Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A miniaturized ion selective electrode (ISE) for Cu2+ ions was developed, specially for application in a microfluidic system. The electrode preparation is based on a silicon wafer substrate which is coated with a Cu deposit in the range of 50 - 200 nm. The Cu layer is quantitatively converted into CuS by treatment in a sulphidic ambient. The chip electrode has a size of 5x5 mm2 and was mounted on a spacer chip coupled to the fluidic microcell using a chip clip technology. The coupling is liquid tight and reversible, admitting an easy exchange of the chip electrodes. The effective electrode area in contact with the liquid of the microsystems flow channel amounts to about 4 mm2.
Sensitivity measurements were performed stationary and in the flow through cell. Good Nernstian response of 29 mV/pCu between pCu 5 and 1 has been found and is in agreement with reference measurements carried out with a commercial ISE.
The rapid response observed also in the most diluted solutions used, is related to the thin, non porous structure of the CuS layer, minimizing diffusion effects during changing the test solutions. The adhesion of the sensitive CuS layer is different for the substrates Si, SiO2 and Si3N4 and depends on their history, roughness and evaporation conditions.

Low-resistivity ( < 0.1 Ohm cm at room temperature), p-type SiC layers were produced by the combination of high dose Al implantation in n-type, 6H-SiC at low temperature, subsequent ion-beam-induced crystallization by means of Si irradiation at 500°C and high temperature annealing at 1500°C. The implanted SiC layers have a nanocrystalline structure consisting of randomly oriented grains of 3C-SiC. The electrical properties of the nanocrystalline and single-crystalline reference samples were investigated by sheet resistance and Hall measurements in dependence on temperature. In comparison with the standard doping process the hole concentration is enhanced by more than one order of magnitude. This can be explained by a higher solid solubility of Al in nanocrystalline SiC. Current-voltage measurements across the vertical p-n-junction in the heavily doped nanocrystalline and single-crystalline samples demonstrated the equivalence of the diode quality.

The aim of this work was to find a correlation between the electrical, optical and microstructural properties of thin SiO2 layers containing group IV nanostructures produced by ion beam synthesis. The investigations were focused on two main topics: The electrical properties of Ge- and Si-rich oxide layers were studied in order to check their suitability for non-volatile memory applications. Secondly, photo- and electroluminescence (PL and EL) results of Ge-, Si/C- and Sn-rich SiO2 layers were compared to electrical properties to get a better understanding of the luminescence mechanism.

The Phi-meson production cross section is measured for the first time at a sub-threshold energy of 1.93 AGeV in ⁵⁸Ni+⁵⁸Ni collisions. The Phi data were obtained within the acceptance of the CDC/Barrel subsystem of the FOPI detector. For a sample of 4.7x10⁶ central events, after background subtraction, 23 Phi candidates were observed. Extensive simulation calculations of the detector performance are shown in a detailed comparison to the data, aiming at a good understanding of the apparatus response and at a reliable determination of the efficiencies, production probability and possible systematic errors. A filter procedure is elaborated, which is meant to facilitate the comparison of any theoretical calculation with the data in the detector acceptance. How to extrapolate the result to a Phi-meson cross section in 4\pi is also discussed. This first result on pseudo-vector mesons can now be compared to existing data for the same reaction at the same incident energy for various outgoing channels, K⁺ and K^- included. It suggests that a significant fraction (at least 20%) of the K^--mesons is originating in the decay of the Phi showing that the two channels are strongly correlated. A first comparison to existing model calculations indicates the possible role of the Rho-meson channels in Phi production.

The quality of single crystals grown by the floating-zone method is strongly determined by the geometry of the solid-liquid phase boundary which, in turn, can be significantly influenced by the convection in the molten zone.
We describe a novel inductor design which allows a strong influence on the flow filed. Numerical simulations are presented for the design of such a two-phase inductor.

We present numerical results of a linear 3-D stability analysis of a square lid-driven cavity flow under the influence of an external magnetic field which is directed parallel to the lid. The Lorentz force has a strong influence on the flow structure, thereby changing number, shape and strength of the eddies inside. Although increasing magnetic fields are able to damp 3-D instability, in a parameter region around Re=3000, several branches of the neutral stabiliy curve do exist. This leads to a non-monotonic behaviour of receptivity to 3-D disturbances as the strength of the magnetic field is increased.

We present the main observable features connected with magnetic field saturation in the Riga dynamo experiment, and try to explain them in terms of a simplified numerical model of back-reaction.

In June 2002, a new series of experimental runs was carried out at the Riga dynamo facility. Compared with the experiments in November 1999 and July 2000, the new experiments have delivered much more magnetic field data with higher radial resolution and with sampling rates up to 10 kHz. The range of propeller rotation rates has been extended to higher values, giving new
information on the kinematic and the saturation regime for higher magnetic Reynolds numbers.

The possibility of velocity reconstruction in electrically conducting fluids from external measurements of different induced magnetic fields is studied numerically. It is shown that for a reliable velocity reconstruction the effect of the electric potential at the fluid boundary on the induced magnetic field should be taken into account.

Stability and transition to turbulence in a flow driven by a rotating magnetic field is studied experimentally. Intermittent signals have been obtained clearly below the linear stability threshold.

Strömungen elektrisch leitfähiger Flüssigkeiten, insbesondere von flüssigen
Metallen und Halbleiterschmelzen, lassen sich mit Magnetfeldern in
kontaktloser Weise stark beeinflussen. Es wird eine Übersicht gegeben zu
diesen Arbeiten im Rahmen des SFB 609 "Elektromagnetische
Strömungsbeeinflussung in Metallurgie, Kristallzüchtung und Elektrochemie"
und am FZR. Die inverse Herangehensweise, maßgeschneiderte Magnetfelder für
die im jeweiligen Prozeß wünschenswerten Strömungen bzw. Wärme- und
Stofftransporte zu entwickeln, wird vorgestellt. Es werden Möglichkeiten zur
Magnetfeldbeeinflussung metallischer Strahlen aufgezeigt, die für das
Sprühkompaktieren interessant sein könnten.

The report gives an overview on the activities of the Institute of Safety Research in 2001.

Bei Anlegen eines elektrischen Feldes an einen Kristall würde der Strom ohne Streuung nicht auf unendlich anwachsen, sondern (fast) auf Null absinken. Dieses im ersten Moment paradoxe Phänomen, das mit der periodischen Struktur des Kristallgitters zusammenhängt, kann semiklassisch als sogenannte Bloch-Oszillation und quantenmechanisch durch die Ausbildung einer Wannier-Stark-Leiter verstanden werden. Beide Beschreibungsweisen führen zu einer Lokalisierung der Elektronen.
Nach einer grundlegenden Darstellung dieses Phänomens möchte ich einen Streifzug durch seine lange Geschichte unternehmen, die ihren Ausgangspunkt in einer Arbeit von Zener aus dem Jahre 1934 hat. Die „Gegenwart“ hat erst um 1990 durch den experimentellen Nachweis in Halbleiterübergittern begonnen. Vieles wurde seither verstanden, viele andere Dinge sind noch offen, wie zum Beispiel die Realisierung eines elektrisch getriebenen Bloch-Oszillators als THz-Quelle oder -Verstärker, wie 1970 von Esaki und Tsu vorgeschlagen. Ich werde aktuelle Experimente, Theorien, Probleme und neue Konzepte diskutieren.

We present the centrality dependence of proton and deuteron rapidity distributions in Ru+Ru collisions at 400A MeV. Data are compared with Isospin Quantum Molecular Dynamics calculations (IQMD) under various assumptions on the nucleon-nucleon cross-section in the medium. The rapidity spectra of both particles can be reproduced by IQMD with a free nucleon-nucleon cross-section for the most central collisions. The ratio of baryon rapidity distributions in isospin asymmetric collision systems shows incomplete mixing and partial transparency of both the projectile and target nuclei at this beam energy.

A novel type of mixed-ligand Tc(III) complexes, [Tc(SCH₂CH₂-E-CH₂CH₂S)(PR₂S)] (E = S, N(CH₃); PR₂S = phosphinothiolate with R = aryl, alkyl) is described. These "3+2"-coordinated complexes can be prepared in a two-step reduction/substitution procedure via the appropriate chloro-containing oxotechnetium(V) complex [TcO(SES)Cl] (E = S, N(CH₃). Tc(III) compounds have been fully characterized both in solid and solution states and found to adopt the trigonal-bipyramidal coordination geometry. The equatorial trigonal plane is formed by three thiolate sulfurs atoms, whereas the phosphorus of the bidendate P,S ligand and the neutral donor of the tridendate chelator occupy the apical positions. The ⁹⁹Tc(III) complexes have been proven to be identical with the ^99mTc-agents prepared at the no-carrier-added level by comparison of the corresponding UV-Vis and radiometric HPLC profiles. Challenge experiments with glutathione clearly indicated that this tripeptide has no effect on the stability of the ^99mTc complexes in solutions. Biodistribution studies were carried out in rats at 5 and 120 minutes post injection. The substituents at the bidendate P,S ligand significantly influenced the biodistribution pattern. Remarkable differences were observed especially in brain, blood, lungs and liver. All the complexes were able to penetrate the blood-brain-barrier of rat brain and showed a relatively fast washout from the brain.

Poster of experimental results of time resolved investigations of nitrogen implanted GaAs

Nanocrystals of silicon carbide were synthesized inside natural diamond using high dose silicon implantation. In order to retain the diamond structure, however, implantation was done at 900 °C. The samples were subsequently annealed in an rf-heated furnace at 1500 °C for 10 minutes. X-ray diffraction (XRD), IR absorption spectrometry and high-resolution cross-sectional transmission electron microscopy (HRTEM) are used to investigate formation and structure of SiC nanocrystallites in the implanted diamond. Raman spectroscopy contributed to trace implantation-induced destruction of the diamond. A first characterization of the electrical properties of the implanted and annealed samples is done by four point probe measurements. The results indicate a highly conductive, buried layer inside the diamond. This layer contains cubic SiC nanocrystals, which are perfectly aligned with the diamond lattice. However, when fluence exceeds a critical value of 5.3×1017 Si+cm-2, the diamond is irreversibly damaged and defect conduction type dominates.

