Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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.

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. 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.

The behavior of PWRs during cold water or boron dilution transients is strongly influenced by the distribution of coolant
temperature and boron concentration at the core inlet. This distribution is the needed input to 3-dimensional neutron kinetics to
calculate the power distribution in the core. It mainly depends on how the plugs of cold or unborated water formed in a single loop
are mixed in the downcomer and in the lower plenum.

To simulate such mixture phenomena requires the application of 3-dimensional CFD (computational fluid dynamics) codes. The
calculations are based on the CFD Code CFX-4. The results of the simulation have to be validated against mixture experiments at
scaled facilities.

Therefore, in the framework of a research project funded by BMBF, the institute created a 1:5 mixture facility representing first the
geometry of a German pressurized water reactor and later the European Pressurized Water Reactor (EPR) geometry.

In the Forschungszentrum Rossendorf a measurements techniques test loop was constructed. Air water flow in a vertical tube was investigated using different two phase flow measuring techniques. The paper describes the used measuring techniques and some performed experiments. The code CFX-4.2 with its implemented two phase models was used, to simulate bubbly flow and to compare calculated void profiles with the measured results.

The behavior of PWRs during cold water or boron dilution transients is strongly influenced by the distribution of coolant temperature and boron concentration at the core inlet. This distribution is required as an input to 3-dimensional neutron kinetics to calculate the power distribution in the core. It mainly depends on how the plugs of cold or unborated water formed in a single loop are mixed in the downcomer and in the lower plenum [1]. The reactivity insertion due to penetration of unborated coolant into the core depends on the degree of mixing. Weak mixing can result in recriticality and possibly in significant power release. The same is true for cold water insertion into the core due to overcooling of a coolant loop in the case of a steam line break. Coolant mixing is also of interest under steady state normal operation conditions. Slight differences in the cold leg temperatures can occur due to small asymmetries in the primary circuit loops.

To simulate such mixture phenomena requires the application of 3-dimensional CFD (computational fluid dynamics) codes. The results of the simulation have to be validated against mixing experiments at scaled facilities. The calculations are accomplished using the CFD Code CFX-4.2 [2].

As a first step, steady state mixing conditions in the downcomer and lower plenum are considered. Qualitatively different flow fields were found in different reactor types depending from the downcomer geometry. Calculated results were compared with experiments.

At the Gesellschaft für Schwerionenforschung in Darmstadt a therapy unit for heavy ion cancer treatment has been established in collaboration with the Deutsches Krebsforschungszentrum Heidelberg, the Radiologische Universitätsklinik Heidelberg and the Forschungszentrum Rossendorf.

For quality assurance the dual-head positron camera BASTEI (Beta Activity meaSurements at the Therapy with Energetic Ions) has been integrated into this facility. It measures ß⁺-activity distributions generated via nuclear fragmentation reactions within the target volume.
BASTEI has about 4 million coincidence channels. The emission data are acquired in a 3D regime and stored in a list mode data format. Typically counting statstics is two to three orders of magnitude lower than those of typical PET-scans in nuclear medicine.

Two iterative 3D reconstruction algorithms based on ISRA (Image Space Reconstruction Algorithm) and MLEM (Maximum Likelihood Expectation Maximization), respectively, have been adapted to this imaging geometry. The major advantage of the developed approaches are run-time Monte-Carlo simulations which are used to calculate the transition matrix.
The influences of detector sensitivity variations, randoms, activity from outside of the field of view and attenuation are corrected for the individual coincidence channels.

Performance studies show, that the implementation based on MLEM is the algorithm of merit. Since 1997 it has been applied sucessfully to patient data. The localization of distal and lateral gradients of the ß⁺-activity distribution is guaranteed in the longitudinal sections. Out of the longitudinal sections the lateral gradients of the ß⁺-activity distribution should be interpreted using a priori knowledge.

