Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We report recent discoveries of superconductivity in Ga-doped germanium fabricated by ion implantation and subsequent flash-lamp or oven annealing. Tuning the preparation parameters allows for varying both charge-carrier and Ga concentration in the resulting roughly 100 nm thin nano- or single-crystalline layers. Transport measurements on systematically prepared samples reveal that besides a needed charge-carrier concentration of more than 0.4 atom%, superconductivity occurs to be sensitive on the implanted Ga content which may also be attributed to a change in the phonon properties. Onset transition temperatures up to 1.4 K have been found for almost 10 atom% Ga. Further, we observe in-plane critical fields exceeding 1 T and being close to the Pauli-Clogston limit. An exceptionally low Cooper-pair density of around 10¹⁵ cm⁻³ turns out the extreme type-II character of superconductivity. Finally, our work adds to our previous report [1] and may help to understand superconductivity in doped elemental semiconductors in general.

Today's available strong magnets allow to study distinct magnetic effects in various electrochemical systems. Lorentz forces and also magnetic gradient forces can be utilized to tailor convection and mass transfer in electrolytic cells, thereby influencing for example the morphology and the structure of the electrodeposits. The presentation will give an overview on recent results of numerical simulations and experimental findings in lab-scale electrochemical systems and will discuss potential applications. Whereas Lorentz forces are often known to enhance mass transfer, new results show that the convection pattern found in simple geometries can already be quite complex. A deeper understanding is required for improved applications. Recently, also magnetic gradient forces gained attention, e.g. for their potential in preparing micro-structured deposits. A detailed discussion of recent results will give further insight. Finally, new investigations of cyclic operation modes or time-dependent magnetic fields are presented which allow for a broad range of new phenomena.

Die Koordinationschemie von Uran(VI) hat in den letzten Jahren vielfältiges Interesse gefunden. Ursachen dafür sind sowohl dessen Bedeutung im Rahmen der Kernenergiegewinnung als auch Probleme bei der Aufarbeitung sowie Lagerung von verbrauchten Kernbrennstoffen. Weitere Fragestellungen beziehen sich auf die Umweltrelevanz von U(VI) als Folge seiner natürlichen Verbreitung sowie bergbaulicher Altlasten. Schließlich werden auch potentielle Anwendungsoptionen von spezifischen Komplexverbindungen des Urans diskutiert.
Wir haben einige Imin-Liganden synthetisiert und drei neue Komplexverbindungen mit UO2(NO3)2 strukturell charakterisiert. Zum Vergleich wurden auch die strukturanalogen Aminderivate in die Untersuchungen einbezogen. Extraktionsexperimente mit den genannten Liganden zeigen differenzierte Extraktionseigenschaften gegenüber U(VI) mit einer ausgeprägten Selektivität gegenüber Eu(III).

Kelvin probe force microscopy (KPFM) is used for the nanoscale characterization of semiconductors. Quantitative dopant profiling by means of KPFM measurements is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions after Mn implantation [2].
In addition, it will be shown that due to surface state formation and charge trapping in a thin native oxide layer the Kelvin bias probed above differently doped regions strongly depends on the measurement frequency [3]. Therefore, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, H. Schmidt, submitted.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

Control over the morphology and spatial correlations at the nanoscale is one of the major challenge of the nowadays nanoscience and nanotechnology. Bottom-up approaches to nanostructured material synthesis are based on self-organization processes to precisely define ordered nanostructures on a large scale. Self-organization occurs via the interplay between two factors - an external constraint acting on internal system processes. During the thin film growth this is translated into the interplay between thermodynamic driving forces and kinetic constraints. In this talk I will summarize the recent research activities of our group on the phase separation during the growth of carbontransition metal thin films. Different processes can be ’switched off/on’ by external control of the experimental parameters such as temperature, substrate type, matrix/dispersed phase chemical affinity or incoming particle energy. This results in a large variety of lateral or vertical composition modulations, such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays. Such self-organization process is versatile as different carbontransition metal systems show this effect. The observed tendencies will be discussed on the basis of the interplay of thermal and energetic ion induced phenomena.

Actinide redox chemistry plays a crucial role in nuclear technology like fuel reprocessing and nuclear waste disposal aspects including predicting of actinide mobility in the environment. Hydrolysis and complex formation of the early actinides are strongly related with their redox behavior in aqueous and nonaqueous solutions. We are interested in understanding the complexation of actinide compounds under controlled redox conditions in presence of inorganic oxo ligands and organic ligands with carboxylic groups.
This study is mainly focused on the use of EXAFS spectroscopy in combination with other supporting methods. The information from EXAFS spectroscopy is restricted to a pair distribution function providing coordination numbers and distances of the next neighbors. Two pathways were used to relate this information to the spatial arrangement of the ligands: (i) EXAFS was combined with DFT calculations which introduce constraints of molecular characteristics [1], and (ii) individual solution species were preserved in crystal structures and determined with single crystal diffraction. EXAFS was used subsequently to quantify differences or identify agreement between the coordination of complex structures in solution and solid state [2-4]. EXAFS is furthermore not very sensitive to differentiate between individual solution species, especially in not a single sample. This problem was solved in the following manner: (i) combination of EXAFS with other more species sensitive techniques, e.g. like UV-Vis spectroscopy [5] and (ii) by using sample series with broad variation of species distribution and subsequent application of statistical analysis techniques to separate the scattering contribution of individual solution species [6]. Finally, we investigated the correlation between the formal redox potential and the stability range of solution species [7].

[1] Hennig et al. The sulfate coordination of Np(IV), Np(V) and Np(VI) in aqueous solution. Inorg. Chem. 48 (2009) 5350-5360.
[2] Hennig et al. Comparative investigation of the solution species [U(CO3)5]6 and the crystal structure of Na6[U(CO3)5]•12H2O. Dalton Trans. 39 (2010) 3744–3750.
[3] Takao et al. First hexanuclear UIV and ThIV formate complexes – structure and stability range in solution. Eur. J. Inorg. Chem. (2009) 4771-4775.
[4] Hennig et al. Coordination of a uranium(IV) monomer in aqueous solution and in solid state. Inorg. Chem. 47 (2008) 1634-1638.
[5] Hennig et al. The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution. Radiochim. Acta 96 (2008) 607-611.
[6] Hennig et al. Species distribution and coordination of uranyl chloro complexes in acetonitrile. Inorg. Chem. 47 (2008) 2987-2993.
[7] Takao et al. Complex formation and molecular structure of neptunyl(VI) and –(V) acetates. Inorg. Chem. 48 (2009) 8803-8810.

The aim of this paper is to present the validation of a new methodology implemented in ANSYS CFX (ANSYS, 2009), that extends the standard capabilities of the inhomogeneous MUltiple-SIze Group model (MUSIG) by additionally accounting for bubble size changes due to heat and mass transfer. Bubble condensation plays an important role in sub-cooled boiling or steam injection into pools among many other applications of interest in the Nuclear Reactor Safety (NRS) area and other engineering areas. Since the mass transfer rate between phases is proportional to the interfacial area density, a polydisperse modelling approach considering different bubble sizes is of main importance, because an accurate prediction of the bubble diameter distribution is required.
The standard MUSIG approach is an inhomogeneous one with respect to bubble velocities, which combines the size classes into different so-called velocity groups to precisely capture the different behaviour of the bubbles depending on their size. In the framework of collaboration between ANSYS and the Forschungszentrum Dresden-Rossendorf (FZD) an extension of the MUSIG model was developed, which allows to take into account the effect of mass transfer due to evaporation and condensation on the bubble size distribution changes in addition to breakup and coalescence effects.
After the successful verification of the model, the next step was the validation of the new developed model against experimental data. For this purpose an experiment was chosen, which was investigated in detail at the TOPFLOW test facility at FZD. It consists of a steam bubble condensation case at 2MPa pressure in 3.9K sub-cooled water at a large diameter (DN200) vertical pipe. Sub-cooled water flows into the 195.3 mm wide and 8 m height pipe, were steam is injected at z=0.0 m and is recondensing. The experimental results are published in (Lucas, et al., 2007). Using a wire-mesh sensor technique the main characteristics of the two-phase flow were measured, i.e. radial steam volume fraction distribution and bubble
diameter distribution at different heights and cross-sections.
ANSYS CFX 12.0 was used for the numerical prediction. A 60 degrees pipe sector was modelled in order to save computational time, discretized into a mesh containing about 260.000 elements refined towards the pipe wall and towards the location of the steam injection nozzles. Interfacial forces due to drag, lift, turbulent dispersion and wall lubrication force were considered. The numerical results were compared to the experimental data. The agreement is highly satisfactory, proving the capability of the new MUSIG model extension to accurately predict such complex two-phase flow.

The objective of this work has been to study the mechanisms governing flow and phase distributions in developing gas/liquid two phase flows in general, and the evolution of different size bubbles in an adiabatic vertical pipe in particular. Flow regimes from bubbly to churn-turbulent have been accounted for. The main emphasis of the work has been on the modeling of various interfacial forces between the dispersed bubbles and the continuous liquid, as well as of bubble/bubble interactions (coalescence and breakup).
The proposed modeling concept uses a complete set of transport equations for each field, such as the continuous liquid and dispersed bubble fields. The overall model has been implemented in a state-of-the-art computational multiphase fluid dynamics code, NPHASE–CMFD. This three-dimensional four-field model, including the continuous liquid field and three dispersed gas fields representing bubbles of different sizes, has been carefully tested for numerical convergence and accuracy, and then validated against the TOPFLOW experimental results.
The NPHASE-CMFD simulations were aimed at demonstrating the capability of the proposed modeling concepts to predict the evolution of bubble concentration from channel inlet to near-equilibrium (fully-developed) conditions downstream. Along with several interfacial closure laws, the effect of elevation on air density has also been included in the model.

In the first part of the contribution, a rather simple design of a conventional, magnetically guided, continuous positron beam will be presented. The moderator is a tungsten mesh and the energy selection is realized using a bent tube. The sample is on ground potential. Further details will be presented during the talk.
In the second part of the talk, the recent progress of the EPOS project at the Research Center Dresden-Rossendorf will be demonstrated. EPOS consists of a pulsed monoenergetic positron beam (MePS), a conventional lifetime/Doppler spectrometer (CoPS), and a setup for gamma-induced positron annihilation spectroscopy (GiPS). While CoPS and GiPS systems are available for user operation, the MePS system is still under construction. First positrons were moderated and fed into the positron lab. At the moment, the chopper/buncher/accelerator system is under construction.

We report on the nature of vacancy complexes and voids involved in H ion-induced splitting of free standing fs-GaN. The fs-GaN wafers were subjected to room temperature implantation with 50 keV H ions at a fluence of 2x10¹⁷ H cm^-2. After implantation, the wafers were annealed at different temperatures ranging from 100 to 600 °C. Variable energy Doppler broadening spectroscopy (VEDBS) was used in order to probe open-volume defects and their thermoevolution. Pulsed low energy positron lifetime spectroscopy (PLEPLS) was employed to qualitively characterize H ion-induced vacancy complexes and to observe their subtle changes during the thermally activated splitting of GaN thin layer. The decomposition of the lifetime spectra of as-implanted and annealed samples up to a temperature of 450 °C resulted in the detection of two vacancy defects: divacancies (260-282 ps) and vacancy clusters (470-650 ps). With increasing temperature, we have noted in addition the existence of other kind of vacancy-type defects, namely, monovacancies (220-236 ps) and a long lifetime which is attributed to positronium. From the values of positronium lifetime equal to 1 ns, 2.2 ns and 3.8 ns, it was possible to estimate the corresponding wall spacing according to the Tao-Eldrup model to be 0.2 nm to 0.4 nm. The fact that positron annihilation spectroscopy can give information about the wall spacing in GaN, leads us to say that this technique is able to predict the phenomenon of splitting in wide band gap semiconductors.

