Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Mn₅Si₃C_x films exhibit antiferromagnetic or ferromagnetic behavior depending on the carbon doping level x. We report a detailed electronic-transport study of films prepared with different x. All films exhibit metallic behavior of the temperature-dependent resistivity ρ(T) with a logarithmic increase towards low temperatures attributed to the structural disorder and the accompanied scattering of conduction electrons by two-level systems. Below 1 K, the Kondo-type behavior ρ(T)~−ln T shows a crossover to Fermi-liquid behavior ρ−T² independent of the type of magnetic order. The magnetoelectronic properties such as Hall effect and magnetoresistance show clear differences characteristic for the different magnetically ordered phases, i.e., antiferromagnetic vs ferromagnetic.

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

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

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

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

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

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

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

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

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

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

Investigation of lateral and vertical element distributions by means of nuclear microprobe:

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

Der Aufbau einer Protonenmikrosonde am Rossendorfer Tandemgenerator wird beschrieben. Testmessungen bei einer Energie von 3 MeV ergaben eine Auflösung von etwa 4 µm bei einem Strahlstrom von etwa 200 pA.

The development of a protonen microprobe at the Rossendorf tandem generator is described. A resolution of about 4 µm with a beam current of 200 pA was reached during first measurements at an energy of 3 MeV.

Hydrogen surface contamination and depth profiles can be measured by the resonant nuclear reactions ¹H(¹⁹F,α y) ¹⁶O and ¹H(¹⁵N,α y) ¹²C. The method was applied to study hydrogen-implanted silicon, amorphous silicon layers and silicon oxide films produced by anodic oxidation.

From the many-body T-matrix the condition for a medium-dependent bound state and its binding energy is derived for a homogeneous interacting Bose gas. This condition provides the critical line in the phase diagram in terms of the medium-dependent scattering length. Separating the Bose pole from the distribution function the influence of a Bose condensate is discussed and a thermal minimum of the critical scattering length is found.

Fluorine surface contamination and depth profiles were studied using the ¹⁹F(p,p'y)¹⁹F resonance reaction. Fluorine implanted silicon samples as well as ZrNb plates and Cr-Al layers after a HF-treatment have been examined. The resonance strengths of the narrow 1088 keV resonance were estimated.

Ion-implantation-induced selective etching of dielectric materials is considerably diminished with increasing hydrogen content.
Making use of the ¹H(¹⁵N,αy)¹²C resonance reaction, low-temperature PECVD Si oxide and Si nitride layers were observed to
contain 12 and 23 at.% H, respectively. For different reagents etch rates were measured regarding the virgin and ion-implanted - He⁺, Ne⁺ at 60, 100 keV - PECVD films.

We show that a Θ+ signal may appear in the [γD, pK−] missing mass distribution in inclusive γD → pK−X reaction when the pK− pair is knocked out in the forward direction and its invariant mass is close to the mass of Λ(1520). We show that the conditions of the recent CLAS experiment reduce the Θ+ formation probability making it difficult to extract a Θ+ peak from the data.

It is widely known that cosmic magnetic fields are produced by the hydromagnetic dynamo effect. Yet it is less well known that cosmic magnetic fields play an active role in cosmic structure formation by means of the magnetorotational instability (MRI). The last ten years have seen tremendous efforts in studying both effects in the laboratory. In 1999, magnetic field self-excitation was observed nearly simultaneously in the liquid sodium facilities in Riga and Karlsruhe. Recently, self-excitation was also obtained in the French "von Karman sodium" (VKS) experiment, although with the help of iron propellers. The helical MRI was recently studied in the ''Potsdam Rossendorf Magnetic Instability Experiment'' (PROMISE), and an improved version of this experiment (PROMISE 2) has provided sharper transitions between stable and unstable regimes. In the talk, the history of dynamo and MRI experiments is delineated, and some interesting directions of future work are discussed.

Plastic materials like polypropylene, polyester (Mylar) and polycarbonate (Lexan or Makrofol E) contain large amounts of hydrogen and their compositions are well known. However, these materials are not stable during ion bombardment. Using the ¹H(¹⁵N,αγ)¹²C and ¹H(¹⁹F, αγ)¹⁶O nuclear resonance reaction at energies E_N = 6.50 MeV and E_F = 6.83 MeV, respectively, we have investigated the behaviour of plastic foils during ¹⁵N and ¹⁹F ion bombardment. By means of a rotating sample holder low current densities of 1–2 nA/cm² and large irradiated foil areas of up to 10 cm² were realized. Under these measuring conditions the γ-ray yields change only slightly and the initial yields, which correspond to the known compositions of the foils, can be determined with good accuracy. In this way the plastic foils can be used as primary standards for hydrogen content calibration. The method was employed to calibrate an a-Si(H) reference target.

We present a high resolution gamma ray computed tomography (CT) system for the measurement of the void distribution in sub-channels in an electrically heated fuel rod bundle at the thermal hydraulic test loop KATHY (AREVA NP GmbH, Germany). This measurement system generates cross-sectional void fraction profiles through the pressure vessel for true-to-scale fuel rod bundles operating under typical nuclear reaction conditions and in steady state. Measurements are non-invasive, thus the two-phase flow in the bundle is not influenced. The gamma ray computed tomography system consists of a collimated 137Cs isotopic source, a gamma radiation detector arc including 320 single elements and a pulse processing unit. The average spatial resolution of the CT system is about 3 mm in plane and 8 mm axial. The thermal design of the detector arc is optimised to keep the temperature of internal components constant under changing environmental conditions. A specially developed gantry was constructed to realise vertical positioning and continuous rotation of the CT system. To determine the void fraction distribution a two-point calibration method is used. Here, data sets at zero and one hundred percent void fraction are required. The non-superposed slice image is generated using the filtered back projection reconstruction algorithm.

The production of eta' mesons in the reactions pp to ppeta' and pn to pn eta' at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. The description of cross section and angular distributions of the available data in this kinematical region in the pp channel is accomplished by including meson currents and nucleon currents with the resonances S_{11}(1650), P_{11}(1710) and P_{13}(1720). Predictions for the pn channel are given. The di-electron production from subsequent eta' Dalitz decay eta' to gamma gamma^* to gamma e^+e^- is also calculated and numerical results are presented for intermediate energy and kinematics of possible experiments with HADES, CLAS and KEK-PS.

In this work, the stability of the Economic Simplified Boiling Water Reactor (ESBWR) has been studied by using a Freon-134a based experimental facility (GENESIS) and two system codes, being ATHLET 2.0a and (to a lesser extent) TRACG. During setting up the GENESIS facility and the numerical calculations, a great effort has been made to approximate the ESBWR system as accurate as possible.
In general, it was found that a sufficient margin to instability exists regarding the ESBWRs nominal point. In addition, a comparison was made between the numerical and experimental results for both the thermal-hydraulic system and the reactor system. Deviations were found between the numerical and experimental results, in spite of the close similarity between the GENESIS facility and the definition of the ESBWR system in the system code. This result shows that predictions regarding real nuclear reactors, based on modeled systems, should be taken with care.

