Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Boron was implanted into 6H-SiC layers to form a 500 nm thick layer with plateau concentrations up to 1.5E21 cm-3. The electrical and microstructural effects were investigated using temperature dependent Hall measurements, XTEM and SIMS. After annealing at temperatures between 1550 and 1750 C for B concentrations above the solubility extraordinary B diffusion and Ostwald ripening is observed forming boron clusters. For B concentrations near the solubility the outdiffusion is reduced. These effects are confirmed by Hall Effect measurements showing a stagnation of hole concentration with increasing B concentration above 1.5E19 cm-3. The electrical activation is limited due to the solubility of boron in 6H-SiC at about 1600 C. Higher B concentrations as well as higher annealing temperatures, including short time annealing at about 2000 C, do not lead to higher activation.

Electromagnetic body (Lorentz) forces originating from a system of permanent magnets and electrodes are used to control the flow of a weakly electrically conducting NaCl solution around a NACA-0017-like hydrofoil. The orientation of the Lorentz force is always parallel to the surface. The effect of a suction-side, streamwise Lorentz force is quantified by means of force balance measurements for chord-length Reynolds numbers of 3 to 8x 10^4. 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 - by 90% at Re=3 10^4 - and a corresponding drag reduction are observed due to separation prevention. The physical tendencies found in the experiments are confirmed by direct numerical simulations at lower Reynolds numbers.

An analysis of the dilepton measurements in the reactions Pb(158 A · GeV) + Au, Pb points to a unique
thermal source contributing to the invariant mass and transverse momentum spectra. Effects of the flow pattern are discussed.

X-ray photoelectron spectroscopy investigation of the interaction of U(VI) and Fe(III) with natural humic acid in aqueous solutions.
Dedicated to Prof. Dr. Egon Uhlig on the occasion of his 70th birthday.
Abstract
Complexes of U(VI) and Fe(III) with natural humic acid (NHA) were studied by X-ray photoelectron spectroscopy (XPS). It follows from the analysis of the uranium and iron concentrations at the surface and in the bulk of the humates that the reaction in solution is heterogeneous. The NHA reacts as a particle. In solutions containing either U(VI) or Fe(III), NHA reacts similar with Fe(III) and U(VI). However, in a mixed solution of Fe(III) and U(VI), NHA reacts predominantly with iron. In comparison to Fe(III) complexes, the complexes with U(VI) are formed mostly in the inner of the NHA particle. Therefore, the concentration ratio U/Fe as measured by XPS increases by powdering of the particles. Salts of Fe(III) can be used to inhibit the uranium migration in form of its soluble humates.

Metals that form dense native surface oxide layers challenge plasma diffusion treatment techniques. Experimental results obtained during nitriding of stainless steel from real-time depth-resolved compositional analysis by elastic recoil detection give insight into the transport kinetics. In agreement with semi-quantitative considerations on the oxide removal and the oxide growth, the interplay of sputtering and oxidation emerges as a key parameter. On this background, suggestions for practical applications and optimization of the modification processes are given for different plasma diffusion treatment techniques.

Aluminium is known as a promising but difficult candidate for successful nitriding. It exhibits a dense native surface oxide layer that acts as a barrier for diffusional nitrogen transport. To investigate the influence of the oxygen partial pressure, samples of pure polycrystalline Aluminum have been ion nitrided at different oxygen partial pressures from a hot filament ion source. Before and during the nitriding process depth profiling of nitrogen and oxygen has been performed by in-situ Real Time Elastic Recoil Detection. The oxygen partial pressure plays a crucial role for the evolution of the surface oxide layer and thus for the nitriding result. If the surface oxide layer is removed an AlN-layer grows. The results are compared to semi-quantitative considerations on the interplay of sputtering and oxidation. A criteria for the removal of the surface oxide layer is given.

Fast Ti-deposition was applied in the gas-dynamic trap (GDT) facility in the regimes with 14-17.5 keV, 2.5-4 MW neutral beam (NB) injection to control gas recycling at the first wall and thereby to reduce charge-exchange losses of energetic ions. The charge-exchange losses of the fast ions turned out to be much less than in former, non-conditioned discharges. The temporal spatial variation of the neutral gas density was measured during typical shots and compared with the results obtained by means of a Monte Carlo transport code. The comparison of the numerical results with the experimental data shows that the recycling coefficient of the chamber wall which has been freshly coated by titanium is close to that of the pure metallic surface.

Based on the Integral Transport Method the code NEUSI calculates the radial-, axial- and time-dependent distributions of fast and slow hydrogen atoms and hydrogen molecules in the plasma region of the GDT facility of the Budker Institute Novosibirsk. The present paper briefly describes the basic features and approximations of the code and gives some calculation results.

The behaviour of the fast ion population is one of the crucial issues of the GDT based neutron generator project proposed by the Budker Institute Novosibirsk. Therefore, the study of the fast ion dynamics is one of the main research objectives at the GDT facility. This research is supported by computational investigations by means of codes that have been specially developed. The present paper briefly describes the fast ion code, demonstrates the capabilities of a fast ion and neutral gas code package and draws computational and physical conclusions from calculations of recent experiments.

The Gas Dynamic Trap (GDT) is an axisymmetric mirror device with a high mirror ratio to confine a collisional plasma and a minority of fast ions. The latter are produced in the trap by oblique, high-power neutral beam (NB) injection into the collisional target plasma. The recent upgrade of the NB system resulted in an increase of the power maximum during the pulse from 2.5 to almost 4.5 MW. Under the new experimental situation were studied: the transport and stability of the high-ß plasma, the cross-field tranport and the detailed energy balance of the fast ions.
The paper reports on the measurement techniques used and on the results achieved.

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. There is considerable effort by many groups to develop agents that will target a variety of receptors, including CNS receptors. As for potential 99mTc based CNS receptor imaging agents, however, low brain uptake is a general problem.
The recent advances in the design of new technetium 99mTc imaging agents illustrate the continued expansion of the use of this class of radiopharmaceuticals.

Bericht der Abteilung Kommunikation und Datenverarbeitung des FZR über ihre Tätigkeit in den Jahren 1997, 1998 und im 1. Halbjahr 1999

A contactless method for velocity determination in electrically conducting fluids is presented. The method is based on the fact that an additional magnetic field is induced if the moving fluid is exposed to a primary magnetic field. Applying the primary magnetic field in two different directions and measuring the corresponding induced magnetic fields the fluid velocity can be reconstructed if some kind of regularization for the velocity field is used. For a spherical shaped conducting fluid analytical expressions for the connection between spherical harmonics expansion coefficients of the induced magnetic fields on one side and of the defining scalars of the velocity on the other side are given. For other geometries a general method for numerical treatment is proposed.

We present a model for the calculation of the hole concentration in boron-doped diamond. It is based on details of the structure of the valence band and on a careful energy balance around the valence band edge. The effect of a variable hole effective mass is first examined. It is found that both the hole concentration and its activation energy increase with increasing hole effective mass. The calculations are then compared to some available experimental data. Good agreement between experiment and calculation is reached. It is concluded that the model rightly describes the thermal generation of the holes from the acceptor levels to the valence band. The difficulty to determine the acceptor and donor concentration independently from the hole effective mass is finally discussed.

Positron affinities, deformation potentials and lifetimes are calculated in diamond, Si, SiC, and BN bulk cubic semiconductors using the first principles pseudopotential and linear-muffin-tin-orbital (LMTO) methods. Both the electron and positron energies are calculated within the local density approximation (LDA) and generalized gradient approximation (GGA). It is observed that the LMTO calculated values of quantities of interest are systematically lower than those calculated with the pseudopotential method. Results further show that the GGA correction for the electron energy levels is not very important in positron calculations. The calculated positron affinity in SiC is found to be in reasonable agreement with experiment. Positron properties for other materials are also compared with experimental data available.

