Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The electrical properties of heavily Al doped single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multi-energy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. Ion beam induced crystallization is used to prepare the nanocrystalline SiC layers. The doping levels are chosen around the solid solubility limit of 2x1020 cm-3 in the range from 5x1019 to 1.5x1021 cm-3. The comparison of the results shows that heavily Al doped single crystalline SiC layers have superior conduction properties. The lowest resistivities measured at room temperature are 0.07 Ohm-cm and 0.8 Ohm-cm for the single crystalline and nanocrystalline samples, respectively. Recent results on enhanced Al acceptor activation in nanocrystalline SiC cannot be confirmed. There is an upper limit for the hole concentration in the nanocrystalline samples independent of the Al supersaturation level in the as-implanted state due to outdiffusion of Al in excess to the solid solubility limit during annealing. In contrast to the nanocrystalline SiC layers the as-implanted Al profile in single crystalline material remains stable after annealing even for concentrations above the solid solubility limit. Therefore, in single crystalline material efficient impurity band conduction due to strongly interacting acceptors can be achieved in the range of supersaturation. For lower doping levels impurity band conduction is more effective in nanocrystalline SiC.

Since high-k insulators appear more and more to be preferable to SiO2 in semiconductor technology, Ge is again becoming of increasing interest, since its carrier mobility is higher than that of Si. Atomistic simulations are a powerful tool to investigate atomic-level physics and to get a better understanding of the processes during the technological steps in integrated electronic device manufacturing.
In the present work different interatomic potentials for Ge are evaluated with respect to their accuracy in describing the structure and energetics as well as the migration of point defects. A number of parameterizations of the Stillinger-Weber (SW) potential and one Tersoff type potential were tested.
The formation energies for different configurations of the interstitial are calculated. Also the formation energy of the vacancy and the bond defect are estimated. It can be shown that the extended 110-dumbbell configuration is the interstitial with the lowest formation energy for most SW parameter sets. In the Tersoff case the tetrahedral interstitial shows the lowest formation energy. For the SW-type potentials the vacancy shows a strong inward-distortion, whereas for the Tersoff potential it shows a slight outwards-distortion.
In recent ab-initio calculations the 110 dumbbell has been found to be the most stable interstitial structure. This is in qualitative agreement with the results for most SW parameter sets, although these calculations predict the extended dumbbell configuration as the interstitial with the lowest formation energy. For the SW parameter sets of W. Yu (model B) and Nordlund, the formation energy of this dumbbell is also in qualitative agreement with the ab-initio result. The formation energy of the vacancy obtained with these SW parameter sets is nearly equal to the ab-initio result. The observed inwards relaxation of the atoms around the vacancy is also found by ab-initio calculations. However, the details of the lattice distortion near the vacancy and the interstitial differ from those predicted by ab-initio calculations.
For the reasons mentioned above, the SW parameter sets of Nordlund et al. and W. Yu et al. are selected for migration investigations. In both cases the vacancy mobility strongly dominates interstitial mobility. Some investigations are also performed with the Tersoff potential, where the vacancy shows a very low mobility.
The results are used to estimate the self-diffusion coefficient. With the SW approach it is shown that self-diffusion in Ge is mediated by vacancies. This stands in good agreement with experimental data. However, the calculated migration energy (2.2 eV) is less than the measured value (3.09 eV). With the Tersoff potential an interstitial dominated mechanism is found. Therefore the Tersoff potential cannot be considered useful for a study of point defect and self-diffusion in Ge.

Detailed experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.

Experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process clearly depends on the initial bubble size. Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area.

Electric potential difference probes (PDP) are mostly applied on laboratory scale to measure local velocities in electrically conducting media. Their principle of operation is based on Ohms law. In the absence of electric currents, and provided a proper orthogonal arrangement, the voltage drop measured between the two electrodes is proportional to the fluids velocity. The measuring magnetic field may be applied globally or by a small permanent magnet at the very tip of the Sensor (VIVES--probe). A typical probe as described in the original work has an electrode spacing of 5 mm while using relatively large CoSm magnets. Because the electrodes are usually mounted on the side of the magnet where the field is weaker, the authors were limited to measure velocities down to 1 cm/s at U =1 mV. They specified a sensitivity of 1 mm/s.

Along with progress in analog electronics, results have recently been published by (GELFGAT) who reported on an increased sensitivity of almost an order of magnitude even for a smaller probe. As stated by the the authors, all measurements were conducted at least five times comprising 200 readings, each. From this averaging it becomes obvious that turbulence measurements have not been possible. The subject of this investigation was the flow driven by a rotating magnetic field (RMF), which may be characterised by the aspect ratio and the magnetic Taylor number.

In the present paper, it is described how the applicable range of PDPs regarding sensitivity can be increased further by about two orders of magnitude. An extremely low-noise preamplifier served as a basis of a multistage measuring chain consisting of another two amplifiers and steep
Butterworth filters. For the differential signal processing required for such small voltages as a few nanovolt it was vital to provide a proper common mode rejection throughout the whole instrumental chain. Since acquisition of velocity fluctuations does not allow any averaging or even the use of integrating amplifiers, potential sources of statistical errors had to be avoided. In particular, the electromagnetic noise was countered by a sophisticated wiring scheme. Systematic errors such as thermoelectric currents are detrimental to the measurement of very small mean velocities. Meticulously avoiding both temperature differences and gradients of Seebeck coefficients, it was possible to reduce thermoelectrical voltages below the velocity signal level.

RMF-driven flows comprise a secondary recirculation in the meridional plane. According to theory, the change-over from a Stokes regime to a laminar boundary one of the primary swirl takes place at a Taylor number of approx. 1000, accompanied by a change of the linear scaling (velocity versus Taylor number) to a power 2/3 characteristic. A sensitivity of 0.01 mm/s permitted to safely determine mean velocities for Taylor numbers commencing with 31.

Besides sensitivity and accuracy, measurements of turbulent velocity fluctuations put a severe
restriction on the size of the sensor in order to resolve all scales of potentially significant vortices. The high sensitivity described above was achieved substantially by state of the art analog instrumentation while the dimensions of the probe were quite small. Having an induction
of 75 mT at the tips of the electrodes, their spacing of 1 mm delivered a signal of 180 nV per cm/s, only. Nevertheless, the performance of the measuring chain allowed for the acquisition of
velocity fluctuations even in the transitional regime slightly above the critical Taylor number. The wavenumber spectra calculated via Taylors hypothesis were well resolved up to the end of the inertial range and showed a steep decrease with an exponent less than 4.

We consider the growth of single crystals by the floating-zone method using a radio frequency (RF) heating magnetic field. The quality of the grown crystals, especially of complicated intermetallic compounds, strongly depends on the growth conditions, particularly on the shape of the solidification front. To obtain single crystals of high physical and chemical precision, a convex to the melt growth interface is desirable. The shape of the solid-liquid interface can strongly be influenced by the convective heat transport in the melt. The major mechanism driving the melt flow is the electromagnetic force due to the RF-heating. This force drives a melt flow directed radially inwards at mid-height of the floating zone. Favourable growth conditions, however, would require the flow to be directed away from the solidification front at the axis of symmetry and, respectively, to be directed against it at the free surface of the floating zone. This flow can be generated by an electromagnetic force directed along the free surface towards the solidification front.
We developed the solution of a two-phase stirrer which allows a flexible control of the melt motion. This stirrer basically consists in an additional coil superimposed to the primary induction coil. The additional coil is not connected to any power supply, but it is part of a secondary circuit with adjustable capacitor and resistance. The current in the secondary coil is solely induced by the primary coil. In that way, an electromagnetic pump is created. Its intensity and resulting flow direction can easily be adjusted to the process needs. The flexible system parameter are the location and distance of the secondary coil with respect to the primary one, and the capacitor and resistance of the secondary circuit.
We present numerical and experimental results for the melt flow and temperature fields resulting from the influence of such a two-phase stirrer. Ni-based single crystals as well as various intermetallic compounds have been grown, and the obtained results are discussed in relation to the provided flow control.

Recently various drag reduction techniques were studied numerically and experimentally in many papers. Among others there is the subtopic of magnetohydrodynamic (MHD) drag reduction where the Lorentz force is used for the purpose of drag reduction in an electrically conducting fluid. In many recently published papers permanent magnets and high electric current densities are used in order to achieve reasonable Lorentz forces. This choice, however, immediately leads to a low efficiency.
We consider a plane channel as the flow configuration. Here, the fully developed turbulent channel flow is homogeneous in the streamwise and spanwise directions, thus, periodic boundary conditions can be applied in these directions. This simplifies the numerical solution of the problem significantly. We present the results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by the interaction of a permanent magnetic field and an electric current from electrodes placed on the bottom wall surface. Two various electromagnetic field cases are considered. In the first case an oscillating electric current and a permanent magnetic field create a spanwise oscillating Lorentz force, whereas in the second case a stationary electric current and a permanent magnetic field create a steady streamwise force.
The reason of the low MHD drag reduction efficiency by a spanwise oscillating Lorentz force, as obtained up to now in literature, is explained. The main result of our work is that using a load factor k ~ 1 leads to a significant efficiency improvement for all considered cases. The efficiency increases when the load factor is close to its optimum value. We show that the time oscillating spanwise Lorentz force reduces the skin-friction drag. The full drag is also reduced, the efficiency is increased by 100 times but is still much less than 1. In this case, the skin-friction drag may be strongly reduced at a very small load factor k < 1, but not the full drag.
The application of the streamwise Lorentz force leads to a much more effective drag reduction if we consider the drag as a full force applied to the body. The skin-friction drag increases but the full drag may be reduced to the zero value with a good efficiency.

The Traveling Magnetic Field (TMF) is a versatile tool to control the flow in an electrically conducting fluid. It introduces a mainly axial Lorentz force into the fluid which leads to meridional flow patterns. Applying the TMF to the Vertical Gradient Freeze (VGF) growth of semiconductor single crystals, the heat and mass transport in the melt can be tailored for growth under optimised flow conditions to improve crystal properties and/or growth yield.
In this paper we present experimental and numerical results on the TMF driven flow in an isothermal model fluid as well as in a VGF melt. The field is created by an equally spaced set-up of six coils of 36 windings each. Induction and frequency can be varied between 0-5 mT and 50-400 Hz, respectively.
Model experiments were carried out at about 20°C with the traveling field applied to InGaSn melts in cylindrical, non-conducting vessels of different diameters. Axial velocity profiles were measured by means of the Ultrasonic Doppler Velocimetry (UDV) method. The basic flow was investigated as a function of the aspect ratio and of the non-dimensional forcing and screening parameters with the focus on the transition from laminar to time-dependent convection. For comparison, numerical calculations were performed using advanced, highly accurate spectral methods as well as commercial codes.
For the growth experiments a VGF furnace was equipped with the TMF set-up. The maximum temperature of the furnace is about 1300°C and crystals with a diameter up to three inches can be grown. Ga doped germanium single crystals were grown under the influence of the field and without field. The TMF impact on the thermal field in the melt was studied on the basis of natural or artificially induced dopant striations which characterise the solid-liquid interface and, thus, the local temperature field. The transition to instationary melt flow which is indicated by the appearance of regular striation patterns in the crystal, was investigated by increasing the TMF forcing parameter intentionally during growth. Numerical results came from a quasi-2D simulation of the melt flow using the commercial code CrysVun++. A global, thermal model of the VGF furnace has been developed for this purpose.

Atomistic computer simulations show that the metastable defect structure formed immediately after ion bombardment of silicon does not only consist of isolated mono-vacancies and mono-interstitials but also of more complex defects. Amongst them a small percentage of very mobile di-interstitials is found. The structure and energetics of these defects as well as their migration are investigated in more detail, and the results are compared with literature data. Mobile and immobile di-interstitial configurations are found. The migration mechanism shows a pronounced dependence on the temperature. The di-interstitial diffusivity and the self-diffusion coefficient per defect are calculated. The di-interstitial migrates much faster than the mono-interstitial.
The high mobility of the di-interstitials and the fact that they can be already formed during the ion bombardment may have implications for the current understanding of many experimental results obtained in the last decade, in particular for the explanation of the implantation-induced migration of interstitial-like defects at room temperature.

As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES).

We investigate different kinds of electro-vortex flows generated in a shallow layer of liquid metal. The metal flow is driven by an externally applied electrical current which interacts with its own magnetic field. Due to symmetry this interaction alone causes not yet a flow as the Lorentz force is purely irrotational. If, however, ferromagnetic C-cores or yokes are applied, the magnetic field distribution is modified and a flow driving action results. An electro-vortex flow occurs with several eddies in this MHD-layer. In the stable case, for some range of electrical current values, these eddies are held in permanent position. The unstable case is characterized by an oscillation of the eddies, which are moving in the plane of the layer. One of the reasons to perform this study is related with the occurrence of similar unstable processes in some devices used for metallurgical purposes including the flat MHD-layer considered here. We have investigated this flow by experimental and numerical methods.
We applied the ultrasound Doppler velocimetry which allows us to measure velocity profiles in non-transparent media. The oxide particles of this alloy were acting as good tracers for ultrasound measurements and allowed us to obtain the time-dependences of the velocity profiles. At higher electrical currents, the profiles showed large-scale low-frequency oscillations. Various types of flows are distinguished depending on the location of the ferromagnetic C-core.
The mathematical model of the processes was based on the MHD-equations, which have been modified using a thin-layer approximation. The numerical calculations support the results obtained in experiments, and showed the behavior of the velocity field with the moving of the eddies.

The production of K+ and of K- mesons in heavy-ion collisions at beam energies of 1 to 2 A GeV has systematically been investigated with the kaon spectrometer KaoS. The ratio of the K+ production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. A comprehensive study of the K+ and of the K- emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K-/K+ ratio is found to be nearly constant as a function of the collision centrality and can be explained by the dominance of strangeness exchange. On the other hand, the spectral slopes and the polar emission patterns are different for K- and for K+. Furthermore the azimuthal distribution of the particle emission has been investigated. K+ mesons and pions are emitted preferentially perpendicular to the reaction plane as well in Au+Au as in Ni+Ni collisions. In contrast for K- mesons in Ni+Ni reactions an in-plane flow was observed for the first time at these incident energies.

The prenyl group is known as an important structural building block in natural and medicinal products. The isotopic substitution of one of the two methyl groups with a [11C]methyl group would provide an access to a large number of interesting 11C-labelled compounds. Here we report a strategy for the synthesis of 11C-labelled prenyl group-containing derivatives starting from methyl-substituted alkynes (1) via a novel 11C-C bond forming reaction. A commonly employed strategy to form a,a’-disubstituted alkenes comprises the formation of alkenylzirconocenes by the syn-insertion of a C-C triple bond into the Zr-H bond of Schwartz reagent [Cp2Zr(H)Cl] followed by metal-mediated C-C bond formation with electrophiles under retention of the configuration of the C-C douple bond [1,2].
In principle the formation of alkenylzirconocenes by syn-addition of Schwartz reagent onto disubstituted alkynes (1) leads to a mixture of regioisomers 2 and 2’. However, treatment of an excess of Schwartz reagent favors the formation of the sterically less hindered isomer 2. Transmetalation with transition metal complexes M(PPh3)4 and conversion with [11C]MeI leads to compound 4.

