Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

In Pressurised Water Reactors (PWRs) the parameters of the coolant may differ from one loop to another and change in time during transients. In case of an undesired decrease of the boron acid concentration we speak about boron dilution transients. In other cases also the coolant temperature may be affected, e.g. by overcooling of a loop if a main steam line break happens. Both kinds of transient lead to a positive reactivity insertion, which may cause a dangerous power excursion. For the analysis of the core behaviour during boron dilution transients and main steam line breaks, coupled neutron kinetic / thermal hydraulic codes are necessary. These codes must contain models of the coolant mixing on its way from the inlet nozzles to the core entrance, because the reactivity insertion strongly depends on the distribution of these parameters at the core inlet. The coolant mixing mainly happens in the three-dimensional flow field inside the complex geometry of the downcomer and lower plenum. It depends signifi-cantly on the construction of the reactor vessel. The modelling of coolant mixing was carried out by detailed computational fluid dynamics (CFD) calculations with the code CFX 4.2. For the validation of the computational results, the ROCOM test facility was built, a fluid dy-namic model of the reactor in the scale of 1:5. The reactor vessel is made of Plexiglas for flow visualisation and LDA measurements. The four loops dispose of separately controllable main coolant pumps. Plugs of coolant with low boron acid concentration are modelled by salt water injection. The use of a system of wire-mesh sensors allows to measure salt concentra-tions at over 1000 locations with a maximum time resolution of 200 Hz. Measuring locations are at the reactor inlet, at the core inlet as well as in the upper part and at the lower end of the downcomer. The experiments as well as the calculations have shown, that the mixing is in-complete. In case of stationary coolant flow in all loops a disturbance of boron concentration or temperature is transferred to a sector of the core inlet plane, which corresponds to the loca-tion of the inlet nozzle. In the steady state, the concentration respectively temperature in the centre of the sector almost reaches the amplitude of the disturbance at the inlet nozzle. A short plug of boron diluted water experiences a better mixing: due to the vortices in the downcomer different portions of the disturbance are transported with different velocities. This causes a dispersion of the front and the end of the plug (axial mixing). If the plug is short enough, the maximum concentration decreases. Further, experiments and calculations are going on to be performed for the investigation of mixing under transient conditions (start of circulation). Response functions will be calculated for the development of a fast running mixing model.

A DC glow charge plasma source was used to implant various types of materials (Al, SS 304, Si) with nitrogen.

High-resolution x-ray diffraction methods have been used to characterize nitrogen-doped silicon obtained by plasma immersion ion implantation.

The formation of iron disilicides by ion implantation at room temperature and the subsequent ion beam induced epitaxial crystallization process was studied by conversion electron Mössbauer spectroscopy. Implantation with 195 keV Fe ions with doses from 7 x 1015cm-2 to 2 x 1017cm-2 at room temperature leads to an amorphized top layer of about 300 nm thickness. The concentration profiles determined by Auger electron sputter depth profiling have maximum iron concentrations from 0.7 at.% for the lowest dose up to 21.1 at.% for the highest dose at about 100 nm depth. The Mössbauer spectra show similar broad quadrupole doublets for each dose which could not be attributed to any known amorphous or crystalline iron silicide phase. The subsequent irradiation with 1 x 1016cm-2 500 keV Si ions at 350°C induces the formation of iron disilicide phases and the crystallization of the Si substrates. For the samples containing the lowest iron content of 0.7, 2 and 5 x 1016cm-2 the metastable g-FeSi2 is produced whereas for doses of 1 x 1017cm-2 and higher the formation of a phase mixture of a- and b-FeSi2 is found.

Magnesium and aluminum were alloyed by implantation with iron ions. The implantation energy was 200 keV while the ion doses ranged over several decades up to 9x1017 cm-2. In this way it was possible to obtain highly disordered alloyed layers with up to 90 at.% iron [1]. To study possible ordering and redistribution processes samples were annealed in vacuum at subsequently increasing temperatures up to 600 °C for aluminium and up to 400 °C for magnesium. The annealing process was observed by conversion electron Mössbauer spectroscopy, Auger electron depth profiling, and x-ray diffraction. In the case of the Fe-Al system iron aluminides are formed. In the case of the Fe-Mg system (insoluble with each other), a-iron is precipited in small clusters.
[1] H. Reuther, M. Betzl, W. Matz, E. Richter, Hyperfine Interactions 113 (1998) 391

Four different combinations of ⁹⁶ ₄₄Ru and ⁹⁶ ₄₀Zr nuclei, both as projectile and target, were investigated at the same bombarding energy of 400 AMeV using a 4pi detector. The degree of isospin mixing between projectile and target nucleons is mapped across a large portion of the phase space using two different isospin-tracer observables, the number of measured protons and the t/³He yield ratio. The experimental results show that the global equilibrium is not reached even in the most central collisions. Quantitative measures of stopping and mixing are extracted from the data. They are found to exhibit a quite strong sensitivity to the in-medium (n,n) cross section used in microscopic transport calculations.

To date most Tc compounds suitable for coupling to biologically active molecules, e.g. CNS receptor targeted agents, are square-pyramidal complexes of the oxo ion [Tc=O]³⁺. However, the properties and thus the in vivo behaviour of such complexes are strongly influenced by the quite polar Tc=O unit offering a free position trans to the oxo ligand for further reaction in vivo. The stricter the requirements for specific agents, the more important is the question whether such a polarity is beneficial or not. Alternatives are oxo-free lower oxidation states. Here we report on prototypic trigonal-bipyramidal mixed-ligand complexes 1, 2 and 3 which are neutral, non-polar and robust since they contain sterically well shielded oxo-free Tc(III). We describe the syntheses and structural analyses of ⁹⁹Tc complexes with simple co-ligands serving as models for functionalized derivatives, the no-carrier-added preparation of the analogous ^99mTc-complexes as well as their stability in aqueous solution and in plasma, and their biodistribution in rats.

Auf dem Wege zu einer ökonomischen und sicheren Energietechnologie muß die Fusionsforschung Materialien entwickeln, die möglichst hohen Strahlenbelastungen standhalten und ein Minimum an langlebiger Aktivierung produzieren. Dazu ist eine geeignete Neutronenquelle als Bestrahlungsgerät unerläßlich. Neben dem Projekt IFMIF bleibt der Vorschlag des Budker-Instituts Novosibirsk für eine Neutronenquelle auf der Grundlage einer gasdynamischen Falle aktuell. Prinzipiellen Vorteilen dieses Quelltyps steht der Nachteil gegenüber, dass seine Funktionsfähigkeit durch die bisher verfügbare Datenbasis noch nicht ausreichend belegt werden kann. Der Vortrag gibt eine Einführung in das Konzept dieser Neutronenquelle und legt die Forschungsergebnisse dar, die in den letzten Jahren, teilweise in Kollaboration mit dem Forschungszentrum Rossendorf, erzielt wurden.

The confinement of the fast, anisotropic ions is one of the basic objectives of the GDT experimental research program. The approach consists in comparing the measured ion parameters with those predicted by computer simulations based on the theory of Coulomb collisions. A broad set of diagnostics for measurements of fast ion parameters has been developed. In particular, it includes the measurement of the local energy distribution function. In parallel the Monte Carlo transport code FIT, which simulates fast ion histories in the frame of the lassical theory has been developed. The comparison of the measured and computed parameters clearly shows that the energy confinement time of the fast ions is governed by Coulomb collisions only and significant anomalous ion losses were not yet observed in GDT experiments up to the present plasma parameters.

