Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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.

In uranium mining piles a number of acidophilic chemolithoautotrophic bacteria has been identified, which are able to oxidize sulphide minerals, elemental sulfur, ferrous iron, and, in presence of uranium minerals, also U(IV). Especially one representative of this group, Acidithiobacillus ferrooxidans, is of particular interest. This organism has been used commercially in metal leaching from ores and decontamination of industrial wastes [1].
Sequence analysis of the 16S rRNA genes of several reference strains and uranium mining waste pile isolates of this bacterium revealed specific signatures which distinguish three types within the species. This allowed to develop a technique for analysis of the distribution of the A. ferrooxidans eco-types in the soil samples of a uranium mining waste pile.
The technique is based on amplification of 16S rDNA fragments in total soil DNA by the use of two A. ferrooxidans species specific primers 16S458F and 16S1473R [2]. The resulting amplicons were then digested with a frequently cutting enzyme RsaI which produced three different type-specific profiles [3; 4]. Using this direct approach we have demonstrated that one of the A. ferrooxidans types (type I) was predominant in the soil samples studied and was found in more polluted sites, whereas the type II was found in less contaminated samples. The type III was found mostly to coexist with the type II.
The objectives of the present work were to determine whether these eco-types differ in their capability to tolerate and accumulate uranium, and also to study the structural complexes formed at the surfaces of A. ferrooxidans eco-types using different spectroscopic techniques as Extended X-ray Absorption Fine Structure (EXAFS), Infra Red (IR) and time-resolved laser-induced fluorescence spectroscopy (TRLFS). In addition, the most efficient desorbing agent for the accumulated uranium was selected.
The uranium accumulation by the above mentioned three types of A. ferrooxidans was studied at different metal concentrations and different pH values (1.5 and 4). The results obtained (Fig.1) demonstrated that the strains from the different types possess different capability to accumulate uranium. The amount of uranium biosorbed by the three types increased with increasing concentration of uranium.
Fig.1: Biosorption of uranium by different types of A. ferrooxidans

Interestingly, the strains W1 (type I) and D2 (type III) are resistant to 8 and 9 mM of uranium, respectively, whereas the strain ATCC 33020 (type II) does not tolerate more than 2 mM of uranium (Table 1).

Strains

Uranium (mM)
Tolerated
MICs
A. ferrooxidans W1
8 9
A. ferrooxidans ATCC 33020
2 4
A. ferrooxidans D2
9 10
Table 1: Minimum Inhibitory Concentrations (MICs) of uranium for the growth of A. ferrooxidans type

On the basis of these results, one may speculate that the strains of the types I and III are more resistant to uranium, probably because they possess a mechanism which limits the uranium binding below the lethal amounts.

The desorption of the accumulated uranium from the bacterial cells was investigated using different desorbing agents as sodium carbonate, sodium citrate and EDTA at different concentrations. The results obtained demonstrated that the sodium carbonate is able to recuperate up to 97% of the uranium sorbed from the cells of A. ferrooxidans type III, and 88.33 and 88.50% from the cells of the types I and II, respectively.

Using EXAFS analysis we have found that no significant structural differences were observed between the uranium complexes formed by the 3 types of A. ferrooxidans. However, the EXAFS spectra are indicating formation of uranium complexes which are different from those formed by bacilli [5; 6].

Acknowledgements
This work was supported by grant 7531.50-03-FZR/607 from the Sächsisches Staatsministerium für Wissenschaft und Kunst, Dresden, Germany

To study the kinetics of Al ion nitriding, a series of experiments has been performed at fixed ion beam parameters using substrate temperatures varied from 250 °C to 400 °C at intervals of 50 °C. The nitride layers have been analysed by nuclear reaction analysis (NRA), elastic recoil detection analysis (ERDA), x-ray diffraction (XRD) and scanning electron microscopy (SEM). Depending on the experimental conditions, the nitriding kinetics shows different character: controlled by the delivery of N ions or by the diffusion of Al atoms. Furthermore, the growth of the nitride layer is limited due to the bad layer adhesion. XRD analysis reveals the formation of a hexagonal AlN-phase plus a small fraction of the cubic AlN-phase.

Im Rahmen eines vom BMBF/BMWi geförderten WTZ-Vorhabens wurde der ukrainischen Aufsichtsbehörde der Programmkomplex ATHLET-DYN3D verfügbar gemacht, welcher eine Anbindung des im FZR entwickelten 3D Kernmodells DYN3D an den thermohydraulischen Systemcode ATHLET der GRS darstellt. Zur Validierung dieses gekoppelten Programmcodes wurde eine Meßdatensammlung angelegt, die entsprechend erarbeiteter Richtlinien Daten von geeigneten Betriebstransienten bereitstellt. Für zwei ausgewählte Transienten wurden Validierungsrechnungen durchgeführt. Dabei wurden die Ergebnisse mit den Meßwerten aus der Datensammlung verglichen.
Der Programmcode DYN3D wurde von den ukrainischen Experten mit einer Ergänzung zur Berechnung von Reaktivitätskoeffizienten im Funktionsumfang erweitert. Diese Programmentwicklung ermöglicht es, den Einfluß der einzelnen Reaktivitätskoeffizienten bei verschiedenen Betriebsprozessen bzw. Störungen zu untersuchen.

Im Rahmen eines vom BMBF/BMWi geförderten WTZ-Vorhabens wurden der Transfer des im Forschungszentrum Rossendorf (FZR) entwickelten Programmcodes DYN3D und seine Integration in die programmtechnische Basis des Instituts für Physik und Energietechnik (IPPE) Obninsk realisiert. Das neutronenkinetische Programmodul von DYN3D wurde von den russischen Experten genutzt, um den im IPPE verwendeten Thermohydraulikcode um die Funktion der 3D Neutronenkinetik zu erweitern. Zur Modernisierung der bisher bei Störfallanalysen verwendeten makroskopischen Wirkungsquerschnitte wurde mit dem Programmcode WIMS/D4 eine neue Datenbibliothek generiert, welche auch die bereits in WWER-Reaktoren umgesetzten Konzepte zu modifizierten Kernbeladungen (abbrennbare Absorber unterschiedlicher Borkonzentration) berücksichtigen kann. Diese Querschnittdatenbibliothek wurde an DYN3D angeschlossen und in ersten Vergleichsrechnungen auf seine Funktionstüchtigkeit sowie Genauigkeit überprüft.
Für das unter Beteiligung von IPPE erstellte integrale Reaktorkonzept ABV-67 wurden sowohl mit DYN3D als auch mit dem gekoppelten Programmkomplex erste ATWS-Analysen durchgeführt.
Der im IPPE entwickelte Fluiddynamikcode DINCOR wurde dem FZR zur Nutzung übergeben und durch gemeinsame Nachrechnungen von Modellaufgaben zum kurzzeitigen Schmelzeverhalten (CORVIS-Experimente) validiert.

The emission pattern of charged pions has been measured in Au+Au collisions at 1 GeV/nucleon incident energy.
In peripheral collisions and at target rapidities, high-energy pions are emitted preferentially towards the target spectator matter. In contrast, low-energy pions are emitted predominantly in the opposite direction. The corresponding azimuthal anisotropy is explained by the interaction of pions with projectile and target spectator matter. This interaction with the spectator matter causes an effective shadowing which varies with time during the reaction. Our observations show that high-energy pions stem from the early stage of the collision whereas low-energy pions freeze out later.

The Master Curve concept allows to quantify the variation of fracture toughness with the temperature throughout the ductile-to-brittle transition region. Limit curves of fracture tough ness for defined failure probabilities and a reference temperatures can be determined using this method. Thus, fracture mechanical values can be supplied for an integrity assessment of structural components. This paper presents the application of the master curve concept to the reference temperature determination over the thickness of RPV steel plate. It was shown that the master curve concept is applicable for the fracture mechanical characterisation of material with different microstructures using small test specimens. The influence of the material homogeneity and the test temperature on the resulting reference temperature was investigated.

