Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We show that the 3D simulation code GPT (General Particle Tracer) can give very detailed results on both the produced radiation and the evolution of the elctron bunch when special subsets of electrons are tracked instead of individual macro- particles. The model and two apllications are presented.

We outline the diagnostic and transport system of the infrared beam produced by the two free-electron lasers of the ELBE facility.

Es werden Entwurf und Rechnungen zu einem partiellen Wellenleiter f"ur den U50 Undulator des Rossendorfer ELBE Projektes vorgestellt.

Die FEL Projekte am FZR werden vorgestellt.

Production cross sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(pi+)/A_part is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/A_part are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/A_part is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K mesons are neglected.

The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its final phase. The project belongs to the AGE-cluster, that also involves the REFEREE project being used as an input to RESQUE. At FISA 97 the reference data on non-reconstituted specimens were presented together with a set of recommendations on temperature measurements (WP1, WP2). Now, the results on the quality and limiting conditions of the reconstituted weld seam are discussed.

Übersichtsvortrag zu Methoden der Nuklearmedizin

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

Only the investigation of reactor pressure vessel steel from operated NPPs offers the opportunity to evaluate the real toughness response of the material to neutron/ gamma radiation. By investigation of material from the formerly Greifswald NPP the evaluation of a standard VVER-440-RPV design and the assessment of the quality of the used as well prediction rules as assessment tools will be possible. The rather different states (irradiated, irradated/annealed, and irradated/annealed/reirradiated) of the RPVs are a special advantage of the four units operated in Greifswald between 1973 and 1990. The paper describes the first results of these investigations and the next steps.

The potential non-equivalent defects in both 3C- and 4H-SiC are classified by a new method that is based on symmetry considerations. In 4H-SiC their number is considerably higher than in 3C-SiC, since the hexagonal symmetry leads to diversification. The different theoretical methods hitherto used to investigate defects in 3C-SiC are critically reviewed. Classical MD simulations with a recently developed interatomic potential are employed to investigate the stability, structure and energetics of the large number of non-equivalent defects that may exist in 4H-SiC. Most of the potential defect configurations in 4H-SiC are found to be stable. The interstitials between hexagonal and trigonal rings, which do not exist in 3C-SiC, are characteristic for 4H-SiC and other hexagonal polytypes. The structure and energetics of some complex and anisotropic dumbbells depend strongly on the polytype. On the other hand, polytypism does not have a significant influence on the properties of the more compact and isotropic defects, such as vacancies, antisites, hexagonal interstitials, and many dumbbells. The results allow conclusions about the energy hierarchy of the defects.

The work was aimed at the experimental investigation and numerical simulation of coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR). For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been designed. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-code CFX-4. For the design of the facility, calculations were performed to analyze the scaling of the model. It was found, that the scaling of 1:5 to the prototype meets both: physical and economical demands. Flow measurements and the corresponding CFD calculations in the ROCOM downcomer under steady state conditions showed a Re number independency at nominal flow rates. The flow field is dominated by recirculation areas below the inlet nozzles. Transient flow measurements with high performance LDA-technique showed in agreement with CFX-4 results, that in the case of the start up of a pump after a laminar stage large vortices dominate the flow. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. At the start-up case of one pump due to a strong impulse driven flow at the inlet nozzle the horizontal part of the flow dominates in the downcomer. The injection is distributed into two main jets, the maximum of the tracer concentration at the core inlet appears at the opposite part of the loop where the tracer was injected. For turbulent flows the CFD-Code CFX-4 was validated and can be used in reactor safety analysis. Due to the good agreement between measured results and the corresponding CFD-calculation efficient modules for the coupling of thermal hydraulic computer codes with three-dimensional neutron-kinetic models using the results of this work can be developed. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.

A better understanding and optimisation of liquid metal processes requires experimental data of the velocity field. Numerical simulations alone are often of limited value. To measure local velocities in liquid metals or to measure channel flow rates in a contact-less way, almost nothing is available commercially.
We report on various measuring technique developments, their test in different liquid metals, and applications in hot melts. For local velocity measurements, a mechano-optical probe working up to temperatures of about 800°C has been developed [1]. It delivers the two mean velocity components perpendicular to the sensor axis. In the presence of an external steady magnetic field, the use of local potential probes allows to analyse the turbulent properties of the flow in addition to the mean velocity [2]. However, both sensor techniques rely on the introduction of probes into the melt and are thus mainly of interest for laboratory purposes.
The Ultrasound Doppler Velocimetry (UDV) became a powerful tool to measure the velocity structure of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In addition, it can principally operate through the channel wall though a direct contact to the melt reduces ultrasonic losses. However, in case of hot metallic melts the user is confronted with several problems: the application of the ultrasonic transducers is usually restricted to maximum temperatures of 200°C, and a good acoustic coupling between the liquid metal and the related interfaces has to be provided. We report on successful measurements in liquid sodium at 150°C [3] which were performed through the channel wall. To overcome the limitation of ultrasonic transducers to temperatures lower than 200°C, an integrated ultrasonic sensor with acoustic wave-guide has been developed. This sensor can presently be applied at maximum temperatures up to 1000°C. Stable and robust velocity measurements have been performed in various PbBi flows at about 250-300°C. We report on first successful measurements in a CuSn melt of about 620°C and in an Al melt of about 750°C.
Evidently, a fully contact-less measuring technique would be most desirable. Such a method has been developed making use of external magnetic field measurements and inverse reconstruction techniques [4]. We will report on a first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure.
For the flow rate measurement in a pipe, a contact-less solution based on a pair of alternating magnetic field transmitter and receiver has been developed. Test results from a laboratory model and an industrial Al casting process will be presented.

We report on laboratory studies using cold liquid metals as a model of realistic light metal processes. The main feature of such cold (temperatures up to about 300°C) liquid metal models is the availability of measuring techniques allowing to analyse the local transport phenomena with a sufficient resolution. Note that water models of liquid metal processes are only meaningful if the melt flow Reynolds number represents the only determining parameter of the transport processes under consideration, which is seldom the case for real casting processes. As soon as temperature gradients, free-surface phenomena, two-phase flows or electromagnetic phenomena play a role, the water model is always of very limited value.
First we present results on the flow modelling of an investment casting process of aluminium alloys. The configuration basically consists in a U-bend, and the main request is to reduce the high flow velocities during the starting phase of the filling process. They are considered as the main source of problems like bubble or inclusion entrapment. The process was simulated using a plexiglas model and the eutectic melt InGaSn which is liquid at room-temperature. Local velocity measurements have been performed using the ultrasonic Doppler velocimetry, whereas flow rates have been determined independently using the contact-less transmitter technique. Measurements and video visualizations clearly show effects like flow rate oscillations or gas bubble entrapment. Depending on geometric and process parameters, the time-scale to get rid of these entrapments may become longer than the process itself. In order to decrease the maximum values of the velocity at the beginning of the process, an external steady magnetic field has been applied. The measurements show that it is capable of reducing these velocity peaks significantly. The experimental results are compared to numerical simulations.
As a second example we report on model experiments of the electromagnetic stirring of liquid metals in a cylindrical cavity. Different types of alternating magnetic fields, like rotating or travelling fields, are employed for such stirrers. The model experiments reveal that by application of just one type of those fields a strong flow results, but this flow is often of a rather rigid type without a noticeable three-dimensional mixing of the melt. An efficient mixing can be obtained by a combination of the field types. Velocity measurements in rotating, travelling, and combined rotating-travelling fields will be presented demonstrating this behaviour.
Third, we report on systematic studies about the influence of a rotating magnetic field (RMF) on the resulting microstructure of Pb-Sn alloys. The RMF strongly influences the flow in the liquid phase and, thus, the local heat transfer. It results in a significant influence on the nucleation and growth processes, leading to a variety of microstructures. Temperature as well as ultrasonic velocity profile measurements have been performed. Main goal is to find a strategy for refining the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. For a Pb-85wt%Sn alloy, the application of the RMF is capable of changing the columnar dendritic microstructure to an equiaxed one.

Transition to turbulence of a rotating magnetic field driven liquid metal flow in a cylinder is studied experimentally by a probe-less method. A sudden, wide frequency band transition as well as intermittency are observed just at the theoretically predicted linear instability limit. A small geometrical imperfection triggers the transition in the linearly stable regime in a control parameter range where additional unstable steady solutions have been detected numerically. We discuss possibilities to predict theoretically the non-normal transition and its characteristics.

Dendrimere sind nanoskalige, dreidimensional verzweigte Moleküle mit sphärischer Architektur, die auf vielfältige Weise funktionalisiert und modifiziert werden können. Die speziellen Eigenschaften der Dendrimere eröffnen zahlreiche neue Anwendungsmöglichkeiten, insbesondere im Pharmabereich (drug delivery systems, tumor targeting etc.) und motivieren damit auch zu umfassenden Untersuchungen der zugrunde liegenden physiko-chemischen Prozesse. Es ist bekannt, dass die Struktur und die Komplexierungseigenschaften von Dendrimeren in wässrigen Lösungen wesentlich von den Säure-Base-Eigenschaften (Protonierungsgrad) der funktionellen Gruppen und damit vom pH-Wert bestimmt werden.
Im Rahmen dieses Beitrages werden Ergebnisse kalorimetrischer und potentiometrischer pH-Titrationsexperimente in wässriger Lösung an Polyamidoamin-Dendrimeren (PAMAM), die an der Peripherie unterschiedlich funktionalisiert sind (-NH2, -OH, -COOH Gruppen), vorgestellt und diskutiert. Die potentiometrischen pH-Titrationskurven können unter Verwendung von minimal drei simultanen Protonierungsgleichgewichten mit guter Genauigkeit beschrieben werden. Die Ergebnisse sind konsistent mit dem typischen Verhalten von Polyelektrolyten.
Die kalorimetrischen pH-Titrationskurven widerspiegeln die komplexe Natur der ablaufenden Prozesse wesentlich deutlicher. Neben unterschiedlichen Stufen in den kalorimetrischen Titrationskurven, die prinzipiell den Protonierungsgleichgewichten zugeordnet werden können, treten zum Teil endotherme Effekte auf, deren Ursachen noch nicht geklärt sind. Die quantitative Beschreibung der Titrationskurven auf der Basis reiner Protonierungsreaktionen gelingt dadurch nicht vollständig.
Weiterhin werden erste kalorimetrische Ergebnisse zur aus pharmakologischer Sicht wichtigen Wechselwirkung von Dendrimeren mit potentiellen Targetmaterialien am Beispiel von Human Serum Albumin (HSA) präsentiert und diskutiert.

