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32227 Publications
Mehrfunktionelle Bispidinderivate für die duale Bildgebung
Fähnemann, S.; Walther, M.; Stephan, H.; Steinbach, J.;
Die Multimodale Bildgebung („Molecular Imaging“) ermöglicht durch die Kombination unterschiedlicher Verfahren eine verbesserte Diagnostik und ist damit Grundlage für eine zielgerichtete personalisierte Therapie von komplexen Krankheiten, wie z.B. Krebs. In diesem Zusammenhang werden insbesondere Computertomographie (CT), Magnetresonanztomographie (MRT), Positronen-Emissions-Tomographie (PET), Single- Photon-Emission-Computed-Tomography (SPECT) und optische Bildgebung eingesetzt [1, 2].
Derivate von 3,7-Diaazabicyclo[3.3.1]nonanen (Bispidine) bieten die Möglichkeit für ein duales Labeling. Sie bilden sehr stabile Komplexe mit radioaktiven Kupferisotopen und gestatten nach entsprechender Funktionalisierung mit Vektormolekülen eine Visualisierung von Tumoren mittels PET [3]. Bispidinliganden verfügen darüber hinaus über weitere funktionelle Gruppen, die die Einführung von Farbstoffen und zielsuchenden Molekülen gestatten.

Die Funktionalisierung der Hydroxygruppe (C9-OH) des Bispidins mit einem Fluoreszenzfarbstoff kann mittels Aktivesterbildung durch Umsetzung mit Chlorameisensäurenitrophenylester und anschießender Urethanbildung mit einem aminofunktionalisierten Farbstoffmolekül realisiert werden.
Es wird über die Synthese derartiger Liganden sowie die Charakterisierung der Fluoreszenzeigenschaften und die Markierung mit dem PET-Radionuklid 64 Cu berichtet.

Literatur:

[1] J.V. Frangioni, J. Clin. Oncol. 2008, 26, 4012-4021.
[2] A. Louie, Chem. Rev. 2010, 110, 3146-3195.
[3] S. Juran, M. Walther, H. Stephan, R. Bergmann, J. Steinbach, W. Kraus, F. Emmerling, P. Comba, Bioconjugate Chem. 2009, 20, 347-359.
  • Poster
    GDCH-Wissenschaftsforum 2011, 04.-07.09.2011, Bremen, D

Publ.-Id: 15962 - Permalink


Multiple Spectroscopic and Microscopic Study on Hydrolysis of Tetravalent Cerium: In-situ Characterization of Ce(IV) Hydrolytic Species in an Aqueous Solution
Ikeda, A.;
Because of its chemical similarity and stable tetravalent oxidation state in solution, cerium (Ce) is often employed as an analogue of tetravalent actinides (An(IV)) in various research fields related with actinides. Besides, its dioxide compound, CeIVO2, has recently attracted considerable attention owing to its wide variety of industrial applications, such as catalysis, oxygen storage, fuel cells, or luminescent materials.
Hydrolysis is one of the most fundamental reactions of metal ions in an aqueous solution. In fact, the hydrolysis behaviour of tetravalent cerium (Ce(IV)) has been studied and often compared with those of An(IV) in order to evaluate its suitability as an analogue of An(IV). Furthermore, the hydrolysis–precipitation process of cerium ions is also of great importance in its industrial applications, since it is one of the most straightforward and simple methods to produce CeO2. However, despite these importance of hydrolysis reaction in the basic- and applied research fields for Ce, most of the precedent studies have focused on its thermodynamical aspects, and still little has been known about the complex structure of Ce(IV) hydrolytic species formed in solution. In this study, multi-spectroscopic (i.e., X-ray absorption spectroscopy (XAS), high energy X-ray scattering (HEXS), dynamic light scattering (DLS)) and microscopic (TEM) techniques have been employed to structurally characterize the hydrolytic Ce(IV) species in an aqueous solution. The results indicate that nanocrystalline CeO2 forms and grows up in an aqueous solution as the hydrolysis proceeds with increasing pH. On the presentation, the results will be also discussed with the corresponding An(IV) hydrolytic species.
Keywords: lanthanides, cerium, Ce(IV), hydrolysis, XAS, HEXS, DLS, TEM
  • Invited lecture (Conferences)
    Lecture (invited), 27.09.2011, Strasbourg, France

Publ.-Id: 15961 - Permalink


Immobilization of uranium in biofilm microorganisms exposed to groundwater seeps over granitic rock tunnel walls in Olkiluoto, Finland
Krawczyk-Bärsch, E.; Lünsdorf, H.; Arnold, T.; Bok, F.; Steudtner, R.; Pedersen, K.; Lehtinen, A.; Brendler, V.;
In the underground rock characterization facility tunnel "ONKALO" in Finland massive biofilms were observed attached to the fractured bedrock at a depth of 70 m. Experiments were performed in the laboratory to study the effect on the behavior of uranium in biofilms by adding uranium to the fracture water with a final uranium concentration (4 x10-5 M) relevant for what can be expected from an injured and leaking waste canister in the far-field during a nuclear event in a HLW repository. The results obtained by analysis, microsensor measurements, TRLFS investigation, EF-TEM/EELS studies and thermodynamic calculations clearly indicate that biofilms have to be considered as microenvironments, which differ significantly from the surrounding medium. Inside the biofilm a pH of 5.37 was recorded, which is about 3.5 units lower than the pH of the surrounding fracture water. Similarly, the redox potential of +73 mV is approximately 420 mV lower than the redox potential measured in the fracture water. The addition of uranium results in an increase of the pH in the biofilm to 7.27 and a decrease of the redox potential to -164 mV mV. The changes of redox potential and pH are influencing the bioavailability of uranium since microbial metabolic processes are sensitive to metals and their speciation. EF-TEM investigations showed that in the biofilm uranium was immobilized intracellular in bacteria by a biologically mediated uranyl phosphate formation similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). In contrast, TRLFS studies of the contaminated fracture water showed aqueous uranium carbonate species, most likely Ca2UO2(CO3)3, which was formed using the available high amount of carbonate from the water. The results are in agreement with the thermodynamic calculation of the theoretical predominance field of uranium species, formed in the uranium contaminated fracture water at the measured geochemical parameters.
Our studies clearly demonstrate that biological systems have to be considered as a part of natural systems in respect to radionuclide immobilization. They are contributing to an improved understanding on the response mechanisms of biofilms towards radionuclides in respect to safety assessments of the radioactive waste repositories.
Keywords: uranium, biofilms, microsensors, TEM, TRLFS, thermodynamic calculation

Publ.-Id: 15960 - Permalink


Electrochemical behaviour of tetrachloro and tetrabromo uranyl complexes in room temperature ionic liquids
Sornein, M.-O.; Cannes, C.; Le Naour, C.; Mendes, M.; Hennig, C.;
The redox properties of tetrahalo uranyl(VI) complexes ([UVIO2X4]2 with X = Cl or Br) have been investigated in the ionic liquids [BuMeIm][Tf2N] and [MeBu3N][Tf2N], where [BuMeIm]+ and [MeBu3N]+ are respectively the 1-butyl-3-methylimidazolium and the tributylmethylammonium cations, both associated with the bis(trifluoromethylsulfonyl)imide anion [Tf2N]. The results suggest that the reduction of [UVIO2X4]2 occurs via an Electron transfer – Chemical reaction – Electron transfer mechanism (ECE mechanism). We have shown by voltammetry that the first electron transfer is quasi-reversible and involves one electron, leading to the tetrahalo uranium(V) complex. This compound undergoes a chemical reaction and its stability depends both on the halide ligand and on the ionic liquid. The most stable complex is [UVO2Cl4]3 in [BuMeIm][Tf2N]. We have assumed that the [BuMeIm]+ cation interacts more strongly by H-bonding than the [MeBu3N]+ cation with the uranium complex, as it is the case for other anionic uranium species. Moreover, in presence of excess chloride ions, the consecutive chemical reaction is not observed anymore by cyclic voltammetry.
Keywords: Uranium, Ionic liquid, Redox properties, Tetrachloro complex, Tetrabromo complex

Publ.-Id: 15959 - Permalink


Uptake and binding of U(VI) by the green alga Chlorella vulgaris
Vogel, M.; Günther, A.; Raff, J.; Bernhard, G.;
For the risk assessment of radionuclides in the environment a comprehensive elucidation of the migration behavior of U(VI) in biosphere is necessary. Aim of this study was the quantitative and structural characterization of the interaction between U(VI) and the green alga Chlorella vulgaris at U(VI) concentrations from 5 μM to 1 mM, and in the pH range of 4.4 to 7.0 with special focus on metabolic activity. The obtained findings of the sorption experiments demonstrate clearly, the interactions with U(VI) are heavily influenced by the U(VI) concentration and the status of the Chlorella cells. Living cells bind in a 0.1 mM U(VI) solution at pH 4.4 within 5 min 14.3±5.5 mg U/g dry biomass and dead cells 28.3±0.6 mg U/g dry biomass. Furthermore, Chlorella cells die at concentration higher than 0.1 mM within 48 h. Interestingly, at lower U(VI) concentration of 5 μM, living cells firstly bind almost all U(VI) within the first 5 min of incubation. But then algal cells mobilize up to 80% of the bound U(VI) during ongoing incubation. The release of metabolism related substances is suggested to cause this mobilization of U(VI). As potential leachates for algal-bound U(VI) oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound U(VI).
The formed U(VI)-algae-complexes were structurally characterized by TRLF, EXAFS and ATR-FTIR spectroscopy. Obtained results demonstrate carboxylic and organic/inorganic phosphate groups were involved in the U(VI) complexation with varying contributions dependent on cell status, U(VI) concentration and pH.
With the help of TEM U(VI) was detected in form of 30-70 nm needle-like deposits in the cell wall of living algae.
Keywords: uranium, algae, Chlorella, biosorption, TRLFS, EXAFS, ATR-FTIR, TEM
  • Lecture (Conference)
    10th symposium on remediation/ 10. Sanierungskolloquium, 03.-05.10.2011, Jena, Deutschland

Publ.-Id: 15958 - Permalink


Long term irradiation phenomena in RPV steels - the LONGLIFE project
Altstadt, E.; Bergner, F.; Hein, H.;
The increasing age of European Nuclear Power Plants and envisaged extensions of reactor pressure vessel (RPV) lifetimes up to 80 years require the accurate prediction and management of RPV neutron irradiation embrittlement. LONGLIFE (“Treatment of long term irradiation embrittlement effects in RPV safety assessment”) is a collaborative project of the 7th Framework Programme of EURATOM. This project has been initiated as the next step forward towards obtaining an improved understanding of irradiation effects in RPV steels under conditions representative of long term operation (LTO) of RPVs. Phenomena which might become important at high neutron fluences (such as late-blooming effects and flux effects) must be considered in detail as part of the process of upgrading safety assessments and embrittlement surveillance procedures to underwrite the safety of LTO of RPVs. The work starts with the collection and evaluation of plant-specific information and data such as target neutron fluences for LTO and the chemical compositions of the materials. This includes a survey of available results of RPV materials data from decommissioned plants of validating surveillance data and studying specific irradiation effects relevant for LTO. Microstructural data are obtained from different techniques with the aim of assessing the adequacy of current dose-damage models with respect to their relevance to the mechanisms of irradiation damage associated with LTO of RPVs. Complementary mechanical tests are performed in order to address gaps in existing experimental data. Microstructural data pertaining to the evolution of irradiation damage are correlated with changes in mechanical properties, and the most important influencing factors will be identified. Surveillance guidelines for LTO of RPV base materials and welds will be developed as one of the principal outputs of the project. The scope of work and the project structure are outlined in the paper. Two LTO relevant phenomena – late blooming effect and flux effect – are discussed more detailed.
Keywords: Reactor Pressure Vessel Steel, Irradiation Embrittlement, Long Term Operation
  • Book chapter
    T. Yamamoto: Effects of Radiation on Nuclear Materials: 25th Volume, STP 1547, USA: ASTM International, 2013, 978-0-8031-7533-4, 096205STP
    DOI: 10.1520/STP104113

Publ.-Id: 15957 - Permalink


Single-ion induced surface nanostructures - A comparison between slow highly-charged and swift heavy ions
Aumayr, F.; Facsko, S.; El-Said, A. S.; Trautmann, C.; Schleberger, M.;
The present topical review focuses on recent advances in the understanding of the formation of surface nanostructures, an intriguing phenomenon in ion - surface interaction due to the impact of individual ions. In many solid targets, swift heavy ions produce narrow cylindrical tracks accompanied by the formation of a surface nanostructure. More recently, a similar nanometric surface effect has been revealed for the impact of individual, very slow but highlycharged ions. While swift ions transfer their large kinetic energy to the target via ionization and electronic excitation processes (electronic stopping), slow highly-charged ions produce surface structures due to potential energy deposited at the top surface layers. Despite the differences in primary excitation, the similarity between the nanostructures is striking and strongly points to a common mechanism related to the energy transfer from the electronic to the lattice system of the target. A comparison of surface structures induced by swift heavy ions and slow highly-charged ions provides valuable insight to better understand the formation mechanisms.
Keywords: highly-charged ions, swift heavy ions, ion-surface interaction, nanostructures, AFM, STM, hillocks, craters, pits, tracks, kinetic energy, potential energy, sputtering, electron emission, KBr, LiF, CaF2, BaF2, SrTiO3, TiO2, mica, polymers, PMMA, HOPG, Si, Au

Publ.-Id: 15956 - Permalink


Design of Radioligands for PET Imaging of Neuropsychiatric and Neurodegenerative Diseases
Brust, P.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    Kolloquium, 03.11.2011, Magdeburg, Deutschland

Publ.-Id: 15955 - Permalink


Numerical study of a bubble plume generated by bubble entrainment from an impinging jet
Zidouni Kendil, F.; Krepper, E.; Bousbia Salah, A.; Lucas, D.; Mataoui, A.;
The current paper presents the prediction results of a bubbly flow under plunging jet conditions using multiphase mono- and poly-dispersed approaches. The models consider interfacial momentum transfer terms arising from drag, lift, and turbulent dispersion force for the different bubble sizes. The turbulence is modeled by an extended k–ε model which accounts for bubble induced turbulence. Furthermore in case of a poly-dispersed air–water flow the bubble size distribution, bubble break-up and coalescence processes as well as different gas velocities in dependency on the bubble diameter are taken into account using the Inhomogeneous MUSIG model. This model is a generalized inhomogeneous multiple size group model based on the Eulerian modeling framework which was developed in the framework of a cooperative work between ANSYS-CFX and Forschungszentrum Dresden-Rossendorf (FZD). The latter is now implemented into the CFD code CFX.
According to the correlation on the lateral lift force obtained by Tomiyama (1998); this force changes its sign in dependence on the bubble size. Consequently the entrained small bubbles are trapped below the jet. They can escape from the bubble plume only by turbulent fluctuations or by coalescence. If the size of the bubbles generated by coalescence exceeds the size at which the lift force changes its sign these large bubbles go out from the plume and rise to the surface.
A turbulent model based on an additional source term for turbulence kinetic energy and turbulence eddy dissipation equation is compared to the common concept for modeling the turbulence quantities proposed by Sato et al. (1981). It has been found that the large bubble distribution is slightly affected by the turbulence modeling which affects particularly the bubble coalescence and break-up process.
Keywords: impinging jet, CFD, experiments, simulations, lift bubble force, population balance model

Publ.-Id: 15954 - Permalink


Structural, Electronic, and Magnetic Properties of Quasi-1D Quantum Magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6-, SbF6-) Exhibiting Ni-FHF-Ni and Ni-pyz-Ni Spin Interactions
Manson, J. L.; Lapidus, S. H.; Stephens, P. W.; Peterson, P. K.; Carreiro, K. E.; Southerland, H. I.; Lancaster, T.; Blundell, S. J.; Steele, A. J.; Goddard, P. A.; Pratt, F. L.; Singleton, J.; Kohama, Y.; Mcdonald, R. D.; Del Sesto, R. E.; Smith, N. A.; Bendix, J.; Zvyagin, S. A.; Kang, J. H.; Lee, C.; Whangbo, M. H.; Zapf, V. S.; Plonczak, A.;
[Ni(HF2)(pyz)2]X {pyz = pyrazine; X = PF6- (1), SbF6- (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN4F2 octahedra. At 298 K, 1 is monoclinic (C2/c) with unit cell parameters, a = 9.9481(3), b = 9.9421(3), c = 12.5953(4) angstrom, and beta = 81.610(3) degrees while 2 is tetragonal (P4/nmm) with a = b = 9.9359(3) and c = 6.4471(2) angstrom and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the c-axis which are linked via mu-pyz bridges in the ab-plane to afford three-dimensional polymeric frameworks with PF6- and SbF6- counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni-F-H bonds are bent (similar to 157 degrees) in 1 but are linear in 2. Ligand field calculations (LFT) based on an angular overlap model (AOM), with comparison to the electronic absorption spectra, indicate greater pi-donation of the HF2- ligand in 1 owing to the bent Ni-F-H bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and lambda-like peaks in d chi T/dT at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (TN). Muon-spin relaxation and specific heat studies confirm these TN's. A comparative analysis of chi vs T to various 1D Heisenberg/Ising models suggests moderate antiferromagnetic interactions, with the primary interaction strength determined to be 3.05/3.42 K (1) and 5.65/6.37 K (2). However, high critical fields of 19 and 37.4 T obtained from low temperature pulsed-field magnetization data indicate that a single exchange constant (J(1D)) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (J(perpendicular)), as mediated by Ni-pyz-Ni, and single-ion anisotropy (D), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of J(perpendicular) and D based solely on powder data, further support offered by related Ni(II)-pyz compounds and our LFT and density-functional theory (DFT) results lead us to a consistent quasi-1D magnetic description for 1 and 2.
  • Inorganic Chemistry 50(2011), 5990-6009

