Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Analyses of the centrality binned identified hadron multiplicities at SPS (Ýa;s = 17 AGeV) and RHIC (Ýa;s = 130 AGeV) within the statistical-thermal model point to strangeness saturation with increasing centrality and energy

Dipole and quadrupole excitations in the semimagic N=50 Nucleus ⁸⁸Sr were investigated at the superconducting Darmsatdt linear accelerator S-DALINAC with bremsstrahlung of an endpoint energy of 6.8 MeV. Many new dipole excitations could be identified, and their reduced transition probabilities were determined. The experimental findings are discussed in the context of quasiparticle-phonon-model and shell-model calculations. A breaking of the N=50 core is essential to describe the structure of the observed excitations. The two-phonon quadrupole-octupole J^pi=1^- state exhibits unusual features which are presently not understood.

Two new octahedral rhenium cluster complexes, [Re₆S₇O(3,5-Me₂PzH)₆]Br₂*3,5-Me₂PzH and [Re₆Se₇O(3,5-Me₂PzH)₆]Br₂*3,5-Me₂PzH, with the organic ligand 3,5-dimethylpyrazole (3,5-Me₂PzH) have been synthesized by reaction of rhenium chalcobromides Cs₃[Re₆(μ₃-Q₇Br)Br₆] (Q = S, Se) with molten dimethylpyrazole. During the reaction all six apical bromine ligands of the cluster complexes are substituted by the organic ligand which is coordinated via the aromatic nitrogen N2. Additionally, the inner ligand μ₃-Br in the cluster core [Re₆(μ₃-Q₇Br)]³⁺ is substituted by oxygen given cluster cores, [Re₆(μ₃-Q₇O)]²⁺, with mixed chalcogene/oxygen ligands.

Two novel star-like cyclam derivatives with appended four amino groups and four PEG-arms have been synthesized. The complex formation of cyclam and the cyclam derivatives and with Cu(II) has been studied by UV-Vis and time-resolved laser-induced fluorescence (TRLFS) measurements. The cyclam ligands investigated form 1:1 complexes with Cu(II). Rapid complex formation was found for cyclam and the pegylated derivative. By way of contrast, complete attainment of complexation between Cu(II) and cyclam ligand having external primary amino groups needs approx. 1 hour. By TRLFS measurements a quench effect of the Cu(II) on the fluorescence of the ligand was found. This behaviour was used to determine the complex formation between Cu(II) and the ligands.

Experimental investigations and Computational Fluid Dynamics (CFD) calculations on coolant mixing in Pressurised Water Reactors (PWR) have been performed within the EC project FLOMIX-R. The project aims at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity. Measurement data from a set of mixing experiments have been gained by using advanced measurement techniques with enhanced resolution in time and space. Slug mixing tests simulating the start-up of the first main circulation pump are performed with two 1:5 scaled facilities: the Rossendorf Coolant Mixing model ROCOM and the Vattenfall test facility. Additional data on slug mixing in a VVER-1000 type reactor have been gained at a 1:5 scaled metal mock-up at EDO Gidropress. Experimental results on buoyancy driven mixing of fluids with density differences have been obtained at ROCOM and the Fortum PTS test facility.
Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests at PWRs and VVER are used together with the data from the ROCOM facility as a basis for the flow distribution studies.
In part 1 of the paper, the experiments performed are described, results of the mixing experiments are shown and discussed. In part 2, efforts on computational fluid dynamics codes validation on selected mixing tests under steady-state flow conditions will be reported about. The application of Best Practice Guidelines in code validation will be demonstrated.

For calculations of Lower Head Failure experiments like FOREVER it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model is developed based on a commercial Finite-Element-code. The CFD module is used to calculate the thermodynamics. The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model is applied.
After pre- and post-test calculations of the ealier FOREVER-experiments, pre-test calculations for the forthcoming experiments were performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.
After analyzing the results of the calculations, it seems to be advantageous to provide a vessel support, which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it may be advantageous to install a passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

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Si-SiO2 structures irradiated with 11-MeV electrons for 10 s and then implanted with B+ ions with an energy of 10 keV at a dose of 1.0×1012 cm-2 through the oxide were annealed at different temperatures. MOS capacitors including such oxide layers were studied by quasi-static C/V and thermally stimulated current (TSC) methods. A comparison of the radiation defect annealing of double-treated (electron-irradiated and ion-implanted) samples and of implanted-only samples was carried out. It is shown that a preceding low-dose high-energy electron irradiation of the samples leads to a lowering of the annealing temperature of radiation defects introduced by ion implantation. After annealing at 500 °C for 15 min, no TSC spectra for the double-treated samples were observed. The spectra of the other samples (which were not previously irradiated) showed that after the same thermal treatment only some of the radiation defects introduced by ion implantation are annealed. The difference between the annealed interface state density of previously electron-irradiated and current MOS structures is also demonstrated. A possible explanation of the results is proposed .

By means of magnetic measurements as a function of temperature and magnetic field, the coordination polymer Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene has been identified as a model system for a homogeneous antiferromagnetic S=1/2 Heisenberg spin chain with a moderate exchange-coupling constant |J| = 21.5 K/k_B. Measurements of the longitudinal elastic constant in pulsed fields up to 50 T, i.e., across the saturation field gmu(B)B(S)=2|J|, reveal a pronounced acoustic anomaly near B_S at T<|J|k_B. We show that this feature is directly related to the shape of the magnetization curve and thus represents a generic property of a one-dimensional S=1/2 Heisenberg antiferromagnet with finite spin-lattice interaction.

Low-dimensional spin systems in high magnetic fields reveal new and unexpected physical phenomena. Typical examples are the distinct plateaus in the magnetization found in quasi- 1d and 2d compounds. Even for the well known case of the quasi-1d homogeneous Heisenberg spin chain or its dimerized variant, unexpected elastic anomalies can be detected in high magnetic fields. Since the exchange constants of these low-dimensional spin systems are of the order of the dominant energy scale, pulse-field experiments are particularly well suited for investigations of the magnetic properties. In this contribution we present and discuss our results for selected low-dimensional compounds such as the homogeneous antiferromagnetic Heisenberg spin chain Cu(II)-bispyrazoldihydroxybenzene, which is a new quasi-1d Cu(II)-coordination polymer, the dimerized spin chain (VO)₂P₂O₇, and the plateau systems SrCU₂(BO₃)₂ and NH₄CUCl₃.

The production and the propagation of K+- and of K--mesons in heavyion collisions at beam energies of 1 to 2 A GeV have systematically been investigated with the Kaon Spectrometer (KaoS) at the SIS at the GSI. The ratio of the K+-production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. At 1.5 A GeV a comprehensive study of the K+- and of the K--emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K-/K+ ratio is found to be nearly constant as a function of the collision centrality. The spectral slopes and the polar emission patterns are different for K- and K+. These observations indicate that K+-mesons decouple earlier from the reaction zone than K--mesons.

The final state in heavy-ion collisions has a higher degree of strangeness saturation than the one produced in collisions between elementary particles such as p-p or p-(p) over bar. A systematic analysis of this phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider and for Au-Au collisions at RHIC and at AGS energies. Strangeness saturation is shown to increase smoothly with the number of participants at AGS, CERN and RHIC energies.

This paper discusses the experimental realisation of two types of X-ray interferometer based on pinhole diffraction. In both interferometers the beam splitter was a thin metal foil containing micrometer pinholes to divide the incident X-ray wave into two coherent waves. The interference pattern was studied using an energy-dispersive detector to simultaneously investigate in a large spectral range the diffraction properties of the white synchrotron radiation. For a highly absorbing pinhole mask the interference fringes from the classical Young's double-pinhole experiment were recorded and the degree of coherence of X-rays could be determined. In the case of low absorption of the metal foil at higher X-ray energies (> 15 keV) the interference pattern of a point diffraction interferometer was observed using the same set-up. The spectral refraction index of the metal foil was determined.

With the Dresden EBIT (electron beam ion trap) a room temperature, compact and long-term stable source of slow highly charged ions (HCIs) has been developed and prepared for small series production. A wide spectrum of ions such as Ar18+, Fe24+ and Xe44+ have been produced and extracted with energies less than q x 10 keV (q - ion charge). At ion-surface interactions the high neutralization energy of the ionic projectiles leads to high power densities of 10(12)-10(13) W/cm(2) at the surface. Thus, these ions can produce nanoscale material modifications and can be used for surface analysis techniques as well. Examples of extracted and magnetically analyzed ion beams are given. Fields of applications of slow highly charged ions are summarized.