Electromagnetic levitation is a well-known technique for containerless processing of metallic samples. If the sample is melted the electromagnetic forces cause a melt motion inside the droplet. This motion is of interest since it influences shape oscillations or heat transfer within the droplet, or may even effect the stability behaviour of the droplet at all. First, the axisymmetric case is considered allowing no variations of quantities around the vertical axis which is the pronounced axis due to the symmetry of the levitating or heating magnetic fields. Typical mean flow strucures are calculated depending on the skin-depth parameter and the magnetic field interaction parameter for the two cases of a uniform or linear magnetic field. The stability of this axisymmetric flow is analyzed showing that those flow fields become unstable only at high numbers of the magnetic field interaction parameter N. This is in contrast to a few experimental observations indicating that oscillatory motions take place already at much lower values of N.
Therefore, the three-dimensional stability of the flow is investigated. This stability analysis is performed using spectral methods. As expected the first instability is characterized by an azimuthal wave number of one. But it is found that the most dangerous three-dimensional instability occures at relatively small interaction parameters being by orders of magnitude lower than the critical values of the axisymmetric case.

This work presents a numerical and experimental study of the growth of single intermetallic-compound crystals by the floating-zone method using a radio frequency (RF) heating magnetic field. The quality of the grown crystals depends strongly on the growth conditions, particularly on the shape of solidification front. To obtain single crystals of complex composition, a convex to the melt growth interface is desirable. The shape of the solid-liquid interface can be strongly influenced by the convective heat transport in the melt. There is a number of mechanisms driving the melt convection: differential rotation of the crystal and the seed, buoyancy, thermocapillarity and electromagnetic forces due to the RF heating. The aim of this work is to find out the growth parameters ensuring a desired shape of the crystalization front. The numerical study consists of two major parts - finding of the electromagnetic field induced by the RF-heater coil and the solution of the coupled heat and hydrodynamic problems. For the solution of the electromagnetic problem a novel boundary-integral method is developed. This method involving integration only along the surfaces is easily applicable to complex geometries at arbitrary skin depth. The heat and hydrodynamic problems are solved by a numerical code based on the control volume technique using a triangular finite-element-like mesh adapting to the solid-liquid interfaces. For small-diameter crystals considered here, only the thermocapillary and electromagnetically-driven convections turn out to be significant for the heat transport. Pure heat diffusion is found to result in the interfaces which are slightly convex over most of the diameter except close to the crystal surface where the interface is always concave to the solid phase. Such a form of the interface is determined by the Ohmic dissipation in the skin-layer and the heat radiation from the surface. A part of the produced heat is emitted directly from the liquid zone that makes the surface colder than the underlaying melt. Therefore the interface is concave in the vicinity of the surface. The rest of the heat released in the skinlayer is conducted radially inwards into the melt from where it enters the crystal to be emitted further away from the liquid zone. This inward heat flux is responsible for the central convex part of the interface. The numerical results give evidence that at the minimal length of the liquid zone, electromagnetically-driven convection may be so weak that it has no significant effect on the heat transfer. Strength of the forced convection rapidly increases with the heating power resulting in a concave interface over the whole diameter. Thermocapillary convection is found to be significant at smaller crystal diameters where it can substantially counterbalance the electromagnetically-driven convection in the bulk of the melt. Numerically found interface shapes are compared with experimental results obtained on a model system of Ni crystals.

Shape oscillations of electromagnetically-levitated metal droplets can be used to measure the surface tension and viscosity of liquid metals. The first determines the frequency while the second accounts for the attenuation rate of the oscillations. Until now the effect of the magnetic field on the frequency spectrum has been considered only in the perfect-conductor approximation where the action of the magnetic field reduces to the magnetic pressure on the liquid surface. In this approximation, magnetic field influences droplet oscillations in two ways. First, it causes a static deformation of the droplet. So the oscillations in the magnetic field occur about an aspheric basic shape. Second, the coupling between the shape variation and the magnetic field gives rise to a new oscillation mode called hydromagnetic surface wave. For small droplets magnetic field causes a slight perturbation of oscillations with both aforementioned effects resulting in the same order small corrections to the frequency spectrum of an inviscid spherical droplet. Magnetic field yields the same order relative correction also for the damping rate of oscillations of a viscous droplet. But there is no direct influence of the magnetic field on the damping rate of oscillations that is a serious drawback of the perfect-conductor approximation. Since for low-viscosity metal droplets the damping rate itself is small, even a weak direct effect of the magnetic field might be significant.
This work is dealt with the effect a high-frequency alternating magnetic field on the damping of the shape oscillations of viscous metal droplet. Conversely to the viscosity, high-frequency magnetic field is found to reduce the damping of the oscillations. We find the leading order solution of the damping rate by assuming the viscosity to be small but the frequency of the magnetic field to be high. The magnetic pressure is considered to be small with respect to the capillary pressure so that the static deformation of the droplet may be neglected. Besides, we assume the Reynolds number of the fluid flow driven by the magnetic field at finite skin depth in the droplet to be small so that the coupling between the base flow and shape oscillations may be neglected. Under these assumptions we formulate a theory for the case when both the magnetic field and oscillations are axisymmetric. The theory is applied to calculate the effect of a uniform magnetic field on the damping of the axisymmetric fundamental mode.

An axially symmetric isothermal liquid metal flow induced by a low frequency low induction rotating magnetic field in a cylindrical cavity is considered. This problem has already been addressed by several investigations but the existing results are still contradicting. We consider the problem numerically employing highly accurate spectral methods. We seek for the steady solution in vorticity-stream function formulation in space of base functions build up from Chebyshev polynomials to satisfy appropriate boundary conditions. The dynamical system is obtained and the spectrum of the linearized problem is found gradually increasing the forcing parameter. We evaluate the critical magnetic Taylor number for the basic solution in 0.1% accuracy as 166300 (for a diameter to height ratio 1). The oscillatory instability is found to be of another type than the expected Taylor-Goertler vortices. Several additional monotonically unstable steady solutions are detected in the range where the basic solution is stable. These additional solutions are marked by an additional couple of secondary vortices counter-rotating in the meridional plane near the side wall at the mid-height. Some of the additional steady solutions are particularly close to the basic steady state and therefore take high spatial resolution to be distinguished. We consider also the time dependent solution that allows much higher spatial resolution. The linear stability results were verified comparing to the dynamical parameters of the time evolution in the near-critical regime. This comparison shows 0.1% agreement. The unstable additional steady solutions close to the basic steady state indicate instability to small finite size perturbations. The closest one gives an estimate from above for the minimum energy of the unstable finite perturbation. This estimate is improved considerably by series of numerical time-dependent solutions developing from additional steady states. The basic state is found to be unstable with respect to a finite size Taylor-Goertler type perturbation of less than 3.0E-8 size (in relative energy terms). Such a small perturbation excites long-lasting non-linear oscillations already at 3/4 of the critical forcing. This excited regime in turn is found to be unstable to another instability that finally reestablishes the basic state. These results predict the possibility of an unpredictably oscillating flow already in the linearly stable regime. The results indicate that an experimental observation of the linear instability is hardly possible. The obtained results also explain the big differences in previous numerical results concerning the stability of the rotating magnetic field driven flow.

Lorentz forces can be used to control the near wall flow of low conducting liquids like sea-water. To achieve force densities strong enough to influence the flow, both magnetic and electric fields have to be applied to the fluid. Here the wall parallel Lorentz force in streamwise direction was generated by means of periodically arranged electrodes and permanent magnet strips of alternating polarity and magnetization direction, respectively. In a first approximation the resulting force is independent of the spanwise coordinate and decays exponentially with the wall distance. Such a force distribution acts as a source of momentum to the flow. It gives the possibility to compensate for viscous losses and to counteract adverse pressure gradients, thereby stabilizing the boundary layer and preventing separation.
Experimental results on the control of a flat plate boundary layer in a sodium chloride solution up to Re=9·105 will be given. LDA measurements show the effect of the Lorentz force on the boundary layer profile. At moderate force strength the mean velocity profiles are characterized by momentum thicknesses smaller than in the unforced case, at high enough Hartmann numbers a wall jet develops. Additionally, a turbulent, but practically non growing boundary layer has been observed for a special combination of Reynolds and Hartmann number. The fluctuating streamwise velocity component is slightly damped due to the accelerating action of the Lorentz force. Force balance measurements on the controlled flat plate show a reduction of the total drag by up to 80% compared to the uncontrolled case. The sole reason for this dramatic drag reduction is the momentum gain caused by the Lorentz force. From the velocity profiles one can conclude on a skin friction increase in the forced cases. However, the momentum gain overcomes the skin friction increase.
The effect of a suction-side, streamwise Lorentz force on a NACA-0017-like hydrofoil is quantified by means of force balance measurements for chord-length Reynolds numbers of 3 to 8·104. Depending on the angle of attack, two different effects are observed. (1) At small angles of incidence, a moderate increase in lift due to additional circulation is observed. Simultaneously, a decrease in the drag of the hydrofoil is caused by the added momentum. (2) At higher angles of attack, where the unforced hydrofoil would normally stall, a more pronounced lift increase (90% at Re=3·104) and a corresponding drag reduction are observed due to separation prevention.
Direct numerical simulations at low Reynolds numbers confirm the physical tendencies of the experiments.