Ion beam induced crystallization was used to transform amorphized, heavily Al doped SiC layers to nanocrystalline material. The morphology of the as-implanted and the annealed layers was studied by XTEM. The electrical properties were analyzed by sheet resistance and Hall measurements and compared with crystalline reference samples. A high-temperature annealing step is necessary to activate the implanted Al acceptor atoms. During annealing the mean grain size of the nanocrystals grow from 3 nm to 37 nm. The Al doped, nanocrystalline SiC has a much lower sheet resistance than the crystalline reference samples. It was found that this is due to the enhanced hole concentration which could be explained by a higher solid solubility of Al in the nc SiC.

We have investigated the synthesis of nanostructures as well as the control of their size and location by means of ion beams. The phase separation and interface kinetics under ion irradiation give new possibilities to control the growth of nanostructures. Additionally, the chemical decomposition of the host matrix by collisional mixing may contribute to self-organization of nanostructures, especially at interfaces. It is shown how collisional mixing during ion implantation affects nanocrystal (NC) synthesis and how ion irradiation through NCs modifies their size and size distribution. An analytical expression for solute concentration around an ion-irradiated NC were found which may be written like the well-known Gibbs-Thomson relation. However, parameters have modified meanings which has a tremendous impact on the evolution of NC ensembles. Thus, inverse Ostwald ripening of NCs resulting in an unimodal NC size distribution is predicted, which has been confirmed experimentally for Au NCs in SiO2 and by kinetic lattice Monte-Carlo simulations. At interfaces, the same ion-irradiation induced mechanism may result in self-organization of NCs in a thin d-layer. Collisional decomposition of SiO2 may enhances the NC d-layer formation in SiO2 at the Si/SiO2 interface. The distance of the self-organized NC d-layer from the SiO2/Si interface makes it interesting for non-volatile memory applications.

Continuing our strategy for a targeted therapy of metastatic renal cell carcinoma (RCC), a tumor which resists chemo- or radiotherapy, we now determined the primary structure of the antigen binding region of the monoclonal antibody 138H11. MAb 138H11, produced against human renal gamma-glutamyltransferase (GGT), stained over 99% clear cell and papillary RCC as well as other carcinomas on frozen sections, showing a membranous expression of the target antigen. In contrast, in normal kidneys GGT is restricted to the brush-border in the lumen of proximal tubules and thus not accessible to the circulation. Human tumor-bearing kidneys perfused in an
extra-corporeal system with 99mTc-138H11 revealed a high, specific uptake into the tumor. In vivo, a 138H11-Calicheamicin theta conjugate was very effective in reducing the tumor size and preventing or significantly delaying the regrowth of residual tumor cells in xenografted nude mice (Cancer Res. 2000, 60, 6089-6094). However, these nude mice are not useful for evaluating ADCC of naked 138H11 or immunoactivating conjugates. For creating a syngenic, immunocompetent mouse model bearing a tumor sensitive to mAb 138H11, we stably transfected the murine RCC RENCA cell line with the human GGT-gene. FACS-analysis revealed that transfected cells were positive for mAb 138H11, in contrast to wild type cells. The transfected cells were growing s.c. in
Balb/c mice without signs of rejection by the host. The mice showed a higher uptake of 99m-Tc-labelled 138H11 into the GGT positive RENCA tumors compared to the wild type tumors. This new model will be usful in the future for evaluating therapeutic effects of potential constructs made with the newly cloned recombinant 138H11-derivatives such as stabilized scFv, diabodies and triabodies.

A method is described for identifying tumor tissue by means of FTIR microspectroscopy and positron emission tomography (PET). Thin tissue sections of human squamous carcinoma from hypopharynx (FaDu) and human colon adenocarcinoma (HT-29) grown in nude mice were investigated. FTIR spectroscopic maps of the thin tissue sections were generated and evaluated by Fuzzy C-Means (FCM) clustering and principal component analysis (PCA). The processed data were reassembled into images and compared to stained tissue samples and to PET. Tumor tissue could successfully be identified by this FTIR microspectroscopic method, while it was not possible to accomplish this with PET alone. On the other hand, PET permitted the non-invasive screening for suspicious tissue inside the body, which could not be achieved by FTIR.

no abstract delivered from author

A detailed investigation of the emission frequency spectra of a gallium Liquid Metal Ion Source (LMIS) is presented. The spectra are correlated with current oscillograms. The current for which pulses appear superimposed on the d.c. level of current is well predicted by existing theory. The pulses are believed to be the result of droplet emission, and their terminal frequency appears to coincide with the frequency of vibrations of the sides of the liquid cone at high currents. Better understanding of the instabilities that develop on the liquid anode can be useful for deposition purposes.

In the paper a novel non-intrusive tomographic method is presented to visualise the gas fraction distribution inside the rotating impeller of an axial pump delivering a two-phase flow. The device has been developed for an axial pump (inducer), which has an impeller with three helical blades rotating at 1500 revolutions per minute. Model fluid is air-water mixture created by a gas distributor upstream the pump inlet nozzle. The developed gamma-tomography set-up consists of a Cs-137 source and an arc of 64 scintillation detectors. Each of the detectors is connected to a number of counters grouped into banks. Each bank is active only during a 100 µs long interval of the rotation period, which corresponds to a well-defined angular interval of the impeller rotation. A trigger pulse, generated at the beginning of each revolution, forces the control unit to restart the counting process from the first bank. In this way, the device is able to measure ensemble averaged projections of the gamma absorption density distribution, which are resolved according to the rotating angle of the impeller. An image reconstruction by filtered back-projection provides density distributions inside the impeller. Void fraction distributions are visualised by means of differential tomography. i.e. by subtracting sets of projections obtained for two-phase operation and for plain liquid.

The processes of deposition and structural relaxation of tetrahedral amorphous carbon (ta-C) films are investigated using atomistic computer simulations. Applying classical molecular dynamics with a modified hydrocarbon potential of Brenner, ion-beam deposition of carbon films was simulated for ion energies E = 10-80 eV, and for substrate temperatures ranging from 100 to 900 K. The dependence of the sp3 content and intrinsic stress in the simulated films on substrate temperature was found to agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp3 fraction increases with ion energy, giving ~80-85% of sp3 bonding at E > 30 eV. Above 200 °C simulations with the Brenner potential predict a sharp transition from ta-C to graphitic carbon with dominating sp2 bonding. Simulating thermal annealing, we show that low-temperature structural relaxation in ta-C is accompanied by a considerable stress reduction with only minor changes in the short-range order.

Reaktivextraktionsverfahren stellen sehr effektive und elegante Trenn- und Anreicherungsverfahren für Metallionen in Lösung dar, die in vielfältiger Weise industriell genutzt werden. Trotz der großen Bedeutung von Anionen in Biologie, Medizin, Umwelt und Technik sind die praktischen Beispiele zur Anionenextraktion relativ begrenzt. Im wesentlichen basieren derartige Prozesse auf einer unspezifischen Ionenpaarbildung mit hydrophoben Ammonium-Kationen, wobei der Phasenübergang durch die Lipophilie der Anionen dominiert wird. Ursache für diese Unterschiede sind eine Reihe von Besonderheiten, die Anionen im Vergleich zu Kationen auszeichnen. Neue Ansätze zu spezifischer Bindung und selektivem Transport anionischer Komponenten beruhen auf einem fortschreitenden Verständnis der biologischen Rolle von Anionen und der dabei wirksamen Prinzipien sowie auf Möglichkeiten, die die supramolekulare Chemie durch Aufbau von vielfältigen Rezeptorarchitekturen mit spezifischen Bindungsstellen für Anionen eröffnet. Ziel der vorliegenden Übersicht ist es, ausgehend von den typischen Eigenschaften der Anionen gegenwärtige Entwicklungstendenzen sowie Einsatzpotentiale neuer potentieller Extraktionsmittel zu diskutieren.

entfällt

Within a transport code simulation for heavy-ion collisions at bombarding energies around 1 AGeV we demonstrate that double-differential di-electron spectra with suitable kinematical cuts are useful to isolate
(i) the ρ meson peak even in case of strong broadening, and
(ii) the in-medium ω decay contribution,
which probe via the di-electron channel the expected in-medium modifications of the vector meson spectral densities.

Low capacitance p+n point diodes were fabricated by combination of sputtering and implantation of a Ga focused ion beam through a thin oxide layer on a silicon substrate. The capacitance of the diodes were determined to be in the range of aF. The current-voltage characteristics show a tendency to a generation / recombination controlled behaviour with increasing dose i.e. with increasing depth of the sputter crater. This is correlated to the big amount of inactive Ga atoms of about 70% in the Si lattice after an annealing of 900°C; 20 min, N2.

Structural relaxation processes in tetrahedral amorphous carbon (ta-C) are examined at the atomic scale using computer simulation techniques and Brenner's bond-order potential. The amorphous carbon networks generated by ion-beam deposition simulation are employed as structural models of as-prepared ta-C. The models possess high intrinsic compressive stresses (~10 GPa) typical of as-grown ta-C films. Simulating annealing by the molecular-dynamics method, structural changes due to the relaxation of the ta-C networks were observed. In agreement with experiment, it is shown that low-temperature structural relaxation in ta-C is accompanied by a considerable stress reduction with only minor changes in the structural disorder and density. A complete stress relief is found to occur at T_a ~1000 K. The stress relief mechanism discussed on the basis of the molecular-dynamics simulations includes structural transformations within the sp³ -bonded constituent of ta-C networks and doesn't require oriented clustering of sp² -bonded atoms.

The paper presents a numerical stability analysis of the flow driven by an alternating (AC) magnetic field in an electromagnetically levitated liquid metal droplet. The basic axisymmetric flow is found to become unstable at Reynolds numbers in the order of 100. The critical Reynolds number Rec and the corresponding most unstable azimuthal wave number m are found for several configurations of the magnetic field depending on the skin-depth d. For a uniform external AC magnetic field the azimuthal wave number of the most unstable mode is m=3. An additional steady (DC) magnetic field imposed along the axis of symmetry increases the stability of the flow.

