Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. This investigation describes the interaction of plutonium in mixed oxidation states (Pu(VI) and Pu(IV)-polymers) with cells of the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis DSM 10631T, which frequently occurs in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. In this study, accumulation experiments were performed in order to obtain information about the amount of Pu bound by the bacteria in dependence on the contact time and the initial plutonium concentration. We used solvent extractions, UV-vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy to determine the speciation of Pu oxidation states. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to study the coordination of the Pu bound by the bacteria. In the first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. Solvent extractions showed that 97 % of the initially present Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves from the cell envelope back to the aqueous solution due to the weak complexing properties of this plutonium oxidation state. Indications were found for a penetration of Pu species inside the bacterial cells.

A new sensor was developed for an improved visualisation and quantification of the coolant mixing in the downcomer of the ROCOM test facility. This sensor spans a measuring grid of 64 azimuthal and 32 positions over the height of the downcomer On behalf of an experiment with the start-up of the main coolant pump the possibilities of the new sensor are demonstrated.

We report the variable temperature vibrational properties of single crystals of the S=1/2 Heisenberg antiferromagnet VOHP O₄ *1/2 H₂O. A pair of peaks in the far infrared spectral response may be due to magnetic excitations. We invoke a dynamic Dzyaloshinskii-Moriya mechanism to explain the activation and polarization dependence of the singlet-to-triplet gap in the far infrared, and we identify the low-energy phonons that likely facilitate this coupling. The spin-gap values are compared to those obtained via magnetic susceptibility, electron spin resonance, and neutron scattering. Vibrational mode splitting in VOHP O4 * 1 / 2 H2 O indicates a weak local symmetry breaking near 180 K , and the low-temperature redshift of V-O and H-O related modes demonstrates enhanced low-temperature hydrogen bonding. The low lattice symmetry is important for the proposed magnetoelastic interactions.

The present paper reports on our efforts in modelling the pressure drop buildup at sump strainers obstructed by mineral fibrous insulation material after a Loss of Coolant Accident (LOCA). Special attention is drawn to the compressibility of the fibrous filter cake. Comparison of numerical results with pressure drop measurements has been provided.

FZR has 10 years of experience using ANSYS CFX software for CFD applications focused on nuclear reactor applications and more recently also chemical process simulations. These CFD activities are very closely connected to experimental investigations at facilities in the institute. Using advanced two-phase flow measurement techniques, a comprehensive data base for CFD code verification is being created. So in addition to single-phase flow nuclear reactor engineering applications, development and verification of physical models for two-phase flows can be performed. FZR is participating in the German initiative on CFD applications in nuclear reactor safety research in close co-operation with the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS, the German nuclear safety authority) and ANSYS. The group of young and highly motivated CFD scientists that has been established at the institute also has a significant portion of the 100 processor Linux cluster of the FZR at its disposal. The FZR coordinated the experimental and analytical investigations of turbulent mixing inside pressurized water reactors (PWRs) performed within the EC project FLOMIX-R (Fluid mixing and flow distribution in the reactor circuit). The purpose of this project was to describe coolant mixing phenomena, particularly for severe accident scenarios. Such scenarios include steam line breaks and boron dilution, where mixing of coolant from different loops moderates the inflow of water with insufficient boron content or temperature into the reactor core. These changes can lead to reactor power excursions (rapid increase in reactor power) due to positive reactivity effects. An example of a typical boron dilution scenario is during start-up of the first main coolant pump after a slug of low borated water has formed in one of the cooling loops, where mixing is largely forced by the momentum introduced by the pump starting. Another safety issue arises during emergency core cooling (ECC) situations, when cold water is injected into a hot cooling loop. In this case, buoyancy-driven mixing is influenced by density differences in the fluid and is typical for so-called pressurized thermal shock (PTS) scenarios. When a streak of cold ECC water touches the reactor pressure vessel (RPV) wall, unacceptable thermal stresses can occur. Measurement data from several sets of mixing experiments, using advanced measurement techniques with enhanced temporal and spatial resolution, improved the basic understanding of turbulent mixing and provided data for CFD code verification.
Selected experiments were then simulated using ANSYS CFX and applying best practice guidelines (BPGs), a set of systematic procedures for quantifying and reducing numerical errors. BPGs were applied when considering computational grid resolution and time step, turbulence models, internal geometry modelling, boundary conditions, numerical schemes, and convergence criteria. These investigations highlighted the importance of grid quality, and also the need to minimize numerical diffusion by using second order discretization. In fact, first order schemes were found
to sometimes even provide physically incorrect results. ANSYS CFX was well able to predict the experimental flow patterns and mixing phenomena for both buoyancy-driven and momentum-driven flows. Two-equation turbulence models like k-ω or SST were found to be suitable for momentum-driven slug mixing, while Reynolds stress models provided better results for buoyancy driven mixing.
Comprehensive multiphase flow models, advanced turbulence models, second order discretization, and scalable parallel performance all combine to make ANSYS CFX a valuable tool at FZR. ANSYS CFX software has been instrumental in the development and verification of best practices guidelines for the use of CFD in nuclear safety analyses.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite (γ-Al(OH)₃).
Two uranyl surface species with fluorescence lifetimes of 330 ± 115 ns and 5600 ± 1640 ns, respectively, were identified.
The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1, 497.4 ± 0.8, 518.7 ± 1.0, 541.6 ± 0.7, 563.9 ± 1.2, and 585.8 ± 2.1 nm. The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH- groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.
Spectroscopic evidence of sorbed U(VI) surface species on quartz and kaolinite, also obtained by TRLFS were presented and compared with the U(VI) gibbsite system.

An overview on applied MHD projects of the Rossendorf MHD department will be given.

Es wird eine Übersicht zur kontaktlosen Kontrolle von Metallschmelzen und zur Messung von Strömungsgeschwindigkeiten gegeben.

This report gives a review on existing experimental data for the development, verification and valida-tion of models for the simulation of a two-phase PTS situation. This includes single effect data, which are useful for the development and validation of closure models for CFD codes as well as integral test data for the validation of the applicability of the code for PTS situations. For the development and validation of closure models for CFD codes, data are required with a high resolution in space and time. There is a need of additional data. Information on the planned TOPFLOW PTS experimental programme is also included in the report.

This report identifies PTS-scenarios for the French 900 MW CPY PWR, the German 1300 MW Kon-voi reactor, the Loviisa 400 MW VVER, the Russian VVER-1000 and the Czech VVER-100. Accord-ing to the resulting basic flow conditions relevant physical phenomena for the simulation of the scenes during Emergency Core Cooling (ECC) injection into the cold leg are identified. The main focus is on two-phase flow phenomena. The state of the art of modelling these phenomena and needs for models improvement are discussed. Thus the report is a suitable basis for the specification of the main topics to be provided in Task T2.1.4 of the NURESIM project.

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At present in-beam PET is the only possibility for an in-situ monitoring of the particle delivery in hadron tumor therapy and there is a unique clinical implementation at the Gesellschaft fuer Schwerionenforschung (GSI) Darmstadt.
Several heavy ion treatment facilities are under construction, which will provide a large variety of ions from protons to oxygen. This requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. For the 3He-case experiments at GSI with three mono-energetic 3He-beams of 130.03 AMeV to 207.92 AMeV have been carried out. The beams were stopped in homogeneous thick targets consisting of PMMA, graphite and water. Results on the production rate and the spatial distribution of 3He ion induced beta+-activity will be presented and compared with data from 12C-irradiation. From these, the accuracy and resolution for determining the range of the 3He primary beams is deduced. Furthermore, energy dependent thick target cross sections for different reaction channels leading to positron emitters will be estimated from the experimental data.

It is shown that the 2pz confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three dimensional Hamiltonian for a quantum well system with random impurities. Intersubband
absorption experiments, which can be nearly perfectly reproduced by the theory, corroborate this interpretation, which also requires re-interpretation of previous data.

Although Electron Paramagnetic Resonance (EPR) has been a very successful method to investigate transition metal ions in coordination complexes and biomolecules, not all such ions can be subject to conventional EPR investigations even if they are paramagnetic. In particular, high-spin (S > 1/2) species pose serious challenges to spectroscopists, and of these, the non-Kramers (integer-spin) ions have been long considered ‘EPR-silent’ at conventional frequencies and fields.
We propose a novel EPR-related technique that takes an advantage of tunable sources operating in the sub-THz range of frequencies in conjunction with very high magnetic fields (up to 25 Tesla) to determine accurate intrinsic spin Hamiltonian parameters not only for a variety of non-Kramers transition metal ions (such as Ni²⁺, Mn³⁺, and Fe²⁺) that have traditionally been termed ‘EPR-silent’, but also for those Kramers (half-integer) species that are poorly characterized in their high-spin states, such as Co2+.
The obtained parameters can serve to better characterize the electronic structure of the ions in question, in combination with other experimental methods.

