Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

X-ray reflectivity investigations of Ga+ ion irradiated Pt/Co/Pt films

Kanak, J.; Stobiecki, T.; Powroznik, W.; Mazalski, P.; Sveklo, I.; Maziewski, A.; Liedke, M. O.; Fassbender, J.; Wawro, A.; Baczewski, L. T.

The effects of Ga+ ion implantation in MBE grown Mo20nm/Pt20nm/Co3.3nm/Pt5nm films were investigated by low and high angle x-ray diffraction methods. The reflectivity measurements were used for characterization of changes in layer thickness and interface Pt/Co structure upon 30 keV Ga ion irradiation in a fluence range between 0 and 6e15 ions/cm2. The layer stack thickness was found to decrease with increase of Ga+ fluence. Mixing of Pt and Co at interfaces leads to a change of interface roughness of the top layers. The results were compared with high-fluence ion implantation simulations, of the dynamic changes of thickness and composition of layers, obtained using TRIDYN.

Keywords: TRIDYN; irradiation; Co; Pt; SRT

  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15208

Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Tripathia, J. K.; Satpatib, B.; Liedke, M. O.; Guptad, A.; Som, T.

Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K

Keywords: Pt/Cr/Co multilayer; Structural property; Magnetic property; Thermal annealing

Publ.-Id: 15207

Quenched-in vacancies in Fe-Al alloys

Melikhova, O.; Cizek, J.; Lukac, F.; Procházka, I.; Kuriplach, J.; Anwand, W.; Brauer, G.

Quenched-in vacancies in Fe-Al alloys with Al content ranging from 24 to 49 at.% were investigated employing two complementary techniques of positron annihilation: slow positron implantation spectroscopy and positron lifetime measurements. It was found that quenched alloys exhibit a very high concentration of vacancies. Although the free positron component cannot be resolved in positron lifetime spectrum in majority of samples, the concentration of quenched-in vacancies can be still determined from the positron diffusion length measured by a variable energy positron beam. The lowest concentration of vacancies was found in a stoichiometric (SM) Fe3Al alloy. The concentration of defects increases with increasing degree of non-stoichiometry with respect to Fe3Al, i.e. in alloys with under-SM and over-SM Al concentration. However, the increase in concentration of quenched-in defects is more pronounced in Al-rich alloys, i.e. alloys containing more than 25 at.% of Al.

Publ.-Id: 15204

Use of superconducting linacs for positron generation: the EPOS system at the Forschungszentrum Dresden-Rossendorf (FZD)

Krause-Rehberg, R.; Jungmann, M.; Krille, A.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Büttig, H.; Kosev, K. M.; Teichert, J.; Wagner, A.; Cowan, T. E.

Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting LINACbased accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system (ELBE Positron Source) at the Forschungszentrum Dresden-Rossendorf (FZD), is described.

Publ.-Id: 15203

Surface nanostructures induced by slow highly charged ions

Facsko, S.; Wilhelm, R. A.; El-Said, A. S.; Heller, R.

Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear or electronic sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation in the surface can thus induce various modifications [1]. Recently, it has been shown that hillock structures are formed on CaF2 by HCI due to a localized phase transition [2].
In the case of the alkali halide crystal KBr we observed the formation of nanostructures resulting by desorption of surface atoms from a single ion impact site [3]. For high enough charge states each ion produces a mono-atomic deep pit with a diameter of 10-30 nm (depending on the charge state) on the atomically flat surface. The desorption of such a high amount of material can not be induced by kinetic sputtering alone, which dominates in this kinetic energy regime, but is induced by the excitation due to the potential energy. For a kinetic energy of 40 keV a threshold in the potential energy of the HCI is found for the formation of these structures between Xe15+ and Xe20+ around 3 keV. Above this threshold the volume of the pits and therewith the potential sputtering yield exhibits a linear dependence on the potential energy. However, the kinetic energy also plays an important role. For higher kinetic energies the threshold shifts to lower values of the potential energy.

Keywords: highly charged ions; nanostructures; surface modifications

  • Invited lecture (Conferences)
    EMMI Workshop "Physics prospects at the ESR and HITRAP", 27.-30.06.2010, Eisenach, Deutschland

Publ.-Id: 15202

SQUID investigations of Ga+ irradiated epitaxial Pt/Co/Pt trilayers

Liedke, M. O.; Shalimov, A.; Fassbender, J.; Mazalski, P.; Maziewski, A.; Wawro, A.; Baczewski, L. T.

Spin reorientation transition in polycrystalline Pt/Co/Pt trilayers, i.e. rotation of the magnetization from an in-plane to out-of-plane orientation and vice versa can be precisely controlled by ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502], similarly to the epitaxial Pt/Co/Pt trilayers exposed to 30 keV Ga+ ions in the fluence range of 1014-1016 ion·cm−2. Magnetic properties of a such irradiated system are studied by means of SQUID magnetometry. Zero field cooling and field cooling dependencies and also magnetization reversal curves are measured and analyzed in the frame of the Preisach model. The model explains structural and magnetic modifications occurring due to ion irradiation. A key magnetic properties, i.e. distribution of coercive and interaction fields, reversible and irreversible magnetic contributions are addressed. The interpretation of the results is also supported by the XRD synchrotron studies.

Keywords: SQUID; spin reorientation transition; Co; Pt; magnetization

  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15201

Magnetic anisotropy engineering: ultrathin Fe films on single crystalline rippled surfaces

Liedke, M. O.; Körner, M.; Lenz, K.; Ranjan, M.; Fassbender, S.; Facsko, J.

Ultrathin Fe films exhibit an excellent epitaxial relation to MgO(100) substrates because of a very low lattice mismatch (~3.8%). Due to a cubic symmetry of the Fe crystal an in-plane fourfold magnetic anisotropy is induced. By means of ion erosion coherently aligned single crystalline patterns (ripples) are created at the MgO surface, which induce an additional uniaxial magnetic anisotropy in the afterwards deposited Fe film. The uniaxial magnetic anisotropy direction and strength is controlled by an arbitrarily chosen irradiation direction with respect to the sample plane and the ion energy dependent ripple wavelength, respectively. Thus an ensemble of twofold and fourfold anisotropy is created and analyzed by ferromagnetic resonance and magneto-optic Kerr effect techniques. Theoretical analysis reveals both the anisotropy fields and their directions that are in a perfect agreement with the experiment.

Keywords: magnetic anisotropy; ripples; MgO; Fe; single crystalline; ion erosion

  • Lecture (Conference)
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15200

Ions for Nanotechnology

Kolitsch, A.

The aim of the nanocenter slovakion is its integration into university research (e.g. STU/MtF, materials research), which is highly required by professional public This will enable university to bring its research closer to the needs of industry and shift it to up-to-date topics on one side, and raise funds from private sources in the industry on the other side, which altogether represents a unique chance to train young qualified researchers in the field of contemporary materials research. The activities of the centre will be equally utilised by both in-house and external research and in a wide scale of services oriented on the support in introducing nanostructures using plasma and ion technologies into production processes for external industrial and other users.
The subject of the research, both basic and applied, will be focused on the modification of surface properties, such as hardness, friction, wear, fatigue, adhesion, as well as electrical, magnetic and optical properties, along with corrosion and bio-compatibility using ion beams technologies in the nanometer range. The research will employ the technologies, such as ion implantation (II), ion beam mixing (IBM) and ion beam assisted deposition (IBAD), as well as plasma assisted pulsing, non-pulsing, reactive and non-reactive processes where energetic ions form a decisive component of this process implementation. Highly topical is the research dealing with the development of nanostructures via ion beams.
Typical fields of utilisation are as follows:

  • Exposed parts in automotive and mechanical engineering industry (injection nozzles, camshafts, bearings, valves and others);
  • Medical and biomedical applications (prosthetics with interesting alloys, even those with the surfaces not sufficiently wear-resistant);
  • Surface nitration of stainless steels via ion implantation with the purpose to improve wear resistance of stainless steels while preserving their high corrosion resistance;
  • Stents (endoluminal catheter protheses), nano-porous stents for additional controlled administration of drugs, biocompatible and blood-compatible materials, etc. for modern medicine;
  • Further possibilities of ion implantation in industry in the fields other than microelectronics, such as precise mechanics, special construction parts of expensive watches;
  • High thermal oxidation protection (Ti AL – alloys, turbine construction);
  • Mould injection of plastics (improvement of safety in the removing of injection-made plastic parts from the mould, as well as wear protection of highly exposed parts of forming tools);
  • Ion implantation of polymers surfaces for the improvement of certain surface properties, such as printability for electric conductivity, biocompatibility, etc.

The important areas of ion beams technology application can be found in the field of ion beam analysis in a nanometer scale as well as in research and industry. Planned procedures are as follows:

  • Rutherford Backscattering (RBS)
  • Elastic Recoil Detection (ERD)
  • Nuclear reaction Analysis (NRA)
  • Proton Induced X-ray Emission (PIXE)
  • Proton Induced Gamma-ray Emission (PIGE)

They provide a possibility of a non-standard depth profile analysis with high precision of nearly all chemical elements. In special cases, such as hydrogen depth profile analysis or light elements (B, C, N, O) analysis in heavy matrix (steel), they are unequalled when compared to other procedures.
Three groups of devices suggested as basic equipment for various uses of ion implantation are as follows:

  • PBII equipment (three machines with various chamber volumes, basic vacuum and pulse voltage);
  • Two linear ion implanters in the energetic range up to 500 kV (standard equipment) and 200 kV as a so-called high current implanter;
  • 6 MV Tandetron Accelerator with experimental stations for high energy ion implantation and ion beam analysis.

The basic equipment for plasma and ion beam assisted separation processes is as follows:

  • IBAD instrumentation with different low energy ion sources;
  • Combination of PBII and thin film deposition
  • Universal magnetron sputtering application systems with possible reactive middle frequency pulsed dual magnetron sputtering and the possibility of choice for typical plasma diagnostics and thin layers diagnostics.
Along with the implantation processes for micro-electronic development of nano-clusters, nano-wires, and nano-arrays, typical surface processes aiming at nano-scale ordered structures such as surface design created by ion erosion, nano-porosity for bio-medicine usage, blistering, etc., play an important role. Anyway, the magnetic nano-scale order of a structure as an indication of ferro-magnetic phases in non-magnetic materials or magnetic domain configuration using ion beams is of certain interest. Ion-beam-assisted separation process or special reactive processes of magnetron sputtering contributed to a significant achievement in the field of fullerene materials, nano-crystalline highly refracting optical materials or in transparent electrical conductive oxides, which play an important role in solar technology and technology of displays. Coating by super hard substances such as a-C or c-BN is impossible without energetic ions.

Keywords: ion implantation; plasma; ion assisted deposition; plasma based implantation; plasma immersion ion implantation; nanotechnology; hard coatings; doping; accelerator; implanter

  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic
  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic

Publ.-Id: 15199

Exploring uranyl(VI) photochemistry by DFT calculations (in Japanese)

Tsushima, S.

no abstract for this publication

  • Lecture (Conference)
    Seminar talk at the Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 08.03.2011, Tokyo, Japan

Publ.-Id: 15198

Time-resolved photoluminescence from GaAs/AlGaAs multiquantum wells quenched by pulsed mid-infrared radiation

Zybell, S.; Schneider, H.; Winnerl, S.; Helm, M.

Several groups have demonstrated the suppression of photoluminescence (PL) from semiconductor quantum wells (QWs) by intense midinfrared radiation (MIR). Since most of the previous studies are done on time-integrated PL the ultrafast changes in the radiative state population are not well understood. We present a detailed study on time-resolved PL from an undoped GaAs/AlGaAs QW sample quenched by MIR pulses from a free-electron laser, which was tuned to the intersubband transition (ISBT) energy. At the arrival time of the MIR pulse a clear sharp dip appears in the PL transient. Free carrier absorption and ISBT are the two processes that take place under MIR excitation and result in an abrupt drop of the radiative state population and consequently in an ultrafast quenching of the PL. Performing polarization sensitive measurements, we were able to discriminate the contributions of free carrier absorption from that of ISBT. A quantitative analysis of the PL dip depth and recovery time as a function of MIR fluence was done using a model based on rate equations.

Keywords: time-resolved photoluminescence; semiconductor quantum wells; intersubband transition

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15197

Voruntersuchungen am HZDR für Filmdickenmessungen an der thermohydraulischen Versuchsanlage KATHY (Karlstein, AREVA NP) mit Gamma-CT

Bieberle, A.; Hoppe, D.; Hampel, U.

Für die Überprüfung des Strömungsregimes im sogenannten Kaminrohr, das in Kernkraftwerken der AREVA NP zur Anwendung kommen soll, müssen zur Überprüfung des Systems im thermohydraulischen Versuchsstand KATHY in Karlstein (AREVA NP) authentische Betriebsszenarien nachgebildet und getestet werden. Grundlage hierfür sind Simulationen und Berechnungen, die mit direkt am Versuchstand gewonnenen Messwerten überprüft werden müssen. Aus diesem Grund soll der mögliche Einsatz des am HZDR entwickelten hochauflösenden Gamma-Computertomographie-Messsystems (Gamma-CT) zur Bestimmung von Wasserfilmdicken überprüft werden.

Keywords: Gamma-CT; Wasser-Dampf Strömung

  • Other report
    HZDR: HZDR, 2011
    20 Seiten

Publ.-Id: 15196

Optimierung des Energiefensters für I-124 anhand von Monte-Carlo Simulationen und PET-Messungen an Kleintier- und Human-Tomographen

Sauerzapf, S.; Zakhnini, A.; Behe, M.; Thomas, L.; Axer, M.; Weber, W.; Pietrzyk, U.; Mix, M.

Die Verwendung des nichtreinen Positronenstrahlers I-124 bietet aufgrund seiner Halbwertszeit von 4,18 Tagen Vorteile bei der Quantifizierung von langsamen biochemischen Prozessen. Nachteilig bei I-124 ist das komplexe Zerfallsschema. Der Anteil an Positronen liegt nur bei 22,8%. Zusätzlich werden koinzidente g -Linien mit Energien emittiert, die innerhalb des am PET-Scanner verwendeten Energiefensters liegen. Ziel dieser Arbeit ist es, das Energiefenster für die PET-Akquisition so zu optimieren, dass ein möglichst geringer Anteil an falschen Koinzidenzen auftritt. Dazu wurden Monte-Carlo Simulationen gerechnet, und Phantome an verschiedenen Kleintier- und Humanscannern gemessen.

Methodik/ Methods:
Die Monte-Carlo Simulationen wurden mit Hilfe von GATE (1) für die Scanner ClearPET (Raytest) und Gemini TF (Philips) sowie für unterschiedliche Phantome durchgeführt. Um die zusätzlich zum Positronenzerfall auftretenden koinzidenten g -Linien im Energiespektrum zu unterscheiden, wurde die I-124 Aktivität nicht als Ionenquelle, sondern alle g -Linien als reine Gammaemitter und die Positronenemission als quasikontinuierliches Energiehistogramm definiert. F-18 wurde als Ionenquelle definiert und als Vergleichsstandard verwendet. Die
Energiespektren wurden für die verschiedenen Bereiche im Phantom hinsichtlich der wahren und gestreuten Koinzidenzen unterschieden. Neben den Messungen mit den o.g. Phantomen für I-124 und F-18 am ClearPET und PET/CT Gemini TF 64 wurden vergleichende Messungen am MicroPET Focus 120 (Concorde) und am ECAT EXACT (Siemens) gemacht.

Ergebnisse/ Results:
Die Simulationen zeigen, dass im Vergleich zu F-18 die I-124 Energiespektren mehr Counts speziell im niederenergetischen Bereich (<350keV) aufweisen. Dies resultiert aus den zusätzlich koinzidenten g -Linien, die als wahre Koinzidenzen gewertet werden. Da die Energieverteilung der g -Linien exponentiell verläuft, wird durch die Wahl einer höheren unteren Energieschwelle (450keV anstatt 250 bzw. 350keV) ein Großteil der falschen
Koinzidenzen herausgefiltert. Die Energieauflösung des PET-Scanners bestimmt dabei die Qualität dieser Maßnahme, was sich in den Phantommessungen an den unterschiedlichen Scannern bestätigt. Besonders deutlich wird dies zwischen dem BGO- und dem LYSOHumanscanner. Durch das engere Energiefenster am Gemini TF wird mit I-124 im Phantom eine auf 10% genaue Quantifizierung sowie annähernd keine Streuanteile in kalten Phantombereichen festgestellt.

Schlussfolgerungen/ Conclusions:
Die Simulationen erlauben eine sehr gute Abschätzung, inwieweit sich bei den PET-Scannern die Akquisition mit dem Isotop I-124 durch Einschränkung des Energiefensters verbessern lässt. Die Phantommessungen zeigen, dass gute quantitative Ergebnisse mit I-124 erreicht werden können.

(1) S. Jan /et al /2004 GATE: a simulation toolkit for PET and SPECT. Phys. Med. Biol. 49

  • Poster
    NuklearMedizin2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15195

Surface nanostructures induced by low energy ion sputtering

Facsko, S.

Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth.
According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.
We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].

[1]W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2]R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3]R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

Keywords: ion sputtering; surface patterns; ripple patterns

  • Lecture (others)
    Birck Nanoscience Center Seminar, 28.04.201, West Lafayette, Indiana, USA

Publ.-Id: 15194

Comprehensive study of the p-type conductivity formation in radio frequency magnetron sputtered arsenic-doped ZnO film

Fan, J. C.; Zhu, C. Y.; Yang, B.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Wong, K. S.; Zhong, Y. C.; Xie, Z.; Ling, C. C.

Arsenic doped ZnO and ZnMgO films were deposited on SiO2 using radio frequency magnetron sputtering and ZnO–Zn3As2 and ZnO–Zn3As2–MgO targets, respectively. It was found that thermal activation is required to activate the formation of p-type conductivity. Hall measurements showed that p-type films with a hole concentration of ∼ 1017 cm−3 and mobility of ∼ 8 cm2 V−1 s−1 were obtained at substrate temperatures of 400–500 °C. The shallow acceptor formation mechanism was investigated using x-ray photoelectron spectroscopy, positron annihilation, low temperature photoluminescence, and nuclear reaction analysis. The authors suggest that the thermal annealing activates the formation of the AsZn-2VZn shallow acceptor complex and removes the compensating hydrogen center.

Keywords: zinc oxide; positron annihilation; ZnMgO; p-type conductivity; nuclear reaction analysis; XPS; PL; AsZn-2VZn shallow acceptor complex

Publ.-Id: 15193

Time-resolved photoluminescence from undoped GaAs/Al0.35Ga0.65As quantum wells quenched by pulsed midinfrared radiation

Zybell, S.; Schneider, H.; Wagner, M.; Winnerl, S.; Köhler, K.; Helm, M.

There is much interest in the development of ultrafast devices with possible applications in optoelectronics. An important goal consists in ultrafast control of luminescence in light-emitting devices; it is therefore interesting to investigate the effect of abrupt changes in the carrier distribution on the luminescence signal. We present an experimental study of the effects of mid-infrared radiation (MIR) on the photoluminescence (PL) from undoped AlGaAs/GaAs quantum wells. Electron-hole pairs, created by weak near-infrared light pulses, were excited in the system while a delayed MIR pulse induces an ultrafast redistribution of free carriers that results in abrupt quenching of the PL with a subsequent PL recovery. The source of the MIR laser pulses was the free-electron laser facility FELBE at the Forschungszentrum Dresden-Rossendorf. In combination with the synchroscan streak camera, collecting the PL from the electron-hole recombination, it turned out to be a great spectroscopic tool for time-resolved measurements. Using a simple fit function we found PL recovery times between 40 and 150 ps depending on the MIR intensity.

Keywords: quantum wells; time-resolved photoluminescence; streak camera; FELBE

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.03.2010, Regensburg, Deutschland

Publ.-Id: 15192

Ordered Ag nanocluster structures by vapor deposition on pre-patterned SiO2

Numazawa, S.; Ranjan, M.; Heinig, K.-H.; Facsko, S.; Smith, R.

Highly ordered Ag nanocluster structures have been grown on pre-patterned amorphous SiO2 surfaces by oblique angle physical vapor deposition at room temperature. Despite the small undulation of the rippled surface, the stripe-like Ag nanoclusters are very pronounced, reproducible and well-separated. Computer modeling of the growth has been performed with a lattice-based kinetic Monte-Carlo (KMC) method using a combination of a simplified inter-atomic potential and experimental transition barriers taken from the literature. An effective transition event classification method is introduced which allows a boost factor of several thousand compared to a traditional KMC approach, thus allowing experimental time scales to be modeled. The simulation predicts a low sticking probability for the arriving atoms, millisecond order lifetimes for single Ag monomers and ~1 nm square surface migration ranges of Ag monomers. It is also shown that metal nucleations can trigger even on defect free surfaces. The simulations give excellent reproduction of the experimentally observed nanocluster growth patterns.

Keywords: Kinetic Monte-Carlo; Physical vapor deposition; nanopatterning

Publ.-Id: 15191

Impact of Slow Highly Charged Ions on Insulating Surfaces

Facsko, S.

Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation can thus induce various effects, like secondary electron emission, potential sputtering, and finally also permanent surfaces modifications [1].
Systematic investigations of surface modifications induced by highly charged ion on different materials have revealed many interesting mechanisms. On CaF2 surfaces hillock structures are formed by the impact of HCI due to a localized phase transition [2]. In the case of the alkali halide crystal KBr the formation of nanostructures results from the desorption of surface atoms from a single ion impact site [3]. In both cases a threshold in the potential energy for the formation of the structure has been identified and could be interpreted in the frame of the applied models. However, still a unified picture of these effects is missing.
This work has been supported by the European Project ITSLEIF (RII3#026015).
[1] S. Facsko, R. Heller, A. S. El-Said, W. Meissl and F. Aumayr, J. Phys.: Cond. Matter 21, 2240122 (2009) .
[2] A. S. El-Said, R. Heller, W. Meissl, R. Ritter, S. Facsko, C. Lemell, B. Solleder, I. C. Gebeshuber, G. Betz, M. Toulemonde, W. Moller, J. Burgdorfer and F. Aumayr, Phys. Rev. Lett. 100 237601 (2008).
[3] R. Heller, S. Facsko, R. Wilhelm, and W. Möller, Phys. Rev. Lett. 101, 096102 (2008).

Keywords: highly charged ions; surface modifications; nanostructures

  • Invited lecture (Conferences)
    24th International Conference on ATOMIC COLLISIONS IN SOLIDS ICACS-24, 18.-23.07.2010, Krakow, Polen

Publ.-Id: 15190

Ion-Induced Surface Patterns as Templates for Thin Film Growth

Facsko, S.; Ranjan, M.; Keller, A.; Oates, T. W. H.; Faßbender, J.; Möller, W.

Nanostructured thin films are of growing relevance for all kind of applications in photovol-taics, plasmonics, or as magnetic materials. Various methods have been used to fabricate these nanostructured thin films with well defined morphology. Besides the top-down ap-proaches using lithographic methods, bottom-up, self-organized methods have been used ex-tensively in the last years because of their fast and easy way of producing patterns with struc-tures down to 10 nm.
Ion beam sputtering has proven to be a promising way to produce self-organized patterns on various surfaces. Depending on the ion incidence angle hexagonally ordered dot patterns as well as ripple patterns oriented perpendicular or parallel to the ion beam direction are formed during the continuous sputtering (see Fig. 1 left). These patterns are excellent templates for the growth of metal thin films. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography (Fig. 1 right top) or as nanoparticles on the substrate surface (Fig. 1 right bottom). Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires [1].
Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favoured. Because of alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [2]. In addition, the magnetic properties of ferromagnetic thin films are drastically change by the presence of the interface and surface periodic roughness [3].

[1] T.W.H. Oates, A. Keller, S. Noda, et al., Appl. Phys. Lett. 93 (2008).
[2] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[3] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

Keywords: ripple patterns; nanostructured thin films; magnetic films; plasmonic material

  • Invited lecture (Conferences)
    PSE 2010, Twelfth International Conference on Plasma Surface Engineering, 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 15189

Cross-Coupling Reactions as Valuable Tool for the Preparation of PET Radiotracers

Pretze, M.; Große-Gehling, P.; Mamat, C.

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of new radiotracers and novel radiolabeling procedures with the most prominent short-lived positron emitters carbon-11 and fluorine-18. Radiolabeling with these radionuclides represents a remarkable challenge. Special attention has to be paid to synthesis time and specific labeling techniques due to the short physical half life of the respective radionuclides 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min). In the past, numerous transition metalcatalyzed reactions were employed in organic chemistry, even though only a handful of these coupling reactions were adopted in radiochemical practice. Thus, the implementation of modern synthesis methods like cross-coupling reactions offers the possibility to develop a wide variety of novel radiotracers. The introduction of catalysts based on transition metal complexes bears a high potential for rapid, efficient, highly selective and functional group-tolerating incorporation of carbon-11 and fluorine-18 into target molecules. This review deals with design, application and improvement of transition metal-mediated carbon-carbon as well as carbon-heteroatom cross-coupling reactions as a labeling feature with the focus on the preparation of radiolabeled compounds for molecular imaging.

Keywords: cross-coupling; radiolabeling; carbon-11; fluorine-18

Publ.-Id: 15188

Surface patterning by low energy ion sputtering

Facsko, S.

The morphology of surfaces after erosion by ion sputtering show very different char-acteristics depending on the ion beam parameters and the material properties. The surface exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns, like periodic rip-ples or hexagonally ordered dots [1,2]. The structures of these patterns have small sizes in the range of 10 to 100 nm and show a high degree of ordering. Therefore, they have attracted strong interest recently as templates for nanostructured thin film deposition [3]. On materials whose surface turns amorphous during the ion erosion the formation of the periodic patterns relies on at least two interplaying processes: roughening of the surface due to the local variation of sputtering yield and smoothing via diffusion processes. Therefore, the surface morphology depends strongly on the details of the energy deposition by the incoming ions and on the details of the surface diffusion.
At the atomic level, the atomic sputtering, the creation of surface defects, and the influence of the ion beam on surface diffusion processes play a decisive role for the morphology evolution. In the case of single charged ions, the energy deposition is dissipated mainly kinetically in a collision cascade which leads finally to the emission of the sputtered atoms and the creation of defects.

[1] A. Keller, S. Rossbach, S. Facsko and W. Möller, Nanotechnology 19, 135303 (2008).
[2] S. Facsko et al., Science 285, 1551 (1999), F. Frost et al., Phys. Rev. Lett. 85, 4116 (2000).
[3] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mucklich, S. Facsko and J. Fassbender

Keywords: Nanostructures; ion sputtering; ripple patterns

  • Lecture (others)
    Seminar der Physikfakultät, 25.11.2010, Cosenza, Italia

Publ.-Id: 15187

In vitro binding profile and radiosynthesis of a novel 18F-labeled azaspirovesamicol analog as potential ligand for imaging of the vesicular acetylcholine transporter

Wenzel, B.; Hiller, A.; Fischer, S.; Sorger, D.; Deuther-Conrad, W.; Scheunemann, M.; Brust, P.; Sabri, O.; Steinbach, J.

Radiolabeled vesamicol analogues are promising candidates as ligands for the vesicular acetylcholine transporter (VAChT) to enable in vivo imaging of early cholinergic degenerations in brain. The 4-fluorobenzoyl substituted azaspirovesamicol derivative FBASV is one out of six novel vesamicol analogs and demonstrated most appropriate in vitro binding data. 18F-radiolabeling was performed by microwave assisted nucleophilic aromatic substitution of the corresponding nitro precursor and two methods were developed for the purification of [18F]FBASV. Utilizing method A, the remaining nitro precursor was reduced to its corresponding amine, which was separated via semi-preparative HPLC on a conventional RP column. In method B a phenyl column was used for the direct separation of [18F]FBASV and its nitro precursor, resulting in a change of the elution order and better separation parameters. Thus, [18F]FBASV was synthesized with a RCY of 16-18%, a specific activity > 300 GBq/µmol, and a radiochemical purity of > 99.5% suitable for future in vivo studies.

Keywords: azaspirovesamicol; [18F]FBASV; VAChT; PET; 18F-labeling; vesamicol; nitro precursor

  • Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 426-432
    DOI: 10.1002/jlcr.1891

Publ.-Id: 15186

Transition metal implanted ZnO: Have we obtained a diluted magnetic semiconductor?

Zhou, S.

Ferromagnetic semiconductor, exhibiting properties of a ferromagnet and a semiconductor simultaneously, is a key material for semiconductor spintronics. To realize diluted ferromagnetic semiconductors, one has to dope semiconductors with transition metal up to several percents. H. Ohno et al. obtained ferromagnetic GaAs:Mn by decreasing the growth temperature in molecular beam epitaxy [1]. In 2000, T. Dietl et al. successfully interpreted the ferromagnetism in GaAs:Mn based on mean-field theory and predicted that p-type wide bandgap semiconductors (ZnO and GaN) can be ferromagnetic above room temperature given the Mn concentration of 5 at.% [2]. This prediction pushed the research on mining for room-temperature ferromagnetic semiconductors as one of the most active topics in the last decade. In this talk, I will present the magnetic and structure properties of transition metal implanted ZnO as well as the opinions from other research groups [3, 4].

1. H. Ohno, et al., Appl. Phys. Lett. 69, 363 (1996).
2. T. Dietl, et al., Science 287, 1019 (2000).
3. K. Potzger, S. Zhou, et al., Appl. Phys. Lett. 88, 052508 (2006).
4. S. Zhou, et al., Phys. Rev. B 77, 035209 (2008).

  • Invited lecture (Conferences)
    Invited talk at Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 08.11.2010, Shanghai, China

Publ.-Id: 15185

On the role of americium in the reduction process in plutonium-americium oxides

Belin, R. C.; Martin, P. M.; Gavilan, E.; Reynaud, M.; Scheinost, A. C.

Innovative mixed oxide (MOX) (U,Pu)O2-x fuels for sodium fast neutron reactors (SFRs) systems are currently studied within the framework of the fourth generation (GEN-IV) nuclear reactors development. SFRs will be able to burn long-lived minor actinides (MA) such as Americium by adding them homogeneously to the fuel in a small amount (2 to 6%). Because oxygen to metal ratio (O/M) has a direct impact on irradiation performance, a thorough knowledge of its correlation with oxygen potential during manufacturing and especially sintering is of major concern.
A study by Osaka et al. [ ] highlights a conflicting redox behaviour of Am and Pu cations responsible for an unusual oxygen potential vs. O/M ratio relationship in Am-doped MOX. The reason might be that interactions between U and Am predominate and those between Pu and Am can be neglected [ ]. According to the authors, this should result in U being oxidized to a pentavalent state since Am is likely to be trivalent [ ].
We recently performed a coupled X-Ray Diffraction (XRD) and X-Ray Absorption Spectroscopy (XAS) characterization on substoichiometric Am-containing MOX [ ]. Our results show that Am reduction to Am+III is completed before any reduction of Pu is yet observed. Surprisingly, no pentavalent U was evidenced and the behaviour of Am tends to solely influence that of Pu.

In the present work, to go deeper into the underlying phenomenon involved in the correlated redox behavior of Pu and Am, we focused on U-free sub-stoichiometric (Pu,Am)O2-x compounds. Three compositions were prepared via conventional solid-state reaction under Ar/5%H2 (1800K; 50h): (Pu0.992Am0.008)O2-x, (Pu0.9Am0.1)O2-x and (Pu0.8Am0.2)O2-x. XRD and XAS analyses were combined to selectively probe the long-range and the short-range order and the local environment of both cations. In particular, X-ray Absorption Near Edge Structure (XANES) allows to quantitatively determining the oxidation states for each cation. XRD shows a monophasic system for each composition. Interestingly, the variation of the cell parameter vs. Am concentration is not linear.
In the presentation, we shall detail and compare XRD and XAS results. Especially, we will focus on the correlation between Am content, cell parameter and ratios of Am+3/Am+4 and of Pu+3/Pu+4. We believe our results will improve comprehension of the role of Americium in the overall reduction process occuring in Americium-doped MOX fuels. They may also contribute to the development of the chemical thermodynamic models used to describe such materials.

Keywords: americium; plutonium; MOX; nuclear fuel; SFR; XAS; XRD

  • Lecture (Conference)
    GLOBAL 2011, 04.-09.09.2011, Nagoya, Japan

Publ.-Id: 15184

CFD simulation of fibre material transport in a PWR under loss of coolant conditions

Höhne, T.; Grahn, A.; Kliem, S.; Weiss, F.-P.

During a postulated cold leg LOCA with hot leg ECC injection, a limited amount of small fractions of the insulation material after passing the sump strainers can enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling. The CFD simulations show that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “brake through channels” located at the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that at the beginning the fibers are not uniformly deposited over the core cross section.

Keywords: CFD; LOCA; PWR

  • Kerntechnik 76(2011), 39-45

Publ.-Id: 15183

Structural characterization of thermodynamically predicted U(VI)-tartrate complexes: Combing Factor Analysis with Landweber inversion method

Rossberg, A.; Lucks, C.; Tsushima, S.; Scheinost, A. C.

An intrinsic problem of EXAFS shell fitting is that the radial pair distribution function (PDF) is approximated by Gaussians functions imitating the coordination shells. Different combinations of shells can yield different structures with similar fit quality, thereby making the structural solution non-unique. Even the so-called F-test often does not yield a unique solution. The shell fit analysis of complicated spectra, as in the case of thermodynamically predicted aqueous complexes of U(VI) with tartaric acid, is much more eased if the PDF for the first shells are computed precisely and independently. Solely based on the FEFF scattering theory, the Landweber inverse method [1] yields the PDF for the aqueous mono-, bi- and tri-nuclear U(VI)-tartaric acid complexes without predefined assumptions about the form of the PDF. With this information and density functional theory (DFT) calculations, the spatial structures of the complexes were determined. Depending on the pH the U(VI)-tartaric acid complexes coexist, hence the EXAFS signal is a mixture of the spectral contributions of the complexes. In order to accomplish this special structural analysis we measured an EXAFS pH-series and isolated the spectra of the single complexes from their mixtures by using factor analysis [2].