A buried layer of iron disilicide was synthesized by ion implantation in (111) Si p-type maintained at 500 degreesC using 195 keV Fe ions with a dose of 2 x 10(17) at./cm(2), followed by annealing in a N-2 atmosphere at 850 degreesC for 90 min. The investigation of the phase composition is carried out by Rutherford backscattering spectrometry (RBS), whereas the structural characterization is obtained by means of both X-ray diffraction (XRD) pole figure and cross-sectional transmission electron microscopy (XTEM). The precipitates favor epitaxial growth with respect to (111) Si planes with epitaxial relationships (220) beta-FeSi(2)parallel to(111) Si and/or (202) beta-FeSi(2)parallel to(111) Si. A mixture of beta-FeSi2 and alpha-FeSi2 Silicides is observed in the as-implanted state. After annealing of the samples at 1000 degreesC, the XRD pole figures show the transition from beta-phase to alpha-phase.

The nucleus-nucleus Liege intranuclear-cascade+percolation+evaporation model has been applied to the C-12+Au-197 data measured by the INDRA-ALADIN collaboration at GSI. After the intranuclear cascade stage, the data are better reproduced when using the Statistical Multiframentation Model as afterburner. Further checks of the model are done on data front the EOS and KAOS collaborations.

The Rh-105 nucleus has been studied with the Mo-100(B-11, alpha2ngamma) reaction at 43 MeV incident energy. A rich variety of structures was observed at high and low spins, using gamma-gamma-t and gamma-gamma-particle coincidences and directional correlation ratios. A gamma-vibrational band was observed for the first time in this nucleus. A new structure based on the intruder 1/2(+)[431] proton orbital was identified. Four magnetic dipole bands have also been observed at high spin, three of which have negative parity and have similar characteristics: they are very regular in energy spacing, presenting nearly constant alignments and large values of B(M1)/B(E2) ratios. Two of them are nearly degenerate in excitation energy and could be chiral partners. The pig(9/2)xnuh(11/2)(g(7/2),d(5/2)) configuration is tentatively assigned for these bands, with the angular momenta of the proton and neutron intruders and the collective angular momentum aligning along the three perpendicular axes of the triaxial core, as predicted by tilted axis cranking calculations.

In previous experiments, diamond-like carbon (DLC) foils which are being produced at Kurchatov Institute, have proven well suited as long-lived stripper foils for high-energy heavy-ion tandem accelerators and ultra-thin secondary-electron (SE) emitting foils for TOF spectrometers. This paper presents the recent advances in DLC targetry with main emphasis given to development and applications of ultra thin foils (maximum diameter up to 70 mm) with high uniformity and minimal possible effective thickness, the latter has been evaluated by measurements of both energy loss and angular scattering of heavy ions transmitting through the foils. Comparative lifetimes of DLC stripper foils irradiated with high intensity (150 muA) He+ beams at 2 MeV are reported, which demonstrate the favorable use of DLC foils as supplemental strippers at RFQ linacs. In conclusion, the attractive results of application of ultra-thin DLC foils to TOF detectors for heavy ion AMS as well as to compact tandem accelerators are presented.

Titanium oxynitride compounds exhibit interesting properties for applications in fields ranging from protective/decorative coatings to solar panels. The properties of TiNxOy are related to the oxide/nitride ratio and can be tailored playing with this ratio. In this work we studied the influence of substrate bias voltage and flow rate of reactive gases (a mixture of N-2 and O-2) on the properties of TiNxOy films. The films were deposited on steel substrates at a constant temperature of 300 degreesC by r.f. reactive magnetron sputtering. The depositions were carried out from a pure Ti target. The composition throughout the entire thickness was determined by Rutherford backscattering spectrometry. To obtain information on the profile of light elements (0, N) and detect the presence of hydrogen on the films, heavy ion elastic recoil detection analysis was performed. The results indicate a nearly constant stoichiometry through the entire analysed depth. The colouration varied from the shiny golden for low oxygen contents (characteristic of TiN films) to dark blue for higher oxygen contents. The electrical resistivity of the samples was obtained at room temperature and the values varied from approximately 120 muOmega cm for a sample with very low oxygen content to values up to 350 muOmega cm, for the highest oxygen contents.

The quadrupole interaction of high-spin isomers in Pb-193 implanted into solid Hg cooled at a temperature T=170 K has been investigated by the time-differential perturbed gamma-ray angular-distribution method. Spectroscopic quadrupole moment values of \Q\=0.22(2) eb and 0.45(4) eb have been deduced for the 21/2(-) and 33/2(+) three-neutron states, respectively. A much higher value \Q(s)\=2.84(26) eb has been determined for the 29/2(-) isomer, the band head of a magnetic rotational band.

High-spin states of the neutron-rich vibrational nucleus Cd-114 have been studied using the incomplete fusion reaction Pd-110(Li-7, p2n) and the GASP spectrometer in conjunction with the ISIS Si ball. About 50 new states with excitation energies up to 7 MeV and angular momentum I less than or equal to (18(+)) were observed and for many of them, spin and parity could be firmly assigned. The band-like stuctures in Cd-114 are compared to the corresponding ones in the even-even neighbour Cd-112.

A continuum model, based on the damped Kuramoto-Sivashinsky equation, is shown to reproduce the morphology evolution during ion sputtering quite successfully. In a very narrow range of the damping parameter alpha, the alignment of the structures into hexagonal domains is obtained under normal incidence of ions with striking resemblance to the experimentally observed dot patterns. The origin of this damping factor is discussed.

Experimental nuclear moments of inertia at high spins along the yrast line have been determined for a large number of nuclei. They are found to systematically differ from the rigid-body values. The difference is attributed to shell effects which are well described by a rotating Woods-Saxon potential. The data and quantal calculations are interpreted by means of the semiclassical periodic orbit theory. From this new perspective, features in the moments of inertia as a function of neutron number and spin as well as their relation to the shell energies can be understood. Gross shell effects persist up to the highest angular momenta observed.

Adding C2H2 gas to nitrogen gas during r.f. plasma processing has significant influence on the properties of 304 austenitic stainless steel. The elemental depth profiles of the compound layer were investigated by glow discharge optical spectroscopy. Different treatment gas compositions of N-2/C2H2 mixtures (0-100% in steps of 10 or 5% in some cases) have been investigated. The total gas pressure during the plasma processing was 8.4 x 10(-2) mbar. The sample temperature was approximately 550 degreesC with an insignificant variation for different gas compositions. A high rate of diffusion of carbonitriding has been obtained without initial sputter removal of the surface oxide layer, which demonstrates that the surface oxide layer does not play a crucial role during r.f. plasma carburizing and carbonitriding of stainless steel. The nitrogen concentration and the compound layer thickness increase, when 10% of C2H2 is added. With further increase in the C2H2 ratio, they decrease again gradually. The carbon depth profiles for the same samples show lower concentration and opposite tendency with respect to the nitrogen content. X-ray diffraction was used to characterize the microstructure of the compound layers. Fe2N, Fe3N, CrN, nitrogen-expanded austenite (gamma(n)) and carbon-expanded austenite (gamma(c)) phases are detected. The relative proportions of the phases are critically dependent on the N-2/C2H2 ratio. Depending on the N-2/C2H2 ratio, the microhardness value increases by a factor between 2 and 6. The carbonitrid layer exhibits a corrosion resistance better than pure nitrided and carburized layers.

The effect of 'double' treatment (plasma immersion ion implantation and subsequent compression plasma flows) on microstructure, element and phase composition, as well as on microhardness properties of AISI M2 high-speed tool steel has been studied. Such methods as Auger electron spectrometry (AES), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis and scanning electron microscopy (SEM) allowed us to obtain the data suggesting that under such treatment a martensite-austenite conversion and the formation of a deep (approx. 35 mum) three-layered structure take place. It has been established that transformations of near-surface regions are associated with the complete dissolution of the initial (Fe, Cr)(3)(W, Mo)(3)C carbide (less than or equal to 5-10 mum) and the formation of gamma(N,M) expanded austenite doped with atoms of nitrogen, carbon and alloying metals M=W, Mo, Cr.

CoFe single and multi-layer systems are diposited by a radio-frequency sputter process. Thickness, roughness, morphology, texture and internal stress state of the layers are determined by X-ray reflectometry, transmission electron microscopy, and diffraction methods. The texture and the internal stress of the layers depend strongly on the parameters of the sputter process. The magnetic properties of the layers are determined from hysteresis curve measurements and magneto-optical Kerr microscopy. A strong correlation between the texture, the internal stress and the magnetic properties of the CoFe layers os observed.