Publ.-Id: 15953 - Permalink


Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4
Tsirlin, A.; Nath, R.; Sichelschmidt, J.; Skourski, Y.; Geibel, C.; Rosner, H.;
We report on the crystal structure and magnetic behavior of the spin-1/2 compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and electron spin resonance measurements identify AgVOAsO4 as a gapped quantum magnet with a spin gap Delta similar or equal to 13 K and a saturation field mu0Hs similar or equal to 48.5 T. Extensive band structure calculations establish the microscopic magnetic model of spin chains with alternating exchange couplings J similar or equal to 40 K and J' similar or equal to 26 K. However, the precise evaluation of the spin gap emphasizes the role of interchain couplings which are frustrated due to the peculiar crystal structure of the compound. The unusual spin model and the low energy scale of the exchange couplings make AgVOAsO4 a promising candidate for an experimental investigation of Bose-Einstein condensation in high magnetic fields.
  • Physical Review B 83(2011)14, 144412

Publ.-Id: 15952 - Permalink


Control of Rectifying and Resistive Switching Behavior in BiFeO3 Thin Films
Shuai, Y.; Zhou, S.; Wu, C.; Zhang, W.; Bürger, D.; Slesazeck, S.; Mikolajick, T.; Helm, M.; Schmidt, H.;
BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed laser deposition using Au as the top electrode. The resistive switching property of the Au/BiFeO3/Pt stack has been significantly improved by carefully tuning the oxygen pressure during the growth, and a large switching ratio of ∼4500 has been achieved. The deposition pressure modifies the concentration of oxygen vacancies and the rectifying behavior of the Au/BiFeO3 junction, and consequently influences the resistive switching behavior of the whole stack. The switching takes place homogeneously over the entire electrode, and shows a long-term retention.
Keywords: resistive switching, BiFeO3, nonvolatile

Publ.-Id: 15951 - Permalink


Coherent control of a THz intersubband polarization in a voltage controlled single quantum well
Wagner, M.; Helm, M.; Sherwin, M. S.; Stehr, D.;
Ultrashort terahertz pulses in the far-infrared spectral region centered around 2 terahertz are used to coherently control an intersubband polarization in a GaAs/AlGaAs quantum well structure at low temperature. While the first pulse excites a macroscopic polarization, a second, temporally delayed pulse switches the polarization off or refreshes it depending on the relative time delay. The switching is directly demonstrated in the time-domain for the few picosecond long free-induction decay of the induced polarization. Additionally, the absorption line is found to be purely homogeneously broadened. Model calculations based on the optical Bloch equations agree well with the experimental data.
Keywords: coherent control, terahertz, intersubband polarization, ultrafast
  • Applied Physics Letters 99(2011), 131109

Publ.-Id: 15950 - Permalink


Metal Nanoparticles/Nanowires Selfassembly on Ripple Patterned Substrate - Mechanism, Properties and Applications
Ranjan, M.;
Plasmonic properties of self-assembled silver nanoparticles/nanowires array on periodically patterned Si (100) substrate are reported with special attention on the mechanism of nanoparticles self-assembly. The advantage of this bottom up approach over other self-assembling and lithographic methods is the flexibility to tune array periodicity down to 20 nm with interparticle gaps as low as 5 nm along the ripple.
Ripple pattern have shallow modulation (~2 nm) still particles self-assembly was observed in non-shadow deposition. Therefore adatoms diffusion and kinetics is important on ripple surface for the self-assembly. PVD e-beam evaporation method used for deposition has proven to be superior to sputter deposition due to lower incident flux and lower atom energy. It was found that particles self-assembly largely dependent on angle of incidence, substrate temperature, and deposition direction due to ripple asymmetric tilt. Ostwald ripening observed during annealing on ripples substrate has striking dependency on ripple periodicity and was found to be different compared to Ostwald ripening on flat Si surface.
In-situ RBS measurements of deposited silver on flat and rippled substrate confirmed different sticking of atoms on the two surfaces. The difference between maximum and minimum of the calculated local flux show a peak at an incidence angle of 70o with respect to surface normal. This explains the best alignment of particles at this angle of incidence compare to others.
Self-assembled nanoparticles are optically anisotropic, i.e. they exhibit a direction dependent shift in LSPR. The reason of the observed anisotropy is a direction dependent plasmonic coupling. Different in plane and out of the plane dielectric coefficients calculated by modelling Jones matrix elements, confirms that nanoparticle/nanowire array are biaxial anisotropic (ex ¹ ey ¹ ez). The nanoparticles are predominantly insulating while nanowires are both metallic and insulating depending on the dimension.
Silver nanoparticles/nanowires self-aligned on pre-patterned rippled substrate are presented for the first time as an active SERS substrate. Anisotropic SERS response in such arrays is attributed to different field enhancement along and across the ripples. Strong plasmonic coupling in elongated nanoparticles chain results in significantly higher SERS intensity then spherical nanoparticles/nanowires and non-ordered nanoparticles. Higher SERS intensity across the nanowires array in comparison to along the array (bulk silver) confirms electromagnetic field enhancement (hot-junction) is responsible for SERS phenomenon.
Self-assembly of cobalt nanoparticle on ripple pattern substrate is also reported. Due to less adatom mobility and higher sticking cobalt self-assembly is possible only at much higher temperature. A strong uniaxial magnetic anisotropy was observed not observed for non ordered cobalt particles.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-007 2011
    ISSN: 1437-322X

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Publ.-Id: 15949 - Permalink


Zur Wechselwirkung von Uran mit den Bioliganden Citronensäure und Glucose
Steudtner, R.;
Um das Verhalten von Actiniden im Menschen (Stoffwechsel), in geologischen und in biologischen Systemen vorherzusagen, ist es erforderlich deren Speziation genau zu kennen. Zur Bestimmung dieser wird das chemische Verhalten des Urans hinsichtlich Komplexbildungsreaktionen und Redoxreaktionen in Modellsystemen untersucht. Anhand der gewonnenen thermodynamischen Konstanten und dem Redoxverhalten können Risikoabschätzungen für das jeweilige untersuchte System getroffen werden.
Das umweltrelevante Uran(IV)-Uran(VI)-Redoxsystem besitzt mit der metastabilen fünfwertigen Oxidationsstufe einen zumeist kurzlebigen Zwischenzustand. Innerhalb dieser Arbeit gelang es erstmalig die Uran(V)-Fluoreszenz mittels laserspektroskopischer Methoden nach zu weisen. Beispielsweise konnte das Bandenmaximum von aquatischem Uranyl(V) im perchlorhaltigem Medium (λex = 255 nm) mit 440 nm, bei einer Fluoreszenzlebensdauer von 1,10 ± 0,02 μs bestimmt werden. Die fluoreszenzspektroskopische Untersuchung eines aquatischen [U(V)O2(CO3)3]5--Komplexes (λex= 255 nm und 408 nm) zeigte bei Raumtemperatur keine Fluoreszenz.
Durch Anwendung der Tieftemperaturtechnik wurden bekannte Quencheffekte des Carbonats unterdrückt, so dass bei beiden Anregungswellenlängen ein für Uran(V) typisches Fluoreszenzspektrum im Bereich von 375 nm bis 450 nm, mit Bandenmaxima bei 401,5 nm (λex = 255 nm) und 413,0 nm (λex = 408 nm) detektiert werden konnte. Darüber hinaus konnte bei 153 K (λex = 255 nm) eine Fluoreszenzlebensdauer von 120 ± 0,1 μs bestimmt werden. Untersetzt wurden diese fluoreszenzspektroskopischen Nachweise durch mikroskopische Studien verschiedener Uran(IV)-Festphasen (Uraninit…UO2, Uran(IV)-Tetrachlorid…UCl4) und einer sulfathaltigen Uran(IV)-Lösung (UIVSO4). Diese wurden durch kontinuierliche Sauerstoffzufuhr zu Uran(VI) oxidiert. Die ablaufende Oxidation wurde mit dem konfokalen Laser Scanning Mikroskop (CLSM) verfolgt, wobei die Proben mit einer Wellenlänge von 408 nm zur Fluoreszenz angeregt wurden. Die auftretenden Bandenmaxima bei 445,5 nm (UO2), bei 445,5 nm (UCl4) und bei 440,0 nm (UIVSO4) konnten eindeutig der Uran(V)-Fluoreszenz zugeordnet werden.
Zur Bestimmung thermodynamischer Konstanten mit Hilfe der Tieftemperaturfluoreszenz wurde zunächst der Einfluss der Temperatur auf das Fluoreszenzverhalten des freien Uranyl(VI)-Ions näher betrachtet. Es zeigte sich, dass mit Erwärmung der Probe (T>298 K) die Fluoreszenzlebensdauer von 1,88 μs (298 K) deutlich absinkt. Die Fluoreszenzintensität verringerte sich dabei um 2,3 % pro 1 K zwischen 273 K und 313 K. Im Gegensatz dazu, steigt die Fluoreszenzlebensdauer um das 150-fache auf 257,9 μs bei einer Verminderung der Temperatur (T <298 K) auf 153 K. Das weitere Absenken der Temperatur (T <153 K) zeigte keinen Einfluss auf die Fluoreszenzlebensdauer. Die Lage der Hauptemissionsbanden des freien Uranyl(VI)-Ions (488,0 nm, 509,4 nm, 532,4 nm, 558,0 nm, 586,0 nm) zeigte bei diesen Untersuchungen keine temperaturabhängige Verschiebung.
Die Validierung der Tieftemperaturtechnik zur Bestimmung thermodynamischer Konstanten mittels zeitaufgelöster laserinduzierten Fluoreszenzspektroskopie erfolgte anhand des Uran(VI)-Citrat-Systems. Im Gegensatz zu bisherigen fluoreszenzspektroskopischen Betrachtungen bei Raumtemperatur wurde das Fluoreszenzsignal bei tiefen Temperaturen mit einsetzender Komplexierung nicht gequencht, woraus die Ausprägung einer gut interpretierbaren Fluoreszenz resultierte. Die Analyse der spektralen Daten mit SPECFIT ergaben mit log β 101 = 7,24 ± 0,16 für den [UO2(Cit)]--Komplex und log β 202 = 18,90 ± 0,26 für den [(UO2)2(Cit)2]2--Komplex exakt die in der Literatur angegebenen Stabilitätskonstanten. Zudem konnten Einzelkomponentenspektren mit Bandenmaxima bei 475,3 nm, 591,8 nm, 513,5 nm, 537,0 nm und 561,9 nm für den 1:0:1-Komplex und 483,6 nm, 502,7 nm, 524,5 nm, 548,1 nm und 574,0 nm für den 2:0:2-Komplex und Fluoreszenzlebensdauern von 79 ± 15 μs (1:0:1) und 10 ± 3 μs (2:0:2) bestimmt werden.
Zur Modellkomplexierung des Uran-Citrat-Systems wurde in dieser Arbeit auch das Komplexbildungsverhalten von U(IV) in Gegenwart von Citronensäure untersucht. Hierbei wurden über den gesamten pH-Wertbereich gelöste Uran-Citrat-Spezies spektroskopisch nachgewiesen und die Stabilitätskonstanten sowie die Einzelkomponentenspektren für die neu gebildeten Uran(IV) und (VI)-Spezies bestimmt. Für die neu gebildeten Citrat-Komplexe des sechswertigen Urans wurden Komplexbildungskonstanten von log β 203 = 22,67 ± 0,34 ([(UO2)2(Cit)3]5-) und log β 103 = 12,35 ± 0,22 ([UO2(Cit)3]7-) und für die Komplexe des vierwertigen Urans von log β 1-21 = -9,74 ± 0,23 ([U(OH)2Cit]-) und log β 1-31 = -20,36 ± 0,22 ([U(OH)3Cit]2-) bestimmt.
Untersuchungen zum Redoxverhalten von Uran in Gegenwart von Citronensäure zeigten unter aeroben und anaeroben Versuchsbedingungen eine photochemische Reduktion vom U(VI) zu U(IV), welche spektroskopisch nachgewiesen werden konnte. Dabei zeigt speziell die Reaktion unter oxidierenden Bedingungen, welchen großen Einfluss vor allem organischen Liganden auf das chemische Verhalten des Urans haben können. Sowohl die Reduktion unter O2- als auch die unter N2-Atmosphäre, weisen ein Maximum bei einem pH-Wert von 3,5 bis 4 auf. Unter anaeroben Bedingungen reduziert die Citronensäure mit ca. 66 %, 14 % mehr Uran(VI) zu Uran(IV) als unter anaeroben Bedingungen mit ca. 52 %.
Ab einem pH-Wert von 7 konnte eine Reduktion nur unter sauerstofffreien Bedingungen festgestellt werden.
Die Wechselwirkung von U(VI) in Gegenwart von Glucose wurde hinsichtlich Reduktion und Komplexierung des Uran(VI) betrachtet. Mit Hilfe der zeitaufgelösten laserinduzierten Fluoreszenzspektroskopie bei tiefen Temperaturen wurde dabei ein Uranyl(VI)-Glucose-Komplex nachgewiesen. Die Komplexierung wurde lediglich bei pH 5 beobachtet und weist eine Komplexbildungskonstante von log β I=0,1 M = 15,25 ± 0,96 für den [UO2(C6H12O6)]2+-Komplex auf. Mit einer Fluoreszenzlebensdauer von 20,9 ± 2,9 μs und den Hauptemissionsbanden bei 499,0nm, 512,1 nm, 525,2 nm, 541,7 nm und 559,3 nm konnte der Uranyl(VI)-Glucose-Komplex fluoreszenzspektroskopisch charakterisiert werden. Unter reduzierenden Bedingungen wurde, ab pH-Wert 4 eine auftretende Umwandlung vom sechswertigen zum vierwertigen Uran durch Glucose in Gegenwart von Licht beobachtet. Der Anteil an gebildetem Uran(IV) steigt asymptotischen bis zu einem pH-Wert von 9, wo das Maximum mit 16 % bestimmt wurde. Als Reaktionsprodukt der Redoxreaktion wurde eine Uran(VI)-Uran(IV)-Mischphase mit der Summenformel [UIV(UVIO2)5(OH)2]12+ identifiziert.
Mit Hilfe der cryo-TRLFS wurde, durch Verminderung von Quencheffekten die Uranspeziation in natürlichen Medien (Urin, Mineralwasser) direkt bestimmt. Proben mit Uran-Konzentrationen von < 0,1 μg/L konnten dadurch analysiert werden. In handelsüblichen Mineralwässern wurde die zu erwartende Komplexierung durch Carbonat nachgewiesen. Im Urin zeigte sich in Abhängigkeit vom pH-Wert eine unterschiedliche Uranspeziation. Die fluoreszenzspektroskopische Untersuchung wies bei niedrigerem pH-Wert (pH<6) eine Mischung aus Citrat- und Phosphat-Komplexierung des U(VI) und bei höheren pH-Wert (pH>6) eine deutliche Beteilung von Carbonat an der Komplexierung auf. Diese Ergebnisse stehen in sehr guter Übereinstimmung mit theoretischen Modellrechnungen zur Uranspeziation im Urin.
Die in dieser Arbeit gewonnenen Ergebnisse zeigen, dass für eine zuverlässigere Prognose des Urantransportes in Geo- und Biosphäre in Zukunft nicht nur Betrachtungen zur Komplexchemie, sondern auch zum Redoxverhalten des Urans nötig sind, um die Mobilität in der Natur richtig abschätzen zu können.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-008 2011
    ISSN: 2191-8708

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Publ.-Id: 15948 - Permalink


Annual Report 2010 - Institute of Ion Beam Physics and Materials Research
von Borany, J.; Heera, V.; Fassbender, J.ORC; Helm, M.
The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of what was called Forschungszentrum Dresden-Rossendorf (FZD) until the end of 2010, but since this year 2011 is called “Helmholtz-Zentrum Dresden-Rossendorf (HZDR)”. This change reflects a significant transition for us: it means that the research center is now member of the Helmholtz Association of German Research Centers (HGF), i.e., a real government research laboratory, with the mission to perform research to solve fundamental societal problems. Often to date those are called the “Grand Challenges” and comprise issues such as energy supply and resources, health in relation to aging population, future mobility, or the information society.
This Annual Report already bears the new corporate design, adequate for the time of its issueing, but reports results from the year 2010, when we were still member of the Leibniz Association (WGL). Our research is still mainly in the fields of semiconductor physics and materials science using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz freeelectron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-002 2011
    ISSN: 2191-8708

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Publ.-Id: 15947 - Permalink


Annual Report 2010 - Institute of Radiochemistry
Bernhard, G.; Foerstendorf, H.; Richter, A.; Viehweger, K.; (Editors)
At the beginning of 2011, the former Forschungszentrum Dresden-Rossendorf (FZD) was fully integrated into the Helmholtz Association, as Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Therefore, the present Annual Report 2010 of the Institute of Radiochemistry (IRC) is published as the first HZDR-Report.

