Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Ziel ist es radioaktive Kupfer(II)-Komplexe hoher Stabilität mit einstellbarer Bioverteilung auf der Basis von 3,7-Diazabicyclo[3.3.1]nonan (Bispidin) zu entwickeln. Voruntersuchungen haben gezeigt, dass insbesondere sechszähnige Liganden ein hohes inhärentes Anwendungspotential für die Radionuklidtherapie aufweisen. [1]
Es wird die Darstellung neuer sechszähniger Bispidinderivate mit Pyridin- und Imidazolgruppen präsentiert. Die Komplexbildungseigenschaften gegenüber Kupfer(II) sowie Möglichkeiten zur Kopplung von Biomolekülen werden diskutiert.
Die Synthese der Bispidinliganden (1) erfolgt durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei Pyridin- und Imidazol-Edukte variieren.

Von ausgewählten Vertretern wurden kristalline Kupfer(II)-Komplexe isoliert und die Struktur mittels Röntgendiffraktometrie gelöst. Weiterhin erfolgten Untersuchungen zur Langzeitstabilität dieser Kupfer(II)-Komplexe in Anwesenheit der Konkurrenzliganden Glutathion und Histidin mittels UV/Vis-Spektroskopie.

Ziel/Aim:

Es sollen radioaktive Kupfer(II)-Komplexe hoher Stabilität mit einstellbarer Bioverteilung auf der Basis von 3,7-Diazabicyclo[3.3.1]nonan (Bispidin) entwickelt werden. Voruntersuchungen haben gezeigt, dass hier sechszähnige Liganden am aussichtsreichsten sind [1]. Durch Modifizierung des Bispidingerüstes ergeben sich günstige Möglichkeiten zur Einführung von Biomolekülen und damit zur gezielten Beeinflussung der Bioverteilung.
Es wird die Darstellung sechszähniger Bispidinderivate mit Pyridin- und Imidazolgruppen vorgestellt. Die Komplexbildungseigenschaften gegenüber Kupfer(II) sowie Möglichkeiten zur Kopplung von Biomolekülen werden diskutiert.
Methodik/Methods:
Die Synthese der Bispidinliganden erfolgt durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei Pyridin- und Imidazol-Edukte eingesetzt werden. Von ausgewählten Vertretern wurden kristalline Kupfer(II)-Komplexe isoliert und die Struktur mittels Röntgendiffraktometrie gelöst. Untersuchungen zur Stabilität dieser Kupfer(II)-Komplexe in Anwesenheit der Konkurrenzliganden Glutathion und Histidin sind mittels UV/Vis-Spektroskopie durchgeführt worden.
Ergebnisse/Results:
Die dargestellten sechszähnigen Bispidinliganden weisen eine schnelle Kinetik für die Komplexbildung mit Kupfer(II) in wässriger Lösung auf. Die kristallinen Kupfer(II)-Komplexe zeigen eine verzerrte oktaedrische Koordinationsgeometrie, wobei das Zentralatom nahezu vollständig von der Umgebung abgeschirmt ist. Die entsprechenden Kupfer(II)-Komplexe mit Bispidinliganden sind auch bei einem Überschuss von Konkurrenzliganden wie Glutathion und Histidin stabil.
Schlussfolgerung/Consequences:
Die dargestellten Kupfer(II)-Komplexe mit sechszähnigen Bispidinliganden weisen eine sehr hohe Stabilität auf und verfügen damit über ein hohes inhärentes Anwendungspotential für radiopharmazeutische Anwendungen in Diagnostik und Therapie. Dazu ist es notwendig, Biomoleküle an das Grundgerüst anzukoppeln, um eine selektive Anreicherung der radioaktiven Kupferkomplexe im Zielgewebe zu erzielen. Radiopharmakologische Untersuchungen zur Optimierung der radioaktiven Markierung der Bispidinderivate mit 64/67Cu sowie zur Biodistribution ausgewählter Radiotracer mittels micro-PET sollen sich anschließen.

Sechszähnige Derivate des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) bilden mit einer Reihe von Übergangsmetallen Komplexe hoher Stabilität [1]. Insbesondere die Kupfer(II)-Komplexe weisen ein hohes inhärentes Anwendungspotential für die Radionuklidtherapie auf.
Zum Verbindungstyp 1 gelangt man durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei durch Variation der Pyridin- und Imidazol-Edukte das Löslichkeits- und Komplexbildungsverhalten gezielt eingestellt werden kann.

Die zeitaufgelöste Laser-Fluoreszenz-Spektroskopie wurde eingesetzt, um Aussagen zur Stabilität von Kupfer(II)-Komplexen mit den Bispidinderivaten 1 zu erhalten. Die Struktur ausgewählter Komplexe konnte mittels Röntgendiffraktometrie aufgeklärt werden. Weiterhin wurden spektroskopische Untersuchungen (UV-Vis) zur Langzeitstabilität der Kupferkomplexe in Anwesenheit der Konkurrenzliganden Glutathion und Histidin durchgeführt.

DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5.

The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D.

Systematic code validation is performed by FZR and independent organizations.

Im Rahmen des Vorhabens SR 2444 wurde eine Nachrechnung des ROCOM Experiments T6655_Y1 mit dem CFD-Programm CFX-5 durchgeführt. Die Anlage ROCOM dient zur Untersuchung der Vermischung hypotethischer Kühlmittelpfropfen mit verringerter Borkonzentration bei unterschiedlichen Schleifendurchsetzen des Primärkreislaufs. Für die Nachrechnung mit CFX wurde der Versuch T6655_Y1 ausgewählt. In diesem Versuch beträgt die Dichtedifferenz zwischen dem, in benachbarten Schleifen 1 und 2, vorgelegten Pfropfen und Umgebung 0,25 %. Das Ergebnis des Experiments besteht hauptsächlich in den mittleren und maximalen relativen Absenkungen der Borkonzentrationen (entspricht mittlerer und maximaler Tracerkonzentration in den Versuchen) am Kerneintritt. Die Ergebnisse der Rechnungen zeigen, dass das Rechenprogramm die Phenomena der Vermischung generell gut erfasst hat.

After successfully commissioning the mid‐infrared FEL (U27) and adjoining a second accelerator unit (up to 35 MeV) at ELBE we have modified our plan how to produce radiation in the far infrared.To ensure the continuous variation of the wavelength up to 150 microns we want to complement the U27 undulator by a permanent magnet undulator with a period of 100 mm (U100). The minimum gap of 24 mm and the hybrid construction consisting of Sm/Co magnets and soft iron poles ensures sufficient radiation resistance and allows rms undulator parameters up to 2.7. The large field variation allows us to cover the whole wavelength range by only two different electron energies (e.g. 20 and 35 MeV). To reduce the transverse beam size we use a partial waveguide which is 10 mm high and wide enough to allow free propagation inhorizontal direction. It spans from the last quadrupole in front of the undulator up to the downstream mirror and is somewhat longer than 8 m. To minimize the coupling losses between free propagation and the waveguide mode appropriate bifocal resonator mirrors will be sed. Detailed calculations and computer simulations predict an outcoupled laser power of roughly 35 W around 40 microns and 20 W at150 microns.

We analyze two types of spin observables in the reaction pi D->->Sigma(->)Theta(+) near the threshold. One concerns the spin-transfer coefficients K-x(x) and K-z(z). The second is the deuteron spin anisotropy. These observables are sensitive to the Theta(+) parity and can be used as a tool for the Theta(+) parity determination.

Invariant mass spectra of di-electrons stemming from bremsstrahlung processes are calculated in a covariant diagrammatical approach for the exclusive reaction Dp to p_spnpe⁺e^- with detection of a forward spectator proton, p_sp. We employ an effective nucleon-meson theory for parameterizing the sub-reaction np to p_spnpe⁺e^- and, within the Bethe-Salpeter formalism, derive a factorization of the cross section in the form dsigma_{Dp to pspnpe⁺e^-} /dM = dsigma_{np to pspnpe⁺e^-} /dM x kinematical factor related solely to the deuteron (M is the e⁺e^- invariant mass). The effective nucleon-meson interactions, including the exchange mesons pi, sigma, omega and rho as well as excitation and radiative decay of Delta(1232), have been adjusted to the process pp to pp e⁺e^- at energies below the vector meson production threshold. At higher energies, contributions from omega and rho meson excitations are analyzed in both, NN and Dp collisions. A relation to two-step models is discussed. Subthreshold di-electron production in Dp collisions at low spectator momenta is investigated as well. Calculations have been performed for kinematical conditions envisaged for forthcoming experiments at HADES.

An algebraic method for evaluating bare nucleon matrix elements of quark operators is proposed. Thereby, bare nucleon matrix elements are traced back to vacuum matrix elements. The method is similar to the soft pion theorem. Matrix elements of two-quark, four-quark and six-quark operators inside the bare nucleon are considered.

Film-forming silica-based materials are potentially useful as tough, abrasion-resistant coatings and fire-retardants. However, these formulations are often solvent-based, and there is an actual tendency to replace them by more environmentally friendly, water-borne coatings. Herein we study surfactant-free and water-borne nanocomposite films consisting of silica nanoparticles (20 nm size) embedded in a vinyl polymer matrix. Highly transparent free-standing films were prepared by copolymerizing of 4-vinlypyridine (4VP) with low glass transition temperature comonomers such as n-butyl acrylate (n-BuA) or n-butyl methacrylate (n-BuMA) in the presence of an ultrafine aqueous silica sol. Films with different silica contents (ranging from 14% to 61%) were prepared with thickness around 100 um. The in-depth distribution of the nanoparticles has been studied by extracting the Si profile from Rutherford backscattering spectrometry (RBS) measurements. Standard RBS with 2 MeV He+ was performed to established the Si profile in the near surface region while a focused 3MeV Li+ ion beam (3-4 um) provided by a nuclear microprobe was used in cross-section specimens to determine the in-depth profile at larger depths.

At the Institute of Safety Research of the FZR a finite element model has been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal hydraulic and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool.
At the Alexandrov Research Institute of Technology in Sosnovy Bor (Russia), the thermo-chemical interaction between molten corium and RPV steel is experimentally investigated. The work is done in the frame of the ISTC project METCOR. The experiments show that the ablation of the steel occurs at interface temperatures below the steel melting temperature. The ablation rate significantly depends on the chemical compostion of the corium melt.
The presentation shows a concept for using the METCOR data within the finite element model of the FZR.