The conditions for the manifestation of transient effects in fission are carefully examined by analysing experimental data where fission is induced by peripheral heavy-ion collisions at relativistic energies. Experimental total nuclear fission cross sections of U-238 at 1 A GeV on gold and uranium targets are compared with the predictions of a nuclear-reaction code, where transient effects in fission are modeled using different approximations to the numerical time-dependent fission-decay width: a new analytical description based on the solution of the Fokker-Planck equation and two widely used but less realistic descriptions, a step function and an exponential-like function. The experimental data are only reproduced when dissipation is considered. The influence of transient effects on the fission process, as well as the deduced value of the dissipation strength P, depends strongly on the approximation applied for the time-dependent fission-decay width. In particular, a metic! ulous analysis sheds severe doubts on the use of the exponential-like in-growth function. Finally, we investigate which should be the characteristics of experimental observables to be most sensitive to transient effects in fission. The pertinence of observables related to the excitation energy at saddle is discussed.

Die Löslichkeitsprodukte kristallinen und amorphen Urandioxids werden durch die Kombination von coulometrischer Titration einer U(IV)-Lösung und der Detektion der bei Überschreitung der Löslichkeit entstehenden Kolloide mittels laserinduzierter Breakdown-Detektion (LIBD) bestimmt. Die Quantifizierung von U(VI)-Spuren erfolgt mittels laserinduzierter Fluoreszenzspektroskopie.
Die Partikelgröße der entstehenden Kolloide und die Ionenstärke wird in den thermodynamischen Berechnungen berücksichtigt. Für die kristalline Modifikation resultiert log K_sp = -59,6, für die amorphe Modifikation log K_sp = -54,4.
Ergänzende Untersuchungen mittels EXAFS-Spektroskopie bestätigen das Vorliegen der kristallinen Modifikation.

The favourable long-half life, the ease of production and the low enery of the emitted positron make ¹⁸F an ideal radionuclide for PET imaging. Radiochemistry of ¹⁸F basically relies of two distinctive types of reactions: nucleophilic and electrophilic reactions. All syntheses of ¹⁸F-labelled radiotracers are based on either [¹⁸F]fluoride ion or [¹⁸F]fluorine gas as simple the primary labelling precursors which are obtained directly from the cyclotron. They can be applied either directly to the radiosynthesis or they can be transformed into more complex labelling precursors enabling the multi-step built up of organic tracer molecules. The topic of this review is a survey on the application of several ¹⁸F-labelled aryl fluorides as building blocks derived from no-carrier-added (n.c.a.) [¹⁸F]fluoride to built up small mono-molecular PET radiotracers at high specific radioactivity by multi-step synthesis procedures.

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Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied.

From the test matrix an experiment with 2% density difference between the de-borated slugs and the ambient coolant was used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used.

The experiment and CFD calculation show a stratification in the downcomer. The less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core.The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.

Our research group has focused on mercaptoimidazole derivatives as the lead structure to design radioactive probes for in vivo imaging of 5-HT_1A receptors. This type of compounds can be labelled directly with ¹¹C or can be used to prepare tripodal ligands suitable to stabilize the fac-[M(CO)₃]⁺ (M = Re, ^99mTc) moieties.^1,2 Interestingly, this versatility allows an easy assessment of the influence of the bulkier metallic fragment on the biological properties of PET (¹¹C) or SPECT (^99mTc) radioligands bearing a common pharmacophore.
Scheme 1
In this communication, we report on the radiosynthesis, characterization and biological evaluation of mercaptoimidazole piperazinyl derivatives labelled with ¹¹C (1) and with ^99mTc (2 and 3) (Scheme 1). It will be discussed their interest as radioactive probes for imaging 5-HT_1A receptors by means of PET or SPECT, as well as the effect of the presence of the organometallic moiety on the affinity and biodistribution profile of the compounds.
Acknowledgments: R. Garcia and L. Maria thank FCT for PhD and Post-Doc grants, respectively. This work has been partially supported by the FCT (POCTI/2001/QUI/42939).
[1] Garcia, R; Xavier, C.; Paulo, A.; Santos, I.; Kniess, T.; Bergmann, R.; Wüst, F. J. Labelled Cpd. Radiopharm. 2005, 48, 301.
[2] Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Ortner, K.; Alberto, R. J.Am Chem. Soc. 2000, 122, 11240.

A solid-state compact pulser of 5kV/2A/5kHz for surface treatment by plasma immersion ion implantation

Effects of low magnetic fields on nitrogen implantation in silicon by plasma immersion

Influence of the plasma density on the performance of plasma immersion íon implantation of silicon surface

Plasma immersion íon implantation with high-energy íons for use in surface treatments

Surface modification of Ti6Al4V alloy by duplex plasma processing

High Temperature Plasma Immersion Ion Implantation of Ti6Al4V

Nitrogen Plasma Immersion Ion Implantation in Ti6Al4V with treatment temperatures ranging from 400 to 800°C

Presentation of recent results describing the interaction of plutonium with cells of Desulfovibrio aespoeensis. Application of solvent extraction and X-ray absorption spectroscopy.

Two nano-sized amorphous layers embedded in perfect crystals have been modeled to study the amorphous-to-crystalline (a-c) transition in the temperature range from 1000 to 2000 K in 4H-SiC by means of classical molecular dynamics methods. The results show that the epitaxial recrystallization of amorphous layers with a-c interface along the c-axis is much faster than that along the basal plane, which suggest the anisotropies in the different activation energies for recrystallization. The recovery of bond defects and the rearrangement of atoms at the interface are important processes driving the epitaxial recrystallization of the amorphous layers. The nano-sized amorphous layer with the a-c interface oriented along the c-axis can be fully recrystallized at all temperatures considered. However, it is observed that second ordered phases, crystalline 3C-SiC, nucleate and grow during the recrystallization process inside the amorphous layer with the a-c interface along the basal plane, and these new phases are stable for long simulation times. Based on a model developed in the previous annealing simulations of 3C-SiC, the range of activation energies are determined to be about 0.35 eV to 2.4 eV, which suggests that the recrystallization consists of multiple recovery processes, rather than a single process proposed previously. The present results are discussed and compared with the annealing simulations of 3C-SiC and experimental observations. The simulation results are in good agreement with previous experimental results in SiC, and thus, provide atomic-level insights into the interpretation of experimentally observed phenomena.

Recently, two different groups have reported independently, that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented, one proposing carrier trapping at grain boundaries and the second putting emphasis on different conformation and packing of the polymer chains in the thin layers.
Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to investigate the structure and crystallization behaviors of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements revealed a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. In order to study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in disordered matrix. In contrast, films of the high molecular weight fraction exhibit partially-ordered domains throughout the whole sample area. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight is largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites.

For details of this talk, please contact the authors.

This paper presents a method for the identification of deformation, damage and fracture properties of ductile materials.
The small punch test is used to obtain the material response under loading. The resulting load displacement curve contains information about the deformation and failure behavior of the tested material. The finite element method is used to compute the load displacement curve depending on the parameters of the Gurson-Tvergaard-Needleman damage law. Via a systematic variation of the material parameters a data base is built up, which is used to train neural networks. This neural network can be used to predict the load displacement curve of the SPT for a given material parameter set. The identification of the material parameters is done by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one predicted by the network function. The identified material parameters are validated by independent tests on notched tensile specimens. Furthermore, these parameters can be used to compute the crack growth in fracture specimens, which finally leads to a prediction of classical fracture toughness parameters.

Die Ausfällung von Sekundärmineralien im Bulk von Umweltwässern durch chemische Reaktionen nach der Mischung von Wässern unterschiedlicher Zusammensetzung oder nach dem Zutritt von Luft zu vorher isolierten Wässern stellt nicht den einzigen Weg zur Bildung von eisenreichen Umweltkolloiden dar. In einer früheren Arbeit zeigten wir, dass ein alternativer Mechanismus die direkte Produktion von Sekundärmineralkolloiden an der Gestein-Wasser-Grenzfläche bei der Verwitterung ist. Er besitzt vor allem für die Kolloidentstehung bei der Verwitterung von frisch zerkleinertem Gestein in der ungesättigten Zone wie z. B. Gestein in Bergwerkshalden Bedeutung. Hier wird demonstriert, dass auch die auf diesem Wege entstehenden Kolloide Einfluss auf das Schadstoffverhalten nehmen können. Als Beispiel dient das Uran(VI)-Verhalten.