Certain bacterial strains can selectively accumulate various metal ions from aqueous systems /1/. Recently, it was demonstrated that two Bacillus strains, B. cereus JG-A30 and B. sphaericus JG-A12, recovered from a uranium mining waste site in Germany are able to accumulate selectively a large variety of heavy metals from the drain waters of the waste site /2/. In particular, it was shown that these strains accumulate large amounts of uranium. The aim of this study is the analysis of the structure of uranium complexes formed at vegetative cells and spores of the above mentioned Bacillus strains using extended x-ray absorption fine structure (EXAFS) spectroscopy. Analytical procedures allow separating radial distribution functions from the EXAFS, which contain information on bond lengths and coordination numbers. However, frequently the EXAFS result is dominated mainly by the major coordination type in the sample. A comparison of the determined structural parameters with those of the uranium structure family allows to determine the type of complex formed in the

Für die kontinuierliche gravimetrische Dosierung feiner Pulver im Bereich kleinster Masseströme ( 50mg/s) mittels Dosierwaage und Schwingrinne wurde ein wissensbasierter Dosierregler entworfen, der die Anpassung an die Fließeigenschaften der Dosiergüter durch Insitu-Messung und qualitative Modellierung
erlaubt. Die Regelung erfolgt PC-gestützt mit dem echtzeitfähigem Simulationssystem
DynStar. Die leistungsfähige Fuzzy-Shell erlaubt die effiziente Generierung und Erprobung nichtlinearer Reglerstrukturen. Damit steht ein komfortables und flexibles Werkzeug für die anwendungsorientierte Forschung auf dem Gebiet der Förderung und Dosierung von Pulvern im Kleinstbereich zur Verfügung.

A setup for radiobiological studies using channeling radiation produced at a beamline of the superconducting electron accelerator ELBE has been optimized in order to reduce the bremsstrahlung and neutron background. The electron beam transport was designed using the code package PARMELA. The interaction of the electrons with the elements of the beam delivery and bremsstrahlung production has been calculated by means of GEANT. These results were used as input for EGS4 to calculate dose distributions in a biological specimen.

Die hochgenaue zeitsynchrone Dosierung feiner Pulver im Bereich kleinster Massenströme (< 100 g/h) ist nur durch gravimetrisch geregelte Masse-Verlaufs-Regelung vorteilhaft realisierbar. Das auf Bruttowägung mit Dosierwaagen basierende Verfahren stellt hohe Anforderungen an die Stell- und Messglieder und an die Regelung.

Im Buch werden der Stand und die Perspektiven der photovoltaischen Stromversorgung dargestellt. Ausgehend von der derzeitigen Energieversorgung wird die Notwendigkeit der Erschließung neuer Energiequellen abgeleitet. Im Kapitel 2 wird das Potential der Solarstrahlung dargestellt. Das Kapitel 3 befaßt sich mit der Technik der photovoltaischen Umwandlung. In den beiden abschließenden Kapiteln werden der Aufbau, die Auslegung und der Betrieb sowohl von photovoltaischen Inselanlagen als auch von netzgekoppelten Photovoltaikanlagen beschrieben. Die Möglichkeiten und Grenzen der photovoltaischen Stromversorgung werden aus energiewirtschaftlicher Sicht verdeutlicht.

The electrical properties of Al, B, N implanted 6H-SiC after flash lamp annealing are discussed in comparison with furnace annealing. The electrical activity of Al is for high concentrations distinctly enhanced using flash lamp annealing. For B implanted layers only a soft enhancement is possible using flash lamp annealing but the dopant outdiffusion is strong reduced. N activated by a two step process. A high temperature short time step follow a furnace step at lower temperatures leads to a soft enhanced electrical activation compared to furnace annealing.

The Ge nanoparticles fabricated by ion implantation technique in SiO2 thin film crystallise after irradiation with high energetic electron beam. The crystallisation process depends on the irradiation dose and intensity. Irradiation with a dose above 6x103 C/cm2 results in cluster growths and above 4x104 C/cm2 in crystallisation. An irradiation of intensity below 150 A/cm2 leads to the crystallisation of Ge nanoparticles in the form of single crystals. For irradiation intensities above this value the formation of twinned and multiply twinned particles (MTP) was observed.

Das Mitte der 90er Jahre im KKW Saporoshje als Pilotprojekt für den 5. Block eingerichtete System zur verbesserten betrieblichen Überwachung wurde auf alle 6 Blöcke erweitert und mittels moderner Kommunikationstechnik an das Informations- und Krisenzentrum der ukrainischen Aufsichtsbehörde in Kiew angeschlossen. Die zur Komplettierung des Rechnernetzes am Standort benötigten aktiven Komponenten wurden einvernehmlich spezifiziert, in Deutschland beschafft, im notwendigen Umfang erprobt, in die Ukraine überführt und dem Partner am Einsatzort unentgeltlich überlassen. Nach der entsprechenden Erweiterung der Software für die Informationsverarbeitung, -übertragung und -bewertung können von jedem der sechs WWER-1000 Blöcke 159 sicherheitsrelevante betriebliche und 25 radiologische Messwerte kontinuierlich erfasst, vor Ort in Form von Tabellen, Grafiken und Schemata online dargestellt und bewertet sowie nach Kiew übertragen werden. Damit steht im Informations- und Krisenzentrum in Kiew der gleiche Informationsumfang für Überwachungszwecke zur Verfügung.

Considering the hypothetical accident scenario of a core melt down for a Light Water Reactor the behaviour of the Reactor Pressure Vessel has to be investigated. The vessel behaviour is governed by multiaxial creep deformation of the three-dimensional vessel with highly non-uniform temperature and stress fields.
Therefore a Finite Element model is developed on the basis of ANSYS/Multiphysics®. Using FLOTRAN® the transient temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain.
The user programmable features (UPF) of the finite element code ANSYS® are used to generate a customized ANSYS-executable including a more general creep behaviour of materials and a damage module. The numerical approach for the creep behaviour is not restricted to a single creep law (e.g. strain hardening model) with parameters evaluated from a limited stress and temperature range. Instead of this strain rate - strain relations can be read from external creep data files for different temperature and stress levels.
The damage module accumulates a damage measure based on the creep strain increment and plastic strain increment of the load step and the current fracture strains for creep and plasticity (depending on temperature and stress level). If the damage measure of an element exceeds a critical value this element is deactivated.
Post test calculations of a scaled core melt down experiment FOREVER-C2 were performed. If the temperature field in the vessel wall is fixed along creeping process, the calculated creep curves disagree with the measurement. Considering the time dependent variation of the temperature field, the calculated results show a good agreement with the measurements.
Currently the FE-Model is improved and validated in the frame of further scaled core melt down experiments.

Ore crystals in clay play a key role in the sulfide oxidation and water mineralization process in abandoned ore mines. Highly mineralized, red-colored solutions are formed by the weathering of the ore particles which causes acid rock drainage (ARD). Major cationic components (>1 g/l) of the ARD solution under study were Zn, Fe, Mg, Al, and Mn. Important minor components were toxic and heavy metals, e.g., As, Cu, Pb, and Cd. This XAS investigation deals with the in-situ characterization of the near-order surrounding of As in ARD solutions containing colloidal particles as well as with the determination of the particle mineralogy. The atomic surrounding of Fe and As in ARD samples is compared to those found in model compounds. The arsenate seems to be bound to the colloids (iron hydroxy sulfate) in a way similar to that of arsenate binding onto ferrihydrite. The presented study is an example for the broad application of XAS techniques to environmental research.

The phase formation in 6H-SiC due to high dose implantation was studied as function of temperature by means of transmission electron microscopy. Two examples demonstrate the feasibility of ion beam synthesis of crystalline phases in 6H-SiC which are epitaxially aligned with the surrounding matrix. In the first example Al+ ions were implanted up to concentrations of 15 at% at temperatures between RT and 800oC. The precipitation of carbon phases due to high dose C+ implantation in 6H-SiC at temperatures between 300°C and 900°C was investigated in the second example.

The influence of growth parameters and melt convection on the solid-liquid interface of intermetallic compounds grown by the RF-floating zone technique was investigated experimentally as well as numerically. Numerical simulations showed that the heat transfer is strongly influenced by the electromagnetically driven and Marangoni convections whereas both the buoyancy and feed rotation have a negligible effect. It was found experimentally that the coil design, the rod diameter and the length of the molten zone influence the solid-liquid interface shape significantly. The electromagnetically driven convection increases dramatically with increasing zone length due to the rapid increase of the non-uniformity of the magnetic field. The minimisation of the zone length and the application of an after heater reduce concave (towards the melt) interface regions which give rise to polycrystalline segments during RF-floating zone crystal growth of complicated intermetallic compounds. However, the adjustment of a complete convex solid-liquid interface shape in RF-floating zone crystal growth requires some additional melt stirring by magnetic forces.

The complexation of neptunium(V) with humic acids at pH 7 was studied by EXAFS and UV-Vis spectroscopy using a natural humic acid from Aldrich as well as a synthetic humic acid model substance (type M42) with well defined functional properties. In addition, we studied the influence of phenolic OH groups on the complexation between humic acids and neptunium(V) in the neutral pH range using Aldrich humic acid in a modified form, i.e., with blocked phenolic OH groups.
The formation of neptunium(V) humate complexes was confirmed for all investigated humic acids by UV-Vis spectroscopy. Neptunium LIII-edge EXAFS spectra were recorded in fluorescence mode at the Rossendorf Beamline (ROBL) at the ESRF in Grenoble. For the first two coordination shells of neptunium(V) the EXAFS spectra were analyzed. The obtained structural information for the axial and equatorial oxygen atoms surrounding the neptunium atom will be presented and compared with results for neptunium(V) hydrates.