To investigate the structural and chemical heterogeneity of dental composites, we analyzed their composition both in whole maps and in selected points by μPIXE, μPIGE and μPBS (Proton Backscattering). Two qualitatively similar biomaterials labeled IV.a and V were studied. Thick disk-shaped, flat-surface samples were prepared by photopolymerization on a glass plate, and investigated at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a ~3 μm spot. Areas of 250 x 250 μm² were mapped, and selected inclusions were analyzed in point mode using three detectors simultaneously. Five areas located ~0.5-2 mm apart of each other and five inclusions from a map for IV.a, as well as one area for V were analysed. Hydroxylapatite and pyrite were used as reference materials. Concentrations from μPIXE spectra were determined by GUPIX calculations. Up to 19 elements were detected, i.e. Ca, Zr, Ba, Yb (major), Fe, Sr, Hf (minor), Mn, Se, Ho (traces) by μPIXE; F, Na, Al, Si by μPIGE; and C, O, F, Al, Si, Ca (and possibly N, Na, Cl) by μPBS. As compared to IV.a, in composite V higher Ca, lower Zr and Ba, and similar Yb levels were found. The mixture in composite IV.a appeared as a heterogeneous map both on a ~1.0 and on a ~0.1 mm scale of the sample. Thus in all μPIXE maps the absolute concentrations of Ca, Zr, Ba and Yb showed rather high dispersion (relative standard deviations ~31-44 %), but the ratios Zr/Ca, Ba/Ca and Yb/Ca were largely constant. The inclusions analyzed in point mode were Zr-rich and although their relative concentrations were roughly constant the absolute ones showed very high dispersion (rel. SD ~120 %). Hence proton microprobe analysis methods are well suited to study the dental composites and to characterize in detail their heterogeneous structure.

While μPIXE of normal and osteoporosis-affected bones was suitable for metals from Ca on (abstract 1 from our group, this volume), it fails to detect low-Z elements. Some of them may be involved in osteoporosis, e.g. F prevents demineralization and N occurs in bone proteins. Here we examined the potential of μPIGE, μPBS and μPIXE to study low-Z elements in the outer surface layer of rat and human bones with osteoporosis. The bone sections were as described (abstract 1), and the μPIGE, μPBS and μPIXE measurements were performed at the Rossendorf nuclear microprobe with 3.1 MeV protons focused to ~3 μm, using concomitantly three detectors.
μPIGE was useful to detect light elements like F, P, Na, S- the concentrations of these elements can be calculated by comparing the characteristic X- ray lines of suitable standards. CaF2, NaCl, pyrite and hydroxylapatite (HA) were used as reference materials. PBS provided information about C, N, O, F, Mg, P and Ca, mainly qualitative at this stage.
Further development would allow N and S analysis, which may help evaluate the bone collagen, supposedly altered in osteoporosis. Only P, S, Cl and Ca were monitored here by PIXE and the concentrations of these elements were calculated by GUPIX. In all bones, a P/Ca ratio of 0.32-0.39 was found, below the 0.46 value of HA, suggesting a fraction of Ca as carbonate in addition to HA. Both P and S concentrations showed variability from bone to bone. The μPIXE maps of P were positively corelated to the Ca maps, evidencing well- ressolved patterns.
Thus the information yielded by μPIGE and μPBS on the light elements from osteoporosis-affected bones was potentially quantitative, complementary to μPIXE, and pathologically relevant, and the three methods complement each other in understanding this bone disease.

In recent studies, PIXE and ERDA showed a high potential for dental composites [1, 2]. However, wide-beam IBA techniques can not explore the biomaterials' granular structure, which requires microbeam methods to be accounted for.
In this report we applied proton μPIXE for mapping the major elements in dental composites, with the aim of evaluating the method's potential. A flat sample with a smooth surface (~ 1 mm thick) of the composite previously labeled IV.a [1,2] was prepared by photopolymerization on a glass plate. Measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ~3 μm. Five areas ~250 x 250 μrn located ~0.5-2 mm apart of each other were mapped on the flat specimen at ~4 μm resolution. The μPIXE maps of Ca, Zr, Ba and Yb clearly evidenced the granular structure of the composite. The mineral particles revealed a polydisperse size distribution and different compositions. Thus while most mineral particles were Ca-rich and not larger than ~8 μm, a small number of much larger inclusions were seen, with size in the ~16-60 μm range and with high levels of Zr, Ba and Yb. Generally the maps of the elements were complementary, but some apparent deviations from this rule were seen in the different areas. This suggests that the mixture of mineral particles may show some degree of heterogeneity visible in the sample on a ~1 mm scale, which is comparable to the diameter of a dental filling. Therefore μPIXE mapping gives structural insight on the dental composites, potentially relevant for the study of their properties and behavior in the oral environment.
[1] E.A. Preoteasa et al., Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 426-430.
[2] E.A. Preoteasa et al., Anal. Bioanal. Chem. 379 (2004) 825-841.

Normal and disease-affected bones have been studied by wide- and microbeam PIXE and other IBA methods, but the biologically-active outer surface layer of bone was not examined in detail. In osteoporosis, the altered metabolism of Ca and trace elements leading to low bone density is not fully understood. μPIXE, μPIGE and μPBS were applied to analyze Ca and other divalent cation-forming metals in the outer layer of femur and tibia from normal and experimental diabetes-affected rats, tibia from humans with osteoporosis-complicated diabetes, clinically sound human femoral neck and normal bovine metacarp. Measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ~3 μm, using concomitantly three detectors. Thick (~1 mm) transversal bone sections were scanned near the surface at ~4 μm effective resolution. Hydroxylapatite was used as a reference. Concentrations were determined from PIXE spectra by GUPIX calculations.
Most elements of the second main group were detected: Mg (at minor levels) by μPIGE and μPBS, and Ca (major) as well as Sr and Ba (traces) by μPIXE.
Other divalent ion-forming trace metals found by μPIXE included Cr, Mn, Fe, Ni, Cu and Zn from the transition groups, and Pb. Only normal bones contained Cr, Mn and Cu. Levels of Ca, Fe, Ni and Zn varied strongly even in the same bone, while Sr showed little change. Ca maps evidenced spatially well-defined patterns of bands, and diabetic rat bones presented Ca-poor regions at the surface. The spatial resolution was weaker in the Fe, Zn and Sr maps and improved in mean profiles normal to the surface.
Near the outer surface of bones the maps, profiles and area concentrations of most divalent metals determined by μPIXE evidenced complex features of element distributions and composition, which may be potentially relevant to the osteoporosis.

To better understand the role of zinc in bone mineralization we studied the distribution of Ca and Zn by microbeam particle-induced X-ray emission (µ-PIXE) profiling and mapping, and of Zn by histochemical mapping and profiling in cortical bovine bone. For µ-PIXE, measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ca. 3 µm, at ca. 4-8 µm effective resolution. Maps, unique scans and side-to-side scan sequences were done for Ca and Zn. The noise in Zn profiles was filtered by Fast Fourier Transform (FFT). For histochemistry, Zn was stained in thick sections by the sulphide-silver reaction. Both µ-PIXE and histochemistry showed that Zn was localized mainly at the surfaces of various structures in bone tissue.

Ion bombardment is a suitable tool to improve tribological properties of polymers. In this study UHMWPE samples were bombarded with 130 keV He ions to the fluences ranging from 1 x 10(14) to 2 x 10(16) cm(-2). RBS and NRA techniques were applied to study compositional transformations induced by ion beam bombardment. Important hydrogen release was observed with increasing ion dose and was correlated with the linear energy transfer (LET). Another important effect observed was the rapid oxidation of samples, which apparently occurs after exposure of implanted samples to the air. Oxygen uptake continues during the prolonged storage of the samples in the air at RT. Up to 10 at.% of oxygen can be incorporated in the implanted layer. Changes of surface layer composition produced important increase in the layer hardness. Scratch tests revealed that the hardening of surface layers does not lead to their higher brittleness.

We report the realization of highly-efficient light emitting MOS devices which are based on hot-electron excitation of rare-earth ions implanted into SiO2. The implantation of Gd+ and Tb+ ions yields emission wavelengths of 316 nm and 541 nm with external quantum efficiencies up to 1% and 16%, respectively. The observed threshold electric fields for observing electroluminescence is in accordance with the injection of hot electrons via Fowler-Nordheim tunneling into SiO2 at field strengths in the range of 8-9 MV/cm. The presence of different electroluminescence bands of the Tb-implanted devices allows us to study details of the hot-electron excitation process.

We study multi-dimensional gravitational models with scalar curvature nonlinearities of types R-1 and R4. It is assumed that the corresponding higher dimensional spacetime manifolds undergo a spontaneous compactification to manifolds with a warped product structure. Special attention has been paid to the stability of the extra-dimensional factor spaces. It is shown that for certain parameter regions the systems allow for a freezing stabilization of these spaces. In particular, we find for the R-1 model that configurations with stabilized extra dimensions do not provide a late-time acceleration (they are AdS), whereas the solution branch which allows for accelerated expansion (the dS branch) is incompatible with stabilized factor spaces. In the case of the R4 model, we obtain that the stability region in parameter space depends on the total dimension D = dim(M) of the higher dimensional spacetime M. For D > 8 the stability region consists of a single (absolutely stable) sector which is shielded from a conformal singularity (and an antigravity sector beyond it) by a potential barrier of infinite height and width. This sector is smoothly connected with the stability region of a curvature-linear model. For D < 8 an additional (metastable) sector exists which is separated from the conformal singularity by a potential barrier of finite height and width so that systems in this sector are prone to collapse into the conformal singularity. This second sector is not smoothly connected with the first (absolutely stable) one. Several limiting cases and the possibility of inflation are discussed for the R4 model.

We discuss the role of gravitational excitons/radions in different cosmological scenarios. Gravitational excitons are massive moduli fields which describe conformal excitations of the internal spaces and which, due to their Planck-scale suppressed coupling to matter fields, are WIMPs. It is demonstrated that, depending on the concrete scenario, observational cosmological data set strong restrictions on the allowed masses and initial oscillation amplitudes of these particles.

In the paper, we report on the status and progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3½ cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. The production of two Nb cavities, with RRR 300 and 40 respectively, has be finished at the beginning of 2005. After delivery, the RF tests will be performed and the preparation of the cavities will be started. At the same time, the design of the cryostat and the fabrication of its components are already finished. Further activities are the design of the diagnostic beam line, the testing of the new photocathode preparation system, and the upgrade of the 262 nm driver laser system.

The distribution of electromagnetic dipole strength in {92, 98, 100}Mo has been investigated by photon scattering using bremsstrahlung from the new ELBE facility. The experimental data for well separated nuclear resonances indicate a transition from a regular to a chaotic behaviour above 4 MeV of excitation energy. As the strength distributions follow a Porter-Thomas distribution much of the dipole strength is found in weak and in unresolved resonances appearing as fluctuating cross section. An analysis of this quasi-continuum - here applied to nuclear resonance fluorescence in a novel way - delivers dipole strength functions, which are combining smoothly to those obtained from (gamma, n)-data. Enhancements at 6.5 MeV and at ca. 9 MeV are linked to the pygmy dipole resonances postulated to occur in heavy nuclei.

We analyze an effect of the coherent Theta+Lambda(1520) photoproduction in gamma D interaction near the threshold. We demonstrate that the coherence effect becomes manifest in a comparison of the nK+ invariant mass distribution when the pK- invariant equals the Lambda(1520) mass. Our model calculations indicate a sizeable contribution of resonant and non-resonant background processes in the gamma D to np K+K- reaction which generally exceed the contribution of the coherent resonant channel. However, we find that the coherent Theta+Lambda(1520) photoproduction is enhanced relative to the background processes in the forward hemisphere of the pK- pair photoproduction. Moreover, the coherence effect does not depend on the Theta+ photoproduction amplitude and is defined by the probabilities of the Lambda(1520) photoproduction and the Theta+ to NK transition. Therefore, this coherence effect may be used as an independent method for studying the mechanism of Theta+ production and Theta+ properties.

