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35173 Publications

Radioaktiv markierte Kern-Hüll-Nanopartikel auf der Basis von Stärke-umhülltem Magnetit

Matterna, M.

kein Abstract verfügbar

  • Lecture (others)
    Seminar, Universität Jena, Institut für Diagnostische und Interventionelle Radiologie, 14.04.2008, Jena, Deutschland

Publ.-Id: 11356

Diagnostik und Therapie mit radioaktiven Substanzen

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Hochschule Zittau/Görlitz (FH), 22.05.2008, Zittau, Deutschland

Publ.-Id: 11355

18F-radiolabeled S100 proteins as potential probes for molecular imaging of inflammatory processes in vivo

Hoppmann, S.; Richter, S.; Pietzsch, J.

Interaction of certain extracellular S100 proteins with the receptor for advanced glycation endproducts (RAGE) is considered to play a crucial role in various inflammatory diseases. However, data concerning the interaction of circulating S100 proteins with RAGE in inflammatory processes in vivo are scarce. One reason is the shortage of suitable radiotracer methods. To address this question, we report a novel methodology using recombinant human S100A1, S100B, and S100A12 for radiolabeling with the positron emitter fluorine-18 (18F) and the use of 18F-S100 proteins in cell association assays in vitro and in dynamic small animal positron emission tomography (PET) studies in Wistar rats in vivo. Human S100 proteins were cloned in the bacterial expression vector pGEX-6P-1, expressed in E. coli BL21, and purified. Purified S100 proteins were radiolabeled with N-succinimidyl-4-[18F]fluorobenzoate. Cellular association studies in human THP-1 macrophages and human aortic endothelial cells (HAEC) showed specific binding of all 18F-S100 proteins to the non-internalizing RAGE as confirmed by inhibitory effects exerted either by other RAGE ligands, e.g., glycated LDL, or by soluble RAGE. Of interest, uptake of 18F-S100 proteins in THP-1 and HAEC mediated by various scavenger receptors was observed. The in vitro data are consistent with in vivo PET data showing a pronounced temporary association of 18F-S100 proteins with tissues expressing RAGE, e.g., lung and vessels. Moreover, a significant accumulation of 18F-S100 proteins in tissues that are rich in cells expressing scavenger receptors (tissue macrophages) such as liver and spleen was observed. In conclusion, 18F-labeling of S100 proteins and the use of small animal PET provide a valuable tool to discriminate the kinetics and the metabolic fate of S100 proteins in vivo. Furthermore, the approach provides novel probes for imaging of RAGE-ligand interaction in inflammatory processes, e.g., in rodent models of disease.

  • Poster
    5th International EDHF Symposium - Endothelium, Vasoactive Factors and Inflammation, 24.-27.06.2008, Tampere, Finland
  • Abstract in refereed journal
    Basic & Clinical Pharmacology & Toxicology 102(2008)S1, 49

Publ.-Id: 11354

Labelling methods in (PET-)Radiopharmacy: Do we need alternatives?

Steinbach, J.

Labelling of molecules was introduced by Georg von Hevesy already decades ago utilizing radiophosphorus. With the availability of C-14 and H-3 a long period of isotopic labelling started in the fifties of the last century following Rudolf Schönheimer´s idea to label biomolecules with deuterium. This was the scientific base of the modern biochemistry enabling detailed study of metabolism and of modern pharmacokinetics. With the use of radioiodine fur human investigations and therapy the era of Nuclear Medicine began during that time.
All these applications require different labelling techniques for the radiotracer synthesis. Most of them have been derived from organic microchemistry and have been further developed for the special radiochemical conditions such as radiation protection and the limited amount of substance matter.
The introduction of radiometals to Nuclear Medicine, first of all Tc-99m, opened a new challenge. This was the need to mimic organic molecules by coordination compounds – utilizing knowledge from inorganic, organic and radiochemistry.
At the end of the seventies the Positron Emission Tomography came into the focus of science and later on of medicine. Completely new methods had to be developed due to the application of the no carrier added positron emitting radionuclides in connection with their short half lifes first of all for F-18 and C-11.

Nowadays thousands of compounds have been labelled – organic and inorganic. Hundreds of methods have been developed to introduce e.g. carbon isotopes, radiohalogens and radiometals into the desired positions of molecules comprising a wide variety of substance classes.
Have we reached a saturation of demand for labelling methods?
Of course – for small molecules the requirements for real new developments may be limited. But new demands are at the horizon: This are biomacromolecules such as proteins, peptides, oligonucleotides which are sensitive to the “classic” conditions of chemical reactions. Other problems are connected with the need for regioselective, site specific labelling.
There is and will be done a lot of work – also in the future for applied purposes.

  • Invited lecture (Conferences)
    15th Workshop "The Synthesis and Applications of Isotopes and Isotopically Labelled Compounds", 12.-13.06.2008, Bad Soden, Deutschland
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)7, 257

Publ.-Id: 11352

Retrospective dosimetry study at the RPV of NPP Greifswald unit 1

Konheiser, J.; Mittag, S.; Noack, K.; Rindelhardt, U.; Borodkin, G.; Borodkin, P.; Gleisberg, B.

For the first time, trepans from a decommissioned VVER-440 (Greifswald-1) reactor pressure vessel (RPV) have been examined. Activities of a trepan, taken at the RPV weld with the highest fast-neutron load, were measured and estimated on the basis of fluence calculations by the codes TRAMO and DORT. A maximum fluence of 4.05*1019 n/cm2 (E>0.5 MeV) was calculated. The average deviation between the two codes is 2.6 %. Activities resulting from the reaction 93Nb(n,n’)93mNb were measured, niobium being a trace element in the RPV steel. Unfortunately, 93mNb is also produced by neutron capture in the alloy component 92Mo, the built-up 93Mo decaying by electron capture. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.42 and 0.97. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.

Keywords: reactor; retrospective dosimetry; neutron; fluence; VVER-440; TRAMO; Greifswald

  • Lecture (Conference)
    13th International Symposium on reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, JRC Petten, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 23-33

Publ.-Id: 11351

Mass occurrence of penetrative trace fossils in triassic lake deposits (Madygen mossil site, Kyrgyzstan, Central Asia)

Voigt, S.; Hoppe, D.

Bioturbation and the breakdown of organic detritus by burrowing macro-invertebrates are key factors for the energy flow in recent freshwater ecosystems due to the acceleration of nutrient cycling. According to the current state of knowledge, food webs similar to those ones of modern lakes were not operating until the Late Mesozoic, when a well-established freshwater infauna evolved. Here we describe laterally extended networks of irregularly branched burrows that constitute the most common ichnofossils in lacustrine deposits of the Middle to Late Triassic Madygen Formation, SW Kyrgyzstan. The shallow penetrative trace fossils assigned to Thalassinoides paradoxicus (Woodward, 1830) give evidence that underground exploitation of lake-bottom sediments by benthic invertebrates set up in the Early Mesozoic at the latest. Architecture and size of the fossil burrows indicate deposit-feeding, worm-like trace makers of similar morphology and behaviour to extant oligochaetes or aquatic insect larvae. Maximum intensity of bioturbation is recorded in mudstones of the transitional sublittoral to profundal lake zone which usually represents the thermocline/chemocline level in modern stratified lakes. Taking into account the low-oxygen tolerance of many recent oligochaetes and insect larvae we propose, that ecospace utilisation of deep-water lacustrine settings was originally impelled by two things: exploitation of additional food resources and avoidance of predation by carnivorous animals from well-aerated lake zones. Spatial restriction of the described fossil traces could offer a basic approach to subdivide the Mermia ichnofacies.

Keywords: Thalassinoides; bioturbation; Mermia ichnofacies; oligochaeta; insect larvae

Publ.-Id: 11350

Quality check of wire-mesh sensor measurements in a vertical air/water flow

Beyer, M.; Lucas, D.; Kussin, J.

Extensive measurements were executed for a vertical upward air/water flow to gen-erate a high-quality database for the development and validation of CFD-Codes for two-phase flows (e.g. for models on bubble forces or on coalescence and break-up). Thereto, in a pipe with a nominal diameter of 200 mm, the wire-mesh sensor technology was used. The present paper aims on the assessment of errors caused by the experimental procedure and especially global errors arising from the use of the wire-mesh sensor technology. Special attention was paid to the plausibility and accuracy of the data regarding the evolution of the vertical multiphase flow. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross-section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. From the measured radial profiles of the void fraction and the velocity of the gas phase, the superficial gas velocity at the wire-mesh sensor integrated over the cross-section is calculated and compared with the set value. Thus, a general error assessment of the sensor data is possible.

Keywords: multiphase flow; bubbly flow; bubble size distribution; wire-mesh sensor; accuracy check; drift velocity

Publ.-Id: 11349

Defect formation in Mn-implanted silicon probed by frequency and temperature dependent capacitance measurements on MOS capacitors

Zhou, S.; Bürger, D.; Beyer, V.; Schmidt, B.; Helm, M.; Schmidt, H.

In order to obtain magnetic Si the doping of it by Mn is one of the topics in this field. This opens the possibility to fabricate Si-based spintronic devices. Most of the research activities focused on material science, e.g. reporting higher Curie temperatures, and on characterizing their structural properties. However exploring the electrical properties after Mn doping is also important, so that the knowledge can be directly transferred to spintronic device fabrication. In these devices, an MIS (metal-insulator-semiconductor) structure is usually used and a high-quality oxide-semiconductor interface is therefore highly demanded. In this contribution, we investigate the defects in Si and in the interface between SiO2 and Si after the doping by Mn implantation into both p-type and n-type Si wafers. The implantation energy was 60 keV with a fluence of 2×10^15 cm^-2, resulting in a peak concentration of 5×10^20 cm^-3. A 15 nm thick SiO2 layer was grown during subsequent thermal oxidation at 900 °C. After this thermal treatment, the Mn atoms are solved in the Si wafer and partially in the SiO2 layer. Additionally, Mn in the region of the implanted profile with a nominal concentration above the solubility limit causes the formation of Mn-silicide nanoparticles [1]. The quality of SiO2/Si interface was checked by frequency dependent CV measurements. A large amount of defects was found at the SiO2/implanted-Si interface. Temperature dependent capacitance transient measurements reveal the formation of deep traps in the implanted Si, with energies of EV+0.54 eV, EV+0.41 eV in p-Si, and EC-0.57 eV, EC-0.23 eV, EC-0.11 eV in n-Si, respectively. All these electrical defects have to be considered when fabricating transition metal/SiO2/Mn-implanted Si structures for spin-dependent tunnelling devices.

[1] Shengqiang Zhou et al., Phys. Rev. B 75, 085203 (2007)

Keywords: Si; Mn; Ion implantation; DLTS

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.08, Dresden, Germany

Publ.-Id: 11348

Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?

Zhou, S.; Potzger, K.; Xu, Q.; Lorenz, M.; Skorupa, W.; Helm, M.; Fassbender, J.; Grundmann, M.; Schmidt, H.

Traditional electronics can be greatly stimulated by a combination of magnetic and semiconducting properties where spins provide an additional degree of freedom. Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with transition metal are diluted magnetic semiconductors (DMS) [1]. In binary DMS materials, transition metal ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit. Ion implantation is a non-equilibrium method, and has been successfully used to create GaAs-based DMS [2]. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between structural and magnetic properties. By synchrotron radiation X-ray diffraction secondary phases (Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as the source for ferromagnetism [3-6]. Due to their different crystallographic orientation with respect to the host crystal these nanocrystals in some cases are very difficult to be detected by a simple Bragg-Brentano scan. This results in the pitfall of using XRD to exclude secondary phase formation in DMS materials. For comparison, the solubility of Co diluted in ZnO films amounts to 10 at.% using pulsed laser deposition (PLD) [7]. Such diluted, Co-doped ZnO films show paramagnetic behaviour. However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d exchange interaction as compared to Co-implanted ZnO single crystals.
[1] T. Dietl, et al., Science 2000; 287:1019.
[2] M. A. Scarpulla, et al, Appl. Phys. Lett. 2003; 82:1251.
[3] K. Potzger, et al., Appl. Phys. Lett. 2006; 88 :052508.
[4] Shengqiang Zhou, et al., J. Appl. Phys. 2008; 103:023902.
[5] Shengqiang Zhou, et al., Phys. Rev. B 2008 ; 77:035209.
[6] Qingyu Xu, et al., Phys. Rev. B 2006; 73:205342.

Keywords: ZnO; diluted magnetic semiconductor; Magnetic nanoparticles; Magnetoresistance

  • Invited lecture (Conferences)
    VII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 16.-19.06.08, Kazimierz Dolny, Poland
  • Vacuum 83(2009), S13

Publ.-Id: 11347

High-Transmission Planar X-ray Waveguides

Salditt, T.; Krüger, S. P.; Fuhse, C.; Bähtz, C.

We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.

Keywords: X-ray optics; X-ray imaging; X-ray scattering

Publ.-Id: 11346

Model experiments on macroscopic thermoelectromagnetic convection

Zhang, X.; Cramer, A.; Lange, A.; Gerbeth, G.

The interaction between a thermoelectric current and an imposed magnetic field may produce thermoelectromagnetic convection (TEMC). In the present paper, an experimental study on TEMC in a generic configuration is reported. While the necessary temperature gradient grad T in a square box was accomplished by heating and cooling of two opposing side walls, respectively, utilising a massive nickel plate for the bottom of the electrically conducting container established a material discontinuity with respect to the liquid metal layer. In first place, such a jump in the related Seebeck coefficient non-parallel to grad T is a pre-requisite for the existence of a thermoelectric current. The second condition for TEMC, which is a non-vanishing curl of the Lorentz force, was fulfilled with a permanent magnet producing an inhomogeneous magnetic field. Ultrasonic Doppler velocimetry was used to quantify the TEMC flow field. The measurements demonstrate that even a moderate temperature difference can produce distinct convection. Locating the magnet, the direction of magnetization of which was parallel to grad T, close to either side wall produced a single vortex spreading throughout the entire box. Moving the magnet to the center led to a modified distribution of the magnetic field, which, in turn, altered the flow structure. A convective pattern consisting of four vortices developed and the velocity fluctuations were intensified. The numerical results for the distribution of the magnetic field in presence of the ferromagnetic bottom support the experimental findings.

  • Magnetohydrodynamics 45(2009), 25-42

Publ.-Id: 11345

Electromagnetic stirring with superimposed travelling and rotating magnetic fields.

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

Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a travelling magnetic field (TMF). The combination of both fields gives rise to an inherent three-dimensional constituent of the electromagnetic force distribution, which implies an intense mixing of the melt.

  • Lecture (Conference)
    XVI International Congress on Electricity applications in modern world - UIE'08, 19.-21.05.2008, Krakow, Poland
  • Contribution to proceedings
    XVI International Congress on Electricity applications in modern world - UIE'08, 19.-21.05.2008, Krakow, Poland, 83-88415-80-8, 41-42

Publ.-Id: 11344

DNA double-strand break signalling: X-ray energy dependence of residual co- localised foci of -H2AX and 53BP1

Beyreuther, E.; Lessmann, E.; Pawelke, J.; Pieck, S.

The foci of gamma-H2AX alone or colocated with 53BP1 are currently used in a lot of different studies to detect DNA double-strand breaks (DSB) after ionizing radiation. The primary objective of our study was to compare the radiation energy, dose dependent induction and kinetics of DNA DSB, in particular with regard to differences between soft and higher energy X-rays with the colocated gamma-H2AX and 53BP1 foci. We chose the human mammary epithelial cell line 184A1 for these experiments due to the medical application of 25 kV X-rays, e.g. in mammography. X-ray energies applied were 25 kV and 10 kV, the latter one by reason of the proposed maximum biological effectiveness at this energy, and 200 kV X-rays as reference radiation source.
The time courses of foci appearance and loss showed a similarity in the kinetics for all energies applied with maxima at 2 h (2 Gy) and 0.5 h for (0.25 Gy) after irradiation. Despite these uniform kinetics, we investigated the dose dependence of the colocated foci, allowing to calculate the RBE of soft X-rays in the range of 1.3 to 2.2 (25 kV) and 2.9 to 6.4 (10 kV).

  • International Journal of Radiation Biology 85(2009)11, 1042-1050
    DOI: 10.3109/09553000903232884
  • Poster
    2nd Workshop on "Radiation and Multidrug Resistance Mediated via the Tumor Microenvironment", 09.-10.02.2009, Dresden, Germany

Publ.-Id: 11343

Characterisation of dissolved thioarsenite complexes and precipitated arsenic species in a low-pH sulphate-reducing bioreactor

Crouzet, C.; Delorme, F.; Battaglia-Brunet, F.; Burnol, A.; Scheinost, A.; Morin, D.; Touzelet, S.

Some mining effluents and mine drainage waters are acidic and highly polluted with arsenic. A bio-process performing the precipitation of arsenic sulphide would be very attractive, because the final solid waste would contain up to 60% arsenic in weight. In the framework of Biomine European Integrated project (contract NMP2-CT-2005-500329), a bacterial population able to reduce sulphate at pH 4.5 was selected and used to inoculate column bioreactors that were continuously fed with arsenic in acidic conditions. Arsenic precipitates with sulphide in acidic and low-sulphide solutions. With excess sulphide, soluble thioarsenite species are expected to form.The present work showed that sulphate-reducing bacteria can mediate the precipitation of arsenic sulphide in acidic conditions. The main part of the precipitate is composed of amorphous orpiment, however crisrtallised phases could be detected. The new method developed here to analyse of thioarsenite species in solution will facilitate the monitoring of anaerobic bioreactors treating arseniccontaining effluents and will allow the biogeochemical modelling of such systems.