Kinematic simulations of the induction equation are carried out for different setups suitable for the von-Karman-Sodium (VKS) dynamo experiment. Material properties of the flow driving impellers are considered by means of high conducting and high permeability disks that are present in a cylindrical volume filled with a conducting fluid. Two entirely different numerical codes are mutually validated by showing quantitative agreement on Ohmic decay and kinematic dynamo problems using various configurations and physical parameters. Field geometry and growth rates are strongly modified by the material properties of the disks even if the high permeability/high conductivity material is localized within a quite thin region. In contrast the influence of external boundary conditions remains small.

Utilizing a VKS like mean fluid flow and high permeability disks yields a reduction of the critical magnetic Reynolds number for the onset of dynamo action of the simplest non-axisymmetric field mode. However this decrease is not sufficient to become relevant in the VKS experiment. Furthermore, the reduction of Rm_c is essentially influenced by tiny changes in the flow configuration so that the result is not very robust against small modifications of setup and properties of turbulence.

Particle Image Velocimetry (PIV) is a powerful measurement technique, suitable for the study of complex flow fields encountered in single- or two-phase flow phenomena. Air entrainment is a widely studied phenomenon, which is encountered in multiple industrial applications, as well as in nature. Results from the successful application of PIV to both impinging region and recirculation zone are presented. Both instantaneous and time-averaged flow fields were obtained. The turbulent kinetic energy is estimated from the averaged velocity fields in the recirculation zone. Simulations of the phenomenon are performed with ANSYS-CFX. The turbulence was modelled using the k-epsilon model. Experimental results were compared with the simulation and showed good agreement.

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We report on measurements of the magnetization up to 7 T, of the specific heat and electrical resistivity in fields up to 14 T, and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh₁₇S₁₅. Our data allow us to complement the superconducting phase diagram. The existence of narrow 4 d-band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the moderately high electronic contribution to the specific heat of about 107 mJ/molK², favoring the existence of a strong superconducting interaction. This fact, and the remarkably high upper critical field (exceeding the simple Pauli limit by a factor of two), give evidence of the uncommon nature of the superconductivity in Rh₁₇S₁₅.

The transverse acoustic wave propagating along the [100] axis of the cubic paramagnet Tb₃Ga₅O₁₂ (TGG) exhibits amplitude oscillations as a function of magnetic field applied in the direction of propagation. This magneto-acoustic Faraday effect shows a linear frequency dependence contrary to theoretical expectation which demands a quadratic frequency dependence. The c₄₄ mode demonstrates also a strong softening of 6% up to 19 T, the magnetic field where an energy level of the CEF triplet branch starts to cross the quasi-doublet branch. This softening has the same origin, the magneto-elastic coupling, as the anomalies in the temperature dependence of the elastic constants and the magneto-acoustic Faraday effect.

We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice spin-1/2 antiferromagnet Cs₂CuCl₄ (T_N = 0.6 K), in external magnetic fields up to 14 T, applied along the b axis, and at temperatures down to 300 mK. The results are analyzed with a quasi-two-dimensional hard-core boson theory based on exchange-striction coupling. There is a good qualitative agreement between theoretical and experimental results.

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area from 90 × 90 μm down to 20 × 20 μm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. MHPs were intensively tested in static (up to 14 T) and pulsed magnetic fields and shown to be appropriate for various applications in the temperature range 2–300 K and in pulsed magnetic fields up to 87 T. The latest version of these probes, with overall cross-section thickness-width dimensions of 150 × 750 μm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged or unpackaged sensors.

We report resistivity and upper critical field B_c2(T ) data for As-deficient LaO_0.9F_0.1FeAs_1−δ in a wide temperature and field range up to 60 T. These disordered samples exhibit a slightly enhanced superconducting transition at T_c = 29 K and a significantly enlarged slope dB_c2/dT = −5.4 T/K near T_c which contrasts with a flattening of B_c2(T ) starting near 23 K above 30 T. This flattening is interpreted as Pauli limiting behavior (PLB) with B_c2(0) ≈ 63 T. We compare our results with B_c2(T )-data reported in the literature for clean and disordered samples. Whereas clean samples show no PLB for fields below 60 to 70 T, the hitherto unexplained flattening of B_c2(T ) for applied fields H || ab observed for several disordered closely related systems is interpreted also as a manifestation of PLB. Consequences of our results are discussed in terms of disorder effects within the frame of conventional and unconventional superconductivity.

We report on pulsed-field magnetization studies of the quasi-two-dimensional spin system [Cu(pyz)₂(HF₂)]PF₆. The magnetization saturates at B^ab _C = 37.5 T and B^c _C= 33.8 T for in-plane and out-of-plane orientations of the applied magnetic field, respectively. In addition, the angular dependence of the g-factor studied by electron-spin resonance reveals orbital overlap in the ab plane suggesting a quasi-two-dimensional square-lattice network of Cu spins. It is argued that the high-field behavior is governed by the two-dimensional nature of the spin correlations due to the large anisotropy of the exchange couplings.

Laser wake¯eld experiments present a unique challenge in measuring the resulting electron energy properties due to the large energy range of interest, typically several 100 MeV, and the large electron beam divergence and pointing jitter >1 mrad. In many experiments the energy resolution and accuracy are limited by the convolved transverse spot size and pointing jitter of the beam. In this paper we present an electron energy spectrometer consisting of two magnets designed speci¯cally for laser wake¯eld experiments. In the primary magnet the ¯eld is produced by permanent magnets while a second electromagnet can be used for electron energies above 75 MeV. The spectrometer has an acceptance of 2.5-400 MeV (Emax=Emin > 100) with a resolution of better than 1% rms for electron energies above 25 MeV. This high resolution is achieved by refocusing electrons in the energy plane and without any post-processing image deconvolution. Finally, the spectrometer employs two complimentary detection mechanisms: 1) absolutely calibrated scintillation screens imaged by cameras outside the vacuum chamber, and 2) an array of scintillating ¯bers coupled to a low-noise CCD.

This review summarizes research into interactions between microorganisms and radionuclides under conditions typical of a repository for high-level radioactive waste in deep hard rock environments at a depth of approximately 500 m. The cell-radionuclide interactions of strains of Pseudomonas species (i.e., Shewanella putrefaciens and Desulfovibrio aespoeensis) with Cm, Pm, and Pu were investigated in vitro and the results were found to agree with literature data. Siderophores are capable of binding actinides strongly and need to be considered in terms of radionuclide mobility in the subsurface. Siderophores and other bioligands were found to have a generally very strong mobilizing effect on Am, Cm, Fe, Np, Pm, Pu, Th, and U. Where reduced groundwater enters an aerobic environment, such as a large open fracture or fracture zone (e.g., in tunnels), there is the possibility of rapid aerobic bacterial metabolism, microbial proliferation, biofilm development, and iron oxide formation. In these environments, the stalk-forming bacterium Gallionella may act as a scaffold for iron oxide precipitation on biological material. In situ work in the Äspö Hard Rock Laboratory tunnel indicated that the concentrations of biological iron oxides, lanthanides, and actinides correlated positively with Gallionella biomass, a finding that compares well to literature data. In deep oligotrophic subsurface granitic rock environments, fracture biofilms reach a threshold of approximately 2-5 x 10⁶ cells/cm². The cells in these biofilms are spatially distinct and are surrounded by an extracellular polysaccharide matrix that constitutes up to 60% of the total organic carbon. Calcium-rich amorphous masses are associated with this base layer of cells and organic exudates. In situ, these biofilms have been found to influence the adsorption and immobilization of Am, Np, Pm, Th, and U. This review demonstrates that microorganisms can influence, and sometimes even control, the migration behavior of radionuclides in deep geological environments typical of future sites for radioactive waste repositories.

Plunging jets play an important role in nuclear reactor safety research. In the present paper the case of the strainer clogging issue is considered. Entrained air caused by a plunging jet has an influence of the liquid flow field and on the fibre transport in the sump. In the paper the amount of entrained air is given as an inlet boundary condition according to correlations in the literature and confirmed by own experiments. The influence of entrained air on the fibre deposition pattern at the bottom of a tank and on the mixing procedure for the case of temperature differences between jet and tank water are investigated by CFD calculations and compared to experiments.
The presented work is part of a joint research project performed in cooperation between the University of Applied Science Zittau/Görlitz and Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow in Zittau and the development of CFD models for its simulation in Rossendorf (Krepper et al. 2008).

Shubnikov-de Haas oscillation and cyclotron resonance were studied for high mobility p-type Ge channels in strained Ge/Si1-x Ge (x) quantum wells, using pulsed high magnetic fields up to 50 T. Fine quantum oscillations were observed in rho (xx) . Reflecting the complex Landau level structure in the nearly degenerate valence bands, the Fourier transform of the oscillatory spectra consists of several peaks. Cyclotron resonance was measured at photon energies between 10 and 17 meV. Two well-defined resonance peaks were observed in two samples with different x, resulting in different strains. A large non-parabolicity and large strain dependence of the effective masses were observed.

Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels.

Silicate materials such as glass, porcelain and ceramics, but also geological findings are characterized by their chemical composition. Corresponding fingerprints of unique pieces - e.g. precious objects of art - have to be studied stringently in a non-destructive manner. Elements along the whole periodic system are of analytical interest. These requirements are met by ion beam analysis (IBA) using protons of 4 MeV energy extracted from vacuum into atmospheric pressure. Atoms of the object of investigation, struck by protons, emit characteristic γ-radiation due to nuclear reactions as well as X-rays via proton-electron interactions. Simultaneous detection of PIGE (Particle Induced Gamma-ray Emission) and PIXE (Particle Induced X-ray Emission) signals allows determination of all chemical constituents. PIGE measures the concentration of the main element Si, consequently the SiO2 content. Moreover, PIGE gives the concentrations of accompanying light elements like Li, B, Na, Mg and Al and their natural oxides; also F can be examined.
Maximum information depths in glass are in the order of 40 µm. Hence, the PIGE results represent the silicate material bulk. PIXE provides concentrations of the elements heavier than Al (Z > 13). Maximum PIXE information depths in glass are only 10 µm, which is due to much higher attenuation of X-rays (E~keV) compared to that of γ-rays (E~MeV). Therefore, the PIXE results stand for the bulk material only if the object surface was not attacked by strong deterioration. PIGE-PIXE analysis of silicate materials must be executed in an interactive manner in order to account for radiation absorption effects. Protons reflected from atoms situated in depth regions near the material surface, i.e. Rutherford Backscattering Spectrometry (RBS), inform of environmental degradation. Thus, IBA is best-suited to calculate both the state of preservation as well as the possible danger of progressive deterioration regarding cultural heritage, especially which made from glass [1].
As is known, K-Ca-silica glass gets decomposed by leaching when being exposed to humid surroundings, even under air conditioning in museum collections. Both, protective storage and preventive conservation have become one of the primary tasks in museum science. The performance of IBA is figuring out glass objects of endangered composition as long as indications of alteration are still not visible. Exhibits sui generis dated from baroque era and treasured inside the museum of applied arts in Dresden were already exposed to the proton beam in air. Several exhibits show visually opacity, some of them a network of fine cracks. The final evaluation of measured data is in the offing. Composition analysis of single obsidian pieces has been a topic of international interest. For their characterization questions have concentrated on fingerprints regarding elements heavier than Fe, being enclosed with low concentrations.
For the bulk materials of interest IBA detection limits are in the order of 5 - 300 µg/g, thus falling for light elements Z < 22 (Ti) below that of X-ray fluorescence spectrometry.