Kinetic 3D lattice Monte Carlo studies are presented on Si nanocrystal (NC) formation by phase separation in 1 keV Si⁺ implanted thin SiO₂ films. The simulation start from Si depth profiles calculated using the dynamic, high-fluence binary collision code TRIDYN. From the initial Si supersaturation, NCs are found to form either by nucleation, growth and Ostwald ripening at low Si concentrations. Or at higher concentrations, non-spherical, elongated Si structures form by spinodal decomposition, which spheroidize by interface minimization during longer annealing. In both cases, the close SiO₂/Si interface is a strong sink for diffusing Si atoms. The NCs align above a thin NC free oxide layer at the SiO₂/Si interface. Hence, the width of this zone denuded of NCs has just the right thickness for NC charging by direct electron tunneling, which is crucial for non-volatile memory applications. Moreover, the competition of Ostwald ripening and Si loss to the interface leads at low Si concentrations (nucleation regime) to a constant width of the denuded zone and a constant mean NC size over a long period of annealing.

In silicon-nanocluster (Si-NC) memories, Si-NC embedded in the gate oxide of a MOSFET are used to store and release electrons thereby modifying the threshold of a transistor. This article describes the formation of its core functional structure, the Si-NC MOS memory capacitor, by annealing a SiO2/SiOX (x < 2) stack, deposited onto a thin direct tunneling oxide on silicon by a sputtering method. To achieve a high density of isolated Si-NC, both, the initial silicon excess in the SiOX layer and the thermal annealing treatment must be optimized. Optimum conditions are expected just at the end of the nucleation stage of the NC ensemble. Therefore the effect of various rapid thermal anneals (RTA) on SiOX/Si structures with different silicon excess x was investigated
focusing on two optical methods: infrared absorption and photoluminescence (PL). The rate of nucleation and phase separation was found to depend strongly on both, silicon excess and annealing temperature. The characteristic size dependence of Si-NC PL was used to differentiate annealing regimes yielding NC ensembles being 'frozen' in the process of nucleation or in their growth/ripening phase respectively. Additionally, Si-NC MOS memory capacitors were prepared and characterized using both, optical and electrical tests. The devices prepared under optimized conditions yield a high flat-band shift and good charge retention characteristics.

For calculations of Lower Head Failure experiments like FOREVER it is necessary to model creep and plasticity processes. Therefore a Finite Element Model is developed using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
The validation of the numerical model is performed by the simulation of and compari-son with experiments. This is done in 3 levels: starting with the simulation of single uniaxial creep tests, which is considered as a 1D-problem. In the next level so called “tube-failure-experiments” are modeled: the RUPTHER-14 and the “MPA-Meppen”-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments.
An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. If these 2 steels show a similar behavior, it should be allowed to transfer experimental and numerical data from one to the other.

Es wird das entwickelte Online-Zustandserkennungssystem MoSys beschrieben, das dem Anlagenfahrer zusätzliche Informationen über den Prozessfortschritt, das voraussichtliche Reaktionsende, die Akkummulation von Edukten oder Zwischenprodukten oder über die Gefahr einer thermischen Explosion bei unzureichender Kühlung zur Verfügung stellt. Das Zustandserkennungssytem, das auf adaptiven Stoff-und Wärmebilanzen basiert, kann sowohl in direkter Kopplung mit dem Prozessleitsystem als auch als Komponente eines komplexen Batch-Informations-Management-Systems betrieben werden. Die Leistungsfähigkeit von MoSys konnte für homogen katalysierte Veresterungsreaktionen in einer Technikumsanlage und für heterogen katalysierte Hydrierprozesse in einer industriellen Chemieanlage nachgewiesen werden. Neben einer Erhöhung der Anlagen- und Umweltsicherheit wird durch den Einsatz von MoSys weiterführendes Prozesswissen generiert, das als Grundlage für eine Prozessoptimierung genutzt werden kann.

There is a considerable interest in the development of ^99mTc radiopharmaceuticals for imaging serotonergic CNS receptors using single-photon emission tomography (SPET). To date most Tc compounds assigned as CNS receptor targeted agents are square-pyramidal complexes of the oxo ion [Tc=O]³⁺. However, the in vivo behaviour of such complexes are strongly influenced by the quite polar Tc=O unit offering a free position trans to the oxo ligand for further reaction in vivo. To reduce this in vivo reactivity, oxo-free Tc complexes containing the metal in lower oxidation states are considered to be appropriate alternatives.
Tc(III) mixed-ligand complexes (1) with tetradentate/monodentate NS₃/isonitrile coordination appear suitable to wrap the metal well in a molecule with receptor-targeting functionality. The here introduced compounds contain a methoxyphenyl-piperazine moiety derived from the selective 5-HT_1A receptor antagonist WAY 100,635 linked to the Tc chelate unit via an alkyl chain [1].

The low-pressure synthesis of a Tc-carbonyl precursor as inaugurated by Alberto et al. allows a convenient exploitation of the potential of the "Tc(CO)₃" moiety in the design of receptor-binding agents [2]. A bidentate N-donor anchor group has been considered well suitable for combining the Tc(I) tricarbonyl center with the antagonist moiety (2). Alternatively, a bidentate thioether group to link the Tc(I) tricarbonyl center with 4,7-dithiaoctanoic acid (3beta-(4-fluorophenyl)tropane-2beta)-methyl ester (3) as receptor-targeting moiety has been chosen [3].
We report the synthesis, in vitro receptor affinity and biodistribution of three candidates in order to demonstrate the suitability of the concept and to elucidate the influence of the building blocks on the biobehaviour of the complexes.

A new approach for a ¹¹C-C bond formation via a Sonogashira-like cross-coupling reaction of terminal alkynes with [¹¹C]methyl iodide was exemplified by the synthesis of 17alpha-(3'-[¹¹C]prop-1-yn-1-yl)-3-methoxy-3,17beta-estradiol. The title compound was obtained in decay-corrected radiochemical yields of 27-47% (n=8) based on [¹¹C]methyl iodide within 21-27 minutes after EOB. In a typical synthesis, 1-2 GBq of 17alpha-(3'-[¹¹C]prop-1-yn-1-yl)-3-methoxy-3,17beta-estradiol was synthesized in radiochemical purity >99%. The specific activity ranged between 10-19 GBq/µmol, and the labeling position was verified by the synthesis of the corresponding ¹³C-labeled compound.

A review will be given on the R&D activities in this field at FZR. Emphasis
will be given to the inverse approach to MHD problems comprising the tools
of model experiments and measuring techniques for metallic melts.
Applications of this approach to crystal growth problems will be presented.

The idea of an inverse design of the heat transfer during the VGF-growth of
GaAs will be presented. Optimization of the solid-liquid phase boundary is,
however, only possible by an additional melt flow control which is provided
here by a rotating magnetic field. Theoretical calculations and experimental
growth results will be compared.

The mechanisms govering the formation of the liquid metal cone that constitutes the basis of a liquid metal ion source (LMIS) are investigated. Cone formation times ranging from < 20 ns up to several hundreds of ms have been reported in the literature. The paper attempts to explain these differences by devising a theoretical model that encompasses inertial and flow effects.

Erkenntnisse zum Verhalten geschmolzener Kernmaterialien im Sicherheitsbehälter und zu deren langzeitiger Kühlung sind für die Begrenzung der Auswirkungen eines schweren Unfalles von erheblicher Bedeutung. Mit dem Bestreben, die Auswirkungen eines Kernschmelzunfalles auf die Anlage zu beschränken, kommt der zuverlässigen Simulation des Verhaltens einer Kernschmelze im Sicherheitsbehälter eine zentrale Bedeutung zu. Nach der Aufbereitung der verfügbaren einschlägigen Versuchsergebnisse und Modellansätze sind auf der Grundlage der dabei gewonnenen Erkenntnisse die zu modilierenden Einzelphänomene identifiziert, verfügbare Modellansätze bewertet und Prioritäten hinsichtlich Neu- bzw. Weiterenrwicklung von Modellen für Einzelphänomene gesetzt worden.

Für die Simulation der Schmelzeausbreitung ist ein auf vulkanologischen Ansätzen basierender Rechencode ausgewählt und unter dem Namen "LAVA" weiterentwickelt worden. In LAVA wird der Immobilisierungsprozess am Ende der Ausbreitung über eine nicht-Newtonsche Materialcharakteristik in Form einer vom Feststoffgehalt des erstarrenden Materials abhängigen Binghamschen Fließgrenze beschrieben. Zur Berechnung der rheologischen Stoffwerte Viskosität und Fließgrenze für erstarrende Schmelzen sind Korrelationen aus der Literatur ausgewählt und Modellparameter abgeschätzt worden. LAVA ist umfassend an den Experimenten der COMAS und KATS Versuchsreihe validiert worden.

Ein Konzept für das Gesamtmodell zum Schmelzeverhalten im Sicherheitsbehälter ist hinsichtlich der physikalischen und programmtechnischen Verknüpfung konzipiert worden, wobei die Randbedingungen für die Implementierung des Gesamtmodells COCOSYS berücksichtigt sind. Dieses Konzept sieht eine Kopplung eigenständiger Module für Schmelzeausbreitung (LAVA) und -kühlung (CCI) vor. Für die Neuformulierung des CCI-Moduls sind in detaillierten Untersuchungen grundlegende Erkenntnisse gewonnen worden: Die Leistungsfähigkeit von CFD-Codes für die Simulation von 3D-Wärmetransportphänomenen in Schmelzepools wurde in einem umfassenden Codevergleich analysiert. Ferner wurde ein Modell zur Beschreibung der bewegten Phasengrenzflächen bei Aufschmelz- bzw. Erstarrungsvorgängen in dem CFD-Code CFX implementiert und angewendet. Aus den hieraus gewonnenen Erkenntnissen ist ein Konzept für die Neuentwicklung des CCI-Moduls in COCOSYS erstellt worden.

