Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Assuming the hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower plenum of a Light Water Reactor (LWR) leads to the question about the behaviour of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
To get an improved understanding and knowledge of the melt pool convection and the vessel creep and possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments (Failure Of REactor VEssel Retention) are currently underway at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm (Sehgal, 1999). These experiments are simulating the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurization scenario. The geometrical scale of the experiments is 1:10 compared to a common LWR.
During the first series of experiments the creep behaviour (FOREVER-C) of the vessel under the thermal attack of the melt pool and varying internal pressure loads is investigated. It is intended to enforce the creep process until vessel failure.
Due to the multi axial creep deformation of the vessel with a non-uniform temperature field these experiments are on the one hand an excellent source of data to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used to optimize the experimental procedure and can help to make on-site decisions during the experiment.
Therefore an axisymmetric Finite Element (FE) model is developed based on the multi-purpose code ANSYS/Multiphysics®. Using the Computational Fluid Dynamics (CFD) module the temperature field within the melt pool and within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a creep model which takes into account large temperature, stress and strain variations.

We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)3(aq.), in uranium mining related waters /1/. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with Na2EDTA.
Slope analysis of the log (fluorescence intensity) versus log [Ca2+] with both methods have shown that two calcium ions are bound to form the complex Ca2UO2(CO3)3(aq.). The formation constants determined from the two independent methods are: i) log ßo213 = 25.26 ± 0.71 and ii) log ßo213 = 25.57 ± 0.37.
A bathochrome shift of 0.35 nm between the UO2(CO3)34- complex and the Ca2UO2(CO3)3(aq.) complex was observed in the UV-vis absorption spectrum and in the laser-induced photoacoustic spectrum (LIPAS), giving additional proof for the formation of the calcium uranyl carbonate complex.
EXAFS spectra at the LII and LIII - edges of uranium in uranyl carbonate solutions with and without calcium did not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex was obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.
This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.

We studied the complexation of neptunium(IV) with various natural and synthetic humic and fulvic acids at pH 1 using X-ray absorption fine structure (XAFS) spectroscopy to observe the local structure around the neptunium ion. The results were compared to the interaction of neptunium(IV) with Bio-Rex70, a cation exchange resin having solely carboxylic groups. For both neptunium humate complexes and neptunium Bio-Rex70 complexes, 11 oxygen atoms were found at a mean distance of 2.36 Å. This verified that the carboxylic groups of humic substances are responsible for binding neptunium(IV) in the acidic pH range. The humic acid carboxylate groups are predominantly monodentately coordinated to neptunium(IV) ions.

Starting from the tripodal ligand 2,2',2"-nitrilotris(ethanethiol) (NS₃) and isocyanides (CNR) as co-ligands neutral mixed-ligand technetium(III) complexes of the general formulation [Tc(NS₃)(CNR)] have been synthesized and characterized. The ⁹⁹Tc complexes can be obtained by a two-step reduction/substitution procedure starting from [TcO₄]^- via the phosphine-containing precursor complex [Tc(NS₃)(PMe₂Ph)]. As shown by X-ray structural analyses the complexes adopt a nearly ideal trigonal-bipyramidal geometry with the trigonal plane formed by the three thiolate sulfurs of the tripodal ligand. The central nitrogen atom of the chelate ligand and the monodendate isocyanides occupy the apical positions.
The no-carrier-added preparation of the corresponding ^99mTc complexes was performed by a one-step procedure starting from ^99m[TcO₄]^- with stannous chloride as reducing agent.
Biodistribution studies in the rat demonstrated for the nonpolar, lipophilic compounds a significant initial brain uptake. In vitro challenge experiments with glutathione clearly indicated that no transchelation reaction occurs. Furthermore, there were no indications for reoxidation of Tc(III) to Tc(V) species or pertechnetate. We propose this type of complexes as a useful tool in designing of lipophilic ^99mTc or ¹⁸⁶Re/¹⁸⁸Re radiopharmaceuticals.

A theoretical investigation is carried out of the temperature and hydrogen concentration as a function of space in an aluminum workpiece during laser beam welding. The driving force for hydrogen transport is thermal diffusion, where a diffusion current is brought about by a temperature gradient. The sign of the respective transport coefficient is negative for H in Al, which implies that hydrogen will accumulate in the heated regions. Analytical solutions are obtained for the temperature and concentration fields which comprise convective and conductive heat transfer, and hydrogen transport by convection, diffusion and thermal diffusion. The spatial characteristics are discussed in detail using various approximations for the upstream and the downstream region as well as the region close to the keyhole.

PURPOSE:

To check the influence of structural characteristics on their permeation through the blood-Brain barrier (BBB), a set of radioactive [^99mTc]chelates bearing amine groups was synthesized and tested in vitro as well as in vivo.

METHODS:

Compounds with different log P and pK_a values were obtained by complex forming reactions of [^99mTc]pertechnetate with varying substituents. Transport was studied in rats and mice, as well as in an ECV304 cell culture model.

RESULTS:

In vitro higher permeation was found for compounds with electron attracting substituents in beta-position to the amine group (pK_a values 7.4 to 8.3) than for those with more basic amine groups (pK_a values > 8.9) even for similar logD_{ph 7.4}. In vivo brain uptake between 0.8 and 4.8% of the injected dose (ID) per organ was found for the former, whereas < 0.4% ID were present for the latter.

CONCLUSIONS:

Three structurally diverse classes of [^99mTc]chelates showed distinct patterns with regard to brain uptake in vivo and BBB permeability in vitro which could not be predicted by their lipophilicity alone. The close correlation between the data from rats and mice and those obtained with cell cultures render the ECV304 cells an attractive model for the screening of new compounds.

The evolution of strongly interacting matter during the cosmological confimement transition is reviewed. Despite of many proposed relics non specific signal from the rearrangement of quarks and gluons into hadrons has been identified by observations. In contrast to this, several observables in heavy-ion collisions at CERN-SPS energies point to the creation of a matter state near or slightly above deconfinement. We focus here on the analysis of dileptons and direct photons. Similarities and differences of the Big Bang and the Little Bang confinement dynamics are elaborated.

Tc(I) thioether tricarbonyl complexes were prepared and characterised by chromatographic and spectrometric methods. The complexes undergo various ligand exchange reactions in aqueous solutions. In Tc(I) dithioether tricarbonyl complexes of the formula [Tc(CO)₃Cl(S-S)] (S-S = bidentate dithioether ligand) chlorine is substituted by water in aqueous solution. Moreover, we found that Tc(I) tricarbonyl complexes containing a bidentate dithioether ligand, [Tc(CO)₃Cl(S-S)], as well as a tridentate carboxylato dithioether ligand, [Tc(CO)₃Cl(S-S-O)], react with histidine and form the complex [Tc(CO)₃His]. EXAFS measurements were performed to estimate structural parameters of the dissolved Tc(I) tricarbonyl complexes and their substitution products with water and histidine.

Gesamtziel des Vorhabens ist es, den Einfluß der Strömungen in der Schmelze auf die Phasengrenze flüssig-fest im Erstarrungsprozeß zu untersuchen und darüber hinaus eine gezielte Beeinflussung der Konvektion durch geeignete, für den jeweiligen Zweck maßgeschneiderte Magnetfelder vorzunehmen. Die Vielfalt der alternierenden (Strömungsantrieb) und statischen (Strömungsunterdrückung) Magnetfelder erlaubt eine Beeinflussung metallischer Schmelzen in sehr weiten Bereichen.
Umfangreiche Erfahrungen liegen z. B. für die Wirkung rotierender Magnetfelder auf die Strömung vor. Der sich daraus ergebende Einfluß auf das resultierende Erstarrungsgefüge bei reinen Metallen oder binären Legierungen ist teilweise aus der Literatur bzw. eigenen Arbeiten bekannt. Langjährige Vorarbeiten für die Schmelzkontrolle bei Halbleiter-Kristallzüchtungsprozessen bis hin zur industriellen Nutzung derart optimierter Magnetsysteme liegen ebenfalls vor.
Im Projekt sollen systematische Untersuchungen zur Beeinflussung der Erstarrung von Nd-Fe-B-Schmelzen über die Kontrolle der Schmelzströmungen durchgeführt werden. Dazu werden die am IFW Dresden vorhandenen Techniken der Floating-Zone-Züchtung und der elektromagnetischen Levitation eingesetzt. Am Beispiel der Floating-Zone-Züchtung wird demonstriert, wie auf der Basis einer theoretisch-numerischen Analyse der prozeßbedingt im System vorhanden Strömungsarten (Marangoni, HF-Heizung, Auftrieb) eine optimierte und flexible Strömungskontrolle über ein zusätzliches Magnetsystem möglich ist.
Für die elektromagnetische Levitation werden Ergebnisse zur Strömung im Tropfen präsentiert, die sowohl für das Verständnis der Erstarrungsvorgänge als auch die Ermittlung thermophysikalischer Parameter aus derart prozessierten Proben wichtig sind.

We discuss the configurations in which singly and doubly quantized vortex lines coexist in a rotating superfluid. General principles of energy minimization lead to the conclusion that in equilibrium the two vortex species segregate within a cylindrical vortex cluster in two coaxial domains where the singly quantized lines are in the outer annular region. This is confirmed with simulation calculations on descrete vortex lines. Experimentally the coexistence can be studied in rotating superfluid 3He-A. With cw NMR techniques we find the radial distrubution of the two vortex species to depend on how the cluster is prepared: (i) By cooling through Tc in rotation, coexistence in the minimum energy configuration is confirmed. (ii) A disordered agglomerate is formed of one starts with an equilibrium cluster of single quantum vortex lines and adds to it sequentially double quantum lines, by increasing the rotation velocity in the superfluid state. This proves that the energy barriers, which seperate different cluster configurations, are too high for metastabilities to anneal.

Results of experimental investigations of thin films and multilayers of binary systems deposited by PLD at room temperature are presented. Poles of sputtering, implantation, rapid quenching, and solid state diffusion in microstructure formation of thin metal an alloy films synthesized prom pulsed erosion jets are considered. Examples of non-conventional microstructure (amorphization, pseudomorphism, superstructures) formation are given.

Reflektometrieuntersuchung von Fe-Cr-Schichten, die durch Laserablation (PLD) auf einem oxidierten Si(100)-Wafer aufgebracht wurden, mittels Synchrotronstrahlung unter Ausnutzung der anomalen Streuung im Bereich der Fe- bzw.Cr-Absorptionskante. Bestimmung der Interfacebreiten (Sigma rms Rauigkeit) und der Rauigkeitsstruktur (laterale Korrelationslänge und Rauigkeitsexponent) der Fe/Cr-bzw.Cr/Fe-Doppelschichten durch Simulationsrechnungen mit dem Programmcode REFS ( Bede Scientific).

An Eisendisilizid-Einkristallen wurden winkelabhängige Mößbaueruntersuchungen durchgeführt.

Eisen und Magnesium sind über den gesamten Konzentrationsbereich nicht miteinander mischbar. Durch Ionenimplantation ist es jedoch möglich, dünne Legierungsschichten mit beiden Metallen herzustellen.
Bei der vorliegenden Untersuchung wurden Eisenionen in Magnesium implantiert (Energie 200 keV, Dosis bis 1018 /cm²). Die Charakterisierung der so hergestellten Schichten erfolgte mittels Augerelektronen-Spektroskopie, Konversionselektronen-Mössbauerspektroskopie sowie Röntgendiffraktion. Es zeigte sich, dass durch die Implantation Eisenkonzentrationen von über 90 Atom-% erreicht werden konnten. Bei solchen hohen Konzentrationen waren die Schichten magnetisch, es entstand eine Schicht aus a-Eisen, in das Magnesium eingelagert war. Bei niedrigen Eisenkonzentrationen wurde das Eisen auf zwei unterschiedlichen Positionen im Magnesium eingelagert. Temperte man die Schichten bei Temperaturen bis 400 °C, schied sich das Eisen erwartungsgemäss aus

Mittels DCEMS wurde eine tiefenselektive Phasenanalyse der Fe-Disilizid-Bildung in Fe-ionenimplantiertem Si durchgeführt.

Silicon was implanted with high doses of nitrogen and carbon Shallow by PIII.

Reciprocal Space Mapping was performed on Silicon Implanted with Nitrogen and Carbon by
PIII

Porous silicon was implanted with N by PIII.