The improbable scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a Light Water Reactor (LWR) Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the containment. One accident management strategy could be to stabilize the in-vessel debris or melt pool configuration in the RPV as one major barrier against uncontrolled release of heat and radionuclides into the containment of the plant.
Based on the successful simulation and analysis work of the FOREVER-experiments the models have been developed further to simulate the prototypical scenario of an In-Vessel-Retention in a large German PWR (KONVOI). As shown in an earlier publication a recursively coupled simulation between the thermal and the mechanical model has to be performed to consider the mutual influence of the heat fluxes respectively the temperatures and the mechanical vessel behaviour.
After the validation of the recursively coupled thermal and mechanical FE-models against the scaled FOREVER-tests the models were improved to simulate a prototypic scenario under certain assumptions. The calculations show that an In-Vessel-Retention might be possible for large PWRs like KONVOI, if the RPV is flooded externally. The remaining vessel wall thickness seems to be sufficient to prevail even higher pressure loads. But in any case a support of the lower head would increase the margin to failure and therefore ensure the integrity of the last barrier within the containment of the plant.

The static and dynamic magnetic properties of 20 nm thick Ni81Fe19 films have been investigated as a function of Ni ion fluence up to 1x1016 Ni/cm2 (~ 5 atom-%). The implantation has been performed at 30 keV in order to implant the Ni ions in the center of the ferromagnetic layer and to achieve a rather homogeneous energy distribution throughout the film. With increasing ion fluence the saturation magnetization and the effective magnetic anisotropies (static and dynamic) are reduced. However, the effective magnetic damping is drastically enhanced for higher ion fluences. This increase can be explained mainly by the drop in saturation magnetization in connection with structural changes. In addition ion implantation in an applied magnetic field allows the setting of the uniaxial anisotropy direction irrespective of the initial orientation.

The transition temperature for the A1 to L10 phase transition of magnetron sputter deposited FePt films in the thickness range between 35 and 130 nm is investigated. Large ordering factors up to S = 0.93 are observed either for a deposition at T = 350°C or a post-deposition annealing at 400°C. These low ordering temperatures are explained by a defect enhanced atomic site exchanges induced by the impact of energetic ions. Due to the use of amorphous substrates no preferential grain orientation and thus only a weak magnetic anisotropy could be achieved.

A novel boundary-layer solution is obtained by the method of matched asymptotic expansions for the solute distribution at a solidification front represented by a disk of finite radius R0 immersed in an axisymmetric converging stagnation point flow. The detailed analysis reveals a complex internal structure of the boundary layer consisting of eight subregions. The development of the boundary layer starts from the rim region where the concentration, according to the obtained similarity solution, varies with the radius r along the solidification front as ~ ln1/3(R0/r). At intermediate radii, where the corresponding concentration is found to vary as ~ln(R0/r), the boundary layer has an inner diffusion sublayer adjacent to the solidification front, an inner core region, and an outer diffusion sublayer which separates the former from the outer uniformly mixed region. The inner core, where the solute transport is dominated by convection, is characterized by a logarithmically decreasing axial concentration distribution. The logarithmic increase of concentration along the radius is limited by the radial diffusion becoming effective in the vicinity of the symmetry axis at distances comparable to the characteristic thickness of the solute boundary layer.

A biofilm of Pseudomonas stutzeri was cultured in a annular rotating reactor /1/ at near-neutral pH conditions on glass slides. After reaching a mature confluent biofilm uranium(VI) was added to the nutrient solution to obtain a final uranium(VI) concentration of 5 ´ 10-6 M. The resulting biofilm was studied by Confocal Laser Scanning Microscopy (CLSM) and a biofilm thickness of 43 µm was recorded. Particles of approximately 5 µm were detected in the biofilm. These particles were excited by an diode laser with an excitation wavelength of 405 nm and the resulting fluorescence signal was recorded. Two kinds of flourescence signals were detected. One with a characteristic fluorecence signal in the range of 490 to 560 nm which is indicative for U(VI) /2/ and a second one with a fluorescence signal from 420 to 470 nm. Since U(IV) requires an excitation wavelength of 245 nm and shows a completely different fluorescence spectrum the formation of uranium(IV) particles was ruled out. However, based on UV-vis measurements of U(V) containing standard solutions these signals were interpreted as U(V) species, indicating that redox processes must have occured within the biofilm.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) were applied to investigate the species of uranyl(VI) adsorbed onto muscovite platelets and muscovite suspensions ( grain size: 63-200 mu m). TRLFS provided evidence for the presence of two adsorbed uranium( VI) surface species on edge-surfaces of muscovite. The two species showed different positions of the fluorescence emission bands and different fluorescence lifetimes indicating a different coordination environment for the two species. HAADF-STEM revealed that nanoclusters of an amorphous uranium phase were attached to the edge-surfaces of muscovite powder during batch sorption experiments. These U-nanoclusters were not observed on {001} cleavage planes of the muscovite. The surface species with the shorter fluorescence lifetimes are interpreted as truly adsorbed bidentate surface complexes, in which the U(VI) binds to alum!
inol groups of edge-surfaces. The surface species with the longer fluorescence lifetimes are interpreted to be an amorphous U(VI) condensate or nanosized clusters of polynuclear uranyl(VI) surface species with a particle diameter of 1 to 2 nm. Depending on the size of these clusters the fluorescence lifetimes vary; i.e., the larger the nanosized clusters, the longer is the fluorescence lifetime.

Three rotational bands in 74 Kr were studied up to (in one case one transition short of ) the maximum spin Imax of their respective single-particle configuratio ns. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin Imax . This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I=Imax .

Aim: Aptamers (synthetic oligonucleotides), can be generated by a combinatorial approach (SELEX1) and are promising probes for radiodiagnostic imaging and therapy due to their high affinity and target specificity. The aptamer, TTA1 is characterized by a low nanomolar affinity and a high selectivity for the human matrix protein tenascin-C. Tenascin-C concentration in normal adult matrix tissue is rather low, whereas it is overexpressed in the stroma of a variety of malignant tumors2, making this target potentially suitable as a multi tumor imaging agent. The aim of this study was to evaluate the pharmacokinetic properties of 99mTc(I) and 188Re(I) carbonyl radiometal chelates attached to TTA1 in tumor animal models in vivo. Material and Methods: [Carboxymethyl-(2-ethylsulfanyl-ethyl)-amino]-acetic acid, an appropriate chelating unit for coordination of 99mTc(I) or 188Re(I), was conjugated to the aptamer and a 99mTc(I) carbonyl precursor was synthesized3. Labeling of the aptamer with the 99mTc(I) carbonyl precursor was achieved in 15 min at 100°C. Synthesis of the 188Re(I) carbonyl labeled aptamer was performed in a one pot reaction at 60°C for 30 min. Both, binding affinity for human tenascin-C and in vitro stability in human plasma were measured. The biodistribution and elimination of the 99mTc-tracer was evaluated in a human U251 xenograft NMRI nude mouse model. Results: The radiochemical purity of the products was >95 % after purification by spin dialysis. Reaction yields ranged from 65 % to 72 % for the 99mTc(I) carbonyl labeled aptamer and from 25 % to 35 % for the 188Re(I) carbonyl labeled aptamer. The specific activity of the Tc(I) carbonyl labeled aptamer was 37 MBq/nmol and the stability in human blood plasma proved to be 65 % after incubation at 37°C for 24h. The binding affinity of the compound against human tenascin-C lies in the low nanomolar range. Significant tumor uptake was observed in the U251 tumor xenograft model after i.v. injection of the 99mTc(I) carbonyl complex. Conclusion: Aptamers can be labeled with both 99mTc(I) and 188Re(I) carbonyls in acceptable yields and good purity. Further investigations are ongoing to fully characterize the potential of the compounds for their use as diagnostic and therapeutic agents. Lit: 1. C. Tuerk, L. Gold, Science, 249, 505-510, 1990; 2. H. P. Erickson, M. A. Bourdon, Annu. Rev. Cell Biol., 5, 71-92, 1989; 3. R. Alberto, R. Schibli, A. P. Schubiger, J. Am. Chem. Soc. 121,6076 - 6077, 1999

Understanding the migration behavior of actinides is important for the reliable long-term risk assessment of potential nuclear waste repositories. Depending on geochemical conditions different materials and processes can influence the behavior of such pollutants in natural aquifer systems. Humic acids (HA) comprise an important part of natural organic materials. HA are soluble in the pH range of natural waters and have the ability for complex and colloid formation. Due to these properties HA can affect the speciation of actinide ions, and therefore, their migration in the environment.
In the present study results from our previous batch experiments (1) were combined with spectroscopic measurements to obtain molecular-level information on the interaction of U(VI) with HA and kaolinite in natural systems.

Clay minerals and organic substances are common components of many soils, sediments, and rocks. However, little is known on the migration behavior of humic substances in clay formations which is supposed to be governed by diffusion processes. Since humic acids (HA) show a strong ability for complex formation they can influence the migration of radioactive and non-radioactive toxic metal ions in clayey environments.
In the present study we investigated the diffusion behavior of humic colloids in compacted clay and its impact on the uranium transport. These studies are of high importance for the reliable risk-assessment of future nuclear waste repositories which requires knowledge on the actinide migration behavior in potential host rock formations. Clay formations as possible host rocks are closely associated with natural organic matter.

A review of ion induced modification of magnetic thin films and multilayers is given.

