Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33508 Publications

The role of a TiN buffer layer on the growth of Ni-Ti sputtered thin films

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
  • Poster
    ESRF Science Days 2006, 07.-08.06.2006, Autrans, France

Permalink: https://www.hzdr.de/publications/Publ-9120
Publ.-Id: 9120


In-situ XRD during sputtering deposition of Ni-Ti Shape Memory Alloys on TiN/SiO2/Si(100)

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
  • Poster
    ESRF User's Meeting 2006, 07.-08.02.2006, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-9119
Publ.-Id: 9119


Modification of bubble-driven liquid metal flows under the influence of a DC magnetic field

Zhang, C.; Eckert, S.; Gerbeth, G.
The paper presents an experimental study devoted to a bubble-driven liquid metal flow under the influence of an external DC magnetic field. Experiments have been performed on laboratory scale at ambient temperature using the ternary alloy GaInSn. Measurements of the bubble-driven liquid metal flow have been carried out using the Ultrasound Doppler Velocimetry (UDV). The magnetic field has been imposed either in vertical direction parallel to the main bubble motion or in horizontal direction, respectively. Whereas a global damping of the flow field was generally observed in the case of the vertical aligned magnetic field, the application of a horizontal magnetic field can provoke a restructuring of the flow pattern with strong, non-steady vortical structures. This finding could attain relevance for metallurgical engineering, for instance the control of the mould flow during the continuous casting of steel by means of an electromagnetic brake.
Keywords: liquid metal, bubble plume, DC magnetic field, Ultrasound Doppler method, velocity measurements
  • Open Access Logo ISIJ International 47(2007)6, 795-801

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Permalink: https://www.hzdr.de/publications/Publ-9118
Publ.-Id: 9118


Texture evolution during annealing of Ni-Ti Shape Memory Alloy

Braz Fernandes, F. M.; Paula, A. S.; Canejo, J.; Mahesh, K. K.; Silva, R. J. C.; Martins, R. M. S.; Cardoso, A. M. A.; Schell, N.
Anisotropy of the shape recovery associated with shape memory effect strongly depends on the type of preferential orientation, that is present, as well as the ‘strength’ of the texture. In the present paper, we report the results obtained by the in-situ study of texture evolution during the annealing process in Ti-rich Ni-Ti Shape Memory Alloys (SMAs) with different thermal and mechanical histories. For this purpose, a Be-dome furnace installed into a 6-circle goniometer at the BM20 beamline (ROBL-CRG) at the ESRF (Grenoble) has been used. It is shown that there is a significant change in the preferential orientation of B2 phase, with the change in microstrain/coherence domain size, as a function of annealing temperature. This effect is also observed in the B19’ phase after cooling. The alpha-fiber II (austenite texture - <110>||RD ({111}<110>-{110}<110>) was present in the as-received alloy, but only up to 400ºC. The evolution of {111}<110> austenite texture component is quite clear for annealing temperatures above 400ºC.
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany
  • Contribution to proceedings
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany
    Proceedings of Shape Memory and Superelastic Technology 2004, Baden-Baden: ASM International, 45-50

Permalink: https://www.hzdr.de/publications/Publ-9117
Publ.-Id: 9117


In-situ study of the preferential orientation of magnetron sputtered Ni-Ti thin films as a function of bias and substrate type

Martins, R. M. S.; Schell, N.; Beckers, M.; Mücklich, A.; Reuther, H.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
The preferential orientation of Ni-Ti thin films is a crucial factor in determining the shape memory behavior. The texture has a strong influence on the extent of the strain recovery. The relationship between structure and deposition parameters is of extreme importance for future device applications. Our approach is in-situ x-ray diffraction during deposition carried out in a process chamber installed at a synchrotron radiation beamline. Near-equiatomic films were co-sputtered from Ni-Ti and Ti targets. Substrate type and bias voltage play an important role for the preferred orientation. On naturally oxidized Si(100) substrates the NiTi B2 phase starts by stacking onto (h00) planes and then changes to (110) fiber texture with increasing film thickness. For thermally oxidized Si(100) substrates, this cross-over is only observed when a bias voltage is applied. The experiments were supplemented by ex-situ transmission electron microscopy and Auger Electron Spectroscopy allowing an additional deeper insight into the film/substrate interface.
Keywords: Ni-Ti; Sputter deposition; In-situ x-ray diffraction; Texture development; Interface
  • Contribution to proceedings
    Conference on Shape Memory and Superelastic Technology 2006, 07.-11.05.2006, Asilomar, U.S.A.
    Proc. of SMST 2006, 363-372
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology 2006, 07.-11.05.2006, Asilomar, U.S.A.

Permalink: https://www.hzdr.de/publications/Publ-9116
Publ.-Id: 9116


Role of the substrate on the growth of Ni-Ti sputtered thin films

Martins, R. M. S.; Schell, N.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.
Ni-Ti thin films have been recognized as promising and high performance materials in the field of microelectromechanical system applications. However, important issues like formation of film texture and its control are still unresolved. Widening the scope of previous experiments concerning the influence of the deposition parameters on the Ni-Ti films structure, here we show how different crystallographic orientations can be obtained by changing the substrate type. The growth of near-equiatomic Ni-Ti films, deposited by magnetron co-sputtering from Ni-Ti and Ti targets on heated substrates ( 470C), has been studied in situ by x-ray diffraction at a synchrotron radiation beamline. As mentioned in other studies for depositions on Si(100), a (110) fiber texture is observed for the B2 phase. However, a preferential stacking of (100) planes of the B2 phase parallel to the film surface was observed when using a MgO(100) substrate. The preferential orientation of B2(100) // MgO(100) was very strong and was kept as such until the end of the deposition, which lasted for 2 hours (~ 900 nm). Ni-Ti films were also deposited on a TiN layer (~ 15 nm) previously deposited on top of a SiO2/Si(100) substrate. In this case, a crossover from (110) oriented grains dominating at small thicknesses, to (211) oriented grains taking over at larger thicknesses was observed. These are promising results concerning the manipulation of the crystallographic orientations of Ni-Ti thin films, since the texture has a strong influence on the extent of the strain recovery.
Keywords: structure and morphology, deposition by sputtering, in-situ x-ray diffraction
  • Poster
    ESOMAT 2006 - European Symposium on Martensitic Transformations and Shape Memory Alloys, 10.-15.09.2006, Bochum, Germany
  • Materials Science and Engineering A 4812-482(2008), 626-629

Permalink: https://www.hzdr.de/publications/Publ-9114
Publ.-Id: 9114


In-situ study of Ni-Ti thin film growth on a TiN intermediate layer by x-ray diffraction

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Pereira, L.; Mahesh, K. K.; Fernandes, F. M. B.
Shape Memory Alloy (SMA) Ni-Ti thin films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. In this study, near-equiatomic films were obtained by co-sputtering from Ni-Ti and Ti targets in a process chamber installed at a synchrotron radiation beamline. In-situ x-ray diffraction during the growth of these films allowed establishing a relationship between structure and deposition parameters. The effect of a TiN layer deposited on top of the SiO2/Si(100) substrate prior to the deposition of the Ni-Ti films was analysed. These experiments show that TiN acts not only as a diffusion barrier, but also induces different crystallographic orientations. A TiN layer with ~ 215 nm thickness induces the preferential growth of (110) planes of the Ni-Ti B2 phase parallel to the substrate from the beginning of the deposition with a constant growth rate during the whole deposition. For a TiN thickness of ~ 15 nm, the diffraction peak B2(110) also appears from the beginning of the deposition but much less intense. In this latter case, the B2(211) peak was also detected having observed a crossover from <110> oriented grains dominating at small thicknesses, to <211> oriented grains taking over at larger thicknesses. The same orientations and similar intensities were observed for a Ni-Ti film deposited on a TiN layer with ~ 80 nm.
Keywords: Shape memory alloy; Ni-Ti; deposition by sputtering; in-situ x-ray diffraction; texture development
  • Poster
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France
  • Sensors and Actuators B 126(2007)1, 332-337

Permalink: https://www.hzdr.de/publications/Publ-9113
Publ.-Id: 9113


Structural in-situ studies of Ni-Ti thin films

Martins, R. M. S.; Braz Fernandes, F. M.; Silva, R. J. C.; Beckers, M.; Schell, N.
Ni-Ti thin films present great advantages for the fabrication of micro-actuators. The phase transformation and precipitation, which are responsible for the shape memory effect, have been widely studied in bulk material and thin films. However, in-situ studies have been limited to the ageing/annealing treatments after deposition. In this study we present a series of results that clearly illustrate the interest of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the ROssendorf BeamLine (ROBL-CRG) at the ESRF, Grenoble, allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer of the ROBL-CRG beamline. This facility allowed us to follow the structural evolution of the films also during the deposition process.
Keywords: Ni-Ti, SMA, x-ray diffraction
  • Contribution to proceedings
    Shape Memory and Superelastic Technologies 2004, 03.-07/10/2004, Baden Baden, Germany
    Proceeding of SMST 2004, Baden Baden: ASM International, 421-426
  • Lecture (Conference)
    Conference on Shape Memory and Superelastic Technology-Europe 2004, 03.-07.10.2004, Baden-Baden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9112
Publ.-Id: 9112


Long-term corrosion and leaching of depleted uranium (DU) in the soil

Schimmack, W.; Gerstmann, U.; Schultz, W.; Geipel, G.
The corrosion and leaching of depleted uranium (DU) was investigated for three years using six DU munitions (145 – 264 g DU) each buried in a column with a soil core of ca. 3.3 kg dry soil mass. The columns were installed in an air-conditioned la-boratory. Each week they were irrigated and 238U was determined in the effluents by Inductively Coupled Plasma Mass Spectrometry. In addition, 235U was measured oc-casionally in order to assure that the origin of 238U was predominantly the DU muniti-on. On average, 14.5 g corresponding to 7.9 % of the initial DU mass was corroded after three years indicating an acceleration of the corrosion as compared to the first year (see Schimmack et al., Radiat Environ Biophysics 44: 183-191 (2005)). The leaching rates increased much stronger than the corrosion by factors of more than 100 resulting in a mean total amount of leached 238U of 13 mg as compared to 0.03 mg after the first year. The uranium species identified by time-resolved laser-induced fluorescence spectroscopy were mainly hydroxo and carbonate compounds in the seepage water and phosphate compounds in the corroded material. It is concluded that the dramatic increase of the leaching and its large temporal and spatial variability do not allow any extrapolation into the future. However, the high level of the 238U concentrations in the seepage water demands further investigations on the transport of 238U through the soil in order to estimate the concentration of 238U from DU muniti-ons in the groundwater for areas affected by DU weapons.
Keywords: depleted Uranium, soil, corrosion, leaching, speciation

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Permalink: https://www.hzdr.de/publications/Publ-9111
Publ.-Id: 9111


Structure, stability and electronic properties of composite Mo_(1-x)Nb_xS_2 nanotubes

Ivanovskaya, V. V.; Heine, T.; Gemming, S.; Seifert, G.
The effect of Mo -> Nb substitution on the electronic structure of MoS2 nanotubes has been investigated using the density functional tight binding method (DFTB). It has been found that composite Mo1-xNbxS2 nanotubes (with Nb contents of 5, 10 and 25 at%) are more stable than the corresponding pure tubes, especially for larger tube diameters. The defect-formation energy indicates that the most stable dopant arrangement is a NbS2 stripe along the tube direction. However, entropy effects may favor a random arrangement of Nb dopant atoms at high temperatures in the tubes with a larger diameter. All of the studied Mo1-xNbxS2 nanotubes have metallic properties, independent of their chirality, diameters and ordering type of substitutional atoms.
Keywords: WS2 NANOTUBES; DISULFIDE NANOTUBES; CARBON NANOTUBES; MOS2; FUNCTIONALIZATION

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Permalink: https://www.hzdr.de/publications/Publ-9110
Publ.-Id: 9110


A study on the two-phase flow in a stirred tank reactor agitated by a gas inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Hessel, G.; Schmitt, W.
Experimental and numerical studies of a gas-liquid two-phase flow were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-ray cone beam computed tomography (CBCT) measurements were taken at five different stirrer speeds starting from 1000 rpm at which the gas inducement occurs for the given operating conditions. The considerable difficulties in acquiring the phase distribution due to beam hardening and radiation scattering effects were overcame by developing a suitable measurement setup as well as by calibration and software correction methods to achieve high accuracy. The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software.
Keywords: stirred tank reactor, gas-inducing impeller, mixing, X-Ray computed tomography, CFD

Permalink: https://www.hzdr.de/publications/Publ-9108
Publ.-Id: 9108


A Method for System Matrix Construction and Processing for Reconstruction of In-Beam PET Data

Shakirin, G.; Crespo, P.; Enghardt, W.
At the experimental heavy ion therapy facility (Gesellschaft für Schwerionenforschung Darmstadt, Germany) an in-beam PET scanner is operated for quality assurance monitoring simultaneously to the therapeutic irradiation. The fixed dual-head PET scanner, which is completely integrated into the treatment facility, registers the annihilation γ-rays following the decay of minor amounts of β+-radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. The quality assurance monitoring of the therapeutic irradiation could profit significantly of a very fast (ideally, real time) reconstruction algorithm and, therefore, an accurate knowledge of the system response function (system matrix) is required. These requirements lead to the development of a dedicated method of system matrix calculation which has to model the system response precisely and deliver system matrix values rapidly. By exploiting the system symmetries, in combination with an optimized interpolation and approximation strategies, the proposed method delivers the system response function in a continuous 3D image space with a high accuracy.
Keywords: Positron emission tomography, image reconstruction, biomedical applications of radiation, in-beam PET
  • Poster
    2006 Nuclear Science Symposium and Medical Imaging Conference, 31.10.-05.11.2006, San Diego, USA
  • Contribution to proceedings
    2006 Nuclear Science Symposium and Medical Imaging Conference, 31.10.-05.11.2006, San Diego, USA
    2006 IEEE Nuclear Science Symposium conference record: Institute of Electrical and Electronics Engineers, 1-4244-0561-0, 3351-3354
  • IEEE Transactions on Nuclear Science 54(2007), 1710-1716

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Permalink: https://www.hzdr.de/publications/Publ-9107
Publ.-Id: 9107


Experimental and numerical prediction of horizontal stratified flows

Höhne, T.; Vallee, C.; Prasser, H.-M.
Slug flow as a multiphase flow regime can occur in the cold legs of pressurized water reactors, for instance after a small break Loss of Coolant Accident (SB-LOCA). Slug flow is potentially hazardous to the structure of the system due to the strong oscillating pressure levels formed behind the liquid slugs. It is usually characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry out a significant amount of liquid with high kinetic energy. For the experimental investigation of air/water flows, a horizontal channel with rectangular cross-section was build at Forschungszentrum Dresden-Rossendorf (FZD). Experimental data were used to check the feasibility to predict the slugging phenomenon with the existing multiphase flow models build in ANSYS CFX. Further it is of interest to prove the understanding of the general fluid dynamic mechanism leading to slug flow and to identify the critical parameters affecting the main slug flow parameters (like e.g. slug length, frequency and propagation velocity; pressure drop).
Keywords: CFD, flow pattern, stratified flow, slug flow
  • Contribution to proceedings
    International Conference on Multiphase Flow ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    CD-ROM, paper S5_Tue_C_23
  • Lecture (Conference)
    International Conference on Multiphase Flow ICMF 2007, 09.07.2007, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-9106
Publ.-Id: 9106


