameters such as e.g. wheel speed and feed rate were varied to yield thin fibres. The analysis of the fibre cross-section showed, if ever, only a small decrease with increasing wheel speed. Highspeed video recording of the meniscus region was employed to investigate this falling short of expectation with respect to the commonly accepted tendencies. The recordings revealed that short fibres may only be produced during duty cycles. As available literature does not provide explanation of the observations, also a simple model was developed.

  • Journal of Materials Processing Technology 204(2008), 103-110

Publ.-Id: 8573

MHD turbulence in electromagnetic processing of materials

Gerbeth, G.

The basics of AC field driven flows will be presented. Examples of turbulent AC driven flows will be discussed

  • Invited lecture (Conferences)
    Graduate School and Workshop on Instabilities and Turbulence in MHD Flows, 26.-30.06.2006, University of Warwick, Great Britain

Publ.-Id: 8572

Use of magnetic fields in aluminum investment casting

Gerbeth, G.; Eckert, S.; Galindo, V.; Willers, B.; Hewelt, U.; Katz, H.-W.; Ziemann, M.

The mould filling process of aluminum investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. We present results on the design and application of a DC magnetic field in order to control this pouring process. Based on numerical simulations and modeling cold metal pre-experiments, DC fields were designed and installed in various casting processes under industrial conditions. The statistics of the casting products show a significant improvement of the casting parts quality. In addition, modeling studies have been performed for an AC magnetic field which may serve for a melt braking at the beginning of the casting process, but a pumping of the melt in a later stage, too.

  • Invited lecture (Conferences)
    EPM 2006, 23.-27.10.2006, Sendai, Japan
  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-930980-55-0 C3057, 323-328

Publ.-Id: 8571

Periodic chains of gold nanoparticles and the role of oxygen during the growth of silicon nanowires

Kolb, F. M.; Berger, A.; Hofmeister, H.; Pippel, E.; Gösele, U.; Zacharias, M.

The introduction of oxygen during the SiO-VLS growth of silicon nanowires causes a shift in SiOx stoichiometry resulting in an increased formation of SiO2 at the nanowire surface. This leads to instabilities of the usual cylindrical nanowire core-shell structure, where the liquid Au/Si alloy droplet at the nanowire tip is incorporated inside a SiO2 nanowire in form of a periodic array of nanoparticles. The structure and the composition of the resulting nanostructure are investigated in detail using high-resolution and analytical transmission electron microscopy. The influence of the oxygen is investigated experimentally and supports our model of the formation mechanism.

Keywords: nanowires; vapor liquid solid growth; self organization

  • Applied Physics Letters (2007)

Publ.-Id: 8570

Laser Interference Lithography Tailored for Highly symmetric arranged ZnO nanowire arrays

Kim, D. S.; Ji, R.; Fan, H. J.; Bertram, F.; Scholz, R.; Dadgar, A.; Nielsch, K.; Krost, A.; Christen, J.; Gösele, U.; Zacharias, M.

Highly symmetric arranged ZnO nanowire arrays are produced by laser interference lithography and chemical vapor transport process. The resulting ZnO nanowires show a narrow diameter distribution as well as a uniform spacing. Liquid-phase assistant vapor-solid mechanism is proposed for one-to-one synthesized ZnO nanowires growth. Scanning cathodoluminescence microscopy is used to characterize the optical properties.

Keywords: Arrays; Chemical vapor transport; Lithography; Nanowires; Semiconductors

  • Small (2007)

Publ.-Id: 8569

Fluorescence Analysis of Actinides: Instrumentation, Applications, Quantification, Future Trends and Quality Assurance

Geipel, G.; Billard, I.

Since the discovery of uranium, the impact of actinides has dramatically increased in our every-day life, firstly through the naturally occurring elements Th, Pa and U, (that were first used mainly as color pigments or cancer-treatment) and secondly through the artificial ones, produced along all steps of the nuclear power process (mostly Pu, Np, Am and Cm). Considering the huge problem of providing safe and sustainable energy in order to supply the fast increasing world demand in the near future, nuclear power will be one of the major concerns of this century. It is therefore of tremendous importance to tackle associated problems, that are related either to the remediation of old mining and milling sites, to the control of fissile products throughout the nuclear power production cycle and finally to the long term disposal of generated wastes. In this field and according to the public concern, quantification and quality assurance are of outmost importance. However, owing to the radioactive properties of actinides, these objectives are liable to even more difficulties than for other, stable elements. Other problems that need to be overcome are mainly related to the complexity of the chemical behaviour of actinides, that display numerous oxidation states, a large tendency to hydrolysis, and, for the short-lived ones (mostly, elements above Cm), handling problems. Furthermore, the range of concentration of these elements which can be found in the environment (as a consequence of mining, milling, nuclear bomb testing and accidents, mainly) limit the use of speciation techniques, that need to be safe, fast, reliable and very sensitive. Fortunately enough, some major actinides display luminescence properties, which can be used for the determination of complex stabilities as well as for the direct detection of the formed species in different environments in a wide concentration range, from ultra traces to chemical usable concentrations up to reprocessing conditions.
In this chapter, we will present an overview of the field of actinide luminescence analysis (Time-Resolved Laser Induced Fluorescence Spectroscopy, TRLIFS), focussing on applications related to the nuclear fuel cycle, from reprocessing to validation of nuclear waste repositories. However, it is not possible to include all publications in this contribution and a personally influenced selection has been made, that highlights applications in solution. Also it should be mentioned that the contribution of laser-induced spectroscopy to actinide speciation has been reviewed recently in several publications [1-6]. Owing to the limited place allocated, the reader is also referred to books on basic actinide chemistry [7] and reviews [8].

Keywords: actinides; luminescence; fluorescence; laser-induced; spectroscopy

  • Contribution to external collection
    Resch-Genger, Ute: Standardization and Quality Assurance in Fluorescence Measurements State of the Art and Future Challenges Series: Springer Series on Fluorescence, Vol. 5, Heidelberg: Springer Verlag, 2008, 978-3-540-75206-6, 465-492

Publ.-Id: 8568

Bromo(tricarbonyl) (15-{[2-(methylthio-S)ethylthio-S} pentadecanoic acid)rhenium(l)

Kraus, W.; Walther, M.; Jung, C. M.; Emmerling, F.; Pietzsch, H.-J.

The title compound, C21H36BrO5ReS2, was synthesized and characterized as non-radioactive surrogate of a novel Tc-containing fatty acid derivative prepared according to the tricarbonyl/dithioether design with the objective to develop new Tc-based radio-pharmaceuticals für the non-invasive diagnosis of myocardial metabolism. The Re chelate contains the metal core in the oxidation state +1 and is attached to the terminal position of a fatty acid. The complex formation was accomplished by ligand exchange reaction using [NBu4]2[Re(CO)3Br3] as starting material

Publ.-Id: 8567

Characterization of deformed and undeformed Al-alloys

Frielinghaus, H.; Ulbricht, A.; Bergner, F.

The experiment is aimed to characterize the nature of the material damage in a mechanically loaded specimen of a ductile aluminium alloy in order to get the input needed for damage mechanics based evaluation of structural components. In the first step the as-received and the homo¬geneously deformed conditions of the aluminium alloy shall be investigated by SANS. The objective is to identify and separate the main features responsible for the measured scattering effects and especially to find out the nature of the additional defects introduced by the mechanical loading procedure.