Keywords: Arsenic; EXAFS; acid mine drainage

  • Poster
    2nd International Congress: As in the environment, 21.-23.05.2008, Valencia, Spain

Publ.-Id: 11342

Megawatt PV plants in Germany: A south-north performance comparison

Rindelhardt, U.; Dietrich, A.; Kedziora, K.; Hahn, A.

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

Locations and design
The plant locations are distributed between 47 and 52 degrees northern latitude (Fig.1), covering Germany from South to North. Some technical features of the investigated plants are given in the table below.

The most plants were built on heavily used or loaded areas (former industrial sites or waste sites). Different types of fundaments and rack support constructions (desks) were used for the module mounting (Fig.2.). The connection with the grid was done in the 10 to 20 kV voltage level, the distance between the plants and the grid was several thousands meters in some cases. The most plants started their operation before 2006. The operation of the plants is monitored by the owners or by professional service providers.

Results and conclusions
The operation results of the year 2007 are exemplarily presented. The solar irradiance in 2007 was higher than the long year average, similar to the years before. The final yield of the plants ranges between 940 and 1180 kWh/kW (Fig. 3). The final yield of the tracked plant in Borna surpasses the yield of the other plants by 25%.
The performance ratios were determined to be between 0.75 and 0.92 (Fig. 4). In the most cases the PR values surprisingly ranges between 0,82 and 0.86. The sources of energy losses are analysed and discussed. Finally a long term estimation of the yield for the different plants will be given.

Keywords: PV plants; performance; MW plants

  • Lecture (Conference)
    23rd European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
  • Contribution to proceedings
    23rd European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
    Proc. of the International Conference held in Valencia, Spain, 1-5 September 2008, München, 3-936338-24-8, 3236-3239

Publ.-Id: 11341

Kernenergie im 21. Jahrhundert

Rindelhardt, U.

Im Vortrag wird einleitend die Entwicklung der Kernenergie im 20. Jahrhundert dargestellt. Ausgehend vom bisher erreichten Stand werden die Perspektiven im 21. Jahrhundert entwickelt. Schwerpunkte dabei sind der Einsatz von Kraftwerken der 3. Generation, der Abfallbehandlung durch Transmutation und die Entwicklung von schnellen Brutreaktoren.

Keywords: Nuclear energy; neclear reactors; electricity

  • Lecture (others)
    Seniorenkolleg TU Chemnitz, 27.05.2008, Chemnitz, Deutschland

Publ.-Id: 11340

Electrochemical and Complexation Behavior of Neptunium in Aqueous Perchlorate and Nitrate Solutions

Ikeda, A.; Hennig, C.; Rossberg, A.; Funke, H.; Scheinost, A. C.; Bernhard, G.; Yaita, T.

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption and Np LIII-edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo the structural rearrangement from spherical coordinating ions (Np3+ and Np4+) to transdioxo neptunyl ions (NpO2n+, n = 1 for Np(V) and 2 for Np(VI)). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate and nitrate solutions. A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10]4+ in 1.0 M HClO4, while Np(V) and -(VI) exist dominantly as pentaaquo neptunyl complexes, [NpO2(H2O)5]n+ (n = 1 for Np(V) and 2 for Np(VI)). A systematic change is observed on the Fourier transforms (FTs) of the EXAF spectra for all the Np oxidation states as increasing the nitrate concentration in the sample, revealing that the hydrate water molecules are replaced by bidentate-coordinating nitrate ions on the primary coordination sphere of Np.

Keywords: Neptunium; Electrochemistry; Complexation; Cyclic Voltammetry; Electrolysis; UV-visible Absorption; X-ray Absorption Spectroscopy; Hydrate; Perchlorate; Nitrate; Aqueous Solution

  • Inorganic Chemistry 47(2008)18, 8294-8305

Publ.-Id: 11339

Magnetfeldkontrollierte Erstarrungsvorgänge in metallischen Legierungen

Eckert, S.; Boden, S.; Räbiger, D.; Willers, B.

Metallschmelzen in industriellen Prozessen unterliegen in der Regel verschiedenen Arten von Strömungen. Diese Strömungen haben einen entscheidenden Einfluss auf den Wärme- und Stofftransport, und damit zumeist auch auf die Effizienz des Prozesses oder die Qualität des Endproduktes. Zukünftige Anstrengungen im Hinblick auf eine Optimierung derartiger Anlagen oder Technologien müssen aus diesem Grund eine wirksame Strömungskontrolle berücksichtigen.
Elektromagnetische Felder eröffnen aufgrund des kontaktlosen Zugangs und der einfachen Regelbarkeit eine attraktive Möglichkeit zur Strömungskontrolle. Eine gezielte Einflussnahme setzt aber ein umfangreiches Wissen über das Strömungsfeld und die Wechselwirkung mit den elektromagnetischen Kraftfeldern voraus. Neben numerischen Simulationen sind Modellexperimente mit sogenannten „kalten“ Schmelzen, d.h. mit Flüssigmetallen mit einem Schmelzpunkt < 300°C, ein unverzichtbares Mittel, um die Strömungsvorgänge besser zu verstehen und geeignete Maßnahmen zur Strömungskontrolle zu ergreifen. Die Röntgenradioskopie hat sich dabei als ein wichtiges diagnostisches Mittel herausgestellt, um Erstarrungsvorgänge in-situ zu visualisieren. Auf Grundlage der Bewertung der Grauwertbilder mit Hilfe der "Optical Flow"-Methode ist es erstmalig gelungen, Strömungsstrukturen in unmittelbarer Umgebung zur Erstarrungsfront während der Erstarrung darzustellen.
Im Vortrag werden am Beispiel der Erstarrung Einsatzmöglichkeiten elektromagnetischer Felder in der Gießereiindustrie erläutert.

Keywords: solidification; metal alloys; electromagnetic fields; X-ray radioscopy; Optical Flow

  • Invited lecture (Conferences)
    Seminar "Struktur und Eigenschaften kondensierter Materie", 20.05.2008, Chemnitz, Deutschland

Publ.-Id: 11338

Complexation of Curium(III) and Europium(III) with Urea and in Human Urine

Heller, A.; Barkleit, A.; Bernhard, G.

The complexation of europium(III) and curium(III) in aqueous urea solution has been studied at pH 1 – 8, I = 0.1 (NaClO4), room temperature and trace metal concentrations using time-resolved laser-induced fluorescence spectroscopy. In case of curium(III) a red shift of the luminescence maximum occurs upon complexation, while for europium(III) emission wavelengths remain unaltered but the peak splitting is changed significantly. Both heavy metals form very weak complexes of the formulae ML3+ which are stable until pH 6. Stability constants were determined to be -0.12 ± 0.05 for europium(III) and -0.31 ± 0.13 for curium(III). In human urine samples the luminescence spectra of both heavy metals differ significantly from those in water and aqueous urea solution. Red shift of the luminescence maximum of curium(III) is more pronounced and peak splitting in case of europium(III) enhanced. Besides that, lifetimes of the species formed in human urine vary markedly from those of the ML3+ complexes with urea. Furthermore, the speciation of the heavy metals seems to depend on the pH of the urine sample.

Keywords: curium(III); europium(III); urea; complexation; urine; heavy metal speciation; TRLFS

  • Contribution to proceedings
    NRC7 - Seventh International Conference on Nuclear and Radiochemistry, 24.-29.08.2008, Budapest, Hungary

Publ.-Id: 11337

Ion irradiation induced local creation of ferromagnetism in Fe60Al40 alloys

Strache, T.; Liedke, M. O.; Fassbender, J.; Möller, W.; Menéndez, E.; Sort, J.; Suriñach, S.; Baró, M. D.; Gemming, T.; Weber, A.; Heyderman, L. J.; Rao, K. V.; Deevi, S. C.; Nogues, J.

Ion irradiation of Fe60Al40 alloys results in the phase transformation from the paramagnetic, chemically ordered B2-phase to the ferromagnetic, chemically disordered A2-phase. The magnetic phase transformation is related to the number of displacements per atom (dpa) during the irradiation. For heavy ions (Ar+, Kr+, Xe+) a universal curve is observed with a steep increase in the fraction of ferromagnetic phase reaching saturation, i. e., a complete phase transformation, at about 0.5 dpa. This proves the purely ballistic nature of the disordering process. If light ions are used (He+, Ne+) a pronounced deviation from the universal curve is observed. This is attributed to bulk vacancy diffusion from dilute collision cascades, which leads to a partial recovery of the thermodynamically favored B2-phase. Comparing different noble gas ion irradiation experiments allows to asses the corresponding counteracting contributions. In addition, the potential to create local ferromagnetic areas embedded in a paramagnetic matrix is demonstrated.

Keywords: magnetism; ion irradiation; binary alloys; intermetallic; FIB; patterning

  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, GSI-Workshop, 11.-12.04.2008, Darmstadt, Germany

Publ.-Id: 11336

Magnetic lithography on paramagnetic FeAl alloys by selective ion irradiation

Sort, J.; Menendez, E.; Liedke, M. O.; Strache, T.; Fassbender, J.; Gemming, T.; Weber, A.; Heydermann, L. J.; Surinach, S.; Rao, K. V.; Deevi, S. C.; Baro, M. D.; Nogues, J.

The atomically-ordered Fe60Al40 (at. %) alloy is paramagnetic at room temperature but it becomes ferromagnetic when subject to structural disorder [1]. This effect has been recently used to generate arrays of sub-100 nm ferromagnetic dots embedded in a paramagnetic matrix. To selectively induce structural disorder, local irradiation procedures, either through lithographed masks or using focused ion beam, have been utilized. Due to the low ion doses used, the irradiation processes do not induce any surface corrugation, thus circumventing tribological problems. The fabricated entities exhibit a range of magnetic properties depending on the size and shape. Furthermore, when the patterned sheets are annealed at sufficiently high temperatures (i.e., around 900 K), the magnetic properties are erased due to the annealing-induced atomic reordering. This method may be extrapolated to a variety of other intermetallic systems such as Fe2AlMn, Ni3Sn2 or CoGa and also to austenitic steels. The obtained magnetic structures may have technological applications, such as magnetic sensors or patterned recording media.
Partial financial support from the Spanish 2005SGR-00401, MAT2007-66302-C02 and MAT2007-61629 research projects, the EU-RITA program “Center for the Application of Ion Beams in Materials Research” (under contract no. 025646) and the Swedish Agencies VINNOVA and SSF is acknowledged. E. M. acknowledges his FPI fellowship from the Spanish Ministerio de Educación y Ciencia, co-financed by the ESF.
[1] J. Nogués et al., Phys Rev. B Phys. Rev. B 74, 024407 (2006)

Keywords: magnetism; ion irradiation; focused ion beam; binary alloys; disordering

  • Invited lecture (Conferences)
    9th International Conference on Nanostructured Materials, 01.-06.06.2008, Rio de Janeiro, Brazil

Publ.-Id: 11334

Structures and Stoichiometry of Actinide Complexes: Challenges of Combining EXAFS and Quantum Chemistry

Tsushima, S.

EXAFS spectroscopy has been proved to be a very powerful tool for studying the structures of actinide complexes in aqueous and non-aqueous systems. The application of EXAFS spectroscopy has been extended to the systems with mixed species and / or species with very dilute concentration. Using EXAFS alone, however, has inherent limitations such as a lack of spatial information of the molecules and rather poor radial resolutions which make it difficult to differentiate two or more bonds with similar distances. Factor analysis by Rossberg et al., for example, was proven to be an effective method for separating individual species from the mixed ones [1]. Such method becomes even more powerful if corresponding 3D structural information can be provided by quantum chemical calculations.
Here, I show two examples in which density functional theory (DFT) calculations are proved to be very helpful for actinide speciation studies. In first case, Th(IV) hydroxo and sulfato complexes were studied by DFT calculations. A significant decrease in the coordination number (CN) was observed as a stepwise hydrolysis reaction of Th4+ ion proceeds. The fourth hydrolysis product, Th(OH)4 0, has a reduced CN of 6 and readily forms a dimeric complex via a Th-OH-Th bridging. The oligomerization makes Th(OH)4 0 to be an unstable aqueous species. In case of sulfate, the CN and the average Th-O distance of Th(SO4)2 0 remains essentially as same as Th4+ aquo ion. This result is in agreement with the EXAFS study by Hennig et al. [2].
In the second example, the reduction potential of Pu(VIII) / Pu(VII) couple was studied as the same way as in a recent study [3]. The geometries and the energies of the complexes were calculated at the B3LYP level. The spin-orbit effect for Pu(VII) species was corrected at the CASSCF level. The redox potential of the PuVIIIO4(OH)2 2-/ PuVIIO4(OH)2 3- couple was found to be as high as ~1.7V in alkaline solution which indicates that it is difficult to obtain Pu(VIII) in aqueous solution.
1. A. Roßberg, T. Reich, G. Bernhard, Anal. Bioanal. Chem. 376, 631-638, (2003).
2. C. Hennig, K. Schmeide, V. Brendler, H. Moll, S. Tsushima, A. C. Scheinost, Inorg. Chem. 46, 5882-5892 (2007).
3. S. Tsushima, U. Wahlgren, I. Grenthe, J. Phys. Chem. A 110, 9175-9182 (2006).

  • Invited lecture (Conferences)
    Actinide XAS 2008, 15.-17.07.2008, Soleil, France

Publ.-Id: 11333

Biogeochemical changes induced by uranyl nitrate in a uranium waste pile

Selenska-Pobell, S.; Geissler, A.; Flemming, K.; Merroun, M.; Geipel, G.; Reuther, H.

Treatments with uranyl nitrate induced strong changes in subsurface bacterial community of a uranium mining waste pile. Most of the bacterial populations, stimulated at the initial stages of the treatment, used the added nitrate for respiration. Mössbauer spectroscopic analyses showed that at the later incubation stages, when nitrate was reduced, reduction of Fe(III) to Fe(II) occurred. Time-resolved laser-induced fluorescence spectroscopic analysis revealed that most of the added U(VI) was bound in phosphate phases of biotic origin.

  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 743-752

Publ.-Id: 11332

Study of the Influence of Humic Acid on the Am(III) Sorption onto Kaolinite

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

In order to determine the influence of humic acid (HA) on the sorption of Am(III) onto kaolinite batch experiments were performed ([Am(III)] = 1x10-6 M, [HA] = 0 or 10 mg/L, I = 0.01 M NaClO4, pH = 3-10, solid/solution ratio = 1 or 4 g/L, pCO2 = 10-3.5 atm). In addition to that, laser-induced fluorescence spectroscopy was applied to study Am(III) kaolinite surface complexes in absence and presence of HA. The obtained results show that the presence of humic acid can affect the Am(III) migration under environmentally relevant conditions.

Keywords: Americium; Am(III); Humic acid; Kaolinite; Clay; Sorption; Batch experiments; Laser-induced fluorescence spectroscopy

  • Lecture (others)
    4th RTDC-1 Meeting of FUNMIG, 20.-21.05.2008, Bürgenstock, Switzerland

Publ.-Id: 11331

Quasifree Lambda, Sigma0, and Sigma− electroproduction from 1,2H, 3,4He and carbon

Dohrmann, F.

A comprehensive study of kaon electroproduction on light nuclei has been conducted in Hall C of the Thomas Jefferson National Accelerator Facility by the E91-016 collaboration. Data were obtained using electron beams of 3.245 GeV impinging on special high density cryogenic targets of 1,2H, 3,4He, as well as on a solid carbon target. Specifically, the measurements on 3,4He are the first performed. Previously, the observation of hypernuclear bound states was discussed [1]. This presentation will give the final results of the data analysis, focussing on the quasifree production cross sections for the Lambda and Sigma hyperons for the various target nuclei [2]. We also derive effective proton numbers from our data and compare these numbers with model calculations. Deviations may indicate possible in-medium modifications of the kaon electroproduction mechanism.

[1] F. Dohrmann et al [E91016 collab.] Phys. Rev. Lett. 93 (2004) 242501
[2] F. Dohrmann et al [E91016 collab.] Phys. Rev. C 76 (2007) 054004

Keywords: electroproduction; quasifree; medium modifications; hyperons

  • Lecture (Conference)
    DPG Frühjahrstagung Darmstadt 2008, 10.-14.03.2008, Darmstadt, Deutschland

Publ.-Id: 11330

Time resolution of radiation hard Resistive Plate Chambers for the CBM experiment at FAIR

Bartos, D.; Caragheorgheopol, G.; Dohrmann, F.; Kämpfer, B.; Kotte, R.; Naumann, L.; Petris, M.; Petrovici, M.; Simion, V.; Stach, D.; Williams, C.; Wüstenfeld, J.

The Compressed Baryon Matter (CBM) experiment at FAIR/Darmstadt studies highly compressed nuclear matter at moderate temperatures in relativistic heavy-ion collisions. CBM uses rare probes for studying fundamental issues of QCD. Currently the technical design of CBM foresees a time-of-flight wall (TOF) equipped with resistive plate chambers (RPCs) 10 m downstream from the target. The inner part of the TOF covers 50-100 mrad around the beam axis with estimated flux densities of charged particles of ~2·10^4 per s and cm², thus radiation hard detector components are indispensable in the forward direction.

RPC tests were conducted at the superconducting electron linac ELBE at FZ Dresden-Rossendorf using MeV electron beams mimicking GeV minimum ionizing particles for detector studies. The pulse width of ~5 ps of the ELBE beam provides the possibility to use its radio frequency directly as a time reference. ELBE also provides high rates (up to 1 mA beam current).

Conventional timing RPCs with standard float glass electrodes are only efficient up to flux densities of < 1·10^3 per s and cm². Accelerating the charge transport requires electrodes with lower volume resistivity while maintaining the time resolution (< 100 ps).

