Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In the last years, there were several reports about the enhanced risk from irradiation with soft X-rays (below 50 keV). This energy range is relevant for diagnostic radiology, such as mammography, radiotherapy, and for the application of novel radiotherapy approaches such as use of miniature X-ray devices. In order to study this phenomenon, the relative biological effectiveness (RBE) of the X-rays in this energy range has to be determined more precisely. Experiments for determination of biological response after conventional X-ray tube irradiation were performed at TU Dresden. Cell survival for NIH/3T3 mouse fibroblasts was measured for soft X-rays (25 kV) and reference X-rays (200 kV). RBE value of 1.28 ± 0.5 was determined from the linear-quadratic model fit at 10% survival level. Further endpoint to be studied is the formation of micronuclei. At present, experiments are performed on human keratinocytes and chinese hamster fibroblasts. However, the precise determination of the energy dependence of RBE has to be performed by means of irradiation with a monochromatic source. One of the applications of the superconducting electron linear accelerator ELBE, at present under construction at Forschungscentrum Rossendorf, will be to provide such X-rays. The first cell irradiation will be performed with X-rays in the range 10 - 50 keV generated by channeling radiation from relativistic electrons in a diamond crystal. The properties of the electron beam (picosecond structure) as well as the intrinsic energy and intensity distribution of the channeling radiation require consideration of precise dose delivery and monitoring, the results of which will be also presented.

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Heat transfer and boiling are key phenomena for power generation facilities. Whereas for 1D thermalhydraulic system codes modeling of boiling was state aof the art from the beginning of their development, the 3D modelling of boiling has not yet reached this maturity. In the paper the boiling model implemented in the CFD-code CFX-4 was applied, to analyse lots of experiments, their results were published in the literature. The validity of the implemented correlations is examined. In many cases the model yields a good agreement to experiments. Especially in the low pressure region, the steam volume fraction is calculated too low. The used models are critical reviewed and compared to alternative solutions. The sensitivity of the calculated results on different influences are compared. Needs for improvements of the model and for further experiments are derived. Main attention should be focused on measuring and modelling of the correct size of the generated steam bubbles.

Gallium nitride is a novel material for short wavelength (blue) optoelectronics. Our previous investigation showed that Mn doped GaN has paramagnetic or antiferromagnetic properties opening new possible applications. The high concentration of magnetic ions possibly allows for the use of such a material in magnetooptic and spintronic devices. GaMnN and GaMnMgN powders were prepared by heating mixtures of gallium and manganese powder or powders of gallium nitride and manganese in a stream of ammonia at the temperature up to 1250°C. The powders have a grain size about 1-10 µm and they contain more than 2% of manganese by weight. Powders of doped GaN were prepared in a series of technological processes at various temperatures, ammonia flow rates and concentration of dopants in initial mixtures. Since hydrogen largely attributes to the passivation of p-dopants it plays an essential role in determination of electrical properties of these materials. Hydrogen content analysis was performed by the NRA method using the 1H(15Na,alpha gamma)12C reaction. This reaction has a sharp resonance of the cross-section at 6.385 MeV. Therefore it is possible by changing the incident 15N beam energy to measure depth distribution of hydrogen. It was found out that hydrogen concentration in our materials was below 1.5at%.

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

It is known that transformation of martensite into austenite (alpha'--> gamma) can take place in the surface layers of steels treated with sufficiently intense pulses of laser, ion or plasma beams. Our present work focuses on the phase transformations in the near-surface layer of various types of steel irradiated with short(µs range) intense (5-6 xE-4 J/m2) argon and nitrogen plasma pulses. The results of CEMS measurements, the pin-on-disc wear tests and SEM observations are presented.

2,6-di(3-alkyl-1,2,4-oxadiazol-5-yl)pyridines, 2,6-di(5-alkyl-1,3,4-oxadiazol-2-yl)pyridines, and 2,6-di(5-alkyl-1,2,4-oxadiazol-3-yl)pyridines were synthesized and tested for their americium(III)-europium(III) selectivity by liquid-liquid extraction. 0.02 M solutions of the compounds extract americium(III) 2-bromohexanoates as monosolvates, AmA3B, from solutions of pH = 2, with an americium(III)-europium(III) separation factor of up to 23. Decreasing the alkyl chain length (butyl < ethyl < methyl) or the polarity of the diluent (chlorobenzene < toluene < tert.-butyl benzene) increased both americium(III) distribution ratio and americium(III)-europium(III) separation factor.

Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution, which are frequently used in industry. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the non-specific ion pair formation with hydrophobic ammonium cations. In this case the phase transfer of anions is dominated by their lipophilicity. The reasons for this situation are closely connected with the specific features of anions in contrast to cations. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to build up receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.

The efficiency of a series of amino-azacryptands for encapsulation and etraction of the oxoanions pertechnetate and perrhenate from aqueous solution is investigated and compared with that of their open-chain counterparts. The aqueous formation constants for oxoanion association with the cryptands were determined by pH potentiometry and/or NMR, and X-ray analysis of single crystals provides evidence for encapsulation. The extractabilities could not be explained solely on the basis of ligand lipophilicity; the level of protonation also plays an important role.

The design and synthesis of anion receptors of technical and biochemical significance is receiving more and more attention.^1-8 Currently, effective binding and selective phase transfer of the oxoanions pertechnetate and perrhenate is of considerable interest from different point of view. Due to its long half-life and environmental mobility, the radioactive pertechnetate is one of the most hazardous contaminants. In this context, effective and selective separation processes are of utmost importance.^9-12 On the other hand, there are some emerging possibilities for the application of the radiochemically active oxoanions pertechnetate and perrhenate in nuclear medicine.^13,14 The most commonly used isotope in diagnostic nuclear medicine ^99mTc is readily available from a ⁹⁹Mo/^99mTc generator system.^15-19 Likewise, the b-emitting ¹⁸⁸Re – discussed as one of the most interesting radionuclides for specific therapeutic applications – is conveniently produced by a ¹⁸⁸W/¹⁸⁸Re generator.^20-22 In both cases the radionuclides are available as oxoanions in isotonic solution, and it appears highly desirable to directly complex ^99mTcO₄ ^- and ¹⁸⁸ReO₄ ^- as they exist in the generator eluate itself. But, the binding of such large, lowly charged anions is a difficult venture. The enthalpic contribution for complexation is rather small. Hence, host compounds being capable to encapsulate these oxoanions are of great interest.
For both directions discussed above, some different requirements have to be fulfilled for the design of ligands. The essential properties of ligands serving as extractants and imaging/therapeutic agents are summarized in Table 1.

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ITO layers with low resistivity and high visible transmittance were produced by means of middle frequency reactive dual magnetron sputtering. The influence of base pressure, Ar/O2 ratio and magnetron pulse duration on the film composition, structure, electrical and optical properties has been investigated. The deposition rate is proportional to the magnetron operation power at changing pulse duration and constant Ar and O2 flows. At enhanced O2 flows an onset of the magnetron target oxidation is discussed as a reason for the decrease of the deposition rate. The presence of water vapor in the residual gas is determined to be a reason for deterioration of resistivity and optical transmittance observed for ITO films produced at base pressures higher than 5×10-4 Pa. It is demonstrated that spectroscopic ellipsometry can be used as a non contact tool to monitor the resistivity of ITO films.

The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic
heavy-ion collisions.

The production of kaons and antikaons in nucleus-nucleus collisions has been studied with the kaon spectrometer at SIS/GSI. The K^-/K⁺ ration was measured in C+C, Ni+Ni, Au+Au collisions at 1.5 AGeV and was found to be almost independent of the system size. In Ni+Ni collisions at 1.93 AGeV we measured the phase-space distributions of K^- and K⁺ mesons. Within the framework of transport models, the measured K⁺ and K^- yields can only be explained if in-medium modifications of the K meson masses are assumed.
In Au-Au collisions at 1 AGeV, we observe non-vanishing elliptic flow near mid-rapidity and in-plane flow at target rapidity for K⁺ mesons. This effect can be explained by transport models when a repulsive in-medium K⁺ N potential is taken into account. The ratio of the K⁺ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energies. This effect is expected for a soft nuclear equation of state.

For the realization of good quality 3C-SiC films, epitaxially grown on Si, the perfection of the film during the early stage of growth is substantial. In this work the beneficial role of Flash Lamp Process (FLP) for defect elimination and strain reduction in the 3C-SiC films is discussed. FLP is a highly transient process with a flash duration of a few milliseconds (ms), preferentially occurring at the SiC/Si interface where the irradiated flux has its maximum absorption. If the energy density is sufficiently high, the temperature at the interface increases above the melting point of silicon. As a result, Si at the interface melts and subsequently dissolves the 3C-SiC in the vicinity of the interface, while the non-melted part of the film is annealed. During the re-solidification phase separation occurs and that part of the SiC film which is already dissolved into silicon is epitaxially deposited on the annealed uppermost part, which acts as the seed layer. The process resembles liquid phase epitaxy (LPE) resulting in substantial improvement of the SiC film. This process also eliminates the cavities and the stress at the 3C-SiC/Si interface. The irradiated 3C-SiC films were characterized by Transmission Electron Microscopy.