The preparation and characterisation of "3+1+1" technetium complexes of the gen-eral formula [Tc(SES)(RS)(PMe₂Ph)] (SES = tridentate dithiol ligand, E = S, O, NMe; RSH = monothiol ligand) at the no carrier added level is described. The Tc(III) com-plexes are prepared in a one-step procedure starting from pertechnetate in yields of 85 - 95 % of radiochemical purity. A comparison of their chromatographic data with the fully characterised ⁹⁹Tc complexes indicate the identity of the investigated com-pounds. Stability studies show that the ^99mTc complexes undergo some alteration in solution. They are oxidised to the 3+1 oxotechnetium(V) complexes and/or decom-pose in aqueous solution. In challenge experiments performed with glutathione, ex-change of the monothiolato ligand occurs in the same manner as known for the 3+1 complexes.

A design study of beam dumps is presented for the 40 MeV superconducting Electron-Linearaccelerator ELBE. Nuclear physical and thermal properties of selected materials are considered. Energy deposition and neutron production were calculated for a special design of the beam dump. For those Monte-Carlo simulations the particle transport rogram packages GEANT, MCNP and FLUKA have been used. The expected activation under beam conditions was estimated for selected dump materials.

A barrel-shaped scintillator hodoscope was developed as part of the time-of-flight spectrometer TOF operated at an external beam line of the cooler synchrotron COSY. The COSY-TOF spectrometer is used mainly to perform kinematically complete experiments on light meson production and proton-proton bremsstrahlung in proton-proton collisions for laboratory energies up to 2.5 GeV.
The newly developed scintillator hodoscope (BARREL1), one of several detector segments of the COSY-TOF spectrometer, consists of one layer of 96 scintillator bars of 15 mm thickness arranged to form a barrel with 3 m in diameter and 2.85 m in length.
For any given interaction process the TOF spectrometer allows to determine the velocity vectors of all charged ejectiles emerging from the target by measuring the time of flight between the start and the stop detector as well as the point of impact on the stop detector. For the BARREL1 detector the position information is obtained by two-sided light read-out of the scintillator bars. For minimum ionizing particles the spatial resolution was measured to be Delta z(FWHM) = 8 cm, corresponding to a polar angle resolution in the range 0.57 to 2.86 degrees, depending on the hit position. The binning in azimuthal angular direction amounts to 360/96 = 3.75 degrees. For the time-of-flight resolution of minimum ionizing particles a value of Delta t(FWHM) = 0.61 ns was obtained.

To study the thermal transport during the ion nitriding of aluminium, samples of pure polycrystalline Al have been subsequently implanted with 14N and 15N. The implantation have been performed by a broad beam ion source with an energy of 1 keV and hihg current density of 1 mA/cm2. The temperature was kept at 500oC which allows fast diffusion. The oxygen partial pressure was below 3 x 10-5 Pa throughout treatment. The samples were analysed by X-ray diffraction grazing incidence technique. The depth profiles of the isotopes were obtained by Nuclear Reaction Analysis. The measurements reveal the formation of a hexagonal AlN-phase and show that the preimplanted isotope is found only in the bulk, while the postimplanted isotope is located near the surface. Thermal transport mechanisms are discussed on the basis of the obtained results.

For developing a dihydropyridine/pyridinium salt redox delivery system that could be useful for SPECT investigations by ^99mTc compounds the synthesis of a mixed-ligand complex of the long-lived isotope ⁹⁹Tc is described. The new compound bearing a pyridinium salt moiety was characterised by NMR-spectrometry and X-ray structure analysis. By reduction with sodium dithionite the corresponding 1,4-dihydropyridine complex was prepared and the stability in buffer, tissue homogenates, blood plasma and cerebrospinal fluid was investigated by UV-VIS spectrometry.

The bfabrication of CoSi₂ - structures by stoichiometric implantation of Co⁺ (E = 30...35 keV, I_ion = 1.3nA) and Co⁺⁺ ions (E = 60 keV, I_ion = 0.6nA) at doses between 0.3 and 5x10¹⁷ cm^-2 and a subsequent two step annealing (600°C, 60 min; 1000°C, 30 min in N₂) is demonstrated. The dose dependence and the influence of the substrate temperature were studied. The quality of the silicide submicron structures was investigated by SEM, EDX and electrical measurements.

For an electrostatic beam blanker the deflection fields are calculated which prevent spurious deflections due to the ion time of flight. The beam blanker consists of two defection electrode pairs arranged symmetrically befor and after the beam cross over. The calculated deflection fields can be realized by declinated surfaces of the blanker electrodes.

The presence of current pulses superimposed on the dc level of the ion current in liquid metal ion sources has been known for a long time. This work investigates the behaviour of the pulses for varying temperature and working liquid metal. Attempts are made to explain the differences observed in the threshold current for the appearance of the pulses and also in their terminal, or saturation, frequency. Differences are also found between sources using the same working metal, although the pulse appearance threshold current is the same for a given metal.
The experimental results indicate that a low source operating temperature is desirable if droplet emission is to be minimized.

Parameters of a lithium liquid metal ion source have been determined. The angular intensity is the higest yet reported for liquid metal ion sources. This high angular intensity and the large range of light ions suggest the liquid metal ion source to be applied for writing beam lithography. PMMA resist layers were exposed by a focused lithium ion beam.

Es wird ein Gittersensor vorgestellt, der die Gasgehaltsverteilung in einer Flüssigkeits-Gas-Strömung mit einer zeitlichen Auflösung von 1200 Messungen pro Sekunde bei einer räumlichen Auflösung von 3 mm erfaßt. Es können einzelne Gasblasen in mehreren aufeinanderfolgenden momentanen Gas-gehalts-ver-teilungen abgebildet werden. Dadurch ist es möglich, Blasengrößenverteilungen zu ermitteln. Der Sensor wurde in einer senkrechten Rohrleitung eingesetzt, in der die Zweiphasenströmung durch Einspeisung von Luft in eine Wasserströmung erzeugt wurde. Der Abstand zwischen Einspeisung und Sensor wurde von ca. 0.5 bis 70 L/D variiert, so daß die Herausbildung der Gasgehaltsverteilung entlang des Strömungs-weges studiert werden konnte. Der vorgestellte Gittersensor erlaubt Dank der erreichten Meßgeschwindigkeit erstmals die quantitative Charakterisierung großer Ensembles von Einzelblasen. Gegenüber den üblicherweise für Blasen-größenmessungen verwendeten lokalen Sonden können die Experimente mit hoher Effektivität durchgeführt werden, da der gesamte Strömungsquerschnitt überwacht wird. Repräsentative Blasengrößenverteilungen lassen sich bereits bei Meßzeiten in der Größenordnung von 10 s ermitteln. Neben den genannten Auswerteverfahren kann auch eine Visualisierung der Strömung in Form einer digitalen Zeitlupendarstellung vorgenommen werden. Der Gittersensor dürfte für vielfältige Anwendungen aus dem Bereich der Verfahrenstechnik interessant sein, die gewonnenen Daten eignen sich zur Modellentwicklung, speziell zur Überprüfung von Koaleszenzmodellen.