Keywords: SANS; Al-alloy

  • Contribution to external collection
    T. Brückel, D. Richter, R. Zorn: Neutron Scattering at FRJ-2, Experimental Reports 2005/6, Jülich: Forschungszentrum Jülich GmbH, 2006, 457-458

Publ.-Id: 8566

Magnetic and structural properties of Fe implanted GaN

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

In order to investigate the possibility to create and stabilize a DMS behavior in the (Ga,Fe)N-system, p-doped GaN was implanted with 200 keV 57Fe+ ions at 350°C, RT and -30°C with fluences Φ = 1*10^16 cm^-2 - 1.6*10^17 cm^-2. Magnetic electronic and structural properties of as implanted as well as subcequently annealed samples were investigated by AES, CEMS, TEM, SQUID and XRD techniques.

Keywords: DMS; Mößbauer; GaN; Fe; Cluster

  • Poster
    Sixth Workshop on Mössbauer Spectroscopy, 07.-11.06.2006, Seeheim, Deutschland

Publ.-Id: 8565

Structural investigation on uranium mine water colloids and their interaction with UO22+

Ulrich, K.-U.; Rossberg, A.; Scheinost, A.; Reuther, H.; Zaenker, H.

Flooding abandoned uranium mines normally involves mixing of shallow groundwater with acidic, iron-rich pore water. A simulation experiment in mesocosm scale showed that nanoparticles of 2-line ferrihydrite formed and took up about 97% of total uranium between pH 5-7. The molecular topology of ferrihydrite and the U(VI) surface complex structure were investigated by EXAFS and ATR-FTIR spectroscopy. The contribution of carbonate to surface sorption was studied by preparing reference samples at varied CO2 partial pressure and pH conditions, and by applying iterative target transformation factor analysis on EXAFS spectra. Surface sorbed UO22+ delayed the thermally induced aqueous phase transformation of ferrihydrite to hematite, shown by Mössbauer spec-troscopy. Desorption of U(VI) from the solid phase was less effective for original colloid and sediment samples from a uranium mine and for aged reference samples than for fresh U(VI)-ferrihydrite precipitates, suggesting that part of the uranium was fixed within the mineral lattice.

  • Lecture (Conference)
    232nd ASC National Meeting, 10.-14.09.2006, San Francisco, United States

Publ.-Id: 8564

Cooling dynamics in multi-fragmentation processes

Liu, T. X.; Lynch, W. G.; van Goethem, M. J.; Liu, X. D.; Shomin, R.; Tan, W. P.; Tsang, M. B.; Verde, G.; Wagner, A.; Xi, H. F.; Xu, H. S.; Friedman, W. A.; Souza, S. R.; Donangelo, R.; Beaulieu, L.; Davin, B.; Larochelle, Y.; Lefort, T.; de Souza, R. T.; Yanez, R.; Viola, V. E.; Charity, R. J.; Sobotka, L. G.

Fragment energy spectra of neutron-deficient isotopes are significantly more energetic than those of neutron-rich isotopes of the same element. This trend is well beyond what can be expected for the bulk multi-fragmentation of an equilibrated system. It can be explained, however, if some of these fragments are emitted earlier through the surface of the system while it is expanding and cooling.

Keywords: Thermal and statistical models; Multifragment emission and correlations

Publ.-Id: 8563

Indirect Radioiodination Increases In Vivo Stability and Tumor Uptake of I-125-L19-SIP

Rother, A.; Sieger, S.; Berndorff, D.; Cyr, J.; Dinkelborg, L.

The extradomain B of fibronectin (ED-B-FN) is an angiogenesis-associated marker of the tumoral extracellular matrix, which can be targeted by the human recombinant, high-affinity antibody fragment L19-SIP. By I-131-labeling L19-SIP becomes a radiotherapeutic agent, which is effective in several tumor models. In this study indirect and direct radioiodination methods were compared with regard to tumor uptake and in vivo stability of the obtained L19-SIP derivatives.

L-19-SIP was directly radioiodinate using the Iodogen methods, as well as indirectly by conjugation of I-125-Boltron Hunter reagent (I-125-BH) or I-125-succinimidylbenzoate (I-125-SIB). Pharmacokinetics and tumor accumulation of the iodinated L19-SIP derivatives were investigated in tumor bearing mice up to 72 h (F9, murine teratocarcinoma and U251, human glioblastoma) with subsequent dosimetry for the therapeutic isotope I-131.

In biodistribution studies the directly iodinated L-19-SIP showed increasing thyroid uptake over time due to dehalogenation of I-125 in vivo, whereas the indirectly iodinated L19-SIP showed improved stability of the iodine label. I-125-BH-L19-SIP and I-125-SIB-L19-SIP exhibited longer retenation in the tumor compared to I-125-L19-SIP. Tumor-to-blood ratios were significantly higher for the indirectly labelled compounds at later time points. It was calculated that activities of 48 MBq I-131-L19-SIP (Iodogen), 47 MBq I-131-BH-L19-SIP and 64 MBq I-131-SIB-L19-SIP could be injected per mouse before reaching the maximum tolerated dose of 2.5 Gy in the bone marrow, and would lead to doses of 42 Gy, 40 Gy and 144 Gy in 100 mg F9-tumors, respectively. The calculated tumor doses were comparable in both tumor models.

I-125-SIB-L19-SIP shows considerably higher in vivo stability and longer tumor retention compared to directly labelled L19-SIP leading to a substantially higher tumor dose.

  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A95

Publ.-Id: 8562

Eine Untersuchung zur Beschreibung kleiner Luftblasen durch Ellipsoide / An investigation concerning the description of small bubbles by ellipsoids

Hoppe, D.; Zaruba, A.

In ruhendem Wasser emporsteigende Luftblasen werden oft durch zweiachsige Ellipsoide beschrieben, ohne dass dies näher begründet wird. Eine Rechtfertigung dafür soll dadurch gefunden werden, dass eine reale Blase erst als dreiachsiges Ellipsoid modelliert und dann geprüft wird, ob sie zu einem zweiachsigen Ellipsoid vereinfacht werden kann. Für diesen Zweck erfolgen zunächst drei orthogonale optische Projektionen der Blase. Diese ebenen Abbildungen werden durch drei Ellipsen beschrieben, aus denen anschließend das gesuchte dreiachsige Ellipsoid berechnet wird.

Bubbles ascending in resting water are often described without further explanation using biaxial ellipsoids. Justification of this practice can be found via primarily modelling a real bubble as triaxial ellipsoid and subsequently checking if it can be reduced to a biaxial ellipsoid. For this purpose three orthogonal optical projections are produced at first. These plane maps are expressed by three ellipses from which in a second step the required triaxial ellipsoid is calculated.

Keywords: Bubble; Three-Axis Ellipsoid; Spheroid

  • Technisches Messen 1(2007), 29-35

Publ.-Id: 8561

Experimental Evidence for Magnetorotational Instability in a Taylor-Couette Flow under the Influence of a Helical Magnetic Field

Stefani, F.; Gundrum, T.; Gerbeth, G.; Rüdiger, G.; Schultz, M.; Szklarski, J.; Hollerbach, R.

A recent Letter [R. Hollerbach and G. Rüdiger, Phys. Rev. Lett. 95, 124501 (2005)] has shown that the threshold for the onset of the magnetorotational instability in a Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, we present results of a Taylor-Couette experiment with the liquid metal alloy GaInSn, showing evidence for the existence of the magnetorotational instability at Reynolds numbers of order 1000 and Hartmann numbers of order 10.

