Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

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

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

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

Surface modification of Ti6Al4V alloy by duplex plasma processing

High Temperature Plasma Immersion Ion Implantation of Ti6Al4V

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

AIM:

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

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

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

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

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

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

kein Abstract..

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Status report concerning WP1 of BioCare project

Status report for ENLIGHT WP 5

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

In this work, nitrogen plasma immersion ion implantation (PIII) treatment of austenitic stainless steels 1.4301 and 1.4571 was performed to investigate the influence of the process conditions on the corrosion properties. Short treatment, high voltage and high temperature result in a decreased corrosion potential while no correlation to layer thickness, nitrogen concentration or lattice expansion was found. Except for the possibility of small CrN agglomerates at high temperatures, no direct explanation for the results can be provided and it is argued that intrinsic stress accumulation and relaxation may be responsible.

An attempt to synthesize superconducting MgB2 inter-metallic compound from the liquid state is presented. The process consists of two steps. In the first one, boron ions are implanted into a magnesium substrate. In the second one, the near-surface region of such system is melted by short, intense hydrogen plasma pulses without necessity of annealing in Mg vapor. A magnetically modulated microwave absorption method was used to detect superconducting regions in the obtained MgB2 layer. Percolation between nano-regions (islands) of MgB2 has not been observed. However, a superconducting state of the insulated islands has been experimentally proven with transition temperatures TC as high as 31 K.

es ist kein Abstrakt vorhanden.

Semiconducting iron disilicide (β-FeSi2) was prepared by ion beam synthesis (IBS) in (111)Si P-type by implantation at 440 ˚C of 195 KeV Fe ions with a dose of 2.1017 Fe+/cm2 followed by annealing in a N2 atmosphere at 900 ˚C for 4 h. Characterization of samples included Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) pole figure, and Raman spectroscopy. A mixture of β-FeSi2 and α-FeSi2 was observed in the as-implanted state. A Photoluminescence (PL) measurement at 12K indicates the luminescence peak at the energy of about 0.81 eV corresponding to the band gap energy of β-FeSi2 phase.

Measuring the resonance strengths of the 25Mg(p,γ)26Al reaction at energies of astrophysical interest poses a very difficult task for the usual prompt γ-ray detection method. Here we describe an alternative method in which targets are first irradiated and the produced 26Al nuclei are off-line counted by means of AMS. An overall efficiency of 4 × 10−5 could be achieved extracting AlO− from the ion source. For this purpose, a careful chemical treatment of the samples and the use of a gas filled magnet were necessary.

The hard Ti-based coating TiAlN has been produced by plasma immersion ion implantation-assisted deposition (PIIIAD) on austenitic stainless steel. In PIIIAD, the substrate is exposed to cathodic arc plasma comprising of metallic ions corresponding to the cathode composition, and the substrate is biased pulsed negative. The pulsed bias of the substrate renders alternate phases of deposition (during the bias off time) and implantation and deposition (during bias on time), thereby controlling deposition temperature, reduction of compressive stresses, increase of crystallinity and enhancing adhesion of coating to substrate. The deposition has been carried out in a neutral as well as reactive nitrogen environment, which leads to nitrogen-containing coatings. In addition to TiAlN, also, Ti, TiN and TiAl were produced to investigate the effect of the different elements. All the coatings are tested for their suitability as biocompatible coatings, and hence, the adherence of osteoblast progenitor cells to these coatings was investigated in correlation with deposition parameters and surface morphology. The results identify the coatings that are wear resistant and suitable for orthopaedic implants.

This work presents selected results from carbon ion implantation into pure Al matrix. The carbon ions were implanted with an ion energy of 25 keV and fluences of 1×1021 and 2×1021 C+/m2 at room temperature (RT) and elevated temperature of 400 °C. Elastic recoil detection analysis (ERDA), grazing incidence X-ray diffraction analysis (GIXRD), Raman spectroscopy and high resolution electron microscopy (HRTEM) show the formation of embedded Al4C3 precipitates with carbon concentrations below its stoichiometric level. At RT ion implantation, the Al4C3 precipitates have an average grain size in the order of 2–4 nm. For carbon ion implantation at 400 °C, the precipitates grow up to approximately 20 nm in diameter and are randomly distributed in the implanted region. The carbon excess, not bound in the Al4C3 precipitates, forms highly disordered C–C clusters of approximately 0.2–0.4 nm in size. Implantation at a temperature of 400 °C reduces drastically the carbon clusters content due to the growth of the Al4C3 precipitates.

