Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Aufgrund der nur unvollkommen erfaßbaren, keineswegs stabilen chemischen Struktur und Funktionalität von Huminsäuren aus natürlichen Recourcen haben operationell mit HS übereinstimmende, synthetische Polymere als Modellhuminsäuren in vielen Bereichen der experimentellen Wissenschaften Eingang gefunden. Sie sind vor dem Hintergrund der Umweltkontaminationen durch toxische und radiotoxische Schwermetalle besonders für Bindungsstudien mit Metallionen interessant, da ihre Funktionalität durch Variation der Precursoren und der Synthesebedingungen in weiten Grenzen "eingestellt" werden kann.

Wir haben FTIR-spektrometrisch die festen Komplexe von Uran(VI) mit unterschiedlichen, gut charaktersierten Huminsäuren, zwei natürlichen Huminsäuren (Aldrich-Huminsäure und eine aus Moorwasser des "Kleinen Kranichsees" isolierte Huminsäure) sowie drei synthetischen Huminsäuren (zwei Melanoidinfraktionen sowie das Oxidationsprodukt von 3,4,5 Trihydroxybenzoesäure), verglichen. Trotz unterschiedlicher Herkunft der Huminsäuren, die in ihren FTIR-Spektren deutlich wird, scheint die Urananbindung an die Huminsäuren sehr ähnlich zu sein, was durch EXAFS-Untersuchungen an Uranylkomplexen natürlicher Huminsäuren und synthetischer Huminsäuren vom Melanoidintyp gestützt wird. Sowohl die asymmetrischen UO22+-Streckschwingungen im mittleren Infrarot, die wir zwischen 933.5 cm-1 und 923.1 cm-1 registrieren, als auch die UO22+-Deformationsschwingungen im fernen Infrarot zwischen 264.8 cm-1 und 260.6 cm-1 sind gut miteinander vergleichbar.
Die Einflußnahmen der strukturellen und funktionellen Unterschiede der Huminsäuren spiegeln sich in unterschiedlichen Verschiebungen der Uranylbanden wieder.

For better understanding of the influence of the deleterious elements on the neutron embrittlement of reactor pressure vessel steels, the microstructural evolution due to neutron irradiation was investigated by SANS experiments at ternary iron alloys with different contents of copper and phosphorus. In every case irradiation produced nanoscaled inhomogeneities. The volume fraction of the inhomogeneities incrases with the copper content but not with the phosphorus content. Surprisingly, the high-pure alloy shows a relatively high irradiation effect. The irradiation defects vary in type and kinetic of evolution for the different alloys.

Al_xGa_1-xAs epitaxial layers grown on semi-insulating GaAs (SI-GaAs) substrates with x=0,25 and on in-doped GaAs with x= 0,45 were implanted at room temperature with 1.5 MeV Se ions to fluences ranging from 0,6x10¹⁴ to 4x10¹⁴ at/cm² . Implanted crystals were analyzed with 1.8 MeV ⁴He ions using the RBS/channeling technique. In order to determine the defect structure and their depth profiles measurements were carried out at two different temperatures: 295 and 105 K. XRD with synchrotron beams was used for structural analysis. White beam topography was used to detect lattice deformation and strain relaxation. The lattice parameters were determined by rocking curve measurements with a monochromatic beam. For all samples a signifcant tetragonalization of the implanted region was observed. For the layers grown on SI-GaAs the lattice distortion increases with increasing ion dose until a critical lattice strain is attained. At that point the complete relaxation of the epitaxial layer occurs. In contrast, no relaxation was observed for layers grown on practically defect free indoped substrates. The mechanism of this transformation is attributed to the much higher dislocation density in the SI-GaAs substrate. Nucleation of new dislocations at defects produced by ion implantation and their interaction with threading dislocations leads to the strain relaxation by plastic
deformation of epitaxial layers.

A computer program was designed for the conversion of element-resolved energy spectra obtained from elastic recoil
detection analysis into composition depth profles. The algorithm is described in detail. An important feature of the
program is that the contribution of the analyzed elements to the stopping power is accounted for self-consistently. Extensions of the algorithm address the problem of the simultaneous analysis of recoil and forward scattering events, respectively, and of distortions in the recoil spectra due to the presence of target constituents with isotopic distributions that cannot be resolved when using standard ionization chambers for recoil detection. Two examples are given to demonstrate how one may benefit from the capabilities of the conversion program in the context of specifc thin film problems. The first example addresses compositional changes in Si3N4/C bilayers due to N-ion implantation, while the second one is dealing with the problem of impurity accumulation at the hexagonal-to-cubic phase boundary in BN films.