[1] A. Rossberg, et al., Journal of Synchrotron Radiation, 17, 280-288 (2010).
[2] A. Rossberg, et al., Analytical and Bioanalytical Chemistry, 376, 631-638 (2003).

Keywords: EXAFS; metal complex; inverse method; Landweber iteration

  • Poster
    Actinide XAS 2011, 02.-04.03.2011, Hyogo, Japan

Publ.-Id: 15182

Numerical simulations of counter-current two-phase flow experiments in a PWR hot leg model using an interfacial area density model

Höhne, T.; Deen, D.; Lucas, D.

In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz–Zentrum Dresden–Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler–Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a k-x turbulence model for each phase. In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD framework for all Code users, with the possibility of the implementation of their own correlations.

Keywords: Slug flow; CFD; AIAD

Publ.-Id: 15181

Herstellung und magnetische Charakterisierung von Co-Nanopartikel auf ionenstrahlerodierten Siliziumsubstraten

Buhl, M.; Körner, M.; Fritzsche, M.; Wiesenhütter, U.; Liedke, O.; Fassbender, J.

Co-Nanopartikel wurden auf den selbstorganisierten Ripplen ionenstrahlerodierter Si-Substrate mittels Molekularstrahlepitaxie deponiert. Im Rahmen der Untersuchung sind Substrattemperatur und nominelle Beschichtungsdicke gezielt variiert worden. Mit Hilfe der longitudinalen magneto-optischen Kerr-Effekt Magnetometrie wurde der Einfluss der Ripple-Oberfläche auf das magnetische Verhalten der Co-Partikel analysiert. Die Auswertung der Messergebnisse von normierter remaneter Kerr-Drehung und Koerzitivfeldstärke zeigt eine uniaxiale magnetische Anisotropie. Die leichte Richtung der Magnetisierbarkeit liegt parallel zu den Ripple-Wellenfronten.

Keywords: Ripple; Co-nanoparticle; MOKE; Co-particle; Kerr Effect; Selforganisation; Magnetism; Anisotropy

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 15180

The trigonal nodal SP3 method of the reactor code DYN3D

Duerigen, S.; Fridman, E.; Kliem, S.

DYN3D is a 3D nodal diffusion code for steady-state and transient analyses of Light-Water Reactors (LWRs) with square and hexagonal fuel assembly geometries. Currently, several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option for square geometry as well as a multi-group diffusion version for hexagonal geometry.
In this work, the multi-group SP3 method based on a trigonal-z geometry was developed. The method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement, which is of particular importance for VVER-type Pressurized Water Reactors (PWRs) as well as for innovative reactor concepts including block type High-Temperature Reactors (HTRs) and Sodium Fast Reactors (SFRs).
In this paper, the theoretical background for the trigonal SP3 methodology is outlined and the results of a preliminary verification analysis are presented by means of two VVER-440 single assembly test examples with different material compositions. The accordant cross sections and reference solutions were produced by the Monte Carlo code SERPENT. The DYN3D results are shown for 2 and 8 energy groups, respectively, and are in good agreement to the reference solutions. The maximum deviation in the nodal power distribution is about 1%.

Keywords: simplified P3; SP3; nodal; trigonal; triangular; hexagonal; DYN3D

  • Contribution to proceedings
    19th International Conference on Nuclear Engineering (ICONE19), 16.-19.05.2011, Chiba, Japan
  • Lecture (Conference)
    19th International Conference on Nuclear Engineering (ICONE19), 16.-19.05.2011, Chiba, Japan

Publ.-Id: 15179

Numerical simulation of the melt flow in the continuous casting process with respect to gas injection and the impact of a DC magnetic field

Miao, X.; Lucas, D.; Gerbeth, G.

The numerical simulation of the melt flow in the continuous casting process with respect to gas injection and the impact of a DC magnetic field is presented. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model.

Keywords: continuous casting; electromagnetic brake; numerical simulation

  • Lecture (Conference)
    Symposium zur Simulation metallurgischer Strömungen an österreichischen und deutschen Universitäten, 17.-18.06.2010, Kirnitzschtal, Germany

Publ.-Id: 15178

Structural characterisation of Er implanted, Ge-rich SiO2 layers using slow positron implantation spectroscopy

Anwand, W.; Kanjilal, A.; Brauer, G.; Wagner, A.; Butterling, M.; Cowan, T. E.; Rebohle, L.; Skorupa, W.

Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, leading to the formation of Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, can lead to an improvement of the luminescent properties. However, the intensity of electroluminescence was found to decrease drastically after exceeding an optimum concentration of the Er doping.
Slow positron implantation spectroscopy (SPIS), both in single (DB) and coincidence (CDB) Doppler broadening mode, was applied to probe processes at a microscopic level which might have an impact on the optical response. It shows that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and also with the improved reverse energy transfer process between Er and Ge.

Keywords: Er doped Ge-rich SiO2; electroluminescence; positron annihilation; Doppler broadening; structural changes

Publ.-Id: 15177

Cu diffusion-induced vacancy-like defects in freestanding GaN

Elsayed, M.; Krause-Rehberg, R.; Moutanabbir, O.; Anwand, W.; Richter, S.; Hagendorf, C.

Positron annihilation spectroscopy was employed to elucidate the nature and thermal behavior of defects induced by Cu in freestanding GaN crystals. Cu atoms were intentionally introduced in GaN lattice through thermally activated diffusion from an ultrathin Cu capping layer. During isochronal annealing of the obtained Cu-doped GaN in the temperature range of 450–850 K, vacancy clusters were found to form, grow and finally vanish. Doppler broadening measurements demonstrate the presence of vacancy-like defects across the 600 nm-thick layer below the surface corresponding to the Cu-diffused layer as evidenced by secondary ion mass spectrometry. A more qualitative characterization of these defects was accomplished by positron lifetime measurements. We found that annealing at 450K triggers the formation of divacancies, whereas further increase of the annealing temperature up to 550K leads to the formation of large clusters of about 60 vacancies. Our observations suggest that the formation of these vacancy-like defects in bulk GaN is related to the out-diffusion of Cu.

Keywords: Cu diffusion-induced vacancy-like defects; GaN; positron annihilation spectroscopy

  • Open Access Logo New Journal of Physics 13(2011), 013029

Publ.-Id: 15176

The DRESDYN project at FZD

Gerbeth, G.; Eckert, S.; Gundrum, T.; Stefani, F.

The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) is intended to become a platform both for large scale experiments related to geo- and astrophysics as well as for safety and thermohydraulic studies related to liquid metal batteries and sodium fast reactors. The most ambitious parts of DRESDYN are a homogeneous dynamo driven solely by precession and a large Tayler-Couette like experiment for the combined investigation of the magnetorotational instability and the Tayler instability.
In the talk we give a short summary of the previous achievements, and we delineate the next steps for the realization of DRESDYN.

  • Lecture (Conference)
    13th MHD-days, 22.-23.11.2010, Dresden, Germany

Publ.-Id: 15175

Experimental and numerical modeling of the steel flow in a continuous casting mould exposed to a transverse DC magnetic field

Timmel, K.; Miao, X.; Lucas, D.; Eckert, S.; Gerbeth, G.

This paper is concerned with numerical and experimental investigations focusing on the fluid flow in the continuous casting process under the influence of an external DC magnetic field. Systematic measurements of the mould flow were carried out using the eutectic alloy GaInSn inside a plexiglass model at room temperature. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mould. The ultrasound Doppler velocimetry (UDV) was applied to obtain a detailed experimental data base with respect to the mean values and transient properties of the velocity fields occurring in the mould. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The comparison between our numerical calculations and the experimental results displays a very well agreement. An important outcome of this study is the feature that the magnetic field does not provide a smooth reduction of the velocity fluctuations at the nozzle outlet.

Keywords: continuous casting; electromagnetic brake; experimental modeling; numerical simulation

  • Lecture (Conference)
    Workshop "Modelling for Material Processing", 16.-17.09.2010, Riga, Latvia

Publ.-Id: 15174

How to circumvent the size limitation of liquid metal batteries due to the Tayler instability

Stefani, F.; Weier, T.; Gundrum, T.; Gerbeth, G.

Recently, a new type of battery has been proposed that relies on the principle of self-assembling of a liquid metalloid positive electrode, a liquid electrolyte, and a liquid metal negative electrode. While this configuration has been claimed to allow arbitrary up-scaling, there is a size limitation of such a system due to a current-driven kink-type instability that is known as the Tayler instability. We characterize this instability in large-scale self-assembled liquid metal batteries and discuss various technical means how it can be avoided.

Publ.-Id: 15173

VGF - type buoyant flow under a Travelling Magnetic Field - Numerical and experimental modelling

Galindo, V.; Niemietz, K.; Paetzold, O.; Gerbeth, G.; Stelter, M.

The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The application of a travelling magnetic field (TMF) allows the temperature and concentration fields to be tailored during growth by introducing an additional melt flow. Detailed knowledge about the flow pattern and stability resulting from the superposition of buoyant and electromagnetic forces is necessary to achieve VGF-TMF growth under optimal convective conditions. Direct measurements of the melt flow in real conditions, however, are extremely difficult because of the enclosed, high-temperature growth environment. In this lecture experimental and numerical modelling of a VGF-type flow under the influence of a TMF are presented. Low-temperature flow experiments at around 70°C were carried out using a GaInSn alloy (melting point: 10.5°C) as the model fluid. Radial heating and cooling of the melt leading to a double vortex buoyant flow like in typical VGF growth, was introduced by means of a model furnace with separately adjustable resistance heaters. The flow was characterized by means of Ultrasonic Doppler Velocimetry (UDV) giving the velocity profile perpendicular to the UDV probe face. The turbulent flow and the temperature distribution in the melt due to the combined action of a travelling magnetic field and the thermal convection were simulated numerically using a finite volume code based on the open source code library OpenFOAM. The k-omega SST RAS turbulence model was used. The distribution of the amplitude of the kinetic energy k, as an expression for the velocity fluctuations, was calculated for different values of the strength and frequency of the applied magnetic field and different heating regimes. The melt flow is systematically studied as a function of axial and radial temperature gradients as well as of strength and frequency of the magnetic field. Particular attention is paid on the effect of the thermal and TMF parameters on the transition to time-dependent melt flow which is a crucial problem in VGF crystal growth. The stability limit is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. It is shown that the TMF-induced flow can be stabilized by natural buoyancy and vice versa, and the conclusions to be drawn for real VGF growth are discussed.

Keywords: crystal growth; vertical gradient freeze; travelling magnetic field

  • Lecture (Conference)
    7. Workshop Angewandte Simulation in der Kristallzüchtung, 23.-24.11.2010, Burghausen, Deutschalnd

Publ.-Id: 15172

Bakterien als Lieferanten für neue Recycling-Technologien: Rückgewinnung von Metallen aus Wässern mit neuen Biokompositmaterialien

Pollmann, K.

Potenzial von Bakterien für neue Technologien

  • Invited lecture (Conferences)
    1. Freiberger Ressourcen-Technologie Symposium, 14.-15.02.2011, Freiberg, Deutschland

Publ.-Id: 15171

Combination of internal and external irradiation: Binding of the monoclonal EGFR-antibody C225 in irradiated tumors

Koi, L.; Brüchner, K.; Bergmann, R.; Helbig, L.; Steinbach, J.; Baumann, M.; Zips, D.

kein Abstract verfügbar

  • Poster
    European Society for Therapeutic Radiology and Oncology (ESTRO), 12.-16.09.2010, Barcelona, Spain

Publ.-Id: 15170

Fundamental and application oriented research on bacterial S-layers from uranium mining waste pile isolates

Weinert, U.; Raff, J.; Günther, T.; Pollmann, K.

Übersicht des Instiutes für Radiochemie und Vorstellung aktueller Forschungsthemen der Nachwuchsgruppe NanoBio

  • Lecture (others)
    Besuch der Arbeitsgruppe von Prof. Betzel, 26.01.2011, DESY Hamburg, Deutschland

Publ.-Id: 15169

Monte-Carlo simulations for timing-system of EPOS at ELBE in Research Centre Dresden-Rossendorf

Butterling, M.; Jungmann, M.; Bondarenko, V.; Sachert, S.; Brauer, G.; Anwand, W.; Krause-Rehberg, R.

Most of the monoenergetic slow-positron beam systems capable for positron lifetime spectroscopy are bunched from a continuous beam (e.g., the PLEPS system in Munich). The EPOS system at the ELBE radiation source will use the original time structure of the 40-MeV electron beam which is utilized for pair production. This is an infinite repetition of very short electron pulses (< 5 ps) with an adjustable repetition rate (typical 77 ns). In both cases, the time structure of the positron beam needs sharpening so that the time focus is located at the sample position. This is realized by the bunching system. Usually, double-slit bunchers are used. They are operated by a sinusoidal RF-voltage. This bunching requires an adjustment according to the final positron energy (0.5...30 keV), since the acceleration of the positrons shifts their time focus. Monte-Carlo simulations were done to investigate the effect of different methods of time focusing. One method is the variation of amplitude of the buncher RF-voltage. Another improvement is the combination of such a buncher voltage variation with a variable drift path acceleration short before the final acceleration which is operated by a DC voltage. Our simulations show that indeed a combination of a buncher variation with a drift path gives the sharpest positron pulses when both devices are supplied with individual voltages for each positron implantation energy.

Keywords: Monte-Carlo simulations for timing-system

Publ.-Id: 15168

Single-magnet rotary flowmeter for liquid metals

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

We present a novel design of a contactless flowmeter using a single cylindrical permanent magnet magnetized perpendicularly to its axis, about which it can freely rotate, and placed close to a duct with a liquid metal flow. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation.
The equilibrium rotation rate, which is attained at a vanishing net electromagnetic torque on the magnet, depends only on the flow rate and the geometry of the system while it is independent of the electromagnetic torque itself.
A laboratory model of such a flowmeter has been built and tested on a liquid metal flow.

  • Journal of Applied Physics 110(2011)3, 034512
    DOI: 10.1063/1.3610440
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 575-579

Publ.-Id: 15167

Quenched-in vacancies in Fe3Al based alloys: a positron annihilation study

Melikhova, O.; Čížek, J.; Kuriplach, J.; Procházka, I.; Lukáč, F.; Cieslar, M.; Anwand, W.; Brauer, G.

In the present contribution, high-resolution positron lifetime spectroscopy and slow positron implantation spectroscopy are used to characterize defects in Fe75.99Al24.01 and Fe71.98Al28.02 alloys. In order to facilitate defect identification, we also perform a theoretical study of basic vacancy-like defects in three phases of the Fe3Al system: ordered (D03), shortrange ordered (B2) and disordered (A2). Positron characteristics, i.e. positron lifetime and positron binding energy to defects are calculated from the first principles for various defect configurations. The results are discussed in the context of experimental data obtained here and available in literature.

Keywords: Fe-Al alloys; defects; positron annihihaltion spectroscopy

Publ.-Id: 15166

Contactless electromagnetic phase-shift flowmeter for liquid metals

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

We present a concept and test results of an induction flowmeter for liquid metals.
The flow rate is determined by applying a weak AC magnetic field to a liquid metal flow and measuring the flow-induced phase disturbance in the external electromagnetic field. The phase disturbance is found to be more robust than that of the amplitude used in conventional AC flowmeters. The basic characteristics of this type of flowmeter are analysed using simple theoretical models where the flow is approximated by a solid body motion. Design of such a flowmeter is presented and its test results reported.

  • Measurement Science and Technology 22(2011)5, 055402

Publ.-Id: 15165

Digital positron lifetime: the influence of noise

Krille, A.; Anwand, W.; Krause-Rehberg, R.

In contrast to the world around where everything seems to go digital as soon as possible, positron lifetime spectrometers are kind of a “last sanctuary” for analog measurements. Only a few of the newer spectrometers use the analog-digital-converters directly after the photomultipliers and extract the timing information via computer. Judging from their results it seems as if the current available converters and the timing mathematics are only as good as the conventional analog setup in the timing resolution. As it is decided that EPOS [1] will use digital positron lifetime, we try to find some reasons for limited timing resolution by simulating anode pulses from the photomultipliers and measuring the FWHM. We create pulses similar to current state-of-the-art 4GS/s digitizers but can control the level of noise and the bit-depth independently. We found that especially the noise (that would come from the analog electronics in/before the converters) has a great influence on the timing resolution. Also we try to use lowpass filtering to reduce that influence with great success.

Keywords: digital positron lifetime spectroscopy

Publ.-Id: 15164

The sensitivity of a travelling magnetic field driven flow to axial alignment

Cramer, A.; Pal, J.; Koal, K.; Tschisgale, S.; Stiller, J.; Gerbeth, G.