There is considerable interest in developing shorter (< 3 mm) wavelength optical devices based on the intersubband transitions (ISBT) such as ultrafast switchers, modulators and quantum cascade lasers. The choice of the suitable system for short-wavelength ISBT is restricted to the combination of materials that provide an appropriate large conduction band offset. In this letter, we report the optical and structural characterization of the InxGa1-x As/AlAs, x>0.6, quantum well (QW) structures grown on InP substrates. In these structures, an increased In content helps to compensate the larger AlAs tensile strain. Secondly, it provides a smaller InGaAs band gap that results in a shift of the 1st G well subband to lower energies relative to the X minimum in the barrier layers even in very narrow wells.
We have grown InxGa1-xAs/AlAs MQW with InAlAs layers between QW's and superlattice (SL) structures with different well thickness by gas source MBE on semi-insulating InP(001) substrates. Since, the compressively strained InxGa1-xAs layers do not fully compensate the tensile strained AlAs barriers, an In0.55Al0.45As slightly compressive strained buffer layer was inserted. The buffer layer was grown at 490 C and the QW structure at 440 C. The InxGa1-x As wells were Si doped to 2.0x1018cm-3.
The X-ray diffraction pattern and a theoretical fit using a dynamical diffraction theory of the MQW sample with 7ML thick In0.7Ga0.3As and AlAs layers, and 20.0 nm In0.55Al0.45As barriers between the QW's is presented in Fig.1. The data show a very good fit to the model using interfaces with little or no compositional grading.
The transmission spectrum of this sample is shown in Fig.2. The band offsets were determined using the model-solid theory, and the energy-level diagram as calculated within the effective mass approximation of the designed structure is shown in the right inset of Fig.2. There is a relatively large deviation between the calculated and measured ISBT wavelength. Due to the large conduction band offset in this system, ~1.4 eV, the monolayer fluctuations of the well thickness can explain the shift to lower energies of the ISBT for the narrow QW structure compared to the calculated on the assumption of abrupt interfaces as well as its broader ISBT spectrum. In addition, the large In composition and the ability of In atoms to segregate at the surface of the growing InGaAs layer probably leads to excess In at the upper interfaces, although the growth temperature of the QW is decreased to 440 C. This causes a nominal decrease of the In composition in the well at the expense of the formation of an In rich composition in the interface and an eventual intermixing with AlAs, i.e. the formation of an additional InyAl1-yAs interface layer at the bottom side of the barrier. When we incorporate a modified band diagram assuming 1-2 ML In intermixing in the upper interfaces we can calculated an ISBT of 1.91 mm (left insert in Fig.2), which is close to the experimental value. Our interpretation of the intermixing at the interfaces is confirmed by photoluminescence spectra.

The strong need for optoelectronic devices which can be integrated into the current silicon technology has initiated an extensive research for silicon-based light emitters. One of the promising approaches is the formation of luminescence centers in dielectric layers by means of ion beam synthesis. In this paper we explore the EL properties of thermally grown SiO2 layers co-implanted with silicon and carbon ions. The main motivation for this work was the expectation of a higher device stability using Si/C compounds within the SiO2 network compared to our former work with Ge and Sn implants. 360 nm thick SiO2 layers were implanted with Si, followed by an intermediate annealing step and a second implantation of C. Finally the structures were annealed at 1100°C. The doses were chosen in order to achieve peak concentrations of excess Si and C of 5-10 %. The devices show a broad PL between 400 and 600 nm with a main peak around 450 nm. The broad EL spectra show additional peaks around 370 nm and between 500-550 nm which are increased with decreasing Si/C concentration. The shape of the EL spectrum does not change with increasing injection currents, which implies that various types of defects occur for the different concentrations. The device stability is improved in comparison to Ge / Sn implanted oxide layers.

Silicon based light emitters are of great interest for future integrated optical systems. One possible approach for the formation of such devices is ion beam synthesis. Thermally grown SiO2 layers (80 nm) were implanted with germanium ions at energies of 30…50 keV to peak concentrations of 1…6 at%. Rapid thermal annealing was performed at 1000°C for 1…150 s under a nitrogen atmosphere in order to form luminescence centers. In previous investigations we observed strong photo- and electro-luminescence (EL) in the blue/violet wavelength range from such layers. In this paper we correlate these optical properties to effects of charge trapping which were observed by using a combination of capacitance-voltage (CV) and current-voltage (IV) methods. Electron trapping occurs at low electric fields. However, at high electric fields (>8MV/cm), which are typically required for the excitation of the defect related EL, positive charge trapping occurs. This might be attributed to hole trapping at oxygen deficiency centers - probably the same defects which cause the EL.

The effect of deposition temperature on the formation of hard amorphous carbon (a-C) films from low and medium energy ions was studied by atomic scale simulation. Applying classical molecular dynamics with a modified hydrocarbon potential of Brenner, ion-beam deposition of carbon films with a thickness of ~3-10 nm was simulated for ion energies E = 10-80 eV, and for substrate temperatures ranging from 100 to 900 K. The dependence of the sp3 content and intrinsic stress in the simulated films on substrate temperature was found to agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp3 fraction increases with ion energy, giving at E > 30 eV a highly sp3-bonded tetrahedral amorphous carbon (ta-C) with a high compressive stress. This trend also remains at room temperature, however with lower values of the sp3 content and stress, whereas above 200 °C simulations with the Brenner potential predict a sharp transition from ta-C to graphitic carbon with dominating sp2 bonding.

The nanocluster (NC) formation by phase separation of implanted impurity atoms from the host matrix has been studied. The deposition of impurity atoms by high fluence Si+ implantation into SiO2 was simulated using the computer code TRIDYN including dynamic target changes due to by sputtering, ion mixing and swelling. The depth profiles differ considerably from that predicted by the TRIM code. The TRIDYN profiles were used as input for kinetic lattice Monte-Carlo simulations of phase separation. The interaction of the Si atoms in the SiO2 layer is approximated by the nearest-neighbor Ising Hamiltonian, while the time evolution of the system is governed by the importance sampling of configurations according the Metropolis algorithm. The simulations show that NC formation proceeds via (i) nucleation and growth at low impurity concentrations, and via (ii) spinodal decomposition and interface minimization at high concentrations. Due to the small distance between the NCs and the SiO2/Si interface, Si atoms condense steadily onto the substrate and a zone denuded by NCs is formed at the interface. As the mass conservation is violated for impurity atoms within the SiO2, the description of the NC coarsening by the Lifshitz-Slyozov-Wagner theory is not applicable. Rather, the evolution of the NCs is determined by the competition of coarsening and dissolution.

The fabrication of regularly arranged nanostructures remains a challenge of today's materials research. In this contribution, Kinetic 3D Lattice Monte Carlo (MC) simulations of the shape evolution of single crystalline nanowires by thermally activated interface diffusion will be presented. Interface minimizations leads to the Rayleigh (or pearling) instability; during annealing nanowires develop peristaltic thickness undulations, which finally results in the decay of the wire into a regular chain of nanocrystals (NC’s). For temperatures above the roughening transition it could be shown that size and spacing of the NC’s are in good agreement with results of the classical stability analysis performed by Rayleigh and Mullins. The competition between peristaltic undulations having different wavelength (modes) results in the decay of the wire into equal-spaced NC’s due to self-selection of the fastest growing mode. This mode selection is demonstrated by the Fourier analysis of the MC results. Other than in the analytical stability analysis it has been found that short-wavelength modes develop first, whereas long-wavelength modes are missing initially. Below the roughening transition, the results differ quantitatively. The spacing between NC’s becomes larger and depend on the crystal orientation of the nanowire, which is due to the anisotropy of the interface energy.

Non-volatile memories concepts based on semiconductor nanocrystals (NC) embedded in the gate oxide of MOS transistors with have attracted much in-terest. In order to synthesize the NC’s, ion implantation followed by annealing is the most compatible method with the current CMOS technology. In this contribution, fundamental studies of NC formation by phase separation in very-low energy ion implanted ultra-thin gate oxides will be presented. Ki-netic 3D lattice Monte-Carlo (MC) simulations show that for low ion fluences (low concentrations) the NC formation proceeds via nucleation, growth and Ostwald ripening. However, for high fluences spinodal decomposition results in a laterally connected network of nanostructures resembling a conventional floating gate memory. In general, the Si/SiO2 interface being in close neighbourhood to the NC’s has substantial influence on the NC evolution. Specifically, it leads to a NC-free tunnel oxide at the interface. Although the analysis of Si NC’s in SiO2 is a challenge for current methods, TEM investiga-tions of Si+ implanted gate oxides on (001) Si are in qualitative agreement with our predictions based on MC simulations. However, quantitatively, the fluence necessary for Si NC formation exceeds the predicted one by up to an order of magnitude. Recent studies have shown that this discrepancy origi-nates from oxidation of a large fraction of implanted Si by moisture absorbed in the damaged SiO2 surface layer.

Corticosteroids regulate a variety of essential physiological functions, such as mineral balance and stress. The great interest in these steroids, especially the glucocorticoids, stems from roles they are thought to play in neuropsychiatric disorders, such as severe depression and anxiety.
The development of glucocorticoid receptor (GR) ligands which are appropriately labeled with short-lived positron-emitting radioisotopes would allow the non-invasive in-vivo imaging and mapping of brain GRs by means of positron emission tomography (PET). In this context we have synthesized a series of novel arylpyrazolo steroids exhibiting different substitution patterns at the D-ring of the steroid skeleton, as ligands for brain GRs. Special attention was given to 4-fluorophenyl pyrazolo steroids, which are known to display high binding affinity toward the GR. The compounds were evaluated in a competitive radiometric receptor binding assay to determine their relative binding affinities (RBA) to the GR. Some compounds show good binding affinities of up to 56% in comparison to dexamethasone (100%). In initial experiments, selected candidates were labeled with the positron emitter fluorine-18 and in one case with the gamma-emitter iodine-131.

Studies of semiconductor nanocrystals (NC's) in the MOS gate oxide received much interest due to their potential application in non-volatile memory devices. However, the detailed charge storage mechanism is still under discussion. Defect-based charge trapping at NC surfaces is hard to distinguish from storage in the conduction band of NC's. For metal NC's in SiO2 the situation is different. Charge traps at the Au/SiO2 interface are assumed to be negligible at first sight. In this contribution, Au NC's serve as a model system for the charge storage phenomena in NC containing gate oxides with dox<40 nm. For the present study, Au NC's were synthesized by low-energy ion implantation followed by annealing. The Au depth distribution was measured by RBS with high depth-resolution. The process of phase separation during annealing is traced by a series of X-TEM images. A fraction of Au diffuses to the Si/SiO2 interface, forms silicon supersaturated by Au and nucleates liquid Au:Si lenses at the interface. The Au NC's in the SiO2 layer above these lenses are stabilized due to the modified detailed balance of Au-atoms detachment/attachment. Additionally, a zone denuded by NC's forms at the interface. Preliminary electrical results will be presented.