A significant wear reduction by several orders of magnitude is the common result for austenitic stainless steels after energetic nitrogen implantation at medium temperatures around 380 °C. In contrast, martensitic stainless steels are rarely investigated. In this investigation, one steel grade, stainless steel AISI 630/DIN 1.4542, is treated using low energy nitrogen implantation at 380 and 600 °C, high voltage nitrogen plasma immersion ion implantation (PIII) and combined carbon/nitrogen PIII at 380 °C. Using PIII, an expanded martensitic lattice extending several micrometers into the sample was observed, whereas Fe4N and CrN were formed after low energy implantation at 380 and 600 °C, respectively. All samples show a hardness of up to 2000 HV and a wear reduction by two orders of magnitude. Additional metallographic cross-sections confirm the microstructure derived from XRD data.

The von Karman sodium (VKS) experiment is intended to investigate the hydromagnetic dynamo effect in a highly turbulent flow. Although much effort has been spent in the optimization of the flow structure and the lateral boundary conditions in order to minimize the critical magnetic Reynolds number, no dynamo effect has been seen in the recent experiments. The measured induced magnetic fields deviate significantly from the computed ones. In order to understand these experimental result, we focus on the role of lid layers, i.e. layers of liquid sodium between the impellers and the end walls of the cylinder. It is shown that static lid layers yield a moderate increase of the criticial Rm by approximately 12 per cent. A more dramatic increase by 100 until 200 per cent can occur when some rotational flow is taken into account in those layers. Possible solutions of this grave problem are discussed for the real dynamo facility.

The FZR performed parallel experimental and numerical investigations in order to better understand the mechanisms leading to slug formation. For the CFD simulation, the code CFX-5 was used, applying the two fluid model with the free surface option. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying slug flow.

The aim of this work is to numerically assess the dynamics of the mixing process of two different density liquids in a stirred tank reactor. The mixing of different density liquids is common operation in the process industry which occurs when a higher density liquid is injected into a tank filled with a lighter density one or in the case of impeller malfunctioning when such a system of different density liquids can get stratified. The process might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses, performed with the CFX-5 numerical package, were carried out for a non-baffled stirred tank reactor, mechanically agitated by a Pfaudler impeller. Although the non-baffled vessel posses an axi-symmetric behaviour on macromixing scale, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. The dynamic mixing behaviour of two miscible liquids with different densities was numerically predicted from initially stratified conditions to complete mixing. The gas phase was involved in the simulations to investigate the effect of the free surface deformation on the mixing process, which was modelled using the free surface model. The multicomponent model was applied to the liquid phase in which the two different density liquids were present. The suitability of the different turbulence models was also addressed but the k-ε turbulence model was finally employed. The numerical simulations were performed on different size grids to ensure obtaining of grid independent results. However, the grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Additionally, the impeller acceleration was taken into account.
The accuracy of the numerical predictions was evaluated experimentally using a video visualisation technique. The initially stratified lighter (alcoholic) coloured component and the heavier (water) transparent one were brought into motion by the rotating impeller. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The procedure was repeated for a number of different initial concentrations of the lighter liquid to obtain the colour-calibration curve. The numerical predictions were evaluated at several locations, close to the vessel central line and wall, for which the optical distortions were minimal. Since the video visualisation technique provides the integral mixing curves at the chosen locations, the predicted concentration values were exported and averaged along the lines corresponding to these locations.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred tank reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation.

In this paper we present a very compact cyclotron resonance (CR) spectrometer based on a GaAs/AlGaAs quantum cascade laser emitting at 11.4m. We show its operation under magnetic fields up to 60T and in temperatures up to 80K. We, finally, illustrate our spectrometer with the measurements of InAsxSb1-x alloy.