The Institute of Radiochemistry is one of the six Research Institutes of this centre. IRC contributes to the research program “Nuclear Safety Research” in the “Research Field of Energy” and performs basic and applied research in radiochemistry and radioecology. Motivation and background of our research are environmental processes relevant for the installation of nuclear waste repositories, for remediation of uranium mining and milling sites, and for radioactive contaminations caused by nuclear accidents and fallout. Because of their high radiotoxicity and long half-life the actinides are of special interest.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-001 2011
    ISSN: 2191-8708

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Publ.-Id: 15946 - Permalink


Quality assurance in accelerator mass spectrometry: Results from an international round-robin exercise for 10Be
Merchel, S.; Bremser, W.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D. L.; Braucher, R.; Caffee, M.; Christl, M.; Fifield, L. K.; Finkel, R. C.; Freeman, S. P. H. T.; Ruiz-Gómez, A.; Kubik, P. W.; Martschini, M.; Rood, D. H.; Tims, S. G.; Wallner, A.; Wilcken, K. M.; Xu, S.;
The first international round-robin exercise for the measurement of the long-lived radionuclide 10Be has been conducted. Ten participating accelerator mass spectrometry (AMS) facilities have each measured three samples at the 10-12-10-14 10Be/9Be level. All results have been made traceable to the NIST SRM 4325 standard to avoid additional discrepancies that arise when different facilities use different calibration materials. Hence, the data concentrates on pure measurement distinctions. Multivariate statistical investigations have been performed to reveal a bias between facilities, i.e. two distinguished groups could be identified. Maximum discrepancies between two single facilities are in the range of 6-31% depending on the absolute 10Be/9Be value. These findings should be considered when comparing 10Be data produced at one AMS facility with that produced at another facility, which is e.g. often the case for in-situ 10Be dating studies. Round-robin exercises are a very helpful tool as part of an overall quality assurance scheme to improve the accuracy, and not only the precision, of AMS data.
Keywords: accelerator mass spectrometry, terrestrial cosmogenic nuclides (TCN), cosmogenic nuclide exposure dating, calibration

Publ.-Id: 15945 - Permalink


Spin-polarized transport in pulsed-laser annealed Ge:Mn
Bürger, D.; Zhou, S.; Kovacs, G. J.; Helm, M.; Schmidt, H.;
The incorporation of transition metal dopants in semiconductors above their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Low temperature molecular beam epitaxy (LT-MBE) is the standard technique for the fabrication of GaAs:Mn. For Ge:Mn the LT-MBE approach seems to be successful to grow Mn rich clusters or nanowires [1]. Nevertheless, hysteretic magnetotransport properties were not observed in such Ge:Mn nanostructures. On the other hand, pulsed laser annealing is a successful annealing method far from thermodynamic equilibrium and a promising technique for the fabrication of ferromagnetic Ge:Mn [2] and for III-V semiconductors [3]. In this work, Mn has been implanted into nearly intrinsic n-Ge substrates up to a depth of around 100 nm at low temperatures and annealed by pulsed laser annealing. We observed the same hysteretic properties up to 30 K via SQUID magnetization as well as via magnetotransport measurements. Furthermore, Ge:Mn films show a spontaneous magnetization in field-cooled SQUID measurements below 250 K. Segregated secondary phases with a regular distance slightly above 50 nm have been detected by HRTEM measurements near the sample surface. At elevated temperatures the confirmation of similar magnetization and magnetotransport properties of the p-Ge:Mn surface layer is hampered by the significant contribution of the underlying n-Ge substrate to the conductivity. Further experiments with insulating substrates and proper etching methods are necessary to clarify the ferromagnetic contribution of each individual layer.

[1] M. Jamet et al., Nature. Mat. 5, 653 (2006)
[2] Shengqiang Zhou et al., Phys. Rev. B 81, 165204 (2010)
[3] M. A. Scarpulla et al., Appl. Phys. Lett. 82, 1251 (2003)
  • Poster
    Spintech VI, 01.-05.08.2011, Matsue, Japan

Publ.-Id: 15944 - Permalink


Spin-polarized hole transport in pulsed laser annealed Ge:Mn up to 30 K
Bürger, D.; Zhou, S.; Kovacs, G. J.; Schmidt, H.;
The incorporation of transition metals dopants in semiconductors over their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Low temperature molecular beam epitaxy (LT-MBE) is the standard technique for the fabrication of GaAs:Mn. Nevertheless, for Ge:Mn [1] the LT-MBE approach seems to be not successful to reach hole concentrations necessary for hole mediated ferromagnetism. On the other hand, pulsed laser annealing is a successful nonequilibrium annealing method and a promising technique for the fabrication of diluted Ge:Mn [2] and for III-V semiconductors, e.g. GaAs:Mn [3]. Recently we fabricated a ca. 100 nm thick Ge:Mn film by low temperature Mn-implantation followed by pulsed laser annealing and observed hole-mediated ferromagnetism up to 30 K via SQUID magnetization as well as magnetotransport measurements. The anisotropy of ferromagnetic Ge:Mn films will be discussed. Moreover, the Ge:Mn films show a remanent magnetization up to 220 K which is lower than the Curie temperature of typical Mn_xGe_y clusters [1]. The confirmation of spin-polarized hole transport up to 220 K becomes difficult because at elevated temperatures the conductivity is mainly determined by the Ge substrate.
[1] M. Jamet et al., Nature. Mat. 5, 653 (2006)
[2] Shengqiang Zhou et al., PRB 81, 165204 (2010)
[3] Danilo Bürger et al., PRB 81, 115202 (2010
Keywords: Ge:Mn, implantation, pulsed laser annealing, ferromagnetic semiconductor
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15943 - Permalink


Hysteretic anomalous Hall effect in a ferromagnetic, Mn-rich Ge:Mn nanonet
Bürger, D.; Zhou, S.; Höwler, M.; Ou, X.; Kovacs, G.; Reuther, H.; Mücklich, A.; Skorupa, W.; Helm, M.; Schmidt, H.;
Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.
Keywords: GeMn, implantation, pulsed laser annealing, ferromagnetic semiconductor, percolation, segregation, instability, nanonet

Publ.-Id: 15942 - Permalink


Magneto-optical properties of ferromagnetic thin films under saturated magnetization conditions
Mok, Kahming; Li, L.; Kovacs, G. J.; Helm, M.; Schmidt, H.;
Vector-magneto-optical generalized ellipsometry (VMOGE) allows to perform generalized Mueller matrix ellipsometry in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. We measured the magneto-optical properties of Fe, Co, and Ni thin films on ZnO substrates and extracted the wavelength dependent magneto-optical dielectric tensor together with the coupling constant Q under saturation magnetization conditions via model analysis. We converted our magneto-optical dielectric tensor of Fe, Co, and Ni into the optical conductivity tensor and the results agreed well with the literature experimental values.
Keywords: magneto-optics, ferromagnet, Mueller matrix, generalized ellipsometry
  • Poster
    6th International School and Conference on Spintronics and Quantum Information Technology (SPINTECH6), 01.-05.08.2011, Matsue, Japan

Publ.-Id: 15941 - Permalink


Advanced tomographic techniques for flow imaging in columns with flow distribution packings
Schubert, M.; Bieberle, A.; Barthel, F.; Boden, S.; Hampel, U.;
Design and optimization of separation units, e. g., distillation and absorption columns with flow distribution packings, require detailed knowledge about the internal flow conditions and their impact on the process behavior. This in turn calls for suitable measuring techniques, which can give a detailed insight into such devices, especially for studies on a laboratory and pilot scale. Traditional instrumentation, such as compartment-type liquid collectors installed below packings, or distributed temperature, pressure and conductivity probes, often falls too short if detailed knowledge on flow conditions is required. This concerns especially local liquid holdup, liquid maldistribution, liquid films thickness, wetting of the packing surface, or bubble size and droplet distribution at trays. Advanced imaging techniques, such as tomography, have found only marginal attention in investigations of separation columns with structured and modern dumped flow distribution packings, mostly due to limited spatial and temporal resolution but also due to prevailing technological problems encountered in such applications. In this study, the potentials and limits of some of the most recently emerged tomographic imaging modalities for multiphase flows have been investigated and reviewed, i.e., ultra-fast X-ray tomography, high-resolution gamma-ray tomography, wire-mesh sensor techniques, and X-ray microtomography with respect to a possible application in separation columns with flow distribution packings.

Publ.-Id: 15940 - Permalink


Unusual non-head-to-tail chains in the crystal structure of glycyl-L-glutamyl-L-phosphoseryl-L-leucine
Heine, K. B.; Fairweather, K. A.; Heine, A.; Clegg, J. K.; Jolliffe, K. A.;
The structure of glycyl-L-glutamyl-L-phosphoseryl-L-leucine, (C16H29N4O11P)2.3H2O, has monoclinic (P21) symmetry. The dimeric structure is characterized by an unusual non-head-to-tail arrangement based on an extended intermolecular hydrogen bonding network. Two of the three H2O molecules included in the network are disordered. The protonation constants of the tetrapeptide were determined as log K1 = 1.50, log K2 =3.63, log K3 =4.32, log K4 =6.08 and log K5 =8.65 by potentiometric pH titration.

Publ.-Id: 15938 - Permalink


Magnetic layer formation on plasma nitrided CoCrMo alloy
Öztürk, O.; Okur, S.; Pichon, L.; Liedke, M. O.; Riviere, J. P.;
In this study structural and magnetic character of the expanded austenite phase (γN) layer formed on a medical grade CoCrMo alloy by a low-pressure Radio-Frequency plasma nitriding process was investigated. The formation of the expanded austenite phase is facilitated at a substrate temperature near 400 °C for 1, 2, 4, 6 and 20 h under a gas mixture of 60% N2–40% H2. The magnetic state of the γN layers was determined by a surface sensitive technique, magneto-optic Kerr effect (MOKE), and with a scanning probe microscope in magnetic force mode (MFM). Strong evidence for the ferromagnetic nature of the γN-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the γN phase observed here ismainly linked to large lattice expansions (~10%) due to high N contents (~30 at.%). As an interstitial impurity, nitrogen dilates the host lattice i.e. the Co–Co (or Fe–Fe) distance is increased, which strongly influences the magnetic interactions. An analogy between the magnetic properties of the expanded phases, γN-(Fe,Cr,Ni) and γN-(Co,Cr,Mo), formed in austenitic stainless steel alloys and the CoCrMo alloy of this study is made, and it is suggested that the ferromagnetic states for the γN-(Co,Cr,Mo) and γN-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively.
Keywords: CoCrMo alloy, expanded austenite structure, plasma nitriding, ferromagnetism, MOKE, MFM
  • Surface & Coatings Technology 205(2011), S280-S285
  • Contribution to proceedings
    12th International Conference on Plasma Surface Engineering, 13.-17.09.2010, Garmisch-Partenkirchen, Germany

Publ.-Id: 15937 - Permalink


Magnetic anisotropy modifi cations of single crystalline rippled Fe
Liedke, M. O.; Körner, M.; Lenz, K.; Shalimov, A.; Strache, T.; Ranjan, M.; Facsko, S.; McCord, J.; Fassbender, J.ORC
Ion erosion as a tool for nanostructuring has proven its versatility with respect to surface morphology modifications. Ion irradiation parameters, e.g. ion energy, fluence, incident angle, and sample temperature, can be varied in order to assemble self-organized periodically ordered arrays of nano-dots and ripples. Particularly, nanopatterning of magnetic materials is meaningful because not only the surface morphology is affected, but the overall magnetic properties are accordingly modified. Here we present a novel bottom-up method of magnetic film patterning, where ordered periodic MgO ripple surfaces with a wavelength on the nanometer scale, ion sculptured along a few arbitrary in-plane orientations and outstandingly fully crystalline upon ion irradiation, are coated by a magnetic Fe layer. Due to a cubic symmetry of Fe an in-plane fourfold magnetic anisotropy is induced and in addition, an uniaxial magnetic anisotropy arises due to the surface morphology. The uniaxial magnetic anisotropy orientation and strength is controlled by an arbitrarily chosen irradiation direction with respect to the sample plane and the ripple wavelength is set by the ion energy, respectively. Thus an ensemble of twofold and fourfold anisotropy is created and analyzed by ferromagnetic resonance, magnetooptic Kerr effect, and X-ray diffraction techniques. Theoretical analysis reveals both the anisotropy fields and their directions that are in agreement with the experiment. This work is supported by DFG FA314/6-1.
Keywords: ion erosion, magnetization, magnetic anisotropy, ripples, Fe, MgO, MOKE, FMR, XRD, GID
  • Lecture (Conference)
    The European Conference PHYSICS OF MAGNETISM 2011, 27.06.-01.07.2011, Poznan, Poland

Publ.-Id: 15936 - Permalink


Magnetic anisotropy investigations in single crystalline Fe films on ripple MgO templates
Liedke, M. O.; Körner, M.; Lenz, K.; Strache, T.; McCord, J.; Ranjan, M.; Facsko, S.; Fassbender, J.ORC
Ion erosion of MgO substrates produces highly ordered surface patterns. The so-called ripples are not only induced along any arbitrary in-plane orientation but outstandingly, they stay crystalline upon ion irradiation. Due to the low lattice mismatch single crystalline Fe films can be grown onto these periodically modulated MgO(100) templates. Despite the intrinsic magnetic property of bcc Fe, i.e. cubic anisotropy, an additional ripple morphology driven uniaxial magnetic anisotropy is introduced. Thus an ensemble of twofold and fourfold symmetry is created, which is confirmed by ferromagnetic resonance and magneto-optic Kerr effect measurements. The orientation and strength of the uniaxial anisotropy, which mainly originates from shape and step-edge contributions, depends on the angle of the ripple ridges elongation with regard to the [100] direction of MgO and on the Fe film thickness, respectively. Theoretical analysis reveals anisotropy fields and orientations of both anisotropy contributions that are in agreement with the experiment.
Keywords: ion erosion, magnetization, magnetic anisotropy, ripples, Fe, MgO, MOKE, FMR
  • Lecture (Conference)
    75th Annual Meeting of the DPG and DPG Spring Meeting, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15935 - Permalink


Formation and structural characterization of thioantimony species and their natural occurrence in geothermal waters
Planer-Friedrich, B.; Scheinost, A. C.;
Previously postulated from laboratory studies, the occurrence of antimony-sulfur species in geothermal waters could now be proven using anion-exchange chromatography-inductively coupled plasma-mass spectrometry. The two thioantimony species detected by AEC-ICP-MS in oxic synthetic antimonite-sulfide solutions were assigned to tri- and tetrathioantimonate based on their S/Sb ratios and structural characterization by X-ray absorption spectroscopy (XAS). XAS confirmed that the initial species formed under anoxic conditions from antimonite at a 10-fold sulfide excess is trithioantimonite. Trithioantimonite rapidly transforms to tetrathioantimonate in the presence of oxygen or to antimonite at excess OH(-) versus SH(-) concentrations, and escapes chromatographic detection. In natural geothermal waters, up to 30% trithioantimonate and 9% tetrathioantimonate were detected. Their occurrence increased at increasingly alkaline pH and with increasing sulfide and decreasing oxygen conce!
ntrations. Considering the large sulfide excess (100 to 10 000-fold) the proportion of thioantimonates formed under natural conditions is lower than expected from synthetic solutions. Together with the observed high thioarsenate concentrations (>80% of total arsenic), this indicates that in direct competition with arsenic for a limited source of sulfide, thioantimonates form less spontaneously than thioarsenates. Interactions of arsenic and antimony with sulfur can therefore be decisive for similarities or differences in their environmental behavior.
Keywords: antimony thiocomplexes thermal waters EXAFS XANES

Publ.-Id: 15934 - Permalink


Annealing of heterogeneous phase TiO2 films: An X-ray absorption and morphological study
Gago, R.; Redondo-Cubero, A.; Vinnichenko, M.; Vázquez, L.;
Heterogeneous TiO(2) films with nanocrystalline (nc-) rutile and amorphous (a-) phases were annealed in vacuum up to 450 degrees C. The structural and morphological changes were studied by in situ X-ray absorption and ex-situ X-ray diffraction and atomic force microscopy. The annealing process leads to phase and morphological changes depending on the initial phase mixture. Films with dominant nc-rutile phase are quite stable whereas in a-TiO(2)-containing films the a-TiO(2) regions crystallize into nc-anatase at 300 degrees C. The latter is attributed to the initial anatase-like character of a-TiO(2). Interestingly, at 450 degrees C nc-anatase or nc-rutile is preferentially promoted for high or low initial a-TiO(2) contents, respectively.