CFD-simulation of thermal hydraulic benchmark V1000CT–2 using ANSYS CFX

Höhne, T.
The OECD/NEA and AER coupled code benchmarks for light water reactors markedly contribute to the testing of best estimate coupled codes in reactivity transients. At the same time, these benchmarks and flow mixing studies indicate that further improvement of the mixing computation tools in the integrated codes is necessary.
Plant measured data from VVER-1000 coolant mixing experiments were used to test and validate CFD codes. The task is to compare the various calculations with measured data, using specified boundary conditions and core power distributions.
The experiments, which are provided for CFD validation, include single loop cooling down or heating-up by disturbing the heat transfer in the steam generator (SG) through the steam valves at low reactor power in the range of 5-14% and with all main coolant pumps (MCP) in operation. They were conducted during the plant commissioning phase at Kozloduy-6, Bulgaria and Kalinin-1, 2, Russia.
CFD calculations have been performed for the thermal hydraulic benchmark V1000CT-2 using ANSYS CFX. The numerical grid model was generated with the grid generator ICEM-CFD and contains 4.7 Mio. tetrahedral elements. The Best Practice Guidelines (BPG) in using CFD in Nuclear Reactor Safety Applications have been used. Different advanced turbulence models were used in the numerical simulation. The best agreement with the Kozloduy heating-up experiment at the core inlet shows the Detached Eddy Simulation (DES). Strong fluctuations occur in the downcomer of the RPV. The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%. Uncertainties are still the estimation and interpolation of experimental values at the core outlet to the core inlet.
Keywords: WWER-1000, CFD, Benchmark, Coolant Mixing
  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
    CD-Rom, ICONE15-10259
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.04.2007, Nagoya, Japan

Permalink: https://www.hzdr.de/publications/Publ-9105
Publ.-Id: 9105


Erzeugung von Nano-Strukturen mit Ionenstrahlen

Schmidt, B.
  • Lecture (others)
    Seminar bei AMD, 27.03.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9103
Publ.-Id: 9103


Materials Science issues for the fabrication of nanocrystal memory devices by ultra low energy ion implantation

Claverie, A.; Bonafos, C.; Ben Assayag, G.; Schamm, S.; Cherkashin, N.; Paillard, V.; Dimitrakis, P.; Kapetenakis, E.; Tsoukalas, D.; Muller, T.; Schmidt, B.; Heinig, K.-H.; Perego, M.; Fanciulli, M.; Mathiot, D.; Carrada, M.; Normand, P.
Nanocrystal memories are attractive candidate for the development of non volatile memory devices for deep submicron technologies. In a nanocrystal memory device, a 2D network of isolated nanocrystals is buried in the gate dielectric of a MOS and replaces the classical polysilicon layer used in floating gate (flash) memories. Recently, we have demonstrated a route to fabricate these devices at low cost by using ultra low energy ion implantation. Obviously, all the electrical characteristics of the device depend on the characteristics of the nanocrystal population (sizes and densities) but also on their exact location with respect to the gate and channel of the MOS transistor. It is the goal of this paper to report on the main materials science aspects of the fabrication of 2D arrays of Si nanocrystals in thin SiO2 layers and at tunable distances from their SiO2/interfaces.
Keywords: Silicon nanocrystals, non volatile memories, Ion implantation, diffusion in SiO2, TEM, Raman spectroscopy, photoluminescence, single electron phenomena
  • Lecture (Conference)
    2nd International Conference on Diffusion in Solids and Liquids, 26.-28.07.2006, Aveiro, Portugal

Permalink: https://www.hzdr.de/publications/Publ-9102
Publ.-Id: 9102


FIB induced cobalt disilicide nanowire growth in silicon

Schmidt, B.; Akhmadaliev, C.; Bischoff, L.
In the present work FIB ion implantation of Co+ ions and subsequent anneaeling was applied to ion beam synthesis of CoSi2 nanowires with feature dimensions of about 20-50 nm in diameter and wire lengths of some µm. Using the CANION 31Mplus FIB column (Orsay Physics) a focusing of the Co++ ion beam down to a spot diameter of 30-50 nm was achieved. The ion energy was chosen to be 60 keV corresponding to a mean ion penetration depth of Rp = 33 nm. For the study of the conventional ion beam synthesis of CoSi2 nanowires (phase separation through precipitation and wire ripening during thermal treatment) and their decay into chains of nanoparticles due to nanowire instabilities the samples were implanted with high doses (1x1016-2x1017 cm-2) and at 420 °C sample temperature. Additionally, the scan direction of the FIB relative to the crystal directions was varied (normal FIB scan-direction was parallel to the [110]-direction on the Si surface). Small misalignment of the FIB trace relative to the [110] orientations leads to the decay of the CoSi2 nanowires into chains of more or less prolonged CoSi2 nanoparticles. Samples implanted at lower ion doses (1014-1016 cm-2) and at room temperature were used to investigate the influence of locally FIB induced irradiation defects on the CoSi2 nanowire growth. In this case, nanowires were again formed during thermal treatment by reacting of cobalt from a thin evaporated layer on the sample back side with defects induced by Co+ ion implantation with the FIB. The nanowires here are self-aligned along the in-plane [110] silicon crystal directions in (001)- and (111)-Si. In contrast to conventional ion beam synthesis of CoSi2 nanowires by high dose FIB implantation along a narrow trace defect-induced and self-aligned nanowire growth seems to be more stable.
Keywords: FIB, ion beam synthesis, CoSi2 nanowires
  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Permalink: https://www.hzdr.de/publications/Publ-9100
Publ.-Id: 9100


Vorstellung des Instituts für Radiochemie und Erläuterungen zum Ablauf des Kernbrennstoffkreislaufes

Steudtner, R.
Erläuterungen zum Kernbrennstoffkreislauf, zur Herstellung von Brennelementen sowie zur Funktionsweise von Reaktoren
  • Lecture (others)
    Vortrag anlässlich des Besuches einer Schülergruppe, 13.06.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9099
Publ.-Id: 9099


Bacteria from extreme environments and their interaction with uranium(VI)

Raff, J.
After a long lasting period of uranium mining and production in Saxony and Thuringia, Eastern Germany, mines have fallen into disuse.
Soil, subsoil and waste waters of former mines and production sites contain still high concentrations of heavy metals and radionuclides, such as uranium. Besides chemical and physical factors influencing the mobility of uranium, also microbial metabolism plays a decisive role in enhancing or retarding migration effects. For instance bacteria are able to bind uranium on the cell surface, to accumulate uranium inside the cell, to reduce or oxidize uranium or to form insoluble uranium precipitates. Intensive studies on the uranium-microbe interaction allow on the one hand to obtain a more detailed understanding of the macroscopic behaviour of uranium in nature and on the other hand the development of new innovative bioremediation strategies for cleaning uranium contaminated water and soil. Starting from several examples of microbes interacting with uranium, the lecture will give an overview about bacterial detoxification strategies, the underlying molecular mechanisms and their application potential for bioremediation.
  • Invited lecture (Conferences)
    Institut für Gewässerschutz/Wassertechnologie, Forschungszentrum für Limnologie (EAWAG), 25.-27.06.2006, Kastanienbaum, Swizerland

Permalink: https://www.hzdr.de/publications/Publ-9097
Publ.-Id: 9097


Solution processable organic field-effect transistors utilizing an alpha,alpha '-dihexylpentathiophene-based swivel cruciform

Zen, A.; Bilge, A.; Galbrecht, F.; Alle, R.; Meerholz, K.; Grenzer, J.; Neher, D.; Scherf, U.; Farrell, T.
A pentathiophene-based swivel cruciform, which allows rotation between the cruciform arms, was synthesized. Homogeneous microcrystalline films were processed from solution, and field-effect transistors utilizing this dimer gave hole mobilities up to 0.012 cm2/V·s.
Keywords: organic field-effect transistors (OFETs), pentathiophene-based swivel cruciform, hole mobilities
  • Journal of the American Chemical Society 128(2006)12, 3914-3915

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Permalink: https://www.hzdr.de/publications/Publ-9096
Publ.-Id: 9096


Investigation of Environmental Colloids/Nanoparticles at the FZD

Zänker, H.
- wird nachgereicht
  • Lecture (others)
    1st meeting of the working group "Aquatic Nanoscience and Nanotechnology", 11.-12.12.2006, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-9095
Publ.-Id: 9095


Joint Project: Migration of Actinides in the System Clay, Humic Substance, Aquifer - Migration Behavior of Actinides (Uranium, Neptunium) in Clays: Characterization and Quantification of the Influence of Humic Substances (Final Report BMWi Project No.: 02 E 9673)

Sachs, S.; Krepelova, A.; Schmeide, K.; Koban, A.; Günther, A.; Mibus, J.; Brendler, V.; Geipel, G.; Bernhard, G.
Objective of this project was the study of interaction processes between humic substances, U(VI), Np(V) and kaolinite KGa-1b. It contributed to the attainment of a better process understanding, the improvement of the knowledge on the interaction of humic substances and metal ions and the enhancement of the thermodynamic database.
With a synthetic humic acid (HA), N-containing functional groups of HA were characterized by 15N-NMR spectroscopy. Based on these results, model studies of the influence of amino groups on the complexation behavior of HA were performed. Spectroscopic studies with amino acids show that the amino group do not contribute to the U(VI) complexation at pH 4.
The impact of kaolinite on the formation of HA and humic substance-kaolinite-sorbates was studied in model syntheses. The results exhibit that the presence of kaolinite during the syntheses mainly influences the yields on HA and their elemental compositions. Synthetic humic substance-kaolinite-sorbates were isolated.
Under exclusion of CO2, the U(VI) complexation by HA was investigated at pH 7 by means of the conventional time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses. Complexation parameters for the ternary complex UO2(OH)HA(I) were determined.
Studies of the Np(V) reduction in presence of HA with different functionalities under anaerobic conditions have shown that Np(V) is reduced to Np(IV) by HA. The redox capacity depends on the HA functionality. Applying a modified HA it was verified that phenolic/acidic OH groups play a dominating role in the Np(V) reduction.
The influence of HA on the U(VI) and Np(V) sorption onto kaolinite was investigated in batch experiments. In dependence on the experimental conditions, HA effects the sorption and consequently the mobility of U(VI) and Np(V). From studies of the U(VI) sorption onto synthetic humic substance-kaolinite-sorbates it was concluded that the structure and functionality of sorbed/associated humic substances considerably influence the sorption behavior of U(VI). The structure of U(VI)-kaolinite-surface complexes in presence of HA was studied by means of X-ray absorption spectroscopy and TRLFS and compared to those of U(VI)-kaolinite-complexes.
Investigations of the migration of HA and U(VI) in the laboratory system kaolinite-water were carried out in diffusion experiments. The migration of HA in compacted clay is governed by diffusion and influenced by its colloidal properties. Humic substances exert an immobilizing effect on the U(VI) transport in compacted kaolinite.
Keywords: Actinides, Uranium, Neptunium, Humic substances, Humic acids, Model substances, Clay, Kaolinite, Complexation, Reduction, Sorption, Migration, Diffusion, Repository
  • Other report
    Dresden: Forschungszentrum Dresden-Rossendorf, 2006
    116 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-460 2007
  • Contribution to external collection
    C.M. Marquardt: Migration of Actinides in the System Clay, Humic Substances Aquifer. Forschungszentrum Karslruhe, Wissenschaftliche Berichte FZKA 7407, Karlsruhe: Forschungszentrum Karlsruhe, 2008, 23-140

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Publ.-Id: 9094


EXAFS spectra analysis: the mother wavelet choice

in Russian
Schabelnikova, S.; Funke, H.; Chukalina, M.
- wird nachgereicht
  • Contribution to proceedings
    International science-technical Conference "Fundamental problems of the radioelectronic instrument-making industry", 24.-28.10.2006, Moscow, Russia
    Book of Proceedings, MIREA, 143-146
  • Poster
    International science-technical Conference "Fundamental problems of the radioelectronic instrument-making industry", 24.-28.10.2006, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-9093
Publ.-Id: 9093


Wavelet analysis of the EXAFS spectra: new wavelet function as a linear combination of two Morlet wavelets

Schabelnikova, S.; Funke, H.; Chukalina, M.
- wird nachgereicht
  • Contribution to proceedings
    Digest Reports of the XVI International Synchrotron RadiationConference., 10.-14.07.2006, Novosibirsk, Russia
    Book of Abstracts, 76
  • Poster
    Digest Reports of the XVI International Synchrotron RadiationConference. Book of Abstracts, 11.-14.07.2006, Novosibirsk, Russia

Permalink: https://www.hzdr.de/publications/Publ-9092
Publ.-Id: 9092


Wavelet transform usage to analyse the signals and images collected by the X-ray techniques

in Russian
Chukalina, M.; Funke, H.
- wird nachgereicht
  • Contribution to proceedings
    International scientific Workshop "Modern techniques for the X-ray diffraction data analysis", 22.-25.05.2006, Velikii Novgorod, Russia, 278-281
  • Lecture (Conference)
    Wavelet transform usage to analyse the signals and images collected by the X-ray techniques, 22.-25.05.2006, Velikii Novgorod, Russia

Permalink: https://www.hzdr.de/publications/Publ-9091
Publ.-Id: 9091


The local structure of soddyite: EXAFS shell fitting and wavelet analysis

Funke, H.; Hennig, C.; Rossberg, A.; Scheinost, A.
- wird nachgereicht
  • Poster
    Actinides XAS 2006, 18.-20.09.2006, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9090
Publ.-Id: 9090


XAFS studies of cobalt(II) binding by solid peat and soil-derived humic acids and plant-derived humic acid-like substances

Ghabbour, E.; Scheinost, A.; Davies, G.
This work has examined cobalt(II) binding by a variety of solid humic acids (HAs) isolated from peat, plant and soil sources at temperatures down to 60 K. The results confirm that X-ray absorption near-edge spectroscopy (XANES) measurements cannot distinguish between aquo and carboxylato ligands in the inner coordination sphere of Co(II). However, between I and 2 inner-sphere carboxylato ligands can be detected in all the peat, plant and soil-derived HA samples by extended X-ray absorption fine structure (EXAFS) measurements, indicating inner-sphere coordination of HA-bound Co(II). The precision of C(carboxylate) detection is limited by the extent and quality of the data and the contribution from inner-sphere O to the Fourier transformed peaks used to detect carbon. Putative chelate ring formation is consistent with a relatively negative entropy change in step A, the stronger Co(II) binding step by HA functional groups, and could relate to 'non-exchangeable' metal binding by HSs.
  • Chemosphere 67(2007)2, 285-291

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Publ.-Id: 9089


Investigation of a TSEE dosimetry system for determination of dose in a cell monolayer

Lehnert, A.; Beyreuther, E.; Lessmann, E.; Pawelke, J.
A prototype system for radiobiological studies has been investigated. It is based on thermally stimulated exoelectron emission (TSEE) detectors and can be used for precise determination of the absorbed dose in a live cell monolayer of several µm thickness. In the present study, five types of BeO detectors, different in structure and method of production, were tested in combination with a Geiger-Müller counter. The dose response and dose range, reproducibility and long-time stability of response, as well as the applicability in a simulated cell culture environment have been studied. The dose response was found to be linear over two orders of magnitude and limited by the counter resolution. However, by a variation of detector sensitivity, the whole dose range of interest for radiobiological experiments can be covered. The irradiation in a simulated cell environment was successful only for one detector type. The system performance was found to be limited by the variation in the system response for time periods longer than several hours, therefore, it is suitable for absolute dose measurement with calibrated detectors if reproducible laboratory conditions are provided.
Keywords: TSEE, exoelectron emission, BeO, Geiger-Müller counter, dosimetry, cell monolayer