The fluoroethyl ester-containing phenyltropane derivative MCL-322 was shown to display high affinity to the dopamine transporter (DAT) (Ki = 2.3 nM). The binding affinities (Ki values) for the serotonin transporter and norepinephrine transporter were determined to be 5.1 nM and 280 nM, respectively [1]. The high binding affinities and selectivities of MCL-322 make the corresponding 18F-labelled compound an attractive PET radioligand for imaging DAT in brain tissue. Here, we report on the radiosynthesis of [18F]MCL-322 and its radiopharmacological characterization involving biodistribution, autoradiography and small animal PET studies.

An increasing number of PET centers is using 6-[18F]fluoro-L-DOPA ([18F]FDOPA) to study presynaptic dopamine metabolism in vivo.
Currently the electrophilic radiofluoro-destannylation reaction of N-Boc-3,4-di(Boc-O)-6-trimethylstannyl-L-phenylalanine ethyl ester with [18F]F2 has emerged as the preparation method of choice for the reliable and reproducible radiosynthesis of [18F]FDOPA (1-5).
Up to now the radiofluorination step of the trimethyltin precursor is carried out in trichlorofluoromethan (CFCl3, Freon 11) as the solvent. De Vries et al. (4) have reported Freon 11 as the superior solvent to provide the highest radiochemical yields for the radiofluorination step. The authors also have investigated the possibility to substitute Freon 11 with other solvents. They observed considerable losses of radioactivity (61-71%) during the evaporation step of the solvents (e.g. chloroform and acetonitrile). They discussed this finding with the formation of volatile radiofluorine compounds originating from the reaction of [18F]F2 gas with the solvents.
For Freon 11 is hardly available in Europe for environmental protection reasons, we investigated the possibility of substituting Freon 11 with chloroform. In contrast to (4) we use 5 M HCl for protecting group hydrolysis. The acid is added directly after the radiofluorination step and the solvent was evaporated at 130°C. First results with chloroform also show increased losses of radioactivity in comparison to Freon 11. However, we found that the rate of radioactivity loss depends on the quality of the chloroform used. The radioactivity losses using chloroform stabilised with ethanol were in the range of 25%, whereas the amylene stabilised chloroform gave losses of 40%. In contrast, using deuterated chloroform (CDCl3) for NMR analysis purposes stabilised with silver no significant losses of radioactivity were observed in comparison with Freon 11. We conclude that no competitive radiofluorination of the solvent chloroform, neither CHCl3 nor CDCl3, with [18F]F2 occures. Instead of that the observed radioactivity losses can be explained by the radiofluorination of stabilisers present in CHCl3.The non-decay-corrected total yield for [18F]FDOPA preparation using Freon 11 as the solvent is 17% (n = 26). Using CDCl3 (silver stabilised) instead of CFCl3 the average non-decay-corrected total yield is slightly higher, being 20% (n = 17).
The use of CDCl3 has further advantages:

• easy handling (boiling point = 61°C) and unlimited availability,
• better environmental protection properties,
• the radiofluoro-destannylation reaction can be carried out at temperatures above freezing-point

AIMS: Corticosteroids are implicated in neuropsychiatric disorders such as severe depression and anxiety. This work investigates the usefulness of nonsteroidal glucocorticoid receptor (GR) ligand [11C]AL-438 as PET ligand for imaging of brain GRs.
METHODS: [11C]AL-438 was synthesised by methylation of the corresponding O-desmethyl labelling precursor with [11C]MeI. Radiopharmacological characterisation of [11C]AL-438 was performed in Wistar rats using biodistribution studies, ex vivo autoradiography and small animal PET studies.
RESULTS: [11C]MeI was trapped in a DMF solution containing the O-desmethyl labelling precursor and NaOH as the base. The methylation reaction was accomplished within 5 min at 100°C. The total synthesis time including HPLC-purification was 40-45 min. [11C]AL-438 was obtained in radiochemical yields of 30-40% (decay-corrected) at a specific radioactivity of 15 to 20 GBq/µmol at the end of the synthesis. The radiochemical purity of [11C]AL-438 exceeded 98%.
Biodistribution studies in rats demonstrated a brain uptake of 1.6 ± 0.4% ID/g after 5 min p.i., which decreased to 0.6 ± 0.1% ID/g after 60 min. Brain to blood ratios at 5 min and 60 min p.i. were 3.0 and 1.0, respectively. The pituitary and adrenals as major GR-containing peripheral organs showed uptake of 2.4 ± 0.5% ID/g and 7.5 ± 1.5% ID/g after 5 min and of 1.8 ± 1.0% ID/g and 3.8 ± 0.6% ID/g after 60 min, respectively. The uptake in the pituitary and adrenals could not be reduced significantly by pretreatment with 10 mg/kg of corticosterone.
Ex vivo autoradiographic studies of [11C]AL-438 on rat brain 5 min after i.v. administration showed specific accumulation of radioactivity in regions rich of GR, such as hypothalamus and various nuclei of thalamus. CONCLUSION: The biodistribution and the brain autoradiographic data of [11C]AL-438 correlated with the expected pattern of GRs in rodents.

The defect structure of Ge-implanted and annealed silicon was investigated. Based on the observation of both, interstitial- and vacancy-type defects, a stacked structure of layers of vacancy and interstitial clusters was detected. These defects form a substructure within the basic dual structure consisting of a vacancy-dominated and an interstitial-dominated region. The appearance of cavities (vacancy clusters) in the interstitial-dominated region indicates significant vacancy–vacancy clustering beside the vacancy–interstitial recombination. Clustering of vacancies and interstitials prevents the vacancy–interstitial recombination. The observed defect structure is in contrast to the widely accepted +1 model which predicts the complete recombination of ion-generated vacancies and interstitials. The limits of the +1 model are discussed.

Postulating an unlikely core melt down accident for a light water reactor (LWR), the possible failure mode of the reactor pressure vessel (RPV) and its failure time have to be investigated for a determination of the load conditions for subsequent containment analyses. Worldwide several experiments have been performed in this field accompanied with material properties evaluation, theoretical, and numerical work.
At the Institute of Safety Research of the FZR a finite element model (FEM) has been devel-oped simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool.
The model was applied to pre- and post test calculations for the FOREVER test series repre-senting the lower head RPV of a pressurized water reactor (PWR) in the geometrical scale of 1:10. These experiments were performed at the Royal Institute of Technology in Stockholm. In this paper the differences between the results of a simple coupled and a recursive coupled FE-simulation are highlighted. Due to the thermal expansion at the beginning and the accu-mulating creep strain later on the shape of the melt pool and of the vessel wall are changing. Despite of the fact that these relative small geometrical changes take place relatively slowly over time, the effect on the temperature field is rather significant concerning the mechanical material behavior and the resulting failure time. Assuming the same loading conditions, the change in the predicted failure time between the simple and the recursive coupled model is in the order of magnitude of the total failure time of the simple model. The comparison with results from the FOREVER-experiments shows that the recursive coupled model is closer to reality than the one-way coupled model.

La polución de aguas por metales pesados es un serio problema ambiental, siendo las principales fuentes de esta contaminación las aguas procedentes de industrias metalúrgicas y mineras. A diferencia de otros contaminantes, una característica preocupante de los metales pesados es la tendencia a persistir indefinidamente en el ambiente, circulando a través de la cadena trófica y acumulándose eventualmente en los organismos superiores.

La búsqueda de soluciones a este tipo de problemas ha hecho que en las dos últimas décadas se haya incrementado notablemente la investigación en relación al potencial biotecnológico de los microorganismos para su eliminación, teniendo en cuenta la capacidad de la biomasa microbiana para concentrarlos y removerlos. Para el tratamiento de aguas dulces se ha ensayado biomasa procedente de bacterias, hongos y algas. No obstante, para el de aguas marinas, si bien hay abundante bibliografía sobre la utilización de algas, apenas hay referencias sobre la utilización de bacterias, por lo que ha parecido de interés realizar una investigación sobre la capacidad de bioadsorción de metales pesados por una cepa bacteriana marina.

Esta comunicación presenta los resultados preliminares obtenidos trabajando con una bacteria aislada de aguas someras del Mar de Alborán, denominada MAH1. Esta cepa bacteriana que crece bien en medios de cultivo comunes y produce abundante cantidad de EPS, presenta la capacidad de desarrollarse en un rango de temperaturas de 2 a 47ºC y a concentraciones de NaCl de 0,6 a 20%. Los ensayos realizados con ella han tenido una doble finalidad: probar, en condiciones estándar, la capacidad de bioadsorción de cromo, plomo, lantano, cobalto, níquel y manganeso y determinar, mediante obresvación con microcopio electronico de transmisión, la localización celular de los metales bioadsorbidos. Los ensayos de bioadsorción se han realizado con biomasa húmeda obtenida en fase exponencial de crecimiento y con soluciones de los metales a concentración 0,5 mM en agua mili- Q y pH 4,5. Los resultados obtenidos indican una buena adsorcion para el cromo y para el plomo (0,91 y 0,78 mmol/gr de biomasa seca, respectivamente), y menor para el resto de los metales ensayados (lantano 0,08 mmol/gr; cobalto 0,1 mmol/gr; manganeso 0,063 mmol/gr y níquel 0,14 mmol/gr). La localización celular de los metales bioadsorbidos ha sido: Pb y Cr, en la pared celular, La en el EPS y los restantes, intracelularmente.

Estos resultados indican que se trata de una bacteria que puede ser buen candidato para desarrollar sistemas de tratamiento de aguas marinas contaminadas por metales pesados, más aún si se tiene en cuenta que son preliminares y que no se han optimizado las condiciones para la bioadsorción de cada metal.

Unusual, S-layer-like gene carrying, mobile elements were localized on the chromosomes of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 and of the closely related strain Bacillus sphaericus NCTC 9602 in the vicinity of the functional S-layer genes. Each of the two almost identical elements designated ISBsph1 (strain 9602) and ISBsph2 (strain JG-A12) possess four ORFs which encode a putative integrase /recombinase, a putative XRE-family like protein containing a DNA binding helix turn helix motif, and a S-layer-like gene copy. Interestingly, the S-layer-like gene copies of the two IS elements are analogous to the coding parts of the previously described plasmid-located, identical between each other, and siltent S-layer genes of the two strains. In the case of the strain JG-A12, however, the ISBsph2 borne s-layer-like gene is truncated.
Comparative analyses of the functional, of the plasmid-located, and of the IS-element-specific S-layer genes of the above mentioned two strains between each other and with the S-layer genes of the other Bacillus sphaericus strains studied up to date revealed that all functional S-layer genes possess mosaic structure and share regions with very high identitiy which are surrounded by regions possessing very low or almost no identity.
Our results strongly suggest that the functional S-layer protein genes in Bacillus sphaericus have evolved via horizontal transfer of genetic information followed by rearrangements which were mediated by mobile elements.
The primary structure of the functional S-layer of the uranium mining waste isolage JG-A12 and in particular its higher capability in comparison to the other S-layers to bind uranium and other metals indicate that the environmental stress factors played an important role in the evolution of its gene.

Interactions of U(VI) with the indigenous bacterial and archael communities of the uranium mining waste pile Johanngeorgestadt in Germany were studied. For this several portions of one sample with a natural content of 40 mg U/kg were supplemented with 60 mg U/kg and 260 mg U/kg in form of uranyl nitrate. Part of the most contaminated portion was additionally incubated under anaerobic conditions. Bothe, selective sequential extraction (SSE) and X-ray absorption spectroscopic analyses, indicated that added U(VI) was bound as uranyl by inner-sphere sorption complexes. No reduction of U(VI) to U(IV) was observed even by the anaerobic treatment.
Analyses of the constructed 16S rRNA gene clone libraries of the untreated and of the U(VI)-supplemented samples revealed changes in the bacterial and in the archaeal parts of the natural microbial community. In the untreated sample the bacterial community was predominated by Alphaproteobacteria and Holophaga/Acidobacterium members. The number of the latter was strongly reduced by increasing the uranium content up to 100 mg U/kg. Instead, a large number of sequences were found representing Gamma-Pseudomonas spp., Arthrobacter ssp. (Actinobacteria) as well as Geobacter spp. (Deltaproteobacteria). The most contaminated portion containing approximately 300 mg U/kg was predominated by represenatives of Cytophaga/Flavobacterium/Bacteroides group. The anaerobic treatment of this sample induced also proliferation of Alpha- and Gammaproteobacteria in it.
The archaeal populations in the original waste sample were rather diverse, whereas the supplemented with U samples wee strongly predominated by a few particular Grenarchaeota species.
Our results indicate that the addition of U(VI) to a low contaminated uranium mining waste sample induces significant shifting in the indigenous microbial populations in dependence on the amount of U(VI) and the redox conditions.

It could be shown that dendritic compounds show the same complex stoichiometry in non-water and water soluble forms. The stability constants in both solution sytems are comparable. As a consequence this demonstrates the possible use of such compounds in for complexation of metal ions aquatic systems.
As the fluorescence decay times change with the concentration of the added metal ion two effects have to be discussed: Dynamic fluorescence quenching, excited state reactions of the ligand. In case of dynamic fluorescence quenching a linear relationship between the concentration of the quencher and the ratio of the fluorescence decay time without and with quencher should be observed.

Summary

During the past decade many studies on speciation of actinides in natural and artificial environments have been done. High demands on the sensitivity in speciation of actinides lead to the development of advanced detection methods. This is connected with intensive use of laser systems as excitation source. Laser can provide any wavelength from the near UV to the NIR (Near Infrared) wavelength range. The development of tunable solid-state lasers overcame some disadvantages of dye laser systems. The application of low temperatures for samples measured with fluorescence spectroscopic methods brought effort in the detection of carbonate species. The availability of modern femtosecond laser systems in combination with ICCD (Intensified Charge Coupled Device) cameras gave the possibility to exploit the fluorescence properties of aromatic organic compounds for the study of their interaction with actinides, especially non-fluorescent metal ions.
The fluorescence of some tetravalent actinides as Pa(IV) and U(IV) in aquatic systems was described firstly. The speciation of actinides in arsenate and several carbonate systems was investigated. The interaction with ligands from life sciences as ATP (adenosine triphosphate) and sugar phosphates became more and more important. Also studies of the speciation of actinides in plants and microorganism cannot be neglected.
In the solid state the speciation of uranium(VI) in several natural and synthetic minerals has been studied as well as the behaviour of depleted uranium in the environment. The interaction of actinides with rock materials and minerals as well as their uptake is also of common interest in actinide chemistry. Especially the sorption and inclusion of Cm into several minerals lead to an improvement in knowledge of minor components in solids.
It is not possible to give a complete overview on the literature about the laser-induced spectroscopy of actinides. The restricted length of this contribution allows only a relatively small and personally influenced selection.