The diagnosis and staging of breast cancer could be improved by the development of imaging radiopharmaceuticals that provide a non-invasive determination of the estrogen receptor (ER) status of tumor cells. Towards this goal, we have synthesized a number of Re and Tc-labeled estradiol (1) mimics based on the conjugated design, which tethers a metal-containing moiety to an existing steroid. In this study, the 7alpha position of estradiol was chosen as the tether site, due to its well known
tolerance of bulky substituents. ¹ The metal was stabilized using either the "3+1" design (2,3), or the cyclopentadienyltricarbonylmetal (CpTM) approach (4,5,6) . In the "3+1" design, a tridentate ligand and a monodentate ligand surround an oxometal core.² In the CpTM design, a substituted Cp and three carbonyls are coordinated to a Re/Tc(I) center.^3,4
The advantages of using the "3+1" and CpTM desings are the well-established stability of both systems, as well as the ability to produce both systems efficiently at the tracer level.^2,4
The first tether used was a hexyl spacer, and the synthesis of the precursors for targets 2-6 started with THP-protected estradiol 7 (Scheme 1). After oxidation to ketone 8 using a previously published method, standard alkylation conditions introduced the hexene side chain to form 9 , with BEt₃ as an additive to stabilize the enolate and prevent O-alkylation.

Small, radiolabeled biomolecules, such as steroids, tracers for the central nervous system and biotin obtained considerable attention in diagnostic nuclear medicine. Nowadays, there are numerous short living isotopes available for SPECT (e.g. ¹³¹I) and PET (e.g. ¹⁸F, ¹¹C) imaging to label such biological vectors. Despite this fact. Tc-99m is still the isotope of choice for diagnostic purpose because of its ideal decay properties. However, unlike iodinated of fluorinated radiopharmaceuticals, Tc-99m requires a highly sophisticated functionalization and coordination chemistry. Attempts to substitute direct covalent bound isotopes by Tc-99m chelates were, apart from peptides, only partially successful. (1,2) The reason is mainly the size of the introduced chelates (interference with active site of the biomolecule) and the redox sensitivity of ^99mTc in the oxidation state +3 and +5. Therefore, alternative approaches are required to overcome these problems by introduction of small, redox inert ^99mTc-cores in combination with simple ligand systems.
Although the idea of labeling e.g. steroids with organometallic Re or Tc-compounds was published by Top et al. In 1995 the attempt failed due to synthetic problems of the precursor on the no-carrier added level.(3) Our group recently pioneered the synthesis of the organometallic Tc(I) complex fac-[M(OH₂)₃(CO)₃]⁺ (M=^99mTc 1a, ⁹⁹Tc 1b, Re 1c) under safe and pressureless conditions in aqueous media in high yields (<95%).(4,5) The compound is characterized by its water solubility, pronounced kinetic inertness (low spin d⁶ system) and the substitution lability of the three coordinated water molecules enabling effective labeling under mild conditions. The small size of the organometallic center will minimize the interference with the binding side of a biomolecule. Therefore, this new label optimi ...

Liquid metal ion sources (LMIS) are one of the key elements in focused ion beam (FIB) technology. For special tasks, alloy LMIS are needed which have to be operated at elevated temperatures. For the adjustment of an optimal beam performance in a FIB system the source parameters, temperature of the ion emitter and the energy spread of the different used ion species are of fundamental importance. Emitters wetted with Au73Ge27, Au77Ge14Si9 and Co36Nd64 alloys were investigated with respect to the influence of the source temperature on the emission current - extraction voltage characteristics, the mass distribution, as well as the energy spread of the different emitted ions using an equipment containing of an ExB mass filter and a retarding field energy analyser. The energy spread significantly determines the available FIB spot size and depends also on the emission current, the charge state, and the mass of ions or clusters. The axial angular intensity and the resulting target current of the FIB were measured as a function of the source parameters. Two operating regimes were found. Whether one works in a high stable target current mode and lower resolution (emission current ~ 10 µA), or in the high resolution, high chromatic angular intensity mode (emission current a few µA), at the risk of lower target current including stability, both at source temperatures some ten degrees above the melting point.

Beim Abriß von Nuklearanlagen fallen große Mengen Bauschutt an, die mit Radionukliden kontaminiert sein können. Da diese Kontaminationen häufig nahe der Freigrenze liegen, ist für die Entscheidung, ob das Material als radioaktiver Abfall behandelt werden muß oder freigegeben werden kann, eine schnelle und exakte Methode notwendig. Die Bestimmung der ( - und $ - Aktivivtät ist mit in-situ Messungen möglich. Eine direkte Messung der " - aktiven Nuklide im stehenden Gebäude ist auf Grund der geringen Reichweite der " -Strahlung und ihrer Absorption im Beton nicht möglich. Die übliche chemische Analyse der " - aktiven Nuklide ist sehr zeitaufwendig.
Im Rahmen dieses Projektes wurde eine Methode der direkten " - Spektrometrie nach nur mechanischer Präparation des Betons entwickelt. In einem aus zwei Schritten bestehendem Zerkleinerungsprozeß wurden Suspensionen mit mittleren Partikeldurchmessern von 0,5 µm erhalten. Die Meßproben mit einem Durchmesser von 20 cm und Schichtdicken zwischen 0,6 und 5 µm wurden durch Gießen oder Sprühen auf die Probenträger und anschließendes Trocknen hergestellt. Die Spektren dieser Proben wurden in einer Gitterionisationskammer aufgenommen. Durch die Verwendung von Standardbeton mit dotierten Actiniden konnten die Selbstabsorption der " - Strahlung und die Peakform in Abhängigkeit der Schichtdicke ermittelt werden. Unbekannte Betonproben gleicher Geometrie konnten mit Hilfe dieser ermittelten Peakform entfaltet werden.
Das für diese Arbeit entwickelte Programm WINKRUM basiert auf einem geometrischen Modell für Partikelgröße, Partikelverteilung und Packungsdichte. Mit Strahlungstransportberechnungen können Spektren simuliert werden, die ebenfalls eine Peakentfaltung von Multielementspektren ermöglichen.
Mit dieser Direktmessung dünner Meßproben können " - aktive Nuklide bis zu 0,02 Bq/g in Multielementspektren innerhalb von 30 h bestimmt werden.

For the analysis of boron dilution transients and main steam line break scenarios the modelling
of the coolant mixing inside the reactor vessel is important. The reactivity insertion due to
overcooling or deboration depends strongly on the coolant temperature and boron concentrati-
on.

The coolant mixing in the downcomer and lower plenum depends significantly on the con-
struction of the reactor vessel and flow conditions are different in each reactor type. In the
German Konvoi type reactors a complicated flow picture with large vortexes was obtained
which is typical probably also for the European Pressurized Water Reactor (EPR). The models
and assumptions for the coolant mixing description used in the coupled neutron kine-
tics/thermohydraulic system codes have to be validated on experimental data from the
Rossendorf coolant mixing model and detailed computational fluid dynamics (CFD) calcula-
tions.

The requirements concerning quality of the experimental results need a non-pressurized test
facility operating with water (room temperature). The reactor vessel is made of Plexiglas? for
flow visualization and LDA measurements. It has to dispose of separately controllable main
coolant pumps in each loop. The measurement instrumentation has to be designed for the
necessary spartial and time resolution.

The three-dimensional flow distribution in the downcomer and the lower plenum of PWRs
was calculated with a computational fluid dynamics (CFD) code (CFX-4).

The paper describes a Positron Emission Tomograph dedicated to the investigation of the behavior of foam in a bubble column as well as the current planning of experiments using this device. In these experiments, foam generation, foam stability and transport phenomena in the liquid phase are the main topics of interest.