We studied the complexation of neptunium(IV) with natural and synthetic humic and fulvic acids at pH 1 by X-ray absorption spectroscopy. Neptunium LIII-edge X-ray absorption spectra were collected in transmission mode at the Rossendorf Beamline (ROBL) at the ESRF in Grenoble. Furthermore, we studied the interaction of neptunium(IV) with Bio-Rex70, a cation exchange resin having solely carboxylate groups, at pH 1. The structural parameters of the near-neighbor surrounding of neptunium(IV) obtained for the interaction of neptunium(IV) with humic substances and with Bio-Rex70 are compared to obtain information on the nature of functional groups of humic substances responsible for binding neptunium(IV) in the acidic pH range.
The results are also compared with structural parameters obtained for neptunium(IV) hydrates as well as for the interaction of thorium(IV) and hafnium(IV) with humic acid and Bio-Rex70.

Soft hadron production is described as a two-step process, where the
interaction of the partonic constituents of the colliding hadrons
leads to the production of intermediate subsystems (fireballs), which
decay subsequently into hadrons. The weights of the various final
states are derived from the corresponding phase-space factors modified
by empirical transition elements. The results compare well with data
at energies between particle production thresholds and ISR
energies. Special emphasis is put on correlation data, which offer the
opportunity to shed some light on the question whether particle
production proceeds via fireballs or strings.

In this conceptual report the idea to establish an European Positron Source for Applied Research ("EPOS") based on new LINAC facilities in Germany (ELBE/Rossendorf or TTF-DESY/Hamburg) is considered. The report contains not only the outline of obvious applications in atomic physics, materials science and surface physics, but also several new methodical developments which are only possible with an intense positron beam. This opportunity will also allow the use and further development of imaging techniques being of special interest for industrial applications.

100 Wissenschaftler und Ingenieure aus elf europäischen Ländern und den USA waren der Einladung des Institutes für Sicherheitsforschung des Forschungszentrums Rossendorf (FZR) zum Fachtag "Wechselwirkungen zwischen Thermofluiddynamik und Neutronenkinetik" gefolgt. Die Tagung fand vom 31. Januar bis 1. Februar 2000 am FZR statt und wurde gemeinsam von den Fachgruppen "Reaktorphysik" und Thermofluiddynamik" der Kerntechnischen Gesellschaft veranstaltet. In 19 Vorträgen wurden Anforderungen an Sicherheitsanalysen aus der Sicht der Wissenschaft, der Industrie und der Gutachter formuliert. Programmschwerpunkte waren die Entwicklung von Methoden zur Kopplung von 3D Neutronenkinetik und Thermohydraulik, die Validierung der Modelle an Hand von Experimenten und die Anwendung für Sicherheitsanalysen von Leichtwasserreaktoren. Am Ende konnte festgestellt werden, dass mit den gekoppelten neutronenkinetisch-thermohydraulischen Systemcodes eine fortgeschrittene Simulationstechnik zur Verfügung steht, die eine wesentliche Erhöhung der Aussagesicherheit von Störfallsimulationen ermöglicht.

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 /1/.

/1/ C. Hennig et al., EXAFS investigation of uranium(VI) complexes formed at Bacillus cereus and Bacillus sphaericus surfaces, Radiochim. Acta (submitted)

Chrome tannage is the most intensively investigated tanning process. Nevertheless, the nature (size) of the chromium - collagen complexes has not been proofed experimentally yet.
We investigated the structure of the chromium complexes in powder and dilute solutions of chromium alum, a basic chrome(III) tannin (Chromosal B), an acetone dehydrated, Chromosal tanned Wet Blue leather, an industrial manufactured leather before and after artificial shrinkage, and gelatin by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy.
It is shown that in solid Chromosal B every Cr atom is surrounded by approximately two other Cr atoms. In 0.2 M Chromosal B solution binuclear, in solid chromium alum and its 0.2 M solution mononuclear chromium complexes are present. In leather and gelatin the bound chromium complexes are approximately binuclear. Partial area shrinkage caused by repeated thermal treatment of the chrome leather did not lead to a significant change of the Cr complex inside the leather. These results support the current theoretical concept of chrome tanning in a direct way and demonstrate the great potential of EXAFS investigations in the leather field.

In a recent paper [1] the hydrolysis and carbonate complexation of Eu(III) was studied by potentiometric titration of 2 ´ 10-4 M Eu(III) solutions in the range pH = 7 - 13. Under the experimental conditions applied in this study, the Eu(III) concentration exceeds the solubility of Eu(OH)3(s) or EuOHCO3(s) by several orders of magnitude. The formation constants derived for numerous aqueous Eu(III) hydrolysis species and ternary hydroxo-carbonate complexes constants must be considered as erroneous. They are the result of misinterpreting the formation of solid Eu(III) particles as hydrolysis or carbonate complexation in solution.

Three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal hydraulic system codes. In the EU Phare project SRR1/95 these codes have been validated against collected real plant transients by the participants from 7 countries. The two experiments chosen for calculation were such that both primary circuit behaviour and fission power behaviour were strongly affected including movements of control rods. Critical boron concentrations, 3-D core power distributions, time behaviour of total fission power, coolant temperatures and pressures were the main parameters utilised in the validation. Good accuracy of the results was generally achieved comparable to the measurement accuracy. Confidence in the results of the different code systems has increased and the consequences of certain model changes could be evaluated.

Classical molecular dynamics simulations were performed to investigate elementary ion-beam-induced defect production in 3C- and 4H-SiC. A modified Tersoff potential was used to model the interactions between the atoms. For cases where C and Si primary knockon atoms (PKAs) start parallel or antiparallel to the [0001] direction the threshold PKA energy for defect formation as well as the final defect configuration and its formation energy were determined. The elementary defects observed in 3C-SiC and 4H-SiC differ significantly whereas the corresponding threshold PKA energies and the formation energies of the configurations are mostly rather similar. In 4H-SiC new sites for C and Si interstitials were found: One site is situated between two C₃Si₃ hexagonal rings, the other between a C₃ and a Si₃ trigonal ring.

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

The transparencies of this lecture can be requested. Email: M.Posselt@fz-rossendorf.de

Results of a 208 Pb (gamma,gamma') experiment are presented aiming at an identification of the 2 + member of the long-sought two-octupole phonon multiplet. Four E2 excitations have been observed below 6.5 MeV excitation energy, two of them for the first time.
However, in contrast to new results of calculations within the quasiparticle-phonon nuclear model (QPM), no obvious candidate for the two-octupole phonon vibration could be found in the present study. We discuss the J pi=2+ states detected in this as well as previous experiments with respect to their possible two-octupole phonon structure.

The diagnosis and staging of breast cancer could be improved by the development of radiopharmaceutical imaging agents that provide a noninvasive determination of the estrogen receptor (ER) status of tumor cells. Agents labeled with ^99mTc would be especially valuable in this regards. In attempting to achieve this goal, we synthesized four ^99mTc-labeled 7alpha-substituted estradiol complexes. One complex utilizes the "3+1" mixed ligand design to introduce the Tc metal, whereas the other three took advantage of the cyclopentadienyltricarbonylmetal (CpTM) design. The Tc moieties were attached to the 7alpha position of estradiol with a hexyl tether, a monoether tether, or a polyether tether. The corresponding rhenium compounds have binding affinities for the ER of 20-45% compared with estradiol. Radiochemical yields of the Tc-labeled compounds ranged from approximately 15% for the CpT-Tc complexes to 95% for the 3+1 inorganic complex. Tissue distribution studies in immature female rats showed low nonreceptor-mediated uptake in the target organs and high uptake in the nontarget organs such as liver and fat. These complexes represent the first time that estradiol has been labeled at the 7alpha position with ^99mTc and provide a further refinement of our understanding of ligand structure-binding affinity correlations for the ER:

Three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal hydraulic system codes. In the EU Phare project SRR1/95 these codes have been validated against real plant transients by the participants from several countries. Data measured during a test in the Balakovo-4 VVER-1000 have been analysed by coupled codes. In the test, one of two working feed water pumps of the steam generators was switched off at nominal power. The steady-state assembly powers measured before and after this transient are reproduced by the codes with a maximum deviation of about 5 %. The time behaviour of the most safety-relevant parameters, such as total fission power, coolant temperatures and pressures is well modelled. Thermal-hydraulic feedback effects observed in the measurement are described by the codes in a consistent manner. The analyses have shown, that an accurate treatment of the heat transfer from the fuel rods to the coolant is important. In all, the results have increased the confidence in the coupled code analyses of VVER-1000 transients.