The sensitivity of a flow that is driven by a travelling magnetic field (TMF) with respect to a shift between the axes of the cylindrical liquid metal column and of the TMF was studied both experimentally and by numerical simulation. In the physical modelling, the generation of the TMF comprised six equidistantly spaced cylindrical coils loaded with ac current having a phase shift of 60 degree, respectively, between them. Ultrasound Doppler velocimetry was used to acquire vertical sections of the vertical velocity component along the beam axis in the centre and at various azimuthal positions for a fixed radial coordinate. The measurements are compared to the according flow data from large eddy simulations. These computations were based on the usual approximations to simplify the magnetohydrodynamical equations, which are low frequency and low induction, and on an analytical expression for the Lorentz force considering the shift between the fluid volume and the field. It is shown that even a small shift between the axes may result in a distinct three-dimensional constituent of the flow structure, and thus changing completely the usually assumed axisymmetric torus-type flow.

Keywords: Fluid flows; Magnetic fields; Stirring; Growth from melt

  • Journal of Crystal Growth 321(2011)1, 142-150

Publ.-Id: 15163

Optimization of the Electron Beam Properties of Dresden EBIT for Charge Breeding

Thorn, A.; Ritter, E.; Sokolov, A.; Vorobjev, G.; Bischoff, L.; Herfurth, F.; Kester, O.; Pilz, W.; Thorn, D. B.; Ullmann, F.; Zschornack, G.

This paper summarizes the results of studies to enhance the performance of Dresden Electron Beam Ion Traps (EBIT) regarding aspects which are important for charge breeding, i.e. injection of externally produced low charged ions and their conversion to highly charged ions. The properties of the electron beam of this compact room-temperature operated EBIT were investigated via position sensitive Xray detection. A detailed analysis of the spatial distribution as well as the energy of the X-ray photons emitted from the electron beam region allowed for the determination of the source parameters needed to guarantee optimal ion trapping conditions and ionization rates. The parameters found in this investigation were applied for the successful realization of charge breeding with the Dresden EBIT.

Keywords: EBIT; charge breeding; X-ray

  • Lecture (Conference)
    International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 18.-23.07.2010, Stockholm, Sweden
  • Open Access Logo Journal of Instrumentation 5(2010), C09006-1-C09006-10
    DOI: 10.1088/1748-0221/5/09/C09006

Publ.-Id: 15162

Some thermophysical properties of the intermetallic Ti40Al60 alloy in the melting-solidification temperature range

Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.

TiAl intermetallic alloys are being developed as potential materials for applications in aerospace and automotive industries and also for chemical and biomedical applications because of their excellent chemical and physical properties such as low density, high modulus and corrosion resistance at high temperatures. The thermophysical properties (electrical conductivity, thermoelectric power and thermal conductivity) of the solid and liquid intermetallic alloy Ti40Al60 have been measured during melting and solidification processes in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.

Publ.-Id: 15161

Raising the temper - μ-spot analysis of temper inclusions in experimental ceramics

Sterba, J. H.; Munnik, F.; Pearce, N. J. G.

Provenancing of ancient ceramics is a highly important scientific tool for archaeological studies. In general, ceramics are not made from the original clay, as it can be found in deposits. To produce the needed physical properties in the finished product, the clay has to be either tempered by adding sands or biological materials or levigated, to remove the coarse fraction. Thus, the chemical composition of the finished ceramic differs from the composition of the original clay bed. To overcome this obfuscation, any information that can be gained about the temper used is useful. In a small series, several pieces of ceramic were produced from known clay and tempers and the resulting ceramics analysed by INAA. As many attempts to physically separate the temper from the clay matrix have failed, μ-spot analysis of temper inclusions were performed at the μ-PIXE (Particle induced X-Ray Emission) facility in Rossendorf and by LA-ICPMS (Laser ablation Inductively coupled plasma mass spectroscopy) in Aberystwyth. It could be shown that from a small number of measurements, a general impression of the temper used could be gained, showing if the temper consists mainly of quartz, feldspars or other main components. With this information, dilution calculations can be greatly facilitated, and a close resemblance of the chemical composition of the clay matrix can be calculated.

  • Poster
    13th International Conference on Modern Trends in Activation Analysis, 13.-18.03.2011, Texas, USA
  • Journal of Radioanalytical and Nuclear Chemistry 291(2012), 25-35
    DOI: 10.1007/s10967-011-1208-6

Publ.-Id: 15160

E. coli filament formation induced by heterologous S-layer expression

Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.

Escherichia coli is a rod-shaped intestinal bacterium which has a size of 1.1-1.5 µm x 2.0-6.0 µm. The fast cell division process and the uncomplicated living conditions turn E. coli into a widely used host in genetic engineering and into one of the best studied microorganism at all. We used E. coli BL21(DE3) as host for heterologous expression of S-layer proteins of Lysinibacillus sphaericus JG-A12 in order to enable a fast and high efficient protein production. The S-layer expression induced in E. coli an unusual elongation of the cells, thus producing filaments with >100 µm in length. In the stationary growth phase, E. coli filaments develop tube-like structures that contain E. coli single cells. Fluorescence microscopic analyses of S-layer expressing E. coli cells that were stained with membrane stain FM® 5-95 verify the membrane origin of the tubes. Analyses of DAPI stained GFP-S-layer expressing E. coli support the assumption of a disordered cell division that is induced by the huge amount of recombinant S-layer proteins. However, the underlying mechanism is still not characterized in detail. These results describe the occurrence of a novel stable cell form of E. coli as a result of a disordered cell division process.

Keywords: Heterologous expression; S-layer; E. coli; morphology; cell division; tube-like structures; Outer membrane; membrane stain; DAPI

Publ.-Id: 15159

GATE goes Material Sciences - ClearPET in Environmental Research

Zakhnini, A.

Es existiert kein Abstract.

  • Lecture (others)
    OpenGATE technical meeting, 17.05.2010, Köln, Deutschland

Publ.-Id: 15158

Reactive Transport Division - scopes and aims

Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    PSI/IRC Meeting, 28.-29.09.2010, Rossendorf, Deutschland

Publ.-Id: 15156

Reactive transport investigations by means of radiotracer applications

Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    Kolloquium der Friedrich-Schiller Universität Jena, 07.12.2010, Jena, Deutschland

Publ.-Id: 15155

PET imaging of σ1 receptors: New F-18-labelled alkyl-substituted spirocyclic piperidine radiotracers

Maisonial, A.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Große Maestrup, E.; Steinbach, J.; Wünsch, B.; Brust, P.

There is evidence that σ1 receptors are involved in the cognitive impairment found in neurodegenerative diseases. Because of considerable drawbacks of the currently used PET ligand for neuroimaging of σ1 receptors, [C-11]SA4503, we have recently developed a new spirocyclic piperidine derivative: [F-18]WMS1813 ([F-18]1'-benzyl-3-(3-fluoropropyl)-3H-spiro[[2]benzofuran-1,4'-piperidine]) with high affinity and selectivity for σ1 receptor binding site (1). Further SAR studies on the fluoroalkyl chain provided three other promising analogues, bearing either fluoromethyl- (WMS1850), fluoroethyl- (WMS1828) or fluorobutyl-(WMS1847) moieties. Herein, we report on radiosyntheses and biological evaluation of these candidates for PET imaging of σ1 receptors.

Radiosyntheses of [F-18]WMS1850, [F-18]WMS1828, and [F-18]WMS1847 were performed by direct nucleophilic substitution of corresponding aliphatic tosylate precursors, using the K[F-18]F-K222-carbonate complex. Biodistribution studies and ex vivo brain autoradiography of the radiotracers were performed in female CD-1 mice. Target specificity was validated by pre-treatment with 1 mg/kg i.p. of the σ1 receptor antagonist haloperidol. In vivo metabolism of each radiotracer was evaluated by radio- TLC/-HPLC.

The three radiotracers were obtained with radiochemical yields of 35-53%, radiochemical purities >98.5%, and high specific activities ≥150 GBq/μmol. In mice, they rapidly accumulated in brain tissue. [F-18]WMS1828 was superior with a brain uptake value of 4.71 ± 1.39 %ID/g (30 min p.i.) in comparison to [F-18]WMS1813, [F-18]WMS1847 and [F-18]WMS1850 (3.18±0.68; 1.78±0.16; 2.65±0.68 %ID/g respectively). For all radiotracers, uptake in brain as well as in peripheral σ1 receptor expressing organs was significantly inhibited by haloperidol. At 30 min p.i., more than 75% of the radioactivity detected in plasma samples corresponded to native [F-18]WMS1850, [F-18]WMS1828 and [F-18]WMS1847. None of the radiometabolites observed crossed the blood-brain barrier. Results of ex vivo autoradiography of brain slices revealed resemblance between radioactivity distribution pattern of all radiotracers and regions with known high σ1 receptors density. The highest target (facial nucleus)-to-nontarget (olfactory bulb) tissue ratio was determined for [F-18]WMS1828 (4.69 at 45 min p.i.).

Within the series of σ1 receptor-specific radiotracers studied, [F-18]WMS1828 ([F-18]fluspidine) appears to be the most promising candidate for PET imaging with even better pharmacological profile than the lead compound WMS1813. Hence, [F-18]fluspidine radiosynthesis is selected for transfer onto an automated radiosynthesis module for further (pre)clinical development.

(1) Maestrup E G et al. J Med Chem 2009; 52, 6062-6072.

Keywords: PET; imaging; F-18; σ1 receptor

  • Lecture (Conference)
    NuklearMedizin2011, 13.-16.04.2011, Bregenz, Österreich
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A39

Publ.-Id: 15154

The Tayler instability of toroidal magnetic fields in a columnar gallium experiment

Rüdiger, G.; Schultz, M.; Gellert, M.

The nonaxisymmetric Tayler instability of toroidal magnetic fields due to axial electric currents is studied for conducting incompressible fluids between two coaxial cylinders without endplates. The inner cylinder is considered as so thin that the limit of Rin → 0 can be computed. The magnetic Prandtl number is varied over many orders of magnitudes but the azimuthal mode number of the perturbations is fixed to m = 1. In the linear approximation the critical magnetic field amplitudes and the growth rates of the instability are determined for both resting and rotating cylinders. Without rotation the critical Hartmann numbers do not depend on the magnetic Prandtl number but this is not true for the corresponding growth rates. For given product of viscosity and magnetic diffusivity the growth rates for small and large magnetic Prandtl number are much smaller than those for Pm = 1. For gallium under the influence of a magnetic field at the outer cylinder of 1 kG the resulting growth time is 5 s. The minimum electric current through a container of 10 cm diameter to excite the instability is 3.20 kA. For a rotating container both the critical magnetic field and the related growth times are larger than for the resting column.

Publ.-Id: 15153

Radiosynthese und physikochemische Bewertung eines 7-(2-[F-18]Fluorethoxy)-6-methoxychinazolin-Derivates für die Darstellung der PDE10A mit PET

Funke, U.; Schwan, G.; Scheunemann, M.; Maisonial, A.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Sträter, N.; Nieber, K.; Briel, D.; Brust, P.

Neurologische und psychiatrische Erkrankungen, wie Schizophrenie und Psychosen werden in Zusammenhang mit Beeinträchtigungen der Aktivität der Phosphodiesterease 10A (PDE10A) gebracht. Selektive und hirngängige PDE10A-Inhibitoren sind daher Ziel der Entwicklung hochwirksamer Therapeutika (1) und geeigneter Diagnostika für die molekulare Bildgebung (2).
Ein Papaverin-basierter chiraler 6,7-Dimethoxychinazolin-Ligand diente in den vorliegenden Arbeiten als Leitstruktur für die Entwicklung eines 7-(2-[F-18]Fluorethoxy)-Analogons [F-18]I zur Darstellung der PDE10A mit PET.

Die Referenzverbindung I sowie die Markierungsvorläufer II und III wurden in Mehrstufen-Synthesen dargestellt und der logD7,0 mittels HPLC ermittelt. Für eine zweistufige Radiosynthese wurde 1,2-Bistosyloxyethan nach einem Standardverfahren zu 2-[F-18]Fluorethyltosylat [F-18]IV umgesetzt und [F-18]IV ohne Aufarbeitung weiterverwendet. Deprotonierung des 7-Hydroxy-Synthesevorläufers II mittels K.222/K2CO3 (2-3 h, 50-60°C, MeCN) und anschließende Veretherung (2 mg; K.222/K2CO3, MeCN/80°C) mit [F-18]IV führten zur Zielverbindung [F-18]I. Die direkte Radiofluorierung erfolgte über Substitution des 7-(2-Tosyloxyethyl)-Präkursors III mit n.c.a. [F-18]F- (2-3 mg; K.222/K2CO3, MeCN/80°C). Nach Aufarbeitung mit FPE (RP-18, MeCN) folgte semipräparative Radio-HPLC (RP-18, 45-50% MeCN, 20 mM NH4OAc) und Formulierung in MeCN, MeOH, EtOH oder wässrigem Puffer. Mit [F-18]I-Lösungen wurde die Stabilität bei 40 und 80°C untersucht sowie der logD7,2-7,4 mittels Extraktion in n-Octanol/Puffer-Systemen bestimmt.

[F-18]IV konnte in 5 min mit Markierungsausbeuten (MA, DC/HPLC) von 50-76% dargestellt werden. Hiermit wurde II in 15-20 min zu 30-45% MA an [F-18]I umgesetzt. Die radiochemische Ausbeute (RCA) betrug nach 2-3 h ohne Aufarbeitung 18-29%.
Mittels Tosylat III wurde n.c.a. [F-18]I in 15 min mit MA von 42-72%, einer chemischen und radiochemischen Reinheit ≥99% (DC/HPLC) sowie spezifischen Aktivität von 110-1110 GBq/μmol (HPLC) erhalten. Die RCA betrug nach 3-4 h Gesamtsynthesedauer 17-40%. Für die Zielverbindung I/[F-18]I wurden ein logD7,0 von 2,63±0,01 mittels HPLC und ein logD7,2-7,4 von 2,59±0,46 mittels Extraktion ermittelt. [F-18]I ist bei 40°C nur in ethanolischer KOH labil und erweist sich in EtOH und MeCN bei 80°C auch nach 120 min als stabil.

Die Zielverbindung konnte sowohl in einer zweistufigen als auch direkten Radiofluorierung dargestellt werden, wobei letztere eine höhere radiochemische Ausbeute lieferte. Ein logD von ∼ 2,6 stellt eine gute Voraussetzung für eine gute Hirnaufnahme des Radioliganden bei ausreichend niedriger unspezifischer Bindung dar. Weiterführende Experimente sind geplant, um die Organverteilung des Radioliganden sowie Bindung in vitro und in vivo zu untersuchen.

(1) Chappie T A et al. J Med Chem 2007; 50: 182-185
(2) Celen S et al. J Nucl Med 2010; 51: 1584-1591

Keywords: PDE10A; PET; 7-(2-[F-18]Fluorethoxy)-6-methoxychinazolin-Derivat

  • Lecture (Conference)
    NulearMedizin2011, 13.-16.04.2011, Bregenz, Österreich
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A38-A39

Publ.-Id: 15152

Investigation of conductive nanostructures on ta-C films made by FIB lithography

Philipp, P.; Bischoff, L.

Tetrahedral amorphous carbon (ta-C) films with high sp3 content produced by mass filtered vacuum arc deposition were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model [1] for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 1016 cm-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290 Ohm/sq was achieved at 1.6 x 1017 cm-2. Investigations of the conduction mechanism were done by Hall-mobility measurements on Van der Pauw and Hall test structures. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 200 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 0.3 GOhm (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.
[1] F. Bosia et al. Nucl. Instrum. Meth. B 268 (2010) 2991.

Keywords: tetrahedral amorphous carbon; ta-C; FIB; nanostructures; graphitization; sheet resistance

  • Lecture (Conference)
    E-MRS 2011 Spring Meeting, 09.-13.05.2011, Strassburg, France
  • Nuclear Instruments and Methods in Physics Research B 282(2012), 121-124
    DOI: 10.1016/j.nimb.2011.08.057

Publ.-Id: 15151

Ein neuer mit Fluor-18 markierter Radioligand für die molekulare Bildgebung der Phosphodieesterase 10A im Gehirn

Funke, U.; Schwan, G.; Scheunemann, M.; Fischer, S.; Hiller, A.; Donat, C.; Sträter, N.; Nieber, K.; Briel, D.; Brust, P.