Publ.-Id: 8560

Contribution of Mössbauer Spectroscopy to the Exploration of Diluted Magnetic Semiconductors

Reuther, H.

Worldwide, semiconductor spin transfer electronics (spintronics) is of strongly increasing interest. One intention is the use of the spin for data storage to increase the possible storage density, another one is to overcome the fundamental limits of the computing speed. To realize such devices polarized carriers can be injected from a ferromagnetic metal into a diluted magnetic semiconductor (DMS). DMS are “conventional” semiconductors doped with transition metal or rare-earth ions which are diluted within the host matrix and ferromagnetically aligned via an indirect magnetic coupling. For applications, it is important that such DMS could be used at practical temperatures, i.e. above room temperature, and that they can base upon an already existing materials technology.

From theory, wide band gap semiconductors like GaN, ZnO, InN, AlP or SiC are the most promising candidates. Doping could be performed by Mn, V, Fe, Co or Ni with concentrations in the range of some %. The magnetism may originate either from a more or less random alloy in which the doping ion substitutes a host atom as interstitial or from small clusters. In the case of 57Fe as doping ion, Mössbauer spectroscopy can be used to investigate how it is built in the host matrix. The 57Fe ion acts both as doping and probe.

In the present study ion implantation is used as doping technique. 57Fe ions were implanted into GaN, ZnO and SiC. The produced layers were investigated by Mössbauer spectroscopy however this method is insufficient for a full characterization. Therefore, samples were studied by transmission electron microscopy, Auger electron spectroscopy, Zero-field-cooled/field-cooled SQUID measurements and by X-ray diffraction too. Depending on the implantation temperature and the annealing conditions diluted magnetic semiconductors could be obtained.

  • Invited lecture (Conferences)
    Sixth workshop on Mössbauer spectroscopy Seeheim, 07.-11.06.2006, Seeheim, Deutschland

Publ.-Id: 8559

RBE of 25 kV X-rays for the Survival and Induction of Micronuclei in the Human Mammary Epithelial Cell Line MCF-12A

Lehnert, A.; Lessmann, E.; Pawelke, J.; Dörr, W.

The broad application of low energy X-rays below about 50 keV in radiation therapy and diagnostics and especially in mammography substantiates the precise determination of their relative biological effectiveness (RBE). A quality factor of 1 is stated for photons of all energies in the ICRP Recommendations. However, the RBE of low-energy X-rays compared to high-energy photons was found to be dependent on photon energy, cell line and endpoints studied, hence varying from less than 1 up to about 4. In the present study, the human mammary epithelial cell line MCF-12A has been chosen due to the implementation of the results in the estimation of risk from mammography procedures. The RBE of 25 kV X-rays (W anode, 0.3 mm Al filter) relative to 200 kV X-rays (W anode, 0.5 mm Cu filter) was determined for clonogenic survival and micronuclei induction. The RBE for clonogenic survival was found to be significantly higher than 1 for surviving fractions in the range between 0.005 and 0.2. The RBE decreased with increasing survival, with an RBE0.1 at 10 % survival of 1.13 ± 0.03. The effectiveness of soft X-rays for micronuclei induction was found to be 1.40 ± 0.07 for the fraction of binuclear cells (BNC) with micronuclei (MN) and 1.44 ± 0.17 for the number of MN per BNC. In contrast, the RBE determined from the number of MN per MN-bearing BNC was found to be 1.08 ± 0.32. This indicates that the effectiveness of 25 kV X-rays results from an increase in the number of damaged cells, which, however, do not have higher number of micronuclei per cell.

Keywords: Soft X-rays; clonogenic survival; micronuclei; human mammary epithelial cells; MCF-12A; RBE

Publ.-Id: 8558

Electronic structure and x-ray spectra of defect oxides LixCoO2

Galakhov, V. R.; Ovechkina, N. A.; Shkvarin, A. S.; Shamin, S. N.; Kurmaev, E. Z.; Kuepper, K.; Takács, A. F.; Raekers, M.; Robin, S.; Neumann, M.; Gavrila, G.-N.; Semenova, A. S.; Kellerman, D. G.; Käämbre, T.; Nordgren, J.

X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band
and core levels have been measured for LixCoO2 (0.6 < x < 1.0). Resonant O K x-ray emission
spectra of LiCoO2 showed localized excitonic states due to a dd transition between unoccupied and
occupied Co 3d states. On the base of measurements of Co 3s x-ray photoelectron and Co 2p and
O 1s x-ray absorption spectra it was established that in defective cobaltites the electronic holes are
localized mainly in O 2p states. Metallic character of conductivity of defective cobaltites LixCoO2 is
confirmed by a combination of x-ray photoelectron and O 1s x-ray absorption spectra. An evidence
of phase separation in LixCoO2 has been found.

Keywords: PACS numbers: 79.60.-i; 78.70.Dm; 78.70.En; 71.28.+d

Publ.-Id: 8557

Ion beam modifications of magnetic films

Fassbender, J.

In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.

1. J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
2. J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
3. J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B 73, 184410 (2006).
4. J. Fassbender, J. McCord, Appl. Phys. Lett. in press (2006).

Keywords: magnetism; magnetic film; ion irradiation; ion implantation

  • Invited lecture (Conferences)
    23rd Summer School and International Symposium on the Physics of Ionized Gases, 28.08.-01.09.2006, Kopaonik, Serbia
  • Invited lecture (Conferences)
    Workshop on Ion Beam Applications for Materials Modification and Analysis, 02.09.2006, Belgrade, Serbia

Publ.-Id: 8556

Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland

Weiß, F.-P.; (Editor)

Die Veranstaltung widmete sich mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial schwerpunktmäßig zwei Themen der Reaktorsicherheit, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext wollten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen beleuchten und die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb darstellen. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort.
Der Fachtag sollte den Teilnehmern aber insbesondere vermitteln, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat.
In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb widmete sich eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden.
Dabei wurden u. a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.

Keywords: reactor safety; emergency core cooling system reliability; cooling sump performance; boron mixing; boron dilution transients; computational fluid dynamics (CFD); CFD methods

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-455 2006
    ISSN: 1437-322X


Publ.-Id: 8555

Coupled fluid-flow and magnetic-field simulation of the Riga dynamo experiment

Kenjeres, S.; Hanjalic, K.; Renaudier, S.; Stefani, F.; Gerbeth, G.; Gailitis, A.

Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electro-conducting fluids, also known as dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment, consisting of a helical motion of sodium in a long pipe followed by a straight back-flow in a surrounding annular passage, which provided adequate conditions for magnetic field self-excitation. We report here on the first attempt to simulate computationally the Riga experiment. The velocity and turbulence fields are modelled by a finite-volume Navier-Stokes solver using a Reynolds-Averaged-Navier-Stokes (RANS) turbulence model. The magnetic field is computed by an Adams-Bashforth finite-difference solver. The coupling of the two computational codes, although performed sequentially, provides an improved understanding of the interaction between the fluid velocity and magnetic fields in the saturation regime of the Riga dynamo experiment under realistic working conditions.