The user programmable features (UPF) of the finite element code ANSYS® are used to generate a customized ANSYS-executable including a more general creep behaviour of materials and a damage module. The numerical approach for the creep behaviour is not restricted to a single creep law (e.g. strain hardening model) with parameters evaluated from a limited stress and temperature range. Instead of this strain rate - strain relations can be read from external creep data files for different temperature and stress levels.
The damage module accumulates a damage measure based on the creep strain increment and plastic strain increment of the load step and the current fracture strains for creep and plasticity (depending on temperature and stress level). If the damage measure of an element exceeds a critical value this element is deactivated.
Examples are given for illustration and verification of the new program modules.

Drag and non-drag forces acting on a bubble depend on the bubble diameter. Recently it was found that the lift force occurring in shear flows changes its sign, when the bubble diameter exceeds a certain critical value. This is probably the main reason for the change from a wall-peaked gas fraction profile to a central-peaked one. The paper presents a new method to obtain bubble size distributions and radial gas fraction profiles decomposed according to bubble size classes. It is based on a wire-mesh sensor, capable in resolving individual bubbles. The sensor delivers time sequences of two-dimensional instantaneous gas fraction distributions in a 51.2 mm diameter pipe with a time resolution of 1200 frames per second. After identifying the bubbles in this data, and after quantifying their effective diameter, the data is decomposed according to given bubble size classes. Partial gas fraction distributions are created by checking each element of the measured data array whether it belongs to a bubble the diameter of which is within a given range, or not. Radial profiles calculated from this partial distributions reflect the quantity of gas carried by the selected bub-ble size class. By varying the axial position of a sensor, the evolution of the bubble size distribution and the decomposed radial profiles in an air-water flow along a vertical pipe was studied. It could be confirmed in a real multi-disperse flow, that bubbles larger than a critical diameter are accumulated in the centre of the pipe, while small bubbles tend to move towards the wall.

For mean-field dynamos, we investigate the possibility of determining the radial dependence of alpha which is assumed to be spherically symmetric. Growth rates for magnetic field spherical harmonics with different orders l are supposed to be known by measurement.
An evolutionary strategy (ES) is used for the solution of the inverse problem. Numerically, we find quite different solutions giving nearly the same eigenvalues. The ES is also applied to find functions alpha(r) yielding zero growth rates for the lowest four l-modes. Additionally, a slight modification of the ES is utilized for an ''energetic'' optimization. The consequences of our findings for inverse dynamo theory and for the design of future dynamo experiments are discussed.

The process of reactive sputtering from a silicon target in an Ar/O2 gas mixture is investigated. An optical plasma regulating circuit using the intensity of the 251.9 nm Si I line as setpoint is employed to stabilize the sputtering process. A phenomenological model of the process is derived that, in contrast to previous models, allows to calculate the composition of the growing SiOx film exclusively from measurable process parameters and accounts for the non-uniform deposition at the substrate. Film compositions X predicted this way for different setpoints were verified by Rutherford back-scattering spectroscopy.
As an example, a SiO2/SiO1.5/SiO2 layer stack was prepared applying an appropriate setpoint sequence. During a subsequent high temperature anneal the stack transformes into an ultrathin layer of nanocrystalline silicon embedded in an oxide matrix, a structure that has high potential for applications in novel optoelectronic and non-volatile MOSFET memory devices (nanocrystal memories).

Aufgrund der spezifischen Eigenschaften metallischer Schmelzen ist die Bestimmung lokaler Strömungseigenschaften wesentlich diffiziler als in Luft oder Wasser. Gegenwärtig gibt es auf dem Markt kaum zuverlässige Meßtechnik, um Geschwindigkeiten in Flüssigmetallströmungen speziell bei höheren Temperaturen zu bestimmen, obwohl gerade für Anwendungen in der Industrie (Stahl, Aluminium, Magnesium, ...) ein großer Bedarf festzustellen ist. Eine weitere Optimierung einschlägiger Produktionstechnologien setzt ein umfassendes Wissen über die Struktur und Transporteigenschaften der Strömung voraus.
Die Ultraschall-Doppler Methode wird bereits kommerziell zur Geschwindigkeitsmessung in Fluiden genutzt. Ein wesentlicher Vorteil des Ultraschall-Doppler Verfahrens besteht in der Möglichkeit, nicht-transparente Fluide zu untersuchen, ohne die Strömung durch den Sensor zu stören. Andererseits ist die heute verfügbare Technik auf Anwendungen bei kleinen Temperaturen (T < 150°C) beschränkt. Aus diesem Grund wurden Anstrengungen unternommen, diese Methode für Flüssigmetallanwendungen bei höheren Temperaturen zu qualifizieren. In unserem Labor wurde die Eignung des Ultraschall Doppler Verfahrens für Strömungen von InGaSn, PbBi, SnPb und Natrium bis zu Temperaturen von 250°C demonstriert, wobei es gelang, die Ultraschallenergie in das Fluid einzukoppeln und verwertbare Echosignale aufzunehmen. Mit einem optimierten Meßaufbau wurden Geschwindigkeitsprofile einer Natriumkanalströmung gemessen.

The rapid development of life sciences connected with biochemical investigations of living processes initiated the research for labelling organic compounds during the fifties of the 20^th century. The need for inserting radioactive carbon-14 atoms into aromatic rings became a matter of interest as more than 50% of naturally occurring and biologically active compounds contain benzenoid and heteroaromatic rings. The radionuclide of choice for labelling was ¹⁴C in many cases due to the need for stable isotopic labelling. A number of useful labelling methods was developed.

For reflecting in vivo processes in man and animal the radionuclide of choice changed: the positron emitter carbon-11 became of interest since the external measurement of biochemical processes using Positron Emission Tomography was developed.
The labelling procedures of carbon-14 radiochemistry could not be transferred to carbon-11 chemistry due to the different radionuclide and radiochemical properties as short half life, low substance amounts and high doses rates. New labelling methods for syntheses of ¹¹C-labelled compounds had to be developed.
Initial investigations from 1982 for ¹¹C-labelling of aromatic compounds were unsatisfactory. First in our systematic work a number of suitable labelling syntheses were developed for carbon-11 introduction into benzenoid and heteroaromatic rings (Figure 1, Steinbach at al. J. Labelled Cpd. Radiopharm., 36 (1995) 33-41, Mäding et al. J. Labelled Cpd. Radiopharm., 41 (1998) 647-656, Zessin et al. J. Labelled Cpd. Radiopharm., 42 (1999) 725-736). The labelling position was determined by ¹¹C/¹³C co-labelling experiments and appropriate ¹³C-NMR investigations for the reaction path 1 and 2.

Not all derivatives of choice are available by this synthetic routes so far. An overall view will be given and the chances and limitations of this methods will be discussed.

16alpha-Fluoroestradiol-3,17beta-disulphamate has proven to be a very strong sulphatase inhibitor. Because the sulphatase activity is high in breast cancer tissue there was much hope to image human mammary tumours by using 16alpha-[¹⁸F]fluoroestradiol-3,17beta-disulphamate ([¹⁸F]FESDS) in PET investigations. For biological characterizing, the new radiotracer had to be made available in high specific activity and in radiochemically pure form. Thus, the module-assisted procedure was developed.

The synthesis of [¹⁸F]FESDS consists of two steps. In a first step, 3-methoxymethyloxy-16beta,17beta- sulphuryldioxy-estra-1,3,5(10)-triene (1) reacted with n.c.a. [¹⁸F]fluoride. The labelled product was deprotected by acid hydrolysis to give 16alpha-[¹⁸F]fluoroestradiol ([¹⁸F]FES). In a second step, [¹⁸F]FES was sulphamoylated to [¹⁸F]FESDS by using sulphamoyl chloride in presence of equivalent amounts of Kryptofix 2.2.2 and potassium carbonate. HPLC purification allowed to obtain pure [¹⁸F]FESDS. The synthesis shown in Figure 1 can be carried out in an automated module as a one-pot procedure.

Results: The synthesis required about 90 min from end of bombardment to the final [¹⁸F]FESDS ready for use. The time was composed of the time of synthesis (60 min) and the time of column purification (about 30 min). The decay-corrected yield of [¹⁸F]FESDS was 22 - 26%. The chemical and radiochemical purity was better than 98%. The specific radioactivity was found to be between 250 and 450 GBq/µmol. When starting with 70 GBq n.c.a. [¹⁸F]fluoride, about 8 - 10 GBq [¹⁸F]FESDS can be produced. A typical radiochromatogram of the HPLC purification is shown in Fig. 2.