Two asymmetric electroluminescence bands with tunable maxima at around 1.044-1.065 and 0.90-1.00 eV are observed at low temperature in silicon pn diodes prepared by boron ion implantation and subsequent high temperature annealing. The intensity of the two bands increases strongly with increasing the boron concentration above the solubility. A large blue shift of the two bands with increasing the injection carrier concentration was attributed to the three-dimensional confinement of holes in p-type doped spikes localized on a nanometer scale. They are produced by the boron clustering at the end of range defects close to the pn junction. The two bands with a smaller binding energy is attributed to the spatially indirect recombination of the excitons confined around the strain-free p-type doped spike. The band with a higher binding energy is associated with highly strained p-type doped spikes around dislocations. A significant enhancement of the room temperature electroluminescence efficiency of the silicon diode is observed which is attributed to the spatial modulation of the band structure around these p-type doped spikes.

Large improvement of the electroluminescence efficiency was observed from silicon pn diodes prepared by boron implantation. The temperature dependence of the EL and PL of the pn diode shows a different behavior compared to the PL from bulk silicon substrates. Two asymmetric EL bands from trap bands below the free exciton emission band are observed at around 1.065 and 0.92-0.96 eV at low temperature in the silicon pn diode. The intensity of the two bands increases strongly with increasing boron concentration. A blue shift of the two bands with increasing the injection current was observed which is similar to EL in deta-doped semiconductors. The temperature dependence of the EL intensity from the different bands shows that the thermal emission of carriers from these traps is responsible for a strong increase of the band edge radiative emission of silicon. These results are consistent with a rate equation model based on the emission, trapping and recombination processes for a system containing free excitons and bound excitons. Our results give an alternative explanation to the strong increase of the EL efficiency in boron implanted silicon pn diodes [1].
[1] W.L. Ng et al., Nature 410, 192 (2001).

A bound-exciton-induced current bistability is observed under forward bias in an efficient silicon light-emitting diode at low temperatures. Two stable states of the S-type differential conductivity correspond to empty and filled states of bound excitons, espectively. The relationship between the current-voltage characteristic and the bound-exciton population can be accounted for using a rate equation model for bound and free excitons. The consistency between the theoretical and experimental results indicates that bound excitons, despite their neutral-charged states, contribute to the current bistability in silicon p-n junction diodes.

Bakterien in stark kontaminierten Umgebungen mussten effiziente Entgiftungsstrategien zum Überleben ausbilden. Diese können zur Entwicklung ebenso effizienter und innovativer Biosanierungsverfahren auf der Basis der immobilisierten Biokomponenten genutzt werden. Ausgewählt wurden Bakterien einer Uranabfallhalde in Form von intakten Zellen, Sporen und Teilen der Zellwand. Diese binden selektiv und reversibel Uran, Kupfer, Blei, Aluminium und Cadmium mit hoher Kapazität. Ausgangspunkt für die Einbettung der Biokomponenten sind Siliciumoxid-Sole, die durch Änderung des pH-Wertes oder durch Temperaturerhöhung schnell gelieren. Durch Trocknung der Biokompositsole entstehen poröse Xerogele, die als selektive und wiederverwendbare Filter in Sanierungsverfahren zum Einsatz kommen können.

Im Bestrahlungsprogramm Rheinsberg II wurden zur Temperaturbestimmung Temperaturmonitoren aus Diamantpulver verwendet. Das Verfahren nutzt den Einfluss der Temperatur auf die bestrahlungsbedingte Änderung der Gitterkonstanten des Diamantgitters und ist in einer russischen Prüfvorschrift standardisiert. Zur Ermittlung der Temperatur wurde die Gitterkonstante mit einem Röntgen-Diffraktometer nach Bestrahlung und anschließenden Ausheilglühungen in isochronenTemperaturstufen von 50 - 100 K bestimmt. Der Unstetigkeitspunkt auf dem linearisierten Temperaturverlauf der Gitterkonstanten liefert einen Wert für die Bestrahlungstemperatur, der gemäß der Prüfvorschrift neutronenflussabhängig zu korrigieren ist. Es werden starke Messwertstreuungen festgestellt, die die Genauigkeit der Bestimmung des Unstetigkeitspunktes erheblich beeinträchtigen. Darüber hinaus treten systematische Fehler auf. Insgesamt ist die Temperaturbestimmung mit Diamantpulver im Bestrah-lungsprogramm Rheinsberg II als nicht zufriedenstellend einzuschätzen. Der wahrscheinlichste Wert liegt im Bereich von 255 - 265 °C und somit nahe dem Wert, der aus den thermischen Randbedingungen der Experimente abgeschätzt werden kann.

Nitrogen ions were implanted into (100)GaAs at high temperature (400 and 600oC) and high dose (2x10^17 and 6x10^17 ions cm-2) in order to synthesize small GaN crystallites. The defective strip due to implantation is about 500 nm thick and stacking faults appeared as the characteristic defect. Selected area diffraction patterns show that cubic GaN was formed in samples implanted at 600oC. The precipitates formed are typically 5 nm large and are epitaxial to the host GaAs. Some larger precipitates are also observed from which the matching of the two lattices could be determined.

In the axially symmetric magnetic mirror device gas dynamic trap (GDT), on-axis transverse beta (ratio of the transverse plasma pressure to magnetic field pressure) exceeding 0.4 in the fast ion turning points has been first achieved. The plasma has been heated by injection of neutral beams, which at the same time produced anisotropic fast ions. Neither enhanced losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. This observation confirms predicted magnetohydrodynamic stability of plasma in the axially symmetric mirror devices with average min-B, like the GDT is. The
measured beta value is rather close to that expected in different versions of the GDT based 14 MeV neutron source for fusion materials testing.

GDT experiments of significance to a GDT based neutron source development are reported in the areas of generation of axially peaked neutron flux profile, stable confinement with on-axis plasma beta ~40%, and radial electric field control. Skew injection of 4 MW 15-17 keV deuterium neutral beams into central cell resulted in generation of strongly peaked axial profile of neutron flux density. This can be described by a model of fast ion relaxation, which involves classical mechanisms of electron drag and binary ion-ion collisions only. Experiments with the radial limiter biasing show that the plasma density profile and radial losses respond to the electric field profile. An increase of plasma energy was achieved with increased magnetic field in the central cell and optimised radial profile of electric field. In these regimes the on-axis plasma beta near the turning points of fast deuterons exceeded ~40%. The plans for future upgrade of the GDT device are discussed. It suggests considerable increase of NB injected power (up to 10 MW) and extension of the pulse duration from 1 ms up to 3-5 ms. After the upgrade, a significant increase of the electron temperature up to 250-300 eV could be obtained. Properties of the plasma with parameters approaching those in the full-scale neutron source are planned to study in experiments with NB injection into an additional mirror cell which will be installed near to one of the standard mirror coils.

Thin films (dB nm)of hydrogenated amorphous silicon carbide (a-SiC:H),deposited by RF reactive magnetron sputtering,have been ion implanted with high doses (D=1E16¿1E17cm^2) of Ga+ as the implant species.The increased disorder and additional structural modi .cation of a-SiC:H,induced by the implantation of Ga+ results in a considerable change of the optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies in the results obtained by optical transmission and re .ection measurements and as derived from photo-thermal-deflection spectroscopy results.This shift may be attributed both to additional defect introduction and to accompanying structural modi .cation effects,as confirmed by optical absorption measurements in the infra-red region and by Raman spectroscopy results.

Proceedings volume!

In order to enable a better description of ballistic and athermal processes occurring in the initial stage of ion-beam-induced defect formation, the repulsive part of the interatomic potentials of Gao and Tersoff is improved. The first modification concerns the two-body part of the potentials. At small interatomic distances it is replaced by the well-tested potential of Ziegler, Biersack, and Littmark (ZBL). For repulsive interactions between zero and some ten electron volt, an exponential spline function is employed to connect the ZBL potential with the two-body parts of the Tersoff and the Gao potential. The modified two-body potentials and their first derivatives are continuous and monotonic over the whole range of repulsive interaction. They are in good agreement with data obtained by density-functional-theory calculations. Furthermore, the three-body part of the Tersoff and the Gao potential is modified in order to avoid the strong dependence of repulsive interactions between two atoms on the bond-order parameter, i.e. on their coordinations. The modification is performed in such a manner that the total potential and its first derivative remain continuous and monotonic for all repulsive interactions.

The present paper deals with advanced conductivity probes for local void measurements, which were equipped with a micro-thermocouple, which is integrated into the probe at the place of the electrode wire. These probes were used for rapid transient condensation tests in a heat exchanger pipe immersed into a cooling water tank. The experiments serve as data sources for the validation of thermal-hydraulic system codes concerning the modelling of the condensation, particularly with respect to the behaviour and effect of non-condensable gases. The present tests were carried out at the pressurizer test facility DHVA of the University for Applied Sciences in Zittau/Görlitz serving as steam source. The slightly downwards inclined condensation tube was connected to the head of the pressure vessel and supplied with steam in this way. The application of a new type of two-phase instrumentation has revealed details about the transient condensation process. Since test were performed with and without the presence of a non-condensable gas (air), the effect of the gas could be studied. The merits of the probes lie in the ability to distinguish between steam and gas. Without the synchronous temperature and void measurement performed by the probes it would have not been possible to clarify the physical background of the temperature jumps found during the experiments with the non-condensable gas.