Carbon (C) and carbon nitride (CNx) films were grown on Si(100) substrates by direct ion beam sputtering (IBS) of a carbon target at different substrate temperatures (RT-450°C) and Ar/N2 sputtering gas mixtures. Additionally, the effect of concurrent nitrogen ion assistance during the growth of CNx films by IBS was also investigated. The samples were analyzed by elastic recoil detection analysis (ERDA) and x-ray near edge absorption spectroscopy (XANES). ERDA results showed that significant nitrogen amount (up to 20 at. %) was incorporated in the films, without any other nitrogen source but the N2-containing sputtering gas. The nitrogen concentration is proportional to the N2 content in the sputtering beam and no saturation limit is reached under the present working conditions. The film areal density derived from ERDA revealed a decrease in the amount of deposited material at increasing the growth temperature, with a correlation between the C and N losses. XANES results indicate that N atoms are efficiently incorporated into the carbon network and can be found in different bonding environments, such as pyridine-like, nitrile-like, graphite-like, and embedded N2 molecules. The contribution of molecular and pyridine-like nitrogen decreases when the temperature increases while the contribution of the nitrile-like nitrogen increases. The concurrent nitrogen ion assistance resulted in the significant increase of the nitrogen content in the film but it induced a further reduction of the deposited material. Additionally, the assisting ions inhibited the formation of the nitrile-like configurations while promoting nitrogen environments in graphite-like positions. The nitrogen incorporation and release mechanisms are discussed in terms of film growth precursors, ion bombardment effects and chemical sputtering.

We determined structural parameters for the near-neighbor surrounding of plutonium(III) in complexes with humic and fulvic acids at pH 1 and for the purpose of comparison also for the plutonium(III) aquo ion by means of X-ray absorption fine structure (XAFS) spectroscopy. It could be shown that in the complexes with humic substances as well as in the Pu3+ aquo ion sample the trivalent oxidation state of plutonium was stable within the time of the experiment. In the humate and fulvate complexes, the plutonium(III) is surrounded by about 8 oxygen atoms with an average Pu-O distance of 2.48 ± 0.02 Å. The structural parameters determined for plutonium(III) humate and fulvate complexes were compared to structural parameters of plutonium(III) and plutonium(IV) aquo ions given in the literature.

Azimuthal distributions of pi+, K+ and K- mesons have been measured in Au+Au reactions at 1.5 AGeV and Ni+Ni reactions at 1.93 AGeV. In semi-central collisions at midrapidity, pi+ and K+ mesons are emitted preferentially perpendicular to the reaction plane in both collision systems. In contrast for K- mesons in Ni+Ni reactions an in-plane elliptic flow was observed for the first time at these incident energies.

500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a correction factor of 0.8 in the electronic stopping power of 4He+ ions along <0001> channel. Full-cascade Crystal-TRIM simulations with the same set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.

This study evaluates chemical trends of seven acidified reservoirs and 22 tributaries in the Erzgebirge from 1993 to 2003. About 85% of these waters showed significantly (p < 0.05) declining concentrations of protons (−69%), nitrate (−41%), sulfate (−27%), and reactive aluminum (−50% on average). This reversal is attributed to the intense reduction of industrial SO2 and NOx emissions from formerly high levels, which declined by 99% and 82% in the German–Czech border region between 1993 and 1999. The deposition rates of protons and sulfur decreased by 70–90%. Since 1993, the dry deposition of total inorganic nitrogen diminished to a minor degree, but the wet deposition remained unchanged. The surface waters reflect a substantial decrease in Al exchange processes, a release of sulfur previously stored in soils, and an uptake of nitrate by forest vegetation. The latter effect may be supported by soil protection liming which contributed to the chemical reversal in almost 20% of the study waters.

The IR, green, and UV electroluminescence from rare-earth (Er, Tb, and Gd) implanted SiO2 MOS devices is studied, exhibiting quantum efficiencies comparable to III-V light emitting diodes.

Different methods of defect engineering are applied in this study for ion beam synthesis of a buried layer of SiC and SiO2 in Si. The initial state of phase formation is investigated by implantation of relatively low ion fluences. He-induced cavities and Si ion implantation generated excess vacancies are intentionally introduced in the Si substrate in order to act as trapping centers for C and O atoms and to accommodate volume expansion due to SiC and SiO2 phase formation. Especially the simultaneous dual implantation is shown to be an effective method to achieve better results from ion beam synthesis at implantation temperatures above 400oC. For SiC synthesis it is the only successful way to introduce vacancy defects. The “in situ” generation of vacancies during implantation increases the amount of SiC nanoclusters and improves crystal quality of Si in the case of SiO2 synthesis. Also the pre-deposition of He-induced cavities is clearly advantageous for the formation of a narrow SiO2 layer. Moreover, in-diffusion of O by surface oxidation can substitute a certain fraction of the O ion fluence necessary to obtain a buried homogeneous SiO2 layer.
The results show that defect engineering for SiC and SiO2 synthesis is working. However, the implementation of a single action is not sufficient to achieve a significant improvement of ion beam synthesis. Only an optimized combination of the different versions of defect engineering can bring about pronounced better results.

Die „Nanopartikel-Zell-Chirurgie“ unter Ausnutzung der Partikelstrahlung von Radionukliden trägt ein großes Potential für die adjuvante Krebstherapie in sich, sofern es gelingt, das entsprechende Radiotherapeutikum im Tumor selektiv zu deponieren und dort eine letale Strahlendosis unter weitgehender Schonung gesunden Gewebes zu erreichen, so dass die Zelle in ihrer Gesamtheit untergeht. In diesem Zusammenhang gewinnen magnetische Kern/Hüll-Nanoteilchen an Bedeutung. Durch zielgerichtete Modifizierung können auf der Oberfläche von magnetischen Ferrit-Nanoteilchen spezielle Haftgruppen zur stabilen Fixierung von Radionukliden angebracht werden. Diese radioaktiv markierten Nanoteilchen können dann durch geeignete Magnetfelder an Tumoren fixiert werden. Bedeutendes Zukunftspotential ist außerdem im zusätzlichen, selektiven Targeting der radioaktiv markierten, magnetischen Nanoteilchen durch Einführung von zielsuchenden Strukturen - wie Antikörper oder spezifische Peptide - in die Hülle der Nanopartikel gegeben.
Für erste Untersuchungen zur radioaktiven Markierung wurden Magnetit-Teilchen mit einem mittleren Kerndurchmesser von 10 nm ausgewählt, die eine DMSA-Hüllschicht tragen. DMSA bildet mit Technetium(V) und Rhenium(V) sehr stabile Komplexe, die eine quadratisch-pyramidale Koordinationsgeometrie aufweisen (s. Abb. 1).
Die Markierung von DMSA mit den therapeutisch relevanten Radionukliden ¹⁸⁶Re und ¹⁸⁸Re liefert die entsprechenden radioaktiven Komplexe in hoher Ausbeute, wobei in der Regel bei Temperaturen von 100°C gearbeitet wird. Für die eingesetzten DMSA-umhüllten magnetischen Nanoteilchen konnten bei Raumtemperatur Markierungs-ausbeuten bis zu 70% für das Generatornuklid ¹⁸⁸Re erzielt werden, wobei das Radionuklid mindestens 24 h stabil an diesen Teilchen gebunden bleibt.

An easy and gentle method for the preparation of ¹⁸⁸Re(V) complexes with bidentate and tetradentate ligands is described starting from the precursor complex ¹⁸⁸Re(III)-EDTA. That complex is prepared at room temperature in acidic solution and reacts by a combined re-oxidation/ligand exchange reaction with appropriate ligands like DMSA or ECD (DMSA = dimercapto succinic acid, ECD = L,L-ethylene dicysteine diethyl ester) or en and cyclam (en = ethylene diamine, cyclam = 1,4,8,11-tetraazacyclotetradecane) to the ¹⁸⁸Re(V)-oxo- and dioxocomplexes, respectively. The chelates were unambiguously identified by chromatographic comparison with spectroscopically characterised samples or known ^99mTc-kit reconstitutions. The reaction succeeds under mild conditions (room temperature, short time, neutral or weak basic solutions) with high yields and has potential for labelling of sensitive biomolecules with ¹⁸⁸Re.

Abstract is not available.

The aim of this work is to optimize the metal/silicon ratio on nickel metal induced crystallization of silicon. For this purpose amorphous silicon layers with 80, 125 and 220 nm thick were used on the top of which 0.5 nm of Ni was deposited and annealed during the required time to full crystallize the a-Si. The data show that the 80 nm a-Si layer reaches a crystalline fraction of 95.7% (as detected by spectroscopic ellipsometry) after annealed for only 2 hours. No significant structural improvement is detected by ellipsometry neither by XRD when annealing the films for longer times. However, on 125 nm thick samples, after annealing for 2 hours the crystalline fraction is only 59.7%, reaching a similar value to the one with 80 nm only after 5 hours, with a crystalline fraction of 92.2%. Here again no significant improvements were achieved by using longer annealing times. Finally, the 220 nm thick a-Si sample is completely crystallized only after 10 hours annealing. These data clear suggest that the crystallization of thicker a-Si layers requires thicker Ni films to be effective for short annealing times. A direct dependence of the crystallization time on the metal/silicon ratio was observed and estimated.

The strain Bacillus sphaericus JG-A12, isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from uranium waste waters. The cells of this strain are enveloped by a surface layer protein (S-layer). The highly regular structure of this S-layer with many pores of identical size offers good binding sites for different kinds of molecules and provides nucleation sites for the formation of metal nanoclusters or minerals. In this study we demonstrate that B. sphaericus JG-A12 cells and their purified S-layer protein were capable to reduce Au to metallic nanoclusters in the presence of reducing agents such as molecular H2. The gold nanoparticles were regularly distributed and sized according to the pores of the protein lattice. The metallic nature of the clusters was confirmed by different techniques such as extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray absorption near edge (XANES) spectroscopy, UV-vis spectroscopy and X-ray powder diffraction (XRD). The size of the gold nanoparticles was estimated to be almost 1 nm. Our results demonstrate that B. sphaericus JG-A12 can be used to prepare gold nanoparticles tailor-made for industrial applications

Der Prozess des natürlichen Grubenholzabbaus in gefluteten Bergwerken führt zu stark reduzierenden Bedingungen im Grubenwasser. Dies hat Konsequenzen für Kontaminanten im Flutungswasser. Insbesondere gelöstes Uran und Arsen könnten reduktiv ausgeschieden werden. Um die künftigen Redoxbedingungen im Grubenwasser zu charakterisieren, wurde das Wasser eines Hochmoors im Erzgebirge in dieser Hinsicht als nahezu gleich gearteter Fall untersucht. Das Redoxpotential im Moorwasser, gemessen mit einer Platinelektrode, sank von der Oberfläche bis in einen Meter Tiefe von etwa 600 mV auf -100 mV. Aus der Tiefenwasseranalyse und der Untersuchung des Sumpfgases, das aus dem Moorgrund extrahiert wurde, errechnete sich ein Redoxpotential von -119  5 mV. Charakteristisch für das stark reduzierende Milieu ist das Auftreten von Methan und Schwefelwasserstoff im Sumpfgas. Aus der Kenntnis dieses Zustands kann für die künftige Situation in der gefluteten Grube hergeleitet werden, dass Uran(VI) und Arsen(V) im Laufe der Zeit reduziert werden und als Uran(IV)-hydroxid und Arsen(III)-sulfid ausgeschieden werden. Durch diesen natürlichen Reinigungsprozess wird die Gefahr der Ausbreitung im unterirdischen Wasserleiter, der als Reservoir für die Trinkwasserversorgung dient, gebannt. Das Hochmoor kann in diesem Sinne als natürliches Analogon zur gefluteten Grube betrachtet werden.

The transition from the application of conservative models to the use of best-estimate models raises the question about the uncertainty of the obtained results. This question becomes especially important, if the best-estimate models should be used for safety analyses in the field of nuclear engineering. Different methodologies were developed to assess the uncertainty of the calculation results of computer simulation codes. One of them is the methodology developed by Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) which uses the statistical code package SUSA. In the past, this methodology was applied to the calculation results of the advanced thermal hydraulic system code ATHLET. In the frame of the recently finished EU FP5 funded research project VALCO, that methodology was extended and successfully applied to different coupled code systems, including the uncertainty analysis for neutronics. These code systems consist of a thermal hydraulic system code and a 3D neutron kinetic core model. Six different working groups applying different coupled code systems performed calculations. The involved system codes were ATHLET and SMABRE. They were used for the calculations together with the 3D neutron kinetic core models DYN3D, KIKO3D, BIPR8 and HEXTRAN.
Two real transients at NPPs with VVER-type reactors documented within the VALCO project were selected for analyses. One was the load drop of one of two turbines to house load level at the Loviisa-1 NPP (VVER-440), the second was a test with the switching-off of one of two main feed water pumps at the VVER-1000 Balakovo-4 NPP. Based on the relevant physical processes in both transients, lists of possible sources of uncertainties were compiled. They are specific for the two transients. Besides control parameters like control rod movement and thermal hydraulic parameters like secondary side pressure, mass flow rates, pressurizer sprayer and heater performance, different neutron kinetic parameters were included into the list of possible sources of uncertainties. These are the burn-up state of the core, the control rod efficiency for different control rod groups and the coefficients for Doppler and moderator density feed back. By use of the SUSA package, sets of input data with statistical variation of the relevant parameter values were generated for a large number of runs of the coupled codes for each transient.
Time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. First of all, these are the core power, upper plenum pressure, core outlet and loop temperatures. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations. This list gives indications for further model improvements and code developments.

The role of the lift force for the stability of a homogeneous bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Non-uniform liquid velocity fields may be induced, if the gas fraction is not equally distributed, e.g. caused by local disturbances. For regions with locally increased gas volume fraction the liquid is accelerated in upwards direction and following a gradient of the liquid velocity occurs. This causes a lateral redistribution of the gas bubbles. Depending on the sign of the lift force coefficient this can act to smooth the spatial bubble distribution or to increase the initial disturbances. It is obvious, that a positive lift coefficient stabilizes the flow, while a negative coefficient leads to unstable gas fraction distributions, and thus it favours the appearance of a heterogeneous bubble column regime. According to the well know correlation obtained by Tomiyama, the lift force coefficient is positive for small bubbles (for air-water at ambient conditions for bubbles with an equivalent diameter < 5.8 mm) and change to negative values for large bubbles. Thus this mechanism may be a possible explanation for the experimentally observed ‘pure heterogeneous’ regime, which occurs when large bubbles are injected. In this case the bubble column is heterogeneous also for small gas volume flow rates.
The above mentioned is feedback mechanism is studied by the means of a linear stability analysis. In addition to the lift force, the turbulent dispersion force is considered, which has always a stabilizing effect, i.e. it partially compensates the destabilisation induced by a negative lift coefficient. The stability analysis for a mono-dispersed system nevertheless showed, that influence of the lift force is much larger, compared to the influence of the turbulent dispersion force, if only bubble induced turbulence is considered. Thus the stability condition is practically the positive sign of the lift force coefficient. The analysis was then extended to two bubbles classes - one being small enough to have a positive lift force coefficient, the other being large enough to have a negative coefficient. The result of the analysis is a condition for the minimum fraction of small bubbles needed for stability. Finally a generalized criterion for N bubble classes and for a continuous bubble size distribution is given.