Die Phosphodiesterase 10A (PDE10A) terminiert die Signalübertragung der Second messenger cAMP und cGMP durch Hydrolyse und wird vorrangig in Gehirn (Striatum) und Schilddrüse exprimiert. Veränderungen der Aktivität der PDE10A werden in Zusammenhang mit Schizophrenie und Psychosen gebracht. Selektive und hirngängige PDE10A-Inhibitoren sind daher Ziel der Entwicklung hochwirksamer Therapeutika und geeigneter Diagnostika für die molekulare Bildgebung, wie unser 7-(2-[18F]Fluorethoxy)-6-methoxychinazolin-Derivat zur Visualisierung der PDE10A mit Positronen-Emissions-Tomographie (PET). Die zur Analytik erforderliche nichtradioaktive Referenzverbindung und die Ausgangsverbindungen für die 18F-Markierung wurden in Mehrstufen-Synthesen dargestellt. Für die 18F-Markierung wurde zunächst ein schneller zugängliches zweistufiges Verfahren entwickelt. Eine verbesserte Darstellung erfolgte anschließend im Einstufenverfahren über die direkte Umsetzung des entsprechenden 7-(2-Tosyloxyethyl)-Präkursors mit trägerfreiem [18F]F-. Die Markierungsausbeute betrug 42-72%, die chemische und radiochemische Reinheit ≥99% und die spezifische Aktivität 110-1110 GBq/µmol. Die zerfallskorrigierte radiochemische Ausbeute lag nach 3-4 h Gesamtsynthesedauer bei 17-40%. Als Kriterium für die Qualität der Hirnaufnahme wurde die Lipophilie des Radioliganden bei pH 7 bis 7,4 mittels HPLC und extraktiven Methoden bestimmt. Ein logD7,0-7,4  2,6 weist auf eine gute Hirnaufnahme bei ausreichend niedriger unspezifischer Bindung hin. Weiterführende Experimente sind geplant, um die Organverteilung des Radioliganden sowie Bindung in vitro und in vivo zu untersuchen.

Keywords: Fluor-18; Phosphodieesterase; molekulare Bildgebung

  • Poster
    9th Research Festival for Life Sciences, 07.12.2010, Leipzig, Deutschland

Publ.-Id: 15150

Fabrication of highly ordered magnetic bio-Au nanoclusters by using SlaA-layer ghosts of Sulfolobus acidocaldarius as a template

Selenska-Pobell, S.; Reitz, T.; Geissler, A.; Herrmannsdörfer, T.; Merroun, M.

The regularly structured paracrystalline surface layers (S-layers) of prokaryotic microorganisms are promising biological templates for production of metal nanoclusters for biotechnological applications. Formerly, we have demonstrated that some bacterial S-layers can effectively bind noble metals and can be used for preparation of palladium, platinum, and gold nanoclusters by using different reduction agents (1, 2) or electron beam (3).
In this work Au-nanoclusters were produced on the extremely stable (against high temperatures, acidity, proteases, and mechanic stress) S-layer of the acidothermophilic Archaeon Sulfolobus acidocaldarius. One additional important characteristic feature of this S-layer, called recently SlaA (4) is the presence of the sulfur containing amino acid cystein in its primary structure. This is in contrast to the above mentioned bacterial S-layers and is of great importance for the effective binding and deposition of Au cations. The purified SlaA-layer fraction was treated initially with tetrachloroauric (III) acid solution. Afterwards the deposited Au(III) cations were reduced to Au(0) by using dimethylaminoburane. The analysis of the obtained Au-nanoclusters by using Transmission Electron Microscopy combined with Energy Dispersive X-ray analyses (TEM-EDX) demonstrated that the nanoclusters have a size in the range of 2-3.5 nm and that they are associated with sulfur atoms (Fig. 1). As measured via SQUID Magnetometer they possess magnetic properties (Fig. 2). No magnetic properties were observed in the case of the Au-nanoparticles formed on the bacterial S-layers possessing no sulfur. We suggest that the sulfur atoms are possibly contributing to the observed magnetic properties. However, the number of sulfur atoms implicated in the Au complexation is extremely low (only a few atoms per nano-particle). On the other hand, the size of the nanoparticles formed on the archaeal SlaA-layer is significantly bigger (about 3 nm) in comparison to those formed on the bacterial S-layer (less then 1 nm). The size difference in the two kinds of nano-particles can be explained with the different size of the pores of the two S-layer lattices, where the initial deposition of the metal cations occurs. The archaeal SlaA-layer possesses p3 lattice symmetry and significantly larger pores (4) then the bacterial S-layer which has p4 symmetry (1, 2). The size of the Au-nanoclusters may play also a role for their magnetic properties. Efforts to understand the reasons for the observed unexpected magnetic behavior of the newly constructed bio-Au nanoparticles are in progress.
To our knowledge, this is the first report on constructing of highly ordered Au nanoparticles on an archaeal S-layer. These bio-Au structures possess some advantageous properties, such as high stability to high temperatures, acidic and mechanical stress, in comparison to those formerly constructed on bacterial S-layers. Moreover, in contrast to Au as a bulk noble metal and to bacterial bio-Au, the archaeal bio-Au nanoparticles possess unique magnetic properties.
1. Fahmy K, Merroun M, Raff J, Pollmann K, Hennig Ch, Savchuk O, Selenska-Pobell S (2006) Biophys J 91:996-1007.
2. Merroun M, Rossberg A, Hennig C, Scheinost A, Selenska-Pobell S (2007) Mater Sci & Engin C27, 188-192
3. Wahl R, Mertig M, Raff J, Selenska-Pobell S, Pompe W (2001) Adv Mater 13, 736-740
4. Veith A, Klingl A, Zolghadr B, Lauber K, Mentele R, Lottspeich F, Rachel R, Alberts S-V, Kletzin A (2009) Mol Microbiol 73, 58-72

  • Contribution to proceedings
    Nano Tech Conference, 13.-16.06.2011, Boston, USA
    Nanotechnology 2011, Vol. 3: NSTI, 978-1-4398-7138-6, 189-192

Publ.-Id: 15149

Dosimetric system for quantitative cell irradiation experiments with laser-accelerated protons

Richter, C.; Karsch, L.; Dammene, Y.; Metzkes, J.; Schramm, U.; Sobiella, M.; Schürer, M.; Weber, A.; Zeil, K.; Pawelke, J.

An Integrated DOsimetry and Cell Irradiation System (IDOCIS) with laser-accelerated proton beams was developed, characterized, calibrated and successfully used for systematic in vitro experiments. Due to the broad exponentially shaped energy spectrum, the low energy range of the protons (< 20 MeV) and the high pulse dose, the absolute dosimetry for this beam quality is challenging. Therefore, a dedicated Faraday cup is used as an energy and dose rate independent absolute dosimeter that has been calibrated consistently with three independent methods. A transmission ionization chamber providing online relative dose information is cross-calibrated against the Faraday cup. Providing both online and absolute dose information the IDOCIS allows for quantitative dosimetric and radiobiological studies at current low-energy laser-accelerated proton beams. Finally, first dosimetric characterizations of a laser-accelerated proton beam with the IDOCIS are presented.

Keywords: laser particle acceleration; proton; dosimetry; faraday cup; radiochromic films

Publ.-Id: 15148

Formation of a ternary neptunyl(V) biscarbonato inner-sphere sorption complex inhibits calcite growth rate

Heberling, F.; Scheinost, A. C.; Bosbach, D.

Neptunyl, Np(V)O2 +, along with the other actinyl ions U(VI)O2 2+ and Pu(V,VI)O2 +,2+, is considered to be highly mobile in the geosphere, while interaction with mineral surfaces (inner- or outer-sphere adsorption, ion-exchange, coprecipitation/structural incorporation) may retard its migration. Detailed information about the exact interaction mechanisms including the structure and stoichiometry of the adsorption complexes is crucial to predict the retention behavior in diverse geochemical environments. Here, we investigated the structure of the neptunyl adsorption complex at the calcite-water interface at pH 8.3 in equilibrium with air by means of low-temperature (15 K) EXAFS spectroscopy at the Np-LIII edge. The coordination environment of neptunyl consists of two axial oxygen atoms at 1.87(±0.01) Å, and an equatorial oxygen shell of six atoms at 2.51(±0.01) Å. Two oxygen backscatterers at 3.50(±0.04) Å along with calcium backscatterers at 3.95(±0.03) Å suggest that neptunyl is linked to the calcite surface through two monodentate bonds towards carbonate groups of the calcite surface. Two additional carbon backscatterers at 2.94(±0.02) Å are attributed to two carbonate ions in bidentate coordination. This structural environment is conclusively interpreted as a ternary surface complex, where a neptunyl biscarbonato complex sorbs through two monodentate carbonate bonds to steps at the calcite (104) face, while the two bidentately coordinated carbonate groups point away from the surface. This structural information is further supported by Mixed Flow Reactor (MFR) experiments. They show a significant decrease of the calcite growth rate in the presence of neptunyl(V), in line with blockage of the most active crystal growth sites, step and kink sites, by adsorption of neptunyl. Formation of this sorption complex constitutes an important retention mechanism for neptunyl in calcite-rich environments.

Keywords: EXAFS; Neptunium; Sorption; Calcite

Publ.-Id: 15147

Bioinspred hybrid nanomaterials based on self-assembling proteins

Raff, J.; Weinert, U.; Günther, T.; Marquard, A.; Lehmann, F.; Kutschke, S.; Pollmann, K.

Many microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example, intensively studied at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf, is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins (figure 1) bind toxic metals and metalloids and thusly protect the cells from being damaged by these elements and their compounds. On other cells, S-layers may act as immobilization matrix for exoenzymes, as molecular sieve, as ion and molecule trap or they protect the cell from being affected by the immune defense of host organism, by other bacteria or by lytic enzymes. These properties makes S-layer, together with their capability to self-assemble in suspension, on surfaces and at interfaces, very interesting building blocks for the construction of new bioinspired nanomaterials for different technical applications. Using the two-dimensional protein arrays, different kinds of surfaces can be nanostructured and multiple functionalized by a layer-by-layer technique. This interdisdisciplinary approach allows the design of novel bio-inorganic hybrid materials. Currently under development are three kinds of materials, namely metal filters, nanocatalysts and sensors. Regarding metal filters the aim is the development of selective materials for the removal of toxic metals and metalloids or the recovery of precious metals. In the case of nanocatalysts, the research is focused on the development of highly efficient catalysts or photocatalysts on the basis of immobilized and regular arranged metal or metal oxide nanoparticles for organic synthesis or the elimination of organic pollutants. S-layer based biosensors were under development to detect chemicals or pharmaceuticals by combining highly specific receptors like aptamers with stable fluorescence dyes.

Keywords: S-layer; biocomposites; nanomaterials

  • Poster
    DFG-NSF Research Conference, 22.-25.03.2011, New York, USA

Publ.-Id: 15146

Advances in Si & Ge millisecond processing: From SOI to superconductivity and carrier-mediated ferromagnetism

Skorupa, W.

This paper reviews the advances that millisecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, namely silicon and germanium, thus enabling the fabrication of novel microelectronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. Opportunities in ultra-shallow junction formation for silicon-on-insulator, superconducting Ge and Si, and diluted ferromagnetic Ge, along with the technical reasons for using annealing times in the ms range are discussed in the context of state-of-the-art materials processing. Whereas these examples base on solid phase processing, the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. As a recent example the controlled surface melting of a Ge enriched silicon substrate is reported.

Keywords: flash lamp annealing; millisecond thermal processing; silicon germanium; ion implantation; silicon-on-insulator; diluted semiconductors; ferromagnetism; superconduction; liquid phase; surface melting; laser annealing

  • Invited lecture (Conferences)
    219th Electrochemical Society Meeting, SYMPOSIUM E1 Silicon compatible materials, processes and technologies for Advanced Integrated Circuits and Emerging Applications, 01.-06.05.2011, Montreal, Kanada
  • Contribution to proceedings
    219th Electrochemical Society Meeting, SYMPOSIUM E1 "Silicon compatible materials, processes and technologies for Advanced Integrated Circuits and Emerging Applications", 01.-06.05.2011, Montreal, Kanada
    Silicon compatible materials, processes and technologies for Advanced Integrated Circuits and Emerging Applications, Pennington, New Jersey, USA: Electrochemical Society, 978-1-56677-863-3, 193-204

Publ.-Id: 15145

In-vivo dosimetry for proton and ion therapy

Fiedler, F.

Abstract not available.

  • Invited lecture (Conferences)
    Retreat - Oncoray Seminar, 11.-12.01.2011, Riesa, Germany

Publ.-Id: 15144

High regiocontrol in the nucleophilic ring opening of 1-aralkyl-3,4-epoxypiperidines with amines – A short-step synthesis of 4-fluorobenzyltrozamicol and novel anilidopiperidines

Scheunemann, M.; Hennig, L.; Funke, U.; Steinbach, J.

Nucleophilic ring-opening reactions of three 1-aralkyl-3,4-epoxy piperidines with a series of aliphatic and aromatic amines have been investigated. Reactions in protic solvents, preferably 2-propanol, gave rise to 3-amino-piperidin-4-ols in ratios up to 20:1. Accordingly, the highly VAChT affine 4-fluorobenzyltrozamicol was obtained directly from an epoxide ring opening in one step, without the need of chromatographic separation. Reactions in acetonitrile assisted by Li-salts, most suitable with LiBr, led regioselectively to trans-4-amino-piperidin-3-ols in high yields. N-Phenethyl substituted anilino-piperidinols as easily obtained by this method were converted into a series of new β-hydroxy substituted anilidopiperidines.

Keywords: 1-aralkyl-3; 4-epoxy piperidines; 4-fluorobenzyltrozamicol; anilidopiperidines

Publ.-Id: 15143

Entwicklung von Radiotracern zur Untersuchung des cholinergen Systems mittels Positronen-Emissions-Tomografie

Brust, P.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    Universität Leipzig - Kolloquium des Paul-Flechsig-Instituts für Hirnforschung, 31.03.2011, Leipzig, Deutschland

Publ.-Id: 15142

Design radioaktiver Sonden zur molekularen Bildgebung bei Hirnerkrankungen

Brust, P.

Es ist kein Abstract vorhanden.

  • Invited lecture (Conferences)
    24. Tagung der KTG-Fachgruppe Nutzen der Kerntechnik, 05.11.2010, Leipzig, Deutschland

Publ.-Id: 15141

Microstructure-property relations of reactively magnetron sputtered VCxNy films

Mitterer, C.; Fateh, N.; Munnik, F.

VCxNy films with a wide range of chemical composition were grown onto silicon and high-speed steel substrates using reactive unbalanced magnetron sputtering from V targets in an Ar/N2/C2H2 atmosphere at a substrate temperature of 500°C. A solid solution of VN and VC is formed for N2 and C2H2 addition, with increasing fractions of an additional amorphous carbon phase for increasing C2H2 flow ratios. While an increase in hardness is observed for low carbon contents due to solid solution hardening, raising the amorphous carbon phase fraction results in a hardness reduction. Dry-sliding ball-on-disc tests yield low friction coefficients with values of 0.22 for those films with the highest content of amorphous carbon phase, while the lowest wear is observed for films with dominating vanadium carbonitride solid solution. The low friction behavior is attributed to the formation of tribo-layers with easy-shearable C-H bonds formed in humid atmospheres, and is not observed in dry nitrogen and synthetic air.

Keywords: Vanadium carbonitride; amorphous carbon; sputtered films; low friction

Publ.-Id: 15140

Magnetisation reversal processes in saturation magnetisation reduced stripes

Basith, M.; Mcvitie, S.; Strache, T.; Fritzsche, M.; McCord, J.; Fassbender, J.

On a continuous 20 nm thick Permalloy film, magnetically softer and harder stripes, which are in direct lateral contact by means of exchange coupling, were fabricated by focused Ga+ irradiation. The irradiation dose was 6.00 x 1015 Ga/ions and the width of the alternative exposed and unexposed stripes were varied from 1000nm to 200nm. Low angle electron diffraction experiment confirmed that due to this amount of ion dose, saturation magnetic induction of the irradiated stripe is reduced to 70 % of the unirradiated stripe, assuming a thickness reduction of 2.5 nm determined by AFM. Magnetisation reversal experiments were carried out using high resolution Lorentz microscopy. For a stripe width of 1000 nm a pronounced 2 step reversal with an intermediate antiparallel orientation of magnetisation in neighboring stripes is found. Differential phase contrast (DPC) images demonstrate a transition from the discrete switching of the wider nanostripes to the collective switching of the narrower stripes of width 200 nm. This can be attributed to the local modification of the magnetic thin film parameters below the intrinsic magnetic length scales associated with the domain wall width. By using DPC mode of Lorentz microscopy, domain wall width was calculated and compared with theory for 20 nm thick continuous Permalloy film.

  • Lecture (Conference)
    Condensed Matter and Materials Physics (CMMP 2010), 14-16 December 2010, 15.12.2010, Warwick, UK

Publ.-Id: 15139

Glacial history of the Pamir Mountains during the Last Glacial cycle along a semi-humid to arid transect based on 10Be surface exposure dating

Röhringer, I.; Zech, R.; Sosin, P.; Abramowski, U.; Aldahan, A.; Kubik, P.; Merchel, S.; Zöller, L.; Zech, W.