Most of the level monitoring systems for pressure vessels containing saturated steam-water mixture use the hydrostatic method. Differential pressure transducers are connected by pulse tubes with nozzles at different height of the pressure vessel. A disadvantage of this method is given by measuring errors cause by evaporation and/or degassing processes in vertical parts of these pulse lines. The error is caused by the decrease of the fluid density in the reference pipe, when a two-phase mixture appears. The present work aimed at the test of a novel differential pressure measuring system that eliminates the influence of density changes in the pulse lines. It is based on two differential pressure transducers, placed accurately at the elevation of the connecting nozzles. They are connected with the pressure vessel only by horizontal pipes. The vertical distance is bridged by a standpipe, the fluid of which is completely separated from the fluid in the vessel. Degassing respectively evaporation effects can therefore completely excluded in the reference column of the new system. The method was tested at the pressurizer test facility of the University of Applied Sciences Zittau/Görlitz on three types of transients including a rapid pressure decrease similar to a loss-of-coolant transient. Traditional differential pressure systems as well as local void probes were used for comparison. The method has proven its advantages compared to the traditional hydrostatic level measurement method.

Im Zuge von Modellbildungen ist es nicht immer möglich, das zu beschreibende Objekt sofort oder direkt durch ein einzelnes Modell vollständig zu erfassen. Vielmehr wird es zunächst mehrere untergeordnete Modelle geben, die jeweils nur verschiedene eingeschränkte Sichten auf das Objekt repräsentieren. Im Beitrag wird untersucht, wie solche Modelle zu einer Modellsymbiose verbunden werden können und wie mit deren Hilfe dann nach einem verbesserten Einzelmodell des zu beschreibenden Objektes gesucht werden kann.

Positron emission tomography (PET) is a powerful imaging technique for the in vivo study of molecular interactions and molecular pathways in the human body. In combination with approprately labelled radiotracers, PET offers exceptional possibilities to study physiology, metabolism, pharmacokinetics and modes of action of novel and established drugs, and food ingredients.

The key element of PET is the PET-radiotracer, a compound labelled with a short-lived positron emitter. The most useful positron emitters for the labelling of organic moleculars are ¹¹C and ¹⁸F which have half-lives measured in minutes, bein 20.4 min and 109.6 min, respectively. Consequently, time dominates all aspects of PET. In this connection the extensive performance of organic radiochemistry using ¹¹C and ¹⁸F is fundamental but also a special challenge. This review will address the recent developemts of organic PET radiochemistry in the synthesis of PET radiotracers with special focus on ¹¹C and ¹⁸F

Examples of a new type of cryptophane molecule incorporating aromatic groups in the bridges (1 - 4) and for the first time, being also supplied with three endo-positional ionizable carboxylic acid function (1) have been synthesized and characterized. The cryptophane triester 2 yielded a solvate (channel inclusion compound) with trichloromethane and water, the X-ray crystal structure of which is reported. The complexation of 1 with low-molecular-weight alcohols in solution was studied, and the liquid-liquid extraction of different metal ions including alkali (Na⁺, Cs⁺), alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), and the lanthanide metal ions Eu³⁺ and Yb³⁺ in an extraction system containing metal nitrate buffer/H₂O/1/CHCl₃ was examined. Molecular modeling calculations of the cryptophanes 1 and 2, and of the Eu³⁺ complex of 1 were carried out contributing to the discussion.

Low concentration of toxic radioactive metals in environmental samples often limits the interpretation of results of infrared studies investigating the interaction processes between the metal ions and environmental compartments. For the first time, we show that photothermal infrared spectroscopy performed with a pulsed free electron laser can provide reliable infrared spectra throughout a distinct spectral range of interest. In this model investigation, we provide vibrational absorption spectra of a rare earth metal salt dissolved in a KBr matrix and a natural calcite sample obtained by thermal beam deflection technique and FT-IR spectroscopy, respectively. General agreement was found between all spectra of the different recording techniques. Spectral deviations were observed with samples containing low concentration of the rare earth metal salt indicating a lower detection limit of the photothermal method compared to conventional FT-IR spectroscopy.

A new method of preparing alumina ceramic surface for brazing it to kovar with conventional Ag-Cu eutectic brazes is presented. The key concept of this approach consists in formation of two inter-layers on the ceramic surface: (i) thin (in nm scale) layer of TiO_x using pulse plasma beams, and (ii) thicker (about 2 µm) layer of TiO_x or metallic Ti using arc PVD technique. Grazing incidence X-ray diffraction (GXRD) analysis shows that the first layer consists most likely of Ti₇O₁₃, whereas the second is either Ti₂O, or metallic Ti - depending on the deposition conditions. Commercial housings of semiconductor diodes have been used as the samples. Brazed housings were tested under routine industrial conditions. The ultimate tensile strength (UTS) of joints reaches the average value of 90 MPa. Vacuum tightness is better than 5x10^-6 mbar l/s. The values of parameters are sufficient to pass the production requirements.

Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreaktor ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können. Es wurden bereits eine Reihe von Experimenten durchgeführt, welche Erkenntnisse hierüber liefern sollen. Begleitend wurden in Einzelversuchen Materialeigenschaften ermittelt, sowie theoretische und numerische Arbeiten durchgeführt.
Für die Simulation von Experimenten zum Versagen der Bodenkalotte, wie OLHF oder FOREVER, ist es notwendig, Kriechen und Plastizität zu berücksichtigen. Gleichzeitig müssen geeignete Modelle das Temperaturfeld in der Behälterwand für die mechanischen Rechnungen bereitstellen. Vom Institut für Sicherheitsforschung des FZR wird ein Finite-Elemente-Modell erstellt, das sowohl die Temperaturfeldberechnung für die Wand als auch die elasto-plastische Mechanik der Behälterwand modelliert. Die bisher durchgeführten Arbeiten werden in diesem Bericht kurz erläutert und mit Beispielen belegt.
Am FZR wurde ein Finite-Elemente-Model entwickelt, das die Verwendung von einfachen Kriechgesetzen, die mit ihren angepassten Konstanten nur für begrenzte Spannungs- und Temperaturbereiche gültig sind, umgeht. Stattdessen wird eine numerische Kriechdatenbasis angelegt, in der die Kriechdehnrate in Abhängigkeit von der Gesamtdehnung, der Temperatur und der Vergleichsspannung abgelegt ist. Eine wesentliche Aufgabe für diese Vorgehensweise besteht in der Generierung und Validierung der Kriechdatenbasis. Zusätzlich wurden alle relevanten temperaturabhängigen Materialeigenschaften mit entsprechenden Modellen in den Code eingegeben. Für die Bestimmung der Versagenszeit wurde ein Schädigungsmodel nach einem Vorschlag von Lemaitre implementiert.
Die Validierung des numerischen Models erfolgt durch die Simulation von und den Vergleich mit Experimenten. Dies geschieht in 3 Stufen: zunächst werden einzelne einachsige Kriechversuche nachgerechnet, was als 1D-Problem bezeichnet wird. In der nächsten Stufe werden sogenannte ¿Rohrversagensexperimente¿ simuliert: das RUPTHER-14 und das ¿MPA-Meppen¿-Experiment. Diese Experimnete werden als 2D-Probleme betrachtet. Schließlich kann das Modell auf skalierte 3D-Versuche angewendet werden, in denen die Bodenkalotte eines Druckwasserreaktors mit ihrer halbkugelförmigen Geometrie wiedergegeben wird. Ein Beispiel hierfür sind die FOREVER-Experimente. In Zusammenarbeit mit den Experimentatoren an der KTH in Stockholm wurden Pre- und Posttest-Rechnungen für diese bisher einzigartigen Experimente durchgeführt, deren Ergebnisse qualitativ und quantitativ sehr zufriedenstellend sind.
Eine wichtige Frage im Rahmen dieser Arbeit ist die Vergleichbarkeit des französischen Reaktordruckbehälterstahls 16MND5 und des deutschen 20MnMoNi5-5, welche chemisch nahezu identisch sind. Da diese beiden Stähle ein ähnliches Verhalten zeigen, sollte es in gewissem Umfang zulässig sein, experimentelle und numerische Daten und Erkenntnisse zwischen beiden zu übertragen.

This paper reports on an extensive study of the characteristics of AuGeSi and CoNd liquid metal alloy ion sources (Focused Ion Beams From Liquid Metal Ion Sources,Research Studies Press,Taunton,Somerset,UK,1991).Such characteristics include current –voltage curves and ion beam mass spectra.A careful investigation has been undertaken where the emitter temperature is the main variable experimental parameter.Theoretical models,or theoretical attempts in certain cases,tend to support the experimental results.The experimental results,in conjunction with existing theories, suggest that simply for reasons of self-consistency two mechanisms must be operative for the production of doubly- charged ions from the AuGeSi source:direct .eld-evaporation and post-ionisation.

We report on the direct measurement of surface plasmon transmissivity of narrow grooves in thin silver films using near-field optical microscopy in an attenuated-total-reflection setup. For different groove widths, we observe characteristic changes in transmissivity that are attributed to resonant gap modes. The results are in good agreement with existing theoretical predictions.