Differential production cross sections of K^- and K⁺ mesons have been measured as function of the polar emission angle in Ni+Ni collisions at a beam energy of 1.93 AGeV. In near-central collisions, the spectral shapes and the widths of the rapidity distributions of K^- and K⁺ mesons are in agreement with the assumption of isotropic emission. In non-central collisions, the K^- and K⁺ rapidity distributions are broader than expected for a single thermal source. In this case, the polar angle distributions are strongly forward-backward peaked and the nonisotropic contribution to the total yield is about one third both for K⁺ and K^- mesons. The K^-K⁺ ratio is found to be about 0.03 independent of the centrality of the reaction. This value is significantly larger than predicted by microscopic transport calculations if in-medium modifications of K mesons are neglected.

Isotope ratios of fragments produced at midrapidity in peripheral and central collisions of 114Cd ions with 98Mo target nuclei at E/A = 50 MeV are compared. The influence of the size (A), density, N/Z, E*/A, and Eflow/A of the emitting source on the measured isotope ratios was explored by comparison with a statistical model (SMM). The midrapidity region associated with peripheral collisions does not appear to be neutron-enriched relative to central collisions.

The defining characteristics of fragment emission resulting from the noncentral collision of 114Cd ions with 92Mo target nuclei at E/A = 50 MeV are presented. Charge correlations and average relative velocities for midvelocity fragment emission exhibit significant differences when compared to standard statistical decay. These differences associated with similar velocity dissipation are indicative of the influence of the entrance channel dynamics on the fragment production process.

The cost-shared project ARVI (assessment of reactor vessel integrity) involves a total of nine organisations from Europe and
USA. The objective of the ARVI Project is to resolve the safety issues that remain unresolved for the melt vessel interaction
phase of the in-vessel progression of a severe accident. The work consists of experiments and analysis development. Four tests were performed in the EC-FOREVER Programme, in which failure was achieved in-vessels employing the French pressure
vessel steel. The tests were analysed with the commercial code ANSYS-Multiphysics, and the codes SYSTUS+ and PASULA, and quite good agreement was achieved for the failure location. Natural convection experiments in stratified pools have been performed in the SIMECO and theCOPOfacilities, which showed that much greater heat is transferred downwards for immiscible layers or before layers mix. A model for gap cooling and a set of simplified models for the system codes have been developed.
MVITA code calculations have been performed for the Czech and Hungarian VVERs, towards evaluation of the in-vessel melt retention accident management scheme.
Tests have been performed at the ULPU facility with organised flow for vessel external cooling. Considerable enhancement
of the critical heat flux (CHF) was obtained. The ARVI Project has reached the halfway stage. This paper presents the results obtained thus far from the project.

For a realistic description of the coolant mixing during stationary and transient processes inside the reactor pressure vessel, a fast running semi-analytical model has been developed. This model is based on the technique of linear superposition of response functions on Dirac impulse shaped perturbation functions. The model has been coupled to the 3D neutron kinetic core model DYN3D.

A parameter study for a hypothetical boron dilution event including stationary and transient core calculations has been carried out. For the analysis a generic core loading pattern of the PWR KONVOI has been used. By varying the initial slug volume was found, that slugs of less than 16 m3 do not lead to over-criticality in stationary calculations. Transient calculations with higher slug volumes revealed a further conservatism of the calculations. An initial slug volume of 20 m3 is necessary to reach over-criticality in transient calculations. This leads to a significant reactivity insertion into the core and results in a power peak of more than 6500 MW. The power excursion is stopped by the Doppler feedback very effectively. The limited integral energy release does not lead to a significant rise of the coolant temperature. In the calculation with the bounding slug volume, the magnitude of the power peak is with about 8500 MW higher than in the previous calculation. The Doppler feedback stops the further power increase, too. Contrary to the 20 m3 case, the power peak occurs even before the boron concentration has reached its minimum. Because the positive reactivity insertion is continued after the power peak, typical secondary power peaks are observed. At the location of the power maximum, coolant boiling with a maximum void fraction of up to 70 % occurs for a short time. However, no heat transfer crisis was obtained.

The influence of the cross section library on the results of the boron dilution transient has been investigated by using an alternative library. Differences in global core parameters lead to quantitative differences in the time and the height of the power excursion.

A special model, based on a particle-in-cell method for the description of the boron transport through the reactor core has been used. It is shown, that a proper description of the boron transport in case of transients with low fluid velocity is absolutely necessary to calculate the neutron kinetic behaviour of the core in a right manner.

According to all calculations, even a reactivity insertion of about 2 $ connected with a 36 m3 slug did not lead to safety relevant consequences. The power excursion is mitigated and stopped by the Doppler feedback.

Ion implantation is one of the major techniques to introduce dopants into Si and SiC in a controlled manner. However, ion irradiation produces defects which prevent their electrical activation. Therefore, subsequent annealing is necessary in order to restore the crystallinity and to obtain dopant activation. The precise knowledge of the spatial distribution of the implanted ions and the radiation damage as well as the understanding of the nature of ion-beam-induced defects are important prerequisites for further improvements in the technology of ion implantation doping. Besides experimental investigations, atomistic computer simulations play an important role to achieve progress in this field. Simulations based on the binary collision approximation (BCA) are employed to determine the depth profile of implanted ions and atomic displacements. The influence of various implantation parameters like energy, direction of ion incidence, dose, dose rate and temperature is considered. A phenomenological model is used to treat the dependence of channeling effects on damage buildup and dynamic annealing during ion bombardment. The implantation profiles determined by the simulations show a good agreement with available experimental data. On the other hand, BCA simulations are limited to the treatment of ballistic processes. They do not yield details of the (meta)stable defect structure formed in subsequent fast relaxation processes. In order to obtain such information, a combined simulation method is employed. Processes in the collision cascade with energy transfers above 100 eV are treated by BCA simulations. Classical molecular dynamics (MD) calculations are applied to consider processes in certain parts of the cascade which start with energy transfers less than 100 eV. Detailed investigations are performed to study the temporal evolution of the defect structure, and to determine the damage morphology obtained after the fast relaxation is finished. The influence of nuclear energy deposition and target temperature is discussed. The combination of BCA and MD methods allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion. The results obtained allow a microscopic interpretation of the phenomenological model employed in conventional BCA simulations to describe the enhanced dechanneling of implanted ions due to damage buildup during implantation. In particular the explicit dependence on the ion mass can be explained. Furthermore, the procedure yields more realistic initial conditions for the simulation of post-implantation annealing than hitherto used.

The project ECOSTAR (acronym for ex-vessel core melt stabilization research) involves in total 17 orgnizations from five European countries. The objective of the project is to demonstrate the technical feasibility of core melt mitigation measures outside the reactor pressure vessel (RPV) as well as the validation of a selected set of codes in order to provide the necessary input for the definition of a convincing safety concept to control corium melts for both existing and future reactors.
The ECOSTAR projects is focused on three key phenomena for ex-vessel mitigation measures, namely melt release from RPV, ex-vessel corium transport and long-term corium stabilization. The extensive work program covers different scenarios and consists of a large number of experiments with both simulant and real materials, code development and validation as well as analytical activities.
This paper presents the progress of work per end of the year 2001 and the results obtained since the launch of the project.

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We show that the 3D simulation code GPT (General Particle Tracer) can give very detailed results on both the produced radiation and the evolution of the elctron bunch when special subsets of electrons are tracked instead of individual macro- particles. The model and two apllications are presented.

We outline the diagnostic and transport system of the infrared beam produced by the two free-electron lasers of the ELBE facility.

Es werden Entwurf und Rechnungen zu einem partiellen Wellenleiter f"ur den U50 Undulator des Rossendorfer ELBE Projektes vorgestellt.

Die FEL Projekte am FZR werden vorgestellt.

Production cross sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(pi+)/A_part is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/A_part are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/A_part is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K mesons are neglected.

The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its final phase. The project belongs to the AGE-cluster, that also involves the REFEREE project being used as an input to RESQUE. At FISA 97 the reference data on non-reconstituted specimens were presented together with a set of recommendations on temperature measurements (WP1, WP2). Now, the results on the quality and limiting conditions of the reconstituted weld seam are discussed.

Übersichtsvortrag zu Methoden der Nuklearmedizin

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Only the investigation of reactor pressure vessel steel from operated NPPs offers the opportunity to evaluate the real toughness response of the material to neutron/ gamma radiation. By investigation of material from the formerly Greifswald NPP the evaluation of a standard VVER-440-RPV design and the assessment of the quality of the used as well prediction rules as assessment tools will be possible. The rather different states (irradiated, irradated/annealed, and irradated/annealed/reirradiated) of the RPVs are a special advantage of the four units operated in Greifswald between 1973 and 1990. The paper describes the first results of these investigations and the next steps.