Differential cross sections for the exclusive reaction pp-->ppeta observed via the eta-->pi(+)pi(-)pi(0) decay channel have been measured at T-beam=2.15 GeV, 2.50 GeV, and 2.85 GeV (excess energies 324 MeV, 412 MeV, and 554 MeV). The influence of the N(1535)S-11 resonance is clearly seen in the invariant mass and momentum dependent differential cross sections. The extracted resonance parameters are compatible with existing data. No significant evidence for further resonance contributions has been found. In addition, angular distributions of the ppeta final state have been measured. The polar angle distribution of the eta shows an anisotropy with respect to the beam axis for the lowest beam energy, which vanishes for the higher energies. The sign of this
anisotropy is negative and expected to be sensitive to the dominant production mechanism. In contrast, the proton polar angle in the pp rest frame tends to be more strongly aligned along the beam axis with increasing beam energy. The analyzing power A(y) is compatible with zero for all beam energies.

Anwendungsbereiche der hier vorgestellten thermodynamischen Sorptionsdatenbank RES³T (Rossendorf Expert System for Surface and Sorption Thermodynamics) sind Deponien unterschiedlichster Art und ihre Sickerwässer, aber auch die Sicherung von kontaminierten Militärstandorten und Industrieanlagen. Neben chemo-toxischen Abfällen wird zudem die Lagerung radioaktiver Abfälle adressiert, wobei sowohl das Wirtsgestein als auch das Deckgebirge erfasst wird, und damit nicht nur für ein einziges Endlagerumfeld (z. B. Salzstock) Relevanz besitzt. Und schließlich stellt die Datenbank auch einen Beitrag dar zur Problematik der Stilllegung, Verwahrung oder Rekultivierung von Bergwerken (Uranerz, Kupferschiefer, Steinkohle) und offenen Tagebauen (Steinkohle, Braunkohle). Die avisierten Anwender umfassen Behörden, Gutachter, die WISMUT GmbH, Ingenieurbüros sowie universitäre und außeruniversitäre Forschungseinrichtungen.

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We present measurements of the excitation function of elliptic flow at midrapidity in Au + Au collisions at beam energies from 0.09 to 1.49 GeV per nucleon. For the integral flow, we discuss the interplay between collective expansion and spectator shadowing for three centrality classes. A complete excitation function of transverse momentum dependence of elliptiv flow is presented for the first time in this energy range, revealing a rapid change with incident energy below 0.4 AGeV, followed by an almost perfect scaling at the higher energies. The equation of state of compressed nuclear matter is addressed through comparisons to microscopic transport model calculations.

The uranium carbonate andersonite Na₂Ca[UO₂(CO₃)₃]*6H₂O was synthesized and identified with classical analytical and spectroscopic methods. The classical methods applied were X-ray powder diffraction (XRD), nitric acid digestion, and Scanning Electron Microcopy combined with Energy-Dispersive Spectroscopy (SEM/EDS). To spectroscopically characterize andersonite, Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS), X-ray Photoelectron Spectroscopy (XPS), and Fourier-Transformed InfraRed spectroscopy (FT-IR) were used. Natural and synthetically prepared andersonite samples were characterized with the non-destructive TRLFS by six fluorescence emission bands at 470.6, 486.1, 505.4, 526.7, 549.6, and 573.9 nm. In addition, andersonite was characterized by FT-IR measurements by the appearance of the asymmetric stretching vibration of the uranyl cation (v₃ UO₂ ²⁺) at 902 cm^-1 with a shoulder at 913 cm^-1 and by XPS measurements. The intensity of the measured XPS lines was used to verify the composition of the synthetic andersonite sample. The measured intensity ratios and the calculated atomic ratios agree with the stoichiometry of Na₂Ca[UO₂(CO₃)₃]*6H₂O. The results of both the qualitative and quantitative XPS analysis confirmed the formation of andersonite. The spectral features of the U 4f electrons and the distinct splitting of the U 6p3/2 electrons can be used to identify the [UO₂(CO₃)₃]^4- structural moiety.

These spectroscopic methods proved to be suitable to identify in a fingerprinting procedure secondary U(VI) phases in mixtures with other phases or as thin coatings on mineral and rock surfaces. The obtained spectroscopic information are of fundamental importance for uranyl(VI) adsorption studies, since such information are useful to identify the coordination environment and structure of unknown adsorbed uranium(VI) surface species on minerals surfaces.

Plasma immersion ion implantation-assisted deposition has been employed to develop Ti-based coatings in the presence of reactive nitrogen environment. When TiN coatings have been developed on Al alloys, it has been observed that a large compressive stress develops in the coating, which can be reduced when the substrate bias is increased. The formation of stress is attributed to atomic peening effect that densifies a coating, whereas thermal spikes generated at high substrate bias reduce the stress. For TiAl coatings delivered from an alloy plasma source, the Al content decreases with increasing negative substrate bias. This is in agreement with the results of TRIDYN ballistic computer simulations, which confirm that the film composition is significantly influenced by preferential sputtering. The results indicate that time-averaged substrate bias is an ill-defined parameter to describe coating properties deposited by the above technique.

The three-dimensional velocity field of a propeller driven liquid metal flow is reconstructed by a contactless inductive flow tomography (CIFT). The underlying theory is presented within the framework of an integral equation system that governs the magnetic field distribution in a moving electrically conducting fluid. For small magnetic Reynolds numbers this integral equation system can be cast into a linear inverse problem for the determination of the velocity field from externally measured magnetic fields. A robust reconstruction of the large scale velocity field is already achieved by applying the external magnetic field alternately in two orthogonal directions and measuring the corresponding sets of induced magnetic fields. Kelvin's theorem is exploited to regularize the resulting velocity field by using the kinetic energy of the flow as a regularizing functional. The results of the new technique are shown to be in satisfactory agreement with ultrasonic measurements.

The bonding structure of highly ordered fullerene-like (FL) carbon nitride (CNx) thin films have been assessed by x-ray absorption near edge spectroscopy (XANES). In particular, samples with different degree of FL character (in terms of graphene plane alignment, extension, and cross-linking) have been analyzed to discern spectral signatures of the microstructure formation. The XANES spectra of FL-CNx films resemble that of graphitic CNx, indicating a sp2 character for C and N atoms. However, the evolution of the FL structure is promoted with the dominance of three-fold N over pyridine-like and cyanide-like bonding environments. In addition, the p*/s* ratio at the C(1s) edge is constant, independent of the change in FL character, while it decreases ~40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp3 hybrids with the development of FL structures and, additionally, that a different spatial localization of p electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could as such explain the outstanding elastic properties of FL-CNx.

A theoretical study is presented of the effect of a radially converging melt flow on the radial solute segregation in simple solidification models. We show that the classical Burton-Prim-Slichter (BPS) theory describing the effect of a diverging flow on the solute incorporation into the solidifying material breaks down for converging flows. The breakdown is caused by a divergence of the integral defining the effective boundary layer thickness which is the basic concept of the BPS theory. The divergence can formally be avoided by restricting the axial extension of the melt to a layer of finite height. This allows us to obtain radially uniform solutions for the solute distributions which, however, are valid only for weak melt flows with an axial velocity away from the solidification front comparable to the growth rate. There is a critical melt velocity for each growth rate at which the solution passes through a singularity and becomes physically inconsistent for stronger melt flows. Thus, the radially uniform solute distribution becomes incompatible with a converging flow exceeding the growth rate, and a radial segregation sets in. The solute distribution is analysed in detail for a solidification front presented by a disk of finite radius R0 subject to a converging melt flow. We obtain similarity and matched asymptotic solutions showing that the radial solute concentration depends on the radius r as ln1/3(R0/r) and ln(R0/r) close to the rim and at large distances from it, respectively. The converging flow causes a solute pile-up forming a logarithmic concentration peak at the symmetry axis which might be an undesirable feature for crystal growth processes.

Die Nutzung der Windenergie zur Stromerzeugung hat in den letzten Jahren ein beachtliches Niveau erreicht. Im Vortrag wird der gegenwärtige technische Entwicklungsstand vorgestellt. Ferner werden die mit der Aufnahme von großen fluktuierenden Mengen Windstromes im Höchstspannungsnetz auftretenden Probleme und Konsequenzen diskutiert.

Even in former East Germany, photovoltaic has being used increasingly for generating electricity. Through weaker buying power the absolute numbers of pv plants are far lower than in the western federal states, but a series of remarkable results was achieved nonetheless. This paper discusses the developments in the federal state Saxony.
It is based on long term results on selected photo-voltaic plants as well as data recorded by the regional electricity supplier Energieversorgung Ostsachsen (ESAG), Dresden, in 2002 and 2003 [1].