The reconstruction of past climate changes in the Pamir Mountains has high potential for identifying the dynamics of circulation systems in Asia and for understanding global environmental changes during the Late Quaternary. The Pamir Mountains are situated in a climatic transition zone between mid-latitude westerlies, the Indian summer monsoon and the Siberian High. Today main moisture to the Pamir comes with SW- cyclones along the westerly jetstream whereas the influence of the Indian monsoon typically ends south of the NW-Himalaya. Up to now the impact of the Indian monsoon on former glaciations of the Pamir Mountains has not yet been adequately examined. Even chronological information about former glaciations in the Pamir is still sparse. The objectives of our study are: To upgrade the present glacial chronology by dating glacial successions along a moisture gradient from the north-western to the southern Pamir Mountain ranges. We present preliminary 10Be ages from moraine successions of three study sites (Iskenderkul area, Muksu-Kyzlsu area, Alichur area). Our first results from the southern Pamir (Alichur area) corroborate and refine previously published findings: Extensive glaciation occurred during MIS 4 and during MIS 2. However our data indicate that glaciers in the southern Pamir also advanced during ~50 to 40 ka. Rapid deglaciation occurred after ~18 ka. So far there is no evidence for glacier advances during the Holocene. Overall, we conclude that the glacial chronology of the Pamir seems to be mainly controlled by temperature, with maxima during ~70 to 60 ka, ~50 to 40 ka and ~20 ka. Because during climatic cold phases the Indian Monsoon was weakened, we assume that glacier advances in the Pamir Mountains during the Last Glacial cycle were mainly triggered by westerly moisture supply. Analyses of further samples, from both the Muksu-Kyzlsu area and the Iskenderkul area are in progress.

Keywords: accelerator mass spectrometry; quaternary; glaciation

  • Poster
    XXVIII INQUA (International Union for Quaternary Research) Congress, 20.-27.07.2011, Bern, Schweiz


Publ.-Id: 15138

Estimation of positron emitter distributions from experimental yields

Priegnitz, M.; Enghardt, W.; Laube, K.; Schöne, S.; Fiedler, F.

At GSI Darmstadt targets of different materials have been irradiated with carbon ions in order to verify an approach for the prediction of positron emitter distribution based on experimental yields. Depth dependent thick target yields calculated with this approach are presented and compared to experimental results.

  • Contribution to external collection
    in: GSI Scientific Report 2010, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2011, 469

Publ.-Id: 15137

Measurement of the inelastic neutron scattering cross section of Fe-56

Beyer, R.; Birgersson, E.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Nolte, R.; Schwengner, R.; Wagner, A.

The (n,n'g) cross section to the 1st excited state of Fe-56 has been measured at the neutron time-of-flight facility nELBE of the Forschungzentrum Dresden-Rossendorf.
The nELBE neutron source delivers neutrons with energies from 100 keV up to 10 MeV. By means of a "double time-of-flight" setup the inealstic scattering cross section of the 1st excited state could be measured over the whole energy range independently of the knowledge about cross sections of higher levels. Plastic scintillators were used to detect the inelastically scattered neutron and BaF2 detectors to detect the correlated gamma-ray. The time of detection of the gamma-ray defines the time-of-flight of the incoming neutron. The time difference between gamma- and neutron-detection gives the energy of the scattered neutron. By this method the excitation of the 1st level can be identified independently from the emitted gamma-ray energy.

Keywords: nELBE; inealstic neutrons scattering; Fe-56

  • Lecture (Conference)
    DPG Frühjahrstagung 2010, 15.-19.03.2010, Bonn, Deutschland

Publ.-Id: 15136

Measuring nuclear data to reduce radioactive waste

Beyer, R.; Birgersson, E.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Nolte, R.; Schwengner, R.; Wagner, A.

It will described how nuclear transmutation will help to reduce the radiotoxicity of nuclear waste.

Keywords: nELBE; transmutation; generation iv

  • Poster
    PhD Seminar 2010, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 15135

A global study of the electric dipole strength in heavy nuclei

Junghans, A. R.; Beyer, R.; Rusev, G.; Schwengner, R.; Wagner, A.; Grosse, E.

The dipole strength function strongly influences neutron capture processes in heavy nuclei and it is of great importance for photon induced processes like electromagnetic disintegration and nuclear resonance fluorescence. Above 10 MeV the absolute value and energy dependence are well known from (g,n) experiments usually described by the Lorentzian shape of the Giant Dipole Resonance (GDR). Below the threshold photon scattering studies on nuclei above mass 80 indicate no decrease of the spreading width with falling energy allows to describe its shape by a continuation of the GDR Lorentzian with constant width. The constant width is in accordance to primary photons observed after neutron capture in deformed nuclei which show a clear double peak structure. Capture data taken for nearly spherical nuclei seem to show a one-component Lorentzian shape with width varying with the square of the gamma-energy Eg. This apparent disaccord between more or less deformed nuclei is reinvestigated with the aid of Average Resonance Capture (ARC) data measured for various transitional nuclei. Our suggestion, a 3-fold Lorentzian for all kinds of deformation, will be explained.

Keywords: ELBE; dipole strength; giant dipole resonance

  • Poster
    International Conference on nuclear data for science and technology 2010, 26.-30.04.2010, Jeju Island, Korea

Publ.-Id: 15134

Fast neutron inelastic scattering

Beyer, R.; Birgersson, E.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Nolte, R.; Schwengner, R.; Wagner, A.

Presenation of latest experiments done at the nELBE facility at Forschungszentrum Dresden-Rossendorf. Preliminary results on Fe-56 and Na-23 inelastic neutron scattering will be shown.

Keywords: nELBE; inelastic scattering; Fe-56

  • Lecture (Conference)
    GEDEPEON WORKSHOP, 29.-30.11.2010, Issy-les-Moulineaux, France
  • Lecture (Conference)
    1st TRAKULA Seminar, 04.-06.10.2010, Braunschweig, Deutschland

Publ.-Id: 15133

Inelastic Neutron Scattering at nELBE

Beyer, R.; Birgersson, E.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Nolte, R.; Schwengner, R.; Wagner, A.

At the superconducting electron linear accelerator ELBE at Forschungszentrum Dresden-Rossendorf the neutron time-of-flight facility nELBE has become operational.
Fast neutrons in the energy range from ca. 0.1 to 10 MeV are produced by the pulsed electron beam from ELBE impinging on a liquid lead circuit as a radiator.
The short beam pulses of ~10 ps provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about < 1~\% at 1 MeV with a short flight path of ~ 5 m.
The neutron intensity on target is ca. 4*104 n/s/cm2 using an electron bunch charge of 77 pC and 203 kHz pulse repetition rate.
The energy range of the neutrons produced is well suited for neutron cross section measurements relevant for the development of Generation IV reactor systems and for the transmutation of nuclear waste.
First measurements of inelastic scattering cross section on natural Fe have been performed using a double time-of-flight method. The cross section for the first excited level of Fe-56 and Fe-54 could be determined.

Keywords: nELBE; inealstic neutron scattering; Fe-56

  • Lecture (Conference)
    Final Scientific EFNUDAT Workshop, 30.08.-02.09.2010, Geneva, Switzerland

Publ.-Id: 15132

Inelastic Neutron Scattering at nELBE

Beyer, R.; Birgersson, E.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Nolte, R.; Schilling, K.-D.; Schwengner, R.; Wagner, A.

At the nELBE facility at Forschungszentrum Dresden-Rossendorf fast neutrons with kinetic energies of 0.1 to 10 MeV will be used to deliver nuclear data on neutron induced reactions necessary for the development of future nuclear transmutation facilities and new types of nuclear reactors. Electrons from the superconducting electron linac ELBE are shot onto a liquid lead target where they produce Bremsstrahlung which in turn liberates neutrons via (gamma,n) reactions. The short pico-second pulse structure of the electron beam enables neutron time-of-flight experiments with very short flight paths of 4-7 meters obtaining energy resolutions of about 1 %.

First experiments on inelastic neutron scattering on 56Fe where performed using a double time-of-flight setup based on proton recoil detectors [2] and an array of 42 BaF$_2$ crystals to detect the emitted photons and neutrons in coincidence. First results will be presented.

Keywords: nELBE; inelastic neutron scattering; Fe-56

  • Lecture (Conference)
    Gemeinsame DPG Frühjahrstagung mit der European Physical Society (EuNPC) 2009, 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 15131

Chlorine-36 interlaboratory comparison - Can we harmonize 36Cl-data on a world-wide scale?

Merchel, S.; Bremser, W.; Alfimov, V.; Arnold, M.; Aumaître, G.; Benedetti, L.; Bourlès, D. L.; Caffee, M.; Fifield, L. K.; Finkel, R. C.; Freeman, S. P. H. T.; Martschini, M.; Matsushi, Y.; Rood, D. H.; Sasa, K.; Steier, P.; Takahashi, T.; Tamari, M.; Tims, S. G.; Tosaki, Y.; Wilcken, K. M.; Xu, S.

As a first step towards using world-wide a common 36Cl standard-type material for the normalization of 36Cl AMS results, we have initiated an interlaboratory comparison, but with differences in the execution of the project compared to other round-robin exercises: a) participants have given up anonymity to better optimize discussion and conclusions, b) preliminary results have been shown at various scientific meetings and workshops to discuss first trends and to increase the number of participants, c) participants had the possibility to repeat their AMS measurements and/or change measurement setups or data evaluation to improve individual data [e.g. 1]. We are aware and acknowledge that these later changes by some of the participants, which led to different overall data compared with the initial results, are not fully consistent with the idea of a normal proficiency test layout. However, these data changes were accepted to better meet the main objectives of the intercomparison: to identify and eliminate differences between AMS laboratories, thus, improving the 36Cl data quality world-wide as soon as possible.
The evaluation of the final results of the eight participating AMS laboratories for three synthetic AgCl samples with 36Cl/Cl ratios at the 10-11 (SM-Cl-11), 10-12 (SM-Cl-12), and 10-13 (SM-Cl-13) level shows no difference in the sense of simple statistical significance [2]. However, more detailed statistical analyses indicate a certain interlaboratory bias and an under-estimation of uncertainties by some of the laboratories. The round-robin data demonstrate that 36Cl/Cl results from two individual AMS laboratories can differ by up to 17% (Fig. 1). Thus, the necessity for further work on harmonizing the 36Cl business on a world-wide scale and on improving the measurements is obvious.

Fig. 1: Regression of normalized results for the three investigated samples in the order of ascending average.
[1] V. Alfimov et al., Ion Beam Physics, ETH Zurich, Annual Report (2009) 13.
[2] S. Merchel et al., Anal. Bioanal. Chem., submitted.

Keywords: accelerator mass spectrometry; round-robin; quality assurance

  • Contribution to external collection
    in: Ion Beam Physics, ETH Zurich, Annual Report 2010, Zürich: Labor für Ionenstrahlphysik, ETH (Herausgeber), 2011, 33

Publ.-Id: 15130

Timing and paleoclimate forcings of Late Quaternary glaciations in the Pamir Mountains: 10Be surface exposure dating of glacial landforms

Roehringer, I.; Abramowski, U.; Zech, R.; Sosin, P.; Aldahan, A.; Merchel, S.; Kubik, P.; Zoeller, L.; Zech, W.

The Pamir Mountains have been extensively glaciated several times in the past. As glaciers are mainly sensitive to variations in temperature and precipitation, they reflect changes in large-scale atmospheric circulation patterns. The Pamir Mountains are situated in a climatic transition zone between mid-latitude westerlies, the Indian summer monsoon and the Siberian High. Today main moisture to the Pamir comes with SW-cyclones along the westerly jetstream. Up to now the impact of the Indian monsoon on former glaciations of the Pamir Mountains has not yet been adequately examined. Even chronological information about former glaciations in the Pamir are still sparse. The objective of our study is: To upgrade the present glacial chronology by 10Be surface exposure dating of erratic boulders on top of moraines along a moisture gradient from the north-western to the southern Pamir Mountain ranges. We present preliminary 10Be ages from moraine successions of three study sites (Iskenderkul area, Muksu-Kyslsu area, Alichur area).
Our first results from the southern Pamir (Alichur area) corroborate and refine previously published findings: Extensive glaciation occurred during MIS 4 and during MIS 2 coinciding with lower insolation intensity. Because during climatic cold phases the Indian Monsoon was weakened we assume that these glacier advances were mainly triggered by westerly moisture supply. However, our data indicate that glaciers in the southern Pamir also advanced during ~58 to ~45 ka as also observed in monsoonal influenced Karakoram and eastern Hindu Kush regions. Our surface exposure ages point to rapid deglaciation after ~18 ka. So far there is no evidence for glacier advances during the Holocene. Analyses of further samples, from both the Muksu-Kyzlsu area and the Iskenderkul area are in progress.

Keywords: accelerator mass spectrometry; glaciation; quaternary

  • Poster
    European Geosciences Union (EGU) General Assembly, Vienna, Austria 2011, 03.-08.04.2011, Wien, Östereich

Publ.-Id: 15129

Development of a reactor dynamics code for block-type HTR at Forschungszentrum Dresden-Rossendorf

Rohde, U.; Merk, B.; Baier, S.; Fridman, E.; Dürigen, S.; Kliem, S.; Weiss, F.-P.

At the Forschungszentrum Dresden-Rossendorf (FZD), the Light Water Reactor (LWR) dynamics code DYN3D is extended and adopted for the application to block-type High Temperature Gas-Cooled Reactor (HTGR). DYN3D is a two-group diffusion code for 3D steady-state and transient core calculations based on nodal expansion methods. In addition to the neutron kinetics, it comprises of a thermal-hydraulics model for flow in parallel coolant channels. Macroscopic cross section data libraries precalculated with variation of burn-up, reactor poisons concentrations and thermal-hydraulic feedback parameters are linked to the code. Recently, a multi-group version of the code was developed.
In this paper, we give an overview of the latest developments of DYN3D concerning block-type HTGR.
The SP3 transport approximation is implemented into the multi-group DYN3D code to take anisotropy of the neutron flux and heterogeneity of the core more precisely into account. The SP3 method previously implemented into DYN3D for square fuel element geometry of LWR is being extended for hexagonal geometry of the graphite blocks, where the hexagons are subdivided into triangular nodes to be able to perform a systematic mesh refinement.
The main challenge in cross section generation for the HTGR core calculations is the treatment of the so-called “double heterogeneity”. The Reactivity-Equivalent Physical Transformation (RPT) approach is applied in order to eliminate the double-heterogeneity of HTGR fuel elements in HELIOS calculations. The main steps of the RPT method are presented. A 3D heat conduction module coupled with a channel-type coolant flow model is implemented to take the temperature reactivity feedback to neutronics physically correctly into account. It is shown that there is significant redistribution of the produced heat by heat conduction between the graphite blocks.

  • Contribution to proceedings
    Fachtag der KTG: "Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland", 07.-08.10.2010, Dresden, Deutschland, 07.-08.10.2010, Dresden, Deutschland
    Tagungsband des Fachtages der KTG: "Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland", CDROM
  • Invited lecture (Conferences)
    Fachtag der KTG: "Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland", 07.-08.10.2010, Dresden, Deutschland

Publ.-Id: 15128

Anisotropy of the elastic and magnetic properties of expanded austenite in AISI 316L stainless steel

Tromas, C.; Stinville, J.-C.; Menendez, E.; Villechaise, P.; Nogues, J.; Sort, J.; Templier, C.; Riviere, J.-P.; Martinavicius, A.; Abrasonis, G.

The correlation between the grain orientation and the magnetic and elastic properties of plasma nitrided polycrystalline 316L austenitic stainless steel (ASS) is investigated.Plasma nitriding was performed at 400°C for 30 minutes under a pressure of 7.5 Pa using a 60 sccm N2 and 40 sccm H2 mixture. The grain orientation in a delimited area was obtained from electron backscatter diffraction (EBSD). The magnetic properties of the assessed grains were locally investigated by polar magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM). Young's modulus Ehkl cartography was obtained in 3D using nanoindentation tomography. Plasma nitriding results in the nitrogen incorporation into the octahedral sites and expansion of the ASS lattice. This induces ferromagnetism at room temperature due to the formation of expanded austenite, where the diverse grains exhibit different magnetic properties, with a resulting effective magnetic easy axis along an unusual direction. Moreover, nitriding results in a complete reversal of the elastic behavior anisotropy: while the non-nitrided 316L ASSshows the typical elastic anisotropy of fcc-type metals with a maximum of Ehkl for the <111> oriented grains, the maximum of Ehkl is observed for the <100> oriented grains in the expanded austenite. These observations are discussed on the basis of the expansion due to the nitrogen incorporation and associated lattice rotation and residual stress effects.

Keywords: plasma nitriding; nanoindentation; magnetism; austenitic stainless steel; elastic anisotropy

  • Lecture (Conference)
    12th International conference on Plasma Surface Engineering, 13.-17.09.2010, Garmisch-Partenkirchen, Germany

Publ.-Id: 15127

First measurements of inelastic scattering at nELBE

Beyer, R.; Birgersson, E.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Mosconi, M.; Nolte, R.; Schilling, K.-D.; Schwengner, R.; Wagner, A.