The nucleation and growth of Ti2AlN thin films on MgO(111) substrates during dual DC reactive magnetron cosputtering from Ti and Al targets in an Ar/N2 atmosphere at a substrate temperature of 690°C have been investigated . Time and thickness dependent in situ specular x-ray reflectivity and x-ray diffraction (XRD) in coplanar scattering geometry in combination with cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy revealed the formation of competing phases. It is found that initially an ~380-Åthick epitaxial cubic (Ti1-xAlx)Ny layer of substoichiometric composition forms with a layer-by-layer growth mode. Nitrogen-vacancy driven diffusion of Ti and Al leads to spinodal decomposition of this metastable solid solution into nano-sized cubic TiNy and AlNy domains as well as to a solid-state reaction where Mg2(Al:Ti)O4 spinel forming below the interface to the MgO(111). Spatial and temporal fluctuations of the nitrogen activity on the (Ti1-xAlx)Ny surface at higher thicknesses yield thermodynamically favored Ti2AlN nucleation and polycrystalline growth. Concurrent Ti2AlN inward grain growth by diffusion of weakly bonded Al atoms along the Ti2AlN basal planes reduces the thickness of the phase-separated (Ti1-xAlx)Ny layer to ~60 Å. Individual Ti2AlN grains retain local epitaxy to the substrate with vertical grain sizes in the range of the final film thickness.

The thermal stability of the first-neighbor antisite pair configurations in 3C- and 4H-SiC is investigated by atomic-level computer simulations. At first the structure and energetics of these defects are determined in order to check the accuracy of the interatomic potential employed. The results are comparable with literature data obtained by the density-functional theory. Then, the lifetime of the antisite pair configurations is calculated for temperatures between 800 and 2500 K. Both in 3C- and 4H-SiC the thermal stability of the antisite pairs is rather low. In contrast to previous theoretical interpretations, the antisite pair cannot be therefore correlated with the DI photoluminescence center that is stable to above 2000 K. The atomic mechanism of the recombination of the antisite pair in 3C-SiC and of three antisite pair configurations in 4H-SiC is a modified concerted exchange. Due to the different sizes of the silicon and the carbon atoms, this process is not identical to the concerted exchange in Si. Two intermediate metastable configurations found during the recombination are similar to the bond defect in Si. Since the SiC lattice contains two types of atoms, there are also two different types of bond defects. The two bond defects can be considered as the result of he incomplete recombination of a carbon vacancy and a neighboring mixed dumbbell interstitial. The antisite pair in 4H-SiC with the two atoms on hexagonal sites has a slightly higher formation energy than the other three antisite pair configurations in 4H-SiC. Its lifetime shows another dependence on the temperature, and its recombination is characterized by a separate motion of atoms. The comparison with results obtained by molecular dynamics simulations that are based on the density-functional theory demonstrates that the atomistic simulations describe the antisite pair and its recombination reasonably well.

Cone-beam type X-ray computed tomography (CBCT) is a potential method to measure three-dimensional phase-distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data is highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transfer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effects of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate measurement of void fraction profiles with CBCT.

A ring of helical vortices is a common feature of the onset of thermal convective instability in a rapidly rotating spherical shell as expected in the Earth's core. In fact, there are good reasons that this kind of fluid motion plays an important role in the generation of earth's magnetic field. On the other hand, this ring of rolls can also result from a spherical Taylor-Couette instability as expected to be reproduced in a sodium experiment in Grenoble, France. In this work, the mean electromotive force (e.m.f) for such kind of flow structure is derived analytically following the lines of the mean field concept. The main idea is to split the basic mechanisms that could generate the dynamo action at large scale. Some numerical examples are also calculated.

The three-dimensional velocity field of a propeller driven liquid metal flow in a cylindrical vessel is reconstructed by a contactless inductive flow tomography (CIFT). A reliable online monitoring of the flow can already be achieved by applying the external magnetic field alternately in two orthogonal directions and by measuring the corresponding sets of induced magnetic fields. The results of the new technique are shown to be in satisfactory agreement with ultrasonic measurements.

The von Karmann sodium (VKS) experiment in Cadarache, France, is intended to study the hydromagnetic dynamo effect in a highly turbulent flow. Up to present, no dynamo effect was measured in this facility, despite the fact that the sodium flow has been carefully optimized. We show that lid layers, i.e. layers of liquid sodium between the impellers and the end walls of the cylinder, and the flow therein are responsible for a dramatic increase of the critical magnetic Reynolds number for cylindrical dynamos of this kind. Possible solutions of this problem are discussed for the real dynamo facility.

It was shown recently that a simple mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha can show a number of features of Earth's magnetic field reversals. This model relies basically on the existence of an exceptional point of the spectrum of the non-selfadjoint dynamo operator. It is shown that highly supercritical dynamos undergo a self-tuning process into a reversal prone state. As a consequence, reversing dynamos might be much more typical and may occur much more frequently in nature than what could be expected from a purely kinematic perspective.

Ion implantation of nitrogen into samples of tempered and quenched H13 steel was carried out by plasma immersion technique. A glow discharge plasma of nitrogen species was the ion source and the negative high voltage pulser provided 10-12 kV, 60 mu s duration and 1.0-2.0 kHz frequency, flat voltage pulses. The temperatures of the samples remained between 300 and 450 degrees C, sustained solely by the ion bombardment. In some of the discharges, we used a N-2 + H-2 gas mixture with 1:1 ratio. PIII treatments as long as 3, 6, 9 and up to 12 h were carried out to achieve as thickest treated layer as possible, and we were able to reach over 20 mu m treated layers, as a result of ion implantation and thermal (and possibly radiation enhanced) diffusion. The nitrogen depth profiles were obtained by GDOS (Glow Discharge Optical Spectroscopy) and the exact composition profiles by AES (Auger Electron Spectroscopy). The hardness of the treated surface was increased by more than 250%, re! aching 18.8 GPa. No white layer was seen in this case. A hardness profile was obtained which corroborated a deep hardened layer, confirming the high efficacy of the moderate temperature PIII treatment of steels.

Experiments comparing nitrogen ion implantations in Al5052 by beam and plasma immersion were carried out. Beam implantation (BI) was carried out using a 100 keV, high current beam implanter while the plasma immersion ion implantation (PIII) was obtained using a glow discharge plasma source coupled to a pulsed high voltage supply. A nitrogen BI dose of 5 x 10(17) cm(-2) at 100 keV was attained with near Gaussian implantation profile while the PIII was performed until we reached similar doses with a maximum energy of 15 keV. Implantation profiles were obtained by Auger electron spectroscopy (AES). X-ray diffraction (XRD) indicated the formation of AlN in both cases but it was more clearly demonstrated by high resolution AES. For BI treatment, a buried AlN layer was achieved while for PIII, a layer of AlNxOy close to the surface was seen. Due to the high temperature reached in the PIII processing (400 degrees C), a softening of the Al5052 bulk resulted while for BI processed sa! mples with < 200 'C an increase in hardness was observed.

When performing nitriding of stainless steels, there is a decrease or even complete depletion of chromium in the nitrogen rich region just beneath the surface, inhibiting the formation of passivated Cr oxide layer, beneficial to withstand corrosive attacks and Cr/Fe nitrides, responsible for hardness enhancement. To overcome this problem, a hybrid technique was used, consisting of depositing a thin chromium film on steel surface and then bombarding it with nitrogen ions. By a complex recoil process, chromium atoms are implanted into the steel matrix. Plasma immersion ion implantation (PIII) was used in this bombardment. The new Cr-rich layer allows the formation of Cr oxides and nitrides. Treated surfaces were characterized by Auger electron spectroscopy (AES) and conversion electron Mossbauer spectroscopy (CEMS), showing formation of a new Cr-rich layer. (c) 2005 Elsevier B.V. All rights reserved.

Electron paramagnetic resonance (EPR) at conventional magnetic fields and microwave frequencies, respectively, B-0 <= 1.5 T, nu <= 35 GHz, has been widely applied to odd electron-number (S = 1/2) transition metal complexes. This technique is less successfully applied to high-spin systems that have even electron configurations, e.g. Fe2+ (S = 2). The recently developed technique of high-frequency and high-field EPR (HFEPR), employing swept fields up to 25 T combined with multiple, sub-THz frequencies readily allows observation of EPR transitions in such high-spin systems. A parallel spectroscopic technique is frequency-domain magnetic resonance spectroscopy (FDMRS), in which the frequency is swept while at zero, or at discrete applied magnetic fields. We describe here the application of HFEPR and FDMRS to two simple high-spin (HS) ferrous (Fe2+) salts: ferrous perchlorate hydrate, Fe(H2O)(6)](ClO4)(2) and (NH4)(2)[Fe(H2O)(6)](SO4)(2), historically known as ferrous ammonium sulfate. Both compounds contain hexaaquairon(II). The resulting spectra were analyzed using a spin Hamiltonian for S = 2 to yield highly accurate spin-Hamiltonian parameters. The complexes were also studied by powder DC magnetic susceptibility and zero-field Mossbauer effect spectroscopy for corroboration of magnetic resonance results. In the case of [Fe(H2O)(6)](ClO4)(2), all the magnetic techniques were in excellent agreement and gave as consensus values: D = 11.2(2) cm(-1), E = 0.70(1) cm(-1). For (NH4)(2)[Fe(H2O)(6)](SO4)(2), FDMRS and HFEPR gave D = 14.94(2) cm(-1), E = 3.778(2) cm(-1). We conclude that the spin-Hamiltonian parameters for the perchlorate best represent those for the isolated hexaaquairon(II) complex. To have established electronic parameters for the fundamentally important [Fe(H2O)(6) 2005 John Wiley & Sons, Ltd.