Permalink: https://www.hzdr.de/publications/Publ-9088
Publ.-Id: 9088


Plutonium incorporation in phosphate and titanate ceramics for minor actinide containment

Deschanels, X.; Picot, V.; Glorieux, B.; Jorion, F.; Peuget, S.; Roudil, D.; Jegou, C.; Broudic, V.; Cachia, J. N.; Advocat, T.; Den Auwer, C.; Fillet, C.; Coutures, J. P.; Hennig, C.; Scheinost, A.
Two ceramics, zirconolite and a monazite-brabantite solid solution (MBss) were studied for the immobilization of minor actinides (Np, Am, Cm) produced by reprocessing spent fuel. Monoclinic zirconolite (CaZrTi2O7) is a fluorite derivative structure and is the primary actinide host phase in Synroc (a titanate composite). Monazite (LnPO(4), where Ln = La, Ce, Nd, Gd, etc.) is a monoclinic orthophosphate containing trivalent cations, and brabantite (Ca(0.5)An(0.5)PO(4)) is ail isostructural monazite compound containing tetravalent cations (An = Th and U). The nominal composition of the ceramics studied in this work is (Ca0.87Pu0.13)Zr(Al0.26Ti1.74)O-7 for zirconolite and (Ca0.09Pu0.09La0.73Th0.09)PO4 for the monazite-brabantite solid solution. These formulas correspond to 10 wt% PuO2 loading ill each material. XANES spectroscopy showed that the plutonium is tetravalent in zirconolite and trivalent in MBss. Thorium, another tetravalent cation, call be incorporated at 10 wt% ThO2 in MBss. Aluminum and calcium balance the excess cationic charge resulting from the incorporation of Pu(IV) in zirconolite and Th(IV) in brabantite, respectively. The relative density of the pellets exceeded 90% of theoretical density. The samples exhibited a homogeneous microstructure even if some minor phases. representing less than 2% of the surface area, were detected. The two ceramics are compared in terms of actinide loading, and preliminary results on their long-term behavior are discussed. (c) 2006 Elsevier B.V. All rights reserved.
  • Journal of Nuclear Materials 352(2006)1-3, 233-240

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Publ.-Id: 9087


Enhancing cerium and plutonium solubility by reduction in borosilicate glass

Cachia, J. N.; Deschanels, X.; Den Auwer, C.; Pinet, O.; Phalippou, J.; Hennig, C.; Scheinost, A.
High-level radioactive wastes produced by spent fuel reprocessing containing fission and activation products as well as actinides are incorporated in a borosilicate glass. To ensure optimum radionuclide containment, the resulting glass must be as homogeneous as possible. Microscopic heterogeneity can arise from various processes including the excess loading of an element above its solubility limit. The current actinide loading limit is 0.4 wt%. Work is in progress to assess the actinide solubility in these glasses, especially for plutonium. Initially the actinides were simulated by lanthanides and hafnium. The results show that trivalent elements (La, Gd) exhibit greater solubility than tetravalent elements (Pu, Hf). Cerium is an interesting element because its oxidation state varies from IV to III depending on the process conditions, such as the temperature and redox potential of the melt. In order to quantify the solubility increase, cerium-doped glass samples were melted under reducing conditions by adding a reducing agent. The solubility observed at 1473 K increased significantly from 0.95 to 13.00 wt%. Several reducing compounds have been tested. This paper deals with this study and the application to reduce Pu(IV) to Pu(III). The reduction state was characterized by X-ray absorption spectroscopy (XANES) for plutonium and by chemical analysis for cerium. The material homogeneity was verified by optical and scanning electron microscopy. Preliminary findings concerning the reduction of Pu-doped glasses fabricated in hot cells are also discussed. (c) 2006 Elsevier B.V. All rights reserved.
  • Journal of Nuclear Materials 352(2006)1-3, 182-189

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Publ.-Id: 9086


The molecular topology of uranium(VI) bonding to iron and aluminium oxyhydroxide nanoclusters revisited by EXAFS spectroscopy

Rossberg, A.; Ulrich, K.-U.; Scheinost, A. C.
Applying a novel approach to the spectral analysis of Extended X-ray Absorption Fine Structure (EXAFS) we were able to derive an advanced 3-D structural model of the uranyl sorption complex on hydrated carbonate-free surfaces of aluminum(III) and iron(III) oxyhydroxide nanoclusters. The calculated molecular model fits the EXAFS data consistently up to a radial sphere of 4.5 Å around the uranium absorber. Being unaware of the physicochemical reasons for the specific complex topology characterized by a slightly tilted and distorted geometry, alternative ideas of EXAFS interpretation are discussed.
Keywords: uranium, sorption, iron oxides, monte carlo simulation, x-ray absorption spectroscopy
  • Poster
    Actinides XAS 2006, 18.-20.09.06, Karlsruhe, Germany
  • Contribution to proceedings
    Actinides XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, 978-92-64-99006-7, 281

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Publ.-Id: 9085


Spectroscopic Studies on Colloid-borne Uranium(VI)

Rossberg, A.; Ulrich, K.-U.; Scheinost, A. C.
wird nachgereicht
Keywords: uranium, mining, sorption, iron oxide, x-ray absorption spectroscopy
  • Poster
    16th Users Meeting, ESRF, 08.-11.02.2006, Grenoble, France, 06.-10.02.2006, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-9084
Publ.-Id: 9084


Production of 86Y and 56Co at the Rossendorf CYCLONE 18/9

Preusche, S.; Wüst, F.; Seifert, S.; Schilling, K.-D.; Wenzel, R.; Dohn, N.; Steinbach, J.
The Rossendorf version of the CYCLONE 18/9 is equipped with a 2 m long external beam transport line (BTL) to have the possibility of producing non-standard PET radionuclides. For this purpose a solid target system was developed and mounted to the BTL. This system increases the flexibility of the CYCLONE 18/9 and enables the production of e.g. 86Y and 56Co for applications in radiochemistry, nuclear medicine and nuclear physics. The solid target system is introduced shortly and the parameters, data and results of the production of 86Y and 56Co are given.
  • Lecture (Conference)
    11th International Workshop on Targetry and Target Chemistry, 28.-31.08.2006, Cambridge, Great Britain
  • Contribution to proceedings
    11th International Workshop on Targetry and Target Chemistry, 28.-31.08.2006, Cambridge, UK
    11th International Workshop on Targetry and Target Chemistry, 86

Permalink: https://www.hzdr.de/publications/Publ-9083
Publ.-Id: 9083


Experimental investigation and CFD validation of horizontal air/water slug flow

Vallee, C.; Höhne, T.
In different scenarios of small break Loss of Coolant Accident (SB-LOCA), stratified two-phase flow regimes can occur in the main cooling lines of pressurized water reactors. Because these flow patterns cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated, especially if they are to be applied to nuclear reactor safety. Because the structure of the interface is strongly connected with the momentum transfer between the phases, the water surface characteristics can be used for validation purposes. Experimental data suitable for CFD validation must satisfy special quality criteria, in particular the boundary conditions and the measurement resolution.

For the investigation of co-current two-phase flows at atmospheric pressure and room temperature, the Horizontal Air/Water Channel (HAWAC) was built at Forschungszentrum Dresden-Rossendorf. At the channel inlet, a special device was designed for a separate injection of water and air into the test-section. A blade separating the phases can be moved up and down to control the free inlet cross-section for each phase. This provides adjustable and well-defined inlet boundary conditions and therefore very good CFD validation possibilities.

The HAWAC facility is designed for the application of optical measurement techniques, which deliver the high resolution required for CDF validation. Therefore, the 8 m long acrylic glass test-section with rectangular cross-section provides good observation possibilities. High-speed video observation and particle image velocimetry (PIV) were applied during slug flow. The camera images show the generation of slug flow from the inlet of the test-section. An algorithm was developed to recognise the interface and the extraction of quantitative values, like water level and slug propagation velocity. The PIV measurements reveal the inner flow rotation inside a slug.

Parallel to the experiments, CFD calculations were carried out. The aim of the numerical simulations is to validate the prediction of slug flow with the existing multiphase flow models built in the commercial code ANSYS CFX. The Euler-Euler two-fluid model with the free surface option was applied to a grid of 600,000 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging, while quantitative comparison show that further model improvement is needed.
Keywords: Horizontal two-phase flow, Slug flow, High-speed video observations, CFD
  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
    Paper ICONE15-10469
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan

Permalink: https://www.hzdr.de/publications/Publ-9082
Publ.-Id: 9082


Impact of optical in-plane anisotropy on near-field phonon polariton spectroscopy

Schneider, S.; Seidel, J.; Grafström, S.; Eng, L. M.; Winnerl, S.; Stehr, D.; Helm, M.
To examine the influence of optical anisotropy on the near-field signal measured in a scattering-type scanning near-field optical microscope, we excite optically uniaxial LiNbO3 close to a phonon resonance at a wavelength of 13 µm in the infrared regime using a tunable free-electron laser. This allows us to excite a phonon polariton resonance in the coupled tip-sample system. We find that the resonance shows a clear dependence on the orientation of the optical axis of the birefringent crystal.
  • Applied Physics Letters 90(2007), 143101

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Permalink: https://www.hzdr.de/publications/Publ-9081
Publ.-Id: 9081


High-resolution rapid-scan THz spectrometer using a large-area photoconductive emitter in combination with asynchronous optical sampling

Dreyhaupt, A.; Winnerl, S.; Schneider, H.; Helm, M.; Bartels, A.; Thoma, A.; Janke, C.; Dekorsy, T.
We present an approach for photoconductive THz generation providing a broad bandwidth and exceptionally high electric-field amplitude. A large-area interdigitated two-electrode structure on a GaAs substrate offers high electric fields at moderate bias voltages. In order to avoid destructive interference of the THz waves in the far field, every second electrode gap is masked by an additional metallization [1]. Thus all semiconductor regions exposed to incident radiation exhibit parallel electric fields and photocarriers excited by a mode locked Ti:Sapphire laser with MHz or GHz repetition rates are accelerated in the same direction. Areas with anti-parallel fields do not contribute to the THz radiation, thus the resulting constructive interference gives rise to an intense THz output. Using electro-optic sampling, we detect a THz field amplitude of 1.7 kV/cm, which is almost one order of magnitude higher as compared to previous photoconductive emitters excited with pulses from an unamplified oscillator. This field value corresponds to an average THz power of 145 µW and yields a NIR-to-THz power-conversion efficiency as high as 2 × 10-4. We have employed this emitter concept in a compact THz spectrometer based on asynchronous optical sampling (ASOPS) [2]. ASOPS allows us to scan the THz electric field over a nanosecond time delay at a kilohertz scan rate without using a mechanical delay stage. To this end, two mode-locked femtosecond lasers with approximately 1 GHz repetition rate are combined at a fixed, stabilized kHz difference frequency ∆f. One laser delivers the THz excitation pulse, the other provides the probe pulses for electro-optic detection. In this way, the relative time delay between the THz pulses and the probe pulses is linearly ramped, thus enabling high-speed scanning over a 1 ns time delay with the scan rate ∆f. At a scan rate of 9 kHz a time resolution of 230 fs is accomplished. High-resolution spectra from 50 GHz up to 3 THz are obtained and water absorption lines with a width of 11 GHz are observed. A dynamic range larger than 3 orders of magnitude is achieved in a few 10 seconds averaging time.
[1] A. Dreyhaupt, S. Winnerl, T. Dekorsy, M. Helm, Appl. Phys. Lett. 86, 121114 (2005).
[2] A. Bartels, A. Thoma, C. Janke, T. Dekorsy, A. Dreyhaupt, S. Winnerl, M. Helm, Opt. Express 14, 430-437 (2006).
  • Poster
    2nd Workshop on Terahertz Technology, 01.-02.03.2006, Kaiserslautern, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-9080
Publ.-Id: 9080


Radiation damage in zirconia investigated by positively charged particles

Grynszpan, R. I.; Anwand, W.; Brauer, G.
nicht vorhanden
  • Lecture (Conference)
    19th International Conference on the Application of Accelerators in Research and Industry (CAARI2006), 20.-25.08.2006, Ft. Worth/Texas, USA

Permalink: https://www.hzdr.de/publications/Publ-9079
Publ.-Id: 9079


Characterization of semi-conducting nanorods by AFM and conducting AFM

Andreev, A.; Hou, Y.; Teichert, C.; Brauer, G.; Djurisic, A.
nicht vorhanden
  • Lecture (Conference)
    56. Jahrestagung der Österreichischen Physikalischen Gesellschaft (ÖPG), 18.-21.09.2006, Graz, Österreich

Permalink: https://www.hzdr.de/publications/Publ-9078
Publ.-Id: 9078


Electrical characterization of deep acceptor states in ZnO

von Wenckstern, H.; Schmidt, H.; Pickenhain, R.; Biehne, G.; Brandt, M.; Brauer, G.; Lorenz, M.; Dadgar, A.; Krost, A.; Grundmann, M.
nicht vorhanden
  • Lecture (Conference)
    MRS Fall Meeting 2006, 27.11.-01.12.2006, Boston/MA, USA

Permalink: https://www.hzdr.de/publications/Publ-9077
Publ.-Id: 9077


Synthesis of Nanowire Structures using Focused Ion Beams

Röntzsch, L.; Heinig, K.-H.; Akhmadaliev, C.; Bischoff, L.; Schmidt, B.
Nanowires (NWs) play an important role as basic components of electronic and photonic devices. Here, theoretical studies using atomistic computer simulations and experi¬mental results are presented on the CMOS-compatible fabrication of metal silicide and semiconductor NWs by focused ion beam (FIB) implantation and subsequent thermal annealing. The FIB implantation along a straight trace leads to a local and surface-near supersaturation in the substrate. Post-implantation annealing causes NW formation by self-organization. It is demonstrated that the evolution of the FIB implantation profile proceeds in three well-separated stages: (1) Phase separation by nucleation and growth, (2) NW formation by coalescence of nanoclusters, (3) NW surface smoothening. Likewise, components for functional devices involving several NWs, like T- or X-junctions, can be obtained by crossing different FIB traces. During long-term thermal annealing, NWs disintegrate into regular chains of nanoparticles (Rayleigh instability) that can be used as surface-plasmon-polariton waveguides. Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors and for multi-gate NW field effect transistors may be fabricated by crossing FIB traces.
Keywords: Nanowire, computer modeling, kinetic Monte Carlo, TRIM, ion beam synthesis, phase separation
  • Invited lecture (Conferences)
    17th Symposium of the MRS-J, 08.-10.12.2006, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-9076
Publ.-Id: 9076


Der Reaktordruckbehälter in der Spätphase eines Kernschmelzunfalls - eine thermomechanische Modellierung

Willschütz, H.-G.
Gibt es Möglichkeiten, die Bevölkerung vor den Folgen eines hypothetischen schweren Kernschmelzunfalls in einem Reaktor zu schützen? Welche Schutzvorkehrungen sind bisher vorgesehen? Neue Antworten auf diese Fragen werden in der Reaktorsicherheitsforschung erarbeitet. In diesem Vortrag werden die Ergebnisse einer Forschungsarbeit zur Rückhaltbarkeit von Kernschmelze im Reaktordruckbehälter eines großen Kernkraftwerks dargelegt.
Keywords: Severe Accident, Nuclear Power Plant, Core Melt Down, Physical Barriers, In-Vessel-Retention
  • Lecture (others)
    Jahresabschlussveranstaltung 2006 der Sektion Sachsen der Kerntechnischen Gesellschaft, 12.12.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9075
Publ.-Id: 9075