The potential non-equivalent defects in both 3C- and 4H-SiC are classified by a new method that is based on symmetry considerations. In 4H-SiC their number is considerably higher than in 3C-SiC, since the hexagonal symmetry leads to diversification. The different theoretical methods hitherto used to investigate defects in 3C-SiC are critically reviewed. Classical MD simulations with a recently developed interatomic potential are employed to investigate the stability, structure and energetics of the large number of non-equivalent defects that may exist in 4H-SiC. Most of the potential defect configurations in 4H-SiC are found to be stable. The interstitials between hexagonal and trigonal rings, which do not exist in 3C-SiC, are characteristic for 4H-SiC and other hexagonal polytypes. The structure and energetics of some complex and anisotropic dumbbells depend strongly on the polytype. On the other hand, polytypism does not have a significant influence on the properties of the more compact and isotropic defects, such as vacancies, antisites, hexagonal interstitials, and many dumbbells. The results allow conclusions about the energy hierarchy of the defects.

The work was aimed at the experimental investigation and numerical simulation of coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR). For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been designed. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-code CFX-4. For the design of the facility, calculations were performed to analyze the scaling of the model. It was found, that the scaling of 1:5 to the prototype meets both: physical and economical demands. Flow measurements and the corresponding CFD calculations in the ROCOM downcomer under steady state conditions showed a Re number independency at nominal flow rates. The flow field is dominated by recirculation areas below the inlet nozzles. Transient flow measurements with high performance LDA-technique showed in agreement with CFX-4 results, that in the case of the start up of a pump after a laminar stage large vortices dominate the flow. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. At the start-up case of one pump due to a strong impulse driven flow at the inlet nozzle the horizontal part of the flow dominates in the downcomer. The injection is distributed into two main jets, the maximum of the tracer concentration at the core inlet appears at the opposite part of the loop where the tracer was injected. For turbulent flows the CFD-Code CFX-4 was validated and can be used in reactor safety analysis. Due to the good agreement between measured results and the corresponding CFD-calculation efficient modules for the coupling of thermal hydraulic computer codes with three-dimensional neutron-kinetic models using the results of this work can be developed. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.

A better understanding and optimisation of liquid metal processes requires experimental data of the velocity field. Numerical simulations alone are often of limited value. To measure local velocities in liquid metals or to measure channel flow rates in a contact-less way, almost nothing is available commercially.
We report on various measuring technique developments, their test in different liquid metals, and applications in hot melts. For local velocity measurements, a mechano-optical probe working up to temperatures of about 800°C has been developed [1]. It delivers the two mean velocity components perpendicular to the sensor axis. In the presence of an external steady magnetic field, the use of local potential probes allows to analyse the turbulent properties of the flow in addition to the mean velocity [2]. However, both sensor techniques rely on the introduction of probes into the melt and are thus mainly of interest for laboratory purposes.
The Ultrasound Doppler Velocimetry (UDV) became a powerful tool to measure the velocity structure of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In addition, it can principally operate through the channel wall though a direct contact to the melt reduces ultrasonic losses. However, in case of hot metallic melts the user is confronted with several problems: the application of the ultrasonic transducers is usually restricted to maximum temperatures of 200°C, and a good acoustic coupling between the liquid metal and the related interfaces has to be provided. We report on successful measurements in liquid sodium at 150°C [3] which were performed through the channel wall. To overcome the limitation of ultrasonic transducers to temperatures lower than 200°C, an integrated ultrasonic sensor with acoustic wave-guide has been developed. This sensor can presently be applied at maximum temperatures up to 1000°C. Stable and robust velocity measurements have been performed in various PbBi flows at about 250-300°C. We report on first successful measurements in a CuSn melt of about 620°C and in an Al melt of about 750°C.
Evidently, a fully contact-less measuring technique would be most desirable. Such a method has been developed making use of external magnetic field measurements and inverse reconstruction techniques [4]. We will report on a first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure.
For the flow rate measurement in a pipe, a contact-less solution based on a pair of alternating magnetic field transmitter and receiver has been developed. Test results from a laboratory model and an industrial Al casting process will be presented.

We report on laboratory studies using cold liquid metals as a model of realistic light metal processes. The main feature of such cold (temperatures up to about 300°C) liquid metal models is the availability of measuring techniques allowing to analyse the local transport phenomena with a sufficient resolution. Note that water models of liquid metal processes are only meaningful if the melt flow Reynolds number represents the only determining parameter of the transport processes under consideration, which is seldom the case for real casting processes. As soon as temperature gradients, free-surface phenomena, two-phase flows or electromagnetic phenomena play a role, the water model is always of very limited value.
First we present results on the flow modelling of an investment casting process of aluminium alloys. The configuration basically consists in a U-bend, and the main request is to reduce the high flow velocities during the starting phase of the filling process. They are considered as the main source of problems like bubble or inclusion entrapment. The process was simulated using a plexiglas model and the eutectic melt InGaSn which is liquid at room-temperature. Local velocity measurements have been performed using the ultrasonic Doppler velocimetry, whereas flow rates have been determined independently using the contact-less transmitter technique. Measurements and video visualizations clearly show effects like flow rate oscillations or gas bubble entrapment. Depending on geometric and process parameters, the time-scale to get rid of these entrapments may become longer than the process itself. In order to decrease the maximum values of the velocity at the beginning of the process, an external steady magnetic field has been applied. The measurements show that it is capable of reducing these velocity peaks significantly. The experimental results are compared to numerical simulations.
As a second example we report on model experiments of the electromagnetic stirring of liquid metals in a cylindrical cavity. Different types of alternating magnetic fields, like rotating or travelling fields, are employed for such stirrers. The model experiments reveal that by application of just one type of those fields a strong flow results, but this flow is often of a rather rigid type without a noticeable three-dimensional mixing of the melt. An efficient mixing can be obtained by a combination of the field types. Velocity measurements in rotating, travelling, and combined rotating-travelling fields will be presented demonstrating this behaviour.
Third, we report on systematic studies about the influence of a rotating magnetic field (RMF) on the resulting microstructure of Pb-Sn alloys. The RMF strongly influences the flow in the liquid phase and, thus, the local heat transfer. It results in a significant influence on the nucleation and growth processes, leading to a variety of microstructures. Temperature as well as ultrasonic velocity profile measurements have been performed. Main goal is to find a strategy for refining the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. For a Pb-85wt%Sn alloy, the application of the RMF is capable of changing the columnar dendritic microstructure to an equiaxed one.

Transition to turbulence of a rotating magnetic field driven liquid metal flow in a cylinder is studied experimentally by a probe-less method. A sudden, wide frequency band transition as well as intermittency are observed just at the theoretically predicted linear instability limit. A small geometrical imperfection triggers the transition in the linearly stable regime in a control parameter range where additional unstable steady solutions have been detected numerically. We discuss possibilities to predict theoretically the non-normal transition and its characteristics.

Dendrimere sind nanoskalige, dreidimensional verzweigte Moleküle mit sphärischer Architektur, die auf vielfältige Weise funktionalisiert und modifiziert werden können. Die speziellen Eigenschaften der Dendrimere eröffnen zahlreiche neue Anwendungsmöglichkeiten, insbesondere im Pharmabereich (drug delivery systems, tumor targeting etc.) und motivieren damit auch zu umfassenden Untersuchungen der zugrunde liegenden physiko-chemischen Prozesse. Es ist bekannt, dass die Struktur und die Komplexierungseigenschaften von Dendrimeren in wässrigen Lösungen wesentlich von den Säure-Base-Eigenschaften (Protonierungsgrad) der funktionellen Gruppen und damit vom pH-Wert bestimmt werden.
Im Rahmen dieses Beitrages werden Ergebnisse kalorimetrischer und potentiometrischer pH-Titrationsexperimente in wässriger Lösung an Polyamidoamin-Dendrimeren (PAMAM), die an der Peripherie unterschiedlich funktionalisiert sind (-NH2, -OH, -COOH Gruppen), vorgestellt und diskutiert. Die potentiometrischen pH-Titrationskurven können unter Verwendung von minimal drei simultanen Protonierungsgleichgewichten mit guter Genauigkeit beschrieben werden. Die Ergebnisse sind konsistent mit dem typischen Verhalten von Polyelektrolyten.
Die kalorimetrischen pH-Titrationskurven widerspiegeln die komplexe Natur der ablaufenden Prozesse wesentlich deutlicher. Neben unterschiedlichen Stufen in den kalorimetrischen Titrationskurven, die prinzipiell den Protonierungsgleichgewichten zugeordnet werden können, treten zum Teil endotherme Effekte auf, deren Ursachen noch nicht geklärt sind. Die quantitative Beschreibung der Titrationskurven auf der Basis reiner Protonierungsreaktionen gelingt dadurch nicht vollständig.
Weiterhin werden erste kalorimetrische Ergebnisse zur aus pharmakologischer Sicht wichtigen Wechselwirkung von Dendrimeren mit potentiellen Targetmaterialien am Beispiel von Human Serum Albumin (HSA) präsentiert und diskutiert.