This paper describes investigations using the Particle Induced X-ray Emission method (PIXE) to evaluate the con-
centration of Ca together with that of other elements (S, Cl, and K) across the articular cartilage of domestic pigs in
order to verify a putative influence of calcium on the structural changes in early arthrotic stage, derived from NMR
microscopic imaging. The measurements were carried out with focused ion beams of a lateral resolution down to
20 lm. The main matrix components (C, N, O) were evaluated from proton backscattering spectra.

The photoluminescence (PL) and electroluminescence (EL) properties of Ge-implanted SiO₂ films thermally-grown on a Si substrate have been investigated and compared to those of Si-implanted SiO₂ films. It is found that the blue-violet PL from both Si and Ge-rich layers reaches a maximum after annealing at 500°C for 30 min. The PL and EL from Ge-implanted SiO₂ are distinctly higher than that from Si-implanted layers and well visible for the naked eye. The EL spectrum from the Ge-implanted oxide annealed at 1000 °C correlates very well with the PL one and shows a linear dependence on the injected current. The neutral oxygen vacancy is assumed to be responsible for the observed luminescence. In the case of Ge the microstructure after high temperature annealing is studied.

We implanted H3+ at 300 eV into Cu-chalcopyrite semiconductors at temperatures between 50 °C and 300 °C. The surface chemistry is similar to the previously reported behavior of CuInS2 implanted with a H2+, H+ low energy ion beam with respect to secondary phase etching. We also found an increase of radiative recombination (photoluminescence), which had been attributed to defect passivation and, hence, as an indicator of hydrogen incorporation. Under the 300 eV H3+ implantation conditions, however, we observed neither a hydrogen concentration in a few hundred nm surface range exceeding the NRA detection limit of about l x exp(19) cm-3 nor a pronounced stoichiometry variation in the ternary material, as proved by Raman measurements.
We conclude, therefore, that a 300 eV H3+ implantation introduces significantly less atomic hydrogen into the volume of the sample than previously reported for other beam compositions under similar temperature and current density conditions. This could be a result of the very low energy of less than 100 eV which can be expected for atomic H produced by dissociation of 300 eV H3+ at the surface, making the instant out-diffusion into the high vacuum of the implantation chamber a favored process.

For measuring sputtering yields with MeV heavy ions only low current densities can be used in order to avoid excessive target heating. Consequently self-cleaning of the target surface during the irradiation cannot be achieved and a contamination free surface has to be maintained by means of UHV conditions. A UHV-setup including a differential pumping system has been designed and operated at a vacuum of 10^-10 mbar during experiments. Sputtered particles were collected on Si catchers and subsequently measured by two different surface analysis methods: Total Reflection X-Ray Fluorescence (TXRF), and Heavy Ion Rutherford Backscattering Spectrometry (HI-RBS). In-situ surface cleaning by 8 keV Xe ions as well as online monitoring by ERDA were found to be essential. With sufficient precautions on the surface conditions reproducible sputtering yields were obtained. First measurements for 230 MeV Au ions on Au, Zr, and Ti targets are presented.

Thin films of Ba3Ca1.18Nb1.82O8.73, prepared in a sol-gel process by multiple dip-coating on silicon wafers were charged with hydrogen by dissociative water
absorption at definite values of water vapour pressures and temperatures. The hydrogen content was determined using nuclear resonance reaction analysis. From the resulting water vapour pressure/hydrogen composition isotherms the absorption enthalpies and the absorption entropy were calculated in the framework of a two site
model, based on Fermi-Dirac statistics. On Ba3Ca1.18Nb1.82O8.73 also impedance spectroscopy was performed yielding the bulk conductivity. From these data
in combination with proton transport numbers and the thermodynamic results as noted above the proton diffusion coefficient could be evaluated.