Development and verification of a nodal approach for solving the multigroup SP3 equations

Beckert, C.; Grundmann, U.
The core model DYN3D which has been developed for three-dimensional analyses of steady states and transients in thermal reactors with quadratic or hexagonal fuel assemblies is based on nodal methods for the solution of the two group neutron diffusion equation. Loading cores with higher content of MOX fuel, the increase of the fuel cycle length, and the consideration of new reactor types are challenging for these standard methods. A nodal expansion method for solving the equations of the simplified P3 (SP3) approximation of the multigroup transport equation was developed to improve the accuracy of the DYN3D code. The method described in the paper is verified with pinwise calculations of a steady state of the OECD/NEA and U.S. NRC PWR MOX/UO2 Core Transient Benchmark. The used 16-group cross section library was generated for DORT calculations with homogenized pin cells. Two different approximations of the diffusion coefficient which occurs in the within-group form of the SP3 equations are investigated. Using the transport cross section for the calculation of the diffusion coefficient gives much better results than those obtained with the removal cross section. The improvement of the results in comparison to a pinwise diffusion calculation is shown. The results are compared with the DORT and the heterogeneous reference solution of the code DeCART. Concerning the SP3 calculation using the diffusion coefficient based on the transport cross section (DYN3D-SP3-TR) the deviations of the eigenvalue keff and the assembly powers from the transport solutions of DORT and DeCART are in the same order as those between the two transport solutions themselves. The improvement of the DYN3D-SP3-TR results in comparison to the diffusion calculation is presented. As the DYN3D-SP3-TR and DORT calculations are performed with homogenized pin cells, the pin powers of the two calculations are closer to each other than to the pin powers of the DeCART solution. To estimate the contribution of higher flux moments, the ratio of the second flux moment to the zeroth flux moment is investigated along a horizontal row of pins. It is shown that it is low in the fuel assemblies with small peaks at the water channels. Considering the baffle and the water reflector regions higher values are obtained in the fast neutron groups.
Keywords: SP3, DYN3D, nodal methods, multigroup, neutron transport, neutron diffusion
  • Annals of Nuclear Energy 35(2008)1, 75-86

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Permalink: https://www.hzdr.de/publications/Publ-9074
Publ.-Id: 9074


The stimulatory effects of low density lipoprotein on steroidogenesis in adrenocortical cells decline with in vitro oxidation and in vivo modification

Kopprasch, S.; Ansurudeen, I.; Krug, A.; Pietzsch, J.; Graessler, J.; Bornstein, S. R.
kein Abstract verfügbar
  • Abstract in refereed journal
    Atherosclerosis 7(2006)Suppl. 3, 522
  • Poster
    XIV International Symposium on Atherosclerosis, 18.-22.06.2006, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-9073
Publ.-Id: 9073


Stimulation of adrenal steroidogenesis by low-density lipoprotein: Impact of oxidative stress and blockage of the ERK signalling pathway

Kopprasch, S.; Ansurudeen, I.; Pietzsch, J.; Graessler, J.; Bornstein, S. R.
kein Abstract verfügbar
  • Abstract in refereed journal
    Diabetes, Stoffwechsel und Herz 15(2006), 28
  • Lecture (Conference)
    2nd Internatinal Symposium on Metabolic Syndrome, 06.-08.10.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9072
Publ.-Id: 9072


Differences in VLDL production in impaired glucose tolerance, Type 2 diabetes and familial combined hyperlipidemia

Julius, U.; Pietzsch, J.
kein Abstract verfügnbar
  • Abstract in refereed journal
    Atherosclerosis 7(2006)Suppl. 3, 507
  • Lecture (Conference)
    XIV International Symposium on Atherosclerosis, 18.-22.06.2006, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-9071
Publ.-Id: 9071


Lipid transfer protein activities in subjects with impaired glucose tolerance

Julius, U.; Jauhiainen, M.; Ehnholm, C.; Pietzsch, J.
Background: Impaired glucose tolerance (IGT) is associated with an increased risk of atherosclerosis that may be due in part to dyslipidemia. The purpose of this study was to assess the regulatory role of lipid transfer proteins in the development of this dyslipidemia. Methods: Activities of cholesterol ester transfer protein (CETP) and phospholipid transfer protein (PLTP), as well as lipid and protein components of the major lipoprotein fractions, were evaluated in probands with IGT and were compared with those in subjects with normal glucose tolerance. The effect of a fat-rich meal on these variables was also investigated. Results: IGT probands had a higher triglyceride content in subfractions of low- (LDL) and high-density lipoprotein (HDL). IGT patients had higher fasting CETP activity. The latter was positively correlated with HDL2 triglycerides and negatively with HDL3 total cholesterol. PLTP activity and mass were not higher in IGT patients. However, PLTP activity correlated with components of VLDL and LDL and was influenced by the type of obesity. Neither CETP and PLTP activities nor PLTP mass were altered by a fat-rich meal. PLTP and CETP activities correlated in both fasting and postprandial conditions. Conclusions: Increased fasting CETP activity may contribute to increased risk of atherosclerosis in subjects with IGT.
  • Clinical Chemistry and Laboratory Medicine 45(2007)2, 237-243

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Permalink: https://www.hzdr.de/publications/Publ-9070
Publ.-Id: 9070


Small-angle neutron scattering study of neutron irradiated Fe and Fe-Ni

Bergner, F.; Ulbricht, A.; Hernandez-Mayoral, M.; Pranzas, P. K.
Nickel plays a key role in the degradation mechanism of neutron-irradiated reactor pressure vessel steels. Binary Fe-Ni alloys are basic for understanding and modeling of the behaviour of more complex steels. The nature of irradiation-induced features in Fe-3wt%Ni was investigated by means of small-angle neutron scattering and Vickers hardness measurements and compared with results for commercially pure Fe. We have observed a vacancy-Ni ratio of 0.4 to 0.5 in the average scatterer. This finding is consistent with the hardness increase observed.

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Permalink: https://www.hzdr.de/publications/Publ-9069
Publ.-Id: 9069


Consequences of different fuel cycle options on the produced plutonium mass in the German reactor park

Merk, B.
In this cycle study the Pu production in the German reactor park will be analyzed and compared to different limiting scenarios. The effects on the Pu production due to a postulated lifetime extension of roughly 10 years are discussed.
Keywords: Plutonium, Cycle Study, German Reactorpark, Lifetime extension, Stockpile Management
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.07, Karlsruhe, Germany
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.07, Karlsruhe, Germany

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Permalink: https://www.hzdr.de/publications/Publ-9068
Publ.-Id: 9068


Der Einfluss von Kolloiden auf den Urantransport in radioaktiven Endlagern und in stillgelegten Uranbergwerken - Ein kritischer Vergleich

Zänker, H.; Ulrich, K.-U.; Opel, K.; Brendler, V.
Durch Laborexperimente und durch den Vergleich mit der geochemischen Erfahrung wird die Rolle von U(IV)- und U(VI)-haltigen Kolloiden für radioaktive Endlager und für stillgelegte Uranbergwerke analysiert. Gezeigt wird, dass in der natürlichen Umwelt sowohl transportunterstützende Einflüsse von Kolloiden auf „immobile“ radiotoxische Kontaminanten wie Uran(IV) als auch transporthemmende Einflüsse auf „mobile“ radiotoxische Kontaminanten wie Uran(VI) möglich sind. Bei Performance-Asssessment-Berechnungen für radioaktive Endlager stehen die transportfördernden Einflüsse der Kolloide im Vordergrund, transporthemmende werden meist vernachlässigt. Für Bergwerke dagegen sind, neben transportfördernden auch transporthemmende Kolloideinflüsse (Natural Attenuation) von großem Interesse, denn sie können in Remediationsstrategien ausgenutzt werden.
Keywords: Colloids, uranium(IV), Uranium(VI), transport-facilitating effects, transport-impeding effects
  • Lecture (Conference)
    Wasser 2007. Jahrestagung der Wasserchemischen Gesellschaft, 14.-16.05.2007, Passau, Germany
  • Contribution to proceedings
    Wasser 2007. Jahrestagung der Wasserchemischen Gesellschaft, GDCh, 14.-16.05.2007, Passau, Deutschland, 14.-16.05.2007, Passau, Germany, ISBN 3-936028-43-5, 68-71

Permalink: https://www.hzdr.de/publications/Publ-9066
Publ.-Id: 9066


Nanocrystals: Catalysts on the edge

Gemming, S.; Seifert, G.
MoS2 nanoplatelets have catalytically active sites along their edegs that are promising for desulfurizing fuels
Keywords: clusters, catalysis, molybdenum sulfide

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Permalink: https://www.hzdr.de/publications/Publ-9065
Publ.-Id: 9065


Changes in hardness and elasticity of a Ti6Al4V alloy under helium irradiation

Chen, S. H.; Schumacher, G.; Xu, Z. Y.; Richter, E.
Ti6Al4V specimens have been irradiated at different temperatures with 200 keV He ions. Microhardness and elastic modulus of the unirradiated and irradiated specimens were measured by means of the nano-indentation technique and analyzed using the Oliver-Pharr method. The indentation depth of all samples is 700 nm, which is comparable in magnitude to the ion range. The subsurface structure of the Ti6Al4V specimens was investigated by the X-ray diffraction technique. The measurements indicate that the microhardness increased with the irradiation temperature from room temperature to 600 degrees C while the elastic modulus almost monotonically decreased. The Irradiation at 700 degrees C, however, caused softening and slight increase of the elastic modulus within the surface layer of the specimens. The hardening and reduction of the elastic modulus of the Ti6Al4V alloy under irradiation conditions used in this study is tentatively explained by a model based on the presence of point defects and dispersed obstacles of P-precipitates. The softening and slight increase of elastic modulus of helium-irradiated Ti6Al4V at 700 degrees C might be related to the coarsening of beta-precipitates and formation of the hybrid gamma-TiH phase in alpha-phase.
  • Journal of Nuclear Materials 358(2006)1, 26-34

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Publ.-Id: 9064


DYN3D-MSR spatial dynamics code for Molten Salt Reactors

Krepel, J.; Rohde, U.; Grundmann, U.; Weiß, F.-P.
The development of spatial dynamics code for Molten Salt Reactors (MSR) is reported in this paper. The graphite-moderated channel type MSR - one of the 'Generation IV' concepts - was selected for the numerical simulation. It has several peculiarities (e.g. the drift of delayed neutrons precursors), which disable the use of standard dynamics codes. Therefore, the own DYN3D-MSR code was developed. It is based on the light water reactor code DYN3D and it allows transients simulation by 3D neutronics and parallel channel thermal-hydraulics. The neutronics and thermal-hydraulics were modified for the MSR peculiarities, where the experience from DYN1D-MSR development was exploited. The code was validated on experimental results from the MSRE experiment done in Oak Ridge National Laboratory and by the comparison with other codes especially with the 1D version. However, by the 3D code transients can be simulated, where space-dependant efforts are relevant, like local blockage of fuel channels or local temperature perturbations.
Keywords: Molten, Salt, Dynamics, MSR, MSRE, MSBR
  • Annals of Nuclear Energy 34(2007), 449-462

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Publ.-Id: 9063


Corrigendum to "Nickel assisted metal induced crystallization of silicon: Effect of native silicon oxide layer"

Pereira, L.; Martins, R. M. S.; Schell, N.; Fortunato, E.; Martins, R.
This work focuses on the role of the native oxide layer (SiO2) on the nickel (Ni)-assisted crystallization of amorphous silicon (a-Si). In some samples, the native oxide was removed using a HF-diluted solution before Ni layers with 0.5 nm be deposited on a-Si. The results show that the presence of a thin SiO2 layer of about 3 nm between the a-Si and the Ni delays the crystallization process. Ellipsometry data show that, after annealing for 5 h at 500 °C, the HF-cleaned sample presents a crystalline fraction of 88%, while the one with the native oxide has only 35%. This difference disappears after 20 h where both samples present similar crystalline fraction. These facts are also reflected on the film's electrical properties, where the activation energy for samples annealed for 5 h rises from 0.42 eV to 0.55 eV, when the oxide layer is removed. After 20 h and 30 h, the activation energy is around 0.55 eV for both kinds of samples, meaning that films with similar electrical properties are now obtained. However, the XRD data suggest the presence of some structural differences attributed to slight differences on the crystallization process.
Keywords: Polycrystalline silicon; Nickel-assisted crystallization; Spectroscopic ellipsometry
  • Thin Solid Films 511-512(2006), 275-279
  • Poster
    E-MRS 2005, 31.05.-03.06.2005, Strasbourg, France

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Publ.-Id: 9062


Novel wire-mesh sensor for the investigation of non-conducting fluids

Da Silva, M. J.; Schleicher, E.; Hampel, U.
Conductivity wire-mesh sensors have been successfully employed in the investigation of two-phase flows in the past. Since the measuring principle requires at least one continuous conductive phase, wire-mesh sensors have almost exclusively been used for the investigation of air-water or steam-water systems. Nevertheless, non-conducting fluids such as oil or organic liquids often occur in industrial applications, for instance, in chemical and petrochemical industry. The experimental investigation of multiphase flows involving non-conducting fluids is therefore of large interest. For this reason we developed a novel wire-mesh sensor based on measurements of the electrical permittivity (capacitance) which is suitable for the investigation of non-conducting fluids. The prototype sensor consists of two layers of 16 steel wires each. The system can at the moment produce cross-sectional phase distribution images with 625 frames per second. Sensor and associate electronic were evaluated showing good accuracy and reproducibility in the permittivity measurement. Initial results of an air-oil bubbly flow as well as a slug flow measurement are presented.
Keywords: capcitance measurement, relative permittivity, wire-mesh sensor, two-phase flow, non-conducting fluid
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Proceedings of 6th International Conference on Multiphase Flow, paper S7_Thu_B_51, 978-3-86010-913-7
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-9061
Publ.-Id: 9061


Analysis of wafer stresses during millisecond thermal processing

Smith, M.; Seffen, K.; Mc Mahon, R.; Voelskow, M.; Skorupa, W.
A flash lamp has been used to uniformly anneal large wafers with diameters approaching 100 mm. The equipment applies a pulse, with duration of 3-20 ms, resulting in large transient thermal gradients in the wafer. In this paper, we present separate models of the thermal reaction of this process and its effect upon the mechanical behavior, in order to predict stresses and shape changes, and to capture practical phenomenon. We further use the model to follow changes in the expected response consequent on altering process conditions, such as preheating and pulse duration, as well as exploring important issues associated with scaling to large wafer sizes. This work presents an initial description of the thermomechanical response of wafers to flash lamp annealing in the millisecond time regime and is therefore fundamental to the use of this technique in the fabrication of semiconductor devices.
Keywords: flash lamp annealing stress silicon model
  • Journal of Applied Physics 100(2006)6, 63515

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Publ.-Id: 9059


Actinide, lanthanide, and fission product speciation and electrochemistry in ionic melts