Two asymmetric electroluminescence bands with tunable maxima at around 1.044-1.065 and 0.90-1.00 eV are observed at low temperature in silicon pn diodes prepared by boron ion implantation and subsequent high temperature annealing. The intensity of the two bands increases strongly with increasing the boron concentration above the solubility. A large blue shift of the two bands with increasing the injection carrier concentration was attributed to the three-dimensional confinement of holes in p-type doped spikes localized on a nanometer scale. They are produced by the boron clustering at the end of range defects close to the pn junction. The two bands with a smaller binding energy is attributed to the spatially indirect recombination of the excitons confined around the strain-free p-type doped spike. The band with a higher binding energy is associated with highly strained p-type doped spikes around dislocations. A significant enhancement of the room temperature electroluminescence efficiency of the silicon diode is observed which is attributed to the spatial modulation of the band structure around these p-type doped spikes.

Large improvement of the electroluminescence efficiency was observed from silicon pn diodes prepared by boron implantation. The temperature dependence of the EL and PL of the pn diode shows a different behavior compared to the PL from bulk silicon substrates. Two asymmetric EL bands from trap bands below the free exciton emission band are observed at around 1.065 and 0.92-0.96 eV at low temperature in the silicon pn diode. The intensity of the two bands increases strongly with increasing boron concentration. A blue shift of the two bands with increasing the injection current was observed which is similar to EL in deta-doped semiconductors. The temperature dependence of the EL intensity from the different bands shows that the thermal emission of carriers from these traps is responsible for a strong increase of the band edge radiative emission of silicon. These results are consistent with a rate equation model based on the emission, trapping and recombination processes for a system containing free excitons and bound excitons. Our results give an alternative explanation to the strong increase of the EL efficiency in boron implanted silicon pn diodes [1].
[1] W.L. Ng et al., Nature 410, 192 (2001).

A bound-exciton-induced current bistability is observed under forward bias in an efficient silicon light-emitting diode at low temperatures. Two stable states of the S-type differential conductivity correspond to empty and filled states of bound excitons, espectively. The relationship between the current-voltage characteristic and the bound-exciton population can be accounted for using a rate equation model for bound and free excitons. The consistency between the theoretical and experimental results indicates that bound excitons, despite their neutral-charged states, contribute to the current bistability in silicon p-n junction diodes.

Bakterien in stark kontaminierten Umgebungen mussten effiziente Entgiftungsstrategien zum Überleben ausbilden. Diese können zur Entwicklung ebenso effizienter und innovativer Biosanierungsverfahren auf der Basis der immobilisierten Biokomponenten genutzt werden. Ausgewählt wurden Bakterien einer Uranabfallhalde in Form von intakten Zellen, Sporen und Teilen der Zellwand. Diese binden selektiv und reversibel Uran, Kupfer, Blei, Aluminium und Cadmium mit hoher Kapazität. Ausgangspunkt für die Einbettung der Biokomponenten sind Siliciumoxid-Sole, die durch Änderung des pH-Wertes oder durch Temperaturerhöhung schnell gelieren. Durch Trocknung der Biokompositsole entstehen poröse Xerogele, die als selektive und wiederverwendbare Filter in Sanierungsverfahren zum Einsatz kommen können.

Im Bestrahlungsprogramm Rheinsberg II wurden zur Temperaturbestimmung Temperaturmonitoren aus Diamantpulver verwendet. Das Verfahren nutzt den Einfluss der Temperatur auf die bestrahlungsbedingte Änderung der Gitterkonstanten des Diamantgitters und ist in einer russischen Prüfvorschrift standardisiert. Zur Ermittlung der Temperatur wurde die Gitterkonstante mit einem Röntgen-Diffraktometer nach Bestrahlung und anschließenden Ausheilglühungen in isochronenTemperaturstufen von 50 - 100 K bestimmt. Der Unstetigkeitspunkt auf dem linearisierten Temperaturverlauf der Gitterkonstanten liefert einen Wert für die Bestrahlungstemperatur, der gemäß der Prüfvorschrift neutronenflussabhängig zu korrigieren ist. Es werden starke Messwertstreuungen festgestellt, die die Genauigkeit der Bestimmung des Unstetigkeitspunktes erheblich beeinträchtigen. Darüber hinaus treten systematische Fehler auf. Insgesamt ist die Temperaturbestimmung mit Diamantpulver im Bestrah-lungsprogramm Rheinsberg II als nicht zufriedenstellend einzuschätzen. Der wahrscheinlichste Wert liegt im Bereich von 255 - 265 °C und somit nahe dem Wert, der aus den thermischen Randbedingungen der Experimente abgeschätzt werden kann.

Nitrogen ions were implanted into (100)GaAs at high temperature (400 and 600oC) and high dose (2x10^17 and 6x10^17 ions cm-2) in order to synthesize small GaN crystallites. The defective strip due to implantation is about 500 nm thick and stacking faults appeared as the characteristic defect. Selected area diffraction patterns show that cubic GaN was formed in samples implanted at 600oC. The precipitates formed are typically 5 nm large and are epitaxial to the host GaAs. Some larger precipitates are also observed from which the matching of the two lattices could be determined.

In the axially symmetric magnetic mirror device gas dynamic trap (GDT), on-axis transverse beta (ratio of the transverse plasma pressure to magnetic field pressure) exceeding 0.4 in the fast ion turning points has been first achieved. The plasma has been heated by injection of neutral beams, which at the same time produced anisotropic fast ions. Neither enhanced losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. This observation confirms predicted magnetohydrodynamic stability of plasma in the axially symmetric mirror devices with average min-B, like the GDT is. The
measured beta value is rather close to that expected in different versions of the GDT based 14 MeV neutron source for fusion materials testing.

GDT experiments of significance to a GDT based neutron source development are reported in the areas of generation of axially peaked neutron flux profile, stable confinement with on-axis plasma beta ~40%, and radial electric field control. Skew injection of 4 MW 15-17 keV deuterium neutral beams into central cell resulted in generation of strongly peaked axial profile of neutron flux density. This can be described by a model of fast ion relaxation, which involves classical mechanisms of electron drag and binary ion-ion collisions only. Experiments with the radial limiter biasing show that the plasma density profile and radial losses respond to the electric field profile. An increase of plasma energy was achieved with increased magnetic field in the central cell and optimised radial profile of electric field. In these regimes the on-axis plasma beta near the turning points of fast deuterons exceeded ~40%. The plans for future upgrade of the GDT device are discussed. It suggests considerable increase of NB injected power (up to 10 MW) and extension of the pulse duration from 1 ms up to 3-5 ms. After the upgrade, a significant increase of the electron temperature up to 250-300 eV could be obtained. Properties of the plasma with parameters approaching those in the full-scale neutron source are planned to study in experiments with NB injection into an additional mirror cell which will be installed near to one of the standard mirror coils.

Thin films (dB nm)of hydrogenated amorphous silicon carbide (a-SiC:H),deposited by RF reactive magnetron sputtering,have been ion implanted with high doses (D=1E16¿1E17cm^2) of Ga+ as the implant species.The increased disorder and additional structural modi .cation of a-SiC:H,induced by the implantation of Ga+ results in a considerable change of the optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies in the results obtained by optical transmission and re .ection measurements and as derived from photo-thermal-deflection spectroscopy results.This shift may be attributed both to additional defect introduction and to accompanying structural modi .cation effects,as confirmed by optical absorption measurements in the infra-red region and by Raman spectroscopy results.

Proceedings volume!

In order to enable a better description of ballistic and athermal processes occurring in the initial stage of ion-beam-induced defect formation, the repulsive part of the interatomic potentials of Gao and Tersoff is improved. The first modification concerns the two-body part of the potentials. At small interatomic distances it is replaced by the well-tested potential of Ziegler, Biersack, and Littmark (ZBL). For repulsive interactions between zero and some ten electron volt, an exponential spline function is employed to connect the ZBL potential with the two-body parts of the Tersoff and the Gao potential. The modified two-body potentials and their first derivatives are continuous and monotonic over the whole range of repulsive interaction. They are in good agreement with data obtained by density-functional-theory calculations. Furthermore, the three-body part of the Tersoff and the Gao potential is modified in order to avoid the strong dependence of repulsive interactions between two atoms on the bond-order parameter, i.e. on their coordinations. The modification is performed in such a manner that the total potential and its first derivative remain continuous and monotonic for all repulsive interactions.