AIM:

With the application of radioactive-labelled aptamers aiming at tumour-specific target structures, a new approach for tumour imaging should be made to increase resolution, sensitivity and specificity in tumour detection. Spiegelmers are synthetic molecules with custom-made properties. They are high-affinity L-enantiomeric oligonucleotide ligands that display high resistance to enzymatic degradation compared with D-oligonucleotides. DOTA is a commonly used chelator for the trivalent radio metals ⁸⁶Y, to form highly stable in vitro and in vivo complexes. In this report, the DOTA-functionalization of a 12-mer L-RNA [Sequenz: 5’-Aminohexyl UGA CUG ACU GAC-3’, MW 3975] (synthesized with a primary amine via an alkyl linker) and a first approach in yttrium-86 labelling is described.
MATERIAL & METHODS: p-SCN-bz-DOTA was used as bifunctional chelator (BFC) to form a stable thiourea-bond with the primary amine of the modified L-RNA. The coupling reaction was carried out in a 0.6 M sodium bicarbonate buffer, pH 8.4 with a 26-fold excess of BFC. The reaction control takes place by IP-RP-HPLC. The preparation achieved a total profit of 97 % of the spiegelmer-derivative DOTA-bz-spiegelmer. The DOTA-bz-spiegelmer was separated from the non-transformed BFC by size exclusion chromatography (SEC). The complexation took place in a 0.5 M ammonium acetate buffer, pH 6.4-7.0 by incubating at 90 °C for 60 min. The transchelation was carried out in 0.5 M ammonium acetate buffer, pH 6.4-7.0 by incubating at 25 °C for 60 min in the presence of 0.1 µmol DTPA. Results: The total labelling efficiency of the DOTA-bz-spiegelmer with 86Y was up to 58%. The non-detachable bound to the DOTA-L-RNA ⁸⁶Y activity was greater than 28%. Experiments with native L-RNA showed, that up to 30% of the RNA bound ⁸⁶Y activity could transchelated to DTPA.
CONCLUSION: DOTA can be coupled to 5’-hexylamine functionalised L-RNA over a thiourea bond and labelled with the trivalent PET-nuclide ⁸⁶Y. The polyanionic nature of the oligonucleotides should be taken into account for non-specific binding of trivalent metal cations. Sponsored by FP6 integrated project BioCare contract no.: 505785

AIM: Positron emission tomography (PET) imaging of animals provides unique possibilities to study normal physiology and pathophysiology of various disease models in vivo. ¹⁸F-FDG PET uptake measurements in regions of interest (ROIs), expressed as percentage ¹⁸F-FDG uptake of the injected dose per gram (%ID/g) of tissue, are simple and easy to obtain, especially in longitudinal studies. These ¹⁸F-FDG uptake measurements may not accurately reflect the true regional rates of glucose utilization because plasma glucose levels and other factors (like anaesthesia) can affect ¹⁸F-FDG uptake. Therefore, we examined and compared the ¹⁸F-FDG uptake and kinetics in rat plasma, brain, heart and liver under urethane anaesthesia with and without simultaneous moderate glucose application to simulate variable food uptake of the rats.
MATERIAL & METHODS: Wistar rats (203+/-41 g body weight) were anesthetized by intraperitoneal application of 1.2 g urethane kg body weight. ¹⁸F-FDG kinetics was studies using a microPET P4 (CTI Concorde Microsystems). The animals were injected intravenously with 0.5 mL ¹⁸F-FDG without (control) or with glucose (55 mg) through a tail vein. One hour after injection the animals were sacrificed and blood samples, heart, and liver were excised, weighted and the activity measured. PET images were reconstructed by 2D-ordered-subset expectation maximization (2D OSEM) algorithm. 3D regions of interest were determined for the subsequent data analysis. The time activity curves of the brain, hear and liver were derived. The curves were corrected for lag time, normalized to the injected and averaged for each organ and animal group.
RESULTS: The plasma glucose concentrations one hour after injections were similar in the control (8.7+/-1.7 mmol/L). At the end of the experiment the ¹⁸F-FDG uptake in the plasma, brain, heart and liver tends to be lower in the glucose group as compared to the controls. However, the time activity curves of the control and glucose groups in the studied organs showed significantly different shapes during the first 15 min, and converged subsequently.
CONCLUSION: A moderate glucose infusion did not influence the distribution pattern of the radiotracer in the blood plasma, heart, brain and liver one hour after injection due to the high glycolysis rate of the rat tissues. It seems to be sufficient to deprive the food of the animals one hour prior to the ¹⁸F-FDG experiments to ensure stable physiological conditions for the PET studies.

Atherosclerosis is a chronic inflammatory disease with increased stress in response to lipid retention in the vessel wall. Diabetes mellitus type 2 is associated with excessive cardiovascular morbidity and mortality. Since atherogenesis already starts before diabetes is diagnosed, we investigated the oxidative stress in the circulation and its associations with dyslipidemia in impaired glucose tolerance (IGT) and diabetes mellitus type 2. Starting from data of a recent study including 125 IGT subjects, 75 patients with newly diagnosed diabetes mellitus type 2, and 403 subjects with normal glucose tolerance (NGT) the pathological consequences of oxidative and metabolic changes in IGT and diabetes mellitus type 2 will be reviewed. The elevated circulating levels of oxidized low-density lipoprotein (oxLDL) in IGT and diabetes mellitus type 2 subjects were not or only weakly related to the oxidative/antioxidative balance in the blood that was characterized by phagocyte oxidant production, serum paraoxonase activity, total antioxidant capacity, and urate-to-allantoin ratio. The close association between oxLDL levels and plasma LDL cholesterol and triglycerides, respectively, favours the hypothesis that dyslipidemia particularly promotes the oxidation of the modified lipoprotein into circulation.

We report the low-temperature multi-frequency ESR studies of copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)]. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of S=1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained.

The dynamo action is generally believed to be the origin of cosmic magnetic field generation. Usually, the numerical treatment of dynamo actions is carried out in the framework of the differential equation approach. In the present work, an integral equation approach is developed to simulate the dynamo actions with arbitrary geometries in general and the von Karman sodium experiment in particular. It is found that the lid layers in VKS experiment facility have an ambivalent effect on the efficiency of the dynamo. The induced magnetic field obtained recently by the integral equation approach shows a good agreement with the experimental result. The integral equation approach demonstrates a number of practical advantages: robust, numerically stable, fast and accurate. These features make it a good forward solver for inverse problems of dynamo experiment and other technical applications of magnetohydrodynamics. A test example to infer the velocity field of Riga dynamo experiment is presented.

Aim: Dose calculation (MIRDOSE) based on a homogeneous distribution of the radiopharmaceutical in the bone metastases and a 50% uptake in the trabecular and cortical bone. In this study we investigated the uptake in bone metastases and skeleton using autoradiography.
Methods: In previous studies a new model for osteoblastic bone metastases was developedand evidenced by histological examination and bone scan. In 15 Copenhagen rats (age 9 +/- 2 month) 100,000 of MatLyLu R-3327 prostate camcer cells were given intra-osseous. Rhenium-188-HEDP (Re-188-HEDP) i.v. (189 +/- 31 MBq) was administrated 17 +/- 1 days after tumor cell application and 2 days later the animals were killed. By all 15 investigated animals macroscopic tumor mass was visualized. Frozen slices were produced (Cryopolycut, Leica, 40µm thickness) and following autoradiographic studies were performed (BAS 500, FuJi; resolution of 0.5 µm). By means of ROI's the uptake of Re-188-HEDP could be estimated in normal skeleton and bone metastases.
Results: In the bone metastases a tumour to muscle ratio (T/M) of 48 +/- 7 and a tumour to non-tumour ratio (T/NT) of 9.7 +/- 1.5 (7.5 to 11.7) was found. The distribution in the metastases was inhomogeneous with a minimal T/NT of 7.0 +/- 1.0 (4.9 to 8.5) and a maximal T/NT of 17.4 +/- 2.7 (11.6 to 22.6). The ratio between the trabecular and cortical bone in non-tumour bone was 68.6 +/- 7.2% to 31.4 +/- 7.2%.
Conclusion: In the study a high and strong inhomogeneous distribution of bone seeking radiopharmaceutical in bone metastases was found. This fact could favour high beta energy radionuclides for a more homogeneous dose distribution in bone metastases. The MIRDOSE calculation underestimates the bone marrow dose, the uptake in the trabecular bone is higher than in the cortical part. The higher uptake in the trabecular bone decreases the hypothetic dose reduction effect of low beta energy radionuclides to the bone marrow.

kein Abstract..