Bhatt, A. I.; Kinoshita, H.; Koster, A. L.; May, I.; Sharrad, C.; Steele, H. M.; Volkovich, V. A.; Fox, O. D.; Jones, C. J.; Lewin, B. G.; Charnock, J. M.; Hennig, C.
We report the results of recent research that we have undertaken to increase our understanding of key actinide and fission product speciation in a range of ionic melts. These results will be used to develop novel electrochemical methods of separation of uranium and plutonium from irradiated nuclear fuel. Our studies in high temperature alkali metal melts (including LiCl and the eutectics LiCl-KCl and CsCI-NaCl) have focussed on in-situ speciation of U, Tc and Ru using both Electronic Absorption Spectroscopy (EAS) and X-ray Absorption Spectroscopy (XAS). The XAS studies have included Extended X-Ray Absorption Fine Structure (EXAFS) and X-Ray Absorption Near Edge Structure (XANES) measurements. We report what could be unusual uranium speciation in high temperature melts and evaluate the likelihood of Ru or Tc volatilisation during plant operation. Our studies in lower temperature melts, commonly known as ionic liquids, have focussed on salts containing tertiary alkyl group 15 cations and the bis(trifluoromethylsulphonyl)imide anion, melts which we know to have exceptionally wide electrochemical windows. We report Ln, Th, U and Np speciation (XAS, EAS and vibrational spectroscopy) and electrochemistry in these melts.
Keywords: MOLTEN-SALTS; LIQUIDS; SPECTROSCOPY; CHLORIDE; COMPLEXES; CHEMISTRY
  • ACS Symposium Series 933(2006), 219-231

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Publ.-Id: 9058


Electrical conductivity surface sensor for two-phase flow imaging in a hydrodynamic coupling

Da Silva, M. J.; Sühnel, T.; Thiele, S.; Schleicher, E.; Hampel, U.; Kernchen, R.
For the measurement of fluid distributions inside a hydrodynamic coupling we have developed a high-speed surface sensor based on the measurement of the electrical conductivity. Two sensors are placed on the pressure-side and the suction-side walls of a blade channel inside the coupling. The sensors are composed by approximately 1000 interdigitated sensing structures. The system is supplied by a battery and has a wireless link to communicate with a PC. Sensor and electronics have been so designed that the whole system can rotate together with the coupling pump wheel. The electronics measures the conductivity of the liquid of each sensing structure in a multiplexed manner which effectively gives images of the instantaneous liquid distribution over the sensor surface. Frame frequencies of up to 10,000 images per second can be reached. We have applied the surface sensor to measure the fluid distribution in a test coupling for different slip conditions. Initial results are presented and discussed.
Keywords: electrical conductivity, surface sensor, fluid distribution, imaging, two-phase flow, hydrodynamic coupling
  • Contribution to proceedings
    International Conference on Multiphase Flow, 09.-13.07.2007, Leipzig, Germany
    Proceedings of 6th International Conference on Multiphase Flow, paper PS7_12, 978-3-86010-913-7
  • Poster
    International Conference on Multiphase Flow, 09.-13.07.2007, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-9057
Publ.-Id: 9057


Time-dependent radioactivity distribution in MAFF

Nebel, F.; Zech, E.; Faestermann, T.; Krücken, R.; Maier-Komor, P.; Assmann, W.; Szerypo, J.; Groß, M.; Kester, O.; Thirolf, P. G.; Grötzschel, R.
The Munich Accelerator for Fission Fragments is planned to be installed at the FRM II in Garching. It will operate a uranium-carbide-loaded graphite matrix as a target for neutron-induced fission. The radioactive reaction fragments leave the ion source as both, atoms and ions. For radiation safety it is imperative to have a basic understanding of the fragment distribution within the beam line.

Atoms leaving the graphite matrix will spread like a gas and stick to surfaces depending on their species. A probabilistic Monte-Carlo approach is used to predict the surface coating of internal surfaces of the beam line for all fission nuclides. To decrease calculation time, the problem is reduced to two dimensions with the surface areas being a measure for the probability, that they are hit by a particle. The program is completely time dependent to implement radioactive decay.

Ions leaving the fission ion source are transported by electrostatic means towards the mass pre-separator, a low-resolution dipole magnet with a complex slit system in the focal plane. All unwanted ions are stopped at the slits, resulting in a high level of radioactive contamination. While it is advantageous for shielding purposes to have the majority of the contamination in one point, precautions must be taken to ensure that it stays that way. Material corrosion caused by sputtering will release previously implanted radionuclides. To reduce this effect, different methods are under investigation, one of which is changing the slit geometry. The considered designs will be described and experimental results will be shown.
Keywords: Radiation damage; Radiation safety; Radioactive beam; Reactor experiment; Ion implantation
  • Nuclear Instruments and Methods in Physics Research A 561(2006)1, 83-89

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Publ.-Id: 9056


Radioactivity distribution at MAFF

Nebel, F.; Szerypo, J.; Zech, E.; Faestermann, T.; Groetzschel, R.; Gross, M.; Habs, D.; Krucken, R.; Maier-Komor, P.; Thirolf, P.; Yakushev, A.
A detailed account on the distribution of radioactive nuclei in the vacuum system of the planned Munich Accelerator for Fission Fragments (MAFF) located at the FRM-II research reactor is presented. Tools used for the simulation of spacial and temporal distribution of radionuclides are explained. The latter allows for a detailed activity budget as well as estimates for the mass-separated ion yields at MAFF. Additionally, a concept to reduce the activity release from the MAFF slit system due to surface sputtering is presented. It is shown, that the use of low-density carbon foam, as a surface coating, reduces sputtering by orders of magnitude.
Keywords: Theory, design, and computerized simulation - Materials - Safety - Beam handling; beam transport
  • European Physical Journal A 29(2006)3, 369-381

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Publ.-Id: 9055


Focused-ion-beam-assisted fabrication of polymer rolled-up microtubes

Luchnikov, V.; Stamm, M.; Akhmadaliev, C.; Bischoff, L.; Schmidt, B.
A focused ion beam (FIB) has been applied to the fabrication of polymer microtubes via the rolling-up technique from poly(4-vinyl pyridine)/polystyrene bilayer films deposited on the top of a sacrificial aluminum layer covering a silicon wafer. The bending forces in the film arise due to different swelling of the bilayer components in acidic water and lead to rolling of the film. The dimensions and position of the rolled-up tubes can be controlled by FIB milling (sputtering) of geometrically well-adjusted openings in the polymer films. This technique can be applied to the structuring of scrolled films formed from different materials without the use of lithographically patterned photoresists. The geometrical patterning of the tube interior can also be done by FIB irradiation.
Keywords: Focused ion beam, polymers, roll-up, nanotubes
  • Journal of Micromechanics and Microengineering 16(2006)8, 1602-1605

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Publ.-Id: 9054


Molecular characterization of actinide oxocations from protactinium to plutonium

Den Auwer, C.; Guilbaud, P.; Guillaumont, D.; Moisy, P.; Le Naour, C.; Trubert, D.; Simoni, E.; Digiandomenico, V.; Hennig, C.; Scheinost, A.
For industrial, environmental and public health purposes, actinide chemistry has been the subject of considerable efforts since the 50’s. Aqueous redox chemistry, ionic selective recognition, uptake by specific biomolecules or compartments of the geosphere are some of the major fields of investigation. The physical-chemical properties of the actinide elements strongly depend on the 5f/6d electronic configuration. Some of them (U, Np, Pu and Am) can form AnO2n+ (n= 1, 2) oxocations, so-called actinyls, with two strong An-O covalent bonds. In any case, the cation polyhedron is characterized by large, flexible coordination spheres with various stable and metastable metal oxidation states. Protactinium, as the first actinide with 5f-electrons involved in bonding, occupies a key position in the actinide series. At formal oxidation state V (its most stable oxidation state in solution as well as in the solid state) Pa(V) corresponds to the formal 5f0 electronic configuration. U(VI) also corresponds to the formal oxidation state 5f0 and is most often encountered as the stable oxocationic form UO22+. The first stable form of U, Np or Pu at formal oxidation state (V) under atmospheric conditions is NpO2+ with formal 5f2 electronic configuration. U(V) is highly unstable under atmospheric conditions and Pu(V) dismutates into Pu(IV) and Pu(VI). On the other hand, the existence of the PaO2+ form in solution and in solid state is highly improbable and has never been reported. In solution, XAFS at the actinide LIII edge is an ideal structural probe of the cation coordination sphere. Furthermore, coupling the XAFS data with molecular dynamics calculations leads to a better description of the cation-solvent interactions. In addition, disorder can explicitly be taken into account using time spaced snapshots of the molecule. This is particularly important when large polyhedra are composed of ligands of similar types as water molecules. This presentation addresses the structural characterization of actinide cations at oxidation states (V) and (VI) as one walks across the periodic table from Z = 91 (protactinium) to Z = 94 (plutonium). For the fist time to our knowledge, the occurrence of the oxocation form of Pa(V) in H2SO4 solution has been inferred from EXAFS and XANES data at the Pa LIII edge. A structural comparison between Pa, U, Np and Pu oxocations in aqueous solution at formal oxidation states (V) and (VI) is carried out. These results are corroborated by quantum chemical and molecular dynamics calculations.
Keywords: Actinides, EXAFS, XANES
  • Lecture (Conference)
    Actinide-XAS, 18.-20.9.2006, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-9053
Publ.-Id: 9053


EXAFS and UV-VIS investigation of the first coordination sphere of the uranyl ion in UO2(NO3)2(TBP)2

Servaes, K.; Hennig, C.; van Deun, R.; Görller-Walrand, C.
The coordination behaviour of the uranyl ion UO22+ has regained interest due to the problem of nuclear waste management and environmental issues. At the end of the nuclear fuel cycle, reprocessing of the spent nuclear fuel mainly occurs by means of liquid-liquid extraction. During the PUREX process, the spent fuel is dissolved in a nitric acid solution. Uranium is extracted from the aqueous nitric acid fuel solution with an organic phase containing tri-n-butylphosphate (TBP; extracting agent). However, little is known about the structure of the chemical species involved in the liquid-liquid extraction process. The first coordination sphere of the uranyl ion UO22+ in UO2(NO3)2(TBP)2 was studied using UV-Vis absorption spectroscopy, EXAFS spectroscopy and 31P-NMR. The characteristic vibrational fine structure in the UV-Vis absorption spectrum points at a high symmetrical complex. The uranium polyhedron is composed of two axial oxygens located at 1.77 ± 0.01 Å, four nitrate (bidentate) oxygens at 2.52 ± 0.01 Å and two phosphate oxygens (TBP) located at 2.38 ± 0.01 Å.
Keywords: UV-vis, EXAFS, uranium
  • Poster
    Actinide-XAS, 18.-20.9.2006, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-9052
Publ.-Id: 9052


Combined techniques for studying actinide complexes in room temperature ionic liquids

Gaillard, C.; Billard, I.; Mekki, S.; Ouadi, A.; Hennig, C.; Denecke, M.
The first coordination sphere of the uranyl cation in room temperature ionic liquids "IL's" results from the competition between its initially bound counterions, the IL anions, and other anions (e.g. present as impurities, or added to the solution). We present a joined spectroscopic (UV-visible and EXAFS) – simulation study of the coordination of uranyl initially introduced either as its UO2X2 salts (X- = nitrate NO3-, triflate Tf-, perchlorate ClO4-) or as UO2(SO4) in a series of imidazolium – based ILs (A- = PF6-, Tf2N-, BF4-), as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. For instance, in the BumimTf2N liquid, UO2(SO4) is insoluble, the UO2(NO3)2 salt dissolves without dissociation, while the UO2(Tf)2 and UO2(ClO4)2 salts are soluble, likely in their complexed and dissociated form, respectively.
Keywords: room temperature ionic liquids, lanthanides, actinides, EXAFS
  • Lecture (Conference)
    Actinide-XAS, 18.-20.9.2006, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-9051
Publ.-Id: 9051


Uranium chloro complexes in hydrophobic room temperature ionic liquid: structural investigation and redox properties

Cannes, C.; Nikitenko, S.; Le Naour, C.; Trubert, D.; Hennig, C.; Moisy, P.
U(IV) hexachloro complexes were studied in hydrophobic room temperature ionic liquids [BuMeIm][Tf2N] and [MeBu3N][Tf2N] to determine their structure, speciation and redox properties (BuMeIm+ and MeBu3N+ are 1-butyl-3-methyl-imidazolium and tri-n-butylmethylammonium respectively, and Tf2N- is bis(trifluoromethyl-sulfonyl)imide).
As the Tf2N- anion is known to be a weak ligand exhibiting oxygen coordination as 1-O or 2-O,O to actinides or lanthanides, the U(IV) chloro complex could be under the general chemical form UClx(Tf2N)y(4-x-y).
The diffuse UV-vis solid state reflectance of both U(IV) complexes agree closely with the absorption spectra obtained in ionic liquids. It is well known that U(IV) hexachloro complex has a centrosymmetric octahedral arrangement in the solid state as well as in acetonitrile solution. It can be concluded that octahedral anion UCl62- is the predominant form of U(IV) in Tf2N- based ionic liquids. EXAFS measurements were also performed to investigate the coordination sphere of U(IV) chloro complex in [BuMeIm][Tf2N]. The results confirmed that the octahedral complex UCl62- is the predominant chemical form of U(IV) in Tf2N- based hydrophobic ionic liquids and a competing reaction with Tf2N- can be excluded. The U-Cl distance measured in [BuMeIm][Tf2N] is 2.632(2) Å and is slightly longer than that in solid state. Probably, it can be related to some stronger H-bonding of UCl62- with BuMeIm+ cation in ionic liquid than that of solid.
Keywords: UV-vis, EXAFS, ionic liquid, uranium
  • Lecture (Conference)
    EuChem conference on molten salts and ionic liquids 2006, 16.-22.09.2006, Hammamet, Tunisia

Permalink: https://www.hzdr.de/publications/Publ-9050
Publ.-Id: 9050


Elemental redistribution and Ge loss during ion-beam synthesis of Ge nanocrystals in SiO2 films

Beyer, V.; von Borany, J.
The elemental redistribution and Ge loss in low-energy Ge+ implanted SiO2 films during wet-chemical cleaning and annealing procedures are investigated. Two effects of major importance for Ge nanocrystal formation have been found. Moisture components (H2O vapor, H+, OH-) penetrate into the damaged oxide during storage, wet chemical cleaning or annealing procedures and lead to a hydrogen and oxygen enrichment in the near-surface oxide. Furthermore, atomic collisions during Ge implantation result in an oxygen excess (with respect to SiO2 stoichiometry) underneath the Ge profile. The local net ratio of Ge and excess oxygen determines, whether the implanted Ge is incorporated into the SiO2 network as spatially fixed GeO2, oxidizes to mobile GeO or remains as elemental Ge forming nanocrystals. Apart from very shallow profiles, where a drastic Ge loss is observed simply by cleaning in chemical solutions containing H2O2, the main Ge loss occurs during annealing. The highly mobile GeO is identified to be responsible for both, Ge redistribution or even loss, if diffusing GeO meets the SiO2 surface and emanates into the annealing ambient. Annealing in Ar/H2 mixtures at < 900°C reduces the Ge loss due to the reduction of Ge oxides. The enhanced Ge mobility (as GeO) is described as an oxygen vacancy assisted mechanism which also explains the influence of the Si/SiO2 interface on the Ge diffusivity. Finally, the consequences of Ge redistribution and loss for Ge nanocrystal memory device fabrication are discussed.
Keywords: ion beam synthesis, germanium, nanocrystal, SiO2, oxygen vacancy, GeODC

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Publ.-Id: 9049


Probing six-fold ring clusters in alloyed sp2 dominated carbon thin films by the means of Raman spectroscopy