The present paper deals with advanced conductivity probes for local void measurements, which were equipped with a micro-thermocouple, which is integrated into the probe at the place of the electrode wire. These probes were used for rapid transient condensation tests in a heat exchanger pipe immersed into a cooling water tank. The experiments serve as data sources for the validation of thermal-hydraulic system codes concerning the modelling of the condensation, particularly with respect to the behaviour and effect of non-condensable gases. The present tests were carried out at the pressurizer test facility DHVA of the University for Applied Sciences in Zittau/Görlitz serving as steam source. The slightly downwards inclined condensation tube was connected to the head of the pressure vessel and supplied with steam in this way. The application of a new type of two-phase instrumentation has revealed details about the transient condensation process. Since test were performed with and without the presence of a non-condensable gas (air), the effect of the gas could be studied. The merits of the probes lie in the ability to distinguish between steam and gas. Without the synchronous temperature and void measurement performed by the probes it would have not been possible to clarify the physical background of the temperature jumps found during the experiments with the non-condensable gas.

Most of the level monitoring systems for pressure vessels containing saturated steam-water mixture use the hydrostatic method. Differential pressure transducers are connected by pulse tubes with nozzles at different height of the pressure vessel. A disadvantage of this method is given by measuring errors cause by evaporation and/or degassing processes in vertical parts of these pulse lines. The error is caused by the decrease of the fluid density in the reference pipe, when a two-phase mixture appears. The present work aimed at the test of a novel differential pressure measuring system that eliminates the influence of density changes in the pulse lines. It is based on two differential pressure transducers, placed accurately at the elevation of the connecting nozzles. They are connected with the pressure vessel only by horizontal pipes. The vertical distance is bridged by a standpipe, the fluid of which is completely separated from the fluid in the vessel. Degassing respectively evaporation effects can therefore completely excluded in the reference column of the new system. The method was tested at the pressurizer test facility of the University of Applied Sciences Zittau/Görlitz on three types of transients including a rapid pressure decrease similar to a loss-of-coolant transient. Traditional differential pressure systems as well as local void probes were used for comparison. The method has proven its advantages compared to the traditional hydrostatic level measurement method.

Im Zuge von Modellbildungen ist es nicht immer möglich, das zu beschreibende Objekt sofort oder direkt durch ein einzelnes Modell vollständig zu erfassen. Vielmehr wird es zunächst mehrere untergeordnete Modelle geben, die jeweils nur verschiedene eingeschränkte Sichten auf das Objekt repräsentieren. Im Beitrag wird untersucht, wie solche Modelle zu einer Modellsymbiose verbunden werden können und wie mit deren Hilfe dann nach einem verbesserten Einzelmodell des zu beschreibenden Objektes gesucht werden kann.

Positron emission tomography (PET) is a powerful imaging technique for the in vivo study of molecular interactions and molecular pathways in the human body. In combination with approprately labelled radiotracers, PET offers exceptional possibilities to study physiology, metabolism, pharmacokinetics and modes of action of novel and established drugs, and food ingredients.

The key element of PET is the PET-radiotracer, a compound labelled with a short-lived positron emitter. The most useful positron emitters for the labelling of organic moleculars are ¹¹C and ¹⁸F which have half-lives measured in minutes, bein 20.4 min and 109.6 min, respectively. Consequently, time dominates all aspects of PET. In this connection the extensive performance of organic radiochemistry using ¹¹C and ¹⁸F is fundamental but also a special challenge. This review will address the recent developemts of organic PET radiochemistry in the synthesis of PET radiotracers with special focus on ¹¹C and ¹⁸F

Examples of a new type of cryptophane molecule incorporating aromatic groups in the bridges (1 - 4) and for the first time, being also supplied with three endo-positional ionizable carboxylic acid function (1) have been synthesized and characterized. The cryptophane triester 2 yielded a solvate (channel inclusion compound) with trichloromethane and water, the X-ray crystal structure of which is reported. The complexation of 1 with low-molecular-weight alcohols in solution was studied, and the liquid-liquid extraction of different metal ions including alkali (Na⁺, Cs⁺), alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), and the lanthanide metal ions Eu³⁺ and Yb³⁺ in an extraction system containing metal nitrate buffer/H₂O/1/CHCl₃ was examined. Molecular modeling calculations of the cryptophanes 1 and 2, and of the Eu³⁺ complex of 1 were carried out contributing to the discussion.

Low concentration of toxic radioactive metals in environmental samples often limits the interpretation of results of infrared studies investigating the interaction processes between the metal ions and environmental compartments. For the first time, we show that photothermal infrared spectroscopy performed with a pulsed free electron laser can provide reliable infrared spectra throughout a distinct spectral range of interest. In this model investigation, we provide vibrational absorption spectra of a rare earth metal salt dissolved in a KBr matrix and a natural calcite sample obtained by thermal beam deflection technique and FT-IR spectroscopy, respectively. General agreement was found between all spectra of the different recording techniques. Spectral deviations were observed with samples containing low concentration of the rare earth metal salt indicating a lower detection limit of the photothermal method compared to conventional FT-IR spectroscopy.

A new method of preparing alumina ceramic surface for brazing it to kovar with conventional Ag-Cu eutectic brazes is presented. The key concept of this approach consists in formation of two inter-layers on the ceramic surface: (i) thin (in nm scale) layer of TiO_x using pulse plasma beams, and (ii) thicker (about 2 µm) layer of TiO_x or metallic Ti using arc PVD technique. Grazing incidence X-ray diffraction (GXRD) analysis shows that the first layer consists most likely of Ti₇O₁₃, whereas the second is either Ti₂O, or metallic Ti - depending on the deposition conditions. Commercial housings of semiconductor diodes have been used as the samples. Brazed housings were tested under routine industrial conditions. The ultimate tensile strength (UTS) of joints reaches the average value of 90 MPa. Vacuum tightness is better than 5x10^-6 mbar l/s. The values of parameters are sufficient to pass the production requirements.

Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreaktor ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können. Es wurden bereits eine Reihe von Experimenten durchgeführt, welche Erkenntnisse hierüber liefern sollen. Begleitend wurden in Einzelversuchen Materialeigenschaften ermittelt, sowie theoretische und numerische Arbeiten durchgeführt.
Für die Simulation von Experimenten zum Versagen der Bodenkalotte, wie OLHF oder FOREVER, ist es notwendig, Kriechen und Plastizität zu berücksichtigen. Gleichzeitig müssen geeignete Modelle das Temperaturfeld in der Behälterwand für die mechanischen Rechnungen bereitstellen. Vom Institut für Sicherheitsforschung des FZR wird ein Finite-Elemente-Modell erstellt, das sowohl die Temperaturfeldberechnung für die Wand als auch die elasto-plastische Mechanik der Behälterwand modelliert. Die bisher durchgeführten Arbeiten werden in diesem Bericht kurz erläutert und mit Beispielen belegt.
Am FZR wurde ein Finite-Elemente-Model entwickelt, das die Verwendung von einfachen Kriechgesetzen, die mit ihren angepassten Konstanten nur für begrenzte Spannungs- und Temperaturbereiche gültig sind, umgeht. Stattdessen wird eine numerische Kriechdatenbasis angelegt, in der die Kriechdehnrate in Abhängigkeit von der Gesamtdehnung, der Temperatur und der Vergleichsspannung abgelegt ist. Eine wesentliche Aufgabe für diese Vorgehensweise besteht in der Generierung und Validierung der Kriechdatenbasis. Zusätzlich wurden alle relevanten temperaturabhängigen Materialeigenschaften mit entsprechenden Modellen in den Code eingegeben. Für die Bestimmung der Versagenszeit wurde ein Schädigungsmodel nach einem Vorschlag von Lemaitre implementiert.
Die Validierung des numerischen Models erfolgt durch die Simulation von und den Vergleich mit Experimenten. Dies geschieht in 3 Stufen: zunächst werden einzelne einachsige Kriechversuche nachgerechnet, was als 1D-Problem bezeichnet wird. In der nächsten Stufe werden sogenannte ¿Rohrversagensexperimente¿ simuliert: das RUPTHER-14 und das ¿MPA-Meppen¿-Experiment. Diese Experimnete werden als 2D-Probleme betrachtet. Schließlich kann das Modell auf skalierte 3D-Versuche angewendet werden, in denen die Bodenkalotte eines Druckwasserreaktors mit ihrer halbkugelförmigen Geometrie wiedergegeben wird. Ein Beispiel hierfür sind die FOREVER-Experimente. In Zusammenarbeit mit den Experimentatoren an der KTH in Stockholm wurden Pre- und Posttest-Rechnungen für diese bisher einzigartigen Experimente durchgeführt, deren Ergebnisse qualitativ und quantitativ sehr zufriedenstellend sind.
Eine wichtige Frage im Rahmen dieser Arbeit ist die Vergleichbarkeit des französischen Reaktordruckbehälterstahls 16MND5 und des deutschen 20MnMoNi5-5, welche chemisch nahezu identisch sind. Da diese beiden Stähle ein ähnliches Verhalten zeigen, sollte es in gewissem Umfang zulässig sein, experimentelle und numerische Daten und Erkenntnisse zwischen beiden zu übertragen.