The ratio between magnetic and nuclear small angle neutron scattering (SANS) can provide additional information about the composition and structure of the scattering inhomogenities. The method fails if the material system does not meet the two-phase approach. In this case, by using the indirect transformation method, the ratio can more generally be defined and related to the dependence of the scattering particle size. The method is derived and applied to model systems with two types of non-magnetic spheric inhomogenities in a ferromagnetic matrix.

Solidified liquid metal ion sources (LMISs) operating with Au alloy wetted hair-pin emitters can be used as high-intensity electron point sources for application in the field of ultrahigh vacuum techniques. A nanotip emitter on a solidified LMIS emitter can be formed by quenching during ion emission mode. I - V characteristics and the performance of the electron emitting LMIS are presented.

Technical Reports on VVER transients were provided by IVO, NRI, KI, STCNRS and INRNE. The present report gives a survey of the transients documented by the five organisations mentioned. The main actions and effects observed during each transient are briefly described. An overview of the information contained in the five Technical Reports is provided in tabular form. The tables comprise information on the initial states, the measured parameters, and the time regime of the measurement. For each reactor type, VVER­440 and VVER­1000, respectively, one transient is recommended for coupled codes validation in the current project.

Despite the great success of dynamo theory during the last decades an experimental verification of magnetic field self-excitation in conducting fluids is still missing. We summarize the outcomes of a workshop held in Riga in June 1998 on various experimental approaches to this topic. The Riga dynamo
experiment is presented in more detail.

We present numerical simulations for the Riga dynamo experiment, which is intended
to verify the magnetic field self-excitation in a helical flow of a conducting fluid.
Testing a wide variety of axial and azimuthal velocity profiles we show the importance
of the global helicity for the efficiency of the dynamo. Predictions are made on
the shape of the arising magnetic field and the back-reaction of the
Lorentz force on the flow.

The critical magnetic Reynolds number (Rm) of the Riga dynamo experiment depends
strongly on the shape of its velocity profiles. For given motor power ressources it is
necessary to optimize these profiles in order to achieve self-excitation of the magnetic
field. We present a number of one- and two-dimensional calculations for a variety of
axial and azimuthal velocities. Particularly, we test velocity profiles with maximal
helicity (Bessel function profile). For these velocity profiles the critical Rm can
be reduced by 20 per cent compared to the value for the solid body rotation profile.
The used two-dimensional finite difference solver allows to study the effect of
axially varying profiles, too. In addition, we present some two-dimensional
calculations for further dynamo experiments in cylindrical geometry, including
the flow topologies s1t1, s2t1 and s2t2. The influence of the flow direction and
the effect of a surrounding conducting medium on the critical Rm is investigated
in detail.

We present numerical results on the control of 2-D and 3-D instabilities in the wake of a circular cylinder by means of externally applied magnetic fields. 2-D instability (vortex shedding) can clearly be suppressed with increasing field strength. However, 3-D instability is influenced in a nonmonotonic way, triggered by changes to the 2-D flow. 3-D instability can exist below the 2-D stability threshold, which may lead to a reversal of the order of instabilities for fixed field strength. Strong fields seem to amplify 3-D instability.

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 thermalhydraulics. Using the code ATHLET which is being developed by "Gesellschaft für Anlagen- und Reaktorsicherheit", pre- and posttest calculations were done to determine the thermalhydraulic 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. Besides the thermalhydraulic standard measuring system, the facility was equipped with needle shaped conductivity probes for measuring the local void fractions.

The OECD has defined a benchmark for coupled Cartesian neutron kinetics/thermohydraulics code systems. In the first phase, a plant simulation with point kinetics was requested. The purpose was to test the model response.
In this presentation, the dependence of the results obtained by means of the ATHLET-code from several important parameters is investigated. It was found, that the nodalization of the steamline in the vicinity of the break has an influence on the pressure behaviour and on the time of the return-to-power.