Publ.-Id: 15933 - Permalink


Al-doped ZnO films grown by reactive magnetron sputtering: properties evolution and secondary phase formation
Vinnichenko, M.; Cornelius, S.; Krause, M.; Gago, R.; Munnik, F.; Kolitsch, A.; Moeller, W.;
Reactive pulsed magnetron sputtering (RPMS) using high metal to oxygen flux ratio is know to provide high-quality transparent and electrically conductive Al-doped ZnO (AZO) films at low temperatures (Ts<200 °C) [1]. However, in this case electrical properties of AZO films strongly depend on deposition temperature and the films even turn insulating at Ts>350 °C [2]. It has been shown that energy deposition during growth due to the elevated TS and from the flux of energetic particles incident on the substrate causes preferential Zn desorption. This leads to a higher Al concentration in the films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. This phase impedes crystal growth (decreasing the grain size) and causes a significant increase of free electron scattering which leads to observed increase of the film electrical resistivity [2]. Little is known about effect of this phase formation on the AZO film optical properties, although it is of special importance for understanding of the influence of the secondary phase formation on the fundamental and above-band gap band-to-band electron transitions in this material.

In order to clarify the problem the films with defined Al concentrations (0-20 at.%) grown by RPMS at temperatures ranging from RT to 550 °C were investigated. They were characterized by Hall-effect measurements, spectroscopic ellipsometry and Raman spectroscopy. These results were complemented by the Rutherford back scattering, elastic recoil detection analysis, X-ray diffraction and X-ray absorption near edge structure (XANES) measurements.

The comparison of undoped ZnO and AZO films with the highest crystallinity shows that an incorporation of ~1 at.% of Al leads to the best electrical properties, although (ZnO)3Al2O3 phase signature appears in its Al K-edge XANES spectra even at this low dopant concentration. This is accompanied by the broadening of the allowed ZnO Raman lines and appearance of the broad band around 565 cm-1 which is interpreted as a defect-enhanced A1 LO mode. Increase of Al concentration up to 8-10 at.% leads to deterioration of the film electrical properties accompanied by an increase of the (ZnO)3Al2O3 phase-related peaks in Al K-edge spectra. At this level of doping the allowed ZnO Raman lines are no longer detectable, but the defect-induced Raman features change their intensity distribution. Finally, increasing cFAl>10 at.% leads to formation of electrically insulating nanocrystalline films, which show even more intense (ZnO)3Al2O3 phase-related XANES peaks. The band gap of these films is significantly broader compared to that of undoped ZnO or conductive AZO layers. The latter may be understood in analogy to optical properties of the metastable wurtzite MgxZn(1-x)O alloys.

[1] B. Szyszka, Thin Solid Films 351, 164 (1999)
[2] M. Vinnichenko et al, Appl. Phys. Lett. 96, 141907 (2010).
  • Lecture (Conference)
    MRS Spring Meeting 2011 (Symposium S: Plasma-assisted Materials Processing and Synthesis), 25.-29.04.2011, San Francisco, USA

Publ.-Id: 15932 - Permalink


Magnetostructural Transitions in a Frustrated Magnet at High Fields
Tsurkan, V.; Zherlitsyn, S.; Felea, V.; Yasin, S.; Skourski, Y.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Lemmens, P.; Wosnitza, J.; Loidl, A.;
Ultrasound and magnetization studies of bond-frustrated ZnCr2S4 spinel are performed in static magnetic fields up to 18 T and in pulsed fields up to 62 T. At temperatures below the antiferromagnetic transition at TN1 ≈ 4 K, the sound velocity as a function of the magnetic field reveals a sequence of steps followed by plateaus indicating a succession of crystallographic structures with constant stiffness. At the same time, the magnetization evolves continuously with a field up to full magnetic polarization without any plateaus in contrast to geometrically frustrated chromium oxide spinels. The observed high-field magnetostructural states are discussed within a H-T phase diagram taking into account the field and temperature evolution of three coexisting spin structures and subsequent lattice transformation induced by the magnetic field.
  • Physical Review Letters 106(2011), 247202

Publ.-Id: 15931 - Permalink


Low-Temperature Elastic Properties of Non-Kramers Doublet Compound PrMg3
Araki, K.; Mitsumoto, K.; Akatsu, M.; Nemoto, Y.; Goto, T.; Suzuki, H. S.; Tanida, H.; Takagi, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.;
We have investigated low-temperature elastic properties of PrMg3 with a non-Kramers Γ3 doublet ground state by using ultrasonic measurements under high field up to 18 T down to 20 mK. A softening of the elastic constant (C11−C12)/2 has been observed below 8 K due to the non-magnetic Γ3 doublet possessing electric quadrupole Ou and Ov with Γ3 symmetry and magnetic octupole Txyz with Γ2. This result appreciably is deviated from a theoretical fitting of the quadrupole susceptibility based on the crystal-electric-field levels below 800 mK. Furthermore, the (C11−C12)/2 shows strange magnetic dependence up to 18 T below 1.7 K, which are inconsistent with the theoretical results
  • Open Access LogoJournal of Physics: Conference Series 273(2011), 012133

Publ.-Id: 15930 - Permalink


Upper Critical Magnetic Field in Ba0.68K0.32Fe2As2 and Ba(Fe0.93Co0.07)2As2
Gasparov, V. A.; Drigo, L.; Audouard, A.; Sun, D. L.; Lin, C. T.; Bud’Ko, S. L.; Canfield, P. C.; Wolff-Fabris, F.; Wosnitza, J.;
We report measurements of the temperature dependence of the radio frequency magnetic penetration depth in Ba0.68K0.32Fe2As2 and Ba(Fe0.93Co0.07)2As2 single crystals in pulsed magnetic fields up to 60 T. From our data, we construct an H–T-phase diagram for the interplane (H || c) and in-plane (H || ab) directions for both compounds. For both field orientations in Ba0.68K0.32Fe2As2 we find a concave curvature of the Hc2(T) lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we can describe Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair breaking is not essential for Ba(Fe0.93Co0.07)2As2. For this electron-doped compound, the data support a Hc2(T) dependence that can be described by the Werthamer–Helfand–Hohenberg model for H || ab and a two-gap behavior for H || c.
  • JETP Letters 93(2011)11, 667-672

Publ.-Id: 15929 - Permalink


Effect of composition and pressure on phase transitions in FexO at low temperature
Glazyrin, K.; Dubrovinsky, L.; Klotz, S.; Uhlarz, M.; Wosnitza, J.; Hansen, T.; Dubrovinskaia, N.;
We report the results of high-resolution neutron powder diffraction studies of FexO (x = 0.925, 0.94) in the vicinity of the low-temperature antiferromagnetic transition and at pressures up to 8 GPa. Our analysis shows that the P-T phase diagram of FexO is strongly affected by the composition and defect structure of the material. We observe the divergence of critical temperatures of magnetic and structural transitions. In contrast to the stoichiometric antiferromagnet MnO, we find no correlation between the magnitude of the magnetic moment of iron and the degree of the rhombohedral distortion in FexO. We suggest that the defect structure of antiferromagnetic FexO significantly influences the temperature of the structural transition.
  • Journal of Applied Physics 110(2011), 026109

Publ.-Id: 15928 - Permalink


High-field magnetization of Ho2Fe17
Skourski, Y.; Kuzmin, M. D.; Skokov, K. P.; Andreev, A. V.; Wosnitza, J.;
The magnetization of a Ho2Fe17 single crystal has been measured along the principal crystallographic directions in pulsed magnetic fields up to 60 T. Stepwise discontinuities in the magnetization occur at 45 and 55 T along the [120] and [100] directions, respectively. The data allowed us to deduce the molecular field at the Ho site. As a cross check, the molecular field was determined as well from a magnetization measurement when the Ho2Fe17 single crystal was let rotate freely. Both values are in good agreement with each other.
  • Physical Review B 83(2011), 214420

Publ.-Id: 15927 - Permalink


Status of proton therapy based on high intensity lasers - the first dose-response curves of laser accelerated protons
Karsch, L.; Baumann, M.; Beyreuther, E.; Burris-Mog, T.; Kraft, S.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Oppelt, M.; Richter, C.; Schramm, U.; Schürer, M.; Zeil, K.; Pawelke, J.;
Fragestellung: Die klassischen Protonenbeschleuniger liefern einige Nanosekunden lange Pulse mit hoher Wiederholfrequenz im Megahertzbereich. Mit der neuartigen Technologie der Laser Beschleunigung werden hingegen kürzere, nur einige Pikosekunden lange Teilchenpakete mit wesentlich geringerer Pulsfrequenz von einigen Hertz bei gleichzeitig viel höherer Pulsintensität erzeugt. Vor einem Einsatz der Laserbeschleunigung in der Strahlentherapie muss die möglicherweise abweichende biologische Wirksamkeit, sei es durch die andere Zeitstruktur oder durch die höhere Pulsdosisleistung, gegenüber den klassischen Teilchenstrahlen untersucht werden. Im Beitrag wird der Stand der neuen Technologie im Hinblick auf eine Protonentherapie diskutiert und die weltweit ersten systematischen Zellbestrahlungen mit Bestimmung von Dosis-Effekt-Kurven für Laser beschleunigte Protonen vorgestellt.
Methodik: Wichtige Voraussetzungen für die Nutzung Laser beschleunigter Teilchen in der klinischen Therapie oder auch für strahlenbiologische Experimente sind die Anpassung des Lasersystems, sowie der Aufbau einer geeigneten Strahlführung und eines Dosimetriesystems. Die Zellbestrahlungen wurden am 150-Terrawatt-Lasersystem DRACO im Helmoltz-Zentrum Dresden-Rossendorf durchgeführt. Die Protonenpulse haben eine Länge von ca. 1 ps und eine Wiederholrate von 0,2 Hz. In einer ersten Serie von in-vitro Zellbestrahlungen mit Strahlendosen im Bereich von 0,3 bis 4 Gy wurde der Anteil der überlebenden Zellen und die 24 h nach Bestrahlung verbliebenen DNA-Doppelstrangbrüche für die Tumor-Zelllinie SKX bestimmt. Zusätzlich wurden Referenzbestrahlungen an einem Tandembeschleuniger mit kontinuierlichen Protonenstrahlen und einer 200 kV-Röntgenröhre durchgeführt.
Ergebnisse: Die neue Technologie bietet ein hohes Potenzial zur Verbesserung der Strahlentherapie mit Protonen. Insbesondere sind kleine, preiswerte Anlagen denkbar, die in bestehende Kliniken integriert werden können. Die präzise dosimetrische Erfassung Laser beschleunigter Strahlen ist möglich. Die biologische Wirksamkeit zwischen konventionell und Laser beschleunigten Protonen zeigt in Zellbestrahlungen keinen signifikanten Unterschied.
Schlussfolgerung: Die ersten Schritte zur Entwicklung einer neuen, auf Hochintensitätslasern basierenden Protonentherapieanlage sind erfolgreich durchgeführt worden. Weitere Untersuchungen zur biologischen Wirksamkeit am Tiermodell müssen erfolgen. Ausserdem sind weitere Entwicklungen und Verbesserungen der Laser Beschleuniger notwendig, damit ein klinischer Einsatz möglich wird.
Die Arbeit wird gefördert durch das BMBF 03ZIK445.
  • Contribution to proceedings
    DEGRO 2011 17. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 02.-05.06.2011, Wiesbaden, Deutschland
    Strahlentherapie und Onkologie 187: Suppl., München: Urban&Vogel, 7

Publ.-Id: 15926 - Permalink


Visualization of spin dynamics in single nanosized magnetic elements
Banholzer, A.; Narkowicz, R.; Hassel, C.; Meckenstock, R.; Stienen, S.; Posth, O.; Suter, D.; Farle, M.; Lindner, J.;
The design of future spintronic devices requires a quantitative understanding of the microscopic linear and nonlinear spin relaxation processes governing the magnetization reversal in nanometer-scale ferromagnetic systems. Ferromagnetic resonance is the method of choice for a quantitative analysis of relaxation rates, magnetic anisotropy and susceptibility in a single experiment. The approach offers the possibility of coherent control and manipulation of nanoscaled structures by microwave irradiation. Here, we analyze the different excitation modes in a single nanometer-sized ferromagnetic stripe. Measurements are performed using a microresonator set-up which offers a sensitivity to quantitatively analyze the dynamic and static magnetic properties of single nanomagnets with volumes of (100 nm)(3). Uniform as well as non-uniform volume modes of the spin wave excitation spectrum are identified and found to be in excellent agreement with the results of micromagnetic simulations which allow the visualization of the spatial distribution of these modes in the nanostructures.

Publ.-Id: 15925 - Permalink


HZDR Developments for Fast Reactor Design
Merk, B.; Duerigen, S.; Rohde, U.; Kliem, S.;
Current work at HZDR will be presented with special emphasis on the development strategy for the DYN3D code as a main component of a diverse 3D coupled core simulation tool for fast reactors and on the work on designable feedback coefficients for sodium cooled fast reactors.
DYN3D is a code for steady-state and transient analysis, currently updated for the use for fast reactors. The code has been extended to multi-group use as well as to the solution of the SP3 equations on rectangular and recently to triangular grid. First verification results for the new triangular multi-group solver will be presented and compared to a HELIOS reference solution. The thermal hydraulics of the code has already been updated with the sodium properties for the steady state and transient core simulation. In an industry funded project the fuel rod modeling will be improved by coupling with a fuel rod analysis code and by extension of the model to consider fuel rod expansion. First full core tests for SFR will be performed within ESFR. LFR validation will be performed on the Guinevere experiments at Mol/Belgium in the project FREYA. Validation of the code for SFR is foreseen in a cooperation project with the IPPE in Obninsk/Russia, already under negotiation. After these validation projects, DYN3D will be a diverse, well validated 3D nodal code for fast reactor steady state and transient analysis.
The new idea of improving the safety coefficients by the insertion of moderating material will be presented. The effect of moderating material on the sodium void effect, the neutron spectrum, and the kinf is investigated. The use of a zirconium hydride ZrH moderator improves the fuel temperature effect, the coolant effect of the system and the sodium void effect significantly. All changes lead to a significant increase in stability of the fast reactor against transients. The effect of different spatial arrangements of the moderating material is investigated. It is demonstrated, that the insertion of the moderating material does not have a significant influence on the fuel element power and burnup distribution. The use of fine distributed moderating material creates a new degree of freedom in the design of sodium cooled fast reactors without implying constraints on the core and the fuel element design. It opens the way to create designable feedback effects in a fast reactor core to optimize the response of the reactor core to transients and incidents. The moderating material has only a small influence on the breeding effect and the MA production.
Keywords: DYN3D, fast reactor, designable feedback coefficients
  • Contribution to proceedings
    IAEA Technical Meeting on “Fast Reactor Physics and Technology", 14.-18.11.2011, Kalpakkam, India
  • Lecture (Conference)
    IAEA Technical Meeting on “Fast Reactor Physics and Technology", 14.-18.11.2011, Kalpakkam, India

Publ.-Id: 15924 - Permalink


Influence of dipolar energy on the magnetization reversal in magnetization-modulated thin film systems: Model and experiment
Martin, N.; Mönch, I.; Schäfer, R.; Fassbender, J.ORC; Schultz, L.; McCord, J.
Laterally patterned magnetic hybrid structures display novel magnetic reversal properties, which are related to the fundamental exchange coupling between material interfaces. We present an analytical model that depicts the influence of dipolar fields inmesoscopic structureswith modulated saturationmagnetization on the magnetization reversal and the local magnetic states, as well as the occurrence of a lateral exchange-spring effect. This is done by confining a lateral array of stripes with alternating saturation magnetizationMS in a micrometer-sized square, introducing external boundary conditions to the system. The calculations were performed for distinct stripe and array sizes, as well as different MS values. From the calculations a stability region of array and stripe sizes is derived, in which the lateral exchange-spring effect occurs. The obtained modeling results were found to be in agreement with the experimental data. The model adds a building block to the fundamental understanding of magnetic hybrid structures.
Keywords: magnetism, hybrid structures, ion irradiation, patterning, Kerr microscopy

Publ.-Id: 15923 - Permalink


Shear and bulk viscosities of the gluon plasma in a quasiparticle description
Bluhm, M.; Kämpfer, B.; Redlich, K.;
Shear and bulk viscosities of deconfined gluonic matter are investigated within an effective kinetic theory by describing the strongly interacting medium phenomenologically in terms of quasiparticle excitations with medium-dependent self-energies. We show that the resulting transport coefficients reproduce the parametric dependencies on temperature and coupling obtained in perturbative QCD at large temperatures and small running coupling. The extrapolation into the nonperturbative regime results in a decreasing specific shear viscosity with decreasing temperature, exhibiting a minimum in the vicinity of the deconfinement transition, while the specific bulk viscosity is sizable in this region, falling off rapidly with increasing temperature. The temperature dependence of specific shear and bulk viscosities found within this quasiparticle description of the pure gluon plasma is in agreement with available lattice QCD results.