A contactless control of melt convection is important for many crystal growth technologies. Typically steady magnetic fields are used to damp such flows and, in particular, turbulent fluctuations. Surprisingly, active flow driving forces due to alternating magnetic fields can be of stabilizing character, too. We present numerical results for the combined action of steady and alternating magnetic fields taking into account rotating, pulsating and travelling magnetic fields. Results will be given for the silicon Czochralski and the vertical Bridgman crystal growth process. For given thermal conditions of the process a typical buoyancy convection takes place. In case of the Czochralski process the convection is additionally determined by crystal and crucible rotations and the thermocapillary driven flow at the free melt surface. We study the influence of different magnetic field combinations on these melt convections. Results will be presented in which way different combinations of fields change the mean flow structure and influence the level of turbulent fluctuations. In order to limit the computational effort, we apply first a zero equation turbulence model based on the Prandtl mixing length hypothesis and afterwards a standard two equations turbulence model (k-omega).

Usually, MHD is understood as the forward problem of determiningvelocity and magnetic fields in the sense of solving the coupled system of Navier-Stokes equations and induction equation if some boundary conditions or types of forcing are given. For most laboratory and technical applications with small magnetic Reynolds number Rm the magnetic field is disturbed only slightly by the flow whereas it can modify the latter significantly via Lorentz forces. For higher Rm, however, the fluid flow can change the magnetic field drastically or can even lead to self-excitation of a magnetic field via the dynamo effect.

In the inverse problems approach one strives to get information about the distribution of certain material parameters or temperature and velocity fields inside the fluid from measurements of appropriate quantities at the fluid boundary and/or outside the fluid. We restrict our interest on the spatial reconstruction of the velocity field (or of related mean-field quantities) purely from magnetic fields and electric potentials which can be measured outside the fluid body and at its boundary, respectively.

For the case of small Rm, which is most interesting for a number of technological applications like metal casting and crystal growth, it is necessary to apply external magnetic fields and to measure the flow induced magnetic fields and electric potentials. Analytical results concerning the uniqueness problem of velocity reconstruction /1/ as well as numerical illustrations /2/ are presented. The need of regularization of the inverse problem is discussed.

Some aspects of generalizing the method to high Rm, i.e. to an inverse dynamo theory, are also discussed. In particaluar, considering a modified Krause-Steenbeck dynamo model with radially varying alpha we show how this radial dependence can be inferred from the growth rates of several magnetic field modes. The connection of this problem with similar problems in quantum mechanics, like isospectral potential deformations, is worked out.

A set of electric arc evaporators has been installed inside the gas dynamic trap experimental facility of the Budker Institute Novosibirsk. It is used for fast Ti-coating of the inner chamber surface. In this way the vacuum conditions could be substantially improved. Under the new conditions special experiments were carried out to measure the temporal and spatial variation of the neutral gas density during typical shots. The results of these measurements are presented and compared with those of numerical simulations by means of the Monte Carlo code TUBE.

The paper reports on the investigations of the confinement of neutral beam heated, high-ß and two-component plasmas in the Gas Dynamic Trap. The set of diagnostic methods which have been developed enabled the characterization of different energy loss channels. To analyze the plasma heating the energy balance models were applied. The measurements of the local energy and angular distributions of the fast ion minority are described and their results are presented. These measurements were done by injecting a focused, diagnostic neutral beam to produce a local charge-exchange target for the fast ions. The resulting charge-exchange atoms were registered by an electrostatic analyzer. The energy distribution function obtained was compared with the results of Monte Carlo and Fokker-Planck simulations.

This report summarizes the results of experimental investigations obtained during the last five years at the Gas Dynamic Trap experimental facility of the Budker Institute Novosibirsk. Due to an essential upgrade of the main components performed in this period, the following plasma parameters have been achieved: electron temperature - 90-110 eV, fast ion density - up to 0.8*10^13 cm^-3, mean energy of fast ions - 5-8 keV, plasma-ß - 15-20%. The paper describes the following investigations: effect of wall conditioning on neutral gas dynamics, longitudinal electron heat flux, confinement of the high-ß two-component plasma, fast ion parameters under high-ß conditions, fueling of the target plasma by gas puffing. It presents results of measurements and of calculations.

By upgrading the high-energetic neutral beam injection system of the gas dynamic trap (GDT) experimental facility of the Budker Institute Novosibirsk the plasma heating could be substantially improved. Now an electron temperature up to 120 eV is attainable compared to 70 eV before. Under the new conditions various heating scenarios and the plasma confinement were studied.

Übersicht über die Methoden und Einsatzmöglichkeiten der Röntgenreflektometrie (XRR). Diskussion der Anwendungen der XRR bei Herstellung und Charakterisierung dünner Schichten und von Vielschichtsystemen. Als Beispiele wurden u. a. Ergebnisse eigener Messungen an der Rossendorfer Beamline (ROBL/ESRF)in Grenoble herangezogen.

Semiconductor nanoclusters embedded in a dielectric matrix are of great interest for future optical and electrical applications in microelectronic circuits. The contribution is focused on the study of Ge-nanoclu-sters generated by ion beam synthesis (IBS) in thermally grown thin SiO2 layers (20-50 nm). TEM and RBS analysis show, that the cluster formation and the elemental Ge distribution is strongly influenced by the annealing condi-tions, which is described in detail for furnace and rapid thermal processing (800°C-1100°C). TEM investigation revealed that in dependence on specific implantation and annealing conditions a broad nanocluster band in the centre of SiO2-layer or a d-like one in the distance of 5-7 nm from the SiO2/Si interface can be generated. HRTEM characterisation of samples emerge that the Ge clusters in the thin SiO2 films are amorphous opposite to earlier results were crystalline Ge nano-cluster were created in 500 nm SiO2 layers [1]. Long-term stability of grown clusters is an important feature for their further use in microelectronics. We identified the preparation conditions where the Ge nanocluster have a high stability and do not change with time and where the cluster are unstable and disappear completely after 2 month storage without any thermal treatment. Experiments with strong electron irradiation performed in a TEM with a FEG show the possibility of in-situ crystallisation of existing cluster as well as crystalline cluster formation in the samples where clusters before irradiation were not observed.
[1] J. v. Borany, R. Grötzschel, K.H. Heinig, A. Markwitz, W. Matz, B. Schmidt and W. Skorupa "Multimodal impurity redistribution and nanocluster formation in Ge implanted silicon dioxide films", Appl. Phys. Lett. 71 (22) 3215 (1997)

We have shown that holes with diameters in the nanometer range may be created in the Al2O3/NiAl(110) substrate if metal clusters deposited on it are irradiated by the intense convergent electron beam in TEM. The localisation and size of holes can be controlled to some extend. The formation of holes can be interrupted by lowering the beam intensity below a critical value. It can be continued by increasing the intensity above the threshold value. We have also disclosed the necessity of clusters' presence on the surface for the start of holes' formation.