Bremsstrahlung photons, produced at superconducting electron accelerator ELBE at the
FZ Rossendorf will be used for the production of neutron-rich nuclei by photo-induced fission. The properties of such exotic nuclei will be studied by decay spectroscopy. The mass and charge identification plays a key role in such experiments and is based on a double time-of-flight (TOF) method for both fission fragments. The reaction products are registered using secondary electrons emitted by thin foils and detected by position-sensitive MCP detectors. Currently a position resolution of 1.8(0.3) mm (FWHM) in both x and y directions and a time resolution of about 330 ps (FWHM) have been deduced using a source of alpha-particles.

A research program has been started to study experimentally the near-threshold photodissociation of nuclides in the chain of cosmic heavy element production with bremsstrahlung from the ELBE accelerator. An important prerequisite for such studies is good knowledge of the bremsstrahlung distribution which was determined by measuring the photodissociation of the deuteron and by comparison with model calculations. First data were obtained for the astrophysically important target nucleus 92-Mo by observing the radioactive decay of the nuclides produced by bremsstrahlung irradiation at end-point energies between 11.8 and 14.0 MeV. The results are compared to recent statistical model calculations.

A new facility for the production of polarised bremsstrahlung has been built at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf. The bremsstrahlung facility and the detector setup are designed such that the background radiation due to scattering of photons and production of neutrons is minimised allowing for experiments close to and above particle separation energies in nuclei.
First results of photon-scattering and photo-dissociation experiments on {92,98,100}Mo are presented.
The results are compared to recent cross-section calculations for astrophysical networks.

Zur Validierung von CFD-Codes bei reaktornahen Versuchsbedingungen wird derzeit das Heißstrang-Modell in der Druckkammer der TOPFLOW-Anlage in Betrieb genommen.
Vorversuche fanden bereits an einem horizontalen Luft/Wasser-Strömungskanal bei Atmosphärendruck statt. Es wurden optische Messungen mit einer Hochgeschwindigkeits-Kamera durchgeführt, die durch synchronisierte dynamische Druckmessungen ergänzt wurden. Außerdem wurden Geschwindigkeitsfelder in einem Schwall mit PIV (Particle Image Velocimetry) gemessen.
Zur Validierung des Codes CFX-5 wurden Nachrechnungen durchgeführt. Diese stimmten mit dem Experiment qualitativ gut überein. Zudem wurde eine Vorrausrechnung zum Heißstrang-Modell gezeigt.

For the investigation of air/water stratified flow, a horizontal channel with rectangular cross-section was build at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter-current flows under atmospheric pressure, especially the slug behaviour.
Optical measurements were performed with a high-speed video camera, and were complemented by simultaneous dynamic pressure measurements. An interface capture technique was developed, which allows to plot the time dependent water level in each cross-section. Further, Particle Image Velocimetry (PIV) measurements where presented, which shows the flow pattern inside of a slug.

We report on the performance of photoconductive THz emitters based on an interdigitated metal-semiconductor-metal finger structure. In every second period of this structure optical excitation is inhibited. Thus carrier acceleration is unidirectional over the whole device area. Excitation with amplified laser pulses leads to THz amplitudes of 6 kV/cm. Saturation of the emission due to screening of the bias field was observed for excitation densities in the 1018 cm-3 range.

The evolution of sp² hybrids in amorphous carbon (a-C) films deposited at different substrate temperatures was studied experimentally and theoretically. The bonding structure of a-C films prepared by filtered cathodic vacuum arc was assessed by the combination of visible Raman spectroscopy, x-ray absorption, and spectroscopic ellipsometry, while a-C structures were generated by molecular-dynamics deposition simulations with the Brenner interatomic potential to determine theoretical sp² site distributions. The experimental results show a transition from tetrahedral a-C (ta-C) to sp² -rich structures at ~500 K. The sp² hybrids are mainly arranged in chains or pairs whereas graphitic structures are only promoted for sp² fractions above 80%. The theoretical analysis confirms the preferred pairing of isolated sp² sites in ta-C, the coalescence of sp² clusters for medium sp² fractions, and the pronounced formation of rings for sp² fractions >80%. However, the dominance of sixfold rings is not reproduced theoretically, probably related to the functional form of the interatomic potential used.

Coherent spin waves in exchange biased bilayers have been excited by ultrafast photomodulation of the exchange bias anisotropy. Vector and time resolved Kerr effect was employed to trace the trajectory of the magnetization vector of the ferromagnetic layer in real time on the picosecond timescale. Photoinduced easy axis precession in CoFe/IrMn samples with different IrMn thicknesses, thus, different exchange bias fields, has been studied. The antiferromagnetic thickness dependence of the decay rate of the induced precession was investigated as a measure of the effective magnetic damping in the system.
The observed increase of the extracted effective damping parameter is proportional to the square of the exchange bias field. Two-magnon scattering of the coherent spin precession of the ferromagnetic layer at local interfacial fluctuations of the exchange bias field can account for an additional dissipation mechanism. The two-magnon damping field in exchange bias systems is proportional to the square of the exchange bias field. Hence, there is time-domain evidence of two-magnon damping involved in magnetic relaxation processes of photoexcited exchange coupled bilayers.

He ion irradiation has been demonstrated to be a versatile tool not only for interfacial mixing in the case of Co/Pt mulilayers [1] but also for low temperature L10-ordering of FePt alloys [2]. L10 ordered NiMn films are due to the high blocking temperature and if exchange coupled to a ferromagnetic material due to the large shift filed a promising candidate for magnetic sensor applications. However, for the creation of the L10 phase an annealing is required. The corresponding thermal budget should be as low as possible to impede the detrimental effect of fast Mn diffusion. In order to reduce the thermal budget for A1 - L10 phase transformation the potential of ion induced vacancy formation has been exploited.
Magnetron sputtered film stacks of 5nm Ta/50(15)nm NiMn/20nm Fe20Ni80 /5nm Ta deposited at Si/SiO2 substrates were subsequently irradiated with He+ ions (30 keV, 10^15-3*10^16cm-2, RT or 250°C). The transition from the paramagnetic NiMn phase (fcc) to the chemically ordered, antiferromagnetic tetragonal L10 phase during annealing (100-500°C, Vacuum) was studied by in-situ X-ray diffraction using synchrotron radiation. A small L10 fraction (< 15%) is already available after deposition. The transformation to a dominating L10 (LRO-parameter S > 0.5) ordered NiMn film takes place between 250-300°C irrespective of the irradiation. Annealing at elevated temperatures (T > 400°C) leads to a loss of L10 ordering due to a complete intermixing of the NiMn and the Permalloy films. A benefit of ion iradiation is the improvement of the crystallinity and the degree of <111> texture in the NiMn films already after low fluence (10^15 cm-2) implantation.

[1] C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280, 1919 (1998).
[2] H. Bernas, J.-P. Attane, K.-H. Heinig, D. Halley, D. Ravelosona, A. Marty, P. Auric, C. Chappert, Y. Samson, Phys. Rev. Lett. 91, 077203 (2003).

Due to the high uniaxial anisotropy L10-ordered FePt is currently the most favoured candidate for future high density storage applications. However, in order to achieve the L10-phase either the deposition or post deposition annealing at temperatures above typically 500°C is required. Many attempts ranging from alternating monolayer deposition [1], different seed or cap layers [2] or doping with third elements [3] have been tried to reduce the ordering temperature with various degree of success.
Here we report on the L10-ordering of stoichiometric 30-125 nm thick FePt films which have been magnetron co-sputtered from elemental targets on SiO2/Si substrates with a deposition rate of (0.30-0.2) Å/s at various temperatures. Surprisingly, already for a deposition at 350°C the films are well chemically ordered in the tetragonal L10 structure with a long- range order parameter S=0.8-0.9 which has been determined by grazing incidence X-ray diffraction. The films exhibit a polycrystalline fiber texture with mean grain sizes of 12-18 nm and a random orientation distribution confirmed by pole figures measurements. In contrast, FePt films deposited at room temperature exhibit the fcc A1-phase with a mean grain size of (5.0 - 0.5) nm. In a sequence of annealing steps with successively increased temperatures, the A1 - L10 transition has been obtained between 300-400°C. After annealing at 400°C the films show nearly complete L10 ordering with S values equivalent to the films deposited at 350°C. During annealing the mean grain size grows to 10-12 nm. Using textured seed layers L10 ordered FePt films with preferred orientation can be realized. One of the key issues in observing the L10-ordering already at rather low temperatures is a combination of low deposition rate and low-energy ion irradiation during deposition.

[1] T. Shima, T. Moriguchi, S. Mitani, K. Takanashi, Appl. Phys. Lett. 80, 288 (2002).
[2] Z. L. Zhao, J. Ding, K. Inaba, J. S. Chen, J. P. Wang, Appl. Phys. Lett. 83, 2196 (2003).
[3] T. Maeda, T. Kai, A. Kiktsu, T. Nagase, J.-I. Akiyama, Appl. Phys. Lett. 80, 2147 (2002).

The fabrication of diluted magnetic semiconductors (DMS) by transition-metal (TM) doping of ZnO has attracted tremendous interest within the last 3 years. However, there are still vivid discussions if the ferromagnetic state stems from Zener-interaction between diluted TM ions or from magnetic secondary phases. In order to prove or exclude the possible formation of TM-secondary phases in ZnO we have investigated iron doping, since Fe-ZnO (n-type) DMS are theoretically predicted to exhibit ferromagnetism [1].
For these investigations Fe-ions have been implanted with an ion energy of 180 keV (projected range Rp=80 nm) at 420 K into ZnO single crystals. Two fluences of either 0.4 or 4x1016 ions per cm2 were chosen which correspond to 0.5 and 5 at%, respectively. The samples were characterized by CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction) using synchrotron radiation, RBS (Rutherford back scattering), TEM (transmission electron microscopy) and SQUID (superconducting quantum interference device) magnetometry.
For the as implanted sample a high solubility of Fe was found, e.g. 100% for the low fluence and ~90% for the high fluence sample. The ionic states are 2+ and 3+ but none of the ionic fractions could be clearly determined to occupy substitutional lattice sites. The high fluence implanted sample exhibits ferromagnetic behavior at room temperature as was observed by CEMS and SQUID. However, CEMS and XRD measurements confirm that the origin of the ferromagnetic behavior is due to Fe-nanocluster formation. These nanoclusters show the magnetic moment and hyperfine field of metallic bcc-Fe. After annealing the samples at 800°C secondary phases (mainly zinc ferrite clusters) form and no ferromagnetic behavior could be detected. For the low fluence implanted sample neither as-implanted nor after annealing a ferromagnetic behavior could be detected although after annealing the Fe-ions develop a 2+ state suggesting an occupation of substitutional lattice sites.