This paper reports on an extensive study of the characteristics of AuGeSi and CoNd liquid metal alloy ion sources (Focused Ion Beams From Liquid Metal Ion Sources,Research Studies Press,Taunton,Somerset,UK,1991).Such characteristics include current –voltage curves and ion beam mass spectra.A careful investigation has been undertaken where the emitter temperature is the main variable experimental parameter.Theoretical models,or theoretical attempts in certain cases,tend to support the experimental results.The experimental results,in conjunction with existing theories, suggest that simply for reasons of self-consistency two mechanisms must be operative for the production of doubly- charged ions from the AuGeSi source:direct .eld-evaporation and post-ionisation.

We report on the direct measurement of surface plasmon transmissivity of narrow grooves in thin silver films using near-field optical microscopy in an attenuated-total-reflection setup. For different groove widths, we observe characteristic changes in transmissivity that are attributed to resonant gap modes. The results are in good agreement with existing theoretical predictions.

Der Aufbau und die erste Nutzung eines kompakten Flugzeitsystems zur energiedispersiven Untersuchung der Wechselwirkung von schnellen Neutronen mit Materialien sind Inhalt eines Vernetzungsprojektes des Forschungszentrums Rossendorf, an dem auch die Technische Universität Dresden im Rahmen eines gemeinsamen DFG-Projektes mitarbeitet. Die geplanten Flugzeit-Experimente mit gepulsten Neutronen werden an der Strahlungsquelle ELBE durchgeführt werden. Erste Ergebnisse zur Entwicklung eines Neutronen-Produktionstargets werden vorgestellt. Mit Hilfe von Strahlungstransport- und Finite-Elemente-Programmen wurden die Verteilungen der Energiefreisetzung des von der Strahlungsquelle ELBE genutzten Elektronenstrahls und der Temperatur im Neutronen-Radiator sowie die zu erwartenden Teilchenspektren und -flüsse am Messplatz berechnet. Überlegungen zur Entwicklung des Strahlfängers werden diskutiert.

RES³T – the Rossendorf Expert System for Surface and Sorption Thermodynamics – is a digitized thermodynamic sorption database utilizing surface complexation models (SCM). It is mineral-specific and can therefore also be used for complex models of solid phases such as rocks or soils. As to the knowledge of the authors there is no such digital thermodynamic database for surface complexation equilibria existent worldwide, despite of the vast amount of available data.
Data records comprise of mineral properties, specific surface area values,characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. An extensive bibliography is also included, providing links not only to the above listed data items, but also to background information concerning surface complexation model theories, surface species evidence, and sorption experiment techniques.
An integrated user interface helps users to access selected mineral and sorption data, to extract internally consistent data sets for sorption modeling, and to export them into formats suitable for other modeling software. It assists the identification of critical data gaps, the evaluation of existing parameter sets, consistency tests and the establishing of selected reference data sets.
RES³T is implemented as a relational database under MS ACCESS. The database is intended for an international use and is currently converted into a WWW-based version.
A system for illustrating the current blind predictive capabilities of SCM using the RES³T database is the Cu²⁺ sorption onto iron oxyhydroxides. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected to account for electrostatics. The calculation was performed with the FITEQL code, version 3.2. The respective SCM parameters from RES³T were the binding site density for the minerals, the surface protolysis constants, and the brutto stability constants for all relevant surface complexes. The model prediction almost always represented the experimental values for the sorbed amount of Cu²⁺, expressed as conventional distribution coefficients K_D as required by PA software.

Mit Batch- und Durchflussexperimenten wurde, unter Einbeziehung der Mineralauflösung und Sekundärphasenbildung, die U(VI) Sorption auf zwei unterschiedlichen Chloritmineralen untersucht. Hierbei handelte es sich um einen nicht alterierten Ripidolith Chlorit (CCa-2) von Flagstaff Hill (El Dorado County, California, USA), der aus einem Chloritschiefer gewonnen wurde und einen hydrothermal alterierten Chlorit von Grimsel (Schweiz), der aus einer granitischen Kluft gewonnen wurde. Die Durchflussexperimente wurden mit 0,5 g des jeweiligen Chloritpulvers (63-200 µm Korngröße), einer 0.1 M NaClO4-Ausgangslösung, einer U(VI)-Konzentration von 1´10-6 M und bei einem pH von 6,5 durchgeführt. Die Ergebnisse zeigten einen deutlichen Unterschied im Sorptionsverhalten der beiden Chlorite. Der nicht alterierte CCa-2 Chlorit zeigte ein Sorptionsmaximum von 90 % und wies damit eine mehr als 20 % höhere Sorption unter vergleichbaren Bedingungen als der hydrothermal alterierte Chlorit auf. Vorangegangene Untersuchungen am CCa-2 Chlorit [1] und Grimsel Chlorit [2] zeigten, dass diese erhöhte Sorption auf die Bildung von Fe-oxyhydroxiden, wie beispielsweise Ferrihydrit, während der Auflösung des nicht alterierten Chlorits zurückgeführt werden können. Ferrihydrit ist aufgrund seiner hohen spezifischen Oberfläche und seiner hohen Sorptionsaffinität ein wichtiger Sorbent für U(VI). Der alterierte Grimsel Chlorit wurde bereits im hydrothermalen Stadium gelaugt, so dass dieser nicht so stark zur Sekundärphasenbildung neigt wie der CCa-2 Chlorit. Die unterschiedlichen U(VI) Sorptionsergebnisse an den beiden Chloriten belegen diese Interpretation.
/1/ Krawczyk-Bärsch et al. (2003): Chem. Geol. (submitted).
/2/ Arnold et al., (1998): Chem. Geol. 151, 129-141.

Bei stark exothermen Batch- und Semibatch-Prozessen ist die Identifikation des aktuellen Prozesszustandes und die frühzeitige Erkennung von unerwünschten Betriebszuständen sowohl unter dem Aspekt der Anlagen- und Umweltsicherheit als auch aus Gründen der Sicherung einer gleichbleibend hohen Ausbeute und Produktqualität von besonderer Bedeutung. Zur Unterstützung des Bedienungspersonals hinsichtlich einer optimalen Anlagenfahrweise wurde ein auf adaptiven Energie- und Stoffbilanzen basierendes Online-Monitoring-System (MoSys) konzipiert. Die Systementwicklung erfolgte anwendungsorientiert für heterogen katalysierte Hydrierprozesse von Nitroaromaten in Rührkesselreaktoren. Für den Einsatz des Systems im Industriemaßstab wurde MoSys in ein komplexes Batch-Informations-Management-System (BIMS) eingebunden. Somit ist die Anzeige der MoSys-Ergebnisse, wie Umsatz- und Konzentrationsverläufe, simultan zu den primären Prozesssignalen und den chargenorientierten Informationen an den verschiedenen Operatorstationen in der Chemieanlage möglich. Der Test des Zustandserkennungssystems erfolgte an einer Mehrzweckanlage der DEGUSSA AG im Werk Radebeul.
Gezeigt werden der prinzipielle Aufbau des Monitoring-Systems (Berechnungsalgorithmus), die Einbindung und Funktion von MoSys innerhalb des Batch-Informations-Management-Systems sowie die Visualisierung der MoSys-Ergebnisse an den Operatorstationen am Beispiel von einzelnen Screenshots. Die Validierung des Systems an der Industrieanlage ist am Beispiel von Konzentrations- und Umsatzverläufen sowie der Zustandsklassifikation für die Zwischenproduktakkumulation dargestellt. Eine Zusammenfassung, in der die Bedeutung des Einsatzes von BIMS/MoSys für die industrielle Praxis aufgezeigt wird, beschließt den Artikel.

Mittels zeitaufgelöster laserinduzierter Fluoreszenzspektroskopie (TRLFS) wurde die Uranyl(VI) Sorption auf dem Schichtsilikatmineral Muskovit angewendet. Ziel dabei war es, die adsorbierten Oberflächenspezies sowohl auf den Basisflächen als auch auf den Kantenflächen nachzuweisen und zu vergleichen.
Die Muskovit Plättchen wurden dazu bei pH 6.3 für ca. 60 h mit einer 1×10-5 M Uranyl Lösung (0,1 N NaClO4) kontaktiert. Etwa 72 % der Ausgangsmenge an Uranyl wurde unter diesen Bedingungen sorbiert.
Auf den Basisflächen wurde kein Uranyl-Fluoreszenzspektrum erhalten, was zeigt, dass Uranyl vernachlässigbar sorbiert wurde (< 10-12 M/cm2). Die Sorption erfolgt dominierend an den Kantenflächen. Die Spektrenauswertung ergab das Vorliegen von zwei sorbierten Uranylspezies mit Lebensdauern von 1,15 bzw. 9,65 µs. Die Lage der Hauptemissionsbanden stimmen innerhalb der Fehlergrenzen für beide Komplexe überein, was auf eine unterschiedliche Anzahl der umgebenden Wassermoleküle hinweist. Aus diesen Ergebnissen und zusätzlich durchgeführten EXAFS Untersuchungen lässt sich die Sorption von Uranyl(VI) an den Muskovit Kantenflächen am besten mit zwei bidentaten mononuklearen Oberflächenspezies beschreiben.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range different ion species are needed. Therefore alloy liquid metal ion sources (LMIS) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions the predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell-time was used for radiation damage investigations in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.

