Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
New developments concerning the fluorine effect for TiAl-alloys
Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.;
The fluorine effect improves the oxidation resistance of TiAl-alloys drastically. The formation of a non protective fast growing mixed oxide scale is suppressed and instead a protective alumina layer is formed after fluorine treatment. Fluorine can be applied by several methods which, however, have to be optimised. An overdoping can lead to enhanced oxidation and worsen the situation. The parameters for an optimised process will be described. An improvement of the already good performance of specimens treated only with fluorine can be achieved e.g. by dipping in inorganic acids containing additional elements to fluorine. The results of high temperature oxidation tests of differently treated TiAl-samples will be presented. Post experimental metallographic investigations reveal the oxide scales formed so that the effect can be rated. Finally the results will be discussed in the view of the models for the fluorine effect.
  • Lecture (Conference)
    European Congress and Exhibition on on Advanced Materials and Processes (EUROMAT 2011), 12.-15.09.2011, Montpellier, France

Publ.-Id: 16278 - Permalink


Development and characterization of advanced coatings for TiAl alloys
Pelic, B.; Bortolotto, L.; Goldberg, S.; Witschel, B.; Rafaja, D.; Masset, P. J.; Donchev, A.; Yankov, R.; Kolitsch, A.; Schütze, M.;
Titanium aluminides exhibit quite good mechanical properties even at elevated temperatures for aeronautic and automobile applications. Their low specific density (half of classical nickel based super alloys) makes them attractive for applications where the mass is a critical parameter, i.e. rotating pieces. At elevated temperatures they suffer of environmental embrittlement by hot gases, which deteriorates drastically their mechanical properties and still hampers their use to temperatures above 500°C in industrial applications. In this work, coatings involving reactive elements such Cr, Y combined with the halogen effect (fluorine surface treatment) have been developed using MO-CVD, CVD, PVD and HVOF techniques. The coatings were characterized as produced and after annealing by means of glancing XRD, GDEOS to analyze their structure, homogeneity and composition, respectively. The adhesion properties of the coatings were measured by using impact tests before and after oxidation. The oxidation behavior of the produced coatings was evaluated in the temperature range of the industrial use, e.g. 600-850°C whereas corrosion tests were conducted using Na2SO4-NaCl mixtures in dry and wet environments. After oxidation/corrosion test post-mortem analysis was carried out using SEM-EDX, EPMA analysis to investigate the oxide layer composition, structure and the corrosion products, respectively. Mechanical properties losses of coated specimens after oxidation/corrosion due to embrittlement were evaluated using 4 point bending test combined with acoustic emission. It was shown that some of the developed coatings reduce the embrittlement sensibility of these alloys.
Keywords: TiAl alloys, coatings, CVD, PVD, HVOF, high temperature oxidation/corrosion
  • Poster
    European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2011), 12.-15.09.2011, Montpellier, France

Publ.-Id: 16277 - Permalink


Surface engineering of Ti and low-Al content Ti-base alloys for high-temperature environmental protection
Yankov, R. A.; Kolitsch, A.; von Borany, J.; Mücklich, A.; Munnik, F.; Steinert, M.; Frenzel, C.; Donchev, A.; Schütze, M.;
An oxygen barrier coating has been developed, which is effective in preventing oxidation and oxygen embrittlement of Ti and several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures. The fabrication process has involved magnetron co-sputtering of titanium and aluminum followed by vacuum annealing and plasma immersion ion implantation of fluorine. The resulting coating consists primarily of γ-TiAl while containing a minor portion of Ti3Al present in the coating/substrate interfacial region. The implantation of fluorine provides the necessary conditions for triggering the halogen effect upon subsequent high-temperature exposure in air. Systematic characterization of the coating material in terms of microstructure, phase formation and element depth distribution has been performed using cross-sectional transmission electron microscopy (XTEM) in conjunction with electron energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and elastic recoil detection (ERD). Overall, the coating fabrication process has been found to be independent of the substrate material making the technique universally applicable at least to the alloys studied. Following oxidation in air at 600°C for 100 h, specimens have been prepared for metallographic analysis, and their cross sections have been characterized by scanning electron microscopy (SEM) in combination with EDX, and electron probe microanalysis (EPMA). The results obtained show that during oxidation exposure the γ-TiAl coating is capable of forming a protective alumina-containing scale, which serves as an oxygen barrier, thereby preventing oxygen embrittlement in the substrate material. In addition, since the only constituents of the coating are Ti and Al, it exhibits excellent chemical substrate compatibility.
  • Poster
    Dresdner Werkstoffsymposium "Werkstoffe für die Mobilität", 08.-09.12.2011, Dresden, Germany

Publ.-Id: 16276 - Permalink


Magneto-optical observation of four-wave scattering in a 15-nm Ni81Fe19 film during large-angle magnetization precession
Nembach, H. T.; Livesey, K. L.; Kostylev, M. P.; Martin-Pimentel, P.; Hermsdoerfer, S. J.; Leven, B.; Fassbender, J.ORC; Hillebrands, B.
Large-angle magnetization precession induced by a short pulsed magnetic field in a 15-nm thick Ni81Fe19 film is observed by use of a time-resolved magneto-optical Kerr effect technique with sensitivity to all three components of the magnetization vector. A reduction of the magnitude of the magnetization vector |M| during large-angle precession is inferred and indicates incoherent dynamics due to excitation of traveling spinwaves with wavelengths smaller than the diameter of the sampling area, that is, the laser spot size for the magneto-optical measurements. The reduction in |M| depends on the magnetic bias field Hbias, which can be qualitatively understood by comparison to the theoretical threshold for observing four-magnon scattering in a small time interval t. We estimate that two-magnon scattering cannot explain the experimental results.

Publ.-Id: 16275 - Permalink


Radiolabelling of commercial Ag0 and TiO2 nanoparticles with 110mAg and 44Ti for life-cycle studies
Hildebrand, H.; Franke, K.;
Vortrag im Rahmen eines Workshops, kein gesonderter Abstract vorhanden.
Dieser Workshop beschäftigt sich speziell mit der Radiomarkierung von Nanopartikeln. Eigene Ergebnisse sollen mit Fachkollegen aus ganz Europa diskutiert werden. Ziel ist es auch, ggf. neue Kooperationen anzubahnen.
  • Lecture (Conference)
    CYCLEUR Workshop, 28.-29.11.2011, Ispra, Italia

Publ.-Id: 16274 - Permalink


Interactive calibration and registration of electromagnetic trackung systems for Virtual Reality
Skripcak, T.; Tanuska, P.; Schmeißer, N.;
This article is aimed on the calibration and registration of electromagnetic tracking system for the purpose of immersive virtual reality application. The first part of the article provides a basic introduction into position and orientation tracking subsystems and denotes problems which are occurring while electromagnetic approach is used for tracking purposes. After that two methods for tracking system calibration are presented and also a solution for position registration of tracking systems with projection space is provided. Second part is focused on interactive calibration application, where the process of development and a resulting application structure is described. Finally results obtained by usage of interactive calibration application are compared. The main goal of this article is to present a way of dealing with static errors in virtual reality application in order to obtain proper alignment of the virtual and real world.
Keywords: virtual reality, electromagnetic tracking system, calibration, registration
  • Contribution to proceedings
    IDS - INTERNATIONAL DOCTORAL SEMINAR, 15.-17.5.2011, Smolenice, Slovakia
    International Doctoral Seminar 2011 : Proceeding. Smolenice Castle, SR, Trnava: AlumniPress, 978-80-8096-145-9, 365-375

Publ.-Id: 16273 - Permalink


Design and Implementation of Interactive Visualisation Configuration using Interaction Paradigms in Virtual Reality Environment
Skripcak, T.; Tanuska, P.; Schmeißer, N.;
This article is aimed on the specific task of interaction with an immerse visualisation application. The first part of the article provides basic introduction into interaction paradigms in 3D space. After that classification and description of standard interaction tasks are presented. We introduce our view of matter on relations between the 3D interaction and standard interaction techniques. The second part describes hardware and software components of our VR system. Furthermore an overview of the architecture and implementation details of system for interactive visualisation configuration is discussed. We describe design specifications of a 3D UI, which helps to make interaction less error prone for inexperienced users. A specific solution for performing numerical input is also provided. The main goal of the article is to describe how 3D user interface paradigms can be implemented in the VR system.
Keywords: VirtualReality visualization, 3d interaction
  • Open Access LogoInternational Journal of Soft Computing and Engineering (IJSCE) 1(2011)5, 57-65

Publ.-Id: 16272 - Permalink


TOPFLOW-Experimente, Modellentwicklung und Validierung von CFD-Codes für Wasser-Dampf-Strömungen mit Phasenübergang
Lucas, D.; Beyer, M.; Krepper, E.; Vallée, C.; Höhne, T.; Seidel, T.; Szalinski, L.; Hampel, U.; Schmidtke, M.; Schleicher, E.; Pietruske, H.; Schütz, P.; Danciu, D.; Zhang, D.; Deendarlianto; Barthel, F.; Zippe, C.; Hänsch, S.; Carl, H.; Weiß, F.-P.;
Das Ziel des Vorhabens bestand in der Ertüchtigung von CFD-Codes für Wasser-Dampf-Strömungen mit Phasenübergang. Während CFD-Verfahren für einphasige Strömungen bereits breite Anwendung in der Industrie finden, steht ein entsprechender Einsatz für Zweiphasenströmungen auf Grund der komplexen Phasengrenzfläche und den davon beeinflussten Wechselwirkungen erst am Anfang. Für die Weiterentwicklung und Validierung geeigneter Schließungsmodelle werden experimentelle Daten mit hoher Orts- und Zeitauflösung benötigt. Solche Daten wurden an der TOPFLOW-Versuchsanlage des HZDR durch Kombination von Experimenten bei praxisnahen Parametern für die Reaktorsicherheit (große Skalen, hohe Drücke und Temperaturen) und innovativer Messtechnik gewonnen. Die Gittersensortechnik, mit der detaillierte Informationen über die Phasengrenzfläche gewonnen werden können, wurde in adiabaten Wasser-Luft-Experimenten sowie Kondensations- und Druckentlastungsexperimenten in einem großen DN200-Rohr eingesetzt. Umfangreiche Datenbasen mit hoher Qualität stehen im Ergebnis des Vorhabens zur Verfügung. Die Technologie für die schnelle Röntgentomographie, die Messungen ohne Strömungsbeeinflussung ermöglicht, wurde weiter entwickelt und in einer ersten Messserie erfolgreich eingesetzt. Hochaufgelöste Daten wurden auch in Experimenten zu verschiedenen Strömungssituationen (z.B. Gegenstrombegrenzung) in einem Modell des heißen Strangs eines Druckwasserreaktors gewonnen. Für die Wasser-Dampf-Experimente bei Drücken von bis zu 5 MPa wurde dabei erstmals die neu entwickelte innovative Drucktanktechnologie eingesetzt. Zur Ertüchtigung von CFD-Codes für Zweiphasenströmungen wurde das Inhomogene MUSIG-Modell für Phasenübergänge in Kooperation mit ANSYS erweitert und anhand der o.g. TOPFLOW-Experimente validiert. Außerdem erfolgten Verbesserungen u.a. für die Turbulenzmodellierung in Blasenströmungen sowie Simulationen zur Validierung der Modelle für Blasenkräfte und Blasenkoaleszenz und -zerfall. Ein wesentlicher Fortschritt wurde bei der Modellierung freier Oberflächen durch die Verallgemeinerung des AIAD-Modells erreicht. Die am Heißstrangmodell ermittelten Flut¬kurven können unter Nutzung dieses Modells in guter Übereinstimmung berechnet werden.
Keywords: CFD, two-phase flow, safety research, experiment, model development, validation
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-011 2011
    ISSN: 1437-322X

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Publ.-Id: 16271 - Permalink


Cyclotron resonance and interband optical transitions in HgTe/CdTe(0 1 3) quantum well heterostructures
Ikonnikov, A.; Zholudev, M.; Spirin, K.; Lastovkin, A.; Maremyanin, K.; Aleshkin, V.; Gavrilenko, V.; Drachenko, O.; Helm, M.; Wosnitza, J.; Goiran, M.; Mikhailov, N.; Dvoretskii, S.; Teppe, F.; Diakonova, N.; Consejo, C.; Chenaud, B.; Knap, W.;
Cyclotron resonance spectra of 2D electrons in HgTe/CdxHg1−xTe (0 1 3) quantum well (QW) heterostructures with inverted band structure have been thoroughly studied in quasiclassical magnetic fields versus the electron concentration varied using the persistent photoconductivity effect. The cyclotron mass is shown to increase with QW width in contrast to QWs with normal band structure. The measured values of cyclotron mass are shown to be systematically less than those calculated using the 8 × 8 Kane model with conventional set of HgTe and CdTe material parameters. In quantizing pulsed magnetic fields (Landau level filling factor less than unity) up to 45 T, both intraband (CR) and interband magnetoabsorption have been studied at radiation wavelengths 14.8 and 11.4 µm for the first time. The results obtained are compared with the allowed transition energies between Landau levels in the valence and conduction bands calculated within the same model, the calculated energies being again systematically less (by 3–14%) than the observed optical transition energies.
Keywords: Semiconductors, cyclotron resonance, quantum wells, topological isolators

Publ.-Id: 16270 - Permalink


Thin film intermetallic compound formation by flash-lamp annealing: an implication of ultra-fast alloying and metallurgy
Yankov, R. A.; Kolitsch, A.; von Borany, J.; Munnik, F.; Voelskow, M.; Schumann, T.; Skorupa, W.; Donchev, A.; Schütze, M.;
Experiments have been undertaken to explore the possibility of rapidly melting and alloying thin metal films by flashlamp annealing (FLA). Aluminum layers of a thickness of 100 to 500 nm have been deposited on α-titanium substrates by magnetron sputtering. The structures have then been heat-treated by FLA in air using flash duration of 20 msec, energy density of 60 to 100 J/cm2, and maximal temperature of 800 to 1660°C. X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA) have been used for sample characterization. The as-deposited Al films are amorphous/nanocrystalline (grain size ~ 5 nm) in nature. Heat treatment by FLA has been found to produce an intermetallic TiAl3 phase. For comparison, under conditions of standard furnace annealing, the formation of this compound in the thin film reaction of Al and Ti necessitates anneal temperatures and times typically in excess of 400°C and 1 h, respectively. Furthermore, the intermetallic TiAl3 phase formed by FLA appears to be present in a region extending from the surface to a depth of a few hundred nm. Importantly, no pure Al phase has been detected either at the surface or in the substrate bulk. XRD measurements have also identified negligibly small amounts of Al and Ti oxide phases. It is expected that one may obtain TiAl phases other than TiAl3 by varying both the film composition (i.e. by co-depositing Al and Ti instead of Al only) and the FLA parameters. The results of this study indicate that FLA of thin metal films is a promising technique for rapid surface alloying and compound formation. For the particular case of the Ti/Al system, t he i ntermetal lc if il ms s o f abricated m ay h ave r el evance t o h igh-temperature m icroel ectronics applications (diffusion barriers, conduction lines etc) as well as to the oxidation protection of titanium and titaniumaluminum alloy surfaces by forming suitable intermetallic TiAl phases.
Keywords: rapid melting and alloying, FLA, intermetallic TiAl3 phase
  • Lecture (Conference)
    subtherm; International Topical Workshop on Subsecond Thermal Prosessing of advanced Materials, 25.-27.10.2011, Dresden, Deutschland

Publ.-Id: 16269 - Permalink


Interactions between GaO4Al12(OH)24(H2O)127+ and cellulosic materials
Sundman, O.; Persson, P.; Banerjee, D.; Ohman, L.-O.;
The adsorption qualities of GaO4Al12(OH)24(H2O)127+, a polycation with ε-Keggin structure, and its stability in contact with anionic cellulosic materials, was investigated under different concentration and ionic strength conditions. The cellulosic materials employed were two different fully bleached fibre materials, carboxyl methyl cellulose (CMC), and a spin coated cellulose model surface. As analytical techniques, pH-measurements, potentiometric titrations, ICP-OES, QCM-D, equilibrium calculations and Extended X-ray Absorption Fine Structure (EXAFS) were used. The adsorption is very strong and the addition of GaO4Al12(OH)24(H2O)127+ to a fibre suspension results in a rapid decrease in pH, followed by a small and slow increase in pH. This behaviour can be explained as due to a rapid and strong adsorption of intact GaO4Al12(OH)24(H2O)127+ ions, followed by a slow, and minor, 3-8 %, decomposition into different monomers. Alternative layer by layer adsorption of this ion, and CMC, on a spin coated cellulose model surface, constitutes further evidence for the strong interactions between the anionic cellulose materials and GaO4Al12(OH)24(H2O)127+. It is shown that the strong adsorption observed could not be described as due to an unspecific Donnan adsorption behaviour, neither of GaO4Al12(OH)24(H2O)127+ nor Ga and Al monomers, and specific surface complex formation is therefore discussed and applied.
Keywords: EXAFS, GaO4Al12(OH)24(H2O)127+, ionic exchange, Donnan equilibrium

