Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

Isospin diffusion in heavy ion reactions

Tsang, M.; Liu, T. X.; Shi, L.; Danielewicz, P.; Gelbke, C. K.; Liu, X. D.; Lynch, W. G.; Tan, W. P.; Verde, G.; Wagner, A.; Xu, H. S.; Friedman, W. A.; Beaulieu, L.; Davin, B.; de Souza, R. T.; Larochelle, Y.; Lefort, T.; Yanez, R.; Viola Jr., V. E.; Charity, R. J.; Sobotka, L. G.

Using symmetric 112Sn + 112Sn, 124Sn + 124Sn collision as references, we probe isospin diffusion in peripheral asymmetric 112Sn + 124Sn, 124Sn + 112Sn systems at incident energy of E/A = 50 MeV. Isoscalic analyses imply that the quasi-projectile and quasi-target in these collisions do not achieve isospin equilibrum, permitting an assesment of the isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical obstacles, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.

  • Michigan State University MSUCL -1273 October 2003

Publ.-Id: 6106

Laboratory astrophysics as examplified by the Riga dynamo experiment

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

It has been proposed to investigate the magnetorotational instability at a large scale liquid sodium facility. This sort of laboratory astrophysics is encouraged by the recent successful dynamo experiments. We report on our experiences with the Riga dynamo experiment where magnetic field self-exciation is achieved in a cylindrical vessel filled with approximately 2 qm of liquid sodium which can reach flow velocities up to 20 m/s. The main experimental results on the kinematic and the saturation regime are compared with numerical modelling. Some focus is also laid on the technical design of the facility and the measurement instrumentation.

  • Lecture (Conference)
    Workshop: MHD Couette flows: experiments and models, 29.02.-02.03.2004, Acitrezza, Catania, Italy

Publ.-Id: 6105

Magnetorotational Instability in Taylor-Dean Flows

Stefani, F.; Gerbeth, G.

The experimental demonstration of MRI in a liquid sodium Taylor-Couette experiment might be hampered by sealing problems at the two end plates whose sophisticated design could be crucial to avoid non-linear instabilities. Thus motivated, we consider alternative flow configurations with respect to their suitability to show MRI. First results for flows that are driven by azimuthal pressure gradients (Dean flows) and for combinations with Couette flows (Taylor-Dean flows) are presented. The influence of an axial magnetic field on the stability of Dean and Taylor-Dean flows with arbitrary gap spacing between the cylinders is considered. For Dean flows with magnetic Prandtl number equal to one it is found that, similar to the result for the Taylor-Couette flow, a significant decrease of the critical Reynolds number occurs for intermediate Hartmann numbers. This MRI is more pronounced for small values of the ratio of the radii of the inner and outer cylinder. For Taylor-Dean flows the onset of the instability in dependence on the ratio of azimuthal pressure gradient and cylinder rotation is investigated.

  • Lecture (Conference)
    Workshop: MHD Couette flows: experiments and models, 29.02.-02.03.2004, Acitrezza, Catania, Italy

Publ.-Id: 6104

Transition strengths between particle hole excitations in 95Ru

Galindo, E.; Hausmann, M.; Jungclaus, A.; Lieb, K. P.; Yordanov, O.; Johnstone, I. P.; Schwengner, R.; Dewald, A.; Fitzler, A.; Möller, O.; de Angelis, G.; Gadea, A.; Martinez, T.; Napoli, D. R.; Ur, C. A.

High-spin states of 95Ru have been populated using the 35Cl+ 64Zn reaction at a beam energy of 135 MeV. In a recoil-distance Doppler-shift experiment, the lifetimes or lifetime limits of 26 high-spin states have been measured, giving information on a total of 49 reduced transition strengths. The results are compared with shell-model calculations with different model spaces and residual interactions. Several families of states with defined proton and neutron seniorities are proposed. The M1 strengths in the negative-parity yrast sequence show a pronounced staggering which is reproduced by the shell-model calculations.

  • Physical Review C 69(2004), 024304

Publ.-Id: 6103

Lorentz force influence on momentum and mass transfer in natural convection copper electrolysis

Weier, T.; Hüller, J.; Gerbeth, G.; Weiss, F.-P.

Momentum and mass transfer during copper electrolysis in a small cell can be significantly influenced by Lorentz forces. Depending on the magnetic field configurations, a multitude of flow fields with an accordingly large range of mass transfer conditions can be arranged. The moderate magnetic field of simple permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. The interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

Keywords: electrochemistry; fluid mechanics; mass transfer; momentum transfer; magnetic field; convection control

Publ.-Id: 6102

An EXAFS and TRLFS investigation on uranium(VI) sorption to pristine and leached albite surfaces

Walter, M.; Arnold, T.; Geipel, G.; Scheinost, A.; Bernhard, G.

Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10−6 M U(VI) showed one silicon atom at a USi distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O)2UO2, on the silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO4, resulting in surface material similar to amorphous silica gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex.

Keywords: uranium(VI); feldspar; albite; leached layer; sorption; EXAFS; TRLFS

Publ.-Id: 6100

Interactions of the U mining waste pile isolate Bacillus sphaericus JG-A12 with U

Raff, J.; Merroun, M.; Rossberg, A.; Soltmann, U.; Böttcher, H.; Selenska-Pobell, S.

Apart from chemical and physical factors influencing mobility of radionuclides, microbial metabolism also plays a decisive role in enhancing or retarding migration effects. Bacteria are able to reduce or oxidize metals and also to accumulate and bind them. In this work biosorption of U by cells, spores and S-layers of a U mining waste pile isolate Bacillus sphaericus JG-A12 was investigated. Furthermore, these three bacterial structures were used for construction of porous biocomponent-silicate hybrids referred to as biological ceramics (biocers) for bioremediation. The results show the highest binding capacity for the spores followed by the cells and the S-layer sheets. The silicate matrix itself binds only small amounts of U. Sol-gel encapsulation does not affect the U binding properties of the cells or the S-layer sheets but strongly reduces the binding capacity of the spores. Spectroscopic analyses of the U complexes demonstrate that U is bound to phosphate and carboxyl groups of the biocomponents and to silanol groups of the silicate matrix.

  • Lecture (Conference)
    11th International Symposium on Water-Rock Interaction, 27.06.-02.07.2004, Saratoga Springs, NY, United States,
  • Contribution to proceedings
    11th International Symposium on Water-Rock Interaction, 27.06.-27.07.2004, Saratoga Springs, NY, Proceedings 1(2004), 697-701

Publ.-Id: 6099

Operational Experiences in Monitoring of Semi-Batch Hydrogenation Using Adaptive Heat and Mass Balances

Hessel, G.; Hilpert, R.; Kryk, H.; Roth, M.; Schmitt, W.; Weiss, F.-P.

This work deals with on-line monitoring of exothermic chemical processes in stirred tank reactors. To support the personnel in the efficient and safe operation of batch processes, the monitoring system (MoSys) based on heat/mass balancing was developed. A model was implemented for estimating concentrations from heat/mass balances. Dimensionless balances with adaptive parameters were used to adapt the heat/mass balances to the chemical target reactor and to realise the scale-up. For industrial testing, MoSys was integrated in a batch-information-management system (BIMS), which was also developed and implemented in the process control system of a multipurpose reactor installation. As a result, the outputs of MoSys can simultaneously be visualised with important process signals on terminals of the process control system. Operational experiences in monitoring an industrial hydrogenation process are represented.

Keywords: On-line monitoring; semi-batch process; modelling; concentration estimation; scale up; chemical industry

  • Lecture (Conference)
    Symposium on knowledge Driven Batch Processes (BATCHPRO), 06.-09.2004, Poros, Greece
  • Contribution to proceedings
    Symposium on knowledge Driven Batch Processes (BATCHPRO),06.-09.06. 2004, Poros, Greece, Proceedings CD-ROM

Publ.-Id: 6098

The HADES Tracking System

Müntz, C.; Markert, J.; Alvarez-Pol, H.; Badura, E.; Bielcik, J.; Bokemeyer, B.; Boyard, J.-L.; Chepurnov, V.; Chernenko, S.; Daues, H.; Dohrmann, F.; Enghardt, W.; Fateev, O.; Garabatos, C.; Glonti, L.; Grosse, E.; Hehner, J.; Heidel, K.; Hennino, T.; Hoffmann, J.; Ierusalimov, A.; Kämpfer, B.; Kanaki, K.; Koenig, W.; Kotte, R.; Naumann, L.; Ott, W.; Pachmayer, Y. C.; Pechenov, V.; Petrov, A.; Pouthas, J.; Ramstein, B.; Rosenkranz, K.; Rosier, P.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Smykov, L.; Stelzer, H.; Stroebele, H.; Sudol, M.; Sturm, C.; Sobiella, M.; Stroth, J.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

The HADES dielectron spectrometer has recently launched its physics program at the heavy ion synchrotron SIS at GSI Darmstadt. The spectroscopy of vector mesons in heavy ion collisions via their dielectron decay channels makes great demands on the HADES tracking system regarding acceptance and spatial resolution. It is formed out of 24 low-mass, trapezoidal multi-layer drift chambers providing about 30 m2 of active area. Low multiple scattering in total four planes of drift chambers before and after the magnetic field is ensured by using Helium-based gas mixtures and aluminum cathode and field wires. First in-beam performance results will be contrasted with expectations from simulations. Emphasis is placed on the energy loss information, exploring its relevance regarding track recognition.

  • Nuclear Instruments and Methods in Physics Research Section A 535(2004)1-2, 242-246

Publ.-Id: 6097

Improvement of low-energy stopping power algorithms in the FLUKA simulation program

Parodi, K.; Squarcia, S.

Monte Carlo methods are actually the best tools to perform the detailed dosimetric and radiobiological calculations required in conformal radiotherapy. In this work we focus our attention on the FLUKA simulation program and on the electronic stopping power calculationsfor protons and alpha particles in materials of interest for therapy. We discovered large inaccuracies (>10%) with respect to the values suggested by ICRU (standard reference) for protons in compounds and alpha particles both in elements and compounds below 1 MeV/amu. These deviations, due to the standard approach based on additivity and scaling rules, could indeed affect radiobiological evaluations for primary charged hadron and neutron beams. Therefore we developed new algorithms based on proper parametric formulae and inserted them in the FLUKA code. The new approach allows an agreement with ICRU data much better than 1% in the entire energy range 1 keV-100 MeV/amu spanned by the old one.

Keywords: electronic stopping power; protons; alpha particles

  • Nucl. Instr. Meth. Phys. Res. A 456 (2001) 352-368

Publ.-Id: 6096

Platinmetall-Führung der Ni-Cu-Sulfidmineralisationen im Bereich der Lausitzer Antiklinalzone

Kindermann, A.; Fiedler, F.; Seifert, T.; Uhlig, S.

The PGE content of liquid magmatic Ni-Cu(-PGE) sulfide mineralization in the Lusatian anticline has been known since the early 20th century. The mineralization occurs only in vein- or stock-like intrusive bodies of gabbroic, dioritic or noritic composition. Mineralization consisting mainly of pyrrhotite, pentlandite and chalcopyrite probably results from gravity segregation of an exsolved sulfide melt. Sulfides occur in general near the contacts of the intrusions. Different types of ore textures can be distinguished. Besides extensive fieldwork at numerous exposures, microscopic, geochemical, and semiquantitative microanalysis was carried out to characterize the sulfide mineralization and the PGE phases. These contain, beside Pt and Pd, remarkable amounts of Sb, Te, Hg and As. The Lusatian Ni-Cu(-PGE) mineralization is genetically similar to Norilsk-Talnakh-type ore deposits.

Keywords: Forschung; Platinerz; Ni-Cu-Sulfidmineralisation; Metallogenese; Gabbro; Diorit; Intrusionskörper; Hauptelementanalyse; Spurenelementanalyse; Lausitzer Antiklinalzone; Sachsen; Oberlausitz

  • Zeitschrift für Angewandte Geologie 2 (2003) 43

Publ.-Id: 6094

A unique parameterization of the QCD equation of state below and above T_c

Bluhm, M.; Kampfer, B.; Soff, G.

We present a unique parameterization of the equation of state of strongly interacting matter in the temperature interval 0.6 T_c \cdots 3 T_c at \mu = 0 within a quasi-particle model based on quark and gluon degrees of freedom.
The extension to non-vanishing baryon-chemical potential is discussed.

Keywords: equation of state; deconfinement; QCD

  • Contribution to HZDR-Annual report
    Bormio Proceedings (2004) 42nd International Winter Meeting on Nuclear Physics


Publ.-Id: 6092

Nucleon resonances and the production of light vector mesons near threshold

Kämpfer, B.; Kaptari, L. P.; Titov, A. I.

The production of the light vector mesons V =ρωφ in the reactions πN → V N and N N → V N N near threshold is studied. The subsequent electromagnetic decay V → γ^* → e^+ e^- is particularly suited for exploring subthreshold ωN resonances.

Keywords: meson production; electromagnetic decay; di-electrons

  • Contribution to HZDR-Annual report
    Hirschegg Proceedings of the International Workshop XXXII on Gross Properties of Nuclei and Nuclear Excitations (2004) 143-150

Publ.-Id: 6091

Surface nanopatterning of metal thin films by physical vapour deposition onto surface-modified silicon nanodots

Azzaroni, O.; Fonticelli, M.; Schilardi, P. L.; Benítez, G.; Caretti, I.; Albella, J. M.; Gago, R.; Vázquez, L.; Salvarezza, R. C.

Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in the development of future technologies. In this work we describe a simple and low-cost method for metal nanostructuring with 50 nm lateral and 6 nm vertical resolutions based on metal film deposition on a silane-derivatized nanostructured silicon master. The silane monolayer anti-sticking properties allow nanopattern transfer from the master to the deposited metal films as well as easy film detachment. The method is non-destructive, allowing the use of the derivatized master several times without damaging. Potential applications of the method are in the field of high-density data storage, heterogeneous catalysis and electrocatalysis, microanalysis (sensors and biosensors) and new optical devices.

Publ.-Id: 6090

On the β-decaying (21+) spin gap isomer in 94Ag

Plettner, C.; Grawe, H.; Mukha, I.; Döring, J.; Nowacki, F.; Batist, L.; Blazhev, A.; Hoffman, C. R.; Janas, Z.; Kirchner, R.; La Commara, M.; Mazzocchi, C.; Roeckl, E.; Schwengner, R.; Tabor, S. L.; Wiedeking, M.

The β decay of 94Ag, a nucleus with three proton and three neutron holes with respect on 100Sn, was investigated at the GSI on-line mass spectrometer by using an array of germanium and silicon detectors. On the basis of an β γ γ coincidence measurement, the previously reported decay scheme has been considerably improved and evidence is presented for a spin-gap isomer with a spin-parity assignment of (21+), i. e., the highest spin ever observed in β decay. The half-life of the low spin-spin isomer (7+) was remeasured to be 0.59(2) s, whereas the half-life of the high-spin isomer was determined as 0.47(8) S. For the states in 94Ag and 94Pd, large-scale shell-model calculations that include up to 4p-4h excitations across the N = Z = 50 shell gap and employ a realistic interaction were carried out. These core excitations play a crucial role in generating the E4 isomerism required for the interpretation of th long half-life of the (21+) state in 94Ag.

  • Nuclear Physics A 733(2004)1-2, 20-36

Publ.-Id: 6089

Develoment and Verification of Dynamics Code for Molten Salt Reactors

Krepel, J.; Grundmann, U.; Rohde, U.

To perform transient analysis for Molten Salt Reactors (MSR), the reactor dynamics code DYN3D developed in FZR was modified for MSR applications. The MSR as a liquid fuel system can serve simultaneously as an actinide burner and a thorium breeder. The specifics of the reactor dynamics of MSR consist in the fact, that there is direct influence of the fuel velocity to the reactivity, which is caused by the delayed neutrons drift. This drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit. This leads to the reactivity loss due to the fuel acceleration or to the reactivity increase in the case of deceleration.
For the first analyses, a 1D modified version DYN1D-MSR of the code has been developed. By means of the DYN1D-MSR, several transients typical for the liquid fuel system were analyzed. Transients due to the overcooling of fuel at the core inlet, due to the reactivity insertion, and the fuel pump trip have been considered. The results of all transient studies have shown that the dynamic behavior of MSR is stable when the coefficients of thermal feedback are negative.
For studying space-dependent effects like e.g. local blockages of fuel channels, a 3D code version DYN3D-MSR will be developed. The nodal expansion method used in DYN3D for hexagonal fuel element geometry of VVER can be applied considering MSR design with hexagonal graphite channels.