Dysfunctions of the serotonin transporter (SERT) may cause numerous psychiatric and neurological diseases. The radiotracer (+)-[¹¹C]McN5652 has the best biological properties for PET investigations of the serotonin transporter state (Suehiro et al., 1993, 53:883-892). Unfortunately, sufficient target-to-nontarget ratios in the human brain were obtained after 115 min (Szabo et al., 1995, 20:37-43), which is out of proportion to the half-life of carbon-11 (20.4 min). Our efforts are therefore directed to develop an ¹⁸F-analogue of (+)-McN5652.
The fluoromethyl analogue of (+)-McN5652 (1) has a similar binding affinity (IC₅₀ 1.5 nM) as ((+)-McN5652. For this reason, we developed a synthesis of the [¹⁸F]fluoromethyl analogue of McN5652 ([¹⁸F]FMe-McN, [¹⁸F]1).
The required fluoromethylation agent [¹⁸F]bromofluoromethane 2 was prepared from[¹⁸F]fluoride and dibromomethane (Eq. 1, decay-corrected radiochemical yield 40%, related to [¹⁸F]F^-). The thioester precursor 3 was hydrolyzed by treatment with TBAH. The resulting thiol 4 was reacted with 2 to yield [¹⁸F]FMe-McN 1 with decay-corrected radiochemical yields of 3-5 % (related to [¹⁸F]F^-) and a specific radioactivity of 1100 - 2400 GBq/µmol.

First autoradiographic ex vivo investigations in rats demonstrated that [¹⁸F]FMe-McN is concentrated in brain regions with a high density of the SERT as raphe nucleus and hypothalamus. After preinjection of the SERT inhibitor fluoxetine, a nonspecific distribution of the radiotracer was observed.
These results indicated that the ¹⁸F-labelled fluoromethyl analogue of (+)-McN5652 has a high potential to be the tracer of choice for imaging of the serotonin transporter.

The tridecapeptide Neurotensin (NT) exhibits a high specific affinity to receptors located on various tumours like small cell lung carcinoma or human colon carcinoma. The purpose of this study was to evaluate the potential of using succinimidyl-4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) for the specific radiolabelling of a non-lysine containing oligopeptide. This was demonstrated using the C-terminal bioactive hexapeptide NT(8-13) as well as its partially reduced stabilised congeners [Arg⁸ps(CH₂NH)Arg⁹]NT(8-13), [Arg⁸ps(CH₂NH)Arg⁹, Tle¹²]NT(8-13). The radiosynthesis of [¹⁸F]SFB started from ethyl trimethylammonium benzoate via a standard three-step procedure. Finally O-(N-succinimidyl) N,N,N',N'-tetramethyluronium tetrafluoroborate was used as activating agent to give [¹⁸F]SFB in 40 % overall radiochemical yield related to [¹⁸F]F^- within 100 min (Wester et al. Nucl. Med. Biol. 1996, 23, 365).
Our labelling experiments revealed that [¹⁸F]SFB reacts with selected N-terminal Arg-peptides with moderate to good chemoselectivities in aqueous buffered solutions (phosphate-borate buffer; pH 7.1 - 8.3). To shorten the period of time necessary for a complete consumption of [¹⁸F]SFB we found it advisable to heat the mixture to 40 - 50 °C for 20 min. The desired products were obtained after HPLC purification in radiochemical yields of 10 to 43 % (80 - 120 min) related to [¹⁸F]SFB. The conditions mentioned above allow the active ester to react specifically with the a-amino group of the N-terminal arginine unit. The radioactive product was identified by chromatographic comparison with a reference compound. The reactions carried out with nonradioactive SFB were shown to give the corresponding 4-FB peptides of which their structural identity was confirmed by proton NMR and MS studies.

The labelled peptides display in vitro affinities to the Neurotensin receptor NTR1 in the nanomolar range (K_D values: 1-9 nM). The accumulation of radioactivity in tumour tissue of tumour bearing mice in vivo is still moderate, demonstrated by tumour/blood and tumour/muscle relations of 2-8 after 30 min (calculated from % D/g tissue).

This work is supported by the European Community (BMH4-CT98-3198)

We report the synthesis of POPAM-dendrimers, bearing up to 64 chromophores at their periphery. For these dendrimers radiotracer technique was used to study the liquid-liquid partition of pertechnetate and ¹⁴C-labeled nucleotides in trichloromethane-aqueous systems. Inclusion and release of guest molecules can be controlled by changing the pH. The extraction efficacy increases with rising generation number.

Es wird eine Übersicht gegeben zu den am FZR durchgeführten Arbeiten zur Nutzung von Magnetfeldern in Kristallzüchtungstechnologien. Auf den bei der Si-Cz-Züchtung erreichten Stand des industriellen Magnetfeldeinsatzes wird
hingewiesen, ohne jedoch auf Einzelheiten einzugehen. Ausführlich dargestellt wird der Einsatz eines rotierenden Magnetfeldes bei der GaAs-Züchtung nach dem VGF-Verfahren, und es werden Verallgemeinerungen zu einem optimalen Rühren der Schmelze, z. B. für das Floating-Zone-Verfahren, diskutiert.

When a quickly rotating wheel is brought in touching contact with the surface of a liquid metal pool which may contain any pure metal or alloy it draws material out of the melt. The molten metal solidifies at the, usually water-cooled, wheel, shrinks, and is flinged away by centrifugal forces. The shape of this rapidly quenched metal is determined by the geometry of the chill wheel. In the direct melt extraction of metallic and intermetallic fibres the extraction wheel is equipped with one or more edges aligned around the circumference of the wheel, the length of the fibres is determined by the distance of the grooves made into these edges.
The industrial production of melt-extracted fibres has two certain limitations which are inevitably coupled with the circumferential speed of the wheel. Besides the production rate most of the applications of such fibres demands them to have diameters in the range of 50mm to 100mm. Increasing the rotation rate decreases their cross-section, but far beyond the desired diameter respectively wheel speed the extraction process becomes unstable due to turbulence within the melt and a wavy motion on the surface.
Many patents are concerned with the stabilisation of the melt pool. They propose submersing mechanical parts directly into the melt to avoid the non-stationary conditions produced by the turbulence within the liquid metal pool. Even made of heat resistant ceramics they suffer from corrosion or cracks and do not work at all.
The present work describes contact-less control mechanism by means of steady magnetic fields of different strength and orientation. They can either be applied globally to damp the flow within the whole melt volume or locally to the meniscus region where the fibre is formed, to reach higher Lorentz forces in this very sensitive region.
Model experiments (In-Ga-Sn, liquid at room temperature; no extraction) with global stabilisation were carried out to study the calm down of the turbulent surface of an inductively stirred melt. The influence of the globally applied field onto the fibres has been investigated in a second model experiment using the low melting Sn-Pb and under real hazardous industrial conditions like induction heating and vacuum. Though the otherwise wavy surface was damped down to a nearly mirror-like plane the goal of significant smaller fibre cross-section could not be reached by the global stabilisation alone.
The clearly observable positive tendency towards smaller fibres is presently investigated with two series of model experiments with additional local stabilisation. The smaller volume which needs to be magnetised allows for a 5 times stronger field which can be achieved either by rare earth permanent magnets or a concentration of the globally applied field with magnetic field guides. First results using the second alternative of field concentration show a significant reduction of the fibre cross-section. Using a global field of 0.14T only we have been able to reach 0.7T at the edge of the wheel the outer parts of which including the edges were made of magnetic iron. The widespread range of extraction parameters, most of which have even been not mentioned here, is far from being investigated. As one typical result Sn-Pb fibres have been extracted with and without the locally concentrated magnetic field at a temperature of T=245oC, keeping even the circumferential speed of 7m/sec constant. The amount of fibres with diameter below 80mm increased from 9% to 51% by applying the magnetic field.