Publ.-Id: 16268 - Permalink


Erfolgreich gegen Krebs – Präzisionsbestrahlungen mit Ionen
Fiedler, F.; (Editor)
no abstract available
  • Lecture (others)
    Physik am Samstag, 19.11.2011, Dresden, Deutschland

Publ.-Id: 16267 - Permalink


The complexation of uranium(VI) and atmospherically derived CO2 at the ferrihydrite-water interface probed by time-resolved vibrational spectroscopy
Foerstendorf, H.; Heim, K.; Rossberg, A.;
The sorption reactions of uranium(VI) at the ferrihydrite(Fh)-water interface were investigated in the absence and presence of atmospherically derived CO2 by time-resolved in situ vibrational spectroscopy. The spectra clearly show that a single uranyl surface species, most probably a mononuclear bidentate surface complex, is formed irrespective of the presence of atmospherically derived CO2. The character of the carbonate surface species correlates with the presence of the actinyl ions and changes from a monodentate to a bidentate binding upon sorption of U(VI). From the in situ sorption experiments under mildly acid conditions, the formation of a ternary surface complex is derived where the carbonate ligands coordinate bidentately to the uranyl moiety (≡UO2(O2CO)x). Furthermore, the release reaction of the carbonate ligands from the ternary surface complex is found to be considerably retarded compared to those from the pristine surface suggesting a tighter bonding of the carbonate ions in the ternary complex. Simultaneous sorption of U(VI) and atmospherically derived carbonate onto pristine Fh shows formation of binary monodentate carbonate surface complexes prior to the formation of the ternary complexes.
Keywords: Ternary surface complex, uranyl, carbonate, ferrihydrite, time-resolved spectroscopy, ATR FT-IR spectroscopy

Publ.-Id: 16266 - Permalink


High Conversion Th-U233 fuel assembly for current generation of PWRs
Baldova, D.; Fridman, E.;
This paper presents a preliminary design of a high conversion Th-U233 fuel assembly applicable for current generation of Pressurized Water Reactor (PWRs). The considered fuel assembly has a typical 17×17 PWR lattice. However in order to increase the conversion of Th232 to U233, the assembly was subdivided into the two regions called seed and blanket. The central seed region has a higher than blanket U233 content and acts as a neutron source for the peripheral blanket region. The latest acts as a U233 breeder. While the seed fuel pins have a standard dimensions the blanket fuel radius was increased in order to reduce the moderation and to facilitate the resonance neutron absorption in blanket Th232. The U233 content in the seed and blanket regions was optimized to achieve maximal initial to discharged fissile inventory ratio (FIR) taking into account the following constrains: 1) target fuel cycle length of 18 months assuming 3-batch reloading scheme, 2) during the fuel cycle the core k-eff should be higher or equal to 1. In this study the neutronic calculations were performed on the fuel assembly level using the Helios deterministic lattice transport code. The fuel cycle length and the core k-eff were estimated with the help of Non Linear Reactivity Model. The applicability of the Helios code for the analysis of the Th-based high conversion designs was confirmed with the help of continuous-energy Monte-Carlo code Serpent. The results of optimization studies show that for the heterogeneous seed and blanket (SB) fuel assembly the FIR of about 0.94 can be achieved.
Keywords: High Conversion Fuel Cycle, Seed-blanket fuel assembly
  • Contribution to proceedings
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA
  • Lecture (Conference)
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA

Publ.-Id: 16265 - Permalink


Influence of low uranium concentrations on Peanibacillus sp. JG-TB8 using calorimetric metabolic monitoring
Obeid, M.; Geissler, A.; Fahmy, K.; Oertel, J.;
The qualitative and quantitative risk assessment of radiotoxicity in contaminated sites plays a key role in radioecological monitoring and for environmental protection. High doses of radioactivity are physically measurable in the near field of nuclear waste disposals. However, it is a major challenge to develop methods for low dose risk assessments typical for the far field, where transmission of radionuclides into the food chain may lead to health risks that are not detectable by conventional methods. To address this problem, a novel approach using metabolic monitoring of bacterial cell growth was established using the Thermal Activity Monitor (TAMIII; TA intruments, USA) as a multichannel microcalorimeter to identify the minimal dose of radionuclides that generates a measurable change in metabolic heat release. In this approach, the toxicity of a radionuclide was defined as a measurable effect on the metabolic activity of Peanibacillus sp. JG-TB8, a gram-positive bacterium isolated from a soil sample of the uranium mining waste pile “Haberland” (Johanngeorgenstadt, Saxony, Germany). Liquid cultures of this strain were exposed to micromolar concentrations of uranium (VI) salts and the metabolic heat release measured as a function of time and temperature. The non-radioactive "heavy metal stress" exerted by europium (Eu(III)) served as reference under the same conditions. Preliminary results show distinct and reproducible effects of uranium and europium on the time-dependent heat release already at 10 µM concentration. The toxicity of uranium and europium caused a decrease of maximal heat flow compared to control samples. In contrast to europium, for which the inhibitory action scales with concentration, uranium influences bacterial growth in a more complicated manner which strongly depends on temperature and pH, probably as a consequence of its different speciations. The results demonstrate that microcalorimetric monitoring is an extremely sensitive tool to investigate the influence of low heavy metal and radionuclide concentrations on the metabolic activity of microorganisms as shown here for Peanibacillus sp. JG-TB8.
Keywords: radiotoxicity microcalorimetry heavy metal
  • Poster
    Uranium biogeochemistry: transformations and applications, 11.-16.03.2012, Monte Verita, Ascona, Switzerland

Publ.-Id: 16264 - Permalink


Long intersubband relaxation times in n-type germanium quantum wells
Ortolani, M.; Stehr, D.; Wagner, M.; Helm, M.; Pizzi, G.; Virgilio, M.; Grosso, G.; Capellini, G.; de Seta, M.;
We measured the non-radiative intersubband relaxation time in n-type modulation-doped Ge/SiGe multi-quantum wells of different thickness by means of degenerate pump-probe experiments. The photon energy was tuned to be resonant with the lowest conduction band intersubband transitionenergy (14-29 meV), as measured by terahertz absorption spectroscopy and in agreement with bandstructure calculations. Temperature-independent lifetimes in excess of 30 ps were observed.
Keywords: intersubband, germanium, free-electron laser, relaxation time, terahertz
  • Applied Physics Letters 99(2011), 201101

Publ.-Id: 16262 - Permalink


Revised Methods for Few-Group Cross Sections Generation in The Serpent Monte Carlo Code
Fridman, E.; Leppänen, J.;
This paper presents new calculation methods, recently implemented in the Serpent Monte Carlo code, and related to the production of homogenized few-group constants for deterministic 3D core analysis. The new methods fall under three topics: 1) Improved treatment of neutron-multiplying scattering reactions, 2) Group constant generation in reflectors and other non-fissile regions and 3) Homogenization in leakage-corrected criticality spectrum. The methodology is demonstrated by a numerical example, comparing a deterministic nodal diffusion calculation using Serpent-generated cross sections to a reference full-core Monte Carlo simulation. It is concluded that the new methodology improves the results of the deterministic calculation, and paves the way for Monte Carlo based group constant generation.
Keywords: Serpent, Monte Carlo, lattice physics, few-group cross-section generation, reflector cross sections, criticality spectrum, 3D core analysis.
  • Contribution to proceedings
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA
  • Lecture (Conference)
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA

Publ.-Id: 16261 - Permalink


Radio- and fluorescence-labelled Cetuximab for multimodal imaging
Zenker, M.; Bergmann, R.; Walther, M.; Pietzsch, H.-J.; Heldt, J.-M.; Steinbach, J.;
Objectives:
Radio (64Cu++) and fluorescence (Alexa Fluor 488) labelled Cetuximab (C225) offers the possibility of multimodal imaging of epidermal growth factor receptor (EGFR). ([64Cu]Cu-NOTA)7-C225-(Alexa Fluor 488)7 was synthesized and the imaging and biodistribution has been proved by small animal PET and ex vivo studies of cryo-sections of xenotransplanted mice.
Methods:
1) Synthesis of (NOTA)x-C225-(Alexa Fluor 488)y (C225-Conjugate). The C225 solution (Erbitux, Merck KGaA, Germany) was buffer-exchanged with a NaHCO3 solution (50 mM, pH 6.0) containing NaCl (150 mM) using a Jumbosep 30 k molecular weight cut-off concentrator (Pall Life Sciences, Germany). NOTA (2-(pisothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid, p-SCN-Bn-NOTA, Macrocyclics, USA) and Alexa Fluor 488 (Alexa Fluor 488 carboxylic acid 2,3,5,6-tetrafluorophenyl ester, Invitrogen, United Kingdom) has been conjugated to C225 lysine amino residues in a single step. Just prior to protein conjugation, NOTA and Alexa Fluor 488 were dissolved in HEPES-buffer (400 μL, 500 mM, pH 7.2) and added to the C225 solution to achieve a molar reaction ratio of 10:1 (NOTA:C225) and gently manually agitated. The reaction mixture was allowed to incubate in the dark at 25°C for 24 h without further stirring. Excess NOTA chelator and dye were removed by passage of the reaction solution through a Jumbosep. The buffer-exchange was performed with an NH4OAc solution (50 mM, pH 6.0) containing NaCl (150 mM). Protein concentration and the number of conjugated dye molecules per mAb were determined by UV/VIS absorption at 280 nm and 495 nm (excitation maxima of Alexa Fluor 488), respectively. The number of NOTA introduced was determined using MALDI-TOFMS. 2) Radiolabeling with 64Cu. A solution of [64Cu]CuCl2 in HCl (0.04 M, 50 MBq) was added to the C225-conjugate (100 μg) plus MES buffer (100 μL, 200 mM, pH 6.1) in 2 mL protein low-binding tubes (Eppendorf, Germany), vortexed immediately and incubated at 30°C for 30 min. Radiochemical yield (RCY) was determined by radio-ITLC. Before ITLC-analyses, free TETA chelator (32 μL; 0.1 μg/μL) was added to the reaction mixture for quenching the labelling reaction and fixing unreacted radionuclide. Therefore a second incubation at 30°C for 30 min was necessary. As stationary ITLC-phase, a 10 cm ITLC-SA strip (Varian GmbH, Germany) and as mobile phase a 0.9% NaCl solution has been used. The radio labelled antibody was purified by spin filtration using Microcon 30 k (Millipore). 3) Biodistribution. Squamous cell carcinoma (FaDu) tumour bearing NMRI nu/nu mice were studied with PET at 24 h p.i. The fine distribution of the probe was then characterized using whole body cryosectioning. The 64Cu-activity was compared with the fluorescence distribution.
Results:
The BFC NOTA and Alexa Fluor 488 were successfully simultaneously conjugated to C225. The resulting conjugate is (NOTA)1-C225-(Alexa Fluor 488)7. Radionuclide labelling was achieved within 30 min with optimization of the molar ratio of NOTA:C225: Alexa Fluor 488 during the conjugation. The radioimmunoconjugate exhibited high accumulation in xenotransplanted FaDu tumours in mice after 24 hours. The 64 Cu-activity concentration correlated well with the fluorescence in most tissues except the liver.
Conclusions:
Dual-labelled immunoconjugates represent a potential probe for translational application in tumour detection, evaluation of long-term distribution and stability studies of the labelled antibody.
Research support: This project was partially supported by “Kompetenzverbund Strahlenforschung” (grant 02NUK006A-E).
  • Poster
    19th International Symposium on Radiopüharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S196

Publ.-Id: 16260 - Permalink


Electron Temperature Scaling in Laser Interaction with Solids
Kluge, T.; Cowan, T.; Debus, A.; Schramm, U.; Zeil, K.; Bussmann, M.;
A precise knowledge of the temperature and number of hot electrons generated in the interaction of shortpulse high-intensity lasers with solids is crucial for harnessing the energy of a laser pulse in applications such as laser-driven ion acceleration or fast ignition. Nevertheless, present scaling laws tend to overestimate the hot electron temperature when compared to experiment and simulations. We present a novel approach that is based on a weighted average of the kinetic energy of an ensemble of electrons. We find that the scaling of electron energy with laser intensity can be derived from a general Lorentz invariant electron distribution ansatz that does not rely on a specific model of energy absorption. The scaling derived is in perfect agreement with simulation results and clearly follows the trend seen in recent experiments, especially at high laser intensities where other scalings fail to describe the simulations accurately.
Keywords: Laser, Electron, Proton, Ion, Temperature, Energy, Scaling, PIC, Model, Analytic, Acceleration, TNSA
  • Physical Review Letters 107(2011), 205003
    DOI: 10.1103/PhysRevLett.107.205003
  • Lecture (Conference)
    Dresden Enlite, 16.-20.04.2012, Dresden, Deutschland
  • Poster
    Dresden Enlite, 16.-20.04.2012, Dresden, Deutschland
  • Poster
    33rd International Workshop on Physics of High Energy Density in Matter, 13.-18.01.2013, Hirschegg, Österreich
  • Lecture (Conference)
    SPIE Optics+Optoelectronics, 15.-18.04.2013, Prag, Tschechische Republik

Publ.-Id: 16259 - Permalink


Radiolabelled cathepsin inhibitors as potential PET tracers for tumour imaging
Löser, R.; Frizler, M.; Bergmann, R.; Dombrowski, L.; Knieß, T.; Gütschow, M.; Steinbach, J.;
Objectives:
Thiol-dependent cathepsins are a class of cysteine proteases that have been shown to be linked to the progression of cancer in multiple ways. Particularly crucial is their involvement in proteolytic pathways that are related to tumour invasion and metastasis [1]. The aim of this study was the design of cathepsin inhibitors based on the structure of the azadipeptide nitrile chemotype [2] that permit the labelling with the positron emitters fluorine-18 and carbon-11 and to evaluate the
potential of this inhibitor class for functional tumour imaging by PET. Additionally, a first insight into the pharmacokinetic behaviour of these inhibitors should be gained.
Methods:
The fluorine atom was linked by an ethylene bridge to the inhibitor core structure. Labelling with fluorine-18 was achieved by fluoroethylation of 1 with different substituted [18F]2-fluoroethyl benzenesulfonates [3]. In addition, the introduction of radiofluorine into 2 was attempted by direct fluorination of the corresponding tosyl and nosyl precursors. The stability of the tracer against chemical and enzymatic degradation as well as its metabolic fate in rat blood was investigated and its biodistribution was studied in vivo by small animal PET. To obtain an 11C-based tracer, the fluoroethyl group of 2 was replaced by methyl. Introduction of carbon-11 was done by conversion of the phenolic precursor 1 with [11C]methyl iodide generated by the gas-phase method. The affinities of the compounds 1-3 to their targets were determined in kinetic enzyme assays.
Results:
The azadipeptide nitriles 1-3 exhibited inhibition constants in the single-digit to subnanomolar range against the oncologically relevant cathepsins L, S, and B. Among the various 18F-fluoroethylating agents tested, [18F]2-fluoroethyl nosylate revealed as the most efficient one. This enabled the two-step radiosynthesis of [18F]2 in an average RCY (d.c.) of 27±5% (n = 13). The direct radiofluorination of the corresponding sulfonate precursors could provide [18F]2 in only low labelling yields. PET studies in rats together with in vitro investigations indicated the trapping of the tracer in erythrocytes, which could be attributed to its inherent thiol reactivity. The tracer [11C]3 could be obtained in labelling yields of 35-42% depending on the employed base. Its radiopharmacological behaviour is under current investigation.
Conclusions:
With the azadipeptide nitriles 2 and 3 highly potent cathepsin inhibitors were found and their labelling with fluorine-18 and carbon-11 could be successfully established. The compounds’ suitability as PET tracers for functional tumour imaging seems to be limited due to their thiol reactivity. The radiolabelling of further cathepsin inhibitors is underway.
References:
[1] Mohamed & Sloane (2006) Nat. Rev. Cancer 6, 764-775, [2] Löser et al. (2008) Angew. Chem.
Int. Ed. 47, 4331-4334, [3] Musachio et al. (2005) J. Label. Compd. Radiopharm. 48, 735-747
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S190

