Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

One potential material system for high density magnetic recording consists of monodisperse, highly anisotropic FePt nanoparticles. In order to exhibit high magnetic anisotropy the fct-L10 phase is required.
FePt nanoparticles (dP = 6 nm) with concentration close to the stoichiometric composition have been prepared by DC magnetron sputtering in Ar and subsequent thermal annealing in the gas phase [1]. Recently, we have shown that under appropriate preparation conditions (pAr = 0.5 mbar, rAr = 100 sccm, Tanneal = 600 – 1000 °C), the obtained particles are monodisperse but unfortunately of icosahedral structure [1,2]. Strikingly, these icosahedra are very stable and even post-deposition annealing of these FePt icosahedra for 30 min at T = 1000 °C did not result in a structural phase transition of the particles, although L10 phase is known to be the thermodynamic equilibrium structure of (bulk) FePt.
In order to investigate both the stability of the icosahedral structure and the potential of He ion irradiation for inducing a structural phase transformation, likewise prepared FePt nanoparticles were deposited onto amorphous carbon films (TEM grids) and irradiated with He ions (5 keV) at room temperature. The ion fluence was varied in the range between 1•1016 and 3•1017 ions/cm2. HRTEM investigations on the irradiated particles show that with increasing fluence, the icosahedral particles become increasingly destabilized at the expense of fcc polycrystalline and single crystal particles. Adjacent particles are observed to coalesce (sinter) under the impact of the ion beam thereby indicating an enhanced diffusivity due to (temporarily) increased defect concentrations. The influence of the modified particle structure (with lower symmetry) on the result of a subsequent post-deposition annealing of the irradiated FePt nanoparticles is discussed.

Part of this work is supported by the Deutsche Forschungsgemeinschaft within SFB 445.

[1] S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, J. Cryst. Growth 252 (2003) 440-450.
[2] S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, Proc. Mat. Res. Soc. Vol. 704, pp. 73-78 (2002).

The alteration of magnetic properties in magnetic thin films by ion radiation has gained increasing attention in recent years. Most of the experiments focus on magnetic multilayers, e.g. Pt/Co [1] or exchange bias [2] systems. Only a few results are obtained from soft magnetic polycrystalline single-layer films [3] using Ga - ions. Here, we present data on the local alteration of the magnetic anisotropy axis in amorphous soft magnetic (Fe9090Fe10)78B10Si12 films by He -ion radiation in an applied magnetic in-plane field. Sputtered CoFeSiB (thickness 30 nm) were irradiated with 5 keV He -ions with a fluence ranging from 5 10^14 ions/cm2 to 5 10^16 ions/cm2. A magnetic field of 600 Oe was applied during irradiation aligned under an angle to the initial easy axis of anisotropy. Above a fluence of 1016 ions/cm2 a rotation of uniaxial anisotropy in the applied field direction in the irradiated areas is observed by MOKE magnetometry and complementary domain observation by Kerr microscopy in the longitudinal mode. No degradation in magnetic properties relative to the as-deposited state is found from the magnetization loops on non-patterned samples. The easy axis coercivity is typically around Hc,ea = 2 Oe and the anisotropy field around Hk = 18 Oe. Using irradiation together with photolithography the films were irradiated locally, thus resulting in "anisotropypatterned" structures. Domain patterns in differently anisotropy-patterned elements with varying angles of anisotropy and edge orientation, separating regions of different anisotropy alignment, are shown. The influence of the patterning on the (still) full film reversal and the resulting border domain structures are discussed in detail.
References:
[1] C. Chappert et al., Science 280, 1919 (1998)
[2] A. Mougin et al., Phys. Rev. B 63, 060409 (2001)
[3] Woods et al., Appl. Phys. Lett. 81(7), 1267-1269 (2002)

An all-optical pump probe technique is used to investigate the magnetization dynamics and the magnetic damping behaviour in the polycrystalline Ni80Fe20/Fe50Mn50 exchange bias system. It is demonstrated that the magnetic damping increases linearly with the exchange bias field magnitude. The results can be understood taking the exchange bias effect as an additional dissipation mechanism into account.
In order to investigate the magnetization dynamics an 8.5 ps laser excitation is used. Within the laser pulse duration the temperature is raised, resulting in a collapse of the exchange bias field. Due to the fast recovery time on the order of 160 ps a magnetization precession is induced and the Gilbert magnetic damping parameter is determined by comparison of the experimental data to macrospin simulations on the basis of the Landau-Lifshitz-Gilbert equation. The exchange bias field dependence is studied employing the antiferromagnetic thickness dependence by preparing a wedge shaped FeMn layer (0 – 10 nm) on top of a 5 nm NiFe layer.

A 8.5 ps short laser excitation (pulse energy: 10 nJ, spot size: 30 µm) is used to thermally control the magnetization of a polycrystalline, mesoscopic NiFe/FeMn exchange biased bilayer system on a picosecond time scale. Due to the creation of a hot spin and phonon gas the exchange coupling across the interface between the ferromagnetic and antiferromagnetic layers is reduced upon arrival of the excitation pulse.

Within 10 picoseconds a fast optical unpinning of the exchange bias coupling is observed for the easy axis geometry as well as for the hard axis case by longitudinal Kerr effect of a time-delayed weak probe pulse. This leads to a reduction of the exchange bias field Heb of about 50 percent (shown in Fig. 1) and to a dramatic increase of the zero-field susceptibility, respectively [1]. A similar time dependence is found for the coercive field Hc of the 50µm x 50µm sample structure under investigation. These effects indicate that the lattice temperature at the FM/AFM interface is elevated close to the blocking temperature Tb (155°C for FeMn) of the exchange coupled system. The fast optical unpinning is followed by a slower recovery of the exchange bias field and the zero-field susceptibility governed by a phenomenological spin-lattice time constant of 160 ps. Pump-probe measurements on a sample with different thicknesses of FeMn, thus different exchange bias field values, show that this relaxation time is independent of the bias field strength.

The exchange coupling across an interface between a ferromagnetic and an antiferromagnetic layer may result in the so-called exchange bias effect evidenced by a shift of the hysteresis loop along the magnetic field axis. To study the role of the exchange interaction at and near the interface, Ni81Fe19/Fe50Mn50 bilayers have been studied, which have an intervening Cu layer of varying thickness and position in the antiferromagnetic Fe50Mn50 layer. The role of the intervening Cu layer is to generate partial exchange decoupling. The main motivation is to investigate in which way each antiferromagnetic monolayer contributes to the total exchange bias and what governs the AF thickness dependence? In general introducing an intervening layer in the antiferromagnet can be understood as a well defined layer of defects. The interpretation of the results might be easier than for dilution experiments [1] and contribute to a deeper understanding of the correlation between exchange bias field and coercivity.
We have prepared and investigated a polycrystalline Ni81Fe19/Fe50Mn50 bilayer with an intervening wedge-shaped (0 – 7 Å) Cu layer. As a growth template a Si(100) wafer with a 150 Å thick Cu buffer layer was used. The thickness of the ferromagnetic Ni81Fe19 layer is 50 Å. On top a wedge (0 – 100 Å) of the antiferromagnetic Fe50Mn50 was grown. Next, a Cu spacer wedge was grown perpendicular to the wedge direction of the Fe50Mn50 film. Finally, an additional wedge of Fe50Mn50 was grown on top with the opposite direction in order to keep the total Fe50Mn50 thickness at 100 Å throughout the whole sample (see the sketches in Fig. 1). For protection a 20 Å thick Cr layer was deposited. As a result, a sample was obtained, where in one direction the position of the intervening Cu layer varies from the interface to the top surface of the Fe50Mn50 layer at constant Cu thickness, and in the other direction the Cu thickness varies. To initialize the exchange bias effect the sample was annealed above the Néel temperature and cooled in an applied field back to room temperature.
Hysteresis loops were measured as a function of position on the sample using longitudinal magneto-optic Kerr effect magnetometry. From the loops the exchange bias field Heb and the coercive field Hc were extracted as a function of the Cu spacer thickness, tCu, and of the thickness tFeMn of the lower Fe50Mn50 layer, which is directly exchange coupled to the Ni81Fe19 layer. The results are shown in Fig.1.
The obtained two-dimensional maps provide us easily with global information about the influence of the partial decoupling of the antiferromagnet as a function of tCu and tFeMn.
To obtain more quantitative information several line scans along the horizontal and vertical axes in Fig. 1 were evaluated (not shown here).
For the exchange bias field two different behaviors appear with increasing tFeMn. On one hand Heb decreases for a small Cu thickness close to the ferromagnetic/antiferromagnetic interface, on the other hand Heb increases for a small Cu thickness distant to the interface. For larger tFeMn the typical antiferromagnetic thickness dependence can be found. With increasing tCu a shift of the Heb maximum to higher tFeMn is observed. For a line scan along the Cu wedge for tFeMn = 0 a good agreement with previous results is found [2].
The evolution of the coercivity is different. For small Cu thickness tCu no variation of Hc is observed for scans along tFeMn. It can be concluded that there is no direct connection between exchange bias field Heb and coercive field Hc. The position of the Heb maximum depends on Cu thickness and position within the antiferromagnetic layer but the maximum in Hc always stays the same. In addition it is found that the exchange bias field also depends slightly on cap layer thickness.

We investigated the damping and spin wave creation in thin NiFe films with time-resolved magneto-optic Kerr effect magnetometry for small and large angle excitations. To gain further insight in the underlying damping process we employ a special measurement procedure, which allows us to determine all three magnetization vector components and therefore the length of the magnetization vector. A reduction of the magnitude of the magnetization vector indicates the creation of spin waves. These spin waves can be created directly by the stripline or by multi-magnon processes.
The experimentally determined magnetization trajectory is compared with numerical simulations based on the Landau-Lifshitz equation, and the damping constant is extracted from these simulations

Vor Kurzem konnte gezeigt werden, dass die magnetischen Eigenschaften von Austausch-Verschiebungssystemen durch Ionenbestrahlung gezielt beeinflusst werden können. Ein Modell wurde vorgeschlagen, welches die Änderung der magnetischen Eigenschaften der bestrahlten Systeme einer ioneninduzierten Änderung ihrer Struktur zuschreibt. Insbesondere wird die Erzeugung von Punktdefekten für die beobachteten Veränderungen verantwortlich gemacht. Um dieses Modell zu testen, wurde das ionenbestrahlte System NiFe/FeMn mit Hilfe von Transmissionselektronenmikroskopie untersucht. Es wurden Hellfeld-, Dunkelfeld- und Beugungsbilder von dem System aufgenommen und ausgewertet. Daraus wurden Morphologie, Partikelgrößen und kristallographische Struktur des Systems bestimmt und deren Abhängigkeit von der Bestrahlung durch 5 keV He+-Ionen und 30 keV Ga+-Ionen untersucht. Es konnte gezeigt werden, dass sich weder Partikelgrößen noch kristallographische Struktur mit zunehmender Ionendosis signifikant verändern. Diese Ergebnisse unterstützen die Theorie der defektinduzierten Modifikation der Austausch-Verschiebung.