Quantum well infrared photodetector (QWIP) technology has opened up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging [1]. High thermal and spatial resolution, low 1/f noise, low fixed-pattern noise, and high pixel operability makes QWIP FPAs appropriate for many applications. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. In this talk, I will report on the development of QWIP structures optimized for thermal imaging applications and on the performance of QWIP cameras which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). Besides imagers for the 8 – 12 micron long-wavelength infrared (LWIR) and 3 – 5 micron mid-wavelength infrared (MWIR) regimes, a LWIR/MWIR dual-band QWIP FPA will also be discussed.
[1] H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors: Physics and Applications, ISBN 3540363238, Springer Series in Optical Sciences Vol. 126, 2007.

Irradiation-induced microstructural features in pure Fe were investigated by a triple of methods: TEM, SANS and PAS. In the talk it will be analyzed, if and how the features detected by the individual techniques reflect themselves in the output of each other method. This information is used in order to derive a coherent picture of irradiation damage in pure Fe.

SANS results for an RPV weld material irradiated at two different neutron fluxes up to the same neutron fluence will be presented. We have observed a remarkable effect of flux on the size of irradiation-induced clusters. A rate theory model is applied in order to give a tentative explanation for the findings. Interestingly, the mechanical properties do not show a corresponding flux effect. The results will be faced with observations for another RPV steel exhibiting a different behaviour.

The L3-edge x-ray absorption spectrum of Pa(V) fluoride in aqueous solution show clear evidence for the double photoexcitation involving 2p and 4f electrons. A comparison with the [2p4f] double-electron excitations observed in the L3-edge x-ray absorption spectra of other actinides (thorium, uranium, neptunium, plutonium and americium) indicates a monotonic increase of the excitation energy. The sharp edge-like structure of the multielectron excitation reveals the origin of a shake-up channel.

ROCOM is a four-loop test facility for the investigation of coolant mixing in the primary circuit of pressurized water reactors. Recently, a new sensor was developed for an improved visualisation and quantification of the coolant mixing in the downcomer. This new sensor spans a dense measuring grid and covers nearly the whole downcomer. In the presented work, special emphasis was given to the comparison of the data of this sensor with the results of calculations using the CFD code ANSYS CFX. A coolant mixing experiment during natural circulation conditions has been conducted. The underlying scenario of this experiment is based on a boron dilution scenario following a SBLOCA event. The corresponding CFD code solution has been obtained using the Best Practice Guidelines. All main effects observed in the measurement are described by the calculation. The detailed comparison reveals that the calculation underestimates the coolant mixing inside the reactor pressure vessel.
The measurement data, boundary conditions of the experiment and facility geometry can be made available to other CFD code users for benchmarking.

Understanding and modelling of two-phase flow is a key issue in nuclear engineering and in many other engineering fields. The Research Centre Dresden-Rossendorf is, amongst others, engaged in safety research for nuclear light water reactors and performs combined experimental and theoretical work on two-phase flow phenomena. In the frame of this work considerable effort has been spent in the past to develop innovative two-phase flow measuring techniques. Special focus has been given to imaging techniques which are able to resolve phase distributions at high temporal and spatial resolution. The presentation introduces the most advanced of these techniques, including different types of wire-mesh sensors, gamma ray tomography and ultra fast electron beam tomography and discusses application of such techniques and systems in basic research as well as industrial applications.

A new ultra fast electron beam X-ray CT scanner has been developed, implemented and tested in different applications. It consists, amongst other components, of an electron beam unit with 10 kHz scanning capability and 1 mm focal spot size and a 240 element circular CZT detector arc. The system is capable to produce slice images at up to 7 kHz frame rate of moderately absorbing objects with maximum 120 mm diameter. The paper introduces the scanner and first results for two-phase flow measurements in a bubble column and a fluidized bed.

We performed wire-mesh and X-ray micro¬tomography studies of the two-phase flow in the mixing chamber of an effervescent atomizer. Flow patterns in the mixing chamber can be revealed by the miniature wire mesh sensor with a temporal resolution of 10 kHz whereas microtomography provides accurate and high-resolution axial-radial gas fraction profiles. The paper describes both measurement techniques and first results of experimental investigation.

We developed an ultra fast X-ray CT scanner based on scanned electron beam technology. The new device enables ultra fast two-dimensional phase fraction imaging in flow cross-sections at frame rates up to 7 kHz. As an example flow measurement in a 60 mm diameter bubble column is presented.

Gamma ray tomography is a valuable tool for multiphase flow analysis in different areas of process, nuclear and mechanical engineering. Here, we introduce the design of a high resolution gamma ray tomography scanner and discuss two application examples from different technical fields.

Alternating current (AC) magnetic fields are commonly used in industrial practice for melt stirring. The requirements arising from the particular metallurgical or casting operation can be manifold. For instance, the electromagnetic stirring is applied to provide an efficient mixing of metallic melts, to control the flow at the mold region in the continuous casting process or to achieve a purposeful alteration of the microstructure of casting ingots.
In the present study we introduce a novel type of electromagnetic stirring using a pulse-modulated rotating magnetic field (RMF). Capabilities of this approach are exemplarily demonstrated for controlling the melt flow during the unidirectional solidification of an Al-7wt%Si alloy. Two variants have been examined. Firstly, we use a succession of pulses that always have the same rotational direction (RMF-PSCD). Secondly, we use an RMF pulse sequence of alternating direction (RMF-PSAD). The latter method is related to a periodic inversion of the sense of rotation between two consecutive pulses. The characteristic period of the inversion for RMF-PSAD and of the pulses for RMF-PSCD is derivable from the spin-up dynamics of a continuously applied RMF.
Numerical and experimental investigations of different configurations applying an RMF either continuously or in form of RMF-PSAD and RMF-PSCD reveal the development of different flow pattern. It was found that the application the time-modulated RMF with suitable modulation frequencies delivers a homogeneous, equiaxed microstructure. Typical segregation pattern or flow-induced gas porosity usually arising from a continuous RMF application can be avoided with the new stirring methods. Essential features of the interplay between the electromagnetically-driven melt flow and solidification parameters such as temperature and mixture mass concentration of Si are discussed. Our results demonstrate that the success of the presented RMF-PSAD technique requires a precise tuning of the magnetic field parameter with respect to the material properties of the alloy, the geometry of the casting or process parameters like the cooling rate.

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In the range of small or moderate void fractions the UDV technique delivers both the bubble and the liquid velocity.

Basing on many years of experience a new extensive high quality database was obtained for stationary upward air-water flows in a vertical pipe with an inner diameter of 195.3 mm using the wire-mesh sensor technology. During the experiments the sensor was always mounted on the top of the test section while the distance between gas injection and measuring plane was varied to up to 18 different L/D by using gas injection chambers at different vertical positions. The gas was injected via holes in the pipe wall. In this new test series the pressure was kept at 0.25 MPa (absolute) at the location of the active gas injection while the temperature was constant at 30°C +- 1K. The experiments were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for water and 0.0025 m/s to 3.2 m/s for air. From the raw data time averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size and the radial profiles of the gas velocity were calculated. All data were checked regarding their consistency. They are characterized by a high resolution in space what makes them suitable for the development and validation of CFD-grade closure models, e.g. for bubble forces and coalescence and break-up. It is also an ideal base to validate CFD approaches for poly-dispersed flow. For this reason it is proposed to use the database as a benchmark for modelling poly-dispersed flows.