Publ.-Id: 16258 - Permalink


Development and fluorine-18-radiolabeling of benzodioxolylpyrimidine EphB4 receptor inhibitors
Mamat, C.; Neuber, C.; Mosch, B.; Pietzsch, J.; Steinbach, J.;
Objectives: Ephrins and Eph receptors were found to be disregulated in several human tumor entities like breast, colon, liver, prostate or melanoma [1]. Concerning Eph/ephrin signalling, the EphB4/ephrinB2 system seems to play a major role in tumor angiogenesis [2]. Several inhibitors were reported based either on peptides which block the extracellular ephrin binding domain [3] or small organic molecules which block the intracellular kinase domain of Eph receptors. For this purpose, promising EphB4 kinase inhibitors based on the dioxolylpyrimidine scaffold were used for the development of a novel radiofluorinated PET tracer candidate [4].
Methods:
Compound 1 (figure 1) represents an advantageous molecule for the development of a fluorine-18 containing radiotracer. It shows an adequate affinity to EphB4 (90 nM) and consists of two structural parts. For the synthesis of the new radiotracer [18F]2, the methylsulfonylphenyl residue in 1 was replaced by a 3-fluoropropylsulfonylphenyl moiety (part B). This part of the molecule was prepared starting from sodium benzenesulfinate and 1-bromopropanol in 5 synthesis steps. Part A of the radiotracer as well as the lead compound containing the benzodioxole moiety was synthesized as described previously [4]. Finally, the non-radioactive reference 2 was obtained after 6 steps, whereas the respective tosylate precursor was prepared within 7 steps. Cellular binding and internalization of [18F]2 was investigated in human A375 melanoma cells as well as A375 cells stably transfected with human EphB4 receptor or mock vector. Furthermore, specific binding and potential transport mechanisms were analyzed by application of different specific inhibitors.
Results:
Starting from a 2 GBq [18F]fluoride batch, 65±5 MBq of [18F]2 were obtained with >95% radiochemical purity within 60 min synthesis time (including HPLC purification tR = 3.9 min, acetonitrile:water, 1:1 + 0.1% TFA). The best conditions for radiolabeling of the tosylate precursor were found to be acetonitrile as solvent at 90 °C for 15 min. Afterwards, water was added and the mixture was filtered prior to the HPLC purification. Cell association studies in melanoma cells showed time dependent increase in binding and internalization of [18F]2. Both inhibition with lead compound 1 and [19F]2 significantly decreased binding and internalization of [18F]2
indicating specific EphB4 binding. However, involvement of other kinases for binding can not be excluded. Moreover, participation of ATP-binding cassette transporters for cellular uptake is indicated.
Conclusions:
A novel potential EphB4 inhibitor based on the dibenzodioxolylpyrimidine scaffold has been synthesized and successfully radiolabeled with fluorine-18. Further biological studies including dynamic small animal PET are currently in progress.
References:
[1] B. Mosch, B. Reissenweber, C. Neuber, J. Pietzsch (2010), J. Oncol., DOI: 10.1155/2010/135285,
[2] E. Pasquale (2010), Nature Rev. Cancer, 10, 165, [3] J. E. Chrencik, A. Brooun, M. I. Recht, G. Nicola, L. K.
Davis, R. Abagyan, H. Widmer, E. B. Pasquale, P. Kuhn, (2007), J. Chem. Biol. 282, 36505, [4] C. Bardelle, T.
Coleman, D. Cross, S. Davenport, J. G. Kettle, E. J. Ko, A. G. Leach, A. Mortlock, J. Read, N. J. Roberts, P.
Robins, E. J. Williams, (2008) Bioorg. Med. Chem. Lett., 18, 2776.
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S178

Publ.-Id: 16257 - Permalink


McMurry cyclization in 18F-labeling - radiosynthesis of a 2,3-diarylsubstituted COX-2 inhibitor
Laube, M.; Kniess, T.; Bergmann, R.; Steinbach, J.; Pietzsch, J.;
Objectives:
Cyclooxygenase-2 (COX-2) is an inducible enzyme overexpressed under inflammatory conditions and is assumed to play a key role in cancerogenesis. Functional imaging of COX-2 expression in vivo by means of COX-2 inhibitors radiolabeled with positron emitters is a challenging approach, e.g., for differentiation of inflammatory processes and cancer1. Despite of different attempts, up to now a suitable radiotracer for COX-2 expression is unavailable. We developed an 18F-labeled COX-2 inhibitor [18F]3 from the type of a 2,3-diarylsubstituted indole via the McMurry cyclization. Thereby, with this labeling approach we got access with [18F]fluoride to the indole system which is, in principle, poorly activated for a nucleophilic substitution.
Methods:
The potent COX-2 inhibitor 3 (IC50=0.02 μmol) was synthesized as reference compound2. The labeling precursor 1 bearing a trimethylammonium leaving group was obtained in a six-step synthesis sequence. The radiolabeling reaction was performed as an one pot-two step procedure starting first by introduction of [18F]fluoride by a nucleophilic substitution at 1 followed by McMurry cyclization to form the indole core structure (Figure 1). The radiosynthesis was carried out with an automated nucleophilic synthesizer TracerLABFXN (GE) and has been optimized with respect of the base, solvent, and temperature. Purification of [18F]3 was performed by semi-preparative HPLC and SPE with C18 cartridges.
Results:
Considering a set of optimization experiments it turned out that for the McMurry cyclization the use of THF is inevitable. Hence, the radiolabeling was performed in acetonitrile at 110-120°C, the solvent was removed under vacuum, and the McMurry reaction was run in pure THF at 90-100°C. Under these conditions the intermediate [18F]2 was formed in 10-15% yield and the cyclization step provided the desired McMurry product [18F]3 in 50-82% yield. A typical module assisted radiosynthesis of [18F]3 starting with 8 GBq of [18F]fluoride and 15 mg precursor 1 yielded 490 MBq of [18F]3 (10% overall yield d.c.) within 80 min synthesis time. The radiochemical purity of [18F]3 after HPLC purification was > 98% and the specific activity was determined to be 74-91 GBq/μmol at end of synthesis.
Conclusions:
A highly potent and selective COX-2 inhibitor from type of a 2,3-diarylsubstituted indole was labeled with fluorine-18 in a two step fully automated radiosynthesis giving a potential PET tracer for functional imaging of COX-2 in vivo. In best to our knowledge, this is the first time that McMurry cyclization was utilized in PET-chemistry as labeling approach to get access to poorly activated compounds by nucleophilic substitutions with [18F]fluoride. In vitro stability studies in rat plasma and blood and in vivo studies in rats showed high stability of [18F]3 over two hours. Cell uptake studies with [18F]3 in THP-1, FaDu, HT29, A2058 and A375 cell lines are under the way as well as small animal PET investigations in HT29 mouse xenograft models.
References:
[1] Kuge et al., (2009), Nucl. Med. Biol., 36, 869-876,
[2] Hu et al., (2003), Bioorg. & Med. Chem.,11, 1153-1160
  • Lecture (Conference)
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S73

Publ.-Id: 16256 - Permalink


Systematic alteration of PEGylation grade of 68Ga- and 64Cu-labeled L-oligonucleotides for tailored pharmacokinetics as prerequisite for tumor pretargeting technologies
Förster, C.; Schubert, M.; Bergmann, R.; Walther, M.; Pietzsch, J.; Pietzsch, H.-J.; Steinbach, J.;
Objectives:
The favorable properties of non-natural, L-configured oligonucleotides (L ON) such as rapid hybridization, the lack of natural hybridization targets in vivo as well as their high metabolic stability [1] award L-ONs as a promising tool for tumor pretargeting technologies. As a result of their oligoanionic nature, 17mer-L-ONs are correlated with very fast blood clearance and high kidney retention [1]. Therefore, improvement of these two parameters was indispensable. To minimize the kidney accumulation and to increase the bioavailability by increasing of the area under the blood curve (AUC), polyethylene glycol (PEG) units of increasing size 2000-20000 Da were conjugated to the 17mer lead structure. Beside effect of PEGylation, the influences of different chelators and labeling ions on the biodistribution behavior of 64Cu- and 68Ga-labeled 17mer-L-ON-PEGs were investigated.
Methods:
17mer-L-DNA (HO-C6H12-S-S-C6H12-5’GCGGCTGTG-CGGTGCGG3’-amino modifier) was 3’-modified with different PEG substituents. By using the mercaptohexyl spacer at 5’-position, new developed NOTA-maleimide derivatives as well as a commercially available DOTA-maleimide were conjugated. After radiolabeling with 64Cu and 68Ga and intravenously administration in healthy Wistar rats, biodistribution data by organ and tissue sampling were determined 5 min p.i. as well as 60 min p.i. Blood clearance half lifes were calculated using of dynamic PET studies. The influence of PEGylation on hybridization was investigated in vitro by gel-electrophoresis.
Results:
The increasing molecular mass of the conjugated PEG units led to significantly decreased kidney retention at 60 min from 56.3±4.1%ID (64Cu; 2 kDa PEG) and 52.4±6.1%ID (68Ga; 2 kDa PEG) to 6.5±0.4%ID (64Cu; 20 kDa PEG) and 6.9±0.6% (68Ga; 20 kDa PEG), respectively. However, the liver uptake was slightly increased at 60 min p.i. from 4.8±0.2%ID (64Cu; 2 kDa PEG) and 2.6±0.4%ID (68Ga; 2 kDa PEG) to 13.3±2.1%ID (64Cu; 20 kDa PEG) and 10.7±2.7%ID (68Ga; 20 kDa PEG). The activity concentrations in all other measured organs, except the blood, were at 60 min p.i. negligible (< 0.5%ID/g or <1 SUV). The biological half-lives in the blood were 10.8 min (2 kDa PEG), 9.6 min (5 kDa PEG), 27.7 min (10 kDa PEG), and 39.4 min (20 kDa PEG) for 68Ga-labeled compounds. Based on gel-electrophoresis investigations, no PEG-induced inhibition of hybridization was found. In vitro hybridization was completed in less than 30 s, whereas the optimal ratio of complementary L DNA single strands was between 1:1 (2-5 kDa) to 1:1,25 (10-20 kDa).
Conclusions:
PEGylation of our 17mer-L-ON resulted in significantly reduced kidney retention, favorable blood circulation half-life, and very low unspecific tissue accumulations. Low kidney and liver accumulations were found for 5 kDa and 10 kDa PEG derivatives. Increasing size of PEG units shifted the hybridization equilibrium to slightly higher DNA ratios without clear hybridization inhibition. The introduction of NOTA or DOTA as chelating moiety enables radiolabeling with various metallic radionuclides for diagnostics and therapy. These results emphasize the high-grade potential of L-ON as a complementary tool for tumor pretargeting technologies.
Reference:
Schlesinger, J. et al., (2008), Lett. Drug Des. Discovery, 3, 330-335
  • Lecture (Conference)
    19th Internatzional Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S62

Publ.-Id: 16255 - Permalink


Effects of very rapid thermal processing on the properties and bonding structure of Al-doped ZnO thin films
Vinnichenko, M.; Hauschild, D.; Lissotschenko, V.; Cornelius, S.; Krause, M.; Gago, R.; Mücklich, A.; Kolitsch, A.;
The combination of low-temperature deposition with very rapid thermal processing (vRTP) at air is a promising approach of synthesis of high-quality thin films of transparent conductive oxides (TCOs) at large areas. However, microscopic mechanisms of TCO film properties modification during such treatment are not understood properly which hampers application of the post-deposition vRTP. In order to resolve this problem, Al-doped ZnO (AZO) films grown onto unheated fused silica substrates by reactive pulsed magnetron sputtering were vRTP processed using a laser source with ~1 ms dwell time. The morphology, bonding structure, electrical and optical properties of as-deposited films were systematically compared with those of the vRTP processed ones. The electrical resistivity of the films drops from 1.4x10-3 to 4.6x10-4 Ohm cm with simultaneous substantial decrease of the film optical extinction in the visible at optimum processing conditions. The resistivity decrease is due to simultaneous increase of the free electron density (from 3.8x1020 to 6.2x1020 cm-3) and mobility (from 12 to 22 cm2V-1s-1). It is also observed that vRTP leads to a substantial decrease of the A1(LO) and E1(LO) disorder-enhanced lines in Raman spectra. This is interpreted in terms of decreasing concentration of point defects because both x-ray diffraction and high-resolution TEM show no improvement of the film crystal quality which might have a similar effect on the Raman spectra. Substantial modification of the O K-edge x-ray absorption near edge structures (XANES) spectra of the vRTP processed AZO films (which are dense and void free already in as deposited state) suggests that these might be oxygen-related point defects or defect complexes. Decrease of concentration of these defects may explain increase of the free electron mobility and decrease of the optical extinction in the visible.
The authors gratefully acknowledge financial support of BMBF under the RainbowEnergy Project.
Keywords: transparent conductive oxides, Al-doped ZnO, diode laser processing
  • Poster
    International topical workshop on “Subsecond thermal processing of Advanced Materials 2011" Subtherm-2011, 25.-27.10.2011, Dresden, Germany

Publ.-Id: 16254 - Permalink


S100A2 in cancerogenesis: a friend or a foe?
Wolf, S.; Haase-Kohn, C.; Pietzsch, J.;
Owing to the exceptional intracellular distribution and the heterogeneous expression pattern during transformation and metastasis in various tumors, the EF-hand calcium-binding protein S100A2 attracts increasing attention. Unlike the majority of S100 proteins, S100A2 expression is downregulated in many cancers and the loss in nuclear expression has been associated with poor prognosis. On the other hand, S100A2 is upregulated in some cancers. This mini review highlights the general characteristics of S100A2 and discusses recent findings on its putative functional implication as a suppressor or promoter in cancerogenesis.
Keywords: Calcium-binding protein; EF-hand; p53 Protein family; Receptor for advanced glycation endproducts (RAGE); Tumor promotor; Tumor suppressor Introduction

Publ.-Id: 16253 - Permalink


Novel Technology of Laser Driven Proton Beams for a Potential Application in Cancer Therapy: in Vitro Dose Response Studies
Laschinsky, L.; Baumann, M.; Beyreuther, E.; Karsch, L.; Lessmann, E.; Oppelt, M.; Richter, C.; Schramm, U.; Schürer, M.; Pawelke, J.;
Background: The development of the new technology of proton and ion acceleration by ultra-high intensity lasers for cancer therapy is the goal of the German joint research project “onCOOPtics”. The laser based acceleration promises compact and economic therapy facilities that are suitable for already existing clinics. In contrast to conventional particle acceleration the laser based method results in beams of very short pulses with ultra-high pulse dose and correspondingly peak dose rate. Within the project multidisciplinary issues like development and optimization of high-intensity laser systems, efficient proton acceleration schemes and proton beam transport are handled. Moreover, the physical and real-time dosimetric characterization as well as the investigation of radiobiological consequences of laser accelerated beams are essential. These imply translational investigations starting from in vitro cell irradiation.

Material and Methods: Systematic in vitro cell experiments were performed at the 150 terawatt laser facility DRACO at HZDR. Proton pulses up to 20MeV were accelerated, whereas the broad proton spectrum was downward limited to 6MeV using an energy-filter-system. An in-house developed integrated dosimetry and cell irradiation system (IDOCIS) was tested and calibrated allowing precise dosimetry as well as the exact positioning of each cell sample. Cell survival and residual DNA double strand breaks were determined after irradiation of the tumour cell line SKX in a dose range from 0.5Gy to 4.3Gy. Additionally, reference irradiation were performed with continuous proton beam at a conventional Tandem accelerator and with a 200 kVp X-ray tube.

Results: A stable and reproducible laser driven proton beam was achieved for experiments over weeks including real-time dose and energy spectrum monitoring as well as precise absolute dosimetry. The comparison of the radiobiological effectiveness of conventional and laser accelerated proton beams show no significant difference for in vitro cell irradiation.

Conclusions: These first systematic in vitro cell response studies with precise dosimetry of laser driven protons represent an important step toward the development of laser accelerated particles for radiotherapeutic application. Further experiments with other human cell lines and in vivo studies are under way.