Abrasonis, G.; Krause, M.; Gago, R.; Kolitsch, A.; Möller, W.
The six-fold ring clustering in sp2-dominated pure carbon (C), nitrogenated carbon (CNx) and nickel alloyed carbon (C:Ni) thin films is investigated by Raman spectroscopy as a function of substrate temperature. Films have been grown by direct and dual ion beam sputtering, ion beam assisted evaporation and magnetron sputtering, resulting in amorphous, graphite-like, fullerene-like, paracyanogenlike, and in the case of C:Ni films – nanocomposite - structures.
Raman spectra in the wave-number region of 900–2000 cm−1 exhibit usually two main peaks positioned at ~1360 and ~1560–1590 cm−1 which are denoted conventionally by D and G, respectively, the G peak corresponding to in-plane bond stretching vibrations (it can be present in aromatic clusters as well as in chain structures) and the D peak corresponding to breathing vibrations of aromatic rings (it can be present only in ring structures). The total intensity of these peaks is proportional to the amount of the sp2 phase, while their relative ratio provides the information on the six-fold ring cluster size.
The results show that each type of atomic arrangement results in a characteristic set of the Raman spectra parameters, which describe the degree of aromatic clustering, bond length and angle distortion and order in sixfold structures1.
In the case of pure C films, the atomic structure evolves with substrate temperature from a disordered network to nanocrystalline planar graphitic configurations, with a progressive promotion in size and ordering of sixfold ring clusters1.
Nitrogen incorporation favors the promotion of sixfold rings in highly disordered networks produced at low temperatures, but precludes the formation of extended graphite-like clusters at elevated substrate temperatures (>400°C). In the latter case, N introduces a high degree of disorder in sixfold ring clusters and enhances the formation of a fullerene-like microstructure1.
The presence of Ni slightly favours the six-fold ring clustering at low temperatures (<300°C), while Raman spectra at higher temperatures have similar features for both C and C:Ni films. For deposition temperatures lower than 300°C, the the absolute intensity of the D-G band decreases by more than one order of magnitude despite the similar total amount of deposited material and one additional Raman line at around 1100 cm-1 appear indicating the presence of new carbon structures in the film. This correlates with the Ni segregation into nickel carbide or nickel nanoparticles occurring at T~300°C, thus segregated Ni and C phases may undergo separate ordering paths at higher temperatures. In contrast, a mixed C-Ni phase is formed at lower temperatures and the precipitation C sp2 phase is hindered.
__________________________
References:
1. G. Abrasonis, R. Gago, M. Vinnichenko, U. Kreissig, A. Kolitsch, and W. Möller, Phys. Rev. B 73, 125427 (2006).
  • Lecture (Conference)
    4th International Workshop on Nanoscale Spectroscopy and Nanotechnology, 17.-21.09.2006, Rathen, Germany

Permalink: https://www.hzdr.de/publications/Publ-9046
Publ.-Id: 9046


Low energy ion accelerated diffusion of interstitial nitrogen in austenitic stainless steel

Abrasonis, G.; Möller, W.; Ma, X. X.; Keller, A.; Facsko, S.
N diffusion in austenitic stainless steel (ASS) under low energy Ar ion bombardment is investigated. ASS samples were ion beam nitrided at 400°C with the N ion energy of 1 keV and flux of 3.11015 s-1 cm-2. The nitriding time was adjusted to obtain a thickness of the nitrided layer of ~1m. The samples were subsequently annealed at 400°C under simultaneous 700 eV Ar+ bombardment with different fluxes (1.3-3.8×1015 s-1 cm-2). N depth profiles were obtained using nuclear reaction analysis, and the phase structure was measured using X-ray diffraction (XRD). XRD reveals the modified layer to be composed of only γN phase in both as-nitrided and Ar+ irradiated samples, with no evidence of nitride formation. It is observed that Ar+ bombardment increases the N mobility in the depths far beyond the ion penetration depth, resulting in an increased broadening of the N depth profile as a function of Ar+ flux. This effect cannot be explained by any established mechanism of radiation enhanced diffusion. Another set of samples was annealed at 400°C under low flux (4×1011 s-1 cm-2) 700 eV Ar ion bombardment of variable charge state (from 1+ to 8+). These charge states correspond to the potential energies of 16-578 eV. The latter is dissipated by electronic excitations in metals. It was found that low flux Ar ion bombardment enhances the N mobility; however, the ion potential energy does not play any role on deep N diffusion. The latter indicates that N diffusion enhancement over large distances (~1 m) is due to nuclear collisional processes during ion stopping in the matter. Tentatively, the observed phenomenon is discussed in terms of collisionally induced quasi-particles which propagate large distances from the layers directly affected by ion bombardment enhancing interstitial N diffusion.
Keywords: radiation enhanced diffusion quasi-particles ion nitriding austenitic stainless steel
  • Lecture (Conference)
    Tenth International Conference on Plasma Surface Engineering, 10.-15.09.2006, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-9045
Publ.-Id: 9045


Construction of an S-layer protein exhibiting modified self-assembling properties and enhanced metal binding capacities

Pollmann, K.; Matys, S.
The functional S-layer protein gene slfB of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 was cloned as a PCR-product into the expression vector pET Lic/Ek 30 and heterologous expressed in E.
coli Bl21(DE3). The addition of His-tags to the N- and C-termini enabled the purification of the recombinant protein by Ni chelating chromatography. The Ni-binding capacity of the His-tagged recombinant S-layer protein was compared with that of the wild-type S-layer. The ICP-MS analyses demonstrate a significantly enhanced Ni-binding capability of the recombinant protein. In addition, the self-assembling properties of the purified modified S-layer proteins were studied by light microscopy and SEM. Whereas the wild-type S-layer proteins re-assembled into regular cylindric structures, the His-tagged S-layer proteins reassembled into regular sheets that formed globular agglomerating structures. The nanoporous structure of the protein meshwork together with its enhanced Ni-binding capacity makes the recombinant S-layer attractive as a novel self-assembling biological template for the fabrication of metal nanoclusters and construction of nanomaterials that are of technical interest.

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Permalink: https://www.hzdr.de/publications/Publ-9044
Publ.-Id: 9044


XPS depth profiling of oxide scales of stainless steels formed in high-temperature aqueous conditions

Ignatova, V. A.; van Dyck, S.; Groetzschel, R.; Moeller, W.
In this work, we studied the oxide scales of AISI 304 and AISI 316 stainless steels formed under hightemperature aqueous conditions using X-ray photoelectron spectroscopy (XPS) together with sputter depth profiling. Two samples of SS 304 and 316 were prepared by exposing them to water at 300 °C containing 100 ppm boric acid and 7 ppm lithium hydroxide in an autoclave. In the case of sputtering with 3 keV argon ions, the elemental distribution as a function of the sputtering time was obtained. The formation of two oxide layers was observed – one mainly iron-based on top, and a second at a greater depth, consisting mainly of chromium-iron oxides. The depth scale of the profiles was calibrated by measuring the oxygen profile using Rutherford backscattering spectroscopy (RBS). On the basis of the distribution of the three oxidised alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, a relative increase of Fe2+ at the surface was found, while the chromium was depleted at the surface and Cr3+ tended to increase at the oxide/substrate interface. In order to estimate possible ion-beam-induced effects due to the ion sputtering, the profiles were compared to the computer-simulated ones obtained by a dynamic TRIM computer code. The simulations included only collisional effects during the sputtering process.

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Permalink: https://www.hzdr.de/publications/Publ-9043
Publ.-Id: 9043


Modelling of the Corium-RPV-Wall Interaction in the Frame of an In-Vessel-Retention Scenario

Altstadt, E.; Willschütz, H.-G.
The improbable scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a Light Water Reactor (LWR) Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the con-tainment. One accident management strategy could be to stabilize the in-vessel de-bris or melt pool configuration in the RPV as one major barrier against uncontrolled release of heat and radionuclides into the containment of the plant.
Based on the successful simulation and analysis work of the FOREVER-experiments the models have been developed further to simulate the prototypical scenario of an In-Vessel-Retention in large PWRs. Based on recently observed results of the METCOR-Experiments it is known that the vessel wall ablation in case of melt-wall-contact can take place well below the steel melting point of T = 1493 °C. The FE-model developed at FZD is now improved to consider the time dependent thermo chemical wall ablation process.
Keywords: severe accident, nuclear power station, core melt down, melt steel wall interaction, corrosion/ablation, residual wall thickness
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Deutschland
    Beiträge zur Jahrestagung Kerntechnik 2007, Proceedings on CD-ROM, Paper 328, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft mbH, 293-299

Permalink: https://www.hzdr.de/publications/Publ-9042
Publ.-Id: 9042


Experimental modelling using low melting point metallic melts: Relevance for metallurgical engineering

Eckert, S.; Gerbeth, G.; Räbiger, D.; Willers, B.; Zhang, C.
This paper describes model experiments with low melting point liquid metals as an important tool to investigate the flow structure and related transport processes in melt flows being relevant for metallurgical applications. Three examples have been selected to demonstrate the benefit of such experiments, namely the electromagnetic stirring of a metallic melt in a pool, the directional solidification of Al-Si alloys under the influence of an electromagnetically driven flow and the behaviour of a liquid metal bubble plume if a vertically traveling field is applied. Results of flow measurements will be presented and the relevance for metallurgical processes will be discussed.
Keywords: liquid metal, magnetic field, electromagnetic stirring, solidification, bubble plume
  • Steel Research International 78(2007)5, 419-425

Permalink: https://www.hzdr.de/publications/Publ-9041
Publ.-Id: 9041


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

Krepelova, A.; Sachs, S.; Brendler, V.; Baumann, N.
Understanding the migration behavior of actinides is important for the reliable long-term risk assessment of potential nuclear waste repositories. Humic acids (HA) comprise an important part of natural organic materials. HA are soluble in the pH range of natural waters and have the ability for complex and colloid formation. Due to these properties HA can affect the speciation of actinide ions, and therefore, their migration in the environment. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite.
We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.
Keywords: U(VI), Humic Acid, TRLFS, Adsorption
  • Lecture (others)
    PSI/LES - FZD/IR Meeting, 05.-06.10.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-9040
Publ.-Id: 9040


Cylindrical anisotropic alpha2 dynamos

Avalos-Zuniga, R.; Xu, M.; Stefani, F.; Gerbeth, G.; Plunian, F.
We explore the influence of geometrical variations on the structure and the time-dependence of the magnetic field that is induced by kinematic alpha2 dynamos in a finite cylinder. The dynamo action is due to an anisotropic alpha tensor which can be derived from an underlying columnar flow. The investigated geometry variations concern, in particular, the aspect ratio of height to radius of the cylinder, and the thickness of the annular space to which the columnar flow is restricted. Motivated by the quest for laboratory dynamos which exhibit Earth-like features, we start with modifications of the Karlsruhe dynamo experiment. Its dynamo action is reasonably described by an alpha2 mechanism with anisotropic alpha tensor. We find a critical aspect ratio below which the dominant magnetic field changes from an equatorial dipole to an axial dipole. Similar results are found for alpha2 dynamos working in an annular space when a radial dependence of alpha is assumed. Finally, we study the effect of varying aspect ratios of dynamos with an alpha tensor depending both on r and z. In this case only dominant equatorial fields are found and most of the solutions are oscillatory, contrary to all previous cases where the resulting
fields are steady.

Permalink: https://www.hzdr.de/publications/Publ-9039
Publ.-Id: 9039


Defect engineering in the initial stage of SIMOX processing

Kögler, R.; Mücklich, A.; Vines, L.; Krecar, D.; Kuznetsov, A.; Skorupa, W.
Defect engineering for SiO2 precipitation was investigated during ion beam synthesis in the first stage of SIMOX fabrication. Vacancy-type defects were created in Si: (i) a buried nanocavity layer was pre-fabricated by He implantation and subsequent annealing, and (ii) excess vacancies were generated during oxide synthesis by an additional simultaneous high-energy Si irradiation.
A narrow nanocavity layer was found to be an excellent nucleation site that favors effectively the SiO2 formation. Such a cavity layer must be adjusted to the excess vacancy profile of the O implant. The excess vacancy generation by simultaneous dual implantation minimizes the defect production in Si. However, it is inappropriate to form a narrow oxide layer due to the too broad distribution of excess vacancies.
Keywords: SOI, SIMOX, ion implantation, defect engineering, Si
  • Lecture (Conference)
    15th International Conference Ion Beam Modification of Materials (IBMM 2006), 18.-22.09.2006, Taormina, Italy
  • Contribution to proceedings
    15th International Conference Ion Beam Modification of Materials (IBMM 2006), 18.-22.09.2006, Taormina, Italy
    Nuclear Instruments and Methods in Physics Research B 257(2007): Elsevier, 161-164

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Permalink: https://www.hzdr.de/publications/Publ-9038
Publ.-Id: 9038


Determination of velocity and angular displacement of bubbly flows by means of wire-mesh sensors and correlation analysis

Hoppe, D.; Grahn, A.; Schütz, P.
For the analysis of air-water bubbly flows in vertical pipes a method is presented which determines the radial profiles of velocity and angular displacement of the gaseous phase. Measurements rely on two so-called wire-mesh sensors, put into the flow behind each other and capturing the electrical conductivity distribution in the pipe cross-section at two different axial positions. The time-resolved signal is directly translated into transient two-dimensional distributions of the gaseous phase at both sensor positions. Sensor data analysis is based on two-dimensional cross-correlation within concentric cylindrical planes. The axial and angular displacement of the gaseous phase manifest themselves as the maximum position of the cross-correlation function.
Keywords: two-phase flow, phase distribution, flow velocity, angular displacement, wire-mesh sensor, cross-correlation

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Permalink: https://www.hzdr.de/publications/Publ-9037
Publ.-Id: 9037


Accurate determination of optical and electronic properties of ultra-thin silver films for biosensor applications

Oates, T. W. H.; Ryves, L.; Bilek, M. M. M.; Mckenzie, D. R.
Ultra-thin metal films are widely utilised for surface-enhanced Raman scattering and surface adsorption spectroscopy. We present in situ spectroscopic ellipsometry investigations of the growth of ultra-thin silver films, from island growth through percolation and continuous film growth. Silver films are deposited using a pulsed filtered cathodic vacuum arc, which provides precise control and reproducibility of the film growth conditions. Plasmon polariton resonances are determined for the growing islands below the percolation threshold. As the surface coverage increases a second oscillator, attributed to bulk plasma resonances, is required to accurately model the ellipsometric data. Postdeposition optical and electronic changes are observed for island films and the origins of these changes are investigated using the ellipsometric data
Keywords: Nanoparticles; Plasmon resonance; Spectroscopic ellipsometry
  • Sensors and Actuators B 109(2005), 146-152

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Permalink: https://www.hzdr.de/publications/Publ-9036
Publ.-Id: 9036


The characteristics of gas/liquid flow in large risers at high pressures

Azzopardi, B. J.; Omebere-Iyari, N. K.; Lucas, D.; Beyer, M.; Prasser, H.-M.
Although, most of the work reported on two-phase flows are limited to small pipe diameters, two-phase flow in large risers are increasingly being encountered in the petroleum and nuclear industries. In the present work, a wire mesh sensor was employed to obtain void fraction and bubble size distribution data and visualizations of steam/water flow in a large vertical pipe (194mm in diameter) at 46bar. For comparison purposes, measurements were made at similar phase velocities and physical properties to the data of Omebere-Iyari et al. (2006), which is for the flow of a nitrogen/naphtha mixture in a similar-sized riser. There exist significant differences between both sets of data. Churn-turbulent flow is observed in the present work instead of slug flow which differs from the intermittent and semi-annular flow patterns reported by Omebere-Iyari et al. (2006). The mean void fraction of the nitrogen/naphtha data is higher that of the present steam/water data. On examination of radial void fraction profiles, core peak distributions are observed for the present work in contrast to the wall peak profiles predicted for the data of Omebere-Iyari et al. (2006) using a power law relationship.
Keywords: two phase flow, nitrogen/naphtha flow, large vertical pipe, steam/water flow, high pressure
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Gas/liquid flow in large risers; paper: S6_Thu_A_47