The experimental realization of dynamo excitation has demonstrated the relevance of boundary conditions and material properties for a self-sustaining dynamo. The consideration of conductivity or permeability inhomogeneities requires a flexible numerical method that utilizes a local discretization scheme. A fast and accurate approach is provided by the constraint transport (CT) approach, a well known realization of a finite volume (FV) method that intrinsically maintains the solenoidal character of the magnetic field. The
problem of laboratory boundary conditions is treated by the boundary element method (BEM) which in combination with the FV scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions.

Test simulations reproduce key results of the induction effects of a von-Karman-like flow and demonstrate the applicability and reliability of the approach.

Current examinations investigate the dynamo process presented by Busse & Wicht (1992, GaFD, 64, 135-144) who showed that a constant flow over a conducting material that exhibits a sinusoidal variation of the conductivity is already sufficient to generate a dynamo.

We report the specific heat, magnetic susceptibility, and magnetization as well as resistivity of hexagonal α-YbPdSn polycrystals down to temperatures T of 50 mK and fields up to 12 T. In the susceptibility χ(T), several different temperature regimes can be distinguished. For 300 K>T>170 K, a Curie-Weiss-like behavior is obtained with the effective moments close to that of Yb>sup>3+. The large Weiss temperature ΘH≈150 K and the leveling off of χ toward low T are indicative of valence fluctuations. Around 30 K, crystal-field excitations manifest themselves in features of χ(T) and the resistivity ρ(T). For 5 K>T>0.2 K, a Curie-Weiss behavior with µ_eff=1.27µ_B/Yb atom and Θ_L=0.41 K is found, signaling the occupation of the lowest crystal-field doublet. A sharp maximum in χ(T) and in the specific heat C(T) indicates antiferromagnetic ordering at 250 mK. The specific-heat peak develops into a broadened Schottky anomaly in moderate magnetic fields. The sizable linear specific-heat coefficient γ=68 mJ/mole K² is attributed to valence fluctuations. Likewise, the magnetization at 10 and 2.3 K measured up to 12 T can be decomposed into a contribution of delocalized electrons and localized magnetic moments. The data can be consistently interpreted in terms of a two-fluid model with ~6% localized and ~94% delocalized moments derived from (nearly) trivalent Yb.

NiCl₂-4SC(NH₂)₂ (known as DTN) is a spin-1 material with a strong single-ion anisotropy that is regarded as a new candidate for Bose-Einstein condensation (BEC) of spin degrees of freedom. We present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase by means of high-field electron spin resonance measurements at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a finite interaction between two tetragonal subsystems and unbroken axial symmetry. The latter is crucial for the interpretation of the field-induced ordering in DTN in terms of BEC.

We present an experiment for the creation of unconventional ferromagnetism in pure ZnO powder by application of mechanical force. The ferromagnetism is related to flake like structures in planar compressed pieces of the powder with easy axis in the plane. It is associated with defect creation and disappears upon annealing in oxygen. Besides cluster formation, such defects might be one of the non-intrinsic origins of ferromagnetism in transition metal doped ZnO.

We report the carbon-isotope effect for boron-doped diamond (BDD). Resistive as well as specific-heat measurements reveal a 0.2 K shift in the superconducting transition temperature T_c between BDDs containing ¹³C and ¹²C. This is more than two times larger than could be expected from the mass difference by the use of the simple BCS formula in case the phenomenon is related to electron-phonon mediated superconductivity in BDD.

Synchrotron-based EXAFS spectroscopy is a powerful technique to obtain structural information on radionuclide bioligand species in solution. As an example pyoverdin-type siderophores are a unique class of bioligands, with a high potential to dissolve, bind, and thus transport uranium in the environment. Pyoverdins are secreted from fluorescent Pseudomonas species which are ubiquitous soil bacteria. The functional groups of the pyoverdin molecule, LH4, participating in metal binding are the catechol group of the chromophore and two ligand sites in the peptide chain, i.e., one or two hydroxamate groups and one or two -hydroxy acid moieties [1]. The formation of complexes of UO22+ with pyoverdins released by the groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m in the Äspö Hard Rock Laboratory, Sweden, was investigated in our previous study [2]. Two UO22+-P. fluorescens pyoverdin species, UO2LH2 and UO2LH-, could be distinguished on the basis of UV-vis spectroscopy and fs-TRLFS.

Little structural information is available regarding the U(VI) pyoverdin species formed in aqueous solutions. We therefore performed U LIII-edge EXAFS measurements of test solutions containing 5x10-4 or 0.001 M UO22+ and pyoverdins or related model compounds at an ionic strength of 0.1 M NaClO4. The pH was varied between 2 and 8 depending on the bioligand. EXAFS measurements were carried out on the Rossendorf Beamline (ROBL) BM20 at the ESRF [3]. The samples were measured at room temperature using a water-cooled Si(111) double-crystal monochromator in channel cut mode (5-35 keV). The spectra were collected either in fluorescence mode using a 13-element Ge solid-state detector or in transmission mode using Ar filled ionization chambers. The model compounds simulate the hydroxamate function (simple hydroxamate and a trihydroxamate compound) and the chromophore of the pyoverdin molecule. The obtained structural information for the axial and equatorial oxygen atoms surrounding the uranium atom will be presented. Estimations of the near order surrounding of uranyl in pyoverdin complexes are based on the comparison with those found in uranium(VI) model ligand species.

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.

For a systematic investigation of the heat- and charge-transport properties of YNi₂B₂C and HoNi₂B₂C, single-crystal measurements of the electrical resistivity, the thermal conductivity, and the thermoelectric power were performed on the same samples. For HoNi₂B₂C, a local maximum of the Lorenz number at 20 K is evidently connected with the occurrence of magnetic fluctuations well above the ordering temperature. For the in-plane thermal conductivity, a kink near the superconducting transition was observed, consistent with an anisotropic gap or a multiband description. For both investigated borocarbides, the electrical resistance is isotropic. In contrast, the thermal conductivity shows a pronounced anisotropy. The thermoelectric power exhibits a minor anisotropy and can be well described by electron-diffusion and phonon-drag contributions over a wide temperature range. Based on an analysis of full-potential local-orbital calculations, a strong influence of the boron z position on the thermoelectric power has been
revealed.

The involvement of gamma amino butyric acid (GABA) receptors in a variety of neurological and psychiatric diseases has promoted the development and use of radiolabelled benzodiazepines (BZ) for brain imaging by PET. However, these radioligands are unable to distinguish between the various subtypes of GABA_A receptors. Novel non-BZ such as the pyrazolo-pyrimidine indiplon proved to be selective for the alpha₁-subunit of the GABA_A receptor. Here, we describe the syntheses of four novel ¹⁸F-labelled indiplon derivatives. Radiosyntheses were performed via n.c.a. ¹⁸F-nucleophilic substitution starting from the tosyl, bromo, and 4-nitrobenzoyl precursors to obtain fluorine substituted N-alkylamide side chain derivatives of indiplon, followed by multistep purification using semi-preparative high-performance liquid chromatography and solid phase extraction. Tosyl and bromo precursors were converted into ¹⁸F-labelled indiplon derivatives with good and reproducible radiochemical yield (RCY) (35–70%, decay corrected), high radiochemical purity (>/= 98.5%), and high specific activity ( > 150 GBq/lmol). By contrast, a low RCY (5–10%) and specific activity (10–15 GBq/lmol) were achieved for the 4-nitrobenzoyl precursor.