Publ.-Id: 8554

Wo stehen wir bei der Integration der PET in die Bestrahlungsplanung der perkutanen Strahlentherapie aus physikalisch-technischer Sicht der Nuklearmedizin?

van den Hoff, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany

Publ.-Id: 8553

Untersuchungen mittels PET bei onkologischen Fragestellungen

van den Hoff, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Workshop: Einsatz der PET in der Bestahlungsplanung, 11.-12.03.2005, Homburg/Saar, Deutschland

Publ.-Id: 8552

Annual Report 2005 - Institute of Nuclear and Hadron Physics

Enghardt, W.; Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; Wünsch, R.; (Editors)

The Forschungszentrum Rossendorf (FZR) at Dresden is a multidisciplinary research center within the Wissenschafts-Gemeinschaft G. W. Leibniz (WGL), one of the German agencies for extra-university research. The center is active in investigations on the structure of matter as well as in the life sciences and in environmental research. The Institute of Nuclear and Hadron Physics (IKH) within the FZR avails for its research the coupling of radiation to matter in subatomic dimensions as well as to tissue, to cells, and to their components. Its research in the field of Subatomic Physics is part of the FZR-program Structure of Matter and its investigations concerning the interaction of Biostructures and Radiation contribute to the bf Life Science program of the FZR. In this field the IKH exploits possibilities for transfer and introduction of experimental and theoretical techniques from particle and nuclear physics to projects in radiobiology and biophysics. Much of this kind of interdisciplinary transfer is connected to the Radiation Source ELBE at the FZR. With its superconducting accelerator for relativistic electrons this large installation provides photons in the wide wavelength range from fm to mm - i.e. bremsstrahlung for the investigation of photonuclear processes, hard X-rays for radiobiological and other studies and infrared light for research on the structural dynamics of biomolecules. The investigation of radiation-induced processes not only dominates the projects in nuclear astrophysics as pursued at ELBE, it also is a central theme of the experimental and theoretical research performed by the IKH in close connection to the heavy ion synchrotron SIS and the upcoming FAIR facility at Darmstadt. ELBE also will deliver compact bunches of secondary neutrons and fission fragments; both offer new possibilities in laboratory studies related to the cosmic breeding of the chemical elements thus complementing the astrophysics-motivated studies with bremsstrahlung photons...

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-442 2006
    ISSN: 1437-322X


Publ.-Id: 8551

CFD simulations and X-ray measurements of the local gas hold-up in a stirred tank reactor agitated by a gas-inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.

The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
The cone-beam type X-Ray tomography is a potential method to measure the phase-distributions in stirred vessels. Three-dimensional information can be gathered within only one tomographic scan. The reconstruction of a rotationally symmetric distribution-field is even possible from a single radiographic image. Such an experimental approach was carefully examined and applied to obtain the quantitative measurements of gas-fraction profiles in a stirred tank reactor. Additionally, a moving slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated x-rays penetrate the fluid-filled tank. An additional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials x-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation. A systematic measurement error of less then 1.5% absolute gas fraction for local gas fractions up to 30% was achieved while maintaining a spatial resolution of better then 1 mm.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.

  • Lecture (Conference)
    ANSYS-FZR Multiphase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Germany
  • Contribution to proceedings
    ANSYS-FZR Multiphase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Deutschland
    Proceedings, CD-ROM

Publ.-Id: 8550

Experimental and numerical assessment of the phase distribution in a stirred tank reactor agitated by a gas-inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.

Over the last century two-phase flow mixing, engineered to take place in mechani-cally agitated tank reactors, has become one of the most common operations in the industry. Traditionally the gas-phase is supplied via a single pipe or a ring sparger mounted beneath the rotating impeller. The gas-inducing impellers provide an alter-native gas injection, in which case the gas is fed directly in the stirrer region.
A non-baffled laboratory-scale tank reactor mechanically agitated by a gas inducing turbine was experimentally and numerically studied. Above a certain impeller speed, at the investigated experimental conditions, the stirrer becomes able to induce gas and consequently disperse it into the bulk liquid phase. The two-phase system under examination comprises air as gas phase into isopropanol as liquid phase at room temperature. The gas-phase distribution was assessed at five different impeller speeds starting from 1000 rpm, at which gas inducement occurs.
The cone-beam type X-Ray tomography, which can provide three-dimensional infor-mation on the gas-phase distribution, was employed to experimentally study the two-phase system. The reconstruction of a rotationally symmetric distribution-field is pos-sible from a single radiographic image. Such an experimental approach was applied to obtain the quantitative measurements of gas-fraction profiles. Additionally, a mov-ing slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated X-rays penetrate the fluid-filled tank. An addi-tional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials X-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation.
The computational fluid dynamics analyses of the stirred tank reactor were performed with CFX 10.0 numerical software. The numerical predictions at 1000 rpm used pre-vious simulation results at lower impeller speed as an initial guess. Starting from 1000rpm, five simulations were performed at stirrer speed thresholds of 50 rpm to be compared with X-Ray cone beam tomography experimental observations. The tetra-hedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer de-scribed by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid with a mean diame-ter of 1 mm and the liquid phase as continuous fluid.
The results demonstrate the X-Ray cone beam tomography and the CFD capabilities to capture the two-phase flow in detail, which can provide valuable information for the industry. In particular the special gas phase distribution can have a crucial impact on the reactor performance. This can be in detail predicted by the computational fluid dynamic software, which can prove to be an essential tool for the reactor optimisation and scale-up.

  • Poster
    DECHEMA 2006 - GVC/DECHEMA-Jahrestagungen 2006, Rhein-Main-Hallen, Wiesbaden, 26.-28.09.2006, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 78(2006)9, 1274

Publ.-Id: 8549

Contactless electromagnetic induction flowmeter based on phase shift measurements

Priede, J.; Buchenau, D.; Gerbeth, G.

This study is concerned with a conceptual design of a new contactless AC induction flowmeter for liquid metal flows. The basic idea is to make use of the fact that the fluid flow disturbs not only the amplitude but also the phase distribution of an applied AC magnetic field. The goal is to consider the possibility of using the fluid flow induced phase shift of an AC magnetic field to measure the flow rate. In order to figure out the basic characteristics of such a flowmeter we consider several simple theoretical models where the liquid flow is approximated by a solid body motion. Based on these ideas a laboratory model of such a flowmeter has been built and tested at a liquid metal flow.

  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-930980-55-0 C3057, 735-740
  • Lecture (Conference)
    EPM 2006, 23.-27.10.2006, Sendai, Japan

Publ.-Id: 8548

Hyperon production in the channel pp→K+Λp near the reaction threshold

Abd El-Samad, S.; Bilger, R.; Böhm, A.; Brinkmann, K.-T.; Clement, H.; Dshemuchadse, S.; Eyrich, W.; Erhardt, A.; Fanara, C.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Geyer, R.; Hauffe, J.; Hassan, A.; Herrmann, P.; Hesselbarth, D.; Jakob, B.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Metzger, A.; Michel, P.; Möller, K.; Morsch, H. P.; Naumann, L.; Roderburg, E.; Schamlott, A.; Schönmeier, P.; Schulte-Wissermann, M.; Schroeder, W.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Wächter, J.; Wagner, G. J.; Wagner, M.; Wilms, A.; Wirth, S.; Zielinski, U.

Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of var epsilon=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the Nasterisk operator(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.