In some PIII devices the sputtering of the surface under treatment is a problem to overcome.

200 keV Fe ions were implanted into Si(111) at 350 °C .

A DC glow discharge plasma source was used in a PIII experiment.

High-resolution X-ray diffraction methods have been used to characterize nitrogen doped silicon obtained by PIII.

A simple industrially feasible screen printing process for bifacial silicon (Si) solar cells has been developed. The process sequence is based on co-firing of front and rear contacts through surface-passivating remote plasma-enhanced chemical vapour deposited (RPECVD) silicon nitride (SiN) antireflection coatings. Due to the thermal stability of the RPECVD silicon nitride films the firing step results in an excellent front and rear surface passivation which is comparable to a high-efficiency process with vacuum-evaporated metal contacts. The proposed rear surface design is also well-suited for the improvement of the front efficiency of screen-printed monofacial Si solar cells presently produced by the photovoltaic industry. Special attention is paid to the optimisation of the rear efficiency as well as to the understanding of the mechanism of contact formation in the firing-through-SiN process.

A simple magnetic spectrometer for high resolution RBS and NRA has been designed and installed at a dual beam facility, where both beams from a 3 MV Tandetron and a 500 kV implanter are available. The spectrometer is attached to an UHV scattering chamber with a precision 5 axes goniometer for channeling experiments. The spectrometer is described and details of the design are discussed.

Uranium (VI) complexes formation at surfaces of Acidithiobacillus ferrooxidans types was studied using uranium LIII-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. In all samples the uranium is coordinated by two axial oxygen atoms (Oax) at distance of 1.77-1.78 Å. The distance between uranium and the equatorial oxygen atoms (Oeq) is 2.35 Å. To within the experimental error, there are no differences in the U-O bond distances between samples from the 3 types of A. ferrooxidans. The coordination number for Oeq is 5-6. The fit to the EXAFS data of samples measured as wet pastes gave the same results as for dried samples. No significant structural differences were observed for the uranium complexes formed by the eco-types of A. ferrooxidans. However, the EXAFS spectra are indicating formation of uranium complexes which are different from those formed by Bacilli. In addition, Time-resolved laser fluorescence spectroscopy (TRLFS) and Infrared spectroscopy (IR) were performed to obtain complementary information about the exact chemical structure of the uranium complexes formed on the surfaces of A. ferrooxidans types.
Fig:1. k3-weighted ULIII-edge EXAFS spectra (left) and the corresponding Fourrier transform (right) of uranyl complexes with A. ferrooxidans type.

INTRODUCTION: The importance of the intrauterine environment for the fetal brain development has been revealed by studies showing persistent behavioral abnormalities in prenatally stressed animals. Inadequate nutritional supply, mainly due to uteroplacental insufficiency or restricted maternal protein intake in the late gestation period, is mostly responsible for asymmetrical intrauterine growth restriction (IUGR). The immature dopaminergic system appears to be sensitive for inadequate prenatal nutritional supply followed by IUGR in offsprings, because the dopamine content in brainstem of fetal IUGR guinea-pigs is increased despite an unchanged oxygen delivery and an altered dopamine release persisted in IUGR born rats after maternal protein malnutrition. This, is suggested to contribute to etiological factors of the attention deficit hyperactivity disorder, a highly prevalent neurodevelopmental disorder with prefrontal and nigrostriatal dysfunction. However, the effects of IUGR on regional in vivo brain dopamine metabolism have yet not been determined. Therefore, we estimated the AADC activity, the ultimate enzyme in dopamine synthesis, together with the regional cerebral blood flow (CBF), the brain tissue PO₂ and the cerebral metabolic rate of oxygen (CMRO₂) in newborn normal weight (NW) and IUGR piglets.
METHODS: PET studies using FDOPA as tracer were performed in two groups of ten anesthetized (0.5% isoflurane, 70% N₂O, 30% O₂), 2-5 days old NW and IUGR piglets [1]. Blood pressure, gases, glucose and lactate, EEG and ECG were monitored. PET scans (three planes, 35 frames between 30 and 600 s) began simultaneously with the FDOPA injection (30-50 Mbq). 49 arterial blood samples were taken and plasma activity was measured. Plasma metabolites of FDOPA were determined by HPLC in 9 samples (between 2 and 120 min p.i.). The blood-brain clearance K₁ ^FDOPA, the clearance rate constant from brain k₂F^DOPA, the decarboxylation rate constant (k₃ ^FDOPA) and a constant for the clearance pathway (k_cl ^FDA+acids) of F-dopamine metabolites were calculated using a compartment model which corrects for the blood-brain transfer of 3-O-methyl-FDOPA [2]. Additionally, the cerebral blood flow (CBF) was measured with colored microspheres in both groups of animals [3].
RESULTS: In IUGR piglets the body weight was pronouncedly reduced (42% of NW group). Naturally occurring growth restriction in swine is asymmetrical with an increase in the mean ratio of brain weight to liver weight from 0.61±0.16 to 1.42±0.24 (P < 0.01). The reduction in brain weight was quite small (83 % of NW group). In contrast, the decrease in liver weight (35 % of NW group) was similar compared to that in body weight (42 % of NW group). All differences in organ weight were significant (P < 0.01). Physiological values measured for newborn NW and IUGR piglets were consistent with other data obtained from mildly anesthetized and artificially ventilated newborn piglets. The arterial blood pressure, the heart rate, and the arterial glucose content were mildly but significantly lower in IUGR piglets (P < 0.05). Other obtained physiological values such as the CMRO₂, the brain tissue PO₂, and the regional CBF were similar in NW and IUGR piglets. PET time curves of ¹⁸F activity accumulated in the striatum showed a distinctly higher tracer amount in IUGR piglets (P < 0.05). The regional transport of FDOPA to the brain indicated by K₁ ^FDOPA and PS^FDOPA, and the clearance rate of labelled metabolites from brain tissue (k_cl ^FDA+acids) were similar in both groups. However, the regional rate constants for backflux from the brain (k₂ ^FDOPA) was markedly increased in IUGR piglets in the striatum (72%) and the frontal cortex (83%) (P < 0.05). Furthermore, the

Due to significant differences in material properties such as density or
surface tension the behavior of gas bubbles reveals some pecularities in
liquid metal applications as compared with ordinary water flows. Moreover,
questions about the wetting of solid surfaces or the role of impurities which
have a minor importance in water systems show a more dominant influence in
metallic melts.
In this lecture some examples with respect to the bubble generation process,
the dispersion of gas bubbles or the momentum and heat transfer properties
of liquid metal bubbly flows will be presented.
The variety of standard measuring techniques to characterize liquid metal
flows is limited due to the nature of metallic melts. A selection of measuring
techniques will be discussed with respect to their capabilities and
restrictions in various applications.
An interesting point is the possibility to control liquid metal two-phase flows
by the application of external magnetic fields. Some examples will be presented
showing the influence of a stationary magnetic field on the generation of gas
bubbles, on the interfacial momentum transfer or on the turbulent dispersion
of gas bubbles.

Die Erzeugung eines Magnetfeldes allein durch die Strömung einer leitfähigen Schmelze wird von Astro- und Geophysik allgemein als Quelle kosmischer Magnetfelder akzeptiert. Dieser grundlegende physikalische Mechanismus wurde jedoch bis vor kurzem noch nie in einem Laborexperiment nachgewiesen. Am Institut für Physik Riga (Lettland) wurde in enger Kooperation mit der Abteilung MHD des Forschungszentrums Rossendorf seit etwa 6 Jahren ein solches Experiment aufgebaut, das im wesentlichen aus einer helikalen Strömung flüssigen Natriums besteht. Bei den Messungen im November 99 wurde erstmals der Effekt der Magnetfeldselbsterregung beobachtet: Bei maximaler Strömungsgeschwindigkeit wurde ein allmählich wachsendes Magnetfeld gemessen. Die charakteristischen Werte der gemessenen Magnetfeldsignale (Frequenz und Wachstumsrate) stimmen sehr gut mit den vorausberechneten überein. Weitere Messungen vom Juli 2000 bestätigten diese Ergebnisse und lieferten ein konsistentes Bild des Rigaer Dynamos: exponentielles Anwachsen des Magnetfeldes oberhalb der kritischen Strömungsrate, stabiles Magnetfeld auf Sättigungsniveaus im Bereich einiger Hundert Gauss, und axial veränderliche Sättigungsniveaus auf Grund der Rückwirkung der Lorentzkraft auf die Strömung

Experimental results for the stability of electromagnetically levitated solid and liquid spheres are presented. It is shown that the stability is solely determined by the non-dimensional frequency as predicted by theory. Quantitative values are derived for the critical frequency threshold above which rotational or oscillatory motions of the levitated sample occur.

Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR) was applied to study the chemical modification process of humic acids (HA) with diazomethane and the subsequent alkaline hydrolysis of the methylated HA, which results in HA with blocked phenolic OH groups. We investigated different chemically modified and unmodified natural and synthetic HA with carbon-13 of natural abundance. In addition, we studied carbon-13 labeled modified synthetic HA, that were synthesized with [13C]diazomethane as methylation reagent, to confirm the assumed modification process and to determine the type of functional groups that have the highest affinity for methylation.
The results of the NMR studies with carbon-13 labeled HA show that carboxyl and acidic (phenolic) OH groups are methylated with diazomethane. Due to the alkaline saponification of the methylated HA, methyl esters of carboxyl groups are hydrolyzed, whereas phenolic OH groups remain methylated. Carboxyl groups show the highest affinity for methylation.
From the spectra of the modified and unmodified HA with carbon-13 of natural abundance it can be concluded that the applied modification procedure causes only the desired structural changes in HA.

Die bildgebende Darstellung funktioneller Vorgänge im lebenden Organismus bei gleichzeitiger Möglichkeit ihrer Quantifizierung ist nur mittels der Positronen-Emissions-Tomographie möglich. Dazu ist die Entwicklung und Anwendung von Radiotracern erforderlich, die mit Positronen emittierenden Radionukliden markiert sind. Das entsprechende Radionuklid mit den günstigsten kernphysikalischen Eigenschaften ist Fluor-18 (Halbwertszeit 110 min)[1]. Eine spezielle Aufgabenstellung ist die Darstellung von Rezeptorarealen, die nur in sehr niedrigen absoluten Stoffmengen vorliegen, weshalb auch der Radiotracer in sehr niedrigen Konzentrationen eingesetzt werden muss. Dementsprechend müssen Fluor-18 - markierte Verbindungen mit einer sehr hohen molaren Aktivität (spez. Aktivität) zum Einsatz kommen. Dies bedeutet ein sehr kleines Verhältnis zwischen den identischen fluorierten Molekülen, die mit nicht-radioaktivem Fluor und Fluor-18 versehen sind.
Anwendungsgebiete sind in der Nuklearmedizin und die Anwendung von deren Methoden in der Pharmakaentwicklung sowie biochemischen Grundlagenforschung.

Der Fluorierungsschritt, die Markierung mit Fluor-18, ist bei der Synthese solcher Radiotracer von besonderer Wichtigkeit.
Zunehmendes Interesse haben Verbindungen, bei denen das Fluoratom an elektrophile Gruppen gebunden ist. Die elektrophile Einführung von Fluor-18 in entsprechende Moleküle wurde bisher stets ausgehend von [¹⁸F]F₂ durchgeführt, wobei die Zugabe einer großen Menge an nicht-radioaktivem Fluor (10...100 µmol F₂) erforderlich ist.

Bei der Suche nach einer Alternative zur Verwendung elementaren Fluors bieten sich elektrophile Fluorierungsmittel an, die ausgehend von [¹⁸F]Fluorid ohne Zusatz von nicht-radioaktiven Fluoriden hergestellt werden müssen [2].

Perchlorylfluorid FclO₃ ist die einzige elektrophile Verbindung, die z.Zt. ausgehend von Fluorid, d.h. ohne die Verwendung elementaren Fluors, hergestellt werden kann. Ausgehend von Literaturdaten wurde eine Synthese erarbeitet die es gestattet, [¹⁸F]FclO₃ ohne Trägerzusatz in Stoffmengen von ca. 50 nmol bei einem hohem Radioaktivitätsniveau herzustellen. Ausgangsprodukt ist stets wässrige [¹⁸F]HF- Lösung.