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Following the possible transport of uranium under environmental conditions we may start with the weathering of uranium compounds in the soil or in a mining waste rock pile. The seepage water contains about 2 mg/L uranium and the speciation is mainly influenced be the formation of the dicalcium-uranyl-tricarbonate species. The input of these seepage water leads to a dilution of the uranium by about three orders of magnitude. Using the cryogenic technique in TRLFS we could also determine the uranium speciation in the river water nearby the former uranium mining area. The uranium concentration was about 2 µg/L uranium and in the river water mainly uranyl-tricarbonate species are formed.
Despite this uranium can migrate down to the groundwater. In this case uranium may come back to the food chain by the production of mineral waters. We have studied the uranium speciation in several German mineral waters with uranium concentrations between 50 ng/L and 5 µg/L. In agreement with speciation calculations the sparkling and the calcium poor waters contain uranium as uranyl-tricarbonate species, whereas the non-sparkling waters if they are rich in calcium show clearly the formation of the dicalcium-uranyl-tricarbonate species. Using cryogenic TRLFS the detection limit for uranium species was estimated to be about 50 ng/L. Additionally a Hungarian medicinical water shows a uranium concentration of 150 µg/L. Due to the high mineralisation of this water also the dicalcium-uranyl-tricarbonate species was determined.
Summarizing it can be concluded that the most natural waters contain uranium as tri-carbonate species. According to investigations of these uranium species are less hazardous than phosphate and citrate species.

Uranium in the environment is ubiquitous. Nevertheless human activities as uranium mining and milling, use of uranium in nuclear power production and as penetrating ammunitions as well as the distribution of uranium with fertilizers lead to an increase of the uranium content in the environment.
Especially the uranium ammunition can generate locally high concentrations of uranium in the environment.
Weathering processes of the uranium metal lead in a first step to the formation of uranium minerals1. Depending on the composition of the soil the formation of several types of minerals can be estimated. Especially the content of phosphate from fertilizers and the aluminium from soil components are involved in the mineral formation.
By use of time-resolved laser-induced fluorescence spectroscopy (TRLFS) the mineral type can be determined without any destruction. A large database of luminescence spectra, obtained from uranium minerals of the collection of the Technical University Mining Academy Freiberg, enables us to identify the formed uranium mineral2. In the experiment, described in (1) we found that mainly the mineral sabugalite was formed. Other experiments with pure calcium and phosphate containing solution lead to the formation of the mineral meta-autunite3.
In a second step the formed minerals than undergo further weathering processes, forming dissolved uranium species.
In the former uranium mining areas of eastern Germany we could discover a new dissolved uranium carbonate species4,5. However, the uranium concentration of about 2 mg/L in these mining related waters is relatively high. Nevertheless the carbonate and calcium concentration are high enough to form a very stable dicalcium-uranyl-tricarbonate species. This species is of great importance, as its existence explains the uranium migration at the Hanford site6.
In addition to the calcium species it can be stated that also the other alkaline earth elements form this type of alkaline earth uranyl carbonate species7,8,910.
Following the uranium migration in the soil we could detect in the experiments that mainly carbonate species are formed. The pure carbonate species do not show any luminescence properties at room temperature. Therefore the samples have to be frozen to temperatures below 220 K11, in order to minimize the dynamic quench effect of the carbonate anion. This increases also the luminescence intensity and the luminescence lifetime of all carbonate containing species.
Nevertheless, in one case of the soil experiment also hydroxo species were found. This may be connected to a non-equilibrium with atmospheric CO2 in this column.
Following the possible transport of uranium under environmental conditions we may start with the weathering of uranium compounds in the soil or in a mining waste rock pile. The seepage water contains about 2 mg/L uranium and the speciation is mainly influenced be the formation of the dicalcium-uranyl-tricarbonate species. The input of these seepage water leads to a dilution of the uranium by about three orders of magnitude. Using the cryogenic technique in TRLFS12 we could also determine the uranium speciation in the river water nearby the former uranium mining area. The uranium concentration was about 2 µg/L uranium and in the river water mainly uranyl-tricarbonate species are formed.

ZnO(0001) single crystals have been implant-doped with maximum 5 atomic % of Co at low temperatures. While as-implanted crystals do not show ferromagnetic properties, post implantation annealing leads to the transformation of the implanted Co ions into small metallic clusters giving rise to a pronounced hysteresis upon magnetization reversal. The dispersed Co ions are in 2+ oxidation state. Positive magneto-resistance could be observed at low temperatures.

A new coupler test bench based on a resonant ring has been built at ELBE in Dresden-Rossendorf to run warm window as well as coupler tests with RF power up to 190 kW (warm window tests up to 250kW) in CW operation. The ring is driven by a 10 kW klystron. This test bench also includes liquid nitrogen cooling of the ceramic cold window of the RF-coupler which allows testing under almost real conditions. A special waveguide to coupler transition was designed to match couplers with different antenna tips. At the beginning with the test bench it was possible to test the warm windows used at ELBE. It has been shown that the used warm windows are usable up to 70kW of CW-RF power with additional air cooling, much more than the 10kW CW used at ELBE. After this test the coupler used at the ELBE cryomodules was tested, in CW operation a power level of about 20kW was reached. More tests are in program and in near future some improvements are planned.

Recent coupled code benchmarks have identified coolant mixing in the reactor vessel as an unresolved issue in the analysis of complex plant transients with reactivity insertion. This issue was one of the main topics in Phase 2 of the recently completed OECD VVER-1000 Coolant Transient Benchmark (V1000CT-2). Exercise 1 of this benchmark is a VVER-1000 V320 vessel mixing problem based on a steam generator isolation experiment at Kozloduy-6 in Bulgaria. Plant data are available for code validation. The validated codes can be used to calculate asymmetric MSLB transients involving similar mixing patterns. A variety of mixing models were tested including multi-1D with cross flow, coarse 3D and fine CFD.
This presentation summarizes a comparison of six submitted CFD results for the V1000CT-2 Exercise 1. The results were obtained with a specified CAD model of the real vessel geometry. Five participants used a solution region from vessel inlet to the core inlet. FZK solved the benchmark for the whole pressure vessel. The comparison is code-to-code and code to experiment. The results show good overall agreement with the experiment and between the codes as well as specific features depending on the turbulence model.

The presentation describes the outline, assumptions and preliminary results of a boron dilution benchmark for pressurized water reactors. In this benchmark the neutron kinetic code DYN3D in combination with three different thermal hydraulic models has been used. Besides the own thermal hydraulic model of DYN3D, models based on the ATHLET and the RELAP5 code were created. The calculations were carried out for a generic PWR core for the subcritical hot zero power state at beginning of an equilibrium cycle. All control rods except the most effective one are inserted into the core. The deboration scenario is based on the start-up of the first main coolant pump with a slug of deborated coolant in the loop. Time dependent core inlet distribution of the boron concentration used as boundary condition for the calculations is based on corresponding experiments at the coolant mixing test facility ROCOM.
Stationary core calculations for the initial state show an excellent agreement between the three calculations. The influence of the different thermal hydraulic models reveals after the return to power. The deboration front causes in all three cases a super-prompt overcriticality jump. The time and the height of the first power peak depend on the ability of the codes to suppress the numerical diffusion of the deboration front. DYN3D and DYN3D/RELAP5 shows with about 30000 MW a considerably lower value than the 53000 MW of DYN3D/ATHLET. This difference has also an influence on the maximum cladding temperature. DYN3D/ATHLET shows with nearly 300 °C the highest value, what is still far from safety relevant conditions.