Studies of the relaxation and confinement of hot anisotropic ions are considered to be the key elements of the gas dynamic trap (GDT) experimental research programme. The method of confinement study described consists essentially in the comparison of measured ion parameters with those predicted by computer simulations. To realize this approach a set of diagnostics for the measurements of local and global parameters of the fast ions has been developed. In particular, this set includes diagnostics to measure the local energy and the angular distribution functions. For numerical studies of the fast ion dynamics a Monte Carlo code based on the theory of two body Coulomb collisions has been elaborated. Comparison of the experimental data with the results of the simulation clearly demonstrates that the fast ion characteristic relaxation times in the warm target plasma are close to those determined by binary Coulomb collisions. Significant anomalous energy losses or scattering of fast ions have not been observed as yet. The measurements provide a maximum density of the fast ions with mean energy of about 8 keV up to 10E+13/cm^3, in good agreement with computer simulations. The increase of the neutral beam power and improved vacuum conditions of GDT made possible the access to plasma ß of as high as 30%.

ZrO2 layers stabilized with 9mol% Y2O3 of 35-100 nmthickness were deposited by sputtering on 200 nm thick Fe layers on Si/SiO2. Ion beam mixing induced by 300 keV Kr ions and 1.5 MeV Br ions bombardement was studied at temperatures ranging from 100 to 300 K. Samples were analysed by means of RBS, GXRD, and SEM techniques. RBS analysis revealed important atomic transport across the ZrO2/Fe interface. The amount of intermixed atoms increases with increasing ion dose. Ion beam mixing was observed at low temperaturesw. Upon 300 keV Kr-ion bombardment the tetragonal structure of as-deposited ZrO2(Y2O3) layers was transformed into the cubic one. High energy ion bombardment produces only transformations of the crystalline structure without any visible atomic transport and the formation of the rare FeO-wuestite phase. Kr blistering was observed from samples implanted with 300 keV Kr ions to fluences exceeding 1e16 at/cm2 at 100 K and 5e16 at/cm2 at RT.

Interface mixing between ZrO2 and Fe by Kr ion irradiation was studies in order to understand atomic effects of adhesion of ceramics on metals. No formation of new phases was observed. The main effect is connected with the redistribution of oxygen near the interface. It was followed with RBS and TEM.

The report gives an overview on the activities of the Institute of Safety Research in 1999.

Ion implantation of Ca and/or P into Ti or Ti alloys is of interest in order to enhance mechanical properties and biocompatibility for medical applications . With this motivation the microstructural changes of the implanted surface layer were studied. Surface near implantation of high doses of calcium results in an oxidation of the modified layer and the formation of CaO. For deeper calcium implantations, precipitation of the metastable hexagonal modification of calcium has been observed instead of the cubic equilibrium phase. Beside these new phases partial amporphization is observed. High dose implantation of phosphorus leads mainly to amorphization of the implanted layer. This hinders the reaction with oxygen during implantation and room temperature aging. High dose double implantation with P followed by Ca also leads to partial amorphization. No indication for new phases containing Ca and P is found.

Overview about the Materials Research Hutch and its instrumentation. Representation of results gained in the first year of operation: powder diffraction on HTSC; formation of SiC in Si; reflectometry on multilayers using anomalous scattering; H in Nd thin films; in-situ study of structural changes in TiAlV;

Populärwissenschaftliche Darstellung von ROBL. Beispiele zu Experimente im Bereich der Ökoradiochemie (Abwässer des Uranbergbaus) und der Materialforschung.

Erzeugung und Eigenschaften von Synchrotronstrahlung und Infrarotstrahlung aus FEL; Ausgewählte Anwendungsbeispieöle aus Physik, Werkstofforschung, Umweltstudien und Medizin.

Description of the experimental set-up of the Materials Research Hutch. Report of first results from structural follow-up during in-situ annealing experiments. Discussion of possibilities for a in-situ deposition chamber.

Description of the Materials Research Set-up of ROBL. Presentation of the results obtained in the first year of operation.

Description of ROBL, its experimental possibilities and the research oppotunities for east European scientist under EC funding.

The project contributed to answer issues which are identified for future BWR plants:

• The design of innovative components
• An enlarged assesment of the performances
• A better understanding of the underlying physical phenomena.

The results of an intercomparison of neutron dosimetry measurements in the ex-vessel cavity of VVER-1000 type reactor are submitted. A good agreement of measured results of different independent participants was found for the different activation reactions. Evaluated absolute dosimetry data are presented. Also good agreement of neutron transport calculation results obtained by as Sn and Monte Carlo methods by independent laboratories with measurements is demonstrated.

: The KORPUS irradiation experiment has been used to test and demonstrate improvements of the pressure vessel dosimetry methodology developed in Rossendorf. The Monte Carlo Code TRAMO has been recently supplied with a new data treatment procedure for elastic scattering and with extended geometries. The new code version has been used to accurately calculate absolute neutron fluence spectra at detector positions in the KORPUS irradiation facility at the RIAR in Dimitrovgrad. The influence of used approximations on the obtained fluences was investigated with calculations for different model variants.
The activation rates calculated with these spectra have been compared with results of activation measurements with detectors irradiated at the International Dosimetry Benchmark at the KORPUS facility. Based on the measured data the calculated fluence spectra have been adjusted with help of the adjustment code system COSA3, a newly extended multispectrum version of COSA2. A comprehensive uncertainty analysis was accomplished for the fluence calculations and the measurements.

The assessment of the uncertainties of neutron transport calculation results caused by uncertainties of the input data is important for the direct use of the calculated fluences and even indispensable for the further improvement of the data by spectrum adjustment on the basis of experimental results. A former work of two of the authors has approached this topic first for a VVER-1000 using a one-dimensional reactor model and applying spectrum adjustment in a single spectrum approximation. In the present work 2D/1D-SN-synthesis calculations have been used to determine the neutron group spectrum covariances including cross-correlations between interesting positions. As possible sources of uncertainties neutron data and reactor model parameters were considered, whereas the uncertainties caused by the calculational method were considered negligible in view of the now available precision of Monte Carlo simulations. The input data uncer-tainties have been updated including newer information.
The calculated absolute group fluence spectra have been adjusted to measured ex-vessel cavity activation rates with help of the COSA3 generalized least squares multispectrum adjustment code. Adjusted fluences for different detector positions have been compared with corresponding fluences obtained with single spectrum adjustments. The results are discussed and conclusions have been drawn. Results obtained with Russian LUND- and ENDF/B-VI-based cross section and fission spectrum covariance data have been compared.

A series of oxorhenium(V) SNS/S mixed ligand complexes [ReO(Lⁿ/L)] carrying different types of tridentate ligand [L¹: C₂H₅N(CH₂CH₂S)₂, L²: (C₂H₅)₂NCH₂CH₂N(CH₂CH₂S)₂, L³: C₂H₅SCH₂CH₂N(CH₂CH₂S)₂ and L⁴: 2,6-(SCH₂)₂NC₅H₃] and the same monodentate coligand (L: C₆H₅S) have been synthesized and characterized by spectroscopic methods and elemental analyses. X-ray structure determination was performed for complexes 3 and 4. Complex 3 adopts the expected distorted trigonal bipyramidal geometry around the metal in a syn configuration, while complex 4, due to the aromatic character of the nitrogen of the SNS donor-atom set, exhibits a distorted square pyramidal geometry. The interaction of complexes 1 - 4 with glutathione (GSH) was studied by high performance liquid chromatography (HPLC), revealing the rapid formation of the respective daughter complexes 5 - 8, wherein the L coligand has been substituted by GS. The daughter complexes 5 - 8 have been characterized by ES-MS and a battery of NMR measurements involving HETCOR, COSY and NOESY procedures. Kinetic aspects of the interaction of complexes 1 ¾ 3 with GSH have been studied by isothermal titration microcalorimetry providing direct measurements of the interaction rate constants as well as the total enthalpy change. The reaction of complex 1 is characterized by the slowest and that of complex 2 by the fastest rate. This is in agreement with previously reported trends for analogous ^99mTc complexes.