It could be shown that both, the introduction of a melt stop layer in any depth behind the Si / SiC interface and the installation of a surface layer, decreasing the silicon melting temperature, are usefull methods to homogenize the melting depth in the bulk silicon.

It could be shown that both, the introduction of a melt stop layer in any depth behind the Si / SiC interface and the installation of a surface layer, decreasing the silicon melting temperature, are usefull methods to homogenize the melting depth in the bulk silicon.

Diese Arbeit ist Teil unserer Bemühungen, Chelatbildner zur stabilen und unkomplizierten Bindung von Rhenium-188 an biologische interessante Strukturen zu entwickeln. Aufgrund der hohen in vivo Stabilität von [¹⁸⁸ReO(DMSA)₂]^- (1) soll dieses Koordinationssystem zum Design von neuen ¹⁸⁸ReO(V) Chelaten, die bezüglich Reoxidation zu Perrhenat und Ligandenaustausch unter allen Bedingungen radiopharmazeutischer Anwendungen stabil sind, ausgenutzt werden. Dieser neuartige Typ tetradentater Liganden wurde durch Überbrückung zweier DMSA-Moleküle mittels einer Alkylentriaminkette dargestellt. Durch Ligandenaustauschreaktionen von NBu₄[ReOCl₄] in Methanol liefert der stereoisomere Tetrathiolato-S₄-Ligand 1 die fünffach koordinierten Oxo-Rhenium(V) Komplexe 2 (exo-cis) und 3 (exo-trans). Ohne Zusatz von Base werden die Verbindungen als Betain, [ReO(S₄)], isoliert. Der protonierte Stickstoff der Brücke dient als internes Gegenion. Röntgenstrukturbestimmungen bieder Isomeren zeigen die quadratisch pyramidale Koordinationsgeometrie des ReOS₄. Die Orientierung des Metall-oxo core ist exo bezüglich der Carbamidgruppen in beiden Isomeren.
Der aktivierte BFC 4 ermöglicht die Kupplung an terminale Aminogruppen von Biomolekülen. Nichtradioaktive Modelladukte mit Tripeptiden wurden mittels Electrospray Massenspektrometrie identifiziert. Die Re-188-Markierungen verlaufen schnell, in guten Ausbeuten und unter milden Bedingungen. Daher bieten diese neuartigen ReOS₄-Komplexe einen weiteren Zugang zu stabilen Rhenium-188-Radiotherapeutika.

A mass separated focused ion beam (FIB) is a very useful tool to fabricate nanostructures by writing implantation within an ion beam synthesis process. In these investigations the IMSA-OrsayPhysics FIB, equipped with a Co36Nd64 alloy liquid metal ion source, was applied. Si(100) and (111) wafers were implanted with 60 keV Co++ ions in the dose range of 2E16 to 2E17 cm-2. Implantation parameters were investigated, like pixel dwell time, relaxation time (time between two cycles), dose rate as well as the pixel overlapping factor. The subsequent annealing was done in a two step process, namely 600°C for 60 minutes and 1000°C for 30 minutes in a N2 ambient. The results obtained by SEM investigations in terms of continuous nanowire structures following the <110> direction and interrupted CoSi2 pattern in the <100> direction show a clear dependence on the time scale as well as the scanning mode of the irradiation. Structure sizes as small as 10 nm are demonstrated. The formation of CoSi2 nanostructures is explained by precipitation, Ostwald ripening and coarsening leading to a shrinking of the initial implanted profile.

Gegenstand des Vortrags sind der aktuelle Stand der Wissenschaft und Technik, eigene Vorarbeiten sowie die Darlegung einer Projektskizze zur Modellierung der bestrahlungsinduzierten Schädigung von RDB-Stählen.

There is experimental evidence for the formation of stable nm-sized vacancy clusters (VC) in low-copper iron alloys irradiated with fast neutrons under in-service conditions of reactor pressure vessels (RPVs) (BÖHMERT et al. 2001, CUMBLIDGE et al. 2003). Modelling of the evolution of VCs in pure iron under neutron irradiation is both of fundamental interest and of practical importance, because vacancies and VCs (even if not present after long-term irradiation) may play an intermediary role in the formation of Cu-rich clusters in RPV steels resulting in an irradiation-induced degradation of mechanical properties. In the present investigation we apply rate theory (RT) to simulate the evolution of VCs in pure bcc iron. Similar work was reported by ODETTE (1998) and HARDOUIN DUPARC et al. (2002). ODETTE (1998) directly solved the master equation with clustering of self-interstitial atoms (SIAs) neglected. HARDOUIN DUPARC et al. (2002) considered both planar SIA clusters and planar VCs and transformed the master equation into a Fokker-Planck equation, which may be a problem at small cluster sizes. The objective of the present investigation is to introduce the effect of lattice relaxation into the framework of ODETTE’s approach. The model can be adjusted in such a way that both volume fraction and mean size of irradiation-induced vacancy clusters measured by means of SANS are reproduced. The values of the specific surface energy of clusters and the dislocation density needed to adjust the model are reasonable estimates for the alloy under investigation. The expectation that the surface energies for the two dose rates considered should agree is fulfilled more closely, if cluster-matrix interaction is taken into account.

In oder to understand relationships between the structure of rhenium-188 '4+1' complexes and their in vitro stability we synthesized a series of rhenium model complexes and determined their stability in human plasma. Rhenium-188 '4+1' complexes were synthesized using different monodentate phosphorus(III) ligands, including both lipophilic and hydrophilic tertiary phosphines and phosphites (188Re1-3) and unsubstituted tetradentate ligands and substituted NS3 ligands bearing a carboxyl group or an isopropyl amide were used as chelators (188Re4-6). As instability in aqueous solution leads always to perrhenate, the amount of 188ReO4- formed after 1h, 24 h and 48 h was determined by TLC. According to our findings 188Re4 was of sufficient stability and therefore used for further investigations. We tried to find out which physico-chemical parameter of the corresponding non-radioactive rhenium complexes Re1-6 may govern the formation of complexes of high in vitro stability. The water-soluble N-hydroxysulfosuccinimidyl activated ester 1 is a useful compound for the conjugation of exclusively water soluble biomolecules. Rhenium-188 labeling of the phosphine-arginine-tyrosine conjugate 2 as model compound was carried out using a labile 188Re(III)-EDTA intermediate. Based on this procedure peptides and proteins shall by labeld and tested in vivo.

Polyoxometallate (POMs) gewinnen zunehmend an Bedeutung im Hinblick auf eine Anwendung in der Medizin [1]. Aufgrund ihrer bekannten antiviralen und antitumoralen Eigenschaften werden insbesondere Clusterverbindungen auf der Basis von Polyoxomolybdaten, -wolframaten sowie -vanadaten intensiv untersucht. Eigenschaften wie hohe Stabilität, geringe Toxizität, hohe Wirksamkeit und eine steuerbare Bioverteilung sind für eine Anwendung von POMs in der Medizin von besonderem Interesse. In diesem Zusammenhang ergeben sich durch Modifizierung der POMs mit organischen Verbindungen vielfältige Möglichkeiten. Besonders aussichtsreich erscheint die Anwendung von Kern/Hüll-Nanoteilchen mit einem Durchmesser von < 100 nm. So ergibt sich im Vergleich zu freien Clusterverbindungen eine höhere antitumorale Aktivität, wenn mit Stärke umhüllte nanometergroße Teilchen eingesetzt werden [2].
Unsere Untersuchungen haben gezeigt, dass die Darstellung von hydrolytisch stabilen Nanoteilchen auf der Basis von Polyoxowolframaten mit dem Biopolymer Chitosan möglich ist. Durch Vermischen von wässrigen Lösungen der Clusterverbindung K7[Ti2W10PO40] und einem Chitosanderivat (Mr ~ 10.000 g/mol) erhält man nanometergroße Assoziate. Diese Nanopartikeln weisen eine definierte Stöchiometrie (~ 5 Clustermoleküle/Molekül Chitosan) auf und die Teilchengröße liegt im Bereich von etwa 40 nm bis 400 nm, wobei der überwiegende Anteil <100 nm ist. Erste Untersuchungen zur Aufnahme in Tumorzelllinien haben ergeben, dass die Assoziate von K7[Ti2W10PO40] mit Chitosan im Vergleich zum freien Polywolframat deutlich besser aufgenommen werden.

[1] J. T. Rhule, C. L. Hill, D. A. Judd, R. F. Schinazi, Chem. Rev. 1999 99, 327.
[2] X. H. Wang, J. F. Liu, M. T. Pope, Dalton Trans. 2003, 957.

This work is part of our efforts to develop chelating agents for stable binding and easy conjugation of rhenium-188 to biologically interesting structures. Keeping in mind the high in vivo stability of [¹⁸⁸ReO(DMSA)₂]^- (1) we want to exploit this coordination system for the design of ¹⁸⁸ReO(V) chelates which are stable towards re-oxidation to perrhenate and towards ligand exchange under all conditions of radiopharmaceutical procedures and applications.
The new type of tetradentate ligand has been synthesized by bridging two molecules of dimercaptosuccinic acid (DMSA) with an alkylene triamine chain. The resulting stereo-isomeric tetrathiolato S₄ ligand 1 forms five-coordinate oxorhenium(V) complexes 2 (exo-cis) and 3 (exo-trans) by ligand exchange reaction of NBu₄[ReOCl₄] in methanol. Without addition of base the compounds will be isolated as “betain”, [ReO(S₄)], with the protonated nitrogen of the bridge as internal “counter ion”. X-ray crystal structure determination of both stereoisomeric forms reveals the square-pyramidal coordination geometry of the ReOS₄ core. The orientation of the metal-oxo core is exo in relation to the carbamido groups in both isomers.
The activated BFCA 4 enables easy linking of biomolecules containing a terminal amino group. Prototypic model conjugates with tripeptides have been identified in non-radioactive form by electrospray mass spectrometry.
The Re-188 labelling procedure runs fast, in good yields and under mild conditions, making the new complexes interesting as a further access to stable rhenium-188 radiotherapeutics.

Ziel: Das klinische Bild der Demenz vom Alzheimer (DAT) wird im Erkrankungsverlauf durch kognitive Einbußen und neuropsychiatrische Auffälligkeiten geprägt. Im Rahmen einer europäischen Multizenterstudie mit Positronen-Emissions-Tomographie (PET) zur Frühdiagnostik der DAT (NEST-DD), sind wir erstmalig der Frage nachgegangen, ob neuropsychiatrischen Symptomen spezifische zerebrale Funktionsstörungen zugrunde liegen könnten.

Methodik: Patienten mit einer beginnenden DAT (NINCDS/ADRDA; n0173; MMSE: 21.2±4.0; Alter: 70.6±8.24) unterzogen sich einer ausführlichen klinischen und neuropsychologischen Untersuchung sowie einer Glukosestoffwechselmessung mittels PET. Die neuropsychiatrischen Symptome wurden mittels standardisierter Fragen an die betreuenden Angehörigen erhoben (Neuropsychiatric Inventory, NPI). Es wurden Einschätzungen zum Vorliegen von Apathie, Depression, Angst, Erregtheit, Euphorie, Wahn, Halluzinationen, Enthemmung, Reizbarkeit und abnormaen motorischen Verhalten erhoben. Die Datenanalyse erfolgte bei den Patienten, die an einer isolierten neuropsychiatrischen Störung klinischer Relevanz litten (NPI-item > 4 Punkte) und wurden mit den Patienten ohne neuropsychiatrische Symptome verglichen (NPI-item < 0 Punkte). Die statistische Auswertung der PET-Bilder erfolgte mittels des interaktiven Programms SPM99 (Statistical Parametric Imaging), nach Normalisierung der einezelnen Studien auf den anatomischen Atlas nach Talairach und einer pixel-basierten statistischen Auswertung (p>0,05; korrigiert).

Ergebnisse: Insgesamt 37 Patienten wiesen keine neuropsychiatrischen Auffälligkeiten auf und dienten als Kontrollgruppe. Drei Patientengruppen konnten untersucht werden: mit klinisch relevanter Apathie (n=20), Depression (n=12) und Angst (n=12). Patienten mit klinisch relevanter Apathie wiesen eine signifikante regionale Stoffwechselminderung im orbitofrontalen Kortex auf. Depressive Patienten zeigten eine signifikante regionale Stoffwechselminderung im dorsolateralen Präfrontalkortex, während bei Patienten mit Angst eine Minderung im ventrolateralen Präfrontalkortex nachgewiesen werden konnte.

Schlussfolgerung: Diese Ergebnisse sprechen dafür, dass bei der frühen DAT den neuropsychiatrischen Auffälligkeiten Apathie, Depression und Angst unterschiedliche regionale Funktionsstörungen im Frontalkortex zugrunde liegen, die sich zum von den Hirnregionen unterscheiden, die mit den kognitiven Einbussen korrelieren.

The use of 3C-SiC wafers for device fabrication has been restricted by the high defect density in the substrates. Flash lamp annealing (the FLASiC process) has been shown to reduce the defect density in 3C-SiC by at least an order of magnitude. This process involves melting a layer of silicon in contact with the 3C-SiC layer on a time scale of milliseconds and the subsequent regrowth of the SiC layer by liquid phase epitaxy. This paper shows how the transport of carbon in the liquid silicon is determined by the structure of the starting substrate and process conditions. The movement of carbon controls the dissolution and regrowth of the SiC and determines the morphology of the regrown film.

Positron emissions tomography studies typically contain serveral hundred tomographic images, which have to be analyzed to derive informations such as the volume of target structures (e.g. tumors). Available programs do not offer the necessary functionality because evaluation is limited to processing of individual tomographic images.

We present a newly developed tool for easy and fast evaluation of regions of interest in a volume orientated way. Examples of typical applications to microPET studies are presented.

To achive the aim the following key functionality was defined and implemented: For acceptance the tool should offer an easy and fast way of navigation through the three dimensional volumes. For that purpose three views are available, an orthogonal view, a multiple plane view and a maximum intensity projection view.

Interesting regions are enclosed by user defined masks to exclude regions of high activity background. A threshold guided automatic delineaction of interesting structures as well as an automatic segmentions of the thresholded data is used to find the target structures. These detected volumes of interest are delineated in realtime in all available views (including, especially, the maximum projection view) with a separate colormap for visual control through the operator. For each detected region the volume and parameters characterizing the tracer accumulation (maximum, minimum, mean, standard deviation, etc.) are provide. For post processing and archiving an export (XML and ASCII) as well as printing of these statistical values is possible.

The coregistration of whole body PET images runs into certain problems. On the one hand if one uses non-rigid transformatin the validity of the data might be compromised. On the other hand if one uses only rigid body transformations, it is hardly possible to take all details of the images into account. We developed a method that circumvents this problem by using piecewise rigid body transformation.