The presentation describes the new results obtained for the asymmetric control rod ejection benchmark defined in the frame of the co-operation inside the AER.

The superconducting CW-LINAC of the Radiation Source ELBE, based on 1.3 GHz-TESLA cavities, has been operational since 2001. An overview of the ELBE facility and of the RF-system of the superconducting CW-LINAC are presented. It is reported on different improvements on RF components to ensure stable operation of this user facility and on experience gathered during 7 years of CW- operation.

The paper presents a study concerning the impact of a turbulent, rotating melt flow on the macrosegregation and the shape of the mushy zone during unidirectional solidification of an Al-7wt%Si alloy. The flow is generated by applying a rotating magnetic field (RMF). Direct numerical simulations (DNS) were performed to study the weakly turbulent flow. The transient heat and mass transfer were simulated using a standard mixture model (Bennon and Incropera, 1987). The treatment of the fluid flow in the mushy zone requires the use of permeability and mixture viscosity models, which also allow for consideration of both columnar and equiaxed solidification. Our results demonstrate that in the case of columnar solidification the Ekman pumping effect causes the development of a Si-enriched liquid channel along the rotational axis . The Taylor-Goertler vortices, which appear randomly along the side wall of the cylinder, amplify the solute transport from the wall to the axis intermittently in the upper part of the mushy zone. This effect leads to a wavy shape of the mushy zone and segregation in the form of a fir tree with a distinct accumulation of silicon along the axis of the cylinder. Moreover, we propose strategies to avoid macrosegregation by using a pulse-modulated rotating magnetic field.

This contribution presents different approaches for the modeling of air entrainment under water by a plunging jet. Since the generation of bubbles happens on a scale which is smaller than the bubbles, this process cannot be resolved in meso-scale simulations, which include the full length of the jet and its environment. This is why the air entrainment has to be modeled in meso-scale simulations.
In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed.
As a first approach the air is modelled as dispersed phase everywhere in the domain. This causes an air entrainment which is obviously determined by numerical effects. Thus, this approach is not suitable for the implementation of a physical model for gas entrainment. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a different drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free parameters included in this model. The calculated gas entrainment can be adapted via these parameters. Therefore, an advanced AIAD approach could be used in future for the implementation of models (e.g. correlations) for the gas entrainment.

Eingeladener Vortrag der Computerwoche Fachkonferenz: Data Center up-to-date 08 - virtualisieren, konsolidieren, outsourcen
Es wird ein Anwendervortrag gehalten, der Fokus liegt auf folgenden Schwerpunkten:

• IT-Profil des Forschungszentrums Dresden-Rossendorf
• Enterprise Storagelösungen
• Virtualisierung im Speichernetzwerk
• Einsatz von Filesystemen
• Lebenszyklus eines Storagesystems

The Ultrasound Doppler Velocimetry (UDV) is a non-intrusive technique to measure velocities of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it becomes very attractive for liquid metal applications. But, in case of hot metallic melts the user is confronted with a number of specific problems: First of all the application of the ultrasonic transducers is usually restricted to maximum temperatures of about 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.
In this presentation various applications of UDV in liquid metal flows will be shown to demonstrate the capabilities and current restrictions of this technique. For instance, we consider single- and multi-transducer arrangements for flow mapping or present velocity measurements obtained during the solidification of a metallic melt. Besides the determination of velocity profiles in the liquid phase the UDV data allow for an assessment of the current position of the solidification front, too. Specific problems arising in the context of UDV measurements in liquid metal experiments will be discussed.

Alternating current (AC) magnetic fields are commonly used in industrial practice for melt stirring. The requirements arising from the particular metallurgical or casting operation can be manifold. For instance, the electromagnetic stirring is applied to provide an efficient mixing of metallic melts, to control the flow at the mold region in the continuous casting process or to achieve a purposeful alteration of the microstructure of casting ingots. However, a purposeful practice of melt stirring requires suitable flow measurements which deliver a detailed knowledge of the magnetic field impact on the flow pattern.
This experimental study considers the transient liquid metal flow which is generated inside a cylindrical container by discontinuously applying a rotating magnetic field (RMF). The focus is on the fluid motion arising from the impulsive spin-up from the resting state, a single pulse or a sequence of RMF pulses. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both the primary, swirling flow and the secondary flow in the radial-meridional plane. The experimental results show an excellent agreement with recently published numerical results. The investigations reveal that the recirculating flow in the radial- meridional plane undergoes characteristic oscillations. Periodic reversals of the meridional flow direction can be observed for a specific length of the RMF pulses.
Our results demonstrate that the utilisation of a time-modulated rotating magnetic field (RMF) offers a considerable potential to provide optimal flow pattern for an efficient melt mixing. For instance, such tailored methods of electromagnetic stirring can be applied during the solidification of metal alloys, where a well-aimed modification of casting properties is achieved by controlling the melt flow in the bulk and adjacent to the solidification front.

Considerable effort is permanently directed to optimise methods and facilities for material processing technologies like melting, refining or casting of metallic alloys. The main goals are an improvement of the final product quality, an enhancement of the process efficiency and an economical consumption of resources and energy. Nowadays it is impossible to imagine such optimisation without performing numerical simulations and a corresponding physical modelling. However, the accuracy of the predictions depends sensitively on the availability of precise and trustworthy data concerning the thermophysical properties of the alloys under consideration. The development of new workable aluminium-based light alloys is a key issue in current materials science. Al-Cu alloys, for instance AlCu₄TiMg (A356), are the most utilized casting alloys in the aluminium industry. The distinctive characteristics of these alloys are low density, high melting temperature, good thermal conductivity and excellent oxidation resistance.
In this work, thermophysical properties (density, viscosity and electrical conductivity) of liquid Al₉₆Cu₄, Al₈₀Cu₂₀, Al₇₀Cu₃₀, and AlCu₄TiMg (wt.%) alloys have been measured in a wide temperature range from the melting point up to 1200 K. Corresponding fit relations have been derived for the density, the dynamic viscosity and the electrical conductivity. All properties are compared to available literature data. An increase of a copper content raises gradually the density and the dynamic viscosity of aluminium suggesting a short-range order in the liquid state. According to the density and viscosity data, no substantial structure rearrangement takes place with admixtures. At the same time, the electrical conductivity results demonstrate that small additions of copper slightly raise the conductivity of liquid Al, while further increase of a copper content decreases predictably the conductivity values.