The paper describes a density measurement technique using positron radiation. The method is appropriate for the determination of densities ranging from 10 kg/m3 to 100 kg/m3, e.g. for determining the density of foams or the humidity of pressurized gases. The focus of this paper is on the results obtained with an optimized low cost detector geometry. The technique makes use of the positron ranges in the measured matter, which is depending on its density.

The lattice damage of silicon produced by ion implantation at extremely high current density of 0.8 A/cm² (2.5 x 10¹⁸ cm^-2 s^-1) was investigated. In a focused ion beam system, implantation was carried out with 70 keV Co ions, fluences of 1.2 x 10¹⁶ cm^-2 and 6.7 x 10¹⁵ cm^-2 into Si (111) at room temperature and elevated temperatures between 355 °C and 400 °C. Radiation damage measurements were performed by Rutherford backscattering/channeling spectroscopy and micro-Raman analysis. The radiation damage was studied as a function of pixel dwell-time and implantation temperature. The critical temperature for amorphization increases with current density. Although the fluence of the focused ion implantation was constant, crystalline layers were obtained for short and amorphous layers for long pixel dwell-times. The critical dwell-time of crystalline/amorphous transition increases with implantation temperature. From the results a typical time for defect annealing of 10^-5 s at 400 °C and an activation energy of (2.5±0.6) eV were deduced.

Bioorganometallic chemistry comprises the combination of an organometallic transition metal complex and a targeting biomolecule. If ever such a combination should be applied, the synthesis has to be convenient, fast and requires one or two steps only. [^99mTc(OH₂)₃(CO)₃]⁺ 1 can be prepared in one step from [^99mTcO₄]^- in saline and bidentate aromatic amines are very efficient chelators for this organometallic precursor. Consequently, we have derivatized a 5-HT_1A (serotonergic) receptor ligand with high affinity and high selectivity for this subclass from the group of the arylpiperazines with a Schiff Base type chelator. In water, 1 radiolabels the receptor ligand in high yield and specific activity.

In the Forschungszentrum Rossendorf the Fast Ion Transport code FIT has been developed on the base of the Monte Carlo method. It allows a detailed analysis of the fast ion field dynamics during GDT experiments [4]. Just, the code has been extended to enable not only the computation of the ion phase space distributions but also that of the neutron source distributions generated by various D-T fusion reactions. By means of FIT calculations the dependencies of the total neutron source strength and of the ion densities on several plasma parameters and operating regimes have been studied. The paper presents the numerical results and gives the physical interpretations.

Studies of hot anisotropic ion confinement is one of the main objectives of the experimental program on the gas-dynamic trap (GDT). Hot ions are produced in the trap by injection of six neutral beams with energy 13-17 keV into collisional target plasma. The total injected power was up to 4.5 MW, pulse duration 1.2 ms. The behavior of hot ions with mean energy 3-10 keV and peak density of 0.5-1.0´ 10¹³ cm^-3 was studied in detail in the experiments with plasma β up to 20%. The method of confinement study consists essentially in comparison of the measured ion parameters with those predicted by computer simulations based on theory of Coulomb collisions. Additionally the measurements of D-D neutron flux were used to measure the hot ion distribution along GDT axis.

In 1995 at the integral test facility ISB-VVER in Elektrogorsk near Moscow natural circulation experiments were performed, which were scientifically accompanied by the Forschungszentrum Rossendorf. These experiments were the first of this kind at a test facility, which models VVER-1000 thermal-hydraulics. Using the code ATHLET which is being developed by "Gesellschaft für Anlagen- und Reaktorsicherheit mbH", pre- and post-test calculations were done to determine the thermal-hydraulic events to be expected and to define and tune the boundary conditions of the test. The conditions found for natural circulation instabilities and cold leg loop seal clearing could be confirmed by the tests. The main thermal-hydraulic phenomena were identified and compared with the results gained during similar experiments on VVER-440 test facilities.

High doses of 350 keV Al+ ions were implanted into 6H-SiC single crystals at 500oC. The phase formation was studied by TEM, SIMS and AES. A critical Al concentration of about 10 at% was found below that the 6H-SiC structure remains stable. The Al atoms
occupy preferentially Si sites in the SiC lattice. The replaced Si atoms seem to be mobile under the given implantation conditions and diffuse out. At higher Al concentrations the SiC matrix is decomposed and precipitates of Si and Al4C3 are formed.
It was found that the Al4C3 precipitates have a perfect epitaxial orientation to the SiC matrix. The phase transformation is accompanied by atomic redistribution and strong volume swelling. The resulting changes in the atomic profiles can be accounted
for by a simple chemical reaction model.

The effects of accumulated radiation damage which arise from the excessive current density employed
during focused ion beam implantation are described. The dwell time during beam scanning significantly
influences the focused ion beam synthesis of CoSi2 in Si. At sufficiently low accumulated damage,
single-crystalline CoSi2 layers are obtained, similarly to conventional ion implantation. A procedure is
described which enables the reduction of radiation damage induced by a focused ion beam to the level of
conventional ion implantation. This is of importance for the formation of single-crystalline CoSi2 layers.

Atomistic computer simulations based on the binary collision approximation (BCA) are very well suited to predict the dependence of as-implanted dopant profiles on implant parameters like energy, dose and direction of incidence as well as on the arrangement of oxide, poly-Si and other materials on the single-crystalline Si substrate. In particular channeling effects, the enhanced dechanneling due to accumulation of radiation defects during ion bombardment and due to preexisting ion-beam-induced defects can be simulated in a reasonable manner. The BCA code Crystal-TRIM was successfully integrated into 1D and 2D process simulators for the Si technology. The application of the trajectory splitting algorithm and the lateral duplicatioin method ensures a high computational efficiency.

Square-planar AuIII complexes are isoelectronic to PtII compounds which are frequently used for cancer therapy. Recently, cancerostatic properties have also been reported for dichloro[2-(dimethylamino-methyl)phenyl-C1,N]gold(III), [Au(damp-C1,N)Cl2] (I) [1], although the mechanism of cytotoxic action may well be different. This encourages us to study the ligand exchange chemistry of this type of compound more in detail.
We have synthesized and structurally characterized a series of AuIII complexes with bi- and tridentate thiosemicarbazones as well as with chelating phosphine thiol ligands which surprisingly stabilize gold in its formal oxidation state "+3".
Reactions of (I) with thiosemicarbazones result in a cleavage of the Au-N bond and protonation of the liberated dimethylamino group. Airstable, zwitterionic compounds are formed. The thiosemicarbazones co-ordinate as deprotonated chelate ligands substituting Cl-. Fig. 1 illustrates an example with the bidentate vanillinethiosemicarbazone. Remaining Cl- ligands can be replaced by further ligand exchange reactions, e.g. with thiolates.