Silicon rich silicon oxide films (SRO) were prepared by co-sputtering from silica and silicon targets in an argon atmosphere. The formation of silicon nanoclusters (Si NCs) by a thermally stimulated phase separation was
investigated. The influence of sample composition and annealing temperature has been studied by optical methods (infrared absorbtion and photoluminescence). Both methods reveal that phase separation proceeds
more quickly in SRO films with a higher Si excess. Additionally MOS capacitors with embedded Si NCs were prepared and investigated by capacitance-voltage measurements.
The embedded Si NCs could be charged by direct tunneling. For optimized samples held at flat-band potential, the charge loss after 2 days at room temperature was below 10%.

The heteroepitaxial growth of TiN on MgO(001), deposited by reactive magnetron sputtering, has been studied in situ. Using real-time specular X-ray reflectivity, layer-by-layer growth was observed, with the surface-roughening decreasing with increasing deposition temperature. Higher temperatures also resulted in lower growth rates. The film thickness was measured with specular X-ray reflectivity. Using off-plane Bragg-Brentano as well as grazing incidence in-plane wide angle scattering, the pseudomorphic growth of TiN to the underlying MgO(001) was established. Transmission electron microscopy reveals atomic planes passing through the MgO–TiN boundary, thus confirming the heteroepitaxial growth.

This article shows that phase transformations in implanted iron may strongly depend on the sample thickness. The effect essentially relies on lower impurity concentration required for given phase formation in thin films as compared with thick layers or bulk samples. The phase transformation in thin films is also more complete. In this work the total transformation of pure iron into iron nitrides was observedn upon nitrogen implantation of thin iron layers, whereas about 20 % of Fe atoms remains in crystalline a-Fe phase in nitrogen-implantedin bulk samples.

Migration of heavy metals in the aquatic environment is often combined with the complex formation of these metals with organic ligands, like humic substances and wood degradation products. To simulate the functionality of these polyelectrolytes simple hydroxybenzoic acids are studied.
The fluorescence properties of organic molecules were used for the determination of metal complexation. Due to short fluorescence lifetimes of the ligand molecules a dedicated spectrofluorimeter using ultra short laser pulses as excitation source was developed. The laser system consists mainly of the oscillator system for generation of femtosecond laser pulses, the amplifier system to increase the pulse energy of the generated pulses to about 2 mJ and an optical parametrical amplifier system to provide tunable laser pulses over a wide wavelength range (280 nm to about 10 µm). The emitted fluorescence was detected using a fast gating intensified CCD-camera based spectrometer. The system allows to determine time-resolved fluorescence spectra in solid and aqueous (solution) systems with fluorescence lifetimes between about 150 ps and about 10 ns and concentrations of the organic ligand down to 1 x10-6 M.
To verify the system the well known protonation constant log K3 = 3.10 ± 0.20 (I = 0.1 M, T = 298 K) [1,2] of the 2,3-dihydroxybenzoic acid was determined.
The fluorescence lifetime of C6H3(OH)2-COO- is determined to be 375 ± 32 ps and the fluorescence emission maximum was found at a wavelength of 438 nm. We obtain from fluorescence data a protonation constant of log K3 = 3.17 ± 0.05 for the first dissociation step at ionic strength of 0.1 M and 294 K exploiting the Stern-Volmer mechanism. The agreement of data and the derived error of the protonation constant demonstrate the accuracy of the developed system.
The complex formation of the 2,3-dihydroxybenzoic acid with neptunium(V) was studied in the range from pH 3.0 to 7.0. At lower pH - values a 1:1 complex was identified, showing only an interaction of the neptunium(V) with the carboxylic group of the ligand. A second 2:1 complex is formed at the higher pH-values. This indicates that the phenolic OH-group also forms complexes with the metal ion. The formation constants are found to be log K11= 0.11 ± 0.04 and log K12 = 6.97 ± 0.10. Also a third intermediate complex was detected by its fluorescence properties.

Literature:

[1] L. Lajunen, R. Portanova, J. Piispanen et al; Pure & Appl.Chem., 1997, 69, 329, [2] H. Harada; Bull.Chem.Soc.Jpn., 1971, 44, 3459

High diversity and significant differences were found in the structures of bacterial communities present in several U mill tailings and U mining waste piles. Many bacterial strains were successfully cultured from those uranium wastes, most of which are unusually effective in different biotransformations of U. The molecular basis for the selective and reversible binding of U and some other toxic metals by one of the natural bacterial isolates was found to be a novel kind of S-layer protein. Our analysis indicates that uranium wastes are a valuable reservoir for unusual microorganisms prospective for bacteria-based bioremediation.

A combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and Infrared (IR) spectroscopy was used to characterize the uranium complexes formed by different bacterial strains of Acidithiobacillus ferrooxidans isolated from uranium mining wastes, and by some reference strains relevant to the predominantly distributed in the wastes Pseudomonas stutzeri, and Pseudomonas migulae. The results demonstrated that all these bacteria accumulate uranium as phosphate compounds with different structural parameters.

Abstract. Cells, spores and the surface layer protein (S-layer) of the Bacillus sphaericus strain JG-A12, recovered from a uranium mining waste pile, were embedded in SiO2 matrices by using sol-gel techniques. Sorption and desorption of uranium and copper by the free biocomponents and the obtained biological ceramics (biocers) were investigated. The biocer with cells possesses the highest binding capacity, followed by the S-layer biocer and the spore biocer. For renewed use of the biocers, the bound uranium and copper can be completely removed by washing with aqueous citric acid.

Biological ceramic composites (biocers) made according to an aqueous sol-gel protocol were used as selective metal binding filters. The biological component of the biocers Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile. Vegetative cells and spores of this strain are known to bind selectively U, Cu, Al, Cd and Pb in large amounts. Sol-gel ceramics were prepared by dispersing vegetative cells, spores and stabilized surface-layer proteins (S-layer) in aqueous silica nanosols, gelling and drying. The biosorption of uranium and copper by the three kinds of biocers and by their single components was investigated in dependence on time, concentration and preparing conditions. Biocers with cells possess the highest binding capacity compared to matrices with spores and S-layer. Freeze drying of prepared biocers or adding water soluble additives as sorbitol lead to higher porosity and faster metal binding. Uranium was bound mainly to the biological component but also to the SiO2 network. In contrast, copper was only bound by the cells, spores or S-layer. Bound uranium and copper were completely removed by washing with aqueous citric acid.

The complexation in the Cm(III) and Eu(III) glycolate systems have been studied by time-resolved laser fluorescence spectroscopy (TRLFS). The measurements have been performed at trace Cm(III) and Eu(III) concentrations (about 10-7 and 10-6 mol/L, respectively) at different concentrations of glycolic acid and at different pH using NaClO4 as background electrolyte. Measurements at higher Eu(III) concentrations (10-3 mol/L) have also been performed in order to study the influence of metal ion concentration on the complexation reaction.
By varying the glycolic acid concentration from 0.1 to 0.5 mol/L at low pH ([H+]=10-3) the stepwise formation of glycolate complexes [Cm(HOCH2COO-)n(H2O)9-2n]3-n with n=1-4 were confirmed spectroscopically. By varying the pH between 4.5 and 12.0 in 1 M glycolate the following three Cm(III) species were identified from the fluorescence emission spectra

• a hydrated tetraglycolate complex [Cm(HOCH2COO-)4(H2O)]- (Cm/complex 1) with a peak maximum at 602.3 nm and a fluorescence emission lifetime of 206 ± 3 µs,
• a mixed hydroxide-glycolate complex [Cm(HOCH2COO-)4(OH)]2- (Cm/complex 2) with a peak maximum at 605.6 nm and the same lifetime as Cm/complex 1 and
• a chelate complex [Cm(HOCH2COO-)3(-OCH2COO-)(OH)]3- or [Cm(HOCH2COO-)2(-OCH2COO-)2(H2O)]3- (Cm/complex 3 ) (peak maximum 611.3 nm) which is generated after deprotonation of one or two of the coordinated a-OH groups of the glycolate with a fluorescence emission lifetime of 295 ± 15 µs. In the europium system there is evidence only for the corresponding Eu/complex 1 and 3. The corresponding europium mixed hydroxide-glycolate complex is not detectable spectroscopically. The fluorescence decay is different in the Cm and Eu systems in the pH range from 7.8 up to 10.5; a bi-exponential decay behaviour was observed for the Cm system, while the Eu system shows mono-exponential decay. This indicates that the kinetics of the chelating process is much slower for Cm(III) than for Eu(III). The rate of protonation of the coordinated a-O- group in the Eu/complex 3 is much faster than in case of Cm/complex 3. Different spectra were observed for Eu(III)/glycolate complexes at europium concentrations of 3x10-6 mol/L and 1x10-3 mol/L indicating the formation of poly-nuclear Eu(III)/glycolate complexes at high metal ion concentration.

Die laserinduzierte Fluoreszenzspektroskopie wird häufig genutzt, um in der Actinidenchemie Untersuchungen bei sehr geringen Konzentrationen durchzuführen. Während dies beispielsweise für Curium(III) und Uran(VI) mit Nachweisgrenzen um 10-9 mol/L bzw. 10-7 mol/L kein Problem ist, sind andere Actinidenelemente auf Grund ihrer fehlenden Fluoreszenzeigenschaften derartigen Untersuchungen nicht zugänglich.
Einen Ausweg bieten Methoden, bei denen nicht die spektroskopischen Eigenschaften des Actinidelementes, sondern die des Liganden im Vordergrund stehen. Als Liganden kommen Verbindungen in Frage, die auf Grund ihrer p-Elektronensysteme über ausgeprägte Fluoreszenzeigenschaften verfügen. Anhand der verschiedenen isomeren Dihydroxybenzoe-säuren kann zudem der Einfluss der phenolischen OH-Gruppe auf die Komplexbildung ermittelt werden. Dies ist von besonderer Bedeutung für das Verständnis der Komplexbildung von Huminstoffen und Holzabbauprodukten.
Berichtet wird über die Komplexbildung von Neptunium(V) und Uran(VI) mit 2,3-Dihydroxybenzoesäure. Da Uran(VI) selbst fluoresziert kann in diesem Fall die Komplexbildung sowohl über die Veränderung der Uranfluoreszenz, als auch über Veränderung der Ligandfluoreszenz beschrieben werden. In diesem Zusammenhang wird die Frage diskutiert, inwieweit andere Prozesse Einfluss auf die ermittelten Komplexkonstanten haben.