The aim of the investigation is the growth of high-precision single crystals of intermetallic compounds using well defined magnetic fields. The fundamental problem is conditional on the fact that especially complicated intermetallic compounds are not producible as single crystals over the whole cross-section by the inductive floating-zone melting technique since the geometry of the zone at the solid-liquid-interface is unfavourable. The controlled adjustment of a solid-liquid-interface of desired curvature and the knowledge of the melt convection in liquids with high conductivity can be arranged by the contact-less influence of electromagnetic fields. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni [1]. The significant influence of the electromagnetically driven flow, which acts opposite to the Marangoni convection, makes the solid-liquid interface concave towards the melt.
Comprehensive investigations of the influence of growth parameters such as zone length, power influence and heated region on the solid-liquid interface geometry during RF floating zone crystal growth were carried out experimentally. It could be shown that undesired concave (towards the melt) interface regions cannot be avoided even at optimised parameter configurations [2].
As a result, a two-phase magnetic field pump, which allows a strong manipulation of the convection and therefore of the solid-liquid interface, was designed. It allows to change the flow structure from the typical double vortex to a single one with a strong influence on the phase boundary shape (Fig. 1). The adjustment of a complete convex solid-liquid interface shape in RF-floating zone crystal growth was tackled with this additional melt stirring resulting in a definite improvement of the solid-liquid-interface.

For the purification of uranium contaminated waters various water purification methods (e.g., application of ion exchangers, direct precipitation, microbiological methods) are usually applied. Also solvent extraction applying calix[6]arenes is suitable to separate uranium from aqueous solution [1]. To facilitate the uranium separation from uranium containing waters in practice, we are developing an alternative procedure. For this, calix[6]arenes are permanently fixed onto textile substrates via spacer groups [2]. This method is advantageous especially for smaller remediation objects and objects with lower contamination levels ([UO22+] ~ 1×10-6 M).
In the present work, the extraction efficiency of various calix[6]arenes including their selectivity towards uranium(VI) is studied in a two phases solvent extraction system in dependence on pH value, ligand concentration and the amount of competing ions. The complex formation between uranium(VI) and calix[6]arenes is further studied at pH 4 by means of TRLFS as well as by TRLFS with ultrashort laser pulses. By these methods it is possible to detect uranium and calixarene species at equilibrium directly in the aqueous and organic phase. Reaction mechanisms are discussed and extraction constants are determined. In the presence of competing ions (e.g., calcium, barium, magnesium) the uranium extraction is only slightly decreased. The suitability of the calix[6]arenes as efficient reagents for selective uranium separation from aqueous solution is shown.

[1] Shinkai, S. et al.: Molecular design of calixarene-based uranophiles which exhibit remarkably high stability and selectivity. J. Am. Chem. Soc. 109, 6371-6376 (1987).
[2] Schmeide, K. et al.: Separation of uranium from aqueous solution by textile bound calixarenes. In: Uranium in the aquatic environment. Springer Verlag, Berlin 2002, p. 417-424.

Heavy ion therapy has two definite advantages: good dose localization and higher biological effect. Range calculation of the heavy ions is an important factor in treatment planning. X-ray CT numbers are used to estimate the heavy ion range by looking up values in a conversion table which relates empirically photon attenuation in tissues to particle stopping power; this is one source of uncertainty in the treatment planning. Use of positron emitting radioactive beams along with a positron emission tomograph or a positron camera gives range information and may be used as a means of checking in heavy ion treatment planning. However, the metabolism of the implanted positron emitters in a living object is unpredictable because the chemical forms of these emitters are unknown and the metabolism is dependent on the organ species and may be influenced by many factors such as blood flow rate and fluid components present. In this paper, the washout rate of ¹¹C activity implanted by injecting energetic ¹¹C beams into thigh muscle of a rear leg of a rabbit is presented. The washout was found to consist of two components, the shorter one was about 4.2+-1.1 min and the longer one ranged from 91 to 124 min. About one third of the implanted positron activity can be used for imaging and the rest was washed out of the target area.

A relative biological effectiveness (RBE) not much larger than unity is usually assumed for soft x-rays (up to ~50 keV) that are applied in diagnostic radiology such as mammography, in conventional radiotherapy and in novel radiotherapy approaches such as x-ray phototherapy. On the other hand, there have been recent claims of an RBE of more than 3 for mammography and respective conventional x-rays. Detailed data on the RBE of soft x-rays, however, are scarce. The aim of the present study was to determine the effect of low-energy x-rays on chromosomal damage in vitro, interms of micronucleus induction. Experiments were performed with 25 kV x-rays and a 200 kV x-ray reference source. The studies were carried out on primary human epidermal keratinocytes (HEKn), human fibroblasts (HFIB) and NIH/3T3 mouse fibroblasts. Micronucleus (MN) induction was assayed after in vitro irradiation with doses ranging from 1 to 5.2 Gy. Compared to the effect of 200 kV x-rays, 25 kV x-rays resulted in moderately increased chromosomal damage in all cell lines studied. This increase was observed for the percentage of binucleated (BN) cells with micronuclei as well as for the number of micronuclei per BN cell.
Moreover, the increased number of micronuclei per micronucleated BN cell in human keratinocytes and 3T3 mouse fibroblasts suggests that soft x-rays induce a different quality of damage. For all cell lines studied the analysis of micronucleus induction by 25 kV soft x-rays compared to 200 kV x-rays resulted in an RBE value of about 1.3. This indicates a somewhat enhanced potential of soft x-rays for induction of genetic effects.

To study of the complex formation of dihydroxybenzoic acids with uranium(VI), we measured the spectra of 2,5-dihydroxybenzoic acid (2,5-DHBA) as a function of pH (2.0 - 4.0) and concentration of uranium (0 - 5x10-3 M). The intensity of the spectra changes with pH and uranium concentration. As we found only spectra with one emission maximum and mono-exponential fluorescence decay, we concluded that no excited state reactions could be observed in the experimental conditions. On the other hand, a change in the fluorescence lifetime could be obtained. The fluorescence lifetimes were found to be in the range from 1.8 ns to 5.7 ns. This means that a dynamic quench process occurred. In order to estimate the formation constant of the 2,5-DHBA with uranium, firstly, we evaluated the protonation constant of the carboxylic group of the 2,5-DHBA. It was found to be log K3 = 2.77 ± 0.05, by taking into account the self-quenching effect. This is in good agreement with literature data (2.82) /1/. The 2,5-DHBA itself and uranium quench the fluorescence of the 2,5-DHBA. We evaluated the dynamic quench constants to be KSV = 216 ± 4 for the ligand itself and KSV = 45 ± 1 for uranium. Both have to be taken into consideration for estimating the complex formation constant. Furthermore, in the pH range 2.0 to 4.0, slopes between 0.91 and 1.39 were found for the validation of the stoichiometry. We conclude, therefore, that a one to one complex forms between uranium and 2,5-DHBA. The dependence of the formation constants on pH values was investigated in order to determine the number of protons involved in the complex formation. Since the slope of the pH dependence was -0.79 ± 0.1, we conclude that one proton at most is involved in this complex formation. This suggests that only the carboxylic group is involved in the complex formation. Based on these considerations, the complex formation constant was assigned to be log K = -0.57 ± 0.26. As uranium shows fluorescence properties, the complex formation can be also confirmed using the changes in the fluorescence behavior of uranium. The formed complex itself does not show fluorescence properties, and only the emission of the non-complexed uranium is observed. As example at pH 4.0, formation constants of log K = 3.29 ± 0.16 were assigned for the ligand study and of log K = 3.17 ± 0.32 for the uranium study, respectively./1/ L. Lajunen, R. Portanova, J. Piispanen et al; Pure & Appl.Chem.,69,329 (1997)

In a former study we analyzed the complex formation between uranium and 2,3-dihydroxybenzoic acid using the fluorescence properties of the ligand. The formation constant was found to be log K11 = -3.11 ± 0.16.We have validated this complex formation using the fluorescence properties of uranium. The formed complex has no fluorescence properties. This is confirmd by a monoexponetial fluorescence decay and also the fluorescence spectra show no shift in the emission maxima.However the fluorescence lifetime of the non-complexed uranium in the solution depends on the concentration of the added ligand. This is due to the dynamic quench effect of the ligand molecule. This quench effect is strongly correlated to the pH of the solution. This leads to the conclusion that only the protonated ligand effects this quench process. Taking this effect into account we are able to calculate the fluorescence intensities of the non-complexed uranium and by use of these data the complex formation between uranium and 2,3-dihydroxybenzoic acid. We obtained a one to one complex formation accompanied by the release of two protons from the ligand, as also found in the study of the fluorescence properties of the ligand. However the derived complex formation constants differ between both methods. The formation constant obtained from the uranium study was found to be log K = -3.99 ± 0.44. This is about 0.9 orders of magnitude lower compared to the constant derived from the study of the ligand. The confidence limits of the two data sets overlap nevertheless the deviation of the both constants leads to the conclusion that other reactions may be involved. From the uranium fluorescence we do not expect such reactions. But the non-complexed ligand may show separate reactions in the excited state, which lead to a change of the fluorescence intensity of the ligand and resulting in an increase of the calculated formation constant. The consequence of the inclusion of these reactions in the examination leads to an exact determination of the ligand concentration accompanied by a much better agreement of the assigned formation constants.