Reference: [1] M. Mäder, C. Neelmeijer, Nucl. Instr. and Meth. B 226 (2004) 110 - 118

Numerical calculations using FLUENT6.3.26 were conducted for steam-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg at FZD, and the results were compared with the FZD data.

Numerical calculations using FLUENT6.3.26 were conducted for air-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg at FZD, and the results were compared with CCFL characteristics in circular tubes.

Author reviews practical aspects of application of quantum cascade lasers (QCL) to high field laser magneto-spectroscopy of semiconductors. The universal QCL based experimental set-up, covering wide spectral region from 5 up to 120mm is presented. The performance of the setup is illustrated with cyclotron resonance measurements of InGaAs/GaAs and InAs/AlSb quantum wells.

Nanomaterials prepared by the sulfurization of Mo₆S₂I₈ nanowires and the time and temperature dependence of the transformation process are investigated by high-resolution transmission electron microscopy, X-ray powder diffraction, and wavelength-dependent Raman spectroscopy. Depending on the temperature, coaxial MoS₂ nanotubes or MoS₂ “mama”-tubes are formed after 2 h of sulfurization. Using a few minutes of sulfurization time, core-shell nanowires composed of well-ordered MoS₂ layers covering a Mo₆S₂I₈ core are formed, proving an outside-to-inside transformation process. The crystallinity of the three MoS₂ nanostructures increases with increasing transformation temperature, i.e., in the sequence from MoS₂/Mo₆S₂I₈ core-shell structures via coaxial MoS₂ tubes to the MoS₂ “mama”-tubes. The analysis indicates a different nature of the defects in the MoS₂-based nanomaterials, originating from the sulfurization of the Mo₆S₂I₈ than in the conventional MoS₂ platelike crystals. A correlation between the Raman spectroscopic parameters and the defect density in MoS₂ is identified.

Synthetic ZrSiO₄ and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV ⁴He²⁺ ions (fluences in the range 1 x 10¹³ – 5 x 10¹⁶ ions/cm²). For comparison, an additional irradiation experiment was done with 30 MeV ¹⁶O⁶⁺ ions (fluence 1 x 10¹⁵ ions/cm²). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO₄) or additional (mildly to strongly metamict natural samples) damage, respectively. The maximum extent of the damage is observed in a shallow depth range approximately 32–33 µm (8.8 MeV He) and ≤ 12 µm (30 MeV O) below the sample surface, respectively, i.e., near the end of the ion trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patters as predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational modes, lowered interference colours (i.e., decreased birefringence), and changes in the optical activity (i.e., luminescence emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels, this centre becomes re-suppressed and samples experience a general decrease of their emission intensity. Most remarkably, there is no indication of any structural recovery process in pre-damaged natural zircon as induced by the light-ion irradiation, which questions the relevance of alpha-assisted annealing of radiation damage in natural zircon.

Experiments were performed in a test facility at NETeF (Thermal-Fluids Engineering Laboratory) of the Engineering School of São Carlos. The facility consists basically of a horizontal glass pipe of 26 mm of inner diameter and 12 m length. Mineral oil (860 kg/m3 density and 100 mPa∙s viscosity) and tap water stored in separated tanks are circulated under controlled conditions through the test pipe. The flow rates of each liquid are individually controlled and measured. After passing the horizontal test section, the mixture flows to a coalescent-plate separator tank. The liquids once separated are returned to their respective storage tanks by gravity. A wire-mesh sensor with 8 x 8 wire configuration was installed close to end of the horizontal pipe at 10.3 m from the entrance. To assemble the wire-mesh sensor in the test pipe, a flange of transparent Perspex was manufactured which allows for optical observations (Fig 1a). A high-speed camera (Optronis, Camrecord 600) was applied to monitor the flow patterns and investigate the influence of wire-mesh sensor in the flow.
Experiments were performed at oil superficial velocity between 0.2 m/s to 1 m/s and water superficial velocity between 1 m/s to 3 m/s. The recording speed was 2000 fps for the high-speed camera and 500 fps for the wire-mesh sensor, whereby data acquisition of both systems was synchronized by a common trigger signal. Figure 1b and 1c show exemplary images of the flow obtained by the both imaging devices. Note that the high-speed camera depicts a lateral view of the flow, while the wire-mesh sensor images show holdup distributions over the cross section of the pipe. From the two-dimensional holdup distribution measured by the wire-mesh sensor we have further determined liquid holdup integrated over different domains thus obtaining time and/or spatially averaged holdup values, e.g. radial profiles or mean holdup. Furthermore, for comparison purposes of holdup measurements, the quick-closing valves (QCV) technique was employed. Good agreement was found between QCV and WMS techniques. In the full paper, a complete description of the measurements will be presented along with a discussion of the accuracy in the measurements.

no abstract available

Phosphopeptides are very useful reagents to study signal transduction pathways related with cellular protein phosphorylation/dephosphorylation. Phosphopeptides have also been identified as important drug candidates to modulate intracellular signaling mechanisms through targeting phosphotyrosine, phosphoserine, or phosphothreonine residue-binding protein domains. In this report, we describe the development of a convenient method for the mild and sufficient radiolabeling of phosphopeptides with the short-lived positron emitter fluorine-18 (¹⁸F) to allow radiopharmacological studies on phosphopeptide metabolism in vivo by means of positron emission tomography (PET). Radiolabeling was accomplished via conjugation of the N-terminus of polo-box domain (PBD)-binding phosphopeptide H-Met-Gln-Ser-pThr-Pro-Leu-OH with the bifunctional labeling agent N-succinimidyl-4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) in reproducible isolated radiochemical yields of 25-28%. Radiopharmacological evaluation in vitro and in vivo of radiolabeled phosphopeptide [¹⁸F]FB-Met-Gln-Ser-pThr-Pro-Leu-OH [¹⁸F]-3 and its non-phosphorylated analog [¹⁸F]FB-Met-Gln-Ser-Thr-Pro-Leu-OH [¹⁸F]-4 involved metabolic stability, cell uptake studies, and small animal PET experiments. Radiolabeled phosphopeptide [¹⁸F]-3 showed a remarkable high metabolic stability in vivo compared to the corresponding non-phosphorylated peptide [¹⁸F]-4. The presented method indicates that radiolabeling of phosphopeptides with [¹⁸F]SFB is a promising approach for studying phosphopeptide metabolism in vivo.

Evidence is provided by photon correlation spectroscopy, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids of a size of 620 nm. A concentration of up to 103 M of colloid-borne U(IV) was observed. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. Electrostatic repulsion due to a negative zeta potential in the near-neutral to alkaline pH range caused by the silicate stabilizes the U(IV) colloids. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. The mechanism of the colloidal stabilization can be regarded as “sequestration” by silicate, a phenomenon well known from heavy metal ions of high ion potential such as iron(III) or manganese(III,IV), but never reported for uranium(IV) so far. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U–O–Si bonds, which increasingly replace the U–O–U bonds of the amorphous uranium(IV) xyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO4. The assessment of uranium behavior in the aquatic environment should take the possible existence of U(IV)-silica colloids into consideration. Their occurrence might influence uranium migration in anoxic waters.

Absorption packing columns employing gas-liquid counter-current flow are widely used across a wide range of industries. Maldistribution of liquid phase could reduce the contact area of both phases, thus lowering column efficiency. Liquid holdup is an essential parameter that influence pressure drop and load capacity of the packing column. Traditional measurements of local liquid holdups using liquid collector strongly disturb the original conditions which make the results less reliable. In this study the local liquid holdup and their distribution was measured with the state-of-the-art technology using wire-mesh sensor installed below the packing.
Wire-mesh sensor contains 16x16 orthogonally arranged wires (up to 32x32), measuring the complex impedance at every sensing point which is related to the local permittivity over the whole cross section. Matrices which denote the local permittivity are obtained with a frequency up to 1000 frames per second. Knowing pure gas and liquid phase permittivity allows calculation of local phase fractions. Unlike ECT or ERT measurement, grid sensor excellently locates the liquid phase position and the area obstruction is lower than 1 percent.
Stochastic behavior of liquid flow at different time was found. It is shown that large scale of maldistribution near the wall was observed and most of liquid phase flows preferentially in the same zones.
The amount of liquid flowing along the column wall was characterized by analyzing liquid holdups of the annular grid points. It is shown that more than 27% of the liquid phase flows improperly and its amount varies dynamically.
Mesurements with wire-mesh sensor could be employed to correct essential parameters such as effective phase contact area, local liquid holdup and etc. Therefore, mass transfer laws suggested by Billet (1995) and hydraulic model by Mackowiak (2009) could be modified.

Recent developments of special models and correlations extended the system TH codes capabilities to simulate 3D phenomena. A code assessment process is always needed whenever the new code features are intended for nuclear reactor design and/or licensing applications. The Korean Thermal-Hydraulic code MARS (developed by Korea Atomic Energy Research Institute) experiences such an improvement, extending the 1D flow field formulation.
In this respect the present paper describes the activity conducted to assess the 3D features of the MARS code by independent users. The adopted experimental data are gathered in a test conducted at the ROCOM (Rossendorf Coolant Mixing Model) experimental facility, which reproduced a pump start-up scenario. In addition, to support the interpretation of experimental data and system code results, a CFD analysis has been also performed.
The assessment activity includes a comparison with RELAP5-3D© code, a set of sensitivity calculations and the use of the FFTBM package.