In order to modify the exchange interaction in a Fe19Ni81/Fe50Mn50 exchange bias system a Cu interlayer of varying thickness and position with respect to the interface has been introduced. In one direction the position of the intervening Cu layer varies from the interface to the top surface of the Fe50Mn50 layer at a constant Cu thickness, and in the other direction the Cu thickness itself varies. The introduction of the Cu layer leads to a partial exchange decoupling. The samples were grown in a UHV MBE system and investigated by magneto-optic Kerr effect magnetometry. Two-dimensional maps are obtained, which provide global information about the influence of the partial decoupling of the antiferromagnet as a function of Cu thickness tCu and FeMn thickness tFeMn. In order to obtain more quantitative information several line scans along the horizontal and vertical axes were evaluated. The influence of the partial decoupling on the origins of exchange bias will be discussed.

Der Einfluss der Bestrahlung von 30 keV Ga+-Ionen auf die magnetischen Eigenschaften des polykristallinen NiFe/FeMn Austausch-Bias-Systems wurde untersucht. In diesem Zusammenhang wurde ein Modell getestet, welches die Änderung der magnetischen Eigenschaften der bestrahlten Systeme einer ioneninduzierten Änderung ihrer Struktur zuschreibt. Dieses Modell war ursprünglich für die Bestrahlung mit He+-Ionen entwickelt worden und macht die Erzeugung von Punktdefekten für die beobachteten Veränderungen verantwortlich. Diesbezüglich wurde auch eine Simulation durchgeführt, die den Beschuss durch He+- und Ga+-Ionen vergleicht. Es konnte gezeigt werden, dass sich das oben genannte Modell auf die Bestrahlung mit Ga+-Ionen übertragen lässt und durch die Ergebnisse der Simulation unterstützt wird. Überdies wurde getestet, ob sich das untersuchte System durch die Bestrahlung mit Ga+-Ionen magnetisch strukturieren lässt. Es konnte nachgewiesen werden, dass auf einer Skala von 10^2 - 10^3 nm eine magnetische Strukturierung mit bestimmten Einschränkungen möglich ist

Eine 9 Pikosekunden kurze Laseranregung (Pulsenergie: 10 nJ, Spotgröße: 25 mm) wird zur thermischen Kontrolle der Magnetisierung eines NiFe/FeMn Bilagensystems auf der Pikosekundenzeitskala eingesetzt. Aufgrund der Erzeugung eines heissen Phononen- /Spingases durch den anregenden Laserpuls wird die Austauschkopplung an der Grenzfläche zwischen Ferro- und Antiferromagnet teilweise unterdrückt. Innerhalb von 20 Pikosekunden wird eine schnelle Reduktion der Austauschkopplung mittels longitudinalem Kerr-Effekt des zeitverzögerten Probepulses sowohl für die magnetisch leichte als auch harte Richtung nachgewiesen. Dies führt zu einer Reduktion des Austausch-Verschiebungsfeldes von ca. 50 Prozent, bzw. zu einem dramatischen Anstieg der Nullfeld-Suszeptibilität. Diese Effekte können durch ein nahe an die sogenannte Blocking-Temperatur Tb (155o C für NiFe/FeMn) erwärmtes Gitter an der FM/AFM-Grenzfläche verstanden werden. Dem schnellen thermischen Unterdrücken der Austauschkopplung folgt eine langsamere Erholung des Austausch-Verschiebungsfeldes bzw. der Nullfeld-Suszeptibilität mit einer Zeitkonstante von ca. 170 ps.

X-ray and neutron scattering studies have been carried out on thermally evaporated FeMn-FeNi exchange bias systems before and after ion irradiation by helium ions. Helium ion dosages of 10^14 - 1017 ions /cm-2 have been used. The ion irradiation has shown to alter the exchange bias characteristics of the samples with dose and rate. X-ray diffraction measurements on the samples were made to assess the epitaxy of the layers to the substrate. In order to assess the effect of ion irradiation on these films, both neutron and x-ray reflectivity measurements were performed and the data modelled simultaneously. A final model was chosen that approximated both sets of data well. The reflectivity data suggest that the samples are prone to etching of the surface layer by the ions and that ion irradiation encourages interlayer mixing resulting in a smearing of the oscillations. Increased ion dosages result in a complete loss of exchange bias properties which is supported with loss in inter-layer definition by ion irradiation.

In the lecture, an overview of the experimental work perfromed at the Rossendorf multi-purpose thermal hydaulic test facility TOPFLOW concerning the flow structure in vertical pipes as well as of the function of wire-mesh sensors was given. Experimental results on the evolution of the radial gas fraction profiles, gas velocity profiles and bubble size distributions in a gas-liquid two-phase flow along a large vertical pipe of 194 mm inner diameter are presented. The tests were performed with two wire-mesh sensors. They were used to record sequences of two-dimensional distributions of local instantaneous gas fraction within the complete pipe cross-section with a lateral resolution of 3 mm and a sampling frequency of 2500 Hz. This data is the basis for a fast flow visualization and for the calculation of the mentioned profiles. The gas fraction profiles were obtained by averaging the sequences over time, velocities were measured by cross-correlation of the signals of the two sensors, which were located on a short (63 mm) distance behind each other. The high resolution of the mesh sensors allows to identify regions of connected measuring points in the data array, which are filled with the gas phase. This method was used to obtain the bubble size distributions.
In the experiments, the superficial velocities ranged from 0.04 to 8 m/s for the gas phase and from 0.04 to 1.6 m/s for the liquid. In this way, the experiments cover the range from bubbly to churn turbulent flow regimes. The evolution of the flow structure was studied by varying the distance between the gas injection and the sensor position. This distance was changed by the help of a so-called variable gas injection set-up. It consists of 6 gas injection units, each of them equipped with three rings of orifices in the pipe wall for the gas injection. These rings are fed with the gas phase from ring chambers, which can be individually controlled by valves. The middle ring has orifices of 4 mm diameter, while the upper and the lower rings have nozzles of 1 mm diameter. In this way, 18 different inlet lengths and two different gas injection geometries can be chosen. The latter allows to vary the initial bubble diameter at identical superficial velocities. The test setup is designed for steam-water operation at up to 7 MPa saturation pressure as well, which will be performed later. The paper presents the results of air-water tests.
A special data evaluation technique allows to study the evolution of radial gas fraction profiles that are decomposed according to bubble size classes. In this way, the behavior of bubbles of different
diameter can be observed, which experience different non-drag forces depending on their diameter. A parallel test section of 52.3 mm inner diameter allows the study of scaling effects.

The lecture presented an overview of the state of art of instrumentation for transient and staedy state multi-phase flows with a special attention to gas-liquid flows. The methods discussed are: impedance probes, wire-mesh sensors, optical fibre probes, gamma tomography, X-ray tomography, 3D pulsed holography, neutron radiography. Short descriptions of the measuring methods developed in Rossendorf were included. This concerns electrical impedance probes, wire-mesh sensors, gamma-tomography for periodically changing transient gas fraction fiels (e.g. in axial pumps and turbo couplings) and highthe status of the development of a -speed X-ray tomography system on the basis of a scanned electron beam.

Wire-mesh sensors have achieved a high spatial and time resolution and can therefore contribute considerably to the development of models for CFD codes

A constant air flow rate was injected into an upwards water flow, while the superficial water velocity was suddenly changed by activating a butterfly valve, the flap of which was perforated. In this way, both a jump-like decrease and increase of the liquid flow rate were studied. Measurements were taken by two wire-mesh sensors mounted at a short distance behind each other. They were placed 3030 mm downstream of the gas injection. Time sequences of the average gas fraction, radial gas fraction and gas velocity profiles as well as bubble size distributions were derived from the wire-mesh sensor data. The velocities were obtained by cross-correlating the signals of the two successive sensors.
Closely after a sudden increase of the liquid superficial velocity, the content of the pipe segment between gas injection and sensor contains still bubbles that were generated before the perturbation. In the first approximation, the cross-section averaged gas fraction should therefore remain the same as before for the duration of the passage of this portion of two-phase mixture. However, the wall peak in the radial gas fraction profile became more pronounced and shifted towards the wall. This was predicted with a CDF code (CFX-4) as well. However, the experimental observations are indicating a significant decrease of the cross-section averaged gas fraction, which can only be explained by an increase of the drift velocity. The latter was supported by gas velocity profiles obtained by cross-correlation of the signals of the two available sensors. We conclude that there is an effect of growing bubble rise velocity with increasing liquid superficial velocity. The nature of this effect is still unclear. In addition, the described effect was observed with inversed tendencies in case of a sudden reduction of the liquid flow rate.

The flow in a rectangular bubble column with a cross-section of 100x20 mm and a height of 1500 mm was studied using a high-speed video system. Series of the images were taken at a frequency of 500 Hz at different elevations. The images were treated by means of a bubble recognition algorithm. It allows the tracking of most of the individual bubbles in a bubble swarm. Time-averaged velocity profiles and turbulent diffusion coefficients were derived as a function of the superficial gas velocity.
To measure the turbulent diffusion coefficient of the gaseous phase the lateral displacement of bubbles traveling over a certain vertical distance was transformed into a probability density distribution. It was found that the shape of distributions fits well to a Gaussean standard distribution. Dispersion coefficients were found to grow nearly proportionally to the square root of the vertical distance. Diffusion coefficients were calculated from the proportionality factor and were compared to correlations from the literature. Experiments were performed at superficial gas velocities ranging from 0.5 to 4 mm/s. The bubbles were generated either by a porous sparger or a set of capillaries placed at the bottom of the column. Measurements were taken at heights between 1 and 1.5 m, where the bubble cloud was occupying the entire cross section.