The fifth dynamic benchmark was defined at the 7th AER-Symposium, held in Hörnitz, Germany in 1997. It is the first benchmark for coupled thermohydraulic system/three-dimensional hexagonal neutron kinetic core models. In this benchmark the interaction between the components of a VVER-440 NPP with the reactor core has been investigated. In this presentation, the first results obtained by means of the codes DYN3D/ATHLET (Forschungszentrum Rossendorf), BIPR8/ATHLET (Kurchatov Institute Moscow) und HEXTRAN/SMABRE (VTT Energy Espoo) were compared. Both thermohydraulics and neutron kinetics parameters show dif-
ferences.

A new nodal method HEXNEM2 for hexagonal geometry is described. The method is based on a two-dimensional expansion of
the intranodal fluxes. Polynomials up to the second order and exponential functions are used in each group. By this method the singular
terms occurring in the transverse integration methods are avoided. Side averaged and corner point values of fluxes and currents are used
for the coupling of nodes. A calculation scheme for the outgoing partial currents at the sides and similar expressions for the corners from
given incoming values are used in the inner iteration which gives a fast running scheme. The method is tested against 2-dimensional
hexagonal benchmark problems for the VVER-type reactors. The results show that the multiplication factor and nodal powers are predicted
accurately. A considerable improvement can be shown of the results for the VVER-1000 benchmarks compared with the method developed
previously for the code DYN3D and the simpler method HEXNEM1.

A summary of magnetic field effects on surface driven flows will be given. Own work in the fields
- hydrothermal waves controlled by magnetic fields,
- Marangoni flows at liquid metal surfaces,
- thermoelectrically driven flows,
- levitated spheres and drops,
- Marangoni motion of drops
will be summarized. In addition, literature results about magnetic field influence on floating zone crystal growth or the use of magnetic fields in laser or electron beam welding bill be given. The second part of the lecture will concentrate on possible experiments with magnetic fields under microgravity. Proposals will be presented for discussion for crystal growth with magnetic fields, thermoelectricity, electromagnetic gas injectors, or magnetic field control of electrochemical processes. Emphasis will be put on the problem of diagnostics being inherent to all activities.

A summary of MHD effects and technical applications will be given based on a classification of the different actions of external magnetic fields and/or external electrical currents. An overview of the different alternating fields (rotating, pulsating, travelling) and static magnetic fields, and their interaction with liquid metal melts will be given. Special emphasis will be put on applications in crystal growth where a contactless melt flow control is important for the convective motions in many growth technologies. Typically steady magnetic fields are used to damp such flows. Surprisingly, active flow driving forces due to alternating magnetic fields can be of stabilizing character, too. Numerical results for the combined action of DC and AC magnetic fields will be presented for two problems: vertical Bridgeman and silicon Czochralski crystal growth. Recent results on MHD turbulence and some destabilizing actions of steady magnetic fields will shortly be mentioned. Special attention will be given to the problem of measuring techniques in liquid metal melts since this is a crucial question for any experimental activities in the field. For instance, any activity for code validation will require model experiments which, in turn, quickly lead to serious measuring problems. Some new results and ideas will be discussed.

Eine kontaktlose Beeinflussung der konvektiven Strömung in der Schmelze ist in vielen Kristallzüchtungstechnologien von großer Bedeutung. Gewöhnlich werden stationäre magnetische Felder benutzt, um solche Strömungen zu dämpfen. Überraschenderweise können auch aktive Strömungsantriebskräfte, die von instationären magnetischen Feldern erzeugt werden, von stabilisierendem Charakter sein. Wir stellen Resultate der numerischen Simulation der kombinierten Wirkung von homogenen und linearen stationären Magnetfeldern für die Silizium-Czochalski-Kristallzüchtung und von homogenen und rotierenden Magnetfeldern für die Bridgman-Anordnung vor. Es werden bei der Czochalski-Geometrie nicht nur die thermische Konvektion und die Rotation des Kristalls und des Tiegels in Betracht gezogen, sondern auch der Einfluß der antreibenden und/oder dämpfenden elektromagnetischen Kräfte sowie der Einfluß des induzierten elektrischen Stromes und der thermokapillar angetriebenen Strömungen an der freien deformierbaren Schmelzoberfläche. Aufgrund der hohen Reynolds-Zahl der Strömung ist die numerische Simulation laminar nicht mehr möglich. Es werden vergleichende Rechnungen mit einem Null-Gleichungs-Turbulenzmodell, das auf der Prandtl´schen Mischungsweg-Hypothese basiert, und einem anisotropen k-epsilon Turbulenzmodell durchgeführt.