3D synthesis based on detailed and improved calculations by SN-codes DORT, ANISN and the BUGLE-96 library has been validated using reference activation data from the Balakovo-3 ex-vessel dosimetry benchmark. The 3D spatial neutron source distribution including pin-to-pin power variations and the complex baffle construction were modeled in detail. All particulars of reactor operation such as coolant temperature changes, assembly power asymmetry and fuel burnup influence on space-energy neutron source distributions were taken into account.
The discrepancies found do not exceed 10%. The average relation between calculated and measured valuse is 0,99. The calculated results show a systematic underestimation for 237Np(n,f) ( -6% on the average), 93Nb(n,n') ( -8%) and systematic overestimation for 58Ni(n,p) and 54Fe(n,p) ( +7%). Generally, the agreement between experiment and calculation is even closer as expected from uncertainty considerations.

A high dose of 1x1018 cm-2, 60 keV carbon ions was implanted into single crystalline 6H silicon carbide (SiC) at elevated temperatures. The formation of carbon phases in the crystalline SiC lattice was investigated by cross sectional transmission electron microscopy. An amorphous, carbon rich phase was produced at 300oC. Precipitates of graphite were obtained at 600oC, whereas at 900oC small diamond grains were produced. These grains are in perfect epitaxial relation with the surrounding SiC lattice.

Pt films on alumina substrates, both in their as-received and annealed states, have been extensively characterized by slow positron implantation spectroscopy (SPIS). Bulk Pt samples have been investigated by conventional positron annihilation spectroscopy (PAS) as well as by SPIS. A variety of state-of-the-art theoretical calculations have been performed to aid the interpretation of experimental findings. The research shows that a re-interpretation of earlier defect studies of bulk Pt by PAS is required in order to achieve a satisfactory agreement with the present experimental findings and theory.

A full power MSLB analysis for the TMI-1 NPP using the coupled code DYN3D/ATHLET was performed in the frame of the OECD Benchmark for coupled neutron kinetics/thermohydraulics codes. The analysis shows a return-to-power after the scram. The impact of the description of coolant mixing inside the reactor pressure vessel was investigated. The exclusion of the coolant mixing enhances this second power peak by about a factor of two in comparison to the first calculation, where the coolant mixing is treated by means of an experimentally determined mixing ratio. The neglection of mixing applied in point kinetics calculations with compatible feedback coefficients shows the opposite effect on the obtained reactor power.

DYN3D is a three-dimensional computer code for calculating transients in light-water reactor cores with quadratic (version DYN3D/R) or hexagonal (version DYN3D/H) fuel assembly geometry. Starting from the critical state (keff - value, critical boron concentration or critical power) the code allows to simulate the neutroniand thermal-hydraulic core response to reactivity changes caused by control rod movements and/or changes of the coolant core inlet conditions. Burn-up calculations can be performed. The depletion state can used as starting point for the transient. The steady state and transient Xe and Sm concentrations can be analyzed. The decay heat is takeinto account.

Extended duality (i.e. the replacement of the thermal dilepton emissivity of hadron matter by that of q bar q annihilation)
is used to explain the dilepton data of heavy-ion experiments at CERN-SPS. Taking into account the background contributions (hadronic cocktail, Drell-Yan, semileptonic open charm decays) the spectral shapes of the CERES, NA38/50 and HELIOS-3 data in experiments with lead and sulfur beams can be well described while the normalizations of the sulfur beam data is problematic.

The structure of dioxouranium(VI) as a function of pH at different (CH3)4N-OH concentrations has been investigated with the aid of U LIII EXAFS. Polynuclear hydroxo species were identified by an U-U interaction at 3.808 Å at pH = 4.1. The precipitate formed at pH = 7 has a schoepite like structure. In solution at high pH [0.5M (CH3)4N-OH], the EXAFS and data are consistent with the formation of a monomeric four coordinated uranium(VI) hydroxide complex UO2(OH)42- of octahedral geometry. The first shell contains two O atoms with a U=O distance of 1.830 Å, and four O atoms were identified at a U-O distance of 2.266 Å.
In strong alkaline solutions [> 1 M (CH3)4N)-OH], 17O-NMR spectra indicate the presence of two species, presumably UO2(OH)42- and UO2(OH)53-, which are in rapid equilibrium with one another at 268 K in aqueous solution.

We analyze the production of Φ mesons in πN and NN reactions in the near-threshold region, using throughoutly the conventional "non-strange'' dynamics based on such processes which are allowed by the non-ideal ω - Φ mixing.
We show that the occurrence of the direct Φ NN interaction may show up in different unpolarized and polarization observables in π N to NΦ reactions. We find a strong non-trivial difference between observables in the reactions pp to ppΦ and pn to pnΦ caused by the different role of the spin singlet and triplet states in the entrance channel for the Φ meson production mechanisms. A series of predictions for the experimental study of this effect is presented.

A covariant model based on the Bethe-Salpeter formalism is proposed for investigating the near-threshold deuteron disintegration via electromagnetic and weak interactions. The solar proton burning process $pp\to De^+\nu_e$ and
its astrophysical low-energy cross section factor $S_{pp}$ areconsidered within this formalism as well.
Results of numerical calculations of the energy dependence of relevant cross sections and of $S_{pp}$ are presented.
Our results confirm previous canonical values. The energy dependence of the $S_{pp}$ factor is rather close to phenomenological extrapolations commonly adopted in computations of solar nuclear reaction rates.

nicht vorhanden

The type of monitoring of nuclear power plants in Ukraine practised early nineties provided the supervisory authority with only inadequate access to information about the current safety status of plants. For the Zaporozhye NPP, unit 5, a technical system to improve the operational monitoring has been designed, installed and commissioned for trial operation at the end of 1995 as a pilot project. The system complements existing operation checking and monitoring facilities by including modern means of information technology. It enables concentration on a continuous monitoring of the state of unit 5 in normal operation and in cases of anomalies or incidents so that when recognisable deviations from the regular plant operation occur, the authority can immediately inquire and if necessary impose conditions on the operator. In 1997 the Information and Crisis Centre of the Ukraine supervisory authority in Kiev has equipped with the most essential technical means necessary for quasi-simultaneous transfer of data and voice and for monitoring purposes and connected the Centre to the Zaporozhye system. A similar monitoring system for both VVER-440 units of the Rovno NPP by analogy with the pilot project was specified, put into operation and connected to the ICC in 1998.

In the Forschungszentrum Rossendorf a measurements techniques test loop was constructed. Air water flow in a vertical tube was investigated using different two phase flow measuring techniques. The paper describes the used measuring techniques and some performed experiments. The code CFX-4.2 with its implemented two phase models was used, to simulate bubbly flow and to compare calculated void profiles with the measured results.
The two phase models of the code version CFX-4.2 are able, to describe void profiles with a near wall void maximum, which will be found for bubbly flow showing a monodisperse bubble size distribution. To model flow regimes showing a bubble size distribution and the occurrence of bubble coalescence and fraction, model extensions would be necessary. The consideration of larger bubbles, which may be deformed, requires the development of improved bubble force models.