This study investigates the characteristics of upward air-water flow for non-symmetric initial condition in the 50 mm vertical tube. Wire Mesh Sensor is utilized to obtain the local properties of the gas phase i.e. void fraction, gas velocity and bubble size. To generate the non-symmetric initial flow condition, air is supplied from a single injecting hole and mixed into the liquid flow inside the pipe through a narrow-ring shaped exit. In this case, large bubble can be generated at the inlet. In this experiment, the characteristics of bubble formation at the inlet and flow evolution along the pipe are emphasized. The results show the capability of the measurement technique to analyze the non-symmetric distribution of the gas phase. The effects of superficial gas and liquid velocity on the bubble distributions and on the local void fraction spreading at the inlet are clarified. The flow evolution dominated by bubble coalescence and break up is discussed in term of the development of Sauter mean diameter over the cross- section of the pipe. The results also show an inconsistency with uniform flow conditions at low gas flux. Hence, the effect of phase distribution spreading is proposed. In addition, the development of rising gas velocity in term of mean bubble size during coalescence and break up is revealed.

The paper reports about air-water tests in two different vertical pipes, one of 52.3 mm inner diameter, the other of 194.1 mm. In both cases, wire-mesh sensors with a measuring frequency of 2500 Hz were applied. They were used to measure radial gas fraction profiles, velocity profiles and bubble size distributions. Scaling effects were found by comparing the results for the two different pipe diameters. A variation of the air injection conditions allowed to study the influence of the primary bubble size. It was found that the kind of gas injection has a deciding influence at the appearance of a wall peak in the gas fraction profile as well as at the establishing gas fraction profiles and bubble size distributions in general.

Die friedliche Nutzung der Kernenergie hat heute einen besonderen Bedarf an Öffentlichkeitsarbeit. In keiner anderen Technologiesparte ist die Diskrepanz zwischen dem Nutzen und dessen Bewertung durch die Öffentlichkeit, zwischen den tatsächlichen Risiken und den Ängsten in der Bevölkerung, zwischen dem Stand der Technik und veröffentlichter Meinung so gravierend, wie hier. Die Ursache liegt zum großen Teil auch in Versäumnissen in der Vergangenheit. Die Kernenergiebefürworter haben durch ihre zurückhaltende Öffentlichkeitsarbeit den mehrheitlich gegen die Kernenergie eingestellten Umweltverbänden und Bürgerbewegungen in den Medien praktisch vollständig das Feld überlassen. Dies hat über eine Reihe von Rückkopplungen zu Verstärkungseffekten geführt, die es nun schwer machen, die Öffentlichkeit mit sachlichen Argumenten zu erreichen. Nur mühsam gelingt es, den verlorenen Boden zurückzugewinnen. Die Kerntechnische Gesellschaft muß den Part der Argumentation für die Kernenergie als Zukunftsoption übernehmen und stärker die in der wissenschaftlich-technischen Weiterentwicklung liegenden Potenzen für Umwelterhalt, Ressourcensicherung und Sicherheit herausstellen.
Die Kerntechnische Gesellschaft stützt sich als gemeinnütziger Verein naturgemäß in hohem Maß auf das Engagement seiner Mitglieder. Das Verfassen von Leserbriefen kann in diesem Zusammenhang gewissermaßen als dezentrale Form der Öffentlichkeitsarbeit angesehen werden. Leserbriefe können und sollen jedoch die persönliche Meinung des Verfassers zum Ausdruck bringen. Leserbriefaktionen, bei denen zentral vorgefasste Parolen an die Öffentlichkeit gebracht werden sollen, entsprechen meiner Meinung nach nicht dem Niveau unserer Kerntechnischen Gesellschaft und seiner Mitglieder. Wohl aber ist es nötig und zulässig, zu einem stärkeren Engagement auf diesem Gebiet aufzurufen. Der vorliegende Beitrag soll deshalb nicht als starrer Leitfaden für eine inhaltliche Gestaltung von Leserbriefen verstanden werden. Es soll vielmehr die persönlichen Ansichten des Autors zur Diskussion stellen und seine Erfahrungen vermitteln, um damit alle diejenigen, die es noch nicht versucht haben, zum Einbringen ihrer persönlichen Meinung auf dem Weg des Leserbriefes zu ermutigen.

Experimental results on the evolution of the radial gas fraction profiles, gas velocity profiles and bubble size distributions in a gas-liquid two-phase flow along a large vertical pipe of 194 mm inner diameter are presented. The tests were performed at the TOPFLOW facility in Rossendorf, where two wire-mesh sensors were used to measure sequences of two-dimensional distributions of local instantaneous gas fraction within the complete pipe cross-section with a lateral resolution of 3 mm and a sampling frequency of 2500 Hz. This data is the basis for a fast flow visualization and for the calculation of the mentioned profiles. The gas fraction profiles were obtained by averaging the sequences over time, velocities were measured by cross-correlation of the signals of the two sensors, which were located on a short (63 mm) distance behind each other. The high resolution of the mesh sensors allows to identify regions of connected measuring points in the data array, which are filled with the gas phase. This method was used to obtain the bubble size distributions.
In the experiments, the superficial velocities ranged from 0.04 to 8 m/s for the gas phase and from 0.04 to 1.6 m/s for the liquid. In this way, the experiments cover the range from bubbly to churn turbulent flow regimes. The evolution of the flow structure was studied by varying the distance between the gas injection and the sensor position. This distance was changed by the help of a so-called variable gas injection set-up. It consists of 6 gas injection units, each of them equipped with three rings of orifices in the pipe wall for the gas injection. These rings are fed with the gas phase from ring chambers, which can be individually controlled by valves. The middle ring has orifices of 4 mm diameter, while the upper and the lower rings have nozzles of 1 mm diameter. In this way, 18 different inlet lengths and two different gas injection geometries can be chosen. The latter allows to vary the initial bubble diameter at identical superficial velocities. The test setup is designed for steam-water operation at up to 7 MPa saturation pressure as well, which will be performed later. The paper presents the results of air-water tests.
A special data evaluation technique allows to study the evolution of radial gas fraction profiles that are decomposed according to bubble size classes. In this way, the behavior of bubbles of different diameter can be observed, which experience different non-drag forces depending on their diameter. A parallel test section of 52.3 mm inner diameter allows the study of scaling effects.

Conservation equations for one or more classes of the interfacial area concentration is one of the concepts to take into account the evolution of the flow structure in a gas-liquid two-phase flow in thermal hydraulic or, respectively, CFD modeling. The measurement of the interfacial area concentration is therefore of large importance for the development and validation of those models. The paper presents the results of an application of wire-mesh sensors to obtain the interfacial area concentration in vertical pipes of 52.3 and 194.1 mm inner diameter as an alternative to the widely used multiple-tip optical fiber probes. The measuring data of a mesh sensor is represented by a threedimensional matrix of local instantaneous gas fractions recorded as a time sequence (sampling frequency 2.5 - 10 kHz) at the crossing points of the wires (resolution in x-y direction: 3 mm).
Velocity information necessary to convert the time axis in an Eulerian z-axis was obtained by means of cross-correlation calculated between the signals of two identical mesh sensors located at a small distance behind each other. Three methods are used to deduce the interfacial area concentration from the wire-mesh sensor data:
• Calculation of the sum of the interfacial area represented by bubbles, which are identified as regions of connected gas filled elements in the data array, where the superficial area of an individual bubble is calculated under the assumption of a ellipsoid bubble shape. This method is restricted to low gas fractions, where bubble shapes are still close to the assumed geometry.
• A second method consists in the calculation of the sum of the contribution of the gas fraction in each local control volume of the sensor formed by two crossing wires. This control volume is approximated by a sphere with a volume-equivalent diameter. Furthermore, it is assumed, that the gas-liquid interface is a plane that cuts this sphere in a part filled with gas and another part that is filled with liquid. In this way, a correlation between the local interfacial area and the local instantaneous gas fraction can be found, in which the local interfacial area concentration is at its maximum at 50 % volumetric gas fraction and decreases to zero at both 0 % and 100 % local instantaneous gas fraction. This method can be applied to large bubbles with an arbitrary shape.
• In order to decrease the measuring error arising from the fact that gas fractions in measuring points inside large bubble as well as inside completely liquid-filled regions are not exactly equal to 100 % or, respectively, 0 %, and which therefore may significantly contribute to an overestimation of the interfacial area, a third method was applied, which is based on the identification of points that belong to the surface of the bubbles.
All three methods were applied to a vertical air-water flow. Since the distance between the sensors and the gas injection was varied, it was possible to characterize the change of the interfacial area concentration along the pipe. By combining the method with bubble size measurements, a decomposition of the interfacial area concentration into more then one bubble size classes was performed as well. The obtained results were compared to the findings reported in literature. The use of mesh sensors proved to be very efficient, since a bubble-size decomposed interfacial area concentration measurement in an entire pipe cross-section can be performed in a few seconds, which is very efficient compared to the use of local probes.

The paper describes the application of high-speed video observation combined with digital image processing techniques to measure the turbulent diffusion coefficient of the gaseous phase in a bubble column. The test channel is a rectangular bubble column with a cross-section of 100x20 mm and a height of 1500 mm. Sequences of the images were taken at different heights of the column with a high-speed video system. A diffuse illumination from the backside of the column was found to produce bubble images with a characteristic bright spot in the center. This bright spot was used for a bubble tracking that tolerates some overlapping of the bubbles. This allows to enhance the applicability of the bubble tracking to higher gas fractions compared to the tracking of the entire bubble shadows. After the bubble trajectories were extracted from the image sequence, the lateral displacement of bubbles between two virtual horizontal measuring planes was calculated for each bubble that crosses both planes. This lateral displacement is caused by the turbulent fluctuations of the bubble velocity. It is analyzed statistically by constructing probability density functions of the lateral displacement, which can be well described by Gaussean standard distributions. The dispersion coefficient of the standard distributions that were fitted to the experimental data shows a linear dependency from the square-root of the vertical distance between the two control planes, which supports the assumption of a diffusion model for the lateral displacement. Deviations from the linear dependency were identified to be the result of deterministic oscillatory motions of the rising bubbles. This effect is typical for low-viscosity liquids, while the bubble oscillations are damped at higher viscosities. Results are presented for different gas flow rates (superficial gas velocity ranged from 0.5 to 4 mm/s), different primary bubble sizes produced by a variation of the sparger and for liquids with different viscosity (water, ethylene glycol, mixtures of both). All measurements were taken at heights between 1 and 1.5 m, where the bubble cloud was occupying the entire cross section. Beside the turbulent diffusion study, the optical observation was used to obtain bubble sizes, gas fractions and rise velocities. Measured diffusion coefficients were compared to correlations from the literature and CFD simulations of the column using the code CFX.