The enrichment of F on Antarctic meteorites is the result of their exposure to the atmosphere, and its measurement allows a subdivision of the terrestrial age into a
duration of exposure on the ice and the time a meteorite was enclosed by the ice. In many cases, the periods of surface exposure are only small fractions of the
terrestrial ages of meteorites collected in Antarctica. The enrichment of F on the surfaces of Antarctic achondrites was investigated by means of nuclear reaction
analysis (NRA): scanning proton beams with an energy of 2.7 and 3.4 MeV were used to induce the reactions F-19(p,alpha gamma)160 and
F-19(p,p'gamma)F-19, respectively. Gamma signals proportional to the F content were measured. The following Antarctic achondrites were investigated: Martian
meteorite ALH 84001; diogenite ALHA77256; the eucrites ALHA81011 and ALHA78132; and in addition, the H5 chondrite ALHA79025. For ALH 84001, our
data indicate a period of exposure on the ice of <500 years. Thus, this specimen was enclosed in the ice >95% of its terrestrial age of 13 000 years.

Due to their unique topology and unusual guest-binding behaviour, dendrimers are promising reagents for use in diagnostic imaging and therapy. We are especially interested in efficient binding and transport of medicinal and biological relevant anions as pertechnetate and the nucleotides AMP, ADP and ATP. Poly(propylenamine)-Dendrimers (POPAM) of different generations have been functionalized at the periphery with the goal to obtain a hydrophobic shell. The dendrimers synthesized (cf. Fig.) were characterized by solvent extraction experiments at the system pertechnetate,(nucleotide)-buffer-H₂O/dendrimer-CHCl₃. A dendritic effect is clearly visible of all dendrimers investigated. The influence of pH and temperature on the extraction of pertechnetate and nucleotides with dendrimers is reported.

Urea-functionalized dendrimers are prepared, which show very efficient phase transfer in particular of the diagnostically relevant anions pertechnetate, perrhenate and ATP. The extractability rates are evaluated quantitavely by tracer methods. Their pH dependancy allows to steer the release of guest molecules from the dendrimer host.

Für die im Forschungszentrum Rossendorf im Bau befindliche Strahlungsquelle ELBE werden die Möglichkeiten zur Erzeugung kohärenter Strahlung mit Hilfe eines Freie Elektronen Lasers im Bereich des mittleren und fernen Infrarot vorgestellt. Mit Hilfe einfacher Modelle werden die Vorgänge bei der Erzeugung und Verstärkung kohärenter Strahlung erläutert und ihre Eigenschaften in Abhängigkeit von den Parametern des Elektronenstrahls und des verwendeten Undulators berechnet. Insgesamt werden 4 mögliche Varianten eines Undulators diskutiert. Anwendbarkeit und Genauigkeit der verwendeten Näherungsformeln werden mit Hilfe eindimensionaler Simulationsrechnungen getestet.

We have conducted systematic experimental studies of K⁺ and K^- production and propagation in nucleus-nucleus collisions at beam energies close to and below the production threshold for free nucleon-nucleon (NN) collisions. In noncentral Au+Au collision, the K⁺ mesons are preferentially emitted perpendicular to the reaction plane and the excitation functions for K⁺ and K^- mesons nearly coincide when correcting for the threshold energy. In contrast, for NN collisions the K⁺ yield exceeds the K^- yield by two orders of magnitude near the respective NN threshold. Both effects are considered to be experimental signatures of a modification of kaon properties in the nuclear medium.

Surface modification of austenitic stainless steel by high current ion nitriding at 400°C has been studied by Slow Positron Implantation Spectroscopy (SPIS). In addition, Nuclear Reaction Analysis (NRA) has been applied to obtain information about the nitrogen depth profile. The results obtained from both methods are compared and discussed with respect to the nature of defects produced by high current ion nitriding and their influence on the formation of a surface layer, called expanded austenite.

The report gives an overview on the scientific work of the Institute of Safety Research in 1998.

Surface water has been studied from the mountain bog 'Kleiner Kranichsee'. This bog is situated in the Johanngeorgenstadt area (Saxony/Germany) close to an abandoned uranium mine and mine tailing piles. The bog water contains about 130 mg/L of organics (primarily humic and fulvic acid).
First, bog water colloids were determined for their particle size and size distribution using photon correlation spectroscopy (PCS) and scanning electron microscopy (SEM) in combination with size fractionation by filtration. Second, about 400 L of the bog water were processed in order to isolate aquatic humic substances. SupeliteTM DAX-8 (Supelco) was used as adsorption resin. The humic material was separated into humic and fulvic acids. A total of 14 g of humic acid and 10 g of fulvic acid were isolated. The humic substances were characterized in terms of their elemental composition, functional properties including proton exchange capacity, charge/size ratios and spectroscopic characteristics. The results were compared with data of a commercial humic acid from Aldrich.