Die Umsetzung erfolgt nach Entfernung des Wassers unter streng wasserfreien Bedingungen als Eintopf-Reaktion. Die wasserfreie HclO₄ wird durch Destillation durch P₄O₁₀ gewonnen, die HF-Lösung mittels Oleum entwässert.
Vorgehensweise: Wasserfreie HclO₄ wird in ein Gemisch von Oleum/[¹⁸F]HF aqu. eindestilliert. Nach kurzer Wartezeit wird das entstandene [¹⁸F]FclO₃ (Gl.1) in eine Vorlage abdestilliert, in der sich eine Lösung eines metalliertern Präkursors (Carbanionen in Form von Na-diethylmalonsäurediethylester oder Phenyllithium) befindet. Durch die Umsetzung mit diesen Substanzen (Gl.2, Gl.3) erfolgt gleichzeitig der Nachweis des gebildeten [¹⁸F]FclO₃ unter Nutzung der Radio-HPLC.

[¹⁸F]HF + HClO₄ _ _ [¹⁸F]FClO₃ (1)
[¹⁸F]FClO₃ + NaCH(COOEt)₂ _ [¹⁸F]FCH(COOEt)₂ (2)
[¹⁸F]FClO₃ + C₆H₅Li _ [¹⁸F]C₆H₅F (3)

Der mögliche Mechanismus wird diskutiert.

Die bisher erreichte radiochemische Ausbeute liegt bei 6 % (zerfallskorrigiert). Damit können erstmals elektrophile Radiofluorierungen mit Fluor-18 ohne Trägerzusatz vorgenommen werden.

Literatur:

[1] Yu-Shin Ding, J. Fluorine Chem.101(2000) 291-295
[2] J. Steinbach, Chr. Fischer, K. Neubert, B. Johannsen, XIIth International Symposium on Radiopharmaceutical Chemistry,
Uppsala, Sweden, June 15-19, 1997, Abstracts S. 14-16

It has been found that phase transformations in implanted iron may strongly depend on the sample thickness. The effect essentially relies on lower impurity concentration required for given phase formation in thin films when compared with thick layers or bulk samples and most likely should be attributed to the stress formed during layer deposition. The phase transformation in thin films is also more complete, for example full transformation of thin iron layers into iron nitrides was observed, whereas in thick and bulk samples about 20 % of Fe atoms in implanted layer remain in crystalline alpha-Fe phase.

Ultrafine-grained (UFG) high purity nickel samples produced by equichannel angular pressing were submitted to thermal treatment and cyclic plastic deformation at different temperatures in order to investigate the stability of the defect structure. After annealing recrystallization already occurs in a temperature range between 425K - 475K. Impurities increase the recrystallization temperature. At room temperature cyclic plastic deformation induces a coarsening of grains and subgrains and at 425K a dynamic recrystallization. Additionally , the mean volume expansion, long-range and short-range internal strains, investigated by synchrotron radiation diffraction for the UFG deformation stage are diminished in consequence of cyclic plastic deformation.

Für die Bewertung des Gefahrenpotentials bei der Herstellung von Grignard-Reagenzien sind neben der sehr hohen Exothermie der Grignard-Reaktionen vor allem deren spontanes Startverhalten von entscheidender Bedeutung. Um Störfälle in industriellen Chemieanlagen zu vermeiden, darf ein Reaktionsstart nicht mehr bei einer hohen Akkumulation des Arylhalogenids erfolgen. Zu diesem Zweck werden die reaktions-technischen Parameter des Startprozesses am Beispiel einer häufig industriell angewendeten Grignard-Reaktion in einem geschlossenen Reaktionskalorimeter untersucht. Die Ergebnisse zeigen, dass neben online-FTIR-Konzentrationsmessungen auch der Anstieg der Reaktortemperatur und des Druckes zur Überwachung des Startens der Grignard-Reaktion genutzt werden können.

The aim of the presentation is to give an overview of the equipment and the experimental activities of the Dep. of Experimental Fluid Dynamics relating to the investigations on exothermic chemical processes.
The experimental equipment consists of several reaction calorimeters, analytical instruments and a modular computer controlled miniplant.
With the help of this equipment a number of processes were investigated on the basis of industrial contracts and research projects.
The research results are presented with two examples:

• the calorimetric investigations of the formation of Grignard reagents
• the characterization of reaction pathways and process kinetics of the catalytic hydrogenation process of a special nitroaromatic compound.

Im Rahmen der externen Validierung des von der Gesellschaft für Anlagen- und Reaktorsicherheit entwickelten Störfallcodes ATHLET, der in der Version Mod 1.2 Cycle C vorlag, wurden zwei Experimente nachgerechnet und analysiert, die an der japanischen Versuchsanlage CCTF durchgeführt wurden.
Die Versuchsanlage CCTF ist ein 1:25 volumenskaliertes Modell eines 1000 MW Druckwasserreaktors. Bei den Experimenten handelt es sich um die Versuche C2-04/62 und C2-19/79, in denen jeweils ein 2F-Bruch im kalten Strang mit kaltseitiger bzw. kombinierter Notkühleinspeisung simuliert wurde. Die Versuchsanlage wurde so ausgelegt, daß die Wiederfüll- bzw. Wiederflutphase bei Druckwasserreaktor-Störfällen mit großem Leck simuliert werden kann.
Die Auswertung der Rechnungen zeigt, daß die wesentlichen Phänomene im Verlauf der Transiente gut wiedergegeben werden. Das betrifft vor allem das zeitliche Verhalten der Wiederbenetzungsfront und die damit verbundene Kühlung der Brennelemente. Wie eine Analyse der experimentellen Daten zeigt, spielen im Reaktorkern radiale Effekte eine wesentliche Rolle. In der CCTF Anlage wird sowohl eine axiale als auch eine radiale Leistungsverteilung im Kern simuliert. Radiale Effekte treten insbesondere bei der kombinierten Notkühleinspeisung auf. Hier wird die Einspeisung über das Obere Plenum durch den in Gegenrichtung strömenden Dampf teilweise behindert. Die Wiederbenetzungsfront schreitet in den Randbereichen schneller voran als im Zentrum. Dieses Verhalten wurde in den ATHLET-Rechnungen durch eine Zweikanal-Modellierung des Reaktorkerns nachgebildet. Die Ergebnisse der ATHLET Rechnungen zeigen sowohl für das Zentrum als auch für die Randbereiche des Kerns eine gute Übereinstimmung mit den experimentellen Daten.
Die Schwachstellen der Rechnungen liegen vor allem bei der Notkühleinspeisung in der Anfangsphase der Transiente. Hier wird kaltes Notkühlwasser in Volumina mit reinem Dampf eingespeist. Die Rechnungen liefern dabei zu hohe Kondensationsraten, welche mit einer unrealistischen Druckabsenkung verbunden sind. Desweiteren wird der Druckaufbau durch die Verdampfung beim Wiederbenetzen der Brennelemente offensichtlich unterschätzt.
Die Ergebnisse der Rechnungen zeigen darüberhinaus, daß die sicherheitsrelevanten Aussagen der Experimente durch den Code ATHLET reproduziert werden.

An overview of the research activities of the FIB group in the Research Centre
Rossendorf is given. More in detail the fabrication technology of alloy LMIS as well
as their characterization is discussed. The FIB system IMSA-100 is briefly
introduced and typical applications are presented: writing implantation of Co ions
into a heated Si target in order to create maskless sub-micron CoSi2 structures,
bombardment of semiconductor materials with different ions in a wide range of
current density, dose and temperature allows to study the damage creation and
dynamic annealing process.

Simplified theoretical models are presented for the highly coupled phenomena of heat transfer, convection and solidification during VGF crystal growth. The models are essential in order to inverse the general approach: optimal conditions at the solidification front can be translated into temperature conditions at the heaters and the corresponding heater regimes. The Stefan problem of the unknown geometry of the solidification front is solved in a simplified analytical way in good approximation with the full numerical solution.

The theory of magnetic field generation in cosmic bodies due to the homogeneous dynamo effect has been widely elaborated during the last decades. However, an experimental verification of this effect was still missing until recently. At the Riga dynamo facility, self-excitation of a magnetic field in a liquid metal flow has been observed for the first time in November 1999. For increasing rotation rate of the driving propeller, the amplification of an applied magnetic field has been measured. At the highest rotation rate of 2150 rpm, an exponentially increasing 1.3 Hz signal has been detected on the background of the amplified 1 Hz signal. Additionally, after switching off the excitation current at a slightly lower rotation rate, a slowly decreasing eigenmode was observed. The results are shown to correspond convincingly with numerical predictions.

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Ein wichtiges Thema der Sicherheitsforschung zum Störfallverhalten von Druckwasserreaktoren sind Reaktivitätsstörfälle. Beispiele für solche Transienten sind Lecks im Frischdampfsystem und Borverdünnungstransienten. Wenn zu kaltes Wasser oder Wasser mit einer zu geringen Borkonzentration in den Reaktorkern gelangt, kann es zu einem so hohen Reaktivitätseintrag kommen, dass der abgeschaltete unterkritische Reaktor wieder kritisch wird. Einerseits kann es bei einem Leck auf der Dampferzeuger-Sekundärseite zu einer Unterkühlung des Kühlwassers auf der Primärseite in dem entsprechenden Loop kommen. Die Unterkühlung kann bis zu 100 K gegenüber der normalen Kereintrittstemperatur betragen. Andererseits besteht die Möglichkeit, dass sich bei einem kleinen bis mittleren Leck im Primärkreis bei teilweisen Ausfall der HD-Notkühlung und Reflux-Condenser-Bedingungen Kondensat in den Dampferzeuger-Kollektoren und den Pumpenbögen ansammelt. Nach dem Wiederauffüllen des Kreislaufes und Anlauf der Kühlmittelzirkulation würde unterboriertes Wasser in den Kern gelangen. Ob der zuvor abgeschaltete Reaktor wieder kritisch wird und wie hoch die Leistungsspitze dabei ist, hängt davon ab, wie weit sich das kalte oder zu schwach borierte Wasser auf dem Wege von den Kühlschleifen durch den Ringraum und das untere Plenum zum Reaktorkern mit dem heißeren und hochborierten Kühlmittel im Reaktor vermischt. Aus diesem Grunde werden an der ROCOM-Versuchsanlage im Institut für Sicherheitsforschung des FZR generische Vermischungsuntersuchungen durchgeführt. Sie dienen vorrangig der Validierung von CFD-Berechungen zur Simulation der verschiedenen Vermischungsszenarien.

We investigate the temperature dependence of the mass spectrum of the ion beam emitted by an Au77Ge14Si9 liquid metal alloy ion source. Our results strongly point towards the co-existance of two mechanisms for the emission of doubly-charged monomer ions: direct field evaporation and post-ionization.

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

After the dynamo experiment in November 1999 had shown magnetic field self-excitation in a spiraling liquid metal flow, in a second series of experiments emphasis was placed on the magnetic field saturation regime. The dependence of the strength of the magnetic field on the rotation rate is studied. Various features of the saturated magnetic field are outlined and possible saturation mechanisms are discussed.

We demonstrate the realization of a quantum cascade laser (QCL) based on strained InGaAs/AlGaAs/GaAs grown on GaAs substrate using molecular beam epitaxy. The material is compared to a GaAs/AlGaAs structure with nominally identical radiative transitions. Lasing at 10 microns was achieved in the strained and the unstrained material. The strained material shows an improved temperature performance with a T0=112K between 125 K and 200 K and a maximum working temperature of T=200 K.

This paper presents a digitized version of a thermodynamic sorption database, implemented as a relational database with MS Access. It is mineral-specific and can therefore also be used for additive models of more complex solid phases such as rocks or soils. An integrated user interface helps users to access selected mineral and sorption data, to extract internally consistent data sets for sorption modeling, and to export them into formats suitable for other modeling software. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. An extensive bibliography is also included, providing links not only to the above listed data items, but also to background information concerning surface complexation model theories, surface species evidence, and sorption experiment techniques.

The monoenergetic positron beamline ‚SPONSOR' at Rossendorf has been used to investigate the positron behaviour in a naturally grown Brasilian quartz, two synthetic quartz crystals of different origin, and synthetic silica glass. The measurements allow to obtain the positron diffusion length of free positrons and Bloch para-positronium (p-Ps), if formed, in these materials.
In addition, hydrothermal treatment of a synthetic quartz has been used to introduce hydrogen into the crystal up to a certain depth. The presence of hydrogen is found to influence the formation of p-Ps. The depth distribution of hydrogen has been measured independently by nuclear reaction analysis (NRA), and will be discussed in comparison with the depth results deduced from the positron studies.