Der Aufbau und die erste Nutzung eines kompakten Flugzeitsystems zur energiedispersiven Untersuchung der Wechselwirkung von schnellen Neutronen mit Materialien sind Inhalt eines Vernetzungsprojektes des Forschungszentrums Rossendorf, an dem auch die Technische Universität Dresden im Rahmen eines gemeinsamen DFG-Projektes mitarbeitet. Die geplanten Flugzeit-Experimente mit gepulsten Neutronen werden an der Strahlungsquelle ELBE durchgeführt werden. Erste Ergebnisse zur Entwicklung eines Neutronen-Produktionstargets werden vorgestellt. Mit Hilfe von Strahlungstransport- und Finite-Elemente-Programmen wurden die Verteilungen der Energiefreisetzung des von der Strahlungsquelle ELBE genutzten Elektronenstrahls und der Temperatur im Neutronen-Radiator sowie die zu erwartenden Teilchenspektren und -flüsse am Messplatz berechnet. Überlegungen zur Entwicklung des Strahlfängers werden diskutiert.

RES³T – the Rossendorf Expert System for Surface and Sorption Thermodynamics – is a digitized thermodynamic sorption database utilizing surface complexation models (SCM). It is mineral-specific and can therefore also be used for complex models of solid phases such as rocks or soils. As to the knowledge of the authors there is no such digital thermodynamic database for surface complexation equilibria existent worldwide, despite of the vast amount of available data.
Data records comprise of mineral properties, specific surface area values,characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. An extensive bibliography is also included, providing links not only to the above listed data items, but also to background information concerning surface complexation model theories, surface species evidence, and sorption experiment techniques.
An integrated user interface helps users to access selected mineral and sorption data, to extract internally consistent data sets for sorption modeling, and to export them into formats suitable for other modeling software. It assists the identification of critical data gaps, the evaluation of existing parameter sets, consistency tests and the establishing of selected reference data sets.
RES³T is implemented as a relational database under MS ACCESS. The database is intended for an international use and is currently converted into a WWW-based version.
A system for illustrating the current blind predictive capabilities of SCM using the RES³T database is the Cu²⁺ sorption onto iron oxyhydroxides. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected to account for electrostatics. The calculation was performed with the FITEQL code, version 3.2. The respective SCM parameters from RES³T were the binding site density for the minerals, the surface protolysis constants, and the brutto stability constants for all relevant surface complexes. The model prediction almost always represented the experimental values for the sorbed amount of Cu²⁺, expressed as conventional distribution coefficients K_D as required by PA software.

Mit Batch- und Durchflussexperimenten wurde, unter Einbeziehung der Mineralauflösung und Sekundärphasenbildung, die U(VI) Sorption auf zwei unterschiedlichen Chloritmineralen untersucht. Hierbei handelte es sich um einen nicht alterierten Ripidolith Chlorit (CCa-2) von Flagstaff Hill (El Dorado County, California, USA), der aus einem Chloritschiefer gewonnen wurde und einen hydrothermal alterierten Chlorit von Grimsel (Schweiz), der aus einer granitischen Kluft gewonnen wurde. Die Durchflussexperimente wurden mit 0,5 g des jeweiligen Chloritpulvers (63-200 µm Korngröße), einer 0.1 M NaClO4-Ausgangslösung, einer U(VI)-Konzentration von 1´10-6 M und bei einem pH von 6,5 durchgeführt. Die Ergebnisse zeigten einen deutlichen Unterschied im Sorptionsverhalten der beiden Chlorite. Der nicht alterierte CCa-2 Chlorit zeigte ein Sorptionsmaximum von 90 % und wies damit eine mehr als 20 % höhere Sorption unter vergleichbaren Bedingungen als der hydrothermal alterierte Chlorit auf. Vorangegangene Untersuchungen am CCa-2 Chlorit [1] und Grimsel Chlorit [2] zeigten, dass diese erhöhte Sorption auf die Bildung von Fe-oxyhydroxiden, wie beispielsweise Ferrihydrit, während der Auflösung des nicht alterierten Chlorits zurückgeführt werden können. Ferrihydrit ist aufgrund seiner hohen spezifischen Oberfläche und seiner hohen Sorptionsaffinität ein wichtiger Sorbent für U(VI). Der alterierte Grimsel Chlorit wurde bereits im hydrothermalen Stadium gelaugt, so dass dieser nicht so stark zur Sekundärphasenbildung neigt wie der CCa-2 Chlorit. Die unterschiedlichen U(VI) Sorptionsergebnisse an den beiden Chloriten belegen diese Interpretation.
/1/ Krawczyk-Bärsch et al. (2003): Chem. Geol. (submitted).
/2/ Arnold et al., (1998): Chem. Geol. 151, 129-141.

Bei stark exothermen Batch- und Semibatch-Prozessen ist die Identifikation des aktuellen Prozesszustandes und die frühzeitige Erkennung von unerwünschten Betriebszuständen sowohl unter dem Aspekt der Anlagen- und Umweltsicherheit als auch aus Gründen der Sicherung einer gleichbleibend hohen Ausbeute und Produktqualität von besonderer Bedeutung. Zur Unterstützung des Bedienungspersonals hinsichtlich einer optimalen Anlagenfahrweise wurde ein auf adaptiven Energie- und Stoffbilanzen basierendes Online-Monitoring-System (MoSys) konzipiert. Die Systementwicklung erfolgte anwendungsorientiert für heterogen katalysierte Hydrierprozesse von Nitroaromaten in Rührkesselreaktoren. Für den Einsatz des Systems im Industriemaßstab wurde MoSys in ein komplexes Batch-Informations-Management-System (BIMS) eingebunden. Somit ist die Anzeige der MoSys-Ergebnisse, wie Umsatz- und Konzentrationsverläufe, simultan zu den primären Prozesssignalen und den chargenorientierten Informationen an den verschiedenen Operatorstationen in der Chemieanlage möglich. Der Test des Zustandserkennungssystems erfolgte an einer Mehrzweckanlage der DEGUSSA AG im Werk Radebeul.
Gezeigt werden der prinzipielle Aufbau des Monitoring-Systems (Berechnungsalgorithmus), die Einbindung und Funktion von MoSys innerhalb des Batch-Informations-Management-Systems sowie die Visualisierung der MoSys-Ergebnisse an den Operatorstationen am Beispiel von einzelnen Screenshots. Die Validierung des Systems an der Industrieanlage ist am Beispiel von Konzentrations- und Umsatzverläufen sowie der Zustandsklassifikation für die Zwischenproduktakkumulation dargestellt. Eine Zusammenfassung, in der die Bedeutung des Einsatzes von BIMS/MoSys für die industrielle Praxis aufgezeigt wird, beschließt den Artikel.

Mittels zeitaufgelöster laserinduzierter Fluoreszenzspektroskopie (TRLFS) wurde die Uranyl(VI) Sorption auf dem Schichtsilikatmineral Muskovit angewendet. Ziel dabei war es, die adsorbierten Oberflächenspezies sowohl auf den Basisflächen als auch auf den Kantenflächen nachzuweisen und zu vergleichen.
Die Muskovit Plättchen wurden dazu bei pH 6.3 für ca. 60 h mit einer 1×10-5 M Uranyl Lösung (0,1 N NaClO4) kontaktiert. Etwa 72 % der Ausgangsmenge an Uranyl wurde unter diesen Bedingungen sorbiert.
Auf den Basisflächen wurde kein Uranyl-Fluoreszenzspektrum erhalten, was zeigt, dass Uranyl vernachlässigbar sorbiert wurde (< 10-12 M/cm2). Die Sorption erfolgt dominierend an den Kantenflächen. Die Spektrenauswertung ergab das Vorliegen von zwei sorbierten Uranylspezies mit Lebensdauern von 1,15 bzw. 9,65 µs. Die Lage der Hauptemissionsbanden stimmen innerhalb der Fehlergrenzen für beide Komplexe überein, was auf eine unterschiedliche Anzahl der umgebenden Wassermoleküle hinweist. Aus diesen Ergebnissen und zusätzlich durchgeführten EXAFS Untersuchungen lässt sich die Sorption von Uranyl(VI) an den Muskovit Kantenflächen am besten mit zwei bidentaten mononuklearen Oberflächenspezies beschreiben.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range different ion species are needed. Therefore alloy liquid metal ion sources (LMIS) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions the predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell-time was used for radiation damage investigations in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.

The aim of the investigation is the growth of high-precision single crystals of intermetallic compounds using well defined magnetic fields. The fundamental problem is conditional on the fact that especially complicated intermetallic compounds are not producible as single crystals over the whole cross-section by the inductive floating-zone melting technique since the geometry of the zone at the solid-liquid-interface is unfavourable. The controlled adjustment of a solid-liquid-interface of desired curvature and the knowledge of the melt convection in liquids with high conductivity can be arranged by the contact-less influence of electromagnetic fields. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni [1]. The significant influence of the electromagnetically driven flow, which acts opposite to the Marangoni convection, makes the solid-liquid interface concave towards the melt.
Comprehensive investigations of the influence of growth parameters such as zone length, power influence and heated region on the solid-liquid interface geometry during RF floating zone crystal growth were carried out experimentally. It could be shown that undesired concave (towards the melt) interface regions cannot be avoided even at optimised parameter configurations [2].
As a result, a two-phase magnetic field pump, which allows a strong manipulation of the convection and therefore of the solid-liquid interface, was designed. It allows to change the flow structure from the typical double vortex to a single one with a strong influence on the phase boundary shape (Fig. 1). The adjustment of a complete convex solid-liquid interface shape in RF-floating zone crystal growth was tackled with this additional melt stirring resulting in a definite improvement of the solid-liquid-interface.