Timing and rate parameters of various RPCs were tested at ELBE, including conventional RPCs with float glass electrodes, as well as RPC electrodes made of special glasses (silicated) with 3-4 orders of magnitude lower volume resistivity than float glass (10^13 Ohm·cm).

Results are reported with emphasis on alternative electrode materials, i.e. polypropylene material and Pestov glass. The NIPNE group developed a prototype RPC with Pestov glass electrodes (10^10 Ohm·cm) read-out via stripe lines or pads.

Also ceramics electrodes are suggested for high rate timing RPCs. New ceramics material have recently become available for laboratory and prototype tests.

These tests will provide data for a decision on the type of high rate RPCs for CBM at FAIR.

Keywords: Gaseous Detectors; Time-of-flight detectors; high rate detectors; new materials

  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
    Conference Record, 978-1-4244-2715-4

Publ.-Id: 11329

Synthesis of inverted spinel ferrite nanocrystals inside ZnO by ion implantation and post-annealing

Zhou, S.; Potzger, K.; Kuepper, K.; Xu, Q.; Schmidt, H.; Helm, M.; Fassbender, J.

The hybrids of magnets and semiconductors show promising magneto-transport properties, and would enable the development of spin-dependent magneto-electronic and magneto-optic devices [1]. The most well studied system is MnAs/GaAs due to its chemically stable interface and the possibility of epitaxy [2]. Large magneto-resistance and Faraday rotation have been observed in GaAs with MnAs nanoclusters. However the Curie temperature of MnAs is 313 K, and limits its application at high temperatures. Spinel ferrites are a group of materials with similar crystal-structure and rich magnetic as well as electronic properties, e.g. NiFeO and CoFeO, are ferrimagnets with large Neel temperatures. Therefore the hybrids of spinel ferrites with semiconductors would allow versatile possibilities for spin-dependent devices. However the integration of ferrites with semiconductors remains challenging due to the fact that the growth of ferrites requires high temperatures and oxygen environment, which is detrimental to conventional semiconductors like Si and GaAs [3]. In this contribution, we show the possibility to incorporate inverted spinel ferrite nanocrystals with ZnO by ion implantation and post-annealing. Their magnetic and electronic properties were investigated by SQUID and x-ray absorption spectroscopy. These nanocrystals are crystallographically oriented inside ZnO, and show superparamagnetic characteristics. Large positive magneto-resistance has been observed, and we will discuss its origin with respect to ordinary magneto-resistance and to magnetic scattering by nano-ferrites. Our results suggest a new magnet-semiconductor heterostructure with potential application in magneto-electronics and microwave devices [3].

[1] G. Prinz, Science 250, 1092 (1990).
[2] L. Daweritz, Rep. Prog. Phys. 69, 2581 (2006).
[3] Z. Chen et al., Appl. Phys. Lett. 91, 182505 (2007).

Keywords: magnetism; diluted magnetic semiconductors; spinell structures; nanocrystals

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11328

Tuning coercivity in CoCrPt-SiO2 hard disk material

Strache, T.; Tibus, S.; Springer, F.; Rohrmann, H.; Albrecht, M.; Fassbender, J.

In order to continuously increase the storage capacity of modern computer disk drives and push the superparamagnetic limit to the smallest achievable bit sizes the material used has to fulfill a number of requirements: i) Maximum perpendicular magnetic anisotropy to guarantee thermal stability. Granular CoCrPt-SiO2 films are currently the material of choice. ii) Large remnant magnetization to achieve a good signal to noise ratio when reading the bit information. iii) Moderate coercive fields to allow for the writing of the bit information with the limited write head fields available. In order to increase the storage density, smaller grains with larger magnetic anisotropies are required for thermal stability which are accompanied by large coercive fields which obstruct the writing process. One route to overcome this problem is to independently reduce the coercive field without altering the magnetic anisotropy and the remnant magnetization by tailoring the intergranular exchange.
Ion irradiation and implantation has recently been demonstrated to be a viable tool to modify magnetic properties of thin magnetic films and multilayers [1, 2]. Here we demonstrate that by means of ion implantation of Co and Ne a continuous reduction of the coercive field can be achieved without significant modification of the remaining magnetic parameters. In addition to the magnetization reversal behavior of the entire film investigated by magneto-optic Kerr effect and SQUID magnetometry also the magnetic domain configuration in the demagnetized state is imaged by magnetic force microscopy. Moreover, these studies are supported by micromagnetic simulations which allow to further extract information about the intergranular exchange coupling which is the source of the modified coercive field.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).

Keywords: magnetism; ion irradiation; magnetic storage; hard disk; coercivity; anisotropy; magnetic domains

  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11327

Magnetic microstructures created by local interface mixing

Strache, T.; Fassbender, J.; Grenzer, J.; Möller, W.; Kaltofen, R.; Mönch, I.; McCord, J.

Magnetic micro- and nanostructures are of great interest due to the fundamental physics involved if the dimension is shrunk as well as due to the application potential in storage, sensing and logic devices. For the creation of such structures typically lithography is used in combination with either etching or lift-off processes. In both cases the magnetic element is defined by isolated topographic structures. An alternative approach relies on the local ion irradiation of a magnetic multilayer structure. As a result of the ion irradiation an interfacial mixing between ferromagnetic layers and non-magnetic interlayers is achieved which consequently reduce and finally fully suppress the ferromagnetism. In order to demonstrate this behaviour Ni80Fe20/Ta multilayers with a different number of repetitions are used. The structural and magnetic properties are investigated by x-ray reflectivity and magneto-optic Kerr effect magnetometry as a function of noble gas irradiation fluence and number of multilayer repetitions. The experimental results are accompanied by TRIDYN simulations. In addition magnetic microstructures are created by means of large area ion irradiation through lithographically defined masks. By choosing the irradiation fluence the exchange coupling between the microstrucutres can be switching on and off. The magnetic domain configuration in these elements is imaged by means of Kerr microscopy and magnetic force microscopy. Thus the modified magnetization reversal curves can be interpreted on the basis of the micromagnetic domain structure.

Keywords: magnetism; ion irradiation; magnetic patterning; intermixing; Kerr microscopy

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11326

Ion beam induced magnetic transformation in layered structures: nonmagnetic to ferromagnetic and vice versa

Dev, B. N.; Fassbender, J.; Grenzer, J.; Schell, N.; Bischoff, L.; Schmidt, B.; Grötzschel, R.; Allenstein, F.; Beddies, G.; McCord, J.

A nonmagnetic to ferromagnetic transformation is observed when a Pt/C multilayer stack (total thickness ~ 60 nm, thickness of individual layers ~ 2 nm) with a small amount of Fe impurity, grown on a glass substrate, is irradiated with 2 MeV Au ions [1]. Using a subnanometer depth resolution technique it was found that ion beam induced preferential migration of Fe from C to Pt layers and the subsequent formation of FePt nanoparticles were responsible for the magnetic transformation [2]. Fe concentration in the C layers decreases exponentially with increasing ion fluence with simultaneous increase of the coercive field in the magnetic hysteresis loop. An example of ion beam induced opposite transformation, namely, ferromagnetic to nonmagnetic, is shown using a Si(5nm)/Ni(10 nm)/Si trilayer system, where ion-beam-induced atomic displacements across the Si/Ni interfaces form a mixed Ni1-xSix layer leading to a ferromagnetic to nonmagnetic transformation. In this case, with increasing ion (30 keV Ga) fluence the coercive field in the hysteresis loop decreases with increasing ion fluence and eventually magnetization is destroyed at a critical fluence. Having identified the critical fluence, a focused ion beam (FIB, 30 keV Ga) was used to fabricate a lateral multistrip pattern in this thin (10 nm) magnetic layer with alternate magnetic/nonmagnetic strips of nanometer dimensions. Magnetooptical Kerr effect microscopy reveals the anisotropy of the magnetic domain structure along and perpendicular to the FIB-patterned strips. In the light of the observed phenomena, future developments in the area of nanotechnology, such as ultrahigh density magnetic storage devices, single-electron spin-valve transistors etc. will be discussed. Some nanoscale structures that can be fabricated using FIB will offer the possibility of exploring new scientific aspects, such as magnons in ordered ferromagnetic spot arrays, in these structures.

[1] B. N. Dev, S. Bera, B. Satpati, D. K. Goswami, K. Bhattacharjee, P. V. Satyam, K. Yamashita, O. M. Liedke, K. Potzger, J. Fassbender, F. Eichhorn and R. Groetzschel,
Microelectronic Engineering 83, 172 (2006).

[2] S. Bera, K. Bhattacharjee, G. Kuri and B. N. Dev
Phys. Rev. Lett. 98, 196103 (2007).

Keywords: magnetism; ion irradiation; magnetic transformation; XRD; Kerr microscopy

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11325

Ga+ ion irradiation-induced changes of magnetic ordering in Pt/Co(3nm)/Pt films

Jaworowicz, J.; Kisielewski, M.; Maziewski, A.; Sveklo, I.; Jamet, J.-P.; Ferre, J.; Mougin, A.; Vernier, N.; Fassbender, J.; Henschke, A.; Bourhis, E.; Gierak, J.

In Pt/Co(d)/Pt ultrathin film structures a spin reorientation transition (SRT) from out-of-plane to in-plane magnetization states is known to occur at a critical Co thickness d=dSRT ~ 1.8nm. For thinner Co thicknesses this SRT can also be forced by ion irradiation. In the present work we demonstrate that also the reverse SRT, i. e. from in-plane to out-of-plane, can be achieved by ion irradiation in certain cases. Therefore, easy-plane magnetized Pt/Co(3nm)/Pt samples were irradiated by 30 keV Ga+ ions with doses D ranging from 1014 to 5x1016 ions/cm2. The ion irradiation induced effects were investigated by polar magnetooptical microscopy, magnetometry and atomic/magnetic force microscopy. At low dose the reverse SRT is observed with a large out-of-plane magnetization component giving rise to a square perpendicular hysteresis loop. Sub-micrometer perpendicular magnetic domain structures either field-induced or in the demagnetized state confirm this new behavior. At higher dose, the easy magnetization direction is turned in-plane again. Topologically, a film swelling effect is first evidenced at low dose, but surface etching dominates at higher dose. Similar effects are also observed under quasi-uniform irradiation performed by scanning a focused ion beam (FIB) on the Pt/Co(3nm)/Pt structure. The results will be also compared to those reported earlier for d < dSRT, where ion irradiation leads to a reduction of the Curie temperature, coercivity and magnetic anisotropy [1,2].
This work was partially supported by EU MC TOK project NanomagLab No MTKD-CT-2004-003177 and EU-RITA program “Centre for Application of Ion Beams in Materials Research” under contract no. 025646. J.J. has benefited of an EC Marie-Curie fellowship (contract MEST CT 2004-51437).

[1] J. Ferré, J.-P. Jamet, in Handbook of Magnetism and Advanced Magnetic Materials, H. Kronmüller, S. Parkin (eds), (2007) John Wiley & Sons, Ltd.
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320 (2008) 579.

Keywords: magnetism; ion irradiation; FIB; magnetic anisotropy; Kerr microscopy

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Poster
    Louis Neel Colloquim, 30.09.-03.10.2008, La Grande Motte, France

Publ.-Id: 11324

Irradiation induced magnetic patterning of soft-magnetic thin films

McCord, J.; Kaltofen, R.; Quandt, E.; Fassbender, J.

Numerous applications of ferromagnetic materials in magneto-electronics are based on multi-layer thin film technology. For most of the relevant applications the magnetic films are patterned by lithographic processes, which result in isolated magnetic elements. Here, we demonstrate the lateral alteration of magnetic properties of soft-magnetic thin films by ion irradiation. In contrast to traditionally patterned thin films, the interaction within the patterned structure occurs through direct magnetic exchange, resulting in novel effective magnetic properties and magnetization states fundamentally differing from conventionally magnetic thin films.
The method and a summary of ion-induced modifications of fundamental magnetic properties of different materials will be shown on single layer crystalline and amorphous thin films, and multi-layered systems. Examples include laterally modulated saturation polarization as well as locally varying magnetic anisotropy alignment, both resembling anisotropic as well as patterned soft-magnetic film behavior. The scaling behavior for the resulting structures will be discussed and the data will be compared to effects known so far only from multi-layered magnetic layers. Moreover it will be shown, that not only the regular static magnetic behavior, but also the magnetization dynamics of systems can be tuned and laterally modified by ion irradiation.
The local modulation of magnetic properties opens exciting new opportunities to the tuning of the integral properties of soft-magnetic thin films and establishes an additional path to thin film magnetic structures with novel functionality.

J. McCord, R. Schäfer, K. Theis-Bröhl et al., J. Appl. Phys. 97, 10K102 (2005).
J. McCord, J. Fassbender, E. Quandt et al., Appl. Phys. Lett. 89, 162502 (2005).
J. Fassbender, J. McCord, JMMM 320, 579–596 (2008).
J. McCord, L. Schultz, J. Fassbender, Adv. Mater., accepted for publication.

Keywords: magnetism; ion irradiation; ion implantation; Kerr microscopy; exchange spring; magnetic domains

  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11323

Generation of micro/nano-scaled magnetic structures on AISI 304L austenitic stainless steel by ion beam nitriding

Menendez, E.; Martinavicius, A.; Liedke, M. O.; Abrasonis, G.; Fassbender, J.; Sommerlatte, J.; Nielsch, K.; Surinach, S.; Baro, M. D.; Nogues, J.; Sort, J.

Nitriding of austenitic stainless steel at moderate temperatures (~400ºC) leads to the formation of the supersaturated nitrogen solid solution often called in the literature “expanded austenite” or γN phase [1]. This causes an enhancement of the microhardness and the wear resistance without loss of the corrosion resistance. Moreover, this phase shows ferromagnetic behavior, whose origin is linked to the expansion of the austenite (γ) lattice due to the incorporation of nitrogen atoms into interstitial positions [2].

The influence of the processing temperature and time on the structural and magnetic properties of AISI 304L austenitic stainless steel, after ion beam nitriding, has been investigated by x-ray diffraction (XRD), nuclear reaction analysis (NRA), magneto-optical Kerr effect (MOKE) magnetometry and atomic/magnetic force microscopy (AFM/MFM). Furthermore, periodic arrays of ferromagnetic structures in the micrometer and sub-micrometer range have been prepared after nitriding through either 2000 mesh Cu transmission electron microscopy grids (mesh size of 7.5 x 7.5 µm2, 12.5 µm pitch, 20 µm thickness and 3.05 mm diameter) or self-assembled porous alumina membranes (5 µm thickness), both acting as shadow masks. The local character of the induced ferromagnetism is confirmed by magneto-optical Kerr effect measurements together with magnetic force microscopy imaging.

[1] G. Abrasonis, et al., J. Appl. Phys. 97, 083531 (2005)
[2] O. Öztürk and D.L. Williamson, J. Appl. Phys. 77, 3839 (1995)

Keywords: magnetism; ion beam processing; nitriding; stainless steel; magnetic patterning

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11322

Direct generation of nanoscale ferromagnetic dots by selective ion irradiation of paramagnetic FeAl alloys

Menendez, E.; Sort, J.; Liedke, M. O.; Strache, T.; Fassbender, J.; Möller, W.; Gemming, T.; Weber, A.; Heyderman, L. J.; Surinach, S.; Deevi, S. C.; Rao, K. V.; Sommerlatte, J.; Nielsch, K.; Baro, M. D.; Nogues, J.

Fe60Al40 (at. %) alloys show an interesting combination of magnetic and structural properties, where atomically ordered Fe60Al40 is paramagnetic at room temperature, whereas disordered Fe60Al40 becomes ferromagnetic [1]. The transformation from paramagnetic B2-phase to the ferromagnetic, A2-phase can be accomplished by means of homogeneous ion irradiation procedures. Furthermore, local ion irradiation procedures (i.e., focused ion beam or ion irradiation through masks) have been also used in order to fabricate periodic arrays of sub-50 nm ferromagnetic structures embedded in a paramagnetic matrix. Due to the low fluences used, this method does not induce any roughening of the surface, leading to topographically featureless dots. The fabricated entities exhibit a range of magnetic properties depending on the size and shape, which were investigated by means of magneto-optical Kerr effect magnetometry, while the local character of the induced ferromagnetism was examined by magnetic force microscopy. Interestingly, when the patterned sheets are annealed at sufficiently high temperatures, the ferromagnetic properties are removed due to the annealing-induced atomic reordering. Hence, these methods may lead to a novel type of patterned recording media free from tribological and exchange coupling effects. Moreover, these approaches can be easily extrapolated to a variety of other systems exhibiting disorder-induced magnetism.

[1] J. Nogués et al., Phys Rev. B Phys. Rev. B 74, 024407 (2006)

Keywords: magnetism; ion irradiation; FIB; magnetic patterning; binary alloys; disordering

  • Invited lecture (Conferences)
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11321

Influence of Cr-ions on the magnetic behaviour of FeCo film

Gupta, R.; Ansari, R.; Khandelwal, A.; Fassbender, J.; Gupta, A.

Implantation of Cr-ions in Fe70Co30 thin film have been performed to modify its structural and magnetic properties. From the XRD results, the lattice constant as well as the grain size of the film is increasing with the ion fluence. 1 X 1017 ions/cm2 Cr-ions reduces the coercivity of the film from 140(3) Oe to 44(3) Oe. Coercivity of the film follows the exponential decay as a function of Cr-ions fluence. 35 keV (projectile range 13.5 nm) and 100 keV Cr-ions (projectile range 34.3 nm) have been used to understand the effects of magnetic Cr-ions and the effects of ballistic collision cascade on the MOKE signal. Similar changes on the coercivity behaviour of the film implanted with these two energies have been observed. It appears that the implantation process creates a solid solution of Cr in FeCo without any other additional treatment in the film. After 5 X 1016 Cr-ions, film exhibit four fold magnetic anisotropy.