Publ.-Id: 15922 - Permalink


Towards the medical application of laser driven particle beams: Establishment of in vitro dose response studies as the first translational step
Beyreuther, E.; Baumann, M.; Burris-Mog, T.; Enghardt, W.; Karsch, L.; Kraft, S.; Laschinsky, L.; Leßmann, E.; Metzkes, J.; Naumburger, D.; Oppelt, M.; Richter, C.; Schramm, U.; Schürer, M.; Zeil, K.; Pawelke, J.;
During the last years, the new laser based technology of particle acceleration was developed at such a rate that medical application, i.e. for cancer therapy, becomes entirely conceivable. Promising more compact and economic proton accelerators, being suitable for existing radiotherapy hospitals, the laser technology however results in ultra-short pulsed particle beams of ultra-high pulse dose and pulse dose rate. Thus, the consequences of laser particle acceleration on beam transport and radiation field formation, dosimetry and radiobiological effects have to be investigated carefully for the whole translational chain from bench to bedside.
Within the German joint research project “onCOOPtics” systematic in vitro cell experiments aiming on the influence of the ultra-high pulse dose rate were firstly established at the Jena 10 terawatt laser system JETI that provides laser accelerated electrons of some ten MeV. Secondly, the increased laser intensity of the 150 terawatt laser system DRACO at the HZDR was applied to accelerate protons to energies of up to 20 MeV. Previous to these experiments, both laser systems had to be extensively optimized in terms of intensity, energy distribution, background reduction, spot size, stability and reliability of the particle beams. The combination of real-time monitoring of dose delivery and a precise retrospective absolute dosimetry enabled the application of defined doses, in spite of the laser based fluctuations of beam intensity and energy. For comparison, reference irradiations with conventionally accelerated, continuous particle beams were performed in parallel to each laser experiment.
In consequence, all key requirements necessary for systematic in vitro cell experiments as the basic translational step towards clinical application of laser-driven particle beams have been fulfilled. Moreover, the dose response curves obtained for pulsed and continuous particle beams show no significant influence of the ultra-high pulse dose rate on the radiobiological response. As next step, animal studies that demand for the translation from 2D to 3D irradiation are in preparation.
The work was supported by the German Federal Ministry of Education and Research (BMBF), grant no. 03ZIK445.
  • Poster
    14th International Congress of Radiation Research, 28.08.-01.09.2011, Warsaw, Poland
  • Lecture (Conference)
    workshop on "Physical and biological basis of hadron radiotherapy", 02.-03.09.2011, Krakow, Poland

Publ.-Id: 15921 - Permalink


Characterization of Structural Changes Associated with Doping Silicon Nanowires by Ion Implantation
Das Kanungo, P.; Kögler, R.; Zhakarov, N.; Werner, P.; Scholz, R.; Skorupa, W.;
Ion implantation can be a very useful technique to dope silicon nanowires heavily to improve their electrical properties. However, heavy implantation can amorphize the nanowires completely. Subsequently, a complete recovery of their crystallinity, which is of utmost importance to ensure their improved electrical properties, becomes nontrivial. We have performed a controlled study of nanowire recrystallization using vertical Si < 111 > nanowires that were amorphized during doping by arsenic ion implantation. Upon a single-step thermal anneal by furnace (500-650 degrees C) or by rapid thermal annealing (800-1200 degrees C), the nanowires turned partly single-crystalline from the bottom and partly polycrystalline from the top, owing to a competition between solid phase epitaxial regrowth from the substrate and random nucleation and growth, probably originating from the free surface. A complete recrystallization of the amorphized nanowires was achieved only after the furnace-annealed nanowires were annealed for a second time at a higher temperature (950-1200 degrees C). The polycrystalline grains formed during the first anneal were successfully aligned to the < 111 > direction, leading to a recovery of the single-crystalline structure of the nanowires.
Keywords: Si-Nanowires, Recristallization, Thermal Annealing

Publ.-Id: 15920 - Permalink


Identification of the main contributions to the conductivity of epitaxial InN
Komissarova, T. A.; Jmerik, V. N.; Ivanov, S. V.; Drachenko, O.; Wang, X.; Yoshikawa, A.;
Complex effect of different contributions (spontaneously formed In nanoparticles, near-interface, surface, and bulk layers) on electrophysical properties of InN epitaxial films is studied. Transport parameters of the surface layer are determined from the Shubnikov-de Haas oscillations measured in undoped and Mg-doped InN films at magnetic fields up to 63 T. It is shown that the In nanoparticles, near-interface, and bulk layers play the dominant role in the electrical conductivity of InN, while influence of the surface layer is pronounced only in the compensated low-mobility InN:Mg films.
Keywords: InN, Shubnikov-de Haas, magneto-transport

Publ.-Id: 15919 - Permalink


Tunable narrowband THz pulse generation in scalable large area photoconductive antennas
Krause, J.; Wagner, M.; Winnerl, S.; Helm, M.; Stehr, D.;
The generation and characterization of narrowband THz pulses by means of chirped pulse difference frequency generation in Auston-switch type photoconductive antennas is reported. Using optical pulses with energies in the range from 1 nJ to 1µJ, we generate THz pulses with up to 50 pJ in energy and electric field strengths on the order of 1 kV/cm. Two emitter concepts are investigated and circumvention of the fast saturation for small area excitation by scaling of the THz emitter is demonstrated.
Keywords: Terahertz, ultrafast
  • Open Access LogoOptics Express 19(2011)20, 19114

Publ.-Id: 15918 - Permalink


Effect of leukotriene inhibitors on evolution of experimental brain contusions
Voigt, C. L. M.; Donat, C. K.; Härtig, W.; Förschler, A.; Arendt, T.; Meixensberger, J.; Schuhmann, M. U.;
Aims: Leukotriene levels increase in cerebrospinal fluid following controlled cortical impact (CCI) injury in rats. We investigated the impact of leukotrienes on contusion size by the effect of two different leukotriene inhibitors in the CCI model.

Methods: 92 male Sprague-Dawley rats were investigated at 24h and 72h after CCI with MRI (n= 40) and immunohistochemistry (n=52). Animals received vehicle or either MK886, an inhibitor of 5-lipoxygenase activating protein, or Boscari, a mixture of boswellic acids, acting as competitive non-redox 5-lipoxygenase inhibitors prior to trauma and then every 8 hours until sacrifice.

Results: Global ICP was within normal limits and unaffected by treatment. T2 weighted MRI showed a reduction of lesion volume in treatment groups at 72h by -21% (p<0.01), which was reflected in a smaller lesion area determined from a NeuN labelled section (-17% to -20%, p<0.05). Qualitative characterization by triple immunofluorescence and Fluorojade B staining showed progressive rarefaction of neurons, glia and vasculature in the contusion core, whereas in the pericontusional zone astro- and microglia were up-regulated in the presence of dying neurons. Treatment resulted in an improved survival of NeuN labelled neurons in the pericontusional cortex (+15% to +20%, p<0.05).

Conclusions: Two differently acting leukotriene inhibitors lead to an attenuation of lesion growth and improved pericontusional neuronal survival following CCI. Therefore, leukotrienes seem to be involved in brain contusion growth and pericontusional secondary injury. Leukotriene inhibition should be further investigated as therapeutic option to counteract secondary growth of traumatic brain contusions and to possibly improve pericontusional neuronal survival.

Publ.-Id: 15917 - Permalink


“yl”-Oxygen Exchange in Uranyl(VI) Ion: A Mechanism Involving (UO2)2(μ-OH)22+ via U-Oyl-U Bridge Formation
Tsushima, S.;
Szabó and Grenthe (Inorg. Chem. 2007, 46, 9372-9378) suggested from NMR spectroscopy that the “yl”-oxygen exchange in dioxo uranium(VI) ion in acidic solution occurs via an OH-bridged binuclear complex (UO2)2(μ-OH)22+. Here, an “yl”-oxygen exchange pathway involving the (UO2)2(μ-OH)22+ is studied by B3LYP density functional theory calculations. The oxygen exchange takes place via an intramolecular proton shuttle between the oxygen atoms in (UO2)2(μ-OH)2(H2O)62+. The direct proton transfer from the hydroxo bridge or from the coordinating water to the “yl”-oxygen in (UO2)2(μ-OH)2(H2O)62+ appears to be negligible because of an exceedingly high activation barrier (~ 170 kJ mol-1). The exchange mechanism in (UO2)2(μ-OH)2(H2O)62+ can be described by a multi-step pathway that leads to the formation of an oxo bridge between two uranyl(VI) centers (U-Oyl-U bridge). The activation enthalpy ΔH of the reaction obtained at the B3LYP level is 94.7 kJ mol-1 and is somewhat larger than the experimental value of 80 ± 14 kJ mol-1. However, the discrepancy between theory and experiment is at the acceptable level. The formation of an oxo bridge between the two uranyl(VI) centers was found to be the key step in proton shuttling, indicating that uranyl(VI) complexes with a stable oxo bridge (such as trinuclear (UO2)33-O)(OH)3+) may have even faster “yl”-oxygen exchange rates than (UO2)2(μ-OH)22+.

Publ.-Id: 15916 - Permalink


Determination of the 60Fe Half-Life – a successful Collaboration in ERAWAST
Rugel, G.;
The radionuclide 60Fe is an important nuclide in nuclear astrophysics. Its half-life has been determined with a sample from a copper beam dump at PSI. After characterization of the beam dump and an intense chemical preparation the final sample material was measured to determine the half-life. This was done with an activity measurement in Munich and a number of 60Fe atoms measurement at PSI. This results in a half-life of (2.62 +/- 0.04) Myr [1].
Some of the important aspects of the work will be reported.
References
[1] G. Rugel, T. Faestermann, K. Knie, G. Korschinek, M. Poutivtsev, D. Schumann, N. Kivel, I. Günther-Leopold, R. Weinreich, M. Wohlmuther, Phys. Rev.Lett. 103, 072502.
Keywords: accelerator mass spectrometry, half-life, astrophysics
  • Lecture (Conference)
    2nd Workshop on Exotic Radionuclides from Accelerator Waste for Science and Technology (ERAWAST II), 29.08.-02.09.2011, Villigen, Schweiz

Publ.-Id: 15915 - Permalink


Determination of uranium(VI) sorbed species in calcium silicate hydrate phases: A laser-induced luminescence spectroscopy and batch sorption study
Tits, J.; Geipel, G.; Mace, N.; Eilzer, M.; Wieland, E.;
Batch sorption experiments and time-resolved luminescence spectroscopy investigations were carried out to study the U(VI) speciation in calcium silicate hydrates for varying chemical conditions representing both fresh and altered cementitious environments. U(VI) uptake was found to be fast and sorption distribution ratios (R-d values) were very high indicating strong uptake by the C-S-H phases. In addition a strong dependence of pH and solid composition (Ca:Si mol ratio) was observed. U(VI) luminescence spectroscopy investigations showed that the U(VI) solid speciation continuously changed over a period up to 6 months in contrast to the fast sorption kinetics observed in the batch sorption studies. Decay profile analysis combined with factor analysis of series of spectra of U(VI) - C-S-H suspensions, recorded with increasing delay times, revealed the presence of four luminescent U(VI) species in C S H suspensions, in agreement with the batch sorption data. Along with the aqueous UO2(OH)(4)(2-) species and a Cauranate precipitate, two different sorbed species were identified which are either bound to silanol groups on the surface or incorporated in the interlayer of the C-S-H structure.
Keywords: uranium, sorption, luminescence

Publ.-Id: 15914 - Permalink


Long-range superexchange in Cu2A2O7 (A = P, As, V) as a key element of the microscopic magnetic model
Janson, O.; Tsirlin, A.; Sichelschmidt, J.; Skourski, Y.; Weickert, F.; Rosner, H.;
A microscopic magnetic model for alpha-Cu2P2O7 is evaluated in a combined theoretical and experimental study. Despite a dominant intradimer coupling J1, sizable interdimer couplings enforce long-range magnetic ordering at TN = 27 K. The spin model for a-Cu2P2O7 is compared to the models of the isostructural beta-Cu2V2O7 and alpha-Cu2As2O7 systems. As a surprise, coupled dimers in a-Cu2P2O7 and alternating chains in alpha-Cu2As2O7 contrast with a honeycomb lattice in beta-Cu2V2O7. We find that the qualitative difference in the coupling regime of these isostructural compounds is governed by the nature of AO4 side groups: d elements (A = V) hybridize with nearby O atoms forming a Cu-O-A-O-Cu superexchange path, while for p elements (A = P, As) the superexchange is realized via O-O edges of the tetrahedron. Implications for a broad range of systems are discussed.
  • Physical Review B 83(2011), 10.1103/PhysRevB.83.094435

Publ.-Id: 15913 - Permalink


EPR study of the two-dimensional quantum magnet Cu(en)(H2O)2SO4
Tarasenko, R.; Orendácová, A.; Cizmár, E.; Orendác, M.; Zvyagin, S.; Wosnitza, J.;
Electron paramagnetic resonance (EPR) spectra of Cu(en)(H2O)2SO4 (en = ethylendiamine) single crystals were measured in the X-band range at temperatures 4 K and 300 K in magnetic fields up to 0.5 T. The angular dependence of the g-factor and EPR linewidths were studied. The analysis of the g-factor confirmed, that coordinating ligands around the Cu(II) ion form a distorted octahedron elongated along the local z axis and the distortion is maintained down to low temperatures. The increase of the linewidth observed at low temperatures can be ascribed to the onset of short-range magnetic correlations previously observed in specic heat studies. The reduction of the period in the angular dependence of the linewidth observed at 4 K cannot be explained by the existence of two crystallographic non-equivalent Cu(II) positions. The analysis of the angular dependence of the linewidth suggests the potential occurence of Dzyaloshinski-Moriya interaction and anisotropic exchange coupling in CUEN.
  • Poster
    The European Conference Physics of Magnetism 2011 (PM´11), 27.06.-01.07.2011, Poznan, Poland

Publ.-Id: 15912 - Permalink


Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field
Zvyagin, S. A.; Ozerov, M.; Wosnitza, J.; Čižmár, E.; Feyerherm, R.; Manmana, S. R.; Mila, F.;
Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous fascinating phenomena in materials with cooperative ground states, in particular, induced by high magnetic fields. The way a magnetic field changes the ground-state properties and, correspondingly, the low-energy excitation spectrum of low-dimensional magnets is one of the fundamental aspects in quantum magnetism. Here, magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of pulsed-field electron spin resonance spectroscopy in fields up to 63 T. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field
  • Invited lecture (Conferences)
    German Estonian Workshop, 13.-15.06.2011, Cottbus, Deutschland

Publ.-Id: 15911 - Permalink


Thermal expansion and magnetostriction of GdAg2, and relations to the magnetoelastic paradox
Mehboob, N.; Rotter, M.; Doerr, M.; Royanian, E.; Müller, H.; Grytsiv, A.; Skourski, Y.;
The antiferromagnet GdAg2 has been shown to be a good model system for the magnetoelastic paradox (MEP), because it exhibits large symmetry conserving magnetoelastic strains and the antiferromagnetic propagation vector breaks the tetragonal lattice symmetry (therefore a large symmetry breaking magnetoelastic strain can be expected in a single q magnetic structure). As in many similar Gd based compounds no symmetry breaking strain has been found in the experiment. In order to investigate this MEP further, we have measured magnetostriction and magnetization on a textured polycrystal. The behaviour closely resembles that of GdNi2B2C, the prototype system for the magnetoelastic paradox (MEP). Our forced magnetostriction data indicate that the crystal distorts in applied magnetic field and gives further evidence that the MEP is a low field effect. The observed phase transitions are in agreement with available specific heat and neutron diffraction data. Moreover, the saturation magnetic field was measured in high pulsed magnetic fields and agrees well with the value calculated from the Standard Model of Rare Earth Magnetism (SMREM).