For the purification of uranium contaminated waters various water purification methods (e.g., application of ion exchangers, direct precipitation, microbiological methods) are usually applied. Also solvent extraction applying calix[6]arenes is suitable to separate uranium from aqueous solution [1]. To facilitate the uranium separation from uranium containing waters in practice, we are developing an alternative procedure. For this, calix[6]arenes are permanently fixed onto textile substrates via spacer groups [2]. This method is advantageous especially for smaller remediation objects and objects with lower contamination levels ([UO22+] ~ 1×10-6 M).
In the present work, the extraction efficiency of various calix[6]arenes including their selectivity towards uranium(VI) is studied in a two phases solvent extraction system in dependence on pH value, ligand concentration and the amount of competing ions. The complex formation between uranium(VI) and calix[6]arenes is further studied at pH 4 by means of TRLFS as well as by TRLFS with ultrashort laser pulses. By these methods it is possible to detect uranium and calixarene species at equilibrium directly in the aqueous and organic phase. Reaction mechanisms are discussed and extraction constants are determined. In the presence of competing ions (e.g., calcium, barium, magnesium) the uranium extraction is only slightly decreased. The suitability of the calix[6]arenes as efficient reagents for selective uranium separation from aqueous solution is shown.

[1] Shinkai, S. et al.: Molecular design of calixarene-based uranophiles which exhibit remarkably high stability and selectivity. J. Am. Chem. Soc. 109, 6371-6376 (1987).
[2] Schmeide, K. et al.: Separation of uranium from aqueous solution by textile bound calixarenes. In: Uranium in the aquatic environment. Springer Verlag, Berlin 2002, p. 417-424.

Heavy ion therapy has two definite advantages: good dose localization and higher biological effect. Range calculation of the heavy ions is an important factor in treatment planning. X-ray CT numbers are used to estimate the heavy ion range by looking up values in a conversion table which relates empirically photon attenuation in tissues to particle stopping power; this is one source of uncertainty in the treatment planning. Use of positron emitting radioactive beams along with a positron emission tomograph or a positron camera gives range information and may be used as a means of checking in heavy ion treatment planning. However, the metabolism of the implanted positron emitters in a living object is unpredictable because the chemical forms of these emitters are unknown and the metabolism is dependent on the organ species and may be influenced by many factors such as blood flow rate and fluid components present. In this paper, the washout rate of ¹¹C activity implanted by injecting energetic ¹¹C beams into thigh muscle of a rear leg of a rabbit is presented. The washout was found to consist of two components, the shorter one was about 4.2+-1.1 min and the longer one ranged from 91 to 124 min. About one third of the implanted positron activity can be used for imaging and the rest was washed out of the target area.

A relative biological effectiveness (RBE) not much larger than unity is usually assumed for soft x-rays (up to ~50 keV) that are applied in diagnostic radiology such as mammography, in conventional radiotherapy and in novel radiotherapy approaches such as x-ray phototherapy. On the other hand, there have been recent claims of an RBE of more than 3 for mammography and respective conventional x-rays. Detailed data on the RBE of soft x-rays, however, are scarce. The aim of the present study was to determine the effect of low-energy x-rays on chromosomal damage in vitro, interms of micronucleus induction. Experiments were performed with 25 kV x-rays and a 200 kV x-ray reference source. The studies were carried out on primary human epidermal keratinocytes (HEKn), human fibroblasts (HFIB) and NIH/3T3 mouse fibroblasts. Micronucleus (MN) induction was assayed after in vitro irradiation with doses ranging from 1 to 5.2 Gy. Compared to the effect of 200 kV x-rays, 25 kV x-rays resulted in moderately increased chromosomal damage in all cell lines studied. This increase was observed for the percentage of binucleated (BN) cells with micronuclei as well as for the number of micronuclei per BN cell.
Moreover, the increased number of micronuclei per micronucleated BN cell in human keratinocytes and 3T3 mouse fibroblasts suggests that soft x-rays induce a different quality of damage. For all cell lines studied the analysis of micronucleus induction by 25 kV soft x-rays compared to 200 kV x-rays resulted in an RBE value of about 1.3. This indicates a somewhat enhanced potential of soft x-rays for induction of genetic effects.

To study of the complex formation of dihydroxybenzoic acids with uranium(VI), we measured the spectra of 2,5-dihydroxybenzoic acid (2,5-DHBA) as a function of pH (2.0 - 4.0) and concentration of uranium (0 - 5x10-3 M). The intensity of the spectra changes with pH and uranium concentration. As we found only spectra with one emission maximum and mono-exponential fluorescence decay, we concluded that no excited state reactions could be observed in the experimental conditions. On the other hand, a change in the fluorescence lifetime could be obtained. The fluorescence lifetimes were found to be in the range from 1.8 ns to 5.7 ns. This means that a dynamic quench process occurred. In order to estimate the formation constant of the 2,5-DHBA with uranium, firstly, we evaluated the protonation constant of the carboxylic group of the 2,5-DHBA. It was found to be log K3 = 2.77 ± 0.05, by taking into account the self-quenching effect. This is in good agreement with literature data (2.82) /1/. The 2,5-DHBA itself and uranium quench the fluorescence of the 2,5-DHBA. We evaluated the dynamic quench constants to be KSV = 216 ± 4 for the ligand itself and KSV = 45 ± 1 for uranium. Both have to be taken into consideration for estimating the complex formation constant. Furthermore, in the pH range 2.0 to 4.0, slopes between 0.91 and 1.39 were found for the validation of the stoichiometry. We conclude, therefore, that a one to one complex forms between uranium and 2,5-DHBA. The dependence of the formation constants on pH values was investigated in order to determine the number of protons involved in the complex formation. Since the slope of the pH dependence was -0.79 ± 0.1, we conclude that one proton at most is involved in this complex formation. This suggests that only the carboxylic group is involved in the complex formation. Based on these considerations, the complex formation constant was assigned to be log K = -0.57 ± 0.26. As uranium shows fluorescence properties, the complex formation can be also confirmed using the changes in the fluorescence behavior of uranium. The formed complex itself does not show fluorescence properties, and only the emission of the non-complexed uranium is observed. As example at pH 4.0, formation constants of log K = 3.29 ± 0.16 were assigned for the ligand study and of log K = 3.17 ± 0.32 for the uranium study, respectively./1/ L. Lajunen, R. Portanova, J. Piispanen et al; Pure & Appl.Chem.,69,329 (1997)

In a former study we analyzed the complex formation between uranium and 2,3-dihydroxybenzoic acid using the fluorescence properties of the ligand. The formation constant was found to be log K11 = -3.11 ± 0.16.We have validated this complex formation using the fluorescence properties of uranium. The formed complex has no fluorescence properties. This is confirmd by a monoexponetial fluorescence decay and also the fluorescence spectra show no shift in the emission maxima.However the fluorescence lifetime of the non-complexed uranium in the solution depends on the concentration of the added ligand. This is due to the dynamic quench effect of the ligand molecule. This quench effect is strongly correlated to the pH of the solution. This leads to the conclusion that only the protonated ligand effects this quench process. Taking this effect into account we are able to calculate the fluorescence intensities of the non-complexed uranium and by use of these data the complex formation between uranium and 2,3-dihydroxybenzoic acid. We obtained a one to one complex formation accompanied by the release of two protons from the ligand, as also found in the study of the fluorescence properties of the ligand. However the derived complex formation constants differ between both methods. The formation constant obtained from the uranium study was found to be log K = -3.99 ± 0.44. This is about 0.9 orders of magnitude lower compared to the constant derived from the study of the ligand. The confidence limits of the two data sets overlap nevertheless the deviation of the both constants leads to the conclusion that other reactions may be involved. From the uranium fluorescence we do not expect such reactions. But the non-complexed ligand may show separate reactions in the excited state, which lead to a change of the fluorescence intensity of the ligand and resulting in an increase of the calculated formation constant. The consequence of the inclusion of these reactions in the examination leads to an exact determination of the ligand concentration accompanied by a much better agreement of the assigned formation constants.

The paper presents examples illustrating the current blind predictive capabilities of surface complexation models (SCM) and respective databases. High-quality experimemtal sorption data sets as provided by Phase II of the NEA Sorption Project for its fitting assessment efforts were used. The systems covered are Np(V) sorption onto hematite, U(VI) sorption onto quartz and Se sorption onto goethite. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected to account for electrostatics. All calculations were performed with the FITEQL code, version 3.2. Based on the information in the sorption database RES³T [1] for the above minerals and chemically similar phases, first a set of relevant species was formed. Then respective surface complexation parameters were taken from RES³T: the binding site density for the minerals, the surface protolysis constants, and the brutto stability constants for all relevant surface complexes. To be able to compare and average thermodynamic constants originating from different sources, the normalization concept as introduced by Kulik [2] was applied. Lacking data was substituted by estimates exploiting chemical analogy. The only system-specific parameters directly going into the computations were the solid-liquid ratio and the specific surface area.

The model prediction almost always represented the experimental values for the sorbed amount of Np, U and Se, expressed as conventional distribution coefficients KD as required by PA software, within one order of magnitude or better, provided an adequate chemical system was assumed. Further improvements may arise from a broader data base eliminating the need for data estimations through chemical analogies.

[1] RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics, V. Brendler, A. Vahle, T. Arnold, G. Bernhard, T. Fanghänel, J.Contaminant Hydrology, in press
[2] Sorption modelling by Gibbs energy minimisation: Towards a uniform thermodynamic database for surface complexes of radionuclides. D. Kulik, Radiochim. Acta, 90 (2002), 815-832

Radiometals play an important role in nuclear medicine^1-3 for the diagnosis or therapy of various diseases. Beside technetium-99m, the most frequently used radionuclide for in-vivo- diagnosis because its optimal nuclide properties, economically supply by the ⁹⁹Mo/^99mTc generator and easy preparation of the ^99mTc-radiopharmaceutical in the clinic, current search for metalloradiopharmaceuticals focuses on both unconventional positron emitting metals (e.g. Cu-64, Ga-66, Y-86, Tc-94m) as potential agents for positron emission tomography (PET) and of radiometal agents labeled with particle emitters for radionuclide therapy³. Since the basic requirement for therapeutic radiopharmaceuticals, namely to induce high effective dose for the target but practically no interference with healthy tissue is not fulfilled yet, the number of therapeutic radiopharmaceuticals for routine use is limited.
Besides the availability of suitable nuclides, the design of chelate systems for stable binding of the radiometal is a crucial point in the development of new metalloradiopharmaceuticals. The chemistry of respective chelates designed in recent years for binding technetium and rhenium at various oxidation states will be discussed. Such chelates involve mixed-ligand complexes containing the metalnitrido core at oxidation state V, Tc(III)/Re(III) and organometallic Tc(I)/Re(I) complexes.
Finally, the application of these chelates for labeling peptides and receptor-affine coordination compounds will be demonstrated.