Im vorliegenden Bericht werden Anwendung und Ergebnisse rauschdiagnostischer Untersuchungen von Schwingungen, die zu Beschädigungen der Einbauten des Reaktordruckgefäßes geführt haben, im Detail beschrieben. Sie waren in den Jahren 1975 bzw. 1985 an den WWER-440/230-Reaktoren der russischen Baureihe der Blöcke 1 und 2 des Kernkraftwerkes Greifswald aufgetreten. Der Bericht enthält die wesentlichen Angaben zum Betriebsverhalten während des gestörten Betriebes, die Inspektionsergebnisse, die charakteristischen experimentellen Befunde unter Verwendung rauschdiagnostischer Analysemethoden, die physikalische Aufklärung des Schwingungsprozesses und seiner Ursachen durch spezielle Untersuchungen sowie einige Empfehlungen zur Schwingungsüberwachung und -minimierung.

The intermetallic compound TiAl is very interesting for high temperature application due to its high temperature strength and low density. Above 700 °C, the use in e.g. aircraft engines is hindered because of a low oxidation resistance. Even though the compound contains 50at% Al, this is not sufficient to form a protective Al2O3 scale. Instead, a mixed oxide scale composed of TiO2 and Al2O3 is formed. Extended alloy development has shown, that additional elements which are beneficial for the oxidation often have a bad influence on the mechanical bulk properties. Cl doping has a strong effect even in very low concentrations of about 500 ppm ("Microalloy"). Ion Implantation of 1016 Cl/cm2 protects TiAl at 900 °C for up to 1000 h against oxidation in a wide range of implantation energies.

In order to apply this effect for complicated shaped parts, the high temperature oxidation behavior after plasma immersion ion implantation of chlorine into different TiAl alloys was investigated. A specialized chamber has been setup up for the strongly etching Cl plasma. Particularly with regard to contaminations, the chamber and the RF- antenna had to be made from aluminum. Since it is known that the Cl effect in TiAl requires a well defined Cl concentration, a variation of the implantation parameters has been performed. The resulting depth profiles of Cl are investigated using depth profiling with Auger electron spectroscopy (AES). After treatment (3*105 to 3*106 30 kV pulses of 5µs at a repetition rate from 150 Hz to 1500 Hz), the Cl is located close to the surface. The process is governed by the interplay between etching and implanting during the HV pulses. Therefore the retained dose depends mainly on the temperature during implantation, which is controlled by the repetition rate of the pulses. Oxidation tests at 900°C in air for 100 h showed a strong reduction of the oxidation, which are comparable to conventional beam line im-plantations of Cl.

In der Energie- und der Verfahrenstechnik spielen Zweiphasenströmungen eine wichtige Rolle. Sie treten in Rohrleitungen und Apparaten auf, und beeinflussen dort chemische Reaktionen, sowie Wärme- und Stoffübergänge. Um die komplexen Vorgänge in den Zweiphasenströmungen modellieren zu können, bedarf es der Ergebnisse umfangreicher Experimente. Zur Ermittlung der charakterisierenden Parameter einer Zweiphasenströmung, wie die Phasenverteilung und die Strömungsgeschwindigkeiten, ist eine Messtechnik notwendig, die eine räumlich und zeitlich hochaufgelöste Visualisierung der Strömung ermöglicht. Für diese Aufgabe eignen sich bspw. konduktive Messverfahren.

Im Institut für Sicherheitsforschung des FZ Rossendorf wurde in den vergangenen Jahren ein Gittersensor zur Untersuchung von Zweiphasenströmungen entwickelt. Dieser basiert auf der Messung der momentanen lokalen elektrischen Leitfähigkeit des Zweiphasengemischs. Er ermöglicht eine hochaufgelöste Visualisierung der Strömung. Bei einer Reihe unterschiedlicher Experimente wurde die Anwendbarkeit des Gittersensors zur Ermittlung der Phasenverteilung in einer Zweiphasenströmung nachgewiesen.

In dieser Arbeit soll die Genauigkeit des Gittersensors bei der Ermittlung von Blasengrößen untersucht werden. Dafür wurde ein Plexiglaskanal angefertigt, in den die Elektroden des Sensors direkt eingebaut wurden. Da es nicht möglich war, für einen Vergleich in der Kanalströmung einzelne Blasen mit einem definierten Volumen zu erzeugen, wurde die Bewegung der Blasen in diesem Kanal mit einer Hochgeschwindigkeits-Videoeinrichtung erfasst. Mit beiden Verfahren wurden synchron Messungen bei unterschiedlichen Strömungsgeschwindigkeiten und mit verschiedenen Blasenvolumen durchgeführt. Mit Hilfe von Rechnerprogrammen wurden aus den Kamerabildern die Durchmesser der Blasen bestimmt und daraus die Volumen berechnet. Damit konnten die ermittelten Blasenvolumen des Gittersensors mit denen der Kameraaufnahmen verglichen werden. Dieser Vergleich ließ qualitative und teilweise quantitative Aussagen über die Genauigkeit des Gittersensors zu.

For the analysis of the core behaviour during boron dilution transients and main steam line breaks, coupled neutron kinetic / thermal hydraulic codes are necessary. These codes (e.g. DYN3D-ATHLET) must contain models of the coolant mixing on its way from the inlet noz-zles to the core entrance, because the reactivity insertion strongly depends on the distribution of temperature and boron concentration at the core inlet. The coolant mixing mainly happens in the three-dimensional flow field inside the complex geometry of the downcomer and lower plenum. The modelling of coolant mixing was carried out by detailed computational fluid dynamics (CFD) calculations with the code CFX 4.3. For the validation of the computational results, the ROCOM test facility was built, a fluid dynamic 1:5 scaled model of the Konvoi reactor. The reactor vessel is made of Plexiglas for flow visualisation and LDA measure-ments. The use of a system of wire-mesh sensors allows to measure salt concentrations at over 1000 locations with a maximum time resolution of 200 Hz. In case of stationary coolant flow in all loops a disturbance of boron concentration or temperature is transferred to a sector of the core inlet plane, which corresponds to the location of the inlet nozzle. A short plug of boron diluted water experiences a better mixing: due to the vortices in the downcomer different por-tions of the disturbance are transported with different velocities. This causes a dispersion of the front and the end of the plug (axial mixing). Further, experiments and calculations are go-ing on to investigate mixing under transient conditions (start of circulation).

Model experiments with low-energy ions under controlled vacuum conditions have been performed in order to identify the surface processes and the diffusion mechanism associated with the nitrogen transport during ion nitriding of stainless steel 316 and pure aluminium. A necessary condition for an efficient nitriding is the transmission of the implanted ions through a surface oxide layer which results from a balance of ion sputtering and re-oxidation from the residual gas. For ion energies around 1 keV and ion current densities around 0.2 mA/cm2, oxygen partial pressures of less than about 3A10-6 mbar and 3A10-7 mbar are required for stainless steel and aluminium, respectively. Diffusion under the influence of traps controls the transport of nitrogen in stainless steel, with dynamic trapping at the Cr atoms of the alloy. In contrast, stoichiometric AlN grows on aluminium due to Al diffusion from the underlying bulk. From the surface and diffusion mechanisms, limitations of plasma nitriding and plasma immersion ion nitriding are derived, and the implications for industrial applications are discussed.

Five-coordinate oxotechnetium(V) mixed-ligand complexes [TcO(SES)(S-p-C₆H₄-OMe)], where SES is a tridentate dithiolato fragment of the type ^-S(CH₂)₂E(CH₂)₂S^- (E = O, 1; E = S, 2; E = NMe, 3) are converted via reduction-substitution reactions in the presence of PMe₂Ph into the corresponding five-coordinate Tc(III) complexes [Tc(SES)(S-p-C₆H₄-OMe)(PMe₂Ph)] (E = O, 4; E = S, 5; E = NMe, 6). Rearrangement of the original square pyramidal '3 + 1' oxo-species to the trigonal bipyramidal '3+1+1' Tc(III) complexes occurs by placing the three thiolate donors on the basal plane, the phosphine phosphorus and the heteroatom of the tridentate ligand at the apexes of the bipyramid. These Tc(III) complexes are diamagnetic species, thereby allowing multinuclear NMR characterization in solution, which confirm their structures to be identical to those observed in the solid state via X-ray determinations.

Introduction:

Choline is the metabolic precursor of neurotransmitter acetylcholine and of the membrane phospholipid phosphatidylcholine. This amine is not synthesized by the brain and is therefore taken up from the blood. It is transported by a specific transport system which is much less characterized than the transporter for glucose and amino acids. Carnitine which is important for the intracellular transport of fatty acids has been found to inhibit the choline transport. On the other hand specific transporters for carnitine are known (OCTN1, OCTN2) which have not been described at the blood-brain-barrier (BBB) up to know. Therefore we have studied the transport of the two amines at an in vitro model of the BBB. In this study, we have demonstrated that at least two different transport systems for choline and carnitine are functionally expressed.
Methods:
The RBE4 cell line was used as an in-vitro model of the BBB and it has been shown that these cells express typical BBB markers such as gamma-glutamyltransferase and alkaline phosphatase(1). Tracer uptake studies were performed in 24 multi-well plates using buffers containing either 25 mM Tris/Hepes (pH 8.5 for choline uptake) or 25 mM Hepes/Tris (pH 7.5 for carnitine uptake), supplemented with 0.5% albumin, 5 mM glucose, 5.4 mM KCl, 1,8 mM CaCl₂, 0.8 mM MgSO₄ and 140 mM NaCl. Whenever Na⁺-free buffers were used, NMDG chloride replaced NaCl isoosmotically. Cells were washed before starting the uptake and then incubated at room temperature (choline uptake) or 37°C (carnitine uptake) with radiolabeled substrates added to the incubation buffer. K_m values and V_max values were calculated from the uptake data. Specific inhibitors of the transporters were added to the incubation buffer to study the specificity of the process.
An RBE4 cell cDNA library was constructed using the Superscript plasmid system. This plasmid cDNA library, grown on NitroPure transfer membranes, was screened by the colony screening method as described by Vogeli and Kaytes (2). The cDNA probe used for screening was 2.1 kb pair long and consisted of most of the coding region of rOCTN2 cDNA. The probe was labeled with [alpha-₃₂P]dCTP using the ready-to-go oligolabeling kit, and used to screen the RBE4 cDNA library under low stringency conditions. The cDNA was functionally expressed in HeLa cells by vaccinia virus expression system (3). Transport measurements were made at room temperature using the same uptake buffer as described above without albumin.
Results:
The RBE4 cells express a Na⁺-independent choline transporter. Hemicholinium, an inhibitor for the Na⁺-dependent choline transporter, also inhibits the choline uptake found in these cells while tetraethylammonium (TEA) does not. The uptake of choline is saturable with a K_m value of 22 µM and a V_max of 515 pmol/(mg protein * 10 min).
We also isolated a full-length OCTN2 clone from the RBE4 cDNA library. HeLa cells transfected with this clone express Na⁺-independent TEA uptake and Na⁺-dependent carnitine uptake. These transfected cells also take up fatty acid esters of carnitine like propionylcarnitine and acetylcarnitine. The K_m value for the carnitine uptake at 37°C in RBE4 cells is about 50 µM. Specific inhibitors for the OCTN2 transporter (MPP⁺ and TEA) inhibit the carnitine uptake in RBE4 cells.
Comments:
In summary, we have found two separate transporters for choline and carnitine are expressed in the RBE4 cells. While the choline transporter is expected to supply the brain with choline for neurotransmitter synthesis OCTN2 is described as an carnitine carrier which also transports short fatty acids as carnitine esters through the cell membrane. The expression of OCTN2 at the BBB may help to understand the way of supplying the brain with acetyl groups for the synthesis of acetylcholine ...

The paper presents a method for the prediction of the radial gas fraction profile in vertical pipe flow for a given bubble size distribution. A large number of bubble classes is considered. An equilibrium of the forces acting on a bubble perpendicular to the flow direction is assumed. On basis of the radial profile of the liquid velocity, radial distributions of the volume fraction are calculated separately for all bubble classes according to a given bubble size distribution. The sum of these distributions is the radial profile of the gas fraction. It again influences the liquid velocity. The final solution is obtained by an iteration process, which consideres the feedback between the gas fraction profile and the profile of the liquid velocity. The model is the basis of a fast running one-dimensional steady state computer code. The results of the model are compared with experimental data for a number of gas and liquid volume flow rates.