[1] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. 40, L334 (2001)

In order to prepare epitaxially oriented Fe nanoparticles near the surface of a single crystalline host material the method of ion beam synthesis has been explored. Two different host matrices, i. e., MgO(001) and Y:ZrO2(001), were employed to study the influence of the lattice misfit, the solubility and the host oxidizing/reducing properties on the formation of the Fe nanoparticles. The Fe ions were implanted at a primary energy of 100 – 110 keV (mean projected range: 50 nm) with a constant fluence of 6x1016 cm-2 at implantation temperatures varying between 25 °C and 1000°C. Structural and magnetic characterization was performed by means of CEMS (conversion electron Mössbauer spectroscopy), XRD (X-ray diffraction), RBS (Rutherford back scattering), TEM (transmission electron microscopy) and MOKE (magneto-optical Kerr effect).
For MgO substrates the fraction of metallic Fe increases from 28% (25°C) to 60% (800°C) as a function of implantation temperature, whilst the Fe depth profile remains the same. For an implantation temperature of 800°C fcc Fe nanoparticles with a mean diameter of 5 nm and an exclusive orientation relationship of -Fe(111)//MgO(111) and -Fe[220]//MgO[220] have been found. However, for an implantation temperature of 1000°C, the amount of Fe incorporated in the calculated depth profile is strongly reduced due to an enhanced mobility and diffusion of the Fe ions in the matrix material. The remaining Fe is found to be in the 3+ oxidation state.
Also in Y:ZrO2 the fraction of metallic Fe increases with increasing implantation temperature reaching 96% at 1000 °C. However, the nanoparticles formed are mainly bcc with a mean diameter of 13 nm. The dominant epitaxial relation is Fe(110)//Y:ZrO2(001) and Fe[001]//Y:ZrO2[100]. The ferromagnetic behavior is reflected by a magnetic hyperfine field of 330 kOe and a hysteretic magnetization reversal. No in-plane anisotropy could be detected.

In order to investigate the relation between shape anisotropy and unidirectional anisotropy in exchange biased lines, the magnetic domain configuration during magnetization reversal was studied as a function of the ratio between both anisotropy contributions. For that purpose a number of glass / Ta 7nm / PtMn 20nm / CoFe 4nm / Ta 4nm samples were sputter deposited. By means of either optical lithography and physical etching or focus ion beam (FIB) milling several line pattern in the range between 0.5 and 2.5 µm width and 20 µm length have been prepared. In order to modify the ratio between both anisotropy contributions the exchange bias field strength was reduced by means of 5 keV He+ ion irradiation. The domain structure during magnetization reversal was then investigated by means of magnetic force microscopy. For the as-prepared samples a mono-domain magnetization state with the magnetization direction aligned along the exchange bias field direction was found regardless of its shape. After irradiation, i. e., reduction of the unidirectional anisotropy, the situation has changed completely. The homogeneous magnetization state broke up into small domains with 360° domain walls in between. The appearance of these domain walls was only observed for the descending branch of the magnetization reversal. In addition it was found that the number of domain walls created depends strongly on the stripe width and orientation.

Pure magnetic patterning by means of ion beam irradiation of magnetic thin films and multilayers result from a post deposition local modification of the interface structure with only minor effects on the film topography. In the study presented here a 50 keV fine focused Co ion beam was used to change the coupling in a Ni81Fe19/Ru/Co90Fe10 structure from antiferromagnetic to ferromagnetic on a micron scale. Thereby an artificial structure with locally varying interlayer coupling and therefore magnetization alignment is produced. High-resolution full-field x-ray microscopy is used to determine the magnetic domain configuration during the magnetization reversal process locally and layer resolved due to the element specific contrast in circular x-ray dichroism. In the magnetically patterned structure there is in addition to the locally varying interlayer exchange coupling across the Ru layer also the direct exchange coupling within each ferromagnetic layer present. Therefore the magnetization reversal behaviour of the irradiated stripes is largely influenced by the surrounding magnetic film. We found that at the boundaries between irradiated and non-irradiated areas magnetic domain walls form during magnetization reversal with a magnetization component perpendicular to the film plane. This can be explained by the stray field generated by this domain wall which is partially compensated by a corresponding domain wall in the second ferromagnetic layer with opposite direction. It is expected that a pure magnetic patterning, as demonstrated here, can provide an additional degree of freedom in tailoring the overall magnetic properties of thin multilayer structures.

Messungen mit leitfähigkeitsbasierter Nadelsondensysteme sind gängige Messverfahren für hochtransiente Zweiphasenströmungen. Leitfähigkeits-Nadelsonden eignen sich jedoch nicht zur Untersuchung nichtleitender Fluide bzw. Mehrphasenströmungen. Um dieses Problem zu behandeln, kann die kombinierte Leitfähigkeits- und Permittivitäts- bzw. Kompleximpedanzmessung eingesetzt werden. Dafür wird in diesem Beitrag eine Impedanznadelsonde und eine dazugehörige Messelektronik vorgestellt. Erste vielversprechende Ergebnisse von Messungen an ausgewählten organischen Fluiden werden dargestellt und diskutiert.

In this work we present a method to study the energy of the phonon modes responsible for nonradiative energy relaxation of electrons in the active zone of quantum cascade lasers (QCLs). The method is based on the analysis of the oscillations pattern of QCLs emission intensity as a function of magnetic field applied along the growth direction. We studied first GaAs/AlGaAs QCLs with different Al concentration in the barriers (33% and 45%). We demonstrated that in the case of high Al concentration the relaxation via AlAs- like LO phonon can be significant. We have also shown that in case of In0.73Ga0.27As/AlAs short-wavelength QCL in spite of the high Al concentration in the barriers and the low GaAs contents in the wells, the nonradiative energy relaxation happens principally via GaAs-like or InAs-like (or mixed modes) phonon emission, while a clear signature of AlAs-like phonons was not observed.

The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the downcomer of a Pressurized Water Reactor (PWR) was analysed at the ROssendorf COolant Mixing (ROCOM) test facility. ROCOM is a 1:5 scaled model of a German PWR, and has been designed for coolant mixing studies. It is equipped with advanced instrumentation, which delivers high-resolution information for temperature or Boron concentration fields.

An experiment with 5 % of the design flow rate in one loop and 10 % density difference between the ECC and loop water was selected for validation of the CFD software packages CFX-5 and Trio_U. Two similar meshes with approximately two million control volumes were used for the calculations. The effects of turbulence on the mean flow were modelled with a Reynolds stress turbulence model in CFX-5 and LES approach in Trio_U. CFX-5 is a commercial code package offered from ANSYS Inc. and Trio_U is a single-phase CFD tool which is developed by the CEA-Grenoble, France.

The results of the experiment and of the numerical calculations show that mixing is dominated by buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this propagation. The ECC water falls in an almost vertical path and reaches the lower down¬comer sen¬sor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWRs. Both CFD codes were able to predict the observed flow patterns and mixing phenomena quite well.

In a Pressurized Water Reactor, negative reactivity is present in the core by means of Boric acid as a soluble neutron absorber in the coolant water. The main functions of the boric acid are to compensate for the fuel burn up and Xenon poisoning during normal operation and to provide the required sub-criticality of reactor shutdown during refueling and maintenance. During a so called Boron Dilution Transient (BDT), the borated coolant water is diluted by mixing with unborated water. The resulting decrease in the boron concentration leads to an insertion of positive reactivity in the core, which may lead to a reactivity excursion. The associated power peak may damage the fuel rods.

The most severe BDT involves scenarios in which a slug of unborated water has been formed in a cold leg in a stationary (Main Coolant Pumps are down) primary circuit. An inadvertent start-up of the MCP of the affected loop causes the transport of the unborated slug into the Reactor Pressure Vessel (RPV). The resulting positive reactivity insertion in the core is governed by the degree of mixing of the unborated slug and the borated water in the cold leg, the downcomer and the lower plenum. This mixing of borated and unborated water is an important process, because it mitigates and determines the degree of reactivity insertion.

The objective of the present study is to develop a validated Computational Fluid Dynamics (CFD) model for the prediction of the boron concentration distribution in the RPV as function of time during a BDT. This CFD model has been validated using the measurement data from the Rossendorf coolant mixing model (ROCOM) experiment. The ROCOM test facility represents the primary cooling system of a KONVOI type of PWR (1300 MWel). The linear scale of the ROCOM experimental facility is 1:5. The RPV is connected with four circulation loops.

A detailed CFD model of the RPV including the inlet nozzles, the downcomer, and the lower plenum has been developed to predict the mixing of unborated and borated water in this RPV. The validation of the model has been achieved by comparison of the calculated and measured relative boron concentration at the core inlet plane as function of time. In spite of the complicated spatial, temporal, and geometrical aspects of the flow in the RPV, the agreement between the calculated and the experimental data is good. In the ROCOM03 experiment, the minimal relative boron concentration measured at the core inlet is 64% and the calculated minimum value is 60%.

The emission of K+ and ± mesons has been studied in the asymmetric collision system Au+C and in the inverse reaction C+Au at 1.0A GeV (and at 1.8A GeV for C+Au only) in order to extract the effective source rapidities based on their distribution in the pt-y plane. The extracted source rapidity of K+ mesons is about ys/ybeam=0.25 at both incident energies [y(Au)=0,y(C)=ybeam]. This corresponds to a reaction volume consisting of the C nucleus and a tube cut out of the Au nucleus. In clear contrast, the source rapidities of ± mesons vary from ys/ybeam=0.5 in peripheral collisions (corresponding to NN interactions) to about ys/ybeam<0.33 in central reactions. The multiplicities of K+ and are compared to symmetric collision systems and, together with detailed transport model calculations, are used to study the sensitivity to the nuclear equation of state.

The Forschungszentrum Rossendorf and the Technische Universität Dresden are working together in a networking project for the construction and the use of a compact time-of-flight facility. The aim is to investigate the energy dispersive interaction of fast neutrons with materials. The planned time-of-flight experiments with pulsed neutrons will be carried out at the radiation source ELBE. First results for the design of a neutron radiator are presented. The distribution of the energy disposal of the used electron beam from the radiation source ELBE, the temperature in the neutron radiator and the expected particle spectra and fluxes at the measuring position were calculated by means of radiation-transport and finite-elements programs. Considerations for the design of the beam dump are discussed.

A new facility for the production of polarised bremsstrahlung has been built
at the superconducting electron accelerator ELBE of the Forschungszentrum
Rossendorf. The bremsstrahlung facility and the setup for photon-scattering
experiments are designed such that the background radiation due to scattering
of photons and production of neutrons is minimised. The sensitive setup in
connection with electron energies up to 20 MeV and average currents up to 1 mA
delivered by the ELBE accelerator enables novel experiments using
photon-induced reactions. First results of photon-scattering experiments are
presented.

Carbon nitride (CNx) thin films were grown by direct N-2/Ar ion beam sputtering of a graphite target at moderate substrate temperatures (300-750 K). The resulting microstructure of the films was studied by high-resolution transmission electron microscopy. The images showed the presence of curved basal planes in fullerenelike arrangements. The achievement and evolution of these microstructural features are discussed in terms of nitrogen incorporation, film-forming flux, and ion bombardment effects, thus adding to the understanding of the formation mechanisms of curved graphitic structures in CNx materials. (C) 2005 American Institute of Physics.

Microorganisms can mobilise radionuclides/metals through autotrophic and heterotrophic leaching, chelation by microbial metabolites and siderophores, and methylation, which can result in volatilisation. Conversely, immobilisation can result from sorption to cell components or exopolymers, intracellular sequestration or precipitation as insoluble organic and inorganic compounds. In this talk, we will present the last results about the spectroscopic and microscopic characterization of interaction mechanisms between radionuclides and bacterial strains isolated from extreme habitats, including uranium mining waste piles. Some of the isolated strains could be used as templates for the formation of metallic nanoparticles (Pd, Au).