Clinical and histopathological findings hint at regional differences in the brain's sensitivity to metabolic changes in cirrhosis. The aim of the present study was to examine regional differences in cerebral ammonia metabolism in patients with cirrhosis and grade 0-to-I hepatic encephalopathy (HE). ¹³N-ammonia, ¹⁵O-water positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed. Quantitative values of cerebral blood flow (CBF) and the initial cerebral ammonia uptake rate (K1) were derived for several regions of interest from images of the desired parameters after interactive coregistration with the patients' MRI-studies. CBF (mL/mL/min), K1 (mL/mL/min), and the ammonia extraction fraction (K1/CBF) showed marked regional variance with the highest levels in the thalamus, the lenticular nucleus, and the cerebellum. In conclusion, the regional differences in cerebral ammonia uptake correspond to the distribution of histopathological changes in the brain of patients with cirrhosis as well as clinical features of HE, characterized by signs of basal ganglia and cerebellar dysfunction with corresponding signs of functional impairment, especially of the frontal cortex and cingulate gyrus.

Boron nitride is a remarkable material both for its fundamental properties and for applications [1]. It exists in different polytypes, the sp2 bonded hexagonal and rhombohedral structure and the sp3 cubic and wurzite phases. All phases are high band-gap semiconductors (>5 eV). Cubic boron nitride, c-BN, is of particular interest for its properties similar to diamond [1,2]. Physical or chemical vapor deposition of boron nitride films can often result in the growth of the less dense hexagonal BN (h-BN). BN nanotubes are also very interesting [3]. Their properties, as for carbon nanotubes, can be derived by studying the wrapping of a single layer of h-BN [3]. Boron Carbon Nitrides (BCN) thin films are also useful for hard coating applications and as semiconductors with variable gap [4]. Raman and Infrared spectroscopy are quick and non-destructive tools to assess the properties of materials. Infrared spectroscopy is the most widely used for boron nitrides. It is very sensitive to polar BN bonds. The spectra for c-BN and h-BN show distinct IR features [1]. Raman spectroscopy is rarely used because of its inferior sensitivity, especially in the case of thin films. This is opposite to diamond-like carbons, where Raman spectroscopy is a standard characterization tool [5]. However, Infrared spectroscopy has limitations. The substrate has to be either transparent or not highly reflective. Raman spectroscopy has no requirement on the substrate properties and can simultaneously give informantion on phase composition, crystallinity, size and stress. In order to successfully apply Raman scattering in boron nitrides its low sensitivity has to be overcome. This can be done by measuring the samples with an excitation energy closer to their band gap. Here we measure BN samples by UV Raman spectroscopy at 5.1 and 5.4 eV. This enhances the BN Raman cross-section and paves the way to making UV Raman scattering a standard tool for boron nitrides characterization. We studied the UV Raman spectra of a variety of boron nitride samples ranging from h-BN (bulk and thin film), c-BN (single crystals, thin and thick films), mixed h-BN and c-BN phases and BCN films with varying B, C and N content. The UV Raman spectra of c-BN and h-BN are so intense that a clear measurement of the second order Raman signal is possible. This allows us to probe for the first time non-zone center phonons and validate the predictions of first-principles calculations of BN properties [3,6]. For h-BN, whilst the high-energy optical phonons are in excellent agreement with theory, the ionic interaction was strongly underestimated for lower energies [6]. The first order UV Raman spectra of thin and nano-crystalline films also show the activation of non-zone center phonons and IR modes, such as the 800 cm-1 mode of h-BN. In BCN films the direct signature of BN bonds can be seen, being no more shadowed by the carbon phase.

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2. W. Zhang, S. Matsumoto, Q. Li, I. Bello, S. T. Lee, Adv. Funct. Mat. 12, 250 (2002)
3. L. Wirtz et al. Phys. Rev. B 68, 045425 (2003)
4. R. Gago et al. J. Appl. Phys. 92, 5177 (2002)
5. A.C. Ferrari, J. Robertson, Phys. Rev. B 61, 14095 (2000); 64 075451 (2001)
6. G. Kern, G. Kresse, J. Hafner, Phys. Rev. B 59, 8551 (1999)

Carbon nitride films have been deposited by ECR-CVD, from Ar/CH4/N2 gas mixtures with different methane concentrations. Infrared Spectroscopy and Elastic Recoil Detection Analysis have been used for films characterisation and Optical Emission Spectroscopy for plasma analysis. Argon concentration in the gas mixture controls the growth rate as well as the composition of the film. In the proposed model, argon plays a key role in the activation of methane molecules. Also, during the growth of the film, two processes may be considered: i) Film formation and ii) Etching of the growing surface. Changing the gas mixture composition affects both processes, which results in films with different composition and structure as well as different deposition rates.

Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2-10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress-release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials.

The paper presents the results of experiments on modification of pure iron by high intense nitrogen pulsed-plasma treatment. The duration of nitrogen plasma pulses is approximately 1 µs, and the energy density amounts to about 5 J/cm². Such pulses are capable to melt the surface layer of the substrate (1-2 µm) and to introduce a significant concentration of nitrogen into the molten layer. Nuclear reaction analysis (NRA), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) were used for characterisation of the treated samples. The main results of the data analysis are as follows:it has been stated that such treatment leads to gradual transformation of initial alpha-phase into austenitic gamma structure in which expanded austenite gamma_N is present. Treatment with 20 pulses results in almost complete transformation and introduces a retained dose of nitrogen estimated as 5.5 x 10¹⁷ N/cm². The susceptibility for expansion of the lattice transformed to austenite in this way is smaller than in the case when the steel subjected to conventional nitriding is orginally of austenite type. The analysis of the ratio of gamma to gamma_N as a function of the nitrogen content provides a firm evidence that strong repulsion forces act between the first and the second nearst-neighbour nitrogen atoms in the fcc austenitic structure as a result of nitriding of pure iron by intense nitrogen plasma pulses.

The scientific analysis of archaeological objects ideally requires the availability of methods, which are simultaneously non-destructive, fast, universal, versatile, sensitive and multielemental. Analyses of source materials combined with analyses of the objects could distinguish from pieces produced in different regions. Our purpose is to help archaeologists to identify objects provenance (workshops, technologies, mines) and to explain different commercial, military and political aspects. We used 241Am source based XRF (X-ray Fluorescence), 3 MeV protons induced PIXE (Particle Induced X-ray Emission), 11 MeV proton activation analysis (PAA) and 3 MeV protons micro-PIXE methods. The above mentioned methods are complementary and they work better together. Some results on pigments from Cucuteni Neolithical and Iznik Medieval ceramics, especially the case of black (Manganese) and blue (Cobalt) colours are presented. We also report a study on ancient Dacian gold coins. The method used were XRF and PAA. Three groups of coins with different composition were found, corresponding to simple, complex and no monogram pieces. Possible historical conclusions are discussed. Finally, micro-PIXE results on some ancient gold objects from Romanian Pietrosa hoard are reported.

New oxotechnetium compleses of general formula [^99mTc(O)(PNS)(S(CH₂)_nOSiR₃] (4-6) were synthesized by direct reduction of [[^99mTcO₄]^- with stannous chloride, in the presence of the tridentate heterofunctionalized phosphine H₂PNS and of the monodentate silylated thiols [HS(CH₂)_nOSiR₃] (n=2, R=Ph (1); n=3, R=Ph (2); n=3, R=Et (3)). The mixed-ligand rhenium and technetium complexes of general formula [M(O)(PNS)(S(CH₂)_nOH] (n=2: M=^99mTc, (7), M=Re, (7a); n=3: M=^99m, (8), M=Re, (8a)) were also prepared. All the ^99mTc complexes were obtained with high radiochemical purity (> 95 %), after purification by HPCL, and were characterized by comparison of their HPLC profiles with the ones obtained for the corresponding Re compounds. The silylated compounds 4-6 are stable in phosphate saline buffer (PBS) pH 7.4; rat plasma, human serum and whole blood, and do not bind to plasmatic proteins, and also do not challenge with glutathione. The biological behavior of [^99mTc(O)(PNS)(S(CH₂)_nOH] (7, 8) and [^99mTc(O)(PNS)(S(CH₂)_nOSiR₃] (4-6) was studied. The effect of the pH on the cleavage of the O-Si bond in complexes 4-6 was also evaluated.

The study of AuSi liquid metal alloy ion sources (LMAIs) for the production of Si ions is not new. However, the present work encompasses in a concise form almost all fundamental aspects of source behaviour, in particular of a Au82Si18 source. A key finding, manifested in the behaviour of the ion extraction voltage with temperature, is the abnormal behaviour of the surface tension coefficient of the alloy with temperature. An important deduction, however, concerns the mechanisms responsible for the creation of doubly charged ions: reasons of self-consistency suggest that while Si++ is directly field-evaporated, Au++ must form by the post-ionization of Au+. (C) 2004 Elsevier B.V. All rights reserved.

The germination rate of sol-gel immobilized spores of B. sphaericus JG-A12 in thin silica layers is 5-8 fold enhanced after pre-incubation with an 1:1 chelate of calcium and dipicolinic acid. This germination potential is conserved during long-time storage of 2.5 years.