The wire-mesh sensor developed by the Forschungszentrum Rossendorf produces sequences of instantaneous gas fraction distributions in a cross section with a time resolution of 1200 frames per second and a spatial resolution of about 2-3 mm. At moderate flow velocities (up to 1-2 m/s), bubble size distributions can be obtained, since each individual bubble is mapped in several successive distributions. The method was used to study the evolution of the bubble size distribution in a vertical two-phase flow. For this purpose, the sensor was placed downstream of an air injector, the distance between air injection and sensor was varied. The bubble identification algorithm allows to select bubbles of a given range of effective diameter and to calculate partial gas fraction profiles for this diameter range. In this way, the different behaviour of small and large bubbles in respect to the action of the lift force was observed in a realistic flow situation.

In this paper we report on the design of a decel lens system for low energy ion implantation. The novel lens system consisting of a converging and a diverging lens in a compact arrangement allows to compensate the spherical aberration. Therefore implantation into large areas at low energies can be performed with high dose uniformity. The implantation chamber with the decel lens system is fitted to the beamline 2 of the medium energy implanter DANFYSIK 1090 at the Forschungszentrum Rossendorf. Using a beam energy of 30 keV the ions can be decelerated up to 2 keV with a dose uniformity of < 5% for 100 mm diameter.

The ever increasing demands for high precision machining and increased cutting performance, in terms of cutting speed and lifetime, require wear resistant tools of large dimensional accu-racy that have very sharp cutting edges. All these requirements can not be fulfilled by the clas-sic PVD and CVD technologies because they result in rather thick overlay coatings.
In this report, first experiments are presented on a hybride plasma immersed ion implantation process (PIII) for depositing thin TiN coatings on hardened and annealed high speed steel or cemented carbides. The layers were produced using a dc-cathodic arc source with a titanium cathode and a nitrogen feed gas. As the cathodic arc generates additional to the metal plasma, a large amount of liquid metal droplets, the plasma was guided to the samples through a 900 magnetic bending field avoiding the deposition of droplets on the samples. The obtained layer thickness was below 1 µm for deposition times of 2 min.
To improve the adhesion of the deposited layers on the substrate materials, of energetic ions were used during the initial phase of the process. Hereto negative high voltage pulses in the range from zero to 5 kV have been applied to the samples during the deposition. The effect of the energy of these ions on the coating structure was also investigated by SEM, TEM and XRD. Mechanical and functional properties were investigated by hardness measurements and fretting wear tests respectively. Finally cutting performance tests of PIII-treated drills were performed, revealing that a 0.8µm thick TiN PIII-coating increased the lifetime of the drills by a factor of 2.5.

We have studied the interminiband absorption and the current-voltage characteristics on the same GaAs/AlGaAs superlattices. The Esaki-Tsu type negative differential resistance is observed as well as the thermal (de)population of the minibands. The possibility of mapping the nonequilibrium electron distribution function through infrared absorption measurements under bias is discussed.

Stress is a common property of thin films. After a brief summary of origins and effects of stresses in thin films the particular situation in amorphous and nano-crystalline films is discussed. The problems related to the extremely high compressive stresses in cubic boron nitride (cBN) have been tackled either by the deposition of buffer layers or by attempts to reduce the stress in the film. These approaches are compared and discussed. Intrinsic stress depth profiles in BN films, as well as the influence of post-deposition thermal treatment and ion irradiation on the global stress, as obtained from in-situ cantilever bending measurements, are reviewed. A technique for the growth of cBN films with significantly reduced compressive stress is demonstrated.

An intensity modulated focused ion beam (FIB) which is hitting the surface of a solid, heats up a small near subsurface region to a temperature which is sufficient for thermal elastic wave generation. The measurement of these waves can be used for analysis and imaging of surface as well as subsurface structures in the material. The modified FIB equipment IMSA-100 working with 35 keV Ga+ and Au+ ions, respectively, and a current of about 3 nA was employed to obtain acoustic images from structures on silicon and glass targets. The acoustic signals were detected using a PZT transducer delivering an output voltage of 50 - 100 nV. The modulation frequency was varied in the range of 60 - 170 kHz. The obtained lateral resolution of the ion acoustic images at these frequencies was about 15 µm on silicon and about 7µm on glass, respectively. Furthermore some estimations due to the reachable resolution and a short description of the set-up is given.

The surface hardness of the titanium alloy Ti-6Al-4V, widely used as construction material, can be improved by nitrogen implantation. The paper reports on a complex study of the structural mechanisms of hardening and its loss at higher temperatures with different methods (grazing incidence X-ray diffraction, in-situ high temperature diffraction with synchrotron radiation, ERDA, hardness and surface inspection by SEM). Plasma immersion ion implantation produces a nitrogen profile directly below the surface. The formation of small TiN crystallites is detected but the hardness increase is only about 40%. Annealing leads to the reduction of the TiN phase and the formation of Ti2N deeper in the material. The in-situ XRD study of the phase formation gives information about the temperature range of the changes. The hardness increases after annealing by a factor of 2.5 compared to the unimplanted state. It is explained by precipitation hardening due to the formation of titanium nitrides in different depths of the material.

Real-time ellipsometry (RTE) in combination with particle flux measurement is applied to ion beam assisted deposition (IBAD) of boron nitride (BN) films. RTE is used as a toll for process diagnostic to improve the deposition stability. A novel technique for the determination of absolute density depth profiles from dynamic growth rate data and film forming particle flux is employed. From real-time cantilever curvature measurement and simultaneously recorded film thickness data instantaneous stress depth profiles are derived with a depth resolution in the nm--range. The synergistic effects on the information obtained from RTE, particle flux, and cantilever bending data are demonstrated. The density of turbostratic BN (tBN) is found to increase slightly with film thickness while the compressive stress decreases, indicating an increasing quality and/or size of crystallites in the course of film growth. Refractive index and density depth profiles in cubic BN (cBN) films correspond perfectly to structural information obtained from dark field TEM graphs. The established tBN/cBN 2-layer model is found to be a crude approximation that has to be replaced by a 3-layer model including nucleation, grain growth, and coalescence of cBN. The instantaneous compressive stress in a homogeneous tBN film is found to decrease while the density increases during growth. The instantaneous compressive stress depth profiles in cBN films are more complex and not easy to understand but reliable information on the structural evolution during growth can be extracted.

Gegenstand der vorliegenden Arbeit ist die Weiterentwicklung von Verfahren zur Ermittlung der Rißeinleitungszähigkeit (Jid) unter schlagartigen Belastungsbedingungen. Als Indikationsmethode für die duktile Rißinitiierung wurde die Messung der unter Beanspruchung im Werkstoff freigesetzten elastischen Energie - der Schallemission (SE) - genutzt.

Die Eignung dieser Methode wurde im instrumentierten Kerbschlagbiegeversuch an modifizierten ISO-V-Proben geprüft. Als zuverlässige Basis für eine Beurteilung der damit bestimmten Kennwerte wird die physikalische Rißinitiierungszähigkeit angesehen. Dieser Referenzwert wird in Verbindung mit der Messung der Stretchzonenbreite aus der nach der Mehrpro-ben-Spaltbruchmethode ermittelten Rißwiderstandskurve gewonnen. Die Bestimmung des SE-definierten Initiierungswertes wurde mit zusätzlichen dynamischen Einprobenverfahren (Laser-COD, magnetische Emission) und ergänzenden Versuchsanordnungen (invertiertes Pendelschlagwerk, dynamischer Dreipunktbiegeversuch) verifiziert. Die Untersuchungen wurden an Stählen mit unterschiedlichen Festigkeits-Zähigkeitseigenschaften durchgeführt.

Die Ergebnisse lassen sich wie folgt zusammenfassen:

• Nach dem Aufprall des Hammers führen die rasch wechselnden Kontaktbedingungen zwischen Finne, Probe und Widerlager zu „schlagbedingter" SE, die frequenzselektiv nicht eliminiert werden kann. Geringfügige Änderungen der Kontaktgeometrie beeinflussen die schlagbedingte SE.
• Unabhängig von der verwendeten Versuchsanordnung (normal, invertiert) wurden grund-sätzlich vergleichbare SE-Signale erhalten.
• Neben der schlagbedingten SE lassen sich reproduzierbar SE-Ereignisse nachweisen, die mit Verformungs- und Bruchprozessen im Werkstoff in Verbindung stehen. Bei prellfreier Belastung konnten solche SE-Ereignisse im Streckgrenzenbereich nachgewiesen werden.
• Vor dem Kraftmaximum treten „rißbedingte" SE-Ereignisse auf, die im Zusammenhang mit der Schädigungsentwicklung vor der Rißspitze stehen. Die damit definierte Rißinitiierungszähigkeit stimmt gut mit dem nach der Mehrproben-Technik bestimmten Referenzwert überein.
• Rißbedingte SE tritt nicht bei jedem Stahltyp oder -zustand mit gleicher Evidenz auf. Tendenziell zeigte sich, daß mit zunehmender Zähigkeit der Nachweis duktiler Rißinitiierung durch SE schwieriger wird. Der kausale Zusammenhang zwischen SE und mikrostruktureller Schädigung ist nicht eindeutig zu belegen.
• Auf der Grundlage der Ergebnisse können Kriterien zur automatisierbaren SE-Auswertung definiert werden.

Der durch rißbedingte SE definierte Zähigkeitsparameter wurde mit der physikalischen Rißinitiierungszähigkeit verifiziert. Obgleich die riß- von der schlagbedingten SE nicht immer ohne Ermessensspielraum zu trennen ist, werden plausible und im Vergleich zu technischen Parametern konservative Jid-Werte bestimmt.

Damage has been observed in 40 keV He ion-implanted Si away from the projected ion range Rp, mainly around Rp/2. Cu gettering has been used for the detection of irradiation defects which are formed during rapid thermal annealing (RTA) of 800°C/10 min. The transmission electron microscopy (TEM) micrographs show no visible defects at Rp/2. The Cu gettering peak at Rp/2 is well known for MeV-ion-implanted and annealed Si (Rp/2 effect). In this study the corresponding effect is observed for low ebergy implantation of a light ion like He.

The formation of Ge nanowires in V-grooves on (001)Si wafers has been studied experimentally as well as theoretically. The V-grooves were formed by anisotropic etching and subsequent oxidation of their surface. The implantation of 1E17 Ge$^{+}$cm$^{-2}$ at 70 keV into the oxide layer leads to an enrichment of Ge in the V-groove bottom. In this Ge rich bottom region, subsequent annealing in N$_{2}$ atmosphere results in the formation of a nanowire by coalescence of Ge precipitates. STEM-EDX investigations of as-implanted samples have confirmed the Ge accumulation at the V-groove bottom, whereas cross-sectional TEM studies of annealed samples prove the formation of a Ge nanowire. The formation mechanisms were studied theoretically by means of a continuum description of sputtering and kinetic 3D lattice Monte-Carlo simulations of phase separation. The preliminary results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations.

Due to their unique structural features and properties dendrimers are ideally suited for use in diagnostic imaging and therapy, transfection, and drug delivery systems.¹ We are especially interested in efficient binding and controlled release of medicinally and biologically relevant anions with dendrimers tailored. In this context poly(propyleneamine)-dendrimers (POPAM) having anion affecting groups at the periphery seems to be very promising. Thus, we could show that urea-functionalized dendrimers are efficient carriers for oxyanions.²

This paper reports the binding behaviour of POPAM-dendrimers having the pH-switchable unit methyl orange at the periphery I. Furthermore POPAM-dendrimers possessing 2,6-diamidopyridine moieties IIa and IIb are investigated. The extractability of the radioactive pertechnetate TcO₄ ^- and the nucleotides AMP, ADP, and ATP with dendrimers are evaluated quantitatively by tracer methods in CHCl₃/H₂O systems. The extraction efficiency is studied in dependence on time, pH, buffer system, dendrimer concentration and generation. A dendritic effect is clearly visible for all dendrimers investigated. Controlled release of anionic guest molecules from the dendrimer host is allowed by alteration the pH.