The work was supported by the BMBF, grant no. 03ZIK445.
  • Open Access LogoContribution to proceedings
    ECCO 16 - ESMO 36 Stockholm Cancer Conference, 23.-27.09.2011, Stockholm, Sweden
    Novel Technology of Laser Driven Proton Beams for a Potential Application in Cancer Therapy: in Vitro Dose Response Studies, 0959-8049
  • European Journal of Cancer 47(2011), S190
    DOI: 10.1016/S0959-8049(11)70964-9

Publ.-Id: 16252 - Permalink


S100 proteins in health and disease
Pietzsch, J.;
kein Abstract verfügbar

Publ.-Id: 16251 - Permalink


Ultrafast X-ray computed tomography of gas-solid fluidized beds
Bieberle, M.; Barthel, F.; Hampel, U.;
Gas-solid fluidized beds find various applications in chemical and process engineering, for instance in fluid catalytic cracking, drying of particulate solids or polyolefin production. The gas-particle flow in fluidized beds is generally complex and difficult to observe, but exact information on voidage distribution and solid transport is urgently needed for assessment, monitoring, modelling and optimization of fluidized bed operation.
Only few of the currently available flow measurement techniques are applicable to dense fluidized beds. Optical imaging and laser-based methods are at the most merely able to capture the peripheral structure of the solids phase or to provide local information by using probes. For tomographic techniques, such as electrical capacitance tomography (ECT), positron emission tomography (PET) or common X-ray CT, it is in general difficult to provide high spatial and high temporal resolution at the same time.
We here introduce a much faster X-ray tomography approach which is based on electron beam scanning. There, an electron beam is rapidly swept along a circular target to produce a moving X-ray source. A static detector ring with 240 detector elements synchronously captures the radiation intensity. From the resulting radiographic projections of the object of interest non-superimposed cross-sectional density distributions are reconstructed. Beside its really fast scanning capability other advantages of this approach are the use of a single electron beam generator and the high versatility of the electron beam with respect to scan patterns and scanning speed. With our approach we have already demonstrated multiphase flow imaging with frame rates of up to 10.000 fps and a spatial resolution in the range of better than 1 mm.
The results presented here include studies at a bubbly fluidized bed with monodisperse spherical particles, in which the capability of the method to visualize the particle dynamics and the internal structure of the fluidized bed in very detail are demonstrated.
Keywords: tomography, ultrafast, fluidized bed, voidage, visualization
  • Lecture (Conference)
    gas-liquid and gas-liquid-solid reactor engineering congress (GLS 10), 26.-29.06.2011, Braga, Portugal

Publ.-Id: 16250 - Permalink


Ultrafast X-ray computed tomography for the analysis of gas-solid fluidized beds
Bieberle, M.; Barthel, F.; Hampel, U.;
Gas-particle flow in fluidized beds is generally complex and difficult to observe. But exact information on voidage distribution and solid transport is urgently needed for assessment, monitoring, modelling, and optimization of fluidized bed operation. So far, there was a lack of suitable measurement and imaging techniques to disclose the complex flow structures in fluidized beds with high spatial and temporal resolution. The recently developed ultrafast X-ray computed tomography technique is superior for such types of multiphase flows and its performance has been demonstrated in this study. Spatial resolution in the range of one millimetre and temporal resolution of several thousand cross-sectional images per second allows at the same time imaging and analysis of voidage structures as well as single particle movement. In this study, the capability of imaging fluidized bed behaviour at different column diameters and gas flow rates has been analysed.
Keywords: tomography, ultrafast, fluidized bed, voidage, visualization

Publ.-Id: 16249 - Permalink


A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media
Hildebrand, H.; Franke, K.;
Nanoparticle (NP) tracking in complex media is still a challenge since NP concentrations are expected to be low compared to elemental background levels as it can be found in environmental matrices. This study presents a new method for radiolabeling of commercial silver nanopowder (Ag0-NPs, dp < 100 nm) with 110mAg radionuclides (t1/2 = 250 d) that provide an adequate time frame for particle detection, localization and tracking under various experimental conditions. The radiolabeling procedure ensures high efficiency, stability and consistency of particle properties. Detection of Ag0-NP in concentrations as low as 125 ng kg-1 could be reached. For the first time, an appropriate tool for life-cycle studies of commercial Ag0-NPs is provided without changing chemical composition of the material. This is of great importance e.g. for research in the field of nanotoxicology.
Keywords: radiolabeling, nanoparticle, silver, nanoparticle detection, nanoparticle tracking

Publ.-Id: 16248 - Permalink


Grain alignment in poly-Si films by means of Plasma Immersion Ion Implantation (PIII) in combination with Flash Lamp Annealing (FLA)
Endler, R.; Voelskow, M.; Skorupa, W.;
A series of experiments have been performed with the aim to improve the electrical and structural properties of CVD – deposited thin polycrystalline silicon films. Using an advanced ion implantation technique like Plasma-Immersion-Ion- Implantation (PIII) in combination with short time Flash-Lamp-Annealing (FLA) it has been shown that in comparison to the as deposited state a significant enlargement of the mean grain size occurs, accompanied by a more pronounced texturizing. Furthermore, the main crystallographic axes of the grains have been found to be mostly parallel to the direction of the particle stream. Whereas the enlargement of the mean grain size due to ion channelling was already reported by Reif et al. in the 80s, in the present work the SSIC technique (Seed Selection though Ion Channelling) was applied for the first time using the PIII process. This technique ensures a high throughput; additionally the costs for the implantation step can be reduced in comparison to conventional ion implantation. Furthermore, in contrast to the well known existing recrystallization techniques like cw-laser annealing or lateral zone melting recrystallization (ZMR), the proposed method circumvents problems arising from several mass transports characteristics of techniques based on melt processes.
Keywords: Flash Lamp Annealing, Poly-Si, SSIC
  • Poster
    Subtherm2011, 24.-27.10.2011, Dresden, BRD

Publ.-Id: 16247 - Permalink


Timing (a) FLASH
Tavella, F.; Stojanovic, N.; Geloni, G.; Gensch, M.;
Many fundamental processes in nature like chemical reactions or phase transitions occur on the few femtosecond time and few nanometres to few angstroms length scale. On a way to their understanding, great hope lies on investigations of their dynamic using the bright, coherent X-ray pulses from free electron lasers (FELs) that have a duration and wavelength commensurate with that of these processes.
We developed a method to measure the arrival time of the X-ray pulses at FLASH with respect to the pump-probe laser in the experimental hall on a few femtosecond timescale, making use of the THz beamline [1]. Method is easily transferable to other advanced light source working with ultrashort electron bunches and therefore of high general interest.
  • Open Access LogoContribution to external collection
    in: DESY Highlights 2011, Hamburg: DESY, 2012

Publ.-Id: 16246 - Permalink


The Rossendorf Beamline at ESRF: A multipurpose X-ray absorption spectroscopy and scattering beamline for Environmental and Materials Sciences
Scheinost, A. C.;
The Rossendorf Beamlines at ESRF is operated since 1997 by the Helmholtz Center Dresden-Rossendorf. As a multipurpose synchrotron x-ray beamline, it serves both inhouse and collaborative research in Environmental and Materials Science. Its optics provide tunable monochromatic x-rays to two experimental stations, the first specialized in bulk x-ray absorption spectroscopy for environmental radionuclide research, and the second specialized in a variety of scattering techniques to elucidate the structure of thin films and other materials. The first focus of my talk will be on the performance of the optics, which are donated to SESAME. I will then show some research examples, and give an overview on the organization, funding and personnel input, and productivity parameters (publications, projects, and outreach).
Keywords: Environmental Sciences, Materials Sciences, ROBL, Synchrotron
  • Invited lecture (Conferences)
    SESAME User Meeting 2011, 12.11.2011, Amman, Jordan

Publ.-Id: 16245 - Permalink


X-ray absorption spectroscopy for environmental sciences: examples and technical challenges
Scheinost, A. C.;
Due to its element specificity, low detection limit, and independence on long-range and crystalline order, X-ray absorption spectroscopy (XAS) is one of the most versatile tools to elucidate the electronic and molecular structure of almost any element in environmental samples. It is fundamental to study the speciation and structure of dissolved (aqueous) complexes, from the most simple solvated ion to polyatomic complexes, to colloids, amorphous and crystalline solids. Furthermore, it is extremely useful to study sorption and redox reactions at the water/solid interface. I will demonstrate its application in environmental chemistry to study the fate of metal contaminants in soils, sediments and water bodies.
Keywords: XAS, XAFS, EXAFS, XANES, environmental sciences
  • Invited lecture (Conferences)
    SESAME User Meeting 2011, 12.11.2011, Amman, Jordan

Publ.-Id: 16244 - Permalink


The Ksar Ghilane 002 shergottite – the 100th registered Martian meteorite Fragment
Llorca, J.; Roszjar, J.; Cartwright, J. A.; Bischoff, A.; Pack, A.; Ott, U.; Merchel, S.; Rugel, G.; Fimiani, L.; Ludwig, P.; Allepuz, D.; Casado, J. V.;
We report on the discovery of a new shergottite from Tunisia, Ksar Ghilane (KG) 002, which is the 100th Martian meteorite fragment registered in the Meteoritical Bulletin. This single stone, weighing 538 g, is a coarse-grained basaltic shergottite, mainly composed of maskelynitized plagioclase (~52 vol.%) and pyroxene (~37 vol.%). It also contains Fe-rich olivine (~4.5 vol.%), large Ca-phosphates, including both merrillites and Cl-apatites (~3.4 vol.%), minor amounts of silica or SiO22-normative K-rich glass, pyrrhotite, Ti-magnetite, ilmenite, and accessory baddeleyite. The largest crystals of pyroxene and plagioclase reach sizes of ~4 mm and ~5 mm. Regarding texture, KG 002 shares some similarities with the evolved NWA 2800 Martian sample. Pyroxene compositions in KG 002 are Fs26-96En5-50Wo2-41 (n=82). They typically range from cores of about Fs29En41Wo30 to rims of about Fs68En14Wo17. Most plagioclases (maskelynites) are Ab41-49An39-58Or1-7 in composition, but some can be as anorthitic as An94. Olivine occurs mainly within symplectitic intergrowths, in paragenesis with ilmenite, or at neighboring areas of symplectites. These minerals are Fa91-96 in composition. Ksar Ghilane 002 is heavily shocked (S5) as indicated by mosaic extinction of pyroxenes, maskelynitized plagioclase, the occurrence of localized shock melt glass pockets and low radiogenic He concentration. Two analyses of oxygen isotopes (delta18O=+5.09 and 5.26‰, delta17O=+3.0 and +3.2‰, and Δ17O=+0.28 and +0.43‰) confirm that this rock is a normal member of the SNC suite of meteorites. Bulk chemical analyses indicate that KG 002 belongs to the main group of basaltic shergottites and it is strikingly similar to the highly-evolved Los Angeles meteorite. According to the K, U, Ba and Sr abundances and fresh appearance of sulfides, KG 002 is not significantly weathered, although a positive Ce anomaly is recognized in the REE pattern. Ksar Ghilane 002 is slightly depleted in LREE and shows a positive Eu anomaly providing evidence for complex magma genesis and mantle processes on Mars. Noble gases with a composition thought to be characteristic for Martian interior may be a dominant component in KG 002. 10Be, 26Al, and 53Mn measurements and comparison with theoretical Monte-Carlo calculations of production rates indicate that KG 002 has been exposed most likely as a single meteoroid body of 35-65 cm radius between 2.8 and 3.7 Ma. Ksar Ghilane 002 strongly resembles Los Angeles and NWA 2800 basaltic shergottites in element composition, petrography and mineral chemistry, suggesting a possible launch-pairing. The CRE ages of KG 002 and Los Angeles may suggest an ejection event at ~3.0 Ma.
Keywords: accelerator mass spectrometry, AMS, cosmogenic radionuclide, Mars, meteorite, noble gases

Publ.-Id: 16243 - Permalink


Influence of storage on the position of the germinal disc in the fertilized unincubated chicken egg
Burkhardt, A.; Meister, S.; Bergmann, R.; Koch, E.;
The breeding of male layer chickens is currently considered to be highly uneconomical. In Germany alone, 40 to 50 million newly hatched male chickens were killed annually immediately after hatching. Therefore, it is necessary to find a method for sexing chickens early in the embryonic development, preferably before incubation. The genotypic sex of an egg can be determined using information found in the germinal disc, so knowledge of the exact position of the germinal disc is essential for further sexing, or for other actions such as the in ovo injection of agents. Previous studies have shown that the germinal disc is located somewhere on top of the yolk. However, no studies have yet been performed that investigate the influence of time spent in horizontal storage on the position of the germinal disc. Magnetic resonance imaging was chosen to determine this influence on the position of the germinal disc. It was found that eggs placed horizontally for long periods of time befor!
e scanning had significant changes in the positions of their germinal discs compared with those of eggs scanned minutes after positioning. The position of the germinal disc in eggs, minutes after horizontal positioning, deviated 14.7 +/- 0.6 mm from the maximum vertical plane of the egg (zero position) in the z-direction; eggs scanned after 96 h of horizontal positioning showed a deviation of only 4.9 +/- 1.6 mm. The x-axis also exhibited changes in the position of the germinal disc over time. Immediately after horizontal positioning, the eggs showed a deviation of 0.4 +/- 0.4 mm in the x-direction, whereas the deviation after 96 h was 2.9 +/- 0.5 mm. These results show that horizontal positioning of the egg hours before the measurement is necessary.

Publ.-Id: 16242 - Permalink


On the effect of different placing ZrH moderator material on the performance of a SFR core
Merk, B.; Weiß, F.-P.;
The structure for the development of a fuel assembly design with reduced sodium void achieved by the use of the moderating material ZrH is investigated. In the study the sodium void effect, as well as the major feedback coefficients are analyzed. Besides the feedback coefficients, the influence on the operational parameters like neutron flux distribution, power distribution, and burnup distribution is investigated for the different possibilities of arranging the moderating material in the fuel assembly. Additionally, the fuel cycle parameters – breeding and minor actinide production – are analyzed. For a first evaluation of the behavior during transients the influence of temperature changes in the ZrH is studied.
Keywords: Sodium void effect, SFR, Fast reactor, Zirconium hydride, designable feedback coefficient.
  • Contribution to proceedings
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA

Publ.-Id: 16241 - Permalink


On the possible gain of the application of the sp3 solution in nodal codes
Merk, B.;
The simplified PN method has attracted much attention in reactor physics. The implementation of an increased order expansion has the potential to improve the results. It is investigated if this potential can be released under the specific features of nodal codes with fuel assembly sized calculation cells.
One dimensional analytical solutions for the one and two energy-group diffusion, SP3 and P3 equations are derived. The results are compared with reference solutions calculated with ONEDANT and HELIOS. Tests are performed on the Brantley, Larsen one-group test case and on a pin cell with real reactor materials. For the evaluation of the differences between the diffusion and the SP3 solutions in the nodal code configuration, benchmark configurations are investigated.
A comparison of the diffusion and the SP3 results show improvements for the test case using fuel element size nodes when compared to a reference solution using the identical cross section basis. Comparing with a multi-group reference solution shows that the diffusion solution sometimes behaves better due to error cancellation. To achieve the full gain of the SP3 method in nodal calculations, a new standard for light water reactor calculations has to be defined with a refined energy-group structure.
Keywords: simplified PN, nodal calculations, reactor physics, analytical solutions, neutron transport.
  • Contribution to proceedings
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA

Publ.-Id: 16240 - Permalink


An analytical solution for the consideration of the effect of adjacent fuel assemblies; comparison of rectangular and hexagonal structures
Merk, B.; Rohde, U.;
A new analytical method is described to deal with the Leakage Environmental Effect. The method is based on the analytical solution of the two group diffusion equation for two adjacent fuel assemblies. The quality of the results for this highly efficient method is demonstrated for quadratic fuel assemblies. In additional tests the transferability of the concept to hexagonal VVER-440 type fuel assemblies is shown and a comparison between the results for rectangular and hexagonal assemblies is given.
Keywords: Analytical solution, Homogenization, Cross-section preparation, Leakage assembly environmental effect, Diffusion equation
  • Contribution to proceedings
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA

Publ.-Id: 16239 - Permalink


An analytical solution for the consideration of the effect of adjacent fuel assemblies; extension to hexagonal fuel assemblies
Merk, B.; Rohde, U.;
A new analytical method is described to deal with the Leakage Environmental Effect. The method is based on the analytical solution of the two group diffusion equation for two adjacent fuel assemblies. The quality of the results for this highly efficient method is demonstrated for quadratic fuel assemblies. In additional tests the transferability of the concept to hexagonal VVER-440 type fuel assemblies is shown.
Keywords: VVER, Analytical Solution, Homogenization, Cross Section Preparation, Leakage Assembly Environmental Effect
  • Contribution to proceedings
    AER Symposium, 19.-23.09.2011, Dresden, Deutschland
  • Lecture (Conference)
    AER Symposium, 19.-23.09.2011, Dresden, Deutschland

Publ.-Id: 16237 - Permalink


Accuracy of MR-based attenuation correction First experience with a whole-body PET/MR system
Schramm, G.; Brüning, E. M.; Langner, J.; Hofheinz, F.; Will, E.; Beuthien-Baumann, B.; Oehme, L.; Platzek, I.; Steinbach, J.; Laniado, M.; Kotzerke, J.; van den Hoff, J.;
Purpose/Introduction: Sequential PET/MR scanners for whole body investigations have been developed only recently and are starting to become commercially available. In 2011, one of the first of these combined systems (Ingenuity TF PET/MR, Philips) was installed at our institute. PET/MR is expected to offer new possibilities, in particular in the field of quantitative bimodal functional imaging [1]. Quantitative PET requires attenuation correction (AC) which is commonly based on a measurement of the photon attenuation using either a radioactive source in standalone PET (RSAC), or CT in PET/CT systems (CTAC). In PET/MR systems such a measurement cannot be performed, therefore AC is based on a dedicated MR measurement (MRAC) plus segmentation and tissue type identification [2]. Here, we report on a first evaluation of MRAC in whole body investigations with the new system.

Subjects and Methods: Evaluation of MRAC is performed by a direct comparison of MRAC maps acquired with the Philips Ingenuity TF PET/MR and RSAC maps acquired with a Siemens ECAT Exact Hr+ PET scanner for 18 patients. Moreover, the quantitative influence of AC on the reconstructed images was investigated.

Results: In most cases the MRAC maps match the RSAC maps very well. Artefacts due to dental implants and sternal cerclages were found. In one case, the algorithm was not able to separate tissue from air in the patients lung. The influence of these artefacts on the reconstructed PET image will be reported.

Discussion/Conclusions: The vendor-provided MRAC algorithms yielded good results in our first patient measurements with respect to soft tissue and air segmentation. However, the algorithm relies on anatomic reference data and thus artefacts arise if the anatomy of the patient does not fit to the reference. In the future, an improved separation between tissue, bone and air without using anatomic reference data might be achieved with ultra short echo time sequences [3,4].