Monolith structures are a promising catalyst carrier to replace conventional catalyst particle packings in many gas-liquid-solid applications, such as hydrogenation, oxidation and enzymatic reactions. Enhanced reactor performance with respect to mass transfer, selectivity and conversion is mainly attributed to the more intense gas-liquid-solid contact within the regular structure and short diffusion distance due to thin liquid film layer. It is obvious that different flow regimes appear within the channels depending on superficial gas and liquid velocities and monolith channel geometry, e.g. bubble and Taylor flow regimes that feature especially high mass transfer rates and complete wetting of the monolith bed. Furthermore, bubble and slug lengths as well as their frequency and velocity can be tuned by operating conditions for optimization of reactor performance depending on the chemical reaction.
Therefore, gas-liquid dynamics in the channels of a monolith block need to be monitored. However, it was shown that design of gas-liquid distributor is the most crucial issue for uniform utilization of all monolithic channels and the hydrodynamic behavior in the monolith can drastically differ from single channel flow.
CREL laboratory applied gamma-ray tomography to study cross-sectional gas-liquid distribution but gives only time-averaged and blurred data while any temporal gas-liquid in-channel formation remains hidden (Roy and Al-Dahhan, 2005). On the other hand, magnetic resonance tomography from Cambridge University (Professor Gladden) drastically improved chemical engineering imaging, e.g. allowing access inside monolithic channels but exclusively for small diameters and non-metallic reactors (Mantle et al., 2002).
In the present work, a novel ultra-fast X-ray tomograph (Fischer et al., 2008) was applied to study gas-liquid distribution in monolithic structures operated in co-current up-flow. Different monolith configurations were installed and the system was operated at different gas and liquid superficial velocities. Normalized bubbles and slug length frequency distributions, gas and liquid fractions and cross-sectional distribution quality were calculated from image sequences. Furthermore, effect of the monolith in the cross-section on gas-liquid flow pattern was studied with respect to the gas-liquid flow in the pipe without structured internals.

In this article, air entrainment as a result of an impinging round water jet and a wall-jet was experimentally studied by means of videometry and image processing methods and also by means of a measuring technique based on a wire-mesh sensor. Therefore, two different experimental setups were utilized. For the first setup, a series of experiments at different conditions was performed and evaluated for both round jets and wall-jets. Jet lengths ranged between 0.01m and 0.2m and jet exit velocities between 0.9 m/s and 3.5 m/s. Image processing algorithms were applied to extract information about jet penetration depth, width of the bubble plume and bubble size distribution. The second facility was used to create a falling film in a square pipe (5 cm x 5 cm). Downstream of the impact point, a wire-mesh sensor was used to measure the gas entrainment characteristics at one axial location. Video image processing was also used in this experiment to gather more qualitative information about the gas entrainment process. Video images were compared with the images obtained by the wire-mesh sensor showing good agreement. The induction trumpet and a thin sheet of gas that is formed around the jet and penetrates into the pool causing the entrainment were clearly identified. Results indicate that the gas void fraction increases and the bubble size decreases as the superficial liquid velocity increases.

Direct numerical simulations were performed of the turbulent flow in a straight square duct in a transverse magnetic field. Without magnetic field the turbulence can be maintained for values of the bulk Reynolds number above approximately Re=1077 [1]. In the magnetohydrodynamic case this minimal value of the bulk Reynolds number increases with the Hartmann number. The flow is laminar at Re=3000 when the Hartmann number is larger than Ha=12.5 and the flow is turbulent for Ha < 12.0. The secondary mean flow structure is analyzed.

Air entrainment by a liquid falling film was experimentally studied by means of videometry, image processing methods, and also by a measuring technique based on wire-mesh sensor. Air was entrained by a plunging liquid film around a stagnant Taylor bubble. Downstream of the impact point, a wire-mesh sensor was used to measure the total gas void fraction, gas void fraction distribution, and bubble size distribution. Results indicate that the gas void fraction increases and the bubble size decreases as the superficial liquid velocity increases. Good agreement was found by comparing video images with the images obtained by the wire-mesh sensor.

Downward bubble flow due to the gas entrainment under a falling film was experimentally investigated using the Wire-Mesh Sensor (WMS) and high speed video camera. The flow pattern was identified using the flow visualization analysis of the WMS. The flow visualization analysis was done in a 2-D (x, y), pseudo 2-D (x, t and y, t), and pseudo 3-D (x, y, t) dimension. The flow pattern observed during the experiments was bubble flow. Good agreement was found by comparing video images with the images obtained by the wire-mesh sensor. Additionally, gas void fraction time series and bubble size distribution are presented. Results show that images obtained from the high speed camera, WMS and experimental observations are in good agreement. Also, it is showed that different approaches for flow pattern recognition can be used. Moreover, results show the influence of the superficial liquid velocity on the gas void fraction and bubble size.

Die industrielle Herstellung von Faserstoffen beinhaltet eine Vielzahl physikalisch-technologischer Prozesse, deren Komplexität vom Holzplatz bis zur Zerfaserung deutlich zunimmt. Die Zerfaserung im Refiner stellt einen hoch komplexen Prozess dar, dessen Wirkungsweise und physikalische Zusammenhänge zum gegenwärtigen Zeitpunkt nur in geringem Maße beschrieben werden können. Das vorhandene Wissen beruht auf Erfahrungen und empirisch gefundenen Zusammenhängen. Das Potential, dass die umfassende theoretische Durchdringung des Zerfaserungsprozesses und die sich daraus ergebenden Optimierungsmöglichkeiten hinsichtlich Einstellung einer definierten Faserqualität und Energieeinsparung bietet, wird nicht ausgeschöpft. Sichere Erkenntnisse zum Einfluss der Faserqualität auf die einzusetzende Bindemittelmenge und die späteren Eigenschaften der Faserplatten sind gleichfalls nicht vorhanden. Angesichts der getroffenen Feststellungen befasst sich das IHD in einem Projekt mit Untersuchungen zur Optimierung des Refinerprozesses hinsichtlich Energieeffizienz und Faserqualität.

In this paper, a high-resolution gamma-ray computed tomography (CT) measurement system is presented that was developed to determine phase fractions and other flow parameters in industrial devices operated under real industrial conditions. From CT scans non-superimposed cross-sectional images are reconstructed, which show the local gamma-ray attenuation coefficients within the scanned object slice. An advanced fast read-out electronics facilitates 2-D visualization of rapidly rotating multiphase distributions, such as in stirred chemical reactors or hydrodynamic machines. Furthermore, the CT measurement system can be applied to non-destructive testing of high-density devices to achieve information about the structure of material, i.e. when exposed to mechanical stress.

In the case of a hypothetical failure of a residual heat removal system under mid-loop operation during shutdown of a pressurized water reactor (PWR), steam generated in a reactor core and water condensed in a steam generator (SG) form a counter-current flow in a hot leg. Though several studies have been carried out to understand counter-current flow limitation (CCFL) in the hot leg, our knowledge on CCFL is still rudimentary. In this study, a scale-down model of the hot leg (one-fifteenth of the actual plant) is used to investigate the effects of fluid viscosity on CCFL in the hot leg. Air and water or air and glycerol-water solutions are used for the gas and liquid phases, respectively. Water levels in the hot leg are also measured using conductivity probes. The gas and liquid flow rates at CCFL are estimated by applying a one-dimensional momentum equation to the flow in the hot leg. As a result, the following conclusions are obtained. (1) CCFL causes a drastic change in the distribution of water level in the hot leg. (2) The liquid viscosity scarcely affects the interfacial force. The interfacial force is mainly due to form drag caused by the presence of large-amplitude waves.

At present, wood fibres for the production of medium density fibreboards (MDF) are produced in acceptable quality, but with high energy consumption. The adjustment of defined fibre properties is quite difficult, because the defibration process in refiners is a very complex one. Currently, its effectiveness as well as physical correlations can only be described to a minor degree. Existing knowledge is based on experiences and empirically retrieved coherences. For this reason, there is still a great demand for optimisation regarding efficiency and defined wood fibre quality. Recently our research group developed a high-resolution gamma-ray computed tomography (CT) measurement system for industrial applications, which has been successfully used in many foregoing projects. It consists of a collimated 137Cs isotopic source, a detector arc, a signal processing unit and a cooling unit. The detector arc contains 320 single detectors based on scintillation technology and the complete measurement system is non-sensitive to electromagnetic fields as well as ambient temperature changes. In a joined project, the CT measurement system of the FZD (Forschungszentrum Dresden - Rossendorf) was applied onto the downscaled refiner of the IHD gemeinnützige GmbH (Institut für Holztechnologie Dresden, Germany). The main objective is to measure wood fibre slurry density differences in the so called ring slit as well as in the refiner gap for the fully working machine. Therefore, classical radiation tomography as well as angular resolved tomography is applied. Results of first experiments will be presented, which were carried out in 2010.

Ultrafast X-ray computed tomography has been developed as a flow imaging technique [1][2] that is able to visualize the phase distribution inside a cross-section of a flow vessel with a spatial resolution of about 1 mm and frame rates of up to 10,000 s-1. The temporal resolution is achieved by fast deflection of an electron beam across an elongated target to produce a moving X-ray source spot. The performance and applicability of this technique has been demonstrated in different two-phase flow experiments such as water-air pipe flows [3], mixing processes or fluidized beds [4] which are of great relevance for the understanding and controlling of various industrial processes. Especially in applications with dense phases, which are opaque to common imaging techniques, ultrafast X-ray tomography can provide important additional information.
Recently, this technique has been advanced towards time-resolved imaging of three-dimensional flow structures. This is achieved by repeated consecutive scanning of a number of tomography planes, which are realised using a stepped target. Thus, several vertically distributed X-ray source paths can be generated. With the reconstructed time-resolved volume data it is possible not only to determine phase distributions but also phase velocities and bubble volumes which are characteristic parameters of the flow. This extended data basis provides the opportunity for an improved validation of computational fluid dynamics codes. The method and first experimental results will be presented.

Ultrafast electron beam X-ray computed tomography (CT) is an imaging technique (Bieberle & Hampel., 2006), which is able to recover the cross-sectional density distribution of multiphase flows with a frame rate of up to 10,000 fps and a spatial resolution of about 1 mm. Originally, electron beam CT was developed for cardiac imaging by Boyd (1983) and modern medical systems reach frame rates of about 20 fps. During the last years, this measurement technique has been advanced and qualified for flow imaging by the Forschungszentrum Dresden-Rossendorf and the University of Stuttgart. Its applicability to different two-phase flows has been demonstrated in a number of experiments (Bieberle et al., 2007, Bieberle et al., 2009). Specifically adapted image reconstruction methods allow to extract the phase boundaries and thus to determine the phase fractions within the tomography plane. The latest developments in ultrafast electron beam X-ray CT include the extension towards two or more tomography planes which enable furthermore to measure phase velocities by using cross correlation techniques. This in turn is essential for determining bubble volumes and volumetric flow rates, which are important parameters for the validation of CFD codes.

In this paper we compare ultrafast electron beam x-ray tomography and wire-mesh sensor imaging for a gas-water two phase flow in a vertical Perspex pipe. A 16 x 16 wire-mesh sensor was applied to measure the flow under controlled conditions in an experimental two-phase flow loop. Part of the flow loop is a two metre tall round pipe of XX mm inner diameter operated with water and air under controlled conditions. A special injector device at the bottom of teh vertical test section provides controlled gasification of the water. This way, different flow patterns and a broad range of void fraction value values can be generated. The ROFEX scanner was installed to visualize the flow just underneath the wire-mesh sensor which is located at a sufficient distance upward the injector to secure a well developed flow.

Experiments were run with flow patterns of bubbly, slug and churn turbulent flow at different liquid and gas superficial velocities. Both sensors produced synchronized data sequences of 10 s at 2,500 frames per second rate. Measured and reconstructed image data was analyzed and compared with respect to cross-sectionally averaged gas fractions, radial as fraction profiles and bubble size distributions. Fairly good agreement between ROFEX scanner and wire-mesh outputs was found for higher mixture superficial velocity while in the lower range some discrepancies were found. Detailed description will be given in the full paper.