Keywords: magnetism; ion implantation; magneto-optic kerr effect; magnetic anisotropy

  • Nuclear Instruments and Methods in Physics Research B 266(2008), 1407-1410

Publ.-Id: 11320

Two-fold origin of the deformation-induced ferromagnetism in bulk Fe60Al40 (at-%) alloys

Menendez, E.; Sort, J.; Liedke, M. O.; Fassbender, J.; Surinach, S.; Baro, M. D.; Nogues, J.

The transition from the atomically ordered B2-phase to the chemically disordered A2-phase and the concomitant deformation-induced ferromagnetism have been investigated in bulk polycrystalline Fe60Al40 (at.%) alloys subjected to compression processes. A detailed correlation between structural, magnetic and mechanical properties reveals that the generated ferromagnetism depends on the stress level but is virtually independent of the loading rate. The mechanisms governing the induced ferromagnetism also vary as the stress level is increased. Namely, in the low-stress regime both lattice cell expansion and atomic intermixing play a role in the induced ferromagnetic behavior. Conversely, lattice expansion seems to become the main mechanism contributing to the generated ferromagnetism in the high-stress regime. Furthermore, a correlation is also observed between the order-disorder transition and the mechanical hardness. Hence, a combination of magnetic and mechanical measurements can be used, in synergetic manner, to investigate this deformation-induced phase transition.

Keywords: magnetism; binary alloys; ordering; disordering; ball milling; lattice expansion

  • Open Access Logo New Journal of Physics 10(2008), 103030

Publ.-Id: 11319

Patterning of magnetic structures on austenitic stainless steel by local ion beam nitriding

Menendez, E.; Martinavicius, A.; Liedke, M. O.; Abrasonis, G.; Fassbender, J.; Sommerlatte, J.; Nielsch, K.; Surinach, S.; Baro, M. D.; Nogues, J.; Sort, J.

Periodic arrays of ferromagnetic structures with micrometer and sub-micrometer lateral sizes have been prepared at the surface of a paramagnetic austenitic stainless steel by means of ion beam nitriding through different types of shadow masks (such as transmission electron microscopy grids or self-assembled porous alumina membranes). This method takes advantage of the formation of the ferromagnetic supersaturated nitrogen solid solution γN phase (i.e., expanded austenite) upon nitriding at moderate temperatures. The local character of the induced ferromagnetism is confirmed by magneto-optical Kerr effect measurements together with magnetic force microscopy imaging. Furthermore, the influence of the nitriding temperature and time on the induced ferromagnetic and structural properties has been analyzed.

Keywords: Magnetism, Ion-beam processing; X-ray diffraction; Austenitic steels; Interstitial diffusion; Magnetic patterning

Publ.-Id: 11318

Dynamic interaction between vortices, antivortices and holes in domain walls investigated by means of time resolved Photoemission Electron Microscopy (PEEM)

Kuepper, K.; Wintz, S.; Buess, M.; Raabe, J.; Quitmann, C.; Fassbender, J.

In this work we study the interaction of vortex cores with either holes in domain walls of Landau structures or other vortices and antivortices, which are also interconnected through the adjacent domain walls of a single cross-tie structure.
During the last few years the investigation of magnetic vortices and their dynamic properties has attracted great attention due to the fundamental interest in the physics of solitons and since they might be used as non volatile memory devices in future applications, e. g. [1,2]. One striking feature of magnetic vortices is that the cores are attracted and can be trapped by artificial defects. If more than one of such defects are created a switching between different vortex core trapped states, which might serve as discrete levels in a multivalent memory device, can be achieved. We report the imaging of the magnetic excitation spectrum in presence of holes, fabricated by focused ion beam milling, in the magnetic domains and domain walls of Landau structures by means of x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). The vortex core in the center of the structure is not modified by ions, here we investigate the interaction of unmodified vortex cores with holes far away (> 1 Mikrometer) in the domain walls and the domains of Landau structures. Due to the very high lateral and temporal resolution the magnetization dynamics and the corresponding Eigen modes (Fig. 1), which are characteristic for the vortex-hole interaction, are investigated in detail [3]. Analyzing the vortex movement unravels an acceleration of the vortex gyrotropic mode if holes are present in the middle of domain walls. The presence of holes in the middle of domains has no significant influence on the vortex speed. The experimental results are compared to micromagnetic simulations.

[1] S. B. Choe et al., Science 304, 420 (2004), J. Raabe et al., Phys. Rev. Lett. 94, 217204 (2005).
[2] B. van Waeyenberge et al., Nature 444, 461 (2006)
[3] K. Kuepper et al., manuscript in preparation.
[4] K. Kuepper et al., Phys. Rev. Lett. 99, 167202 (2007)

Keywords: magnetism; magnetization dynamics; vortex; antivortex; defects; time-resolved; magnetic imaging

  • Invited lecture (Conferences)
    IEEE International Magnetics Conference - Intermag 2008, 04.-08.05.2008, Madrid, Spain
  • Invited lecture (Conferences)
    Workshop on high temporal and spatial resolution studies of magnetic nanostructures, 27.06.-02.07.2008, Augustow, Poland

Publ.-Id: 11317

Ga+ ion irradiation-induced out-of-plane magnetization in Pt/Co(3nm)/Pt films

Jaworowicz, J.; Kisielewski, M.; Maziewski, A.; Sveklo, I.; Jamet, J.-P.; Ferre, J.; Mougin, A.; Vernier, N.; Fassbender, J.

Ion beam irradiation under weak or moderate fluence allows to modify and even control the magnetic properties of thin film structures [1–2]. So, this method stands now as an elegant technique for magnetic nanopatterning [3].Spin reorientation transition form in-plane to out-of-plane state in Pt/Co/Pt film with cobalt thickness 3nm after irradiation by 30 keV Ga+ ions with doses of 0.5 x 1015 and 1015 ions/cm2 was observed. Experiments were made with magneto-optical base microscopy and magnetic force microscopy.

[1] C. Chappert, H. Bernas, J. Ferré, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280 (1998) 1919.
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320 (2008) 579
[3] J. Ferré, J.-P. Jamet, in Handbook of Magnetism and Advanced Magnetic Materials, H. Kronmüller, S. Parkin (eds), (2007) John Wiley & Sons, Ltd, p 1710

Keywords: magnetism; ion irradiation; perpendicular anisotropy; Kerr microscopy; MFM

  • Poster
    IEEE International Magnetics Conference - INTERMAG 2008, 04.-08.05.2008, Madrid, Spain

Publ.-Id: 11316

Single Pi- production in np collisions for excess energies up to 90 MeV

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.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Teufel, A.; Ucar, A.; Ullrich, W.; Wintz, P.; Wüstner, P.; Zupranski, P.

The quasifree reaction np -> pppi- was studied in a kinematically complete experiment by bombarding a liquid-hydrogen target with a deuteron beam of momentum 1.85GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector Pn which differed from event to event. A range of almost 90MeV excess energy above threshold was covered. Energy-dependent angular distributions, invariant-mass spectra as well as fully covered Dalitz plots were deduced. Sizeable pp FSI effects were found as were contributions of p and d partial waves. In comparison with existing literature data the results provide a sensitive test of the spectator model. The behavior of the elementary cross-section σ01 close to threshold is discussed in view of new cross-section data.

Keywords: 13.75.Cs - Nucleon-nucleon interactions (including antinucleons and deuterons etc.); 25.10.+s - Nuclear reactions involving few-nucleon systems

  • European Physical Journal A 36(2008), DOI: 10.1140/epja/i2007-10543-x

Publ.-Id: 11315

Radiation Source ELBE – Electromagnetic Radiation for Fundamental Research

Justus, M.

Since 2003, the Radiation Source ELBE at the Research Centre Dresden-Rossendorf (FZD) delivers infrared light, X-rays and Bremsstrahlung of high intensity for fundamental research. The experimental proposals are associated with the FZD programs “Advanced Materials Research”, “Cancer Research” as well as “Nuclear Safety Research and come from the institute itself, as well as from international guests.
The design and the technical implementation of the 40 MeV superconducting electron beam linear accelerator are explained with regard to the generation of the different types of secondary radiation. The article also highlights beam diagnostics and optimization of the beam quality and availability with respect to the different demands on its main properties (energy, bunch charge, emittance, time structure) and the ongoing installation of facility parts.

Keywords: ELBE

  • Lecture (Conference)
    DPG Frühjahrstagung Freiburg 08, 03.-07.03.2008, Freiburg, Deutschland


Publ.-Id: 11314

Die numerische Auswertung von Kleinwinkelstreukurven

Küchler, R.

Aus dem Streubild der Kleinwinkelstreuung kann im Allgemeinen, die die Streuvertei-lung erzeugende Struktur nicht eindeutig rekonstruiert werden. Die Ursache dafür wird erörtert und die damit verbundenen Einschränkungen bei der rechnerischen Auswertung der Streukurven an Beispielen veranschaulicht. Dies geschieht an Streukurven, die mit bekannten Größenverteilungen berechnet wurden. Weiterhin wird untersucht, welche Fit- Ansätze sich zur Auswertung der Kleinwinkelstreuexperimente am besten eignen. Als Fit- Ansätze wurden Reihenentwicklungen nach Trigonometrischen- und Polynomfunkti-onen und eine theoretisch motivierte Funktion verwendet. Neben dem entscheidenden Vergleich mit der Streukurve der Ausgangsfunktion werden die Ergebnisse auch den Rechnungen gegenübergestellt, die mit der weit verbreiteten Glatter- Methode erzielt werden.

Keywords: small-angle scattering; data evaluation; indirect fourier transformation; density distribution

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-496 2008
    ISSN: 1437-322X


Publ.-Id: 11313

First CoMFA Characterization of Vesamicol Analogs as Ligands for the Vesicular Acetylcholine Transporter

Szymoszek, A.; Wenzel, B.; Scheunemann, M.; Steinbach, J.; Schüürmann, G.

Vesamicol derivatives are promising candidates as ligands for the vesicular acetylcholine transporter (VAChT) to enable in vivo imaging of cholinergic deficiencies if applied as positron emission tomography radiotracers. So far, optimization of the binding affinity of vesamicol-type ligands was hampered by the lack of respective quantitative structure–activity relationships. We developed the first quantitative model to predict, from molecular structure, the binding affinity of vesamicol-type ligands toward VAChT employing comparative molecular field analysis (CoMFA) for a set of 37 ligands, covering three different structural types (4-phenylpiperidine, spiro, and tropan derivatives of vesamicol). The prediction capability was assessed by leave-one-out cross-validation (LOO) and through leaving out and predicting 50% of the compounds selected such that both the training and the prediction sets cover almost the whole range of experimental data. The statistics indicate a significant prediction power of the models (q2 (LOO) = 0.66, q2 (50% out) = 0.59–0.74). The discussion includes detailed analyses of CoMFA regions critical for ligand−VAChT binding, identifying structural implications for high binding affinity.

Publ.-Id: 11312

A population balance approach for polydispersed bubbly flows considering size dependent bubble forces

Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, P.

A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. By simulating a poly-dispersed gas-liquid two-phase flow, the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation as well as the momentum exchange due to bubble size dependent bubble forces have to be considered. Particularly the lift force has been proven to play an important role for establishing a certain bubble size distribution dependent flow regime.
The derived model has been validated against experimental data from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The wire-mesh technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid phases was applied. Numerous tests investigating air-water flow and steam-water flow at saturation conditions in vertical pipes having a length up to 8 m and a diameter up to 200 mm were performed and used for model validation. Furthermore in order to check the model framework for a more complex flow situation, further experiments on the flow field around a half moon shaped asymmetric obstacle were performed and the flow conditions were simulated by applying the inhomogeneous MUSIG model in direct comparison.
The paper describes the main concepts of the CFD model approach and presents model validation and application cases. The inhomogeneous MUSIG model approach was shown to be able to describe bubbly flows with higher gas content. Particularly the separation phenomenon of small and large bubbles, which was proven to be a key phenomenon for the establishment of the corresponding flow regime, is well described. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated.

Keywords: bubbly flow; CFD; non-drag forces; bubble breakup; bubble coalescence; population balance; validation

  • Lecture (Conference)
    6th International Conference on COMPUTATIONAL FLUID DYNAMICS in the Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway
  • Contribution to proceedings
    6th International Conference on COMPUTATIONAL FLUID DYNAMICS in Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway

Publ.-Id: 11311

A study of uranium phosvitin complexation using ATR FT-IR and EXAFS spectroscopy

Li, B.; Raff, J.; Rossberg, A.; Foerstendorf, H.

Phosvitin is a highly water soluble 34 kDa protein containing 10 % (w/w) phosphate groups. It serves as an ideal model for the investigation of the interaction of U(VI) with phosphorylated proteins by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and EXAFS spectroscopy.
In our study, phosvitin and its complex with U(VI) were first studied in aqueous solution at various pH values by ATR FT-IR. In order to understand the inter-atomic coordination of the U(VI) to the functional groups of the protein, in particular to phosphate groups, the samples containing U(VI) phosvitin complex with different U(VI) concentrations were additionally investigated by EXAFS spectroscopy.
Different protonated states of phosphate groups on the protein have been first identified by infrared spectra of phosvitin in solution at different pH. Comparing the spectra with those of inorganic phosphate solutions, it is obvious that at pH 4 the phosphate groups appear as dihydrogen phosphate, and at pH 8 as hydrogen phosphate.
Upon the adsorption of uranium onto phosvitin the protein is irreversible denatured. Infrared spectra of the protein, which were denatured thermally in the absence of U(VI) or denatured by other bivalent metal ions, recorded at pH 4 demonstrate that deprotonation occurs during the protein denaturation. Among those spectra, the U(VI) phosvitin complexes with lower U(VI) concentrations (10−4 M, and 10−5 M) show a unique peak at or even lower than 918 cm−1, while this peak appears at 925 cm−1 for the complex with higher U(VI) concentration (10−3 M). As the characteristic νas(UO22+) mode representing a U(VI) complexation to carboxylic groups appears at 923 cm−1 on the IR spectra, the discovered unique peak indicates coordination of the U(VI) predominately to phosphate groups of the phosvitin.
The EXAFS spectra of the U(VI) phosvitin complex are in good agreement to the spectra of other organic U(VI) phosphate complexes confirming the results from IR spectroscopy. The formation of a U(VI) complex, which is similar to the so-called “Feldman complex” is discussed.

Keywords: Phosvitin; uranium; phosphorelated protein; ATR FT-IR; EXAFS

  • Contribution to proceedings
    BioMetals 2008, 14.-18.07.2008, Santiago de Compostela, Spain
  • Poster
    Biometals 2008, 14.-18.07.2008, Santiago de Compostela, Spain

Publ.-Id: 11310

MULTIMAG - A MULTIpurpose MAGnetic system for physical modelling in magnetohydrodynamics

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

At laboratory scales, liquid metal model experiments are an important tool to understand the details of the flow structure and the transport properties of flows occurring in real-scale facilities, as well as to validate the multitude of numerical codes for flow simulations. Our MULTIpurpose MAGnetic field system facility is based on a compact coil system to investigate the influence of different magnetic fields on electrically conducting fluids. Several features distinguish MULTIMAG from other systems: (i) With its large experimental volume of H = 400 mm and D = 365 mm industrially relevant parameter can be achieved. (II) Due to the absence of any ferromagnetic materials, the possibility of linear superposition of different magnetic field types (rotating, traveling, pulsating, DC-homogen and -cusp) exists. (III) Special developed current sources allow arbitrary waveforms for each of the field types in any phase relation. Besides the main aim to describe MULTIMAG, the present paper instances results of performed flow measurements.

Keywords: Magnetohydrodynamics; Stirring device; Tailored magnetic fields

  • Flow Measurement and Instrumentation 20(2009), 241-251

Publ.-Id: 11309

Non-covalent interactions between nucleosides and molecular clips – comparison of phosphate, phosphonate and sulphate containing clips

Raditzky, B.

Water-soluble clips are possible molecules to study the weak, non-covalent interactions, responsible for many biological processes. The association between nucleosides and sulphate containing clips, with naphthalene or anthracene sidewalls, has been studied by time-resolved laser-induced fluorescence spectroscopy with ultrafast pulses (fs-TRLFS). The determined association constants for the 1:1 complexes range from log Ka = 3.9 – 4.2. The measured spectra assumes the appearance of excited state species.

Keywords: moleculare clips; nucleosides; sulphate clips; fs-TRLFS; association

  • Lecture (Conference)
    5th SUPRAPHONE/4th WG Meeting COST D31, 29.-31.05.08, Prague, Czech Republic

Publ.-Id: 11308

Ion bombardment of shape memory alloy (SMA) Ni-Ti films

Martins, R. M. S.; Schell, N.; von Borany, J.; Mücklich, A.; Siva, R. J. C.; Mehesh, K. K.; Braz Fernandes, F. M.

Ni-Ti films were deposited by magnetron cosputtering using a chamber installed into the six-circle goniometer of the Rossendorf BeamLine at ESRF. The in-situ XRD studies enable us to identify different steps of the structural evolution during growth and annealing. The use of diverse type of substrates and the effect of the application of a bias voltage to the substrate during film deposition were major tools in this study. When a negative bias voltage is applied, it causes a higher energetic ion bombardment of the growing film, resulting in an enhanced surface-atom mobility, but at sufficiently high voltage, leads to defect formation. Cross-sectional TEM and SEM micrographs have shown a change in the morphology of the films linked with different levels of bias voltages (0, -45 and -90V in this study). The transformation behaviour of the sputtered Ni-Ti films (as shown by electrical resistivity measurements) is influenced by the energy of the bombarding ions. The microstructure details resulting from the deposition using different bias values are discussed.
Additionally, it has been commissioned an ion gun allowing post-deposition ion irradiation or ion bombardment during sputter deposition. In this first series of experiments, a Ni-Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e. reduced surface oxide formation) thus modifying deliberately the microstructure of the film locally. A layer of approximately 50% of the thickness of the film was selectively removed at the irradiated region (6 x 6 mm²).
This type of studies will be very useful for the easier design and miniaturization of Ni-Ti films based devices in the field of micro-electro-mechanical systems (MEMS).