Publ.-Id: 15910 - Permalink


Safety Monitoring of Components and Materials of Nuclear Power Plants
Gokhman, A. R.; Bergner, F.;
Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 1.5 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. For both alloys a saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC for the doses above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. CD modeling of Cr precipitates has been done with taking into account of deviation of this system from the ideal cluster gas. A specific surface tension of about 0.17 J/m2 between the alpha matrix and the Cr-rich alpha' precipitate and the rate at which Cr monomers are absorbed about 7.94 m-1 were found as best fit values for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS. Taking into account the formation and migration of Fe-Cr interstitial as additional link between the CD master equations for the self-defects and the CD master equations for the Cr precipitates, may lead to improve CD results for irradiated Fe-9at%Cr alloy. The assumption on the constant composition of Fe-Cr precipitates under neutron irradiation has been checked by means of new master equation of CD respect of the distribution function of clusters not only on size but also on composition. The slight dependence of the composition on the size of Fe-Cr precipitates is found.
  • Invited lecture (Conferences)
    NATO Advanced Research Workshop “Nanodevices and Nanomaterials for Ecological Security”, 20.-23.06.2011, Riga-Jurmala, Latvia

Publ.-Id: 15909 - Permalink


Transport studies at the Mott transition of the two-dimensional organic metal κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1−x
Yasin, S.; Dumm, M.; Salameh, B.; Batail, P.; Mézière, C.; Dressel, M.;
The two-dimensional organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1−x undergoes a transition from an insulator to a superconductor upon substituting Cl by Br. We have performed in and out-of-plane electric-transport measurements on the alloyed series with x = 20%, 40%, 70%, 80%, 85%, and 90% as a function of temperature in order to explore the bandwidth-controlled phase transition between the Mott insulator and the Fermi-liquid. All crystals exhibit a similar semiconducting behavior of ρ(T) from room temperature down to 100 K. Below approximately 50 K, a metal-to-insulator transition is found for compounds with x < 70%. Out of this Mott insulating state, magnetic order develops below TN ≈ 25 K. The Br-rich samples cross a bad-metal regime before they become coherent metals and eventually superconducting at Tc ≈ 12 K. For these systems the resistivity at Tc ≤ T ≤ T0 reveals a ρ(T) ∝ T2 dependence associated with a strongly correlated Fermi-liquid, limited by some characteristic temperature T0. The conclusions are corroborated by data from microwave, magnetic and optical experiments.
  • European Physical Journal B 79(2011), 383-390

Publ.-Id: 15908 - Permalink


Interplay of spin and lattice degrees of freedom in the frustrated antiferromagnet CdCr2O4: High-field and temperature-induced anomalies of the elastic constants
Bhattacharjee, S.; Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Moessner, R.; Zhitomirsky, M. E.; Lemmens, P.; Tsurkan, V.; Loidl, A.;
Temperature and magnetic field studies of the elastic constants of the chromium spinel CdCr2O4 show pronounced anomalies related to strong spin-phonon coupling in this frustrated antiferromagnet. A detailed comparison of the longitudinal acoustic mode propagating along the [111] direction with a theory based on an exchange-striction mechanism leads to an estimate of the strength of the magnetoelastic interaction. The derived spin-phonon coupling constant is in good agreement with previous determinations based on infrared absorption. Further insight is gained from intermediate and high magnetic field experiments in the field regime of the magnetization plateau. The role of the antisymmetric Dzyaloshinskii-Moriya interaction is discussed.
  • Physical Review B 83(2011), 184421

Publ.-Id: 15907 - Permalink


Magnetic and magnetoelastic anomalies of an Er2Co17 single crystal in high magnetic fields
Andreev, A. V.; Skourski, Y.; Kuzmin, M. D.; Yasin, S.; Zherlitsyn, S.; Daou, R.; Wosnitza, J.; Iwasa, A.; Kondo, A.; Matsuo, A.; Kindo, K.;
A high-field study of magnetization (up to 68 T) and magnetoelastic properties (up to 60 T) of Er2Co17 is reported. The most significant effect, a first-order transition from the collinear ferrimagnetic to a canted state, is observed at about 40 T with H || [001]. The transition is accompanied by a prominent magnetization jump as well as by step-wise anomalies of the magnetoelastic properties. Thus, the volume of the crystal reduces by about 4 per mil, while the speed of transverse sound in the [001] direction increases by as much as 5 per mil. At higher temperatures the anomalies gradually become smaller and less sharp before they finally disappear at ∼50 K. The anisotropy constants of the Er sublattice and the molecular field thereon have been determined from the magnetization curves.
  • Physical Review B 83(2011), 184422

Publ.-Id: 15906 - Permalink


NMR signal averaging in 62 T pulsed fields
Meier, B.; Greiser, S.; Haase, J.; Herrmannsdörfer, T.; Wolff-Fabris, F.; Wosnitza, J.;
Nuclear Magnetic Resonance (NMR) experiments in pulsed high magnetic fields up to 62 Tat the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden) are reported. The time dependence of the magnetic field is investigated by observing various free induction decays (FIDs) in the vicinity of the maximum of the field pulse. By analyzing each FID's phase and its evolution with time the magnetic field's time dependence can be determined with high precision. Assuming a quadratic or cubic dependence on time near the field maximum its confidence is found to be better than +/- 0.03 ppm at low fields and +/- 0.8 ppm near 62 T. In turn, the thus obtained time dependence of the field can be used to demodulate and phase-correct all FIDs so that they appear phase-locked to each other. As a consequence signal averaging is possible. The increase in signal-to-noise ratio is found to be close to that expected theoretically. This shows that the intrinsic time dependence of the pulsed fields can be removed so that the NMR signals appear to be taken at rather stable static field. This opens up the possibility of performing precise shift measurements and signal averaging also of unknown, weak signals if a reference signal is measured during the same field pulse with a double-resonance probe.
  • Journal of Magnetic Resonance 210(2011), 1-6

Publ.-Id: 15905 - Permalink


Recent ultrasound results obtained in pulsed magnetic fields
Nemoto, Y.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    User Meeting und Midterm Review EuroMagNET II, 22.-24.06.2011, Toulouse, Frankreich

Publ.-Id: 15904 - Permalink


High-field ESR in low-dimensional spin systems
Zvyagin, S.;
Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous fascinating phenomena in materials with cooperative ground states, in particular, induced by high magnetic fields. In this presentation I will focus on high-frequency and high-field Electron Spin Resonance (ESR) studies of copper pyrimidine dinitrate (Cu-PM), a spin-1/2 Heisenberg antiferromagnetic chain system with alternating g-tensor and Dzyaloshinskii-Moriya interactions in magnetic fields up to 63 T. Due to the alternations, this material exhibits a field-induced gap, observed by us directly. Signatures of three breather branches and a soliton are identified in magnetic fields up to 25 T. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum field sine-Gordon theory. We report also on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field.
  • Invited lecture (Conferences)
    International Conference "Resonances in Condensed Matter", 21.-25.06.2011, Kazan, Russia

Publ.-Id: 15903 - Permalink


Coexistence of ferromagnetism and superconductivity in single-phase Bi3Ni nanostructures
Herrmannsdörfer, T.; Skrotzki, R.; Wosnitza, J.; Köhler, D.; Boldt, R.; Ruck, M.;
Superconductivity and magnetic order, two fundamental ground states of condensed matter, are observed to be competitive in many materials. In the case of predominantly ferromagnetic exchange interactions, superconductivity is suppressed in almost any representative. The quantity of materials, however, in which a coexistence of superconductivity and ferromagnetism might be studied, could be larger than ever thought.
Here we demonstrate the coexistence of superconductivity and ferromagnetism in Bi3Ni nanostructures which have been prepared by making use of novel chemical-reaction paths. We have characterized their magnetic and superconducting properties by means of magnetometry and electrical-transport measurements. Other than in bulk geometry, submicron-sized particles and quasi one-dimensional nanoscaled strains of single-phase Bi3Ni undergo ferromagnetic order [1]. Superconductivity in confined Bi3Ni emerges in the ferromagnetically ordered phase and is stable up to remarkably high magnetic fields. Uniquely, ferromagnetic hysteresis at zero resistance is observed in nanostructured Bi3Ni. As a result, a magnetic hysteresis loop occurs while the material is in the superconducting state.
The coexistence of superconductivity with ferromagnetic order would most likely be possible in the case of triplet pairing. The absence of an inversion center of the lattice of confined Bi3Ni would allow for the formation of an antisymmetric spatial component of the electron-wave function and could lead to a significant admixture of a spin-triplet component of the order parameter. However, as the lattice of bulk Bi3Ni is centrosymmetric, the question remains as to whether the loss of structural long-range order at the surface of confined nanostructures could induce antisymmetry of the charge carrier wave function. Nuclear magnetic resonance experiments in high magnetic fields* may now open a chance to get deeper insight in the symmetry of the superconducting wave function in k space.
  • Invited lecture (Conferences)
    International Conference "Resonances in Condensed Matter", 21.-25.06.2011, Kazan, Russia

Publ.-Id: 15902 - Permalink


NMR Signal Averaging in Pulsed Fields
Meier, B.;
The first Nuclear Magnetic Resonance (NMR) experiments at the Helmholtz-Zentrum Dresden-Rossendorf in pulsed high magnetic fields that peak at maximum flux-density up to 62 Tesla are described. The temporal properties of the magnetic field B(t) in the vicinity of the field maximum are characterized using 1H and 2H NMR single-pulse excitation. The error in B(t) is smaller than 0.1 ppm, which allows making precise predictions concerning the initial and time evolution of the NMR signal’s phase near the field maximum. We demonstrate that the various free induction decays that are excited near a single field pulse maximum, e.g., during 25 milliseconds, can be demodulated from the intrinsic time dependence and corrected for the initial phase making signal-averaging possible in pulsed fields.
  • Invited lecture (Conferences)
    User Meeting and Midterm Review EuroMagNET II, 22.-24.06.2011, Toulouse, Frankreich

Publ.-Id: 15901 - Permalink


Annual Online Report 2009
Bartho, A.;
Internet-Jahresbericht 2009 des FZD
Keywords: Annual Online Report 2009 of the FZD
  • Communication & Media Relations
    Internet-Jahresbericht 31.05.2010

Publ.-Id: 15900 - Permalink


AER Working Group D on VVER Safety Analysis – Report of the 2011 Meeting
Kliem, S.;
The AER Working Group D on VVER reactor safety analysis held its 20th meeting in Stockholm, Sweden, during the period 12-13 April, 2011. The meeting was hosted by the Royal Institute of Technology (KTH) and was held in conjunction with the third workshop on the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and the fifth workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 18 participants attended the meeting of the working group D, 12 from AER member organizations and 6 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.

The meeting started with a general information exchange about the recent activities in the participating organizations.

The given presentations and the discussions can be attributed to the following topics:

• Code validation and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
• Thermal hydraulic analyses
• Safety analyses and code developments
• Future activities

A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files can be obtained from the chairman.
  • Contribution to proceedings
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany
    Proceedings of the 21st AER Symposium, Budapest: MTA KFKI, 9789633726464, 417-423
  • Lecture (Conference)
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany

Publ.-Id: 15899 - Permalink


Viscosities of the quasigluon plasma
Bluhm, M.; Kämpfer, B.; Redlich, K.;
We investigate bulk and shear viscosities of the gluon plasma within relaxation time approximation to an effective Boltzmann-Vlasov type kinetic theory by viewing the plasma as describable in terms of quasigluon excitations with temperature dependent self-energies. The found temperature dependence of the transport coefficients agrees fairly well with available lattice QCD results. The impact of some details in the quasigluon dispersion relation on the specific shear viscosity is discussed.

Publ.-Id: 15898 - Permalink


Benzenedithiol: A Broad-Range Single-Channel Molecular Conductor
Kim, Y.; Pietsch, T.; Erbe, A.; Belzig, W.; Scheer, E.;
More than a decade after the first report of singlemolecule conductance, it remains a challenging goal to prove the exact nature of the transport through single molecules, including the number of transport channels and the origin of these channels from a molecular orbital point of view. We demonstrate for the archetypical organic molecule, benzenedithiol (BDT), incorporated into a mechanically controllable break junction at low temperature, how this information can be deduced from studies of the elastic and inelastic current contributions. We are able to tune the molecular conformation and thus the transport properties by displacing the nanogap electrodes. We observe stable contacts with low conductance in the order of 10E-3 conductance quanta as well as with high conductance values above ∼0.5 quanta. Our observations show unambiguously that the conductance of BDT is carried by a single transport channel provided by the same molecular level, which is coupled to the metallic electrodes, through the whole conductance range. This makes BDT particularly interesting for applications as a broad range coherent molecular conductor with tunable conductance.
Keywords: Single molecule, break junction, inelastic electron tunneling spectroscopy, benzenedithiol, single-level model

Publ.-Id: 15897 - Permalink


Proceedings 6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and the 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS)
Steinhauser, G.; Merchel, S.; Knappik, R.; (Editors)
kein Abstract, Editoren von Proceedings
  • Contribution to proceedings
    Proceedings 6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and the 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS), 06.-09.09.2011, Dresden, Deutschland
    6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS)

Publ.-Id: 15896 - Permalink


Photoneutron Cross Sections for Au Revisited: Measurements with Laser Compton Scattering gamma-Rays and Data Reduction by a Least-Squares Method
Itoh, O.; Utsunomiya, H.; Akimune, H.; Kondo, T.; Kamata, M.; Yamagata, T.; Toyokawa, H.; Harada, H.; Kitatani, F.; Goko, S.; Nair, C.; Lui, Y.;
Photoneutron cross section measurements were made for Au in the entire energy range of the (gamma,n) channel based on a direct neutron counting with quasi-monochromatic gamma-rays produced in inverse Compton scattering of laser photons with relativistic electrons. The data were analyzed by a least-squares method to deduce photoneutron cross sections. The analysis significantly reduced experimental uncertainties compared with those resulting from the photon difference method. The result is compared with the previous data by direct neutron counting with gamma-rays produced in positron annihilation in flight and by photoactivation with bremsstrahlung. The present data are in good agreement with the previous data near the neutron threshold, while there remain some discrepancies between the present and the previous data above 10 MeV
  • Journal of Nuclear Science and Technology 48(2011)5, 834-840

Publ.-Id: 15895 - Permalink


Editorial Nuclear analytical methods: We've got the hammer for your nail
Steinhauser, G.; Merchel, S.; Knappik, R.;
From 6 to 9 September 2010, the 6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and the 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS) were jointly held in Dresden Rossendorf (Germany). In fact, we observe that not only the conferences grow together but also our research fields constantly expand to other areas and seek collaboration in topics that are all but traditionally “nuclear”. The spectrum of the presentations ranged from classical archaeometry to tests on cable fires in power plants. From provenance studies of traffic-related particulate matter to nutritional studies on trace elements in honey. From activation studies for the decommissioning of nuclear facilities to the application of mobile neutron sources for future moon explorations. The remarkable variety of different topics is the best evidence for the universal applicability of nuclear techniques, notably nuclear analytical techniques. With numerous non-nuclear analytical methods being ubiquitously available, we feel that the analytical community sometimes seems to oversee the advantages nuclear techniques (such as activation or ion beam analysis) may offer for their specific problems. We are sure that in many cases, a nuclear technique can be the method of choice for certain analytical challenges.

Thus, we are looking forward to keep on the tradition of these nuclear-based workshops and seminars. The 7th RCA will be held again at Dresden-Rossendorf, whereas the 24th SAAGAS will probably move on to the Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II) at Munich. We are looking forward to these events with keen anticipation and wish the organisers all the best. We hope the upcoming seminars will be as successful as the joint SAAGAS & RCA – event in 2010 with 30 oral presentations – including two invited contributions by Rolf Michel (University of Hanover, Germany) and Sönke Szidat (University of Berne, Switzerland) and one evening lecture for the public by Max Bichler (Atominstitut Vienna, Austria)—and 17 posters!

This special issue in Applied Radiation and Isotopes contains seven selected contributions from RCA-SAAGAS. We thank our sponsors and co-organisers (AMETEK/ORTEC, AREVA, CANBERRA, Dr. Westmaier GmbH, Fachverband für Strahlenschutz, Gesellschaft Deutscher Chemiker, Landeshauptstadt Dresden, Kerntechnische Gesellschaft, Wirtschaftsverband Kernbrennstoff Kreislauf) for their support of RCA-SAAGAS and especially for supporting this issue. The hard work of numerous reviewers is highly appreciated: Thanks to all of you. We finally thank Elsevier for providing a forum for our cumulative contributions. We are sure that this issue will be highly visible in the analytical community. Besides, we hope it will stimulate further collaborations between nuclear and non-nuclear sciences.