Experimental tests were conducted recently to test both the capacitance and conductance wire mesh sensors against gamma densitometry. Similar techniques were utilised in the past at FZD to test the accuracy of the wire mesh sensor (Prasser et al 1998). It is interesting to note that comparisons of the wire mesh sensor have also been done with other measurement devices e.g. ECT (Azzopardi et al, 2009). A small closed loop test facility was utilised. This consisted of a vertical round pipe approximately 1 metre in length, and around 50mm in diameter. A 16 x 16 wire mesh sensor was used, giving a spatial resolution of 3.1mm. This sensor was placed approximately 1 metre above the injector. Temporal resolution or sampling frequency of the sensor was set at 1000 Hz throughout the experiments. Deionised water was used and hence both types of WMS could be utilised. There was a small gas injector at the inlet of the vertical pipe, this allowed compressed air to be injected, and two-phase gas-liquid mixture was generated. The gas superficial velocity was varied between 0.05m/s to 1.4m/s at two liquid velocities of 0.2 and 0.7m/s. The gamma densitometer consisted of collimated source and also a collimated detector to minimise scattering. The source was Cs 137; this generated a gamma beam of 5mm in diameter. The detector used was a NaI scintillation crystal with photomultiplier read-out. The measuring period was 120s (similar methodology was used previously by Prasser et al 1998). The gamma densitometer was placed on a moving platform approximately 1cm below the plane of wires of the sensor, in order to align it accurately using a counter mechanism, with each of the wires of the WMS, and the platform could scan the full section of the pipe. One half of the pipe i.e. 8 wires of the sensor were measured with capacitance WMS and gamma densitometer, and the other half of the pipe was measured with conductance WMS and gamma densitometer. Calibration was carried out for each position i.e. 16 points and data collected for each of the 16 wires at the stated gas and liquid flow rates. In total there were 224 runs. Different flow regimes were observed e.g. bubbly and slug. The count rate from the gamma densitometer detector was converted to void fraction (Stahl et al, 2004). For the cross-sectional void, along each wire, there was good agreement between sensors and the gamma densitometer near the centre of the pipe, however there wasn’t a good agreement near the circumference or edge of the pipe. There was consistent agreement between the capacitance and conductance wire mesh sensors throughout the experiment. This experiment also demonstrated how limited gamma densitometry actually is, i.e. it provides no visualisation. The wire mesh sensor in return gave void fractions at each crossing point i.e. a 16x 16 matrix, at a very high sampling rate, together with visualisation of flow. It also gave bubble identification and size distribution of the bubbles.

The complexation of protactinium(V) by oxalate is studied by X-ray absorption spectroscopy (XAS), capillary electrophoresis coupled with ICP-MS (CE-ICP-MS ) and solvent extraction. XAS measurements show unambiguously the presence of a short single oxo-bond. CE-ICP-MS results indicate the formation of a highly charged anionic complex. The formation constant of PaO(C2O4)+, PaO(C2O4)2– and PaO(C2O4)33– are determined from solvent extraction data by using protactinium at tracer scale (CPa < 10–10M) and different temperatures. Complexation reactions of Pa(V) with oxalate are found to be exothermic with relatively high positive entropic variation.

By coupling EXAFS, UV-vis spectroscopy and molecular dynamics and quantum mechanical calculations, we studied the complexation of uranyl cations with nitrate and chloride ions in a water immiscible ionic liquid, C4mimTf2N. Both anions are shown to be stronger uranyl ligands than the ionic liquid Tf2N- or triflate anions. Structural parameters of the trinitrate-complex of uranyl are similar to those obtained in organic solvents like acetonitrile. When chloride and nitrate anions are simultaneously present, one never observes “limit” complexes like UO2(NO3)3- or UO2Cl42- alone. At a U/ NO3 /Cl ratio of 1 /2 /2, the dominant species is likely UO2Cl(NO3)2-. When chlorides are in excess over uranyl with different nitrate concentations (U/ NO3 /Cl ratio of 1/2/6, 1/4/4, 1/12/4) the solution contains a mixture of UO2Cl42- and UO2Cl3(NO3)2- species. Furthermore, it is shown that the experimental protocol for introducing these anions (either as uranyl counterion, as added salt, or as ionic liquid component) influences the UV-vis spectra, pointing to kinetic equilibration issues in the ionic liquid.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section.
Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264°C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments.
This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison.
Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes the effect of viscosity into account.

We investigated the adsorption of the L-Lysine (200 mmol) molecule to a silanized SiO₂ surface as a function of the pH value. The SSC (spraying spin coating)-method [Cherkouk et al, J. of Col. and Int. Sci., 337(2009)] was applied to functionalize the SiO₂ surface by using the (3-Aminopropyl)trimethoxysilane (APMS) as coupling agent with a NH2 functional group. We adsorbed lysine molecules for the pH-values of 2.5, 7.5, 8.7, 9.5 and 13 to the silane film. The infrared spectroscopy is not suitable to investigate the system because the NH3+ signal at 1600 cm-1 originating from the silane film overlaps with the infrared signal of the deprotonated carboxyl group of the lysine molecule. X-ray photoelectron spectroscopy (XPS) was used to measure the binding energies C1s and N1s as function of the pH value. This pH change affects the charge state which was fitted in the XPS spectra to obtain the optimal adsorption conditions at pH= 7.5 via carboxyl groups of the lysine to the functionalized SiO₂ surface.

In the Euler/Eulerian approach simulating bubbly flow, the influence of the bubbles on the turbulence of the liquid has to be modelled. Vice versa, the structures of the turbulent liquid flow influence the gas void fraction distribution, which is expressed as a turbulent dispersion force. Reliable models for turbulence are an urgent precondition for the improvement of models describing bubble coalescence and bubble breakup in any population balance model. In the present work the different approaches simulating the influence of bubbles on the turbulence are revised and compared to measurements using ANSYS-CFX. Models for the turbulent dispersion force are validated.

In crystal structure of the title compound, {[UO2NO3(C4H7NO)2]2O2}, two UO22+ ions are connected by mu-ita2:ita2-O22–. An inversion center is located at the middle point of a O—O bond in the O2 moiety. As a result, the centrosymmetrically expanded dimeric structure is afforded. The O2 unit shows "side-on" coordination and connects two U, i.e., mu-ita2:ita2-O2. The bond lengths between U and the axial O are 1.78 Å (mean), indicating that oxidation state of U is exclusively 6+, i.e., UO22+. Furthermore, the O—O distance in the dioxy­gen moiety is 1.491 Å, which is typical of the peroxide, O22–. Each U atom is eight-coordinate in a hexagonal-bipyramidal geometry. The coordinating atoms of nitrate, pyrrolidine-2-one and mu-ita2:ita2-O22– are located on the equatorial plane, and form an irregular hexagon. The inter­molecular hydrogen bonds are found between N—H of 2-pyrrolidone and the coordinating O of the same ligand in the neighboring complex.

no abstract for this presentation

Di-Elektronen in relativistischen Schwerionenkollisionen

In recent years, many NPPs have developed and implemented severe accident management guidelines (SAMG). A primary objective of SAMG is prevention or mitigation of the consequences of severe accidents by keeping the reactor pressure vessel (RPV) integrity and reducing the load to the containment.

In-vessel melt retention (IVR) by ex-vessel reactor cooling (EVC) is one of the possible strategies for mitigation of a severe accident. This concept has already been approved by the Finnish Regulatory Agency (STUK) to be a part of the severe accident management procedures for the Loviisa NPP, Finland, with a VVER-440 reactor [1]. Besides its feasibility for such smaller power reactors, the concept is also investigated for some GEN III+ advanced light water reactors with higher core powers, such as the Westinghouse AP-1000. By applying the strategy of in-vessel retention of corium, the possible fuel-coolant interaction in the reactor cavity and thus the pressure loads in the cavity could be avoided.

The late in-vessel phase of a VVER-1000 reactor, applying external cooling of the RPV wall as mitigative severe accident management measure (SAMM), is investigated. The study is based on the FEM computer code ANSYS. Without flooding, the vessel wall would fail, as the necessary temperature for a balanced heat release from the external surface via radiation is near to or above the melting point of the steel. A crucial question regarding the feasibility of the IVR is whether all the decay heat could be transferred through the vessel wall into the water in the reactor cavity. The heat flux distribution from the molten corium to the RPV wall is therefore of high importance.

We have developed a versatile software package for the simulation of di-electron production in pp and dp collisions at SIS energies. Particular attention has been paid to incorporate different descriptions of the Dalitz decay \Delta \to N e⁺e^- via a common interface. In addition, suitable parameterizations for the virtual bremsstrahlung process NN \to NN e⁺e^- based on one-boson exchange models have been implemented. Such simulation tools with high flexibility of the framework are important for the interpretation of the di-electron data taken with the HADES spectrometer and the design of forthcoming experiments.

We report the first demonstration of a solid state laser passively mode-locked through the saturable absorption of short-wavelength intersubband transitions in doped quantum wells: a continuous wave Ti:sapphire laser end-pumped Tm,Ho:YAG laser at the center wavelength of 2.091 μm utilizing intersubband transitions in narrow In0.53Ga0.47As/Al0.53As0.47Sb quantum wells. Stable passive mode-locking operation with maximum average output power of up to 160 mW for 2.9 W of the absorbed pump power could last for hours without external interruption and a mode-locked pulse with duration of 60 ps at repetition rate of 106.5 MHz was generated.

The geochemical fate of selenium is of key importance for today’s society due to its role as a highly toxic essential micronutrient and as a significant component of High Level Radioactive Waste (HLRW) originating from the operation of nuclear reactors. Understanding and prediction of the long-term behavior of Se in natural environments requires identification of the in situ speciation of selenium. This article describes an XAS-based investigation into the solid phase speciation of Se upon interaction of Se(IV) with Boom Clay, a reducing, complex sediment selected as model host rock for clay-based deep geological disposal of HLRW in Belgium and Europe. Using a combination of long-term batch sorption experiments, linear combination XANES analysis and ITFA-based EXAFS analysis allowed for the first time to identify Se0 as the dominant solid phase speciation of Se in Boom Clay systems equilibrated with Se(IV).