References:

[1] Pichler, B.J. et al., 2008, Sem. Nucl. Med., 199-208
[2] Martinez-Möller, A. et al., 2009, J. Nucl. Med., 520-526
[3] Catana, C. et al., 2010, J. Nucl. Med., 1431-1438
[4] Keereman, V. et al., 2010, J. Nucl. Med., 812-818
  • Lecture (Conference)
    ESMRMB Congress 2011, 06.-08.10.2011, Leipzig, D
  • Abstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 24(2011), 199

Publ.-Id: 16236 - Permalink


Synthesis, colloidal stability and 64Cu labeling of iron oxide nanoparticles bearing different macrocyclic ligands
Barreto, J. A.; Matterna, M.; Graham, B.; Stephan, H.; Spiccia, L.;
The synthesis, solution stability and 64Cu2+ labeling of magnetite nanoparticles (NPs) coated with different macrocycles is reported, together with the stability of the resulting radioisotope-labeled NPs to transchelation by the competing ligand cyclam, and their stability in blood serum. Three macrocycles, 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane (dmptacn),1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,7,10-tetraazacyclododecane (cyclen), and
3-aminopropyltriethoxysilane were used to modify the magnetite NPs. The ligands were covalently linked to the surface of the NPs with high efficiency by reaction of the corresponding
3-(3-(triethoxysiloxy)propoxy)propan-2-ol derivatives with the NPs. According to transmission electron microscopy (TEM), the uncoated magnetite NPs and macrocycle-functionalized congeners have an average diameter of 6 to 7 nm. The NPs form stable colloidal suspensions in 0.05 M aqueous 2-(N-morpholino)ethanesulfonic acid (MES) buffer, which consist of larger aggregates with a mean hydrodynamic size of about 200 nm. The NPs with the appended macrocycles can be efficiently labeled with 64Cu2+ ions and the radioactivity persists in rat plasma for at least 24 h. Challenge experiments with cyclam also indicate that the radiocopper complexes are highly stable, with the dmptacn-functionalized NPs showing the highest resistance to metal ion leakage. Overall, the dmptacn-functionalized iron oxide NPs provide an excellent platform for the development of robust multimodal cancer imaging/therapeutic agents.
  • New Journal of Chemistry 35(2011), 2705-2712

Publ.-Id: 16235 - Permalink


Concomitant targeting of cyclooxygenase-2 and oxidant stress pathways for radioprotection of endothelial cells.
Pietzsch, J.; Laube, M.; Pietzsch, F. J.; Bergmann, R.; Knieß, T.;
kein Abstract verfügbar
  • Contribution to external collection
    Lewis BS, Flugelman MY, Halon DA (eds.): Coronary Artery Disease: 2011 Update, Bologna: Medimond S. r. l - Monduzzi Editore International, 2011, 978-88-7587-619-7, 107-110

Publ.-Id: 16234 - Permalink


Site-selective radiolabeling of peptides by 18F-fluorobenzoylation with [18F]SFB in solution and on solid phase - a comparative study
Kuchar, M.; Pretze, M.; Knieß, T.; Steinbach, J.; Pietzsch, J.; Löser, R.;
Peptides labeled with short-lived positron-emitting radionuclides are of outstanding interest as probes for molecular imaging by positron emission tomography (PET). Herein, the site-selective incorporation of fluorine-18 into lysine-containing peptides using the prosthetic labeling agent N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) is described. The reaction of [18F]SFB with four biologically relevant resin-bound peptides was studied and optimized. For comparison, each peptide was 18F-fluorobenzoylated in solution under different conditions and the product distribution was analyzed confirming the advantages of the solid phase approach. The method's feasibility for selective radiolabeling either at the N-terminus or at the lysine side chain was demonstrated. Labeling on solid phase with 18F]SFB resulted in crude 18F-fluorobenzoylpeptides whose radiochemical purities were typically greater than 90 % and that could be prepared in synthesis times from 65 to 76 min.

Publ.-Id: 16233 - Permalink


Biosorptive Kompositmaterialien für die Rückgewinnung von Wertstoffen: Neue Konzepte und Anwendungspotenziale
Pollmann, K.; Raff, J.; Kutschke, S.;
Es werden Konzepte zur Entwicklung von biosorptiven Materialien für die (Rück-)gewinnung von Metallen vorgestellt.
  • Invited lecture (Conferences)
    Biomining von Sekundärrohstoffen - Workshop 3 des Innovationsforums "Geobiotechnologie - mikrobiologische Verfahren in Bergbau und Umweltschutz", 14.-15.12.2011, Hannover, Deutschland

Publ.-Id: 16232 - Permalink


Herstellung von 61Cu mit hoher spezifischer Aktivität über die 64Zn(p,α)61Cu-Reaktion
Thieme, S.; Walther, M.; Rajander, J.; Pietzsch, H.-J.; Solin, O.; Steinbach, J.;
Ziel:
Die Herstellung von 61Cu hoher spezifischer Aktivität erfordert besonders aufwändige Maßnahmen, um Metallkontaminationen sowohl durch Cu-Isotope als auch durch andere Metalle zu minimieren. Dementsprechend müssen die herkömmlichen Methoden verfeinert werden, um 61Cu sowohl in hoher Qualität als auch effektiv herstellen zu können. Vergleichswerte über spezifische Aktivitäten von 61Cu sind in der Literatur selten zu finden. McCarthy et al. berichten zu spez. Aktivitäten von 61Cu im Bereich von 47 bis 190 GBq/µmol; erzeugt durch 61Ni(p,n)61Cu und 60Ni(d,n)61Cu-Reaktion. Eine Alternative dazu stellt die 64Zn(p,α)61Cu-Reaktion dar. Das hierfür genutzte Targetmaterial 64Zn (99,3% Isotopenanreicherung) ist im Vergleich zu angereichertem 61Ni weitaus weniger kostenintensiv.
Methoden:
Für die Bestrahlung am Zyklotron wird ein massiver Targetträger aus Gold verwendet, auf dem ca. 100 mg angereichertes 64Zn (99,3% Isotopenanreicherung) abgeschieden sind. Die radiochemische Trennung erfolgt über Ionenaustauschtechniken nach Literaturangaben. Die angewandte Methode nutzt eine Ionenaustauscherkaskade, die aus zwei Kationenaustauscher-Säulen und einer Anionenaustauscher-Säule besteht. Dabei sorgt der doppelte Kationenaustauscherschritt für die effektive Abtrennung von Galliumisotopen (66/67/68Ga) und die Anionenaustauscher-Säule für die Trennung des 61Cu vom Zn-Targetmaterial. Der Gesamtprozess zur Gewinnung des gereinigten 61Cu dauert eine Stunde. Die Methode umfasst die Wiedergewinnung des eingesetzten 64Zn, welches danach zur erneuten Verwendung zur Verfügung steht. Das optimierte Verfahren nutzt kleinere Ionenaustauschersäulen als bisher und ausschließlich wässrige Salzsäure; Details vgl. Thieme et al.. Die Ermittlung der spezifischen Aktivität erfolgt über TETA-Titrationen und ICP-MS-Analysen. Es wurden Bestrahlungen an zwei verschiedenen Zyklotronen durchgeführt: am Cyclone 18/9 (IBA, Belgien) des Instituts für Radiopharmazie, Dresden-Rossendorf und am CC 18/9 (Efremov Institut, St. Petersburg, Russland) des Turku PET Centre in Turku, Finnland.
Ergebnisse:
Die Bestrahlungen mit dem Cyclone 18/9 wurden mit 12 µA und 16 MeV durchgeführt. Dies führte innerhalb von 30 Minuten zu Ausbeuten von ca. 300 MBq 61Cu (EOB). Am CC 18/9 wurde mit 30 µA, 13 MeV, 30 Minuten gearbeitet. Dabei wurden ebenfalls 330-400 MBq 61Cu (EOB) erzeugt, bei einer Bestrahlungszeit von 3 Stunden bis zu 1150 MBq 61Cu (EOB). Am CC 18/9 wurde eine extrem hohe spezifische Aktivität des 61Cu von über 1000 GBq/µmol erreicht. Demgegenüber fielen die spezifischen Aktivitäten am Cyclone 18/9 deutlich ab, es konnte nur eine spezifische Aktivität von ca. 2 GBq/µmol erzielt werden. Wahrscheinlich tritt in diesem Fall eine Kontamination mit stabilem Kupfer schon während der Bestrahlung auf. Möglicherweise geht diese von der Targethalterung am Zyklotron aus, da sie nicht wie beim CC 18/9 komplett aus Aluminium, sondern größtenteils aus Messing besteht. Bisherige Versuche zum Schutz des Targetträgers und des Targetmaterials vor derartigen Kontaminationen bzw. der Versuch, Kontaminationen während des Trennprozesses zu verhindern, blieben erfolglos.
Schlussfolgerungen:
Die Ergebnisse zeigen, dass es prinzipiell möglich ist, 61Cu mit hoher spezifischer Aktivität mit Hilfe der 64Zn(p,α)61Cu-Reaktion herzustellen. Die genutzte radiochemische Trennmethode bietet sich hervorragend für eine routinemäßige Herstellung von 61Cu an.
  • Lecture (Conference)
    19. Jahrestagung der Arbeitsgemeinschft Radiochemie/Radiopharmazie der DGN, 15.-17.09.2011, Ochsenfurt, D

Publ.-Id: 16231 - Permalink


Materialcharakterisierungen mit Antimaterie: Atomaren Defekten auf der Spur
Wagner, A.;
Materialcharakterisierungen mit Antimaterie: Atomaren Defekten auf der Spur
  • Lecture (others)
    Tagung des Fachausschusses Materialcharakterisierung der Deutschen Gesellschaft für zerstörungsfreie Prüfung e.V., 07.-08.11.2011, Dresden, Deutschland

Publ.-Id: 16230 - Permalink


SiC growth modification and stress reduction in FLASiC assisted liquid phase epitaxy
Pezoldt, J.; Stauden, T.; Morales, F.; Polychroniadis, E. K.; Voelskow, M.; Skorupa, W.;
The defect density of the epitaxial SiC layers on Si result from the high defect density in the seeding layer formed by carbonization of the Si substrate. A method to reduce the defect density is flash lamp annealing. The recrystallisation can be improved if a three layers stack consisting of 3C-SiC/Si/3C-SiC/Si-substrate is used (iFLASiC-process). To improve the recrystallization C, Ge or both elements were added to Si. Ge and C additions to the Si and subsequent FLASiC processing l ead t o a s ubstantial increase o f t he m ass t ransfer. T he g rowth r ate r eached 1 0.0 μm/s. T he a chieved thickening of the lower layer strongly depends on the Si composition and is caused by the modification of the optical properties and the mass transport properties of the Si. Ge incorporation into Si and therefore into the Si melt enhance the mass transport from the upper SiC layer to the lower one. C incorporation into Si increases the available C contributing to SiC growth. Both elements lower the Si band gap increasing light absorption. Beside the growth modification the in plane strain in the 3C-SiC layer turns from tensile strain with a value of 0.0004 in the non buckling case to an in plane compressive strain with a strain value of - 0.0046. Non annealed layers of comparable thickness deposited under the same conditions exhibit tensile residual strain in the range of 0.002 to 0.006. FLASiC is not only able to improve the layer quality but also reduces the residual stress.
Keywords: Flash Lamp Annealing, SiC, Liquid Phase Epitaxy
  • Poster
    subtherm 2011 - International Topical workshop on Subsecond Thermal Processing of Advanced Materials, 25.-27.10.2011, Dresden, BRD

Publ.-Id: 16229 - Permalink


Synchrotron-based X-ray techniques for radioactive materials research: Understanding the chemical behaviour of radionuclides in solution
Ikeda, A.;
Treatment of spent nuclear fuels (SNFs) is one of the critical issues in the world’s nuclear power industry. The international consensus thus far is that the SNFs are supposed to be reprocessed to extract reusable nuclides (e.g., Pu or U) by solvent extraction, or buried deep in the ground to permanently isolate them from human contact. The basic- and applied research related with these SNFs treatments always requires fundamental information on the chemical behaviour of radionuclides in solution, since most chemical processes relevant to the treatment of SNFs (e.g., solvent extraction or geological disposal) occur in solution.
As one of the powerful experimental probes for radioactive materials research, synchrotron-based X-ray techniques have been extensively employed for the last few decades. This seminar will focus on the application of synchrotron-based X-ray methods to the study of radionuclides in solution systems, including the following three sub-topics: (1) X-ray absorption spectroscopy (XAS) and high energy X-ray scattering (HEXS) for characterizing the hydrolytic species of tetravalent cerium (Ce(IV)) in aqueous solution, (2) X-ray absorption spectroscopy for understanding the redox behaviour of actinides in aqueous solution, (3) multiple spectroscopic (XAS and UV-visible-NIR) and quantum chemical approach for acquiring structural information of individual chemical species in the mixed system.
Keywords: Synchrotron, XAS, HEXS, Actinides, Lanthanides, Solution, Spectroscopy
  • Invited lecture (Conferences)
    CLS internal seminar, 23.11.2011, Canadian Light Source, Saskatoon, Canada

Publ.-Id: 16227 - Permalink


ATHLET models for the Emergency Condenser and the Containment Cooling Condenser of the INKA test facility
Hristov, H. V.; Kozmenkov, Y.; Schäfer, F.;
The ATHLET code (GRS®) has been used for the numerical analyses of the EC (Emergency Condenser) and the CCC (Containment Cooling Condenser) performance at the INKA (INtegralversuchsanlage KArlstein) test facility. Three ATHLET 2.2 Cycle A models have been developed: EC, CCC and Integral model.
The EC model predictions for the postulated steady state scenario (EC characteristic curves) were compared with the old simulations (ATHLET 2.1 Cycle A model for of the EC). INKA EC transient run at 45 bar primary pressure was used as second validation step for the assessment of the different ATHLET versions influence on the numerical predictions. The EC ATHLET Cycle 2.2 A model validation was extended further with the transient EC INKA experiment at 80 bar primary pressure.
Technically, the CCC ATHLET model was based on the old CCC ATHLET 2.1 Cycle A one. However, significant improvements have been accomplished in order to make it capable of adequately representing the INKA CCC experimental layout and conditions. Two models have been developed to account for the different sparger designs. Experimental data (information) analyses have been in addition carried out due the initial poor model performance. The CCC ATHLET 2.2 Cycle A model ability to correctly capture the CCC heat transfer and in general the process has been demonstrated. Second CCC ATHLET model has been developed to incorporate the new sparger design. The model has been partly validated against the provided experimental data. While it was able to calculate well the initial stage of the experiment, it failed to represent the final one.
An integral INKA ATHLET model, which includes both the EC and the CCC, has been developed. This model incorporates the CCC one with new sparger design. Two LOCA scenarios have been postulated for the investigation of the EC-CCC performance under the INKA configuration. These scenarios include RPV (Reactor Pressure Vessel) and RSL (Reactor Steam Line) break. The EC – CCC joined operation under the break scenarios has been analysed.