The flow around bodies moving in weakly electrically conducting fluids can be controlled by applying electromagnetic forces originating from electrodes and permanent magnets suitably placed on the surface of the body. Here we consider the
possibility of separation control for a two-dimensional bluff body and an inclined flat plate by inducing Lorentz forces parallel to the surface. We present physical and numerical experiments at diameter/chord Reynolds numbers in the range of 300--4,000 for the circular cylinder and 2,000--20,000 for the plate. Both steady and time-periodic forcing are applied. The physical experiments are conducted in an open channel with sodium hydroxide as the working fluid. Dramatic separation delays are observed on both bodies for a modest expenditure of energy. Special attention is drawn to lift enhancement due to separation delay for the inclined plate. Direct numerical simulations at low Reynolds numbers confirm the physical tendencies of the experiments.

The flow around bodies (cylinder, plate) can be controlled by applying electromagnetic forces originating from electrodes and permanent magnets suitably placed on the surface of the body. There is a large variety for applying those forces with respect to the geometrical arrangement and the electrical current feeding the electrodes. The goals of this approach are flow stabilization, drag reduction or manoeuvrability of the body in an electrically low-conducting fluid like seawater. We present experimental and numerical results for a low Reynolds-number range of 200 < Re < 4000. Experiments were performed using a copper sulphate electrolytic solution and a sodium hydroxide loop. Flows are considered around a cylinder and over a plate, with
Lorentz forces being parallel to the body surface. Experimental results will be presented for the body drag and the wake flow structures depending on different
regimes of electromagnetic forcing. In particular, we distinguish between the
regimes of direct, frequency-variable sinusoidal or pulsed electric currents. Numerical results confirm the physical tendencies at least for lower Reynolds numbers. Parameter ranges will be given for an optimal electromagnetic flow control in terms of drag reduction and flow laminarization. The energetic balance will be discussed.

Specimen reconstitution, i.e. the incorporation of a small piece from a previously tested specimen into a compound specimen, allows to multiply the number of tests. That is especially important if the available material is restricted and new parameters have to be measured. For this purpose a technique was developed to reconstitute Charpy size single-edge notch specimens (SENB) from broken halves of Charpy V-notch specimens. The essential tools for producing reconstituted specimens are a stud arc welding set-up and an electric wire discharge machine. The reconstitution technique applied is in accordance with the ASTM- guideline E-1253. The fraction of the insert that is affected by the reconstitution technique is determined by measurements of temperature and hardness gradients and by metallographic examination. The specimen reconstitution technique has been validated for SENB specimens of Charpy geometry. The test methods comprised instrumented impact testing of Charpy V specimens and elastic- plastic fracture toughness testing with precracked and side grooved SENB specimens.

Der Traum von magnetohydrodynamischen (MHD)-Generatoren und MHD-Schiffsantrieben hat sich nicht erfüllt. Die magnetisch gesteuerte Kernfusion läßt auf sich warten. Doch die Stille trügt:; MHD-Technologien halten erfolgreich Einzug in Metallurgie und Verfahrenstechnik, MHD-Experimente eröffnen neue Perspektiven für die nichtlineare Physik und Turbulenzforschung, und selbst das klassische Problem der Entstehung des Erdmagnetfeldes scheint seiner experimentellen Verifikation nahe zu sein.