Metal hexacyanoferrates are well known molecular solids for a large variety of cations, although very little has been described for actinide adducts. Two new members of actinide(III) hexacyanoferrates have been synthesized with americium and californium cations. They have been structurally characterized by infrared spectroscopy, X-ray diffraction and X-Ray absorption spectroscopy. Combined EXAFS data at the iron K edge and actinide L_III edge lead to propose a three-dimensional model for these two new compounds. Structural data in terms of bond distances have been compared to those reported for the lanthanide(III) hexacyanoferrates. A comparison between the actinide and lanthanide homologues has been carried out, based on ionic radii considerations. Consequently, Am(III)/Nd(III) and Cf(III)/Gd(III) complexes have been compared : the americium adduct with KNdFe^II(CN)₆.4H₂O and the californium adduct with KGdFe^II(CN)₆.3H₂O. Comparison between the present EXAFS data and reported X-ray diffraction data suggests that the americium and neodymium environments are very similar, resulting in a tri-capped trigonal prism polyhedron (CN = 9) where the americium is bonded to six nitrogen atoms and to three water molecules. For the californium adduct, EXAFS derived bond length and angle suggest that the californium cation sits in a bi-capped trigonal prism (CN = 8) as in the gadolinium homologue of known structure. Using EXAFS spectroscopy, this is one of the rare evidences of californium/lanthanide similarities in a molecular compounds. A discussion about actinide(III)/lanthanide(III) comparison and coordination number decrease from Am to Cf is also provided, based on previous crystallographic results reported for the actinide(III) hydrate series

The present work is concerned with ultrasound and temperature measurements in a Czochralski crystal growth model experiment. In the Czochralski growth, primary strong horizontal temperature gradients are present at the solidification front, which should lead to an axisymmetric flow pattern in the melt volume. To study the flow structure a modified Rayleigh-Bénard configuration was built up in which the upper thermal boundary condition in a Czochralski system is accounted for by a partially cooled surface. The measurements show, that rather a large scale flow pattern develops known as wind in real Rayleigh–Bénard configurations. The wind was always found as the only stable flow pattern for all performed Grashof numbers. Applying a rotating magnetic field (RMF) to the melt volume, the wind starts to co-rotate with the RMF. By analogue with the superposition of the primary and the secondary flow in an RMF, the swirl evoked by the RMF is also superimposed to the wind without any remarkable interaction. Not until the weaker secondary flow produced by the RMF becomes similar in vigour to the buoyant wind does the flow structure in the modified Rayleigh-Bénard system change basically. The results show the applicability of the Ultrasound Doppler Velocimetry (UDV) in the detection and identification of complex flow patterns.

The present experimental study is concerned with the sensitivity of the flow driven by a travelling magnetic field (TMF) to axial alignment. Referring to the center axis of the TMF generating coil system the fluid volume was stepwise dealigned. Because the flow induced in a TMF is, basically, of a torus type, vertical velocity components are representative for the motion in the meridional plane. To acquire velocity profiles the Ultrasound Doppler velocimetry (UDV) was used which allows gathering the whole profile along the ultrasonic beam. Several transducers were mounted at the bottom of the fluid covering vessel and connected to the multiplexer channels of the UDV device. Eutectic GaInSn was used as working fluid. Analysing mean velocity profiles and the spatiotemporal properties of the flow, the study shows, that already for small deviations from coaxial conditions the flow topology changes.

We present the main features of PIConGPU, the - to our knowledge - first scalable particle-in-cell (PIC) code for relativistic laser plasma interactions written for graphical processing units (GPUs). We show that it is possible to use PIConGPU on standard compute clusters equipped with GPUs and introduce the main features that are important to reach good weak scaling when increasing both the size of the system simulated and the number of GPUs.

We have analyzed the acceleration of laser-generated protons, produced at the rear surface of flat-cone targets irradiated by anultra-intense (I~5 x 10¹⁹ W/cm²) short (400fs) laser pulse. We used different target sizes and shapes in order to find the optimum target layout. We find that for targets with a too narrow cone structure, the production of the hot electrons, driving the proton acceleration, islocated prior to the accelerating rear surface of the target, resulting in a reduced maximum proton energy.

We have conducted two sets of laser-ion acceleration experiments at the LANL 200 TW Trident short-pulse laser comparing regular size flat foils, reduced mass targets and new Cu micro-cone targets to elucidate the production of hot electrons and ions in these targets. Results from the latest experiment show proton energies in excess of ~65 MeV for the cones, compared to ~55 MeV for reduced mass targets and ~45 MeV for regular flat foils for high contrast. Data from Cu K-alpha 2D imaging crystal, an X-Ray single hit CCD, proton beam images on RCF film stacks, and an electron spectrometer are presented.

Ion irradiation is turning out as a very useful tool for producing nanoparticles in phases that are hard or impossible to obtain otherwise. In addition to promoting chemical ordering in, for instance, FePt particles [1], irradiation has recently been shown to provide a means to remove grain boundaries from alloyed (CuAu, FePt) multiply twinned particles, turning them single-crystalline [2,3]. Irradiation can also be used to densify porous cluster-assembled films without dramatically increasing the grain size [4]. Thus, irradiation provides a versatile tool for controlled engineering of nanoscale systems. We will give an overview of our recent work on radiation effects in nanoparticles. Specifically, the multiply-twinned to single-crystalline transformation, which has been shown to occur via transient amorphization of the alloyed particles, is discussed [3]. The transformation is surprising, as it occurs in alloys, which are known not to amorphize in bulk. In addition to phase transitions, we will review defect production by, on one hand, cascade-producing irradiation [5] (e.g., 25 keV Ga on Au) and, on the other, irradiation in the single knock-on regime [6,7] (e.g., 3 keV He on Pt). The defect production mechanisms and the differences between irradiation response of nanosized and bulk systems are discussed.

[1] U. Wiedwald et al., Appl. Phys. Lett. 90, 062508 (2007).
[2] O. Dmitrieva et al., J. Appl. Phys. 97, 10N112 (2005).
[3] T. T. Järvi et al., EPL 85, 26001 (2009).
[4] K. Meinander and K. Nordlund, Phys. Rev. B 79, 045411 (2009).
[5] T. T. Järvi et al., EPL 82, 26002 (2008).
[6] T. T. Järvi et al., Phys. Rev. B 80, 132101 (2009).
[7] T. T. Järvi et al., J. Appl. Phys. 102, 124304 (2007).

In pp collisions at 1.25 GeV kinetic energy, the HADES collaboration aimed at investigating the di-electron production related to $\Delta$ (1232) Dalitz decay ($\Delta⁺ \to pe⁺e^-$). In order to constrain the models predicting the cross section and the production mechanisms of $\Delta$ resonance, the hadronic channels have been measured and studied in parallel to the leptonic channels. The analyses of $pp\to np\pi⁺$ and $pp\to pp\pi⁰$ channels and the comparison to simulations are presented in this contribution, in particular the angular distributions being sensitive to $\Delta$ production and decay. The accurate acceptance corrections have been performed as well, which could be tested in all the phase space region thanks to the high statistic data. These analyses result in an overall agreement with the one-$\pi$ exchange model and previous data.

Laser cooling of ion beams at relativistic energies at the Experimental Storage Ring (ESR) at GSI has shown that in order to address the complete phase space of an initially hot ion beam, laser systems have to deliver light at a wide range of frequencies. If all ions are cooled by the laser force, the beam momentum spread can be reduced to a level that cannot be resolved by standard accelerator diagnostics. In our talk we introduce new laser systems and optical diagnostics that are currently set up for an upcoming laser cooling experiment at ESR. We discuss the impact of these new developments on the detection of beam ordering referring to laser cooling experiments previously performed at the ESR.

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger in n+p reactions as compared to p+p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.

The time evolution of vector-meson spectral-functions is studied within a kinetic theory approach. We implement this formalism in a BUU type transport model. Applications focus on rho and omega mesons being important pieces for the interpretation of the di-electron invariant mass spectrum measured by the HADES collaboration for the reaction C + C at 2 AGeV bombarding energy. Since the evolution of the spectral functions is driven by the local density, the in-medium modifications are tiny for small collision systems within this approach.

The production of strange mesons in collisions of Ar+KCl at a kinetic beam energy of 1.756 AGeV is studied within a transport model of Boltzmann-\"Uhling-Uhlenbeck (BUU) type. In particular, phi, K⁺ and K^- yields and spectra are compared to the data mesured recently by the HADES collaboration and the phi yield measured previously by the FOPI collaboration. Our results are in agreement with these data thus presenting an interpretation of the subleading role of phi decays into K^-'s and confirming the importance of the strangeness-exchange channels for K^- production.

Results of a study of charged pion production in 12C+12C collisions at incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using the spectrometer HADES at GSI, are presented. We have performed a measurement of the transverse momentum distributions of pi+- mesons covering a fairly large rapidity interval, in case of the C+C collision system for the first time. The yields, transverse mass and angular distributions are compared with a transport model as well as with existing data from other experiments.

Inclusive production of e+e--pairs in pp and dp collisions at a kinetic beam energy of 1.25 GeV/u has been studied with the HADES spectrometer. In the latter case, the main goal was to obtain data on pair emission in quasi-free np collisions. To select this particular reaction channel the HADES experimental setup was extended with a Forward Wall hodoscope, which allowed to register spectator protons. Here, the measured invariant mass distributions demonstrate a strong enhancement of the pair yield for M > 140 MeV/c2 in comparison to pp data.

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics.

For the first time Am(III) complexation with a small organic ligand could be identified and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature and trace metal concentration. With pyromellitic acid (1,2,4,5-benzene-tetracarboxylic acid, BTC) as ligand spectroscopic characteristics for the Am BTC complex system as well as for the Am3+(aq) ion were determined at pH 5.0, an ionic strength of 0.1 M (NaClO4) and room temperature. The fluorescence lifetimes were determined to be 20.8 ± 3.4 ns for Am3+(aq) and 27.3 ± 2.3 ns for the Am BTC 1 : 1 complex; the emission maximum for the 5D1 7F1 transition is 691 nm for both species. The complex stability constant for the Am BTC 1 : 1 complex was calculated to be log β110 = 5.42 ± 0.09.

The silverpoint drawing technique had its cumulating period in the late Middle Ages and the Renaissance. However, some undoubtful Rembrandt drawings were made on prepared vellum by the master with this already obsolete technique in the Golden Age. Among these drawings is the best-known portrait of his wife Saskia, 1633 (KdZ1152, Berlin). It is, thus, especially interesting to investigate these drawings. In addition to art historical studies, it was also important to get new insights into the graphical material employed in order to know whether it was different from that one used in former periods, which in turn can give information on the genesis and dating of the drawings.
Silverpoint drawings belong to the most valuable treasures of graphical art collections. They are generally very precise drawings of excellent quality. Therefore, only completely non-destructive analytical methods are applicable. Moreover, they need to be very sensitive because of the low quantity of matter present in the strokes (less than some hundreds of μg/cm²). Several preliminary tests showed that only Particle induced X-ray Emission (PIXE) spectrometry and Synchrotron radiation induced X-ray fluorescence analysis (SR-XRF) fulfil the analytical requirements for the investigations of these drawings meaning that they are sensitive enough, feasible in air and require no sampling.
Synchrotron radiation induced X-ray fluorescence results obtained at the BAMline, BESSY II, HZB, Berlin on three Rembrandt silverpoint drawings of the collection of the Kupferstichkabinett Staatliche Museen zu Berlin will be presented (Reiche et al. 2006).
The chosen method will be explained as well as the requirements for studying non-destructively valuable works of art such as these silver point drawings. The main part of the presentation focusses on the meaning of the results and illustrates how SR-XRF analysis can reinforce art historical assumptions on the genesis, the dating of the drawings and their connection. Additional information can be gained from such analytical studies on the conservation state of the drawings.
The results will also be compared to those available on other silverpoint drawings by Van Eyck, Dürer and the Holbein family (Reiche and Roth, 2008, Ketelsen et al. 2005, Reiche et al. 2004).

References :

I. Reiche and M. Roth, Berliner Beiträge zur Acrhäometrie 21 (2008) 81.
I. Reiche et al., Appl Phys. A 83 (2006) 169.
T. Ketelsen et al., The Burlington Magazine CXLVII, #1224 (2005) 170.
I. Reiche et al., NIMB 226 (2004) 83.