This method evaluates the alignment of the images by the correlation of intensities and the mutual information of the data. The best transformation parameters are searched for by a modified conjugate gradient method.

The complete functionality is implemented in form of a libarary, which might be linked to an application. A command line and graphical user interface is provided. This program allows to define several areas in the images on which a separate coregistration is performed. All areas can be viewed in the same transformed image. The regions in between are interpolated by a Fermi box for each area in order to keep as much of the original information as possible.

The user interaction is reduced to a minimum, besides the coregistration areas only some information about the image content used for optimization and acceleration might be provided. However, the method will lead to improved alignment even without this additional information.

We will present the method as well as result for the different fields of application, e.g. follow up studies or dynamical studies.

Ziel: In (1) wurde bereits ein Auswertesystem vorgestellt, welches zur Eingrenzung, Analyse und quantitativen Auswertung dreidimensionaler Strukturen (VOIs) innerhalb von PET-Bildvolumen dient. Im Rahmen eines fortdauernden Projektes zur verbesserten quantitatischen volumetrischen Auswertung in 3D PET Daten wurden zusätzliche Module entwickelt, um die Visualisierung und interaktive Befundung zu verbessern

Methodik: Um dem Anwender bessere Auswertemöglichkeiten zu bieten, wurden zwei zusätzliche Ansichten der Volumen geschaffen. Die erste ist ein Überblick über alle Schichten ("Multipe Planes View") einer zu spezifizierenden Ansicht (Transaxial, Coronar, Sagittal). Die zweite Ansicht stellt eine rotierende Maximum Intensität Projektion (MIPS) bereit. Hierbei besteht die Möglichkeit, alternativ zur ungewichteten Maximum Projektion eine frei wählbare Abstandsgewichtung entlang der jeweiligen Projektionsrichtung vorzunehmen, um die bei der MIPS mögliche Abschirmung interner Strukturen, z. B. im Gehirn, zu verhindern.

Ergebnisse: Da in beiden neuen Ansichten die VOIs in Echtzeit und mit Hilfe eienr zweiten Farbtabelle eingeblendet werden, behält der Anwender auch hier einen Überblick übe die bereits ausgewerteten Volumina. Insbesondere die Abgrenzung der Volumina in der MIPS mittels einer zweiten Farbtafel erleichtert die Demonstration und Dokumentation von Befunden. Zusätzlich bleiben in der Multiple Plane Ansicht alle Funktionalitäten wie Masken setzen und die VOI-Detektion erhalten. Die Gaußsche Gewichtung der Intensitäten in der MIPS Ansicht schafft die Möglichkeit, heiße Bereiche, wie zum Beispiel den Cortex, auszublenden. In allen drei Ansichten besteht die Möglichkeit, Entfernungen zu messen, um Aussagen über Größen oder Abstände treffen zu können. Zur Dokumentation wurde ein Bilderexport (PNG, JPG, etc) mit verschiedenen Enstellmöglichkeiten und eine Druckfunktion für alle drei Ansichten implementiert.

Schlussfolgerungen: Die Erweiterung der Software um fehlende Funktionalitäten erlaubt die Integration des Softwarepaketes in den Routinebetrieb. In weiteren Entwicklungen soll die Möglichkeit geschaffen werden, mehrere PET-Studien zu koregistrieren und einmal erzeugte VOIs auf diese abzubilden. Dadurch sollen Aussagen über den Therapieerfolg in Follow Up Studien vereinfacht werden.

Ziel: ACS2-basierte PET-Scanner wie der weit verbreitete ECAT HR+ unterliegen auf Grund von Hardwarelimitationen nicht nur einigen allgemein bekannten Stabilitätsproblemen, sondern auch der Problematik, dass ein Netzwerkzugriff auf die akquirierten Daten nur mit 0,5 MB/s möglich ist. Besonders bei der Verarbeitung von Listmodedaten, z. B. bei einer event-basierten Bewegungskorrektur, ist dies nicht tolerierbar und behindert die Überführung dieser Methoden in die Routine in erheblichem Makße (1). Unsere Studie greift dies auf und soll am Beispiel des ECAT HR+ überprüfen, inwieweit die Entwicklung von hard- und softwarenahen Methoden die Stabilität des ACS2 verbessern, vor allem aber den Zugriff auf die Daten wesentlich beschleunigen kann.

Methodik: Beim ACS werden die akquirierten Daten über einen SCSI-2 Bus auf eine Festplatte abgespeichert. Dieser Bustyp bietet eine Höchstgeschwindigkeit von 10 MB/s, wobei er jedoch bei einer Datenübertragung per Netzwerk durch die Limitationen des ACS2 kaum an sein Limit gerät. Um dies zu verbessern, wurde das ACS2 mit einem von zwei getrennten Hostanschlüssen eines SCSI-RAID System verbunden. Ferner wurde ein auf Linux basierender Rechner an den zweiten Anschluss angeschlossen, um beide Rechnersystemen einen physischen Zugriff auf das RAID System zu ermöglichen. Im Rahmen einer Softwareentwicklung wurde dann das vom ACS2 verwendete Dateisystem auf Linux portiert, um von dort aus auf die Daten zugreifen zu können. Um einen transparenten Zugriff auf die Daten zu erhalten und diese unmittelbar nach jeder Messung vom ACS2 auf die Akquisitionsworkstatin zu verschieben, wurden Shellskripte in Messprotokolle des PET-Scanners integriert.

Ergebnisse: Durch den Einsatz eines Ultra1 60 SCSI-RAID Systems konnten mit Hilfe eines parallel betriebenen Linux-Rechners beträchtliche Geschwindigkeitenszuwächse erzielt werden. Im Gegensatz zu der vormals auf 0,5 MB/s limitierten Methode, ist es nun möglich, mit einer Transferrate von 70 MB/s die Akquisitionsdaten zu übertragen bzw. Zugriff darauf zu erhalten.

Schlussfolgerungen: Durch die erzielte Geschwindigkeitssteigerung konnte ein langjähriger Limitationsfaktor beim akquirieren großer Datenmengen mit ACS2-basierten PET-Scannern eliminiert werden. Die entwickleten Methoden erlauben es nun, im vertretbaren Zeitrahmen Zugriff auf die Akquisitionsdaten zu erhalten und dsind darüber hinaus in der Lage, den wie verbreiteten Stabilitätsproblemen des ACS2 entgegenzuwirken.

Ziel: Im Gegensatz zur intraindividuellen Koregistrierung von PET-Kopfaufnahmen, bei der zumindest die Außenkonturen des Kopfes in verschiedenen Aufnahmen konstant sind, steht man bei der Koregistrierung von PET-Großkörperaufnahmen vor dem Problem, dass sich die zu vergleichenden Datensätez beträchtlich voneinander unterscheiden können. Versucht man alle Unterschiede durch elastische Transformationen zu berücksichtigen, kann es leicht zu Verfälschungen der Bilder kommen. Beschränkt man sich lediglich auf starre Transformationen, gelingt lokal keine gute Anpassung der Intensitäten. Unser Ziel war die Entwicklung einer routinefähigen Methode, die PET-Ganzkörperaufnahmen bestmöglich bei vollständigem Informationserhalt gegeneinander koregistriert. Der Fokus der Entwicklung lag auf der Registrierung von Follow Up Studien. Die Algorithmen sollten über ein benutzerfreundliches graphisches Interface gesteuert werden können.

Methodik: Bei dem von uns verfolgten Ansatz wird eine der beiden Aufnahmen in verschiedene Areale unterteilt. Diese Areale werden dann unabhängig voneinander gegen die andere Studie registriert. Dabei werden nur starre Transformationen verwendet. Die gesamte Transformation ist damit eine stückweise starre Transformation und der stetige Übergang zwischen den Arealen wird durch Interpolation realisiert. Die besten Transformationsparameter werden mit Hilfe einer modifizierten Methode der konjugierten Gradienten gesucht, wobei die Übereinstimmung der Bilder mittels der Korrelation der Voxelintensität und der "Mutual Information" der Bilder bewertet wird.

Bei allen durchgeführten Koregistrierungen konnte eine Verbesserung der Übereinstimmung der PET-Daten erreicht werden. Insbesondere wenn die Areale ganze Organe umschließen, lassen sich auf der Grundlage dieser quasi elastischen Transformation auch starke Unterschiede in den Bildern erfassen und verlustfrei aufeinander abbilden. Die Größe der Areale beeinflusst dabei die Qualität der Ergebnisse. Umfasst ein Areal den gesamten Datensatz, kann nur mit einer mäßigen Güte der Koregistrierung gerechnet werden. Je kleine die Areale umso besser die Resultate. Die Rechenzeiten liegen typischerweise bei zwei bis fünf Minuten. Die Benutzerinteraktion reduziert sich auf die Wahl der interessierenden Areale. Zusätzlich kann der verwendete Algorithmus über Informationen zum Inhalt der Aufnahmen beschleunigt bzw. optimiert werden.

Schlussfolgerungen: Das hier vorgestellte Koregistrierungsprogramm lierfert bei kurzen Rechenzeiten stabile und genaue Ergebnisse und erscheint somit für den Routineeinsatz geeignet.

Das Löslichkeitsprodukt von wäßrigem, amorphem Urandioxid UO2•xH2O(am) wurde mit Hilfe der laserinduzierten Breakdown-Detektion (LIBD) bestimmt. Dazu wurden U(VI)-Lösungen bei pH-Werten um 1 elektrochemisch reduziert, das Fortschreiten der Reduktion wurde durch UV-Vis-Spektroskopie und Laserfluoreszenzspektroskopie verfolgt. Die Erhöhung des pH-Wertes erfolgte durch coulometrische Titration der Lösung, die einsetzende Bildung von U(IV)-Kolloiden wurde durch die LIBD detektiert. Der pH-Wert an diesem Punkt lieferte die Grundlage zur Berechnung des Löslichkeitsproduktes. Die Ergebnisse von zwei Titrationen zeigt die folgende Tabelle.

Tabelle: Ergebnisse der coulometrischen Titrationen
[U(IV)]tot/mol•l-1 pHkoll log Ksp°
1,06•10-4 2,57 -54,27
3,37•10-5 2,80 -54,34

Das Löslichkeitsprodukt wurde gemäß folgender Gleichung berechnet:

log Ksp° = [U4+]*[OH-]^4*g(U4+)*g(OH-)^4

Die Berechnung der Aktivitätskoeffizienten erfolgte mit Hilfe der Specific Ion Interaction Theory, die in [1] dargelegt ist. Zur Bestimmung von [OH-] wurden pHkoll und das Ionenprodukt von Wasser herangezogen. Die Berechnung von [U4+] wurde unter Berücksichtigung der unter diesen Bedingungen wichtigen Hydrolysespezies des U(IV) durchgeführt. Der Anteil der einzelnen Spezies wurde über die in [2] aufgeführten Bildungskonstanten der Spezies quantifiziert und von der analytisch bestimmten Gesamtkonzentration des Urans subtrahiert.

Der berechnete Mittelwert des Löslichkeitsproduktes von UO2•xH2O(am) liegt bei log Ksp° = -54,31 und bestätigt Ergebnisse früherer Untersuchungen, bei denen die Reoxidation von U(IV) zu U(VI) wirksam unterbunden wurde [3].

[1] Grenthe, I. et al., Chemical Thermodynamics, Vol. 1. Chemical Thermodynamics of Uranium, 1992, Elsevier, Amsterdam.
[2] Neck, V. et al., Radiochim. Acta 89 (2001) 1.
[3] Rai, D. et al., Radiochim. Acta 79 (1997) 239.

From a fluid mechanical point of view, the filling of the mould during aluminum investment casting processes comprises in essence a flow in a U-bend. It is characterized by a high value of the pouring velocity in the early stage, which decreases in the course of the process. This initial high velocity poses distinct problems such as entrapment of bubbles or debris. At present, different types of filters are used for the removal of inclusions, a desired secondary effect of which is a reduction of the melt velocity.
A non-invasive contact-less solution to control the flow of liquid aluminum is the application of a static (DC) magnetic field. Numerical calculations were performed to simulate the filling process and in particular the influence of the field. The free surface problem, which occurs in the riser of the casting unit, was taken into account by a volume-of-fluid method. 3D transient calculations employing the commercial finite-element code FIDAP were carried out for a simplified model system as well as for the real aluminum casting unit. The term for the electromagnetic force was implemented via a user defined subroutine while an additional equation for the electrical potential was solved. End effects owing to the limited size of the magnet poles were taken into account.
In parallel to the simulations, model experiments were performed using the eutectic alloy InGaSn (Tmelt = 10oC). The casting unit was modeled by a perspex pattern, and ultrasonic Doppler veloci­metry was applied for detailed acquisition of velocity data. Such measurements constitute a profound basis for the validation of the numerical simulations. On account of the excellent agreement, an up- scaling towards the realistic aluminium casting process is justified.
Finally, realistic tests with liquid aluminium were performed at an industrial installation. The primarily aimed at influence of the magnetic field, i.e. the attenuation of velocity peaks in the beginning of the process, could be clearly demonstrated. In a second set of experiments, the strength of the DC field was adapted to the process. At start-up, the maximum braking force was applied for a fixed time, followed by a reduction with increasing filling-level of the casting unit. This schedule provided a distinct damping of the peak velocities without the drawback of a significant prolongation in filling time. A remarkable diminishment of defects in the casting product could be achieved.

Bright green electroluminescence with luminance up to 2800 cd/m2 is reported from indium-tin-oxide/SiO2:Tb/Si metal-oxide-semiconductor devices. The SiO2:Tb3+ gate oxide was prepared by thermal oxidation followed by Tb+ implantation. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and the annealing temperature. The optimized device shows a high external quantum efficiency of 16 % and a luminous efficiency of 2.1 lm/W. The excitation processes of the strong green electroluminescence are attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent cross-relaxation from 5D3 to 5D4 energy levels. Light emitting devices with micrometer size fabricated by the standard metal-oxide-semiconductor technology are demonstrated

Ziel: In (1) wurde ein Verfahren vorgestellt, welches zur Eingrenzung, Analyse und quantitativen Auswertung dreidimensionaler Strukturen (VOIs) innerhalb von PET-Bildvolumen dient. Hierbei werden die VOIs halbautomatisch über eine Schwellwertanalyse detektiert und segmentiert. Da der Schwellwert durch den Anwender festgelegt wird, unterliegt das gesamte Verfahren in bestimmtem Umfang der Subjektivität des Anwenders mit entsprechender Konsequenz für die Inter-Observer-Variabilität. Das Ziel dieser Arbeit war es, die vorhandene Schwellwertanalayse so zu modifizieren, dass sie die Volumina von VOIs und hiervon abhängige Größen wie die mittlere Tracerakkumulation/SUVs reproduzierbar bestimmt.