Ausgehend von der Hintergrundkonzentration in den Eintrag von Uran in geochemische und biologische Systeme, wird über die Bestimmung der Speziation des Urans in kontaminierten Wässern, die aus dem ehemaligen Uranerzbergbau resultieren, berichtet.

Trigonal-bipyramidal Re(III) complexes with tetra-dentate/monodetate NS3/P ‘4+1’-coordination are inter-esting agents for the development of rhenium-188 com-plexes for potential therapeutic application. In order to understand relationships between the structure of rhenium-188 ‘4+1’ complexes and their in vitro stability we synthesized a series of rhenium model complexes 1, 2 and determined their stability in human plasma.
The complexes were prepared as described in [1] using various combinations of NS3 derivatives and mono-dentate phosphorus(III) ligands.
Since instability in aqueous solution always leads to the formation of perrhenate, we determined the amount of perrhenate formed after 1h, 24 h and 48 by TLC.
By means of physico-chemical parameters of the corres-ponding non-radioactive rhenium complexes we tried to find factors which may govern the formation of complexes showing high in vitro stability.
Finally, the most stable representative 3 was studied in 188Re labeling experiments with a phosphine-arginine-tyrosine model conjugate using the water-soluble N-hydroxysulfosuccinimidyl ester of the monodentate phosphine.

Bor ist ein starker Absorber für thermische Neutronen und wird dem Kühlmittel von DWR zugesetzt, um die Überschussreaktivität des Reaktorkerns zu kompensieren. Die unbeabsichtigte Verringerung der Borkonzentration, die sog. Borverdünnung, im Kern hat deshalb eine Reaktivitätserhöhung zur Folge und könnte im Extremfall die Rekritikalität des abgeschalteten Reaktors nach sich ziehen.

Inert, so-called “4+1” trigonal-bipyramidal coordinated mixed–ligand complexes of the trivalent technetium and rhenium with tetradentate and monodentate ligands proved to be more stable than the pentavalent “3+1” mixed–ligand complexes with the (M=O)3+ core. They have appeared not to undergo a substitution in vivo with SH groups of such species as cysteine or glutathione [1].
In the presented paper we describe the synthesis of novel 99mTc(III) and 188Re(III) complexes containing the tripodal chelator 2,2’,2’’-nitrilotris(ethanethiol), NS3, and a dendritic modified monodentate isocyanide, CN-R(den). The reaction course was monitored with TLC and the radiochemical purity was monitored by HPLC. As a reference compound we have synthesized also the non-radioactive rhenium(III) complex which has been characterized by elemental analysis, IR, MS, 1H and 13C NMR.

The title compound, [Re(C7H12NO2S3)(C18H15P)]center dot C3H6O, crystallizes from a solution in chloroform - acetone - cyclohexane with enantiomers disordered equally over each molecular site. Hydrogen bonds between the carboxyl groups form dimers in the crystal structure.

Force field parameters for the modeling of oxotechnetium(V) and oxorhenium(V) complexes with amine, amide, imine, carboxylate and thiolate donors have been derived and optimized with 131 published solid state structures. An automated procedure, based on a simplex algorithm, was used to optimize the 35 sets of metal-dependent structural parameters for each metal ion. These were introduced into the established MOMEC97 force field. The application of the new force field in the prediction of a novel radio-pharmaceutical’s structure was successful; the predicted structures of the two isomers compared well with the corresponding crystal structures obtained (RMS around the metal core: 0.153 and 0.035 Å, respectively).

We introduce a model of rotating magnetic field with a weak axial gradient which approximates the field generated by a slightly conical and sufficiently long inductor. The axial variation of the free-space field is assumed to be weak and its amplitude is approximated by the first linear term of expansion in a power series of the axial coordinate. This allows us to obtain an analytic solution for the azimuthal harmonics of the induced scalar electric potential and the azimuthal driving force in a cylinder of finite length. The results are verified by comparison with a numerical solution obtained by a Chebyshev-tau method.

This work is part of efforts to develop chelating agents for stable binding and easy conjugation of rhenium-188 to biologically interesting structures. Starting from the well-known high in vivo stability of [188ReO(DMSA)2]- we want to exploit this coordination system for the design of 188ReO(V) chelates which are stable towards re-oxidation to perrhenate and towards ligand exchange under all conditions of radiopharmaceutical procedures and applications. Therefor a new type of tetradentate ligand has been synthesized by bridging two molecules of N,N’-diisobutyl-2,3-dimercaptosuccinamide with N-(3-aminopropyl)propane-1,3-diamine. The resulting stereoisomeric tetrathiolato S4 ligand of the composition (iBu)2N(O)C-C(SH)-C(SH)-C(O)NH-(CH2)3–NH-(CH2)3–NHC(O)-C(SH)-C(SH)-C(O)N(iBu)2 forms anionic five-coordinated oxorhenium(V) complexes by ligand exchange reaction of NBu4[ReOCl4] in methanol. Without addition of base the compounds will be isolated as “betain”, [ReO(S4)], with the protonated nitrogen of the bridge as internal “counter ion”. Two representatives have been fully characterized both in solid and solution states and found to adopt the expected square-pyramidal coordination geometry. The equatorial plane is formed by four thiolate sulfur atoms, whereas the oxygen occupies the apical position. The orientation of the metal oxo group is exo in relation to the carbamido groups in both isomers. Both complexes are stereoisomeric regarding the junction of the triamine chain.

Das Projekt liefert einen Beitrag zum Kenntnisstand der Wirkung von Bestrah-lung und Umgebungseinflüssen auf den Reaktordruckbehälter und dient zur Aufrechterhaltung eines hohen Sicherheitsstandards. Bis heute ist der Me-chanismus der Versprödung von RDB-Stählen nicht vollständig verstanden. Gesichert ist die Wirkung des Neutronenfeldes auf die Zähigkeitsabnahme von RDB Stählen. Zunehmend wird aber ein synergistischer Effekt zwischen Wasserstoff und den durch Bestrahlung erzeugten nanodispersen Strukturde-fekten diskutiert.
Ziel des Projektes war es eine experimentellen Nachweis über die Wechsel-wirkung von Wasserstoff und den bestrahlungsbedingten Strukturdefekten zu erbringen, den möglichen Einfluss auf die Zähigkeitsabnahme von RDB Stäh-len zu untersuchen und Unterschiede im Verhalten gegenüber dem unbe-strahlten Zustand auszuweisen.
Zur Untersuchung des Einflusses von Wasserstoff auf das Zähigkeitsverhal-ten von Reaktordruckbehälterstählen wurden einachsige Zugversuche bei verschiedenen Dehnraten an unbestrahlten und bestrahlten, wasserstoffvor- und in-situ beladenen Proben bei Raumtemperatur und 250°C durchgeführt. Die Bestimmung der mechanischen Eigenschaften wurde durch fraktografi-sche Untersuchungen der Bruchflächen ergänzt.
Mit SANS-Untersuchungen, der Analyse von Wasserstoffgehalten und Ther-modesorptions-untersuchungen wurde geprüft, ob Strahlendefekte als Haft-stellen für Wasserstoff wirksam werden.
Es konnte gezeigt werden, dass die Empfindlichkeit gegenüber Wasserstoff-versprödung von der chemischen Zusammensetzung des RDB-Stahles, der Fluenz bis zu der bestrahlt wurde, der Bestrahlungstemperatur und der Art der gebildeten Strahlendefekte bestimmt wird. Eine verstärkte Anfälligkeit ge-genüber Wasserstoffversprödung wird bei RT, in-situ Wasserstoffbeladung und langsamen Dehnraten sowie geringen Bestrahlungstemperaturen beo-bachtet. Bei 250°C ist eine Versprödung durch Wasserstoff nicht mehr nach-weisbar. Aus den Ergebnissen ist abzuleiten, dass bestrahlungsinduzierte De-fekte keine bevorzugten Plätze für eine höhere Aufenthaltswahrscheinlichkeit für Wasserstoff unter Betriebstemperaturen von RDB darstellen. Sie sind so-mit keine internen Quellen für Wasserstoff. Bei Betriebstemperaturen ist des-halb nicht mit einer erhöhten Versprödungsanfälligkeit zur zu rechnen. Durch die höheren Festigkeiten der bestrahlten Stähle steigt aber allgemein die Empfindlichkeit gegenüber Wasserstoffversprödung.
Der Integritätsnachweis von RDB’s außerhalb des Leistungsbetriebes unter Wasserstoffwirkung ist deshalb noch zu erbringen.

wird nachgereicht

Two new octahedral cluster complexes – [Re6S8(3,5-Me2PzH)6]Br2·2(3,5-Me2PzH) (1) and [Re6Se8(3,5-Me2PzH)6]Br2·2(3,5-Me2PzH) (2), where 3,5-Me2PzH is 3,5-dimethyl-pyrazole, have been synthesized using reaction of rhenium chalcobromide complexes Cs4[Re6S8Br6]·2H2O and Cs3[Re6Se8Br6]·H2O respectively with molten 3,5-dimethylpyrazole. Both compounds synthesized were characterised by X-ray single-crystal diffraction and chemical analysis, IR and luminescent spectra.

Resveratrol (3,4',5-trihydroxy-trans-stilbene) is a naturally occurring phytoalexin and polyphenol existing in grapes and various other plants, and one of the best known 'nutriceuticals' . It shows a multiplicity of beneficial biological effects, particularly, by attenuating atherogenic, inflammatory, and carcinogenic processes. However, despite convincing evidence from experimental and clinical studies, data concerning the role of resveratrol and other members of the large polyphenols family for human health is still a matter of debate. One reason for this is the lack of suitable sensitive and specific methods, which would allow direct assessment of biodistribution, biokinetics, and the metabolic fate of these compounds in vivo. The unique features of positron emission tomography (PET) as a non-invasive in vivo imaging methodology in combination with suitable PET radiotracers have great promise to assess quantitative information on physiological effects of polyphenols in vivo. Herein we describe the radiosynthesis of an 18F-labelled resveratrol derivative, 3,5-dihydroxy-4'-[18F]fluoro-trans-stilbene ([ 18 F]-1), using the Horner-Wadsworth-Emmons reaction as a novel radiolabelling technique in PET radiochemistry for subsequent functional imaging of polyphenol metabolism in vivo. In a typical "three-step/one-pot reaction, 18F-labelled resveratrol derivative [ 18 F]-1 could be synthesized within 120-130 min including HPLC separation at a specific radioactivity of about 90 GBq/mumol. The radiochemical yield was about 9% (decay-corrected) related to [18F]fluoride and the radiochemical purity exceeded 97%. First radiopharmacological evaluation included measurement of biodistribution ex vivo and positron emission tomography (PET) studies in vivo after intravenous application of [ 18 F]-1 in male Wistar rats using a dedicated small animal PET camera with very high spatial resolution. Concordantly with data on bioavailability and metabolism of native resveratrol from the literature, these investigations revealed an extensive uptake and metabolism in the liver and kidney, respectively, of [ 18 F]-1. This study represents the first investigation of polyphenols in vivo by means of PET.