Technetium and rhenium co-ordination chemistry is of particular interest due to the favourable nuclear properties of 99mTc (Eg = 140 keV, half-life t1/2 = 6.02 h) which makes this isotope the workhorse for diagnostic nuclear medicine. The b-emitting rhenium nuclides 186Re and 188Re are under investigation for possible applications in radioimmunotherapy. Fundamental co-ordination chemical studies form the basis for the development of new Tc and Re radiopharmaceuticals.
Diphenyl(2-pyridyl)phosphine (PPh2py) and tris(2-pyridyl)phosphine (Ppy3) are a versatile ligands which can co-ordinate as a monodentate or chelating ligands depending on the requirements of the metal center.
The potentially bidentate ligand PPh2py reacted with (NEt4)2[MI(CO)3X3] complexes (M = Re, Tc) to give (NEt4)[MI(CO)3X2(PPh2py-P)] or [MI(CO)3X(PPh2py-P)2] depending on the amount of the ligand used. The reaction with (NBu4)[TcVINCl4] yielded [TcVNCl2(PPh2py-P)2] whereas from the reaction with (NBu4)[ReOCl4] the complexes [ReVOCl3(PPh2py-P,N)], [ReVOCl3(OPPh2py-O,N)], [ReIVCl4(OPPh2py-O,N) and [ReIVCl3(OH)(OPPh2py-O,N)] have been isolated. Reduction of the metal center and formation of diphenyl(2-pyridyl)phosphine oxide (OPPh2py) occurs using an excess of PPh2py and heating of the reaction mixtures under reflux.
All products have been characterised spectroscopically and by X-ray structure analysis. Monodentate co-ordination via phosphorus has been found for the rhenium(I) carbonyl complexes and [TcVNCl2(PPh2py-P)2]. In the latter compound a trigonal-bipyramidal coordination sphere is formed with the phosphines as axial ligands. The chelated complexes show small N-Re-P and N-Re-O bite angles due to the 4-membered or 5-membered chelate rings. The pyridine nitrogen occupies the axial position (trans to "O2-") in [ReOCl3-(PPh2py-P,N)] whereas equatorial co-ordination is found in [ReOCl3(OPPh2py-O,N)].
The reaction of (NEt4)2[ReI(CO)3Br3] with Ppy3 gave [Re(CO)3Br(Ppy3-N,N')] whereas with o ...

In aeroben Batchexperimenten wurde der Einfluß von Huminsäure auf die Sorption von U(VI) u. a. auf dem Schichtsilkat Muskowit im pH-Bereich zwischen 3,5 und 9,5 untersucht (SCHMEIDE et al., 1998). Hierbei wurden 0,5 g der pulverisierten Probe (63µm - 200µm Körnung) in Kontakt mit einer Uranyl(VI)-Konzentration von 1.10-6 M und einer Huminsäure-konzentration von 5 mg/L gebracht, während die Ionenstärke mit 0,1 M NaClO4-Lösung konstant gehalten wurde. Aus den Ergebnissen ergibt sich eine pH-Wert abhängige Huminsäure-Sorption, die ihr Maximum (~ 83 %) bei einem pH von 4,5 bis 5 aufweist. Verglichen mit den U-Sorptionsversuchen, die in Abwesenheit von Huminsäure durchgeführt wurden (Zorn, 1999), wird die Sorption von U in Gegenwart von Huminsäure im pH-Bereich von < 5,8 vergrößert (67 % bei pH 5,5).

Elektronenmikroskopische Untersuchungen (REM) sollten im Anschluß an die Batch-experimente Aussagen zum Sorptionsverhalten an den Kristallflächen der Minerale liefern. Hierzu wurden einzelne Muskowitplättchen in Kontakt mit einer Huminsäure-Lösung der Konzentration von 40 mg/L für jeweils 1 und 18 Stunden gebracht. Die Huminsäure wurde zuvor filtriert (50 nm Filterporengröße), um u. a. Bakterien abzutrennen Die Einstellung der pH-Werte richtete sich nach den Ergebnissen aus den Batchexperimenten und wurde bei pH 4 für hohe Adsorption und zum Vergleich bei pH 7 für geringe Adsorption gewählt. Die Ergebnisse zeigen trotz starken Spülens der Proben mit entionisiertem H2O einen Überzug ("coating") des gesamten Bereiches der Mineralplättchen mit Huminsäure bei einer Verweildauer von 18 Stunden und einem pH von 4 in der Versuchsanordnung. Es kann daraus geschlossen werden, daß eine Sorption von U(VI) in diesem Fall überwiegend an der Huminsäure und nicht am Mineral stattgefunden hat. Im Gegensatz dazu zeigen die Proben, die lediglich für 1 Stunde in der Huminsäure verweilten kein vollständiges "coating". Erkennbar sind einzelne kugelige Huminsäurepartikel sowie Agglomerate v ...

A TEM technique was employed for the in-situ observation the Ge-clusters ripening process. Subsequent irradiation with electron beams of 200kV and 300kV acceleration energy lead to formation of a nanocluster band in the middle of thermally grown SiO2 thin layer implanted with Ge+. A number of micrographs taken during the ripening show the detailed information about process. The velocity of ripening can be controlled by changing of the irradiation intensity. The performed experiments pointed that ripening take place even for sample temperatures far below 1000K the activation threshold of thermal processes.

The usefulness of ¹⁸F-labelled carbohydrates, especially 2-deoxy-2-[¹⁸F]fluoro-D-glucose, to study pathophysiological processes in man non-invasively using positron-emission-tomography (PET) led to a widespread investigation of different ¹⁸F-labelled sugars and sugar derivatives. In consideration of the short half-life of fluorine-18 (T_1/2=110 min) synthetic strategies concerning precursor design, labelling conditions and deprotection of the intermediate compounds were developed to guarantee an efficient high radiochemical yield synthesis for diagnostic purposes. Besides some aspects of medical application of 2-deoxy-2-[¹⁸F]fluoro-D-glucose, a few synthetic strategies are described reflecting development work on promising ¹⁸F-labelled sugars for diagnostic purposes during the last two decades

A new one-dimensional Particle-In-Cell transport model for multiphase flow in a vessel is presented. The model aims at the consistent simulation of discontinuities as the top level of a multi-phase mixture. That makes it possible to include models for the transient behaviour of a foam layer on top of a mixture for example. The transport model, which is the basic component of a new computer code will be described. Flexible interfaces allow the implementation of models, constitutive laws or correlations for extra effects like phase transfer, generation and coalescence of bubbles or drops, foam behaviour, heat transfer, discharge from the vessel a.s.o. Due to these interfaces and a transparent code structure the code is a suitable basis for the development, test and validation of models. It allows the completion or the replacement of such models according to the specific application.

Die Reaktion von [ReNCl₂(Me₂PhP)₃] 1 mit zwei Äquivalenten Dimercaptobernsteinsäuredimethylester (DMSMe₂) in Aceton führt zur Bildung eines neutralen, diamagnetischen Rhenium(V)-DMSMe₂-Komplexes unter Anlagerung einer Phenyldimethylphosphanisopropyl-Gruppierung am nukleophilen Nitrid-Stickstoff. Der entstehende Komplex 2 [Re{NC(CH₃)₂(Me₂PhP)}(DMSMe₂)₂] kristallisiert triklin in der Raumgruppe P1, a = 12,334(7), b = 12,412(7), c = 12,414(8) Å; alpha = 60,14(3)°, beta = 67,98(3)°, gamma = 80,63(6)°; Z = 2. Das Rhenium befindet sich in einer quadratisch-pyramidalen Anordnung der Donoratome. Die beiden meso-DMSMe₂-Liganden sind in syn-endo-Stellung angeordnet. Die Rhenium-Stickstoff-Bindung ist mit 1,697(12) Å nur wenig länger als in Nitridokomplexen und vergleichbar mit anderen Re-N-C-Bindungsabständen. Der Angriff des Lösungsmittels am Nitridostickstoffatom wird in Aceton (2) und Methylethylketon unter Bildung von 3 beobachtet. Massenspektrometrisch wird darüberhinaus nachgewiesen, daß auch eine Reaktion des Nitridostickstoffatoms mit dem Kondensationsprodukt des Methylethylketons erfolgt unter Bildung von [ReN{C(CH₃)(C₂H₅)CH₂C(O)C₂H₅(Me₂PhP)}(DMSMe₂)₂]) 4.