Visualisation of primary prostate cancer and its metastases remains a clinical important problem, state-of-the-art methods like CT, MRI, TRUS (transrectal ultrasound) and ¹⁸F-FDG PET notwithstanding. The difficulties are even more pronounced in case of local recurrence as ¹⁸F-FDG PET, while useful in the detection of metastases, is not considered helpful in the investigation of relapse. The aim of this study was to evaluate the efficacy of ¹¹C-acetate and ¹⁸F-FDG-PET in the detection of prostate cancer and its metastases in patients treated with or without hormonal ablation.
25 patients (age: 54 to 82 years) were investigated during follow-up of a primary prostate cancer, suspected relapse, or metastatic disease using ¹¹C-acetate PET and 15 with ¹⁸F-FDG PET additionally. 14 Patients had antiandrogen treatment at the time of the investigation, the other 11 patients were drug-naive.
Primary tumours were detected in 20/24 (83%) patients using ¹¹C-acetate PET and in 10/15 (75%) patients using ¹⁸F-FDG PET. Based on the results of both PET scans, one patient was diagnosed with a lung cancer as second malignancy. Median ¹⁸F-FDG uptake exceeded that ¹¹C-acetate in distant metastases (SUV=3.2 vs. 2.3, respectively). ¹¹C-acetate uptake, however, was higher in local recurrence and in local lymph node metastases (median SUVs = 2.9 and 3.8) compared to ¹¹C-acetate (median SUVs = 1.0 and 1.1, respectively). ¹¹C-acetate and ¹⁸F-FDG uptake was lower in patients on antiandrogen therapy compared with the drug-naïve patients but ¹¹C-acetate uptake was not significantly impaired. A close correlation of serum PSA level and Gleason score on the one hand and both ¹¹C-acetate uptake and ¹⁸F-FDG uptake on the other hand was observed.
These data confirm that ¹¹C-acetate is more useful than ¹⁸F-FDG in the detection of local recurrences and localised lymph node metastases. ¹⁸F-FDG, however, appears to be more accurate in visualising distant metastases. Antiandrogen therapy reduces tumour metabolic activity and therefore overall PET accuracy but detection of local recurrences by ¹¹C-acetate is not severly compromised. Ultimately, there may be a role for combined ¹¹C-acetate/¹⁸F-FDG PET in the follow-up of patients with prostate cancer and persisting or increasing PSA.

no abstract

The influence of the formation of secondary iron phases on the sorption behavior of U(VI) on chlorite was investigated in batch sorption experiments with two different types of chlorites: an unaltered chlorite from Flagstaff Hill (CCa-2) and a hydrothermally altered chlorite from Grimsel/Switzerland. The easily extractable ions have not been removed in the CCa-2 chlorite and it therefore tends to form secondary phases. In contrast, the hydrothermally altered chlorite is relative resitant to weathering as discussed in Arnold et. al. [1] and therefore does not tend to form secondary phases. The batch sorption experiments were carried out under ambient temperature and pressure using a solid concentration of 0,5 g chlorite in 40 mL 0,1 M NaClO4 solution. The higher sorption capacity of the unaltered CCa-2 chlorite of more than 20 % of the initially added 1´10-6 M U(VI) compared to the hydrothermally altered chlorite is especially striking in the pH region from 6,5 to 8,5 and was attributed to the generation of secondary Fe and Al phases forming during the two months period of the batch sorption experiments. As a consequence of the formation of a new phase additional mineral surface area is generated [2] which serves as a substrate for further uranium sorption. It is well known that Fe-oxyhydroxide particles show a very high affinity for sorbing U(VI) [3]. Our results clearly show that newly-forming secondary phases may increase the sorption capacity of primary minerals. The Diffuse Double Layer Model (DDLM) was applied to model the U(VI) sorption on the two chlorites including the newly-formed secondary phases.

This class of flows is characterized by the feeding of strong electrical currents into a volume of liquid metal. A prominent example of industrial interest is the electrode-welding where the current is supplied via a locally restricted area, leading to high current densities. The interaction of these currents with their own magnetic field drives flows which exhibit phenomena like formation of jets and pinch-effect. Further increasing the current may lead to disruption of the melt column accompanied with a discharge. This can be used for a liquid metal current limiter with self-healing properties.
Local measurements of the flow structures are of obvious interest for a better understanding of these phenomena. The paper will give results from a systematic study of the flow structure performed by means of our mechano-optical velocity probe. The measured flow structure of the evolving jet was found to be in a reasonable agreement with our numerical simulations.

Passing an electrical current through a volume of conducting fluid drives flow via the interaction with its own magnetic field. Among this class of electro-vortical flows the electrode-welding is a prominent example of industrial interest. In such configurations where a strong current is supplied locally, the resulting high current densities show phenomena like formation of jets and pinch-effect. The latter may disrupt the melt column in the case of very strong currents, accompanied by a discharge. Thus pinching can be used for a liquid metal current limiter with self-healing properties.
Local flow measurements are important for a better understanding of these phenomena. This paper gives results from a systematic study of the fluid motion performed with our mechano-optical velocity probe. The measured flow structure of the evolving jet was found to be in a reasonable agreement with our numerical simulations. Local pressure measurements have been consistent with the experimental and numerical results for the flow field.

Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon frequency. Measuring this frequency and comparison to a theoretical model allows the determination of competing higher-order lattice forces.

195-keV Fe+ Ionen wurden mit einer nominellen Dosis von 5x10E16 cmE-2 bei Raumtemperatur in einen GaN(0001)-Wafer implantiert.

Half-sandwich complexes of the type (RCOCp)M(CO)₃] with M ) Re and ^99(m)Tc were synthesized from [M(OH₂)_3-(CO)₃]⁺ in water. The R group can be an organic residue or a receptor binding biomolecule with a spacer to cyclopentadienyl (Cp). This provides a general route to Cp complexes of technetium without the need for starting from [TcBr(CO)₅].
The X-ray structure of [{C_6H5CH₂COC₅H₄}Tc(CO)₃] has been elucidated. The compound crystallizes in the monoclinic space group P2₁/c with a = 16.1454(9), b = 7.6300(6), and c = 12.3922(7) Å and beta = 107.792(6)°. We have chosen a serotonergic receptor ligand (WAY) as an example for the derivatization of Cp with a bioactive molecule. WAY is linked to Cp by an aliphatic chain of variable length. The half-sandwich complexes were prepared from water and organic solvents. The structure of [(WAY4-Cp)Re(CO)₃] could be elucidated. The compound crystallizes in the monoclinic space group P2₁/c with a = 15.7112(6), b = 6.8775(3), and c = 25.5217(12) Å and beta = 103.778(5)°. Quantification of inhibition constants gave a clear structure-activity relationship. A single methylene group between the receptor binding site and the half-sandwich complex gave an IC₅₀ of 217 nM for T_1A, whereas a butylene linker resulted in retention of the inhibition constant with an IC₅₀ of 6 nM with respect to underivatized WAY. For use as radiopharmaceuticals, the compounds have also been prepared with ^99mTc in quantitative yield.

The [¹⁸F]fluoromethyl analogue of (+)-McN5652 ([¹⁸F]FMe-McN) has recently been developed as a radioligand for imaging the neuronal serotonin transporter (SERT) with positron emission tomography (PET). We describe here the autoradiographic evaluation of [¹⁸F]FMe-McN in the brain of rats and pigs. Autoradiographic studies of [¹⁸F]FMe-McN performed on rat and pig brain in vitro showed a high accumulation of radioactivity in the regions rich in SERT, such as amygdala, hypothalamus, superficial gray layer of the superior colliculus, various nuclei of thalamus and substantia nigra. The binding of [¹⁸F]FMe-McN was reduced by citalopram, a highly selective inhibitor for SERT. Similar regional specific binding densities of [¹⁸F]FMe-McN were observed in both species. The regional distribution and specific binding of this radiotracer correlates well with the distribution and regional brain binding of [³H]citalopram. Region-to-cerebellum ratios of [¹⁸F]FMe-McN in vitro reached a maximum value of 20.6 in the rat and 14.5 in the pig. In addition, ex vivo autoradiography of the rat brain was performed 90 min after i.v. administration of [¹⁸F]FMe-McN. The highest regional uptake of [¹⁸F]FMe-McN was observed in the hypothalamic area, substantia nigra and amygdaloid area. There is a high correlation between the in vitro and in vivo binding. The region-to cerebellum ratio in vivo reached a maximum value of 5.1 in the substantia nigra, the highest yet reported for a ¹⁸F-labelled SERT tracer in vivo in this region. Furthermore, the distribution volume of [¹⁸F]FMe-McN calculated from the PET data in various regions of the porcine brain is highly correlated with the SERT density as determined by in vitro autoradiography with [³H]citalopram. Thus, [¹⁸F]FMe-McN has a clear potential as a radiotracer for studies of the SERT distribution in man with PET.