Keywords: Associated strangeness production; Total cross-section; Angular distribution; Dalitz plot

  • Physics Letters B 632(2006)1, 27-34

Publ.-Id: 8547

Complex formation of uranium(VI) with the amino acids L-glycine and L-cysteine: A fluorescence emission and UV-vis absorption study

Günther, A.; Geipel, G.; Bernhard, G.

The complexation of uranium(VI) with the amino acid L-glycine and L-cysteine has been investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV-vis spectroscopy at low pH range. The identified 1:1 and 1:2 uranyl-L-glycine complexes fluoresce and have similar absorbance properties. In contrast to the glycine system, uranyl forms with L-cysteine two different non-fluorescent 1:1 complexes showing individual absorbance properties under the given experimental conditions.The corresponding complex formation constants were calculated using the spectroscopic data.

Keywords: uranium; complexation; amino acid; TRLFS; UV-vis spectroscopy

  • Polyhedron 26(2007), 59-65

Publ.-Id: 8546

Effect of an external magnetic field on the flow in a liquid metal bubble plume

Zhang, C.; Eckert, S.; Gerbeth, G.

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In the range of small or moderate void fractions the UDV technique delivers both the bubble and the liquid velocity.
In our experiments we investigated the consequences of an application of both DC and AC magnetic fields on the velocity field of bubble plumes. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. The application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction. AC magnetic fields can be applied to generate flow structures being different from the recirculating flow known from classical bubble plumes. A tailoring of the flow using magnetic fields obviously allows a control of the heat and mass transfer in bubble plumes.

Keywords: bubble plume; DC magnetic field; AC travelling magnetic field; electromagnetic stirring; velocity measurements; ultrasound Doppler technique

  • Lecture (Conference)
    CHISA 2006, 27.-31.08.2006, Praha, Czech Republic
  • Contribution to proceedings
    17th International Congress of Chemical and Process Engineering, CHISA 2006, 27.-31.08.2006, Praha, Czech Republic

Publ.-Id: 8545

Upper limits on resonance contributions to proton-proton elastic scattering in the c.m. mass range 2.05-2.85 GeV/c^2

Rohdjeß, H.; Altmeier, M.; Bauer, F.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Busch, M.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Ernst, J.; Eversheim, P. D.; Eyser, K. O.; Felden, O.; Gebel, R.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Langkau, R.; Lindlein, J.; Maier, R.; Mosel, F.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schulz-Rojahn, F.; Schwandt, F.; Schwarz, V.; Scobel, W.; Trelle, H.-J.; Ulbrich, K.; Weise, E.; Wellinghausen, A.; Woller, K.; Ziegler, R.

Recently published excitation functions in proton-proton (pp) elastic scattering observables in the laboratory energy range 0.5-2.5GeV provide an excellent data base to establish firm upper limits on the elasticities ηel = Γel/Γtot of possible isovector resonant contributions to the nucleon-nucleon (NN) system. Such contributions have been predicted to arise from dibaryonic states, with c.m. masses between 2.1-2.9GeV/c2, but have not been confirmed experimentally. A method to determine quantitatively the maximum value of ηel compatible with experimental data is presented. We use energy-dependent phase shift fits to the pp data base to model the non-resonant interaction. Based upon the differential cross-section data measured by the EDDA Collaboration an unbiased statistical test is constructed to obtain upper limits on ηel, that exclude larger values with a 99% confidence level. Results in the c.m. mass range 2.05-2.85GeV/c2 and total widths of 10-100MeV/c2 in the partial waves 1S0, 1D2, 3P0, 3P1, and 3F3 are presented and discussed.

Keywords: PACS. 25.40.Cm Elastic proton scattering; 13.75.Cs Nucleon-nucleon interactions (including antinucleon and deuterons etc.); 14.20.Pt Dibaryons; 11.80.Et Partial-wave analysis

Publ.-Id: 8544

Determining beam parameters in a storage ring with a cylindrical hodoscope using elastic proton–proton scattering

Rohdjeß, H.; Albers, D.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Eversheim, P. D.; Gasthuber, M.; Greiff, J.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Igelbrink, M.; Langkau, R.; Maier, R.; Mosel, F.; Müller, M.; Münstermann, M.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Trelle, H. J.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R.

The EDDA-detector at the cooler-synchrotron COSY/Jülich has been operated with an internal CH2 fiber target to measure proton–proton elastic scattering differential cross-sections. For data analysis knowledge of beam parameters, like position, width and angle, are indispensable. We have developed a method to obtain these values with high precision from the azimuthal and polar angles of the ejectiles only, by exploiting the coplanarity of the two final-state protons with the beam and the kinematic correlation. The formalism is described and results for beam parameters obtained during beam acceleration are given.

Keywords: Vertex reconstruction; Fiber target; Elastic proton–proton scattering; Storage ring

Publ.-Id: 8543

Radiation damage of polypropylene fiber targets in storage rings

Rohdjeß, H.; Albers, D.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Eversheim, P. D.; Greiff, J.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Igelbrink, M.; Langkau, R.; Maier, R.; Mosel, F.; Müller, M.; Münstermann, M.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Trelle, H. J.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R.

Thin polypropylene fibers have been used for internal experiments in storage rings as an option for hydrogen targets. The change of the hydrogen content due to the radiation dose applied by the circulating proton beam has been investigated in the range 1 × 106–2 × 108 Gy at beam momenta of 1.5–3 GeV/c by comparing the elastic pp-scattering yield to that from inelastic p-carbon reactions. It is found that the loss of hydrogen as a function of applied dose receives contributions from a fast and a slow component.

Keywords: Radiation damage; Polypropylene; Fiber target; Elastic proton–proton scattering; Storage ring

Publ.-Id: 8542

Determination of the flow structure in bubble-driven liquid metal flows using ultrasound Doppler method

Zhang, C.; Eckert, S.; Gerbeth, G.

The ultrasound Doppler velocimetry (UDV) was validated for its capability to measure both gas and liquid velocities in transparent as well as opaque two-phase flows. A special threshold method has been tested successfully for processing of UDV data acquired from bubble-driven flows. Our experimental work presented here is focused on the influence of a transverse static magnetic field on a bubble plume in a cylindrical vessel. The liquid flow field has been measured by means of the ultrasound Doppler velocimetry. Despite the well-known damping effect of a DC magnetic field, it was observed, that the application of a moderate magnetic field may also cause an intensification of the liquid recirculation. The global flow field was found to be dominated by quasi-two-dimensional large scale vortex structures, whose axes are parallel aligned with the magnetic field direction. Therefore, the time-averaged flow field shows a distinct anisotropy. Local recirculating zones are found in the meridional plane perpendicular to the magnetic field lines, while velocity distributions become more uniform in the other plane parallel to the magnetic field.

Keywords: bubble plume; liquid metal; magnetic field; ultrasound Doppler velocimetry

  • Lecture (Conference)
    5th International Symposium on Ultrasound Doppler Methods (ISUD), 12.-14.09.2006, Zürich, Swizerland
  • Contribution to proceedings
    ISUD5, 5th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics, 12.-14.09.2006, Zürich, Swizerland
    Proceedings: ETH Zürich, 51-54

Publ.-Id: 8541

Electron beam monitoring for channeling radiation measurements

Neubert, W.; Azadegan, B.; Enghardt, W.; Heidel, K.; Pawelke, J.; Wagner, W.