AC magnetic fields are used in industrial practice for melt stirring. The requirements are manifold for miscellaneous metallurgical operations or casting technologies, mainly the magnetic field application should provide an efficient mixing of the melt in order to achieve homogeneous distributions of solute and/or temperature. The rotary stirring during solidification has been proved to be a striking method to achieve a purposeful alteration of the microstructure of casting ingots, such as a distinct grain refining or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET). Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Al-Si alloys from a water cooled copper chill. A modulated rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. The velocity field in the liquid phase was determined by means of Ultrasound Doppler velocimetry (UDV). The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results demonstrate that the modulated magnetic field enables an effective control of the flow field and the structure of the solidified samples.

The rotary stirring during solidification has been proved to be a striking method for achieving a purposeful alteration of the microstructure of casting ingots, such as grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET). However, the imposition of a rotating magnetic field (RMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface leading to surface defects or the entrainment of gas. A permanent radial inward flow along the solidification front is responsible for the transport of solute to the axis of the ingot resulting in typical freckle segregation pattern in form of vertical channels filled with alloy of eutectic composition. We present a new innovative method of electromagnetic stirring using a modulated RMF which offers a considerable potential for a well-aimed modification of casting properties. This paper considers the directional solidification of Al-Si alloys from a water cooled copper chill. Modulated AC magnetic fields were applied for melt agitation. The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results demonstrate that the modulated magnetic field enables an effective control of the flow field and the structure of the solidified samples.

Capabilities of the X-ray attenuation contrast radioscopy were utilized to provide a real-time diagnostic technique for observations of dendritic growth and the melt flow during solidification of a Ga-30wt%In alloy. The solidification process was visualised using a microfocus X-ray tube. The X-ray facility provided shadow radiographs at spatial resolutions of about 10 µm and frame repetition rates up to 25 Hz. We used the optical flow approach to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns appearing during the X-ray image sequence. Experiments have been carried out to solidify the Ga-In alloy unidirectionally either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection. Buoyancy-driven flow patterns were found at length scales being larger than the length scales of the solidifying microstructure. A strong coupling between convection and dendritic growth became apparent via flow-induced modifications of the concentration profile in the liquid. Dendritic fragmentation can be observed during the solidification in the reverse top-down direction. Variations of the applied cooling rate evoked a transition from a columnar to an equiaxed dendritic growth (CET).

A well-tuned Galerkin melody about fluid flows requires a piano with the right keys (called modes, e.g. POD), musical notes (physics resolution), an audience (observer), and a composer (control law) in case the music shall be changed. Here, we briefly review new key enablers for these tasks. Then, a finite-time thermodynamics is proposed bridging fluid mechanics disciplines and theoretical physics treasures. This formalism opens the path to fully nonlinear attractor control, as required for turbulence manipulation in experimental demonstrators. Presented studies include shear flows with simple to complex dynamics.

Focus ion beam (FIB) patterning of Fe60Al40 provides the potential to create arrays of microscopic ferromagnetic regions embedded in a paramagnetic matrix. As the consequence of low fluence irradiation such a method does not affect the surface roughness. Due to the ion damage distribution the phase transition from the chemically ordered B2-phase to the chemically disordered, ferromagnetic A2-phase is setup. The magnetic phase transformation is studied as a function of noble gases mass and is directly related to the number of displacements per atom (dpa) during ion irradiation. In case of heavy ions (Ar+, Kr+ or Xe+) the phase transformation originates purely from ballistic nature of the disordering process. For light ions (He+, Ne+) the disordering conditions deviates from the former case. The bulk vacancy diffusion from dilute collision cascades, that leads to a partial recovery of the thermodynamically favored B2-phase, plays a major role. Furthermore, by means of moderately high temperature annealing (about 900 K) the paramagnetic phase is completely recovered due to the annealing-induced atomic reordering. Therefore, local ion irradiation may lead to a novel type of patterned recording media free from tribological and exchange coupling effects.

We demonstrate a scattering-type scanning near-field optical microscope (s-SNOM) with broadband THz illumination. A cantilevered W tip is used in tapping AFM mode. The direct scattering spectrum is obtained and optimized by asynchronous optical sampling (ASOPS), while near-field scattering is observed by using a space-domain delay stage and harmonic demodulation of the detector signal. True near-field interaction is determined from the approach behavior of the tip to Au samples. Scattering spectra of differently doped Si are presented.

Introduction:

The development of the escalated BEACOPP regimen let to an improved outcome in patients with advanced Hodgkin Lymphoma (HD9 study of the GHSG). However, the application of high dose etoposide (cumulative 4,8 g/m2 per 8 cycles) seems to be associated with an increased incidence of secondary MDS and AML, respectively. Therefore, the aim of our multicenter pilot study was to evaluate the efficacy and toxicity of the etoposide free as well as dose intensified BACOPP-D protocol.

Methods:

Since May 2000 a total of 115 patients with Hodgkin Lymphoma (HL) stage IIB, III, and IV were treated with BACOPP-D which included cyclophosphamide 1250 mg/m2 (d1), adriamycin 25 mg/m2 (d1+2), dacarbazine 250 mg/m2 (d1-3), procarbazine 100 mg/m2 (d1-7), prednisolone 40 mg/m2 (d1-14), bleomycin 10 mg/m2 (d8) and vincristine 1,4 mg/m2 (maximum 2 mg, d8) at three-weekly intervals with granulocyte colony-stimulating factor (G-CSF). A consolidating involved field radiation (30 Gy) was performed only in patients who achieved less than CR following chemotherapy. Post-treatment follow-up included PET imaging.

Results:

Until now 97 patients (median age 35 years, range 17-65; 61 male, 36 female) are assessable for toxicity and treatment outcome. We analyzed the acute toxicity for 728 cycles of BACOPP-D. CTC/WHO grade III/IV haematological toxicities per patient were observed as follows: leukopenia 93%, anemia 39%, and thrombocytopenia 33%. CTC grade III/IV non-haematological side effects included documented infection (4%) and lung toxicity (one patient). A total of 85 patients (88%) achieved complete remission, 9 patients (9%) achieved partial remission, three patients (3%) had progressive disease. At a median observation time of 39 months (0,9-77 months), five patients have relapsed, and nine deaths were documented (4 HL-specific and 3 treatment related deaths, 1 death due to ruptured Meckel diverticulum with peritonitis, one 65 year-old woman died in CR following myocardial infarction). One patient developed a second neoplasia (hypopharyngeal carcinoma in an alcoholic). The overall survival and freedom from treatment failure rates at 39 months were 91% and 85%, respectively. FDG-PET scans after BACOPP-D chemotherapy were performed in 68 of 97 patients. PET scans revealed no increased FDG uptake in 48/68 patients (71%), in 20 patients (29%) increased FDG uptake was detected. In the group of patients with increased FDG uptake, one patient developed progressive disease and four patients relapsed. In the group with PET-negative findings no patient relapsed.

Diskussion:

BACOPP-D regimen appears as a feasible and effective treatment which induced a complete morphologic and metabolic remission in a high proportion of patients with advanced HL. The treatment was associated with moderate acute toxicity. No secondary AML or MDS occurred until now.

Footnotes

Disclosure: No relevant conflicts of interest to declare.

Die Umsetzung des neuen Urheberechts für den Bereich der Dokumentenbereitstellung durch Bibliotheken ist äußerst problematisch. Die Einschränkungen der Verfügbarkeit elektronischer Lieferungen bedingen umfangreiche Schulungen des Bibliothekspersonals, Informationen der Bibliotheksbenutzer, zusätzlichen Bearbeitungsaufwand der Bestellungen und Bestelleingangs- und Rechnungsverwaltung und wesentlichen finanziellen Mehraufwand. Im Vortrag wird am Beispiel des Subito-Rahmenvertrages auf die aktuellen Probleme eingegangen.