Binary collision simulations of high-fluence 1 keV Si⁺ ion implantation into 8 nm thick SiO₂ films on (001)Si were combined with kinetic Monte Carlo simulations of Si nanocrystal (NC) formation by phase separation during annealing. For nonvolatile memory applications, these simulations help to control size and location of NCs. For low concentrations of implanted Si, NCs form via nucleation, growth and Ostwald ripening, whereas for high concentrations Si separates by spinodal decomposition. In both regimes, a self-adjusted oxide layer denuded of NCs forms at the SiO₂/Si interface, which has just the right thickness for NC charging by direct electron tunneling. However, only in the nucleation regime the width of the tunneling oxide and the mean NC diameter remain constant during annealing. This stability originates in the competition of Ostwald ripening and Si loss to the Si/SiO₂ interface. Based on the process simulations, its is predicted that the technological demands on the NC synthesis for nonvolatile memories are fulfilled best in the nucleation regime.

Within the PWR safety analyses, attention has increasingly focussed in recent years on boron dilution events which could potentially lead to reactivity transients. Mixing of the diluted water with the ambient coolant of higher boron content provides an important mitigation mechanism before the diluted water enters the core.
Experimental support is needed to validate the computational tools to be applied to analyze the mixing of the low-boron water. Experiments were performed in the three test facilities UPTF, PKL and ROCOM in Germany.
The relevant PKL and UPTF tests were focussed on small break loss of coolant accident (SB-LOCA) scenarios with reflux-condenser mode and restart of natural circulation. The two test facilities represent a typical western-type PWR and are/were operated by Siemens/KWU now Framatome ANP in Germany. While the restart of natural circulation was investigated in the PKL system test facility (volume 1:145, height 1:1), the UPTF experiments dealt with the mixing of water flows with different boron concentration in the cold legs, reactor pressure vessel (RPV) downcomer and the lower plenum (all these components were full-scale models).
The results from the PKL test facility demonstrate, that in case of a postulated SB-LOCA with reflux condensation phase, natural circulation does not start up simultaneously in all loops. This means, that slugs of condensate, that might have accumulated in the pump seal during reflux condenser mode of operation, would reach the RPV at different points in time. The UPTF tests showed an almost ideal mixing of water flows with different boron concentration in the RPV downcomer.
The ROCOM test facility has been built in a linear scale of 1:5 for the investigation of coolant mixing phenomena in a wide range of flow conditions in the RPV of the German KONVOI type PWR. The test results presented are focussed on the mixing of a slug of deborated water during the start-up of the first reactor coolant pump. Based on experimentally determined pulse responses, a semi-analytical model for the description of coolant mixing inside the KONVOI RPV has been developed. Calculations for a presumed boron dilution event during the start-up of the first reactor coolant pump have been carried out by means of the semi-analytical model and independently by means of the CFD-code CFX-4. The semi-analytical model is able to describe the time dependent behaviour of the deboration front at each fuel element position in a good agreement with the experiment. All main mixing effects, observed in the experiment, are also reproduced by the CFX-calculation.

Die Verwendung von großflächigen Gamma-Detektoren zeichnet sich durch hohe Effektivität und damit geringe Messzeit aus. Dagegen sind mit ihnen keine hohen Ortsauflösungen bei der Rekonstruktion der Aktivitätsverteilung möglich. Zur Untersuchung der Rekonstruierbarkeit unbekannter Aktivitätsverteilungen werden zwei in der Tomographie gebräuchliche Verfahren verglichen, ein algebraisches (iterativ) und ein analytisches (gefilterte Rückprojektion). Beide Verfahren erbringen qualitativ ähnliche Ergebnisse. Reale Aktivitätsverteilungen werden nach beiden Verfahren zufriedenstellend rekonstruiert.

Die Verwendung von großflächigen Gamma-Detektoren zeichnet sich durch hohe Effektivität und damit geringe Messzeit aus. Dagegen sind mit ihnen keine hohen Ortsauflösungen bei der Rekonstruktion der Aktivitätsverteilung möglich. Zur Untersuchung der Rekonstruierbarkeit unbekannter Aktivitätsverteilungen werden zwei in der Tomographie gebräuchliche Verfahren verglichen, ein algebraisches (iterativ) und ein analytisches (gefilterte Rückprojektion). Beide Verfahren erbringen qualitativ ähnliche Ergebnisse. Reale Aktivitätsverteilungen werden nach beiden Verfahren zufriedenstellend rekonstruiert.

The interaction of a pulsed ion beam with a solid leads to a small temperature variation in the near subsurface region. Due to the local heating of the target thermal elastic waves were generated. The measurement of these waves gives informations about the internal structure and properties of the sample. Experiments were carried out using an intensity modulated beam of high energy ions from a TANDETRON accelerator for the investigation of elastic waves in aluminum, steel, copper and silicon samples as well as for a pulsed low energy focused ion beam (FIB) for acoustic imaging from structures on different targets. The detection of the acoustic signal was provided by piezoelectric transducers based on lead zirconium titanium (PZT) ceramic or on polyvinylidene fluoride (PVDF) films which can be applied in the scanning ion acoustic microscopy. In this case the modulation frequency was varied in the range from 60 kHz to 2 MHz. A lateral resolution of the ion acoustic images near the samples surface of a few micrometers could be obtained.

The A(e,e'K+)YX reaction has been investigated in Hall C at Jefferson Laboratory for 6 different targets. Data were taken for Q²ࣈ 0.35 and 0.5 GeV² at a beam energy of 3.245 GeV for ³H, ²H, ²He, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of Lambda and Sigma⁰ hyperon production off the proton, and Sigma^- off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for
^3,4He targets.

The electrical conduction mechanism of Ge-implanted SiO2 films exhibiting room-temperature blue electroluminescence with a power efficiency of up to 0,5 % [Appl.Phys.Lett.71(1997)2809] is investigated. In detail it will be shown that the current–voltage characteristic of Ge-implanted SiO2 layers for applied electric fields between 4.5 and 7 MV/cm can be modeled very well with the space charge limited (SCL)conduction mechanism in the trap-filled-limited (TFL) region.The current density j shows a power law dependence j ~ E^a of the applied electric field E, and the temperature dependence of a exhibits the typical behavior of TFL injection currents. For applied electric fields above 7 MV/cm the charge transport mechanism is explained by SCL currents which are superimposed by effects of field emission, impact ionization, and electron–hole recombination.

The spherical MHD mean-field dynamo is considered from a mathematical
viewpoint. It is shown that the corresponding 2x2 operator matrix lives in a Krein
space (a Hilbert space with indefinite metric) and has paired complex
eigenvalues.
A no-go theorem is discussed which forbids isospectral classes of dynamo
operators for a linear factorization ansatz in a supersymmetric intertwining
approach.
A detailed compatibility analysis is presented for the associated matrix
Riccati differential equations.

no abstract delivered from author

We present new experimental data on directed flow in collisions of Au+Au, Xe+CsI and Ni+Ni at incident energies from 90 to 400 A MeV. We study the centrality and system dependence of integral and differential directed flow for particles selected according to charge. All the features of the experimental data are compared with Isospin Quantum Molecular Dymnamics (IQMD) model calculations in an attempt to extract information about the nuclear matter equation of state (EoS). We show that the combination of rapidity and transverse momentum analysis of directed flow allows to disentangle various parametrizations in the model. At 400 A MeV, a soft EoS with momentum dependent interactions is best suited to explain the experimental data in Au+Au and Xe+CsI, but in case of Ni+Ni the model underpredicts flow for any EoS. At 90 A MeV beam energy, none of the IQMD parametrizations studied is able to consistently explain the experimental data.

With the invention of the liquid metal ion source (LMIS) in the sixties the focused ion beam (FIB) technique started an impressive development from the laboratory level to high performance industrial equipments. At present, the FIB is a very useful and versatile tool in microelectronics industry for mask and integrated circuit repair and modification, failure analysis or TEM specimen preparation, as well as in the material science for radiation damage and sputtering investigations, for grain size and distribution analysis in metals and alloys, for the formation of silicides or the fabrication of micro-tools. For special purposes in the field of research and development, like writing ion implantation or ion mixing in the µm- or sub-µm range different ion species are needed. Therefore alloy LMIS are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of the FIB equipment. Different source materials like Au73Ge27, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and temperature T. For single charged ions the predicted dependence of the energy spread according to DE µ I2/3 m1/3 T1/2 found for Ga could be confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. So a Co-FIB was applied for the ion beam synthesis of CoSi2 micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell-time was used for radiation damage investigations in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. All these examples underline the importance of a FIB in modern research and the new possibilities given by a mass separated system applying a broad spectrum of ion species.

An efficient semi-analytical model for the description of the coolant mixing during stationary and transient processes inside the reactor pressure vessel (RPV) of pressurised water reactors (PWR) has been developed. This model is based on the technique of linear superposition of response functions on Dirac impulse shaped perturbation functions. In the model, the RPV is represented formally by a group of transfer systems (for each combination of inlet nozzle position and fuel element position one) with one input and one output each. An experimental way of obtaining the transfer properties is shown on the example of the German PWR KONVOI. The validation of the model against experimental data from the 1:5 scaled coolant mixing test facility ROCOM is presented.
The semi-analytical model for the description of coolant mixing has been used in combination with the 3D reactor dynamics code DYN3D for the analysis of a hypothetical boron dilution event after start-up of the first main coolant pump in a generic four-loop PWR. The model provides realistic time-dependent boron concentration fields at the core inlet. By varying the initial slug volume it was found, that for the given core configuration slugs of less than 20 m3 do not lead to a re-criticality of the shut-off reactor. Calculations with the bounding slug volume of 36 m3 show, that the corresponding reactivity insertion does not lead the safety relevant consequences.

At the Research Center Rossendorf near Dresden a superconducting electron accelerator is under construction and will start its operation in the course of this year. The electron beam with an energy of 20 (later up to 40) MeV is intended to provide the "source" for several types of secondary radiation: (1) gamma photons for nuclear spectroscopy, (2) X-rays for studies of cell damage, (3) neutrons for fusion-related research, (4) positrons for applications mostly in solid state physics, and finally (5) intense, coherent infrared radiation by means of two free-electron lasers, which will span the wavelength range between 5 and 150 microns. While giving a brief overview about all the above topics, I will concentrate on the free-electron lasers and the solid state spectroscopy we are planning to use them for. A focus will be time resolved studies of semiconductor quantum structures. It is intended to develop ELBE into a user facility, open to users worldwide, but of course in particular to researchers in central Europe.