The present interest in the 5-HT_1A receptor is due to its implicated role in several major neuropsychiatric disorders such as depression, eating disorders and anxiety. For the diagnosis of these pathophysiological processes it is important to have radioligands in hand able to specifically bind on the 5-HT_1A receptor in order to allow brain imaging. Due to the optimal radiation properties of ^99mTc there is a considerable interest in the development of ^99mTc radiopharmaceuticals for imaging serotonergic CNS receptors using single-photon emission tomography (SPET) [1,2].
Here we introduce two cyclopentadienyl technetium tricarbonyl conjugates of piperidine derivatives which show high accumulation of radioactivity in brain areas rich in 5-HT_1A receptors. The complexes have been synthesized starting from the ferrocene complexes N-(alkyl)piperidino-4-[bispentahaptocyclopentadenyl)iron]carboxylate (with alkyl = methyl, isopropyl) [3]. Their chemical identity was confirmed by chromato-graphic methods and electrospray mass spectrometry.
The in vivo uptake of the ^99mTc ligands in the whole rat brain and into brain regions was investigated. To determine the pharmacological specificity and selectivity, a group of rats was pretreated with several receptor ligands. The evaluation was carried out by quantitative digital ex vivo autoradiography.
Furthermore, we report the in vitro receptor affinity and biodistribution of the two candidates in order to demonstrate the suitability of the concept and to elucidate the influence of the building blocks on the biobehaviour of the complexes.

Trigonal-bipyramidal Tc(III) and Re(III) mixed-ligand complexes of the general formula [M^III(L¹)(L²)] (M = Tc, Re; L¹ = 2,2‘,2“-nitrilotris-(ethanethiol) NS₃ or NS₃-COOH; L² = isocyanide or phosphine) are stable against ligand exchange with cysteine or glutathione and in vitro incubations with plasma as well as whole blood of rats. Therefore, such complexes represent an interesting tool concerning the possibilities of designing biologically relevant ^99mTc or ¹⁸⁸Re labelled compounds. The introduction of a carboxyl group into the tetradentate ligand and/or the monodentate ligand enables the conjugation of biomolecules as well as fine-tuning of lipophilicity. Improved methods for n.c.a. preparations will be presented. To avoid formation of reduced-hydrolysed species of both metals the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand (NS₃) or its carboxyl derivative (NS₃-COOH) and the monodentate phosphine or isocyanide to the so-called ‘4+1’ complexes. The isocyanides are used in form of their copper(I) complexes, [Cu(CN-R)₄]Cl. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of ¹⁸⁸Re isocyanide complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labelling of interesting molecules. The stability of various ^99mTc and ¹⁸⁸Re complexes will be discussed. The described approach allows the functionalization of a biomolecule with the tripodal as well as the monodentate ligand. The isocyanides and phosphines offer the possibility to vary the length and type of spacer for coupling the biomolecule.

Introduction: In an effort to develop technetium-labelled fatty acid analogues for myocardial metabolism imaging rhenium model complexes and their ^99mTc analogues were synthesized according to the '4+1' mixed-ligand approach and investigated in vitro and in vivo.

Materials and Methods: The rhenium model complexes were completely characterised by NMR, IR, MS, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid head structure was determined by single crystal X-ray analyses. To estimate the diagnostic value of the ^99mTc-labelled fatty acids the compounds were investigated using the isolated constant-flow-perfused guinea pig heart model (see presentation A. Heintz et al.), in cell-uptake experiments and in biodistribution studies using male Wistar rats (5 - 6 weeks old, body weight 151 ± 15 g).

Results: The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the omega-position of a fatty acid chain. This structural feature is considered to be a good imitate of the well-established iodinated phenyl fatty acid. The formation of the rhenium models was accomplished by ligand exchange reactions using different pre-formed rhenium precursors. Noticable heart uptake of the ^99mTc tracers being in the order of 2 % ID/g 5´p.i. and accompanied by a good heart to blood ratio of 8.6 confirms the remarkably results of the perfused heart experiments. A significant time-dependent cell uptake in HepG2 cells is shown for two representatives.

Conclusion: Further species such as mice and guinea pigs will be involved to characterise in vivo patterns of those derivatives, that show high extraction rates in the isolated constant-flow-perfused guinea pig heart model. While the tracers are superior to other described Tc-fatty acid imitates with regard to good heart to blood ratios, heart to liver ratio has to be improved. For this, chemical modifications will be performed at the chelating part as well as at the alkyl chain.

Introduction: Newly developed technetium-labeled fatty acid analogues are promising agents for myocardial metabolism imaging. We tested the myocardial extraction of ^99mTc analogues of rhenium model complexes synthesized according to the '4+1' mixed-ligand approach (see presentation M. Walther et al.) in a guinea pig heart LANGENDORFF model

Materials and Methods: Firstly 30 min of steady state perfusion with 10 ml/min of normotherm Krebs-Henseleit-Buffer enriched with 0,1 % albumin was performed. Isolated guinea pig heart were then perfused with fatty acid tracers for 180 seconds in a 1:100 ratio. The venous effluate was collected in intervals of 15 s for 225 s following the start of tracer infusion. Perfusion was stopped, the heart was dissected into atria and ventricle compartments and γ-activity was measured. Eight new (C₁₁, C₁₂, C₁₅, C₁₀S, C₁₁S, C₁₂S, C₁₄S, C₁₆S) and for known control substances (¹²³I-IPPA, ¹²³I-BMIPP, ^99mTc-MIBI, ^99mTc-DTPA) were tested in this model (n=3-5).

Results: All eight substances showed acceptable extractions rates. Especially experiments with the C₁₁ (39.8 %), but also C₁₂ (14.8 %)and C₁₁S (17.1 %) fatty acid analogues showed excellent results.

Conclusion: When compared with extraction rates for IPPA determined with the same set-up, extraction for the C₁₁ and ₁₁S compounds is 3 fold and 1.3 fold, respectively. These results confirm our hypothesis that the "4+1" Tc(III) chelate unit is promising tool for the Tc-labelling of fatty acids. Further experiments with different species are planned to elucidate exact myocardial uptake mechanisms.

The new radiation source ELBE at Research Center Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to 1 mA at energies between 12 MeV and 40 MeV can be delivered with a wide variability in the electron pulse structure. The maximum pulse frequency is 13 MHz with a pulse width less than 10 ps. The small emittance of the electron beam permits the irradiation of very small volumes. These main beam parameters led to the idea to convert the intense picosecond electron pulses into sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and to produce neutrons by bremsstrahlung photons through (gamma,n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n,p), (n,alpha) and (n,f) with a time-of-flight arrangement with a short flight path of only a few meters, it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons which would broaden the neutron pulses. It is the primary physics objective of this neutron source to determine neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select radiation hard materials, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. In addition, the distribution of fragments can be analyzed which are produced by neutron-induced transmutation of long-lived radioactive nuclides. Furthermore experiments can be performed which address problems of nuclear astrophysics.
The energy deposition of the electron beam in the small neutron radiator is that high that any solid material would melt. Therefore, the neutron radiator consists of liquid lead flowing through a channel of 11.2×11.2 mm² cross section. From the thermal and mechanical point of view molybdenum turned out to be the most suited channel wall (thickness 0.5 mm) material. Depending on the electron energy and current up to 20 kW power will be deposited into a radiator volume of 3 cm³. This heating power is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are in the range of 2 m/s in the radiator section. The electrons that are not stopped in the radiator and the secondary radiation are dumped in an aluminum beam dump. To reduce the radiation background in the measuring direction, the neutrons are decoupled from the radiator at an angle of 90° with respect to the impinging electrons. Particle transport calculations were carried out using the Monte Carlo codes MCNP and FLUKA. These calculations predict a neutron source strength of 7.88e+12 and 2.67e+13 n/s for electron energies between 20 and 40 MeV. At the measuring place 362 cm away from the radiator, neutron fluxes of 1.7e+7 n/(cm² s) will be obtained. The mentioned time-of-flight distance allows for an energy resolution better than 1%. The maximum usable neutron energy is about 7 MeV.

An international project, whose aim was the development of a transparent and robust method for evaluating and ranking restoration strategies for radioactively contaminated sites (RESTRAT), was carried out under the Fourth Framework of the Nuclear Fission Safety Programme of the EU. The evaluation and ranking procedure used was based on the principles of justification and optimisation for radiation protection. A multi-attribute utility analysis was applied to allow for the inclusion of radiological health effects, economic costs and social factors. Values of these attributes were converted into utility values by applying linear utility functions and weighting factors, derived from scaling constants and expert judgement. The uncertainties and variabilities associated with these utility functions and weighting factors were dealt with by a probabilistic approach which utilised a Latin Hypercube Sampling technique. Potentially relevant restoration techniques were identified and their characteristics determined through a literature review. The methodology developed by this project has been illustrated by application to representative examples of different categories of contaminated sites; a waste disposal site, a uranium tailing site and a contaminated freshwater river.