A Wire Mesh Sensor system has been employed on a vertical 67 mm diameter pipe up which air and water mixtures flow. This enables an examination of the flow to be carried out at several levels of complexity. The measuring system provides time and cross-sectionally resolved information about the spatial distribution of the phases. The information can be used to obtain space and time averaged void fractions, radial profiles of time averaged void fraction and cross-sectional averaged time series of void fraction. This last yields Probability Density Function information as well as other statistical information. It also yields data of the frequency of periodic structures within the flow. More powerfully, the fully resolved data can give deep insights into the structure of the gas/liquid interface. A hitherto unreported structure has been seen in churn flow which could be linked to the wisps in wispy-annular flow.

The rapid progress in the field of laser particle acceleration has stimulated a debate about the promising perspectives of laser based ion beam sources. For a long time, the beams produced exhibited quasi-thermal spectra. Recent proof-of-principle experiments demonstrated that ion beams with narrow energy distribution can be generated from special target geometries. However, the achieved spectra were strongly limited in terms of monochromacity and reproducibility. We show that microstructured targets can be used to reliably produce protons with monoenergetic spectra above 2 MeV with less than 10% energy spread. Detailed investigations of the effects of laser ablation on the target resulted in a significant improvement of the reproducibility. Based on statistical analysis, we derive a scaling law between proton peak position and laser energy, underlining the suitability of this method for future applications. Both the quality of the spectra and the scaling law are well reproduced by numerical simulations.

Various defect studies of hydrothermally grown (0001) oriented ZnO crystals electrochemically doped with hydrogen are presented. The hydrogen content in the crystals is determined by nuclear reaction analysis and it is found that already 0.3 at. % H exists in chemically bound form in the virgin ZnO crystals. A single positron lifetime of 182 ps is detected in the virgin crystals and attributed to saturated positron trapping at Zn vacancies surrounded by hydrogen atoms. It is demonstrated that a very high amount of hydrogen (up to similar to 30 at. %) can be introduced into the crystals by electrochemical doping. More than half of this amount is chemically bound, i.e., incorporated into the ZnO crystal lattice. This drastic increase of the hydrogen concentration is of marginal impact on the measured positron lifetime, whereas a contribution of positrons annihilated by electrons belonging to O-H bonds formed in the hydrogen doped crystal is found in coincidence Doppler broaden!
ing spectra. The formation of hexagonal shape pyramids on the surface of the hydrogen doped crystals by optical microscopy is observed and discussed.

At present positron emission tomography (PET) is the only feasible method of an in situ and non-invasive monitoring of patient irradiation with ions. At the experimental carbon ion treatment facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt an in-beam PET scanner has been integrated into the treatment site and lead to a considerable quality improvement of the therapy. Thus, it is highly desirable to extend in-beam PET also to other therapeutic relevant ions which requires an extensive knowledge on the spatial distribution of generated positron emitters. Therefore, by means of the in-beam PET scanner at GSI the beta+-activity induced by 7Li3+ ions has been investigated for the first time. Targets of PMMA, water, graphite and polyethylene were irradiated with monoenergetic, pencil-like beams of 7Li3+ with energies between 129.1 AMeV and 205.3 AMeV and intensities ranging from 3.0 e7 to 1.9 e8 ions s-1. This paper presents the measured beta+-activity profiles as well as depth dependent thick target yields which have been deduced from the experimental data. The beta+-activity induced by 7Li ions was found to be a factor of 1.9 higher than the one induced by 12C ions at the same physical dose and particle range.

In this paper the development of a new thermal design for a high resolution gamma ray computed tomography detector is presented. The new design has become necessary due to stringent requirements on count rate accuracy under varying thermal conditions at thermal hydraulic test loops. The components of the existing tomography detector have been analysed with respect to their thermal response and a new arrangement has been devised that is optimized with respect to efficient heat conduction from internal as well as external heat sources to a cooling circuit.

The population balance equation (PBE) has been combined with a steady-state gas phase momentum equation to model the operation of an air-water bubble column. Instead of solving a bubble number density constitutive equation, a population balance equation with coalescence term has been solved. The system of equations has been linearized by successive iteration and solved by the least-squares method with high accuracy and fast convergence. The bubble size distribution along the column axis has been investigated and compared to the corresponding experimental data, showing good agreement.

The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions for a self-sustaining dynamo. Within the interior of a field producing domain geometric constraints or varying material properties (e.g. electrical conductivity of the container walls or localized high-permeability material) might also play a role. Combining a grid based finite volume approach with the boundary element method in a hybrid FV-BEM scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions in almost arbitrary geometries at comparatively low costs. Kinematic simulations of dynamo action generated by a well known prescribed mean flow demonstrate the reliability of the approach.

Future examinations are intended to understand the behavior of the VKS-dynamo experiment where the field producing flow is driven by ferrous propell lers and the induction effects of conductivity/permeability inhomogeneities might provide the required conditions for the measured dynamo characteristics.

The velocity field of a propeller-driven liquid metal flow is reconstructed by a contactless inductive flow tomography (CIFT). A robust reconstruction of large scale velocity fields is already achieved by applying the external magnetic field in two orthogonal directions. The results of this technique are shown to be in satisfactory agreement with ultrasonic measurements.

Uranium is an ubiqutous element. Besides this depleted uranium amunition as well as uranium mining and milling and manifold other use of uranium leads to an increase of uranium contamination in the environment.
Application of laser-induced and time-resolved methods allow the direct determination of uranium speciation at extremely low concentrations. This behaviour can be directly observed due to the properties extraorbitant luminescence properties of uranium-(VI). Contact of dissolved uranium with living cells at ambient conditions changes dramatically the uranium speciation.
Some examples fluorescence properties of uranium species relevant to the environment are shown. The change of this speciation can be observed then due to a change in luminescence properties. Besides of several organic phosphate binding forms although other uranium species were found as uranium bond to phenolic and thiol groups. Some of them do not emit any luminescence at room temperature. Nevertheless low temperature measurements allow the assignment of species not fluorescing at room temperature, due to strong dynamic quench effects of H2O molecules and COO- groups.

Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed specific extracellular defence reactions after uranium exposure. These include characteristic pH-shifts of the culture medium caused by contact with the heavy metal. At the same time a transient release of fluorescent compounds from the cells occurred. These phytoalexins probably belong to the widespread group of flavonoids detected by HPLC and thin layer chromatography (TLC). They are able to interact with uranium and hence can protect the cell against heavy metal poisoning. To gain an insight in these interactions time-resolved laser-induced fluorescence spectroscopy (TRLFS) was performed. Further investigations are under way to identify intracellular defence mechanisms, e.g. spatial patterns of a possible cytoplasmic pH-shift, the formation of proteins possessing thiol groups (phytochelatins), respectively.

Results of high-field ESR and magnetization studies of the new spin-1 Haldane-chain material Ni(C2H8N2)2NO2 are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding Δ/kB = 17.4 K, gk = 2.14, D/kB = 7.5 K, and |E/kB| = 0.7 K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, which
origin is discussed.