- vertraulich -
Nachfrage bei Dr. S. Kliem
  • Other report
    Dresden: HZDR, 2011
    94 Seiten

Publ.-Id: 16226 - Permalink


Synchrotron radiation-based X-ray diffraction during magnetron co-sputtering of Ni-Ti films
Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.;
The study of Ni-Ti shape memory alloy films is of great technological interest for applications in the field of microengineering. They can work as sensors and actuators at the same time. However, there are still important issues unresolved like formation of film texture and its control. Films exhibiting the two-way shape memory effect are also required. A better understanding of the underlying growth mechanisms and their microstructural development requires sophisticated in-situ techniques. A two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the Rossendorf Beamline at the European Synchrotron Radiation Facility has been used for the processing of the Ni-Ti films. The in-situ x-ray diffraction studies enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth. It has been found that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. In some cases they exhibit a pronounced depth dependence of their preferential orientations. Amorphous SiO2 and TiN buffer layers have been used to successfully control their crystallographic orientations. This is an important achievement since the texture has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented. The deposition of graded Ni-Ti films by changing deliberately the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, has also been performed. The aim has been the optimization of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). It will lead to the development of smaller devices due to an optimal design of microdevices regarding size and weight (i.e., no consideration has to be paid to a resetting spring).
  • Poster
    EUROMAT 2011 (Symposium A54: Shape Memory Alloys (SMA) - Materials and Devices), 14.-15.09.2011, Montpellier, France

Publ.-Id: 16225 - Permalink


Optimising the efficiency of pulsed diode pumped Yb:YAG laser amplifiers for ns pulse generation
Ertel, K.; Banerjee, S.; Mason, P.; Phillips, P.; Siebold, M.; Hernandez-Gomez, C.; Collier, J.;
We present a numerical model of a pulsed, diode-pumped Yb:YAG laser amplifier for the generation of high energy ns-pulses. This model is used to explore how optical-to-optical efficiency depends on factors such as pump duration, pump spectrum, pump intensity, doping concentration, and operating temperature. We put special emphasis on finding ways to achieve high efficiency within the practical limitations imposed by real-world laser systems, such as limited pump brightness and limited damage fluence. We show that a particularly advantageous way of improving efficiency within those constraints is operation at cryogenic temperature. Based on the numerical findings we present a concept for a scalable amplifier based on an end-pumped, cryogenic, gas-cooledmulti-slab architecture.
Keywords: Laser amplifiers; Lasers, pulsed; Lasers, ytterbium; Pumping

Publ.-Id: 16224 - Permalink


Simultaneous time and wavelength resolved spectroscopy under two-colour near infrared and terahertz excitation
Bhattacharyya, J.; Wagner, M.; Zybell, S.; Winnerl, S.; Stehr, D.; Helm, M.; Schneider, H.;
Time and wavelength resolved spectroscopy requires optical sources emitting very short pulses and a fast detection mechanism capable of measuring the evolution of the output spectrum as a function of time. We use table-top Ti:sapphire lasers and a free-electron laser (FEL) emitting ps pulses as excitation sources and a streak camera coupled to a spectrometer for detection. One of the major aspects of this setup is the synchronization of pulses from the two lasers which we describe in detail. Optical properties of the FEL pulses are studied by autocorrelation and electro-optic sampling measurements. We discuss the advantages of using this setup to perform photoluminescence quenching in semiconductor quantum wells and quantum dots. Carrier redistribution due to pulsed excitation in these heterostructures can be investigated directly. Sideband generation in quantum wells is also studied where the intense FEL pulses facilitate the detection of the otherwise weak nonlinear effect.
Keywords: Photoluminescence quenching, streak camera, time and wavelength resolved spectroscopy

Publ.-Id: 16223 - Permalink


Thickness independent magneto-optical coupling constant of nickel films in the visible spectral range
Mok, K. M.; Scarlat, C.; Kovacs, G. J.; Li, L.; Zviagin, V.; McCord, J.; Helm, M.; Schmidt, H.;
Magneto-optical properties of nominally 10, 20, and 30 nm thick ferromagnetic Ni films have been investigated at room temperature by vector-magneto-optical generalized ellipsometry under saturated magnetization conditions in the sample surface plane. The magneto-optical dielectric tensor of Ni has been determined by reflection Mueller matrix ellipsometry in the spectral range from 300 to 1100 nm. Different sets of magnetic field induced Mueller matrix elements enable us to identify the magnetization directions in the sample. The extracted magnetic field and thickness independent magneto-optical coupling constant is useful for modeling the Mueller matrix and complex Kerr angle of magnetized Ni thin films in layered sample systems in dependence of the incident angle of light, wavelength, and magnetization.
Keywords: Mueller matrix, generalized ellipsometry, magneto-optics, nickel

Publ.-Id: 16222 - Permalink


Formation of U(VI) lactate and citrate complexes and their sorption onto Opalinus Clay between 10 and 60°C
Schmeide, K.; Steudtner, R.; Bernhard, G.;
Results to the U(VI) complexation with lactate and citrate and the influence of these ligands on U(VI) sorption onto Opalinus Clay (OPA) (Mont Terri, Switzerland) between 10°C and 60°C are shown.
Keywords: Complexation, sorption, uranium(VI)
  • Poster
    Workshop "HiTAC – High Temperature Aqueous Chemistry", 09.11.2011, Karlsruhe, Germany

Publ.-Id: 16221 - Permalink


Wechselwirkungen von Actiniden mit Biomolekülen
Barkleit, A.;
Die Komplexierung von Uran(VI) und Cm(III) mit den Zellwandkompartimenten Lipopolysaccharid und Peptidoglycan, charakterisiert durch TRLFS, EXAFS und FT-IR, wird dargestellt.
Keywords: uranyl, curium, lipopolysaccharide, peptidoglycan, TRLFS, EXAFS, FT-IR
  • Invited lecture (Conferences)
    2. Workshop zum Innovationsforum Geobiotechnologie, 03.-04.11.2011, Dresden, Deutschland

Publ.-Id: 16220 - Permalink


Field- and current-induced domain-wall motion in permalloy nanowires with magnetic soft spots
Meier, G.; Vogel, A.; Wintz, S.; Gerhardt, T.; Bocklage, L.; Strache, T.; Im, M.-Y.; Fischer, P.; Fassbender, J.ORC; McCord, J.
New concepts of high-density and ultrafast nonvolatile data storage devices involve the controlled motion of magnetic domain walls (DWs) in nanowires [1]. To realize such a device, reproducible and reliable pinning sites for individual DWs are required. Geometric constrictions are widely used to create local confining potentials acting as pinning sites [2]. As an alternative, pinning sites can be induced via a local modification of magnetic properties by ion irradiation [3]. In this case, a variation in the wire geometry on the nanoscale is not required. Implantation of chromium ions into permalloy is known to cause alloying and structural defects which lead to a reduction in the saturation magnetization MS, and the magnetic anisotropy as well as to a change in the exchange constant and the damping parameter [4]. The strength of the pinning potential can be tuned by the chromium ion fluence applied to induce the so-called magnetic soft spots [3].
Micromagnetic simulations, high resolution magnetic transmission soft X-ray microscopy at beamline 6.1.2 of the Advanced Light Source in Berkeley, CA, USA, and electrical measurements of the anisotropic magnetoresistance are employed to characterize the pinning potential which significantly differs for transverse and vortex walls. We demonstrate field-induced DW pinning and depinning as well as reliable DW depinning by single current pulses in a permalloy nanowire containing a square-shaped magnetic soft spot [5]. Lower requirements on the lithography in comparison to geometric constrictions on the nanoscale, a smaller distribution of properties due to parallel processing during implantation, and fine tunability of the pinning potential via the chromium ion fluence make the magnetic soft spots a promising candidate for applications.
Financial support by the Deutsche Forschungsgemeinschaft via Grant Nos. FA314/3-2 and MC9/7-2, the SFB 668 and the GrK 1286 as well as the Forschungs- und Wissenschaftsstiftung Hamburg via the Exzellenzcluster “Nano- Spintronik” is gratefully acknowledged. Operation of the X-ray microscope is supported by the US Department of Energy under Contract No. DE-AC02-05-CH11231.
References: [1] D. A. Allwood, Gang Xiong, M. D. Cooke, C. C. Faulkner, D. Atkinson, N. Vernier, R. P. Cowburn, Science 296, 2003 (2002); S. S. P. Parkin, U. S. Patent No. US 683 400 5 (2004).
[2] M.-Y. Im, L. Bocklage, P. Fischer, and G. Meier, Phys. Rev. Lett. 102, 147204 (2009).
[3] A. Vogel, S. Wintz, J. Kimling, M. Bolte, T. Strache, M. Fritzsche, M.-Y. Im, P. Fischer, G. Meier, and J. Fassbender, IEEE Trans. Mag. 46, 1708 (2010).
[4] J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[5] A. Vogel, S. Wintz, T. Gerhardt, L. Bocklage, T. Strache, M.-Y. Im, P. Fischer, J. Fassbender, J. McCord, and G. Meier, Appl. Phys. Lett. 98, 202501 (2011).
Keywords: domain wall; soft spot
  • Lecture (Conference)
    56th Annual Conference on Magnetism & Magnetic Materials, 30.10.-03.11.2011, Scottsdale, Arizona, USA

Publ.-Id: 16219 - Permalink


Microorganisms in potential nuclear waste disposal host rocks
Geissler, A.; Moll, H.; Bachvarova, V.; Lütke, L.; Selenska-Pobell, S.; Bernhard, G.;
It is known that microorganisms exist in host rocks of potential nuclear waste disposals. In this talk, some results will be presented from the current project about the microbial diversity in clay (Opalinus clay) and the interactions of dominant microorganisms with actinides. Especially the interactions of a Sporomusa sp. clay isolate with Curium(III) will be shown. In the second part of the talk, some information’s will be given about Halophiles in general and future plans to investigate the microbial diversity in salt rocks.
  • Lecture (Conference)
    ABC Salt Workshop, 07.-08.11.2011, Karlsruhe, Germany

Publ.-Id: 16218 - Permalink


Kinetics and Thermodynamics of Defects and Nanostructures
Posselt, M.;
Computer simulations using classical interatomic potentials are an efficient tool to investigate and understand atomic-level properties and processes in advanced materials. They allow the consideration of length and time scales which are often hardly accessible by experiments. However, the accuracy of the interatomic potentials employed in such type of simulations determines decisively the quality of the obtained results. Therefore, these potentials must be continuously improved and evaluated.
In the talk two applications of atomistic computer simulations are illustrated. The focus is on kinetics and thermodynamics of defects and nanostructures in materials for micro- and nanoelectronics and in structural materials for fission reactors.
The first example deals with the investigation of basic migration mechanisms of mono- and di-(self-)interstitials in Si using molecular dynamics simulations. Both the atomic mobility due to the presence of the defect and the defect mobility itself were determined. The mechanism of di-interstitial migration depends on temperature, in contrast to that of the mono-interstitial.
The subject of the second example is the structure, energetics and thermodynamics of coherent nanoclusters in bcc-Fe containing vacancies, Cu and Ni. For clusters up to a size of 200 monomers (vacancies, Cu and Ni atoms) the most stable configurations at T=0 are determined by Metropolis Monte Carlo simulations and their formation and binding energies are calculated. The temperature-dependent free formation and free binding energies of the nanoclusters are determined by taking into account configurational contributions which are calculated using the Wang-Landau Monte Carlo method.
Keywords: Si, mono-interstitials, di-interstitials, kinetics, Molecular Dynamics, Fe-based alloys, nanoclusters energetics, thermodynamics, Monte-Carlo simulations
  • Lecture (others)
    Seminarvortrag, Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, 24.10.2011, Livermore, USA
  • Lecture (others)
    Seminarvortrag, Materials Science Laboratory, Los Alamos National Laboratory, 27.10.2011, Los Alamos, USA

Publ.-Id: 16217 - Permalink


Structure, Energetics and Thermodynamics of Embedded Nanoclusters
Posselt, M.;
not available, please contact the author
Keywords: embedded nanoclusters, structure, energetics, thermodynamics
  • Lecture (others)
    Seminarvortrag, Department of Mathematical Sciences, Loughborough University, 20.10.2011, Loughborough, UK

Publ.-Id: 16216 - Permalink


Ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures
Bracht, H.; Radek, M.; Kube, R.; Knebel, S.; Posselt, M.; Schmidt, B.; Haller, E.; Bougeard, D.;
Gallium (Ga) implantation induced self-atom mixing in crystalline and amorphous germanium (Ge) is investigated utilizing isotopically controlled Ge multilayer structures grown by molecular beam epitaxy. The distribution of the Ga ions and the ion-beam induced depth-dependent mixing of the isotope structure was determined by means of secondary ion mass spectrometry. Whereas the distribution of Ga in the crystalline and amorphous Ge is very similar and accurately reproduced by computer simulations based on binary collision approximation (BCA), the ion-beam induced self-atom mixing is found to depend strongly on the state of the Ge structure. The experiments reveal stronger self-atom mixing in crystalline than in amorphous Ge. Atomistic simulations based on BCA reproduce the experimental results only when unphysically low Ge displacement energies are assumed. Analysis of the self-atom mixing induced by silicon implantation confirms the low displacement energy deduced within the BCA approach. This demonstrates that thermal spike mixing contributes significantly to the overall mixing of the Ge isotope structures. The disparity observed in the ion-beam mixing efficiency of crystalline and amorphous Ge indicates different dominant mixing mechanisms. We propose that self-atom mixing in crystalline Ge is mainly controlled by radiation enhanced diffusion during the early stage of mixing before the crystalline structure turns amorphous, whereas in an already amorphous state self-atom mixing is mediated by cooperative diffusion events.
Keywords: ion-beam mixing, germanium, amorphous germanium

Publ.-Id: 16215 - Permalink


A Technology Platform for Translational Research on Laser Driven Particle Accelerators for Radiotherapy
Enghardt, W.; Bussmann, M.; Cowan, T.; Fiedler, F.; Kaluza, M.; Pawelke, J.; Schramm, U.; Sauerbrey, R.; Tünnermann, A.; Baumann, M.;
It is widely accepted that proton or light ion beams may have a high potential for improving cancer cure by means of radiation therapy. However, at present the large dimensions of electromagnetic accelerators prevent particle therapy from being clinically introduced on a broad scale. Therefore, several technological approaches among them laser driven particle acceleration are under investigation.
Parallel to the development of suitable high intensity lasers, research is necessary to transfer laser accelerated particle beams to radiotherapy, since the relevant parameters of laser driven particle beams dramatically differ from those of beams delivered by conventional accelerators: The duty cycle is low, whereas the number of particles and thus the dose rate per pulse are high. Laser accelerated particle beams show a broad energy spectrum and substantial intensity fluctuations from pulse to pulse. These properties may influence the biological efficiency and they require completely new techniques of beam delivery and quality assurance.
For this translational research a new facility is currently constructed on the campus of the university hospital Dresden. It will be connected to the department of radiooncology and host a petawatt laser system delivering an experimental proton beam and a conventional therapeutic proton cyclotron. The cyclotron beam will be delivered on the one hand to an iso-centric gantry for patient treatments and on the other hand to an experimental irradiation site. This way the conventional accelerator will deliver a reference beam for all steps of developing the laser based technology towards clinical applicability.
Keywords: Radiotherapy, photons, electrons, protons, ions, cyclotron, synchrotron, laser particle acceleration
  • Contribution to proceedings
    SPIE Optics + Optoelectronics, 18.-21.04.2011, Czech Republic, Prague
    Proceedings of the SPIE, Vol. 8079, 79681

Publ.-Id: 16214 - Permalink


CFD-Modellierung von Wandsieden und technische Anwendung
Krepper, E.; Rzehak, R.;
Die Verifikation von Auslegungsverbesserungen an Brennelement-Abstandhaltern und ihr Einfluss auf den kritischen Wärmestrom erfordert kostspielige Experimente. Deswegen ist die Ergänzung oder sogar der Ersatz dieser Experimente durch numerische Analysen von großem Interesse. CFD-Modelle haben das Potential der Entwicklung von Modellansätzen unabhängig von der bestimmten Geometrie.
Der Vortrag beschreibt den aktuellen Stand der CFD-Modellierung wan Wandsieden und mögliche Beiträge zur Brennelementauslegung. Mit dem aktuellen Stand ist zumindest die vergleichende qualitative Analyse möglich. Bessere quantitativ zuverlässige Resultate sind mit verbesserten Modellen möglich, die auf CFD-tauglichen Experimenten basieren. Der kürzliche Fortschritt bei der Kopplung des Wandsiedemodells mit einem Populationsbilanzmodell wurde gezeigt. Vieleversprechende Reultate sind mit der in Entwicklung befindlichen schnellen Röntgentomographie zu erwarten.
Keywords: CHF, CFD, mixing vanes, subcooled boiling, fuel assembly design, DEBORA tests, MUSIG model
  • Invited lecture (Conferences)
    Kompaktkurs "Kavitation", 27.-28.10.2011, Dresden, Deutschland

Publ.-Id: 16213 - Permalink


CFD-Modelling of subcooled boiling and their technical application
Krepper, E.; Rzehak, R.;
The verification of design improvements of a fuel assembly of a nuclear reactor core and their influence on the critical heat flux require expensive experiments. Therefore the supplementation or even the replacements of experiments by numerical analyses are of relevant interest in fuel assembly design. The CFD modeling has the potential of simulation independent on the certain geometry.
The presentation describes the actual state of CFX modeling of subcooled boiling and their possible contribution for rod bundle design. The comparative investigation of different designs is possible at least qualitatively. For more quantitatively reliable results the models have to be improved. In the presentation the demands on the accuracy of measured values are established. Most promising results are expected by tomographic methods like by fast X-ray tomography.
Keywords: CHF, CFD, mixing vanes, subcooled boiling, fuel assembly design, DEBORA tests
  • Invited lecture (Conferences)
    ANSYS Conference & 29. CADFEM Users’ Meeting 2011, 19.-21.10.2011, Stuttgart, Deutschland

Publ.-Id: 16212 - Permalink


An analytical solution of the time dependent diffusion equation in a composite slab
Glivici-Cotruta, V.; Merk, B.;
The time-dependent, one-dimensional diffusion equation is solved for a finite slab of two layers. An external source is supplied to one of the layers. The differential equations are subject to the reflecting boundary conditions at the two outer boundary surfaces. The flux and the current density are continuous across the interface between two media. The exact analytical solution is expressed in terms of a Green's function. The solution is developed by the application of the Laplace transformation.
Keywords: Green's function, diffusion, Laplace transformation, composite slab

Publ.-Id: 16211 - Permalink


Terrestrial cosmogenic radionuclides for geomorphology applications
Merchel, S.;
ohne Abstract, eingeladener Vortrag
Keywords: cosmogenic radionuclides, TCN, AMS accelerator mass spectrometry
  • Lecture (others)
    Seminar, School of Geography, Politics and Sociology, 02.11.2011, Newcastle upon Tyne, UK