A secondary emission monitor and an auxiliary Faraday cup necessary for calibration purposes have been constructed and installed at the radiation physics beam line of the electron accelerator ELBE. These devices are to be applied for the precise beam-current monitoring in measurements of channeling radiation. Miscellaneous simulations of underlying interactions of the beam electrons with the target material as well as with the materials of the monitor equipment have been performed to optimize the design and to evaluate possible correction factors inherent to transmission monitoring.

Keywords: electron beam monitor; secondary electrons; channeling radiation

  • Nuclear Instruments and Methods in Physics Research B 254(2007), 319-328

Publ.-Id: 8540

Magnetic turbulence in the Riga dynamo experiment

Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.

The Riga dynamo experiment demonstrates that a strong enough and appropriately directed flow of a fluid electroconductor generates a magnetic field very similar as the Earth and other celestial bodies do. Two 100 kW motors are driving a propeller which forces molten sodium to circulate inside an annular vessel, a part of which is located in the basement of the sodium lab. The sodium flow is directed by two thin coaxial electroconducting cylindrical partition walls. In the central channel sodium is swirling down from the propeller. In the coaxial counter-flow channel the flow is raising straight up to the propeller. In an outer part of the vessel the sodium is at rest, it serves only for better electric boundary conditions. Depending on sodium temperature at a propeller speed of 1800-2000 rpm (flow-rate about 0.6 qm/s) the zero state for the magnetic field is becoming unstable and a field appears seemingly from nothing. The magnetic field values are recovered from coil voltage records by means of Fast Fourier processing. For finer spectral resolution two small coils were inserted alternately in a narrow channel tip penetrating deep inside the central flow. Examples for recorded signals and FFT processed fields are presented.

  • Invited lecture (Conferences)
    Workshop: Modelling MHD Turbulence: Application to Planetary and Stellar Dynamos, 27.-30.06.2006, Boulder, United States

Publ.-Id: 8539

Some aspects of a Krein space related perturbation theory for MHD α²-dynamos and the resonant unfolding of diabolical points

Kirillov, O.; Günther, U.

The spectrum of the spherically symmetric α²-dynamo is studied in the case of idealized boundary conditions. Starting from the exact analytical solutions of models with constant α-profiles a perturbation theory and a Galerkin technique are developed in a Krein-space approach. With the help of these tools a very pronounced α-resonance pattern is found in the deformations of the spectral mesh as well as in the unfolding of the diabolical points located at the nodes of this mesh. Non-oscillatory as well as oscillatory dynamo regimes are obtained. A Fourier component based estimation technique is developed for obtaining the critical α-profiles at which the eigenvalues enter the right spectral half-plane with non-vanishing imaginary components (at which overcritical oscillatory dynamo regimes form). Finally, Fréchet derivative (gradient) based methods are developed, suitable for further numerical investigations of Krein-space related setups like MHD α²-dynamos or models of PT-symmetric quantum mechanics.

Keywords: Krein space; MHD dynamo; diabolical point; exceptional point; spectral deformation; perturbation theory; resonance; Galerkin method

  • Lecture (Conference)
    International Summer School and Workshop "Operator algebras, operator theory and applications" (WOAT 2006), Satellite conference to the International Congress of Mathematicians, Madrid 2006, 01.-05.09.2006, Madrid, Portugal

Publ.-Id: 8538

New results on the spectrum of the MHD α²-dynamo and on Jordan algebra related canonical structures of PT-symmetric matrices

Günther, U.; Kirillov, O.

The talk consists of two parts.

The results reported in the first part concern some unexpected properties of the spectrum of the α²-dynamo operator. In a work from February 2006 we investigated the unfolding of diabolical points in the spectrum of a dynamo operator with idealized boundary conditions (BCs). Similar to the Hamiltonians of PT-symmetric Quantum Mechanics this operator is selfadjoint in a Krein space. For constant α-profiles α₀ its spectrum λ[α₀] forms a mesh-like structure in the (α₀,Re λ)-plane with diabolical points (degeneration points of geometric and algebraic multiplicity two) at the nodes of the mesh. Under inhomogeneous perturbations of the α-profile the spectral mesh undergoes deformations which are accompanied by a resonant unfolding of the diabolical points. It was shown that each Fourier component of an α-profile α(x) induces a selective unfolding of diabolical points located on a specific parabola in the (α₀,Re λ)-plane. In recent research we extended this analysis to dynamo operators with realistic boundary conditions. Unexpectedly, it was found that the parabolas related to the resonant unfolding of diabolical points in models with idealized BCs coincide exactly with the spectral branches of dynamo operators with realistic BCs. We discuss some first aspects of the underlying mechanism responsible for this coincidence and indicate some of its possible implications.

In the second part of the talk, canonical representations of Jordan normal forms of PT-symmetric matrices are presented. These canonical representations are derived with the help of Jordan-algebra based conjugations which map Jordan blocks and Jordan chains into corresponding explicitly PT-symmetric matrices and their eigenvectors and associated vectors.

Keywords: Krein space; MHD dynamo; PT-symmetric Quantum Mechanics; diabolical point; resonance; Jordan algebra; Jordan normal form

  • Lecture (Conference)
    5th International Workshop on pseudo-Hermitian Hamiltonians in Quantum Physics, 03.-08.07.2006, Bologna, Italy

Publ.-Id: 8537

Transitional and weakly turbulent flow in a rotating magnetic field

Stiller, J.; Frana, K.; Cramer, A.

The early stage of the turbulent flow driven by a rotating magnetic field is studied via direct numerical simulations and electric potential measurements for the case of a cyindrical geometry. The numerical results show that the undisturbed flow remains stable up to the linear stability limit, wheras small perturbations may initiate nonlinear transition at subcritical Taylor numbers. The observed instabilities occur randomly as isolated pairs of Taylor-Görtler vortices, which grow from spots to long tubes until they are dissipated in the lid boundary layers. At 7.5 times the critical Taylor number, the flow is governed by large-scale 3D fluctuations and may be characterized as weakly turbulent. Taylor-Görtler vortices provide the major turbulence mechanism, apart from oscillations of the rotation axis. As the vortices tend to align with the azimuthal direction, they result in a locally two-dimensional turbulence pattern.

  • Physics of Fluids 18(2006), 074105

Publ.-Id: 8536

Container-less melt extraction of metallic fibres

Cramer, A.; Priede, J.; Galindo, V.; Andersen, O.; Kostmann, C.

A method for the production of metallic fibres is proposed that uses melt extraction from a pending molten edge at the lower end of a metal sheet. Melting the sheet at its edge rather than between the two opposing branches of the inductor is achieved by a tailoring of the induction heating magnetic field. The basic feature of the configuration is the same direction of the electric current in both branches of the inductor. A proper choice of geometry, electrical conductivities of both extraction and substrate material, and the frequency of the alternating magnetic field have proven to be essential for the extraction process. Melting a platinum sheet at the edge and extraction of fibres only 20 micron in effective cross-section from a tin sheet were successfully demonstrated in model experiments.

  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Processing of Materials (EPM2006), Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-93 980-55-0 C3057, 335-340
  • Lecture (Conference)
    EPM 2006, 23.-27.10.2006, Sendai, Japan

Publ.-Id: 8535

Positron lifetimes in ZnO single crystals

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

Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.

Keywords: ZnO; positron lifetime; vacancy defects; hydrogen-defect interaction

  • Invited lecture (Conferences)
    VIth International Conference "Ion implantation and other applications of ions and electrons", 26.-29.06.2006, Kazimierz Dolny, Polen

Publ.-Id: 8534

Positron lifetimes in ZnO single crystals

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

Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.