Surface modification with ion beams is a well established technique to create self-organized regular patterns like ripples and dots [1,2]. The pattern can be controlled by the kind of ion species as well as by their energy, fluence and angle of incidence. Future applications in electronic or optoelectronic nanodevices are under discussion [3]. In this contribution we present a novel approach, the irradiation with focused dimer and trimer beams of heavy ions, in particular Bi₂ ⁺ and Bi₃ ⁺⁺. These clusters from a liquid metal ion source were mass separated in a CANION 31Mplus FIB system from Orsay Physics and focused onto a Ge surface. The acceleration voltage of 30 kV corresponds to energies of 10-15 keV/atom, fluences from 10¹⁵ to 10¹⁷ cluster/cm² were applied.
For normal incidence up to an angle of ~30° dot patterns with a pronounced short-range order have been found. The dots are crystalline (as confirmed by Raman measurements), enriched with Bi and have a diameter of 30 nm. The inter-dot distance is about 50 nm. A new quality of the dots is their large aspect ratio of ~1. Using the same fluence and energy/atom, irradiation with single Bi+ ions resulted in the well-known porous Ge surface. Therefore, this new kind of pattern should be caused by cluster effects, not by single ion impacts. The Bradley-Harper model is obviously not valid, in contrast to the fabrication of regular 3-4 nm deep holes in Ge by a 5 keV FIB irradiation with monomer Ga-ions [4]. According to a first analysis, the energy density deposited per volume by the cluster impact cascade must exceed a threshold value to form this new kind of surface pattern. The threshold energy deposited per Ge atom coincides with the heat per atom required for Ge melting. Thus, each cluster impact yields to a small melting pool of <1000nm³ volume. A model based on such pools explains the segregation of Bi into the dots. The Ge surface undulation is caused by a decrease of the Ge volume of 5% during melting. A Ge flux into the Bi rich region occurs due to the Bi concentration dependent Ge melt temperature.
In the range from 30° to 60° no structures occur. The surface becomes very smooth by the heavy cluster beam. Increasing the angle further leads to the formation of ripples perpendicular to the beam direction with a wavelength of about 100 nm and a height of 30 nm. Measurements with back scattered electrons reveal that the top of the ripples is Bi enriched. At still higher angles a transition from ripples to a shingle structure has been found, which are also perpendicular to the beam direction. A rotation into ripple pattern parallel to the beam has been not observed.
References: [1] R.M. Bradley and J.M.E. Harper, J. Vac. Sci Technol. A 6 (1988) 2390-2395. [2] S. Facsko, T. Dekorsy, C. Koerndt, C. Trappe, H. Kurz, A. Vogt, H.L. Hartnagel, Science 285 (1999) 1551-1553. [3] R. Gago et al. Phys. Rev. B 73 (2006) 155414-1-9. [4] Q. Wei et al., Adv. Mat. 21 (2009) 2865-2869.

Two features of our heavy-ion-irradiation-induced surface patterns differ drastically from patterns formed on Ge with ions so far: The surface remains crystalline as proven by Raman measurements, and the dots and ripples heights equal their wavelengths (aspect ratio ~1).
The self-organisation of these very regular, high-amplitude dot and ripple patterns on (001)Ge has been found under bombardment with heavy ions of bismuth dimers and trimers. The Bi₂ ⁺, Bi₃ ⁺ and Bi₃ ⁺⁺ ions are formed in a Liquid Metal Ion Source, they were accelerated, focused and scanned by a Focused Ion Beam system. 30 kV acceleration voltage and up to 10¹⁷ ions/cm² have been used.
In the ion impact angle range from normal to ~30° incidence, hexagonal patterns of dots with ~30 nm diameter and ~40 nm height are found. Using a Bi monomer ion beam having the same atomic energy and fluence like the dimer and trimer beams, an amorphous Ge nanosponge is found. In the incidence range from 30° to 60° Bi₃ ⁺⁺ ions smoothen the Ge surface, whereas we found for 60° to 80° and more grazing incidence ripples and shingles perpendicular to the beam, respectively.
The Bi₃ ⁺⁺ ions are 16 times heavier than Ar⁺ ions, and still 5 times heavier than Xe⁺ ions. This high ion mass leads to a patterning mechanism different from the Bradley-Harper model, which becomes strikingly apparent by the crystalline Ge surface. An identified threshold of this new patterning mode could help to understand the mechanism: The ion-impact-induced deposition of energy per volume (as estimated by SRIM) must exceed a value which coincides with the energy needed for melting. Thus, Bi segregation during melt pool resolidification and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.

In safety assessments for radioactive waste repositories in deep geological formations the host formation and/or the sedimentary overburden might act as a barrier, since sorption on mineral surfaces of the sediments can retard the transport of many radionuclides. So far, the retention of radionuclides has been described in respective computer programs by temporally constant distribution coefficients.
A coupling of reactive transport programs with a full geochemistry code is currently not practical due to the high computing costs for the calculation of large model areas and very long time scales as required in long-term safety analysis. Therefore, the present study develops and implements a different methodology to extend the existing 3D transport program r3t [FEI 04] towards a more realistic description of the radionuclide migration under temporal variable geochemical conditions. Such changes might be caused in a sedimentary overburden by a marine transgression or the thawing of permafrost.

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Zur Aufrechterhaltung der Kernkühlung bei Kühlmittelverluststörfällen (KMV) in Leichtwasserreaktoren wird das aus dem Leck im Primärkreislauf austretende Kühlwasser im Reaktorsumpf gesammelt und über Notkühlpumpen in den Kühlkreislauf zurückgeführt. Auf der Saugseite der Notkühlpumpen befinden sich Sumpfsiebe zur Rückhaltung von im Kühlwasser suspendierten Fremdstoffen. Im Fokus von Arbeiten zur Gewährleistung einer gesicherten Kernkühlung bei KMV-Störfällen steht seit Jahren die Erforschung von Transport- und Verblockungsprozessen von Isoliermaterialfasern im Reaktorsumpf bzw. an entsprechenden Rückhaltevorrichtungen. Im Verlauf eines KMV-Störfalles können neben dem Isoliermaterial weitere Feststoffe im Kühlwasser sowohl das Verblockungsverhalten an den Sumpfsieben als auch die Wasserchemie beeinflussen. Speziell der Langzeitkontakt des Leckwasserstrahls mit feuerverzinkten Lichtgitterrosten kann zur Bildung löslicher und partikelförmiger Korrosionsprodukte führen. Im Rahmen eines vom BMWi geförderten Forschungsvorhabens soll der Einfluss derartiger Korrosionsprozesse auf die chemische Zusammensetzung des Kühlwassers und auf das Sumpfsieb-Verstopfungsverhalten untersucht werden. Ziel ist die Unterstützung der Modellierung für eine konsistente Strömungssimulation von KMV-Störfällen unter Einbeziehung von chemischen Langzeiteffekten.
Neben grundlegenden Aussagen zur Korrosionschemie verzinkter Stahloberflächen und Einflussfaktoren auf die Korrosionsprozesse beinhaltet der Vortrag die geplanten Versuchsstrategien und die darauf aufbauenden Auslegungskriterien für die am FZD zu errichtenden Versuchsanlagen für korrosionschemische Experimente unter störfallspezifischen Bedingungen. Weiterhin wird die Mess- und Analysentechnik für die Untersuchung der Korrosionsvorgänge vorgestellt und diskutiert.

Tumor cells are characterized by their loss of growth control resulting from alterations in regulating pathways of the cell cycle, such as a deregulated cyclin-dependent kinase (Cdk) activity and/or Cdk expression. Appropriately radiolabeled Cdk4 inhibitors are discussed as promising molecular probes for imaging cell proliferation processes and tumor visualization by PET. This work describes the design, synthesis and radiopharmacological evaluation of two ¹²⁴I-labeled Cdk4 inhibitors as potential radiotracers for imaging of Cdk4 in vivo. Treatment of a solution containing labeling precursors with [¹²⁴I]NaI gave radiolabeled Cdk4 inhibitors [¹²⁴I]CKIA and [¹²⁴I]CKIB in radiochemical yields of up to 35%. ¹²⁴I-labeled radiotracers [¹²⁴I]CKIA and [¹²⁴I]CKIB were used in cell uptake studies as well as biodistribution studies in Wistar rats and small-animal PET in tumor-bearing mice. In vitro radiotracer uptake studies in adherent tumor cells using [¹²⁴I]CKIA showed substantial uptake in HT-29 and FaDu cells (750–850 %ID/mg protein [¹²⁴I]CKIA and 900–1000 %ID/mg protein [¹²⁴I]CKIB) after 1 h at 37 °C. Biodistribution of [¹²⁴I]CKIA and [¹²⁴I]CKIB showed rapid blood clearance of radioactivity and an accumulation as well as metabolization in the liver. Both radiotracers were administered intravenously to mouse FaDu xenograft tumor model and imaging studies were performed on a small-animal PET scanner. Both imaging techniques showed only little uptake of both radiotracers in the FaDu tumor xenografts.

Electromagnetic Processing of Materials (EPM) relates to all branches of materials processing where some benefit could be attained from an electromagnetic influence on the process. This covers traditional areas such as liquid metal processing, metal casting and solidification, induction heating, but also crystal growth from the melt, plasma processes, etc. The series of EPM conferences was initiated in 1994 by S. Asai (Japan) and M. Garnier (France).

We report recent discoveries of superconductivity in p-type-doped germanium which has been fabricated by implantation of gallium ions into near-intrinsic cubic Ge. Depending on the detailed preparation and annealing conditions, we demonstrate that superconductivity can be generated and tailored in thin p-doped layers of the Ge host. By carefully adjusting the annealing parameters, we have been able to raise the onset temperature of superconductivity to about 1.4 K at a Ga peak concentration of ∼10 at.%. This progress and the large in-plane critical magnetic field of about the size of the Chandrasekhar–Clogston limit makes thin-film Ga-doped Ge (Ge:Ga) even more attractive for technological applications. There might be particular interest to utilize on-chip thin-film superconductivity in a semiconducting environment as our preparation method of Ge:Ga is fully compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining ‘islands of the periodic table of elements’ on which superconductivity has not been found so far.

Increased plasma levels of S100 proteins and interaction of S100 proteins with receptor for advanced glycation end products (RAGE) have been associated with a number of disease states, including chronic inflammatory processes and atherosclerosis. However, data concerning the role of circulating S100 proteins in these pathologies in vivo are scarce and, furthermore, it is currently not known whether RAGE is the sole receptor for extracellular S100 proteins in vivo. We report a novel methodology using recombinant human S100 proteins radiolabelled with fluorine-18, particularly, ¹⁸F-S100A12, in receptor binding studies and cellular association studies in vitro, and in dynamic small animal positron emission tomography (PET) studies in rats in vivo. Association to both human aortic endothelial cells and macrophages revealed specific binding of ¹⁸F-S100A12 to RAGE, but, furthermore, provides evidence for interaction of ¹⁸F-S100A12 to various scavenger receptors (SR). PET data showed temporary association of ¹⁸F-S100A12 with tissues overexpressing RAGE (e.g., lung), and, moreover, accumulation of ¹⁸F-S100A12 in tissues enriched in cells overexpressing SR (e.g., liver and spleen). Blockade of overall SR interaction by maleylated BSA (malBSA) clearly shows diminished in vivo association of ¹⁸F-S100A12 to these tissues as well as a significant increment of the mean plasma residence time of ¹⁸F-S100A12 (4.8 ± 0.4 h vs. 2.3 ± 0.3 h). The present approach first demonstrates that besides RAGE also scavenger receptors contribute to distribution, tissue association and elimination of circulating proinflammatory S100A12.