Publ.-Id: 16210 - Permalink


The Emerging Opportunities of New Multimeric Cyclam Based Copper Chelators in Multimodal Imaging
Kubeil, M.;
kein Abstract verfügbar
  • Lecture (Conference)
    8th Supraphone Meeting, 07.-10.09.2011, Funchal, Portugal

Publ.-Id: 16209 - Permalink


Radioaktive Substanzen helfen beim Suchen und Zerstören von Tumoren
Kubeil, M.;
Der Vortrag bietet eine Übersicht und befasst sich mit den Möglichkeiten und der Bedeutung von Radiopharmaka hinsichtlich ihres Einsatzes für die nuklearmedizinische Diagnostik und Therapie von Krebserkrankungen.
  • Lecture (others)
    Dresdner Lange Nacht der Wissenschaften, 01.07.2011, Dresden, D

Publ.-Id: 16208 - Permalink


Radiopharmazie am Helmholtz-Zentrum Dresden-Rossendorf
Kubeil, M.;
kein Abstract verfügbar
  • Lecture (others)
    Patiententag im Ärztehaus, 04.05.2011, Sebnitz, D

Publ.-Id: 16207 - Permalink


Cyclampropionsäure-Derivate: Neue Chelatsysteme für nuklearmedizinische Anwendungen?
Kubeil, M.; Lehmann, T.; Stephan, H.; Steinbach, J.;
Die Entwicklung von mehrfunktionellen Komplexbildnern für Radiometallnuklide im Hinblick auf eine medizinische Anwendung stellt ein intensiv bearbeitetes Forschungsgebiet dar. Als sehr interessant erweisen sich makrocyclische Tetraamin-Systeme, die eine Mehrfachfunktionalisierung mit löslichkeitsvermittelnden, fluoreszierenden und zielsuchenden Einheiten am selben Molekülkern gestatten. Komplexe des 1,4,8,11-Tetraazacyclotetradecans (Cyclam) mit radioaktiven Kupferisotopen nehmen einen besonderen Stellenwert ein, da diese eine hohe thermodynamische Stabilität aufweisen, kinetisch inert sind und den Zugang zur nuklearmedizinischen Radiodiagnostik (64Cu) sowie Radiotherapie (67Cu) eröffnen.
Umfangreiche Untersuchungen zur Anwendung in der Radiopharmazie sind bisher zu Essigsäure-Derivaten des Cyclams - insbesondere zum 1,4,8,11-Tetraessigsäure-1,4,8,11-tetraazacyclotetradecan (TETA) - durchgeführt worden [1, 2]. Demgegenüber sind Propionsäure-Derivate I - IV in diesem Zusammenhang wenig untersucht [3]. Wir konnten zeigen, dass die Cyclamtetrapropionsäure IV unter physiologischen Bedingungen sehr stabile Komplexe mit 64CuII bildet und durch Kupplung von spezifischen Peptiden an dieses Ligandgerüst ein Targeting in biologischen Systemen möglich ist [4].

Es werden die Synthese von Cyclampropionsäure-Derivaten vorgestellt sowie koordinations- und radiochemische Aspekte dieser Liganden mit CuII diskutiert.

Literatur:

[1] R. Delgado, V. Felix, L. M. P. Lima, D. W. Price, Dalton Trans. 2007, 2734-2745.
[2] X. Liang, P. J. Sadler, Chem. Soc. Rev. 2004, 33, 246-266.
[3] M. Kuhlmann, H. Stephan, J. Steinbach, A. Röhrich, In “Technetium and other Radiometals in Chemistry and Medicine“, U. Mazzi, W. C. Eckelman, W. A. Volkert (Eds.), SGE Editoriali, Padova, Italy, 2010, 77-80.
[4] A. Röhrich, R. Bergmann, A. Kretzschmann, S. Noll, J. Steinbach, J. Pietzsch, H. Stephan J. Inorg. Biochem. 2011, submitted.
  • Lecture (Conference)
    GDCh-Wissenschaftsforum Chemie 2011, 04.-07.09.2011, Bremen, D

Publ.-Id: 16206 - Permalink


Nanomaterials: Applications in Cancer Imaging and Therapy
Stephan, H.;
kein Abstract verfügbar
  • Lecture (Conference)
    8th SUPRAPHONE Meeting, 07.-10.09.2011, Funchal, Portugal
  • Invited lecture (Conferences)
    Seminar, Beijing Normal University, College of Chemistry, 23.04.2013, Beijing, China

Publ.-Id: 16205 - Permalink


Pyridin-haltige Liganden des 1,4,7-Triazacyclononans (TACN): Vielseitig einsetzbare bifunktionelle Chelatoren für Radiokupfer
Stephan, H.; Ruffani, A.; Steinbach, J.;
Dreizähnige makrocyclische Liganden auf der Basis des 1,4,7-Triazacyclononans (TACN) bilden mit Metallionen Koordinationsverbindungen sehr hoher Stabilität. Aufgrund der kleinen Ringgröße des Makrocyclus sind die Zentralionen außerhalb der Ringebene in der Weise angeordnet, dass die Donoratome eine maximale Überlappung der Bindungsorbitale gestatten [1]. Dadurch wird eine hohe thermodynamische Stabilität bei gleichzeitig schneller Komplexbildungskinetik erzielt. Derartige Liganden weisen damit günstige Eigenschaften für einen Einsatz in der nuklearmedizinischen Diagnostik und Therapie auf. Der bekannteste Vertreter ist hier der hexadentate Ligand 1,4,7-Triessigsäure-1,4,7-triazacyclononan (NOTA), der sehr stabile Komplexe mit Radionukliden der dreiwertigen Metalle GaIII, InIII und YIII bildet, aber auch in der Diskussion für CuII ist [2].
Wir konnten zeigen, dass insbesondere Pyridin-haltige Derivate des TACN I sehr stabile Komplexe mit dem Radionuklid 64CuII bilden und damit nach entprechender Funktionalisierung mit spezifischen Peptiden und Proteinen in der nuklearmedizinischen Diagnostik eingesetzt werden können [3].
Es werden Arbeiten zur Synthese von kupplungsfähigen Markierungsbausteinen Ia – Ic sowie Konjugationsreaktionen mit geeigneten Biomolekülen vorgestellt. Der Einfluss von Pyridineinheiten auf die Koordinationsgeometrie und Stabilität von CuII-Komplexen sowie die Eignung ausgewählter radioaktiv markierter Komplexe für die Tumordiagnostik werden diskutiert.

Literatur:
[1] P. Chaudhuri, K. Wieghardt, Prog. Inorg. Chem. 1987, 37, 329-436.
[2] T. J. Wadas, E. H. Wong, G. R. Weisman, C. J. Anderson, Chem. Rev. 2010, 110, 2858-2902.
[3] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran,, M. Walther, J.-U. Künstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 19, 719-730.
  • Lecture (Conference)
    GDCh-Wissenschaftsforum Chemie 2011 , 04.-07.09.2011, Bremen, D

Publ.-Id: 16204 - Permalink


Copper-mediated cross-linking of S100A4, but not of S100A2, results in proinflammatory effects in melanoma cells
Haase-Kohn, C.; Wolf, S.; Lenk, J.; Pietzsch, J.;
The aim of this study was to investigate the response to and the physiological consequences of copper-mediated cross-linking of S100A2 and S100A4, two members of the S100 family of EF-hand calcium-binding proteins. As demonstrated by electrophoresis and mass spectrometry techniques S100A2 and S100A4 show formation of cross-links due to copper-mediated oxidation of cysteine residues. For S100A4, but not for S100A2, this results in both increased activation of NFκB and secretion of TNF-α in human A375 and, to a higher extent, in RAGE-transfected melanoma cells. The data suggest that a prooxidative tumor microenvironment enhances proinflammatory and prometastatic action of S100A4.

Publ.-Id: 16203 - Permalink


Production of 61Cu via the 64Zn(p,α)61Cu reaction with high specific activity
Thieme, S.; Walther, M.; Rajander, J.; Pietzsch, H.-J.; Solin, O.; Steinbach, J.;
Objectives:
Optimized production and separation parameters, use of only ultra-pure reagents with ppt-levels of metal traces are necessary for the production of high specific activities (SA) 61Cu. From previous studies regarding production of 61Cu there is little data on SA published. McCarthy et al. [1] measured SA ranging from 47 to 190 GBq/µmol for 61Cu produced via 61Ni(p,n)61Cu and 60Ni(d,n)61Cu reaction. An alternative method for production is the use of the 64Zn(p,α)61Cu reaction [2]. The use of 99% enriched 64Zn is considerably cheaper than use of enriched 61Ni.
Methods:
A target setup was developed using approximately 100 mg enriched 64Zn electroplated on a massive gold disk for proton irradiation. The radiochemical separation technique included recycling of the target material and was based on ion exchange methods described in the literature [3-8]. It consisted of a system of cation and anion exchange columns. This ion exchanger cascade included a twofold cation exchange step developed for effective removal of gallium by-products (66/67/68Ga) and one anion exchange step to separate 61Cu from the target material. This separation procedure took one hour. After the recycling procedure for the target material a new electrodeposition of the 64Zn could be carried out. The method used small ion exchange columns, aqueous hydrochloric acid solutions and is described in detail by Thieme et al. [2]. The SA was evaluated by TETA binding assay with radio TLC. Two different cyclotrons were used for the irradiations: a Cyclone 18/9 (IBA, Belgium) at the Insitute of Radiopharmacy in Dresden-Rossendorf with a home-made solid target holder and a CC 18/9 (Efremov Institute, St. Petersburg, Russia) at Turku PET Centre in Turku also with a home-made solid target holder.
Results:
With the Cyclone 18/9 the irradiations were performed with 12 µA of 16 MeV protons on target for 30 min and yielded about 300 MBq 61Cu at EOB. The CC 18/9 irradiations with 30 µA of 13 MeV protons on target for 30 min yielded 330-400 MBq 61Cu, and with 3 hours 1150 MBq 61Cu, respectively. SA of 500 GBq/µmol were achieved with the CC 18/9 which is equipped with a solid target holder completely made of aluminum preventing contamination of the target disk with non-radioactive copper. Compared to the low specific activities, less than 1 GBq/µmol was achieved at the Cyclone 18/9. This low SA is most likely caused by contamination with non-radioactive copper from the currently used solid target holder containing brass/copper parts.
Conclusions:
These results show the possibility to produce high SA 61Cu (SA up to 500 GBq/µmol) via the 64Zn(p,α)61Cu reaction at low proton energies. Together with the used radiochemical separation method it is possible to produce high quality 61Cu routinely.
  • Poster
    19th International Symposium on Radiopharmaceutical Scieneces (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S237

Publ.-Id: 16202 - Permalink


H-F hydrogen bonds as synthons in polymeric quantum magnets
Beyer, R.; Manson, J. L.; Schlueter, J. A.; Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Poster
    2nd EuroMagNET Summer School, 05.-11.09.2010, Ameland, The Netherlands
  • Poster
    Phd Seminar, 22.-24.09.2010, Meissen, Deutschland

Publ.-Id: 16201 - Permalink


Magnetization in Magnetic Molecules
Kampert, E.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    2nd EuroMagNET Summer School, 05.-11.09.2010, Ameland, The Netherlands

Publ.-Id: 16200 - Permalink


THz-range free-electron laser ESR spectroscopy: techniques and applicatons in high magnetic fields
Ozerov, M.; Cizmar, E.; Kamensky, D.; Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.; Zvyagin, S. A.; Wünsch, R.; Seidel, W.;
es hat kein Abstract vorgelegen
  • Lecture (Conference)
    2nd EuroMagNET Summer School, 05.-11.09.2010, Ameland, The Netherlands

Publ.-Id: 16199 - Permalink


Specific Heat at mK Temperatures and DC fields up to 16 T
Götze, K.; Wolff-Fabris, F.; Uhlarz, M.; Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Poster
    Phd Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 16198 - Permalink


Magnetic quantum oscillations in the normal and superconducting state of borocarbide superconductors
Bergk, B.;
es hat kein Abstract vorgelegen
  • Lecture (Conference)
    22. Edgar Lüscher-Seminar, 12.-18.02.2011, Klosters, Switzerland

Publ.-Id: 16197 - Permalink


De Haas-van Alphen investigations of iron pnictides: first results
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Kick-off meeting of the SPP 1458 "High-temperature superconductivity in iron pnictides", 24.-25.02.2011, Dresden, Deutschland

Publ.-Id: 16196 - Permalink


Research at High Magnetic Fields
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    22. Edgar Lüscher-Seminar, 12.-18.02.2011, Klosters, Switzerland

Publ.-Id: 16195 - Permalink


Activities at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    HGF-PNI Workshop at the Helmholtz-Zentrum Berlin, 17.01.2011, Berlin, Deutschland

Publ.-Id: 16194 - Permalink


Fluctuation conductivity in melt-textured YBaCuO samples under low magnetic fields
Dias, F. T.; Vieira, V. N.; Pureur, P.; Rodrigues Jr., P.; Obradors, X.; Wolff-Fabris, F.;
We have studied thermal fluctuations of the electrical conductivity in melt-textured YBa2Cu3O7 (YBCO) samples under low magnetic fields. Measurements were performed either for current applied parallel or perpendicular to the c-axis and fluctuation conductivity was studied in the proximity of the superconducting transition. Two melt processed samples were prepared with different concentrations of Y2Ba1Cu1O5 (Y211) phase. For the sample with lower concentration, 3D-Gaussian and genuine critical 3D-XY-E fluctuation regimes were identified in the conductivity parallel to the ab plane and a regime beyond 3D-XY was also observed. The 3D-XY-E scaling was also identified in the fluctuation conductivity along the c-axis. In the sample with higher concentration of the Y211 phase, disorder effects are relevant. The results indicate that the superconducting state in YBCO has a three-dimensional character, and suggest the presence of a sub-dominant order-parameter component that has an appreciable projection along the c-axis.

Publ.-Id: 16193 - Permalink


Enhanced magnetic properties of Bi-substituted cobalt ferrites
Franco, J. A.; Machado, F. L. A.; Zapf, V. S.; Wolff-Fabris, F.;
In this paper we present a magnetic study of Co1-xBixFe2O4 nanoparticles obtained by applying magnetic fields up to 14 T and for temperatures in the range of 5 to 340 K. Hysteresis loops yield a saturation magnetization (Ms), coercive field (Hc), and remanent magnetization (Mr) that vary significantly with temperature and bismuth content. The T-dependence of Ms obtained for H = 5 T presents a maximum at 150 K and a minimum at 25 K that are also dependent on the value of x. However, for H = 14 T, this anomalous behavior disappears and the magnetization smoothly approaches saturation down to 5 K. The magnetic cubic anisotropy constant for different Bi contents, determined by a “law of approach” to saturation, was found to be smaller than those values for pure cobalt ferrite nanoparticles and strongly dependent on temperature. A discussion on the implications of the anomalous behavior in the determination of the anisotropy constant in these sample materials is also presented.
  • Journal of Applied Physics 109(2011), 07A745

Publ.-Id: 16192 - Permalink


In situ monitoring of convection effects on segregation freckle formation
Shevchenko, N.; Eckert, S.; Boden, S.; Gerbeth, G.;
Visualizations of the solidification process were obtained by means of X-ray radioscopy within a Hele-Shaw cell filled with Ga-25wt%In alloy. The complete temperature field was measured in additional experiments by an infrared camera (Trotec IC 080 LV). The evolution of segregation channels (so-called ‘chimneys’) and microstructure of mushy zone was investigated and convection effects were highlighted. In the case of thermo-solutal convection the probability of chimney formation depends sensitively on variations of the horizontal temperature distribution. The temperature difference between the central part and the periphery of the solidification cell may cause a modification of the natural circulation inside the melt.
The second part of this study concerns the case when the natural convection is superimposed by an electromagnetically driven flow perpendicular to the dendrites growth direction. The main effects of forced melt flow are a modification of the dendritic structure and flow-induced redistribution of the solute concentration.
A quantitative assessment of the melt convection directly at the solid-liquid interface was obtained by applying the optical flow approach, which provided information about the velocity field. This quantitative analysis and experimental data of flow field and temperature distribution gives a better understanding of the interplay be-tween melt flow and solidification process.
Keywords: solidification, X-ray radiography, melt convection, segregation
  • Lecture (Conference)
    Modeling of Casting, Welding and Advanced Solidification Processes 2012 (MCWASP XIII), 17.-22.06.2011, Schladming, Österreich
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 33(2012), 012035
    DOI: 10.1088/1757-899X/33/1/012035