[1] D.A. Tomalia, A.M. Naylor, W.A Goddart III, Angew. Chem. Int. Ed. Engl. 1990, 29, 138; Y. Kim, S.C. Zimmermann, Curr. Opin. Chem. Biol. 1998, 2, 733; O.A. Matthews, A.N. Shipway, J.F. Stoddart, Prog. Polym. Sci 1998, 23, 1; M. Fischer, F. Vögtle, Angew. Chem. Int. Ed. Engl. 1999, 38, 884; A.W. Bosman, H.M. Janssen, E.W. Meijer, Chem. Rev. 1999, 99, 1665.
[2] H. Stephan, H. Spies, B. Johannsen, L. Klein, F. Vögtle, Chem. Commun. 1999, 1875-1876

A nuclear resonance fluorescence experiment on the spherical N=50 nucleus 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy using two EUROBALL CLUSTER detectors. Dipole excitations observed in the energy region 4.5 MeV $\leq Ex \leq$ 5.5 MeVare proposed to be scissors-like excitations on top of the dynamically deformed quadrupole vibrational state.

FOREVER (Failure Of Reactor Vessel Rentention) experiments has been carried out in order to simulate the behaviour the lower head of a reactor pressure vessel under the conditions of a depressurized core melt down scenario. In particular the creep behaviour and the vessel failure mode have been investigated. Metallographic post test investigations have complemented the experimental programme. Samples of different height positions of the vessel of the FOREVER-C1 and -C2 experiments were metallographically examined and characteristic microstructural appearances were identified. Additionally samples with uneffected microstructure were annealed at different temperatures and cooled by different rates and afterwards investigated. In this way the microstructural effects of the temperature regime, the thermo-mechanical loads and the environmental attack could be characterized. Remarkable effects were characteristic for the FOREVER-C2 experiment where the highest-loaded region below the welding joint reached temperatures of approx. 1100°C and a strong creep damage occured. In the FOREVER-C1 experiment creep damage could not be observed and the maximum temperature did not exceed 900°C. Environmental attack generated decarburization and oxidation but the effect was restricted to a narrow surface layer. There was almost no chemical interaction between the oxidic melt and the vessel material.

High-spin states in 72Br and 73Br were studied with the EUROBALL III spectrometer.
The negative-parity band observed in 72Br displays a signature inversion around spin I = 16. Fully consistent cranked Nilsson-Strutinsky calculations show that this signature inversion can only be understood if the nuclear shape evolves from a triaxial shape with rotation around the intermediate axis at low spin through a collective prolate shape to a triaxial shape with rotation around the shortest principal axis at high spin. Rotational bands in 73Br
were observed up to spins of I = 65/2 at excitation energies of 26 MeV. Cranked Nilsson-Strutinsky calculations indicate that one of the negative-parity bands terminates at spin 63/2. Since this spin coincides with the maximum spin observed in the corresponding experimental band, we conclude that we observed this band up to its termination.

A quasi-particle model is presented which describes QCD lattice results for the 0, 2 and 4 quark-flavor equation of state.
The results are mapped to finite baryo-chemical potentials.
As an application of the model we make a prediction of deconfined matter with appropriate inclusion of strange quarks and consider pure quark stars.

Der Beitrag ist der Zwischenbericht des von der DFG geförderten gleichnamigen Forschungsvorhabens, Kennwort Prozessführung bei Pulverhandhabung.
Es wird auf folgende Bearbeitungsschwerpunkte näher eingegangen:

• Auswahl und Charakterisierung der für die Untersuchungen ausgewählten Pulver
• Untersuchungen zu Möglichkeiten der Insitu-Messung des Schüttgutverhaltens auf Basis von:

• Untersuchungen zum Strecken- und Regelverhalten eines entwickelten Schwingförderers sowie zur Schüttgutabhängigkeit der Reglerparameter, Erprobungsergebnisse eines fuzzy-adaptiven Dosierreglers (s. FWS 00-04)
• Entwurf eines fuzzy-adaptiven und eines Fuzzy-Reglers für die kontinuierliche Dosierung durch masse-Verlaufsregelung im Kleinstdosierbereich (<40mg/s), siehe FWS 00-01

Es werden die Eigenschaften des Schwingförderers als Förder- und Dosierorgan beschrieben. Aus dem Übertragungsverhalten des Schwingförderers werden die Aufgaben für den Einsatz in einer Dosierwaage formuliert. Anstelle der sonst üblichen Massestrom-Regelung wird die Masse-Verlaufs-Regelung als Folgeregelung eingesetzt, da sie für Dosierprozesse, die eine Zeitsynchronisation und eine Massebilanzierung erfordern, von Vorteil ist. Es wurde als Labormuster eine Dosierwaage, bestehend aus einer kommerziellen Präzisionswaage und einem Schwingförderer (Eigenentwicklung FZR) aufgebaut. Als Dosierregler wurde ein fuzzy-adaptiver PI-Regler entwickelt, der PC-implementiert im Echtzeit- Simulations- und Reglersystem DynStar der Hochschule Zittau realisiert wurde. Damit wurde der Prototyp eines universellen und flexiblen adaptiven Dosierreglers geschaffen, der für die kontinuierliche Dosierung von Pulvern im Kleinstbereich (< 40 mg/s) eingesetzt werden kann.
Der Beitrag entstand im Rahmen des von der DFG geförderten Forschungsvorhabens Prozessführung bei Pulverhandhabung.

Es wird ein Messverfahren zur Erfassung der Haufwerksrückwirkung und damit der Schüttguteigenschaften aus den Schwingungsgrößen eines Resonanzsystems beschrieben und Untersuchungsergebnisse an einem aufgebauten Labormuster vorgestellt. Das Verfahren ist zum Patent angemeldet. Es wird gezeigt, dass zwischen Fließverhalten und den am Resonanztopf gemessenen Merkmalen Frequenz und Tastverhältnis ein signifikanter Zusammenhang besteht. Damit kann es für die Klassifizierung und Parameteradaption bei Dosierreglern in Abhängigkeit vom Schüttgut verwendet werden. Das Messverfahren ist geeignet, als Insitu-Messung in eine Prozesslinie zur Schüttgutdosierung zu integrieren.
Der Beitrag entstand im Rahmen des von der DFG geförderten Forschungsvorhabens Prozessführung bei Pulverhandhabung.

Es werden die Eigenschaften des Schwingförderers als Feder-Masse-System beschrieben. Daraus wird das Förderverhalten von Schüttgütern bzw. Pulvern abgeleitet. Für die Förderung bzw. Dosierung von Pulvern kleiner Mengen wird ein speziell entwickelter Förderer, der als Patent angemeldet ist, vorgestellt. Für die Beschreibung des Förderverhaltens wird die empirische Größe Diskontinuität abgeleitet. Es wird anhand von Untersuchungen gezeigt, wie Förderbarkeit und Fließverhalten sowie Förder- und Regelverhalten zusammenhängen. Durch die qualitative Beschreibung des Förderverhaltens ist der Vergleich der Fördergüter mit unterschiedlichen Eigenschaften sowie der Vergleich verschiedener Förderorgane möglich. Es ist vorgesehen, die als Insitu-Messgröße gewonnene Diskontinuität für die Klassifizierung und damit Prozessoptimierung, d.h. für die schüttgutabhängige Parametereinstellung bei Dosierreglern zu verwenden.
Der Beitrag entstand im Rahmen des von der DFG geförderten Forschungsvorhabens Prozessführung bei Pulverhandhabung.

The phase formation and annealing behaviour are reported after nitrogen PIII in two austenitic stainless steels, DIN 1.4541
(X6CrNiTi18.10) and DIN 1.4571 (X6CrNiMoTi17.12.2), differing only in the Mo content. The treatment parameter were
pulses of 10 s and 40 kV for a nitrogen dose of 4×1018 cm-2 at a temperature of 380°C. In 1.4541, without Mo, the modified
layer is limited to 1.5 m while the 2 wt.% Mo-containing 1.4571 exhibits a layer thickness of 15 m. No difference in the
hardness (corrected for the layer thickness) and the wear behaviour was observed. Using X-ray diffraction (XRD) a lattice
expansion between 5 and 11%, was observed, not correlated with the nitrogen content (as determined by glow discharge
optical spectroscopy ¯¯ GDOS). After annealing at 400 and 425°C for different times, the lattice constant is slightly reduced,
albeit no phase transformation was observed in 1.4571. In 1.4541 at a temperature of 425°C a strong reduction of the lattice
expansion, coupled with an inward diffusion of the nitrogen was observed. No mechanism explaining this behaviour is available
at the moment.

Stainless steels show excellent corrosion resistance, which is lost during conventional hardening processes at temperatures
above 500°C, like gas or plasma nitriding, to improve the low hardness and to reduce the high wear rate. For aluminium alloys
it is impossible to improve the mechanical properties by traditional nitriding. Plasma immersion ion implantation (PIII) of
nitrogen is successfully used for hardening both austenitic stainless steels and aluminium alloys. Compared to the untreated
materials the hardness and the wear resistance can be improved significantly. For austenitic stainless steels an `expanded
austenite' layer of up to several tens of micrometer thickness and for aluminium alloys an AlN layer of more than 10-m
thickness were formed over a few hours. Corrosion tests showed no or only small changes in the corrosion behaviour for
stainless steel. The AlN layer can be used as a supporting layer for the deposition of hard materials like CrN on aluminium
alloys. It is shown that the partial pressure of oxygen in the residual gas in the vacuum chamber plays an important role for the
nitriding of both stainless steel and aluminium alloys

Das vorliegende Projekt wurde im Rahmen einer Kooperationsvereinbarung zwischen dem Forschungszentrum Rossendorf (FZR) und der wissenschaftlichen Gruppe von Prof. Melnikon von der Technischen Universität Nishny Novgorod (TUNN) der Russischen Föderation durchgeführt. Es ist Teil des Wissenschaftsunterstützungsprogramms / FSU der Bundesregierung im Rahmen der Beratungshilfe für den Aufbau von Demokratie und sozialer Marktwirtschaft (TRANSFORM). Neue Methoden der Instrumentierung für Zweiphasenströmungen wurden entwickelt: Ultraschall-Wellenleitersonden können zur lokalen Gas- bzw. Dampfgehaltsmessung eingesetzt werden. Der neue Ultraschall-Gittersensor erlaubt eine Visualisierung der Zweiphasenströmung mit ca. 250 Bildern/Sekunde. Sowohl die lokalen Sonden als auch der Ultraschall-Gittersensor können erfolgreich unter den Bedingungen von Wasser-Dampf-Gemisch bei hohem Druck und hoher Temperatur, sowie in anderen Fluiden, wie organischen Flüssigkeiten und Kältemitteln, eingesetzt werden. Darüber hinaus wurden berührungslos arbeitende Wellenleitersonden für die Durchschallung von Rohrleitungen und Dichtesensoren, die auf der Messung der Ausbreitungsgeschwindigkeit von Ultraschall in Wellenleitern beruhen, die sich im Messmedium befinden, entwickelt und getestet. Bei dem gegenwärtigen Stand der Entwicklung können die berührungslosen Sensoren lediglich als qualitativer Nachweis von Gas in einer Flüssigkeitsströmung dienen. Die Funktion der Dichtesensoren wurde anhand von Messungen in verschiedenen einphasigen Flüssigkeiten unterschiedlicher Dichte demonstriert. Für einen praktischen Einsatz ist die weitere Verbesserung der elektronischen Signalerfassung erforderlich. Die hauptsächliche Innovation wird durch den Ultraschall-Gittersensor verkörpert, dessen Auflösung mit der von schnellen elektrischen Gittersensoren und ultraschnellen Röntgentomographen vergleichbar ist, während das Gerät selbst sehr robust und preiswert ist.

The 6th dynamic benchmark concerns a double ended break of one main steam line (asymmetric MSLB) in a VVER-440 plant. The core is at the end of its first cycle in full power conditions. The control rods of group K6 are at position 175 cm from bottom of the core. All other groups of control rods are out of the core. The initial state conditions of the core in the beginning of the transient are given. The isothermal re-criticality temperature of the core is defined to be 210°C. It should be achieved by tuning the worth of all control rods. Otherwise, own best estimate nuclear data are to be used. The main geometrical parameters of the plant and the characteristics of control and safety systems to be considered are given. Otherwise, own input data decks developed for a VVER-440 plant and for the applied codes can be used. The objective is to calculate the behaviour of the core during this re-criticality event using coupled codes, which combine a three-dimensional neutron kinetics code for the core with a thermohydraulics system code. This benchmark is a logical continuation of the work in the 5th dynamic benchmark. Additional new features include asymmetric operation of the feed water system, effects of coolant mixing in the reactor vessel, and the definition of a fixed isothermal re-criticality temperature for normalising the nuclear data.