Methodik: Der Anwender muss einen ersten Schwellwert festlegen, der in etwa dem subjektiv als korrekt betrachteten Wert entspricht. Die nähere Umgebung des Volumens definiert den Untergrund und schränkt gleichzeitig den zu betrachtenden Bereich ein. Ausgehend von diesem Hintergrund lassen sich lokale Schwllwerte definieren. Um diese Schwellwerte zu finden, muss das Niveau des Untergrundes ermittelt werden. Dies geschieht über einen Least-Squares-Fit gegen eine 3D-Hyperfläche, welcher mittels multilinearer Regression berechnet wird.

Ergebnisse: Bei den betrachteten Testdatensätzen lieferte die Methode erste viel versprechende Ergebnisse. Untersucht wurden zum einen Studien mit ortinvariante, sowie solche mit stark ortsabhängigem Untergrund. Für einen um 40 Prozentpunkte variierenden Schwellwertbereich wurden die Volumina jeweils mit und ohne Bestimmung des Untergrundes berechnet. Es zeigte sich, dass bei Studien mit ortinvariantem Untergrund die Schwankungsbreite der ermittelten Volumina von 150 Prozent auf 10 Prozent reduziert werdn konnte. Bei Studien mit stark ortsabhängigem Untergrund, z. B. an Organgrenzen, konnte eine Verminderung von 280 Prozent auf 60 Prozent erreicht werden. Hierbei spielt die Höhe des untergrundes in beiden Fällen keine Rolle, solange der Startschwellwert über dem Untergrundniveau liegt.

Schlussfolgerung: Die Methode liefert bei hinreichend ortsinvariantem Untergrund stabile Ergebnisse. Bei stark ortsabhängigem Untergrund sind Erweiterungen nötig. Vorstellbar wäre eien ortsabhängige Gewichtung des Untergrundes im Bereich zwischen Startvolumen und Untergrund, was in weiteren Tests zu untersuchen ist.

The nanostructural evolution during heat treatments of DC magnetron-sputtered Cu films deposited at different substrate bias voltages was experimentally studied. A growth chamber equipped with two magnetrons and Kapton windows for in-situ X-ray diffraction was mounted on a six-circle goniometer at a synchrotron beam line. Using Bragg–Brentano X-ray diffraction, the grain size,the texture, and the lattice constant were monitored during thermal annealing.Increasing the substrate bias voltage, the grain growth rate lowered, and the change in texture with time became smaller due to a decrease in the defect concentration. Furthermore, the grain size in the as-deposited films decreased with increasing bias voltage. The activation energy for grain growth was, within experimental errors, the see in all the films.

Recently, an enhanced optical transmission (EOT) through 2D periodic arrays of sub-wavelength holes in a metal layer was found. It generated intense theoretical and experimental research, but its physical nature is still not elucidated. In this communication, we report experimental investigations on ID relief gratings, and numerical analysis of the composite structure of randomly distributed dielectric nanoparticles embedded in a thin metallic matrix. We show that EOT is also present in such structures.

Annealing of thin films of amorphous indium tin oxide (ITO) in vacuum is known to decrease their resistivity. The amorphous-to-crystalline transition is often assumed as the reason for this improvement due to a Sn donor activation, but the physical mechanisms behind the experimental observation are not clear. In present work, the films were studied during heating in vacuum within the temperature range Ta=20-330 °C at a constant rate of 5 °C/min as well as at isothermal annealing at Ta=210 °C. This study is focused on in situ spectroscopic ellipsometry (SE) monitoring of the film properties during annealing. In addition, the films were investigated by in situ four point probe resistivity measurement technique and the in situ X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA). The observed temperature dependences of the ellipsometry parameters and resistivity indicate several stages with features at Ta=110, 150, 280, and 310 °C, in contrast to the more simple two-stage behavior of these characteristics obtained during isothermal annealing. Even in the XRD-amorphous state, the film resistivity significantly decreases with increasing temperature due to a free-electron density enhancement as shown by SE. It is likely caused by the generation of oxygen vacancies, because ERDA showed decrease of the oxygen content in the film on this stage of annealing. A rapid crystallization within the temperature range of 250-280 °C leads to a further decrease of the resistivity due to Sn donor activation. The amorphous-to-crystalline transition is accompanied by a film roughening as it is shown by in situ SE and corroborated by atomic force microscopy.

The agostic B-H...Re bond in complexes [Re{kappa(3)-R(mu H)B(tim(Me))(2)}(CO)(3)] (R= H (1), Ph (2), tim(Me) = 2-mercapto-1-methylimidazolyl) is readily cleaved by t-butylisonitrile or cyclohexylisonitrile leading to the mixed-ligand complexes [Re{kappa(2)-Ph(mu-H)B(tim(Me))(2)}(C equivalent to (NBu)-Bu-t)(CO)(3)] (3) and [Re{kappa(2)-H(mu-H)B(tim(Me))(2)}(C equivalent to N-cyclohexyl)(CO)(3)] (4), respectively. Bearing in mind the so-called [2 + 1] mixed ligand approach for the development of target-pecific radiopharmaceuticals, reactions of 1 with isonitriles carrying the (2-methoxyphenyl)piperazine pharmacophore (part of WAY 100635) were also studied and the complexes [Re{kappa(2)-H(mu-H)B(tim(Me))(2)}(C equivalent to N-R'-WAY)(CO)(3)] (R' = butylene (5), pentylene (6) or hexylene (7)) isolated. The novel mixed Re(I) tricarbonyl complexes (3-7) have been characterized by the usual analytical techniques, which included X-ray diffraction analysis in the cases of 3, 4 and 5. The affinity of the complexes 5-7 toward the 5-HT1A receptors was tested in competitive receptor binding assays and the IC50 values found were in the 21.9-66.5 nM range. Complex 7, with the longest spacer length between the isonitrile function and the pharmacophore, has shown an improved selectivity towards the 5-HT1A subtype of receptors when compared with 5 and 6.

Ziel: Wenigstens 5 % der Bevölkerung verlieren im Laufe des Lebens ihren Geruchssinn. Bei diesen Patienten stellt der Nervus trigeminus die einzig verbliebene intranasale chemosensorische Modalität dar. Bisherige Studien beschäftigen sich überwiegend mit olfaktorisch-trigeminalen Mischreizen, zum tieferen Verständnis der Verarbeitung intranasaler trigeminaler Reize fehlt es bisher an Informationen. Ziel dieser Studie ist es zu überprüfen, in wiefern die O-15-H2O-PET für den Nachweis einer gezielten Reizung des N. trigeminus geeignet ist.

Methodik: Es wurden 15 männliche Probanden (Alter 30 - 58 Jahre, mittleres Alter 36) ohne internistische oder neurologische Vorerkrankungen und ohne Erkrankung im HNO-Bereich untersucht. Die PET-Messungen erfolgten an einer dedizierten PET-Kamera (ECAT EXACT HR+). Pro Proband waren 4 dynamische Messungen über 5 min vorgesehen, alternierend Ruhemessungen und Aktivierung nach Applikation von 1,7 GBq O-15-H2O i.v. und mind. 15 min Pause zwischen den Einzelmessungen. Für die Reizung des N. trigeminus wurden per Nasensonde CO2-Pulse (Reizdauer 1 s, Intervall 3 s) in das linke Nasenloch beginnend 20 sec vor Injektion und über den gesamten Messzyklus appliziert. Die Auswertung erfolgte mittels parametrischer Flow-maps, die unter Benutzung einer Standard-Inputfunktion erzeugt wurde. Für den Vergleich Ruhemessung - Aktivierung kam das Softwareprogramm SPM99 zum Einsatz. Die Studie war durch die lokale Ethikkommission und das Bundesamt für Strahlenschutz genehmigt.

Ergebnisse: Bei 12 Probanden konnten je 2 Ruhe- und Aktivierungsmessungen akquiriert werden, bei 3 Probanden konnten auf Grund technischer Schwierigkeiten nur mindestens je 1 Ruhe- und Aktivierungsstudie aufgenommen werden. In der noch andauernden Auswertung zeigt sich in einer ersten Auswertung aller Probandenmessungen eine deutliche Aktivierung im Projektionsfeld des N. trigeminus am Fuse des postzentralen Gyrus, die rechsseitig stärker ausgeprägt ist als in der linken Hemisphäre.

Schlussfolgerung: Nach trigeminaler Reizung der Nasenschleimhaut des linken Nasenloches zeigt sich in einer ersten Auswertung aller Probandenmessungen der H2O-PET eine Perfusionssteigerung im Bereich der postzentralen Projektionsfelder bds. die kontralateral zur Reizung stärker ausgeprägt ist. Die Prüfung der Stabilität der intra-individuellen Aktivierung ist noch Gegenstand der Auswertung.

Apoptosis imaging with PET plays an increasing role in various medical fields like oncology, cardiology, transplant rejection, and inflammation, but the radiotracer distribution in the tis-sues is influenced by various mechanisms. In this study a recombinant annexin-V (courtesy N. Budisa, Max Planck Institute of Biochemistry) derivative and human serum albumin (HSA) were radiolabelled using N-succinimidyl-4-F-18-fluorobenzoate (SFB), and characterized. Mechanism and specificity of both F-18-annexin-V and F-18-HSA biodistribution and accu-mulation were examined in rodents.

Recombinant annexin-V derivative and HSA were radiolabelled using SFB and the products were confirmed by size exclusion chromatography and SDS-PAGE. The radiotracer distribu-tions in animals were studied in rats and mice ex vivo by organ extraction, autoradiography, and in vivo with animal PET. For apoptosis imaging, F-18-annexin-V or F-18-HSA were in-travenously applied in 4 groups of mice that received either intraperitoneal 100 µg Anti-Fas antibody in 200 µL isotonic NaCl or 200 µL isotonic NaCl 2 hours before the radiotracer. The degree of liver apoptosis was characterized by plasma ALAT and ASAT activity measure-ments.

The radiochemical yield was in the range of 10 to 30% (corrected for decay) with a specific activity of more than 20 GBq/µmol. The accumulation of F-18-annexin-V and F-18-HSA, respectively in the apoptotic livers (4 – 16%ID/g) were correlated to the ASAT and increased up to 4 times in comparison to control. The biodistribution of the tracers were comparable except for the renal elimination of F-18-annexin-V, which was up to 3 times higher than of F-18-HSA.

Due to the lattice misfit between the silicon and the silicon carbide lattices the epitaxial deposition of SiC layers normally results in a highly defected carbide layer. Short time annealing seems to be an effective method to improve the crystal structure of the epitaxial layer using intense light pulses from flash lamps.
From the present point of view the annealing mechanism is based on the rapid melting of a thin silicon interface layer due to the intense light pulse, giving the non molten SiC layer the possibility for relaxation and annealing. Consequently, after the pulse is over and the liquid silicon intermediate layer solidifies epitaxially on the monocrystalline substrate one receives a high temperature annealed epitaxial SiC on silicon structure.
Although the annealing of the SiC layer due to the flash irradiation could be verified by TEM investigations a serious problem remains, connected with the facetted melting of the monocrystalline silicon surface after rapid heating above the melting temperature. Due to the layer by layer crystallisation within the molten pyramides, including a lateral growth component and due to the 5 % higher density of liquid silicon in comparison to solid silicon a surface relief will be formed after the solidification process is completed.
Two techniques were tested to circumvent the deep facetted melting.
The first procedure to homogenize the melting depth is based on the introduction of a so called melt stop layer in a certain depth below the SiC / Si interface. For this purpose carbon admixture which increases the melting temperature of silicon was implanted at a dose of 2*1017cm-2 and a energy of 140 keV through a 30 nm thick SiC layer into silicon, forming a approximately 200 nm thick melt barrier in a depth of 400 nm.
As a further possibility to prevent the facetted melting ion implantation of germanium admixture as a element reducing the melting temperature of silicon was tested.
It could be experimentally shown that both, the introduction of a melt stop layer at any depth behind the Si / SiC interface as well as the modification of the silicon surface, leading to a decrease of the silicon melting temperature, are usefull methods for the homogenization of the melting depth at the bulk silicon surface.

Einleitend wird im Rahmen des Vortrags auf Methoden und Ergebnisse zur Bestimmung der bakteriellen Diversität in Uranafallhaden eingegangen. Darauf aufbauend werden Möglichkeiten zur Untersuchung der Wechselwirkungen von Bakterien mit Radionukliden und Schwermetallen aufgezeigt und die Ergebnisse einzelner Analysen vorgestellt. Der letzte Teil umfasst Arbeiten zur Anwendung der Metallbindung in der Biotechnologie und Nanotechnologie.

Recently it has been demonstrated that ion irradiation of ultrathin magnetic films and multilayer structures is a versatile tool to modify the magnetic properties of these systems in laterally confined areas [1–3]. In most cases the modification of the magnetic anisotropy or the different exchange coupling contributions present in multilayered films are due to a post deposition modification of the interface structure. Depending on the enthalpy of mixing light ion irradiation may result in a roughening or a sharpening of the interface on the atomic level. Due to the local nature of the ion-solid interaction these modifications can be restricted to confined areas resulting in magnetically patterned films without a modification of the surface topography.
An alternative route to ion-driven magnetic nanostructures relies on ion implantation. By doping magnetic thin films in a percentage range with Cr or rare earth transition metals either the Curie temperature [4] or the magnetic damping behavior [5] can be adjusted. In combination with focused ion beam techniques magnetic nanostructures can be written directly into the film structure.
In the presentation I will review the current status of these investigations with respect to magnetic nanostructure formation.

[1] C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280, 1919 (1998).
[2] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[3] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[4] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).
[5] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003).

The Sb speciation in soil samples from Swiss shooting ranges was determined using Sb K-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and advanced statistical data analysis methods (Iterative Transformation Factor Analysis, ITFA). The EXAFS analysis was supported by a spectral data base of 13 Sb minerals and 4 sorption complexes. In spite of a high variability in geology, pH (3.1 – 7.5), Sb concentrations (1000 – 17000 mg/kg) and range history, the spectra of all nine samples could be reconstructed with only two components, indicative of two Sb species. In the first species, Sb is surrounded solely by other Sb atoms at radial distances of 2.90, 3.3.5, 4.30 and 4.51 Å, which are typical for metallic Sb(0). The Sb(0) metal species prevailed in a very acidic (pH 3), organic matter-rich soil. Since no metallic Pb, but Pb2+ bound to soil organic matter was found in this soil by Pb LIII-edge EXAFS spectroscopy, the Pb component of the bullet PbSb alloy may have dissolved more rapidly than the Sb component, leaving metallic Sb behind. In the second species, Sb is coordinated to 6 O atoms at a distance of 1.98 Å, indicative of Sb(V). Iron atoms at radial distances of 3.10 and 3.56 Å are in line with edge-sharing and bidentate corner-sharing linkages between Sb(O,OH)6 and Fe(O,OH)6 octahedra, similar to structural units in the Fe antimonate tripuhyite. This local arrangement, the prevalence of Fe backscatterers and the small coordination numbers suggest formation of clusters of Fe-rich antimonate. This pentavalent Sb species was present in all samples, suggesting that it is the prevailing species after weathering of metallic Sb(0) in oxic soils.