Thermocapillary Marangoni convection of liquid gallium was studied experimentally and analytically. Using a sophisticated high-vacuum technique, liquid gallium was filled into the container with an optical window. The main idea was to obtain an oxide-free surface. For this purpose the working container was made as small as possible, so as to minimize the number of residual gas molecules. The amount of gallium introduced into the container was such as to form a layer of 2 mm thickness. This finite-volume technique is the principal advantage and innovation versus all other methods used before. It worked so well that no deterioration of the surface quality was noticeable over 6 months after preparation of the facility. This enabled us to monitor the motion of tracer particles along the free surface and to measure the corresponding velocity profiles.
It turned out that the movement along the free surface is directed from the cold toward the hot area for some temperature range just above the melting temperature. This finding was quite unexpected, since it means that surface tension increases with temperature. In the most investigations, however, the surface tension of gallium is found to decrease with increasing temperature.
This anomalous direction of the thermocapillary flow could be explained by the presence of a small amount of a surface-active contaminant. Despite the high purity of the gallium, laser-ablation analysis of the solidified sample of gallium done after opening of the container revealed 0.5% of lead in the layer of 50 microns depth at the free surface, but no lead in the bulk of the sample was found. Lead is known to be strongly surface-active with respect to gallium, and even a very small admixture can significantly change the surface tension of the latter.
A novel physical model was devised for the flow driven by the gradient of the surface tension induced additionally by the concentration of the adsorbed layer of contaminant, which in turn depends on the temperature. The observed anomalous direction of the flow can be explained as follows: In the hot region of the container the adsorbed layer partly dissolves and its concentration decreases, so that the surface tension increases, driving the surface towards the hot region of the container. This centripetal flow advects the adsorbed layer and restores its concentration, and at the same time reduces the gradient of the surface tension. When the surface concentration exceeds its equilibrium level, the surfactant on the surface begins to dissolve, increasing the bulk concentration. The resulting non-uniformity of the latter is smoothed out by diffusion and advection of the impurity in the liquid bulk. Thus there is a balance between contraction and stretching of the adsorbed layer, as well as between adsorption and desorption of the impurity - which is controlled by its diffusion from and to the surface. Since the diffusion of the impurity is much slower than the thermal or even the viscous one, the flow has a very strong feedback on the driving force. This is different from pure thermocapillary convection in low-Prandtl-number fluids where the coupling between the velocity and the driving temperature field is weak. The strong coupling in the present case could account for the heavily concave surface velocity profile observed in the experiment.

In the first run of the Riga Dynamo experiment an intense flow of liquid sodium produced by an outside driven propeller has generated a slowly growing magnetic field eigenmode. For a slightly decreased flowrate the observed field is slowly decaying. The measured results correspond satisfactorily with theoretical predictions for the growth rates and frequencies. In the report will be presented computational base, optimisation, the detailed design of the experiment, current results and next experimental steps.

Fourfold Al+ implantations into 6H-SiC have been carried out in order to create a laterally structured p-doped layer. This way, a 400 nm thick box-shaped Al profile with a concentration plateau of 5x1019 cm-3 buried 200 nm below the SiC surface could be realized. The defects caused by the ion implantation should be minimized by implantation at higher substrate temperatures and post implantation annealing. In addition to the traditional furnace annealing a flash lamp annealing has been used. The defect structure after implantation and annealing has been investigated by Slow Positron Implantation Spectroscopy (SPIS). It could be shown that vacancies and vacancy agglomerates can be removed using furnace annealing at 1650 0C. However, dislocation loops in the implantation region remain stable at this temperature. Using flash lamp annealing a further defect removal could be observed.

We studied the interaction of uranium(VI) with humic and fulvic acids to obtain information on the binding of uranium(VI) onto functional groups of humic substances. Therefore, various natural and synthetic humic acids (HAs) were chemically modified resulting in HAs with blocked phenolic OH groups. From the original and modified HAs, solid uranyl humate complexes were prepared at pH 2. FTIR spectroscopy and U LIII-edge extended X-ray absorption fine structure (EXAFS) analysis were applied to study the derivatization process of HAs, to study the structure of the uranyl humates and to evaluate the effect of HA functional groups (carboxylic and phenolic OH groups) on the uranyl complexation.
By FTIR spectroscopy it could be shown that the synthesis of modified HAs with blocked phenolic OH groups was successful. These modified HAs are suitable model substances to study the complexation of actinides by humic substances, especially to study the role of phenolic OH groups in dependence on pH.
By EXAFS, identical structural parameters were determined for all uranyl humates. Axial U-O bond distances of 1.78 Å were determined. In the equatorial plane approximately five oxygen atoms were found at a mean distance of 2.39 Å. The blocking of phenolic OH groups of HAs did not change the near-neighbor surrounding of uranium(VI).
The comparison of results obtained by FTIR spectroscopy and EXAFS analyses for uranyl humates prepared from original and modified HAs confirmed that predominantly HA carboxylate groups are responsible for binding of uranyl ions at pH 2. These carboxylate groups are monodentate coordinated to uranyl ions. The influence of phenolic OH groups is insignificant.

High-spin states of the nucleus $^{88}$Sr have been studied via the
reaction $^{80}$Se($^{11}$B,$p$2$n$) at a beam energy of 45 MeV. Gamma-rays
were detected with the six-detector array OSIRIS CUBE. The level scheme of
$^{88}$Sr has been extended up to $E \approx$ 11 MeV and $J = 17$.
Mean lifetimes of three levels have been determined using the
Doppler-shift-attenuation method. The level structures in $^{88}$Sr have
been interpreted in terms of the shell model. The calculations were performed
in the configuration space $(0f_{5/2}, 1p_{3/2}, 1p_{1/2}, 0g_{9/2})$ for
the protons and $(1p_{1/2}, 0g_{9/2}, 1d_{5/2})$ for the neutrons. These
calculations describe the high-spin level sequences linked by $M1$ transitions
with strengths of $B(M1) \leq 1.4$ W.u. as multiplets of seniority
$\upsilon$ = 4 and 6 states including proton configurations and neutron-core
excitations.

Five different species, namely B, Si, P, Ge, and As, have been implanted at MeV energies into (100)-oriented n-type CZ-Si, in order to form deep gettering layers during the subsequent annealing. Then the samples have been contaminated with Cu by implanting the impurity on the backface and an additional annealing. The resulting Cu depth distributions have been measured by secondary ion mass spectrometry. Surprisingly, strong gettering of Cu atoms beyond the projected ion range RP and formation of a well-defined separate Cu gettering band therein has been found for P and As implants. We call this phenomenon the "trans-RP effect". It is an indication of a significant amount of defects in the regions much deeper than RP. Their gettering ability is higher than that of the extended defects around RP, since the amount of Cu atoms gettered beyond RP is, especially for the P implants, much greater than that in the implanted gettering layer at RP. These deep defects have not been detected by transmission electron microscopy and we suggest that they are small interstitial clusters. A mechanism responsible for the migration of self-interstitials from RP into the trans-RP region and their clustering therein is proposed. An explanation is given of the possible reasons for the differences in the results for the phosphorous and arsenic implants.

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 a uranium mining waste pile called "Haberlandhalde" situated near the town of Johanngeorgenstadt, Germany. For this study both culture-dependent and direct (culture-independent) molecular approaches were applied.

In uranium mining waste piles a number of acidophilic chemolithoautotrophic bacteria have been identified, which are able to oxidise sulphide minerals, elemental sulfur, ferrous iron, and in presence of uranium minerals, also U(IV). Especially one representative of this group, Acidithiobacillus ferrooxidans, is of particular interest. This organism has been used industrially in metal leaching from ores and decontamination of industrial wastes.
Sequence analysis of the 16S rRNA genes of several reference strains and uranium mining waste pile isolates of this bacterium revealed specific signatures which distinguish three types within the species. This allowed to develop a technique for analysis of the distribution of the A. ferrooxidans eco-types in the soil samples of a uranium mining waste pile.
The technique is based on amplification of 16S rDNA fragments in total soil DNA by the use of two A. ferrooxidans species specific primers 16S458F and 16S1473R [1]. The resulting amplicons were then digested with a frequently cutting enzyme RsaI which produced three different type-specific profiles [2; 3]. Using this direct approach we have demonstrated that one of the A. ferrooxidans types (type I) was predominant in the soil samples studied and was found in more polluted sites, whereas the type II was found in less contaminated samples. The type III was found mostly to coexist with the type II.
The objectives of this work were to determine whether these eco-types differ in their capability to tolerate and accumulate uranium, and also to study the structural complexes formed at the surfaces of A. ferrooxidans eco-types using spectroscopic techniques as Extended X-ray Absorption Fine Structure (EXAFS), Infra Red (IR) and Raman Spectroscopy. In addition, the most efficient desorbing agent for the accumulated uranium was selected.
The uranium accumulation by the three types of A. ferrooxidans was studied at different metal concentrations and at pH 1.5 and 4. The results obtained (Fig.1) demonstrated that the strains from the three different types possess different capability to accumulate uranium. The amount of uranium biosorbed by the three types increased with increasing concentration of uranium and pH.