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Permalink: https://www.hzdr.de/publications/Publ-9034
Publ.-Id: 9034


Uranyl Coordination in Ionic Liquids: The Competition between Ionic Liquid Anions, Uranyl Counterions, and Cl- Anions Investigated by Extended X-ray Absorption Fine Structure and UV-Visible Spectroscopies and Molecular Dynamics Simulations

Gaillard, C.; Chaumont, A.; Billard, I.; Hennig, C.; Ouadi, A.; Wipff, G.
The first coordination sphere of the uranyl cation in room-temperature ionic liquids (ILs) results from the competition between its initially bound counterions, the IL anions, and other anions (e.g., present as impurities or added to the solution). We present a joined spectroscopic (UV-visible and extended X-ray absorption fine structure)-simulation study of the coordination of uranyl initially introduced either as UO2X2 salts (X- ) nitrate NO3 -, triflate TfO-, perchlorate ClO4 -) or as UO2 (SO4) in a series of imidazolium-based ILs (C4mimA, A- ) PF6 -, Tf2 N-, BF4 - and C4mim ) 1-methyl-3-butyl-imidazolium) as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. The addition of Cl- anions promotes the solubilization of the nitrate and triflate salts in the C4mimPF6 and the C4mimBF4 ILs via the formation of chloro complexes, also formed with other salts. The first coordination sphere of uranyl is further investigated by molecular dynamics (MD) simulations on associated versus dissociated forms of UO2X2 salts in C4mimA ILs as a function of A- and Xanions.
Furthermore, the comparison of UO2Cl4 2-, 2 X- complexes with dissociated X- anions, to the UO2X2, 4
Cl- complexes with dissociated chlorides, shows that the former is more stable. The case of fluoro complexes is also considered, as a possible result of fluorinated IL anion’s degradation, showing that UO2F4 2- should be most stable in solution. In all cases, uranyl is found to be solvated as formally anionic UO2XnAmCl p 2-n-m-p complexes, embedded in a cage of stabilizing IL imidazolium or ammonium cations.
Keywords: Ionic liquids, uran, complexation, EXAFS
  • Inorganic Chemistry 46(2007), 4815-4826

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Permalink: https://www.hzdr.de/publications/Publ-9033
Publ.-Id: 9033


Structural investigation of Neptunium(V) in toxicological processes

Den Auwer, C.; Moisy, P.; Guillaumont, D.; Vidaud, C.; Funke, H.; Hennig, C.
General understanding needs to be deepened of intramolecular interactions engaged in molecular actinide species, i.e. physical chemical mechanisms that drive the affinity of chelating ligands for actinide cations still needs to be deepened. In this field, X-ray absorption spectroscopy has been extensively used as a structural and electronic metal cation probe. Combination with more traditional spectroscopic techniques such as spectrophotometry is an ideal tool for the understanding of the chelation mechanism. Metallobiomolecules are considered elaborate inorganic complexes with well-designed metal active sites. Although the various interaction processes between essential cations important to biology and proteins are widely studied, focus on the actinides is more seldom. Actinide impact on biological cycles has been motivated by risk assessments related to the wide use of nuclear fuel sources and industrial or military applications. In particular, the interaction between these cations with the biological active complexation sites are only partially understood.
Keywords: EXAFS, Neptunium(IV)
  • Materials Research Society Symposium Proceedings 893(2006), 315-323

Permalink: https://www.hzdr.de/publications/Publ-9032
Publ.-Id: 9032


Speciation of technetium and rhenium complexes by in situ XAS-electrochemistry

Poineau, F.; Fattahi, M.; Den Auwer, C.; Hennig, C.; Grambow, B.
A spectro-electrochemical cell was developed in order to study the speciation of radio-elements in thermodynamic unstable redox states using in situ XAS spectroscopy. This cell was used for the speciation of Re and Tc complexes in chloride media. Experiments on Re were carried out with the aim to validate the functionality of the experimental set-up. During electro-reduction of Re(VII) in HCl media, EXAFS and XANES studies were performed in order to reveal the formation of chloro-oxygenated compounds of Re(IV). The speciation of technetium in aqueous solutions of deep geological deposits for radioactive waste is important to predict its mobility under reducing conditions. XANES spectra showed that electro-reduction of Tc(VII) in chloride media leads to a position of K-edge absorption which agrees with a Tc(IV)/Tc(III) mixture.
Keywords: Technetium, Rhenium, EXAFS, Speciation, Spectro-electrocemistry

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Permalink: https://www.hzdr.de/publications/Publ-9031
Publ.-Id: 9031


Eine Frage der Kühlbarkeit / A question of cooling ability (coolability)

Willschütz, H.-G.
Wie kann die Bevölkerung vor den Folgen eines hypothetischen schweren Kernschmelzunfalls in einem Reaktor geschützt werden? Welche Schutzvorkehrungen sind vorgesehen? Neue Antworten auf diese Fragen werden in der Reaktorsicherheitsforschung erarbeitet. Dass Forschungsaktivitäten im Bereich hypothetischer Ereignisse mit äußerst geringer Eintrittswahrscheinlichkeit eine Sicherheitskultur auf hohem Niveau unterstützen und weitere Verbesserungsvorschläge auch für bestehende Anlagen ermöglichen, belegen Ergebnisse einer Forschungsarbeit zur Rückhaltbarkeit von Kernschmelze im Reaktordruckbehälter.
Keywords: Nuclear Power Plant, Severe Accident, Core Melt Down, Physical Barriers, In-Vessel-Retention
  • Brennstoff, Wärme, Kraft: BWK 58(2006)12, 27-30

Permalink: https://www.hzdr.de/publications/Publ-9030
Publ.-Id: 9030


A toy model of PT-symmetric Quantum Mechanics, the Squire equation and UV-IR-duality

Günther, U.; Stefani, F.; Znojil, M.
Some facts about the spectrum of a PT-symmetric quantum mechanical (PTSQM) toy model with potential V(x)=Gx2(ix)ν in a box x∈[-L,L] are presented for the parameter region ν∈[-2,0]. The corresponding Hamiltonian is selfadjoint in an appropriately chosen Krein space and for ν=-1 the spectral problem maps into that of the hydrodynamic Squire equation. It is shown that in the limit L→∞ a spectral singularity occurs and that the PTSQM ⇄ Squire mapping can be interpreted as a special type of strong-coupling ⇄ weak-coupling (UV-IR) duality. Finally, the system behavior in the vicinity of a spectral triple point is sketched.
partially based on:
J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.
Keywords: PT-symmetric Quantum Mechanics, Krein space, spectral analysis, spectral triple point, UV-IR duality
  • Invited lecture (Conferences)
    6th Workshop "Operator Theory in Krein Spaces and Operator Polynomials", 14.-17.12.2006, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-9029
Publ.-Id: 9029


What can we learn from diffuse scattering about actinide coordination in solutions?

Hennig, C.
The presentation comprises an introduction in the theory of diffuse scattering, experimental conditions, classical technique and difference technique, LAXS and HEXS. Several typical examples and potential applications will be discussed.
Keywords: Actinides, Uranium, diffuse scattering, LAXS, HEXS
  • Lecture (others)
    ROBL Seminar, 21.11.1006, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-9026
Publ.-Id: 9026


Application of EXAFS spectroscopy for structural analysis of actinide compounds in solution

Hennig, C.
An overview on EXAFS on applications on actinide structure investigation in solution will be given.
Keywords: EXAFS, Actinides
  • Invited lecture (Conferences)
    Chemistry Department of the Argonne National Laboratory, 31.10.2006, Chicago, United States

Permalink: https://www.hzdr.de/publications/Publ-9025
Publ.-Id: 9025


Bacterial S-layers as template for the formation of Pd nanoclusters

Hennig, C.; Fahmy, K.; Merroun, M.; Pollmann, K.; Raff, J.; Savchuk, O.; Selenska-Pobell, S.
Nano-catalysts made from palladium and other noble metals promise to accelerate chemical reactions even at low temperatures. Critical for the efficiency of such nano-catalysts is a perfect control of their cluster-size. By using the surface protein layer (so-called S-layer) of a bacterium, particles with a uniform size distribution of 50 to 80 Pd atoms can be generated. For the first time, the bonding sites between the metal and the S-layer protein have been characterized. Hereby, the prerequisite is given to manipulate this protein by genetic engineering enabling the design of materials with new optic, magnetic and catalytic properties.
The uranium uptake mechanism were investigated by EXAFS performed at the Rossendorf Beamline. The measurements revealed that the purified S-layer proteins of this bacterium coordinate uranium through phosphate groups of phosphorylated serine and threonine in a monodentate mode as well as through carboxyl groups of aspartic and glutamic acids in a bidentate mode.
The heavy metal binding capacity of the S-layer led to the idea to use it as template for the formation of Pd nanoclusters. Within the pores of the S-layer, isolated from vegetative bacteria, Pd(II) solutions are reduced to metallic palladium by the use of hydrogen.
In order to investigate the metal-protein interactions and their impact on the secondary structure, a solution of Pd(II) ions has been sorbed on the S-layer matrix. The combination of Fourier transform infrared spectroscopy and EXAFS spectroscopy revealed that the surface Pd(II) is predominantly coordinated by aspartic and glutamic residues through 4 nitrogen and oxygen atoms at a distance of 2.01 Å. In contrast to U(VI), that binds to carboxyl and phosphate groups, Pd(II) binds exclusively to the carboxyl groups of the S-layer. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate the binding of heavy metals to aspartic and glutamic acids. These side chains are thus targets for the design of engineered S-layer based nanoclusters.
Keywords: EXAFS, Rossendorf Beamline, Palladium, S-layer
  • Contribution to external collection
    in: ESRF Highlights 2007, Grenoble: ESRF, 2007, 83-84

Permalink: https://www.hzdr.de/publications/Publ-9024
Publ.-Id: 9024


The effect of flash lamp annealing on Fe implanted ZnO single crystals

Potzger, K.; Anwand, W.; Reuther, H.; Zhou, S.; Talut, G.; Fassbender, J.ORC; Brauer, G.; Skorupa, W.
The effect of flash lamp annealing applied to ZnO single crystals implanted with 3.6 at. % Fe has been studied. For intermediate light power, the implantation induced surface defects could be annealed without creation of secondary phases within the implanted region. At the same annealing temperatures, however, ion beam induced open volume defects start to increase in size. Recrystallization is initiated for the highest light power applied, i.e. the ion beam induced lattice disorder reflected by the minimum channelling yield of Rutherford backscattering spectroscopy decreases from 76 % to 46 % and the open volume defects are annealed. At the same time, the Fe3+ fraction increases at the cost of the Fe2+ states. Weak ferromagnetic properties are induced, that are mainly associated with nanoparticles
Keywords: ZnO, Diluted magnetic semiconductors, ion implantation, flash lamp annealing
  • Journal of Applied Physics 101(2007)3, 033906
  • Lecture (Conference)
    71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.3.2007, Regensburg, Germany

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Permalink: https://www.hzdr.de/publications/Publ-9023
Publ.-Id: 9023


Resonance effects in α2-dynamos

Kirillov, O.; Günther, U.
First results on a perturbation theory for α2-dynamos with non-constant spherically symmetric α-profiles are presented. The basics of the mathematical technique is demonstrated on a simplified model with idealized boundary conditions (BCs). Such BCs allow for a full semi-analytical treatment of the problem due to the selfadjointness of the dynamo operator in a so called Krein space --- a Hilbert space with an additional indefinite metric structure.
Starting point of the consideration is the model with constant α-profile α₀ which is exactly solvable. The eigenvalues λ of such a model form a mesh-like branch structure in the (α₀,Re λ)-plane. The nodes of this mesh (the intersection points of the branches) are double semi-simple eigenvalues (diabolical points) of algebraic and geometric multiplicity 2.
A Krein space related perturbation theory as well as a Galerkin technique for the numerical treatment of inhomogeneous perturbations of the α-profile have been developed. With the help of these tools, a very pronounced α-resonance pattern has been found in the deformations of the spectral mesh as well as in the unfolding of the diabolical points. The selection rules of this resonance pattern are defined by the Fourier coefficients of the perturbations leading to a strong correspondence between the characteristic length scale of the α-perturbations and the decay rates of the coherently induced field excitations. Such correlations will exist also in models with realistic BCs and may provide a qualitative explanation for some specifics of field reversal processes --- supporting corresponding numerical simulations on more realistic dynamo setups.
Furthermore, an estimation technique has been developed for obtaining optimal α-profiles for which α2-dynamos can become overcritical in oscillatory regimes. This basic technique is demonstrated explicitly for a simplified monopole (l=0) model, where it leads to a bound on the Fourier components of the α-profile. The capability of the used Galerkin approach is demonstrated in extending the strength of the α-perturbations from weakly perturbed regimes to strongly perturbed ones.
Extensions of the presented techniques to spherically symmetric α2-dynamos with realistic boundary conditions are in preparation.
Keywords: MHD dynamo, Krein space, perturbation theory, spectral analysis, spectral singularities, diabolical points, exceptional points
  • Lecture (Conference)
    9th MHD Days 2006, 04.-05.12.2006, Heidelberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-9022
Publ.-Id: 9022


Boron dilution analyses at reactor shutdown conditions using the coupled code DYN3D/ATHLET

Kliem, S.; Rohde, U.
A parameter study of a hypothetical boron dilution event during the work of the RHRS was performed. Based on a validated coolant mixing model for the lower plenum of the RPV, realistic boron concentration curves at the inlet into each fuel assembly were obtained and used for a number of stationary and transient core calculations. For the generic core loading pattern used in the calculations, in the stationary calcu-lations recriticality is reached for slug volumes of about 8 m3 if the realistic core inlet boron concentration distribution is used. Transient core calculations from 8 to the maximum initial slug volume of 15 m3 showed, that the maximum calculated fuel and cladding temperature values are below critical values. Although in all calculations local coolant boiling occurs over several tenths of seconds, the integrity of the fuel is always ensured according to the calculation results.
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2007, 22.-24.05.2007, Karlsruhe, Germany
    Proceedings of the Annual Meeting on Nuclear Technology 2007: INFORUM GmbH, 51-57

Permalink: https://www.hzdr.de/publications/Publ-9018
Publ.-Id: 9018


Silicon-on-insulator microcavity light emitting diodes with two Si/SiO2 Bragg reflectors

Potfajova, J.; Sun, J. M.; Schmidt, B.; Dekorsy, T.; Skorupa, W.; Helm, M.
Light emitting pn-diodes were fabricated on a 5.8 µm thick n-type Si device layer of a silicon-on-insulator (SOI) wafer using standard silicon technology and boron implantation. The thickness of the Si device layer was reduced to 1.3 µm, corresponding to a 4λ-cavity for λ = 1150nm light. Electroluminescence spectra of these low Q-factor microcavities are presented. Addition of Si/SiO2 Bragg reflectors on the top and bottom of the device (3.5 and 5.5 pairs, respectively) is predicted to lead to spectral emission enhancement by ∼270.
Keywords: Silicon; Electroluminescence; Resonant cavity
  • Journal of Luminescence 121(2006)2, 290-292
    DOI: 10.1016/j.jlumin.2006.08.006
  • Poster
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nizza, Frenkreich