Measurements were conducted in a vertical pipe with an inner diameter of 51.2 mm and a length of about 3 m for air/water bubble and slug flow. The use of a wire-mesh sensor allows a high resolution of the gas fraction data in space as well as in time. From these data time averaged values for the two-dimensional gas fraction profiles decomposed according to a large number of bubble size classes were calculated. This allows to extract data for the radial gas fraction profiles for a given range of bubble sizes as well as data for local bubble size distributions. The measurements were done for up to 10 different inlet lengths and for about 100 combinations of gas and liquid volume flow rates. Further experiments are planned. The data will be used for the development of models for the forces acting on a bubble in a shear field of the liquid flow and models for bubble coalescence and break-up.

The ultrasound Doppler velocimetry (UDV) has been used to measure flow velocities at temperatures up to 620°C. To overcome the thermal restriction of the ultrasonic transducers an acoustic wave guide has been used. The acoustic wave guide and the piezoelectric element are combined in form of an integrated sensor. This approach allowed the first successful application of the ultrasound Doppler technique in liquid metals at temperatures above 200°C. The feasibility of this integrated sensor concept was demonstrated in experiments with metallic melts. Measurements were performed in a PbBi bubbly flow and in CuSn.

Considering the phase 2 of the OECD/NRC BWR Turbine Trip Benchmark several analyses were performed with the help of the DYN3D code. Thermal-hydraulic boundary conditions of the core are given for this part of the benchmark. Concerning the modelling of the BWR in the DYN3D code several simplifications and their influence on the results were investigated. The standard calculations with DYN3D were performed with 764 coolant channels (1 channel per fuel assembly). It is shown that the power peak obtained for the given boundary conditions is close to the measured value. For numerical stability reasons, preliminary calculations were carried out neglecting the instationary mass balance equation. This approximation provided a stronger reduction of the core void that results in a higher power peak. The impact of the assembly discontinuity factors (ADF) was studied. It is shown that the influence on core-averaged values of the steady state and the transient is small. Considering local parameters the influence is not negligible. Several participants of the benchmark perform calculations with 33 thermal-hydraulic channels. The influence of the number of coolant channels has also a small effect on the core averaged values, but local parameters as axial power distribution in single fuel assemblies are affected. The phase slip model of MOLOCHNIKOV is the standard model of DYN3D for void fraction calculation. The ZUBER-FINDLAY model shows only small deviations from the standard case for both global and local values, however not in the direction of the measurement. Using the thermal-hydraulic boundary conditions the best agreement with the experiment was obtained for the standard model.

The paper links the Master Curve (MC) concept and the Charpy-V impact test to determine dynamic fracture mechanical parameters of ASTM A 533 B Cl. 1 nuclear pressure vessel steel. Pre-cracked and side-grooved Charpy size specimens were tested under impact loading using the instrumented impact pendulum test. J-integral based fracture toughness values, KJc, were determined at cleavage failure of the specimen. MC based reference temperatures, T0dy, were determined on the basis of measured KJc values.
The change in T0dy was determined in dependence on the thickness position of a steel plate and compared with the quasi-static reference temperature, T0st, and the Charpy-V transition temperature (TT). All three parameters increased from the surface towards the middle of the steel plate in the same course. However, in the middle section of the plate T0dy is in average approximately 26 K higher than TT41J and 72 K higher than T0st. Different T0 were found when tested at different temperatures, but the trend is ambiguous.
The results show that the MC based T0 is sensitive to reflect rather small microstructural differences by testing small Charpy size specimens and, thus it is applicable for the fracture mechanical characterisation of materials.

We report on investigations of spin-coated peat humic acid solutions by scanning force microscopy allowing, for the first
time, direct imaging of individual single humic acid molecules with a minimum diameter of 1.5-3.5 nm. The measured
height of the molecules deposited onto a mica substrate increases with decreasing pH value of the solution. This behaviour
can be explained by means of the random coil model if one takes the existence of charge carriers in organic macromolecules
into consideration. With increasing humic acid concentration the molecules arrange into a few monolayer-thick
agglomerates formed during the process of film deposition. In unfiltered solutions and in 1000 nm filtrates we find
additional particles well distinct from the above-mentioned molecules in size and properties. They possess an equivalent
spherical diameter of 70-160 nm and behave inert when the ambient conditions are changed.

The influence of dose rate and temperature on the dose dependence of the shape of Ge depth profiles obtained by channeling implantation into Si and SiC is investigated. A focused ion beam system is employed which enables the application of two widely different dose rates (1011 and 1018 cm-2 s-1). Implantations into Si are performed at room temperature (RT) and 250 0C. SiC is implanted at RT, 225, 450, and 580 0C. The Ge depth distributions are measured by secondary ion mass spectrometry. The shape of the channeling implantation profiles is affected by the formation and evolution of complex defects formed during ion bombardment, since these defects cause significant dechanneling of the implanted particles. The competing influence of dose rate and temperature on the shape of Ge depth profiles is explained in terms of intracascade defect relaxation. The time scale for the reduction of complex defects is estimated. At RT, in Si some defect relaxation occurs within the first 100 s after an ion impact. At temperatures of 225 and 250 0C, in SiC and Si, a considerable defect reduction is found within the first 10 ms as well as between 10 ms and 100 s after an ion impact. The complex defects in Si vanish entirely between 10 ms and 100 s, whereas in SiC some of them survive. At 450 and 580 0C, defects in SiC relax mainly within the first 10 ms after an ion impact. The defect reduction increases with growing implantation temperature. Different mechanisms which may be responsible for the dynamic annealing in Si and SiC are discussed. A phenomenological model is developed in order to treat the dose rate and temperature dependence of the defect-induced dechanneling within the framework of atomistic computer simulations of ion implantation. The simulated Ge depth profiles agree very well with the measured data.

Als alternative Ionenquellen für Feinstrahlanlagen werden zur Ga-LMIS (liquid metal ion source) Flüssigmetall-Ionenquellen vorgestellt, die mit metallischen Legierungen arbeiten und so das Spektrum verfügbarer Ionen erweitern. Die Wirkungsweise sowie die Herstellungstechnologie werden diskutiert sowie vielfältige Anwendungen eines massenseparierten Ionenfeinstrahls (FIB = focused ion beam) dargestellt.

Unsaturated flows within subsurface regions control many large-scale hydrological and environmental processes. This contribution presents and discusses the results of numerical calculations dealing with the flow of water, the chemical reaction at the water-mineral interface and the transport of chemical species caused by such flows. The source of the water flow through the soil is solely the rainfall. The water motion is calculated for two different soil classes and for a typical annual precipitation. The codes which were used are based on the following model: The transport of chemical species is described by a set of partial differential equations, and the homogeneous chemical processes, under the assumption of equilibrium, are described by a set of nonlinear algebraic equations. The source terms of these partial differential equations are given by rate laws of the chemical weathering. Rainfall and chemical weathering are therefore the sources of the transport of reactive multispecies in this model.

The rock phyllite is commonly encountered in uranium tailings associated with the former uranium mining activities in the Western Erzgebirge in Germany. Currently, many of these mines are being flooded. The flood water, which contains concen-tration of uranium penetrates through cracks and fissures of the phyllite and leads to a dissolution of several minerals. One of the major components in the phyllite is an iron-rich chlorite [1], which dominates the sorption behaviour for heavy metals.
During the dissolution of the chlorite a reaction causes the loss of octahedral layer cations, primarily Fe. Ferrous iron is released in the aqueous solution, where it is oxidized rapidly to ferric iron. Hydro-lysis of ferric iron leads to Fe-oxyhydroxide, which precipitates from the solution as due to the low solubility of iron in the pH region higher 4. By scanning electron microscopy, these precipitates of Fe-oxyhydroxide are detected as small spherical particles of ferrihydrite that are preferentially situated as immobile coatings on the most reactive edge surfaces of the chlorite crystals [2]. During the dissolution of chlorite a mobile component of ferrihydrite is formed, too. These are colloids, which are found under similar geochemical conditions. The mobile colloids are aqueous species that do not adsorb to rock surfaces. The adsorption of contaminants, for example uranium onto the colloidal particles of ferrihydrite influences and enhances the rate of contaminant transport. In previous investigations the uptake of uranium on ferrihydrite reaches almost 95-100 % in a pH range from 5.0 to 7.5 [1]. Conclusively, the formation of secondarily formed ferrihydrite as mobile colloids and as immobile coatings during the dissolution of chlorite in the rock phyllite is an important process which has to be considered in risk management.

References:

[1] Arnold, T. et al. (1998): Chemical Geology 151,
129-141.
[2] Krawczyk-Bärsch, E. et al. (2002): Chemical
Geology (submitted).

QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of mass parameters
for the lightest vector mesons ρ, ω and Φ in a strongly interacting medium. For conditions relevant for the starting experiments at HADES we find that the in-medium mass shifts of the ͦ and ω mesons are governed, within the Borel QCD sum rule approach, by the density and temperature dependence of the four-quark condensate. In particular, the variation of the strength of the density dependence of the four-quark condensate reflects directly the decreasing mass of the ρ meson and can lead to a change of the sign of the ω meson mass shift as a function of the density. In contrast, the in-medium mass of the Φ-meson is directly related to the chiral strange quark condensate which seems correspondingly accessible.