At the nELBE facility at Forschungszentrum Dresden-Rossendorf fast neutrons with kinetic energies of 0.1 to 10 MeV will be used to deliver nuclear data on neutron induced reactions.
First experiments on inelastic neutron scattering on 56Fe where performed using a double time-of-flight detector setup. This setup is based on proton recoil detectors and an array of 42 BaF2 crystals. The emitted photons and neutrons can be detectd in coincidence. First results will be presented.

Keywords: nELBE; inelastic scattering; iron; 56-Fe

  • Contribution to proceedings
    EFNUDAT Fast Neutrons - Scientific Workshop on Neutron Measurements, Theory and Applications, 28.-30.04.2009, Geel, Belgium
    Proceedings of the Scientific Workshop on Neutron Measurements, 978-92-79-11705-3, 27-31
  • Lecture (Conference)
    EFNUDAT Fast Neutrons - Scientific Workshop on Neutron Measurements, Theory and Applications, 29.04.2009, Geel, Belgium

Publ.-Id: 15126

Selbstorganisierte Oberflächenmuster auf Germanium durch schwere Clusterionen

Bischoff, L.; Heinig, K.-H.

Ionenstrahlinduzierte Oberflächenstrukturen von bisher nicht erreichter Qualität wurden Ende 2009 am FZD bei der routinemäßigen Untersuchung der Oberflächenerosion von Ge mit schweren Bi2+ und Bi3++ Ionen-Clustern entdeckt. Die neue Qualität betrifft die sehr gute Nahordnung und die große Amplitude der „Dot“-Muster, die deutlich über dem bisher Erreichten liegt (siehe Abb.). Das implantierte Bi ist in den Dots angereichert.
Auch ein qualitativer Sprung wird bei der Cluster-Ionenerosion beobachtet: Während bei senkrechter Fokussed-Ion-Beam-Bestrahlung mit Bi+-Ionen die Ge-Oberflächenschicht die bekannte Schwammstruktur erhält, finden wir mit Bi3++-Clustern bei gleicher Energie pro Bi-Atom (10 keV) selbstorganisierte (kristalline) „Dots“, deren Abstand untereinander weniger als 50nm beträgt und die 30-40nm hoch sind.
Die von uns entdeckte Selbststrukturierung basiert also auf einem Clustereffekt, nicht auf Einzel-Ioneneinschlägen. Das Kuramoto-Sivashinsky Modell ist daher nicht anwendbar, anders als für die reguläre Selbststrukturierung von Ge mit 3-4nm flachen Löchern durch Beschuss mit 5keV Ga-Ionen (Wei et al., Adv. Mat. 21 (2009) 2865).
Erste theoretische Analysen zeigen, dass die durch die Stoßkaskade deponierte Energiedichte einen Schwellwert überschreiten muss um den neuartige Selbststrukturierungsprozess auszulösen. Der Schwellwert koinzidiert mit der pro Atom benötigten Energie zum Schmelzen des Ge, d.h. jeder Bi-Clustereinschlag erzeugt einen Ge-Schmelzpool von einigen 100nm3. Unsere erste Modellvorstellung erklärt die Bi-Konzentrierung in „Punkte“ durch eine Bi-Ge-Entmischung der Oberflächenschicht mittels vielfacher Bi-Segregation in den erstarrenden Schmelzpools. Die topografische Aufwölbung in den „Punkten“ wird durch die ca. 5%ige Ge-Volumenänderung beim Schmelzen bewirkt. Die Bi-konzentrationsabhängigen Schmelztemperatur des Ge führt zu einem asymmetrischen Erstarren der Schmelzpools und wegen der Volumenänderung zu einem Ge-Massentransport in Richtung hoher Bi-Konzentration.

Keywords: FIB; cluster ions; surface pattern

  • Lecture (others)
    DFG Forschergruppe 845 Projektantragsrunde, 20.-21.05.2010, Leipzig, Germany

Publ.-Id: 15125

Focused ion beams

Bischoff, L.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance with the development of the ano-technology. For special purposes like writing ion implantation for doping or ion beam synthesis (IBS) in the µm- as well as in the nm-range without any lithographic steps ion species other than gallium become more and more relevant. Therefore mass separated FIB systems equipped with alloy liquid metal ion sources (LMIS) play an increasing role.
Modern FIB systems and related liquid metal ion sources are introduced in detail and the broad spectrum of applications, like processes for the fabrication of nanstructures, templating, 3D ion milling or the combination of FIB implantation and wet chemical anisotropic etching as well as sample preparation techniques will be presented and discussed.

Keywords: Focused ion beam; liquid metal ion source; nanostructures

  • Lecture (others)
    SPIRIT Tutorial “Ion Implantation and Irradiation", 13.-14.12.2010, Dresden, Germany

Publ.-Id: 15124

Buried superconducting films in Si containing Ga-rich precipitates

Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.

Recently a lot of research has been done in revealing the nature of intrinsic superconductivity in highly p-type doped silicon and germanium. However, the studies presented here, demonstrate the feasibility of embedding extrinsic superconducting nanolayers in commercial (100) silicon wafers due to Ga precipitation. With the ion implantation technique a high Ga fluence (2x1016 cm-2 or 4x1016 cm-2) is introduced in Si through a 30 nm SiO2 cover layer. This leads to amorphous layers containing Ga peak concentrations far beyond the equilibrium solid solubility limit. To initiate Ga precipitation and recrystallization rapid thermal annealing (RTA) is used. At optimized processing conditions (4x1016 cm-2, 600 - 700°C) the samples become superconducting. Critical temperatures of 7 K and in plane critical fields up to 14 T are reached [1]. A detailed investigation of the layer microstructure by means of RBS/C and TEM will be presented. These structural investigations reveal polycrystalline Si layers containing amorphous Ga-rich precipitates and that the superconductivity arises because of a high density of precipitates at the Si/SiO2 interface. As the ion implantation with subsequent annealing is compatible with standard microelectronic technology it could be possible to develop new superconducting devices, which operate above liquid He temperature.
[1] Skrotzki R. et al., Appl. Phys. Lett. 97 (2010) 192505

  • Poster
    E-MRS 2011 Spring Meeting Symp B, 09.-13.05.2011, Nice, France

Publ.-Id: 15123

Two-dimensional ultrasound Doppler velocimeter for flow mapping of unsteady liquid metal flows

Franke, S.; Lieske, H.; Fischer, A.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.

We present a novel ultrasound Doppler system for fluid flow engineering being able to determine two-dimensional, two-component velocity fields. Electromagnetically-driven liquid metal flows appear as an attractive application field for such a measuring system. Two linear ultrasound transducer arrays each equipped with 25 transducer elements are used to measure the flow field in a square plane of 67 x 67 mm². The application of advanced processing techniques like a simultaneous excitation of multiple transducer elements and a segmented array technique enable high data acquisition rates as well as a high spatial resolution, which have not been obtained so far for flow measurements in liquid metals. Essential operation principles such as the multiplexing electronic concept will be presented within this paper. The capabilities of the measuring system makes it suitable for investigations of nontransparent, turbulent flows. Here, we present measurements of liquid metal flows in a rotating magnetic field for demonstration purposes. The measuring setup realized here delivers details of the swirling fluid motion in a horizontal section of a cube. Frame acquisition rates up to 30 fps were achieved for a complete two-dimensional flow mapping.

Keywords: ultrasound Doppler velocimetry; flow field measurements; ultrasound flow mapping; liquid metal flows; rotating magnetic field

Publ.-Id: 15122

Actinides chemistry in mixed oxide nuclear fuel

Martin, P.; Belin, R.; Robisson, A. C.; Dumas, J.-C.; Scheinost, A. C.

Innovative Mixed OXide (MOX) (U,Pu)O2-x fuels for Sodium Fast neutron Reactors (SFR’s) systems are studied within the framework of GEN-IV nuclear reactor systems. SFRs will also be able to burn long-lived minor actinides (MA) such as Am, Np and Cm. Among MA, americium is of main concern. One solution currently considered is to homogeneously add americium in small amount to the fuel. Because it significantly affects sintering properties as well as irradiation performances, the oxygen to metal (O/M) ratio is an important factor to be considered when designing oxide fuels. Therefore, a thorough knowledge of the correlation between oxygen potential fixed during fuel sintering and O/M ratio is essential. The aim of this work is to follow the chemistry of uranium, plutonium and americium in (U0.750Pu0.246Am0.004)O2-x samples sintered for 4 h at 1700°C in various moisture-added Ar containing 5% of H2 atmospheres Thanks to XAS experiments performed at U, Pu and Am edges, the O/M ratio values were determined and are in very good agreement with those derived from XRD analysis. Furthermore, both XANES and EXAFS results show that O/M evolution in MOX samples is only supported by the reduction of plutonium. Thus, with this methodology, we are able to obtain O/M ratio without further thermal treatment as opposed to TGA. By using thermochemical modeling based on Lindemer and Besmann formalism [1], determination of thermodynamical conditions leading to these O/M values are estimated. Our results are compared to the study of Osaka et al. [2] highlighting a discrepancy between modeled and experimental oxygen potential vs. O/M ratio curve for Am-doped MOX system.

[1] T.B. Lindemer and T.M. Besmann, J. Nucl. Mat. 130, 489-504 (1985).
[2] M. Osaka et al., J. Alloys Comp. 428, 355-361 (2007).

Keywords: Nuclear fuel; Mixed Oxides; XAS

  • Contribution to proceedings
    Actinide XAS 2011, 02.-04.03.2011, Harima Science Garden City, Japan
    Workshop Proceedings
  • Contribution to proceedings
    E-MRS Spring Meeting, 09.-13.05.2011, Nice, France

Publ.-Id: 15120

Generic experiments at the sump model “Zittauer Strömungswanne” (ZSW) for the behaviour of mineral wool in the sump and the reactor core

Alt, S.; Hampel, R.; Kästner, W.; Kratzsch, A.; Renger, S.; Seeliger, A.; Zacharias, F.; Cartland-Glover, G.; Grahn, A.; Hoffmann, W.; Krepper, E.; Kryk, H.

The investigation of insulation debris transport, sedimentation, penetration into the reactor core and head loss build up becomes important to reactor safety research for PWR and BWR, when considering the long-term behaviour of emergency core cooling systems during loss of coolant accidents. Research projects are being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The projects include experimental investigations of different processes and phenomena of insulation debris in coolant flow and the development of CFD models. Generic complex experiments serve for building up a data base for the validation of models for single effects and their coupling in CFD codes. This paper includes the description of the experimental facility for complex generic experiments (ZSW), an overview about experimental boundary conditions and results for upstream and down-stream phenomena as well as for the long-time behaviour due to corrosive processes.

Keywords: reactor safety; fibres; coolant; LOCA; experiments

  • Kerntechnik 76(2011)1, 20-29

Publ.-Id: 15118

Aqueous coordination chemistry of excited state uranyl(VI)

Tsushima, S.

Photoexcitation of uranyl(VI) ion occurs via singlet-to-singlet transition. After rapid internal conversion and intersystem crossing, it converges to the lowest-lying triplet state which has relatively long lifetime of ~ μs. The relaxation process of excited state uranyl(VI) has been a subject of investigation by Ghosh et al. [1] using picosecond transient absorption spectroscopy. Time-resolved X-ray absorption spectroscopy is well-suited for such investigation, however, to the best of my knowledge there has been no such application to uranyl(VI) systems.
Here, excited state chemistry of uranyl(VI) has been explored by density functional theory calculations mainly focusing on the lowest-lying triplet states. The structures of the lowest-lying triplet states were found to predict photochemical reactivities of uranyl(VI) complexes, e.g. photochemical reduction [2], luminescence quenching [3], and photochemical decomposition [4]. The lowest-lying triplet state of uranyl(VI) ion in the presence of ethanol was found to have an asymmetric bond distances in its transdioxo O-U-O unit with the U-O distances of 1.791 and 1.962 Å, and the formal oxidation state of uranium was found to be U(V). These theoretical findings were experimentally confirmed by Ghosh et al. using transient absorption spectroscopy [1].
[1] R.Ghosh et al., J. Phys. Chem. A 114, 5263-5270 (2010).
[2] S.Tsushima, Inorg. Chem. 48, 4856-4862 (2009).
[3] S.Tsushima et al., Chem. Eur. J. 16, 8029-8033 (2010).
[4] S.Tsushima et al., Dalton Trans. 39, 10953-10958 (2010).

Keywords: DFT; triplet state; photochemistry

  • Lecture (Conference)
    Actinide XAS 2011 (6th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources and Other Quantum Beam Sources), 02.-04.03.2011, Harima Science Garden City, Hyogo, Japan

Publ.-Id: 15117

Preparation of domain walls in Co/Pt multilayer wires

Kimling, J.; Vogel, A.; Kobs, A.; Bocklage, L.; Wintz, S.; Strache, T.; Fassbender, J.; Im, M.-Y.; Fischer, P.; Merkt, U.; Oepen, H. P.; Meier, G.

Current-induced domain wall motion for systematic studies of spin momentum transfer requires the reliable preparation of domain walls. Since high current densities can change or destroy the structures investigated, weak pinning potentials allowing the controlled and reliable depinning of domain walls at low current densities are desirable. A prerequisite for the preparation of a domain wall at such pinning sites is, that the domain wall nucleates at fields smaller than the field required to depin the domain wall. We suggest methods to tune the nucleation field of lithographically patterned Co/Pt multilayer wires. An up to fourfold reduction of the nucleation field could be achieved through altering the lateral shape of the wires or by depositing iron stripes on top. Furthermore we explored the applicability of geometric constrictions and ion implantation for the creation of pinning sites. The magnetization reversal of the structures was imaged by transmission X-ray microscopy at the Advanced Light Source in Berkeley, CA, USA. The authors gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft via SFB 668 and GrK 1286 as well as by the DOE.

Keywords: magnetic nanowires; domain wall pinning; perpendicular magnetization

  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15116

Domain-wall motion in permalloy nanowires with magnetic soft spots

Vogel, A.; Wintz, S.; Gerhardt, T.; Bocklage, L.; Strache, T.; Im, M.-Y.; Fischer, P.; Fassbender, J.; McCord, J.; Meier, G.

The controlled motion of magnetic domain walls in nanowires is of scientific and technological relevance since it is necessary for new concepts of ultrafast, high-density, and nonvolatile data storage devices. Locally well-defined confining potentials, e.g., created by notches, act as pinning sites for individual domain walls. Magnetic configurations can be manipulated by external magnetic fields and by spin-polarized currents via transfer of spin-angular momentum.
The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites without geometric constrictions. Implantation of chromium ions into permalloy nanowires causes alloying and structural defects which leads to a reduction of the Curie temperature and the saturation magnetization Ms as well as small changes of the magnetocrystalline anisotropy.
The energy associated with the domain wall is locally reduced and a position at the so-called magnetic soft spot is energetically favorable in comparison to the environment, Field- driven pinning and depinning of a domain wall at the soft spots has been directly observed using magnetic transmission soft X-ray microscopy (MTXM) at beamline 6.1.2. of the Advanced Light Source in Berkeley, CA, USA. Magnetic contrast is provided via X-ray magnetic circular dichroism (XMCD) at the Ni L3-absorption edge. We have shown that the strength of the pinning potential and thus the depinning field can be tuned by the chromium ion fluence applied to induce the soft spots.

Keywords: Domain walls and domain structure; Intrinsic properties of magnetically ordered materials; Magnetic properties of nanostructures; Magnetization reversal mechanisms

  • Poster
    Intermag 2011 (IEEE International Magnetics Conference), 25.-29.04.2011, Taipeh, Taiwan
  • Poster
    19th international conference on magnetism (ICM 2012), 08.-13.07.2012, Busan, Korea

Publ.-Id: 15115

Interlayer Coupled Magnetic Vortices

Wintz, S.; Puzic, A.; Strache, T.; Bunce, C.; Körner, M.; Liedke, M. O.; Banholzer, A.; Buhl, M.; Bernert, K.; Moench, I.; Mattheis, R.; McCord, J.; Raabe, J.; Quitmann, C.; Erbe, A.; Fassbender, J.

Micromagnetic structures have been a focus of both fundamental and technological research for several decades. As a part of this effort, spin vortices (which are characterized by an in-plane magnetization curl and a small out-of-plane core region) have attracted much attention due to their chiral nature and the variety of dynamic phenomena associated with them. Although the static and dynamic properties of individual vortices are now reasonably well understood, there have been relatively few studies addressing their mutual interactions, particularly for the case of a vertically stacked arrangement. Here we present experimental findings on vortex coupling in trilayer elements, where two ferromagnetic layers are separated by a nonmagnetic spacer. For these systems the relative configurations of the in-plane flux senses (circulations) as well as the core orientations (polarities) of layered vortices have been identified by means of scanning transmission x-ray microscopy (STXM). The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling (IEC).

Keywords: magnetic vortex; vortex coupling; vortex dynamics; STXM; interlayer exchange coupling

  • Lecture (Conference)
    Intermag 2011 (IEEE International Magnetics Conference), 25.-29.04.2011, Taipeh, Taiwan

Publ.-Id: 15114

Combined 3D high-resolution PET and CT measurements with lattice Boltzmann simulations of fluid flow in heterogeneous material

Wolf, M.; Kulenkampff, J.; Enzmann, F.; Gründig, M.; Richter, M.; Lippmann-Pipke, J.