NiTi Shape Memory Alloy (SMA) thin films have been recognized as promising materials in the field of microelectromechanical systems (MEMS). Previous studies on the NiTi/Si(100) interface have shown that during high temperature deposition there exist interfacial diffusion and chemical interactions at the interface where Ni and Ti silicides form [1]. Since the NiTi film required for MEMS applications is usually a few micrometers thick, a relatively thin reaction layer could have significant adverse effects on shape memory properties. An intermediate SiO2 layer was found to serve as an effective diffusion barrier but at the expense of film adhesion [2].

For the present study, NiTi thin films were prepared by magnetron co-sputtering from NiTi and Ti targets in a specially designed chamber mounted on the 6-circle goniometer of the ROssendorf BeamLine (ROBL-CRG) at ESRF, Grenoble (France) [3-5]. The depositions were made at a temperature of  470°C on Si(100), Si(111) and poly-Si substrates and a detailed High-Resolution TEM (Philips TEM CM300) analysis of the interfacial structure has been performed. When NiTi is deposited on Si(100) substrate, a considerable diffusion of Ni into the substrate takes place, resulting in the growth of semi-octaeder NiSi2 silicide (Fig. 1). In the case of NiTi deposited on Si(111), there appears an uniform thickness plate, due to the alignment between substrate orientation and the [111]-growth front (Fig. 2). For NiTi deposited on poly-Si, the diffusion is inhomogeneous. Preferential diffusion is found along the columnar grains of poly-Si, which are favorably aligned for Ni diffusion (Fig. 3). These results show that for the NiTi/Si system, the morphology of the diffusion interface is strongly dependent on the type of substrates.

For the long-term performance assessment of nuclear waste repositories, knowledge about the interactions of actinide ions with mineral surfaces such as iron oxides is imperative. The mobility of released radionuclides is strongly dependent on the sorption/desorption processes at these surfaces and on their incorporation into the mineral structure. In this study the interaction of Am(III) with 6-line-ferrihydrite (6LFh) was investigated by EXAFS spectroscopy. At low pH values (pH 5.5), as well at higher pH values (pH 8.0), Am(III) sorbs as a bidentate corner-sharing species onto the surface. Investigations of the interaction of Am(III) with Fh coated silica colloids prove the sorption onto the iron coating and not onto the silica substrate. Hence, the presence of Fh, even as sediment coating, is the dominant sorption surface. Upon heating, Fh is transformed into goethite and hematite as shown by TEM and IR measurements. The results of the fit to the EXAFS data indicate the release of sorbed Am(III) at pH 5.5 during the transformation and likely a partial incorporation of Am into the Fh transformation products at pH 8.0.

The complex formation of uranyl UO₂ ²⁺ with chloride ions in acetonitrile was studied by UV-vis and U L_III EXAFS spectroscopy.
The investigations unambiguously point to the existence of a [UO₂Cl₄]^2- species in solution with D_4h symmetry. The distances in the U(VI) coordination sphere are U-O_ax ) 1.77 ± 0.01 Å and U-Cl ) 2.68 ± 0.01 Å.

The unique properties of water-stable room temperature ionic liquids (RTIL) create an opportunity to obtain the fundamental data on actinide chemistry without interference from the hydrolysis reactions. These solvents also offer the possibility to develop the new processes for the recovery and purification of actinides.The contribution reports the first EXAFS measurements of UCl62- in hydrophobic ionic liquid [BuMeIm][Tf2N], where BuMeIm+ is 1-butyl-3-methyl-imidazolium cation, and in a solid complex [BuMeIm]2[UCl6]

Strahlungsinduzierte Defekte können die Eigenschaften von Festkörpern stark verändern. Die physikalischen Prozesse bei der Bildung und Evolution dieser Defekten laufen auf sehr unterschiedlichen Zeit- und Längenskalen ab und sind dem Experiment nur teilweise direkt zugänglich. Multiskalen-Computersimulationen tragen zum besseren Verständnis der genannten Vorgänge und ihres Einflusses auf die Materialeigenschaften bei. Die atomistische Modellierung spielt dabei eine wichtige Rolle. Im Vortrag wird das am Beispiel der ionenstrahlinduzierten Defektbildung und der Defektmigration in Silicium erläutert. Die methodischen und inhaltlichen Verbindungen zwischen diesen Untersuchungen und der atomistischen Simulation von strahlungsinduzierten Defekten im Reaktorstahl werden aufgezeigt und diskutiert.

The intention of the "von Karman sodium" (VKS) experiment is to study the hydromagnetic dynamo effect in a highly turbulent and unconstrained flow. Much effort has been devoted to the optimization of the mean flow and the lateral boundary conditions in order to minimize the critical magnetic Reynolds number and hence the necessary motor power. The main focus of this paper lies on the role of "lid layers", i.e. layers of liquid sodium between the impellers and the end walls of the cylinder. First, we study an analytical test flow to show that lid layers can have an ambivalent effect on the efficiency of the dynamo. The critical magnetic Reynolds number shows a flat minimum for a small lid layer thickness, but increases for thicker layers. For the actual VKS geometry it is shown that static lid layers yield a moderate increase of the critical magnetic Reynolds number by approximately 12 per cent. A more dramatic increase by 100 until 150 per cent can occur when some rotational flow is taken into account in those layers. Possible solutions of this problem are discussed for the real dynamo facility.

Isotopic effects in the fragmentation of excited target residues following collisions of 12C on 112,124Sn at incident energies of 300 and 600 MeV per nucleon were studied with the INDRA 4 detector. The measured yield ratios for light particles and fragments with atomic number Z5 obey the exponential law of isotopic scaling. The deduced scaling parameters decrease strongly with increasing centrality to values smaller than 50% of those obtained for the peripheral event groups. Symmetry-term coefficients, deduced from these data within the statistical description of isotopic scaling, are near =25 MeV for peripheral and <15 MeV for central collisions.

In the first topic the superconducting RF (SRF) photo-injector projects are reviewed. The DC SC photo-injector at the Peking University Accelerator Facility, the all-niobium SRF gun of Brookhaven and the high current SRF photo-injector project of AES and Brookhaven are discussed. Special attention is paid to the project of the FZ Rossendorf. The experimental set-up with a 1.3 GHz half-cell cavity has demonstrated the stable operation of a SRF photoelectron gun for the first time. The manufacture and the warm tuning of two 3 1/2 cell niobium cavities for the new photo-injector project are finished. A new cryostat with a special tuning and cathode transfer system has been designed. The status of manufacture for different components is shown. In future it is planed to operate this SRF gun with an energy of 9.5 MeV as a low-emittance photo-injector for the ELBE accelerator. In the second topic of the review some special points are discussed, which are specific for superconducting RF guns. The advantages and disadvantages of different shapes for the first cavity cell (gun cell) are discussed. Different kinds of photo-cathodes (normal conducting, superconducting, all niobium) and their integration into a superconducting cavity are explained. Different possibilities (RF focussing, magnetic RF field (TE - mode), static magnetic field outside the cavity) are discussed for beam focussing and emittance compensation inside the superconducting cavity.

For the investigation of air/water slug flow, a horizontal channel with rectangular cross-section was built at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter-current flows at atmospheric pressure, especially the slug behaviour. Optical measurements were performed with a high-speed video camera, and were complemented by simultaneous dynamic pressure measurements. Moreover velocity-fields were measured using Particle Image Velocimetry (PIV).

A CFD simulation of the stratified co-current flow was performed using the code CFX-5, applying the Euler-Euler two fluid model with the free surface option. The grid contains 400000 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. To achieve wave generation in such a short channel, the inlet water level had to be varied in time. For this purpose, the water level history was taken from a recorded image sequence and set as time-dependent boundary condition at the model inlet. The results show a wave formation up to slug development with closure of the whole channel cross-section and consequently an increase of the pressure level behind the slug. Despite unsteady conditions at the inlet of the test channel and simplified initial conditions in the model, the slug simulation with CFX is in good qualitative agreement with the experiment, while the slug length increases during its progression, witch was not observed in reality.