Fig.1: Biosorption of uranium by three types of A. ferrooxidans

On the basis of the results obtained studying the uranium tolerance by the three eco-types by the determination of the Minimum Inhibitory concentrations (MICs) of uranium for the growth of the strains studied, one may speculate that the strains of the types I and III are more resistant to uranium, probably because they possess a mechanism which limits the uranium binding below the lethal amounts.
The recovery of accumulated uranium by desorption was investigated using different desorbing agents as sodium carbonate, sodium citrate and EDTA at different concentrations. The results obtained demonstrated that sodium carbonate is able to recuperate up to 97% of the uranium sorbed from the cells of A. ferrooxidans type III, and 88.3 and 88.5 % from the cells of the types I and II, respectively.
Using EXAFS analysis we have found that no significant structural differences were observed between the uranium complexes formed by the thee types of A. ferrooxidans. However, the EXAFS spectra are indicating formation of uranium complexes which are different from those formed by bacilli [4; 5] and other bacteria.
References:
[1] De Wulf-Durand, P. et al., (1997) Appl. Environ. Microbiol. 63, 2944-2948
[2] Selenska-Pobell, S. et al., (2000) Antonie van Leewenhuek (in press)
[3] Selenska-Pobell, S. et al., (1999) Report FZR-285, p. 52
[4] Hennig, C. et al., (2000) Radiochemica Acta. (submitted)
[5] Hennig, C. et al., (1999) Report FZR-285, p. 70

Bacteria in uranium waste piles are of special interest for bioremediation, because they are adapted to the high concentrations of radionuclides and heavy metals which occur in those environments. A large number of Bacillus strains was recovered from the 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 analyses of this protein show that its primary structure differs significantly from those described for the B. sphaericus strains 2362, P-1 and CCM 2177 (EMBL Ac. Nos. M28361, A45814 and AF211170, respectively). However, the B. sphaericus JG-A 12 S-layer protein shares the N-terminal surface layer homology domain with the S-layer protein of B. stearothermophilus PV 72 p2 [2].
Fig. 1: TEM micrograph of the negatively stained na-tive surface layer, isolated from the uranium waste pile isolate Bacillus sphae-ricus JG-A 12.
Additionally one can see fragments of the bacterial flagellum (see the arrow).

The S-layer of B. sphaericus JG-A 12 has a p4 symmetry with a lattice constant of 12.5 nm [1]. S-layers may interact with different metal ions by forming metal clusters [3; 4; 5; 6]. We have demonstrated that the treatment of the native S-layer sheets of B. sphaericus JG-A 12 with Pt- or Pd-salt solutions leads to metal nanocluster formation. The latter is of great interest for the nanotechnology.
Vegetative cells and spores of B. sphaericus JG-A 12 are selectively accumulating large amounts of U, Pb, Cd, Cu and Al from the highly polluted drain waters of the above mentioned waste pile [7]. Using a sol-gel-process we have prepared a nanoscale bio-ceramic, which contains intact bacterial cells or extracted S-layer proteins. First results on heavy metal binding properties of this bio-ceramic will be presented.
References
[1] Raff, J. et al. (1999) 99TH General Meeting of the American Society for Microbiology,
May 30 - June 3, 1999, Chicago, Illinois, USA, J-12, p. 398
[2] Engelhardt, H. et al. (1998) Journal of Structural Biology 124, 276-302
[3] Brown A. D. et al. (1998) FEMS Microbiology Ecology 26, 297-310
[4] Diluweit, S. et al. (1998) Supramolecular Science 5, 15-19
[5] Pompe W. et al. (1999) Zeitschrift für Metallkunde 90 (12), 1085-1091
[6] Shenton W. et al. (1997) Nature 389, 585-587

Bacterial diversity was studied in soil and water samples drawn from different sites and depths of several uranium mining waste piles, mill-tailings and disposal sites by the use of 16S rDNA and RISA retrievals. These studies demonstrated significant differences in the structure of the natural communities and in the degree of bacterial variability between the environments studied. The predominant bacterial groups in the samples analysed were in general site-specific. However, many samples share common bacterial groups, belonging mainly to the g subgroup of Pseudomonas; to the sulfate and metal reducing genera such as Desulfovibrio and Geobacter (d-Proteobacteria); to the Gram-positive bacteria with a low DNA G+C content (Bacillus/Clostridium); to the aerobic chemolithoautotrophs oxidising iron and/or sulfur compounds (Acidithiobacillus); or to those oxidising nitrite (Nitrospina) and ammonium (Nitrosomonas) b-Proteobacteria. Interestingly, 16S rDNA sequences indicating the presence of the recently discovered anaerobic chemolithotrophic ammonium oxidising bacteria named Anammox were found to be ubiquitous in many of the uranium waste samples studied [1]. The Anammox was identified as a novel autotrophic member of the order Planctomycetales, one of the major distinct divisions of Bacteria [2].
In all three kinds of uranium polluted wastes the presence of a large variety of not yet cultured representatives belonging to Holophaga/Acidomicrobium and Cytophaga/Flexibacter clusters was also shown. In addition, many 16S rDNA sequences were affiliated with various undefined so called "candidate" bacterial divisions.

In parallel to the above described culture independent approach, the classical method of enrichment culturing was applied to analyse the bacteria present in the uranium polluted environments. The aim was to culture and study particular bacterial groups which are of interest because of their ability to biotransform heavy metals and radionuclides.
Among the cultured bacterial strains predominant were those belonging to the genera Acidithiobacillus, Agrobacterium, Bacillus, Desulfovibrio, Desulfotomaculum, Leptospirillum, Pseudomonas, Rhizobium, and Stenotrophomonas. Many of the strains cultured are representing novel species within the above mentioned genera.
These natural bacterial isolates are prospective for in situ bioremediation of the uranium mining wastes piles, because they are well adapted to the extremely complex conditions in those heavily polluted environments.

References:

[1] Radeva, G., et al., (1999) Annual Report FZR 285, 56
[2].

A wire-mesh sensor with a time resolution of 1.2 kHz is used to measure bubble size distributions in a gas-liquid flow. The sensor consists of two electrode grids with 16 electrodes each, put in flow direction behind each other. The local instantaneous electrical conductivity is directly measured between all pairs of crossing wires, a tomographic image reconstruction is not necessary. The resulting 16 x 16 sensitive points are equally distributed over the cross section. This resolution is sufficient to detect individual bubbles, which are imaged in several successive frames during its transition through the measuring plane of the sensor. A comparison with high-speed video observations has shown that the sensor causes a significant fragmentation of bubbles. Nevertheless, the measured signals still represent the structure of the two-phase flow before it is disturbed by the sensor. Bubble sizes can therefore be determined by integrating local instantaneous gas fractions over an area of measuring points occupied by the bubble. Bubble size distributions can be obtained if large assemblies of bubbles are analysed. The method was applied to study the establishing slug flow along a vertical tube. The obtained bubble size distributions show the effect of coalescence as well as bubble fragmentation.

A unique parameterization of secondary dilepton yields in heavy-ion experiments at CERN-SPS is proposed.
This parameterization resembles a thermal q \bar q annihilation rate and is supported by the ''dual'' description of hot, strongly interacting matter within either a hadronic or partonic base. Adding the thermal yield and the background contributions (hadronic cocktail, Drell-Yan, correlated semileptonic decays of open charm) the spectral shapes of the CERES/NA45, NA38, NA50 and HELIOS/3 data in experiments with lead and sulfur beams can be well described.

The data of direct single-photon measurements of the WA98 collaboration in the reaction Pb(158 AGeV) + Pb are analyzed within a thermal model with a minimum number of parameters adjusted to the dilepton data obtained by the CERES and
NA50 collaborations in the reactions Pb(158 AGeV) + Au, Pb.
The agreement of our model with the WA98 data points to a unique large thermal source emitting electromagnetic radiation observable in both the real and virtual photon channels.

The unique mechanical properties of ta-C films such as high hardness and Young modulus are directly related to the atomic structure of amorphous carbon. Atomic-scale modeling is a valuable tool to study both growth mechanisms of amorphous carbon films and the properties sensitive to details of their structure, primarily to the content of sp ³-bonded atoms. As it has been recently demonstrated, the steady-state growth of ta-C thin films can be modeled using the molecular dynamics method with realistic empirical interatomic potentials. It was shown that the experimentally observed high contents of i>sp ³-bonded atoms ( up to 90%) can be achieved using a potential function of Brenner with a slightly increased interaction radius. This provides a possibility to investigate the mechanical properties of amorphous carbon networks generated by a realistic growth process simulation, rather than by quenching the liquid carbon at high pressures as was done in previous
studies.

In this contribution we present results of the investigation of average and atomic-level elastic moduli of amorphous carbon networks with different sp ³-contents, corresponding to C⁺ ion energies of E = 30-80 eV in the ion-beam deposition process.
For the sake of comparison, the calculation of the elastic moduli was performed using not only the potential functions of Brenner, but also the potential function of Tersoff. The relaxational part of elastic moduli was computed using 3D-supercells with about
1000 atoms and an accurate iterative method for the solution of large linear systems. The elastic moduli tensor was found to show only small deviations from the elastic isotropy. Taking into account that the Brenner potential functions underestimate the bulk modulus of crystalline diamond, the results are in an agreement with experimental measurements.