The migration behavior of uranium in a sandy aquifer system rich in humic substances was studied in laboratory column experiments. For the investigations we used a Pleistocene aeolian quartz sand and groundwater GoHy-532 from the Gorleben site (Germany). The column experiments were performed in a glove box under anaerobic conditions (Ar + 1 % CO₂). ²³²U(VI) was used as a tracer. The migration behavior of uranium was investigated as a function of the uranium/groundwater equilibration time before injection into the column, the groundwater flow velocity and the column length.
From the breakthrough curves one can conclude that a part of the injected uranium migrates slightly faster than groundwater. The observed migration behavior is attributed to the association of a part of uranium with humic colloids, which move faster due to size exclusion processes. Depending on the experimental conditions the recovery of humic colloid-bound transported uranium amounts to 0.4 up to 7.6 %. The recovery of non-retarded colloid-borne uranium increases with increasing uranium/groundwater equilibration time before injection into the column. Beyond it, the recovery of humic colloid-borne uranium decreases with decreasing groundwater flow velocity and increasing column length, which corresponds to an increasing residence time in the column.
The results refer to the fact that the migration behavior of uranium is strongly influenced by kinetically controlled interaction processes of uranium with humic colloids.

Die Untersuchung des Ausbreitungsverhaltens von Actinidionen in wäßrigen Systemen ist unabdingbar zur Erstellung von Risikoabschätzungen zur Langzeitsicherheit von ober- und untertägigen Einrichtungen des ehemaligen Uranerzbergbaus sowie von Endlagern für radioaktiven Abfall. Das Migrationsverhalten von Actinidionen in einem natürlichen Aquifer wird stark von den vorherrschenden Bedingungen beeinflußt. Dabei können Huminstoffe als ubiquitäre, organische Komplexbildner einen entscheidenden Einfluß auf die Immobilisierung bzw. Mobilisierung der Actinidionen ausüben.
Die vorliegende Arbeit zeigt Ergebnisse von Säulenexperimenten zur Untersuchung des Einflusses aquatischer Huminstoffe auf das Migrationsverhalten von Uran(VI) in einem sandigen Grundwasserleiter. Für die Untersuchungen wurden ein Grundwasser (GoHy-532, DOC: 30 mg C/l) sowie pleistozäner Flugsand aus dem Gebiet Gorleben verwendet. Der in Säulen (Länge 25 cm und 50 cm; Durchmesser 5 cm) eingebaute Sand wurde unter Inertgasbedingungen (Ar + 1 % CO₂) mit dem Grundwasser konditioniert. Zur Bestimmung der hydraulischen Parameter der Säulen wurde tritiertes Wasser als Tracer verwendet. Die Migrationsuntersuchungen erfolgten in Abhängigkeit von der Kontaktzeit des Grundwassers mit Uran(VI) (²³²UO₂Cl₂) bis zur Injektion auf die Säule, der Grundwasserfließgeschwindigkeit sowie der Säulenlänge.
Die Uran-Durchbruchskurven der Säulenexperimente zeigen, daß ein Teil des Urans ungehindert, an Huminstoffe gebunden und dabei bis zu 5 % schneller als das Wasser durch das Sediment transportiert wird. Der Wiedererhalt an Uran liegt für die durchgeführten Experimente im Bereich zwischen 2 % und 9 %.
Der ungehinderte, huminstoffgetragene Urantransport ist von der Kontaktzeit des Grundwassers mit Uran(VI) abhängig und steigt mit Erhöhung der Konditionierungszeit. Darüber hinaus nimmt der Wiedererhalt mit abnehmender Grundwasserfließgeschwindigkeit sowie zunehmender Säulenlänge, d.h. mit Erhöhung der Kontaktzeit mit dem Sediment, ab. Dieses Ergebnis deutet auf eine kinetisch kontrollierte Wechselwirkung des huminstoffgebundenen Urans mit der Sandoberfläche hin.