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Permalink: https://www.hzdr.de/publications/Publ-9017
Publ.-Id: 9017


Asymptotic methods for spherically symmetric MHD α2-dynamos

Kirillov, O.; Günther, U.
We consider two models of spherically-symmetric MHD α2-dynamos --- one with idealized boundary conditions (BCs) and one with physically realistic BCs. As it has been shown in our previous work, the eigenvalues λ of a model with idealized BCs and constant α-profile α₀ are linear functions of α₀ and form a mesh in the (α₀,Re λ)-plane. The nodes of the spectral mesh correspond to double-degenerate eigenvalues of algebraic and geometric multiplicity 2 (diabolical points). It was found that perturbations of the constant α-profile lead to a resonant unfolding of the diabolical points with selection rules of the resonant unfolding defined by the Fourier coefficients of the perturbations. In the present contribution we present new exact results on the spectrum of the model with physically realistic BCs and constant α₀. For non-degenerate (simple) eigenvalues perturbation gradients are found at any particular α₀. We present a detailed study of the spectral behavior of the α2-dynamo operator over a family of homotopic deformations of the BCs between idealized ones and physically realistic ones. Furthermore, we demonstrate that although the spectral singularities are lifted, a memory about their locations remains deeply imprinted in the homotopic family of the spectral deformations due to a hidden underlying invariance.
Keywords: MHD dynamo, homotopic deformation, homotopic invariance, non-Hermitian operator, spectral analysis
  • Lecture (Conference)
    6th International Congress on Industrial and Applied Mathematics (iciam 07), 16.-20.07.2007, Zürich, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-9016
Publ.-Id: 9016


Single-pion production in pp collisions at 0.95 GeV/c (I)

Abd El-Samad, S.; Bilger, R.; Brinkmann, K.-T.; Clement, H.; Dietrich, M.; Doroshkevich, E.; Dshemuchadse, S.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Geyer, R.; Gillitzer, A.; Hauffe, J.; Hesselbarth, D.; Jaekel, R.; Jakob, B.; Karsch, L.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Meier, R.; Möller, K.; Morsch, H. P.; Naumann, L.; Roderburg, E.; Schönmeier, P.; Schulte-Wissermann, M.; Schroeder, W.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Wächter, J.; Wagner, G. J.; Wagner, M.; Weidlich, U.; Wilms, A.; Wirth, S.; Zhang, G.; Zupranski, P.
The single-pion production reactions pp → dπ+, pp → npπ+ and pp → ppπ0 were measured at a beam momentum of 0.95GeV/c ( T p ≈ 400MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus, all pion production channels were recorded with 1-4 overconstraints. The total and differential cross-sections obtained are compared to previous data and theoretical calculations. Main emphasis is put on the discussion of the ppπ0 channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement with recent phenomenological and theoretical predictions. In particular, we observe very large anisotropies for the π0 angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip transitions associated with π0 s and d partial waves and emphasizing the important role of π0 d-waves.
Keywords: PACS. 13.75.Cs Nucleon-nucleon interactions - 25.10.+s Nuclear reactions involving few-nucleon systems - 25.40.Ep Inelastic proton scattering - 29.20.Dh Storage rings

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Publ.-Id: 9015


Study of spectator tagging in the reaction np → ppπ- with a deuteron beam

Abdel-Bary, M.; Brinkmann, K.-T.; Clement, H.; Doroshkevich, E.; Dshemuchadse, S.; Erhardt, A.; Eyrich, W.; Freiesleben, H.; Gillitzer, A.; Jäkel, R.; Karsch, L.; Kilian, K.; Kuhlmann, E.; Möller, K.; Morsch, H. P.; Naumann, L.; Paul, N.; Pizzolotto, C.; Ritman, J.; Roderburg, E.; Schönmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sun, G. Y.; Teufel, A.; Ucar, A.; Wagner, G. J.; Wagner, M.; Wintz, P.; Wüstner, P.; Zupranski, P.
The reaction dppppπ- has been studied in a kinematically complete experiment at a single beam momentum pd =1.85 GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free nppppπ- reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.
Keywords: PACS. 13.75.Cs Nucleon-nucleon interactions - 25.10.+s Nuclear reactions involving few-nucleon systems - 29.20.Dh Storage rings - 29.90.+r Other topics in elementary-particle and nuclear physics experimental methods and instrumentation

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Permalink: https://www.hzdr.de/publications/Publ-9014
Publ.-Id: 9014


Scanning probe microscopy with cantilever arrays

Rangelow, I.; Ivanov, T.; Volland, B.; Dontsov, D.; Sarov, Y.; Ivanova, K.; Persaud, A.; Filenko, D.; Nikolov, N.; Schmidt, B.; Zier, M.; Gotszalk, T.; Sulzbach, T.
This paper reports on to the realization of piezoresistive cantilever-Arrays used in scanning probe microscopy (SPM). Sensors for the SPM are peculiar microsystems since the combination of physical and microtechnological principles allows to gain an insight into the material science at nanoscale. Moreover SPM technology is opening new horizons in fundamental research and gives a chance to employ new interaction principles for the realization of new sensors and sensor arrays. Physical, biological, and chemical values and interactions can effectively be detected and analyzed using cantilevers, where the nanomechanical interactions can be transformed into an electric signal. The basic issues for the realization of a complete system of self-actuated, piezoresistive cantilever arrays are described.
Keywords: Piezoresistive cantilever arrays, scanning force microscopy, microsystems, nanosystems

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Permalink: https://www.hzdr.de/publications/Publ-9013
Publ.-Id: 9013


Bubble recognition algorithms for the processing of wire-mesh sensor data

Prasser, H.-M.; Beyer, M.
Wire-mesh sensors deliver sequences of instantaneous, two-dimensional gas fraction distributions from a measuring cross-section. The spatial and temporal resolutions are high enough to reflect individual bubbles in much more than one measuring frame during their passage through the sensor plane. The bubbles can therefore be detected by a pattern recognition method based on the identifications of connected areas of gas-filled elements in the array of local instantaneous gas fractions, available as a function of the lateral co-ordinates x,y and as function of time. Algorithms were presented in earlier publications, which are based on a recursive fill procedure that assigns individual bubble numbers to the elements of the gas fraction array. This procedure has to rely on a threshold for the cancellation of the recursive fill, because the gas fraction data are affected by noise. The choice of the correct threshold is difficult, since a too high gas fraction threshold leads to unrealistic bubble fragmentation, while a too low threshold provokes unrealistic unification of bubbles. In previous papers an optimum approach was found by introducing a differential threshold determined for each bubble individually from the maximum gas fraction inside the given bubble to identify the cores of the bubbles. This is combined with an agglomeration step, where elements with a gas fraction below the threshold are assigned to already existing bubble cores, if these elements were not yet assigned to a bubble in the recursive fill step.
In the present paper, the algorithm will be analysed by applying it to synthetic measuring data, which is generated by placing bubbles of known geometrical parameters into the discretization measuring grid defined by the wire-mesh geometry. The discretization is performed with due care to reflect the fact that the gas-liquid interface at the periphery of the bubbles crosses control volumes of the measuring grid, producing local instantaneous void fractions of intermediate values. The synthetic signals are furthermore superposed by synthetic white noise. It is shown that the original bubble recognition algorithm needs to be improved in certain cases: (a) Unrealistic fragmentation in axial (time) direction may occur, when bubbles cross the sensor plane with a low velocity. (b) non-realistic coalescence becomes dominating at very high gas fractions, where bubbles of complex shape occur. Different improvements were tested. Unrealistic coalescence is avoided by introducing a criterion to terminate the recursive fill algorithm, which are based on the local gradient of the gas fraction. A second approach relies on a repair algorithm, which unites unrealistic fragments in an additional processing step after the preliminary bubble recognition. This repair algorithm takes benefit from a-priory knowledge to distinguish realistic close neighbour bubbles from unrealistic bubble fragments divided by an early truncation of the bubble recognition. After the check against synthetic bubbles, the algorithms are applied to real measuring data from gas-liquid flows in vertical pipes and the results obtained by the different algorithms are compared.
Keywords: wire-mesh sensor, measurement technique, bubble identifikation, bubble recognition algorithm
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    paper:S7_Thu_B_50
  • Lecture (Conference)
    International Conference on Multiphase flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

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Publ.-Id: 9012


A globally diagonalizable α2-dynamo operator, SUSY QM and the Dirac equation

Günther, U.; Samsonov, B.; Stefani, F.
A new class of semi-analytically solvable MHD α2-dynamos is found based on a global diagonalization of the matrix part of the dynamo differential operator. Close parallels to SUSY QM are used to relate these models to the Dirac equation and to extract non-numerical information about the dynamo spectrum.
Keywords: MHD dynamo, Krein space, operator theroy, supersymmetric Quantum Mechanics, Dirac equation, quasi-exactly solvable model, perturbation theory, Jordan structure

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Publ.-Id: 9011


A bubble size distribution model for the numerical simulation of bubbly flows

Ruyer, P.; Seiler, N.; Beyer, M.; Weiss, F.-P.
This study carried out at the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) concerns the bubbly flow numerical simulation. One of the determining features of the two-phase flow is the topology of the flow. Local interfacial area concentration, say ai, allows to determine the exchange surface for momentum, heat and mass transfers between liquid and vapor. In the case of bubbly flow the size of the inclusion, say D, (through the non-dimensional Eötvös number) determines essential liquidvapor momentum transfers such as the lift force (e.g. (Tomiyama et al. 1995)). The corresponding fields ai and D are functions of history, flow conditions, as well as local events such as coalescence, break-up and phase change. This justifies to model their evolution thanks to additional transport equations (in addition to momentum, mass and energy balance equations). Several approaches can then be distinguished, namely the population balance (Coulaloglou and Tavlarides 1977), the two-group interfacial area transport (Fu and Ishii 2002) or the moment densities (Kamp et al. 2001). The purpose of the present study is to examine the ability of the NEPTUNE_CFD code to predict bubble size distribution in complex flow configurations.
A series of experiments performed at FZD in the frame of the TOPFLOW project allows to determine the local structure of the two-phase flow including the bubble size local distribution. We focus more particularly on bubbly air-water flows around an asymmetric obstacle in the section of a vertical pipe (see (Prasser et al. 2006)). The presence of the obstacle induces a pronounced three-dimensional effect as well as coalescence events. We perform numerical simulations with the NEPTUNE_CFD code of these experiments. The NEPTUNE_CFD code (see (Guelfi et al. 2005)) is based on the two-fluid model formulation. It is developed in the frame of a research program supported by EDF, CEA, IRSN and AREVA_NP. In the present study, two different levels of description of the bubble size distribution in space and time are considered. At the first level of description, the bubble size distribution is determined thanks to an interfacial area equation allowing to define locally a single bubble size (monodisperse flow). At the second level we consider locally a spectrum of bubble sizes (polydisperse flow) with the help of a moment densities approach. We incorporate the model within NEPTUNE_CFD and present the resulting gain in accuracy of the simulation. Perspectives concerning improvement of the numerical modelling of bubble size distribution are discussed.
Keywords: two-phase flow, NEPTUNE_CFD, bubble size distribution
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    paper: S6_Thu_A_48

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Publ.-Id: 9009


Crystallographically oriented magnetic ZnFe2O4 nanoparticles synthesized by Fe implantation into ZnO

Zhou, S.; Potzger, K.; Reuther, H.; Talut, G.; Eichhorn, F.; von Borany, J.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
In this paper, a correlation between structural and magnetic properties of Fe-implanted ZnO is presented. High fluence Fe+ implantation into ZnO leads to the formation of superparamagnetic α-Fe nanoparticles. High vacuum annealing at 823 K results in the growth of α-Fe particles, but the annealing at 1073 K oxidizes the majority of the Fe nanoparticles. After a long term annealing at 1073 K, crystallographically oriented ZnFe2O4 nanoparticles are formed inside ZnO with the orientation relationship of ZnFe2O4(1 1 1)[1 1 0]//ZnO(0 0 0 1)[11 2 0]. These ZnFe2O4 nanoparticles show a hysteretic behaviour upon magnetization reversal at 5 K.
Keywords: ZnO; Magnetism of nanostructures; Ferrite
  • Journal of Physics D: Applied Physics 40(2007), 964-969

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Publ.-Id: 9008


Annual Report 2005 - Institute of Safety Research

Weiss, F.-P.; Rindelhardt, U.; (Editors)
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-457 2006

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Publ.-Id: 9007


Synthesis of 18F-labeled neurotensin(8-13) via copper-mediated 1,3-dipolar [3+2]cycloaddition reaction

Ramenda, T.; Bergmann, R.; Wüst, F.
The copper(I)-mediated 1,3 dipolar [3+2]cycloaddition between terminal alkynes and azides, also referred to as click-chemistry, was used to synthesize a 18F-labeled neurotensin(8-13) (NT(8-13)). 4-[18F]Fluoro-N-(prop-2-ynyl)benzamide [18F]1 as novel terminal alkyne building block could successfully be coupled with azide-functionalized NT(8-13) 4 to give the corresponding 18F-labeled NT(8-13) derivative [18F]5 product in 66% yield as determined by radio-HPLC. The in vitro binding affinity of 18F-labeled NT(8-13) derivative [18F]5 was determined to be 66 nM.
  • Letters in Drug Design & Discovery 4(2007)4, 279-285

Permalink: https://www.hzdr.de/publications/Publ-9005
Publ.-Id: 9005


Investigations into the Formation of Intrinsic Colloids and Pseudocolloids of Uranium(IV)

Zänker, H.; Opel, K.; Weiß, S.; Hübener, S.; Bernhard, G.
Investigations into the formation of intrinsic colloids and pseudocolloids of uranium(IV) were performed. Coulometric titrations of strongly acidic U(IV) solutions in HClO4/NaClO4 medium were carried out in order to find the pH of first colloid formation. Laser-induced breakdown detection (LIBD) was applied for the detection of traces of uranium colloids as the pH was increased. The pH values at the onset of colloid formation were used for thermodynamic calculations aimed at determining the solubility products of crystalline and amorphous uranium dioxide. Furthermore, the UO2·xH2O(am) colloids were investigated for their colloidal stability. Zeta potentials of ≥ 30 mV were found for pH values of less than 4. The point of zero charge was found at pH ~ 6.9. Colloidal suspensions of 1 mMol/L UO2·xH2O(am) at a pH value of 2.5 proved to be stable over > 1.5 years. The interaction of the forming UO2·xH2O(am) colloids with other colloid-forming species was tested. Therefore, coulometric titrations of U(IV) solutions in the presence of (a) dissolved Al(III) and (b) dissolved silicate were carried out. The presence of Al(III) does not significantly influence the formation of the UO2·xH2O(am) colloids, and the presence of U(IV) does not significantly influence the behaviour of Al(III). Also silicate does not significantly influence the pH of UO2·xH2O(am) colloid formation. However, the presence of U(IV) significantly influences the behaviour of the silicate (formation of pseudocolloids). The nature of the interaction between the silicate and the U(IV) is not yet known (adsorption? formation of a coffinite precursor?). EXAFS experiments to elucidate the local structure around the U(IV) atoms in the pseudocolloids are under preparation.
Keywords: Uranium(IV), uranium dioxide, intrinsic colloids, pseudocolloids, aluminum, silicate
  • Lecture (Conference)
    2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-9004
Publ.-Id: 9004


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