In order to study the role of the exchange interaction at and near the interface, Ni81Fe19/Fe50Mn50 bilayers have been studied, which have an intervening layer of varying thickness and position in the anti ferromagnetic Fe50Mn50 layer. The role of the intervening layer is to generate partial exchange decoupling. As a result, samples were obtained, where in one in-plane direction the position of the intervening layer varies from the interface to the top surface of the Fe50Mn50 layer at a constant intervening layer thickness, and in the other in-plane direction the intervening layer thickness varies. Two-dimensional maps of the resulting exchange bias field and the coercive field were obtained from magneto-optic Kerr effect magnetometry measurements. The role of the position and strength of the partial decoupling within the anti ferromagnetic layer on the exchange bias effect and the coercive field is discussed.

The influence of 30 keV Ga+ ion irradiation on the magnetic properties of polycrystalline NiFe/FeMn exchange bias layers were investigated. In this context, it was of particular interest to determine whether a previously observed enhancement of the bias field value for the irradiation with 5 keV He+ ions is a material-specific or an ion-specific effect. Moreover, the capability of magnetic micropatterning using Ga+ ions from a Focused Ion Beam source was tested. It could be demonstrated that magnetic patterning with a lower limit in the range of 100 – 1000 nm is possible.

X-ray reflectivity, neutron reflectivity studies and Magneto-Optic Kerr Effect measurements (MOKE) have been carried out on thermally evaporated FeMn-FeNi exchange biased films before and after ion irradiation by helium ions. MOKE shows that ion irradiation reduces the exchange bias characteristics of the samples with increased dose. Modelling of the reflectivity data infers that atoms from the buffer layer are displaced by the ions and imbedded into the substrate material. The correlation between these strong structural modifications by irradiation with the reduction of the exchange bias will be discussed.

Due to the reduced dimension, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range from 5 – 150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Similar effects can also be observed using Ga+ ion irradiation, which is the common ion source in focused ion beam lithography. Examples for ion induced modifications of magnetic properties in exchange bias systems are presented.

Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may have an applied interest. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic leading to new phenomena at their mutual interface.

Most of the material systems discussed here are important for technological applications. It will be shown that light-ion irradiation has many advantages for design of new material properties and the fabrication technology of actual devices.

Due to the reduced dimension, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range from 5 - 150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may have an applied interest. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic leading to new phenomena at their mutual interface. An overview over the present status will be presented.

A 9 ps long laser pulse (energy: 10 nJ, spot diameter: 25 µm) is used to thermally control the magnetization of a NiFe/FeMn exchange bias bilayer system on the ps-time scale. The short laser pulse creates a hot phonon/spin gas. Consequently the exchange coupling across the interface between the ferro- and antiferromagnetic layer is reduced within 20 ps. This fast reduction of the exchange coupling is sensed by a time delayed probe pulse and analyzed with longitudinal magneto-optic Kerr effect. The time evolution of the exchange bias field in the easy magnetization direction and of the zero field suszeptibility in the hard magnetization direction is investigated. Within the first 20 ps a reduction of the exchange bias field of about 50 percent is observed. In addition a drastic increase of the zero field suszeptibility is found. The results can be understood concerning that the crystal lattice is heated close to the blocking temperature of the FeMn film (150°C). After the fast thermal reduction of the exchange coupling a slow recovery of the exchange bias field and the zero field suszeptibility is observed with a time constant of 170 ps.

A 9 ps long laser pulse (energy: 10 nJ, spot diameter: 25 µm) is used to thermally control the magnetization of a NiFe/FeMn exchange bias bilayer system on the ps-time scale. The short laser pulse creates a hot phonon/spin gas. Consequently the exchange coupling across the interface between the ferro- and antiferromagnetic layer is reduced within 20 ps. This fast reduction of the exchange coupling is sensed by a time delayed probe pulse and analyzed with longitudinal magneto-optic Kerr effect. The time evolution of the exchange bias field in the easy magnetization direction and of the zero field suszeptibility in the hard magnetization direction is investigated. Within the first 20 ps a reduction of the exchange bias field of about 50 percent is observed. In addition a drastic increase of the zero field suszeptibility is found. The results can be understood concerning that the crystal lattice is heated close to the blocking temperature of the FeMn film (150°C). After the fast thermal reduction of the exchange coupling a slow recovery of the exchange bias field and the zero field suszeptibility is observed with a time constant of 170 ps.

Ausgehend von einer ausführlichen Beschreibung der Mehrzweckversuchsanlage TOPFLOW und der zu ihrem Betrieb erforderlichen Bedien- und Sicherheitshinweise enthält dieses Betriebshandbuch Anweisungen zur Inbetriebnahme der Versuchsanlage sowie für die Vorbereitung und Durchführung von Experimenten zur Untersuchung von transienten Zweiphasenströmungen mit den Medien Dampf-Wasser bzw. Luft-Wasser. Erläuterungen über Sonderbetriebsfälle schließen das Betriebshandbuch ab. Eine Auflistung der technologischen Verriegelungen und Visualisierungen der Anlagenschemata aus dem Prozessleitsystem sind als Anlagen angefügt.

After the first theoretical proposal in 1971, it took more than two decades until the first laser based on intersubband transitions in semiconductor quantum structures was demonstrated. The progress since then has indeed been spectacular with lasers now spanning the range from 3.5 to 140 microns. The physics of these devices will be elucidated and some crucial achievements will be highlighted. Finally the perspectives for closing the still existing wavelength gap (25-60 microns) and extending the covered range to even longer as well as shorter wavelength will be discussed.

Low-emissivity coatings on glass, which provide highly efficient heat isolation, are nowadays extensively used in windows in offices and residential buildings for the purpose of saving energy in air conditioning. In this paper, multilayer low-emissivity coatings with the structure glass/SnO2/Ni–Cr/Ag/Ni–Cr/SnO2 were deposited onto large glass substrates in an industrial sputtering system. The extremely low thickness of the layers which compose such structures, as well as the large substrate area, causes the structure and impurity content of the films and interfaces to play an important role in providing efficient energy-saving performance as well as high optical transmittance. Thus, in-depth characterization was performed by spectroscopic ellipsometry, Rutherford backscattering spectroscopy and Auger electron spectroscopy. The use of these characterization techniques provides the great advantage of allowing the investigation of the whole multilayer system, including the interfaces. However, the properties of the individual layers (density, composition and optical behaviour) were also determined independently and compared to the values of corresponding bulk materials. Special attention is devoted to inter-diffusion of species.

Invited Lecture

Determination of structures using X-ray powder diffraction is complicated if the reflection intensities are mainly influenced by the scattering from heavy atoms and the atomic coordinates of light atoms remain uncertain. A method like EXAFS, which is sensitive to short range order, gives reliable atomic distances in the surroundings of heavy atoms with a precision of ± 0.02 Å. The probability for obtaining the complete structure from X-ray powder diffraction increases if one includes parameters derived from EXAFS measurements as restraints during the procedure of structure solving. We demonstrate the potential of combining EXAFS and X-ray powder diffraction by solving the structure UO2[H2AsO4]2×H2O. The procedure starts with the determination of space group and cell parameters from XRD powder data. In a second step the absolute values of the structure factor |F| are separated by iterating a decomposition formula. The heavy atom positions are determined by direct methods. In the third step atomic distances of coordination polyhedra are estimated using EXAFS. Subsequently, the complete coordination geometries around the heavy atoms including reliable distances are used as restraints in the structure solving and refinement procedure.

Le couplage SAZ - Elèctrochimie s'avère être une méthode pour la spéciation des espèces réduites du technetium. Cette méthode pourra être étendue à l'étude des espèces instables des actinides et des produits de fission.

Uranium(VI) consists predominantly of two double bonded oxygen atoms in axial direction (Oax) and 4, 5 or 6 oxygen atoms in the equatorial plane (Oeq). This anisotropic coordination leads to a strong polarization dependence of XAFS. Responsible for the polarization dependence are the electron waves with different impulse-momentum at the L1 and L3 edges. We investigated this effect by comparing experimental data with the theory. The Theory and experiment are in good agreement. The polarization dependence of L1 edge is significantly stronger that of L3 edge.

Spectroscopic extended X-ray absorption fine structure (EXAFS) evidence was obtained on the chemical environment of 99Tc(IV) atoms formed upon introduction of TcO4 - into four types of laboratory-scale synthetic and natural systems which mimic in situ natural reducing conditions in humicrich geochemical environments: (a) magnetite/pyrite in synthetic groundwater in the absence of humic substances (HSs), (b) magnetite/pyrite in natural Gorleben groundwater in the presence of HSs, (c) Boom clay sediment mixed with synthetic groundwater, and (d) Gorleben sand mixed with natural Gorleben groundwater. The investigated systems obey to pH 8-9 conditions, and all measured samples show similar EXAFS spectra for Tc, which could be fitted by a hydrated TcO2¿ xH2O phase. The results are interpreted as follows: upon introduction of high concentrations (millimolar to micromolar) of TcO4 to chemically reducing environments, small Tc(IV) oxidic polymers are formed, which either may aggregate into larger units (colloids) and finally precipitate or may interact in their polymeric form with (dissolved and immobile) humic substances. This latter type of interactionsTc(IV) colloid sorption onto HSssdiffers significantly from the generally accepted metal-humate complexation and therefore offers new views on the possible reaction pathways of metals and radionuclides in humic-rich environments.

Technetium, uranium and neptunium may all occur in the environment in more than one oxidation state (IV or VII, IV or VI and IV or V respectively). The surface of mackinawite, the first-formed iron sulfide: phase in anoxic conditions, can promote redox changes so a series of laboratory experiments were carried out to explore the interactions of Tc, U and Np with this mineral. The products of reaction were characterised using X-ray absorption spectroscopy. Technetium, added as TcO4-, is reduced to oxidation state IV and forms a TcS2-like species. On oxidation of the mackinawite in air to form goethite, Tc remains in oxidation state IV but in an oxide, rather than a sulfide environment. At low concentrations, uranium forms uranyl surface complexes on oxidised regions of the-mackinawite surface but at higher concentrations, the uranium promotes surface oxidation and forms a mixed oxidation state oxide phase. Neptunium is reduced to oxidation IV and forms a surface complex with surface sulfide ions. The remainder of the Np coordination sphere is filled with water molecules or hydroxide ions.

Extended X-ray absorption fine structure (EXAFS) spectroscopy at the uranium LIII-edge was used for determining the structural environment of aqueous uranyl sorbed onto montmorillonite. The study reveals that uranyl uptake at pH ~ 5- ~ 7 and at an initial uranyl concentration of 5×10-5 M takes place at amphoteric surface hydroxyl sites as inner-sphere complex. The measured bond distances between uranium and the equatorial oxygen atoms are in the range of 2.34 Å and 2.37 Å indicating an inner-sphere coordination. At ~ 3.4Å the presence of a U-Al backscattering pair was determined. This backscattering pair indicates that the binding of the uranyl unit to amphoteric surface hydroxyl sites occurs preferred as a bidentate inner-sphere complex on aluminol groups.