The joint research project „Dynamics of drowned and flooded salt mines and their overlaying rocks“ aimed at exemplarily and comprehensively clarifying causes, processes and effects of damages caused by abandoned historical potassium mining in Staßfurt, Germany [1]. Funded by the BMBF (Bundesministerium für Bildung und Forschung) ten universities, research facilities and companies were coordinated by the BGR (Bundesanstalt für Geowissenschaften und Rohstoffe). The IRC - Research Site Leipzig contributed small scale laboratory experiments of flow and transport process observations in drilling cores from hydrologic relevant regional lithologies and the matching of fluid flow patterns with high resolution CT imaging data and structure-controlled model simulations obtained and conducted by colleagues from JGUM [2]. This close collaboration aimed at enhancing the comprehension of small scale fluid flow in heterogeneous natural porous media.

Visualization of fluid flow in homogeneous porous as well as in fractured heterogeneous media was conducted with a preclinical PET scanner with a spatial resolution of 1 mm and a temporal resolution of 1 minute [3]. Drill cores from anhydrite, sandstone and rock salt formations of the Staßfurt salt dome were examined with continuous flow-through experiments. Pulses of radiotracer solutions ([18-F]KF and [124-I]KI) were injected and in situ PET-observations of the tracer propagation were conducted throughout the course of several hours and weeks, depending on the sample permeability. The flow behavior can be described with heterogeneous and process-dependent parameter distributions, like effective volume, permeability and dispersion rates. Based on µXCT measurements with a spatial resolution of 65.3 µm the percolating pore space, including all connected pores and fractures and the maximal inner surface, was quantified [2].

This “GeoPET” method is an excellent tool for direct quantitative spatiotemporal visualization of tracer transport in heterogeneous rocks on core scale [3, 4]. Combined interpretation of µXCT PET data enables deepened understanding on causes and effects of the structural constraints (pore space, cleavages etc.) and fluid flow patterns, enables to stereotype combined structural characteristics and flow path topologies and to determine the ratio between total and effective pore volume. The latter is for instance revealed by observable fingering phenomena in extended fractures. The fraction of the internal surface of a rock sample in contact with the mobile fluid – the effective reactive surface area – decreases with increasing localization of actual transport paths. Therefore, combined PET-CT data interpretation enables to realistically describe the considerably narrowed potential of dissolution and sorption reactions in heterogeneous and fractured media. In combination with simulated data the flow velocity patterns were quantified along the pathways, and they appeared highly variable within the fractures. In saline rocks we observed that localized high flow velocities may locally stimulate the salt dissolution and cause the widening of fracture cross sections. Such self energizing mechanisms may lead to increasing permeabilities, flow velocities and flow rates.

The complex flow patterns and the different resolutions of the data sets require scale independent comparison methods. We thus applied variography [4], which also could be applicable as simple method for upscaling to the field scale.

[1] Gerardi, J. (2006) Report BGR, p. 79.
[2] Enzmann, F. et al. (2010) EDGG, 244, p. 213-224.
[3] Kulenkampff, J. et al. (2008) Phys. Chem. Earth, 33, p. 937-942.
[4] Wolf, M. et al. (2010) EDGG, 244, p. 200-212.

  • Poster
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Wien, Österreich

Publ.-Id: 15113

Induction of DNA-double Strand Breaks via 90Y-DTPA-Cetuximab in Human Squamous Cell Carcinoma Cell Lines to establish EGFR directed Therapy for Tumour Inactivation

Saker, J.; Zenker, M.; Heldt, J.-M.; Baumann, M.; Steinbach, J.; Kasten-Pisula, U.; Dikomey, E.

Molecular targeting is a novel approach in radiotherapy with great potential to increase local tumour control. The epidermal growth factor receptor (EGFR) is a suitable target for such strategies, due to its overexpression in many solid tumours.
The aim of the project is an increased inactivation of tumour cells, including EGFR overexpressing metastases. Therefore the radioactive isotope 90Yttrium was bound to the EGFR directed antibody Cetuximab (C225). This allows a specific induction of DNA damage in EGFR overexpressing tumour cells with low side effects in normal tissue expressing low EGFR.
In this study double strand breaks (DSB) induced by 90YDTPA-Cetuximab were determined. Therefore γH2AX foci formation in human squamous cell carcinoma cells of head and neck differing in EGFR expression were detected after treatment with 90Y-DTPA-Cetuximab.

Summary & Conclusion:

  • The binding of Cetuximab to cells depends on their membranous EGFR expression level.
  • The chelator DTPA attached to the antibody Cetuximab reduces the affinity to EGFR about 30% compared to native Cetuximab. This effect can be avoided by using saturating concentrations of antibody.
  • 90Y-DTPA-Cetuximab induces DNA double strand breaks in human squamous cell carcinoma cell lines.
  • The dose applied by 90Y-DTPA-Cetuximab, and thereby the amount of DNA double strand breaks induced, depends on the time of treatment and seems to be related to the membranous EGFR expression.
  • The repair of DNA double strand breaks in human squamous cell carcinoma cell lines shows comparable kinetics after treatment with 90Y-DTPA-Cetuximab and irradiation with X-ray.
__> 90Y-DTPA-Cetuximab can be used to generate DNA-double strand breaks in human cell lines expressing high EGFR. The data shows that this EGFR directed targeting strategy using a radioactive labelled antibody has the potential to increase tumour control. Experiments in tumour model systems (respective xenografts) to investigate the therapeutic benefit (with and without external radiation) and possible side effects are currently done by our cooperation partners.
This project is supported by BMBF (02 NUK 006 C) & DFG (PAK-190)
  • Poster
    13. Jahrestagung der Gesellschaft für Biologische Strahlenforschung, 01.-02.09.2010, Hamburg, D

Publ.-Id: 15112

Magnetic properties of mixed property magnetic thin films prepared by selective ion irradiation

McCord, J.; Hamann, C.; Strache, T.; Mönch, I.; Fassbender, J.

The control of the magnetic properties like magnetic anisotropy, saturation magnetization, and especially the dynamic magnetic properties in ferromagnetic thin films are of significant importance for spintronics applications. For instance, the magnetic anisotropy, e.g. uniaxial anisotropy or unidirectional anisotropy, in ferromagnetic single or multi-layers is initialized by applying a magnetic field during film deposition or by a magnetic field anneal.
Here, we give an overview on novel ways of tailoring ferromagnetic thin film properties by ion irradiation. In addition, additional tuning is obtained by patterning the magnetic films in terms of laterally varying magnetic properties [1]. Results from different samples patterned in terms of anisotropy [1, 2, 3], exchange bias [1, 4], and saturation magnetization [5] are presented. The main emphasis of the investigations is on the role of magnetic domain formation and domain wall effects in stripe-like magnetic hybrid structures on the overall static and especially dynamic magnetic properties [6, 7].
The presented paths of ferromagnetic film preparation provide an additional degree of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films

  • Invited lecture (Conferences)
    INTERNATIONAL CONFERENCE on Ion-Beam Induced Nanopatterning of Materials - IINM-2011, 06.-10.02.2011, Bhubaneswar, India

Publ.-Id: 15111

Study of dipole strength distributions at the ELBE accelerator

Schwengner, R.

Dipole strength functions up to the neutron-separation energies S_n of the N=50 isotones 88Sr , 89Y, 90Zr, the even-mass Mo isotopes from 92Mo to 100Mo, the N=82 nuclide 139La and the doubly magic 208Pb have been studied in photon-scattering
experiments using the bremsstrahlung facility [8] at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. To estimate the distribution of inelastic transitions from high-lying levels at high level density to low-lying levels, simulations of $\gamma$-ray cascades were performed. On the basis of these simulations, intensities of inelastic transitions were subtracted from the experimental intensity distributions that include the resolved peaks as well as a quasicontinuum formed by unresolved transitions, and the intensities of elastic transitions to the ground state were corrected for their branching ratios.
The photoabsorption cross sections obtained in this novel way are combined with (gamma,n) and (gamma,p) data and give detailed information about the dipole strength functions in the energy range from about 4 MeV up to the
giant dipole resonance (GDR). In all nuclides enhanced strength compared to Lorentzian-like approximations of the tail of the GDR is found in the energy range from about 5 MeV up to about the respective particle thresholds.
Calculations in the framework of the quasiparticle-random-phase approximation (QRPA) underestimate the dipole strength at low energy and show strong fluctuations in the whole energy range up to the giant dipole resonance (GDR). A new approach is presented that calculates the dipole strength for nuclei with shape fluctuations by combining the interacting boson approximation (IBA) with
QRPA. Based on the slow shape dynamics and the fast dipole vibrations an Instantaneous Shape Sampling (ISS) is performed that describes the photoabsorption at a fixed shape with QRPA with probabilities given by IBA.
The ISS-QRPA improves the description of the experimental photoabsorption cross sections but still requires additional smearing. Predictions of ISS-QRPA for isotopic chains with changing nuclear deformation are presented.
Shell-model calculations including (2p-2h) excitations performed for the case of 208Pb show that the higher-order excitations are the main mechanism for the fragmentation of the strength and hence for the spreading of the GDR.

Keywords: ELBE accelerator; bremsstrahlung; photon scattering; photodissociation; photoactivation; dipole strength; absorption cross section; RPA

  • Invited lecture (Conferences)
    Workshop "N-N interaction and the Nuclear Many-Body Problem", 18.-27.11.2010, Mumbai, India

Publ.-Id: 15110

Bruchmechanische Untersuchungen an bestrahltem Reaktordruckbehälterstahl der stillgelegten Reaktoren des KKW Greifswald

Houska, M.; Viehrig, H.-W.

The paper presents initial results of the post mortem investigations performed on the reactor pres-sure vessels (RPV) of 1st generation WWER-440/V-230 reactors. Trepans were taken from the beltline weld and the base metal of the units 1, 2 and 4 RPVs, which represent different material conditions (irradiated, annealed and re-irradiated. From the trepans were manufactured standard SE(B) and Charpy V-notch specimens and investigated by Master Curve (MC) and Charpy V-notch testing. Specimens from defined locations through the thickness of the welding seam and the base metal ring were tested. The reference temperature T0 was calculated using the measured fracture toughness values KJc at brittle failure of the specimen. In addition Charpy V-notch specimens were tested in order to determine the Charpy-V ductile-to brittle transition temperatures.

Keywords: Nuclear Safety; reactor pressure vessel; fracture mechanics; neutron embrittlement; Master Curve

  • Contribution to proceedings
    43. Tagung des DVM Arbeitskreises Bruchvorgänge, 22.-23.02.2011, Rostock, Deutschland
    Tagungsband der 43. Tagung des DVM Arbeitskreises Bruchvorgänge, Berlin: Deutscher Verband für Materialforschung und -prüfu
  • Lecture (Conference)
    43. Tagung des DVM Arbeitskreises Bruchvorgänge, 22.-23.02.2011, Rostock, Deutschland

Publ.-Id: 15109

Aspects of magnetic heterostructures - statics, dynamics, and magnetic domains

McCord, J.

  • without abstract -
  • Invited lecture (Conferences)
    Seminar des Sonderforschorschungsbereichs SFB 668, 01.02.2011, Hamburg, Deutschland

Publ.-Id: 15108

On the role of the lateral lift force in poly-dispersed bubbly flows

Lucas, D.; Tomiyama, A.

An extensive experimental database comprising air-water as well as steam-water upwards vertical pipe flows for a pressure up to 6.5 MPa was used to investigate the effect of the lateral lift force on turbulent poly-dispersed flows with medium or high gas volume fraction. It was clearly shown that the lift force plays an important role also in such flows. Dynamic effects such as bubble coalescence and breakup as well as fast rising large bubbles which push small bubbles towards the pipe wall superpose the effect of the lift force but can be separated from this effect. The predictions of the correlation by Tomiyama et al. (2002) on the critical bubbles size at which the lift force changes its sign are obviously also valid for turbulent air-water and steam-water flows with medium and high void fraction and a broad spectrum of bubbles sizes. The values for this critical bubble diameter are confirmed by the experimental data within the frame of the uncertainty of the data. Consequences of the action of the lateral lift force on flow structures in different flow situations are discussed. From the investigations can be concluded that the lift force including the bubble size dependent change of its sign should be considered in a proper numerical 2D or 3D-simulation on flows in which bubbles in the range of several millimeters are present.

Keywords: lift force; bubble; poly-dispersed flow; CFD

Publ.-Id: 15106

Slow-mode gas/liquid-induced periodic hydrodynamics in trickling packed beds derived from direct measurement of cross-sectional distributed local capacitances

Schubert, M.; Kryk, H.; Hampel, U.

Hydrodynamics of a periodically operated trickling packed bed was studied with a high-speed wire-mesh sensor technique based on direct measurement of cross-sectional distributed local capacitances Liquid cycles in the alumina packing were generated by periodic induction of gas and/or liquid phase in distinctive slow-mode Hydrodynamics were characterized with respect to liquid saturation and liquid saturation distribution varying period length split and time-averaged superficial gas and liquid velocities The sensors technique allows direct access to local phenomena during liquid pulse breakthrough to distribution patterns and their reproducibility at different cycle positions that were studied based on transient liquid saturation distribution data of different periodicity variables Due to simultaneous measurement at four different axial reactor positions pulse attenuation along the reactor and pulse velocity could be analyzed Furthermore hydrodynamics of different modes of gas-induced periodic cycling e. g. gas cycling only asynchronous and synchronous cycling of gas and liquid flow rate and alternating gas-liquid cycling were studied.

Publ.-Id: 15105

Erosion patterns in the Nepal Himalayas from river gauging, cosmogenic nuclides and precipitation data

Andermann, C.; Gloaguen, R.; Bonnet, S.; Crave, A.; Merchel, S.

The distribution of erosion in the Himalayas is mainly controlled by the spatial distribution of relief and possibly precipitation intensity. However, both parameters might depend on each other. Today we do not have a good understanding of the effects of this controlling parameters on erosion in complex topographic settings and active mountain belts such as the Himalayas. The conjunction of independent erosion proxies can help to understand recent (today-104 years) erosion distribution and its eventual dependency on topography, precipitation and uplift.

For our analysis we have validated the precipitation dataset APHRO_MA_V1003R1 (Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of Water Resources, Monsoon Asia, Version 10, hereafter referred to as APHRO), which is interpolated from rain gauging stations. It was evaluated to be the best dataset of precipitation estimates at the scale of the Himalayas. APHRO data, with a daily temporal resolution and 0.25° spatial resolution, is available since 1951.

Here, we present a compiled analysis of spatio-temporal erosion evaluation from suspended river discharge fluxes, its relation with precipitation and rainfall induced landsliding. The analysis is based on data from 14 hydrological stations in Nepal, which cover nearly all major rivers, spanning a rainfall gradient from East to West along the Himalayan front. The annual hydrograph of the Himalayan rivers is controlled by the South Asian summer monsoon. The average increase of discharge during monsoon is one to two orders of magnitude with respect to winter base-flow. Considerable suspended concentrations (102–103 mg/l) are observable during monsoon season. Short lasting events, however, can catapult concentrations for few short periods above 103 mg/l. In general, few above 95 % quantile events account for more than the half of all suspended material transported in one year. These above threshold events are generated by precipitation driven landslides. A direct linkage between annual suspended fluxes and precipitation intensity distribution is also observed. Denudation rates calculated from suspended sediment fluxes are in the range of 2.1 to 5.6x3 t km-2 a-1.

We will present cosmogenic erosion rates, deduced from 10Be analyses from quartz, for several small and associated large catchments across the Himalayan range. Sample locations for large river basins correspond with the hydrological station location mentioned above. Our cosmogenic erosion rates are in the same range as the ones derived from suspended sediment fluxes, 1-4 mm/a. In general, erosion rates are higher within the Himalayan range close to the Himalayan ride crest.

The combination of these methods gives a good overview on the erosion processes and its distribution across the Himalayan mountain belt. Mass wasting is indeed the dominant process driving erosion and shaping topography. Furthermore, the source and transport pathways can be determined, which is a first step to understand the linkage between topography and precipitation distribution on a large scale.

Acknowledgments: Beryllium-10 measurements by accelerator mass spectrometry at the French CEREGE-ASTER-LN2C is highly appreciated.

Keywords: accelerator mass spectrometry

  • Poster
    European Geosciences Union (EGU) General Assembly 2011, 03.-08.04.2011, Wien, Austria

Publ.-Id: 15104

Physics Concepts for Simulation - Prediction of Signals for in-beam PET and SPECT during Proton and Ion Therapy

Priegnitz, M.; Müller, A.; Fiedler, F.

Overview of the physical basics of in-beam PET and SPECT during proton and ion therapy. Current investigations of signal prediction and preliminary results are presented.

  • Poster
    OncoRay Retreat Meeting 2011, 12.-13.01.2011, Riesa, Deutschland

Publ.-Id: 15102

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