The first attempt to chemically identify one of the recently discovered long-lived isotopes of superheavy elements, namely ²⁸³112 (3 min, SF), made at FLNR, Dubna is reported. The nuclide was produced by fusion of accelerated ⁴⁸Ca with a target of natural U, which contained some Nd to simultaneously produce also short-lived Hg nuclides. According to test experiments with Hg, the expected lighter homologue of element 112, both elements can be isolated from the products of the bombardment in metallic state, and transported from the target in flowing He gas to a detection system, where spontaneous fission and alpha decays 49-s ¹⁸⁵Hg) were registered using PIPS detectors. The surface of the detectors was covered with a thin layer of Au or Pd which ensured the detection of Hg with high efficiency due to its chemisorption on these surfaces. While about three SF events could be expected, not a single one was detected at an upper limit for the production cross section of about one picobarn. This may point to a "Rn-like" rather than "Hg-like" behavior of element 112. A new experiment is planned, in which both a "Rn-like" and a "Hg-like" species could be detected.

Structures of uranyl hydroxide monomeric UO₂(OH)₂ ⁰, and dimeric (UO₂)₂(OH)₂ ²⁺ were studied by hybrid density functional theoretical calculations. It was found out that both the monomeric ortho-UO2(OH)20 and dimeric (UO₂)₂(OH)₂ ²⁺ complexes have bent O=U=O angles (~170°). This is attributed to significant donation from the equatorial OH⁻ ligands to the uranyl moiety. It was also found that the ortho- and meta-UO₂(OH)₂(H₂O)₃ ⁰ complexes lie very close in energy, and that both isomers may exist in normal aqueous media.

Our aim in the present work was to investigate changes of the defect structure of bulk niobium induced by hydrogen loading. The evolution of the microstructure with increasing hydrogen concentration was studied by x-ray diffraction and two complementary techniques of positron annihilation spectroscopies (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with the measurement of the Doppler broadening, in defect-free Nb (99.9%) and Nb containing a remarkable number of dislocations. These samples were electrochemically loaded with hydrogen up to xH=0.06 [H/Nb], i.e. in the alpha-phase region, and it was found that the defect density increases with hydrogen concentration in both Nb samples. This means that hydrogen-induced defects are created in the Nb samples. A comparison of PAS results with theoretical calculations revealed that vacancy-hydrogen complexes are introduced into the samples due to hydrogen loading. Most probably these are vacancies surrounded by 4 hydrogen atoms.

The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under an Ar atmosphere at an ionic strength of 0.1 M NaClO₄. The pH is varied between 2 and 10 and the metal ion concentration between 2.7×10⁻⁸ and 4.5×10⁻⁵ mol/L. With increasing pH, two Cm(III)–alumina surface species are identified which are attributed to≡Al–O–Cm²⁺(H₂O)₅ and≡Al–O–Cm+(OH)(H₂O)₄. The two curium–alumina surface complexes are characterized by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110s). In the concentration range investigated, the surface complex formation is not dependent on the metal ion concentration but only on the pH. Additionally, the concentration ratio of the two surface species is found to be independent of the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.

Single crystal X-ray diffraction measurements are complicated in the presence of heavy atoms. In these cases the structure factors are mainly influenced by the heavy catterers and the error in determination of atomic coordinates increases for light atoms. The difficulties grow if the unit cell dimensions or the space group symmetry remain uncertain. If the structure model is similar to the correct structure, it is difficult to find an independent criterion for the accuracy of the bond-length determination. We demonstrate that extended X-ray absorption fine structure (EXAFS) spectroscopy is a useful tool for the investigation of local bond lengths in the environment of heavy atoms.

The ⁷Be activity concentrations measured from 1996 to 1998 at four high-altitude stations, Jungfraujoch—Switzerland, Zugspitze—Germany, Sonnblick—Austria and Mt. Cimone—Italy, were analyzed in combination with a set of, meteorological and atmospheric parameters such as the tropopause height, relative and specific humidity and also in conjunction with 3D back-trajectories in order to investigate the climatological features of ⁷Be. A frequency distribution analysis on ⁷Be activity concentrations revealed the existence of two concentration classes around 1.5 and 6 mBq m−3 and a transition class between the two modes of the distribution at 3–4 mBq m−3. Cross-correlation analysis performed between ⁷Be and a number of meteorological and atmospheric parameters at the first three stations showed a strong negative correlation with relative humidity (−0.56, −0.51, −0.41) indicating the importance of wet scavenging as a controlling mechanism. Also, the positive correlation with the height of 3-days back-trajectories and tropopause height (+0.49/+0.43, +0.59/+0.36, +0.44/+0.38) shows that downward transport from the upper or middle to lower troposphere within anticyclonic conditions plays also an important role. Trajectory statistics showed that low ⁷Be concentrations typically originate from lower-altitude subtropical ocean areas, while high concentrations arrive from the north and high altitudes, as is characteristic for stratospheric intrusions. Although the ⁷Be activity concentrations are highly episodic, the monthly means indicate an annual cycle with a late-summer maximum at all stations. The correlation coefficients calculated for monthly means of the ⁷Be and atmospheric data suggest that the main predictor controlling the seasonality of the ⁷Be concentrations is tropopause height (+0.76, +0.56, +0.60), reflecting more vertical transport from upper tropospheric levels into the lower troposphere during the warm season than during the cold season.

A growing interest in the phytotoxic effects of trichloroacetic acid (TCA) has led us to develop a small-scale (<1 mmol) one-pot synthesis of [1,2-¹⁴C]TCA with >70% yield and specific activity of 3.7 GBq/mmol

The sorption of uranyl ions onto amorphous silica has been studied in the presence of atmospheric CO₂ by laser-induced time-resolved fluorescence spectroscopy at trace concentrations (1.0 and 0.1 M). Two fluorescent uranyl surface complexes have been identified in the pH range 4 to 9. Both complexes could be differentiated by lifetimes (170±25 s at low pH and 360±50 s at high pH) and fluorescence emission spectra. Within the constant capacitance model framework they are described by mononuclear (1 : 1) complexes with release of two and three protons, respectively. When fluorescence data were compared to wet chemistry sorption data, a third “silent” ternary uranyl–silica–carbonate surface complex had to be postulated to account partly for adsorption between pH 8.0 and 9.0. Three independent data sets led therefore to the identification of three surface complexes, postulated as &tbond;SiO₂UO₂°,&tbond;SiO₂UO₂OH^-, and &tbond;SiO₂UO₂OHCO₃ ^3-.

The molecular changes of phytochrome during red far-red and reverse photoreactions have been monitored by static infrared difference spectroscopy using the recombinant 65 kDa N-terminal fragment assembled with a chromophore chemically modified at ring D or with a chromophore isotopically labeled with 18O at the carbonyl group of ring A. This allows the identification of the C=O stretching vibrations of rings D and A. We exclude the formation of an iminoether in Pfr. The positions of both these modes show that the chromophore always remains protonated. The upshift of the C=O stretch of ring D in the first photoproducts is explained by a twisted methine bridge connecting rings C and D. The changes in the vibrational pattern during the red far-red conversion show that the backreaction is not just the reversal of the forward reaction. The infrared difference spectra of the fragment deviate very little from those of the full-length protein. The differences which are related to the lack of the C-terminal half of the protein constituting the signaling domain are possibly important for the understanding of the signaling mechanism.

The sorption of U(VI) onto low-grade metamorphic rock phyllite was modeled with the diffuse double layer model (DDLM) using the primary mineralogical constituents of phyllite, i.e. quartz, chlorite, muscovite, and albite, as input components, and as additional component, the poorly ordered Fe oxide hydroxide mineral, ferrihydrite. Ferrihydrite forms during the batch sorption experiment as a weathering product of chlorite. In this process, Fe(II), leached from the chlorite, oxidizes to Fe(III), hydrolyses and precipitates as ferrihydrite. The formation of ferrihydrite during the batch sorption experiment was identified by Mössbauer spectroscopy, showing a 2.8% increase of Fe(III) in the phyllite powder. The ferrihydrite was present as Fe nanoparticles or agglomerates with diameters ranging from 6 to 25 nm, with indications for even smaller particles. These Fe colloids were detected in centrifugation experiments of a ground phyllite suspension using various centrifugal forces.