In conclusion we are proud to say: We are the Nuclear Analytical Methods: We may have gotten the hammer for your nail! So do not hesitate to contact us.
Keywords: activation analysis, nuclear

Publ.-Id: 15894 - Permalink


FZD Journal 05: Meilensteine - Forschen für die Welt von morgen
Bohnet, C.; Bartho, A.; Hampel, U.; Knauer, R.; Bradbury, M. H.; Schuster, N.; Urban-Eicheler, B.; Gebel, S.;
Das Journal des Forschungszentrums Dresden-Rossendorf
  • Communication & Media Relations
    Journal 31.03.2010
    23 Seiten

Publ.-Id: 15893 - Permalink


Internet-Jahresbericht 2009
Bartho, A.;
Jahresbericht 2009 des FZD
  • Communication & Media Relations
    Jahresbericht 31.03.2010

Publ.-Id: 15892 - Permalink


Annual Report Highlights 2010
Bartho, A.; Bohnet, C.; Bilow, U.;
Annual Report of the HZDR 2010
  • Communication & Media Relations
    Annual Report 31.05.2011

Downloads:

Publ.-Id: 15891 - Permalink


Jahresbericht Highlights 2010
Bartho, A.; Bohnet, C.; Bilow, U.;
Jahresbericht des HZDR 2010
  • Communication & Media Relations
    Jahresbericht 30.04.2011
    27 Seiten

Publ.-Id: 15890 - Permalink


Insider 1/2011
Bartho, A.;
Mitarbeiterzeitung des HZDR
  • Communication & Media Relations
    Mitarbeiterzeitung 31.01.2011
    4 Seiten

Publ.-Id: 15889 - Permalink


Standortplan
Bohnet, C.;
Standortplan des HZDR
Keywords: Site Plan of the HZDR
  • Communication & Media Relations
    Standortplan 31.01.2011

Publ.-Id: 15888 - Permalink


Forschen für die Welt von morgen
Bohnet, C.;
Imageflyer des HZDR
  • Communication & Media Relations
    Imageflyer 30.06.2011
    23 Seiten

Publ.-Id: 15887 - Permalink


Research for the World of Tomorrow
Bohnet, C.;
Imageflyer des HZDR
Keywords: Image Flyer of the HZDR
  • Communication & Media Relations
    Imageflyer 31.07.2011
    23 Seiten

Publ.-Id: 15886 - Permalink


FZD intern 56
Bartho, A.; Bohnet, C.;
Mitarbeiterzeitung des FZD
  • Communication & Media Relations
    Mitarbeiterzeitung 30.06.2010
    12 Seiten

Publ.-Id: 15885 - Permalink


FZD intern 55
Bartho, A.; Bohnet, C.;
Mitarbeiterzeitung des FZD
  • Communication & Media Relations
    Mitarbeiterzeitung 31.03.2010
    12 Seiten

Publ.-Id: 15884 - Permalink


Diffusion, degradation or on-site stabilisation – identifying causes of kinetic processes involved in metal-humate complexation
Lippold, H.; Eidner, S.; Kumke, M. U.; Lippmann-Pipke, J.;
The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal-humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites.
In this work, we focused on the competition effect of aluminium(III) on complexation of terbium(III) or europium(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. While the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived “diffusion theory” turned out to be inapplicable, since it cannot explain an increase in competition for the “initial” sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.
Keywords: Aluminium; Competition; Complexation; Humic substances; Kinetics; Lanthanides

Publ.-Id: 15883 - Permalink


FZD intern 58
Bartho, A.; Bohnet, C.;
Mitarbeiterzeitung des FZD
  • Communication & Media Relations
    Mitarbeiterzeitung 31.12.2010
    10 Seiten

Publ.-Id: 15882 - Permalink


Insider 2/2011
Bartho, A.;
Mitarbeiterzeitung des HZDR
  • Communication & Media Relations
    Mitarbeiterzeitung 30.06.2011
    10 Seiten

Publ.-Id: 15881 - Permalink


Struktur-Affinitäts-Studien zu VAChT-Liganden: Synthese und In-Vitro-Bindung neuer Vesamicolanaloga
Barthel, C.; Wenzel, B.; Sorger, D.; Schweiger, S.; Deuther-Conrad, W.; Jäckel, P.; Sabri, O.; Schüürmann, G.; Brust, P.; Steinbach, J.;
Ziel:
Ein wichtiges neuropathologisches Merkmal der Alzheimer Demenz ist die Degeneration cholinerger Nervenzellen. Als Bestandteil des cholinergen Transmittersystems wird der vesikuläre Acetylcholintransporter (VAChT) als mögliches Target zur bildgebenden Darstellung cholinerger Funktionsveränderungen im Hirn angesehen. Vesamicol (2-(4-Phenylpiperidin-1-yl)cyclohexanol) ist ein hoch-affiner, nicht-kompetitiver Inhibitor für den VAChT. Obwohl diese Verbindung auf Grund der vorhandenen Affinität zu Sigma-Rezeptoren (σ1/σ2) eine geringe Selektivität aufweist, dient sie als Leitstruktur bei der Entwicklung von PET-Radioliganden für den VAChT. Es ist bisher keine andere Verbindung bekannt, die mit annähernd hoher Affinität an den VAChT bindet. Ziel dieser Struktur-Affinitäts-Studie ist es, eine Vielzahl systematisch strukturell modifizierter Vesamicolanaloga zu synthetisieren und die Affinität zum VAChT und zu Sigma-Rezeptoren zu bestimmen. Diese Daten bilden die Grundlage für die Entwicklung eines 3D-QSAR-Modells, das erstmals beide Targets einbeziehen wird und somit erlauben sollte, einen hochaffinen und selektiven VAChT-Liganden zu entwickeln.

Methoden:
Die Synthese der Analoga erfolgte ausgehend von geeigneten Epoxidvorläufern durch nukleophile Epoxidringöffnung mit strukturell verschiedenen Aminen. Durch den Einsatz von Lithiumsalzen konnte ein Teil der Synthesen regioselektiv gesteuert werden. Die Produkte der nicht-regioselektiven Synthesen wurden mit Hilfe präparativer HPLC getrennt. Die Identifizierung der Analoga erfolgte durch HPLC, NMR und MS. Die Bindungsaffinitäten (Ki-Werte) zum VAChT wurden mit Hilfe kompetitiver Bindungsassays an mit Ratten-VAChT-cDNA stabil transfizierten PC12-Zellen und (-)-[3H]Vesamicol als Radioligand bestimmt.

Ergebnisse:
Es wurden zunächst die drei Klassen der Vesamicole, F-Benzylethervesamicole und Aminobenzovesamicole synthetisiert und deren Affinität zum VAChT bestimmt. Die neuen Analoga weisen strukturelle Veränderungen mit sowohl sterischen als auch elektronischen Einflüssen in den Ringen A, B und C des Vesamicolgrundgerüstes auf. Modifikationen am Ring A wurden durch die Synthese unterschiedlicher Epoxidvorläufer ermöglicht. Der Einsatz strukturell verschiedener Amine zur nukleophilen Epoxidringöffnung führte zu Änderungen in den Ringen B und C. Die untersuchten drei Klassen von Vesamicolanaloga zeigten sehr unterschiedliche VAChT-Bindungsaffinitäten. Sie lagen im Bereich von Ki = 96,5 ± 19,3 nM bis Ki > 400 µM. Wie erwartet, wurden innerhalb der Klassen (Derivate unterscheiden sich in Ring B oder C) große Affinitätsunterschiede beobachtet. Allerdings wurden auch unerwartete Werte bei vergleichbaren Derivaten der drei Klassen (Unterschied in Ring A) beobachtet. Im Vergleich zum (-)-Vesamicol (Ki = 24,4 ± 4,4 nM) wiesen alle untersuchten Verbindungen eine geringere Affinität zum VAChT auf.

Schlussfolgerungen:
Bereits nach diesen ersten Ergebnissen hat sich deutlich gezeigt, dass Vorhersagen bezüglich der Affinität zum VAChT von Klasse zu Klasse nicht möglich sind und der Einfluss struktureller und elektronischer Änderungen am Vesamicolgrundgerüst tendenziell nicht vorausgesagt werden kann. Dies bestätigt die Notwendigkeit der geplanten quantitativen Struktur-Affinitäts-Studie, bei der die Daten systematisch strukturell modifizierter Verbindungen zu Grunde gelegt werden.
  • Lecture (Conference)
    19. Jahrestagung der Arbeitsgemeinschaft Radiochemie/Radiopharmazie der DGN, 15.-17.09.2011, Ochsenfurt, Deutschland

Publ.-Id: 15880 - Permalink


Interaction of humic acid with actinides: Influence of heteroatomic functional groups other than carboxylic groups
Sachs, S.; Schmeide, K.; Bernhard, G.;
The role of heteroatomic functional groups other than carboxylic groups on the interaction behavior of humic acids (HA) with actinides is widely unconsidered. Applying synthetic HA the influence of reduced sulfur functionalities on the U(VI) complexation and the Np(V) reduction by HA was studied. Reduced sulfur functionalities have been identified as complexing and redoxactive sites in HA.
Keywords: Humic acid; Uranium; Neptunium; Complexation; Reduction; Sulfur; Reduced sulfur; Humic acid model substances; Synthetic humic acid
  • Contribution to proceedings
    Workshop peat and humic substances: Current research in chemical, physical and biological characterization of peat, 28.-30.09.2011, Zittau, Germany
    Workshop Peat and Humic Substances Current research in chemical, physical and biological characterization of peat, Zittau: University of Applied Sciences Zittau/Görlitz, 978-3-941521-01-8, 17-20
  • Invited lecture (Conferences)
    Workshop peat and humic substances: Current research in chemical, physical and biological characterization of peat, 28.-30.09.2011, Zittau, Germany

Publ.-Id: 15879 - Permalink


Constitutive expression of hydrophobin HFB1 from Trichoderma reesei in Pichia pastoris and its pre-purification by foam separation during cultivation
Kottmeier, K.; Günther, T. J.; Weber, J.; Kurtz, S.; Ostermann, K.; Rödel, G.; Bley, T.;
Hydrophobins are small surface-active proteins that have considerable potential for use in applications ranging from medical and technical coatings, separation technologies, biosensors, and personal care. Their wider use would be facilitated by the availability of recombinant tailor-made hydrophobins. We successfully expressed the class II hydrophobin HFB1 from Trichoderma reesei in Pichia pastoris under the control of the constitutive GAP (glyceraldehyde 3-phosphate dehydrogenase) promoter. Avoiding the use of the AOX1 (alcohol oxidase 1) promoter prevents the costs and risks associated with the storage and delivery of methanol used as an inducer. Efficient secretion of hydrophobin was achieved using either the alpha-factor prepro-peptide or the native secretion signal of HFB1. The secreted hydrophobins have been isolated with a purity of up to 70% using in situ foam separation during the cultivation process. Coating experiments and surface pressure measurements demonstrated the activity of the hydrophobins. An immunodot assay showed the accessibility of carboxyterminally fused tags of the hydrophobin, which is necessary for potential applications using functionalized hydrophobins. The presented data show that Pichia pastoris is a suitable system for production of constitutively expressed and secreted active hydrophobin, allowing for in situ pre-purification using foam separation.
Keywords: Hydrophobin, HFB1, Pichia pastoris, heterologous expression, foam separation, surface active protein

Publ.-Id: 15878 - Permalink


Insider extra Juli 2011
Bohnet, C.;
Mitarbeiterzeitung des HZDR
  • Communication & Media Relations
    Mitarbeiterzeitung 15.07.2011
    2 Seiten

Publ.-Id: 15877 - Permalink


Terahertz nonlinear optics of intra-exciton transitions in quantum wells
Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Teich, M.; Andrews, A. M.; Schartner, S.; Strasser, G.; Helm, M.;
In our contribution we investigate nonlinear optics related to the hydrogen-like intraexciton 1s-2p heavy-hole (hh) transition in GaAs/AlGaAs quantum wells. Tuning intense terahertz (THz) light of the Dresden free-electron laser around this resonance we report (i) efficient sideband generation and (ii) clear evidence of the Autler-Townes effect.
Keywords: free-electron laser, sideband generation, Autler-Townes, AC Stark
  • Invited lecture (Conferences)
    EP2DS19/MSS15, 25.-29.07.2011, Tallahassee, USA

Publ.-Id: 15876 - Permalink


Coherent control of a THz-intersubband polarization in a quantum well
Wagner, M.; Helm, M.; Sherwin, M. S.; Stehr, D.;
Ultrashort terahertz pulses in the far-infrared spectral region centered around 2 terahertz are used to coherently control an intersubband polarization in a GaAs/AlGaAs quantum well structure at low temperature. While the first THz pulse excites a macroscopic polarization between the quantum well first and second subband, a second, temporally delayed, control pulse switches the polarization off or refreshes it depending on the relative time delay between the pulses. The switching is directly demonstrated in the time-domain for the few picosecond long free-induction decay of the induced polarization. Model calculations based on the optical Bloch equations agree well with the experimental data.
Keywords: terahertz, ultrafast, coherent control, intersubband polarization, free-induction decay
  • Poster
    EP2DS19/MSS15, 25.-29.07.2011, Tallahassee, USA

Publ.-Id: 15875 - Permalink


Microfocus infrared ellipsometry characterization of air-exposed graphene flakes
Weber, J. W.; Hinrichs, K.; Gensch, M.; van de Sanden, M. C. M.; Oates, T. W. H.;
Graphene and ultrathin graphite flakes prepared by exfoliation were characterized by microfocus synchrotron infrared mapping ellipsometry. The dielectric function of graphene in a dry-air atmosphere is determined and compared to that of ultrathin graphite, bulk graphite and gold. The imaginary part of graphene was revealed to be about an order of magnitude higher than that of graphite. Comparing the conductivity to an optical model considering intraband transitions we discuss the effects of environmental exposure, relevant for real-world applications.

Publ.-Id: 15874 - Permalink


NanoTrack - Untersuchung des Lebenszyklus von Nanopartikeln anhand von [45Ti]TiO2 und [105Ag]Ag0
Franke, K.; Hildebrand, H.; Mehnert, R.; Mai, E.; Freyer, A.; Bilz, E.; Isaacson, C.; Schirmer, K.; Ammann, A.; Sigg, L.;
Die Herstellung und Nutzung von nanopartikelhaltigen Polymersystemen hat in den letzten Jahren deutlich zugenommen. Während die Vorteile und gewünschten Eigenschaften von Nanokompositmaterialien vielfach gezeigt werden konnten (z.B. selbstreinigende, kratzfeste Oberflächen, antibakterielle Wirkung des Ag+ aus Ag0-NP), sind die erforderlichen Kenntnisse zur Risikobewertung der typischerweise in Lacksystemen und Beschichtungen eingebrachten Nanopartikel (z.B. TiO2, Ag0) bisher unzureichend. Für nanopartikuläres TiO2 und Ag0 bietet sich zur Technologiefolgeabschätzung der Einsatz von radioisotopischen Sonden an. Die Radiomarkierung von Nanopartikeln eröffnet eine hoch sensitive Nachweismöglichkeit und eignet sich für ein qualitatives und quantitatives Prozessmonitoring, z.B. hinsichtlich des Verhaltens von Nanopartikeln während Alterung und Verschleiß der Kompositmaterialien bis hin zu einer Abschätzung der Freisetzungsraten und des Transports der Nanopartikel in der Umwelt sowie Wechselwirkungen mit Organismen. Die modellhafte Erfassung relevanter Prozesse ermöglicht im Ergebnis Schlussfolgerungen für die Weiterentwicklung von Nanokompositmaterialien.
Im Verbundprojekt NanoTrack werden nanopartikelhaltige (TiO2, Ag0) Modelllacksysteme auf Acrylat-Basis hergestellt und einer beschleunigten Bewitterung ausgesetzt. Dabei konnte für ein Lacksystem mit nanoskaligem TiO2 (P 25, Evonik Industries, dp,TiO2 ≈ 21 nm, Maschinenauftrag mit einer Nassschichtdicke von 4 µm) nach ca. 500 h UV-A-Bestrahlung (Intensität ~ 15 mW/cm2) festgestellt werden, dass die organische Lackmatrix nahezu vollständig zerstört wurde und ein Nanopartikelaustrag somit erfolgen könnte. In Abbildung 1 ist der zeitliche Verlauf des Abbaus einer Polyacrylat-TiO2-Nanokomposit-Beschichtung durch UV-A-Bestrahlung dargestellt. Mittels Infrarot¬spektroskopie (FTIR-ATR) und thermogravimetrischen Messungen konnte dieses Ergebnis eindeutig bestätigt werden. Des Weiteren konnte gezeigt werden, dass die freigesetzten Partikel meist nicht als Primärpartikel, sondern mindestens als Verbünde von wenigen Teilchen, überwiegend jedoch als mikroskalige Aggregate vorliegen.
Modellrechnungen ergaben, dass die im Vergleich zur Schwerkraft sehr starke Dipol-Anziehung der polaren, nanoskaligen TiO2-Teilchen praktisch das Auftreten freier Primärpartikel verhindert.