Keywords: thin films; shape memory alloy; ion irradiation; X-ray studies; ROBL

  • Lecture (Conference)
    Microscience 2008, 23.-26.06.2008, London, United Kingdom

Publ.-Id: 11307

Synchronized force and PIV measurements on an electromagnetically forced separated flow

Cierpka, C.; Weier, T.; Gerbeth, G.

Periodic addition of momentum by wall--parallel electromagnetic forces has a strong influence on the separated region of a stalled airfoil. The controlled flow possesses typically a small number of relatively large vortices, which are believed to be related to the control mechanism.
In the present paper synchronized force and particle image velocimetry measurements of the excited flow at a NACA 0015 (\alpha = 20^{\circ}, Re = 1\cdot10^{5}) will be presented.

Keywords: flow separation control; PIV; NACA0015

  • Lecture (Conference)
    ICTAM2008 - International Congress of Theoretical and Applied Mechanics, 24.-30.08.2008, Adelaide, Australia
  • Contribution to proceedings
    ICTAM2008 - International Congress of Theoretical and Applied Mechanics, 25.08.-29.09.2008, Adelaide, Australia, 978-0-9805142-1-6

Publ.-Id: 11306

Was misst die „Perfusion-CT“?

van den Hoff, J.; Hietschold, V.; Abramyuk, A.; Abolmaali, N.; Kotzerke, J.

Dynamische CT-Untersuchungen nach Kontrastmittelgabe (KM) bilden die Grundlage der als „Perfusion-CT“ bezeichneten Quantifizierungsverfahren, welche zunehmend zur Bewertung der Gewebeperfusion genutzt werden. Diese Ansätze finden z.Zt. v.a. Beachtung bei onkologischen Untersuchungen an PET/CT-Geräten, um simultan Informationen zu Tumorstoffwechsel (PET)
und -perfusion (CT) zu erhalten. Ziel dieser Arbeit war eine Analyse der Aussagekraft der verwendeten Modelle unter Beachtung messtechnisch gegebener Randbedingungen.

Zwei Modelle wurden betrachtet: 1. das in der Perfusion-CT als Patlak-Modell bezeichnete, 2. die adiabatische Lösung des „tissue homogeneity“ Modells (vgl. z.B. [2]). Aus den Lösungen der Modellgleichungen wurden Gewebeantwortkurven berechnet und im Hinblick auf Parameteridentifizierbarkeit und korrekte Parameterinterpretation analysiert.

Der als „Patlak-Modell“ bezeichnete Ansatz ist identisch mit einem irreversiblen 1-Kompartment-Modell zzgl. eines Blutvolumenterms, welches auf die frühe Phase des KM-Transits angewandt wird. Eine Analyse verfügbarer Daten (z.B. [1)) zeigt, dass die allgemein als Perfusion interpretierte Steigung K des entsprechenden Patlak-Plots numerisch typischerweise um den Faktor 5-10 von realistischen Perfusionswerten abweicht. Wir interpretieren dies dahingehend, dass dieser Parameter, welcher dem unidirektionalen KM-Transport in den Extravasalraum entspricht, i.a. unkorreliert zur Gewebeperfusion ist, da die effektive Extraktion des KM sehr klein ist (typischerweise kleiner als etwa diejenige von FDG). Vielmehr entspricht dieser Parameter eher dem PS-Produkt des KM im Zielgewebe. Das „tissue homgeneity“ Modell enthält die Perfusion explizit als freien Parameter. Die Quantifizierung setzt jedoch voraus, dass die Boluspassage durch das Kapillarbett mit so hoher zeitlicher Auflösung erfasst wird, dass diese vom Zeitverhalten im arteriellen Blut unterscheidbar bleibt. Dies erscheint aufgrund der beschränkten statistischen Genauigkeit und verschiedener systematischer Fehlerquellen (wie Bewegungsartefakten) praktisch kaum möglich.

Der Begriff Perfusion-CT suggeriert die Fähigkeit, die Perfusion aus der Gewebediffusion von Kontrastmitteln analog zum Einsatz diffusibler Tracer in der PET bewerten zu können. Diese Fähigkeit ist aber im Allgemeinen nicht gegeben. Eine kritische Bewertung der Aussagekraft des Verfahrens, namentlich im Hinblick auf den Einsatz an PET/CT-Geräten bei onkologischen Fragestellungen erscheint dringend geboten.

(1) Ng, QS et al.: „Lung cancer perfusion at multi-detector row CT: reproducibility of whole tumor quantitative measurements.“, Radiology 239(2), pp. 547-53 (2006).
(2) Stewart et al.: „Correlation between hepatic tumor blood flow and glucose utilization in a rabbit liver tumor model.“, Radiology 239(3), pp. 740-50 (2006).

  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A60

Publ.-Id: 11305

Vergleich einer 2D- und 3D-basierten ROI-Auswertung beim F-18-DOPA-Hirn-PET in einem Normalkollektiv

Oehme, L.; Hofheinz, F.; Wolz, M.; Pötzsch, C.; van den Hoff, J.; Kotzerke, J.

Die in der Parkinsondiagnostik relevanten Strukturen, Nucleus caudatus und Putamen, sind komplexe dreidimensionale Strukturen. Ziel der Untersuchung war es, die Ergebnisse der bisherige 2D-basierte ROI-Auswertung (CAPP-Software, Siemens/CTI) mit einer ROI-Auswertung im 3D-Datensatz (Softwarepaket ROVER, ABX Radeberg) zu vergleichen.

Ausgewertet wurden neun F-18 -DOPA-Hirn-PET-Datensätze gesunder Kontrollpersonen (positives BfS-Gutachten und Ethikvotum). 60 min nach 150 mg Carbidopa per os sowie nach 10 min Transmissionsmessung erfolgte die dynamische Akquisition über 90 min mit Injektion von 185 MBq F-18-DOPA i.v. (ECAT EXACT HR+, Siemens/CTI). Die Auswertung erfolgte in einem Pseudo-2D-Verfahren (Summenbild 10-90min p.i., Ausrichtung Putamen horizontal, Addition von 4 Schichten auf Höhe von Nucl. Caudatus und Putamen, Positionierung von ROIs vordefinierter Größe und Anzahl über Nucl. Caudatus, Putamen, Referenzgewebe occipital) und in einem 3D-Datensatz (freie Positionierung o.g. ROIs vordefinierter Größe und Anzahl in allen 3 Raumebenen). Die Dopamin-Einstromraten wurden mittels Patlak-Analyse bestimmt. Beide Auswerteverfahren wurden verblindet von zwei Untersuchern ausgeführt. Verglichen wurden die Abweichungen innerhalb einer Auswertemethode zwischen den Untersuchern (U1, U2) sowie die Abweichungen zwischen den zwei Auswertemethoden (2D, 3D).

Die Auswertung mit der 3D-Methode war schneller und wurde als einfacher empfunden. Weder innerhalb einer Auswertemethode zwischen den 2 Untersuchern noch zwischen den 2 Auswertemethoden eines Untersuchers waren signifikante Unterschiede zu finden. Über das Kollektiv gemittelt betrugen die Einstromraten (1/min, m+/-sd) für U1-2D; U2-2D; U1-3D; U2-3D: Nucl. Caudatus rechts 0,0181+/-0,0010; 0,0174+/-0,0018; 0,0175+/-0,0022; 0,0174+/-0,0017; Nucl. Caudatus links 0,0185+/-0,0013; 0,0180+/-0,0019; 0,0179+/-0,0013; 0,0183+/-0,0020; Putamen rechts 0,0185+/-0,0006; 0,0180+/-0,0018; 0,0185+/-0,0013; 0,0185+/-0,0017; Putamen links 0,0185+/-0,0013; 0,0180+/-0,0018; 0,0182+/-0,0018; 0,0183+/-0,0015. Die relativen Abweichungen (Differenz/Summe) liegen für alle Paarvergleiche jeweils (gemittelt über alle ROIs) innerhalb +/-2 % (sd < 5 %), allerdings gibt es auch Ausreißer mit Unterschieden größer als +/- 10 %.

Die 2D- als auch die 3D-basierte Auswertung mittels Standard-ROIs definierter Anzahl und Größe lieferten in diesem Normalkollektiv vergleichbare Ergebnisse, wobei die 3D-Methode einen geringeren Zeitbedarf erfordert und als einfacher empfunden wird. In einem weiteren Schritt werden beide Auswertemethoden auf Datensätze von Patienten mit M. Parkinson mit unterschiedlicher Krankheitsintensität angewendet, um die Variabilität der Ergebnisse in Abhängigkeit von Auswertemethode und Untersucher abschätzen zu können.

  • Poster
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A108

Publ.-Id: 11304

Determination of harmonic and pulsed eddy current distributions in a liquid metal

Forbriger, J.; Galindo, V.; Gerbeth, G.; Stefani, F.

The spatio-temporal distribution of harmonic and pulsed eddy currents in the liquid metal alloy GaInSn positioned above an excitation coil is determined by measuring the corresponding voltage drop in an electric potential probe. The resulting spatio-temporal eddy current field is compared with the corresponding analytical expressions for a conducting half-space. Deformations of the eddy current distribution due to a non-conducting ring immersed into the liquid metal are measured and compared with numerical results.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Proceedings of the 7th International PAMIR Conference on Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 809-813
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11303

Constraining the geodynamo by sequences of field reversals

Fischer, M.; Gerbeth, G.; Stefani, F.

Using a spherically symmetric mean field dynamo model with a quenched helical turbulence parameter alpha under the influence of noise and external periodic forcing we try to constrain its essential parameters by typical features of field reversal. Our results indicate that the geodynamo works in a highly supercritical state, that the relative strength of the periodic forcing due to the Milankovic cycle of the Earth’s orbit eccentricity is approximately 15 per cent of the general dynamo strength, and that the magnetic diffusion time is significantly reduced in comparison with the diffusion time resulting from the molecular conductivity.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Proceedings of the 7th International PAMIR Conference on Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 225-229
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11302

Liquid metal experiments on the helical magnetorotational instability

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

The magnetorotational instability (MRI) plays an essential role in the formation of stars and black holes. By destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs. We present the results of a liquid metal Taylor-Couette experiment under the influence of helical magnetic fields that show typical features of MRI at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10. Particular focus is laid on an improved experiment in which split end caps are used to minimize the Ekman pumping.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Proceedings of the 7th International PAMIR Conference on Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 97-101
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Magnetohydrodynamics 45(2009)2, 135-143

Publ.-Id: 11301

Synthese und radiopharmakologische Charakterisierung von Kohlenstoff-11 markierten Chromenderivaten als neuartige nicht-steroidale Liganden für den Glucocorticoidrezeptor (GR)

Steiniger, B.; Bergmann, R.; Pietzsch, J.; Wüst, F.

Glucocorticoidrezeptoren (GR) nehmen innerhalb der Hypothalamus-Hypophysen-Nebennieren (HHN)-Achsenregulation eine wichtige Rolle ein. Störungen dieses wichtigen neuroendokrinen Regelsystems sind charakteristisch für verschiedene neuropsychiatrische Erkrankungen, wie z.B. Depression [1]. Ziel der vorliegenden Arbeit war die Entwicklung von Radiotracern für die Darstellung von GR im Gehirn mittels PET. Dabei sollten besonders verschiedene GR-bindende Chromenderivate als neueuartige nicht-steroidale GR-Liganden mit 11C markiert und radiopharmakologisch charakteri-siert werden.

Ausgehend von chromenbasierten Sulfonamiden wurden verschiedene nicht-steroidale Verbindungen als Liganden für den GR synthetisiert. Die Markierung der Desmethyl-Vorstufen erfolgte in einem automatisierten Synthesemodul über eine regioselektive O-Methylierung mit [11C]MeI. Die radio-pharmakologische Charakterisierung der hergestellten Verbindungen umfasste Bioverteilungs-untersuchungen, Autoradiographie und dynamische Kleintier-PET-Untersuchungen mit normalen Wistar-Ratten.

Die Radiomarkierung mit [11C]MeI konnte durch die Verwendung von NaH als Base und DMF als Lösungsmittel regioselektiv als O-Methylierung durchgeführt werden. Die als Konkurrenzreaktion stattfindende N-Methylierung konnte dadurch weitgehend unterdrückt werden. Die 11C-markierten Chromenderivate konnten in radiochemischen Ausbeuten von 33% und spezifischen Aktivitäten von 15 GBq/µmol erhalten werden. Bioverteilungsstudien zeigten Hirnanreicherungen von bis zu 1.6 %ID/g nach 5 min und 0.6 %ID/g nach 60 min. In den Kleintier-PET Aufnahmen waren GR-reiche Gehirnareale wie der Cortex gut sichtbar.

Das vorgestellte Chromengerüst eignet sich als vielversprechende Leitstruktur für die Entwicklung neuer GR-bindender Radiotracer mit moderater Lipophilie. Weitere radiopharmakologische Untersuchungen sind für eine abschließende Bewertung der vorgestellten Verbindungen als PET-Radiotracer für die Darstellung von GR im Gehirn notwendig.

[1] E. R. De Kloet et al. Endocr. Rev. 1998 19(3):269-301.

  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A31

Publ.-Id: 11300

A Novel Approach for Predicting the Positron Emitter Distributions Produced during Therapeutic Ion Irradiation

Priegnitz, M.; Fiedler, F.; Kunath, D.; Laube, K.; Parodi, K.; Sommerer, F.; Enghardt, W.

In-beam PET is a valuable method for a beam-delivery independent dose monitoring in radiation therapy with ion beams. The clinical feasibility of in-beam PET has been demonstrated for carbon and proton beams up to now. From radiobiological point of view it is highly desirable to perform tumor irradiation also with other ions. To extend the application of in-beam PET also to these ions, extensive knowledge about positron emitter production via nuclear fragmentation reactions during ion irradiation is necessary. To model the positron emitter production correctly, cross
sections for all possible nuclear reactions occurring in the tissue during irradiation and leading to positron emitters are required. Since for many ions of therapeutic interest these cross sections are not available in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced. The prediction of positron emitter distributions is based on depth dependent thick target yields, which are deduced by linear superposition of measured yields in water, graphite and polyethylene as reference materials. First results on the prediction of positron emitter distributions in polymethyl methacrylate (PMMA) targets induced by Li and C irradiation are presented. By comparison with data deduced from experiments, it is shown that a rather accurate prediction of positron emitter distribution in PMMA is possible with this method.

  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany

Publ.-Id: 11299

Synthesis and in vitro evaluation of new diphenyl ether derivatives as serotonin transporter ligands

Guo, Y.; Chen, X.; Jia, H.; Deuther-Conrad, W.; Brust, P.; Steinbach, J.; Vercouillie, J.; Liu, B.

For the development of new ligands as potential imaging agents for the serotonin transporter (SERT), a series of diphenyl ether derivatives have been synthesized, characterized, and evaluated for their in vitro binding affinities to the SERT. Among the above compounds, 2-(2-((dimethylamino)methyl)-4-fluorophenoxy)-5-bromobenzenamine (15) and 2-(2-((dimethylamino)methyl)-4-fluorophenoxy)-5-iodobenzene amine (16) show high binding affinities for the SERT with K i values of 0.28 and 0.20 nmol·L−1, respectively. They can be further labeled with carbon-11, fluorine-18, iodine-123 or bromine-76, and evaluated as useful imaging agents for the SERT. Moreover, the study of the structure-activity relationship (SAR) provides some useful information for the future design of new ligands.

Keywords: serotonin transporter; diphenyl ether; imaging agents; in vitro evaluation

Publ.-Id: 11298

Bacterial and archaeal communities' composition of uranium-contaminated soils in Bulgaria

Radeva, G.; Kenarova, A.; Buchvarova, V.; Flemming, K.; Selenska-Pobell, S.

The uranium mining waste piles, mill tailing, and disposal sites in several regions of Bulgaria are highly contaminated with toxic metals as a result of the U mining and milling performed in the past. In order to suggest appropriate bioremediation strategies for such environments, the phylogenetic composition and structure of the microbial communities in two uranium-contaminated sites were characterized by using molecular approaches. Three soil samples were studied: two of them were collected from different depths of a U mill tailings (Metallurg Buhovo, located in western Bulgaria), and the third - from a former U mining site (mine Sliven, South-Eastern Bulgaria). 16S rRNA gene libraries were generated from total community DNA, using universal bacterial and archaeal oligonucleotide primer sets. Four hundred fifty bacterial clones were analyzed and grouped in sixty eight operational taxonomic units (OTUs). Three hundred ninety two archaeal clones of the clone libraries from the two U mill tailings soil samples were organized in fourteen archaeal OTUs. Rarefaction analysis indicated a high diversity of bacterial sequences, while the archaeal sequences were less diverse. Most of the bacterial sequences were affiliated with Proteobacteria from Alpha- Beta-, and Gamma- subdivisions. 16S rRNA gene sequences representing Bacteroidetes, Acidobacteria, Verrucomicrobia, Actinobacteria, and Gemmatimonadete were found in various numbers as well. Our results showed that the composition of the microbial communities in the two different studied ecosystems was diverse and environment-specific. Acidobacteria and Bacteroidetes were predominant in the soil samples collected from the U mill tailings, whereas Gammaproteobacteria and Actinobacteria were characteristic for the soil from the U mining waste. All archaeal 16S rRNA gene sequences retrieved from the U mill tailings soil samples were affiliated with the group 1.1b of the mesophilic soil Crenarchaeota which still does not contain any cultured representatives. Closely related 16S rRNA gene sequences were repeatedly found earlier in soil samples from different U mining waste piles and mill tailings in the east part of Germany.
Taken into account the significance of Crenarchaeota in the global nitrogen cycle, the studied soil samples were assayed also for the presence of ammonia monooxygenase subunit A (amoA) gene. Using PCR primers targeting archaeal amoA genes, two clone libraries were constructed and analyzed.