This paper describes the current status of the 3 1/2 cell SRF gun. The SRF photo injector will produce short pulses with high bunch charges and low transverse emittance like the traditional photo injector. The requirement for the ELBE superconducting electron linear accelerator is to provide low emittance electron beam with 1 mA current and 9.5 MeV energy. Additionally, it will easily operate in the CW-mode caused by the low RF power losses in the superconducting material. This is an exceptional property of the mid infrared ELBE-FEL to work in such a regime. Therefore, the normal conducting copper cathode must be cooled by liquid N2 in order to preserve the temperature of the cavity at 2 K. The estimated power input from the RF field into the cathode amounts 10 W. First results of temperature distributions on the cathode respectively the cooling system by a heat load of 10 W are presented.

The paper describes the development of a fully PC-controlled bead-pull measurement device based on LabView software. The device is part of a cavity tuning test stand and has been used successfully to measure the field profile and the shunt impedance of the prototype Nb-cavities for the 3 1/2 cell SRF-Gun project at FZ-Rossendorf.

Vorlesung zum Kosten- und Finanzmanagement/Controlling an der HTW Dresden mit folgenden Schwerpunkten: Das deutsche Wissenschaftssystem, Change-Management-Prozesse, Instrumente zur Managementunterstützung, Leistungs- und Erfolgsbewertung.

We report on the study of a two-dimensional dot lattice structures which was produced on GaAs and Si (001) substrates using a Ga⁺ focused ion beam in normal incidence with a spot size of about 50 nm, an energy of 25 keV and a dose of 10¹⁴ cm^-2. The fabricated 2D-lattice structures consist of dots of almost circular shape with an area of about 2000 nm² and a period of 250x250 nm². The whole implanted area has a size of less than 0.2 mm². We have investigated the interaction of the implanted ions with the host lattice as a function of the implantation conditions using grazing incidence diffraction at the ID10 and ID1 beam lines at the ESRF. The low-dose implantation creates interstitials and vacancies below the surface generating a weak displacement field resulting in a 2D periodical strain field in case of Si substrate. For the GaAs substrate we found a much more complex scattering pattern which depends on the in-plane orientation of the 2D dot lattice with respect to the crystallographic orientation of the crystal. A much stronger scattering contrast can be found if the 2D dot lattice misaligned by 14° degree. A simulation taking the interaction between the implanted ions and the host lattice into account shows an enhanced channelling of the ions into low-index crystallographic directions. Thus the dependence of the profile of implantation damage on the crystalline structure influences the scattering patterns.

ABSTRACT
The dual implantation chamber (DIC) at Rossendorf Center for Application of Ion Beams in Materials Research allows materials to be implanted using two ion beams simultaneously. This facility is located at the 45o cross point of two beam lines, one from a single ended HVEE 500 kV ion implanter and the other from a HVEE 3 MV Tandetron accelerator. Each beam line is equipped with independent ion fluence and current control. The special design of the beam sweeping system, enables both ion beams to scan the target surface simultaneously in synchronous mode, i.e. both ion spots are kept at coincident positions over the target. Experiments, concerning the formation of SiC nanoclusters in Si by high dose C and simultaneous Si implantation, are reported.

Our quasi-particle model is compared with recent lattice QCD data at finite temperature and baryon number density with emphasis on the coefficients in the Taylor series expansion of thermodynamic observables. The inclusion of static critical end point effects into the equation of state is discussed.

The effect of parameter consistency and uncertainty (protolysis constants, equilibrium constants) in surface complexation modeling (SCM) is illustrated. As example the blind prediction of Cu(II) sorption onto goethite was selected, applying the Diffuse Double Layer Model (DDLM) as the electrostatic model requiring the smallest set of parameters.
All randomly generated normal distributed pK parameter sets did predict the experimentally determined conventional distribution coefficients KD within one order of magnitude or better. Thus, the formally large spreading of the pK values as extracted from literature is actually not critical. Concerning the uncertainty of the formation constant of the surface species the effect of using parameters linked to electrostatic models other than DDLM was investigated. In case of sparse SCM data matrices such inconsistencies may be tolerated.
We conclude, that the application of DDLM can indeed be used for estimating distribution coefficients for contaminants in well-defined mineral systems.

Alloys made of CrCoMo and CrNiMo are commonly used materials with UHMWPE (Ultra High Molecular Weight Polyethylene) as joint couple components in the orthopedic prosthesis. We have applied the plasma immersion ion implantation (PIII) to the samples made of these alloys to enhance their tribological properties and hence to make it possible to extend considerably their lifetime as joint components when implanted in humans. As a result, we obtained CrCoMo surface with 70% improvement in hardness and 10% in modulus of elasticity and CrNiMo surface with 250% improvement in hardness and practically no change in modulus. Peak nitrogen concentrations as high as 40% and 30% were achieved by nitrogen PHI for CrCoMo and CrNiMo, respectively. Formation Of gamma(N) phases in CrNiMo sample was clearly seen by XRD. (c) 2005 Elsevier B.V. All rights reserved.

Status report concerning WP1 of BioCare project

Status report for ENLIGHT WP 5

At present in-beam PET is the only possibility for an in-situ monitoring of the particle delivery in hadron tumour therapy. It has been implemented for clinical application at the carbon ion therapy facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt. Several heavy ion treatment facilities are in planning or even construction stage. They will provide a variety of ions from protons to oxygen. The application of in-beam PET requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. For the 3He-case experiments at GSI with three monoenergetic 3He-beams of 130.03 AMeV to 207.92 AMeV and mean intensities varying from 2.0 • 108 to 3.5 • 108 ions / s have been carried out. The beams were stopped in homogeneous thick targets consisting of PMMA, graphite and water, which were placed in the centre of the field of view of the PET-scanner at the experimental carbon ion therapy at GSI. Results on the production rate and the spatial distribution of 3He-ion induced +-activity are presented and compared with data from 12C-irradiation. The accuracy and resolution for determining the range of the 3He primary beams is deduced. Furthermore, energy dependent thick target cross sections for different reaction channels leading to positron emitters have been estimated from the experimental data.

At the clinical heavy ion treatment facility, which is under construction in Heidelberg, beams of He will be used for tumor irradiation. These will be monitored by means of in-beam PET for quality assurance. This requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. For this an experiment at the Gesellschaft für Schwerionenforschung (GSI) with three mono-energetic {rm³He}-beams of 130.03 it A\rm M it e\rm V
to 207.92 it A\rm Mit e\rm V and mean intensities varying from 2.0 cdot 10⁸ to 3.5 cdot 10⁸ ions/s has been carried out. The beams were stopped in homogeneous thick targets consisting of lucite, graphite and gelatine, which were placed in the center of the field of view of the PET-scanner at the experimental carbon ion therapy at GSI [1]. Results on the production rate and the spatial distribution of {\rm³He} ion induced beta^a-activity will be presented. From these, the accuracy and resolution for determining the range of the {rm³He} primary beams is deduced. Furthermore, energy dependent cross sections for different reaction channels leading to positron emitters will be estimated from the experimental data.

Experimental and theoretical β-decay properties of 103, 105Sn are discussed.

The β-decay of 102Sn was studied by using high-resolution germanium detectors as well as a Total Absorption Spectrometer (TAS). A decay scheme has been constructed based on the γ-γ coincidence data. The total experimental Gamow-Teller strength BGTexp of 102Sn was deduced from the TAS data to be 4.2(9). A search for β-delayed γ-rays of 100Sn decay remained unsuccessful. However, a Gamow-Teller hindrance factor h = 2.2(3), and a cross-section of about 3nb for the production of 100Sn in fusion-evaporation reaction between 58Ni beam and 50Cr target have been estimated from the data on heavier tin isotopes. The estimated hindrance factor is similar to the values derived for lower shell nuclei.

Because of today’s micro- and optoelectronics need for functional structures in submicron range the research in creating those structures gained much interest during the past years. In order to produce such nanometer sized devices there are two complementary approaches: the “top-down” and the “bottom-up” approach. The first case is represented by conventional processes like lithography, whereas the latter one makes use of self-organization phenomena. It has been shown that low energy (typically 0.1 – 10 keV) ion sputtering induces such a self-organized process at the irradiated surface which leads to the formation of periodic structures of size ranging from 10 to 100 nm [1]. This way periodic ripple patterns can be achieved for oblique ion beam incidence and hexagonally ordered dot arrays for normal incidence. The evolution of ripple structures on different semiconductor, metal and other surfaces has been studied extensively during the last decades [2]. Although both effects can be described by the same theoretical approach based on the Bradley-Harper model [3], the formation of nanodots has been discovered only very recently [4].
In the presented work, the evolution of GaSb(001) surface under normal incidence ion sputtering has been studied in-situ by surface sensitive X-ray techniques. The Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Diffraction (GID) measurements have been performed at the beam line ID01 at the ESRF. These techniques were used to study the temporal evolution of the dots for ion energies from 100 to 1000 eV. With GISAXS the morphology and the correlation of the dots could be observed, with GID information about the dots shape, crystalline structure and present strain was obtained.