Abbildung 1: Zeitlicher Verlauf des Abbaus einer Polyacrylat-TiO2-Nanokomposit-Beschichtung (TiO2 P 25, Evonik Industries); A) original, B) t = 2 d (50.000 fache Vergrößerung); C) t = 4 d, D) t = 8 d, E) t = 16 d (75.000 fache Vergrößerung); REM-Aufnahmen: IOM

Für den sensitiven Partikelnachweis werden radiomarkierte Nanopartikel des gleichen Typs (P 25, [44Ti]TiO2 bzw. [110mAg]Ag0) eingesetzt. Die authentische Markierung erfolgte mittels diffusiven Eintrags von Radionukliden in Nanopartikel. Dabei konnten radiochemische Ausbeuten von über 98 % erreicht werden. Die Stabilität der Radiomarkierung wurde in wässrigen Systemen in Abhängigkeit vom pH-Wert der Suspension und der Zeit untersucht. Dabei konnte gezeigt werden, dass die radioisotopischen Sonden physikalisch und chemisch stabil mit den Nanomaterialien verbunden sind und dem Chemismus der Partikel folgen (z.B. Lösungsgleichgewicht Ag0-NP ⇄ Ag+).
Die Radiomarkierung erlaubt auch den Nachweis von Nanopartikeln in komplexen Medien. Im Projekt werden die Wechselwirkungen der Partikel mit Geomatrizes und der Transport in durchströmten Systemen untersucht. Ein weiterer wichtiger Aspekt ist die Beurteilung der Ökotoxizität der freigesetzten Nanopartikel. Werden diese in Oberflächengewässer eingetragen, kann es zu Wechselwirkungen mit lebenden Organismen kommen. Biofilme werden als potenzielle Senke für technische Nanomaterialien beschrieben. Diese sind ein wichtiger Bestandteil von Ökosystemen und könnten dazu beitragen, dass Partikel über die Nahrungsaufnahme höherer Organismen (z.B. Daphnien) in Nahrungsketten eingetragen werden. Systematische Studien sollen zu detaillierten Erkenntnissen hinsichtlich der Mobilität und möglicher Risiken der eingesetzten TiO2 und Ag0-NP für die Umwelt führen.
Die ganzheitliche Betrachtung von Nanopartikeln in Lacksystemen und Beschichtungen hinsichtlich Produktion, Alterung und Verschleiß, Partikelfreisetzung und deren Verbleib in der Umwelt soll als Datengrundlage für eine Risikoabschätzung dienen und zur Validierung und ggf. Anpassung von Lackformulierungen beitragen.
  • Poster
    WING.DE 2011, 04.-06.10.2011, Berlin, Deutschland

Publ.-Id: 15873 - Permalink


Fast propagation of weakly pinned domain walls and current-assisted magnetization reversal in He+-irradiated Pt/Co/Pt nanotracks
Cormier, M.; Mougin, A.; Ferré, J.; Jamet, J.-P.; Weil, R.; Faßbender, J.ORC; Baltz, V.; Rodmacq, B.
No abstract available
  • Poster
    MORIS 2011, 22.06.2011, Nijmegen, The Netherlands

Publ.-Id: 15872 - Permalink


Radiolabeling of phosphatidylserine-binding peptides with prosthetic groups N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide ([18F]FBAM) and N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB)
Kapty, J.; Kniess, T.; Wuest, F.; Mercer, J. R.;
The widely used (18)F-prosthetic group N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB) and the recently developed N-[6-(4-[(18)F]fluorobenzylidene)aminooxyhexyl]maleimide ([(18)F]FBAM) were investigated for radiolabeling of two representative phosphatidylserine-binding peptides. The prosthetic groups were compared with respect to required reactions conditions for optimum labeling, radiolabeling yield and chemoselectivity. The N-terminus labeled product produced by reaction of [(18)F]SFB with binding peptide LIKKPF was produced in 18% radiochemical yield while no N-terminus labeled product could be isolated following [(18)F]SFB reaction with PDGLSR. When the peptides were modified by addition of a cysteine residue at the N-terminus they provided almost quantitative radiochemical yields with [(18)F]FBAM. Results indicate that for the peptides in this study, [(18)F]FBAM is a more useful prosthetic group compared to [(18)F]SFB due to its excellent chemoselectivity and high radiochemical yield.
Keywords: Apoptosis; Phosphatidylserine; PET; [18F]SFB; [18F]FBAM

Publ.-Id: 15871 - Permalink


Vorstellung des Instituts für Radiochemie zum Dies academicus
Steudtner, R.;
Vorstellung des IRC, Arbeitsgebiete des IRC, Präsentation möglicher Semesterarbeiten
  • Lecture (others)
    Dies academicus 2011, 08.06.2011, Zittau, Deutschland

Publ.-Id: 15868 - Permalink


Late Quaternary rock uplift rate at the northern margin of the Central Anatolian Plateau: inferences from pediment surfaces and multiple cosmogenic nuclides
Yildirim, C.; Schildgen, T. F.; Echtler, H. P.; Strecker, M. R.; Melnick, D.; Niedermann, S.; Merchel, S.; Martschini, M.; Steier, P.;
The northern margin of the Central Anatolian Plateau spans the northward arched part of the Pontide Mountains between the North Anatolian Fault to the south and the Black Sea to the north. Crustal deformation between the North Anatolian Fault and the Black Sea is integrally tied to the evolution of the Central Anatolian Plateau. The asymmetric topographic pattern, coupled with the spatial distribution and geometry of faults, suggest that the northern margin of the plateau has constituted an active accretionary orogenic wedge with northward polarity between the North Anatolian Fault and the abyssal plain of the Black Sea (Figure). To explore the mode and rate of rock uplift that is associated with internal deformation in the accretionary orogenic wedge, we dated incised and deformed pediments by measuring in situ produced 10Be, 21Ne and 36Cl concentrations.
The key target area for our analysis is the Kastamonu intramontane basin. We mapped a suite of six gravel-covered pediment surfaces in the basin that rise 175-180m (P1), 115-130 m (P2), 70-80 m (P3), 45-54 m (P4), 25-35 m (P5) and 12-22 m (P6) above the river. One set of samples was collected along the trunk stream of the Kastamonu basin to estimate trunk stream incision rates, and a second set of samples was collected from local surfaces that have been deformed and incised in response to faulting in the accreationary orogenic wedge.
The surfaces within the basin have exposure ages that range from about. (7.8±0.9) ka to (437 ±64) ka. The temporal distribution of the abandonment ages suggests that specific climatic conditions do not promote abandonment of pediment surfaces in the Kastamonu Basin. The abandonment ages and strath heights of the surfaces yield incision rates that range from 0.20 to 0.49 mm/yr along the trunk stream of the Kastamonu Basin. We used an average fluvial incision rate to calculate rock uplift rate, i.e., incision between the 70-80 m (P2) and 12-22 m (P6) pediments along the trunk stream of the Kastamonu Basin. This gives ~0.27 mm/yr of average vertical rock uplift rate between ca. 437 and 22 ka in the internal part of the Central Pontides.
The highest incision rates (1.04 to 3.16 mm/yr) in the basin are obtained from local surfaces deformed by faults along the basin margins. Topographic profiles across the local pediment surfaces show discernable warping in evidence of out of sequence faulting and partial accommodation of internal deformation in the orogenic wedge. We believe that out-of-sequence faulting and internal deformation indicate a subcritical state of the orogenic wedge at the northern margin of the Central Anatolian Plateau.
Keywords: dating, TCN, in-situ, cosmogenic radionuclides, AMS
  • Poster
    7th TOPO-EUROPE Workshop - A forum investigating the cause and creation of the topography of Europe, 06.-09.10.2011, Davos, Schweiz

Publ.-Id: 15867 - Permalink


Experimente zur Entstehung und Wirkung kosmischer Magnetfelder
Stefani, F.;
Seit langem ist bekannt, dass die Magnetfelder von Planeten, Sternen und Galaxien durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden, den sogenannten hydromagnetischen Dynamoeffekt, erzeugt werden. Weniger bekannt ist hingegen die bedeutende Rolle, die Magnetfelder bei der kosmischen Strukturbildung spielen. So sind die beobachteten hohen Wachstumsraten von Sternen und Schwarzen Löchern nur erklärbar, wenn die Akkretionsscheiben, aus denen sie gefüttert werden, turbulent sind und damit Drehimpuls effektiv nach außen transportieren können. Die Ursache dieser Turbulenz liegt in der destabilisierenden Wirkung von Magnetfeldern auf rotierende Strömungen, die als Magneto-Rotations-instabilität bezeichnet wird.
Der Vortrag gibt zunächst eine kurze Einführung in die Theorien zur Entstehung und Wirkung kosmischer Magnetfelder. Im Mittelpunkt stehen dann die Flüssigmetall-Experimente des letzten Jahrzehnts, in denen sowohl der Dynamoeffekt als auch die Magneto-Rotationsinstabiliät untersucht worden sind. Im Detail werden insbesondere das Rigaer Dynamo-Experiment und das PROMISE-Experiment am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) besprochen.
Zum Schluss werden die Pläne für ein neues großes Dynamoexperiment am HZDR vorgestellt, in dem Selbsterregung in einer nur durch Präzession getriebenen Strömung von flüssigem Natrium nachgewiesen werden soll.
  • Invited lecture (Conferences)
    Greifswalder Physikalisches Kolloquium, 23.06.2011, Greifswald, Deutschland

Publ.-Id: 15866 - Permalink


Theory of a liquid metal Tayler experiment
Rüdiger, G.; Gellert, M.; Stefani, F.;
The nonaxisymmetric Tayler instability of toroidal magnetic fields is studied for conducting incompressible fluids between two coaxial cylinders. The inner cylinder is assumed as thin. The outer radius of the container is 5 cm. The electric current may be homogeneous so that the azimuthal magnetic field is proportional to the radius. Endplates are not considered. The azimuthal mode number of the perturbation is fixed to m = 1.
  • Lecture (Conference)
    17th International Couette-Taylor Workshop, 25.-27.07.2011, Leeds, United Kingdom

Publ.-Id: 15865 - Permalink


Radiosynthesis of a 18F-labeled 2,3-diarylsubstituted indole via McMurry coupling for functional characterization of cyclooxygenase-2 (COX-2) in vitro and in vivo
Kniess, T.; Laube, M.; Bergmann, R.; Graf, F.; Steinbach, J.; Wuest, F.; Pietzsch, J.;
The radiosynthesis of 3-(4-[18F]fluorophenyl)-2-(4-methylsulfonylphenyl)-1H-indole [18F]3 as PET radiotracer for functional characterization of cyclooxygenase-2 (COX-2) in vitro and in vivo is described. [18F]3 was prepared by McMurry cyclization of a 18F-labeled intermediate with low valent titanium and zinc via a two-step procedure in a remote controlled synthesizer unit including HPLC purification and solid phase extraction. In this way [18F]3 was synthesized in 80 min synthesis time in 10% total decay corrected yield from [18F]fluoride in radiochemical purity >98% and a specific activity of 74-91 GBq/µmol. [18F]3 was evaluated in vitro using pro-inflammatory stimulated THP-1 and COX-2 expressing tumor cell lines (FaDu, A2058, HT-29), where the radiotracer uptake was shown to be consistent with up regulated COX-2 expression. The stability of [18F]3 was determined by incubation in rat whole blood and plasma in vitro and by metabolite analysis of arterial blood samples in vivo, showing with 75% of original compound after 60 min an acceptable high metabolic stability. In vivo kinetics and tumor uptake were investigated by dynamic small animal PET studies on HT-29 tumor-bearing mice, and revealed in contrast to the in vitro results no substantial tumor accumulation of [18F]3. These data indicate that the radiotracer is not suitable for functional imaging of COX-2 in rodent models in vivo. However it should be noted that McMurry cyclization in PET chemistry gives access to 18F-labeled diaryl-substituted heterocyles that hold promise as new radiolabeled COX-2 inhibitors.

Publ.-Id: 15864 - Permalink


Characterization and local magnetic modification of ion irradiated GaMnAs
Li, L.; Yao, S. D.; Roshchupkina, O.; Prucnal, S.; Akhmadaliev, S.; Campion, R. P.; Rushforth, A. W.; Fassbender, J.ORC; Helm, M.; Gallagher, B. L.; Timm, C.; Schmidt, H.; Zhou, S.
We study the influence of ion irradiation on magnetic, magneto-transport and structural properties in Ga0.94Mn¬0.06As films. The carrier concentration is accurately controlled by defects introduced via ion irradiation. Magnetic properties strongly depend on the hole concentration. We present the modification of coercivity, magnetic anisotropy, and magnetotransport properties during such a procedure. By x-ray diffraction and Raman spectra, we exclude the effects from structural changes. Using lithograph made resist mask, one can realize planar local structures with different magnetic properties, indicating the promising future of ion irradiation for spintronics device fabrication.
Keywords: GaMnAs, ferromagnetism, ion irradiation

Publ.-Id: 15863 - Permalink


The correlation between structure and magnetism of Ni-implanted TiO2 annealed at different temperatures
Ding, B.; Cheng, F.; Pan, F.; Fa, T.; Yao, S.; Potzger, K.; Zhou, S.;
In this paper, the structural and magnetic properties of Ni metal implanted TiO2 single crystals are discussed. Ni nanocrystals (NCs) have been formed in TiO2 after ion implantation. Their crystalline sizes were increased with increasing post-annealing temperature. Metallic Ni nanocrystals inside the TiO2 matrix are stable up to an annealing temperature of 1073 K. The Ni NCs forming inside TiO2 are the major contribution of the measured ferromagnetism.
Keywords: Diluted magnetic oxides, Ion implantation, TiO2

Publ.-Id: 15862 - Permalink


The influence of temperature and small organic ligands on the sorption of Eu(III) on Opalinus Clay
Schott, J.; Acker, M.; Barkleit, A.; Brendler, V.; Taut, S.; Bernhard, G.;
The influence of temperature up to 50°C and small organic ligands (citrate, tartrate) on the sorption of Eu(III) on the natural clay rock Opalinus Clay (OPA) under aerobic (p(CO2) = 10^(-3.5) atm) synthetic OPA pore water conditions (pH 7.6, I = 0.4 M) was investigated. Batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were used to study these influencing factors on the Eu(III) sorption.
Sorption isotherms and distribution coefficients Rd (15°C: log Rd = 4.50 ± 0.05 … 50°C: log Rd = 5.54 ± 0.06) at 2•10^(-9) M Eu(III) as a function of the solid-to-liquid ratio (up to 3 g•L^(-1)) and temperature were determined. A significant temperature dependency of the Eu(III) sorption was observed. With rising temperature the Eu(III) sorption increases. The surface reaction is endothermic (sorption enthalpy ~ 50 kJ•mol^(-1)). Using TRLFS, a surface species with a luminescence lifetime of (201 ± 9) microseconds was identified.
In the presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution, with citrate having a more pronounced influence on the sorption than tartrate. With the batch sorption experiments it can be shown that at a citrate concentration larger than 10^(-5) M and at a tartrate concentration larger than 10^(-4) M an increasing Eu(III) desorption occurs. This result is supported by TRLFS measurements, which show the correlation between the complexation of Eu(III) by citrate or tartrate in solution and the Eu(III) desorption process. Possible Eu(III) citrate or Eu(III) tartrate surface species on OPA could not be detected using TRLFS.
Keywords: Europium(III)/citrate/tartrate/temperature dependence/batch sorption experiments/TRLFS

Publ.-Id: 15861 - Permalink


Fracture mechanics characterisation of the beltline welding seam of the decommissioned WWER-440 reactor pressure vessels of nuclear power plant Greifswald Unit 4
Viehrig, H.-W.; Altstadt, E.; Houska, M.; Valo, M.;
The paper presents data measured for trepans sampled from decommissioned WWER-440 reactor pressure vessel of the NPP Greifswald Unit 4 the main focus being on fracture toughness characterisation according to test standard ASTM E1921. Large variation of the evaluated reference temperature values T0 across the wall of the multilayer beltline welding seam was observed. Generally, the through wall variation of the T0-values does not follow the ductile-to-brittle transition temperature (TT) shift predicted by the Russian code and in fact the non-fluence dependent variation of the T0-values is comparable to the variation predicted by the code. Metallographic investigations show that the T0-values measured with TS oriented Charpy size SE(B) specimens from different thickness locations of the multilayer welding seams strongly depend on the metallographic structure at the specimen crack tip. The RPV integrity is accessed taking into account a pressurised thermal shock scenario.
Keywords: decommissioned reactor pressure vessel, weld metal, fracture toughness, Master Curve, specimen orientation, integrity assessment

Publ.-Id: 15860 - Permalink


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