Keywords: MSR; MSRE; MSBR; salt; Dynamics; Neutronics; Thermal-hydraulics; delayed; neutron; drift

  • Contribution to proceedings
    ICONE 12 - 12th International Conference on Nuclear Engineering, ASME, 25.-29.04.2004, Arlington, Virginia, United States, CD-ROM, paper 49130
  • Lecture (Conference)
    ICONE 12 - 12th International Conference on Nuclear Engineering, 25.-29.04.2004, Arlington, Virginia, United States
  • Poster
    ICONE 12 - 12th International Conference on Nuclear Engineering, 25.-29.04.2004, Arlington, Virginia, USA

Publ.-Id: 6088

3D computation of the shape of etched tracks in CR-39 for oblique particle incidence and comparison with experimental results

Dörschel, B.; Hermsdorf, D.; Reichelt, U.; Starke, S.; Wang, Y.

Computation of the shape of etch pits needs to know the varying track etch rate along the particle trajectories. Experiments with alpha particles and 7-Li ions entering CR-39 detectors under different angles showed that this function is not affected by the inclination of the particle trajectory with respect to the normal on the detector surface. Track formation for oblique particle incidence can, therefore, be simulated using the track etch rates determined for perpendicular incidence. 3D computation of the track shape was performed applying a model recently described in literature. A special programm has been written for computing the x, y, z coordinates of points on the etch pit walls. In addition, the etch pit profiles in sagittal sections as well as the contours of the etch pit openings on the detector surface have been determined experimentally. Computed and experimental results were in good agreement confirming the applicability of the 3D computational model in combination with the functions for the depth-dependent track etch rates determined experimentally.

Keywords: Light ions; Track shape; Computation model; Track etch rate; CR-39

  • Radiation Measurements 37 (2003) 563-571

Publ.-Id: 6085

Fluid mixing and flow distribution in the reactor circuit (FLOMIX-R)

Rohde, U.; Weiss, F.-P.; Karlsson, R.; Hemström, B.; Lillington, J.; Scheuerer, M.; Tuomisto, H.; Toppila, T.; Dury, T.; Cvan, M.; Muehlbauer;, P.; Toth, I.; Elter, J.; Bezrukov, Y.

The project aims 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. Measurement data from a set of mixing experiments, gained by using advanced measurement techniques with enhanced resolution in time and space help to improve the basic understanding of turbulent mixing and to provide data for Computational Fluid Dynamics (CFD) code validation. Slug mixing tests simulating the start-up of the first main circulation pump are performed with two 1:5 scaled facilities: The Rossendorf coolant mixing model ROCOM and the VATTENFALL test facility, modelling a German Konvoi type and a Westinghouse type three-loop PWR, respectively. 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 are made available.
Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests (Sizewell-B for PWRs, Loviisa and Paks for VVERs) are used together with the data from the ROCOM facility as a basis for the flow distribution studies. The test matrix on flow distribution and steady state mixing performed at ROCOM comprises experiments with various combinations of running pumps and various mass flow rates in the working loops.
Computational fluid dynamics calculations are accomplished for selected experiments with two different CFD codes (CFX-5, FLUENT). The applicability of various turbulence modelling techniques is studied for transient and steady state flow. Best practice guidelines (BPG) are referenced 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. The computational grid generation for the test facilities and first calculations on the benchmark tests have been performed.

Keywords: turbulent mixing; boron dilution; test facility; computational fluid dynamics; code validation; nuclear reactor; safety analysis

  • Lecture (Conference)
    Symposium FISA-2003 - EU research in reactor safety, Luxembourg, November 10-13, 2003; Pre-proceedings pp. 198-204
  • Contribution to proceedings
    Symposium FISA-2003 - EU research in reactor safety, Luxembourg, November 10-13, 2003; Pre-proceedings pp. 198-204

Publ.-Id: 6084

Influence of gas pressure and substrate temperature on PIII nitrocarburizing process of AISI 304 stainless steel

Abd El-Rahman, A. M.; El-Hossary, F. M.; Negm, N. Z.; Prokert, F.; Richter, E.; Möller, W.

Plasma immersion ion implantation (PIII) has been used to modify the surface properties of 304 austenitic stainless steel (AISI). The influence of working gas pressure, 0.2 - 1.0 Pa, and substrate temperature, 300 - 500 oC, on the microstructure, treating rate, nitrogen/carbon concentration depth profile, and surface microhardness was investigated. A gas composition of 25 % C2H2, 75 % N2, rf plasma power input of 350 W, and a negatively biased potential of 30 kV were fixed during the experiment. The experimental results show that the substrate temperature and the diffusion process of nitrogen and carbon depend on gas pressure inside the plasma chamber. The thickness of the modified layer has been found to be more than 30 µm after 60 minutes plasma processing time. The results provide recent values of diffusion coefficient and surface microhardness are 3.4 x 10-1 µm2/sec and 1880 kg/mm2 respectively.

Keywords: Plasma immersion ion implantation (PIII); PIII working gas pressure; PIII sample temperature; GDOS; AISI microstructure; AISI surface hardness

Publ.-Id: 6083

Determination of Low Concentrated Small-Sized Colloids by Laser Induced Breakdown Detection

Opel, K.; Hübener, S.; Zänker, H.

Colloids of some nanometers in size are interesting for the transport of contaminants in natural waters because of their high specific surface. Optical and acoustic detection of plasmas induced by laser pulses on individual particles allows determining of size and concentration of smallest colloids in the ppt-range. The apparatus for laser induced breakdown detection established in the Institute of Radiochemistry at FZR is described. First results of measurements on particle standards, de-ionized waters and nearly colloid-free environmental samples are presented.

Keywords: LIBD; colloids; environmental samples; contaminants

  • Poster
    12. Wolfgang-Ostwald-Kolloquium, Inorganic Colloid Science - Importance of Layered Materials, Kiel, 25. und 26. März 2004

Publ.-Id: 6082

In-beam PET for in-situ dose quantification in carbon ion therapy and possible extension to proton therapy

Parodi, K.; Enghardt, W.

  • Lecture (Conference)
    DPG-Frühjahrstagung, 22.-26.03. 2004, München, Germany

Publ.-Id: 6081

Interaction of bacteria with metals: EXAFS studies

Merroun, M.; Raff, J.; Pollmann, K.; Rossberg, K.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.

Poster - kein Abstract

  • Poster
    14th ESRF Users Meeting Grenoble, 10.-11.2.2004

Publ.-Id: 6080

Interaction of U(VI) with bacterial strains isolated from uranium mining piles: spectroscopic and microscopic studies

Merroun, M.; Raff, J.; Rossberg, A.; Hennig, C.; Reich, T.; Selenska-Pobell, S.

Bacteria, ubiquitous in all aquatic and soil systems, can interact in many ways with actinides. They can mobilize or immobilize actinides in the environment, leading to their dissolution or precipitation. Knowledge of bacteria-actinide interactions is important for understanding the migration behaviour of the latter in the biogeosphere. In this work, a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared (IR) spectroscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) was used to conduct a molecular and atomic analysis of the uranium complexes formed by different bacterial strains isolated from uranium mining waste piles. EXAFS analysis showed that the cells of Stenotrophomonas maltophilia JG-2, Pseudomonas rhodesiae R5 and Myxococcus xanthus precipitate U(VI) as autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, in the case of B. sphaericus JG-A12 the uranium bonding was consistent with the formation of a ternary complex with phosphate and carboxylate. These results are in agreement with those found by Infrared measurements. TEM and EDS analysis showed strain-specific extracellularl and/or intracellularl uranium accumulation to varying degrees. In B. sphaericus JG-A12 the uranium is located at the cell wall, while the cells of S. maltophilia JG-2 and P. rhodesiea R5 accumulate uranium both extracellularly on the cell surface and intracellularly as electron-dense granules.

  • Lecture (Conference)
    14th Goldschmidt Conference 2004, 05.-11.06.2004, Kopenhagen, Denmark
  • Geochimica et Cosmochimica Acta 68(2004)11, 499-499
    ISSN: 0016-7037
  • Contribution to proceedings
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark

Publ.-Id: 6079

Prozesskinetische Untersuchungen zur Modellierung reaktionsgetriebener Druckentlastungen

Kryk, H.; Schmitt, W.; Hessel, G.; Tefera, N.

Zur Dimensionierung von Schutzeinrichtungen und nachgeschalteten Anlagenteilen von Rührkesselreaktoren sowie für die sicherheitstechnische Bewertung unerwünschter Betriebszustände ist die Kenntnis der bei Druckentlastungen ablaufenden hydro- und thermodynamischen sowie reaktionskinetischen Prozesse unabdingbar. Die Qualität der Simulationsergebnisse existierender Computercodes (z. B. SAFIRE/ Vent, BRICK) ist von der Genauigkeit der Untermodelle zur Berücksichtigung von Wärme- und Stofftransport, Reaktionskinetik, Mischphasenthermodynamik sowie Aufwall- und Schaumverhalten abhängig. Reaktionskinetische Modelle zur Simulation von Druckentlastungsprozessen wurden bisher meist auf der Grundlage von Experimenten in adiabatischen Kalorimetern ermittelt. Wie eigene Untersuchungen unter isothermen Bedingungen zeigen, geben diese Formalkinetiken den thermischen Reaktionsverlauf oft nur unzureichend wieder.

Ziel der Arbeiten ist eine Verbesserung der Modellierung der Einzelphänomene unter Berücksichtigung der spezifischen Prozessbedingungen der Druckentlastung. Die Modelle werden in den am FZ Rossendorf entwickelten 1D-Code BRICK eingebunden. Hierdurch soll eine Ertüchtigung des Codes für die Simulation von Druckentlastungsprozessen siedend aufwallender bzw. schäumender reaktiver Stoffsysteme erfolgen.

Als Modellprozess wurde die Veresterung von Essigsäureanhydrid mit Methanol gewählt. Die Modellbildung bzw. –auswahl erfolgt auf der Grundlage isothermer und isoperiboler Experimente im Reaktionskalorimeter RC1, wobei zur Erfassung der Konzentrationsverläufe während der Reaktion, Messungen mit einem In-Situ-FTIR-Spektrometer erfolgen. Die Ausdehnung des Gültigkeitsbereiches der Modelle erfolgt anschließend durch ergänzende Experimente im adiabatischen Kalorimeter PhiTecII. Gleichzeitig werden zur Berücksichtigung thermodynamischer Einflüsse Mischungsenthalpien und Mischleistungsverläufe im RC1 gemessen, modelliert und in das Prozessmodell integriert.
Zur Bewertung von Druckentlastungsprozessen hinsichtlich des Gefährdungspotenzials, verursacht durch aus dem Reaktor austretende Substanzen, ist die quantitative Zusammensetzung des bei der Druckentlastung austretenden Stoffgemisches von entscheidender Bedeutung. Darüber hinaus ist die Kenntnis der Konzentrationen hilfreich zur Validierung der Simulationssoftware und zur Charakterisierung des thermodynamische Zustandes des Reaktionsgemisches zum Zeitpunkt der Druckentlastung. Die Konzentrationsmessungen erfolgen mittels Offline-FTIR, wobei die Gemischzusammensetzungen der ausgetragenen Substanzen unmittelbar nach der Duckentlastung und die Konzentrationen der im Reaktor verbliebenen Gemische ermittelt werden. Hierzu erfolgen Druckentlastungsexperimente im PhiTecII, wobei zum Abstoppen der Reaktion die ausgetretenen Substanzen in ein mit flüssigem Stickstoff gekühltes Quench-Gefäß eingeleitet werden.

Es werden die unter isothermen, isoperibolen und adiabatischen Bedingungen experimentell ermittelten thermischen Reaktionsverläufe und die Konzentrationsverläufe im Vergleich zu den mittels Literaturdaten berechneten und den auf Grundlage des entwickelten Prozessmodells unter Einfluß der Mischungsenthalpie simulierten Daten dargestellt und diskutiert. Weiterhin werden die Methodiken für die Konzentrationsmessungen bei den Druckentlastungsexperimenten vorgestellt und die Messergebnisse diskutiert.

Keywords: Druckentlastung; Reaktionskinetik; Reaktionskalorimetrie

  • Abstract in refereed journal
    Chemie Ingenieur Technik 76(2004)9, 1312

Publ.-Id: 6078

Real-time evolution of the ITO film properties and structure during annealing in vacuum

Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Prokert, F.; Cantelli, V.; Kolitsch, A.; Moeller, W.

Indium tin oxide films produced by reactive middle frequency dual magnetron sputtering were annealed in vacuum at a constant rate of the temperature enhancement. The film electrical and optical properties have been studied in situ along with direct characterization of the structure. Even in amorphous state the film resistivity significantly decreases at increasing temperature due to a free electron density enhancement likely by oxygen vacancies creation. The rapid crystallization within the temperature range 250-280 °C leads to further decrease of the resistivity due to a Sn donor activation. The resistivity and optical properties depend non-linearly on the crystalline fraction.

Keywords: indium tin oxide; resistivity; structure; optical properties; annealing; in situ characterization

  • Applied Physics Letters 85(2004)2, 212-214

Publ.-Id: 6076

DYN3D Calculations for the V-1000 Test Facility and Comparisons with the Measurements

Grundmann, U.; Mittag, S.

In the framework of the EU project VALCO, measurements at the V-1000 test facility of the Russian Research Centre 'Kurtschatov Institute' are used for the validation of three-dimensional neutronic calculations. Experimental results of steady states and kinetic experiments are available for comparisons with calculations. Respective DYN3D calculations have been performed by using the cross section libraries generated with the codes HELIOS, CASMO and WIMS.
Results obtained by the DYN3D code are compared with steady-state measurements for two different configurations of the V-1000 facility. Pin-power distributions measured within one fuel assembly are compared to the results of the pin power reconstruction implemented in DYN3D.
Two kinetic experiments performed in the V-1000 facility were simulated by the DYN3D code. Comparisons of the calculated results with the measurements at the in-core detector positions are given. The calculated fast flux of the nodes, situated near to the ionisation chambers of the two reactimeters, is compared with the detector signal. The results of the relative detector rates coincide with the measurements. The dynamical reactivities are obtained from the core-averaged flux by inverse point kinetics. It is compared with reactivity curves, provided by the two reactimeters.

Keywords: three-dimensional neutron kinetics; steady states; kinetic experiments; code validation; VVER-reactors; reactivity

  • Contribution to proceedings
    PHYSOR-2004 - The Physics of Fuel Cycles and Advanced Nuclear Systems: Global Developments, 25.-29.04.2004, Chicago, USA
    Proceedings of PHYSOR-2004, La Grange Park, Illinois: American Nuclear Society, 0-89448-683-7
  • Lecture (Conference)
    PHYSOR-2004 - The Physics of Fuel Cycles and Advanced Nuclear Systems: Global Developments, 25.-29.04.2004, Chicago, United States

Publ.-Id: 6074

Neues aus der Bibliothek

Reschke, E.

Die Bibliothek ist die zentrale Stelle für wissenschaftliche Literatur- und Fachinformation des Forschungszentrums Rossendorf. Mit ihren spezifischen Leistungen unterstützt sie die Forschung und trägt damit zur Sicherung der Attraktivität des Forschungsstandortes Rossendorf im internationalen Standortwettbewerb bei. Davon ausgehend werden die neuesten elektronischen Informationsservices dargestellt: Zugang zum "Web of Knowledge" und zu einer Vielzahl elektronischer Zeitschriften im Volltext. Durch Umbau der ehemaligen Buchbinderei im Haus der Bibliothek konnte ein IT-Schulungsraum eingerichtet werden.

Keywords: Library; Information services; Database availability

  • FZR intern (2004) Februar

Publ.-Id: 6072

Layer morphology and Al implant profiles after annealing of supersaturated, single crystalline, amorphous and nanocrystalline SiC

Heera, V.; Mücklich, A.; Dubois, C.; Voelskow, M.; Skorupa, W.

Al supersaturated SiC layers (5x10^20 Al cm-3) were produced by multi-energy, high dose ion implantation into 6H- and 4H-SiC. Several implantation schemes with varying implantation sequence and temperature were investigated. In dependence on the implantation conditions damaged single-crystalline, amorphous or nanocrystalline layers were formed. The layer morphology and Al distribution in the as-implanted state as well as structural changes and related Al redistribution after high temperature annealing (1500-1700°C) were characterized by XTEM, RBS/C, AFM and SIMS analysis. Remarkable Al redistribution effects have been found after annealing of Al supersaturated SiC. During high temperature annealing Al atoms in excess to the solid solubility (2x1020 Al cm-3) tend to precipitate in single crystalline SiC whereas they diffuse out in amorphous or nanocrystalline SiC. Redistribution of Al with concentration below the solid solubility is governed by transient enhanced diffusion which can be controlled by the annealing scheme. Amorphization of SiC is advantageous in the case of Al doping to levels higher than the solid solubility because it prevents Al precipitation during annealing and helps to form box-like Al profiles with smooth plateau and abrupt edge.

Keywords: implanted SiC; heavy Al doping; layer morphology; high temperature annealing; Al redistribution

Publ.-Id: 6071

Complex formation of U(VI) with amino acids studied by UV-vis spectroscopy, TRLFS and EXAFS

Günther, A.; Geipel, G.; Rossberg, A.; Bernhard, G.

wird nachgereicht

  • Lecture (Conference)
    Sixth International Conference on Nuclear and Radiochemistry 29.8.-03.9.2004, Aachen, Germany
  • Contribution to proceedings
    Sixth International Conference on Nuclear and Radiochemistry, 29.08.-03.09.2004, Aachen, Germany

Publ.-Id: 6070

Investigations of uranyl sorption onto gibbsite

Baumann, N.; Brendler, V.; Arnold, T.; Geipel, G.