[1] M. Navez, D. Chaperot and C. Sella, C. R. Acad. Sci. 254 (1962), 240
[2] G. Carter and V. Vishnyakov, Phys. Rev. B 54 (1996), 17647; C. Boragno et al., Phys. Rev. B 68 (2003), 094102; S. Habenicht, Phys. Rev. B 63 (2001), 125419
[3] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6 (1988), 2390; B. Kahng, H. Jeong and A.-L. Barabási, Appl. Phys. Lett. 78 (2001), 805
[4] S. Facsko et al., Science 285 (1999), 1551; F. Frost, A. Schindler and F. Bigl, Phys. Rev. Lett. 85 (2000), 4116

In the series of self-organized processes for the fabrication of nanostructures the pattern forma-tion during ion erosion of surfaces has attracted much interest in the last years. In the continuous sputtering process, induced by the bombardment with low-energy ions, periodic surface patterns appear in form of ripples under off-normal incidence or arrays of hexagonally ordered dots at normal incidence. The dimension of the pattern is related to the size of the typical collision cas-cade and lies in the range of ten to tens of nanometers, depending on ion energy. The self-organization mechanism relies on the interplay between a surface instability caused by the sput-tering, and surface diffusion processes. Regular ripple and dot array morphologies have been produced in this way on very different materials including semiconductors, insulators, and met-als, demonstrating the universality of the mechanism.

Layers of Ti nitride, Ti oxynitrides TiNxOy and Ti oxide were produced by means of metal plasma immersion ion implantation and deposition (MePIIID) from a plasma produced by cathodic arc evaporation of Ti under addition of nitrogen and/or oxygen to the ambient near the substrate. The phase composition and structure of the layers are strongly dependent on the relation of the gases partial pressure. To study the correlation between blood compatibility and physical properties of the coating the thrombocyte adhesion and fibrinogen adsorption on the surface as well as wettability and surface energy were investigated. Thrombocyte adhesion and fibrinogen adsorption are lower for TiNxOy than for TiO2. This correlates with a lower hydrophobicity and higher polar component of the surface energy for TiNxOy. (c) 2005 Elsevier B.V. All rights reserved.

Plasma immersion ion implantation (PIII) has been employed for nitrocarburizing 304 stainless steel. The sample was treated at relatively low gas pressure of nitrogen and acetylene in the range of 10(-3) mbar. The microstructure variation, the austenite lattices spacing and the phase transformations were studied in-situ during heating up to 800 degrees C and after cooling, using synchrotron X-ray diffraction. Glow discharge optical spectroscopy (GDOS), optical microscopy and hardness profile measurements have been used before and after thermal treatment to analyse the nitrocarburized layer. (c) 2005 Elsevier B.V. All rights reserved.

Most of the proposed electron accelerator projects for FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. In all of the projects photo guns will be applied: DC-photoguns, normal conducting RF photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF gun development still possesses a high risk. Challenges are the thermal and contaminant isolation needed between the cathode and superconducting cavity, the choice of the right photocathode and its life time, the difficulty of coupling high-average power into the gun, and beam excitation of higher order cavity modes. But in combination with SRF-linacs, the SRF-guns are best solution for high current and CW operation is simply possible. Thus, several R&D projects of SRF-gun have been launched. The talk will give an overview of the history and progress of the SRF-gun development. In detail the technical concept, performance, and status of the Rossendorf superconducting rf gun project, a collaboration of BESSY, DESY, MBI and FZR, will be presented.

A Multiple Field Multiple Size Group Model for industrial poly-dispersed gas-liquid flows has been developed in the commercial code CFX10.0. This model is based on the multi-fluid approach and the population balance method and is efficient for solving large-scale industrial flow problems. Compared with the previous CFX Multiple Size Group Model, the current model is applicable for inhomogeneous flow. In the first part, the model concepts and governing equations are presented.

The atomic arrangement in sp2-dominated carbon (C) and carbon nitride (CNx) thin films has been studied by Raman spectroscopy as a function of substrate temperature and, in the case of CNx, different N incorporation routes (growth methods). In this way, materials composing graphitelike, fullerenelike (FL), and paracyanogenlike structures have been compared. The results show that each type of arrangement results in a characteristic set of the Raman spectra parameters, which describe the degree of aromatic clustering, bond length, and angle distortion and order in sixfold structures. In the case of C films, the atomic structure evolves with substrate temperature from a disordered network to nanocrystalline planar graphitic configurations, with a progressive promotion in size and ordering of sixfold ring clusters. Nitrogen incorporation favors the promotion of sixfold rings in highly disordered networks produced at low temperatures, but precludes the formation of extended graphiticlike clusters at elevated substrate temperatures (>700 K). In the latter case, N introduces a high degree of disorder in sixfold ring clusters and enhances the formation of a FL microstructure. The formation and growth of aromatic clusters are discussed in terms of substrate temperature, N incorporation, growth rate, film-forming sources, and concurrent bombardment by hyperthermal particles during growth.

The successful application of reaction transport algorithms to calculating the chemical evolution of natural systems requires accurate methods to compute the rates of mineral/fluid surface reactions. Regarding the transport of radio-nuclides in mining dumps the dissolution of minerals is of special importance. The use of a kinetic rate law of the mineral dissolution verified for unsaturated conditions will allow a realistic modeling of the mineral weathering in the environment. Dissolution rates of minerals in an aqueous solution are determined by surface reaction rates, the morphology of the mineral’s surface and, in case of the unsaturated zone, by the degree of the water saturation. For this process, it is decisive which portion of the particle surfaces is in con-tact with percolating water. To study the differences of mineral dissolution under saturated and unsaturated conditions batch and column experiments were carried out with a pyrite/calcite mixture. The experimental results were verified by calculations. Comparing the dissolution in batch with that in the column experiment, which was performed with a water flow velocity of 0.64 cm/d and analyzed in the region with a water saturation of 0.11, one can conclude that only the small portion of about five per cent of the grain surface is chemically reactive in this unsaturated flow.

The ELBE electron beam at Forschungszentrum Rossendorf, Dresden, with energies up to 40 MeV, can be used to produce a beam of intense neutron pulses in a liquid-lead radiator, where bremsstrahlung photons created by the electrons produce neutrons in (gamma,xn) reactions. The 5 ps electron beam pulses create very short neutron pulses, giving an energy resolution of less than 1 % with a flight path of 3.9 m. A beam repetition rate of 1.6 MHz enables measurements with neutron energies from 200 keV to 10 MeV – an interval where neutron cross section measurements are needed for fission, fusion, and transmutation. The neutron beam will be shaped by a 2.4 m long collimator made from borated polyethylene and lead, reducing the background of scattered neutrons and of photons at the sample position. Monte Carlo simulations with MCNP4C3 were performed to optimise the collimator composition. About 92 % of the neutrons at the experiment site retain their correct energy-to-ToF correlation. The neutron energy resolution is 0.4 % (FWHM) at the maximum intensity. For neutron-capture gamma rays, a BaF2 scintillation detector array of up to 60 crystals is being built, whereas for neutron detection, Li-glass scintillators and a 1 m2 plastic scintillator wall will be used.

Bereits seit einiger Zeit ist bekannt, dass man durch gezieltes Rühren einer erstarrenden, metallischen Schmelze mit mechanischem Antrieb oder mit Hilfe zeitabhängiger Magnetfelder in aktiver Weise Einfluss auf die Gefügeausbildung nehmen kann. Diese sogenannte, erzwungene Konvektion begünstigt beispielsweise globulitisches gegenüber dendritischem Wachstum und bewirkt eine Kornfeinung. Allerdings können Strömungen im Schmelzbad während der Erstarrung auch unerwünschte Makroseigerungen hervorrufen.
Der Einsatz elektromagnetischer Felder zum Rühren des Schmelzbades ist vor allen Dingen aus zweierlei Gründen attraktiv: (a) diese Methode bietet die Möglichkeit einer völlig kontaktlosen Einflussnahme und (b) eine unmittelbare und einfache Kontrolle der Intensität der Strömung kann über die elektrischen Regelparameter Strom und Frequenz vorgenommen werden. Zusätzlich sind verschiedene Arten von Magnetfeldern (Wanderfelder, pulsierende Felder, statische Felder) im Prinzip beliebig kombinierbar. Damit ergibt sich die Möglichkeit, grundsätzlich verschiedene Strömungsmuster je nach Bedarf zu erzeugen.
Das Ziel unserer Forschung besteht in der Anwendung maßgeschneiderter Magnetfelder während der Erstarrung zur effizienten Herstellung homogener, feinkörniger, globulitischer Gefüge. Zunächst soll mit Hilfe von Modellexperimenten, die die Komplexität des Problems überschaubar halten, mehr Informationen über die physikalischen Zusammenhänge zwischen der Erstarrung metallischer Legierungen und einer erzwungenen Konvektion in der Restschmelze gesammelt werden. Dazu wurden Pb-Sn-Legierungen in einer einfachen zylindrischen Geometrie unter Einwirkung eines rotierenden Magnetfeldes (RMF) gerichtet erstarrt.