The basis for the successful interpretation of the experimental sorption data of uranyl(VI) on phyllite were: (1) the determination of surface complex formation constants of uranyl with quartz, chlorite, muscovite, albite, and ferrihydrite in individual batch sorption experiments, (2) the determination of surface acidity constants of quartz, chlorite, muscovite, and albite obtained from separate acid–base titration, (3) the determination of surface site densities of quartz, chlorite, muscovite, and albite evaluated independently of each other with adsorption isotherms, and (4) the quantification of the secondary phase ferrihydrite, which formed during the batch sorption experiments with phyllite. The surface complex formation constants and the protolysis constants were optimized by using the experimentally obtained data sets and the computer code FITEQL. Surface site densities were evaluated from adsorption isotherms at pH 6.5.

The uranyl(VI) sorption onto phyllite was accurately modeled with these newly determined constants and parameters of the main mineralogical constituents of phyllite and the secondary mineralization phase ferrihydrite. The modeling indicated that uranyl sorption to ferrihydrite clearly dominates uranyl sorption, showing the great importance of secondary iron phases for sorption studies.

Aluminiumknetlegierungen haben sich seit langem im Bereich der Außenhaut des Rumpfes und der Tragflächen von Verkehrsflugzeugen bewährt. Klassische Vertreter sind die hochfeste Legierung 7075 T6 sowie die als schädigungstolerant geltende Legierung 2024 T3. In den letzten Jahren hat sich vor dem Hintergrund des Erfordernisses der Gewichtsreduzierung sowie der Einführung neuer Bauweisen und Fertigungsverfahren der Blick auf ein breiteres Spektrum von Aluminiumlegierungen geöffnet. Für eine fundierte Bewertung dieser Legierungen werden zuverlässige Materialdaten benötigt, wobei im Rahmen des Schädigungs-Toleranz-Konzeptes die Ermüdungsrissausbreitung von besonderem Interesse ist. Unglücklicherweise sind zuverlässige Rissaubreitungsdaten nicht ohne weiteres aus der Literatur beschaffbar. Eine diesbezügliche Studie [Sinclair und Pieri, On obtaining fatigue crack growth parameters from the literature, Int. J. Fatigue 12 (1990) 57-62] kam zu dem ernüchternden Urteil, dass für nominell gleiche Werkstoffe die Streubreite der Literaturangaben deren praktischen Nutzen ernsthaft in Frage stellt. Folgerichtig kommt der Angabe der Messbedingungen sowie der Bekanntgabe der Originalmessdaten große Bedeutung zu.

Im vergangenen Jahrzehnt wurde in einem breit angelegten Versuchsprogramm eine neue Datenbasis mit Ergeb-nissen von Ermüdungsrissausbreitungsmessungen aufgestellt. Die Datenbasis beruht weitgehend auf Messungen mit konstanter Spannungsamplitude (Spannungsverhältnis R=0,1) an mittenangerissenen Proben (Probenbreite 160 mm) aus gewalzten dünnen Blechen (Blechdicke 1,5 bis 3 mm) unterschiedlicher Aluminiumknetlegierungen. Der Riss-fortschritt wurde lichtoptisch gemessen, die Auswertung erfolgte im Rahmen der linear-elastischen Bruchmechanik gemäß Norm ASTM E647. Die Datenbasis enthält neben den Originalmesswerten (Risslänge a, Lastspielzahl N) und den berechneten Werten der Rissausbreitungskurve (Rissausbreitungsrate da/dN über der Schwingbreite des Spannungsintensitätsfaktors DK) auch Zugversuchskennwerte und Restfestigkeiten. Sofern die Materialmenge ausreichte, wurden für jeden Werkstoffzustand in den Orientierungen längs bzw. quer zur Walzrichtung mindestens je fünf Zugversuche und fünf Rissausbreitungsversuche durchgeführt. Für ausgewählte Aluminiumlegierungen wurde auch das Spannungsverhältnis (R=0,5) oder das Umgebungsmedium (3,5%ige NaCl-Lösung) variiert. Speziell für die Aluminiumlegierung 6013 T6 erfolgten Messungen in 3,5%iger NaCl-Lösung im Frequenzbereich von 4 mHz bis 40 Hz.

Ziel des Beitrages ist es, die Datenbasis einem breiteren Interessentenkreis bekannt und zugänglich zu machen. Sie enthält unter anderem Ermüdungsrissausbreitungsdaten für jeweils mehrere 2000er (Hauptlegierungselement Cu), 6000er (Hauptlegierungselemente Mg und Si) und 7000er (Hauptlegierungselement Zn) Aluminiumknetlegierungen im kalt- sowie im warmausgelagerten Zustand. An ausgewählten Beispielen soll gezeigt werden, wie die Materialdaten zur vergleichenden Bewertung der einzelnen Werkstoffe herangezogen werden können. Sofern die Belastungsbedingungen (konstante Spannungsamplitude, Spannungsverhältnis) eine Übertragung auf ein Bauteil zulassen, können durch Integration der Ermüdungsrissausbreitungskurven Restlebensdauern für das betreffende Bauteil abgeschätzt und geeignete Inspektionsintervalle festgelegt werden.

The one-step radiosynthesis of 4-([¹⁸F]fluoromethyl)-2-chlorophenylisothiocyanate ¹⁸F-7 as a novel bifunctional ¹⁸F-labelling agent is described. Optimised reaction conditions in a remotely controlled synthesis module gave isothiocyanate ¹⁸F-7 in radiochemical yields of 45 % (decay-corrected) within 40 min and high radiochemical purity of > 95 % after solid-phase-extraction. Coupling of compound ¹⁸F-7 with the primary amine benzylamine as a model reaction afforded the corresponding ((4-[¹⁸F]fluoromethyl)-2-chloro-phenyl)-benzyl thiourea ¹⁸F-8 in a high radiochemical yield of > 90 %. Stability studies of thiourea ¹⁸F-8 in terms of radiodefluorination showed appreciable buffer stability at pH 7.4, whereas significant radiodefluorination was observed when ¹⁸F-8 was incubated in buffers af pH 3.6 and pH 9.4. Preliminary dynamic PET studies with thiourea ¹⁸F-8 in male Wistar rats showed high bone accumulation, indicative of high in vivo radiodefluorination.

Uranium LIII-edge extended X-ray absorption fine structure (EXAFS) analysis was carried out on aqueous uranium(VI) complexes with monomeric intermediates of the natural wood-degradation process such as protocatechuic acid (3,4-dihydroxybenzoic acid), catechol (2-hydroxyphenol), pyrogallol (1,2,3-trihydroxybenzol), and vanillic acid (4-hydroxy-3-methoxybenzoic acid). The structural parameters of the 1:1 complexes with protocatechuic acid and vanillic acid in weakly acidic solution indicate that the carboxylic group coordinates the uranyl cation in a bidentate mode in the equatorial plane. Based on the identical structural parameters observed for protocatechuic acid, catechol and pyrogallol in alkaline media, we conclude that the coordination with uranium occurs via the neighboring OH groups of the phenols under formation of a five-membered ring.

Albian carbonate mud-mound limestones exposed near Iraneta, northern Spain, show a fabric- and particle-specific fluorescence. Intense fluorescence is restricted to in situ precipitated microcrystalline (automicritic) fabrics, calcified demosponges, and coralline sponges. Intermediate intensity derives from micritized bioclasts, pellets, and a rim of marine bladed cement. Most invertebrate skeletons, late-diagenetic equant cement, and crosscutting zones of dolomitization are weakly to nonfluorescent. Internal microcrystalline sediment (allomicrite) and red algae debris have variable fluorescence. Correlation between rock fluorescence and soluble humic substances was evaluated from 3 g of automicrite, allomicrite, and cement. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) with ultra-short pulses on two extracrystalline fractions (NaOH-soluble) and two intracrystalline fractions (HCl-soluble and NaOH-soluble) showed that most of the soluble humic substances of automicrite are within the crystals; but conversely, are significantly enriched on outer surfaces of allomicrite. Spar cement is close to detection limits. Fluorescence lifetimes are in the range of 0.5–2 ns and 3.5–6 ns. We conclude that precipitation of automicrite took place during oxidative organic matter diagenesis, i.e., during condensation reactions of degradation products of marine biopolymers. By contrast, allomicrite formed by skeletal breakdown followed by ingestion, organic coating, and reingestion during deposit feeding. A humic-substance–based model of marine polymer gels represents a new approach for the understanding of ancient polygenetic carbonate muds, so typical of Phanerozoic mud-mounds in deeper water settings.

The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and 17O-NMR spectroscopy. Uranium LIII edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Å. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Å. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22+ + SO42- ⇔ UO2SO4 (k1), (2) U*O22+ + UO2SO4 ⇔ U*O2SO4 + UO22+ (k2), (3) UO22+ + UO2(SO4)22- ⇔ 2 UO2SO4 (k3), and (4) UO2SO4 + SO42- ⇔ UO2(SO4)22- (k4). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their 17O chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.