The application of surface complexation models (SCM) towards real-world problems requires not only a reliable parameter database but also information about the chemical structure of surface species and the crystallographic location of binding sites. This study focused on the sorption behavior the uranyl cation UO2 2+ on aluminol and silanol groups in model substances for clays, namely gibbsite: γ-Al(OH)3.
Batch sorption experiments were carried out at an ionic strength of 0.1 M NaClO)4 and at different pH values with a stepping of 0.5 from 3.5 to 9.5 under air. After a contact time of 2 days in the overhead shaker gibbsite was separated by centrifugation and the uranium contend in the separated solution was measured by ICP-MS. The concentration of uranium adsorbed on gibbsite was calculated in accounting for uranium sorbed on the container wall. The sorption curve indicates a maximum sorption between pH 5.5 and 7.5.
For the spectroscopic investigations with TRLIF (Time-resolved laser-induced fluorescence) the gibbsite from the batch experiments was re-suspended in a solution with pH and ionic strength being identical to the original solution. So it was guaranteed, that the fluorescence signals were only caused from uranium sorbed on the gibbsite, and not from uranium in solution. After a second centrifugation the solution was also measured to ensure the absence of dissolved uranyl species.
The TRLIF spectra, excluding the wavelength range between 525 and 540 nm influenced by the laser dispersion peak, were integrated and then fitted to a sum of exponential decay terms. The best approximation for the fluorescence decay gave a bi-exponential decay function yielding two fluorescence decay times: t)1. in a range between 200 and 450 ns (this indicates the formation of UO)2.(OH))3+) and t)2. between 3200 and 7900 ns (indicates UO)2.(OH))2.).
The peak maxima (at approximately 498, 521, 543 and 557 nm) differ slightly at varying pH, but do not show systematic shifts. The uranium surface species are therefore assumed to be similar throughout the investigated pH range. They should have identical numbers of hydroxyl groups in their first coordination sphere and differ only in the respective water content. This is valid both for the short lived and the long lived species.

  • Poster
    SORPO Workshop, Karlsruhe 25./26.3.2004; FZKA Report 6986, 13-16
  • Contribution to proceedings
    14th Goldschmidt Conference, 05.-11.6.2004, Copenhagen, Denmark Proceedings
  • Contribution to proceedings
    SORPO Workshop, 25.-26.03.2004, Karlsruhe, Germany; FZKA Report 6986, 13-16
  • Contribution to proceedings
    Tagung der Deutschen Mineralogischen Gesellschaft, 19.-22.09.2004, Karlsruhe, Germany
    Beiheft zum European Journal of Mineralogy 16(2004)1, 9
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 68(2004)11, A509

Publ.-Id: 6069

Einfluss von Wasserstoff auf die Zähigkeit von bestrahlten Reaktordruckbehälterstählen

Müller, G.; Ulbricht, A.; Böhmert, J.; Uhlemann, M.

Niedriglegierte ferritische Stähle gelten ebenso wie die hochlegierten austentischen Stähle als anfällig gegen Wasserstoffversprödung. Im Kernreaktor können Korrosion oder Radiolyse zur Bildung von atomaren Wasserstoff an der inneren Oberfläche des Reaktordruckbehälters und folglich zur Wasserstoffaufnahme während des Reaktor-betriebes führen. Werden die als Folge der Bestrahlung entstehenden Strukturdefek-te auch als Wasserstoff-Traps wirksam, sind sicherheitsgefährdende Synergismen zwischen dem Phänomen der Strahlen- und Wasserstoffversprödung nicht auszu-schließen. Frühere Untersuchungen haben gezeigt, dass Wasserstoffgehalte > 2,5 ... 4 ppm eine deutliche Zähigkeitsabnahme bewirken und vor allem hochfeste Zustän-de in diesem Fall bei Raumtemperatur vollständig verspröden.

Mit dem einachsigen Zugversuch wurden die mechanischen Eigenschaften verschie-dener unbestrahlter und vor allem bestrahlter, mit Wasserstoff beladener RDB-Stähle bestimmt. Das Ziel der Untersuchungen bestand darin, einen potenziellen Zusam-menhang von Versprödungseffekten infolge Neutronenbestrahlung und Wasserstoff aufzudecken. Fraktografische Untersuchungen der Bruchflächen ergänzten das Pro-gramm. Mit SANS-Untersuchungen sollte überprüft werden, ob die Strahlendefekte als Haftstellen für den Wasserstoff wirksam werden.
Für die mechanischen Untersuchungen standen T3-Kleinzugproben der RDB-Stähle A 533 B cl.1, A 508 cl.3 und 15Kh2MFA (KAB, Skoda) im bestrahlten und unbestrahl-ten Zustand zur Verfügung. Die Proben wurden elektrolytisch im simulierten Reak-tordruckwasser bis zur Sättigung mit Wasserstoff beladen. Die Zugversuche wurden bei RT und 250°C und verschiedenen Dehnraten durchgeführt.

Das Verformungsverhalten der bis zu hohen Neutronenfluenzen und bei reak-torbetriebsnahen Temperaturen bestrahlten RDB-Stahlmarken bzw. –chargen des Untersuchungsprogrammes wird nicht signifikant durch eine Wasserstoff-vorbeladung beeinflusst. In Übereinstimmung damit liefern auch SANS-Messungen keinen Hinweis auf eine Wechselwirkung zwischen dem strukturellen Strahlendefekt und den Wasserstoffatomen. Die SANS-Methode erwies sich aber als geeignet, Wasserstoffeinlagerungen in RDB-Stählen zu detektieren.
Ein deutlicher Versprödungseffekt der Wasserstoffvorbeladung tritt nach Bestrahlung bei niedrigerer Temperatur auf. Das Ergebnis zeigt, dass der Typ der Strahlendefek-te entscheidend für die Effektivität der Defekt-Wasserstoff-Wechselwirkung ist. Die bisherigen Ergebnisse haben sich vorzugsweise auf Proben konzentriert, bei denen die Strahlendefekte vor allem mit dem Typ der Cu-reichen Ausscheidungen identifi-ziert werden müssen. Im weiteren werden Proben mit Strahlendefekten des sog. Matrixtyps (Leerstellenkomplexe) untersucht, um die Frage zu beantworten, ob unter bestimmten Bestrahlungsbedingungen ein sicherheitsrelevanter Versprödungseffekt von Wasserstoff nicht auszuschließen ist.

Keywords: Wasserstoffversprödung; RPV-Stahl; Zähigkeit; einachsige Zugversuche; Fraktographie; Abdruckverfahren

  • Contribution to proceedings
    Proceedings CD, Vortrag, 3. Workshop Kompetenzverbund Kerntechnik 8. Oktober 2003

Publ.-Id: 6068

Optimizing Nanocrystal Synthesis For Multi-Dot Floating Gates of Novel Nonvolatile Memories

Müller, T.; Heinig, K.-H.

The synthesis of a single monolayer of nanocrystals (NCs) with a maximum density but no in-plane electrical percolation paths is a challenging task. Such layers are required for the fabrica-tion of multi-dot nonvolatile memories. Here, compared to the conventional nonvolatile memory, the floating gate is replaced by a layer of Si NCs allowing for distributed charge storage and, therefore, lower operation voltages, faster programming, etc. These advantages are lost at too high NC densities when NC’s charge can spread over neighboring NCs by electron tun-neling, i.e. due to electrical in-plane percolation paths.
In this contribution, studies on the synthesis of Si NCs by low energy Si+ implantation into thin gate oxides of NC memories are presented. Using a kinetic 3D lattice Monte Carlo code, the nucleation, growth and Ostwald ripening of the Si NCs in Si supersaturation is simulated. On the basis of these simula-tions, the dependence of the Si NC density, the distribution of the NC spacing as well as the threshold for extended electron tunneling paths are predicted. Thus, process conditions could be identified, where NCs align in a thin layer at high density but sufficient electrical isolation.

  • Lecture (Conference)
    E-MRS Spring Meeting 2003, Symposium E: Ion beams for nanoscale surface modifications, Strasbourg, France, June 10 - 13, 2003

Publ.-Id: 6067

Basic processes in deposition and annealing of ta-C films as predicted by molecular-dynamics simulations

Jäger, H. U.; Belov, A. Y.

The results of classical molecular-dynamics simulations of amorphous carbon films are reviewed. An analytic interatomic potential of Brenner was adopted, but with an increased C-C interaction range. Deposition of films with a thickness of up to 10 nm was simulated for ion energies Eion=10-80 eV and for a wide range of substrate temperatures. The thermodynamically favoured structural transformations in these films during post-deposition annealing at low temperatures (less than ~600 °C) were carefully examined. The approach used describes quite accurately the properties of highly tetrahedral amorphous carbon (ta-C) films, overestimating, however, density of graphitic films, since the potential does not account for the long-range repulsion between non-bonded pi-orbitals.

The film deposition simulations revealed a short-term temperature-dependent relaxation stage (t~70-1000 fs), where the film formation is considerably influenced by substrate temperature Ts. During this stage, depending on Ts, the carbon atoms coming to rest at metastable highly coordinated sites can relax to either three- or fourfold coordinated positions. In agreement with experiment the molecular-dynamics simulations predict a sharp (within the range of about 50 K) transition from ta-C to graphitic carbon as Ts exceeds a critical temperature Tc. The as-deposited ta-C films contain many small clusters (mostly pairs) of sp2 bonded atoms, but some extended sp2 networks are also found in the films. The ring statistics within these networks will be presented.

During low-temperature annealing the potential energy and stress of the as-deposited ta-C films are released with only minor changes in the short-range order and density. It is demonstrated that as a result of annealing the volumes of sp3 atoms decrease, which is consistent with experiment. The change of potential energy with annealing time can be fit by an exponential function, which enables to analyse the relaxation kinetics in ta-C, in particular, to obtain the dependence of the relaxation time on annealing temperature.

  • Invited lecture (Conferences)
    5th Specialist Meeting on Amorphous Carbon,ITC-irst, Sept. 9-10, 2004, Povo-Trento, Italy

Publ.-Id: 6066

Complex Formation of Curium with Adenosine 5’-Triphosphate (ATP) Studied by TRLFS

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

We investigated for the first time the complex formation of curium(III) with adenosine 5’-triphosphate (ATP) by time-resolved laser fluorescence spectroscopy (TRLFS). The interaction between soluble species of curium(III) with ATP was studied at trace Cm(III) concentrations (10-7 M), at different concentrations of ATP and at different pH using 0.154 M NaCl as background electrolyte. Predominant 1:1 complex formation reactions were observed. Taking the dissociation of H4ATP into consideration, we found evidence for the existence of three Cm – ATP species: CmH2ATP+, CmHATP and CmATP-.

Keywords: Curium; TRLFS; Complexation; ATP

  • Poster
    Sixth International Conference on Nuclear and Radiochemistry (NRC 6), 29 August to 3 September 2004, Aachen, Germany
  • Contribution to proceedings
    Sixth International Conference on Nuclear and Radiochemistry (NRC 6), 19.08.-03.09.2004, Aachen, Germany

Publ.-Id: 6065

Redox Stability of Uranium(VI) in Presence of Synthetic and Natural Humic Acids

Sachs, S.; Geipel, G.; Bernhard, G.

Based on the oxidation of phenolic compounds (e.g., hydroquinone, catechol) we developed synthetic HA model substances with pronounced redox functionalities in order to study the redox behavior of HA and the redox stability of actinide humate complexes. In the present work we studied the redox stability of U(VI) humate complexes applying these synthetic HA in comparison to purified natural HA from Aldrich.

Keywords: humic acids; complex formation; uranium; redox stability; laser-induced photoacoustic spectroscopy

  • Poster
    12th International Meeting of the International Humic Substances Society. 26.-30. Juli 2004, Sao Pedro, Brazil.
  • Contribution to proceedings
    12th International Meeting of the International Humic Substances Society, 25.-30.07.2004, Sao Pedro, Sao Paulo, Brazil
    Humic Substances and Soil and Water Environment, 172-174

Publ.-Id: 6064

Thermochromatographic Volatility Studies of Actinide Oxides

Hübener, S.; Bernhard, G.; Fanghänel, T.

The volatility of plutonium oxides in the O2-H2O(g)/SiO2(s) system has been studied by thermo-chromatography in the temperature range 1475 to 600 K. Oxides of thorium, protactinium, uranium, neptunium, and americium in trace amounts have been studied for comparison. Oxide samples containing 105 – 1016 actinide atoms were heated in the starting position of the ther-mochromatographic silica columns. Mixtures of helium, oxygen and water vapor were applied as reactive mobile gas phase. Resulting from thermochromatography the volatile actinide spe-cies are deposited in the column downstream, thus creating inner chromatograms along a temperature gradient. At the end of each experiment the actinide chromatograms were meas-ured by alpha spectrometry. Gamma spectrometry was used to measure protactinium.
Plutonium was found to be volatile in humid oxygen at temperatures above 1300 K. The Pu volatility is lower than that of uranium, but higher as one would expect for stable Pu(IV) which is nonvolatile under the applied experimental conditions. The Pu volatility is assigned to PuO2(OH)2(g). The experimental results give evidence of the oxidation of PuO2 and NpO2 to higher oxides by moist oxygen.

Keywords: plutonium dioxide; oxidation; actinide oxide hydroxide; volatility; thermochromatography

  • Poster
    Sixth International Conference on Nuclear and Radiochemistry, 29.08.-03.09.2004, Aachen, Germany
  • Contribution to proceedings
    Sixth International Conference on Nuclear and Radiochemistry, 29.08.-03.09.2004, Aachen, Germany

Publ.-Id: 6063

Determination of Effective Diffusion Parameters in Compacted Kaolinite

Mibus, J.; Lambarki, M.; Küchler, R.

Clay minerals are main components of many soils, sediments, pelitic rocks, as well as fracture filling material in crystalline rocks. Furthermore, clays are used in geo-engineering, particularly to design hydraulic and geochemical barriers in contaminated sites, landfills or underground repositories for toxic or nuclear wastes. Due to the low permeability of clay molecular diffusion is the main transport mechanism of dissolved or colloidal substances at natural hydraulic gradients. This process has to be studied to assess the long-term behavior of geoengineered barrier systems.
In order to determine effective transport parameters in kaolinite diffusion experiments with a conservative tracer were performed. Kaolinite from Hirschau (Germany) was filled in a diffusion cell (cross sectional area 78.6 cm2, layer thickness 1.8 cm), compacted to a dry density of 1.1 g cm-3 and fixed between two filter plates. The through-diffusion of tritiated water (HTO) was observed applying a tracer reservoir with a starting activity of 4·105 Bq in 100 mL. The tracer activities of the high and the low concentration side were measured in intervals by liquid scintillation counting.
An analytical solution of the one dimensional transport equation was developed to determine the diffusion coefficient and the effective porosity. Two variable boundary conditions accounted for the changing concentrations in the transient phase.
A diffusion coefficient of De = 3.2·10-10 m2s-1 and an effective porosity of e = 0.6 were determined from the measured concentration versus time. These results are compared with stationary diffusion experiments using reactive tracers (Cu2+, Zn2+ Pb2+, AsO43-) and natural sealing material (loess loam) and kaolinite (Hamad, 2003). For instance, in loess loam De was found to be 2.47, 3.04, and 4.14·10-10 m2s-1 for Cu, Pb, and Zn, respectively. These results indicate that the diffusion parameters in the natural and the engineered barrier material are in the same order of magnitude.

  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 68(2004)11, A165.
  • Poster
    Goldschmidt Conference 2004, Copenhagen
  • Contribution to proceedings
    14th Goldschmidt Conference 2004, 05.-11.06.2004, Copenhagen, Denmark

Publ.-Id: 6062

Subthreshold antiproton production in pC, dC and αC reactions

Müller, H.; Komarov, V. I.

Data from KEK on subthreshold bar{p} as well as on π± and K±production in pC, dC and αC reactions at energies between 3.5 and 12.0~AGeV are described for the first time within a unified approach. We use a model which considers a nuclear reaction as an incoherent sum over collisions of varying numbers of projectile and target nucleons. It samples complete events and thus allows for the simultaneous consideration of all final particles including the decay products of the nuclear residues. The enormous enhancement of the bar{p} cross section as well as the moderate increase of meson production in dC and αC compared to pC~reactions is well reproduced. In our approach, the observed enhancement near the production threshold is mainly due to the contributions from the interactions of few-nucleon groups.