The regional density of serotonin uptake sites in porcine brain was determined by quantitative radioluminography. Brain cryostat sections 30 mm thick were cut in the sagittal plane and were incubated with [³H]citalopram for selective labelling of serotonin uptake sites. The autoradiograms were quantified using tritium-sensitive radioluminography. The apparent affinity (K_D) of [³H]citalopram for its binding sites in various brain regions ranged from 2.3 - 5.6 nM. The density of serotonin uptake sites was highest (200 - 300 fmol/mg tissue) in the amygdala, superior colliculus and substantia nigra. Intermediate binding (100 fmol/mg tissue) was present in the dorsomedial thalamus, basal ganglia, and entorhinal cortex. Traces of specific binding (10 fmol/mg tissue) were detected in the neocortex and cerebellar cortex. The findings show that the anatomic distribution of serotonin uptake sites in the porcine brain is similar to that reported in other mammals. The density was close to that reported in human brain and in rat brain.

Introduction:

Loss of 5-HT transporter (SERT) sites has been implicated in various brain diseases. Therefore, the development of suitable radioligands for neuroimaging of the SERT in the human brain is important. ¹¹C](+)McN5652 is the only PET radioligand which is available for clinical use. However this compound is not optimal because of its rather slow kinetics and high non-specific binding in the human brain. For the evaluation of further radioligands in animal experiments a comparison with [¹¹C](+)McN5652 is recommendable. Therefore we have studied the binding and distribution of [¹¹CMcN5652 in various animal species.

Methods:

The in vitro binding of ¹¹C](+)McN5652 was studied on tissue homogenates and slices of rat and porcine brain and on the SERT expressing human placental cell line JAR. The in vivo binding of [¹¹C](+)McN5652 was investigated in rats, mice and pigs. 35 Wistar rats (age: 8 weeks) were injected with 20 MBq [¹¹C](+)McN5652 and sacrificed at 5, 30, 60, or 90 min p.i. 11 rats were treated additionally with 5 mg/kg i.v. fluoxetine or citalopram 5 min before tracer injection. Additionally 6 mice were injected with 80-200 MBq [¹¹C under general anesthesia (0.5-0.75% isoflurane in N₂O/O₂. 46-48 arterial blood samples were obtained at defined time points. Additional arterial samples were withdrawn for detection of metabolites using thin-layer chromatography.

Results:

Evidence for a significant binding of ¹¹C](+)McN5652 not only to SERT but also to the norepinephrine (NET) and dopamine transporters (DAT) was found in vitro. IC₅₀ values of 6.6 and 9.4 nM for NET and DAT were measured. Binding equilibrium at JAR cells was reached after about 60 min. Nonspecific binding (defined by 10 µM citalopram) was 76%. In rats a high brain uptake was found with the highest values measured in thalamus, colliculi and olfactory bulb (~1.3 % g^-1). Only in these regions a significant inhibition (38-48%) by fluoxetine and citalopram was found. Similar results were obtained by autoradiography in mice. Also the PET data obtained in pigs revealed a high blood-brain transfer of ^[11C](+)McN5652 (K₁: 0.22-0.43 ml g^-1 min^-1). Rapid metabolism was observed. More than 50% metabolites were found at 12 min p.i. Significant binding of [¹¹C. The highest binding potential was found in thalamus and colliculi. Preinjection of citalopram or fluoxetine reduced k₃ by 30-70%.

Comments:

A high consistency exists between the in vitro and in vivo studies in various animal species. The data reveal a displaceable binding in target regions but also a rather high nonspecific binding of ¹¹CMcN5652. Binding to other targets such as NET and DAT may contribute to this. The location of serotonin uptake sites in the porcine brain appears to be similar to that found in rats and mice which makes pigs a suitable animal model for the development of radioligands for studying serotonergic functions with PET.

Self-interstitials were introduced by additional Si+ implantation into the vacancy-dominated depth range around half of the projected ion range, RP/2, of high-energy ion-implanted Si in order to balance radiation-induced excess vacancies. The undesired gettering of Cu atoms in this region (RP/2 effect) could be suppressed. The threshold was determined necessary to remove the Cu gettering at RP/2. It does approximately agree with the number of the calculated excess vacancies. Additional interstitial-type dislocation loops were formed during annealing at RP/2 as the Si+ fluence exceeds this threshold. Interstitial clusters were not approved to be the gettering centres for Cu trapping

Introduction
The activity concentration of small lesions with diameters comparable to the spatial resolution (FWHM) is underestimated in PET measurements. This resolution is determined by the camera characteristics and also by the reconstruction and filter conditions used. For simple formed lesions the underestimation can be corrected, if the size of the lesion and the spatial resolving in the recon-structed picture are known and appropriate phantom measurements are present.
The aim of the study was to determine the resolution as well as the recovery coefficients( HSRC) for small spheres by phantom measurements and to prove, whether the underestimation is possible to correct by means of the quotient of the two measured lesion values for reconstructions with clearly different picture resolution.

Methods
All measurements took place at the PET camera ECAT EXACT HR+ with the software V7.1 (Siemens, CTI) in the 2D-Mode. For the measurement of the HSRC the EEC head phantom with the hollow spheres insert was used. Additionaly 8 thin-walled glass spheres with inside diameter values between 5.0 mm and 8.6 mm were examined. The reconstruction of the phantom measurements took place with FBP and OSEM.
The transversal resolution was measured with three line sources in water and the average values from radial and tangential values were calculated.
From ROIs with the diameter equal to the FWHM the recovery coefficients (phantom measurements) and the contrast values (patient measurements) were determined.

Results and Discussion
The transver-sal resolution was measured for axial distances up to 11.5 cm. For distances larger than 7 cm the radial component is increased.
If the HSRC from two reconstructions with significantly different image resolution are used to calculate a quotient HSRC1/HSRC2 then spheres with diameters smaller approximatly 15 mm can be distinct.
This method can be used to correct the recovery of a lesion in a patient study by determination of the image contrast. Fore the application of the procedure to lesions in the periphery of the body the dependence of the resolution from the axial distance must be considered.
Further investigation should be done to show the limits of this method.

'3+1' Mixed-ligand [^99mTc]oxotechnetium complexes with affinity for melanoma were synthesized in a one-pot reaction. Complexation of technetium-99m with a mixture of N-R(3-azapentane-1,5-dithiol) [R = Me, Pr, Bn, Et₂N(CH₂)₂] and N-(2-dialkylamino)ethanethiol [alkyl] = X = Et, Bu, morpholinyl] using Sn²⁺ as the reducing agent resulted in the formation of '3+1' mixed-ligand technetium-99m complexes [TcO(SN(R)S)(SNX₂)] in high radiochemical yield (60-98%). In vitro uptake studies in B16 murine melanoma cells indicated a moderate tumor-cell accumulation (40%) of compound 1 [R = Me, X = Et] and a higher accumulation (69%) of compound 2 [R = Me, X = Bu] after a 60-min incubation. In vivo evaluation of compounds 1-6 in the C57B16/B16 mouse melanoma model demonstrated tumor localization. Compound 2 displayed the highest accumulation with up to 5% ID/g at 60 min after injection. In vivo, 2 also showed a low blood-pool activity and high melanoma/spleen (4.3) and melanoma/lung (1.9) ratios at 1 h. These results suggest that small technetium-99m complexes could be useful as potential melanoma-imaging agents.

'3+1' Oxorhenium(v) complexes [ReO(SN(R')S)(SR)] (R' = Me, Et, Pr or Bu; SR = aminoalkane thiolate) have been synthesized by ligand exchange at trans-trichloromonooxo-bis(triphenylphosphine)rhenium(v) with a mixture of HSN(R')SH and RSH in alkaline methanolic solution. The complexes were purified by column chromatography and characterized by elemental analysis, mass and IR spectroscopy and for selected compounds by ¹H NMR spectroscopy. The structures of those complexes have been determined by X-ray diffraction analysis and revealed a change in the co-ordination geometry from square pyramidal to trigonal bipyramidal, depending on the chelating (SN(R')S) moiety. The alkyl group (R') was found to be arranged "syn" to the oxorhenium group.

The global stresses in turbostratic and cubic boron nitride films are studied during annealing up to 670 °C. It is observed that the stress relaxation starts when the deposition temperature is exceeded. The compressive intrinsic stress in tBN and cBN decreases exponentially with the same time constant of . Depth resolved analysis of the stress before and after annealing reveals that the features in the stress depth profile do not smear out during annealing. The stress relaxation in the interfacial turbostratic boron nitride exceeds that in the cubic boron nitride on top by a factor of 1.5±0.2 and is thus not significantly affected by the capping cubic boron nitride. The specific thermal stresses in turbostratic and cubic boron nitride films are not altered after thermal treatment up to 670 °C. It is concluded that the decrease in stress is mainly due to changes in strain, whereas the elastic properties of boron nitride films remain largely constant under annealing.

The pollution of the environment with toxic metals is one of the most severe problems of our industrial century. The uranium mining waste piles are a subject of particular attention, because in soils, sediments, and drain waters of these environments significant amounts of many hazardous metals such as uranium, caesium, strontium, selenium, molybdenum, arsenic, cadmium, chromium, mercury, lead, copper, nickel, zinc, etc. are present (Francis, 1990). In addition, significant amounts of thorium, radium, and polonium might also be present at the so called uranium "mill tailings" where the extraction of uranium from the ores was performed.
It was demonstrated that even in the most heavily polluted uranium wastes large numbers of bacteria are present (Cerda et al., 1993; Goebel & Stackebrandt, 1994; Shippers et al., 1994). Moreover, different groups of bacteria are interacting in various ways with metals and radionuclides. Some of the most important mechanisms by which bacteria can biotransform and influence the mobilisation and/or immobilisation of metals are listed below:
1) Direct oxidation and/or reduction of metals, which affect their solubility (DiSpirito & Tuovinen, 1982; Lovley, 1993; Nelson et al., 1999; Sharma et al. 2000; Wildung et al., 2000);
2) Direct or indirect oxidation of metal sulfides and solubilization of certain elements (Bosecker, 1997; Krebs & Brandl, 1997);
3) Indirect alteration of metal ionic states caused by bacterial induced pH and Eh changes in the medium (Bosecker, 1997; Bacelar-Nicolau & Johnson, 1999);
4) Bioaccumulation [biosorption by cell surface polymers (DiSpirito et al., 1983; Douglas & Beveridge, 1998; Macaskie et al., 1992; Panak et al., 1999; Selenska-Pobell et al., 1999; Valentive et al., 1996) and/or uptake of metals inside the cells (Klaus et al., 1999; Marques et al., 1991; Purchase et al., 1997)].
5) Bio-mineralization, which includes induction of metal precipitates by particular metabolic functions of some bacteria and consequent generation of minerals (Brown and Beveridge, 1998; Douglas and Beveridge, 1998; Francis, 1998);
6) Release of the biosorbed metals by chelation, alkylation, or decomposition (Bosecker, 1997; Francis, 1990; Francis et al., 1998).
It is clear that the above described bacterial activities are strongly influencing the fate and the migration of toxic metals in and outside of the sites where uranium mining was performed.
In addition to the living cells, significant amounts of different bacterial metabolites are present in the wastes which are also interacting with the heavy metals and influencing their behaviour.
For these reasons, the knowledge about the diversity and about the activity of the indigenous bacteria in the uranium waste piles is of basic importance for understanding the bio-geo-chemical processes occurring in these environments and especially for modelling the process of migration of the heavy metals and radionuclides in nature.

Bacteria in uranium waste piles are of special interest for bioremediation, because they are adapted to high concentrations of radionuclides and heavy metals which occur in these environments. A large number of Bacillus strains was recovered from a uranium mining waste pile "Haberland" near the town of Johanngeorgenstadt in Saxony, Germany. One isolate, Bacillus sphaericus JG-A 12, possesses a surface layer protein with a molecular weight of 135 kDa [1]. Sequence analysis of a part of the gene of this protein, coding 184 amino acids from the N-terminal region of its matured S-layer product, demonstrated that the protein shares only a limited homol-ogy (less than 35%) to the known S-layers of the other Bacillus sphaericus strains WHO 2362, CCM 2177 and P-1 (see Fig. 1).