Rare earth-nickel-borocarbides have attracted much interest in the last years because the compounds show the interplay of superconductivity and magnetic ordering. LuNi2B2C can be considered as non-magnetic reference system of such magnetic borocarbides as HoNi2B2C in which superconducting and antiferromagnetic ordering temperatures, Tc and TN, are similar.
So far, LuNi2B2C crystals were only prepared by a flux method. For growing larger crystals we used an optical floating zone (FZ) technique, which already was successful in crystal growth of other RNi2B2C (R = Y,Tb,Ho,Tm,Er) compounds. In the case of LuNi2B2C, the primary crystallization field is far from the stoichiometric composition, and adjacent to the properitectic LuB2C2 phase field an extended region of LuNiBC occurs. Systematic studies of polycrystalline samples revealed that samples with nominal compositions LuNi5B3.5C and LuNi5B3C0.5 are free of the properitectic LuB2C2 and LuNiBC phases.
Thus in the FZ crystal growth experiments we used a molten zone which corresponds to these compositions. From the grown LuNi2B2C rods single crystalline pieces have been prepared to investigate Fermi surface peculiarities by magnetoresistance measurements and to study the electronic band structure.

We present specific heat and torque-magnetization data of the layered organic superconductor κ-(BEDT-TTF)₂Cu(NCS)₂ in high magnetic fields up to 28 T and at low temperatures down to 1.5 K. The magnetic field was aligned perfectly parallel to the superconducting planes of the sample. In that orientation and at low temperatures the upper critical field, B_c2, gets close to the Pauli limit which is about 21 T. But instead of the expected saturation at this field value we observe an upturn of B_c2 towards low temperatures. This comes along with a change of the order of the phase transition from second order to first order. In addition, another first-order phase transition appears below B_c2 in the superconducting state. These features strongly point to the formation of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in the state above the Pauli limit. Our results are in line with the behaviour predicted for FFLO states in two-dimensional systems.

Quantum phase transitions are one of the important topics in the understanding of condensed matter. These transitions are driven by quantum fluctuations in contrast to classical phase transitions which are accompanied by thermal fluctuations. Recently, the heavy fermion system YbRh2Si2 was intensively studied, because it is a clean and stoichiometric metal situated on the magnetic side (TN = 72 mK), but very close to a quantum critical point, which can be crossed by applying a tiny magnetic field. Therefore, this system presents both an antiferromagnetic phase transition driven by thermal fluctuations as well as pronounced quantum fluctuations due to the vicinity to the quantum phase transition. In this contribution, we show accurate measurements of the specific heat C around TN on a single crystal of highest quality (RRR ~ 150). We observe a very sharp peak at TN with absolute values as high as C/T = 8 J/molK2. A detailed analysis of the critical exponent α around TN reveals α = 0.37 which differs significantly from those of the conventional universality classes in the Landau theory α < 0.11. We will discuss in detail the analysis and possible mechanism.

Results of systematic tunable-frequency ESR studies of the spin dynamics in NiCl₂-4SC(NH₂)₂ (known as DTN), a gapped S = 1 chain system with easy-plane anisotropy dominating over the exchange coupling (large-D chain), are presented. We have obtained direct evidence for two-magnon bound states, predicted for S = 1 large-D spin chains in the fully spin-polarized (FSP) phase. The frequency–field dependence of the corresponding excitations was calculated using the set of parameters obtained earlier [S.A. Zvyagin, et al., Phys. Rev. Lett. 98 (2007) 047205]. Very good agreement between the calculations and the experiment was obtained. It is argued that the observation of transitions from the ground to two-magnon bound states might indicate a more complex picture of magnetic interactions in DTN, involving a finite in-plane anisotropy.

We report on resistance and Hall-effect measurements of the half-Heusler compound CeBiPt in pulsed magnetic fields up to 70 T. The band structure of the semimetal CeBiPt depends highly sensitively on temperature, magnetic field, and stoichiometry. This is reflected by the observed sample-dependent threshold fields above which the Shubnikov–de Haas signal disappears and at which clear changes of the Hall coefficient occur.

Abstract. Results of magnetization and high-field electron spin resonance (ESR) studies of the new spin-1 Haldane-chain material [Ni(C2H8N2)2NO2] (BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency–field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding ∆/kB = 17.4 K, g = 2.14, D/kB = 7.5K and |E/kB| = 0.7K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap; their origin is discussed.

The combination of magnetic and semiconducting properties in oxides is currently one of most popular fields in materials research. Besides the expected gain of knowledge about basic physics, such materials have a large application potential in spin electronics. We present a summary of our results on transition metal doping of ZnO single crystals and thin films by means of ion implantation. We found that none of the samples investigated represents a diluted magnetic semiconductor as predicted by theory [1]. The observed ferromagnetism mainly originates from secondary phase formation (metals or inverted spinel ferrites). We highlight the suppression of secondary phase formation by means of deliberately lowering the crystalline quality prior to the doping. Moreover, bombardment with transition metal ions leads to defects which create weak ferromagnetism without participation of the transition metal implanted. We discuss the possibility that such defects are also responsible for ferromagnetism observed in transition metal doped ZnO thin films. Thus, interpretations of ferromagnetic DMS reported in the past are often misleading.

[1] K. Sato and H. Katayama-Yoshida, Physica E 10, 251 (2001).

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides external users with the possibility of performing diverse experiments in pulsed magnetic field. Various experimental techniques, such as electrical transport, magnetization, ultrasound and magnetic-resonance measurements are available or are under installation at the HLD. A particular feature of the laboratory is a nearby free-electron laser facility which enables high-field infrared spectroscopy in pulsed magnetic fields [1].
A 50 MJ modular capacitor bank with a maximum charging voltage of 24 kV is in operation at the HLD. This capacitor bank allows to energize independently up to four sub-coils in multi-coil configurations and the energy pulses can be switched to five experimental cells. A program of the non-destructive pulsed magnets for the HLD includes a wide spectrum of coils designed for energies between 1 and 46 MJ, magnetic fields of 60 – 100 T, pulse durations of 10 - 1000 ms, and magnet bores in the range from 20 to 40 mm. In order to fulfill this program the necessary infrastructure accounting for the technical and technological aspects of pulsed-magnet design and fabrication has been established at the HLD. A pulsed-magnet core design has been developed [2]. In spite of the strong external mechanical support, our magnets are designed in a compact way which is suitable both for a mono-coil and a multi-coil configuration. With this design we are trying to achieve higher fields with longer pulse duration and high field homogeneity as well as to provide adequate space inside the magnet for the experimental installations. Important issues of the pulsed-magnet design are numerical simulations of the magnet performance. Both analytical approaches and finite-element analysis are used for these simulations.
Currently a number of 60 T /1.44 MJ and 70 T /8.5 MJ pulsed-magnets are available for external users and for in-house research [3]. A fabrication of a 60 T /43 MJ “long pulse” mono-coil is near to completion. A few double-coil prototypes have been designed, constructed and tested in frame of our 100 T project. Using the test results some improvements have been implemented in the multi-coil configuration. New double-coil prototypes targeting magnetic field above 90 T are under construction now.