In this paper EXAFS was used to determine bond lengths in the structures of zeunerite and meta-zeunerite. The atomic distances between heavy and light scatterers observed using EXAFS in meta-zeunerite deviate approximately 0.1 _A from literature data of single-crystal X-ray diffraction measurements. Because this difference is significant higher than the error limits of EXAFS measurements, the complete crystal structure of meta-zeunerite, Cu[UO2AsO4]2 _ 8 H2O, is revised by X-ray structure analysis. The bond length determinations by EXAFS and the revised XRD data agree within the experimental error limits. In this study EXAFS spectroscopy has proven to be an useful tool for determining precise local bond lengths in the environment of heavy atoms. Moreover, the crystal structure of zeunerite, Cu[UO2AsO4]2 _ 12 H2O, hitherto not been described in the literature, was investigated. Reflex broadening effects and intergrowth relationship between zeunerite and meta-zeunerite show that meta-zeunerite grows in nature due to dehydration of zeunerite. The structural transition from zeunerite to meta-zeunerite is connected with a change in the uranyl arsenate layer arrangement and the crystal water content.

The structure parameters of the Am3+ aquo ion and of Am(III) sorbed onto smectite and kaolinite at varying pH are analyzed using EXAFS. An Am-O distance of 2.47-2.49 Å is found and a coordination number of 8-9 oxygen atoms is observed for the Am3+ and its hydration sphere. Combined TRLFS (Cm(III)) and EXAFS (Am(III)) results show that An(III) sorbs onto smectite at pH 4, forming an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere sorption onto smectite and kaolinite occurs. The overall number of oxygen atoms coordinating the actinide ion remains about the same at pH 6, with four water molecules being replaced by oxygen atoms from the mineral surface during inner-sphere complex formation. The coordination number of sorbed Am(III) at pH 8 exhibits an apparent decrease, which may be affected by the formation of ternary OH-/Am/clay mineral surface species.

Epitaxial SiC nanocrystals are fabricated by high-fluence Si-implantation into natural diamond at elevated temperatures between 760 °C and 1100 °C. Fluences under investigation range from 4.5 to 6.2 x 10¹⁷ Si cm^-2 . This implantation scheme yields a buried layer rich of epitaxial aligned SiC- nanocrystals within slightly damaged diamond. The generation of a small fraction of graphitic sp²-bonds of up to 15 % in the diamond host matrix can not be avoided. Unintentional coimplantation with nitrogen results in a very high doping level of more than 10²¹ cm^-3 . Resistivity and Hall measurements in van der Pauw geometry reveal a high, thermally stable n-type conductivity with electron concentrations exceeding 10²⁰ cm^-3and mobilities higher than 2 cm²/Vs. It is supposed, that both the SiC regions as well as the diamond matrix exhibit n-type conductivity and that the electron transport occurs across the low-resistivity SiC nanograins. In the SiC nanocrystals the electrons originate from nitrogen donors whereas in diamond defects are responsible for the electron conductivity. The formation of disordered graphite, which leads to low electron mobility, is substantially reduced.

Void fraction distributions of air-water two-phase flow in 3 different diameter vertical tubes (0.042 m, 0.1 m, and 0.2 m) were measured by 16x16 wire-mesh sensors with a sampling frequency of 1 kHz. Also, predictions under the same flow conditions were made by a 3D extended two-fluid model, generating a time-series of cross-section averaged void fraction at the same frequency with the experiment. Fluctuation characteristics from experiments and simulations were analysed in view of the probability density function, frequency spectrum, and Trajectory Parallel Measures (TPM). The analyses of TPM showed that dynamics is well-established for large nunnles whose fiameter is on the order of Taylor wave length in an air-water system, although small bubble void fraction signal is almost random in dynamical point of view. It is shown that the fluctuation component in void fraction time series can be used as one of criteria for validation of numerical models.

Die Ortssektion Sachsen der Kerntechnischen Gesellschaft bemüht sich kontinuierlich um eine aktuelle und attraktive Präsens im Internet. Mit der eigenen Internetseite "www.ktgsachsen.de", die seit Oktober 2001 besteht, wird versucht, neben der Information für die Mitglieder - in erster Linie Ankündigungen und Auswertungen von Veranstaltungen - mit Diskussionsbeiträgen zur Kernenergie ein breiteres Publikum zu erreichen. Dabei werden unter der Rubrik ARGUMENTE Themen, wie Nachhaltigkeit, CO2-Emissionen und Energieressourcen berührt. Unter der Überschrift NEWS wird über aktuelle Ereignisse informiert. Insgesamt
bleibt die Resonanz auf diese Internetseite jedoch gering. Nur sehr selten trifft Post ein, die auf die publizierten Argumente eingeht oder auch Widerspruch anmeldet. Um die Attraktivität der Internetseite zu erhöhen und dabei gleichzeitig einen Beitrag zum allgemeinen Informationsstand über die physikalischen Grundlagen der Reaktortechnik in der Bevölkerung zu leisten, wurde im November 2003 ein neuer Weg beschritten. Es wurde ein Programm zur On-line Simulation der Kettenreaktion in einem Kernreaktor entwickelt und ins Netz gestellt. Die Ortssektion Sachsen strebt damit die folgenden Ziele an:
(1) Durch eine attraktive Darstellung der physikalischen Prozesse in einem Kernreaktor, die durch interaktive Eingriffe über die Steuerorgane beeinflusst werden können, entsteht eine Art Computerspiel, mit dem es gelingen soll, interessierten Personen - insbesondere Kindern und Jugendlichen - Einblicke in die Reaktorphysik zu ermöglichen. Dabei wird Wert darauf gelegt, die Grundprozesse qualitativ möglichst korrekt und umfassend darzustellen, um einen hohen Bildungseffekt zu erreichen.
(2) Durch die spielerische Erschließung des Stoffes soll die emotionale Barriere, die häufig gegenüber der Kerntechnik besteht, abgebaut werden, um die Besucher der Internetseite an weitergehenden Informationen zu interessieren und die Aufgeschlossenheit für weitere Diskussionen und Argumente zu erhöhen.
(3) Durch ständige Weiterentwicklung sollen in monatlichen Abständen jeweils neue Versionen des Programms mit erweiterten Möglichkeiten angeboten werden, um eine Art Fangemeinde entstehen zu lassen, die der Internetseite ihre Treue hält. Das Programm wurde in der Programmiersprache DELPHI erstellt. Der unter WINDOWS ausführbare Code (EXE) kann zusammen mit einem Manual, welches die physikalischen
Hintergründe in populärwissenschaftlicher Weise beschreibt und dem Anwender numerische Experimente vorschlägt, von der Webseite www.ktg-sachsen.de heruntergeladen werden.

SiC nanoclusters are synthesized in Si by simultaneous dual implantation using two ion beams, of C and Si ions. This implantation mode is associated with extra excess vacancy generation. The effect of vacancies on SiC synthesis is investigated in this study. The amount of synthesized SiC is compared for different implantation modes, simultaneous and sequential ones. Sequential pre-deposition of vacancy defects in Si before the C implantation is performed by additional Si and He implantation. The simultaneous dual beam implantation is found to be the only method to improve SiC synthesis. The introduction of vacancies, both excess vacancies and He induced vacancies, by a sequential implantation process is disadvantageous for SiC nanocluster formation. The pre-deposition of vacancy defects is accompanied with higher crystal damage and/or the defects are annealed out during the subsequent C implantation at temperatures above 400oC. Vacancies must be created “in-situ” during C implantation to achieve enhanced output of SiC.

The process of formation of excess vacancies by ion implantation is explained. Moreover, the simulation of the process, the experimental detection of excess vacancies and their application for defect engineering is described.

Zum Studium der Wechselwirkungen von Schwermetallen mit Biofilmen in der Umwelt ist die reproduzierbare Präparation und detaillierte Charakterisierung von Biofilmen auf Mineral- und Gesteinsoberflächen notwendig. Die initialen Aufwachsstadien von auf Biotit erzeugten Pseudomonas aeruginosa Biofilmen wurden mit Rasterelektronenmikroskopie (SEM) und Rasterkraftmikroskopie (AFM) visualisiert. Zum Studium des reifen Biofilms wurden Fluoreszenzmikroskopie und konfokale Fluoreszenzmikroskopie (CLSM) eingesetzt. Die Unterscheidung zwischen lebenden und toten Bakterien erfolgte mit Hilfe eines LIVE/DEAD - Kit. Zur Visualisierung von Polysacchariden innerhalb der EPS wurden Lektine gekoppelt mit Fluoreszenzfarbstoffen verwendet. Hierbei konnten die einzelnen Polysaccharide der EPS unterschieden werden in solche, die direkt an Zellwände der Bakterien gebunden sind und weitere, die eine diffuse Verteilung der EPS im Biofilm aufzeigen. Die Dicke der erzeugten Biofilme auf den Biotitoberflächen wurde mit CLSM bestimmt. Sie schwankte zwischen 5,3 µm für Biofilme, die unter Nährstoffmangel angezogen wurden, und 16,6 µm bei ausgereiften Biofilmen.

Closure laws are needed for the qualification of CFD codes for two-phase flows. In case of bubbly and slug flow, the momentum transfer between the phases is usually modelled by forces acting on the bubbles. These forces depend on the liquid flow field as well as on the size and the shape of the bubbles. To validate models for these forces a detailed database for vertical pipe flow is used. It contains not only the information on the radial distribution of bubbles of different size, but also information on the bubble size distribution. Measurements were done for a large number of combinations of gas and liquid superficial velocities and for two different pipe diameter (DN50 and DN200). An one-dimensional model, which resolves the variables in radial direction and which considers a large number of bubble size classes to account for the size effect, is used for an analysis of models for these forces. The results obtained by this model were compared to 3D results obtained by the commercial code CFX-5.7 for simplified cases with only one bubble class. The effect of the number of bubbles classes as well as the effect of the lateral extension of the bubbles were analysed. For the validation of the bubble forces measured bubble size distributions were taken as an input for the model. On basis of the assumption of an equilibrium of the lateral bubble forces, radial volume fraction profiles were calculated separately for each bubble class. In the result of the validation of different models for the bubble forces, a set of Tomiyama lift and wall force and the Favre averaged turbulent dispersion force was found to reflect the experimental data with best agreement. Some discrepancies remain at high liquid superficial velocities.