It is planned to build a 50 MJ pulsed field laboratory at the Forschungszentrum Rossendorf (near Dresden) to obtain magnetic fields up to 100 T with 10 ms pulse duration. This facility would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free electron lasers (5m to 250m) now under construction at the radiation source ELBE in Rossendorf. For gaining experience in the construction and operation of pulsed magnets, a smaller pulsed field laboratory was established at the Institute for Solid State Physics and Materials Research Dresden (IFW Dresden) in 1999. The laboratory includes pulse magnets with peak fields up to 50 T in a 24 mm bore and a rise time of about 10 ms, and a 40 T long pulse magnet with a 24 mm bore and rise time of about 80 ms. The coils are energized by a 1 MJ, 10 kV capacitor bank with thyristor switches. The bank is subdivided into four identical and independent units. A particular advantage is the possibility to reverse the polarity of the magnetic field pulse by means of a novel circuit with industrial circuit breakers. The design of the power supply is explained in detail. High precision measurements of magnetization and magnetotransport in the temperature range of 1.5 to 300 K have been performed.

The incident energy at which the azimuthal distributions in semi-central heavy ion collisions change from in-plane to out-of-plane enhancement is studied as a function of mass of emitted particles, their transverse momentum and centrality for Au+au collisions. The analysis is performed in a reference frame rotated with the sideward flow angle relative to the beam axis.

The ratio of K^- and K⁺ meson yields has been measured in the systems ⁹⁶Ru+⁹⁶Ru at 1.69 AGeV, ⁹⁶Ru+⁹⁶Zr at 1.69 AGeV, and ⁵⁸Ni+⁵⁸Ni at 1.93 AGeV incident beam kinetic energy. The yield ratio is observed to vary across the measured phase space. Relativistic transport-model calculations indicate that the data are best understood if in-medium modifications of the kaons are taken into account.

Ausgehend von der Entdeckung der Elemente 114, 116 und 118 im Jahre 1999 in Dubna und Berkeley [1, 2] wird ein Überblick über die experimentellen Techniken und die Ergebnisse der letzten 20 Jahre gegeben, die die Entdeckung der Elemente 107 bis 112 in Darmstadt einschließen [3]. Anhand des jahrelangen Prioritätsstreites über die Entdeckung der Elemente 102 bis 105, der durch die verbindliche Namensgebung durch die IUPAC bis einschließlich Element 109 im Jahre 1997 beendet wurde [4], werden die Kriterien für die Entdeckung eines neuen Elementes erläutert.
Im Hauptteil des Vortrages werden anhand eigener experimenteller Arbeiten zur physikochemischen Charakterisierung des Seaborgiums die Grundprinzipien, Methoden und Probleme der Erforschung der chemischen Eigenschaften der schwersten Elemente erläutert [5-7].
In einem Ausblick werden Konzepte zur chemischen Identifizierung der superschweren Elemente 112 und 114 vorgestellt [8,9].

[1] Yu. Ts. Oganessian et al., Physical Review Letters 83 (1999) 3154
[2] V. Ninov et al., Physical Review Letters 83 (1999) 1104
[3] S. Hofmann, G. Münzenberg, GSI Preprint 2000 - 02, submitted to Rev. Mod. Phys.
[4] Pure & Appl. Chem., 69 (1997) 2471
[5] M. Schädel et al., Nature 388 (1997) 55
[6] A. Türler et al., Angew. Chem. 111 (1999) 2349
[7] S. Hübener et al., TAN 99, Seeheim 1999, Extended Abstracts
[8] H.W. Gäggeler et al., GSI UNILAC Proposal, 2000
[9] S. Hübener et al., unveröffentlichte Mitteilung

Eine wesentliche Sanierungsaufgabe in der sächsischen und thüringischen Uranbergbauregion ist die Flutung von ausgedehnten Untertagebergwerken, die in hohem Maße mit Holz ausgebaut sind. Im Flutungsprozess wird das Grubenholz zunehmend vom Luftzutritt abgeschnitten und der natürliche Holzabbau unter der Einwirkung des Grubenwassers findet statt. Bei diesem Vorgang wird Sauerstoff verbraucht und es entstehen reduzierende Bedingungen [1].
Um diesen Prozess zu untersuchen, wurden Redoxpotenzialmessungen und Redoxtitrationen mit Kaliumhexacyanoferrat(III) an hydrothermalen Holzauszügen, Fichtenlignin und Huminsäu-ren unter Verwendung einer Platinelektrode in Kombination mit einer Silber-Silberchloridelek-trode in einer Zelle mit Überführung ausgeführt. Die Redoxpotenziale des Lignins und der Huminsäure wurden in Abhängigkeit vom pH-Wert und der Konzentration untersucht. Nach Extrapolation auf pH 0 und unendliche Verdünnung wurde für beide ein Redoxpotenzial (Eh) von 570"5 mV mit einem negativen pH-Gradienten von 54,0"1 mV/pH erhalten. Dieses Potenzial zeigt, dass organische Zersetzungsprodukte des Holzes Uran(VI) zu Uran(IV) reduzieren können.
Das Reduktionsprodukt Uran(IV) wurde sowohl spektrophotometrisch als U(IV)-arsenazo(III)-Komplex als auch mit Hilfe der laserinduzierten photoakustischen Spektroskopie (LIPAS) nachgewiesen. Photoakustisch fanden wir die für U(IV) typischen Absorptionsbanden bei 630, 650 and 670 nm. Das Vermögen des Lignins Uran(VI) zu reduzieren stieg im pH-Bereich 5-8 von 0,13@10-4 auf 5@10-4 mval/g. Im Falle von Eisen(III) erhielten wir bei pH 4,5 eine Reduktions-kapazität von 0,15 mval/g.
Um die durch den natürlichen Holzabbau im wässrigen Milieu verursachten reduzierenden Eigenschaften zu charakterisieren, wurden Untersuchungen im Hochmoor AKleiner Kranischsee@ am Erzgebirgskamm bei Johanngeorgenstadt durchgeführt. Bei Feldmessungen fanden wir, dass das Redoxpotenzial von der Oberfläche bis zu einer Tiefe von einem Meter um mehr als 800 mV abfiel. Aus der Analyse des Sumpfgases (49,6% CH4, 3,28% CO2, 1,65@10-3% H2S) konnte für das Redoxpotenzial im Moorgrund (pH 5,3, 4°C) ein Eh-Wert von -120 mV hergeleitet werden. Schließt man hiervon auf das Flutungswasser mit seinem höheren pH und seiner höheren Temperatur, so müssten Redoxpotenziale unter -200 mV möglich sein. Würde als Folge des Holzabbaus die Sulfatreduktion in Gang kommen und Sulfid in mikro-molarer Konzen-tration auftreten, so entspräche das einem Redoxpotenzial von -220 mV. Das würde bedeuten, dass so stark anoxische Bedingungen auftreten, das zur Uran(VI)-Reduktion die reduktive Immobilisierung von Arsen(V) als As2S3 (Auripigment) hinzu kommen kann [2].
In tieferen Wasserschichten gefluteter Bergwerke wurden Potenzialerniedrigungen um etwa 700 mV gemessen. Dies wird aber ausschließlich der Oxidation sulfidischer und arsenidischer Erze und Mineralien, wie beispielsweise Pyrit, Markasit und Arsenopyrit zu geschrieben. Diese Potenzialverminderung bewirkt, dass Uran(VI), als Carbonatokomplex vorliegend, unter Gruben-wasserbedingungen zu Uran(IV) reduziert wird, das als Uran(IV)-hydroxid ausfällt und sedimen-tiert.
Die vorliegenden Ergebnisse zeigen, dass die Zersetzung großer Holzmengen in den gefluteten Gruben mithilft reduzierende Bedingungen zu erzeugen und aufrecht zu erhalten. Der natürli-chen Holzabbau im Grubenwasser der zur Uranimmobilisierung beiträgt und u.U. weitergehende reduktive Ausscheidungen verursacht, entspricht damit einem eminent wichtigen natürlichen Reinigungsprozess.
Literatur:

[1] SMWK-Projektbericht 4-7541.83-FZR/512, Juni 1998: AUntersuchung des Einflusses der in Gruben- wässern gelösten organischen Verbindungen auf den Valenzzustand von Radionukliden@

[2] Baraniak et al.: ARedox Reaction Sequence in Flooded Wood-Supported Mines@, Report FZR-272 (1999) p. 51