The lecture summarizes efforts to deliver a chemical base for safety analysis and risk assessment. One major aspect is the substitution of conventional distribution coefficients (Kd values) for the empirical description of sorption processes by surface complexation models (SCM).
The general strategy and examples for current blind predictive capabilities of SCM and the respective database RES³T – the "Rossendorf Expert System for Surface and Sorption Thermodynamics"- are explained.
RES³T is a digitized version of a thermodynamic sorption database as required for the parametrisation of SCM, namely in risk assessment studies.
The approach for the compilation of numerical data includes the collection of the mineral surface characteristics, the selection of reliable data records, the extrapolation to infinite dilution, the normalization to a reference site density and the averaging of selected thermodynamic data records.
The Cu(II) sorption onto goethite and the Np(V) sorption onto hematite were chosen as systems illustrating the blind predictive capabilities. The model predictions represent the experimental values for the adsorbed amount of Cu(II) and Np(V), respectively, expressed as conventional distribution coefficients K_D as required by most performance assessment software, are within one order of magnitude or better.
As an example to illustrate the effect of parameter uncertainty in blind predictions the Np(V) sorption onto haematite was selected. The formally large scatter of pK values as extracted from literature is actually not critical. Even the use of inconsistent values from other electrostatic models will yield similar results.
We can conclude, that for well-defined mineral systems, provided a suitable database is accessible, the SCM approach seems to be promising. More realistic (thermodynamic) approaches can and have to amend the K_D concept.

Based on a classification of the various magnetic field actions on metallic melts, the idea of tailored flow control is presented. Examples will be given for this approach ranging from crystal growth applications, metal casting, electromagnetic levitation, liquid metal two-phase flows to solidification studies. Special emphasis is put on recent developments in velocity measuring techniques for metallic melts as they provide the essential clue for experimental investigations.

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of about 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the single bubble wake. Within the whole present parameter range, the bubble Strouhal number was decreased in the longitudinal magnetic field while increased in the transverse magnetic field. On the other hand, the bubble drag coefficient was found to be increased or decreased depending on the bubble size and the magnetic interaction parameter.
In a next step the gas flow rate was increased leading to the formation of weak bubble plumes. The interest was mainly focused on the effect of both longitudinal and transverse magnetic fields on the global flow structure in the container. The UDV results revealed that the velocity field of the liquid phase was completely reorganized by the external DC magnetic field. The magnetic field application does not result exclusively in a plain damping of the recirculating flow. Especially in the case of a transverse magnetic field new flow pattern were observed in both planes parallel and perpendicular to the magnetic field lines. The tendency was found to align and elongate the flow structures along the magnetic field direction. Magnetic damping effects become important with increasing magnetic field strength.

The HADES spectrometer installed at GSI Darmstadt is devoted to the study of the production of di-lepton pairs from vector meson decays in relativistic nucleus-nucleus collisions, as well as proton- and pion-induced reactions. Extraction of rare lepton pairs in high hadron multiplicity events requires an efficient particle identification (PID). In HADES charged particles momentum is measured by a tracking system surrounding the toroidal super conducting magnet, and velocity and energy loss is provided by a TOF detector. Leptons are identified by a Rich as well as a Shower detector. The particle identification method is using full experimental information from all subdetectors. To demonstrate the method performance, single particle spectra of charged hadrons and leptons from C+C at 2 AGeV will be presented and compared with results of corresponding simulations. The proton and pion yields an m_T and rapidity distributions will be compared with existing data. Very preliminary results of lepton analysis will be shown as well.

Electromagnetic fields provide an attractive tool for a contact-less control of flows in metallurgical and crystal growth processes. The presentation starts with a classification of magnetic field actions on melt flows and with a summary of the recently developed velocity measuring techniques for opaque metallic melts. Emphasis will be given to the Ultrasonic Doppler Velocimetry (UDV) as it provides full profiles of the mean velocity and is applicable even through channel walls.
Based on such experimental and numerical modelling capabilities, we first consider the design and application of various magnetic fields for the inflow control of the mould filling process of aluminum investment casting. This process consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical 3d transient calculations were performed to simulate the filling process and the effect of the magnetic field. In parallel, model experiments with a plexiglas model have been performed using the low melting eutectic GaInSn. UDV was applied to carry out detailed velocity measurements in the model. Those measurements served for the validation of the numerical calculations, thus allowing to scale up the simulations to the realistic aluminium casting process. Tests with molten aluminium have been performed at an industrial investment caster. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly demonstrated. The amplitude of the DC field was tuned during the process as the braking action is only needed during the first part of the process. In this way, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time. Eventually, a remarkable diminishment of defects in the casting products was achieved.
A more active influence on the overall process can be obtained by application of a travelling magnetic field which brakes the flow at the beginning but allows to pump the melt at the end of the filling process. First numerical and experimental results will be presented showing the superimposed stirring action of such an electromagnetic pump besides its integral pumping action. For a homogeneous breaking or pumping a special design of the AC magnetic field is inevitable.
The application of electromagnetically driven flows during solidification improves the quality of casting ingots by promoting the formation of fine, equiaxed grains. However, the lack of detailed knowledge on the transient flow dynamics obstructs the optimisation of solidification processes by electromagnetic flow control and is consequently one of the reasons for the rather empirical application of melt agitation until now. Our results show that the forced convection influences significantly the concentration as well the temperature profile ahead of the solidification front. A flow effect can be supposed both on the presence of free nuclei in the melt and suitable conditions allowing them to grow as equiaxed crystals in competition with the columnar front.

The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed forced crucible rotation technique. Samples were subjected to well-defined forced rotation and vibration, respectively, during induction heating and solidification. A concerted microstructure evolution is possible by enhancement or suppression of the melt convection. As a result, the microstructure pattern, mainly the volume fraction of the soft magnetic a-Fe phase, vary strongly with the strength of the internal flow motion. A distinct reduction of the a-Fe volume fraction in samples with strong melt rotation was observed by measuring the magnetic moment. Moreover, the melt flow was studied numerically taking into account the coupled heat and fluid flow fields. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.

Experimental set-ups for magnetohydrodynamic dynamo involve usually complex configurations of fluid flow and magnetic field, designed to achieve the critical magnetic Reynolds number sufficient for magnetic self-excitation, but with minimum energy input and at scales manageable in a laboratory. Computer simulations that could be used to optimize the design and to complement the experiments have, however, been limited to much simplified geometries and flow conditions, which inevitably limit their applicability. In this paper, we report on progress in the coupled finite difference (Maxwell solver)/finite volume (Navier-Stokes solver) computer simulations of the full-scale real Riga dynamo experiment

In Analogie zu den Systemen für die KKW Saporoshje und Rovno wurden für die drei Blöcke des KKW Südukraine und für den ersten Block des KKW Chmelnitzky technische Systeme zur verbesserten betrieblichen Überwachung eingerichtet. Dazu werden der Aufsichtsbehörde vor Ort und im Krisenzentrum in Kiew einmal pro Minute für jeden Block bis zu 51 sicherheitsrelevante technologische und 16 radiologische Parameter zur Bewertung mittels moderner technischer Ausrüstungen online zur Verfügung gestellt. Die entwickelte Auswertesoftware gestattet die Darstellung der Bewertungsergebnisse in Form von Tabellen, Grafiken und Schemata. Außerdem ermöglicht ein Archivmodus Trendanalysen.
Mit der Integration der für die geschützte Warte gelieferten Ausrüstungen in das am Standort des KKW Saporoshje betriebene Fernüberwachungssystem ist es nunmehr möglich, die wesentlichen sicherheitsrelevanten Parameter des gesamten Standortes auch bei außergewöhnlichen Ereignissen mit Hilfe moderner Technik zu erfassen und zu bewerten.

The phenomenon of sudden and irregular reversals of the Earth's magnetic field has attracted much interest in the last decades. It is known that the mean reversal rate varies from approximately zero in the Permian and Cretaceous supercrons to approximately 5 per Myr in the present. There is some observational evidence for the facts that the reversals are asymmetric in time and that the overall distribution of the field intensity has a bimodal behaviour. In an attempt to explain these features in a paradigmatic model we investigate a mean-field dynamo model of the alpha^2 type. Field saturation is guaranteed by alpha-quenching, and the influence of noise is taken into account. In order to keep the model simple and to allow for very long simulations, we choose the helical turbulence parameter alpha as spherically symmetric. We show that reversals occur in the vicinity of so-called exceptional points of the spectrum of the dynamo operator, where two real eigenvalues coalesce and continue as a pair of complex conjugate eigenvalues. We describe the reversal mechanism, and all the above mentioned features, in terms of a self-accelerating field decay, followed by the rapid recovery of the field with opposite polarity. We point out that the reversal mechanism can be attributed to the square-root character of exceptional points in the spectrum. Hence it is not restricted to our particular model but should be identifiable also in more realistic models of the Earth dynamo.

Exposing a moving electrically conducting fluid to an external magnetic field, one can measure the induced magnetic field in the exteriour of the fluid with the aim to reconstruct the flow field of the fluid. The application of two different external fields represents a certain minimum for the identification of the main topological structure of the flow. After delineating the theory of this measurement method in the framework of the integral equation approach to kinematic MHD, we report on an experiment with a propeller driven flow of InGaSn. In the basic version of this experiment, an axial and a transverse external field are produced by two orthogonal pairs of Helmholtz coils. The externally induced fields are measured by Hall sensors at 49 positions which cover the vessel rather homogeneously. By comparison with ultrasonic Doppler measurements, the method is shown to provide correct and robust results on the main topological structure and the magnitude of the flow. First results of an alternative variant using one homogeneous and one cusp field are presented. The potential advantages of using AC fields instead of DC fields to achieve a better depth resolution and to make the method applicable in rough industrial environments are also indicated.

no abstract available

Mit dem Ziel, die Migration des Radiums im Umfeld des Endlagers Morsleben zu beschreiben, wurde (1) die Löslichkeit des (Ra, Ba)SO₄ in den spezifischen Salzlösun-gen (gesättigte NaCl-Lösung, Magnesialauge) bestimmt und (2) die Adsorption des Radiums am Leinetal-Sediment (grauer Salzton) untersucht.
Die Salzlösungen bestanden aus einer 5,35 molaren NaCl-Lösung und einer quinären Lösung mit den Bestandteilen Magnesium (3,8 molar), Kalium (0,8), Natrium (0,4) als Chlorid und Sulfat. Die Lösungen wurden mit den Verfüllmaterialien (Salzbeton und Magnesiabinder) und dem Salzton voräquilibriert.
Die Bestimmung der Löslichkeit wurde nach Einstellung des Löslichkeitsgleich-gewichts (über 360 Tage) durch Bestimmung des 226Ra in der gesättigten Lösung mit-tels Flüssig-Szintillations-Messung durchgeführt. Hierzu wurde zum einen ein Überschuss (²²⁶Ra, Ba)SO₄ zur Salzlösung gebracht und zum anderen RaCl₂-Lösung zugegeben, wobei mit dem in der Lösung vorhandenen Sulfat die Ausfällung des (²²⁶Ra, Ba)SO₄ erfolgte. Die Gehalte an Barium wurden durch ICP-MS und die des Sulfats durch Ionenchromatografie ermittelt. Die vorkonditionierten Salzlösungen sind zu 95 bis 99% mit BaSO₄ gesättigt. Weniger als 5% (Ra, Ba)SO₄ lassen sich in diesen Lösungen noch zusätzlich auflösen („mobilisieren“). Die Auflösungen führen zu Ra²⁺-Konzentrationen im Bereich 1,2∙10^-8 bis 4,7∙10^-8 mol/l. Die Summenkonzentration von Ba²⁺ und Ra²⁺ liegt dann bei 1,1∙10^-7 bis 1,3∙10^-6 mol/l. Die nach der Ausfällung verbliebenen Ra²⁺-Konzentrationen sind geringer. Sie liegen im Bereich 1,2∙10^-8 bis 4,7∙10^-8 mol/l. Durch den Fällvorgang entstandene Übersättigungszustände werden abgebaut. Die hieraus folgenden Löslichkeitsprodukte liegen bei log K_sp,298 = 7,07 ± 0,21 im Falle der Auflösung und bei log K_sp,298 = 7,39 ± 0,21 bei der Ausfällung. Das Löslichkeitsprodukt für unendliche Verdünnung (-10,3 ± 0,1) [1,2] liegt um drei Größenordnungen niedriger.
Die Sorption des Radiums am Salzton wurde an Proben untersucht, die 1,5 bis 2,5 g Salzton in 15 ml Salzlösung enthielten. Die Ausgangskonzentration des Radiums in der flüssigen Phase lag bei 1,3∙10^-9 mol/l. Die ²²⁶Ra-Konzentration verringerte sich im Zeitraum von etwa 400 Tagen auf 2,7∙10^-10 bis 8,6∙10^-10 mol/l. Dabei ist die Sorption aus der NaCl-Lösung mit Verteilungskoeffizienten (R_S) von 9,6 bis 22,7 ml/g stärker als aus der Magnesialauge, für die R_S-Werte von 4,4 bis 7,5 ermittelt wurden. Der Verlauf der Experimente zeigte, dass das Sorptionsgleichgewicht in keinem Falle erreicht war. Es zeigt sich, dass alle Ionenprodukte größer sind als das entsprechende Löslichkeits-produkt, d.h. sowohl die Ausgangslösungen als auch die Lösungen nach der Sorption liegen in jedem Falle im Zustand der Übersättigung vor. Außer der ²²⁶Ra-Sorption am Grauen Salzton wurde auch festes (Ra,Ba)SO₄ ausgeschieden. Beide Mechanismen tragen im Belastungsfall zur ²²⁶Ra-Immobilisierung bei.
[1] Langmuir, D., Riese, A.C.: Geochim. Cosmochim. Acta 49 (1985) 1593.
[2] Paige, C.R. et al.: Geochim. Cosmochim. Acta 62 (1998) 15.

Förderung: BfS-Projekt: Nuklidmigration im Deckgebirge des ERAM, PSP-Nr.: 9M 212230-62.

Recently it has been demonstrated that ion irradiation of ultrathin magnetic films and multilayer structures is a versatile tool to modify the magnetic properties of these systems in laterally confined areas [1–3]. In most cases the modification of the magnetic anisotropy or the different exchange coupling contributions present in multilayered films are due to a post deposition modification of the interface structure. Depending on the enthalpy of mixing light ion irradiation may result in a roughening or a sharpening of the interface on the atomic level. Due to the local nature of the ion-solid interaction these modifications can be restricted to confined areas resulting in magnetically patterned films without a modification of the surface topography.
An alternative route to ion-driven magnetic nanostructures relies on ion implantation. By doping magnetic thin films in a percentage range with Cr or rare earth transition metals either the Curie temperature [4] or the magnetic damping behavior [5] can be adjusted. In combination with focused ion beam techniques magnetic nanostructures can be written directly into the film structure. Applications in the area of patterned storage media are evaluated currently.
The third approach makes use of ion beam synthesis of magnetic nanoparticles in a nonmagnetic single crystalline oxide host matrix [6]. Magnetic ions are implanted into the host material which leads to a supersaturation of these ions. During implantation at elevated temperatures or a succeeding annealing step the metallic precipitates grow and form, depending on their size and structure, ferromagnetic nanoparticles.
The current status of these different techniques with respect to magnetic nanostructure formation will be reviewed.
References:
[1] C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280, 1919 (1998).
[2] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[3] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett., 86, 162502 (2005).
[4] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).
[5] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003).
[6] C. W. White, S. P. Withrow, J. M. Williams, J. D. Budai, A. Meldrum, K. D. Sorge, J. R. Thompson, L. A. Boatner, J. Appl. Phys. 95, 8160 (2004).