Keywords: ZnO; positron lifetime; vacancy defects; hydrogen-defect interaction

  • Vacuum 81(2007), 1314-1318

Publ.-Id: 8531

Indentation response of single-crystal GaAs in the nano-, micro-, and macroregime

Bergner, F.; Schaper, M.; Hammer, R.; Jurisch, M.; Kleinwechter, A.; Chudoba, T.

Fabrication, handling and processing of wafers of intrinsically brittle and anisotropic single-crystalline GaAs require a high level of control of the material’s response to different loading conditions. The present work is focused on the response to hardness indentation. A short overview on the behaviour of (100) GaAs wafers in several doping conditions over a wide range of indentation loads from nano-indentation up to macro-indentation including sharp and blunt indenters is given. Special attention is paid to the pop-in effect in depth-sensing nano-indentation, to the anisotropy of indentation-induced radial crack formation and to the material’s crack resistance obtained from the indentation fracture mechanics approach. We have observed that, under certain conditions, the frequency of formation of radial cracks is essentially different for the two in-plane <110> directions. This observation is attributed to the occurrence of two different kinds of dislocations and to the lack of inversion symmetry. The effect turns out to be closely related to a left-right asymmetry in the material removal caused by wire sawing. This insight has paved the way to the optimization of the process of wire sawing of GaAs single crystals.

Publ.-Id: 8530

Atomistic simulation of interstitial cluster migration in silicon

Posselt, M.

The state-of-the-art interpretation of physical processes during post-implantation annealing, such as defect evolution and transient-enhanced boron diffusion assumes that ion implantation produces a supersaturation of single vacancies and self-interstitials. They are supposed to be mobile and may recombine or may form immobile clusters. On the other hand, atomistic simulations demonstrated that implantation may generate not only single vacancies and self-interstitials but also more complex defects. Furthermore, recent theoretical studies showed that small interstitial clusters may be mobile as well. The present work gives an overview on the latter investigations. Due to the complex structure of the interstitial clusters, methods based on the estimation of migration barriers by considering the potential energy surface at 0 K are hardly applicable. Molecular dynamics (MD) simulations must be used to get a thorough understanding of the migration mechanisms. Ab-initio MD simulations are presently not practicable since they require a tremendous computational effort. Therefore atomic-level MD simulations are applied. The diffusivity of the small interstitial clusters, the self-diffusion coefficient per defect, and the corresponding effective migration barriers are determined. The implications of the present results for the explanation of experiments on post-implantation annealing and on room-temperature migration of implantation-induced self-interstitial defects are discussed.

Keywords: defects; diffusion; silicon; atomistic simulation; interstitial clusters

  • Invited lecture (Conferences)
    E-MRS IUMRS ICEM Spring Meeting 2006, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8529

Equilibrium concentration and diffusivity of vacancies in Ge: An atomistic study with an improved interatomic potential

Gessner, H.; Posselt, M.

An improved Stillinger-Weber-type potential for Ge is developed by adjusting the three-body parameters in such a manner that lattice parameter and cohesive energy are preserved, and the elastic constants and the melting point are reproduced satisfactorily. The dependence of the equilibrium concentration and the diffusivity of vacancies on the temperature as well as the contribution of vacancies to self-diffusion are determined by atomistic simulations and by thermodynamic considerations. The calculations are performed in the temperature range between 600 and 1100 K. The enthalpies and entropies for formation and migration are estimated. Similar investigations are performed for self-interstitials in order to check whether their contribution to self-diffusion in Ge can be neglected, as shown experimentally. Finally, the self-diffusion coefficient and the equilibrium concentration of vacancies are compared with experimental data from the literature.

Keywords: defects; diffusion; germanium; computer simulation

  • Poster
    E-MRS IUMRS ICEM 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8528

Dose rate and temperature dependence of ion-beam-induced defect evolution in germanium

Posselt, M.; Bischoff, L.; Grambole, D.; Herrmann, F.; Grötzschel, R.

To investigate the effect of dose rate and irradiation temperature on defect evolution in germanium during the ion implantation process a focused ion beam system is used. Channeling implantation of Ga is performed at two very different dose rates (3.5x1011 and 1.6x1019 cm-2s-1), at two temperatures (RT and 250 0C), and at five different doses, ranging from 5x1012 to 5x1014 cm-2. The depth distributions of Ga and of the implantation damage are determined by SIMS and micro-RBS/C, respectively. The shape of the measured range and damage profiles is strongly influenced by the dose rate and the implantation temperature. These results are explained by the competition between damage buildup and dynamic annealing during the ion bombardment. For the two implantation temperatures considered, the time scale for intracascade defect relaxation can be estimated. The measured Ga depth profiles can be reproduced by atomistic computer simulations using a phenomenological model to describe the probability that an implanted ion collides with a target atom of a damaged region in dependence on the total nuclear energy deposition per target atom.

Keywords: ion implantation; damage; defects; germanium

  • Lecture (Conference)
    E-MRS IUMRS ICEM Spring Meeting 2006, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8527

Phase distribution in a stirred tank reactor mechanically agitated by gas-inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.

The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
Cone-beam type X-ray computed tomography is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. However, there are considerable difficulties for accurate quantitative measurements, for instance of average gas fraction in a fluid, due to beam hardening and radiation scattering effects. We have developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate void fraction measurement.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.

  • Lecture (others)
    VDI-GVC-Fachausschusssitzung "Mehrphasenströmungen" und "Computational Fluid Dynamics", 01.-03.03.2006, Überlingen, Germany

Publ.-Id: 8526

Low-lying E1, M1, and E2 strength distributions in 124,126,128,129,130,131,132,134,136Xe:Systematic photon scattering experiments in the mass region of a nuclear shape or phase transition

von Garrel, H.; von Brentano, P.; Fransen, C.; Friessner, G.; Hollmann, N.; Jolie, J.; Käppeler, F.; Käubler, L.; Kneissl, U.; Kohstall, C.; Kostov, L.; Linnemann, A.; Mücher, D.; Pietralla, N.; Pitz, H. H.; Rusev, G.; Scheck, M.; Schilling, K. D.; Scholl, C.; Schwengner, R.; Stedile, F.; Walter, S.; Werner, V.; Wisshak, K.

Systematic nuclear resonance fluorescence (NRF) experiments on all nine stable (seven even-even and two odd-mass) Xe isotopes have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator. For the first time thin-walled, high-pressure gas targets (about 70 bar) with highly enriched target material were used in NRF experiments. Precise excitation energies, transition strengths, spins, and decay branching ratios were obtained for numerous states, most of them previously unknown.
The systematics of the observed E 1 two-phonon excitations (2+,3-) and M1 excitations to 1+ mixed-symmetry states in the even-even isotopes are discussed with respect to the new critical point symmetry E(5). The fragmentation of these fundamental dipole excitation modes in the odd-mass isotopes 129,131 Xe is shown and discussed. In the even-even nuclei several low-lying E2 excitations were observed.

Keywords: Nuclear structure; nuclear spectroscopy; photon scattering

Publ.-Id: 8525

18F-labelling, cellular uptake and biodistribution of novel acyclic purine nucleosides for monitoring HSV1-tk based gene therapy

Oswald, J.; Noll, S.; Bergmann, R.; Noll, B.