The paper presents examples illustrating the current blind predictive capabilities of surface complexation models (SCM) and respective databases. High-quality experimemtal sorption data sets as provided by Phase II of the NEA Sorption Project for its fitting assessment efforts were used. The systems covered are Np(V) sorption onto hematite, U(VI) sorption onto quartz and Se sorption onto goethite. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected to account for electrostatics. All calculations were performed with the FITEQL code, version 3.2. Based on the information in the sorption database RES³T [1] for the above minerals and chemically similar phases, first a set of relevant species was formed. Then respective surface complexation parameters were taken from RES³T: the binding site density for the minerals, the surface protolysis constants, and the brutto stability constants for all relevant surface complexes. To be able to compare and average thermodynamic constants originating from different sources, the normalization concept as introduced by Kulik [2] was applied. Lacking data was substituted by estimates exploiting chemical analogy. The only system-specific parameters directly going into the computations were the solid-liquid ratio and the specific surface area.

The model prediction almost always represented the experimental values for the sorbed amount of Np, U and Se, expressed as conventional distribution coefficients KD as required by PA software, within one order of magnitude or better, provided an adequate chemical system was assumed. Further improvements may arise from a broader data base eliminating the need for data estimations through chemical analogies.

[1] RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics, V. Brendler, A. Vahle, T. Arnold, G. Bernhard, T. Fanghänel, J.Contaminant Hydrology, in press
[2] Sorption modelling by Gibbs energy minimisation: Towards a uniform thermodynamic database for surface complexes of radionuclides. D. Kulik, Radiochim. Acta, 90 (2002), 815-832

Radiometals play an important role in nuclear medicine^1-3 for the diagnosis or therapy of various diseases. Beside technetium-99m, the most frequently used radionuclide for in-vivo- diagnosis because its optimal nuclide properties, economically supply by the ⁹⁹Mo/^99mTc generator and easy preparation of the ^99mTc-radiopharmaceutical in the clinic, current search for metalloradiopharmaceuticals focuses on both unconventional positron emitting metals (e.g. Cu-64, Ga-66, Y-86, Tc-94m) as potential agents for positron emission tomography (PET) and of radiometal agents labeled with particle emitters for radionuclide therapy³. Since the basic requirement for therapeutic radiopharmaceuticals, namely to induce high effective dose for the target but practically no interference with healthy tissue is not fulfilled yet, the number of therapeutic radiopharmaceuticals for routine use is limited.
Besides the availability of suitable nuclides, the design of chelate systems for stable binding of the radiometal is a crucial point in the development of new metalloradiopharmaceuticals. The chemistry of respective chelates designed in recent years for binding technetium and rhenium at various oxidation states will be discussed. Such chelates involve mixed-ligand complexes containing the metalnitrido core at oxidation state V, Tc(III)/Re(III) and organometallic Tc(I)/Re(I) complexes.
Finally, the application of these chelates for labeling peptides and receptor-affine coordination compounds will be demonstrated.

Visualisation of primary prostate cancer and its metastases remains a clinical important problem, state-of-the-art methods like CT, MRI, TRUS (transrectal ultrasound) and ¹⁸F-FDG PET notwithstanding. The difficulties are even more pronounced in case of local recurrence as ¹⁸F-FDG PET, while useful in the detection of metastases, is not considered helpful in the investigation of relapse. The aim of this study was to evaluate the efficacy of ¹¹C-acetate and ¹⁸F-FDG-PET in the detection of prostate cancer and its metastases in patients treated with or without hormonal ablation.
25 patients (age: 54 to 82 years) were investigated during follow-up of a primary prostate cancer, suspected relapse, or metastatic disease using ¹¹C-acetate PET and 15 with ¹⁸F-FDG PET additionally. 14 Patients had antiandrogen treatment at the time of the investigation, the other 11 patients were drug-naive.
Primary tumours were detected in 20/24 (83%) patients using ¹¹C-acetate PET and in 10/15 (75%) patients using ¹⁸F-FDG PET. Based on the results of both PET scans, one patient was diagnosed with a lung cancer as second malignancy. Median ¹⁸F-FDG uptake exceeded that ¹¹C-acetate in distant metastases (SUV=3.2 vs. 2.3, respectively). ¹¹C-acetate uptake, however, was higher in local recurrence and in local lymph node metastases (median SUVs = 2.9 and 3.8) compared to ¹¹C-acetate (median SUVs = 1.0 and 1.1, respectively). ¹¹C-acetate and ¹⁸F-FDG uptake was lower in patients on antiandrogen therapy compared with the drug-naïve patients but ¹¹C-acetate uptake was not significantly impaired. A close correlation of serum PSA level and Gleason score on the one hand and both ¹¹C-acetate uptake and ¹⁸F-FDG uptake on the other hand was observed.
These data confirm that ¹¹C-acetate is more useful than ¹⁸F-FDG in the detection of local recurrences and localised lymph node metastases. ¹⁸F-FDG, however, appears to be more accurate in visualising distant metastases. Antiandrogen therapy reduces tumour metabolic activity and therefore overall PET accuracy but detection of local recurrences by ¹¹C-acetate is not severly compromised. Ultimately, there may be a role for combined ¹¹C-acetate/¹⁸F-FDG PET in the follow-up of patients with prostate cancer and persisting or increasing PSA.

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The influence of the formation of secondary iron phases on the sorption behavior of U(VI) on chlorite was investigated in batch sorption experiments with two different types of chlorites: an unaltered chlorite from Flagstaff Hill (CCa-2) and a hydrothermally altered chlorite from Grimsel/Switzerland. The easily extractable ions have not been removed in the CCa-2 chlorite and it therefore tends to form secondary phases. In contrast, the hydrothermally altered chlorite is relative resitant to weathering as discussed in Arnold et. al. [1] and therefore does not tend to form secondary phases. The batch sorption experiments were carried out under ambient temperature and pressure using a solid concentration of 0,5 g chlorite in 40 mL 0,1 M NaClO4 solution. The higher sorption capacity of the unaltered CCa-2 chlorite of more than 20 % of the initially added 1´10-6 M U(VI) compared to the hydrothermally altered chlorite is especially striking in the pH region from 6,5 to 8,5 and was attributed to the generation of secondary Fe and Al phases forming during the two months period of the batch sorption experiments. As a consequence of the formation of a new phase additional mineral surface area is generated [2] which serves as a substrate for further uranium sorption. It is well known that Fe-oxyhydroxide particles show a very high affinity for sorbing U(VI) [3]. Our results clearly show that newly-forming secondary phases may increase the sorption capacity of primary minerals. The Diffuse Double Layer Model (DDLM) was applied to model the U(VI) sorption on the two chlorites including the newly-formed secondary phases.

This class of flows is characterized by the feeding of strong electrical currents into a volume of liquid metal. A prominent example of industrial interest is the electrode-welding where the current is supplied via a locally restricted area, leading to high current densities. The interaction of these currents with their own magnetic field drives flows which exhibit phenomena like formation of jets and pinch-effect. Further increasing the current may lead to disruption of the melt column accompanied with a discharge. This can be used for a liquid metal current limiter with self-healing properties.
Local measurements of the flow structures are of obvious interest for a better understanding of these phenomena. The paper will give results from a systematic study of the flow structure performed by means of our mechano-optical velocity probe. The measured flow structure of the evolving jet was found to be in a reasonable agreement with our numerical simulations.

Passing an electrical current through a volume of conducting fluid drives flow via the interaction with its own magnetic field. Among this class of electro-vortical flows the electrode-welding is a prominent example of industrial interest. In such configurations where a strong current is supplied locally, the resulting high current densities show phenomena like formation of jets and pinch-effect. The latter may disrupt the melt column in the case of very strong currents, accompanied by a discharge. Thus pinching can be used for a liquid metal current limiter with self-healing properties.
Local flow measurements are important for a better understanding of these phenomena. This paper gives results from a systematic study of the fluid motion performed with our mechano-optical velocity probe. The measured flow structure of the evolving jet was found to be in a reasonable agreement with our numerical simulations. Local pressure measurements have been consistent with the experimental and numerical results for the flow field.

Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon frequency. Measuring this frequency and comparison to a theoretical model allows the determination of competing higher-order lattice forces.