Keywords: Nuclear eaction models and methods; Monte Carlo simulations; Nucleon-induced reactions; 2H-induced reactions; 3H-, 3He-, and 4He-induced reactions

Publ.-Id: 6061

Shape parameters of the participant source in Ru + Ru collisions at 400 AMeV

Bastid, N.; Dupieux, P.; Benderag, A.; Barret, V.; Crochet, P.; Lopez, X.; Alard, J. P.; Andronic, A.; Basrak, Z.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Devismes, A.; Dzelalija, M.; Finck, C.; Fodor, Z.; Gasparic, I.; Gobbi, A.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kang, D.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Leifels, Y.; Manko, V.; Matulewicz, T.; Merschmeyer, M.; Moisa, D.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; de Schauenburg, B.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolarkiewicz, M. M.; Smolyankin, V.; Soliwoda, I. J.; Stockmeier, M. R.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Yushmanov, I.; Zhilin, A.

New results on nuclear collective flow are presented for central and semi-central Ru + Ru collisions at 400 AMeV measured with the FOPI detector at GSI Darmstadt. The source shape parameters, flow angle and aspect rations, are extracted from Gaussian fits to in-plane and out-of-plane momentum distributions. The orientation and the shape of the source exhibit different trends according to the investigated phase space region. The shape parameters of the participant source are studied as a function of the particle mass and collision centrality. The flow angle is found to be independent of the particle mass. Both the flow angle and the aspect ratios depend sensitively on the impact parameter. Detailed comparisons with the predictions of the Isospin Quantum Molecular Dynamics model are performed. It is shown in particular that the source shape parameters permit to extract information on the in-medium nucleon-nucleon cross section.

Publ.-Id: 6060

Validation of Eulerian Multiphase Flow Models for Nuclear Safety Applications

Frank, T.; Shi, J.-M.; Burns, A.

The CFD package CFX-5 has been used to predict the development of upward directed gas-liquid flows in a vertical pipe. Under the assumption of monodisperse bubbles the dilute gas-liquid flow has been predicted using the Eulerian framework of multiphase flow modeling. The capabilities of the CFX-5 flow solver have been extended by taking into account additional non-drag forces like lift, turbulent dispersion and wall lubrication forces. Range of applicability and accuracy of the numerical model have been validated against measured gas void fraction profiles obtained at the MT-Loop test facility of the Forschungszentrum Rossendorf (FZR) in the bubbly flow regime. Best agreement of numerical results with experimental data could be obtained for a wide range of experimental conditions, if Menter s k-w Shear Stress Transport (SST) turbulence model has been used in combination with the Favre averaged drag (FAD) turbulent dispersion force model as derived by Burns [1]. Furthermore results of extensive numerical experiments [2] for the examination and comparison of different model formulations for the wall lubrication and turbulent dispersion forces are presented in this paper.

Keywords: Lift force; turbulence dispersion force; wall lubrication force; turbulence model; grid dependence analysis

  • Contribution to proceedings
    3rd International Symposium on Two-Phase Flow Modeling and Experimentation, 22.-24.09.04, Pisa, Italy
    Conference Proceedings CD-ROM, 1-9

Publ.-Id: 6059

Numerical investigations of insulation debris transport phenomena in water flow

Krepper, E.; Grahn, A.

The investigation of insulation debris generation, transport and sedimentation gains importance regarding the reactor safety research for PWR and BWR considering all types of LOCA as well as short and long term behavior of emergency core coolant systems.
A common project in cooperation with IPM-Zittau deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow (see ref. 1). The activities are funded by the German Federal Ministry of Economy and Technology. While experiments are performed at the IPM-Zittau, theoretical work is concentrated at Forschungszentrum Rossendorf.
In the present paper the basic concepts are described and first feasibility studies are shown. During the ongoing work further results are expected.

Keywords: nuclear power reactor; insulation debris; computational fluids dynamics; two-fluid approach

  • Lecture (Conference)
    Debris Impact on Emergency Coolant Recirculation, Workshop Proceedings, 25.-27.02.2004, Albuquerque, NM, United States
  • Contribution to proceedings
    Debris Impact on Emergency Coolant Recirculation, Workshop Proceedings, 25.-27.02.2004, Albuquerque, NM, United States, OECD 2004/NEA No 5468, 271-229

Publ.-Id: 6058

Experimental and Numerical Studies of Void Fraction Distribution in Rectangular Bubble Columns

Krepper, E.; Reddy Vanga, B. N.; Prasser, H.-M.; Lopez De Bertodano, M.

Bubbly flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. The presence of a second phase, re-circulating flow, instabilities of the gas plume and turbulence, complicate the hydrodynamics of bubble column reactors. This paper describes experimental and numerical results obtained in a rectangular bubble column with a cross-sectional area of 20 cm2. Images obtained from a high speed camera have been processed to calculate bubble velocities, bubble turbulence parameters and bubble size distributions. Gas disengagement technique was used to obtain the volume averaged gas fraction over a range of superficial gas velocities. A wire mesh sensor was applied, to measure the local volume fraction. Numerical calculations were performed with an Eulerian-Eulerian two-fluid model approach using the commercial code CFX.
The paper details the effect of various two-fluid model interfacial momentum transfer terms on the numerical results. The inclusion of a lift force was found to be necessary to obtain a global circulation pattern and local void distribution that was consistent with the experimental measurements. The nature of the drag force formulation was found to have significant effect on the quantitative volume averaged void fraction predictions.

Keywords: Bubble column; experiments; wire mesh sensor; high speed video camera CFD; drag bubble forces; non-drag bubble forces

  • Lecture (Conference)
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy
  • Contribution to proceedings
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy, paper MS11

Publ.-Id: 6057

The integral equation approach to kinematic dynamos in finite domains

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

The usual method to treat kinematic dynamos numerically is to solve the induction equation. For celestial bodies of spherical shape, like the Earth and the Sun, the boundary conditions for the magnetic field can be formulated separately for every degree and order of the spherical harmonics. However, there are a number of aspherical dynamos as, e.g., galactic dynamos and the laboratory dynamos in Riga, Karlsruhe and Cadarache, for which the correct handling of the non-local boundary conditions is a notorious problem. Several methods have been used to deal with this problem, including the use of simplified local boundary conditions, the embedding of the very dynamo region into a spherical region with lower conductivity, or the full solution of the Laplace equation in the exterior.
An alternative way to implement the correct boundary conditions is based on Biot-Savart's law. We present the general formulation of the integral equation approach to both steady and time-dependent dynamos. For spherical dynamos we show the numerical equivalence of this approach with the differential equation approach. The suitability of the method to cope with dynamo problems in arbitrary finite domains is exemplified by the treatment of mean-field dynamos in rectangular boxes.
For flows with small magnetic Reynolds numbers, that are exposed to an external magnetic field, the integral equation approach can be cast into a linear inverse problem for the determination of the flow velocity from externally measured induced magnetic fields. This inverse problem is the basis of the "Contactless Inductive Flow Tomography" (CIFT) which has been demonstrated in a recent experiment. In a cylindrical vessel filled with InGaSn a flow is produced by a motor driven propeller. The moving liquid is exposed alternately to an axial and an transversal magnetic field. The two corresponding sets of induced magnetic fields measured at 49 external Hall sensors are processed in an inverse problems solver to give a rough, but reliable, picture of the flow.

  • Lecture (others)
    Joint meeting of COST-P6-Working Group 1 and CNRS-GDR "Dynamo" , 22.-23.01.2004, Paris, France

Publ.-Id: 6056

Incorporation of nitrogen in thin tantalum films using plasma immersion ion implantation

Peikert, M.; Wieser, E.; von Borany, J.; Reuther, H.; Dittmar, K.; Gehre, D.

The incorporation of nitrogen into thin (10 nm) Ta layers using plasma immersion ion implantation (PIII) have been studied. PIII was carried out using a low-pressure (0.3 Pa) plasma and ion energies between 6 and 25 keV. The depth distributions of nitrogen were measured by Auger Electron Spectroscopy and compared with those obtained by numerical simulations (Profile Code). The experimental profiles do not show a maximum at the projected range of the implanted ions, but a high nitrogen concentration at the surface decreasing into depth. The influence of implantation parameters such as high-voltage pulse rise and fall times, voltage amplitude, and plasma pulsing on the shape of the nitrogen profile is investigated and discussed.

Keywords: Plasma immersion ion implantation; Tantalum; Diffusion Barrier

  • Surface & Coatings Technology, 200(2005)(7), p. 2253-2259

Publ.-Id: 6053

Colloid-borne uranium in an abandoned uranium mine in the stage of flooding

Ulrich, K.-U.; Zänker, H.; Jenk, U.

Abandoned uranium mines which underwent or just undergo flooding may represent a severe source of radioactive contaminants against groundwater, surface water, and the atmosphere. The uranium mines operated until 1990 in Saxony and Thuringia left a total void volume of more than 100 million m3 to be flooded. Prognosis of radionuclide emission via the water path needs detailed knowledge about the hydrological regime of the mine and the speciation of the contaminants. The adsorption of radionuclides on colloidal phases may stimulate or delay their transport and migration. Neglecting the colloidal phases may have the following consequences on environmental hazard prognosis:

a) The radionuclide is fully mobile, i.e. it is not adsorbed onto solid phases: colloidal transport is irrelevant and the model description is correct.
b) The radionuclide is regarded as fully mobile in the model, but it adsorbs on colloids which aggregate and settle (‘natural attenuation’): the prognosis is too pessimistic.
c) The radionuclide is regarded as immobile in the model due to adsorption on the host rock, but in part it adsorbs on colloids which are transported: the prognosis is too optimistic.
Based on their chemical and colloidal composition, mine waters usually range between the following water types:
i) Type ‘acid pore water’ (acid rock or mine drainage, sometimes called ‘yellow boy’): Very acidic (pH 1-3) and usually anoxic waters with a high salt loading.
ii) Type ‘bulk water’: Near-neutral, oxic or suboxic waters with a moderate salt loading, typically represented by gallery or adit water.
Mine flooding is accompanied with a transition of type (i) into type (ii) water, which is crucial for colloid-chemical processes changing the partitioning of heavy metals and radionuclides. Due to pH increase and access of oxygen, colloids of Fe(III) and Al compounds are formed known to adsorb trace metals.
To assess the uranium migration in the stage of flooding and afterwards, we performed neutralization experiments by mixing acid floodwater from an uranium mine with oxic groundwater from an aquifer above the mine and studied the formation and composition of colloids as well as the adsorption of uranium onto these colloids by using spectroscopic methods.

Keywords: mine flooding; acid mine drainage; groundwater; neutralization experiment; uranium mobility; adsorption; colloids; ironoxyhydroxides; ferrihydrite; tangential flow ultrafiltration; XAFS spectroscopy

  • Contribution to external collection
    Qaim, S.M., Coenen, H.H. (Eds.), Advances in Nuclear and Radiochemistry, Extended Abstracts of NRC 6, Schriften des Forschungszentrums Jülich, Reihe Allgemeines und Interdisziplinäres 3(2004), 645-647
  • Lecture (Conference)
    Sixth International Conference on Nuclear and Radiochemistry (NRC 6), 29.08.-03.09.2004, Aachen, Germany

Publ.-Id: 6052

Capability of SCM and RES3T Database for Blind Predictions

Richter, A.; Brendler, V.

The paper presents the general strategy and an example for the current blind predictive capabilities of surface complexation models (SCM) and the respective database RES3T - the "Rossendorf Expert System for Surface and Sorption Thermodynamics"[1]. The approach for the elucidation of numerical data includes the collection of the mineral surface characteristics, the selection of reliable data records, the extrapolation to infinite dilution, the normalization to a reference site density and the averaging of selected thermodynamic data records.
The copper(II) sorption onto goethite was chosen as system illustrating the blind predictive capabilities. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected accounting for electrostatics. The calculations were performed with FITEQL code [2].
The model prediction represents the experimental values for the adsorbed amount of Cu(II), expressed as conventional distribution coefficients KD as required by most performance assessment software, within one order of magnitude or better.

  • Lecture (Conference)
    SOPRO 2004, 25.-26.03.2004, Karlsruhe, Germany
  • Contribution to proceedings
    SOPRO 2004, 25.-26.03.2004, Karlsruhe, Germany
    Proceedings, 127-131

Publ.-Id: 6051

Multi-Dot Floating-Gates in MOSFETs for Nonvolatile Memories - Their Ion Beam Synthesis and Morphology

Müller, T.; Bonafos, C.; Heinig, K.-H.; Tencé, C.; Coffin, H.; Cherkashin, N.; Ben Assayag, G.; Schamm, S.; Zanchi, G.; Colliex, C.; Möller, W.; Claverie, A.

Scalability and performance of current flash memories can be improved substantially by novel devices based on Multi-Dot Floating Gate MOSFETs. The multi-dot layer in the very thin gate oxide can be fabricated CMOS-compatibly by ion beam synthesis (IBS). Here, we present both experimental and theoretical studies on IBS of multi-dot layers consisting of Si nanocrystals (NCs). The NCs are produced by ultra low energy Si ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this su-persaturation leads to phase separation of the excess Si from the SiO₂. Till now, the study of this phase separation suffered from the weak z contrast between Si and SiO₂ phases in Transmission Electron Microscopy (TEM). Here, this imaging problem is solved by Energy Filtered Scanning Transmission Electron Microscopy (EFSTEM). Additionally, kinetic lattice Monte Carlo simula-tions of Si phase separation have been performed and compared with EFSTEM images. It has been predicted theoretically that the morphology of the multi-dot Si floating gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These pat-tern agree remarkably with EFSTEM images. However, the predicted fluence for spinodal pattern is lower than the experimental one. Because oxidants of the ambient atmosphere penetrate into the as-implanted SiO₂, a substantial fraction of the implanted Si is lost due to oxidation.

Publ.-Id: 6050

Angewandte Medieninformatik: Workshop Digitale Fotografie

Joehnk, P.

  • Lecture (others)
    Hochschule Anhalt, Köthen, Fachbereich Informatik gehalten am 20.1.2004

Publ.-Id: 6049

Control of Separated Flows by Time Periodic Lorentz Forces

Weier, T.; Gerbeth, G.

Electromagnetic, i.e. Lorentz forces, may be used to influence the flow of electrically conducting fluids. The present paper investigates the application of time periodic Lorentz forces to the control of the suction side flow on a NACA 0015 hydrofoil.
Experimental results, consisting of flow visualizations and force measurements, characterizing the control effect in the low Reynolds number range of 10^4 < Re < 10^5, are presented. A comparison of the forcing effect with stationary Lorentz forces on one hand and conventional oscillatory blowing on the other hand is given as well.

  • European Journal of Mechanics B23(2004)6, 835-849

Publ.-Id: 6048

Non-normal nonlinear transition to turbulence in a magnetically driven swirling flow

Grants, I.; Gerbeth, G.

It is well-known that several shear flows become turbulent far below their linear stability limit. The transition to turbulence is triggered by unavoidable finite-amplitude disturbances. Although all infinitesimal disturbances eventually decay, their amplitude can grow temporarily. The lower limit of the control parameter when the amplitude of disturbances can grow initially is called limit of energetical instability [1]. As a rule, this limit considerably underestimates the threshold when the transition to turbulence is observed experimentally in various shear flows. Only recently certain clues of theoretical prediction of the phenomenon of non-linear non-normal transition have been found [2]. However, a routine method to predict this so-called non-normal non-linear transition is still a challenge.
We consider the flow of an electrically conducting melt driven by a rotating magnetic field (RMF) in a cylindrical cavity. Our numerical analysis evidenced that the intermittency route may take place also for this example of a rotating flow [3]. A pronounced flow sensitivity and additional unstable saddle type steady solutions have been detected at control parameters several times below the critical value for the onset of linear axisymmetric instability. The presence of such additional solutions is a sign of a possible non-linear non-normal transition due to finite perturbations despite the linear stability of the basic flow.
We present experimental and numerical results for the transition to turbulence in the RMF driven flow in a cylindrical cavity. The experimental approach is based on a non-invasive examination of the sensitive flow field by hanging the cavity on a torsion wire [4]. Under carefully prepared, clean conditions the occurrence of first flow oscillations was observed at a control parameter close to the linear stability threshold. If an artificial perturbation like a thermocouple was installed at the inner cavity wall, the transition was observed at a considerably lower forcing in the linearly stable parameter range. Examples of the typically intermittent onset of transition will be given. The numerical results will comprise the linear stability analysis based on a highly accurate spectral method and, in particular, the investigation of additional unstable steady solutions. Current evidence suggests that the lowest possible control parameter for the non-linear transition may be reasonably associated with the first bifurcation of such solutions. Indeed, a good quantitative agreement was found between experiments and numeric for the value of this global stability threshold.
Further results will be presented for the linear as well as global stability limits if the RMF driven flow in the cylinder is additionally exposed to a heating from below or a superimposed steady magnetic field. The latter typically delays the transition. The stability analysis of such flows is of particular interest in crystal growth technologies from the melt, for which the occurrence of a turbulent flow should often be prevented.