Bei der Entwicklung von ^99mTc-Radiopharmaka für Hirnfunktionsuntersuchungen stellt der Transport durch die Blut-Hirn-Schranke einen wesentlichen Faktor dar. Das gilt insbesondere für die Klasse von "3+1"-Gemischtligandkomplexen, die gegenwärtig im Mittelpunkt der Rezeptorligandforschung mit Technetium steht. Zum Verständnis der Strukturabhängigkeit des Transports wird anhand einer systematisch variierter Verbindungsreihe untersucht, wie sich Modifizierung des monodentaten Thiolliganden in neutralen, hirngängigen ^99m/99Tc-(3+1) Gemischtligandkomplexen der angegebenen Struktur auf Lipophilie und Höhe der Aufnahme im Rattenhirn auswirken.
Alle Komplexe enthalten protonisierbare Aminogruppen, die entsprechend ihrem pK_a-Wert, bei pH 7,4 in unterschiedlichem Maße geladen sind. Aus diesem Grunde wurde hier der pK_a-Wert der Komplexe als ein relevanter Parameter für die Hirnaufnahme bewertet. Er wurde durch RP-HPLC bei unterschiedlichem pH ermittelt. Der Verteilungskoeffizient bei pH 7,4 (logD), wurde als Ausdruck der Lipophilie in die Betrachtungen einbezogen. Die Initiale Hirnaufnahme wurde bei der Ratte 2 min nach Tracerinjektion geprüft. (i.v.; männl. Wistar-Ratten; 5-6 Wochen alt).
Die pK_a-Werte der Komplexe A und C lagen bei 10,1 bis 9,6. Diese nahezu vollständige Ionisation, bei relativ niedriger Lipophilie (logD 0,3 - 0,7), spiegelte sich in einer niedrigen Hirnaufnahme von 0,2 - 0,5 % ID wieder. Die Einführung eines Ether-Sauerstoffes in die Komplexe (D) erhöhte deren Lipophilie beträchtlich (logD 1,40-1,60)und brachte pK_a-Werte von 9,5 bis 8,9. Diese Änderungen ließen die Hirnaufnahme signifikant auf Dosiswerte um 1% ansteigen. In ähnlicher Weise verbesserte die Einführung einer Morpholingruppe (B und E) die Lipophilieparameter der Komplexe (pK_a 7,9/7,2, logD 1,2/2,6). Auch hier folgte eine gute initiale Hirnuptake von mehr als 1% ID. Ein zweites Sauerstoffatom im Komplex (F) beeinflusste dessen Lipophilieeigenschaften (pK_a 8,3, LogD 2,3) ebenfalls drastisch. Mit diesem Tracer konnte eine sehr gute Aufnahme von 2,1% ID im Hirn registriert werden. Diese Ergebnisse zeigen, dass speziell die Einführung von Sauerstoffatom(en) in die monodentaten Thiol-Liganden der betrachteten Tc-(3+1) Gemischligandkomplexe zu günstigeren Lipophilieeigenschaften führt, die sich positiv auf deren Hirnaufnahme auswirken.

Im Rahmen unserer Arbeiten zu Technetium- und Rheniumkomplexen mit Affinität zu Rezeptoren von Neurotransmittern wird die Eignung des Ergolinsystems für das Design Dopamin D₂-rezeptorbindender Technetiumtracer untersucht. Ausgehend von 6-Methyl-8alpha-aminoergolin wurden erstmalig Re- und Tc-Komplexe synthetisiert, die sich an Ergotalkalioden als Leitverbindung orientieren. Nach Einführung des als Haftatom benötigten Schwefels durch Mercapotoacetylierung der 8alpha-Aminogruppe bindet das Ergolin als monodentater Ligand an Re(V) bzw. Tc(V), die restlichen Metallvalenzen werden durch tridentate Komplexbildner unter Bildung neutraler Gemischtligandkomplexe abgesättigt. Die Rheniumverbindung wurde als kristalline Verbindung isoliert, Technetiumspecies wurden als radiochemisch reine Lösungen hergestellt.

Alle synthetisierten Verbindungen haben hohe Affinität zu Dopamin D₂-Rezeptoren mit K_i-Werten zwischen 0.38 und 6.9 [Mn] für die organischen Komplexvorstufen bzw. 19.5. [Mn] für den Rheniumkomplex. Bioverteilungsuntersuchungen (Wistarratten) der technetiumkomplexe zeigen geringen Hirnuptake (0.19% Dosis/Organ 5 min p.i.) mit konstanter Speicherung in Putamen und Hippokampus über 10 bis 120 min. Die vorläufigen Ergebnisse zeigen, dass die Verbindungsklasse eine Basis für weitere potentiell Dopamin D₂-bindende Radiotracer darstellt.

Our work over the past few years has been focused on the design and evaluation of novel chelating systems suitable for oxorhenium and/or oxotechnetium that may lead to useful radioagents. Several ^99mTc mixed ligand complexes carrying the SNS/S or the SNN/S donor atom set have shown promising biological properties for future application. The in vivo stability and thereby biological properties of these complexes is greatly dependent on the electronic and lipophilic character of the monothiol.
We report here on the comparative resistance to cysteine substitution of two parallel series of ^99mTcO{Et₂NCH₂CH₂N(CH₂CH₂S)₂. The electronic influence on cysteine substitution rate can thus be investigated.
All above complexes are prepared at tracer level using glucoheptonate as transfer ligand and are purified by organic extraction and HPLC. Their structure has been previously resolved by comparison with authentic samples. The ^99mTc complexes are stable in solution in the absence of thiol for long periods of time. Competition experiments with cysteine are performed in aqueous medium at pH 7.4 and using two different cysteine concentrations, 10 mM and 1 mM, by incubation at 37°C. Aliquots of the incubate withdrawn at 0, 15, 30, 60, 120 min and 24 h time intervals are subjected to HPLC analysis. A RP C18 column is eluted by TEAP buffer pH 7.4/EtOH gradient system, whereby all radioactive ingredients are well separated.
All complexes are attacked by cysteine under the above conditions forming mixtures of intermediates, that with time lead to total loss of the original ^99mTc compounds. Relative resistance to cysteine substitution is directly proportional to monothiol nucleophilicity in both series of complexes: -NH₂ > -H> -NO₂. Since the free thiol content - mainly cysteine and its derivatives - varries in vivo, mixed ligand systems as the above can be used for directing and trapping ^99mTc in tissues of choice by finely monitoring stability via the monothiol.

A combination of FTIR spectroscopy and positron emission tomography (PET) is shown to provide new information on tissue. Here we give a first demonstration on the potential of this combination in discriminating tumor tissue from healthy tissue. Examples are taken of cancer grown in muscle tissue in mice. Immediately before thin sections of the cancer tissue were prepared, a radiotracer was injected in the living mouse. Subsequently a native section was immobilized on a CaF₂ window and an autoradiographic image was recorded from that immobilized section. FTIR maps of the thin sections were obtained by using an infrared microscope equipped with computerized XY stage and MCT detector. Principal component analysis was chosen for chemometric evaluation of the spectra. Evaluated data were reassembled into two dimensional maps and compared with the corresponding PET image.

99mTc labelled nucleobases are expected to be precursors for in vivo radioactive labelling of DNA. This offers the possibility for visualization of tumours developing in surroundings of non-dividing tissue as e.g. brain.
The aim of the study was achieve uptake of 99mTc complexes of derivatized nucleic acid precursors, especially mercaptoamide functionalized uracil derivatives, into proliferating cells.
The 99mTc complexes were prepared by ligand exchange on 99mTc(V) gluconate both as mixed ligand complexes according to the "3+1 principle" and as complexes formed by (MAG)_n chelators coupled to nucleobases.
Uptake of 7 selected compounds into the crude cytosolic and nuclear fractions of cultured V79 cells was checked. Pulse labelling for 4 hrs showed cellular uptake of some compounds. Best results were about 20% cellular uptake, and thereof up to 40% in the nuclear fraction. The corresponding results with ³HTdR controls were 20% and 75% respectively.
Postincubation experiments showed an increase of the percent 99mTc radioactivity in the nuclear fraction by a factor of 2. This means integration of the complex in the nucleus from the pool present in the cytosol after the initial incubation. No radioactivity was released into the postincubation medium.
The results are encouraging, making evident that complex compounds of this kind can be taken up into the cell nucleus.