Das vorliegende Projekt hatte die Ermittlung der räumlichen und zeitlichen Verteilung der Kühlmittelparameter am Spaltzoneneintritt bei transienten Prozessen zum Ziel, bei denen an den einzelnen Kühlmitteleintrittsstutzen des Reaktors Unterschiede in der Borkonzentration bzw. in der Kühlmittel-temperatur auftreten. Die Sicherheitsrelevanz ist durch die Auswirkungen von Deborierungs- und Kaltwassertransienten auf die Leistungsfreisetzung im Reaktorkern gegeben.Mit Hilfe von Experimenten an einem Reaktormodell sowie durch Validierung und Nutzung eines dreidimensionalen Fluidynamikcodes (CFX-4) und durch Entwicklung eines vereinfachten Vermischungsmodells (SAPR) wurden die für die Ermittlung der reaktordynamischen Systemantwort notwendigen Tools zur Beschreibung der Verhältnisse am Kerneintritt geschaffen. Mit der Modellierung der räum-lich und zeitlich aufgelösten Bor- bzw. Temperaturverteilung im RDB wurden die Voraussetzungen für die gekoppelte neutronenkinetisch-thermohydraulische Simulation von Deborierungs- und Kaltwas-sertransienten und deren Sicherheitsbewertung entwickelt. Das Vorhaben beschränkt sich auf Vor-gänge ohne Verdampfung des Kühlmittels, die Vermischung innerhalb des Reaktorkerns bleibt aus-geklammert. Um Mehrfachzirkulationen von Temperatur- bzw. Borkonzentrationsstörungen im Pri-märkreis adäquat abbilden zu können, wurde auch die Vermischung im oberen Plenum behandelt. Zur Lösung der Aufgabe wurde die Versuchsanlage ROCOM (Rossendorf Coolant Mixing Model) aufgebaut. ROCOM ist ein 1:5-Modell eines KONVOI DWR. Durch die volle Abbildung aller vier Um-wälzschleifen, die flexible Versuchssteuerung sowie die speziell für ROCOM entwickelte Gittersen-sormesstechnik zur räumlich und zeitlich hochauflösenden Bestimmung von Konzentrationsverteilungen stellt ROCOM heute eine weltweit führende Versuchsanlage dar. Bei den Experimenten wurden transiente Konzentrationsverteilungen am Kerneintritt für alle gemäß Arbeitsplan zu betrach-tenden Szenarien ermittelt und zur Validierung von CFX-4 genutzt. Das vereinfachte Vermischungs-modell SAPR dient zur effizienten Kopplung zwischen dem thermohydraulischen Systemcode und dem dreidimensionalen neutronenkinetischen Kernmodell.

Proper characterization of tin doped indium oxide (ITO) films prepared at various deposition parameters is important to produce the layers with low resistivity and high luminous transmittance. Therefore, thin ITO films were grown on insulating substrates by means of pulsed reactive dual magnetron sputtering at different base pressure, magnetron pulse duration and Ar/O2 ratio. To characterize the layers after deposition, spectroscopic ellipsometry (SE) was applied in combination with optical transmittance and resistivity measurements. Surface roughness obtained by SE was corroborated by atomic force microscopy. A significant variation in film deposition rate was observed for experiments with different magnetron pulse duration due to SE results. It agrees with Auger depth profiling data. The latter also showed that the O/In ratio values close to 1.5 correspond to the lowest film resistivity. For ITO films produced at various deposition conditions it was observed that SE derived free electron parameters ratio demonstrates certain minimum. It corresponds to the lowest film resistivity and high transmittance. SE was also applied in situ as a non contact technique to monitor ITO film resistivity optimization during annealing.

Reactive magnetron sputtering provides possibility of high-quality tin doped indium oxide In2O3:Sn (ITO) film deposition on a large substrates at low temperature. Although resistivity and transmittance of ITO films prepared by this technique greatly depend on the deposition parameters [1], which have to be optimized. Unique combination of the ITO properties is controlled by its electronic band structure parameters [2]; the latter can be characterized by optical methods. That is why, this work is focused on application of spectroscopic ellipsometry (SE) for probing of ITO layers.

The ITO films were grown by sputtering of metallic In (90%) - Sn (10%) alloy targets in atmosphere of Ar and O2 mixture by using pulsed dual magnetron system. Base pressure, Ar/O2 ratio and magnetron pulse duration have been varied during the deposition. The films were prepared on Si (100) covered with 500 nm SiO2 and soda lime glass substrates. Spectroscopic ellipsometry was applied within the wavelength range 300-1700 nm in combination with optical transmittance measurements. The spectral dependences of ellipsometric parameters were acquired in autoretarder mode. SE data were fitted simultaneously with transmittance data by using the model of rough graded layer [3] on substrate.

Such approach yielded ITO film thickness and roughness values, which were corroborated by profilometry and atomic force microscopy respectively. A significant variation in film deposition rate was observed only for experiments with different magnetron pulse duration. This parameter is minimal at 50 µs magnetron on-time, than it reaches maximum at 125 µs followed by further decrease at longer pulse durations. Such behavior can be related to changes in plasma density with variation of pulse length that was obtained by Langmuir probe measurements. The film lowest resistivity at high transmittance was achieved at pulse length 100-150 µs. The ITO optical constants were parameterized in Drude-Lorentz approach that permitted to obtain free electron parameters (plasma, wp, and relaxation, wt, frequencies) and interband transition characteristics. Vertical grading of optical constants through the film was quantified. During variation of base pressure, Ar/O2 ratio and pulse duration the minimum values of wt/wp^2 were reached at optimal deposition parameters that provided the lowest resistivity (3.2 mOhm·cm) of the film along with the high transmittance (0.84 for 180 nm thickness). For non optimal deposition parameters the behavior of wt/wp2 ratio qualitatively resembled resistivity dependence. Only in the vicinity of optimal deposition parameters resistivity is proportional to the ratio wt/wp^2 that points on the applicability of free electron approach in this case. For non optimal deposition parameters mechanisms of electric resistivity are more complex and require more detailed investigation of the film structure.

[1] R.B.H. Tahar, T. Ban, Y. Ohya, Y. Takahashi, J. Appl. Phys., 83 (1998) 2631
[2] O.N. Mryasov, A.J. Freeman, Phys. Rev. B, 64 (2001) 233111.
[3] R.A. Synowicki, Thin Solid Films 313-314 (1998) 394.

Investigations of processes involving actinides and bacteria in environments around nuclear waste repositories are needed for improvement of the scientific basis for performance of safety assessments. Sulfate reducing bacteria (SRB) are of special interest due to their ability to reduce many metals and actinides. Motamedi and Pedersen showed that SRB are frequently distributed in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (HRL, Sweden) [1]. The presented work is focussed on interactions of curium (III) and uranium (VI) with the strain Desulfovibrio äspöensis, DSM 10631T, recovered from the deep granitic groundwater at the Äspö site [1].
The interaction of D. äspöensis with Cm (III) was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. No evidences were found for changes in the oxidation state of Cm (III). At pH 3, no interaction between Cm (III) and bacteria was detected. With increasing pH, a surface complexation of Cm (III) occurs at the cell walls. The Cm (III)/bacteria surface complex is characterized by its emission spectrum (peak maximum at 600 nm) and its fluorescence emission lifetime (160 ± 15 µs).
80 % of the U (VI), solved initially (0.02 mM) in a liquid medium supplemented with lactate (10 mM) and bacterial biomass (1.10 g/L), was removed by the cells of D. äspöensis after 72 h of incubation at pH 5. Kinetic studies showed that the main amount of U (VI) was removed from the medium during the first 24 h. The microbial activity depended on pH, initial U (VI), and biomass concentration. By using X-ray absorption spectroscopy (XAS), we demonstrated that, in contrast to the above mentioned case with Cm (III), changes of the oxidation state of U (VI) in the precipitate formed by D. äspöensis occurred. The cellular localization of uranium removed from the medium was studied by using Transmission Electron Microscopy (TEM) and Electron-Disperse X-ray (EDX) analyses.

[1] Motamedi, M., Pedersen, K., Int. Syst. Bacteriol. 1998, 48, 311-315.

This work was funded by the BMWi under contract number: 02E9491.The authors are indebted for the use of the 248Cm to the U.S.. Department of Energy, Office of Basic Energy Sciences, through the transplutonium element production facilities at Oak Ridge National Laboratory which was made available as part of a collaboration between FZR and the Lawrence Berkeley National Laboratory (LBNL).

To protect the health of the population, knowledge is necessary about the transfer of radioactive heavy metals, like uranium, via the food chain soil-water-plant-animal-human. The overall process of uptake of heavy elements into plant tissues from contaminated soils is quantified using the soil-to-plant transfer factor (TF). The transfer factor of uranium for lupine and dandelion is in the range of 10-2 to 10-3. To obtain a more mechanistic understanding of the uptake of heavy metals in plants knowledge about the individual physical-chemical processes is needed. This study focuses on the determination of uranium speciation after uptake of uranium by plants (lupine, dandelions, lamb¢s lettuce). For the first time, laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy were used to determine the chemical speciation of uranium in plants. Information on the spatial distribution of uranium in the plant was achieved by scanning electron microscopy, coupled with energy-dispersive X-ray microanalysis. Differences were detected between the uranium speciation in the initial solutions (hydrophonic and pore water of soil) and inside the plants. The oxidation state of uranium remained hexavalent after the uptake. The chemical speciation of uranium was identical in the roots, shoot axis, and leaves and was independent of the various investigated plants. First results are reported concerning the speciation of uranium in cell sap and solid cell components after separation. Spectroscopic data of relevant model compounds (e.g. sugar phosphates, inorganic phosphates, carboxylic acids, proteins) are compared with the uranium complexes in the different compartments of the plants.The results indicate that the uranium is predominantly bound to phosphoryl groups but in dependence on the experimental conditions the formation of uranium carboxylate complexes cannot be excluded.