Resonant electron-LO phonon assisted depopulation of the lower lasing state is one of the common approaches to ensure population inversion and gain of quantum cascade lasers (QCLs) [1]. As a consequence, understanding of the dominating energy relaxation channels is important for development and optimizing of the active region of QCLs, especially built with new or modified materials. In this work we present a method to study the energy of the phonon modes responsible for nonradiative energy relaxation of electrons in the active zone of QCLs. The method is based on the spectrum analysis of the oscillations pattern of QCLs emission intensity as a function of magnetic field applied along the growth direction. These oscillations known as intersubband magnetophonon resonance (IMPR) originate from the resonant phonon assisted scattering of electrons from the upper lasing state into the Landau ladders of lower subbands whenever it is allowed by energy conservation [2] (Fig.1). The IMPR oscillations are periodic in the reciprocal magnetic field. Each lower subband and each phonon mode results in a maximum of the oscillation spectra. Each maximum corresponds to resonant scattering of electrons into the first Landau level of one of the bottom subbands, therefore the difference between intersubband and cyclotron energies gives the energy of phonon modes ensuring the relaxation.
In our experiments we have studied three sets of samples. The first two ones are GaAs/AlGaAs QCLs with different Al concentration in the barriers (33% and 45%) [3]. We clearly demonstrated that in the case of high Al concentration the relaxation via AlAs-like LO phonon can be significant (Fig. 2.). The third set is a In0.73Ga0.27As/AlAs short-wavelength QCL [4]. In this case we found that in spite of the high Al concentration in the barriers and the low GaAs contents in the wells, the nonradiative energy relaxation happens principally via GaAs-like or InAs-like (or mixed modes) phonon emission, while a clear signature of AlAs-like phonons was not observed.

[1] J. Faist et al., IEEE J. Quantum Electronics 38, 533 (2002).
[2] D. Smirnov et al., Phys. Rev. B 66, 125317, (2002); D. Smirnov et al., Phys. Rev. B 66, 121305(R) , (2002)
[3] P. Kruck et al. Appl. Phys. Lett. 76, 3340 (2000) ; H. Page et al., Appl. Phys. Lett. 78, 3529 (2001)
[4] M. P. Semtsiv et al., Appl. Phys. Lett. 85, 1478 (2004).

The investigations of insulation debris generation and transport gain in importance regarding the reactor safety research for PWR and BWR considering all types of LOCA as well as short and long term behaviour of emergency core coolant systems.
The background of experimental investigations consists of the generation of a wide data base developing and validating the CFD-models for the description of particle transport phenomena in flow (e.g. drift, subsidence, sedimentation, resuspension, agglomeration and head loss at hold-up devices) under various geometric and fluidic boundary conditions. Separate effect experiments for the investigation of particle transport phenomena in multidimensional water flow, sedimentation and resuspension processes were carried out at plexi glass test facilities (Column, Ring Channel) using modern flow measurement and digital image processing technologies. The behaviour of gravitating insulation particles in aqueous solution (sink rates or settling velocities) and sedimentation processes were observed at the test facility “Column” in 2D-geometry. Experiments for the determination of 2D-transport behaviour of different particle sizes in horizontal carrier flow were realised at facility “Ring Channel”. Experimental results were generated with constant cross section area along the whole channel length as well as with varied cross section areas (e.g. barriers) and strainers.
Model developments for CFD simulations of insulation material transportation, suspension, resuspension and the clogging and penetration at strainers are described. The check of model parameters and functions based on the separate effect experiments.
The paper includes the presentation of experimental results generated at the facilities, the theoretical concepts for modelling these phenomena with CFD-codes and the comparison between simulated and measured data.