An energy resolution of 4.38+-0.11% was obtained for 662 keV gamma-rays with a 3x3x20 mm³ YAP:Ce crystal with its long face coupled to an XP2020Q photomultiplier. The measured number of photoelectrons of 5290+-80 phe/MeV implies a photoelectron statistical contribution of 4.18+-0.04% and hence a YAP intrinsic energy resolution of 1.3+-0.5%, the lowest value ever observed for scintillators. The relative light output of the YAP crystal measured for energies between 14.4 keV and 1.275 MeV was constant withing +-2%. These observations are consistent with the assumption that there is a direct correlation between energy resolution of scintillators and nonproportionality of their light output versus energy.

In ^99mTc labelling of specific peptides, ^99mTc has to be introduced at a position of the peptide molecule which would tolerate inclusion of the label without adversely affection the receptor or other specific binding. Although for direct labelling of peptides Tc-binding sequences remote from the receptor-binding sequence have been successfully introduced, the corrdination mode of such peptides is still poorly understood. The aim of our studies was I) to clarify for simple N,S-donor building blocks, such as cysteine derivatives, how the ligands bind Tc(V) and II) to determine in solution the coordination mode of a ⁹⁹Tc-labelled endothelin derivative, containing the sequence -Cys-Gly-Cys-, which is a potential agent for imaging atherosclerosis. X-ray asorption spectroscopy proved to be a valuable tool in obtaining direct structural information from the noncrystalline material and solution species. The performed studies have shed more light on the subtle interplay of the donor groups of the ligand, including the hitherto uncommon occurrence of both a deprotonated and a neutral nitrogen donor group in bis-bidentate S,N oxometal(V) complexes. EXAFS analysis of the ⁹⁹Tc-labelled Cys-containing endothelin derivative revealed that coordination of the [TcO]³⁺ core is restricted to the sequence -Cys-Gly-Cys-. Under the labelling condition used (ligand exchange reaction with Tc(V) gluconate), the preferred coordination by the cysteinyl thiol group surprisingly prevents involvement of any donor atom other than sulphur, thus forming purely S-coordinate 1:2 complexes in form of two isomers.

There is evidence that the dopaminergic system is sensitive to asphyxia. However, the respective enzyme activities have not been measured in the living neonatal brain yet. In this study, FDOPA was used to estimate the activity of the aromatic amino acid decarboxylase (AADC) and the relative changes of monoamine oxidase (MAO) and catechol-o-methyl-transferase (COMT) in the neonatal pig brain.
Two PET studies were performed under control conditions and under 2-hour asphyxia in each of 6 piglets and combined with measurements of cerebral blood flow (CBF) and volume (CBV). Plasma metabolites of FDOPA were also determined by HPLC.
As expected asphyxia elicited a 3-fold elevation of the CBF and increased the CBV by 40%. The blood-brain transfer of FDOPA, K₁, and the clearance rate constant from brain, k₂, were unchanged. However, the rate of [F-18]fluoro-dopamine synthesis, k₃, was increased in striatum from 0.038±0.016 min^-1 to 0.056±0.028 min^-1. Also, the rate of conversion of FDOPA to 3-O-methyl-FDOPA (OMFD) by COMT in plasma decreased during asphyxia from 0.0080±0.0015 min^-1 to 0.0046±0.0010 min^-1. Measurement of metabolites in tissue indicates that similar changes occurred also in the brain. Furthermore, the amount of FDOPAC as product of brain MAO activity was significantly decreased under asphyxia.
Increase of the extracellular level of dopamine is expected to be involved in severe disturbances of neuronal metabolism during asphyxia, e.g. by generating free radicals and quinones. In this study, evidence for an increase of the AADC activity and a decrease of MAO activity during asphyxia was obtained which may contribute to the increase of extracellular dopamine.

Reactions of [Au(PPh3)Cl], (Bu4N)[AuCl4] and the organometallic gold complex [Au(damp-C1,N)Cl2] (damp- = 2-(N,N-dimethylamino-methyl)phenyl) with the potentially tri- and tetradentate proligands PhP(C6H3-SH-2-R-3)2 (H2L1a: R = SiMe3, H2L1b: H) and P(C6H3-SH-2)3 (H3L2) result in the formation of mono- or dinuclear gold complexes depending on the precursor used. Monomeric complexes of the type [AuL1Cl] are formed upon the reaction with [Au(damp-C1,N)Cl2], but small amounts of dinuclear [AuL1]2 complexes with gold in two different oxidation states, +I and +III, have been isolated as side-products. The dinuclear compounds are obtained in better yields from [AuCl4]-. A dinuclear complex having two Au(III) centres can be isolated from the reaction of [Au(PPh3)Cl] with H3L2, whereas from the reaction with H2L1b the mononuclear [Au(Ph3P)HL1b] is obtained which contains a three-coordinate gold atom.
Comparatively short gold-gold distances have been found in the dinuclear complexes (2.978(2) A and 3.434(1) Å). They are indicative of weak gold-gold interactions, which is unusual for gold(III).

Surface modification of titanium is of interest considering the necessary improvement of mechanical properties of this material for applications as e.g. medical implants. This work is devoted to the formation of a layer with a high content of the titanium aluminides Ti₃Al and TiAl below the surface by high dose aluminium implantation. If the maximum aluminium concentration exceeds 20 at.% precipitation of Ti 3Al is detected by XRD already in the as-implanted state. For maximum aluminium concentrations between 50 and 55 at.% the phase TiAl is found beside Ti₃Al after annealing at 700^oC. For a double implantation resulting in an aluminium concentration of about 60 at.% in the depth range between 100 and 200 nm a disordered fcc TiAl phase is observed after implantation as precursor for the ordered tetragonal TiAl formed by subsequent annealing at 600^oC. The influence of a pre-implantation of 3x10¹⁷ V/cm² on the phase formation is also reported.
The depth dependent maximum hardness in the near surface range increases with increasing Al dose up to a factor 4. Significantly enhanced wear resistance is observed for Al doses >10¹⁸ cm^-2 after annealing. High dose implantation of Al into Ti results in an enhanced corrosion in 5 M HCl. However, subsequent annealing reduces the corrosion current compared to unimplanted Ti.

Das Performance Ratio (PR) als wichtigste Kenngröße einer netzgekoppelten Photovoltaikanlage wird analysiert. Durch Unterscheidung zwischen der nominalen Generatorleistung und der Nennleistung des Generators können einerseits gemessenen Werte des PR interpretiert und andererseits aus gemessenen Werten des PR auf relativ einfache Weise die Generatornennleistung ermittelt werden. Das Verfahren wird an verschiedenen Anlagen verifiziert.
Die qualifizierte Ermittlung des PR einer Anlage ist wichtige Voraussetzung für eine belastbaren Ertragsvorhersage einer PV-Anlage.

Na ions were implanted into pure Ti surfaces. New surface phases were shown to be incorporated into the surface: sodium titanates Na2TiO3 (in the as-implanted state) and Na2Ti6O13 (after 20 min heating at 700 °C in air). A variable level of rugged surface in porosity and roughness was observed depending on the applied ion dose and energy. Upon exposing to simulated body fluid, such ion-implanted surfaces were revealed to enhancedly elicit hydroxyapatite nucleation and growth.

The replacement of the external high voltage modulator by an integrated plasma based modulator recently presented, would appreciably reduce the costs of plasma immersion ion implantation equipment. Hence an inherent restriction of the integrated modulator is the limited maximum current supplied by the integrated modulator during the application of the high voltage pulse to the sample. The aim of the present publication is to investigate possibilities to overcome this limitations. Detailed investigations are presented on the response of a plasma if electrons are extracted by a large electrode with special emphasis on the processes near the wall and near the control grid of the modulator.
Switching off the negative bias voltage of the grid, controlling the electron flow to the anode, results in an increase of the plasma floating potential from -8V to about 60V, as revealed by probe measurements. All electrons leaving the plasma are collected by the anode. Further during the off - time of the grid voltage a 2 to 3 fold increase of the plasma density was observed.