A measuring system based on potential difference probes is presented which makes possible the determination of very small values of the velocity in liquid metal flows. On the one hand, a large size of the sensor and a high induction of the static measuring field, respectively, and resolution on the other hand has always been a compromise. These opposite demands were countered with state of the art analog instrumentation, and by avoiding meticulously potential sources of error such as induced noise and the even more detrimental thermoelectricity. The present paper instances the flow driven by a rotating magnetic field, in which the scaling of velocity versus strength of the driving electromagnetic force was examined. The measurement of the transition from the Stokes regime to a laminar boundary one demonstrates the obtained improvement of the velocity resolution by about two orders of magnitude.

The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to water. Secondary mineral colloids of 10E+1 to 10E+2 nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, aluminosilicates, amorphous Al(OH)3 and gibbsite with possible additions of iron silicates and iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock-water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity.

The effect of flux and Ar pretreatment during ion beam nitriding of austenitic stainless steel is investigated. The ion energy and temperature were 1.2 keV and 400°C, respectively, the ion current densities were 0.5, 0.67, and 0.83 mA∙cm-2. The nitrogen distribution profiles were measured using nuclear reaction analysis. The obtained nitrogen distribution profiles were analyzed by the means of the nitrided layer thickness evolution due to sputtering and diffusion and the model of trapping-detrapping. Both approaches could fit well the experimental results, however different diffusion coefficients have to be assumed for each current density. In addition, the diffusion coefficients are higher for higher current densities. On the other hand, it is shown that the pretreatment with Ar ion beam at nitriding temperatures produces only a thermal effect without any other influence on the following nitrogen diffusion. The results are discussed in relation with surface and temperature effects and atomic transport mechanisms.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMIS`s discussed above have been used for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB is applied for the ion beam synthesis of CoSi2 micro-structures down to 30 nm. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials. Especially this direct patterning was used for the fabrication of various kinds of micro-tools as well as recently for nano-holes in AFM cantilever tips.
Running and future activities will be discussed which are focused to the preparation and investigation of plasmonic structures, like nano-wires and nano-chains in the sub-micron scale down to a few ten nanometers.

Electromagnetic levitation is a well-known technique for container-less processing of molten metals and their alloys. In experiments, the levitated bodies often exhibit various kinds of instabilities. In the simplest case of static instability, a small displacement of the body from its equilibrium position can cause the failure of levitation. In some other cases the levitated bodies are observed to start to oscillate with growing amplitude or rotate with increasing rate that also can result in failure of levitation. This work presents a theoretical study of oscillatory and rotational instabilities of a solid sphere levitated electromagnetically in 3D coil systems. We have developed a combined numerical and analytical approach to analyze the static and dynamic stability of a sphere depending on the AC frequency and configuration of the magnetic system which is modeled by linear current filaments. First, we calculate numerically the magnetic vector potential in a number of points on the surface of the sphere and use Legendre and fast Fourier transforms to find the expansion of the magnetic field in spherical harmonics about the center of the body. Second, the numerically obtained expansion coefficients are substituted into the analytic solution describing the perturbation of the total electromagnetic force depending on both the displacement of the body from its equilibrium position and its velocity of motion. Thus we find the effective electromagnetic stiffness coefficients which characterize the frequency of small-amplitude oscillations of the body. Each equilibrium position is characterized by three mutually orthogonal principal directions of oscillations and three corresponding principal stiffness coefficients which all have to be positive for the equilibrium state to be statically stable. Dynamic instabilities are characterized by critical AC frequencies which, when exceeded, may result either in a spin-up or oscillations with increasing amplitude. The effective electromagnetic friction coefficients which are usually small are found by classical perturbation theory approach. For the spin-up instability we propose a new theoretical model applicable for arbitrary field configurations. This model yields three critical AC frequencies for rotations around three mutually orthogonal principal axis found respectively as eigenvalues and eigenvectors of the effective electromagnetic friction coefficient matrix. Our approach may be useful for analysis and design of electromagnetic levitation systems.

The forced crucible rotation technique has been applied to the solidification of Nd-Fe-B alloys. Specially sealed samples were subjected to well-defined forced rotation during induction heating and solidification. The resulting microstructure of the Nd-Fe-B alloys in consideration of melt convection has been investigated using scanning electron probe microscopy. The determination of the α-Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the α-Fe volume fraction in samples with high crucible rotation frequencies. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.

Für die Untersuchung von mehrphasigen Strömungen steht am Forschungszentrum Rossendorf eine Röntgenanlage mit einem zweidimensionalen Bildaufnehmer und einer eindimensionalen schnellen Detektorzeile zur Verfügung. In dieser Arbeit soll die Eignung dieser Anlage zur Bestimmung der lokalen Gasphasenverteilung in einem begasten chemischen Rührkesselreaktor, der aus der Verfahrenstechnik her bekannt ist, untersucht werden. Dazu wird zunächst die Signalcharakteristik des Aufnahmesystems untersucht, um die zu erwartende Genauigkeit der tomographischen Messung beurteilen zu können. Ein Algorithmus für die Rekonstruktion von zwei- und dreidimensionalen Projektionsdaten wurde implementiert. Mit einem Phantom wurde die quantitative Genauigkeit der Bestimmung zeitgemittelter Gaspahsenanteile überprüft. Zur Korrektur der Strahlaufhärtungsartefakte wurde eine Kalibriermethode entwickelt, mit der es möglich ist, die Gasphasenanteile direkt aus den bestimmten Schwächungskoeffizienten zu bestimmen. Es konnte gezeigt werden, dass die quantitative Genauigkeit der Kegelstrahl-Tomographie durch den hohen Anteil an Streustrahlung beeinträchtigt ist. Mit der schnellen Detektorzeile wurden schnell rotierende Objektstrukturen sichtbar gemacht.

Bacteria in nature do not usually occur as single individual bacterial cells but rather in large communities of bacteria glued together by Extracellular Polymeric Substances (EPS). Such aggregates are called biofilms. They may significantly influence the transport of heavy metals in the geosphere by changing the geochemical conditions within the biofilm or simply by adsorption onto biological surfaces. For these biofilm studies we generate thick biofilms in a rotating annular bioreactor that provides a well mixed liquid phase, turbulent flow and constant shear fields [1]. For biofilm sampling, removable microscopic slides with affixed mineral platelets are placed in recessed slots on the outside of the inner cylinder. These slides can be removed via a port in the top of the reactor. The nutrient solution includes a bacteria cocktail (Pseudomonas stutzeri, Pseudomonas fluorescens, Flavobacterium aquatile, Bacillusus thuringiensis) was pumped through the reactor at 0.02 mL per minute into the base of the reactor, triggering a circulation from bottom to top at room temperature. After the experiment the mature confluent biofilm was removed from the reactor and the biofilm thickness of approximately 150 µm was determined by using Confocal Scanning Laser Microscopy (CLSM).

To measure the electrochemical conditions such as redox potential and/or pH in situ within the biofilm and in the surrounding bulk solution an experimental setup has been developed. Previous work has been carried out by means of several sensors, mainly focused on the interface basis material/biofilm to investigate microbial induced corrosion [2]. Because of low lateral dimensions for an analytical study of concentration profiles in biofilms only micro sensors with extremly small diameters are applicable. It is essential that the biofilm is not affected by the use of the grooved sensor and that the front surface exclusively acts sensitively. In our experiments an investigation concept is introduced, where the electrochemical micro sensor forms a unit with an integrated micrometer screw (advantage: not rotable spindle). In this way during the measurement the micro sensor can be moved in the biofilm in µm-steps vertically. The sensor systems to determine the redox potential and the pH value consist of indicator electrode and reference electrode, which are arranged sidewise and possess a ceramic diaphragm. The applied redox sensors have been developed in different constructions. On the one hand glass coated Pt sensors with an outer diameter of 300 µm have been constructed; on the other hand we applied micro sensors covered with wax and resin having an outer diameter of 120 µm. In both cases the diameter of the sensitive area amounts to 80 µm.
In our experiments we used the newly constructed micro sensors to determine the redox potentials and pH values within the biofilm generated in the rotating annular bioreactor. In the near future it is planned to develop micro sensors for measuring concentration gradients of other substances such as Cl- and NO3- [3], too.

Ion implantation and subsequent thermal annealing are the standard processes for the electrical doping of semiconductors. Ion implantation is characterized by fast ballistic processes which lead to the deposition of the implanted atoms and to displacements of the target atoms. After the fast relaxation of the displaced atoms a (meta)stable defect structure is formed. Long-term thermally activated processes, especially during thermal annealing, cause defect reduction, rearrangement, and migration. In my talk I will show that computer simulations on the atomic level are a useful tool for the theoretical description of the different physical processes occurring during ion implantation and thermal annealing. The ballistic processes are simulated by the Crystal-TRIM code which is based on the binary collision approximation (BCA). This code is part of different process simulators. Classical molecular dynamics (MD) simulations are employed to investigate defect migration over a period of 10 - 100 ns. The defect diffusivity as well as the microscopic migration mechanisms are studied. A combination of BCA and MD simulations is used to determine the complex defect morphology after the fast relaxation processes are finished. This method allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion.

We describe the design and implementation of a broad-gain and low-threshold (Jth = 860 A/cm2 at 8 K) quantum-cascade laser based on strain-compensated In0.73Ga0.27As-AlAs on InP. Laser emission between 3.7 and 4.2 um is achieved because of the very large Gamma-valley conduction band discontinuity with narrow quantum wells, allowing large intersubband energy differences. Furthermore, the design inhibits carrier loss from the upper lasing state into the continuum even at elevated operating temperatures, resulting in room-temperature operation. Laser operation in pulsed mode is achieved up to a temperature of 330 K with maximum single-facet output peak powers of 6 W at 8 K and 240 mW at 296 K. The temperature coefficient T0 is 119K. The 30-period structure exhibits an external differential efficiency of 13 (40% per period) at low temperatures and a maximum wall-plug efficiency of 24%. The lasing transition takes place from several upper states to several lower states, resulting in a relatively broad (300 cm-1) gain spectrum and could allow the design to be used in external tuning configurations.

At the radiation source ELBE (Electron accelerator producing a quasi-continuous electron beam of high Brilliance and low Emittance) of the FZR a neutron source is being constructed. The electron beam with energies of up to 40 MeV and pulse frequencies of up to 13 MHz is converted into sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator with a small volume. The neutrons are generated by bremsstrahlung photons through (gamma,n)-reactions. The energy deposition of the electron beam in the small neutron radiator is that high that any solid material would melt. Therefore, the neutron radiator consists of liquid lead flowing through a channel of 11.2×11.2 mm² cross section. From the thermal and mechanical point of view molybdenum turned out to be the most suited channel wall (thickness 0.5 mm) material. Depending on the electron energy and current up to 20 kW power will be deposited into a radiator volume of 3 cm³. This heating power is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are in the range of 2 m/s in the radiator section. The electrons escaping from the radiator and the secondary radiation are dumped to a large extent in an aluminum beam dump. To reduce the radiation background in the measuring direction, the neutrons are decoupled from the radiator at an angle of 90° with respect to the impinging electrons.
Particle transport calculations were carried out to determine the volumetric heat generation in the liquid lead, in the channel wall and in the Al beam dump. Subsequent fluiddynamic and thermo-mechanic finite element analyses are performed to proof the mechanical integrity of the radiator channel. It could be shown that the equivalent plastic strain of the radiator channel can be kept sufficiently small, i.e. less than 1 %. Thermal analyses of the water cooled Al beam dump proved, that the maximum temperatures do not exceed 200 °C, thus a sufficient distance from the melting point is maintained.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the surface of a depleted uranium (DU) disc immersed in a Ca-phosphate solution for 182 days. The weathering solution contained 2.49 · 10^-3 M calcium and 1.05 · 10^-3 M phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that meta-autunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. This secondary U(VI) mineral phase was identified using a fingerprinting procedure by comparing it with TRLFS-spectra from an in-house U(VI) TRLFS database, including U(VI) oxides, U(VI) hydroxides, U(VI) sulphates and U(VI) phosphates. Its TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50 ± 5 ns and 700 ± 25 ns.

Ion irradiation is a versatile tool to modify magnetic properties like anisotropy or exchange coupling in thin magnetic films and multilayers on a local scale. The presentation will review the present status of magnetic anisotropy and domain patterning in amorphous CoFeSiB films and the ion irradiation induced phase transformation in FePt nanoparticle systems.

Review about the present status regarding magnetization dynamics investigations of magnetic tunnel junctions and exchange bias systems.

The paper contributes to the advanced CFD simulation of subcooled boiling in forced convective flows, with special attention given to the momentum transfer between continuous liquid and vapour bubbles. A wall boiling model, implemented in CFX-5 (Egorov, Menter, 2004) and based on the two-fluid approach, is used here together with the state-of-the-art model correlations for the non-drag forces, available in CFX-5. The paper describes the main concepts of modelling mass, heat and momentum transfer between the phases. Published experimental results for flow in a pipe are used for the model validation.
The model is applied to the simulation of subcooled boiling flow in a hot channel of a fuel rod bundle. Influence of mixing vanes, attached to the spacer grids of fuel assembly in order to enhance the heat transfer, is taken into account. The simulation results demonstrate the capability of the model to estimate the effects of geometrical design on the flow physics.

High energy, high dose Ge ion implantation in silicon results after rapid thermal annealing in a defect structure which shows a stacked structure consisting of sequential layers of vacancy-type defects (cavities) and interstital-type defects (dislocation loops). This structure is in contrast to the predictions of the so called +1 model. The conditions for the formation of such defects and the limits of the +1 model are discussed.

Ion implantation is a well-known standard procedure in electronic device technology for precise and controlled introduction of dopants into silicon. However, damage caused by implantation acts as effective gettering zones, collecting unwanted metal impurities. This effect can be applied for "proximity gettering reducing the concentration of impurities in the active device region. In this study the consequences of high-energy ion implantation into silicon and of subsequent annealing were analysed by means of secondary ion mass spectrometry (SIMS). Depth profiles were recorded of such impurities as copper, oxygen and carbon to obtain information about their gettering behaviour. The differences in impurities gettering behaviour were studied as a function of the implanted ions, P and Si, of the implantation dose and annealing time at T=900degreeC. Besides impurities gettering at the mean projected range (Rp) of implanted ions, Rp-effect, defects at around half of the projected ion range, Rp/2-effect, and even in some cases beyond Rp, trans-Rp-effect, have also been found to be effective in gettering of material impurities.