As a contribution to Task 1 (Sampling and Characterization), we have characterized Derwent Reservoir fulvic acid by means of FTIR spectroscopy and capillary zone electrophoresis and compared to Kranichsee humic and fulvic acid and Aldrich humic acid.
Our contribution to Task 2 (Complexation) consists of two parts. First, we studied the complexation of Kranichsee humic acid (HA) and fulvic acid (FA) with uranyl(VI) ions by laser-induced fluorescence spectroscopy at pH 4 and an ionic strength of 0.1 M (NaClO4). The loading capacities were determined to be 14 ± 1 % and 13 ± 1 % for humic acid and fulvic acid, respectively. The complexation constants for Kranichsee humic acid and fulvic acid were found to be log ß = 6.35 ± 0.22 and log ß = 6.21 ± 0.20, respectively. These results were compared to the uranyl complexation behavior of other natural humic acids such as Aldrich HA and GoHy-573 HA. Second, we investigated original bog water of the mountain bog 'Kleiner Kranichsee' by ultrafiltration to determine the hydrodynamic particle size distribution, i.e., the 'apparent molecular weight' distribution of the organic substances in the bog water. Furthermore, the influence of uranyl complexation on this particle size distribution of humic colloids was investigated. No significant influence of the uranyl ions on the molecular weight distribution of the humic substances was found.

The effect of humic acid (HA) on the uranium(VI) sorption onto phyllite and onto its individual main mineralogical constituents, muscovite, albite, and quartz was studied in air-equilibrated batch experiments in the pH range of 3.5 to 9.5. The uranyl(VI) and HA concentration was 1×10-6 M and 5 mg/L, respectively. The ionic strength was held constant at 0.1 M (NaClO4 solution). A size fraction of 63 to 200 µm of the solids was used, the mass loading was 12.5 g/L, and the experimental volume was 40 mL.
The rock material phyllite shows both the highest HA sorption over the entire pH range and the highest uranyl sorption in the neutral pH range compared to the pure mineral phases muscovite, albite and quartz. In contrast to the minerals the maximum of the uranium sorption on phyllite is not shifted to lower pH values but remains largely unchanged in the pH range from 6 to 7.8 when HA is present at 5 mg/L. This is attributed to ferrihydrite a secondary mineral phase formed during the sorption experiments.
The humic acid and uranyl sorption on the mineral surfaces of the constituents of phyllite decreased in the sequence: muscovite > albite > quartz. Below pH 5, the uranium uptake is generally increased in the presence of HA. This is attributed to the fact that the HA is sorbed on the mineral surface thereby providing additional sorption sites due to their complexing ability and/or due to adsorption of uranyl humate complexes on the mineral surface. In the neutral pH range, the HA sorption decreases with increasing pH. The dissolved HA forms aqueous uranyl humate complexes thereby decreasing the uranyl uptake on the solids. At alkaline pH values, the HA has little or no effect on the amount of uranium sorbed by muscovite, albite and quartz. Inorganic carbonates with its high complexing ability towards uranyl ions predominate the influence of HA under the given experimental conditions. We conclude that the uranium sorption is determined by the kind of rock material or mineral and is strongly affected by both the pH and the presence of organic material.
In addition, the uranium adsorption on phyllite was studied as a function of the HA concentration (5 and 60 mg HA/L). Below pH 5.7, the uranium sorption is enhanced in the presence of 60 mg HA/L compared to experiments carried out with 5 mg HA/L. From pH 5.4 to 9.4, the uranium uptake, on a percentage basis, decreased as the humic acid concentration increased. Thus, a strong relationship between the initial humic acid concentration in solution and the amount of uranium adsorbed at a given pH was found.