We report on high-field magnetization, specific heat, and electron-spin-resonance (ESR) studies of the quasi-two-dimensional spin- 1/2 Heisenberg antiferromagnet [Cu(pyz)₂(HF₂)]PF₆. The frequency-field diagram of ESR modes below T_N = 4.38 K is described in the frame of the mean-field theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the interplane/intraplane exchange interaction ratio, J´ /J = 1/ 16. It is argued that despite the onset of three-dimensional long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Néel temperature) are strongly affected by two-dimensional spin correlations.

Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state. In spite of its topologically simple magnetic structure, the [Cr^IIIMn^II ₃(PyA)₆Cl₃] (CrMn₃) molecule, in which PyA represents the monoanion of syn-pyridine-2-aldoxime, exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. In the present work, we elucidate the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn₃ molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, and ligand-field multiplet calculations. Quantum-model calculations based on a Heisenberg Hamiltonian augmented with local anisotropic terms enable us not only to improve the accuracy of the exchange interactions but also to determine the dominant local anisotropies. A discussion of the various spin Hamiltonian parameters not only leads to a validation of our element selective transition metal L edge XMCD spin moments at a magnetic field of 5 T and a temperature of 5 K but also allows us to monitor an interesting effect of anisotropy and frustration of the manganese and chromium ions.

dimers by the dominant antiferromagnetic intrabilayer coupling. The dimers are coupled three dimensionally by frustrated interdimer interactions. A structural distortion from hexagonal to monoclinic leads to orbital order and lifts the frustration giving rise to spatially anisotropic exchange interactions. We have grown large single crystals of Sr₃Cr₂O₈ and have performed DC susceptibility, high-field magnetization and inelastic neutron scattering measurements. The neutron scattering experiments reveal three gapped and dispersive singlet to triplet modes arising from the three twinned domains that form below the transition thus confirming the picture of orbital ordering. The exchange interactions are extracted by comparing the data to a random phase approximation model and the dimer coupling is found to be J₀ = 5.551(9) meV, while the ratio of interdimer to intradimer exchange constants is J´/J₀ = 0.64(2). The results are compared to those for other gapped magnets.

In my talk I will present a short review of our recent high-field Electron Spin Resonance (ESR) studies of spin systems with competing magnetic interactions. This topic will cover Antiferromagnetic Resonance in the multiferroic hexagonal antiferro-magnet YMnO₃, ESR in the anisotropic triangular antiferromagnet Cs₂CuBr₄, and organic spin-1/2 chain systems [Cu(C₄H₄N₂)(NO₃)₂ and (C₆H₉N₂)CuCl₃], in which an additional frustration term originates either from interchain or next-nearest-neighbor exchange interactions. A brief introduction into the recent development of the high-field ESR program at the High Magnetic Field Laboratory in Dresden will be also given.

Multiphase flows denote flowing mixtures of different fluids, solids and gases, such as oil, water and air. A phase is defined in a thermo dynamical sense as a physically homo-geneous portion of a material. Multiphase flows are to be found in many industrial proc-esses and plants, for instance in oil production, chemical reactors, energy production or driving systems. In many cases, process efficiency as well as safety is directly coupled with the flow behaviour inside industrial facilities. Therefore, there was and is a strong development of invasive and non-invasive measuring and imaging techniques with the aim to improve our understanding of physical flow phenomena and achieve flow optimi-sation and control wherever necessary. Furthermore, flow measurement technology plays an important role in the derivation of physical models for flow simulation with so called CFD (computational fluid dynamics) codes.
Computed tomography (CT) is a non invasive imaging technique that produces non superimposed cross sectional images using analytical, algebraic or statistical reconstruc-tion algorithms. Radiation based transmission tomography therefore employs a radiation source, such as a nuclide or an X-ray source, and a spatially resolving radiation detec-tor. Such as measurement system must acquire radioscopic projections from different angular positions, which can be accomplished either by rotating it around the object of investigation or by rotation of the object itself. In industrial applications nuclide sources with photon energies higher than 500 keV are often used. Such radiation can penetrate metal housings and still gives sufficient contrast between the phases that have to be analysed.
In this work, a new high resolution gamma radiation computed tomography system that uses a 137Cs source was developed. The design and the electronic parts were carefully developed for the application in harsh industrial environments (e.g. temperature and humidity variation as well as electrical and magnetic fields respectively) and high meas-urement accuracy. The spatial resolution of the detector arc is about 2 mm, the stop-ping efficiency for gamma photons with 662 keV energy is about 75% and the deviation of measuring repetition is lower than 1%. The detector arc operates in pulse mode al-lowing excluding scattered gamma photons to a certain degree from the measurement by a pulse height discriminator stage. The developed measurement system was success-fully applied in industrial and laboratory measurement campaigns, for instance meas-urements on an electrically heated rod bundle, a fluid coupling and a chemical reactor. Due to the quantum limitations of the radiation source and slow rotation of the heavy scanner elements the developed gamma radiation computed tomography system can only be used for time-averaged flow measurement with integration times in the range of one minute or more. However, within the frame of this work an extension of the system to the measurement of rapidly rotating fluid distributions is shown. Here, the principle of angle-resolved data acquisition has been implemented which was highly challenging for this type of high resolution radiation detector from an electronic point of view. The developed gamma ray tomography system is not only valuable for flow measurement but has a much wider application range, such as high-energy non-destructive testing of materials and components, such as castings, vehicle constructions or palaeontological objects.

Ion irradiations combined with nanoindentation provide a means to characterize irradiation damage in a wide range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe9at%Cr and Fe-12.5at%Cr irradiated at 300°C up to 1 and 10 dpa. The effect of Cr content and fluence are discussed. Hardening features were characterized by means of transmission electron microscopy. The ion-induced damage is compared with the damage created by neutron irradiation for the same alloys.

Messtechnik für Mehrphasenströmungen steht heutzutage verstärkt im Fokus der Forschung, da Mehrphasenströmungen einerseits maßgeblich die Sicherheit und Effizienz vieler industrieller Prozesse beeinflussen und andererseits - aufgrund der erhöhten Rechenleistung heutiger Computer - zentrales Thema bei der Entwicklung verbesserter Strömungsmodelle für Simulationscodes sind. Die ultraschnelle Röntgen-Computertomographie ist ein neuartiges Messverfahren, das erstmalig eine nicht-invasive sowie zeitlich und räumlich hochauflösende Abbildung von transienten Mehrphasenströmungen erlaubt. Die zu Grunde liegende Limited-Angle-Anordnung stellt dabei besondere Anforderungen an die Bildrekonstruktion, da ein Teil der hierfür benötigten Projektionsinformationen fehlt.
Kernthema dieser Ausgabe der Reihe "Dresdner Beiträge zur zerstörungsfreien Prüftechnik" ist die Entwicklung eines Bildrekonstruktionsalgorithmus', der in der Lage ist, fehlende Projektionsinformationen durch a-priori-Informationen über das Untersuchungsobjekt auszugleichen und somit die Ausprägung von Bildartefakten stark zu reduzieren. Der auf Basis der Level-Set-Methode entwickelte Algorithmus erreicht dieses Ziel durch die Rekonstruktion von Phasengrenzflächen anstelle von Dichteverteilungen. Gleichzeitig umfasst er einen Glättungseffekt, der eine Minimierung des durch die kurzen Messintervalle hervorgerufenen Rauschens bewirkt. Die ultraschnelle Röntgen-Computertomographie sowie der neu entwickelte Level-Set-Rekonstruktionsalgorithmus wurden an diversen Zweiphasenströmungsexperimenten erprobt. Zudem wurde das Messsystems erfolgreich für die Zweiebenen- und Volumentomographie erweitert.

Nanocrystalline 3mm thick Cu1–xNix (0.45 < x < 0.87) films are electrodeposited galvanostatically onto Cu/Ti/Si (100) substrates, from a citrate- and sulphate-based bath containing sodium lauryl sulphate and saccharine as additives. The films exhibit large values of reduced Young’s modulus (173 < Er < 192 GPa) and hardness (6.4 < H < 8.2 GPa), both of which can be tailored by varying the alloy composition. The outstanding mechanical properties of these metallic films can be ascribed to their nanocrystalline nature - as evidenced by X-ray diffraction, transmission electron microscopy, and atomic force microscopy - along with the occurrence of stacking faults and the concomitant formation of intragranular nanotwins during film growth. Due to their nanocrystalline character, these films also show very low surface roughness (root mean square deviation of around 2 nm). Furthermore, tunable magnetic properties, including a transition from paramagnetic to ferromagnetic behavior, are observed when the Ni percentage is increased. This combination of properties, together with the simplicity of the fabrication method, makes this system attractive for widespread technological applications, including hard metallic coatings or magnetic micro/nano-electromechanical devices.

This paper describes laboratory experiments aimed at investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. Experimental results will be presented which have been obtained using a physical model operating with the room temperature alloy GaInSn. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied up to Hartmann numbers of about 400. The effect of the magnetic field on the flow structure turned out to be rather complex. The flow measurements do not manifest a smooth braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould volume. Variations of the wall conductivity showed a striking impact on the resulting flow structures. The experiments provide a substantial data base for the validation of respective numerical simulations.

In the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, the super-conducting state can survive even at high magnetic fields above the Pauli paramagnetic limit. The quasi-two-dimensional (2D) organic superconductors have been suggested as good can-didates for exhibiting the FFLO state. When applying the magnetic field exactly parallel to the conducting layers the orbital pair breaking is greatly suppressed and the Pauli limit is reached. We performed high-resolution specific-heat and torque-magnetization experiments in magnetic fields up to 32 T for such 2D organic superconductors. In a very narrow angular region close to parallel-field orientation we observe additional anomalies below the upper critical field sig-naling the existence of an additional superconducting phase. The specific-heat data for kappa-(BEDT-TTF)₂Cu(NCS)₂ with T_c = 9.1 K show that the superconducting transition becomes first order for fields above 21 T indicating that the Pauli limit is reached. Below about 3 K, the upper critical field increases sharply and a second first-order transition appears within the superconducting phase. These results are corroborated by magnetic-torque data which allowed to follow the phase diagram to lower temperatures and higher fields. Our results give strong evidence for the realization of the FFLO state in organic superconductors.
Work done in cooperation with R. Lortz, B. Bergk, Y. Wang, A. Demuer, I. Sheikin, G. Zwicknagl, and Y. Nakazawa.

A resistive plate counter for timing purposes in the high rate environment of the Compressed Baryonic Matter Experiment has been developed at the Forschungszentrum Dresden-Rossendorf. The detector electrodes are made of a ceramics composite, whose volume resitivity can be tuned in the production process over five orders of magnitude. The detector prototype has been tested with single electrons of 32MeV. It shows an all-time high rate capability for electron fluxes up to 5·10 ⁵s⁻¹cm⁻².