Publ.-Id: 16191 - Permalink


Research at High Magnetic Fields - Activities at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument in condensed-matter physics. For the observation of many phenomena very high magnetic fields are es-sential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), that in 2007 has opened its doors for external users, pulsed magnetic fields up to about 72 T are readily available and a European record field of 87.2 T has been reached. The laboratory has set the ambitious goal of reaching 100 T on a 10 ms timescale. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 µm. Cryotech-niques and different sample probes for a broad range of experimental techniques custom designed for the pulsed magnets are available for users. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Besides introducing some highlights of the HLD experimental infra-structure, some recent scientific research results will be presented. This includes the determination of the doping-dependent evolution of the Fermi surface of elec-tron-doped high-temperature superconductors by means of Shubnikov de Haas measurements. The observed reconstruction of the Fermi surface gives evidence for the existence of a superlattice potential, the origin of which is still under debate. Fur-ther, the recently found evidence for the Fulde Ferrell Larkin Ovchinnikov state in an organic superconductor will be presented. Emphasis will be laid on such examples where neutron research at high fields might be able to contribute in unravelling topical open questions.
  • Invited lecture (Conferences)
    Workshop "Present Status and Perspectives of Neutron Research in High Magnetic Fields", 31.03.-01.04.2011, Berlin, Deutschland

Publ.-Id: 16190 - Permalink


Adjustment and verification of macroscopic melt flow during solidi-fication by means of various AC magnetic fields
Eckert, S.; Räbiger, D.; Vogt, T.; Gerbeth, G.;
AC magnetic fields unlock an enormous potential to realize a variety of flow structures in molten metals, which makes the electromagnetic stirring attractive for control-ling the melt flow during solidification. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macro-scale especially in solute-rich alloys showing different equilibrium concentrations of solute in the mixed crystal and the surrounding melt. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification, which in turn requires a detailed knowledge of the flow structures and a profound understanding of the complex interaction between melt flow, temperature and concentration field.
Previous investigations considered the use of time-modulated AC magnetic field to control the heat and mass transfer at the solidification front. It has been shown recently under laboratory conditions, that an accurate tuning of the magnetic field parameters can avoid segregation effects, however, a mismatch of the relevant modulation parameter may lead to worse results. Further investigations in form of numerical simulations accompanied by model experiments are necessary to achieve a quantitative understanding of the effect of fluid flow on the microstructure evolution.
This paper presents an experimental study which at first is focused on obtaining quantitative information about the isothermal flow field exposed to various magnetic field configurations. In a second step solidification experiments are carried out to verify the effect of a certain flow field on the solidification process. Furthermore, a new experimental set-up has been constructed to investigate electromagnetically-driven flows under realistic conditions of directional solidification, in particular the behaviour of the flow pattern in case of a propagating interface.
Keywords: solidification, electromagnetic stirring, rotating magnetic field, flow control
  • Lecture (Conference)
    Modeling of Casting, Welding and Advanced Solidification Processes 2012 (MCWASP XIII), 17.-22.06.2012, Schladming, Österreich
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 33(2012), 012047
    DOI: 10.1088/1757-899X/33/1/012047

Publ.-Id: 16189 - Permalink


Recent Developments at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
At the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), that in 2007 has opened its doors for external users, pulsed magnetic fields up to 70 T on a timescale of 150 ms as well as 60 T with 1.5 s pulse duration are available and a European record field of 87.2 T has been reached [1,2]. The laboratory has set the ambitious goal of reaching 100 T on a 10 ms timescale. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed-field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 µm. Cryotechniques and different sample probes for a broad range of experimental techniques custom designed for the pulsed magnets are readily available for users. These techniques include magnetization, ultrasound, electron spin resonance, cyclotron resonance, as well as nuclear magnetic resonance and specific-heat measurements. Recent improvements in signal-to-noise ratios allow to resolve relative resistance changes in electrical-transport measurements of about 10-4 [3] and relative length changes in magnetostriction experiments of about 10-7 [4]. In reply to the very strong user demand an extension of the HLD with additional pulse-field cells, capacitor bank, and improved infrastructure will be built starting from 2011. In-house research of the HLD focuses on electronic properties of strongly correlated electron systems at high magnetic fields. Besides introducing some highlights of the HLD experimental infrastructure, some recent scientific research results will be presented.
  • Invited lecture (Conferences)
    2nd International Workshop on Frontier Science in Pulsed Magnetic Fields, 20.-22.04.2011, Wuhan, China

Publ.-Id: 16188 - Permalink


Flow oscillations driven by a rotating magnetic field in liquid metal columns with an upper free surface
Travnikov, V.; Eckert, K.; Nikrityuk, P. A.; Odenbach, S.; Vogt, T.; Eckert, S.;
Oscillatory flow instabilities in a liquid metal cylinder with a free upper surface, exposed to a rotating magnetic field (RMF), are analysed by numerical simulations of the axisymmetric Navier-Stokes equations. The critical Taylor number designating the onset of the oscillatory flow regime decreases with increasing aspect ratio A= H/R while the Taylor-number interval, where the flow oscillations occur, becomes narrower. The instability is initiated near the free surface, where an oscillatory variation of the size and position of the upper vortex in the secondary flow can be observed accompanied by a horizontal oscillation of the azimuthal velocity maximum at the free surface. The predicted flow regimes have been observed in corresponding model experiments with GaInSn using the Ultrasound Doppler Velocimetry (UDV) for flow field measurements. The occurrence of the oscillatory flow regime depends sensitively on the cleanliness of the liquid metal surface.
Keywords: computer simulation, fluid flows, magnetic fields, stirring

Publ.-Id: 16187 - Permalink


Polarization option for the Time-of-Flight Spectrometer FOCUS
Ackermann, R.; Filges, U.; Horisberger, M.; Holitzner, L.; Bollhalder, A.; Keller, P.; Schneider, M.; Stahn, J.; Straessle, T.; Embs, J. P.; Hempelmann, R.;
es hat kein Abstract vorgelegen
  • Poster
    ECNS 2011 (5th European Conference on Neutron Scattering), 19.-22.07.2011, Prague, Czech Republic

Publ.-Id: 16186 - Permalink


Status of the Pulsed-Magnet-Development Program at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.; Wustmann, B.; Herrmannsdörfer, T.; Wosnitza, J.;
The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which offers to researches a variety of experimental techniques combined with nondestructive pulsed magnetic fields. Recently a new, 9.5 MJ dualcoil magnet has been commissioned. This magnet has achieved magnetic field of 91.4 T in a 16 mm bore and it is available for users now. In this paper, we report on some key upgrades in the magnet design which have led to breaking the 90 T limit at the HLD. Further possible design improvements are discussed. In addition, we share our operational experience obtained with the pulsed magnets.
  • Lecture (Conference)
    MT22, 12.-16.09.2011, Marseille, France

Publ.-Id: 16185 - Permalink


Manganese-doped (1-x)BiScO3-xPbTiO3 high-temperature ferroelectrics: Defect structure and mechanism of enhanced electric resistivity
Drahus, M.; Jakes, P.; Erdem, E.; Schaab, S.; Chen, J.; Ozerov, M.; Zvyagin, S.; Eichel, R.;
The effect of multivalency manganese doping on the defect structure and enhanced electrical resistivity is studied for the high-temperature piezoelectric (1 - x)BiScO3-xPbTiO3 (BSPT) solid-solution system by means of multifrequency electron paramagnetic resonance spectroscopy combined with conductivity measurements. The results show that manganese is rather incorporated on a scandium than a titanium site as an isovalent substitute (MnScx) instead of acceptor-type centers, such as Mn(Ti)', Mn(Ti)'', or Mn(Sc)'. The enhanced electric resistivity is found being on the one hand due to the trapping of conduction electrons at the manganese functional center sites (Mn(Sc)(x) + e' -> Mn(Sc)'). On the other hand, through the formation of (Mn(Sc)' - V(O)(center dot center dot))(center dot) defect complexes the ionic conductivity is reduced. Concerning the overall mechanism of charge compensation in that material, both kinds of defects mutually compensate.
  • Physical Review B 84(2011), 064113

Publ.-Id: 16184 - Permalink


Metastable Bi8Ni8S by Reductive Pseudomorphosis of Bi8Ni8SI2
Kaiser, M.; Isaeva, A.; Skrotzki, R.; Schwarz, U.; Ruck, M.;
The bimetallic subsulfide Bi8Ni8S was synthesized by reduction of Bi8Ni8SI2 with n-BuLi. Bi8Ni8S is metastable and decomposes exothermically at about 180°C. In a pseudomorphosis, the shiny black crystals of the precursor were preserved, while the iodide ions were extracted and the pre-formed 1\infinity[Bi8Ni8S] fragments rearranged into a pseudo-hexagonal rod packing [space group Pbam, a = 1750.14(7) pm, b = 1007.7(2) pm, c = 419.6(3) pm]. The rods have an effective diameter of about 1 nm and consist of an outer octagonal tube of bismuth atoms and an inner octagonal tube of nickel atoms. This arrangement markedly resembles the columnar Ta4Te4Si structure type. The difference comes with the disulfide groups that reside on the cen-tral axis. Interatomic distances inside the rods are almost not affected by the reduction, and thus the electronic band structure is not much altered. Yet, the additional electrons raise the Fermi level into a local maximum of the density of states and occupy predominantly antibonding Ni–Ni and S–S states. The dominant Bi–Ni multicenter bonding is accompanied by localized two-center bonds between nickel atoms. The charges of the nickel atoms as well as ELI-D basin populations of Ni– Ni and Ni–Bi bonds change considerably, indicating that the tube is (un)charging quite flexibly and acts as an electron reservoir. In contrast to the iodide precursor, the weak Pauli paramagnetism of Bi8Ni8S is slightly enhanced and spin correlations are observed below 20 K.

Publ.-Id: 16183 - Permalink


Uniaxial R2Co17 Ferrimagnets in High Magnetic Fields
Skourski, Y.; Andreev, A. V.; Kuz’Min, M.; Wosnitza, J.;
Rare-earth intermetallic compounds R2Co17 and R2Fe17 form an interesting group of magnetic materials and their properties have been extensively studied in the last decades. In these compounds, as generally in R-T transition-metal compounds, the strongest interaction is the 3d-3d interaction which primarily determines TC. The 4f-3d interaction, although much weaker than the 3d-3d interaction, is of special importance since it couples the strongly anisotropic R-sublattice moment to that one of much less anisotropic T-sublattice. R2Co17 and R2Fe17 compounds (crystallizing in the hexagonal Th2Ni17-type structure), where R is a heavy rare-earth element, are ferrimagnetic and high magnetic fields are needed to induce changes in the magnetic configuration.
  • Lecture (Conference)
    MISM (Moscow International Symposium on Magnetism), 21.-25.08.2011, Moscow, Russia

Publ.-Id: 16182 - Permalink


Field-Induced Gap in Quantum Spin-1/2 Chains in Strong Magnetic Fields
Zvyagin, S. A.; Ozerov, M.; Wosnitza, J.; Cizmar, E.; Feyerherm, R.; Manmana, S. R.; Mila, F.;
The low-temperature excitation spectrum in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a eld-induced spin gap, is probed by means of ESR spectroscopy in magnetic elds up to 63 T. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48:5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully conrmed by the quantitative agreement over the entire eld range of the experimental data with the DMRG calculations for spin-1/2 Heisenberg chain with a staggered transverse field.
This work was partly supported by the DFG and EuroMagNET II under the EU contract 228043.
  • Poster
    26th International Conference on Low Temperature Physics, 10.-17.08.2011, Beijing, China

Publ.-Id: 16181 - Permalink


Anisotropic Dirac Fermions in a Bi Square Net of SrMnBi2
Park, J.; Lee, G.; Wolff-Fabris, F.; Koh, Y. Y.; Eom, M. J.; Kim, Y. K.; Farhan, M. A.; Jo, Y. J.; Kim, C.; Shim, J. H.; Kim, J. S.;
We report the observation of highly anisotropic Dirac fermions in a Bi square net of SrMnBi2, based on a first-principles calculation, angle-resolved photoemission spectroscopy, and quantum oscillations for high-quality single crystals. We found that the Dirac dispersion is generally induced in the (SrBi)+ layer containing a double-sized Bi square net. In contrast to the commonly observed isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a large momentum-dependent disparity of Fermi velocities of ~8. These findings demonstrate that a Bi square net, a common building block of various layered pnictides, provides a new platform that hosts highly anisotropic Dirac fermions.
  • Physical Review Letters 107(2011), 126402

Publ.-Id: 16180 - Permalink


Magnetic phase diagram of CeAu2Ge2: High magnetic anisotropy due to crystal electric field
Fritsch, V.; Pfundstein, P.; Schweiss, P.; Kampert, E.; Pilawa, B.; von Löhneysen, H.;
CeAu2Ge2 single crystals (with tetragonal ThCr2Si2 structure) have been grown in Au-Ge flux (AGF) as well as in Sn flux (SF). X-ray powder diffraction and EDX measurements indicate that in the latter case, Sn atoms from the flux are incorporated in the samples, leading to a decrease of the lattice constants by ≈0.3% compared to AGF samples. For both types of samples, a strong anisotropy of the magnetization M for the magnetic field B parallel and perpendicular to the c direction is observed with M||/M⊥ ≈ 6–7 in low fields just above 10 K. This anisotropy is preserved to high fields and temperatures and can be quantitatively explained by crystal electric field effects. Antiferromagnetic ordering sets in around 10 K as previously found for polycrystalline samples. From the magnetization data of our single crystals we obtain the phase diagrams for the AGF and SF samples. The magnetic properties depend strongly on the flux employed. While the AGF samples exhibit a complex behavior indicative of several magnetic transitions, the SF samples adopt a simpler antiferromagnetic structure with a single spin-flop transition. This effect of a more ordered state induced by disorder in form of Sn impurities is qualitatively explained within the anisotropic next-nearest neighbor Ising (ANNNI) model, which assumes ferromagnetic and antiferromagnetic interactions in agreement with the magnetic structure previously inferred from neutron-scattering experiments on polycrystalline CeAu2Ge2 by Loidl et al.
  • Physical Review B 84(2011), 104446

Publ.-Id: 16179 - Permalink


Stacking-order dependent transport properties of trilayer graphene
Jhang, S. H.; Craciun, M. F.; Schmidmeier, S.; Tokumitsu, S.; Russo, S.; Yamamoto, M.; Skourski, Y.; Wosnitza, J.; Tarucha, S.; Eroms, J.; Strunk, C.;
We reportmarkedly different transport properties ofABA- andABC-stacked trilayer graphenes. Our experiments in double-gated trilayer devices provide evidence that a perpendicular electric field opens an energy gap in the ABC trilayer, while it causes the increase of a band overlap in the ABA trilayer. In a perpendicular magnetic field, the ABA trilayer develops quantum Hall plateaus at filling factors of nu = 2,4,6, . . . with a step of Δnu = 2, whereas the inversion-symmetric ABC trilayer exhibits plateaus at nu = 6 and 10 with fourfold spin and valley degeneracy.
  • Physical Review B 84(2011), 161408(R)

Publ.-Id: 16178 - Permalink


Saturation Field of Frustrated Chain Cuprates: Broad Regions of Predominant Interchain Coupling
Nishimoto, S.; Drechsler, S.-L.; Kuzian, R. O.; van den Brink, J.; Richter, J.; Lorenz, W. E. A.; Skourski, Y.; Klingeler, R.; Büchner, B.;
A thermodynamic method to extract the interchain coupling (IC) of spatially anisotropic 2D or 3D spin-1/2 systems from their empirical saturation field Hs(T = 0) is proposed. Using modern theoretical methods we study how Hs is affected by an antiferromagnetic (AFM) IC between frustrated chains described in the J1-J2-spin model with ferromagnetic 1st and AFM 2nd neighbor in-chain exchange. A complex 3D-phase diagram has been found. For Li2CuO2 and Ca2Y2Cu5O10, we show that Hs is solely determined by the IC and predict Hs \apprx 61 T for the latter. With Hs \approx 55 T from magnetization data one reads out a weak IC for Li2CuO2 close to that obtained from inelastic neutron scattering.
  • Physical Review Letters 107(2011), 097201

Publ.-Id: 16177 - Permalink


The impact of heavy Ga doping on superconductivity in germanium
Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Fiedler, J.; Mücklich, A.; Helm, M.; Wosnitza, J.;
We report new experimental results on how superconductivity in gallium-doped germanium (Ge:Ga) is influenced by hole concentration and microstructure. Ion implantation and subsequent flash-lamp annealing at various temperatures have been utilized to prepare highly p-doped thin films consisting of nanocrystalline and epitaxially grown sublayers with Ga-peak concentrations of up to 8 at.%. Successive structural investigations were carried out by means of Rutherford-backscattering spectrometry in combination with ion channelling, secondaryion-mass spectrometry, and high-resolution cross-sectional transmission electron microscopy. Hole densities of 1.8·1020 to 5.3·1020 cm-3 (0.4 to 1.2 at.%) were estimated via Hall-effect measurements revealing that only a fraction of the incorporated gallium has been activated electrically to generate free charge carriers. The coincidence of a sufficiently high hole and Ga concentration is required for the formation of a superconducting condensate. Our data reflect a critical hole concentration of around 0.4 at.%. Higher concentrations lead to an increase of Tc from 0.24 to 0.43 K as characterized by electrical-transport measurements. A short mean-free path indicates superconductivity in the dirty limit. In addition, small critical-current densities of max. 20 kA/m2 point to a large impact of the microstructure

Publ.-Id: 16176 - Permalink


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