Die Bewertung des Einflusses von Huminstoffen auf die Mobilität von Radionukliden in natürlichen Aquifersystemen ist von großem Interesse und ermöglicht beispielsweise eine Einschätzung zur Langzeitsicherheit stillgelegter Uranbergwerke bzw. Endlagerstätten für radioaktive Stoffe. Infolge der Komplexierung von Radionukliden durch Huminstoffe kann deren Löslichkeit erhöht und somit ihre Mobilität in der Geosphäre erhöht werden. Zur Quantifizierung der Wechselwirkung zwischen Huminstoffen und Radionukliden kann die Komplexbildungskonstante genutzt werden.
Aquatische Huminstoffe wurden aus dem Oberflächenwasser des Hochmoores 'Kleiner Kranichsee' isoliert, welches im ehemaligen Uranbergbaugebiet bei Johanngeorgenstadt (Sachsen, D) liegt. Die Huminstoffe wurden in Humin- und Fulvinsäurefraktionen getrennt und hinsichtlich ihrer Elementarzusammensetzung, funktionellen Eigenschaften einschließlich der Protonenaustauschkapazität, Ladungs-Größenverhältnisse und spektroskopischer Eigenschaften charakterisiert.
Die Komplexierung von Uranyl(VI) durch Huminsäure (HS) und Fulvinsäure (FS) wurde bei pH 4 und einer Ionenstärke von 0.1 M mittels zeitaufgelöster Laserfluoreszenzspektroskopie (TRLFS) untersucht. Mit Hilfe des Ladungsneutralisationsmodells wurden Komplexbildungskonstanten (log ß) und Beladungskapazitäten (LC) der Huminstoffe mit UO₂ ²⁺ bestimmt. Folgende Ergebnisse wurden erhalten:
HS: log ß = 6.35±0.22, LC = 14%; FS: log ß = 6.21±0.20, LC = 13%.
Weiterhin wurde der Einfluß von SO₄ ^2- als anorganischer, konkurrierender Ligand auf die Uranyl-Huminstoff-Komplexierung untersucht, da Sickerwässer sächsischer Uranbergbauhalden neben anderen Ionen relativ hohe Konzentrationen an Uran (10^-5 M) und Sulfat (3x10^-2 M) enthalten. Dabei wurde festgestellt, daß das Sulfat-Ion auf die Komplexierung zwischen Uranyl und Huminstoff keinen Einfluß hat, da die Uranyl-Huminstoff-Komplexbildungskonstanten trotz steigender Sulfat-Konzentrationen (0, 10^-3, 10^-2 M) innerhalb des experimentellen Fehlers unverändert bleiben. Dagegen sinkt die Beladungskapazität der Huminstoffe gegenüber Uranyl-Ionen mit steigender Sulfat-Konzentration. D.h., das Sulfat-Ion muß einen Einfluß auf die komplexierenden Gruppen der Huminstoffe ausüben.

Die Auslegung von Apparaten der chemischen Verfahrenstechnik erfolgt in der Praxis oft noch auf der Grundlage experimenteller Untersuchungen oder mit groben Abschätzungen. Mit der Verbesserung der Rechentechnik nimmt jedoch die Bedeutung der numerischen Simulation der gekoppelten strömungsmechanischen, thermodynamischen und chemischen Prozesse in diesen Apparaten zu. Ziel der vorliegenden Modellentwicklung war es, einen weitgehend allgemeingültigen Programmkern, der die Transportgleichungen löst, zur Verfügung zu stellen. Spezielle Modelle für einzelne Phänomene oder Apparate sollen leicht über Interfaces ankoppelbar sein. Das ermöglicht insbesondere Untersuchungen zum Einfluß spezieller Phänomene und Modelle auf das Simulationsergebnis. Dreidimensionale Rechnungen erfordern i.a. einen sehr hohen Aufwand und sind meist nur für spezielle Probleme praktisch anwendbar. Bei dem vorgestellten Simulationstool für Mehrphasenströmungen in einem Behälter erfolgte daher eine Beschränkung auf die axiale Behälterkoordinate. Ausgangspunkt war die Simulation von Druckentlastungsvorgängen. Das Behältermodell muß das Aufwallen des Behälterinhalts wiedergeben und Aussagen zur Zusammensetzung des in die Abblaseleitung eintretenden Fluids liefern. Diese hängt von der Phasenseparation einschließlich des Schaumverhaltens des Fluids ab. Schäume treten in einer Vielzahl technischer Apparate wie Rührreaktoren, Blasensäulen, Trennkolonnen, Elektrolysezellen oder Bioreaktoren auf. Die Beschreibung von Schaumentstehung und Schaumzerfall am Gemischspiegel war ein spezielles Ziel der Modellentwicklung. Durch die Anwendung einer speziellen Partikelmethode für die Modellierung der Transportvorgänge wird zum einen die numerische Diffusion vollständig unterdrückt, zum anderen das Transportproblem weitgehend von den anderen Prozessen entkoppelt. Das Fehlen der numerischen Diffusion bringt Vorteile bei der Beschreibung von Diskontinuitäten, wie dem Übergang zwischen dem Mehrphasengemisch und dem Gasraum und damit bei der Modellierung der Schaumzone. Um das Modell einfach zu halten, wurden statt der Impulserhaltung nur ein zeitabhängiger Behälterdruck (ggf. mit Beachtung des geostatischen Drucks) und die Relativbewegungen der Phasen auf der Grundlage empirischer oder halbempirischer Ansätze (Driftbeziehungen) berücksichtigt.

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.