Knowledge of the migration of intrinsic point defects is crucial to understand defect recovery, various annealing stages and microstructural evolution after irradiation or ion implantation. Molecular dynamics (MD) and the nudged-elastic band method have been applied to investigate long-range migration of point defects in SiC over the temperature range from 0.36 to 0.95 Tm , and the defect diffusion coefficient, activation energy and defect correlation factor have been determined. The results show that the activation energies for C and Si interstitials in 3C-SiC are about 0.74 and 1.53 eV, respectively, while it is about 0.77 eV for a C interstitial in 4H-SiC. The minima energy paths reveal that the activation energies for C and Si vacancies are about 4.1 and 2.35 eV, respectively. Finally, the results are discussed and compared with experimental observations and available ab initio data.

The aim was to characterize the damage zone ahead a crack tip in technical aluminium alloys using Small Angle X-ray Scattering. Experiments were conducted at the Austrian beamline at ELETTRA in Trieste from 18th-24th of February 2003. Four specimens of 2024-T351 aluminium alloy, different in shape, deformation condition and grain size, were investigated. Anisotropic grain boundary scattering of the CT-specimen was observed.

A method has been developed for the simultaneous determination of ²²⁶Ra, ²³³U and ²³⁷Np by liquid-scintillation (LS) spectrometry. This method consists in the evaluation of strongly overlapped multi peak spectra by a special peak fit function, considering the deviation of the LS-peak shape from the pure Gaussian distribution. First ²³⁷Np is determined using its daughter ²³³Pa by analyzing the ß-spectrum. ²²⁶Ra follows from the α-spectrum recorded 6 weeks after sample preparation. The peak of the three short-lived daughters ²²²Rn, ²¹⁸Po and ²¹⁴Po corresponds to the ²²⁶Ra activity under radioactive equilibrium conditions. Finally the ²³³U activity results from the joint α-peak at 4.8 MeV of the deconvoluted spectrum by subtracting the activity of ²²⁶Ra and ²³⁷Np. A second option uses the characteristic double peak of ²³⁷Np near 4.8 MeV. Due to the fact that the position is accurately known the pure α-spectrum can be analyzed for the determination of the given nuclides.

Bacterial diversity was studied in a water sample collected from a depth of 290-324 m below the land surface from the monitoring site S15 near the city of Tomsk, Siberia, Russia. In order to overcome the problems of culturability of bacteria, we applied a direct molecular approach based on PCR amplification and cloning of the 16S rDNA of the members of the natural bacterial communities. 65% of the cloned sequences were almost identical to the 16S rRNA genes of Dechlorosoma sp. belonging to the Rhodocyclus group of b-subclass of Proteobacteria. Relatively high was the number of the sequences which shared high identities with the 16S rRNA genes of some cultured g-Proteobacteria (6.9%), a-Proteobacteria (4.6%) and with the sequences of mostly uncultured members of Cytophaga/Flavobacterium/Bacteroides (5.4%), Actinobacteria (4.6%) and Planctomycetales (2.3 %). The rest of the retrieved sequences were clustered in small groups, each containing about 1 % of the total number of clones, and they matched with 16S rDNA sequences of Bacillales, Holophaga/Acidobacteria, Nitrospira, and d-Proteobacteria, respectively.

Dynamo action is generally accepted as the source of cosmic magnetic fields, such as the fields of planets, stars and galaxies. The understanding of dynamos has considerably progressed during the last decades. Recently, the hydromagnetic dynamo effect has been demonstrated experimentally in large liquid sodium facilities in Riga and Karlsruhe.
The electrically conducting fluid is usually confined to a finite domain which is surrounded by an insulator. For only a few cases, such as spheres or cylinders with infinite length, the boundary conditions for the magnetic field are easily implementable. In most cases, including finite cylinders which are relevant for the liquid sodium experiments in Riga, Karlsruhe, Cadarache and New Mexico, the correct handling of the non-local boundary conditions is far from trivial. We have re-formulated Pre-Maxwell's equations to an integral equation system under the assumption that the velocity field is stationary.
The main advantage of this approach is that the numerical solution of the integral equation system does not require any discretization of the exterior region.
In the present work, the integral equation approach is performed on a group of Beltrami flows (and some modifications) with the topologies s2t2, s2t1 and s1t1 in a finite cylinder. Beltrami flows are characterized by maximum helicity for a given magnetic Reynolds number. Due to the axisymmetry of these flows, the integral equation system in the cylindrical system is reduced to a two-dimensional form.
The calculated results show a good agreement with those obtained by a differential equation approach. This integral equation approach exhibits attractive features such as robustness and stability.
The impact of a stagnant conducting layer surrounding the cylinder is also investigated. Such a layer can reduce the critical magnetic Reynolds number significantly, and it can even transform no-dynamos into dynamos. Interestingly, the presence of a layer can also change an oscillatory dynamo to a steady dynamo.

Gamma tomography has been used to investigate the fluid distribution within multiple axial planes of a hydrodynamic test coupling under operating conditions. The tomographic data was obtained by phase correlated averaging of projections from the homogeneously rotating parts of the coupling. By application of the filtered backprojection reconstruction technique to the data we reconstructed average fluid fraction distributions in the transversal planes at different operating points of the coupling.

A status report on the SRF photo-injector activities at FZR within the CARE/PHIN project will be given. The new SRF gun has been designed for CW operation at the ELBE linac with an average current of 1 mA, 77 pC bunch charge, and 10 MeV energy. The basic concept of the gun, operating a normal conducting, thermally insolated photo-cathode within a superconducting cavity, have been taken from the first SRF half-cell gun [1] which was successfully tested. In this report the design layout of the SRF photo-injector, the parameters of the superconducting cavity and the expected electron beam parameters are presented. The SRF gun will have a 31/2-cell niobium cavity working at 1.3 MHz and will be operated at 2 K. The cavity consists of three full cells with TESLA-like shapes and a half-cell in which the photocathode is situated.

HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal, show first experimental results obtained from C+C reactions at 2 A GeV and shortly discuss physics programme of up-coming experimental runs.

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. Similarly to some other Bacillus isolates from this site, cells and spores of B. sphaericus JG-A12 bind selectively and reversibly large amounts of different toxic metals, such as uranium /1/. The cells of the B. sphaericus strain JG-A12 are covered by a surface layer (S-layer) protein. The latter forms a highly ordered lattice with distinct structural and chemical properties. Because it was shown that S-layers may work as protective coat, matrix for biomineralization, molecular sieve or as ion and molecule trap /2, 3, 4/ their special importance for the interaction of cells with radionuclides and heavy-metals in the surrounding environment is evident. As a consequence of the above mentioned properties, B. sphaericus JG-A12 was investigated with regard to its suitability to work as a binding matrix for bioremediation of uranium mining waste waters. A fundamental requirement for biotechnological application is the complete immobilization of the biomass in a porous structure. In this work, sol-gel techniques were used for embedding B. sphaericus JG-A12 cells, spores and S-layer protein in a SiO2-matrix in order to obtain a novel kind of biological ceramic (biocer) /5/. To select the appropriate filter material, uranium sorption and desorption experiments were carried out with free and immobilized cells, spores and S-layer protein of B. sphaericus JG-A12. Besides quantification of the available binding sites, the formed uranium complexes were investigated also by using infrared and extended X-ray absorption fine structure (EXAFS) spectroscopy. The latter revealed that the binding of uranium by free cells, spores and S-layer occurred via phosphate and carboxyl groups. The presence of phosphate groups was confirmed by different methods not only for cells and spores but also for the S-layer protein. The spectroscopic analysis of the uranium complexes formed by the biocer demonstrates the metal binding via phosphate groups and the formation of a uranium precipitate, what is of special interest for the binding capacity of the biocer. In case of the xerogel uranium was bound to silanol groups. Analyses of the uranium sorption by cells, spores and S-layer protein of B. sphaericus JG-A12 and of the xerogel itself (without biocomponent) showed highest binding capacity for spores followed by cells, S-layer protein and xerogel. In case of embedded biocomponents only the binding capacity of spores is significantly reduced and is lower than for cell- and S-layer-ceramics. Uranium bound to biocers can be completely removed by washing with citric acid.

1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
2. Beveridge, T.J. 1979 J. Bacteriol. 139 (3): 1039-1048
3. Schultze-Lam, S. et al. (1992) J. Bacteriol. 174 (24): 7971-7981
4. Sára, M. & Sleytr, U.B. 1987. J. Bacteriol. 169 (6): 2804-2809
5. Raff, J. et al (2003) Chem. Mater 2003; 15(1):240-4

Bacterial diversity was studied in a soil sample collected from a uranium mining waste pile situated near the town of Johanngeorgenstadt, Germany. As estimated by ICP-MS analysis the studied sample was highly contaminated with Fe, Al, Mn, Zn, As, Pb and U. The 16S rDNA retrieval, applied in this study, demonstrated that more than the half of the clones of the constructed 16S rDNA library were represented by individual RFLP profiles. This indicates that the composition of the bacterial community in the sample was very complex. However, several 16S rDNA RFLP groups were found to be predominant and they were subjected to a sequence analysis. The most predominant group, which represented about 13% of the clones of the 16S rDNA library, was affiliated with the Holophaga/Acidobacterium phyllum. Significant was also the number of the proteobacterial sequences which were distributed in one predominant alpha-proteobacterial cluster representing 11% of the total number of clones and in two equal-sized beta- and gamma-proteobacterial clusters representing each 6% of the clones. Two smaller group representing both 2% of the clones were affiliated with Nitrospira and with the novel division WS3. Three of the analysed sequences were evaluated as a novel, not yet described lineage and one as a putative chimera.

A ribosomal intergenic spacer amplification (RISA) retrieval was applied to analyze the natural bacterial communities in drain waters of two uranium mill tailings - Gittersee/Coschütz in Germany and Shiprock in the USA. About 35% of the clones from the RISA library constructed for the samples of the German tailings represented a microdiverse population of Planctomycetales. The rest of the clones were affiliated with rather diverse bacterial groups including g- and d- Proteobacteria, Cytophaga/Flavobacterium/Bacteroides (CFB), Nitrospira, Verrucomicrobia and Actinobacteria. 8% of the cloned sequences represented a novel bacterial lineage from the recently described division NC3.
Bacterial diversity in the Shiprock mill tailings was found to be significantly lower. The RISA library constructed for those samples contained only two larger groups of clones, representing b-proteobacterial species and one small group, which was affiliated with d-Proteobacteria.

Vector meson (V=ω , φ) production in threshold-near elementary nucleon-nucleon collisions pp to ppV, pn to pnV and pn to dV is studied within an effective meson-nucleon theory.
It is shown that a set of effective parameters can be established to explain fairly well the available experimental data on angular distributions and the energy dependence of the total cross sections without explicit implementation of the Okubo-Zweig-Iisuka rule violation. Isospin effects are considered in details and compared with experimental data whenever available.