Positron emission tomography (PET) is a medical imaging technique using compounds labelled with short-lived positron emitting radioisotopes to obtain functional information of physiological, biochemical and pharmacological processes in vivo. The need to understand the potential link between the ingestion of individual dietary agents and the effect of health promotion or health risk requires the exact metabolic characterization of food ingredients in vivo. This exciting but rather new research field of PET would provide new insights and perspectives on food chemistry by assessing quantitative information on pharmocokinetics and pharmacodynamics of food ingredients and dietary agents. To fully exploit PET technology in food chemistry appropriately radiolabelled compounds as relevant for food sciences are needed. The most widely used short-lived positron emitters are 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min). Longer-lived radioisotopes are available by using 76Br (t1/2 = 16.2 h) and 124I (t1/2 = 4.12 d). The present review article tries to discuss some aspects for the radiolabelling of food ingredients and dietary agents either by means of isotopic labelling with 11C or via prosthetic group labelling approaches using the positron emitting halogens 18F, 76Br and 124I.

Mixed - ligand model complexes of general formula [Tc-99m(O)(kappa(3) -SPh)(kappa(1)-SPh))] [X = O (1a), S (2a)] were prepared in a one-step procedure from [(TcO4-)-Tc-99m] using stannous chloride as reducing agent. Stability studies and challenge experiments with glutathione showed that complex 2a presented promising features for pursuing animal studies. The activity in the brain (% dose injected/organ) at 5 min (0.14% +/- 0.03) and 120 min (0.11% +/- 0.02) pi encouraged the synthesis of several mixed-ligand "3 + 1" oxo complexes of general formula [M(O)(kappa(3)-PNS)(kappa(1)-SL))] (M = Tc-99m, 3a-6a, Re, 3-6), in which the tridentate ligand is the heterofunctionalized phosphine 2-(diphenylphosphanyl)-N-(2-thioethyl)benzamide (PNS) and the co-ligands are different arylpiperazine derivatives (HSL1-HSL4). The Tc-99m complexes have been characterized by comparison of their retention times in the HPLC chromatogram (gamma-detection) with the retention times of the analogous Re complexes (UV detection at 254 nm). The 99mTc complexes, obtained with radiochemical purity higher than 95%, after HPLC purification, are stable in saline, 0.01 M PBS (pH 7.4), rat plasma (4 h, 37 degrees C), and glutathione (10 mM solutions, 2h, 37 degrees C). Binding affinity and selectivity for 5-HT1A receptors (relative to the 5-HT2A receptor) were determined, complex 5 demonstrating the best values (IC50 for the 5-HT1A 2.35 +/- 0.02 nM; competitor 5-HT2A 372 +/- 11 nM). Biodistribution and stability studies in mice indicated a preferred hepatobiliary excretion, a high in vivo stability, but a poor brain uptake.

The structure of a steam-water flow in a vertical pipe of 195.3 mm inner diameter was studied using novel wire-mesh sensors for high-pressure / high-temperature operation (max. 7 MPa / 286 °C). Tests were carried out at pressures of 1 and 2 MPa under nearly adiabatic conditions as well as with slightly sub-cooled water. The evolution of radial gas fraction profiles and bubble-size distributions along the pipe in a high-pressure steam-water flow was measured for the first time. The experimental data allow to correlate the intensity of steam condensation in contact with sub-cooled water with the structure of the interfacial area and the bubble size distribution, which is very important for the model development.

The surface layer (S-layer) protein genes of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 and of its relative B. sphaericus NCTC 9602 were analyzed. The almost identical N-termini of both S-layer proteins possess a unique structure, comprising three Nterminal S-layer homologous domains (SLH). The central parts of the proteins share a high homology and are related to the S-layer proteins of B. sphaericus CCM 2177 and P-1. In contrast, the C-terminal parts of the studied S-layer proteins differ significantly between each other. Surprisingly, the C-terminal part of the S-layer protein of JG-A12 shares a high identity with that of the S-layer protein of B. sphaericus CCM 2177. In both strains the chromosomal S-layer protein genes were followed by a newly identified putative insertion element comprising three ORFs, which encode a putative transposase, a putative integrase/recombinase, a putative protein containing a DNA binding helix turn helix motif, and the S-layer protein-like gene copies sllA (9602) or sllB (JG-A12). Interestingly, both studied B. sphaericus strains were found to contain an additional, plasmid located and silent S-layer protein gene possessing the same sequence as sllA and sllB. The primary structures of the corresponding putative proteins are almost identical in both strains. The N-terminal and central parts of these S-layer proteins share a high identity with those of the chromosomally encoded functional S-layer proteins. Their C-terminal parts, however, differ significantly. These results strongly suggest that the S-layer protein genes have evolved via horizontal transfer of genetic information followed by DNA rearrangements mediated by mobile elements.

Uranium mining waste piles, heavily polluted with radionuclides and other toxic metals, are a reservoir for bacteria that have evolved special strategies to survive in these extreme environments. Understanding the mechanisms of bacterial adaptation may enable the development of novel bioremediation strategies and other technological applications. Cell isolates of Bacillus sphaericus JG-A12 from a uranium mining waste pile in Germany are able to accumulate high amounts of toxic metals such as U, Cu, Pb, Al, and Cd as well as precious metals. Some of these metals, i.e. U, Cu, Pd(II), Pt(II) and Au(III), are also bound by the highly orderd paracrystalline proteinaceous surface layer (S-layer) that envelopes the cells of this strain. These special capabilities of the cells and the S-layer proteins of B. sphaericus JG-A12 are highly interesting for the clean-up of uranium contaminated waste waters, for the recovery of precious metals from electronic wastes, and for the production of metal nanoclusters. The fabricated nanoparticles are promising for the development of novel catalysts. This work reviews the molecular biology of the S-layer of the strain JG-A12 and the S-layer dependent interactions of the bacterial cells with metals. It presents future perspectives for their application in bioremediation and nanotechnology.

¹⁸F-labeled amino acids represent a promising class of imaging agents in tumors visualized by means of positron emission tomography (PET). Because of the high uptake it is still problematic to clear differentiate between tumors and inflammation.
The high enrichment in tumor tissues assumed the uptake of the tracer via a tumor-specific amino acid transporter, which is not or different expressed in inflammatory cells suggesting a different endowment of neutral amino acids. As previously shown, L-type amino acid transporter 1 (LAT1) is playing a key role because of its high up-regulation in malignant tumors. For the functional expression of LAT1 a single membrane-spanning protein, the heavy chain of 4F2 antigen (4F2hc), essentially forms a heterodimeric complex via disulfide bonds.
The present study investigated the amino acid transport mechanism of LAT1 for 3-O-methyl-6-¹⁸F-Fluoro-L-DOPA (OMFD), a novel ¹⁸F-labeled phenylalanine derivative, into tumor cells.
For molecular characterisation of L-type amino acid transporters focusing on the LAT1-4F2hc subtype we used two different tumor cells like FaDu (squamous cell carcinoma)/HT29 (colorectal adenocarcinoma) and tumor bearing mice performing quantitative RT-PCR, Western-Blot, and immunhistochemistry. In vitro uptake assays with HT29 and FaDu were performed with OMFD under physiological amino acid concentrations.
OMFD demonstrated a saturable and sodium- and energy-independent accumulation in vitro in different tumor cell lines, suggesting its uptake to be mediated exclusively by sodium-independent LAT1.
Our data emphasize the relevance of OMFD as a PET tracer for imaging of specific amino acid transport via LAT1 in tumors. Furthermore, the identification and characterization of tumor specific amino acid transporters like LAT1 will be a helpful tool for therapeutic implications. The inhibition of LAT1 activity in tumor cells could be effective in the inhibition of tumor cell growth by depriving tumor cells of essential amino acids, too.

Hypoxia is a common feature of various human tumor entities. Hypoxic tumor tissue can be studied by nuclear medicine imaging techniques like PET and SPECT. In this study we analyzed in vitro the influence of experimental hypoxia on the radiotracer uptake of various primary endothelial cells, which play an essential part in tumor angiogenesis.
Experimental hypoxia was induced by cultivating cells for 24 hours in presence of 2% oxygen in a special incubator (Gasboy C40, Labotect). Cellular uptake of [99mTc]MIBI, [18F]MISO and [18F]FDG was determined after one or four hours incubation and measured after cell lysis with a gamma counter Cobra II (Perkin Elmer). Radiotracer uptake was normalized to the cell protein. Three types of primary endothelial cells were used: human umbilical vein endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines, being FaDu (squamous cell carcinoma) and HT29 (colorectal adenocarcinoma), respectively. Cellular expression of hypoxia-inducible factor-1a (HIF-1a) and vascular endothelial growth factor (VEGF) was monitored with quantitative PCR (RotorGene 2000).
In our experiments we found that under hypoxic conditions the uptake of [99Tc]MIBI was decreased in all cell types. The uptake of the hypoxia-specific radiotracer [18F]MISO was slightly increased in all primary endothelial cell types. Furthermore, primary endothelial cells incorporated significant higher amounts of [18F]FDG under experimental hypoxic conditions in comparison to normoxic conditions. Especially HDMECs showed a marked response to hypoxia with an approximately two-fold higher [18F]FDG uptake. Also HUVECs and HAECs responded to experimental hypoxia, whereas tumor cell lines FaDu and HT29 showed only moderate increase of [18F]FDG uptake under hypoxic conditions.
We conclude that experimental hypoxia represents a much higher stimulus for primary endothelial cells than for cultivated tumor cells to accumulate [18F]FDG and also to incorporate [18F]MISO in vitro. Our data emphasize the relevance of endothelial cells as one important part of the tumor micromilieu and stimulate further studies on the different patterns of radiotracer uptake in neoplastic or neovascularized lesions.

Aim:

Hypoxia is a common feature of various human tumor entities and the enhanced uptake of specific radiotracers in hypoxic tissues can be visualized by means of positron emission tomography (PET). In this study we analyzed the influence of experimental hypoxia on the [¹⁸F]FDG uptake of various primary endothelial cells and tumor cell lines.
Material and Methods:
Experimental hypoxia was induced by cultivating cells for 24 hours in presence of 2% oxygen in a special incubator (Gasboy C40, Labotect). Cellular [¹⁸F]FDG uptake was determined after one hour incubation and measured after cell lysis with a Cobra II spectrometer (Packard). [¹⁸F]FDG uptake was correlated to protein concentration. Three types of primary endothelial cells were used: human umbilical cord endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines, being FaDu (squamous cell carcinoma) and HT29 (colorectal adenocarcinoma), respectively.
Results:
In our experiments we found that primary endothelial cells incorporate significant higher amounts of [¹⁸F]FDG under experimental hypoxic conditions in comparison to normoxic conditions. Especially HDMECs showed a marked response to hypoxia with an approximately two-fold higher [¹⁸F]FDG uptake. Also HUVECs and HAECs responded to experimental hypoxia, whereas tumor cell lines FaDu and HT29 showed only moderate increase of [¹⁸F]FDG uptake under hypoxic conditions.
Conclusion:
Experimental hypoxia represents a much higher stimulus for primary endothelial cells than for cultivated tumor cells to incorporate [¹⁸F]FDG. Our data emphasize the relevance of endothelial cells as one important part of the tumor micromilieu and stimulate further studies on the different patterns of radiotracer uptake in neoplastic or neovascularized lesions.