[1] D. D. Joseph, Stability of Fluid Motions Vol. I, Springer, Berlin, 1976.
[2] S. Grossmann, The onset of shear flow turbulence, Rev. Mod. Phys. 72, 603, 2000.
[3] I. Grants, G. Gerbeth, Stability of axially symmetric flow driven by a rotating magnetic field in a cylindrical cavity, J. Fluid Mech. 431, 407, 2000.
[4] I. Grants, G. Gerbeth, Experimetal study of non-normal nonlinear transition to turbulence in a rotating magnetic field driven flow, Phys. Fluids 15, 2803, 2003.

  • Lecture (Conference)
    10th European Turbulence Conference, 29.06.-02.07.2004, Trondheim, Norway
  • Contribution to proceedings
    10th European Turbulence Conference, 29.06.-02.07.2004 Trondheim, Norway, H.I. Andersson, P.-A. Krogstad (Eds.): Advances in Turbulence X, 161-164

Publ.-Id: 6047

Depth profiling of ZrO2/SiO2/Si stacks - a TOF-SIMS and computer simulation study

Ignatova, V. A.; Conard, T.; Möller, W.; Vandervorst, W.; Gijbels, R.

This study is dedicated to a better understanding of the processes occurring under ion bombardment of ultra-thin ZrO2/SiO2/Si gate dielectric stacks. Complex-shaped depth profiles were obtained by using TOF-SIMS with dual beam (500 eV for sputtering and 10 keV for analysis) Ar+ ions. The SIMS intensities of all the elements depend critically on the amount of oxygen at any moment of the sputtering process. Increased intensity is observed at the surface and at the ZrO2/SiO2 interface. A long tail of the Zr signal is present in the Si substrate, even after the second (SiO2/Si) interface, and a double bump structure in the 90Zr and ZrO dimer is observed, which is more pronounced with increasing thickness of the interfacial SiO2 layer.

Computer simulations using the dynamic Monte Carlo code (TRIDYN) are performed in order to distinguish the ion-bombardment-induced effects from changes in the ionization degree. The original code is extended with simple models for the ionization mechanism and for the molecular yield during sputtering. Oxygen preferential sputtering at the surface and ballistic transport of Zr towards and through the interface are clearly demonstrated, but there is also evidence that due to recoil implantation oxygen gets piled-up near the ZrO2/SiO2 interface.

Publ.-Id: 6046

Intrinsic stress and preferred orientation in TiN coatings deposited on Al using plasma immersion ion implantation assisted deposition

Mukherjee, S.; Prokert, F.; Richter, E.; Möller, W.

TiN coatings were deposited on Al substrates using the plasma immersion ion implantation and deposition (PIIIAD) technique, employing a filtered Ti cathodic arc in a nitrogen atmosphere. Negative pulsed bias voltages between 0 to –4.0 kV were applied with varying duty cycles, at a constant time-averaged bias. Stress measurements using X-ray diffraction reveal an increase and then a decrease in the intrinsic compressive stress at increasing on-time bias. A bias dependent preferred orientation of TiN is observed i.e., {111}, {200} and {220} at low bias and predominantly {200} at higher bias. The hardness reduces from 29 GPa at lower bias to 20 GPa at higher bias. Thus, the time averaged energy of ion bombardment does not uniquely determine the properties of the growing coating, which can be adjusted by the on-time substrate bias applied for very short durations. A subplantation model of stress development is applied to explain the results.

Publ.-Id: 6045

Neptunium(V) sorption onto granite and its mineral constituents in the absence and presence of humic acid

Schmeide, K.; Bernhard, G.

The sorption of neptunium(V) onto granite and its main mineral constituents quartz, orthoclase, albite, biotite, and muscovite is studied under anaerobic conditions as a function of pH in a series of batch equilibrium experiments. Furthermore, the effect of humic acid on the neptunium(V) sorption is studied applying a 14C-labeled synthetic humic acid (type M42) for the experiments. The data suggest that the neptunium sorption onto granite is affected by both the pH and the presence of organic material. In the absence of humic acid, the neptunium sorption starts between pH 7 and pH 8 and increases with increasing pH value. Due to addition of humic acid the neptunium sorption onto granite is decreased in the neutral to alkaline pH range, which is attributed to complexation of neptunium by humic acid in solution. Thus, in this pH range the neptunium mobility is increased by humic substances. The neptunium(V) sorption onto granite and onto its mineral constituent biotite is nearly equal, suggesting that the sorption of neptunium(V) is controlled by the minor amount of biotite which, however, is reactive.

Keywords: neptunium; humic acid; sorption; reduction

  • Contribution to external collection
    Humic Substances in Performance Assessment of Nuclear Waste Disposal : Actinide and Iodine Migration in the Far-Field. Second Technical Progress Report, Wissenschaftliche Berichte FZKA 6969, Forschungszentrum Karlsruhe, Karlsruhe 2004, 85-94

Publ.-Id: 6044

Comparative Study of Charge Trapping in High-Dose Si and Ge-Implanted Al/SiO2/Si Structures

Nazarov, A.; Skorupa, W.; Osiyuk, I. N.; Tjagulskii, I. P.; Lysenko, V. S.; Yankov, R. A.; Gebel, T.

We have studied the trapping of negative and positive charge in Si-implanted SiO2 layers of Al/SiO2/Si-based devices during high-field electron injection from the Si substrate under conditions typically used for obtaining electroluminescence. The location, capture cross-section and concentration of negatively and positively charged traps have been determined in dependence on the time of heat treatment by rapid thermal annealing (RTA). A comparison between the results obtained from Si- and Ge-implanted oxide layers has been made. It has been shown that in the case of Si-rich oxides an increase in the RTA time leads to the formation of hole and electron traps of high concentration, both of which are located within the oxide. For Ge-rich oxide layers, however, the hole traps are found primarily in the vicinity of the SiO2/Si interface while the electron traps are present within the oxide. The nature of these traps has been discussed.

Keywords: charge trapping; ion implantation; silicon; germanium; electroluminescence; silicon dioxide; trapping cross section

  • Journal of the Electrochemical Society 152(2005)2 F20

Publ.-Id: 6042

Comparison of two HSV1-tk-based approaches for PET of cardiac transgene expression

Miyagawa, M.; Simoes, M. V.; Städele, C.; Haubner, R.; Reder, S.; Lehner, T.; Noll, S.; Noll, B.; Grote, M.; Gambhir, S. S.; Gansbacher, B.; Schwaiger, M.; Anton, M.; Bengel, F. M.

Objectives: PET imaging of cardiac reporter gene expression holds promise for noninvasive monitoring of gene therapy. Two approaches based on herpesviral thymidine kinase gene(HSV1-tk) habe been applied. Wild-type HSV1-tk was imaged with 2´-fluoro-2´-deoxy-5[124I]-iodo-arabinofuranosyluracil([124I]FIAU), and mutant HSV1-sr39tk was imaged with 9-[4-[18F]-fluoro-3-(hydroxymethylbutyl)guanine([18F]FHBG).
Methods: Adenovirus expressing wild-type HSV1-tk(Adtk), mutant HSV1-sr39tk (Adsr39tk), or control gene (AdLacZ) were directly injected into myocarcardium of 24 rats and 8 pigs. Two days later, dynamic PET imaging was performed for 120 min after injection of [124I]FIAU or [18F]FHBG with a clinical scanner. Imaging with [13N]-ammonia was performed to identify cardiac regions of interest. Pig hearts were sliced into 5 short-axis slices for ex vivo imaging, and regional tracer uptake was analyzed.
Results: For [124I]FIAU, the largest difference of cardiac uptake between Adtk rats and controls was found at 10-30 min after injection (1.7±0.25 vs 0.87±0.22 %dose/ml, p=0.035). No difference was observed at later imaging times due to [124I]FIAU washout. For [18F]FHBG, difference between Adsr39tk rats and controls continuously increased over time and was largest at 105-120 min (1.45±0.45 vs 0.35±0.05 %dose/ml, P=0.0066). Global cardiac reporter probe kinetics in rats was confirmed by regional myocardial analysis in pigs. Transgene expression was specifically visualized by both approaches. Highest target/background ratio of [124I]FIAU in Adtk infected myocardium was 1.50±0.20 vs 2.64±0.49 for [18F]FHBG in Adsr39tk infected areas (P=0.01). In vivo results of rats were confirmed by ex vivo counting and autoradiography. In vivo segmental reporter probe uptake in pigs correlated well with those in ex vivo images.
Conclusions: Both combinations were feasible for PET of cardiac transgene expression in different species. Specific probe kinetics suggests different myocardial handling of pyrimidine ([124I]FIAU) and acycloguanosine ([18F]FHBG) derivatives. Results are in favour of [18F]FHBG because of continuous accumulation over time and higher imaging contrast.

  • Lecture (Conference)
    51st Annual Meeting, Society of Nuclear Medicine Philadelphia, 19.-23.06. 2004, Philadelphia, USA

Publ.-Id: 6041

Coexpression of Herpesviral Thymidine Kinase Reporter Gene for Nonivasive Monitoring of Therapeutic Gene Transfer - In Vivo- and Initial In Vivo-Evaluation

Anton, M.; Wittermann, C.; Haubner, R.; Simoes, M.; Reder, S.; Essien, B.; Wagner, B.; Henke, J.; Erhardt, W.; Noll, S.; Hackett, N. R.; Crystal, R. G.; Schwaiger, M.; Gansbacher, B.; Bengel, F. M.

Background: Coexpression of a reporter gene and therapeutic gene may allow for non-invasive monitoring of cardiac gene therapy. We sought to evaluate the usefulness of an adenoviral vector expressing mutant herpesviral thymidine kinase reporter gene(HSV1-sr39tk) and VEGF121 in independent expression cassettes(Ad4tk).
Methods and Results: Accumulation of [14C]FIAU and [18F] FHBG as reporter probes, and VEGF secretion into medium were determined for Ad4tk-infected H9c2 rat cardiac cells in vitro. Tracer uptake increased with increasing vector concentration and over time, and was comparable to cells infected with adenovirus expressing only wild-type HSV1-tk(reporter probe: [14C]FIAU) or mutant HSV1-sr39tk(reporter probe: [18F]FHBG). No significant uptake was observed in uninfected cells or cells infected with adenovirus expressing VEGF alone. With increasing vector concentration, Ad4tk-infected cells increasingly released VEGF into medium. VEGF production correlated significantly with cellular reporter uptake (r=.98). In an initial in vivo experiment, Ad4tk and control vector were injected directly into two separate myocardial areas of a healthy pig following thoracotomy. Two days later, PET imaging was performed using [124I]FIAU, allowing for specific visualization of the area of Ad4tk injection. Identification of regional reporter gene expression was accompanied by significant increase of plasma VEGF concentration.
Conclusion: The usefulness of a vector coexpressing HSV1-tk and VEGF for noninvasive imaging of the expression of a therapeutic transgene has been demonstrated for the first time. This approach may allow for in vivo monitoring of cardiac angiogenesis gene therapy in the future.
Condensed Abstract: Usefulness of an adenoviral vector(Ad4tk) expressing mutant herpesviral thymidine kinase reporter gene and VEGF121 was evaluated. Accumulation of radiolabelled reporter probes increased for Ad4tk-infected rat cardiac cells with increading vector concentration and over time, and was comparabel to cells expressing reporter gene alone. No significant uptake was observed in cells expressing VEGF alone. VEGF production after Ad4tk-infecion correlated significantly with reporter probe uptake in vitro. In vivo, PET yielded specific visualization of Ad4tk injection area in a pig. This approach may allow for noninvasive monitoring of cardiac angiogenesis gene therapy.

Keywords: imaging; gene therapy; radioisotopes; reporter genes; VEGF

  • Journal of Nuclear Medicine 45(2004)10, 1743-1746

Publ.-Id: 6040

Positron Emission Tomography of Cardiac Transgene Expression - Comparison of two Approaches Based on Herpesviral Thymidine Kinase Reporter Gene

Miyagawa, M.; Anton, M.; Haubner, R.; Simoes, M. S.; Städele, C.; Erhardt, W.; Reder, S.; Lehner, T.; Wagner, B.; Noll, S.; Noll, B.; Grote, M.; Gambhir, S. S.; Gansbacher, B.; Schwaiger, M.; Bengel, F. M.

Background: PET imaging of reporter gene expression holds promise for noninvasive monitoring of gene therapy. Previously, two approaches based on the herpes simplex virus type 1 thymidine kinase gene(HSV1-tk) have been applied to the heart. Wild-type HSV1-tk was imaged with [124I]-fluoro-deoxy-iodo-arabinofuranosyluracil(FIAU) and mutant HSV1-sr39tk with [18F]-fluoro-hydroxymethylbutyl-guanine(FHBG), but a direct comparison has not yet been performed.
Methods and Results: In H9c2 cardiac cells, in vitro FIAU accumulation was superior to FHBG following infection with adenovirus expressing wild-type HSV1-tk(Adtk), while FHBG uptake was superior to FIAU using adenovirus expressing mutant HSV1-sr39tk(Adtk). Subsequent in vivo studies employed dynamic PET two days after intramyocardial vector injection. FIAU was used after Adtk infection. Highest cardiac uptake compared to negative controls occurred at 10-30min after tracer injection. Specific uptake disappeared at later times due to FIAU washout. FHBG was used after Adsr39tk infection. Specific tracer uptake continuously increased over time and was highest vs controls at latest imaging times(105-120min). Global cardiac reporter probe kinetics in rats were confirmed by regional analyses in pigs. Transgene expression was specifically visualized by both approaches. Highest traget/backgrounde ratio of FIAU in Adtk infected pig myocardium was 1.50±0.20 vs 2.64±0.49 for FHBG in Adsr39tk infected areas(P=0.01). In vivo results were confirmed by ex vivo counting and autoradiography.
Conclusions: Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression in different species. Specific probe kinetics suggest different myocardial handling of pyrimidine(FIAU) and acycloguanosine(FHBG) derivatives. Results are in favour of FHBG and mutant HSV1-sr39tk because of continuous accumulation over time and higher imaging contrast.
Condensed Abstract: Two approaches for PET imaging of cardiac reporter gene expression based on herpesviral thymidine kinase gene (HSV1-tk) were compared in small and large animals. Using wild-type HSV1-tk, dynamically imaged with [124I]-fluoro-deoxy-iodo-arabinofuranosyluracil (FIAU), highest myocardial FIAU uptake occurred early after injection, but tracer washout was observed at later times. Using mutant HSV1-sr39tk, imaged with [18F]-fluoro-hydroxymethylbutyl-guanine (FHBG), specific uptake increased over time and was highest at late imaging. Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression, but results are in favour of FHBG because of continuous accumulation over time and higher imaging contrast.

Keywords: imaging; genes; gene therapy; HSV1-tk radioisotopes

  • Journal of Nuclear Medicine 45(2004) 11, 1917-1923

Publ.-Id: 6039

Influence of humic acid on the neptunium(V) sorption onto granite and its mineral constituents

Schmeide, K.; Bernhard, G.

To evaluate the influence of humic substances upon the extent of neptunium(V) sorption by granite, the sorption of neptunium(V) on granite in the absence and presence of humic acid was studied under anaerobic conditions as a function of pH in a series of batch equilibrium experiments. The neptunium and humic acid sorption onto the mineral constituents of granite (quartz, orthoclase, albite, biotite, and muscovite) was also studied to identify the mineral component which dominates the sorption of neptunium and humic acid on granite. The study showed that the neptunium sorption is affected by both the pH and the presence of humic acid. An increased mobility of neptunium was found between pH 7 and pH 11 in the presence of humic acid. As dominating mineral phase in the granite for the neptunium sorption, biotite was identified.

Keywords: neptunium; humic acid; sorption; reduction

  • Poster
    International workshop on sorption processes at oxide and carbonate mineral water interfaces - SOPRO 2004, Karlsruhe, 25.-26.03.04
  • Contribution to external collection
    in: Wissenschaftliche Berichte FZKA 6986, Karlsruhe: Forschungszentrum Karlsruhe, 2004, 132-136

Publ.-Id: 6038

Investigation of thick 3C-SiC films re-grown on thin 35nm "Flash Lamp Annealed" 3C-SiC

Ferro, G.; Panknin, D.; Stoemenos, J.; Balloud, C.; Camassel, J.; Polychroniadis, E.; Monteil, Y.; Skorupa, W.

We report on the formation of thick 3C-SiC films on 3C-SiC/Si substrates which were produced by flash lamp processing (FLP). Employing a three step process, firstly a 35nm thick 3C-SiC film on a <100>-Si substrate is deposited which is followed, secondly by FLP. This leads to a melting of the SiC/Si interface region within 20ms followed by epitaxial solidification. Then, in a third step, this film is used as a seed for the deposition of a second, 3 µm thick, 3C-SiC layer. This newly developed process including FLP is called FLASiC (Flash LAmp supported deposition of Silicon Carbide). Compared with standard 3 µm thick layers directly grown on silicon, both transmission electron microscopy and low temperature photoluminescence evidence improvement of the re-grown material.