Bacterial diversity was assessed in water samples collected from several uranium mining wastes in Germany and in the USA by using 16S rDNA and RISA retrievals.
The results obtained using the 16S rDNA retrieval showed that the samples collected from the uranium mill tailings Schlema/Alberoda, Germany, were predominated by Nitrospina-like bacteria, whereas those from the mill tailings Shiprock, New Mexico, USA, were predominated by g-Pseudomonas and Frateuria spp. Additional smaller populations of CFB, a-, and d-proteobacteria were identified in the Shiprock samples as well. Proteobacteria and CFB were also predominant in the third uranium mill tailings studied, Gittersee/Coschütz in Germany, but the groups of the predominant clones were rather small. Most of the clones of the Gittersee/Coschütz samples represented individual sequences that indicated a high level of bacterial diversity. The samples from the fourth uranium waste studied, namely Steinsee Deponie B1 in Germany, were predominantly occupied by Acinetobacter spp.
The RISA retrieval provided results complementary to those obtained by the 16S rDNA analyses. For instance, in the Shiprock samples an additional predominant bacterial group was identified and affiliated to Nitrosomonas sp., whereas in the Gittersee/Coschütz samples Anammox-populations were identified which were not retrieved by the used 16S rDNA approach.

The migration behavior of U(IV)/U(VI) in the presence of humic acids was studied in a laboratory quartz sand system by column experiments. It was found that humic acid influences the transport of U(IV) and U(VI). In presence of humic acid both redox species migrate nearly as fast as the groundwater flow. Retardation factors of 1.11 ± 0.03 and 1.14 ± 0.03 as well as eluate recoveries of 0.83 ± 0.09 and 0.65 ± 0.07 were determined for U(VI) and U(IV), respectively. In case of U(VI) humic acid exhibits a clear mobilizing effect compared to the humic acid-free system. There are also strong indications for a similar effect on the U(IV) transport.
The present study demonstrates that humic acids can play an important role in the migration of tetravalent actinides. Consequently, the humic colloid-borne transport of actinides has to be taken into account in performance assessment.

Objectives: PET imaging of cardiac reporter gene expression holds promise for noninvasive monitoring of gene therapy. Two approaches based on herpesviral thymidine kinase gene(HSV1-tk) habe been applied. Wild-type HSV1-tk was imaged with 2´-fluoro-2´-deoxy-5[¹²⁴I]-iodo-arabinofuranosyluracil([¹²⁴I]FIAU), and mutant HSV1-sr39tk was imaged with 9-[4-[¹⁸F]-fluoro-3-(hydroxymethylbutyl)guanine([¹⁸F]FHBG).
Methods: Adenovirus expressing wild-type HSV1-tk(Ad_tk), mutant HSV1-sr39tk (Ad_sr39tk), or control gene (Ad_LacZ) were directly injected into myocarcardium of 24 rats and 8 pigs. Two days later, dynamic PET imaging was performed for 120 min after injection of [¹²⁴I]FIAU or [¹⁸F]FHBG with a clinical scanner. Imaging with [¹³N]-ammonia was performed to identify cardiac regions of interest. Pig hearts were sliced into 5 short-axis slices for ex vivo imaging, and regional tracer uptake was analyzed.
Results: For [¹²⁴I]FIAU, the largest difference of cardiac uptake between Ad_tk rats and controls was found at 10-30 min after injection (1.7±0.25 vs 0.87±0.22 %dose/ml, p=0.035). No difference was observed at later imaging times due to [¹²⁴I]FIAU washout. For [¹⁸F]FHBG, difference between Ad_sr39tk rats and controls continuously increased over time and was largest at 105-120 min (1.45±0.45 vs 0.35±0.05 %dose/ml, P=0.0066). Global cardiac reporter probe kinetics in rats was confirmed by regional myocardial analysis in pigs. Transgene expression was specifically visualized by both approaches. Highest target/background ratio of [¹²⁴I]FIAU in Ad_tk infected myocardium was 1.50±0.20 vs 2.64±0.49 for [¹⁸F]FHBG in Ad_sr39tk infected areas (P=0.01). In vivo results of rats were confirmed by ex vivo counting and autoradiography. In vivo segmental reporter probe uptake in pigs correlated well with those in ex vivo images.
Conclusions: Both combinations were feasible for PET of cardiac transgene expression in different species. Specific probe kinetics suggests different myocardial handling of pyrimidine ([¹²⁴I]FIAU) and acycloguanosine ([¹⁸F]FHBG) derivatives. Results are in favour of [¹⁸F]FHBG because of continuous accumulation over time and higher imaging contrast.

The radiosyntheses of 5-(4´-[¹⁸F]fluorophenyl)-uridine [¹⁸F]-11 and 5-(4´-[¹⁸F]fluorophenyl)-2´-deoxy-uridine [¹⁸F]-12 are described. The 5-(4´-[¹⁸F]fluoro-phenyl)-substituted nucleosides were prepared via a Stille cross-coupling reaction with 4-[¹⁸F]fluoroiodobenzene followed by basic hydrolysis using 1 M potassium hydroxide. The Stille cross-coupling rreaction was optimized by screening various palladium complexes, additives and solvents. By using optimized labelling conditions (Pd₂(dba)₃/CuI/AsPh₃ in DMF/dioxane (1:1), 20 min at 65 °C), 550 MBq of [4-¹⁸F]fluoroiodobenzene could be converted into 120 MBq (33 %, decay-corrected) of 5-(4´-[¹⁸F]fluorophenyl)-2´-deoxy-uridine [¹⁸F]-12 within 40 min, including HPLC purification.

A comprehensive study on the migration of di- and tri-interstitials in silicon is performed using classical molecular
dynamics simulations with the Stillinger–Weber potential. The initial di- and tri-interstitial configurations with the lowest
formation energies are determined, and then, the defect migration is investigated for temperatures between 800 and
1600 K. The defect diffusivity and the self-diffusion coefficient per defect are calculated. Compared to the mono-interstitial,
the di-interstitial migrates faster, whereas the tri-interstitial diffuses slower. The migration mechanism of the diinterstitial
shows a pronounced dependence on the temperature. Like in the case of the mono-interstitial, the mobility of
the di-interstitial is higher than the mobility of the lattice atoms during the defect diffusion. On the other hand, the triinterstitial
mobility is lower than the corresponding atomic mobility. The implications of the present results for the
analysis of experimental data on defect evolution and migration are discussed.

Ni was surface-alloyed with Cu, Ti or Cu + Ti by ion implantation. This material was examined for its redox and electrocatalytic activity by cyclic voltammetry. The surface was characterized by X-ray photoelectron spectroscopy, X-ray and electron diffraction, and electron and atomic force microscopy. This type of materials exhibited a unique voltammetric response of Ni and was shown to stabilize the ß modification of the Ni oxide/hydroxide. Cu modified the anodic oxidation of glucose and the oxygen evolution to a higher degree than Ti. The morphology and microstructure differed from those of bulk materials.

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Information on the local structure of the flow is also required by 1D thermal-hydraulic codes. Gas-liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up. E.g. the Lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. Basing on extensive experimental data with a high resolution in space and time the applicability and the limits for the simulation of bubble flow with current CFD-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model, parametric studies can be conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.

The paper includes the description of separate effect test facilities used for investigations with regard to the fragmentation and the transport behaviour of different insulation materials in multidimensional aqueous flow. The instrumentation of the rigs is specified, in particular modern digital image processing technologies. First experimental results are shown and discussed generated at three acrylic glass test facilities. The experimental data will be use for CFD-modelling and validation. The anticipated modeling concepts are presented and their feasibility is demonstrated. During the ongoing work further results are expected.

TOPFLOW is a new thermal fluid-dynamic multipurpose test facility designed for generic and applied studies of transient two phase flow phenomena.
The paper presents results obtained in air-water tests which were started in December 2002. The experiments aimed at studying the structure of a gas-liquid two phase flow in pipes of large diameter. The experimental data is used for the visualisation of the two phase flow structure as well as to obtain void fraction profiles and bubble size distributions. Additionally, a new visualisation technique is presented, that consists in the creation of virtual side projection of the flow.

Momentum and mass transfer during electrochemical reactions in a small cell can be significantly influenced by Lorentz forces. Depending on the magnetic field configurations, a multitude of flow fields with an accordingly large range of mass transfer conditions can be arranged. The moderate magnetic field of simple permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. The interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

Our activities were directed to the investigation of some diffusion controled electrochemical reactions like [Fe(CN)6]3+/[Fe(CN)6]4+, Ce4+/Ce3+ and the electrodeposition of Cu2+.

Since Faradaic currents are inherently coupled to electrochemical processes, the mass transfer enhancement attainable by Lorentz force induced convection does not increase the running costs. Therefore it seems attractive to perform further studies in order to determine the underlying scaling laws.

In a second part of the discussion a fluidic microsystem is presented. The silicon-glass wafer system is produced in a micromechanic planar technology and consists of a network of microfluidic channels. The microsystem can be coupled with microsensors and actuators.

Still, the K_D concept of empirical distribution coefficients is the most often utilized approach for description of sorption phenomena. However, as an empirical concept it can not correctly portray the complex processes on the surfaces. A better approach is a Surface Complexation Models (SCM) capable of describing the sorption processes at the mineral-fluid interface on a scientific, quasi-thermodynamic basis. SCM are available in various versions, in which the Diffuse Double Layer Model (DDL), Constant Capacitance Model (CC) and Triple Layer Model (TL) are the most important and applied submodels.
Certainly, during the next decade SCM will replace K_D only in some simple systems or systems dominated by one mineral. However, SCM can help to verify measured K_D's, to identify the most sensitive experimental parameters, to assign uncertainty limits, to fill gaps difficult to access in sorption experiments, and to help to gain a better process understanding.
RES³T [1]– the Rossendorf Expert System for Surface and Sorption Thermodynamics - is a digitized version of a thermodynamic sorption database as required for the parametrisation of SCM, namely in risk assessment studies.
As an example to illustrate the effect of parameter uncertainty in blind predictions the Np(V) sorption onto haematite was selected.

Slow Positron Implantation Spectroscopy (SPIS), based on the generation, implantation and subsequent annihilation of mono-energetic positrons in a sample, is used to study depth dependent vacancy-type damage in ion-implanted 6H-SiC. The derivation of physical information from the Doppler-broadened annihilation lineshape is exemplified. It is found that the depth profile of vacancy-type damage formed in SiC co-implanted by Al+ and N+ at 800 °C, and subsequently annealed at 1200 °C and 1650 °C, strongly depends on the sequence of implantations and on annealing conditions. These studies show that annealing at 1650 °C for 10 minutes is not sufficient to remove the vacancy-type damage created by ion implantation.