Suicide gene therapy utilizing herpes simplex virus type 1 thymidine kinase gene (HSV1-tk) requires careful monitoring of the successful transfection. 18F-labelled nucleoside analoga, especially acyclic nucleosides such as 9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]FHPG) and 9-[(4-[18F]fluoro)-3-hydroxymethylbutyl]guanine ([18F]FHBG) are currently used as PET tracers for monitoring and quantification of HSV1-tk expression. To improve the tracer properties, two new precursors have been synthesized by introduction of bromine in order to get the new substrates 8-bromo-9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]FHBrPG) and 8-bromo-9-[(4-[18F]fluoro)-3-hydroxymethylbutyl]guanine ([18F]FHBrBG) for monitoring gene expression of HSV1-tk.

Materials and methods
The precursors as well as the nonradioactive reference compounds were prepared by introduction a p-toluenesulphonyl leaving group and trityl protecting groups into the brominated derivatives of ganciclovir and penciclovir. In a further step the precursors reacted with a K[18F]F kryptofix complex to trityl-protected intermediates. Then, the protecting groups were removed by heating in methanolic acetic acid solution. Both tracers were purified by RP HPLC separation. The identity of the tracers with the nonradioactive reference compounds was proved by HPLC. The in vitro uptake of all compounds was evaluated in a glioblastoma cell line stably transfected with the HSV1-tk gene and in the respective non-transfected cell line. The biodistribution and biokinetics of the radiotracers have been studied in mice and rats by small animal PET.

The radiochemical yield of the 18F-tracers amounts to 10-15% (decay corrected) after a synthesis time of 85 95 min, the radiochemical purity was > 98%. The average specific activity was 19 GBq/µmol at the end of synthesis. Cell-uptake studies were carried out with both the brominated and the non-brominated derivatives of ganciclovir and penciclovir as standards. The relative cellular uptake (ratio HSV-tk-positive/controls) was 12.4±4.5 after 1 h of incubation with [18F]FHBrBG. In contrast, the uptake ratio of the other tracers [18F]FHBrPG (1.7±0.4), [18F]FHBG (4.0±2.3) and [18F]FHPG (1.6±0.3) was significantly lower than that of [18F]FHBrBG. Renal elimination was the main route of tracer clearance from the body, however with increasing lipophilicity of the tracers, increasing amounts were also eliminated through liver and bile into the intestine.

The novel tracer [18F]FHBrBG showed a superior uptake in HSV1-tk transfected cells compared to the clinically tested PET-tracer [18F]FHBG. Therefore [18F]FHBrBG appears to be a novel tracer for an improved monitoring of HSV1-tk based gene therapy approaches with PET.

  • Lecture (Conference)
    EANM'06 Annual Congress of the European Association of Nuclear Medicine, 30.09.-04.10.2006, Athens, Greece
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 33(2006)Suppl. 2, 624

Publ.-Id: 8524

Expression of VEGF and VEGF receptors and radiotracer uptake in tumor cells and primary endothelial cells under experimental hypoxia

Oswald, J.; Treite, F.; Haase, C.; Bergmann, R.; Schwenzer, B.; Pietzsch, J.

Vascular-endothelial growth factor (VEGF) is expressed in response to various stimuli like hypoxia and plays a key role in tumor angiogenesis. In this study we analyzed the influence of experimental hypoxia on the upregulation of VEGF and its receptors in primary endothelial cells and tumor cell lines. Furthermore we quantified the uptake of radiotracers in these cells in response to experimental hypoxia in vitro.
Material and Methods:
Three types of primary endothelial cells were used: human umbilical vein endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines FaDu (squamous cell carcinoma) and HT-29 (colorectal adenocarcinoma), respectively. Experimental hypoxia was induced by cultivating cells for 24 to 72 hours in presence of <1% oxygen in a special incubator (Gasboy C40, Labotect). Expression of VEGF, and of the VEGF receptors FLT-1, KDR, FLT-4 and neuropilin 1 and 2 were quantified with quantitative PCR (Realplex, Eppendorf). Cellular uptake of [99mTc]sestamibi, [18F]FDG, and [18F]F-misonidazole was determined after one to four hours incubation and measured after cell lysis with a Cobra II gamma counter (Packard).
After 48 h of experimental hypoxia all cell lines showed a significant upregulation of VEGF expression. VEGF receptors FLT-1, KDR and FLT-4 were expressed in endothelial cells but absent in tumor cells. Cellular uptake of [99mTc]sestamibi was reduced under hypoxic conditions in all cell lines. Furthermore, we found that primary endothelial cells incorporated significantly higher amounts of [18F]FDG under experimental hypoxic conditions in comparison to normoxic conditions.
When compared to normoxia [18F]FDG uptake after 48h hypoxia was increased 4.3-fold in HUVECs, 3.4-fold in HDMECs, and 3.5-fold in HAECs. These values were substantially higher than the values for the tumor cells FaDu (1.9-fold) and HT-29 (2.1-fold).
Our data show VEGF to be a suitable indicator for enhanced oxygen demand in both tumor and endothelial cells in vitro. Moreover, the results emphasize the particular relevance of endothelial cells as one important part of the tumor micromilieu.

  • Lecture (Conference)
    EANM'06 Annual Congress of the European Association of Nuclear Medicine, 30.09.-04.10.2006, Athens, Greece
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 33(2006)Suppl. 2, 661

Publ.-Id: 8523

Central depression in nuclear density and its consequences for the shell structure of superheavy nuclei

Afanasjev, A. V.; Frauendorf, S.

The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean-field theory. A large depression leads to the shell gaps at the proton Z = 120 and neutron N = 172 numbers, whereas a flatter density distribution favors N = 184 and leads to the appearance of a Z = 126 shell gap and to the decrease of the size of the Z = 120 shell gap. The correlations between the magic shell gaps and the magnitude of the central depression are discussed for relativistic and nonrelativistic mean field theories.

  • Physical Review C 71(2005), 024308

Publ.-Id: 8522

Description of rotating N=Z nuclei in terms of isovector pairing

Afanasjev, A. V.; Frauendorf, S.

A systematic investigation of the rotating N=Z even-even nuclei in the mass A=68-80 region has been performed within the frameworks of the cranked relativistic mean field, cranked relativistic Hartree-Bogoliubov theories, and cranked Nilsson-Strutinsky approach. Most of the experimental data are well accounted for in the calculations. The present study suggests the presence of strong isovector np pair field at low spin, whose strength is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar t=0 np pairing has been obtained in the present investigation performed at the mean field level.

  • Physical Review C 71(2005), 064318

Publ.-Id: 8521

Reappearance of the pairing correlations at finite temperature

Sheikh, J. A.; Palit, R.; Frauendorf, S.

Rotational and deformation dependence of isovector and isoscalar pairing correlations at finite temperature are studied in an exactly solvable cranked deformed shell model Hamiltonian. It is shown that isovector pairing correlations, as expected, decrease with increasing deformation and the isoscalar pairing correlations remain constant at temperature, T=0. However, it is observed that at finite temperature both isovector and isoscalar pairing correlations are enhanced with increasing deformation. It is also demonstrated that the pair correlations, which are quenched at T=0 and high rotational frequency reappear at finite temperature. The changes in the individual multipole pairing fields as a function of rotation and deformation are analyzed in detail.

  • Physical Review C 72(2005), 041301

Publ.-Id: 8520

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