Tritium depth profiling measurements by accelerator mass spectrometry have been performed at the facility installed at the Rossendorf 3 MV Tandetron. In order to achieve a uniform erosion at the target surface inside of a commercial Cs ion sputtering source and to avoid edge effects, the samples were mechanically scanned and the signals were recorded only during sputtering at the centre of the sputtered area. The sputtered negative ions were mass analysed by the injection magnet of the Tandetron. Hydrogen and deuterium profiles are measured with the Faraday cup between the injection magnet and the accelerator, while the tritium is counted after the accelerator with semiconductor detectors. Depth profiles have been measured for carbon samples which had been exposed to the plasma at the first wall of the Garching fusion experiment ASDEX-Upgrade and from the European fusion experiment JET, Culham/UK. The tritium contents of the samples from JET were one up to five orders higher compared to the samples from ASDEX-Upgrade. The problem of the detector overloading during measurements of samples with a high tritium content has been solved by installation of a scanning system in the AMS beamline, which enables defined scanning of the tritium beam over an aperture in front of the detector.

The synthesis of 16alpha-[¹⁸F]fluoroestradiol-3,17beta-disulphamate ([¹⁸F]FESDS) being a new potential radiotracer for investigations in positron emission tomography is described. 16alpha-[¹⁸F]Fluoroestradiol ([¹⁸F]FES) is converted with excessive sulphamoyl chloride in absolute acetonitrile in presence of an alkali. Using kryptofix 2.2.2 and K₂CO₃ as alkali, [¹⁸F]FESDS was obtained in yields of 50 - 60%.

The influence of fluid-structure interaction (FSI) on vibration modes is investigated using the finite element method. The method of modelling is verifyed by comparing the finite element results with the exact analytical solution of a simple fluid-shell test system. It is shown that the method of coupling between structural and fluid elements is important for the accuracy of the eigenfrequencies. The vibration modes of the reactor pressure vessel and its internals of a WWER-1000 type reactor are calculated. The FSI causes a considerable down shift of the shell mode frequencies of pressure vessel, core barrel and thermal shield. Some bending modes which exhibit a relative displacement between pressure vessel and core barrel or between core barrel and thermal shield are significantly affected too. Some simple analytical approaches to consider the FSI are discussed on the basis of the numerical results.

During two­phase blowdown from pressure vessels considerable pulsations of the discharged mass flow rate were found. Regions of instability were predicted by a linear stability analysis. The oscillations are caused by the following feedback circuit: boil up ­ level movement ­ void fraction of the discharged mixture ­ critical discharge rate ­ velocity of pressure decrease ­ boil up. They were also found at transient simulations. Finally the instabilities were confirmed by experiments. The possibility of the occurence of oscillations increases with the volume of the ventline and the volume void fraction of the discharged mixture. They may influence the pressure relief from pressure vessels as well as from chemical reactors.

The effect of ion beam implantation and plasma immersion ion implantation of chlorine on the high temperature oxidation of titanium aluminides above 800 °C in air was investigated. Thermogravimetric oxidation tests (TGA) were performed to examine the long term protection. Depth profiling with Auger electron spectroscopy (AES) was used to investigate Cl diffusion and oxide formation during the first stage of oxidation. A microscopic model of the chlorine effect will be discussed. A systematic variation of the implantation energy and fluence shows that there is a narrow regime of the Cl concentration for optimum protective effect at 900°C in air. The oxidation rate after this incubation time is reduced by about 2 orders of magnitude compared to untreated Ti50Al and is nearly independent of the fluence. The effect is almost independent of the implantation energy in the range of 15 keV to 1 MeV. First results of plasma immersion ion implantation of chlorine show that it is possible to use this technique to implant also large and complex surfaces.

The interface water vapour-titanium was employed for a controlled synthesis of surface-supported hydroxyapatite. In this approach, a Ti surface was doped with Ca and P by ion implantation and then subjected to a hydrothermal treatment in a water vapour autoclave. Ion implantation served to prepare a reactive blend of finely dispersed reactants in a stoichiometric ratio incorporated within the network of an outermost layer of the substrate surface. Needle-like carbonate hydroxyapatite in an overlayer was identified to deposit on the surface. The results suggest interface-mediated thin film formation and phase transformation.

Subsequent studies have identified many scenarios which can lead to reactivity excursions due to boron dilution. The comparative study, presented in this paper, deals with the so-called "restart of the first reactor coolant pump" scenario and its reactor-dynamic consequences for the both VVER reactor types - VVER-440 and VVER-1000. The transient simulations were performed using the three-dimensional core dynamics code DYN3D. The DYN3D modeling features, including recent developments, as well as the cross-section generation methodology, involved in these calculations, are described. The analyzed accident scenario is outlined together with the assumptions made. The results of core response in this boron dilution accident for both VVER reactors have been compared within ranges, determined by the two reactivity values of interest: the criticaly limit and the reactivity initiated accident (RIA) limit.

Alkaline hydrolysis of 1,3,4,6-tetraacetyl-2-(¹⁸F]fluoro-deoxy-D-glucose in the course of 2-[¹⁸F]fluoro-deoxy-D-glucose (¹⁸FDG) synthesis offers special advantages over acidic hydrolytic procedures, because the reaction time is short and thermal requirements are very mild. In view of the possible epimerization of 2-[¹⁸F]fluoro-deoxy-D-glucose a multi-centre study has been performed to check the safety of this method for routine production of ¹⁸FDG in view of the quality standards set by the European Pharmacopoeia. The study revealed that in using 0.33 M NaOH for the hydrolysis, a limitation of the reaction temperature to 40°C and a restriction of the reaction time to 5 min represent reaction conditions, which reliably limit the epimerization of ¹⁸FDG to ¹⁸FDM to 0.5%. Regarding the quality requirements on FDG as set forth by pharmacopoeial standards, alkaline hydrolysis of the intermediate in routine ¹⁸FDG production is a safe and efficient reaction pathway, which furthermore obviates the requirement to check for other 2-substituted deoxy-D-glucose derivatives.

This paper reports on self-organization of narrow bands of Ge nanoclusters in thin thermally grown SiO₂ layers by means of ion beam synthesis. Although the implanted Ge profile is distributed over almost the whole SiO2, a delta-like nanocluster band very close to, but well separated from the Si/SiO₂ interface is formed under specific implantation and annealing conditions. The evolution of this band can be explained by a model taking into account collisional ion beam mixing and reactions near the Si/SiO₂ interface, which describes in good agreement the experimental results. The reliable fabrication of such cluster bands are the basis for new memory applications.

Dendrimere sind aufgrund ihrer Fähigkeit zur Wirt/Gast-Wechselwirkung und ihrer einzigartigen Oberflächenfunktionalität in der nuklearmedizinischen Diagnostik sowie als synthetische kationische Liposomen von großem Interesse.

Durch Einbau spezieller Haftgruppen für Technetium in divergent aufgebaute Dendrimere auf Basis eines Poly(aminoamido)- bzw. Poly(propylenimin)-Grundgerüstes kann sowohl die spezifische Aktivität erhöht als auch die Bioverteilung gesteuert werden. Das Komplexbildungsverhalten dieser neuartigen Dendrimere soll im homogen wäßrigen Einphasensystem studiert sowie die Transporteigenschaften im organisch-wäßrigen Zweiphasensystem charakterisiert werden. Außerdem sind in-vitro-Bestimmungen der radiopharmakologisch relevanten Größen wie Proteinbindung und Lipophilie sowie in-vivo-Untersuchungen zur Bioverteilung vorgesehen.