Bacterial diversity was studied in drain waters and soil samples drawn from different sites and depths of three uranium mill-tailings - Schlema/Alberoda, Gittersee/ Coschütz (Germany), and Shiprock, New Mexico (USA) as well as in samples drawn from two uranium mining waste depository sites, "Haberlandhalde" near the town of Johanngeorgenstadt and Deponie B1, Germany. For this study both culture-dependent and culture-independent i.e. direct molecular approaches were applied.
The direct molecular analyses involved PCR based rep-APD, 16S rDNA and RISA retrievals [1, 2, 3].
Three parallel rDNA clone libraries (16S rDNA I, 16S rDNA II, and RISA) were constructed for each of the samples studied using three different sets of PCR primer pairs (see Fig. 1).Fig. 1. Clone libraries constructed for the soil and water samples from the uranium wastes analysed

The clones of each of the above mentioned three libraries constructed from the same sample usually indicated the presence of different, not overlapping bacterial groups. This demonstrates the necessity of using more than one PCR primer pair in the construction of the environmental rDNA libraries, because as mentioned by others [4] in such complex mixtures of DNA templates the regions flanking the PCR amplification products are strongly influencing the effectivity and the preferences of the PCR reaction. As a result of these so called biases of the preferential PCR on the end of each amplification an enrichment with particular fragments preferred by the process occurs.
For example, in some samples of the uranium wastes the RISA retrieval demonstrated the predominance of the aerobic ammonia oxidisers Nitrosomonas (b-Proteobacteria) and of the anaerobic chemolithotrophic ammonia oxidizing bacteria named Anammox (Planctomycetales) which were "overseen" by the 16S rDNA retrievals.
The direct molecular approach has demonstrated that, in general, the bacterial populations in the environmental samples studied possess different grade of variability. The highest variability was found in the soil samples drawn from depths between 2.5 m and 5 m below the surface and also in the water sediment samples. Despite the fact that the predominant bacterial species in the studied environments are in general site-specific, many samples share common bacterial groups. These groups belong mainly to the g subgroup of Pseudomonas; to the sulfate and metal reducing genera such as Desulfovibrio, and Geobacter (d-Proteobacteria); to the aerobic chemolithoautotrophs oxidizing iron and sulfur compounds (Acidithiobacillus); or to those oxidizing nitrite (Nitrospina) and ammonium (Nitrosomonas), d- and b-Proteobacteria, respectively. A large number of diverse 16S rDNA sequences was related to various not yet cultured representatives of Holophaga/Acidomicrobium and Cytophaga/ Flexibacter clusters. In addition, many 16S rDNA sequences were affiliated with novel so-called "candidate" bacterial divisions.
Both the RISA and the 16S rDNA retrievals revealed many cases of bacterial microdiversity, i.e. presence of closely related strains belonging to the same species predominating in the natural community.

Analyzsing different individual bacterial isolates as well as mixed enrichment bacterial cultures we have demonstrated the presence of strains belonging to the genera Acidithiobacillus, Agrobacterium, Bacillus, Clostridium, Desulfovibrio, Leptospirillum, Pseudomonas, Rhizobium, Stenotrophomonas, etc. in the samples of the uranium wastes. The exact phylogenetic affiliation of the individual strains studied was performed by the use of the 16S rDNA RFLP and sequence analyses. Many of the strains cultured represent novel bacterial species within the above mentioned genera. In addition, several pure cultures of isolates which are closely related to some previously uncultured bacterial species were cultured.
Interactions of several of the natural uranium waste isolates with uranium (VI), in particular, sor...

The main problem of the direct molecular approaches for studying environmental samples is the so called preferential PCR amplification which can mask the presence of some DNA templates in the samples.
For this reason the application of the classical approach of the enrichment cultures, in parallel to the molecular retrievals, for studies on bacterial diversity in the environment may be helpful. Of course, here the limitation to analyze only those strains of the community which are able to grow individually exists. It is a compromise to analyze enriched biofilm cultures or mixed cultures instead of pure cultures, because most of the bacteria in the extreme environments are living in consortia which are described as symbiotic [1, 2]. The identification of the members of such mixed cultures using the 16S rDNA retrieval may provide very important information in addition to those, derived by the direct methods, about the bacteria present in the samples studied.
Our studies on phylogenetic diversity of bacteria cultured as pure and/or mixed cultures from the uranium wastes are presented in Table 1.
From these results one can see that bacterial strains known for their ability to biotransform metals were recovered from the samples. For example, different types of Acidithiobacillus ferrooxidans, which are oxidizing iron and sulfur compounds and Leptospirillum ferrooxidans , oxidizing iron, were cultured. These two groups of bacteria play a significant role in the mobilization of many metals and radionuclides in the wastes, because as a result of their physiological activity large amounts of H2SO4 are produced and the pH in their surrounding is extremely low.
Individual cultures representing sulfate reducing bacteria of the genus Desulfovibrio which are able to reduce also uranium and other metals were cultured from the uranium mining waste samples as well.
In addition, strains belonging to the species Pseudomonas stutzeri, Pseudomonas migulae, Erwinia herbicola (g-Proteobacteria) as well as isolates related to Agrobacterium and Sphingomonas (a-Proteobacteria) were cultured.
In addition to the above described individual bacterial isolates several enrichment mixed cultures were recovered. One of them, called initially "JG1", from which the sulfate reducing Desulfovibrio isolate JG1 was purified, consisted of 11 diverse representatives of Clostridium (see the series of clones IrT-JG1 affiliated to the Bacillus/Clostridium group in Table 1) and the two clones IrT-JG1-58 and IrT-JG1-71 closely related to the isolate Desulfovibrio JG1.
Formerly we have reported that the mixed culture of "JG1" is able to reduce and precipitate amounts of about 1.5 g of U(VI) per g of dry weight bacterial biomass from a liquid medium independently on its pH value in the range between 2.8 and 6.0 [3]. Our recent results demonstrated, however, that the U(VI) reducing capacity of the pure culture of Desulfovibrio sp. JG1 does not differ significantly from those published for the other uranium reducing bacteria, Desulfovibrio vulgaris, D. desulfuricans, and Geobacter metallireducens which is about five times lower and, in addition, it is pH dependent with an optimum of pH 6.8 [4, 5]. This indicates that the higher capability of the mixed culture "JG1" to precipitate uranium at a wider range of environmental conditions (pH for example) is a result of the combined function of the different bacterial members of which it consists. We suppose that in addition to the U(VI) reduction performed by the above mentioned natural strains of Desulfovibrio sp. (JG1, IrT-JG1-58 and JrT-JG1-71) some other processes occur, as bio-precipitation or/and bio-minearalisation stimulated by the metabolic functions of the described Clostridia present in the mixed culture.
Another mixed culture "JG14" consisted of different a-Proteobacteria (Agrobacterium and Rhizobium) and a microdiverse population of environmental strains of Stenotrophomonas maltopilia (d-Proteobacteria). ...

Bacterial diversity in soil and drain water samples of uranium mining waste piles was studied by two direct (culture-independent) approaches, the16S rDNA and the ribosomal intergenic spacer amplification (RISA) retrievals. A large number of samples was studied which were drawn from the following heavy metal and radionuclide polluted sites: the uranium mill-tailings Schlema /Alberoda, Gittersee/Coschütz, in Germany, and Shiprock/New Mexico in the USA, as well as two uranium mining disposal sites, Haberlandhalde near the town of Johanngeorgenstadt and Deponie B1/Weisse Elster (Germany).
Both methods demonstrate significant differences in the microbial diversity between the samples studied. The highest diversity was found in the drain water and soil samples from the mill-tailing Gittersee/Coschütz, followed by those from Schlema/Alberoda and the Haberlandhalde. The predominant 16S rDNA fragments in those samples were affiliated to Pseudomonas, Geobacter, and to different uncultured sulfate reducing and Cytophaga-like bacteria. Interestingly, in the samples of the Gittersee/Coschütz site the presence of the recently discovered anaerobic chemolithotrophic ammonium oxidizing bacteria named Anammox [1] was demonstrated by the use of the RISA approach. Using the same approach, an abundance of Nitrosomonas sp., nitrifying bacteria belonging to b-subclass of Proteobacteria was found in the water samples from Shiprock. Both groups of bacteria were "overseen" when the 16S rDNA retrieval was applied for analyzing the same samples. These results clearly demonstrate the utility of using at least two primer pairs for PCR amplifications of environmental rDNA fragments in order to overcome the masking effect of the preferential amplification, which depends on the structure of the flanking regions of the templates.
In all kinds of uranium polluted wastes the presence of a large variety of not yet cultured bacteria belonging to Holophaga/Acidobacterium and Cytophaga/ Flexibacter clusters was shown. In addition, many 16S rDNA sequences were affiliated with various unidentified so- called "candidate" bacterial divisions such as OP1, and OP6 [2].

Acknowledgements
This work was supported by grants 7531.50-03-FZR/607 from the Sächsisches Staatministerium für Wissenschaft und Kunst, Dresden, Germany and GRP/9816 from the European Science Foundation. The authors thank David Balkwill, Florida State University, Tallahassee, USA for providing some of the water samples.

A large number of acidophilic chemolithoautotrophic iron oxidizing bacterial isolates recovered from two uranium mining waste piles was classified as Leptospirillum ferrooxidans. For this purpose a combination of classical and molecular microbiological methods was applied. The letter involved Amplified Ribosomal DNA Restriction Endonucleases analysis (ARDREA) and 16S rDNA sequence analysis. In the ARDREA two sets of primers were involved: one universal -16S7f and 16S1406r, and one species specific -16S176f and 16S679r (De-Wulf-Durand et al,.1997, Tzvetkova et al., 1999). In both cases using endonuclease RsaI, two groups were discriminated among the isolates studied. These groups correspond to the recently characterized RsaI RFLP types I and II of L. ferrooxidans, which include the type strain of the species L. ferrooxidans DSM 2705T (type I) and the strains L. ferrooxidans DSM 2391 and Lf30A (type II); (Fig.1 and Tzvetkova et. al., 1999);
An additional extensive comparative sequence analysis of the variable region 3 of a series of natural isolates and the deposited sequences of this region in the EMBL allowed to distinguish seven L. ferrooxidans groups. Each group possesses a specific signature in the helix 18 of the variable region 3 (Fig.2). These signatures discriminate particular types of the species and possibly reflect the genetic adaptations of different parts of the natural L. ferrooxidans populations to different concentrations of heavy metals and other components of their natural environment. The variability of the helix 18 influences target sites of several frequently cutting endonucleases and allows discrimination of some of the above mentioned groups.
The interaction of some L. ferrooxidans natural isolates with uranium was studied at different concentrations of the metal and at two pH values. Results demonstrating accumulation of U(VI) at unusually low pH values are presented and discussed in the poster

Bacteria express a wide variety of complex molecules on their surfaces, which, at physiological pH values, contain numerous charged chemical groups (such as phosphoryl, carboxyl, and amino groups) that usually give the cell surface a net of anionic (negative) charge density. Since the cell surface is in direct contact with the environment, the charged groups within the surface layers are able to interact with ions or charged molecules present in the external milieu. As a result, metal cations can become electrostatically attracted and bound to the cell surface [1].

Uranium (VI) complexes formation at surfaces of three Acidithiobacillus ferrooxidans types was studied using uranium LIII-edge extended x-ray absorption fine structure (EXAFS) spectroscopy. In all samples uranium is coordinated by two axial oxygen atoms (Oax) at distance of 1.77-1.78 Å. The average distance between uranium and the equatorial oxygen atoms (Oeq) is 2.35 Å. The coordination number for Oeq is 5-6. In comparison to the uranium crystal structure data, the U-Oeq distance indicates a coordination number of the equatorial oxygen of 5.

Within the experimental error, there are no differences in the U-O bond distances between samples from the 3 types of A. ferrooxidans investigated. The fit to the EXAFS data of samples measured as wet pastes gave the same results as for dried samples. No significant structural differences were observed for the uranium complexes formed by the three eco-types of A. ferrooxidans. However, the EXAFS spectra are indicating a formation of uranium complexes which are different from those formed by Bacilli [2] where the bond length of 2.28 Å indicates a coordination number of 4 for the equatorial oxygen atoms.