Keywords: 16S rRNA; bacterial diversity; Archaea; uranium mining wastes

  • Contribution to proceedings
    XII International Congress of Bacteriology and Applied Microbiology, 05.-09.08.2008, Istanbul, Turkey

Publ.-Id: 11297

Accumulation of Heavy Metals by Microorganisms: Biomineralization and Nanocluster Formation

Selenska-Pobell, S.; Merroun, M.

Bacteria and archaea are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the metal binding potentials of their cell wall components.
This chapter is focused on cell wall dependent accumulation and biomineralization of iron and uranium. By using transmission electron microscopic analysis in combination with x-ray absorption and time-resolved laser-induced fluorescence spectroscopic analyses it is demonstrated that the Gram-negative and most of the Gram-positive bacteria as well as some archaea immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. However, some Gram-positive bacteria which possess highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) not only by phosphate groups mainly from their peptidoglycan but also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In addition, the cell wall supported formation of metallic palladium nanoclusters by some bacteria is presented as well. Despite the different mechanisms of the biological deposition of Pd by Gram-negative and Gram-positive bacteria, the nanoparticles formed by both organisms have almost identical size and catalytic activity.

  • Contribution to external collection
    König, H., Claus, H., Varma, A.: Prokaryotic Cell Wall Components – Structure and Biochemistry, Heidelberg: Springer Verlag, 2010, 483-500

Publ.-Id: 11295

Biodistribution and metabolism of hCT-derived cell-penetreting peptides

Bergmann, R.; Rennert, R.; Közle, I.; Franke, J.; Schlesinger, J.; Neundorf, I.

Cell-penetrating peptides (CPP) derived from the native peptide hormone human calcitonin (hCT) represent a high potential drug delivery system for in vivo intracellular targeting of diagnostic and therapeutic compounds. Cell penetration of hCT-derived substances was
verified in vitro, however, the knowledge about CPP in vivo distribution and metabolism is very limited. Therefore we studied the in vivo radiopharmacology of 68Ga radiolabeled DOTAmodified, hCT-derived CPP in rats using small animal PET.

Three hCT-derived peptides (hCT(9-32), LGTYTQDFNKFHTFPQTAIGVGAPNH2; [f12,16]-hCT(9-32), LGTfTQDfNKFHTFPQTAIGVGAP-NH2; random (rd)-hCT(9-32), FLTAGQNTIQTPVKTGGHFPFADY-NH2) were at the N-terminus modified with DOTA. The biodistribution and kinetics of the radiolabeled 68Ga-DOTA-hCT(9-32) or 68Ga-DOTA-[f12,16]-hCT(9-32) or 68Ga-DOTA-rd-hCT(9-32) were studied with small animal PET. The arterial blood at different time points, and urine were analyzed for radio-metabolites.

The radio-peptides were eliminated mainly by the renal system, more than 50% of the injected dose was found at 60 min after injection in the urine, only small amounts of the activity were detected in the intestine. The general activity retention in the body was low, except the kidneys. The blood clearance of the original peptides reached terminal half-lifes of 68Ga-DOTAhCT(9-32) 15.9 min, 68Ga-DOTA-[f12,16]-hCT(9-32) 20.9 min, 68Ga-DOTA-rd-hCT(9-32) 15.8 min; the relative AUC in comparison to 68Ga-DOTA-hCT(9-32) were 100%, 170%, and 51%, respectively. The patterns of metabolic cleavage in the arterial blood were different. The 68Ga-DOTA-[f12,16]-hCT(9-32) was metabolized to three radio-metabolites after 30 min, the other radiopeptides were degraded to more than five radioactive metabolites.

It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex. The blood clearance and the elimination of the 68Ga-DOTA-peptides were relatively high and should be decreased by
structural changes to enhance the tissue uptake of this drug carrier system.

  • Lecture (Conference)
    19th Meeting of the International Research group in Immuno-Scintigraphy and Therapy (IRIST), 25.-28.06.2008, Krakow, Poland

Publ.-Id: 11294

Bacteria Heavy Metal Interactions: Biomineralization and Nanoclusters Formation

Selenska-Pobell, S.

Bacteria exhibit fascinating resistant mechanisms to extreme temperatures, acidity, alkalinity, high metal, radionuclide, and salt concentrations. For this reason, they occupy not only the moderate habitats of humans, animals, plants, and insects but also extremely harsh environments such as hot springs, permafrost, acidic mine drainages, “dead” sees, etc.
Due to their ubiquitous distribution in terrestrial and aquatic environments bacteria play a major role in deposition and weathering in the earth’s crust of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the differences in their cell wall organization.

  • Invited lecture (Conferences)
    Invited talk at Ben Gurion University of the Negev, 02.04.2008, Negev, Israel

Publ.-Id: 11293

A comparative study of n.c.a. sodium [18F]fluoroacetate and sodium [11C]acetate in xenotransplanted tumor bearing mice

Bergmann, R.; Richter, S.; Pietzsch, J.; Beuthien-Baumann, B.; Wüst, F.

Objectives :
This study describes the radiosynthesis of [18F]fluoroacetate (18F-FAC), radiopharmacological characterization, and molecular imaging of oxidative metabolism in tumor bearing mice using 18F-FAC in comparison with 11C-ACE.

Methods :
The radiosynthesis of n.c.a. sodium 18F-FAC was performed in two step reaction sequence and subsequent SPE purification in a remotely controlled synthesis module.
Biodistribution, metabolism and small animal PET studies of 18F-FAC and 11C-ACE were carried out in rats and HT-29 tumor-bearing mice.

Results :
18F-FAC was obtained in radiochemical yields of 20-25% within 50 min. Biodistribution data showed higher initial radioactivity uptake in most organs and tissues for 18F-FAC; the initial brain uptake of 0.67 %ID/g at 5 min p.i. followed by a 22% clearance at 60 min p.i. Both radiotracers can clearly delineate the tumor. The tumor-to-muscle ration was 1.8 for 18F-FAC and 1.5 for 11C-ACE. Unlike 11C-ACE, 18F-FAC shows a slow transport of the free radiotracer from the blood pool into the tumor, and 10% of the free fraction of 18FFAC is trapped in tumor tissue.

Conclusions :
The highly reproducible remotely-controlled two step/one pot synthesis of 18FFAC represents an alternative to previously published synthesis routes. The successful PET imaging of xenotransplanted human colorectal adenocarcinoma tumor HT-29 by means of 18F-FAC shows that the radiotracer may not only be restricted for imaging of previously reported prostate cancer tumors. However, the exact mechanism of 18F-FAC tissue uptake remains unclear and should be subject of further studies.

Research Support : Supported in part by the EU FP6 ‘‘BioCare’’, proposal #505785.

  • Lecture (Conference)
    2008 SNM Annual Meeting, 14.-18.06.2008, New Orleans, USA

Publ.-Id: 11292

The impact of implantation defects in SIMOX processing

Kögler, R.; Ou, X.

The impact of implantation induced point defects in SIMOX (Separation by IMplantation of OXygen) processing is explained. The origin of the so-called energy-dose window is shown to be the point defects generated by the oxygen implantation.

Keywords: Oxygen implantation; SIMOX; point defects

  • Lecture (Conference)
    Arbeitstreffen "Punktdefekte", 03.-04.04.2008, Dresden, Deutschland

Publ.-Id: 11291

CFD simulation of convective flow boiling of refrigerant in a vertical annulus

Koncar, B.; Krepper, E.

In this paper a forced convective boiling of Refrigerant R-113 in a vertical annular channel has been simulated by a custom version of the CFX-5 code. The employed subcooled boiling model uses a special treatment of the wall boiling boundary, which assures the grid invariant solution. The simulation results have been validated against the published experimental data. In general a good agreement with the experimental data has been achieved, which shows that the current model may be applied for the Refrigerant R-113 without significantly changing the model parameters. The influence of non-drag forces, bubble diameter size and interfacial drag model on the numerical results has been investigated as well.

Keywords: forced convective boiling; refrigerant R-113; CFD simulations; validation

  • Nuclear Engineering and Design 238(2008), 693-706

Publ.-Id: 11290

Fluctuations due to nonlocal collisions

Morawetz, K.

It is shown that the collision integral describing the nonlocal character of collisions leads to the same mean-field fluctuations in the one-particle distribution as proposed by Boltzmann-Langevin pictures. It is argued that this appropriate collision integral contains the fluctuation-dissipation theorems in equilibrium itself and therefore there is no need to assume additionally stochasticity. This leads to tremendous simplifications in numerical simulation schemes.

  • Poster
    International Workshop on Chaos and Collectivity in Many-Body System, 05.-08.03.2008, Dresden, Germany

Publ.-Id: 11288

The concept of correlated density and its application

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.; Schreiber, M.

The correlated density appears in many physical systems ranging from dense interacting gases up to Fermi liquids which develop a coherent state at low temperatures, the superconductivity. The underlying quantum statistical theory in nonequilibrium is the nonlocal kinetic theory developed earlier. One consequence of the correlated density is the Bernoulli potential in superconductors which compensates forces from dielectric currents which allows to access material parameters.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11287

Contribution of the surface dipole to deformation of superconductors

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.; Schreiber, M.

The interaction of the ionic lattice with the superconducting condensate is treated in terms of the electrostatic force in superconductors. It is shown that the surface dipole supplies the force responsible for the volume difference of the normal and superconducting states. Assuming this mechanism we argue
that the usual parametrization of the theory of deformable superconductors should be revisited.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11286

Enhancement of pairing near reasonant atoms

Morawetz, K.

A correlated fermion system is considered surrounding a finite cavity with virtual levels. The pairing properties are calculated and the influence of the cavity is demonstrated. To this end the Gell-Mann and Goldberger formula is generalized to many-body systems. We find a possible enhancement of pairing temperature if the Fermi momentum times the cavity radius fulfills a certain resonance condition which suggests an experimental realization.

  • Poster
    International Workshop on Chaos and Collectivity in Many-Body Systems, 05.-08.03.2008, Dresden, Germany

Publ.-Id: 11285

Surface deformation and magnetocapacitance of superconductors

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.

Electrostatic potentials have been measured at surfaces of superconductors in order to access directly the gap and material parameters. The reason why no thermodynamic corrections are measured as predicted by the theory, e.g. by Rickayzen, has remained a puzzle for almost 30 years. The solution is found in the Budd-Vannimenus theorem due to the surface dipoles. To access thermodynamic corrections one has to look deeper in the bulk like in an experiment by Kumagai et al measuring the quadrupole shift of the NMR in YBCO. The found large magnitude and unexpected sign is explained by the charge transfer between Cu chains and planes. To this end we develop the theory of electrostatic potentials above the Abrikosov vortex lattice within Bardeen's extension of the Ginzburg-Landau theory to low temperatures including the surface dipole.
As applications it is proposed:
(i) The deformation of the crystal due to the presence of vortices is calculated and the corresponding effective mass of vortices is suggested to be measured.
(ii) We found a jump of the magnetocapacitance at the surface critical magnetic field which should be experimentally accessible.

The experimentally confirmed Bernoulli potential is a consequence of the correla ted density which follows from the concept of nonlocal kinetic theory. Therefore we see this Bernoulli potential as a justification of our kinetic equation of nonlocal and non-instantaneous character which has unified the achievements of transport in dense gases with the quantum transport of dense Fermi systems.

  • Invited lecture (Conferences)
    1st Bilateral Estonian-German Workshop, 30.04.-02.05.2008, Tartu, Estland

Publ.-Id: 11284

Phase diagram for interacting Bose systems

Maennel, M.; Morawetz, K.; Schreiber, M.

no abstract available

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11283

The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface po tential step and BCS-BEC crossover

Morawetz, K.; March, N. H.; Squire, R. H.

The chemical potential $\mu$ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for $\mu$ for a three-dimensional electron liquid in terms of average kinetic and potential energies per particle. The difference between $\mu$ and the energy per particle is found to be exactly the electrostatic potential step at the surface. We also present calculations for an integrable one-dimensional many-body system with delta function interactions, exhibiting a BCS-BEC crossover. It is shown that in the BCS regime the chemical potential can be expressed solely in terms of the ground-state energy per particle. A brief discussion is also included of the strong coupling BEC limit.

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11282

Dominant motion vs. localization in quasiperiodic chains

Morawetz, K.; Schreiber, M.

Chains of coupled clusters arranged in a quasiperiodic sequence are analyzed with respect to the dynamics of wave packets. The recurrence probability is shown to show characteristic plateaus described by an interplay of localization and dominant motion. A three-mode model is developed which allows to understand the features of the recurrence probability as well as of the time-dependent width of the wave packets. The relation to waiting probabilities and anomalous diffusion is worked out. The consequences for the transmission coefficient realizable in experiments by sequences of quasiperiodic chains are discussed and the generalizations towards two-dimensional tilings are presented.

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11281

Surface superconductivity and capacitance of superconductors under electric and magnetic fields

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.; Schreiber, M.

A superconducting layer exposed to a perpendicular electric and parallel magnetic field is considered within the Ginzburg-Landau (GL) approach. The GL equation is solved near the surface and the surface energy is calculated. The nucleation critical field is shown to be changed in dependence on the magnetic and electric field. Special consideration is payed to the induced magnetic-field effect caused by diamagnetic surface currents. The latter effect constitutes the main contribution to the effective inverse capacitance which determines the effective penetration depth.
The surface energy becomes strongly dependent on the width of the sample.
An experimental realization is suggested for determining the change in the effective capacitance of the layer.

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11280

VVER-1000 main steam line break analysis using the coupled code system DYN3D/ATHLET

Kliem, S.; Kozmenkov, Y.; Höhne, T.; Rohde, U.; Weiß, F.-P.

Calculations using the coupled code system DYN3D/ATHLET were performed in the frame of the OECD/NEA MSLB benchmark for a VVER-1000 reactor. The coolant mixing inside the reactor pressure vessel was treated using a validated empirical mixing model implemented into the DYN3D/ATHLET code.
Using very conservative boundary conditions (reduced scram worth, two stuck rods, running MCP throughout the whole transient) a return-to-power was predicted.
For the assessment of the empirical mixing model a time dependent calculation using the computational fluid dynamics code CFX-10 was performed. For that analysis, a detailed model of the reactor pressure vessel consisting of the inlets nozzles, downcomer, lower plenum and a part of the core and having 4.67 million unstructured tetra cell elements was used. For the considered case with running main coolant pumps, this calculation shows a sector formation at the core inlet with a certain amount of mixing at the edges of the sector.
A core calculation using these CFX results as boundary conditions predicted also a return-to-power with a maximum value being about 200 MW lower than in the coupled code calculation. This variation calculation confirms the applicability of the empirical mixing model. The comparison shows also, that in this way results with a reasonable degree of conservatism can be obtained.

  • Contribution to proceedings
    International Conference on the Physics of Reactors (PHYSOR'08), 14.-19.09.2008, Interlaken, Switzerland
    Proceeedings of the International Conference on the Physics of Reactors 2008, CDROM paper 311, Villigen: Paul Scherrer Institut, 978-3952140956
  • Lecture (Conference)
    International Conference on the Physics of Reactors (PHYSOR'08), 14.-19.09.2008, Interlaken, Switzerland

Publ.-Id: 11279

Nanocluster in implantierten Lichtemitter-Bauelementen durch ms-Temperung

Skorupa, W.; Rebohle, L.; Prucnal, S.; Kanjilal, A.; Sun, J. M.; Cherkouk, C.; Helm, M.; Nazarov, A.; Behar, M.

Die effiziente Erzeugung silizium-basierter Elektrolumineszenz ist eine Schlüsselproblematik, die für den avisierten Übergang von der Nanoelektronik zur Nanophotonik von entscheidender Bedeutung ist. Im Vortrag wird über die Korrelation von Temperzeit, der Größe von Seltenerde-Nanoclustern und deren Einfluß auf die Elektrolumineszenz-Ausbeute in Lichtemitter-Bauelementen berichtet, die auf implantierten, thermisch gewachsenen SiO2-Schichten auf Si-Wafern basieren.

Keywords: nanocluster; rare earth; ion implantation; electroluminescence; silicon-based light emitting devices

  • Lecture (Conference)
    Workshop Ionenstrahlphysik und Nanotechnologie, 11.-12.04.2008, Darmstadt, Germany

Publ.-Id: 11278

Assembly, structure, and performance of an ultra-thin film organic field-effect transistor (OFET) based on substituted oligothiophenes

Haubner, K.; Jaehne, E.; Adler, H.-J.; Koehler, D.; Loppacher, C.; Eng, L. M.; Grenzer, J.; Herasimovich, A.; Scheinert, S.