The Riga dynamo experiment is an attempt to show the
self-excitation of a magnetic field in an electrically conducting fluid.
Due to the absence of any scale separation effects, the precise shape of
the velocity profile has a strong influence on the values
of the critical magnetic Reynolds numbers (Rm).
Several numerical codes have been developed and used for the determination
of these critical Rm for arbitrary velocity profiles.
Helicity maximizing
profiles are shown to provide smaller critical Rm than the
solid body rotation flow. We outline how the velocity profiles
have been optimized in an iterative process including flow measurements,
constructive improvements and numerical calculations.

On the NOKO (emergency condenser) test station constructed at Jülich Research Centre, the operating performance and
effectiveness of the emergency condenser of the boiling water reactor 1000 have been determined in well over 200 tests. It has been
possible to check that the tests were in close agreement with a modified version of ATHLET

Thermocapillary Marangoni convection of liquid gallium was studied experimentally and numerically. A specially designed experimental setup ensured an oxide-free surface of the liquid gallium for a very long time. The convective flow at the free surface was found to be directed opposite to both buoyancy-driven and ordinary thermocapillary convection. The anomalous direction of the thermocapillary flow was explained by the presence of a small amount of a surface-active contaminant - lead adsorbed at the free surface. Two different approaches were used to describe the observed phenomenon. First, the flow was treated as a pure thermocapillary convection with a modified dependence of the surface tension on temperature so that to reproduce the measured velocity distribution. Second, a novel physical model was devised for the flow driven by the gradient of the surface tension induced by the temperature dependence of the concentration of the adsorbed layer of contaminant. In contrast to the ordinary thermocapillary convection in low-Prandtl-number liquids, there is a strong coupling between the flow and the driving force in the proposed model resulting in velocity profiles very similar to those observed in the experiment.

Neutral Re(I) carbonyl complexes with multidentate thioethers of the general formula [ReBr(CO)₃(R-S(CH₂)₂S-R')] were obtained by ligand exchange reaction starting from [ReBr₃(CO)₃]^2-. The thioether ligands bear functional groups (R, R'', such as the carboxyl, propargyl and hydroxyl moiety, which can act as anchor groups for biologically active molecules. First representatives of Re(I) and Tc(I) carbonyl thioether complexes, meant to target CNS neuroreceptors and hormone receptor-positive breast tumors, are described.

Two different instability mechanisms of electromagnetically levitated bodies are analyzed. The first is due to the virtual coupling between the electric current passing through the magnetic system and the variation of position of the body. This mechanism can result in unstable mass center oscillations of a levitated solid body. Another type of instabilities may occur because of the coupling beween the motion and the electric currents induced in the body. This effect can cause a spontaneous rotation of the body setting in as the frequency of the alternating magnetic field exceeds certain critaical threshold depending on the configuration of the field. This instability can be suppressed by an axial steady magnetic field of strength comparable to that of the levitating field.

We study the linear stability of a thermocapilary-driven convection in a planar unbounded layer of an electrically conducting low-Prandtl-number liquid heated from the side and subjected to a transverse magnetic field. The thresholds of convective instability for both longitudional and oblique disturbances are calculated numerically and also asymptotically by considering the Hartmann and Prandtl numbers as large and small parameters, respectively. The magnetic field has a stabilizing effect on the flow with the critical temperature gradient for the transition from steady to oscillatory convection increasing as square of the the field strength. So increases also the critical frequency, while the critical wavelength reduces inversely with field strength. These asymptotics develop in a strong enough magnetic field when the instability is entirely due to the jet of the base flow confined in the Hartmann layer at the free surface. In contrast to the base flow, the critical disturbances, having a long wavelength at small Prandtl numbers, extend from the free surface into the bulk of the liquid layer over a distance exceeding the thickness of the Hartmann layer O(Pr-1/2) times. For Ha ? Pr-1/2 the instability is influenced by the actual depth of the layer. For such moderate magnetic fields the instability threshold is sensitive to the thermal properties of the bottom of the layer and the dependences of the critical parameters on the field strength are more complicated. In the latter case, there is a number of various instability modes possible depending on the thermal boundary conditions and the relative magnitudes of Prandtl and Hartmann numbers.