In flow-through reactor experiments the dissolution of a ripidolite chlorite (CCa-2) from Flagstaff Hill (El Dorado County, California, USA) was studied with the intention to approach mineral dissolution conditions occuring in the unsaturated zone of an uranium tailing. The experiments were conducted under atmospheric conditions, a temperature of 25 °C, an ionic strength of 0.1 M, and a pH of 7. In addition the experiments were conducted with and without 1.10-6 M uranium and also with and without a humic acid concentration of 5 mg/L.
During the first eight hours of the experiments high initial dissolution rates calculated from Mg, Si, Al and Fe concentrations were determined. These initial dissolution rates are attributed to reactive surface sites on the freshly crushed chlorite platelets /1/. High initial dissolution rates were obtained when using an aqueous solution with a humic acid or uranium concentration. The initial dissolution rates for Mg and Si are 250 times and 400 times greater than the initial dissolution rates determined in experiments with solutions free of humic acid. In uranium containing solutions an initial dissolution rate for Al was 50 times greater than in solutions free of uranium. It seems that humic acid as well as uranium ions initiate a fast dissolution of the chlorite mineral. A constant dissolution rate was obtained after 8 hours which is almost similar to experiments with solutions free of humic acid and uranium. Average dissolution rates of 3,18.10-12 and 1,86.10-11 mol.m-2.sec-1 were calculated for Mg and Si, respectively. The average dissolution rates for Fe and Al of 7,86.10-13 and 2,87.10-12 mol.m-2.sec-1 respectively seem to be very low. In fact they are primarily higher. But however, they are based on the concentration of Fe and Al in solution and do not consider precipitated Fe and Al phases. Due to the low solubility of Fe and Al in aqueous solutions with a pH > 5 Fe-oxyhydroxides and Al(OH)-phases are precipitating. Fe-oxyhydroxide particles have been detected on the {hk0}-faces of chlorite crystals and as well as immobile colloids in the surrounding solution /2/. Due to their very high specific surface area and their affinity to bind heavy metals the formation of secondary Fe-minerals may significantly influence as Fe-coatings and Fe-colloids the migration of uranium and other toxic heavy metals in uranium tailings. Additional EXAFS investigations of sorbed uranium on chlorite platelets were performed to find out if chlorite or the newly formed Fe-phases are responsible for the immobilization of uranium in the environment of uranium tailings.

/1/ Rochelle, C.A. et al., 1995. Mat. Res. Soc. Symp. Vol. 353, p. 149-156.
/2/ Krawczyk-Bärsch et al.: Formation of secondary iron oxyhydoxide phases during the
dissolution of chlorite - effect on uranium sorption. In: Chemical Geology (submitted).

Das Standardverfahren für die Füllstandsmessung von Flüssigkeiten in druckführenden Anlagenkomponenten von Kraftwerksanlagen basiert seit vielen Jahrzehnten auf einer Differenzdruckmessung. Am Siedewasserreaktor hat die Füllstandsmessung eine besonders hohe sicherheitstechnische Relevanz. Daher empfiehlt die Reaktorsicherheitskommission, eine diversitären Füllstandsmessung vorzusehen. Diversität bedeutet, dass das angewandte Verfahren nach einem andersartigen physikalischen Wirkprinzip funktionieren muss. Als diversitäres Messprinzip wurde die lokale Leitfähigkeitsmessung gewählt, mit der eine binär arbeitende Füllstandsdetektion zu realisieren war. Der Messwertgeber des vorgestellten Füllstandswächters ist für den Einbau in ein Standrohr vorgesehen. Der Nachweis der Flüssigphase geschieht durch Detektion deren elektrischer Leitfähigkeit. Der Füllstandswächter wurde entsprechend den Anforderungen an störfallfeste Instrumentierung für die Einbindung in den Reaktorsicherheitskreis entsprechend KTA 3505 ausgelegt. Weiterhin wurde er mit einem Selbsttest ausgestattet, die den Ausfall infolge Isolationsabfall oder Leitungsbruch signalisiert. Wesentliches Element des Messwertgebers ist eine isolierte Durchführung aus Aluminiumoxid-Sinterkeramik. Der Füllstandswächter wurde an einem Teststand der Hochschule Zittau/Görlitz unter Einsatznahen Bedingungen erprobt. Bei diesen und weiteren Tests wurde eine Standzeit von mindestens 5 Jahren bereits jetzt experimentell nachgewiesen. Die Qualifizierung des Füllstandswächters für den Einsatz im Kernkraftwerk ist im Gange. Sie umfasst hauptsächlich abschließende Entwicklungsschritte, die Durchführung der theoretischen und praktischen Prüfungen zur Bauartzulassung gem. KTA 3505 /3507 sowie die Untersuchung des Zusammenhangs von Füllstand im Standrohr und Füllstand im Reaktor zur Erarbeitung einer Konzeption zur Einbindung der Signale. Die Arbeiten zur Qualifizierung werden von Framatome ANP durchgeführt.

The trapping effects of negative and positive charges in Ge-enriched SiO2 layers during high-field electron injection from the Si-substrate of Al-SiO2-Si structures are studied. The capture cross-section and the concentration of negatively and positively charged traps are estimated and the location of the positively charged traps is determined. It is shown that increasing rapid thermal annealing (RTA) time from 6 s to 150 s at 1000°C leads to an enhanced diffusion of Ge towards the SiO2-Si interface and the increase of negatively and positively charged trap concentration. The mechanisms of the trap generation are discussed.

We investigate ultrafast reflectivity changes of a near-optimally doped YBa2Cu3O7-x (123) superconductor. The amplitude of coherently excited phonons show strong changes as a function of temperature above the superconducting transition temperature. These changes give evidence for two crossover temperatures within the pseudogap regime. In addition, these crossover temperatures exhibit a clear hysteretic behavior as a function of temperature.

SiC and diamond are semiconductor materials with unique physical properties for very promising applications for high frequencies, high power and extreme environment (radiation, high temperature). However, the possibility of doping these materials are limited and complementary to each other. Only n-doped SiC and p-doped diamond can be produced in a reliable way [1]. It is found that p-n-junctions can be formed by ion beam synthesis of buried nanocrystallites, especially diamond in SiC [2] and SiC in diamond [3].
The materials studied were 6H-SiC(0001) implanted with 1x1018 cm-2 C+ (60 keV) at 900 °C and diamond(001) implanted with 5.3x1017 cm-2 Si+ (120 … 170 keV) at 900 °C. In this high temperature implantation processes nanocrystals of diamond are grown in 6H-SiC at a depth of (110 ± 30) nm below the surface and 3C-SiC nanocrystals in diamond at a depth of (90 … 130 ± 30) nm, respectively. At lower implantation temperatures it was not possible to grow diamond in 6H-SiC.
Various x-ray scattering techniques like coplanar diffraction, grazing incidence diffraction, texture studies, measurement of specular reflectivity, and reciprocal space mapping were used at laboratory and synchrotron (ROBL at ESRF) sources to study structural details of the material.
The nanocrystals of diamond have a diameter of 5 … 6 nm, and those of 3C-SiC a diameter of 7 … 8 nm. They are oriented completely heteroepitaxially according to
diamond < 1 1 1 > || substrate 6H-SiC < 0 0 0 1 >
diamond < 1 1 0 > || substrate 6H-SiC < 1 1 -2 0 >
3C-SiC < 0 0 1 > || substrate diamond < 0 0 1 >: all crystallographic directions of both cubic materials coincide.
The mosaicity (angular fluctuation of the alignment) is anisotropic to the surface and lies for diamond crystals in 6H-SiC in the range from 2° (220) to 6° (111) and for 3C-SiC crystallites in diamond in the range from 5° (111) to 12° (002), respectively.
The heteroepitactic growth is favoured by a partial coherence of the neighbouring crystal lattices: in both systems a 4:5 coherence between the crystal lattices of synthesized crystallites and substrate is observed:
5 x ddiamond(111) » 4 x d6H-SiC(0006) (1.027 nm » 1.004 nm)
5 x ddiamond(220) » 4 x d6H-SiC(11-20) (0.629 nm » 0.615 nm)
4 x a3C-SiC » 5 x adiamond (1.744 nm » 1.780 nm).
In all cases the strain does not exceed 2.3 %.
In conclusion it can be stated that well aligned nanocrystals can be grown by the ion beam synthesis at high temperatures in 6H-SiC as well as in diamond.

References
[1] - R. Kalish, Diamond and Related Materials 10, 1749 (2001)
[2] - V. Heera, W. Skorupa, B. Pécz and L. Dobos, Applied Physics Letters 76, 2847 (2000)
[3] - V. Heera, F. Fontaine, W. Skorupa, B. Pécz and A. Barna, Applied Physics Letters 77, 226 (2000)

To study the kinetics of Al ion nitriding, a series of experiments have been performed at an ion energy of 1.6 keV, an ion current density of 0.2 mA/cm2 and substrate temperatures varied from 250 °C to 400 °C. The nitride layers have been analyzed by nuclear reaction analysis (NRA) and scanning electron microscopy (SEM). Binary collision computer simulations have been performed to calculate the sputtering yields of N and Al. Depending on the experimental conditions, the nitriding kinetics is either controlled by the supply of N atoms from the ion beam or by the diffusion of Al atoms trough the growing nitride layer. Solutions of rate equations describing the growth of the nitride layer are fitted to the experimental data, from which diffusion and activation parameters are obtained for the transport of the Al atoms.

We investigate the energy spread, dE½, vs emission current, i, of the doubly-charged ions emitted by a Au77Ge14Si9 Liquid Metal Alloy Ion Source (LMAIS). For the ionic species of main interest, namely Ge++, two modes were found with regard to the dependence of dE½ on i. In the first mode dE½ ~ i^ 0.3 and in the second dE½ ~ i . The difference is attributed to changes in the composition of the alloy during field-evaporation. Au++ an Si++ were also found to obey a dE½ ~ i^ 0.3 law; in the case of Si++ however, there is a deviation from this law at high currents.

The A(e,e'K⁺)YX reaction has been investigated in Hall C at Jefferson Laboratory for 6 different targets. Data were taken for Q²)approx 0.35 and 0.5 GeV²) at a beam energy of 3.245GeV for ¹)H, ²)H, ³)He, ⁴)He, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of Lambda and Sigma⁰) hyperon production off the proton, and Sigma^-) off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for ^3,4)He targets.

Boron carbon nitride films (BCN) were grown by B4C evaporation under concurrent N2 ion beam assistance (IBAD). The films were characterized by x-ray absorption near edge spectroscopy, IR and Raman spectroscopy and high-resolution transmission electron microscopy. The bonding structure and film composition correlate with the momentum transfer per incoming atom during deposition. As the momentum transfer is increased, the film structure evolves from an amorphous boron carbide network towards a hexagonal ternary compound (h-BCN) with standing basal planes. The growth of h-BCN takes place for momentum transfer in the window between 80 and 250 (eVxamu)1/2. The characteristic vibrational features of the h-BCN compounds have also been studied. Finally, the solubility limit of carbon in the hexagonal BN structure, under the working conditions of this report, is found to be ~15 at. %.