We report on the improved assembly and characterization of a small molecule organic field-effect transistor (OFET). Novel alpha-omega-dicyano substituted beta-beta'-dibutylquaterthiophene molecules (DCNDBQT) were synthesized and characterized by UV–Vis spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and cyclic voltammetry. The ultra-thin organic film formation on TiO2 templates was effectively promoted through the specifically designed bifunctional self assembly molecules (SAM) 5-cyano-2-(butyl-4- phosphonic acid)-3-butylthiophene (CNBTPA). Excellent structural properties were found for up to 9 DCNDBQT molecule thick films prepared through UHV vacuum sublimation as investigated with UHV non-contact atomic force microscopy (nc-AFM) and X-ray diffraction. Both X-ray and nc-AFM data indicate that the DCNDBQT molecules form a well-ordered terraced structure exhibiting step heights of 1.5 nm to 2.0 nm layers. Hence, the DCNDBQTmolecules are linked to the functional SAM interface layer by H-bond interactions (see structure model) standing quasi perpendicular to the TiO2 template, and thus providing optimal orbital overlap neigh-bouring thiophene rings. The vacuum sublimated DCNDBQT molecules form a closed packed and dense molecular layer that was used to construct and operate a nanoscopic OFET-structure. The resulting field mobilities of 10^–5 cm^2 /V /s reflect a high current density in our ultrathin but highly ordered structure.

Keywords: organic field-effect transistor (OFET)

Publ.-Id: 11277

Flow structure and concentration distribution in seemingly parallel magnetic and electric fields

Weier, T.; Cierpka, C.; Eckert, K.; Uhlemann, M.; Bund, A.

We aim to show that flow field and concentration measurements are a valuable aid in understanding magnetoelectrochemical phenomena. Two examples, the flow field in a cylindrical cell and the concentration distribution near a circular millielectrode, will be discussed. Both cases have in common that at first sight electric and magnetic fields seem to be parallel. However, in reality, Lorentz forces are generated at locations, where the assumption of parallelism is locally violated, inducing convection phenomena of surprising complexity.

  • Lecture (Conference)
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Contribution to proceedings
    7th International pamir Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France, 333-337

Publ.-Id: 11276

Biodiversität im Filter: Wie Forscher helfen, Uran-Altlasten zu beseitigen

Raff, J.; Pollmann, K.

Mikrobiologen im Forschungszentrum Dresden-Rossendorf entwickeln intelligente Filtersysteme zur Entfernung oder Rückgewinnung von Metallen aus Wässern, indem sie den Überlebensmechanismus von Bakterien nutzen. Vor wenigen Jahren fanden sie Bakterien mit verblüffenden Eigenschaften auf einer Uran-Abfallhalde im sächsischen Johanngeorgenstadt. Wie am Beispiel des Isolates Lysinibacillus sphaericus JG-A12 gezeigt werden konnte, haben die Bakterien im Laufe der Evolution eine spezielle Schutzschicht entwickelt, um sich vor dem toxischen Schwermetall Uran zu schützen. Die Schicht besteht aus besonderen Hüllproteinen, die auf der Zelloberfläche nanoskalige Gitter ausbilden und dazu dienen, giftige Metalle am Eindringen in die Zelle zu hindern, für das Überleben des Bakteriums wichtige Substanzen jedoch passieren zu lassen.
Die Forscher kopieren für ihre neuartigen Filtersysteme diese genialen Vorbilder aus der Natur. Sie stellen Bioverbundmaterialien aus Hüllproteinen auf der Grundlage von konventionellen Immobilisierungsverfahren her bzw. beschichten herkömmliche Filtermaterialien mit den Hüllproteinen. Im Ergebnis erhalten sie Filter, die nur die Metalle aus dem Wasser holen, die entfernt oder gewonnen werden sollen, und das selbst bei niedrigsten Konzentrationen. Durch die Verwendung unterschiedlicher Proteine sollen zukünftig Filtermaterialien für verschiedene Metalle hergestellt werden und derartig miteinander kombinierbar sein, dass schließlich eine individuelle Wasserbehandlung möglich wird. Bis zur großtechnischen Anwendung dieser Verfahren werden jedoch noch einige Jahre vergehen.

  • Poster
    Parlamentarischer Abend der Leibniz-Gemeinschaft, 06.05.2008, Berlin, Deutschland

Publ.-Id: 11275

Simulation von ATWS-Transienten in Druckwasserreaktoren

Kliem, S.; Mittag, S.; Rohde, U.; Grundmann, U.; Weiß, F.-P.

Im Rahmen von Sicherheitsanalysen für KKW werden auch Transienten mit unterstelltem Ausfall der Reaktorschnellabschaltung (RESA) betrachtet. Bei diesen ATWS-Transienten (Anticipated Transients Without Scram) wird angenommen, dass das mechanische Einfahren der Regel- und Abschaltstäbe vollständig versagt, wenn es infolge eines bestimmten Ereignisses angefordert wird. Bei einem derartigen Versagen der RESA wird die Leistungsentwicklung im Reaktorkern ausschließlich durch die neutronenkinetische Rückkopplung über Brennstofftemperatur, Moderatortemperatur und –dichte sowie Borkonzentration bestimmt.
Die ATWS-Transiente „Ausfall der Hauptspeisewasserversorgung mit Nichtabschalten der Hauptkühlmittelpumpen“ wurde mit dem gekoppelten neutronenkinetisch/thermohydraulischen Programmkomplex DYN3D/ATHLET analysiert. Dabei wurde der Einfluss systemtechnischer und neutronenkinetischer Randbedingungen auf die Rechenergebnisse untersucht. Bei den durchgeführten Rechnungen handelt es sich um methodische Untersuchungen und nicht um Nachweisführungen.
Die Reduktion der Abblasemenge aus dem Primärkreislauf, welche die Unsicherheiten beim zweiphasigen kritischen Ausströmen abdecken soll, hat unter den ausgewählten Variationen den größten Einfluss auf den Druckverlauf im Primärkreislauf, der bei der betrachteten Transiente der wichtigste Sicherheitsparameter ist.
Die Veränderung der Kernbeladung (Variation der Anzahl der MOX-Brennelemente) hat einen großen Einfluss auf die Reaktivitätskoeffizienten der Brennstofftemperatur und der Moderatordichte. Über diese zwei Koeffizienten wird der Primärdruck stark beeinflusst. Wesentliches Ergebnis ist, dass das berechnete Druckmaximum mit Erhöhung der Anzahl der MOX-Brennelemente deutlich niedriger ausfällt.
Mit einer statistischen Variation der globalen Rückkopplungsparameter wurden für eine konkrete Kernbeladung die Auswirkungen von Unsicherheiten, die sich bei der Erstellung der Zweigruppen-Wirkungsquerschnittsdaten ergeben können, auf den Verlauf der betrachteten Transiente analysiert. Die Bereiche für die statistische Variation der Daten wurden auf Grund von Erfahrungswerten vorgegeben. Die Variation des Reaktivitätskoeffizienten der Moderatordichte bewegt sich dabei in einem ähnlichen Bereich, wie er sich bei der Variation der Anzahl der MOX-Brennelemente er-gab, der Variationsbereich des entsprechenden Koeffizienten der Brennstofftemperatur ist ungefähr doppelt so groß. Im Ergebnis ergibt sich eine größere Streuung des berechneten Maximaldrucks. Eine Streuung der Koeffizienten um ± 20 % ergibt eine Streubreite im Maximalwert des Drucks im Primärkreislauf von 2.17 MPa, die entsprechenden berechneten Toleranzgrenzen sind 18.26 und 20.43 MPa. Eine Sensitivitätsanalyse ergab, dass der Primärdruck in größerem Maß vom Dichtekoeffizienten abhängt, der Koeffizient der Brennstofftemperatur beeinflusst das Druckmaximum bei gleicher relativer Variation nur halb so stark.

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany
    Tagungsband der Jahrestagung Kerntechnik 2008, CDROM, Berlin: INFORUM GmbH
  • Invited lecture (Conferences)
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany
  • atw - International Journal for Nuclear Power 54(2009)2, 100-110

Publ.-Id: 11274

Study of the L-shell ionisation of gold by 3.0-18.2 MeV nitrogen-ion bombardment

Palinkas, J.; Sarkadi, L.; Schlenk, B.; Török, I.; Kalman, G.; Bauer, C.; Brankoff, K.; Grambole, D.; Heiser, C.; Rudolph, W.; Thomas, H. J.

The angular distributions of the L x-ray line intensities of gold have been measured by nitrogen-ion bombardment in the 3.0-18.2 MeV energy region. From the measured data absolute subshell ionisation cross sections and the anisotropy parameter of the Ll x-ray line have been deduced. Comparing the experimental data with the first-order perturbation theories significant deviations have been found, especially for the L2-subshell ionisation cross section and for the anisotropy parameter of the Ll x-ray line.

  • Journal of Physics B 17(1983), 131-145

Publ.-Id: 11273

CO2 laser nitriding of titanium

Raaif, M.; El-Hossary, F. M.; Negm, N. Z.; Khalil, S. M.; Kolitsch, A.; Möller, W.; Höche, D.; Kaspar, J.; Schaaf, P.; Mändl, S.

Samples of pure titanium were laser nitrided by continuous wave CO2 laser irradiation in mixtures of nitrogen and argon gas with different ratios. In all cases, TiN formed in the surface. The properties and the characteristics of the processed samples were evaluated using nanoindentation technique, optical microscopy, surface roughness measurements, X-ray diffraction and wear resistance measurements. It was found that the nitrogen content in the gas atmosphere has a massive effect on the microstructure and the mechanical properties of the laser nitrided samples. For all treated samples, the mechanical properties are improving with the nitrogen content in the gas atmosphere. Moreover, the thickest TiN layers with high values of the microhardness and good wear resistance were obtained for the titanium sample that was treated in 80% N2 and 20% Ar. In addition, the strain and the grain size of the coatings formed at the surface of the laser nitrided titanium samples were determined from X-ray data.

Keywords: laser nitriding; TiN

  • Journal of Physics D: Applied Physics 41(2008), 085208

Publ.-Id: 11272

Ion implantation followed by laser/pulsed plasma/ion beam annealing: a new approach to fabrication of superconducting MgB2 thin films

Piekoszewski, J.; Werner, Z.; Barlak, M.; Kolitsch, A.; Szymczyk, W.

The paper presents a new approach to formation of superconducting MgB2 thin films: ion implantation followed by annealing in an unconventional second step treatment using pulsed laser, plasma, or ion beams. Merits and drawbacks of individual approaches are discussed.

Keywords: superconductivity

  • Nukleonika 53(2008)1, 7-10

Publ.-Id: 11271

Infrared spectroscopic identification of aqueous neptunium species

Müller, K.; Foerstendorf, H.; Brendler, V.

In the safety assesment of underground disposal of radioactive waste neptunium (Np) is one of the most relevant radionuclides. Due to its long half-life, its hazardous to human health and its mobility under aerobic conditions Np-237 is considered as a possible long-term pollutant of the ecosystem from the safety point of view. The distribution of aqueous neptunium species, as there are the free neptunyl ions of Np(V) and Np(VI) and various complexes arising from hydrolysis or carbonate complexation, primarily defines its geochemical reactions and migration behavior in the environment.

Current knowledge about Np speciation is mainly based on data obtained by non-structural experiments such as potentiometric titration [1]. A spectroscopic verification of these Np species is still incomplete. There are only few EXAFS and Raman spectroscopic studies [2-4], using very high Np concentrations. Attenuated Total Reflectance Fourier-transform Infrared (ATR-FTIR) spectroscopy is a useful technique for the identification of different molecular species and it allows the direct measurement of liquid samples to obtain important spectral information even at low neptunyl concentrations relevant to environmental conditions.

In this study we investigate the Np speciation in aqueous solution using ATR-FTIR spectroscopy focusing on micromolar neptunyl concentrations. We work with varied experimental conditions, i.e. Np oxidation state (Np(V) and Np(VI)), wide pH range (pH 2 – 10), inert gas atmosphere, ionic strength. We present the first IR spectra of aqueous Np solutions and compare our results critically to thermodynamic calculations.

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

  • Lecture (Conference)
    V Ibero-American Congress of Environmental Physics and Chemistry, 14.-18.04.2008, Mar del Plata, Argentina
  • Contribution to proceedings
    V Ibero-American Congress of Environmental Physics and Chemistry, 14.-18.04.2008, Mar del Plata, Argentina
    Las Fronteras de la Física y Química Ambiental en Ibero América: libro de actas del V congreso iberoamericano de física y química ambiental, Buenos Aires, Argentina: Universidad Nacional de San Martin, 978-987-1435-05-0, 39

Publ.-Id: 11270

Enhanced electric dipole strength below particle-threshold as a consequence of nuclear deformation

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

Photoabsorption cross sections up to the neutron-separation energy were measured for the stable even-mass isotopes 92-100Mo in photon-scattering experiments. The photon-scattering data were analyzed in a novel way by taking into account the intensity of unresolved levels at high excitation energy and high level density. Simulations of gamma-ray cascades were performed to estimate the intensity distribution of inelastic transitions to low-lying levels and, hence, to deduce intensities and branching ratios of the ground-state transitions needed for the determination of the absorption cross section. The present (gamma,gamma') data can be combined for the first time with (gamma,n) data which allows us to obtain the absorption cross section in the energy range from about 4 MeV up to the giant dipole resonance for a series of isotopes. The absorption cross section below the neutron-separation energy increase with the number of neutrons above the neutron shell closure at N = 50. Calculations using a quasiparticle-random-phase approximation in a deformed Woods-Saxon potential describe this effect as a consequence of the increasing nuclear deformation.

Keywords: photon scattering; photoabsorption cross section; dipole strength function; nuclear deformation; random phase approximation

Publ.-Id: 11269

Sorption von U(VI) in Abwesenheit und Gegenwart von Huminsäure an Kaolinit und Opalinuston

Joseph, C.

Die Sorption von Uran(VI) an Kaolinit in Abhängigkeit der Ionenstärke und des Salzsystems (NaClO4, Opalinustonwasser) wurde untersucht. Zusätzliche Uran(VI)-Sorptionsversuche fanden in Abwesenheit oder Gegenwart von C-14-markierter Huminsäure statt. Die Huminsäuresorption an Kaolinit wurde zusätzlich untersucht. Erste Ergebnisse zur Uran(VI)-Sorption an Opalinuston (optimales S/L-Verhältnis) konnten vorgestellt werden.

Keywords: uranium(VI); humic acid; kaolinit; opalinus clay; sorption

  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 01.-02.04.2008, München, Germany

Publ.-Id: 11268

Komplexierung von U(VI) durch stickstoffhaltige Modellliganden

Raditzky, B.

Im Vortrag werden Ergebnisse zur spektroskopischen Bestimmung von Stabilitätskonstanten für die U(VI)-Komplexierung durch organische Modellliganden vorgestellt. Insbesondere werden die stickstoffhaltigen Liganden Anthranilsäure und Nicotinsäure betrachtet.

Keywords: Uran; hexavalent; Benzolsulfonsäure; 4-Phenolsulfonsäure; Anthranilsäure; Nicotinsäure; TRLFS

  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 01.-02.04.2008, München, Germany

Publ.-Id: 11267

Current without external bias and diode effect in shuttling transport of nanoshafts

Morawetz, K.; Gemming, S.; Luschtinetz, R.; Eng, L. M.; Seifert, G.; Kenfack, A.

A row of parallely ordered and coupled molecular nanoshafts is shown to develop a shuttling transport of charges at finite temperature. The appearance of a current without applying an external bias voltage is reported as well as a natural diode effect allowing unidirectional charge transport along one field direction while blocking the opposite direction. The zero-bias voltage current appears above a threshold of initial thermal and/or dislocation energy.

Keywords: Current without bias; ratchets; OFET; nanotubes; shuttling transport

  • Open Access Logo New Journal of Physics 10(2008)103014, 1-8

Publ.-Id: 11266

International Co-operation in Research - a German View onto the Challenges of Management

Joehnk, P.; Gilge, B.

Actually there is a worldwide competition for the best ideas and for the best outcome. By now large-scale equipment for research is so expensive, that it’s nearly impossible to buy and run it single nations going it alone. A way out are international co-operation. Thereby appear a lot of new questions that concern particularly the management of such co-operation. The author gives a review about the requirements of research co-operation, some examples from a German institution and the management of programmes and projects. Also the author points out the importance of co-operation for evaluation.

Keywords: International co-operation; Reqiurements of research co-operation; Role of the State; Management of programmes; Management of projects; Evaluation; Management

  • Contribution to proceedings
    Technical Universities: Integration with European and World Education Systems, 22.-24.04.2008, Izhevsk, Russia, 978-5-7526-0353-2, 12-19

Publ.-Id: 11265

A new database on the evolution of two-phase flows in a large vertical pipe

Lucas, D.; Beyer, M.; Szalinski, L.; Schütz, P.

A comprehensive database with high quality was obtained for stationary upward air-water flows in a vertical pipe with an inner diameter of 195.3 mm using the wire-mesh sensor technology. During the experiments the sensor was always mounted on the top of the test section while the distance between gas injection and measuring plane was varied to up to 18 different L/D by using gas injection chambers at different vertical positions. The gas was injected via holes in the pipe wall. The pressure was kept at 0.25 MPa (absolute) at the location of the active gas injection while the temperature was constant at 30°C 1K. This procedure exactly represents the evolution of the flow along the pipe, as it would be observed for an injection at a constant height position and a shifting of the measurement plane. The experiments were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for water and 0.0025 m/s to 3.2 m/s for air. From the raw data time averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size and the radial profiles of the gas velocity were calculated. Due to the combination of the new experimental procedure with the high spatial and temporal resolution of the wire-mesh sensor technology the data are have new quality especially regarding their consistency in the evolution with increasing L/D. This closes a gap for data suitable for the development and validation of closure models for two-phase flows and especially for models on bubble coalescence and break up.

Keywords: multiphase flow; bubbly flow; churn turbulent flow; annular flow; bubble size; pipe flow

  • International Journal of Thermal Sciences 49(2010), 664-674

Publ.-Id: 11264

Reduction of antimony by nanoparticulate magnetite and mackinawite

Kirsch, R.; Scheinost, A. C.; Rossberg, A.; Banerjee, D.; Charlet, L.