Erste Ergebnisse liegen für Harnstoff-funktionalisierte Dendrimere vor. Diese Verbindungsklasse (vgl. Abb.) ist deutlich lipophiler als kommerziell erhältliche PAMAM- und PPI-Dendrimere.

Insbesondere die Alkylharnstoff-Dendrimere binden Oxoanionen effektiv und sind in der Lage, Pertechnetat aus einer wäßrigen Lösung in Chloroform zu extrahieren.
Biologisch relevante Substrate wie AMP, ADP und ATP werden mit bemerkenswerter Abstufung in die organische Phase überführt. Dabei konnte mittels massenspektrometrischer Untersuchung nachgewiesen werden, dass von einem Dendrimer 5 Moleküle ATP gebunden werden.

In dem neu entwickelten 1-D-Behältermodell BRICK werden die Transportvorgänge in
Behältern auf der Grundlage einer neu entwickelten Partikelmethode gelöst.
Die Methode zielt auf die Vermeidung numerischer Diffusion, was insbesondere bei der Berücksichtigung von Diskontinuitäten, wie z. B. dem Gemischspiegel, von
Vorteil ist. Die implizite Wiedergabe der aktuellen Position des Gemischspiegels sowie ein spezielles Interface ermöglichen die Beachtung der Entwicklung einer
Schaumkrone am Übergang zwischen dem Zweiphasengemisch und dem Gasraum.

Es wurden für die Simulation die DWR Konvoi und WWER-440 ausgewählt, wobei hierbei sich auf die Netzgenerierung des Downcomerbereiches und des untereren Plenums beschränkt wurde. Hierbei wurde das dreidimensionale Strömungsberechnungsprogramm CFX 4.1 eingesetzt, welches die Navier-Stokes-Gleichungen löst. Das verwendete Turbulenzmodell war das k-Epsilon-Modell. Die Strömung des Kühlmittels wurde inkompressibel gerechnet. Es wurde Wert auf eine möglichst originalgetreue Gestaltung des Stutzenbereiches / Schrägen bzw. Erweiterungen im Downcomer und Rundungen der Stutzenpartien gelegt. Der Bereich hoher Geschwindigkeitsgradienten wurde mit einem dichteren Grid generiert.

The three-dimensional flow distribution in the downcomer and the lower plenum of PWR's was calculated with a computational fluid dynamics (CFD) code (CFX-4) and the results were presented at the conference

Boron nitride (BN) based composite thin films have been prepared by ion beam assisted deposition (IBAD) employing two electron beam evaporators. 3~5 at.% either Ti or Al was incorporated into the BN composite films. Fourier transform infrared (FTIR) spectroscopy was used for phase identification of the BN composite films. The influences of the Ti and Al additions on the cubic phase formation in the BN films are reported. It has been found that the Al incorporation has a strong negative effect on cubic BN (cBN) formation. No cubic phase can be obtained under the presently chosen ion-bombardment parameters. However, the disturbance of 3~5at.% Ti addition depending on the preparation conditions for the BN thin films, only shifts the threshold of ion/atom ratio of the IBAD process which is required for cBN formation to a higher value. In order to understand the different behaviors of the Ti and Al incorporations, the chemical states of the Ti and Al additions in the BN composite films were examined by X-ray photoelectron spectroscopy (XPS), indicating preferential formation of TiB2 and AlN, respectively.

High oxidation resistance of gamma titanium aluminides can be achieved by the formation of a continuous scale of slowly growing Al2O3. The formation of such a scale was stimulated by the addition of small amounts of chlorine. The additions were incorporated by ion implantation into the sample. The g-TiAl samples were oxidized at 1173 K in air for 100 h. Even if chlorine is present in very small quantities, it has a highly beneficial effect on the oxidation resistance (microalloying effect). The kinetics are changed from mixed TiO2/Al2O3- kinetics for unimplanted specimens to pure Al2O3- kinetics for chlorine implanted specimens.

The effect of ion beam implantation and plasma immersion ion implantation of chlorine on the high temperature oxidation of titanium aluminides above 800 °C in air was investigated. Thermogravimetric oxidation tests (TGA) were performed to examine the long term protection. Depth profiling with Auger electron spectroscopy (AES) was used to investigate Cl diffusion and oxide formation during the first stage of oxidation. A microscopic model of the chlorine effect will be discussed. A systematic variation of the implantation energy and fluence shows that there is a narrow regime of the Cl concentration for optimum protective effect. The time to form a protective Al2O3 layer depends on the local Cl concentration. The oxidation rate after this incubation time is reduced by about 2 orders of magnitude compared to untreated Ti50Al and is nearly independent of the fluence. The implantation energy is not a sensitive parameter, because the implanted chlorine profile changes very quickly during high temperature oxidation.

The influence of microalloying on the oxidation behavior of gamma-TiAl based alloys was studied. The microalloying elements were added by ion implantation. Oxidation tests at 1173 K in air showed that the addition of chlorine into TiAl improves the oxidation resistance resulting in a decrease of the oxidation rate by about 2 orders of magnitude compared to unalloyed TiAl. Microstructural investigations revealed that the formation of an protective alumina layer on top of Cl-implanted TiAl is the cause for the decrease in the oxidation rate. AES measurements in the initial stage of oxidation showed that chlorine is located under the alumina layer in the metal phase. Thermodynamic calculations, investigations on the temperature dependence of the chlorine effect and the oxidation kinetics of preoxidized Cl-implanted samples support the model of a selective Al-transport via AlCl. Furthermore, the influence of small additions (in the ppm range) of P, B, C and Br on the oxidation kinetics of g-TiAl-based alloys has been investigated. P, B and C implanted TiAl showed a different oxidation behaviour and oxide scale microstructure compared to Cl and Br microalloyed TiAl. Especially the P implanted sample revealed an extensive nitride formation connected with a breakaway oxidation after 100 h.

New reactor designs comprise passive elements for decay heat removal. Computational-Fluid-Dynamics codes are an appropriate tool for the assessment of the efficiency of those components. Most of these codes are based either on the Finite-Volume or the Finite-Element method. Because of the importance for reactor safety these numerical tools have to be thoroughly validated using results from experimental setups.
The governing mechanism in passive components for decay heat removal is natural convection and heat transfer with internal heating. To assess the capability describing mixed convection flow, post test calculations of an IAHR benchmark exercise were performed (Kamide et. al, 1991). The commercial codes CFX-4® and ANSYS/FLOTRAN® were used, representing the Finite-Volume Method and the Finite-Element Method respectively.
This paper presents a discussion of the problems and capabilities of each code to calculate complex flow regimes and temperature fields.

There has been considerable interest in the development of technetium-99m radiopharmaceuticals for imaging CNS receptors.
Apart from [^99mTc]TRODAT-1 for the dopamine transporter (1), the strategies applied so far for specific CNS radiotracers failed in the ultimate goal of providing imaging agents. Both in the integrated approach with the chelate meant to be part of the pharmacophore and the pendant approach simply attaching the chelate moiety to highly potent antagonists, the chelate unit often proved to be more crucial than initially anticipated. Although the currently available chelate units make it possible to alter and adjust overall properties such as size, shape, charge, polarity (oxo, dioxo, oxo-free) and lipophilicity, insufficient receptor affinity or negligible initial brain uptake remain an unsolved problem. The introduction of the small organometallic "Tc(CO)₃" moiety into the design of ^99mTc radiopharmaceuticals (2-4) considerably extend the versatility in designing new technetium or analogous rhenium complexes. The low-pressure synthesis of a Tc-carbonyl precursor as inaugurated by Alberto et al. (2) allows a convenient exploitation of the potential of the "Tc(CO)₃" moiety in radiotracer design. We became particularly interested in studying the suitability of the new building block for the synthesis of Tc and Re based receptor-binding agents. Based on earlier work on thioether ligands (5) we have chosen a bidentate thioether group to link the Tc(I) tricarbonyl center with a receptor-ligand moiety. In a previous work, we applied this concept already to a steroid (6). Alternatively, a bidentate N-donor anchor group has been considered well suitable for combining the Tc(I) tricarbonyl center with the antagonist moiety.
Here we report the synthesis and in vitro receptor affinity of three candidates (Fig. 1) for the 5-HT_1A receptor, 5-HT_2A receptor, and dopamine transporter, respectively, in order to demonstrate the suitability of the concept.