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

The sheet resistance and structural properties of high-fluence Si-implanted diamond were investigated. In order to minimize the radiation damage and to facilitate SiC formation the implantation was performed at 900 °C. All samples were subsequently annealed in an rf-heated furnace at 1500 °C for 10 minutes in order to remove defects and thermally unstable phases. X-ray diffraction, infrared absorption spectrometry and high-resolution cross-sectional transmission electron microscopy revealed the formation of a buried layer inside the implanted diamond, which contains SiC nanocrystallites. These SiC nanocrystals have a cubic structure and are nearly perfectly aligned with the diamond lattice. Raman spectroscopy was applied to analyze radiation-damage-induced graphitization in dependence on the implantation conditions. The sheet resistance of the samples was measured as function of temperature by four point probe technique in van-der-Pauw geometry. The decrease of the sheet resistance with increasing ion fluence unambiguously shows the influence of implantation-induced damage. The behavior of the sheet resistance can strongly be modified by additional nitrogen implantation The resulting higher conductivity is interpreted as partial incorporation of the nitrogen donor into the SiC nanocrystals. However, when the Si fluence exceeds a critical value of 5.3×1017 Si+cm-2 at 900 °C the diamond is irreversibly damaged and defect related conductivity dominates.

The mobility of actinides in the environment is determined by their speciation which is strongly influenced by their oxidation states. Humic acids (HA) influences the speciation of actinides by complexation. However, they have also significant redox properties which can affect the oxidation states of actinides and consequently their migration in the environment. Thus, it is very important to understand both the complexation and the redox properties of HA in natural systems.
In order to study the redox behavior of HA in more detail we synthesized HA model substances with distinct redox functionalities based on the oxidation of diphenolic compounds in the absence and presence of amino acids. These humic acid-like model substances are characterized by elemental compositions and structural elements that are comparable to natural HA. However, they show phenolic/acidic OH group contents that are higher than those of natural HA. For characterization of the redox properties of these synthetic products, their Fe(III) and ferricyanide redox capacities (RC) were determined at pH 3 and pH 9.2, respectively, and compared to that of purified natural HA from Aldrich. The synthetic products show RC that are up to a factor of 11 and 4 higher than that of Aldrich HA at pH 3 and pH 9.2, respectively. Additionally, we modified, i.e., etherified the phenolic OH groups of these HA by methylation with diazomethane. Applying these modified HA we verified the dominating role of phenolic OH groups in the redox behavior of these HA.
The synthesized HA model substances with distinct redox functionalities are applied to further improve the knowledge on the impact of HA on the redox stability of actinides in the environment. We study the redox stability of uranium(VI) complexes of these HA depending on pH. Uranium(IV) that is formed due to the redox process is spectroscopically determined both directly by laser-induced photoacoustic spectroscopy and indirectly in form of the uranium(IV) arsenazo(III) complex.

a-Si:H films prepared by plasma-enhanced CVD with 10% SiH4 in hydrogen have been studied concerning the effect of film thickness on the hydrogen concentration, interconnected void network and mechanical stress. The hydrogen concentration was determined by nuclear reaction analysis. The interconnected void network was studied by the method of ion exchange in glass substrate. The films were prepared at a substrate temperature in the range of 150 - 270°C. The results show that at the substrate temperature of 150°C the film structure develops as the void network decreases with the film thickness. At the substrate temperature of 270°C the film starts to grow with a dense structure and its structural improvement is manifested by the increase of the intrinsic compressive stress with the film thickness. The hydrogen concentration does not depend on the film thickness at any substrate temperature.

The interaction of the two chemical homologues (Cm (III) and Eu(III)) with calcium silicate hydrates (CSH phases) at pH 13.3 has been investigated in batch-type sorption studies using Eu(III) and complemented with time-resolved laser fluorescence spectroscopy (TRLFS) using Cm(III). The sorption data for Eu(III) reveal fast sorption kinetics and a strong uptake by CSH phases with distribution ratios of (6±3)·105 L kg-1. Three different Cm(III) species have been identified: A non-fluorescing species, which was identified as a curium hydroxide (surface) precipitate, and two fluorescing Cm(III)/CSH sorbed species. The fluorescing sorbed species have characteristic emission spectra with main peak maxima at 618.9 nm and 620.9 nm and fluorescence emission lifetimes of 289 ± 11 µs and 1482 ± 200 µs, respectively. From the fluorescence lifetimes it was calculated that the two fluorescing Cm(III) species have one to two and no water molecules left in their first coordination sphere suggesting that these species are incorporated into the CSH structure. A structural model for Cm(III) and Eu(III) incorporation into CSH phases is proposed based on the substitution for Ca at two different types of sites in the CSH structure.
Key words : curium, europium, CSH, sorption, incorporation, TRLFS

A nuclear resonance fluorescence experiment with two highly efficient EUROBALL Cluster detectors has been performed on the Gamma-soft nucleus 194Pt. Dipole excitations were observed between 2 and 4 MeV excitation energy. They are tentatively interpreted as the main fragments of the scissors mode based on the measurec excitation strengths and a comparison to microscopic calculations in the framework of the quasiparticle random phase approximation (QRPA). The data indicate large differences to the neighbouring isotope 196Pt: a doublingof the observed dipole strength and a shift of the energy centroid by about 600 keV. None of the currently available models is able to reproduce these features consistently in both nuclei.

An investigation in the field of the crack initiation determination for Charpy size specimens was carried out. An extensive literature survey of published methods for the crack initiation was performed. Methods based on the stretch zone width measurement, blunting line, multiple gauge measurement, electric potential drop, compliance changing rate, acoustic emission, ultrasonic method and magnetic emission are discussed in the theoretical part of the report. Analytical methods for the critical J-integral evaluation were also taken into account, as well as the expressions for the J-integral calculation. On the basis of the theoretical survey suitable measurement methods were chosen and applied in the experimental programme to several different materials. Namely blunting line related methods, multiple gauge methods, electric potential drop and compliance changing rate methods were used. The initiation J-integrals were evaluated with use of wide range of evaluation procedures and compared together in order to find a reliable method for the crack initiation determination. There was not found a universal method for the crack initiation determination. The performance of the methods was varying in dependence on the investigated material, so the results enable to choose perspective method for considered case.

Low energy X-rays (Eph < 50 keV) are widely used in diagnostic radiology and radiotherapy. However, data on their relative biological effectiveness (RBE) are scarce. Of particular importance for risk estimation are the RBE value of X-rays in the range which is commonly used in mammography (10 - 30 keV). In the present study we have determined clonogenic survival after low-energy X-ray irradiation for 3 cell lines: primary human epidermal keratinocytes (HEKn), mouse fibroblasts (NIH/3T3) and Chinese hamster fibroblasts (V79). Experiments were performed with a 25 kV X-ray tube and compared to 200 kV X-rays as a reference. Compared to the effect of 200 kV X-rays, irradiation with 25 kV X-rays resulted in a decreased survival rate in the murine fibroblasts but not the human epithelial cell line. RBE value was calculated for 10 % surviving fraction. For HEKn cells, RBE was 1.33 ± 0.27, for NIH/3T3 cells 1.25 ± 0.07 and for V79 cells 1.10 ± 0.09. In conclusion, no consistently increased RBE was observed in the various cell lines. Nevertheless, a potential of increased cytogenetic changes has to be considered for risk estimation of low-energy X-rays.

Intersubband transitions in InP-based (Ga,In)As/(Al,In)As MQWs cover the wavelength range beyond 3.5 micron. Application of enhanced conduction band edge discontinuity allows for a reduced intersubband transition wavelength. This can be accomplished by replacing (Al,In)As by Al(As,Sb) barriers that can be grown lattice-matched to InP. (Ga,In)As/Al(As,Sb) MQWs were deposited by MBE and characterised using a combination of x-ray diffraction, photoluminescence and IR absorption measurements. Influence of well thickness and doping behaviour were systematically investigated. By
comparison with simplified theoretical calculations, the electronic band structure (interband and intersubband system) was deduced. Based on the corresponding results, the potential of (Ga,In)As/Al(As,Sb) MQWs for implementation in quantum cascade lasers will be discussed.

Mixed Oxide (MOX) fuel is usually considered as a solid solution formed by uranium and plutonium dioxides. Nevertheless, some physico-chemical properties of (U_1-y, Pu_y)O₂ samples manufactured under industrial conditions showed anomalies in the domain of plutonium contents ranging between 3 and 15 at.%. Cerium is commonly used as an inactive analogue of plutonium in preliminary studies on MOX fuels. Extended X-ray Absorption Fine Structure (EXAFS) measurements performed at the European Synchrotron Radiation Facility (ESRF) at the cerium and uranium edges on (U_1-y, Ce_y)O₂ samples are presented and discussed. They confirmed on an atomic scale the formation of an ideal solid solution for cerium concentrations ranging between 0 and 50 at.%.

The spatial coherence of hard X-rays provided by a bending magnet of the storage ring BESSY II was investigated performing Young's interference experiment. The interference pattern was created by the diffraction of two 2 µm pinholes drilled into a thin tantalum foil by focused ion sputtering. Using an energy-dispersive detector with an energy resolution of 200 eV the interference pattern were detected simultaneously between 5 keV < E < 16 keV scanning a 5 µm pinhole through the detector window. The set-up is suitable to characterise the coherence properties of the beamline in a simple manner, i.e. to deduce parameters as the effective source size, the coherence length and the visibility. For the present case the visibility is near 100% at 5 keV and decreases to 20% at 16 keV.

The spatial coherence of hard X-rays provided by a bending magnet of the storage ring BESSY II was investigated performing Young's interference experiment. The interference pattern was created by the diffraction of two 2 µm pinholes drilled into a thin tantalum foil by focused ion sputtering. Using an energy-dispersive detector with an energy resolution of 200 eV the interference pattern were detected simultaneously between 5 keV < E < 16 keV scanning a 5 µm pinhole through the detector window. The set-up is suitable to characterise the coherence properties of the beamline in a simple manner, i.e. to deduce parameters as the effective source size, the coherence length and the visibility. For the present case the visibility is near 100% at 5 keV and decreases to 20% at 16 keV.