For further model development and the validation of CFD codes for two-phase flow applications experiments were carried out with a sudden change of the superficial velocity of water in a vertical pipe of 51.2 mm diameter. Measurements of the cross sectional gas volume fraction distributions were taken by two wire-mesh sensors (24x24 points, 2500 Hz) mounted in a short distance (16 mm) behind each other. This sensor assembly was placed 3030 mm downstream of the gas injection. The change of the superficial water velocity was jump-like reduced and in a second series of tests jump-like increased. The tests enable the observation of the restructuring process of bubbly flow between two steady state conditions. The experimental results for tests showing a monodisperse bubble size distribution were compared to CFD calculations using the code CFX-5. Applying the two fluid approach, the momentum interaction between the liquid and gas phase was considered. For the experimental conditions of dispersed bubbly flows without or with neglectable bubble coalescence & breakup the main flow features observed in the experiments could be reproduced qualitatively and quantitatively by the numerical simulation. Further research will be undertaken for the investigation of flow regime transition from gaseous phase volume fraction wall peak to core peak dominated flows. Further investigations will also include compressibility effects for the disperse bubbly phase.

The hydrodynamics of a rectangular bubble column operating in the dispersed bubbly regime has been numerically investigated using a two-fluid model Large Eddy Simulation (LES). Experimental data was obtained to validate the numerical model. LES computational fluid dynamic calculations of the transient flow for the bubble column were performed to account for the turbulence in the liquid phase. The computational mesh is of the same scale as the bubble size. The sub-grid scale Reynolds stresses were calculated using the Smagorinsky model. Furthermore, the effect of the bubbles on the turbulence in the continuous phase was modeled using Sato’s eddy viscosity model for bubble-induced turbulence. LES facilitates the direct numerical resolution of length scales that play an important role in the transport of bubbles, avoiding the need for constitutive models like the turbulent diffusion force to account for diffusion of the gas phase under the influence of the large eddies. Mean quantities, in particular the void fraction and the average velocity of the bubbles, were computed by averaging over a time period that was longer than the dynamic time scales of the turbulence. A systematic analysis of the effect of the interfacial momentum transfer terms on these quantities has been conducted. The bubble column was locally aerated using a sparger located in the center of the bottom plate. The model was validated with experimental data (Reddy Vanga, 2004) obtained using wire-mesh tomography measurements for void fraction and bubble size distributions. The experiments were performed for various aspect ratios (height of water column to width ratio) and superficial gas velocities.

The investigation of insulation debris generation, transport and sedimentation gains importance regarding the reactor safety research for PWR and BWR considering the long term behaviour of emergency core coolant systems during all types of LOCA. The insulation debris released near the break during LOCA consists of a mixture of very different particles concerning size, shape, consistence and other properties. Some fraction of the released insulation debris will be transported into the reactor sump where it may affect emergency core cooling. Open questions of generic interest are e.g. the sedimentation of the insulation debris in a water pool, possible re-suspension, transport in the sump water flow, particle load on strainers and corresponding difference pressure.
A joint research project in cooperation with Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While experiments are performed at the IPM-Zittau, theoretical work is concentrated at Forschungszentrum Rossendorf.
In the present paper the basic concepts for CFD modelling are described and first results including feasibility studies are shown. During the ongoing work further results are expected.

In this work a general-purpose CFD code CFX-5 was used for simulations of subcooled flow boiling. Some important modelling issues were investigated: heat flux partitioning, turbulence modelling and non-drag forces. The subcooled boiling model, available in a custom version of CFX-5, has been used here. The special treatment of the wall boiling boundary, based on analytical temperature wall function, assures the grid invariant solution. The calculations been validated against the published experimental data of high-pressure flow boiling in a vertical pipe covering a wide range of conditions (relevant also to the pressurized water reactor).

Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, where one of the phases is a continuous liquid and the other phase consists of gas or vapour of the liquid phase. In the range of low to intermediate volume fraction of the gaseous phase the multiphase flow under consideration is a bubbly or slug flow, where the disperse phase has to be characterized by an evolving bubble size distribution due to bubble breakup and coalescence processes. The paper presents a generalized inhomogeneous Multiple Size Group (MUSIG) Model, where the disperse gaseous phase is divided into N inhomogeneous velocity groups (phases) and where each of these groups is subdivided into M bubble size classes. Bubble breakup and coalescence processes between all bubble size classes are taken into account by appropriate models. The derived inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility at the Research Center Rossendorf (FZR). Comparisons of gas volume fraction and velocity profiles with TOPFLOW-074 testcase data are provided, showing the applicability and accuracy of the model for polydispersed bubbly flow in large diameter vertical pipe flow.