The successful development of [^99mTc]TRODAT as ligand for the dopamine transporter has shown the feasibility to image specific transporters in the brain with radiotracers based on Tc-99m (1). In contrast to this achievement and despite the efforts many groups have devoted so far, the search for Tc-99m complexes with affinity to post-synaptic CNS receptors have not yet reached the same stage of development (2). As one of the consequences for the design of serotonin-5-HT_2A receptor binding Tc-99m complexes an affinity of < 1nM is believed to be a prerequisite for further progress. Aiming at such a high affinity, we have pursued our design concept starting from ketanserin as lead structure for 5-HT_2A receptor binding ligands (3, 4).
Here we report on the synthesis of a new high-affinity Tc-99m ligand that meets the requirement of picomolar affinity. The complex is evaluated in various receptor binding assays and by in vitro autoradiography.

The most important activities of the Institute of Safety Research regarding to the development sensors two-phase flow measurement and pressure relief are presented. A new developed electrode-mesh sensor allows a very fast (1024 frames per second) tomographic measurement of the void or gas fraction. The sensor is used e.g. for investigations on the transition between flow regimes. For the transient simulation of pressure relief the BLDN code and the BRICK code are available. The BRICK code bases on a new Particle-In-Cell (PIC) transport model, which avoids numerical diffusion. This is advantageous in case of the consideration of generation and decay of foam. A special interface allows to include a foam model. Investigations on the influence of short living foams on the pressure relief process are presented as well as investigations on pulsations of the mass flow rate, which may occur during the blowdown process under certain conditions.

Die Nachrechnungen von Druckentlastungsexperimenten bei durchgehender Reaktion dienen Validierung des Computerprogramms BRICK. Dafür stehen experimentelle Daten der Inburex GmbH Hamm (Kalorimeterversuche), des Wilhelm-Jost-Instituts Hamm (Entlastung eines 280 l Reaktors) sowie eigene kleinmaßstäbliche Experimente (Entlastung eines 1,95 l Reaktors) zur Verfügung. Als Reaktionssysteme wurden die Methanol/Essigsäureanhydridveresterung (verdampfendes System), die Ammoniumperoxodisulfatzersetzung (gasbildendes System) und Wasserstoffperoxidzersetzung (sowohl gasbildend als auch verdampfend) genutzt. Die Übereinstimmung zwischen den Rechnungen und den experimentellen Daten ist gut. Einen wesentlichen Unsicherheitsfaktor stellen die Wärmeströme über die Behälterwand vor. Daher sollten insbesondere die Korrelationen für die Wärmeübergänge sowohl für die Behälterinnenwand als auch an der Außenwand erweitert und ergänzt werden.

Das Programm BRICK beruht auf einer neuen Lösungsmethode für die Modellierung
von Transportvorgängen in Behältern. Die Grundgedanken der Methode, welche zur Klasse der Particle-In-Cell (PIC) Methoden gehört, werden vorgestellt.

Das Programm BRICK gestattet die Berechnung des zeitlichen Verlaufs wichtiger Größen (Druck, Temperatur, Massenaustrag) bei der Druckentlastung chemischer Reaktoren auf Grundlage einer Particle-In-Cell (PIC) Methode. Die wichtigsten Einzelmodelle des Programms werden erläutert. Beispiele zur Validierung werden diskutiert.

Im Forschungszentrum Rossendorf wurde ein Gittersensor entwickelt, der die Ermittlung von momentanen Gasverteilungen mit einer örtlichen Auflösung von ca. 3 mm bei einer Meßfolge von derzeit 1200 Hz erlaubt. Er basiert auf der Messung der momentanen örtlichen elektrischen Leitfähigkeit des Zweiphasengemischs. Mit dem Sensor wurde eine Luft-Wasser-Strömung in einer vertikalen Rohleitung in weiten Bereichen der Leerrohrgeschwindigkeiten visualisiert und Voidanteile gemessen. Durch die gute Auflösung des Sensors werden Gasblasen in mehreren, zeitlich aufeinanderfolgenden Verteilungen abgebildet, was die Untersuchung von Blasengrößenverteilungen und deren Evolution entlang des Strömungsweges ermöglicht. Mit zwei hintereinander angeordneten Sensoren wurden durch Anwendung der Kreuzkorrelation Profile der Gasgeschwindigkeit gemessen.

Im Forschungszentrum Rossendorf wurde ein Gittersensor entwickelt, der die Ermittlung von momentanen Gasverteilungen mit einer örtlichen Auflösung von ca. 3 mm bei einer Meßfolge von derzeit 1200 Hz erlaubt. Er basiert auf der Messung der momentanen örtlichen elektrischen Leitfähigkeit des Zweiphasengemischs. Mit dem Sensor wurde eine Luft-Wasser-Strömung in einer vertikalen Rohleitung in weiten Bereichen der Leerrohrgeschwindigkeiten visualisiert und Voidanteile gemessen. Durch die gute Auflösung des Sensors werden Gasblasen in mehreren, zeitlich aufeinanderfolgenden Verteilungen abgebildet, was die Untersuchung von Blasengrößenverteilungen und deren Evolution entlang des Strömungsweges ermöglicht. Mit zwei hintereinander angeordneten Sensoren wurden durch Anwendung der Kreuzkorrelation Profile der Gasgeschwindigkeit gemessen.

Für den Zweck der Modellbildung wird es im Beitrag als einfacher angesehen, erst Teilmodelle des zu beschreibenden Objektes zu erzeugen und diese nachher zu einer gesamtheitlichen Struktur miteinander zu verknüpfen, als das Objekt unmittel bar in seiner Gesamtheit zu modellieren. Aus dieser Sicht wird untersucht, wie die Verknüpfung von vorgegebenen Teilmodellen auf systematische Weise mit Hilfe der sogenannten Dimensionsanalyse durchgeführt werden kann. Das Strukturierungs problem wird dabei auf das Lösen eines linearen algebraische Gleichungssystems zurückgeführt. Strukturelle Restriktionen werden entweder durch eine geeignete Problemformulierung oder dadurch berücksichtigt, daß der formal gefundene Lö sungsraum nachträglich eingeschränkt wird. Anwendungsmöglichkeiten dieses Kon zeptes werden an verschiedenartigen Beispielen gezeigt.

Experiments were performed to investigate heating up processes of fluids in storage tanks under the influence of an external heat source. As a consequence of an external fire, the heat-up of the inventory may lead to the evaporation of the liquid and to release of significant quantities of dangerous gases into the environment. Several tests were performed both with heating from the bottom and with heating from the side walls. In recent tests in addition to thermocouples, the tank was equipped with needle probes for measuring of the local void fraction. The paper presents experimental and numerical investigations of single and two phase heating up processes of tanks with side wall heating. The measurement of the temperature and of the void fraction makes interesting phenomena evident. which could be explained by an own 2D model. The gained experimental results may be used for the validation of boiling models in 3-D CFD codes.