The lecture is splitted into three parts. In its first part, a brief introduction is presented into the underlying physics of the dynamo effect of magnetohydrodynamics (MHD), in order to make clear the motivation of the subsequent mathematical considerations. Paleomagnetic evidences for fields reversals of the geomagnetic field are discussed, as well as the results of the Riga dynamo experiment. Special emphasis is laid on the planned next generation dynamo experiments.

In the second part of the lecture, the basic operator-theoretic properties of the 2×2 operator matrix of the spherically symmetric α²-dynamo are discussed: its pseudo-Hermiticity in the case of idealized boundary conditions (with corresponding representation of the operator in a Krein space as indefinite generalization of a Hilbert space), and the general lack of symmetry and Hermiticity for physically realistic boundary conditions. A brief summary is given of the results of Ref. [1] on testing the operator struture on its compatibility with an operator intertwining technique as descriptive tool for possibly existing isospectral classes of dynamo operators. A corresponding no-go theorem is discussed for first-order differential operators as intertwiners.

Subject of the third part of the lecture are recent results on spectral phase transitions. Such phase transtions from non-oscillating dynamo regimes to oscillating regimes occur at two-fold degenerate level-crossing points of the spectrum (exceptional points), where two real-valued branches of the spectrum cross and leave the real axis to develop as pair of complex conjugate branches. Some general properties of the spectrum in the vicinity of the exceptional points are discussed. For this purpose, the linear eigenvalue problem of the 2×2 operator matrix is reformulated as equivalent eigenvalue problem of an associated quadratic operator pencil. Special emphasis is laid on the differences of exceptional points for quantum mechanical operators in Hilbert spaces and for pseudo-Hermitian operators in Krein spaces.

The lecture is completed by a discussion of open operator theoretic problems with relevance for the planned next generation dynamo experiments.

[1] Günther U. and Stefani F., Isospectrality of spherical MHD dynamo operators: pseudo-Hermiticity and a no-go
theorem, J. Math. Phys. 44, 2003, 3097, math-ph/0208012.

At the Forschungszentrum Rossendorf the build-up of the superconducting 1.3 GHz accelerator ELBE is still in progress. Furthermore a new sc photo injector (SRF gun) is under development, which should accelerate electrons up to 10 MeV at 1.3 GHz frequency. The use of electron accelerators is also more and more interesting for applications where the destructive potential of the electrons are used like sterilization of medical waste and medical products, food irradiation or decontamination of sewage. For these processes a high power is required to achieve a high product throughput in a plant. The aim is therefore to use beam powers of around 100 kW or more. Since the applications of electron accelerators in industrial environments are steadily increasing one can speculate about transferring the above named state of the arte technology to industrial electron accelerators. At the FZR a feasibility study of such a table top electron accelerator (TTE) has been performed to investigate its technical limits and marketabilitys.

For 10 years an irradiation measuring field has been operated at FZR near Dresden. It consisted of 12 modules with different tilt and azimuth angles. The yearly mean values of the generated DC-energy are presented and directly compared with the predictions of the PEREZ model. The main result of the measurements is the providing of typical module DC power distributions. This distributions can be used to determine the optimal module/inverter power ratio of grid connected PV plants. For nearly optimal orientated generators this ratio should be one. Further a revision of the widely used “European Efficiency” of inverters is suggested, which is based on new weighting factors derived from the measurements. For PV plants a maximum performance ratio of 84% could be estimated. Finally the matching of the daily electricity load with PV plants in Germany is discussed. The load peak in Germany can be covered by an installed PV capacity of 45 GW.

Zur Verbesserung des Korrosionsverhaltens von Baustahl wurde versucht, durch Rückstoßimplantation bzw. Ionenstrahlmischen seine Oberfläche mit einer chromreichen Schicht zu versehen. Dazu wurde polierter Baustahl (SAE 1020) mit Chrom bedampft und anschließend mit Stickstoffionen bestrahlt. Der Ionenbeschuß erfolgte sowohl durch direkte Ionenimplantation als auch durch Plasmaimmersions-Ionenimplantation.

Die so hergestellten Proben wurden mittels Augerelektronenspektroskopie, Konversionselektronen-Mößbauerspektroskopie und Röntgendiffraktometrie untersucht. Die Kombination dieser Verfahren gestattete eine ausreichende Charakterisierung der erzeugten Oberflächenschichten. Während die Schichtung Chrom/Stahl durch die direkte Ionenimplantation kaum verändert wurde, entstand durch die Plasmaimmersions-Ionenimplantation eine (Eisen/Chrom)-Nitridschicht auf der Stahloberfläche.

Nach der Behandlung wurden die Oberflächenhärte und das Korrosionsverhalten bestimmt und mit dem Ausgangszustand verglichen. Während sich bei den direkt implantierten Proben nur die Härte leicht erhöhte, nahm bei den durch Plasmaimmersions-Ionenimplantation behandelten Proben die Korrosionsbeständigkeit zu, so dass für den gewünschten Zweck dieses Verfahren das geeignetere ist.

Zwei asynchron rotierende Objekte sollen gemein-sam tomografisch rekonstruiert werden. Dafür werden tomografische Projektionen immer nur dann vorgenommen, wenn beide Objekte eine bestimmte Relativposition zueinander aufweisen. Die Objekte erscheinen dadurch wie fest miteinander verbunden. Vorhandene radiale Symmetrien der Objekte können ausgenutzt werden. Als praktisches Anwendungsbeispiel dient eine hydrodynamische Kupplung.

Bei tomografischen Bildrekonstruktionen können zu große Detektorabstände oder zu wenige Projektionen Aliasing-Artefakte hervorrufen. Betrachtet werden Objekte, die eine drehsymmetrische Struktur enthalten. Von ihr entsteht neben dem reellen auch ein virtuelles tomografisches Abbild. Gezeigt wird, dass es schwierig sein kann, ein solches virtuelles Abbild als Aliasing-Artefakt zu identifizieren.

The improved resolution of potential probe measurements allowed to investigate the turbulent properties of flows driven by various types of alternating magnetic fields. Results will be presented on the turbulent spectra of such flows and the spatio-temporal changes of the mean velocity profiles.

The magnetic control of aluminium investment casting is presented as an example of metallurgical applications of external magnetic fields.

Recent results on separation control with steady and unsteady Lorentz forces will be presented, embedded into the 40 years history of electromagnetic seawater flow control.

The preliminary results of the REDOS project participants for neutron and gamma fluence spectrum integrals obtained for two VVER-440 pressure vessel benchmarks at the LR-0 reactor in Rez have been analyzed. The results of different calculations have been compared with each other and with experiments. The influence of the scintillation detectors on the measurement results was discussed.

The existence of hydrogen in Pd–O-bearing aggregates, which together with iron oxides form the characteristic dark encrustation of an ouro preto nugget of Gongo Soco, Minas Gerais, Brazil, is confirmed by elastic recoil detection analysis with a heavy-ion microbeam (micro-ERDA). Hydrogen is lost from Pd–O-bearing areas during the micro-analyses, but not from goethite.
The data indicate that the Pd–O–H phase is unstable compared to goethite, giving support to previous observations that it is a transient phase in a transformation to native palladium.

The final results of the REDOS project participants for neutron and gamma fluence spectrum integrals obtained for the VVER-1000 pressure vessel benchmark at the LR-0 reactor in Rez had been analyzed. The comparison of different calculations with each other and of calculations with experiments showed in both cases reasonable agreement.

Neutron and gamma fluence results for the VVER-440 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached.

The start-up of the Munich high-flux reactor FRM-II is going on. At the beam tube SR-2 the spectrometer PANDA has been installed. It is a three-axis neutron spectrometer looking onto a slightly under-moderated cold neutron source. For polarization analysis PANDA is equipped with a vertical cryo-magnet producing fields up to 14.5 Tesla at the sample. To get an appropriate shielding of the high-intensity instrument one had to take into account the large cross-section of the primary beam, several restrictions using magnetic materials, limitations in loading the site and, finally, one had to keep the lateral extent of the shielding small to allow for high scattering angles. The shielding has been designed on the base of results which were achieved by the combined use of both the Monte Carlo code MCNP-4B2 and an analytical method based on one-dimensional dose transmission functions.

Neutron and gamma fluence results for the VVER-1000 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached. Additionally, results obtained with different energy group structures were compared.

A new neutron dosimetry benchmark of the NEA SINBAD Data Base is described. This full-scale reactor benchmark, based on VVER-1000 ex-vessel neutron activation measurements performed at the Balakovo NPP, Unit 3 (Balakovo-3), is a result of several years of thorough measurements and calculations. With regard to evaluation of measured and calculated results an international intercomparison study played a key role. This interlaboratory comparison produced the reference measured data expressed as end-of-irradiation activities of reaction products of the reactions: 237Np(n,f), 238U(n,f), 93Nb(n,n'), 58Ni(n,p), 54Fe(n,p), 46Ti(n,p) and 63Cu(n,a). A comprehensive analysis of reactor data used for creating the computational models has been performed. Special attention was paid to the analysis of the reliability of the absolute neutron source distributions. Results of calculations performed by various discrete ordinates and Monte Carlo codes have been used for the benchmark evaluation. It turned out that these calculation results are in agreement within 12 % with the reference measured data. The experience gained by creation and evaluation of the full-scale power reactor benchmark is discussed in the paper.

Ni-Ti thin films (SMA) formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as microvalves, microfluidic pumps and micromanipulators. Successful implementation of Ni-Ti micro-actuactors requires a good understanding of the relationship among processing, microstructure and proprieties of Ni-Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at the ESRF, we carried out a series of experiments that clearly illustrate the benefit of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the Materials Research Hutch (MRH) allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer [1]. This facility allowed us to follow, almost in “real time”, the structural evolution of the deposited thin film as a consequence of changing deposition parameters.

The real-time structural design of magnetron sputtered NiTi SMA (shape memory alloy) thin films is reported. During deposition the phase content was followed in situ by synchrotron x-ray diffraction and controlled by varying the power of co-sputtering NiTi plus Ti for otherwise fixed deposition parameters. This method allows an optimization of the thin film in respect to its functional properties like phase transition temperature or adhesion as well as an understanding of the actual growth process by revealing temporary intermediate growth states (precipitates) and diffusion processes during film growth. The method is neither restricted to the sputter material (NiTi) nor to the controlling parameter (power) chosen, but immediately applicable to a large class of materials as well as general enough for other deposition parameters.