During the archaeological work in summer 2000 a spectacular hoard of silver coins could be excavated at the medieval site Becin, next to Ephesos / Turkey. This hoard, whose total weight amounted to approximately 30 kg, includes about 60.000 Islamic coins as well as 830 European coins and represents the largest finding of coins ever made in Turkey. One of the most outstanding features of the Becin hoard is the fact that almost all mint places recorded for the Ottoman Empire and all rulers of the second half of the 16th century up to the beginning of the 17th century are represented in this treasure. Thus, the numismatic evaluation and the material analysis of the coins will provide a general insight in the monetary and economic history of the Ottoman Empire in this time.
In a first step of the investigations a collection of 450 samples was analyzed quantitatively. Photon, electron and proton induced X-ray analysis provide complementary information on the chemical composition of the coins. Using EDXRF, the content of both the major constituent Ag and the minor elements Cu and Pb were determined. The advantage of SEM/EDX is the ability to analyze small areas of the cross-sections. Finally, PIXE measurements were carried out in order to characterize also the trace elements, like Au, Bi, Fe, Ni. The initial results show on the one hand an arrangement in different groups of coins concerning their chemical composition. On the other hand the findings illustrate frequent devaluations in the fineness of the silver coins described in the Ottoman written sources.

The role of hydrogen in hydrogenated amorphous silicon (a-Si:H) has been studied from the viewpoint of its specific contribution to mechanical stress in the material. Hydrogen ion implantation has been used to increase the hydrogen concentration. In order to distinguish the effect of the changed hydrogen concentration/bonding configuration from the accompanying implantation-induced defects, a-Si:H samples with corresponding number of displacements have been studied, created using proper doses of silicon ion implantation. The experimental results have shown that it is the silicon-bonded hydrogen that essentially affects the stress, as the major contribution has its clustered bonding configuration.

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The γ decay of the 12+ yrast trap in 52Fe has been measured for the first time. The two E4 γ-branches to the 8+ states are hindered with respect to other B(E4) reduced transition probabilities measured in the f 7/2 schel. The interpretation of the data is given in the full pf shell model framework, comparing the results obtained with different residual interactions. It is shown that measurements of hexadecapole transition probabilities constitute a powerful tool in discriminationg the correct configurration of the involved wavefunctions.

Die Sorption von Uran (VI) an das komplexe Gestein Phyllit wurde gründlich untersucht. Dominierender Prozess der Sorption ist die Bindung an das Sekundärmaterial Ferrihydrit. Anhand der gewonnenen experimentellen Daten gelang die Bestimmung von Oberflächenkomplexbildungskonstanten für die mineralischen Bestandteile Quarz, Muskovit, Albit und Chlorit. Diese log K-Werte können in chemischen Transportprogrammen Verwendung finden.

Diese Arbeit beschäftigt sich mit der Entfernung von organischen Stoffen aus Wässern durch Anionenaustauscher. Dabei werden C-14-markierte Modellsubstanzen eingesetzt. Die Aufnahme von Durchbruchskurven erfolgt bei verschiedenen Bedingungen (Variation von Beladungstemperatur, Salzgehalt und Organikakonzentration).

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Flash lamp annealing of heteroepitaxial silicon carbide on silicon structures involves melting the silicon below the SiC layer but the facetted nature of the liquid-solid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by using a melt stop created at a controlled depth below the Si / SiC interface by implanting a high dose of carbon, which significantly increases the silicon melting temperature. Results confirm the effectiveness of the technique in reducing roughness.

Swirling flows generated by the application of a rotating magnetic field (RMF) during the solidification significantly modify the heat and mass transport in the melt. Their enormous potential to modify the microstructure is known since long but was systematically studied only recently [1,2]. However, the understanding of flow field driven by the RMF in the solidifying melt and the corresponding temperature and concentration distributions is far from being complete. By means of a combination of experiments and numerical simulations important relations shall be established.
To calculate the flow field we use a code based on the SIMPLE algorithm which has been carefully validated on the isothermal problem of the RMF-driven acceleration of a melt from rest [3,4]. The solidification is treated by using a mixture-theory-model following Voller et al. [Int. J. Heat Mass Transfer 32 (1989), 1719]. The geometry studied is a Pb-Sn melt in a cylindrical cavity directionally solidified from below. The simulations cover Taylor numbers, Ta, up to 2*106 where Ta determines the magnitude of the bulk flow.
The solidification in the RMF depends on the degree of development of the forced convection (spin-up problem). The flow fields belonging to characteristic stages are discussed. Generally, the RMF significantly modifies the solidification as soon as the average flow velocity of the meridional flow becomes comparable or larger as the velocity of the solidification front. We discuss the impact of the flow on heat transfer in the melt thereby providing a detailed comparison of experimental and numerical date with respect to cooling rates and temperature gradients. Emphasis is given to the temperature gradients in vicinity of the solidication front which are hardly accessible in experiments. Their tendency with growing Ta is examined and linked with the accelerated onset of the transition from columnar to equiaxed growth (CET) found in the experiments [2]. Furthermore the macrosegregation to be expected in the RMF case are discussed.

The application of time varying magnetic fields can be considered as an effective tool to organize a well-defined flow structure in the liquid phase affecting the nucleation and solidification parameters. Main goal of our activities is to elucidate a strategy to control the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. The development of fine, globular grains is preferred. Structures containing textured columnar grains and zones of macrosegregation should be avoided.
Solidification experiments as well as numerical simulations were carried out dealing with Pb Sn alloys solidified directionally from a water cooled copper chill. A rotating magnetic field (RMF) was chosen for melt agitation, because the essential features of an RMF-driven flow have already been intensively investigated for the isothermal case. The magnitude of the bulk flow in the melt generated by the RMF varies with the magnetic Taylor number Ta. The forced convection causes distinct modifications of the temperature and concentration field such as a reduction of the temperature gradient ahead of the solidification front. Without electromagnetic stirring the alloy solidifies solely in form of dendrites aligned parallel to the heat flow direction. In contrast, a transition from a columnar to an equiaxed growth (CET) is observed if the solidifying ingot is exposed to an RMF. The position of the CET is shifted towards the bottom of the casting by increasing the Ta number. The CET was found to occur for a cooling rate of about 0.4 K/s and temperature gradients in the range between 0.6 and 1.0 K/mm
The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. Our results show that the velocity profiles undergo distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case. Furthermore, the UDV data allow an assessment of the current position of the columnar solidification front.

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids , especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. Powerful optical methods are obviously not available for measurements in liquid metals. The majority of measurements in liquid metal two-phase flows published until now was obtained using local conductivity probes, hot wire anemometer or optical fiber probes to determine quantities such as void fraction, bubble and liquid velocity or the bubble size. However, measurements with any local probe disturb the flow in a significant way, especially if the structures to be investigated reach dimensions comparable to the probes. In the case of opaque liquids the application of acoustic or ultrasonic sensors offers a possibility to get information about the flow structure and bubble quantities. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications.
In our experiments we investigated the consequence of an application of a DC magnetic field on both the bubble and the liquid velocity. The motion of single argon bubbles rising in GaInSn were analyzed in terms of the terminal velocity, the drag coefficient, the oscillation frequency of the bubble velocity and the Strouhal number. Because the gas bubble is electrically non-conducting, it does not experience the effect of the electromagnetic force directly. However, the bubble behaviour is influenced by the magnetically induced modifications in the liquid flow structure around the bubble. The measurements reveal a distinct effect of the magnetic field on the bubble velocity as well as the bubble wake. The magnetic field application leads to a mitigation of the horizontal components of the bubble velocity resulting in a more rectilinear bubble path. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. As a result of the interaction between magnetic field and liquid flow electric currents were induced inside the liquid causing a damping of the flow by Joule dissipation. However, a characteristic feature of the electromagnetic dissipation is the anisotropy. Thus, the application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction.

Bakterien sind winzig klein, sehr leistungsfähig und es gibt keinen noch so extremen Lebensraum, den sie nicht besiedeln könnten. Als wahre Alleskönner liefern sie der Bionik (Verbindung aus Biologie und Technik) viele neue Impulse. Am Beispiel faszinierender Hüllstrukturen verschiedener Bakterien wird dies exemplarisch aufgezeigt.

Nanowires have fascinating properties. Also the kind and strength of driving forces for their structural evolution differ from macroscopic systems, thus opening new routes for their synthesis. And, with respect to interface energy, nanowires are unstable, during their decay new selforganized 1D structures evolve.
This presentation summarizes reaction pathways of the formation and decay of 1D nanostructures predicted by atomistic computer simulations. It will be shown that nanowire synthesis by phase separation from supersaturated 1D traces relies on different time scales of different processes involved: (i) phase separation is faster than long-range diffusion, thus, initially small nanodroplets form. (ii) Short-range diffusion is fast, thus, lateron the minority phase is concentrated/unified to a wire (ripening, coalescence). (iii) On a long time scale, the wire lowers its surface energy by peristaltic undulations and decays finally into large droplets (Rayleigh instability). Each process can be governed in order to fabricated functional structures. For instance, crosspoints of nanowires accelerates the wire instability locally, which leads to a nanodot separated by nm gaps from the four nanowires. Such a Si structure embedded in SiO2 might operate as a room temperature single electron transistor.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied regarding their potential application in nanoelectronics. CoSi2 nanostructures in Si are particularly interesting because of the full compatibility of CoSi2 with CMOS technology.
Here, we present predictive atomistic computer simulations on the ion beam synthesis of CoSi2 NWs in Si and their decay into chains of CoSi2 NCs which are applicable as plasmon waveguides. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely-focused Co ion beam of 50nm in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described. From an evolutionary viewpoint, NW synthesis and decay proceed on different time scales. The NW decay into a NC chain (Rayleigh instability) is driven by the minimization of interfacial free energy. In this regard, it will be demonstrated that the orientation of the Co implantation profile to the single crystalline Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain.

An abstract was not required.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied for photonic and nanoelectronic applications. In this respect, CoSi2 NWs and NC chains are of particular interest because of their full CMOS compatibility, the low damping of surface plasmons at the CoSi2-Si interface, and the transparency of Si at the plasmon frequency.
Here, we present results of atomistic computer simulations which describe the ion beam synthesis of CoSi2 NWs in Si and their thermally activated decay into chains of CoSi2 NCs. The Co implantation is simulated with the binary collision codes TRIDYN and TRIM adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described. From an evolutionary viewpoint, NW synthesis proceeds on a shorter time scale than its decay. The NW decay into a NC chain (Rayleigh instability) is driven by the minimization of interfacial free energy. Moreover, we demonstrate that the orientation of the Co implantation profile to the single crystalline Si matrix strongly influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)-Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain. Thus, intentional misalignment between the focused Co ion beam and the Si substrate is suggested as way to a controlled decay of the ion beam synthesized CoSi2 NW into a chain of monodisperse and equidistant CoSi2 NCs.

An abstract was not required.