Keywords: 3C-SiC; flash lamp annealing; epitaxy; TEM; LTPL

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 313-316

Publ.-Id: 6037

Formation of 3C-SiC films embedded in SiO2 by sacrificial oxidation

Panknin, D.; Godignon, P.; Mestres, N.; Polychroniadis, E.; Stoemenos, J.; Ferro, G.; Pezoldt, J.; Skorupa, W.

The formation of SiC on Insulator (SiCOI) using a tool wet sacrificial oxidation is studied. The wet oxidation in 3C-SiC is very anisotropic strongly depended on the defect density, especially the inversion domain boundaries (IDBs). The SiCOI structure was realized by depositing of 35 nm thick 3C-SiC film on (100)-Si substrate by APCVD subsequently the film was annealed by flash lamps. The flash lamp annealing system consists of Xe lamps powered by discharging capacitors producing pulses of 20 ms. After radiation two zones can be distinguished, upper and lower, exhibiting high and low defect density, respectively. The highly defected upper zone was etched by wet sacrificial oxidation at 1150°C for 16 min. forming a 50nm thick oxide layer on the top of a good quality, 20nm thick, 3C-SiC film. In parallel, a buried oxide layer having a mean thickness of 44nm was formed by oxidation of the Si substrate through existing channels created in the SiC by the preferential wet oxidation of the IDBs which touch the SiC/Si interface. Through the oxided channels the Si substrate is oxided fast forming a continuous buried oxide layer realizing the SiCOI structure.

Keywords: 3C-SiC; SiCOI; flash lamp annealing

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 1515-1518

Publ.-Id: 6036

Flash lamp supported deposition of 3C-SiC (FLASiC) - a promising technique to produce high quality cubic SiC layers

Skorupa, W.; Anwand, W.; Panknin, D.; Voelskow, M.; Ferro, G.; Monteil, Y.; Leycuras, A.; Pezoldt, J.; Mcmahon, R.; Smith, M.

The production of cubic SiC (3C-SiC) layers in device quality through the epitaxial growth on (100)-Si wafers has remained a challenging task yet. Recently, it was demonstrated that the use of Flash Lamp Processing (FLP) can support the production of high quality 3C-SiC layers in a promising manner. The FLASiC team organized within a project of the V. Framework of the European Community is currently extending this early work as a broader approach with the following main aspects: a) Development of the epitaxial process including FLP, b) Development of a prototype equipment for the FLP, and c) Demonstrating the improved quality at dedicated devices. In this talk a short overview will be given regarding the latest advancements of this new approach.

Keywords: +3C-SiC; flash lamp annealing epitaxy; microstructure; modelling

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 175-180

Publ.-Id: 6035

Structural characterization of thin 3C-SiC films annealed by flash lamp process

Polychroniadis, E.; Stoemenos, J.; Ferro, G.; Monteil, Y.; Panknin, D.; Skorupa, W.

The formation of 3C-SiC epitaxially grown on Si wafers is still a considerable problem. Due to the 20% misfit between Si and 3C-SiC the defect density in the film is very high. the partial melting and subsequent recrystallization of the film by the flash lamp process can improve the quality of the thin 3C-SiC films. In this paper the microstructure of the annealed and partially recrystallized 35 nm thick films is studied by transmission electron microscopy. The films were grown by APCVD using Silane and Propane. The flash lamp annealing system consists of Xe lamps powered by discharging capacitors producing pulses of 20 ms. After irradiation almost free of defects 3C-SiC trapezoidal protrusions (TPs) are formed at the lower part of the film. In the uppermost part of the film the defect density was also reduced. The good quality of the TPs is shown by high resolution cross-section TEM observations. The good quality of the films was also confirmed by Plane View TEM observations of the moiré patterns in the as grown and annealed films. Moiré patterns are formed when the electron beam penetrates both the Si and the SiC lattices and are very sensitive to any lattice distortion or defects.

Keywords: 3C-SiC; flash lamp annealing; epitaxy; microstructure

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 351-354

Publ.-Id: 6034

Examination of the charge storage of Si- and Ge nanoclusters in SiO2 films by scanning probe techniques

Beyreuther, E.; Beyer, R.; Beyer, V.; von Borany, J.; Weber, J.

Embedded Si or Ge nanoclusters in SiO2 films might be a future alternative to conventional floating gate memories. Si or Ge implanted 20nm SiO2 layers were annealed to generate nanoclusters with sizes of 3-4 nm. The charge storage of the implanted layers was studied by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM). Local charge injections were accomplished by a biased conductive tip.
The amount of the injected charge was estimated from the shifts of the local dC/dV curves acquired with scanning capacitance spectroscopy (SCS). The SCS data were compared with CV-measurements on planar MOS structures. The decay of the SCM- and EFM-contrasts was monitored and the retention time was determined.

  • Poster
    DPG Frühjahrstagung des Arbeitskreises Festkörperphysik (AKF) 2003 Dresden, 24.-28. März 2003

Publ.-Id: 6032

Ladungsrelaxation in MOS-Strukturen mit Ge Nanoclustern

Beyer, R.; Beyer, V.; von Borany, J.; Weber, J.

Mittels Kapazitästransientenspektroskopie (DLTS) wurde die Umladung von Grenzflächen- und Isolatorzuständen in MOS-Strukturen mit eingebetteten Ge-Nanoclustern untersucht. Die Clusterbildung in den 20 nm dicken SiO2-Schichten erfolgte durch Ionenstrahlsynthese, wobei Ge mit verschiedenen Dosen (5x10^15, 1.5x10^16 cm^-2) und Energien (12, 18 keV) implantiert wurde und die Proben bei 950°C/1050°C in N2-Atmosphäre getempert wurden. TEM-Messungen zeigen die Bildung und Verteilung der Nanocluster im SiO2. Die DLTS-Messungen ergaben eine signifkante Abhängigkeit der Zustandsdichte an der Si-SiO2-Grenzfläche von den Ausheilparametern. Ein Trapniveau ~0.32 eV oberhalb der Valenzbandkante des Siliziums wurde in allen implantierten Proben gefunden. Durch Variation der elektrischen Anregungspulse kann der Beitrag der langsam relaxierenden grenzflächennahen Oxidzustände separiert und die für die Clusterumladung relevante Tunneloxidschicht an der Interface charakterisiert werden.

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Festkörperphysik (AKF) 2003 Dresden, 24.-28. März 2003

Publ.-Id: 6031

Comparison of the Charge Storage Properties of Ion Beam Sythesized Si and Ge Nanoclusters in Thin Gate Oxides

Beyer, V.; von Borany, J.; Knobloch, K.; Mücklich, A.

Semiconductor nanoclusters (NCs) embedded in thin gate dielectrics are of fundamental interest for future integrated memory concepts. In this contribution we compare the properties of Ge and Si NCs embedded in thin SiO2 films (d = 20 nm) with respect to their charge storage behaviour. Those NCs were prepared by ion beam synthesis combining low energy ion implantation (6-18 keV, 5x1015-2x1016cm-2) with subsequent rapid thermal processing (950 or 1050°C, 30-120 s) choosing identical ion ranges and peak concentrations for both elements. Electrical characterization based on CV, IU, pulsed Ct and It measurements were performed at MOS capacitors. The investigations reveal significant differences for Ge and Si NC containing gate oxides. Ge NCs near the Si/SiO2 interface are characterized by fast charging / decharging and a flatband voltage shift of several volts. In contrast, Si implanted oxides show memory effects with a smaller flatband voltage shift, but considerably improved data retention. In both cases charging is possible for electrical field strength of 4-6 MV/cm, well below the Fowler-Nordheim tunnelling region. The varying electrical properties correlate with differences in the spatial distribution of ion beam synthesized Ge and Si NC in thin SiO2 films, which were investigated by XTEM and RBS. The change of spatial distribution during annealing is due to different thermodynamics of NC evolution and chemical processes especially in thin SiO2 films.

  • Lecture (Conference)
    E-MRS 2003 Spring Meeting / Strasbourg (Frankreich), 10.-13. Juni 2003
  • Lecture (Conference)
    EUROMAT 2003 Lausanne (Schweiz), 01.-05. September 2003

Publ.-Id: 6029

Charge Storage Behavior of Ion Beam Synthesized Au Nanocrystals

Beyer, V.; Müller, T.; von Borany, J.; Heinig, K.-H.

Studies of semiconductor nanocrystals (NC’s) in the MOS gate oxide received much interest due to their potential application in non-volatile memory devices. However, the detailed charge storage mechanism is still under discussion. Defect-based charge trapping at NC surfaces is hard to distinguish from storage in the conduction band of NC’s. For metal NC’s in SiO2 the situation is different. Charge traps at the Au/SiO2 interface are assumed to be negligible at first sight. In this contribution, Au NC’s serve as a model system for the charge storage phenomena in NC containing gate oxides with a thickness of less than 40 nm. For the present study, Au NC’s were synthesized by low-energy ion implantation followed by annealing. The formation of well-separated NCs (4..5 nm diameter) were observed by X-TEM studies. Additionally, a zone denuded of NC’s forms at the interface. Thus, the formed NC-layer has the right distance from the Si/SiO2 interface for charging by direct electron tunneling. On prepared MOS capacitor structures, charge storage behavior was successfully demonstrated by capacitance-voltage measurements.

  • Poster
    Jahrestagung der Deutschen Physikalischen Gesellschaft DPG, 24.-28. März 2003, Dresden

Publ.-Id: 6028

Interaction Processes of Tetravalent Actinides in the System Humic Acid / Quartz Sand / Solution

Krepelova, A.; Mibus, J.; Sachs, S.; Nebelung, C.; Bernhard, G.

In the present work the influence of HA on the interaction of tetravalent actinides onto quartz sand was investigated in batch and column experiments. HA can affect the sorption of actinides onto mineral surface as a complexing ligand for cations in solutions, and as an adsorbent by modifying the properties of the mineral surface.
Batch experiments were performed with Th(IV) as stable tetravalent actinide element. Column experiments were carried out with uranium which is less stable in the tetravalent state under laboratory conditions. Results of the U(IV) migration were compared to the U(VI) migration.
HA shows a pH-dependent influence on the Th(IV) sorption onto quartz sand. At pH < 4 HA may immobilize Th(IV) due to HA sorption and/or precipitation onto the surface. Between pH 4 and pH 5 the Th(IV) sorption is decreased in the presence of HA which can be attributed to the formation of dissolved Th(IV)-humate complexes. For higher pH values a comparable effect is assumed. The experimental proof was not possible by the performed batch experiments.
From the column experiments it can be concluded that HA affects the migration of both U(IV) and U(VI). In the presence of HA U(VI) is significantly mobilized. A similar effect is supposed for U(IV). This is in accordance with the results of the batch experiments.

  • Poster
    SOPRO 2004, 25.-26.3.2004, Karlsruhe, Germany
  • Contribution to proceedings
    SOPRO 2004, International Workshop on Sorption Processes at Oxide and Carbonate Mineral Water Interfaces, 25.-26.03.2004, Karlsruhe, Germany
    Book of extended abstracts, 75-79

Publ.-Id: 6027

Perspectives for biotechnological applications of the uranium mining waste pile isolate Bacillus sphaericus JG-A12

Merroun, M.; Raff, J.; Pollmann, K.; Hennig, C.; Rossberg, A.; Foerstendorf, H.; Scheinost, A.; Selenska-Pobell, S.

The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt. The most prominent properties of this strain are reversible and selective binding of U, Cu, Pb, Al and Cd and the presence of a surface layer protein as outermost cell wall component. Mass spectroscopical, colorimetric and phosphor specific staining methods showed phosphorylation of the S-layer protein. EXAFS analysis and Infrared spectroscopy of the uranium complexes formed by the cells and S-layer of this bacterium demonstrated that this metal is coordinated to carboxyl and phosphate groups. In this work we present analysis of Pd nanoclusters formed on the cells of B. sphaericus JG-A12 in the presence of H2 as a reducing agent. These nanoclusters are interesting for the development of bionanocatalysts and biosensors. Further, by embedding cells, spores or S-layers using sol-gel techniques bioceramics particles were produced. These bioceramics can be used for bioremediation of heavy metal contaminated waters.

  • Lecture (Conference)
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany

Publ.-Id: 6026

Microbial diversity in uranium contaminated soils

Geißler, A.; Tzvetkova, T.; Selenska-Pobell, S.

Contamination of soils with heavy metals and radionuclides is a severe environmental problem. Bacteria are involved in migration and detoxification of a large number of toxic metals due to their ability to interact with and to biotransform them. Total DNA was extracted from soils of one uranium mining waste pile near the town of Johanngeorgenstadt (Germany) and of one uranium mill tailings near Shiprock, NM in the USA. Universal bacterial, archael and also Geobacter-specific primers were used to construct 16S rDNA libraries. We found that natural microbial communities at the two uranium wastes differed significantly. Alpha-Proteobacteria and representatives of the Holophaga/Acidobacterium phylum were predominant in the U mining waste pile, whereas the Shiprock U mill tailings was occupied mainly by Bacillales, Gamma-Proteobacteria and Green non-sulfur bacteria. The most related sequences to ours in the GenBank were those of not yet cultured bacteria or archaea. Representatives of the genus Geobacter were identified in the U waste pile by using Geobacter-specific primers and in the U mill tailings by both Geobacter-specific and universal primers. Because these bacteria are able to reduce and immobilize a large number of heavy metals, we are performing a quantification of them via Real time PCR. Efforts to cultivate some bacterial isolates from the U wastes are in progress in our laboratory.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig

  • Poster
    VAAM-2004 vom 28.03-31.03.04 in Braunschweig
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany

Publ.-Id: 6025

Bacterial diversity in waters at the Siberian deep-well monitoring site Tomsk-7

Nedelkova, M.; Selenska-Pobell, S.

Bacterial diversity was studied in water samples collected at depths of 290 to 324 m from the Siberian deep-well radioactive waste disposal site S15 near the Russian city of Tomsk by using the 16S rDNA retrieval. Bacterial clone libraries were constructed for the DNA isolated from the biomass collected on filters with a pore size of 0.45µm and 0.22µm. Comparative analyses of the two libraries revealed significant differences in the predominant bacterial groups and in the species composition. In the 0.45µm clone library a dominance of Dechlorosoma spp. was found, whereas in the 0.22µm library populations of Chrysobacterium spp. belonging to Cytophaga/Flavobacterium/ Bacteroides (CFB) group were predominant. Many of the identified 16S rDNA sequences were affiliated to uncultured members of different bacterial lineages. Effort to culture some of them is in progress in our laboratory.
In addition, using CFB-specific primers and applying semi-nested PCR a clone library was generated for the total DNA extracted from the same site. Our previous study of this DNA, applying universal bacterial primers, indicated a presence of relatively small CFB population there. The estimation of the real amount and the significance of this bacterial group via real-time PCR is also in progress.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig

  • Poster
    VAAM-2004 vom 28.03-31.03.04 in Braunschweig
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany
  • Contribution to external collection
    Tsang, C. F.; Apps., J. A.: Developments in Water Science, Underground Injection Science and Technology, Amsterdam: Elsevier, 2005, 0-444-52068-6, 521-536

Publ.-Id: 6024

Molecular analysis of the S-layer protein of the uranium mining waste pile isolate Bacillus sphaericus JG-A12

Pollmann, K.; Raff, J.; Schnorpfeil, M.; Fahmy, K.; Selenska-Pobell, S.

Cells of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 are capable of selective and reversible accumulation of heavy metals.
The cells of B. sphaericus JG-A12 are enveloped by a surface-layer (S-layer). S-layers, which are composed of identical protein monomers with the ability to self-assemble into two-dimensional crystalline arrays, are one of the most commonly observed surface structures of archaea and bacteria.
In case of the strain JG-A12 our analyses showed that the S-layer is capable of binding metals. Thus, it is probable that the S-layer contributes to heavy metal resistance.
Sequence analyses showed, that the S-layer proteins of B. sphaericus JG-A12 and its closest relative, B. sphaericus NCTC9602, possess an unusual high identity of the N-terminus and the central domain, whereas the C-terminal parts differ significantly between the two strains. Further, both strains contain a second truncated S-layer gene-like copy which is possibly encoded by large plasmids. These results indicate a horizontal transfer of parts of the gene between different strains.
The S-layer proteins show a high content of aspartate and glutamate, especially in the C-terminal part. IR analyses demonstrated that the carboxylgroups of these residues are involved in Pd-binding.

VAAM 2004
Braunschweig 28.03.-31.03.2004

  • Lecture (Conference)
    VAAM 2004, 28.3.-31.3.2004, Braunschweig, Germany
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany

Publ.-Id: 6023

Models for the forces acting on bubbles in comparison with experimental data for vertical pipe flow

Lucas, D.; Shi, J.-M.; Krepper, E.; Prasser, H.-M.