Speciation of Sb is strongly influenced by its oxidation state (V, III, 0, -III). Redox processes under anerobic groundwater conditions may therefore greatly alter the environmental behavior of Sb. Employing X-ray absorption and photon spectroscopy, we show here that Sb(V) is reduced to Sb(III) by magnetite and mackinawite, two ubiquitous Fe(II)-containing minerals, while Sb(III) is not further reduced. At the surface of magnetite, Sb(III) forms a highly symmetrical sorption complex at the position else occupied by tetrahedral Fe(III). The Sb(V) reduction increases with pH, at values above pH 6.5 Sb(V) is completely reduced to Sb(III) within 30 days. In contrast, Sb(V) is completely reduced at the mackinawite surface across a wide pH range and within 15 days. Sb(V) reduction proceeds solely by oxidation of surface Fe(II), while the oxidation state of sulfide is conserved. Independent of whether Sb(V) or Sb(III) was added, an amorphous or nanoparticulate SbS3-like solid forms.

Keywords: antimony; reduction; Fe(II); magnetite; mackinawite

  • Mineralogical Magazine 72(2008)1, 185-189
  • Contribution to proceedings
    Geochemistry of the Earth's Surface 8 (GES8), 18.-22.08.2008, London, UK
    abstracts published in "Mineralogical Magazine"
  • Poster
    Geochemistry of the Earth's Surface 8 (GES8), 18.08.2008, London, UK

Publ.-Id: 11262

Reduction of antimony by nanoparticulate Fe3O4 and FeS

Kirsch, R.; Scheinost, A. C.; Rossberg, A.; Banerjee, D.; Charlet, L.

Antimony finds a wide range of industrial applications, e.g. in flame retardants, brake pads and as a lead-alloy in storage batteries and ammunition and is widely distributed in the environment. Sb may occur in several oxidations states (-III, 0, III, V). Under oxic conditions, Sb0 oxidizes prevalently to SbV, forming the anionic species Sb(OH)6- which is strongly sorbed by Fe oxides[1]. In contrast, SbIII forms an uncharged complex Sb(OH)3(aq), which is more mobile. Under anoxic conditions, SbV and SbIII may be reduced by FeII-bearing minerals. Magnetite (FeIIFeIII2O4) and mackinawite (FeS) have been shown to reduce e.g. Se[2], As[3], and Pu[4]). We therefore investigated the reaction of SbIII and SbV with these two minerals at <1ppm O2 (v/v) using Sb-K XAS.
When SbIII was reacted with magnetite at pH 4.7 to 7.6 during 1 h to 67 d, the oxidation state was stable and only one Sb species was identified by EXAFS. SbIII is coordinated with 4 to 5 iron atoms at a distance of 3.6 Å. FEFF Monte Carlo simulations revealed formation of a highly ordered surface complex on the {111} faces of magnetite. The trigonal pyramidal SbO3 units occupy positions of FeIII tetrahedra, that would be ideally coordinated to six Fe06 octahedra via corner-sharing. The experimental Fe coordination numbers below six suggest that Sb occupies positions near edges of the {111} faces. When SbV was reacted with magnetite, reduction to SbIII increased linearly between pH 4.5 and 6.5, with little influence of reaction time. The SbIII produced by the surface reaction formed the same surface complex as after direct addition of SbIII.
In the presence of mackinawite, SbV was completely reduced to SbIII within 30 d and in the pH range 4.3 - 8.4. The local structure shows SbIII surrounded by three sulfur atoms at a distance of 2.5 Å as in Sb2S3. The lack of more distant atomic shells suggests a highly dissordered structure. Again the resulting surface complex is the same as after direct addition of SbIII. Cryo-XPS measurements of shock-frozen samples show that the S 2p spectra remain unchanged before and after SbV reduction, while a FeIII-shoulder emerged in the Fe 2p spectra after reduction, indicating that SbV was reduced by FeII and not by S. In no case, reduction to an oxidation state below III was observed.

[1] Scheinost et al., Geochim. Cosmochim. Acta 70 (2006) 3299-3312. [2] Scheinost & Charlet, Environ. Sci. Technol. (2008) online. [3] Gallegos et al., Environ. Sci. Technol. 41 (2007) 7781-7786. [4] Powell et al., Environ. Sci. Technol. 38 (2004) 6016-6024.

Keywords: antimony; reduction; mackinawite; magnetite

  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A476

Publ.-Id: 11261

Electronic transport in magnetically ordered Mn5Si3Cx films

Gopalakrishnan, B.; Sürgers, C.; Montbrun, R.; Singh, A.; Uhlarz, M.; von Löhneysen, H.

Mn5Si3Cx films exhibit antiferromagnetic or ferromagnetic behavior depending on the carbon doping level x. We report a detailed electronic-transport study of films prepared with different x. All films exhibit metallic behavior of the temperature-dependent resistivity ρ(T) with a logarithmic increase towards low temperatures attributed to the structural disorder and the accompanied scattering of conduction electrons by two-level systems. Below 1 K, the Kondo-type behavior ρ(T)~−ln T shows a crossover to Fermi-liquid behavior ρ−T2 independent of the type of magnetic order. The magnetoelectronic properties such as Hall effect and magnetoresistance show clear differences characteristic for the different magnetically ordered phases, i.e., antiferromagnetic vs ferromagnetic.

  • Physical Review B 77(2008), 104414

Publ.-Id: 11260

The Atomic Layer Deposition of HfO2 and ZrO2 using advanced metallocene precursors and H2O as an oxidant

Dezelah, C. L.; Niinistö, J.; Kukli, K.; Munnik, F.; Lu, J.; Ritala, M.; Leskelä, M.; Niinistö, L.

The atomic layer deposition of HfO2 and ZrO2 thin films was investigated using (CH3C5H4)2Hf(CH3)2, (CH3C5H4)2Hf(OCH3)(CH3), (CH3C5H4)2Zr(CH3)2, and (CH3C5H4)2Zr(OCH3)(CH3) precursors at deposition temperatures between 300 and 500 °C using water vapor as the oxidant. A surface-limited growth mechanism was confirmed at 350 °C for all metal precursors examined. The processes provided nearly stoichiometric HfO2 and ZrO2 films with carbon and hydrogen concentrations below 0.5 and 1.0%, respectively, for representative samples. All films were polycrystalline as deposited and possessed a thin interfacial SiO2 layer. The capacitance-voltage and current density-voltage behavior is reported and discussed for capacitor structures containing films from this study.

Keywords: ALD; hafnium oxide; zirconium oxide; cyclopentadienyl (Cp) complexes; high-k dielectric

Publ.-Id: 11259

Prozessautomatisierung des Versuchsstandes TOPFLOW des Forschungszentrums Dresden Rossendorf

Lenk, S.; Carl, H.; Beyer, M.

Der Vortrag beschreibt das Steuerungs- und Messdatenerfassungssystem der Versuchsanlage TOPFLOW. Beginnend bei der ursprünglichen Konfiguration des Automatisierungssystems werden die bis heute ausgeführten Erweiterungen und Optimierungen ausführlich erläutert. Des Weiteren beinhaltet der Vortrag Erklärungen zu den an TOPFLOW eingesetzten Hardware- und Softwarelösungen. Außerdem werden die Systemdokumentation und Maßnahmen zur Qualitätssicherung erklärt. Ausgewählte Beispiele zur Anlageninstrumentierung und Erläuterungen zur online Berechnung wichtiger thermo-physikalischer Stoffdaten schließen den Beitrag ab.

Keywords: process automation; OPC interface; ethernet communication; interbus

  • Lecture (others)
    Frühjahrstagung der Studiengruppe für Elektronische Instrumentierung, 07.-09.04.2008, Karlsruhe, Deutschland

Publ.-Id: 11258

Speciation and coordination of U(VI) and U(IV) sulfate in aqueous solution

Hennig, C.

The abandoned uranium mine Königstein near Dresden/Germany, where uranium ore has been leached by sulfuric acid, is even nowadays concerned from the problem of heavy metal mobility affecting adjacent aquifers used for recovering drinking water. A rising interest can be observed worldwide to use such in situ leaching techniques to obtain uranium from ore mines. At the other hand, the thermodynamics of uranium in presence of high sulfate concentration is actually not well understood, especially under reduced conditions. The extended Debye-Hückel formalism, commonly used to estimate the species distribution and to correct activity coefficients, is above the validity limit in case of high ionic strength originated by the sulfuric acid. The specific ion interaction theory (SIT) and the Pitzer model are useful at higher ionic strengths but partly not to the extent in the directly concerned rock areas. In this study were combined therefore EXAFS, HEXS, XRD, TRLFS and UV-vis spectroscopy to extract the species distribution and the coordination of U(VI) and U(IV) sulfate complexes from model systems with low pH values and high sulfate concentrations [1-3]. For that purpose a spectro-electrochemical cell has been constructed that allowed the investigation of the solutions under controlled redox conditions. The study revealed that in contrast to neutral pH conditions, where U(VI) is highly soluble but U(IV) is nearly insoluble, even U(IV) becomes highly soluble at low pH by forming stable complexes resulting in an enlarged migration capacity.

[1] C. Hennig, K. Schmeide, V. Brendler et al.: EXAFS investigation of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution. Inorg. Chem. 46, 5882 (2007).
[2] C. Hennig, W. Kraus, F. Emmerling et al.: The coordination of a U(IV) sulfate monomer in aqueous solution and in solid state, Inorg. Chem. 47, 1634, (2008)
[3] C. Hennig, A. Ikeda, K. Schmeide et al.: The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution. Radiochim. Acta, submitted.

Keywords: Uranium; Sulfat; U(IV); U(VI); EXAFS; HEXS; XRD; TRLFS; UV-vis

  • Lecture (Conference)
    Uranium Mining and Hydrogeology V, 14.-18.09.2008, Freiberg, Germany

Publ.-Id: 11257

Coordinatiom of actinides in aqueous sulfate solution

Hennig, C.; Ikeda, A.; Tsushima, S.; Le Naour, C.; Den Auwer, C.; Wilson, R.

Structural information on the sulfate coordination of actinides in aqueous solution is actually rather scarce. At the other hand there is often a high sulfuric acid concentration in the environment mines containing pyrite, because pyrite, exposed to aerobic conditions, undergoes a weathering followed by sulfuric acid release. An artificial source of sulfate in natural environment is in situ leaching, so-called solution mining, where sulfuric acid is injected into the ore deposit, as has been used especially for uranium mining in sandstone formations. Due to the lack of information on the coordination of sulfate with actinides in aqueous solution, we investigated Th(IV), Pa(V), U(IV), U(VI), Np(IV), Np(V) and Np(VI) complexes in aqueous sulfate solution by L3-edge EXAFS, high energy x-ray scattering (HEXS), and UV-Vis spectroscopy using samples of 10-50 mM of actinide and total sulfate concentrations, 0.05 ≤ [SO42-] ≤ 10 M. In contrast to the coordination of actinides with carbonate where bidentate coordination always prevails, the coordination with sulfate comprises monodentate and bidentate linkage with a wide variety of combinations. In general, with increasing [SO42-]/[Ann+] ratio the bidentate coordination becomes dominant in solution. As example, at low [SO42-]/[UO22+] ratio, where the UO2SO4(aq) species prevails, the sulfate coordinates in a monodentate and only to a less extend in bidentate fashion. At high [SO42-]/[UO22+] ratio, where UO2(SO4)22- species prevails, bidentate sulfate coordination with the species [UO2(SO4)2bid]2- becomes dominant [1]. In oxidation state IV, up to five coordinating sulfate groups have been observed, mostly with predominant bidentate coordination as for example in the high-charged complex [U(SO4bid)3(SO4mon)2]6- [2]. Pa(V) shows in high excess of sulfate a coordination of monodentate and bidentate sulfate, e.g. the complex [PaO(SO4bid)2(SO4mon)3]7- [3]. Np(IV) and Np(VI) follows the tendency of U(IV) and U(VI), whereas Np(V) is weakly coordinated by sulfate, in accordance with its low formation constant. The attempt to preserve solution species in crystal structures led in most of the cases to a rearrangement of bidentate sulfate groups in solution to monodentate–bridging coordination in solid state. The coordination of the solution complexes was optimized by DFT calculation and the results were compared with the experimental observations.

[1] C. Hennig, K. Schmeide, V. Brendler, H. Moll, S. Tsushima, A.C. Scheinost, Inorg. Chem. 46, 5882, 2007.
[2] C. Hennig, W. Kraus, F. Emmerling, A. Ikeda, A.C. Scheinost, 47, 2987, 2008
[3] C. Le Naour, D. Trubert, M.V. Di Giandomenico, C. Fillaux, C. Den Auwer, P. Moisy,C. Hennig, Inorganic Chemistry 44, 9542, 2005

Keywords: Th; Pa; U; Np; sulfate; EXAFS; HEXS; UV-vis; XRD

  • Lecture (Conference)
    Plutonium Futures "The Science" 2008, 07.-11.7.2008, Dijon, France

Publ.-Id: 11256

Infrared absorption strengths of ion-implanted hydrogenated amorphous silicon

Danesh, P.; Pantchev, B.; Schmidt, B.

Silicon and hydrogen ion implantations have been used to affect the absorption of the infrared stretching modes in hydrogenated amorphous silicon (a-Si:H). Hydrogen ions have been implanted with ion energy of 16 keV and the doses in the range of 2.2 x 1014 -7.2 x 1016 cm-2. Silicon ion implantation has been carried out with the energy of 160 keV and the doses in the range of 9.5 x 1012 cm-2 -1.7 x 1015 cm-2. The a-Si:H films have been prepared by plasma-enhanced chemical vapor deposition. Nuclear reaction analysis has been used for the determination of the hydrogen concentration in the as-deposited and ion-implanted samples. It has been established that the values of the absorption strengths of stretching modes of the isolated monohydrides, A(2000), and clustered hydrogen forms, A(2100), are not equal and remain constant for all ion implantation doses. A(2100) has been considered as a weighted average of the absorption strengths of polyhydrides and clustered monohydrides, A(2100,SiHx) and A(2100,(SiH)n). It has been established that the ion implantation does not induce any change in the ratio between polyhydrides and clustered monohydrides. It has been suggested that the absorption strengths do not vary when a post-deposition treatment of samples is associated with the introduction of structural defects in the amorphous silicon network.

Keywords: hydrogenated amorphous silicon; ion implantation; infrared absorption spectroscopy; nuclear reaction analysis

  • Thin Solid Films 516(2008)10, 3383-3386

Publ.-Id: 11255

Bacteria –Actinide Interactions: an Environmental Perspective

Merroun, M.; Selenska-Pobell, S.

Soils, sediments, and waters heavily polluted with radionuclides and other toxic metals, are a reservoir of unusual bacteria well adapted to these toxic environments. These bacteria possess fascinating mechanisms for interaction with and bio-transformation of radionuclides and other heavy metals, thus regulating the mobility of the metals in the environment. Microorganisms can mobilize radionuclides and metals through autotrophic and heterotrophic leaching, chelation by microbial metabolites and siderophores, and methylation, which can result in volatilization. Conversely, immobilization can result from sorption to cell components or exopolymers, intracellular sequestration, or precipitation as insoluble organic and inorganic compounds, e.g. oxalates, sulfides, or phosphates. The present work is intended to give a brief overview of the key processes implicated in the interaction of uranium with bacterial strains isolated from different extreme environments including uranium mining waste piles as well as groundwater of a radioactive repository. For this purpose, a combination of spectroscopic (EXAFS, XANES, TRLFS), microscopic (TEM), microbiological and wet chemistry techniques is used. Elucidating the interaction mechanisms microbe/metals is helpful for understanding the role which bacteria play in the transport and mobility of toxic metals in the environment as well as their biotechnological application in the bioremediation of heavy metal contaminated waters.

  • Lecture (Conference)
    38èmes Journées des Actinides 2008, 12.-15.04.2008, Wroclaw, Poland

Publ.-Id: 11254

Search for exotics in γD => φnp reactions near threshold

Titov, A. I.; Kämpfer, B.

We discuss coherent and incoherent -meson photoproduction off the deuteron at low energy and small momentum transfer with the aim to check whether the recent experimental data need for their interpretation an inclusion of exotic channels. Our analysis of the differential cross-section and spin-density matrix elements shows that new data on the D → X reaction at Eγ ∼ 2GeV may be understood on the basis of conventional dynamics.

Publ.-Id: 11253

Untersuchung von lateralen und vertikalen Elementverteilungen mittels Kernmikrosonde

Grambole, D.; Herrmann, F.; Klabes, R.; Böhmert, J.; Klemm, W.; Plier, F.

Die Kernmikrosonde, die am 5 MV Tandembeschleuniger des Zentralinstituts für Kernforschung Rossendorf installiert ist und über eine laterale Auflösung von ca. 4 µm für 3 MeV Protonen verfügt, wurde zur Mikrobereichsanalytik in der Medizin, Werkstofforschung und Geologie eingesetzt. Tiefenprofile von F im menschlichen Zahnschmelz und von O in Zr-Legierungen wurden bestimmt. Mikroeinschlüsse fester und flüssiger Phasen im Quarz wurden ebenfalls analysiert.

Investigation of lateral and vertical element distributions by means of nuclear microprobe:
The nuclear microprobe at the5 MV tandem accelerator of the Central Institute for Nuclear Research Rossendorf with a lateral resolution of about 4 µm for 3 MeV protons was used for microanalysis in medicine, material science, and geology. Depth profiles of F in human tooth enamels and of O in Zr alloys were determined. Microinclusions of solid and fluid phases in quartz were also investigated.

  • Beiträge zur elektronenmikroskopischen Direktabbildung und Analyse von Oberflächen 23(1990), 263-266

Publ.-Id: 11252

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