Series of carbon steels with various contents of carbon were irradiated with high intensity 5-6 J cm-2, short (µs range) nitrogen and argon plasma pulses. In all samples the near surface layer of the thickness in µm range was melted. The paper reports the results of investigation of changes induced by such treatment. The identified phases, profiles of retained nitrogen concentration, microhardness and wear resistance of the modified layer are presented and discussed.

The experiments to synthesize thin MgB2 inter-metallic compound with the use of ion implantation and plasma pulse treatment are presented. Mg was implanted with 3e18 cm-2 of 80 keV and 5e18 cm-2 of 100 keV B+ ions and next treated with hydrogen and argon plasma pulses of duration of about 1 mu s and fluence between 2 and 4 J/cm2. Superconducting properties were examined by magnetically modulated microwave absorption (MMMA), magnetic moment and electrical conductivity measurements. The structural properties of the implanted and pulse-treated samples were examined by the X-ray diffraction (XRD) and Rutherford backscattering (RBS) methods. The main result consists in observation of MMMA hysteresis loop demonstrating the existence of superconducting regions with T-c as high as 32 K. However, the zero-resistance effect has not been obtained due to incomplete global connectivity between the superconducting regions.

Neutron and gamma field functionals were studied by means of deterministic Sn and stochastic Monte Carlo calculations and by neutron activation measurements that were carried out in the ex-vessel cavity of the VVER-440 reactor Greifswald-1. The paper presents and analyses the results. The influence of different numbers of energy groups for the description of the cross sections is pointed out. A good agreement was found both between the results of deterministic and Monte Carlo calculation and between numerical and measurement results.

Laser-Induced spectroscopic methods were often used in actinide chemistry as tool to study the speciation of these elements in aquatic environments. The main goal of the application of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and laser-induced photoacoustic spectroscopy (LIPAS) is to achieve detection limits of the actinide species as low as possible or in concentration ranges expected under environmental conditions.
With laser sources can it is possible to provide any wavelength from the near UV to the NIR (Near Infrared) wavelength range. The development of tunable solid-state lasers overcame some disadvantages of the dye laser systems as short tunable wavelength range and the use of hazardous chemicals. The application of low temperatures for samples measured with fluorescence spectroscopic methods brought effort especially in the detection of carbonate species.
In this contribution the focus will be mainly on the fluorescence spectroscopy of lower actinides, as it is not possible to include all literature in this field.

The processes of electro- (EL) and photoluminescence (PL) and charge trapping in Er-implanted SiO2 containing silicon nanoclusters have been studied. It is shown that in Er-doped SiO2 with an excess of silicon nanoclusters of 10 at. %, a strong energy transfer from silicon nanoclusters results in a ten-fold increase of the PL peak at 1540 nm from Er luminescent centers, whereas the EL is strongly quenched by the excess silicon nanoclusters. It is further shown that the implantation of Er creates in the oxide positive charge traps with a giant cross section (σ(h0) > 10(-13) cm(2)). Introducing subsequent silicon nanocrystals in the oxide leads to the formation of negative charge traps of a giant cross section (σ(e0) > 10(-13) cm(2)). The possible reason for the EL quenching in the Er-doped SiO2 by silicon nanoclusters is discussed. (C) 2005 American Institute of Physics.

The oxygen concentration in Nd-Fe-B alloy was determined with secondary ion mass spectrometry (SIMS) using Cs+-ions. The SIMS measurements were calibrated with oxygen-implanted single crystals. The depth profile of Nd2Fe14B single crystals displays a 0.5 μ m thick surface layer with elevated oxygen concentration which can be distinguished from the matrix with an oxygen content c(O) = 0.006&PLUSMN; 0.002 at%. Polycrystalline samples can exceed this value by far and are sensitive to processing parameters and sample handling. SIMS measurements revealed the oxygen content of the Nd2Fe14B phase considerably lower than the total oxygen content of Nd-Fe-B samples. © 2004 Elsevier B.V. All rights reserved.

The complexation of Cm(III) and Eu(III) with n-C3H7-BTP in non-aqueous organic solution was studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum chemical calculations performed at different levels support this finding. On the other hand, the Cm•(n-C3H7-BTP)3 complex is formed at much lower metal-to-ligand concentration ratio than the Eu•(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP’s high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.

Electromagnetic processing comprises the influence of Lorentz forces in the molten state. Whereas the action of static magnetic fields is solely damping in most cases, alternating fields offer the potentiality of active control mechanisms such as pumping, stirring, homogenization, and the like. Among the latter, various field types have to be distinguished based on the number of poles and geometric arrangement. Neither for one type, and more than ever for a combination thereof, might the resulting flow tagged well known.
Numerous, often non-validated numerical simulations overwhelm the few experiments done on liquid metals. In the present work, the ultrasonic Doppler velocimetry (UDV) and local potential probes have been employed to study the flow of an alloy in single-phase, traveling, and rotating fields. The area-wide results conveyed by the UDV technique will be presented as flow visualization whereas potential probe measurements may answer questions of more quantitative nature regarding turbulence characteristics.

At the experimental carbon ion tumour therapy facility at GSI Darmstadt, in-beam positron emissions tomography (PET) is used to monitor the dose delivery precision. A dual head positron camera has been assembled from commercial detector components in order to measure the β+-activity, induced by the irradiation, simultaneously to the dose application. Despite the positive clinical impact, the image quality is limited by the low counting statistics, orders of magnitude below that in standart PET applications to nuclear medicine. This paper investigates the origin for the noisy acquisition during particle extraction from the synchrottron of GSI. The results demonstrate the failure of standard random correction techniques due to a γ-ray background correlated in time with the carbon ion beam microstructure. This prevents the use of data acquired during beam extraction for imaging. The loss of counting statistics is expected to rise further at the future hospital-based facility at Heidelberg, due to a more efficient utilisation of the accelerator resulting in shorter beam pauses and a reduced treatment time. In respect, this paper provides the basis for a new data acquísition concept tailored to the unconventional application of in-beam PET imaging to therapy monitoring at radiofrequency pulsed radiation sources.

The subjects of electromagnetic flow control and ship propulsion are reviewed, and possibilities for further developments are sketched.

The possibilities for local velocity measurements in liquid metal flows are reviewed. Special emphasis is put on local potential probes and the ultrasonic velocimetry.

Ausgehend von den physikochemischen Grundlagen der Grignard-Chemie werden Einflussfaktoren für eine sichere Prozessführung beschrieben. Bei Grignard-Synthesen tritt das größte Gefahrenpotential in der ersten Reaktionsstufe, der Herstellung der Grignard-Reagenz, auf. Insbesondere muss das Anspringen der Reaktion bei einer unzulässig großen Akkumulation von organischem Halogenid verhindert werden, wenn keine ausreichende, schnell wirksam werdende Kühlleistungsreserve vorhanden ist.
Vor der Überführung einer neuen Grignard-Synthese in den großtechnischen Maßstab sollten umfassende Untersuchungen der Grignard-Reaktionsstufe in Laborreaktoren durchgeführt werden. Mit Hilfe isothermer und adiabatischer kalorimetrischer Messungen konnten die wichtigsten Prozessparameter, wie molare Reaktionsenthalpie, adiabatische Temperaturerhöhung, Induktionszeit, Anstiegsgeschwindigkeit der Wärmeleistung und Dauer der Startphase, ermittelt werden. Sie sind notwendig, um die maximal zulässige Akkumulation des organischen Halogenids für die verfügbare Kühlleistung der Produktionsanlage bestimmen zu können.
Die Untersuchungen zeigten, dass gleiche Werte der molaren Reaktionsenthalpie sowohl bei isothermer als auch adiabatischer Kalorimetrie gemessen wurden. Als Ursache für die gemessenen größeren Enthalpiewerte während der isotherme Startreaktionsphase konnten noch vorhandene Wasser-Restmengen identifiziert werden, die infolge ihrer exothermen Folgereaktion mit der gebildeten Grignard-Reagenz einen zusätzlichen Wärmebeitrag lieferten. Eine Temperaturabhängigkeit der molaren Reaktionsenthalpie konnte im Temperaturbereich von 25°C bis 120°C nicht festgestellt werden.
Um subjektive Fehleinschätzungen des Anspringens der Grignard-Reaktion zu vermeiden, wurden die Anwendungsmöglichkeiten verschiedener Messmethoden zur Online-Überwachung getestet. Mit der in situ-Infrarotspektroskopie ließ sich das Anspringen der Grignard-Reaktion eindeutig und empfindlich detektieren. Ebenso könnte das spätere Einschlafen der Reaktion infolge zudosierter oder eindringender Verunreinigungen erkannt werden. Das Leistungsvermögen der Stoff- und Energiebilanzen als Methode zur Online-Überwachung konnte sowohl für die Startphase als auch für die Hauptreaktionsphase im Vergleich mit der Infrarotspektroskopie nachgewiesen werden. Die Wärmebilanzierung liefert eine viel versprechende Alternative zur in situ-Infrarotspektroskopie für den Einsatz an Produktionsanlagen, weil sie mit einer ausreichend empfindlichen Betriebsmesstechnik realisiert werden kann, quasi im Echtzeitbetrieb arbeitet und wesentlich kostengünstiger ist. Der Vorteil der in situ-Infrarotspektroskopie ist die parallele Online-Messung von störenden Wasseranteilen im Reaktionsmedium. Beispielsweise könnte das Nichtstarten der Grignard-Reaktion aufgrund von zu großen Wasserrestmengen in der Mehrzweckanlage erkannt werden. Durch geeignete Sicherheitsmaßnahmen und Sicherheitsverriegelungen sollte die Überdosierung von organischem Halogenid und das Eindringen stark exothermer Verunreinigungen (wie z. B. Wasser) während der ersten Grignard-Reaktionsstufe unbedingt verhindert werden. Aus Sicherheitsgründen sollte Wasser durch Öl als Kühlmedium möglichst ersetzt werden.

The impact of organic matter on the migration of actinides in argillaceous media is relevant for the risk assessment of future nuclear waste repositories. The diffusion of a 14C-labelled synthetic humic acid in compacted Georgia kaolinite and its influence on the uranium(VI) migration was studied.
The migration of humic acid in clay is governed by diffusion. The colloidal properties of humic acid result in a size exclusion from small pores. Thus the accessible pore space decreases and the tortuosity of the diffusion path increases compared to a conservative tracer. Furthermore, the compacted clay filters large humic colloids. Both effects restrict the diffusive flux of humic acid in the clay.
Diffusion experiments on the time scale of several weeks could not demonstrate a humic colloid-borne migration of uranium(VI) in the clay system. The competition of the humate and surface binding sites for uranium as well as the kinetics and reversibility of the complexation govern the actinide migration in this system.

We propose scanning near-field optical microscopy as a novel technique for characterizing the ion-implanted patterns fabricated in amorphous silicon carbide (a-SiC:H). Different patterns have been fabricated in a-SiC:H films with a focused Ga+-ion beam system and examined with scanning near-field optical microscopy and atomic force microscopy. Although a considerable thickness change (thinning tendency) has been observed in the ion-irradiated areas, the near-field measurements confirm increases of optical absorption in these areas. The observed values of the optical contrast modulation are sufficient to justify the efficiency of the method for optical data recording using focused ion beams.