As a consequence of the averaging process constitutive models for the interaction between the phases are required in the multi-fluid modelling. For the simulation of bubbly flows this concerns models for the forces acting on bubbles. Detailed experimental data for vertical pipe flow, obtained by an advanced wire-mesh sensor, were used to assess such models for a wide range of combinations of superficial velocities. A simplified one-dimensional model, which considers a number of bubble classes is used for the prediction of radial gas fraction profiles from a given (measured) bubble size distribution. A comparison of these profiles with the measurements allows the evaluation of the models for the non-drag forces. In contrast to common CFD codes the simplified model also allows to consider the extension of the bubbles. This is important, if large bubbles or slugs occur. A good agreement is achieved for liquid superficial velocities up to 1 m/s using the lift- and wall force models from Tomiyama and the Favre averaged drag model for the turbulent dispersion force. For larger liquid superficial velocities an intermediate peak occur in the measured radial gas fraction profile, which cannot be reproduced by the available models.

Keywords: two-phase flow; modelling; bubble forces; vertical pipe flow

  • Lecture (Conference)
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy
  • Contribution to proceedings
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy, paper ha04

Publ.-Id: 6022

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern ermöglicht. In Anrege-Abfrage Experimenten ist damit die Zeitskala zugänglich, in der sich wichtige elementare Wechselwirkungen abspielen. In Halbleiter Quantenstrukturen können durch fs-Laserpulse z. B. kohärente elektronische Wellenpakete präpariert werden, deren Untersuchung die Überprüfung elementarer Vorhersagen zur Existenz von Bloch Oszillationen erlaubt. Desweiteren werde ich auf Beiträge zur technologischen Weiterentwicklung des Feldes, wie die Realisierung des kompaktesten fs-Lasers auf Festkörperbasis, und dessen Anwendungen eingehen.

  • Lecture (others)
    Physikalisches Kolloquium, Universität Konstanz, Januar 2004, Konstanz, Deutschland

Publ.-Id: 6021

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie eröffnet. Über nichtlinear-optische Prozesse lassen sich ultrakurze optische Pulse in nahezu jeden Frequenzbereich konvertieren. Insbesondere im niederenergetischen Terahertz Bereich (1 THz entspricht 4 meV) erlaubt dies die zeitaufgelöste Spektroskopie von wichtigen Elementaranregungen in Festkörpern.
In Anrege-Abfrage Experimenten an Halbleitern und Halbleiter Quantenstrukturen ist somit die Zeitskala zugänglich, in der sich Elektron-Elektron Wechselwirkungen, Elektron-Phonon Streuung und Kohärenzzerfall abspielen. So lassen sich zum Beispiel kohärente elektronische Wellenpakete präparieren, die mit einer kohärenten Intrabandpolarisationen verbunden sind. Diese Intrabandpolarisation ist von Interesse für die Erzeugung elektrisch abstimmbarer THz Emission von Bloch Oszillationen in Halbleiter-Übergittern.
Zukünftige Perspektiven der Femtosekunden Spektroskopie werden im Hinblick auf die Untersuchung von Halbleiter-Nanostrukturen diskutiert.

  • Lecture (others)
    Universität Stuttgart, Dezember 2003

Publ.-Id: 6020

Reliability test of a PAL spectrometer - selected results on Fe

May-Tal Beck, S.; Brauer, G.; Anwand, W.; Berant, Z.; Shahal, O.; Ganor, M.; Israelashwily, I.

A positron lifetime spectrometer for defect studies in bulk, with time resolution of 185 +-7 ps, is described. Its reliability, tested on 4N Fe samples in various states, is demonstrated. For comparison, the same samples are studied also by Slow Positron Implantation Spectroscopy.

Keywords: defects; iron; positron lifetime spectroscopy; slow positron implantation spectroscopy

  • Contribution to external collection
    Material Science Forum 445-446 (2004), 495-497

Publ.-Id: 6019

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern eröffnet. Über nichtlineare optische Prozesse lassen sich ultrakurzen optischen Pulse in nahezu jeden Frequenzbereich konvertieren. Insbesondere im niederenergetischen Terahertz Bereich erlaubt dies die Entwicklung von zeitaufgelöster Spektroskopie mit hoher Empfindlichkeit.
In Anrege-Abfrage Experimenten an Halbleitern ist somit die Zeitskala zugänglich, in der sich wichtige elementare Prozesse, wie zum Beispiel Elektron-Phonon Streuung und Kohärenzzerfall, abspielen. In Halbleiter Quantenstrukturen können durch die Anregung mit Femtosekunden Pulsen kohärente elektronische Wellenpakete präpariert werden, die mit kohärenten Interband- und Intrabandpolarisationen verbunden sind. Die Dephasierungszeit der Intrabandpolarisation ist von Interesse für die auf Bloch Oszillationen basierende THz Emission aus Übergittern. Besonders interessant sind Untersuchungen für den Resonanzfall, wenn die Frequenz der Intrabandpolarisation auf die LO Phononfrequenz abgestimmt wird.

  • Lecture (others)
    Universität Regensburg, Mai 2003

Publ.-Id: 6018

Hydrogen-induced defects in niobium studied by positron annihilation spectroscopy

Cizek, J.; Prochazka, I.; Kuzel, R.; Becvar, F.; Cieslar, M.; Brauer, G.; Anwand, W.; Kirchheim, R.; Pundt, A.

Changes of the defect structure of niobium induced by hydrogen loading are presented in this work. The evolution of the microstructure with increasing hydrogen concentration was studied by X-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS). A comparison of PAS results with theoretical calculations revealed that complexes consisting of a vacancy, surrounded likely by four hydrogen atoms, were introduced into the samples due to hydrogen loading.

Keywords: hydrogen; niobium; vacancies

  • Contribution to external collection
    Materials Science Forum, 445-446 (2004), 60-62
  • Journal of Alloys and Compounds 404-406(2005), 580-583

Publ.-Id: 6017

Fluence dependence and thermal stability of defects in helium-implanted cubic zirconia

Saude, S.; Grynszpan, R. I.; Anwand, W.; Brauer, G.; Grob, J. J.; Le Gall, Y.

Slow positron implantation spectroscopy investigations of yttria-stabilized cubic zirconia implanted with 50 keV He ions detect, at 60% of the projected range, a concentration of defects maximum, which may constitute a barrier for the diffusion of helium towards the surface. The Doppler broadening lineshape dependence on the fluence suggests a change in the nature of defects above 4 x 10**16 ions/cm**2, with an enhancement of the trapping efficiency. These defects evolve into large bubbles by Ostwald ripening after annealing at temperatures higher than 573 K, as suggested by their distribution narrowing. Above 973 K, a breaking-up of the bubbles occurs, with He release and diffusion towards the surface and eventual out-gassing.

Keywords: ion implantation; zirconia; radiation effects; positrons

Publ.-Id: 6016

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern ermöglicht. In Anrege-Abfrage Experimenten ist damit die Zeitskala zugänglich, in der sich die wichtigsten elementaren Wechselwirkungen, zum Beispiel Elektron-Phonon Kopplung und Kohärenzzerfall, abspielen. Über nichtlineare optische Prozesse lassen sich diese ultrakurzen optischen Pulse in nahezu jeden Frequenzbereich vom niederenergetischen Terahertz Bereich bis ins UV konvertieren, was die Entwicklung neuer spektroskopischer Anwendungen ermöglicht.

In Halbleiter Quantenstrukturen können durch die Anregung mit Femtosekunden Pulsen kohärente elektronische Wellenpakete präpariert werden, deren Untersuchung die Überprüfung elementarer Vorhersagen der Quantenmechanik in Festkörpern zur Existenz von Bloch Oszillationen ermöglicht. Desweiteren werde ich auf Beiträge zur technologischen Entwicklung des Feldes, wie die Realisierung des kompaktesten Femtosekunden Lasers auf Festkörperbasis, und dessen Anwendungen eingehen.

  • Lecture (others)
    Universität Paderborn, März 2003

Publ.-Id: 6015

Electroluminescence from silicon pn diodes

Dekorsy, T.

The indirect band gap of silicon makes this material an inherently bad light emitter. However, since silicon is the key material of electronics, there is a tremendous effort for realizing silicon based light emitters in order to take full advantage of silicon process technology. The different routes pursued so far include porous silicon, 2 dimensional silicon nanostructures, silicon nanocrystals in a SiO2 matrix [1], Er3+ doped silicon, and silicon-germanium quantum cascade lasers.
Recently, the light emission from bulk silicon received considerable interest [2,3]. We pursue a similar route for preparing silicon pn-diodes via high-dose boron implantation. Under forward bias these diodes emit electroluminescence close beneath the silicon bandgap. The origin of the electroluminescence is based on high local boron concentration, which leads to the localization of holes at doping spikes similar as observed in delta doped layers produced by MBE. The relevance of excitons bound at the B doping spikes on the electrical [4] and optical properties will be discussed with respect to the prospects of obtaining efficient room temperature light emitters.

[1] L. Pavesi, et al., Optical gain in silicon nanocrystals, Nature 408, 440 (2000).
[2] W.L. Ng et al., An efficient room temperature silicon based light emitting diode, Nature
410, 192 (2001).
[3] M.A. Green et al., Efficient silicon light-emitting diodes, Nature 412, 805 (2001).
[4] J. Sun et al, Bound-exciton-induced current bistability in a silicon light-emitting diode, Appl. Phys. Lett. 82, 2823 (2003).

Keywords: silicon based light emission; pn diodes; boron implantation

  • Lecture (others)
    Seminarvortrag, Gruppe Prof. J. Feldmann, LMU München, Juni 2003

Publ.-Id: 6014

Vergleich der ELBE - FELs mit Table Top Lasersystemen

Dekorsy, T.

not available

  • Lecture (others)
    ELBE Palaver, Forschungszentrum Rossendorf, Juli 2003

Publ.-Id: 6013

Mehr Licht...aus Silizium

Dekorsy, T.

not available

  • Lecture (others)
    Festkolloquium anläßlich des 60. Geburtstages von Prof. H. Kurz, RWTH Aachen, Dezember 2003

Publ.-Id: 6012

Ultra-fine grained copper prepared by high pressure torsion: spatial distribution of defects

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

High-purity bulk ultra-fine grained (UFG) metals of grain size of " 100 nm and of no porosity can be produced by high-pressure torsion (HPT) technique. In the present contribution a study of spatial distribution of defects in HPT made UFG copper is reported. Positron annihilation spectroscopy (slow-positron implantation, lifetime and Doppler broadening spectroscopies) was utilized together with transmission electron microscopy, x-ray diffraction and microhard-ness measurements to investigate lateral distributions as well as depth profiles of defects.
Two types of defects were identified: dislocations situated in distorted regions along grain boundaries and microvoids of size comparable to 3-5 vacancies inside grains. No lateral changes in grain size and mean dislocation density were observed. Close to the specimen sur-face, the mean coherent domain size was found to be 80±20nm and it slightly increased with depth. As a consequence, a decrease in volume fraction of distorted regions takes place, which results in a decrease of the mean dislocation density with depth. These changes were observed at depths below 35 mm. At higher depths, the mean dislocation density tends to independence of depth. Contrary to lateral behavior of dislocations, concentration of microvoids was found to vary with distance from center of the specimen disk.

Keywords: High-pressure torsion; ultra-fine grained copper; spatial distribution of defects; positron annihilation

  • Contribution to external collection
    Proc. Second Int. Conf. on Nanomaterials by Severe Plastic Deformation: Fundamentals - Processing - Applications, Vienna 2002, eds. M.J. Zehetbauer, R.Z. Valiev (Wiley, Weinheim, 2003) pp. 407-412

Publ.-Id: 6010

Electroproduction of Strangeness on 3,4He

Dohrmann, F.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J.; Asaturyan, R.; Assamagan, K.; Avery, S.; Bailey, K.; Baker, O. K.; Beedoe, S.; Bitao, H.; Breuer, H.; Brown, D. S.; Carlini, R.; Cha, J.; Chant, N.; Christy, E.; Cochran, A.; Cole, L.; Collins, G.; Cothran, C.; Crowder, J.; Cummings, W. J.; Danagoulian, S.; Duncan, F.; Dunne, J.; Dutta, D.; Eden, T.; Elaasar, M.; Ent, R.; Ewell, L.; Fenker, H.; Fortune, H. T.; Fujii, Y.; Gan, L.; Gao, H.; Garrow, K.; Geesaman, D. F.; Gueye, P.; Gustafsson, K.; Hafidi, K.; Hansen, J. O.; Hinton, W.; Jackson, H. E.; Juengst, H.; Keppel, C.; Klein, A.; Koltenuk, D.; Liang, Y.; Liu, J. H.; Lung, A.; Mack, D.; Madey, R.; Markowitz, P.; Martoff, C. J.; Meekins, D.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mohring, R.; Mtingwa, S. K.; Mueller, B.; O'Neill, T. J.; Niculescu, G.; Niculescu, I.; Potterveld, D. H.; Price, J. W.; Raue, B. A.; Reimer, P. E.; Reinhold, J.; Roche, J.; Roos, P.; Sarsour, M.; Sato, Y.; Savage, G.; Sawafta, R.; Segel, R. E.; Semenov, A. Y.; Stepanyan, S.; Tadevosian, V.; Tajima, S.; Tang, L.; Terburg, B.; Uzzle, A.; Wood, S.; Yamaguchi, H.; Yan-1, C.; Yan-2, C.; Yuan, L.; Zeier, M.; Zeidman, B.; Zihlmann, B.

The A(e,e'K+)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q{2} approx 0.35 rm GeV2 at a beam energy of 3.245 rm
GeV for 1H,3He and 4He targets. Missing mass spectra are fitted with Monte Carlo simulations taking into account the production of Lambda and Sigma0 hyperon production off the proton, and Sigma- off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for 3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed.

Keywords: Electroproduction; Strangeness; Hyperons; Hypernuclear boundstates

  • Contribution to external collection
    Proceedings of HYP2003

Publ.-Id: 6008

Lateral and depth distribution of defects in ultra fine grained copper prepared by high pressure torsion

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

Ultra-fine grained copper prepared by high-pressure torsion has been studied by means of positron annihilation techniques (slow positron implantation spectroscopy,conventional positron lifetime and Doppler broadening measurements) combined with transmission electron microscopy, X-ray diffraction and microhardness measurements. Dislocations in distorted regions along grain boundaries and microvoids of size 3-4 vacancies inside grains were identified and their lateral distribution and depth profile were investigated in detail. The concentrationof microvoids has been found to decrease with depth and to vary slightly with the distance from specimen axis, being lowest in the centre of the specimen disc. No position dependence of the concentration of dislocations was observed.

Keywords: ultra-fine grained copper; high-pressure torsion; dislocations; microvoids; slow positron implantation spectroscopy; positron lifetime; Doppler broadening

  • J. Metastable Nanocryst. Mater. 17 (2003) 23-28

Publ.-Id: 6006

Sampling and Characterization of Rock Material from Uranium Mining Waste Rocks for Study and Modeling of Release and Migration of Uranium

Sachs, S.; Benes, P.; Vopalka, D.; Stamberg, K.; Mibus, J.; Bernhard, G.; Bauer, A.

To study the effects of humic substances on the leaching and migration of uranium from uranium mining waste a natural rock material was sampled from a uranium rock pile situated in the mining region Schlema/Alberoda (Saxony, Germany). This report describes the sampling and characterization of the <1 mm grain size fraction of the rock material. The main focus is on the characterization of the sampled material with regard to its elemental and mineralogical composition and its amount of uranium that is accessible from the rock material by leaching processes.

Keywords: Uranium; migration; humic substances; uranium mining; rock pile; rock material; characterization

  • Contribution to external collection
    Humic Substances in Performance Assessment of Nuclear Waste Disposal : Actinide and Iodine Migration in the Far-Field. Second Technical Progress Report, Forschungszentrum Karlsruhe, Wissenschaftliche Berichte, FZKA 6969, Karlsruhe 2004, 73-84

Publ.-Id: 6005

Spatial distribution of defects in ultra-fine grained copper prepared by high pressure torsion

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

A study of ultra-fine grained copper produced by high-pressure torsion is presented. Positron annihilation spectroscopies (slow-positron implantation, lifetime and Doppler broadening spectroscopies), transmission electron microscopy, X-ray diffraction spectroscopy and micro-hardness measurements have been employed in order to identify defects and their spatial dis-tribution, i.e. lateral distribution and depth profile, in the specimens. Two types of defects could be identified: dislocations in the distorted regions along grain boundaries and micro-voids of size of 3-4 vacancies inside the grains. No change in grain size as a function of the distance from the center of the sample disk was observed. The mean coherent domain size close to the surface was found to be 80 ± 20 nm and it slightly increases with depth. The con-centration of microvoids has been found to decrease with depth and it slightly varies with the distance from the center of the disk, being lowest in the center. No position dependence of the concentration of dislocation was observed.

Keywords: High-pressure torsion; ultra-fine grained copper; spatial distribution of defects; positron annihilation spectroscopy

  • phys.stat.sol.(a) 195 (2003) 335-349

Publ.-Id: 6004

Metallographical and Numerical Investigation of the EC-FOREVER-4 Test

Willschütz, H.-G.; Altstadt, E.; Mueller, G.; Boehmert, J.; Sehgal, B. R.