In the Forschungszentrum Rossendorf a measurements techniques test loop was constructed. Air water flow in a vertical tube was investigated using different two phase flow measuring techniques. Air was injected into an upward water flow at normally conditions applying different injection modes. Different tests with different relations of air and water superficial velocity were performed. For each test stationary conditions were settled. The paper describes the measuring techniques used and some experiments performed. Applying a wire mesh sensor, developed in FZR, the cross section of the void fraction could be determined. The time resolution achieved by the signal processing unit is 1024 frames per second. The spatial resolution equals 3 mm. At the investigated flow velocities, the bubble diameter distributions could be determined. Using the code CFX-4.2, void profiles over the tube cross section were calculated. The development of the void profiles is mainly influenced by bubble forces, which act perpendicular to the flow direction. Therefore the comparison of the calculated with the measured results for bubble flow regimes is a good validity test for the implemented two phase flow models. The two phase models of the code version CFX-4.2 are able to describe void profiles with a near wall void maximum, which will be found for bubbly flow showing a monodisperse bubble size distribution. To model flow regimes showing a bubble size distribution and the occurrence of bubble coalescence and diffraction, model extensions would be necessary. The consideration of larger bubbles, which may be deformed, requires the development of improved bubble force models.

The appreciation of short-lived radionuclides in nuclear medicine has led to the development of radionuclide generators that serve as a convenient source of these radionuclides to prepare a wide range of radiopharmaceuticals. Of all the potentially useful generator systems, the ^99mTc generator has found the most widespread use. Although originally chosen because of its excellent disintegration characteristics and its ready availability, ^99mTc would not be so widely used today were it not for its ability to exhibit a versatile coordination chemistry.
During the first phase of research into the development of ^99mTc based imaging agents in the 1970s the agents were relatively simple in nature (pertechnetate, colloids, particles, albumin, and complexes with DTPA, phosphonates). Then new complexes have been developed which provide images of flow and metabolism, e.g. kidney and liver functions as well as regional heart and brain perfusion. Antibodies, antibody fragments and numerous peptides have been successfully labelled with ^99mTc. Progress in technetium chemistry has led to an assortment of building blocks in the form of various cores and valuable combinations of donor groups in a number of chelating ligands. Research is still going on to extend and improve these tools. Using new concepts and methods, current research is being directed at an area of technetium chemistry well beyond perfusion tracers to open a window on biochemistry. The recent advances in the design of new technetium ^99mTc imaging agents illustrate the continued expansion of the use.

Rhenium and technetium belong to the same group of the periodic table and have similar chemical properties. Radioisotopes of rhenium (¹⁸⁶Re and ¹⁸⁸Re) have been suggested as radiopharmaceuticals for therapy. Similar to the in-house use of the ^99mTc generator for the preparation of a great variety of ^99mTc labeled diagnostic agents, the ¹⁸⁸Re generator can provide the therapeutically useful radionuclide for the preparation of ¹⁸⁸Re agents for bone pain palliation, cancer therapy, radiotherapy of chronic degenerative joint diseases and brachytherapy to reduce restenosis risks after coronary dilatation.

The third workshop on Measuring Techniques for Steady State and Transient Multiphase Flows took place at the Forschungszentrum Rossendorf (FZR) at the 14 Oktober 1999. This series of meetings was initiated by the Institute for Safety Research of the FZR and by the Institute of Process Technology, Process Automation and Measuring Techniques of the University of Applied Science Zittau. The workshop was supported by the Deutsche Gesellschaft für Chemisches Apparatewesen, Chemische Technik und Biotechnologie (DECHEMA) and the Section Thermo and Fluiddynamics of the Kerntechnische Gesellschaft. Two main lectures and 9 technical papers dealt with wall thermography, acoustic and gamma source water level measurement, electro diffusion, optical tomography and velocity and mass flow measurements with wire mesh sensors.

Bis Mitte der 90er Jahre wurde in den USA an der Entwicklung eines Höchstflußreaktors (ANSR: Advanced Neutron Source Reactor) gearbeitet, dessen Neutronenfluß den der derzeit betriebenen Hochflußreaktoren (z. B. dem HFR in Grenoble) um mindestens eine Größenordnung übertreffen sollte. Der aus 15 kg hochangereichertem Uran bestehende Kern besaß eine Leistung von 330 MWth, ein Volumen von 67,5 l sowie eine Kernstandzeit von 17 Tagen.

Zur thermohydraulichen Auslegung der Brennelemente des ANSR wurde am Oak Ridge National Laboratory die THTL (Thermal Hydraulic Test Loop) Versuchsanlage aufgebaut. Die hierbei durchgeführten Experimente dienten dazu, die Auslegungsgrenzen gegen Einsatz von Strömungsinstabilität (THI) und Überschreitung der kritischen Heizflächenbelastung (DNB) im unterkühlten Siedebereich zu bestimmen. Die Experimente sind durch sehr hohe Wärmestromdichten (bis zu 1680 W/cm²) sowie Strömungsgeschwindigkeiten (bis zu 28 m/s) bei einem Systemdruck von 17 bar charakterisiert.

Im nachfolgenden Beitrag soll nun die Nachrechnung ausgewählter THTL-Experimente mit dem von der Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH entwickelten Thermohydraulikprogrammsystems ATHLET beschrieben. Dieses wurde hierzu um ein von Hainoun entwickeltes Modell zur Beschreibung der Dampfbildung beim unterkühlten Sieden erweitert und anhand der Nachrechnung von Experimenten zur Strömungsinstabilität und Voidverteilung im Bereich niedriger Drücke (kleiner 2 bar) und mäßiger Geschwindigkeiten (kleiner 5 m/s) validiert. Die hier vorgestellte Nachrechnung der THTL-Experimente stellt somit eine umfangreiche Ereiterung des Anwendungsbereiches dar. Zukünftig ist es somit möglich, mit ATHLET Sicherheitsanalysen für Hochflußreaktoren durchzuführen.

In the Crystal-GRID (Gamma Ray induced Doppler Broadening) technique one uses the fact that atomic nuclei can be excited by a
thermal neutron capture reaction. The de-excitation process takes place via the emission of gamma-quanta. The emission of the first
gamma-quantum after the neutron capture leads to a recoil of the excited nucleus. Typical recoil energies are
in the range of several hundreds of eV and therefore much higher than the displacement threshold of the atom. The recoiling atom will start to
collide with its neighbours losing successively kinetic energy until
thermal energies are reached.

During the collision process a second gamma-ray might be emitted by the atomic nucleus and, as the emitter was moving, the energy of the
gamma-quantum
will be Doppler shifted. The Doppler-shift is a very direct indicator to study the motion of the emitting particle and yields information on the
recoil
process of the atom. However, due to the isotropic orientation of the recoil direction one observes a
Doppler-broadening of the the Intensity distribution I(Eg2). The sensitivity of the technique to the study of atomic collision processes is
enhanced if single crystalline targets are used. In this case the microscopic anisotropy of the slowing down process induces a characteristic
fine structure of the Doppler-broadened line shapes. Measurements with differently aligned targets with respect to the axis of observation give
different line shapes I(Eg2) and allow therefore to accumulate information on the microscopic collision processes. A detailed description of the
experimental technique will be given together with an overview on already performed experiments. In these experiments the comparison of
experimental data to predictions deduced from Molecular Dynamics simulations has allowed to obtain new repulsive interatomic potentials.

Currently, the measurement of I(Eg2) is carried out using a double flat crystal geometry, which allows to obtain a relative energy resolution of
(Delta E)/E = 10-6. The very small solid angle of 10-11 of this geometry requires the use of massive targets. This limits significantly the variety
of compounds, which can be studied by this technique. The use of a double Dumond geometry would allow to overcome this problem. Recent
technical improvements of the GAMS5 spectrometer towards a double bent crystal geometry will be demonstrated. The current status of the
spectrometer and the expected capabilities will be presented.