Assuming the hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower plenum of a Light Water Reactor (LWR) leads to the question about the behavior of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
To get an improved understanding and knowledge of the melt pool convection and the vessel creep and possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments (Failure Of REactor VEssel Retention) are currently underway at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm. These experiments are simulating the behavior of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurization scenario. The geometrical scale of the experiments is 1:10 compared to a common LWR.
Accompanying the experiments metallographical and numerical work is performed at the Forschungszentrum Rossendorf. An axisymmetric Finite Element model is developed based on the multi-purpose code ANSYS/Multiphysics®. First the temperature field within the melt pool and within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a creep model which takes into account large temperature, stress and strain variations. For a failure prediction it is necessary to introduce a damage measure. This is done according to a model proposed by Lemaitre. The microstructural investigation gives an insight to the material state of the vessel wall at different positions. This can be compared with the numerical damage value calculated in the Finite Element Model.
This paper deals with the experimental, numerical, and metallographical results of the creep failure experiment EC-FOREVER-4, where the American pressure vessel steel SA533B was applied for the lower head. For comparison the results of the experiment EC-FOREVER-3B are discussed, too.

Keywords: metallographic investigations; creep; crack; RPV; vessel failure

  • Lecture (Conference)
    International Congress on Advances in Nuclear Power Plants (ICAPP '04),13.-17.06.2004, Pittsburgh, PA, United States
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP '04),13.-17.06.2004, Pittsburgh, PA, United States, Proceedings on CD-ROM, paper 4006

Publ.-Id: 6003

Depth resolved investigations of boron implanted silicon

Sztucki, M.; Metzger, T. H.; Milita, S.; Berberich, F.; Schell, N.; Rouviere, J. L.; Patel, J.

We have studied the depth distribution and structure of defects in boron implanted silicon (001). Silicon wafers were implanted with a boron dose of 6e15 ions/cm2 at 32 keV and went through different annealing treatments. Using diffuse X-ray scattering at grazing incidence and exit angles we are able to distinguish between different kinds of defects (point defect clusters and extrinsic stacking faults on {111} planes) and to determine their depth distribution as a function of the thermal budget. Cross-section transmission electron microscopy was used to gain complementary information.
In addition we have determined the strain distribution caused by the boron implantation as a function of depth from rocking curve measurements.

Keywords: Diffuse X-ray scattering; Transmission electron microscopy; Ion implantation; Defects

Publ.-Id: 6002

The nanostructure evolution during and after magnetron deposition of Au films

Schell, N.; Jensen, T.; Petersen, J. H.; Andreasen, K. P.; Bottiger, J.; Chevallier, J.

The evolution of the nanostructure of magnetron sputtered Au films has been experimentally studied. At a synchrotron-radiation beam line, during growth and subsequent annealing, in-situ X-ray diffraction has been carried out to follow the texture, the grain size, the microstrain and lattice-plane distances. With Bragg–Brentano geometry, only (111) grains, having a (111) plane parallel to the film surface, have been observed, while, with glancing incidence and exit X-ray diffraction, (111)* grains, having one of their (111) planes perpendicular to the film surface, have also been observed. Both during growth and subsequent annealing, the (111) texture changed, and some (111)* grains recrystallized and/or the orientation of the grains changed. The microstrain decreased drastically during the first few minutes of growth (300 A) while, simultaneously, the size of the coherently diffracting domains increased. Subsequently, the microstrain became constant, and the rate of increase of the size of coherently diffracting domains leveled off. Initially, during the first few minutes of annealing, a large decrease in the microstrain was observed simultaneously with a dramatic rise of the size of the coherently diffracting domains. After this initial annealing period, as during film growth, the microstrain became constant, and the rate of increase of the size of coherently diffracting domains leveled off.
The activation energy for the initial growth of the coherent diffracting domains was found to be Q=(0.25 +/- 0.03) eV, and the activation energy for normal grain growth was found to be Q=(0.99 +/- 0.04) eV.
Finally, the thin-film stress was followed during growth and subsequent annealing. A tensile contribution to the stress was observed during island coalescence.

Keywords: Nanocrystalline Au; Nanostructure; In-situ X-ray diffraction; Growth; Magnetron sputtering

  • Contribution to HZDR-Annual report
    ERSF Highlights 2003 (2004) 39-40
  • Thin Solid Films 441 (2003) 96-103


Publ.-Id: 6001

On the development of texture during growth of magnetron-sputtered CrN

Schell, N.; Petersen, J.; Bottiger, J.; Mücklich, A.; Chevallier, J.; Andreasen, K. P.; Eichhorn, F.

During growth of CrN films deposited by reactive magnetron sputtering, the development of the microstructure, especially the texture, was studied.By ex-situ Bragg–Brentano X-ray diffraction measurements, the texture, the grain size and the microstrain were measured as a function of film thickness.In addition, in-situ Bragg–Brentano X-ray diffraction and reflection measurements were carried out with synchrotron radiation, including measurements where the dynamic development of the microstructure was followed in real-time. Below a transition deposition temperature of approximately 550°C, it was found that the <002> preferred orientation dominated, while a mixture of <111> and <002> preferred orientations was found above the transition temperature. The development of texture with film thickness was controlled by a recrystallization mechanism.With increasing film thickness, the grain size increased while the microstrain decreased.The real-time measurements with synchrotron radiation revealed that several different dynamic processes took place both during and after depositions.After a long-time interruption of the growth,major changes in the texture were observed.

Keywords: Texture development; CrN; Magnetron sputtering

  • Thin Solid Films 426 (2003) 100-110

Publ.-Id: 6000

In situ high temperature synchrotron-radiation diffraction studies of silicidation processes in nanoscale Ni layers

Rinderknecht, J.; Prinz, H.; Kammler, T.; Schell, N.; Zchech, E.; Wetzig, K.; Gessner, T.

The formation of nickel silicides has been studied by X-ray diffraction experiments using synchrotron radiation (SR). A high temperature chamber was used to investigate the phase formation and transition processes under quasi-static conditions at temperatures from 200 to 650 °C. Samples with different dopants, several metal layer thicknesses as well as samples with and without a 150 A TiN capping layer on single-crystal (001) and polycrystalline silicon substrates were examined. While n-type dopants like P and As had no significant impact on the silicidation processes, boron decreased the range of thermal stability of the low-resistivity phase NiSi. A TiN capping layer shifts both these formation and transition temperatures to higher values.

Keywords: Nickel silicide; Phase formation; Transition temperatures; Dopants; Capping layer

  • Microelectronic Engineering 70 (2003) 226-232

Publ.-Id: 5999

Analysis of the biaxial strain state of Al-doped c-BN films using diffraction experiments with synchrotron radiation

Linss, V.; Halm, T.; Hoyer, W.; Richer, F.; Schell, N.

Thin films of cubic-boron nitride with a small amount of aluminum were produced by rf magnetron sputtering of a h-BN target and an additional Al ring-shaped electrode. Then the strain state of the biaxially stressed films was measured using synchrotron X-ray diffraction and the lattice spacing that unstressed films would have was calculated for different amounts of aluminum. This unstressed lattice spacing gets larger with increasing Al-amount. There is much evidence that the aluminum atoms are substitutionally incorporated at boron sites. This article provides an insight into the method of determining the unstressed lattice spacing using a slightly changed sin2_psi method.

Keywords: Cubic boron nitride (c-BN); Al-doping; Unstressed lattice spacing; Synchrotron radiation; sin2_psi-method

  • Vacuum 70 (1) (2003) 1-9

Publ.-Id: 5998

Dynamo experiments: where we stand and where we go

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

It was a nice coincidence that, after years of preparations, the liquid sodium dynamo facilities in Riga and Karlsruhe had become operative nearly simultaneously at the end of 1999. Since those pioneering times, there have been many additional runs in either place, yielding a wealth of reproducible data on the kinematic as well as on the saturated regime. The accompanying numerical work has got some maturity and shows, by now, a reasonable correspondence with the experimental results. The results of the two experiments are complementary rather than redundant as they cover the paradigmatic cases of a large scale dynamo (Riga) and a mean-field dynamo (Karlsruhe). With the main focus on the results and the interpretation of the Riga dynamo experiment, we give a summary of what has been achieved so far and what is left for future dynamo experiments. In particular, we demonstrate that the saturation mechanism of the Riga dynamo experiment is already a non-trivial one as it relies heavily on the change of the flow structure due to the back-reaction of the self-excited magnetic field. We comment on the envisioned dynamo experiments in non-rotating and rotating spheres and ask what geodynamo simulation could learn from

  • Abstract in refereed journal
    Geophysical Research Abstracts 6(2004), 02933
  • Invited lecture (Conferences)
    European Geosciences Union, 1st General Assembly, 25.-30.04.2004, Nice, France

Publ.-Id: 5996

Relaxation kinetics in amorphous carbon films: an insight from atomic scale simulation

Belov, A. Y.; Jäger, H. U.

Depending on temperature, thermodynamically favoured structural relaxations in as-deposited tetrahedral amorphous carbon (ta-C) films can either essentially retain the content of sp3 bonded atoms or result in a transition to a graphitic phase with dominating sp2 bonding. The structural relaxation occurs at low temperatures (less than ~ 600 °C) and is accompanied by reduction of the grown-in film stress. The most recent NMR spectroscopy investigation [1] shows that the structural changes in highly tetrahedral a-C films due to low-temperature annealing don't reduce to simple sp3-to-sp2 or sp3-to-sp2 conversions and have more complicated nature than it was previously believed. We present results of long-term simulated annealing studies of the relaxation processes in ta-C using molecular dynamics with a modified Brenner potential for C-C interactions and the structural models of as-deposited (unrelaxed) ta-C generated by an ion-beam film deposition simulation [2]. It is shown that during low-temperature annealing the potential energy and stress of the as-deposited ta-C films are released with only minor changes in the short-range order and density. It is demonstrated that as a result of annealing the volumes of sp3 atoms decrease, which is consistent with experiment [1]. It is also found that the change of potential energy with annealing time can be fit by an exponential function, which enables to analyze the relaxation kinetics in as-deposited ta-C, in particular, to obtain the dependence of the relaxation time on annealing temperature.
[1] T.M. Alam, T.A. Friedmann, P.A. Schultz, D. Sebastiani, Phys. Rev. B 67, 245309 (2003)
[2] H.U. Jäger, A.Yu. Belov, Phys. Rev. B 68, 024201 (2003)

  • Lecture (Conference)
    European Materials Research Society 2004 Spring Meeting, Symposium J : Synthesis, Characterisation and AdvancedApplications of Amorphous Carbon films, 24-28 May 2004, Strasbourg France, contr. J-V.6

Publ.-Id: 5995

Hydrogen bonding and structural order in hydrogenated amorphous silicon prepared with hydrogen-diluted silane

Danesh, P.; Pantchev, B.; Antonova, K.; Liarokapis, E.; Schmidt, B.; Grambole, D.; Baran, J.

A study of the structural development of hydrogenated amorphous silicon (a-Si :H) during plasma-enhanced chemical vapour deposition with hydrogen-diluted silane has been carried out with focus on the variations in the hydrogen bonding configuration and in the amorphous silicon network with increasing film thickness. In addition, the hypothesis of a high fraction of non-bonded (molecular) hydrogen in a-Si :H has been tested. The total hydrogen concentration and its silicon-bonded fraction have been estimated by means of nuclear reaction analysis and infrared spectroscopy, respectively. It has been shown that the presumable molecular hydrogen is not detectable within the limits of the measurement accuracy of the methods used. The hydrogen concentration is uniformly distributed along the growth direction, and the infrared absorption modes at 2000 and 2100 cm-1 are not affected by increasing the film thickness. Raman spectroscopy has been used to follow the variations in the structure of the silicon network. The increase in the film thickness leads to an improved ordering of the amorphous network on the short and medium range scale for films deposited at low substrate temperatures. In films deposited at high substrate temperatures, the tendency of structural improvement has been detected only on the medium range scale.

Keywords: H:a-Si; NRA; Raman spectroscopy; hydrogen bonding

  • Journal of Physics D 37(2004), 249-254

Publ.-Id: 5993

Effect of post-hydrogenation on the structural properties of amorphous silicon network

Pantchev, B.; Danesh, P.; Liarokapis, E.; Schmidt, B.; Schmidt, J.; Grambole, D.

Post-hydrogenation of magnetron sputtered amorphous silicon films has been carried out with the aim to study the effect of hydrogen interaction with amorphous silicon network on its short and medium range order. Raman spectroscopy has been used to study the variations in the amorphous structure. Nuclear reaction analysis (NRA) has been used to determine the total amount and depth distribution of the penetrated hydrogen atoms. The concentration of the silicon-bonded hydrogen and the bonding configurations have been established by means of infrared (IR) transmission measurements. The values of hydrogen concentration evaluated by NRA and IR spectroscopy coincide within the measurement accuracy, suggesting that the hydrogen diffusion proceeds via interaction with the host silicon atoms. This interaction is accompanied by a rearrangement of the strained Si-Si bonds which leads to an improvement of the amorphous network.

Keywords: amorphous silicon; post-hydrogenation; hydrogen depth distribution; Raman spectroscopy

Publ.-Id: 5990

NIR Spectroscopic Study on the Influence of Phenolic OH Groups on the Neptunium(V) Humate Complex Formation

Sachs, S.; Bernhard, G.

We investigated the influence of phenolic OH groups on the Np(V) complexation by humic acids at pH 7 and pH 8. The studies were performed by near-infrared (NIR) absorption spectroscopy applying unmodified and chemically modified humic acids with blocked phenolic/acidic OH groups. The experimental data were evaluated with the metal ion charge neutralization model. For all humic acids under investigation comparable complexation constants were determined. However, compared to the original humic acids, modified humic acids with blocked phenolic/acidic OH groups show significant lower loading capacities for Np(V) under the applied experimental. This result indicates a lower amount of maximal available humic acid ligand sites for the complexation of Np(V). Thus, it can be concluded that humic acid phenolic/acidic OH groups contribute to the interaction between humic acid and Np(V) under the studied conditions.

Keywords: Humic substances; Humic acids; Actinides; Complexation; Neptunium

  • Contribution to external collection
    Humic Substances in Performance Assessment of Nuclear Waste Disposal : Actinide and Iodine Migration in the Far-Field. Second Technical Progress Report, Forschungszentrum Karlsruhe, Wissenschaftliche Berichte, FZKA 6969, Karlsruhe 2004, 61-71

Publ.-Id: 5989

Some metallurgical applications of magnetic fields. The role of model experiments and velocity measuring techniques.

Gerbeth, G.

Magnetic fields provide the possibility of a tailored flow control for metallurgical and crystal growth processes. Two examples will be presented: the application of a specially shaped steady magnetic field in the melt extraction process of thin metallic fibres, and the control of the flow filling process in the investment casting of aluminium alloys. The role of cold model experiments and the development of velocity measuring techniques for metallic melts will be stressed. As a final example, velocity measurements in a liquid metal switcher will be presented.

  • Lecture (Conference)
    Coventry University, 12.01.2004, Coventry, Great Britain

Publ.-Id: 5988

Differentiation between recurrent tumor or radiation necrosis in a child with anaplastic ependymoma after chemotherapy and radiation therapy

Beuthien-Baumann, B.; Hahn, G.; Winkler, C.; Heubner, G.

Background: In patients after treatment for malignant brain tumors, a clear distinction between tumor recurrence and radiation necrosis can be challenging. This case report describes the diagnostic workup in child with anaplastic ependymoma and inconclusive MRI (magnetic resonance imaging) and PET (positron emission tomography) findings.
Case Report: 1.5 years after resection, hyperfractionated radiotherapy and chemotherapy of an anaplastic ependymoma in the right parietal region, the cranial MRI of an 11-year-old girl showed multiple small contrast-enhanced lesions in the frontal cortex. In the following months, these lesions increased in number and size and neurologic symptoms developed. Diagnostic workup included repeated MRI scans, PET with an 18F-amino acid and 18F-fluorodexyglucose (FDG), as well as a brain biopsy.
Results: Amino acid PET, performed when the lesions were still small, showed multiple small areas of mild uptake in close correlation to the MRI lesions. Although not typical, this result was suspicious of tumor seeding, the more since the lesions appeared in gray matter areas outside the high-dose-rate irradiation field. A biopsy, performed 6 months later when the clinical appearance worsened, showed no tumor tissue. FDG PET, performed after the size and number of the lesions has increased, showed no intensely increased glucose metabolism, a high-grade recurrent tumor was therefore very unlikely. In the following months, the clinical picture stabilized.
Conclusion: The final interpretation of the lesions was multiple focal radiation necrosis based on perfusion abnormalities after chemotherapy and conformal hyperfractionated radiotherapy, probably due to an individually enhanced of the cerebral vessels.

Keywords: Anaplastic ependymoma; Magnetic resonance imaging; Positron emission tomography; Hyperfractionated radiotherapy; Radiation necrosis

  • Strahlentherapie Onkologie (2003) 179: 819-822

Publ.-Id: 5987

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