We studied the fluorescence properties of 120 uranium minerals in order to provide a data base of potential secondary solids that may form in the flooding process of defunct uranium mines. This data base may provide a link of the fluorescence spectra of the minerals to solution spectra containing so far unknown tertiary and quaternary solution complexes in environmental uranium(VI)-containing waters. In our initial effort to establish the data base, we are focusing on phosphate- and arsenate-containing uranium(VI) minerals. Except for chernikovite [(H3O)2(UO2)2(PO4)2 · 6H2O], these minerals show intensive fluorescence emissions bands with a bathochromic shift of up to 18 nm compared to the fluorescence of the uranyl ion in solution. We found hypsochromic shifts of the fluorescence emission for the uranyl phosphates and bathochromic shifts for the uranyl arsenates. The band spacing of the fluorescence emissions from the 20502 cm-1 level are comparable to the vibrational frequency available from IR-data. Using these data we estimated the axial U-O bond lengths. The decrease of the vibration frequency from 813 cm-1 (saleiite, [Mg(UO2)2(PO4)2 · 10(H2O)]) to 794 cm-1 (uranocircite, [Ba(UO2)2(PO4)2 · 12(H2O)]) is related to a slight increase of the U-O bond length by 3 pm. In both series, the fluorescence lifetime decreases with decreasing crystal water. This is different compared to solution spectra where the lifetime increases as water is displaced from the inner coordination shell. Comparing the fluorescence data of the mineral troegerite [H2(UO2)2(AsO4)2 · 8(H2O)] with the fluorescence spectra of uranyl arsenate solutions, we identified one of the three uranyl arsenate complexes in solution as HUO2(AsO4)(aq.).batch experiment at anoxic conditions proved that pyrite can immobilise U(VI).

The spectral branching behavior of the 2×2 operator matrix of the magneto-hydrodynamic α²-dynamo is analyzed numerically. Some qualitative aspects of level crossings are briefly discussed with the help of a simple toy model which is based on a Z2-graded-pseudo-Hermitian 2×2 matrix. The considered issues comprise: the underlying SU(1,1) symmetry and the Krein space structure of the system, exceptional points of branching type and diabolic points, as well as the algebraic and geometric multiplicity of corresponding degenerate eigenvalues.

The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected1-3: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties. The synthesis of increasingly heavy elements4-6, now including that of elements 114, 116 and 118, allows the investigation of this effect, provided sufficiently long-lived isotopes for chemical characterization are available7. In the case of elements 104 and 105, for example, relativistic effects interrupt characteristic trends in the chemical properties of the elements constituting the corresponding columns of the periodic table8, whereas element 106 behaves in accordance with the expected periodicity9-12. Here we report the chemical separation and characterization of six atoms of element 107 (bohrium, Bh), in the form of its oxychloride. We find that this compound is less volatile than the oxychlorides of the lighter elements of group VII, thus confirming relativistic calculations13 that predict the behaviour of bohrium, like that of element 106, to coincide with that expected on the basis of its position in the periodic table.

A new experimental method is presented for the determination of solubility data, which is based on the laser-induced breakdown detection (LIBD). The method is capable of monitoring the initial colloid generation when the metal ion concentration reaches or just exceeds the solubility at given pH. The application is made to determine the solubility of Th(IV) in acidic solutions at I = 0.5 M (NaCl) and 25 °C. The initial colloid formation is determined as a function the H+ concentration in a series of 2.8 × 10-2 - 8.9 × 10-5 M thorium solutions. The conditional solubility product (log K'sp = -49.54 ± 0.22) obtained in this study corresponds to an equilibrium between solution and colloidal thorium dioxide particles. The solubility product at I = 0 (log K°sp = -52.8 ± 0.3) is calculated with the SIT coefficients of the NEA-TDB. It corresponds to the known value for crystalline ThO2(cr), in particular if the small particle size of about 20 nm is taken into account. The present results indicate that the high thorium solubilities measured in the previous studies for amorphous Th(IV) hydroxide or hydrous oxide are primarily caused by the inclusion of polynuclear species or Th(IV) colloids of very small size.

A series of alkaline uranyl carbonates, M[UO2(CO3)3]•nH2O (M = Mg2, Ca2, Sr2, Ba2, Na2Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). For the first time, the molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba2[UO2(CO3)3]•6H2O was obtained for the first time. The EXAFS analysis showed that this compound consists of (UO2)(CO3)3 clusters similar to the other alkaline earth uranyl carbonates. The average U-Ba distance is 3.90±0.02 Å. Fluorescence wavelengths and life times were measured using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The U-O bond distances determined by EXAFS, TRLFS, and XPS agree within the experimental uncertainties. The spectroscopic signatures observed could be useful for identifying uranyl carbonate species adsorbed on mineral surfaces.

Radioecological research at the Institute of Radiochemistry, FZR

Transfer of Uranium to Plants - Aspects of Chemical Speciation

Wechselwirkung von Uran mit Biosystemen

The paper presents examples illustrating the current blind predictive capabilities of surface complexation models (SCM) in combination with a respective database RES3T (Rossendorf Expert System for Surface and Sorption Thermodynamics).
The general strategy for the selection of numerical data is discussed. Based on the information about the minerals collected in the sorption database RES3T, first a set of relevant surface species must be formed. Then respective surface complexation parameters are taken from RES3T: the binding site density for the minerals, the surface protolysis constants, and the stability constants for all relevant surface complexes. To be able to compare and average thermodynamic constants originating from different sources a normalization concept is applied.
In a second part the current capabilities of SCM is demonstrated based on a blind prediction exercise. The system covered is the Cu(II) sorption onto goethite, with the predictions compared to raw data from three independent experimental investigations. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected to account for electrostatics. The calculations were performed with the FITEQL code, version 3.2.
In most cases the model prediction represented the experimental values for the sorbed amount of Cu(II), expressed as conventional distribution coefficients KD, within one order of magnitude or better.
We conclude, that the application of SCM can indeed be very valuable for estimating distribution coefficients for contaminants in well defined mineral systems. The SCM database so far assembled within the RES3T project is able to provide the respective parameter sets following the outlined stepwise strategy of species selection, data collection, normalization and averaging.

One of the serious problems encountered in the use of various materials in technology is the occurrence of fatigue phenomena as an undesirable material damage under cyclic mechanical load. For aluminium alloys this issue is of extremely high importance in case of their utilisation for aircraft purposes, e.g., where a very wide spectrum of frequencies occur. Moreover, the cyclic loading may be joined by the presence of specific electrolyte media. Therefore, the material candidates must be thoroughly examined in view of their sensitivity to fatigue as well as to corrosion fatigue. Usually, the Cu-containing alloy EN-AW 2024 T3 is applied besides 7075 T6 in Airbus aircrafts, but the weldable alloy 6013 T6 is considered to be a potential alternative. Referring to former investigations on the environmental sensitivity in the fatigue behaviour this paper brings up experimental findings as well as expanded considerations about damaging mechanisms and modelling. The situation with the alloy 6013 T6 is emphasized. The propagation of cracks under cyclic load in different environments, such as vacuum, air or aqueous media, is described by means of fracture mechanics. This enables discrimination in view of the influence of environmental factors and, hence, the participation of corrosion processes.

A silicon pn -diode was embedded into a microcavity composed of a buried metal silicide as bottom reflector and a Si/SiO 2 Bragg mirror as top reflector. Spectral narrowing and an increased intensity of the Si bandgap electroluminescence was observed.

The melt convection during solidification has a considerable influence on the nucleation process and the grain structure. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow in a Sn-15wt%Pb alloy solidified directionally from a water cooled copper chill. The flow is driven by a rotating magnetic field. We present velocity profiles measured during the solidification process. Moreover, from the UDV measurements the current position of the solidification front can be estimated.

A detailed analysis of the strong room-temperature photoluminescence (PL) signal of size controlled nc-Si is reported. The size control of nc-Si is realized by evaporation of SiO/SiO2 superlattices and subsequent thermally induced phase separation. By this method the synthesis of completely SiO2 passivated Si nanocrystals with a controlled size is demonstrated. A strong blueshift of the photoluminescence signal from 1.3 to 1.65 eV with decreasing crystal size is observed. Resonant photoluminescence measurements prove the breakdown of the k-conservation rule for nc-Si by showing an increase in the no-phonon transition probability with decreasing crystal size. A no-phonon to phonon assisted transition probability ratio above 1 is detected at 4.5 K. These results confirm quantum confinement as the origin of the investigated luminescence signal. The size dependence of the different luminescence properties and the very high no-phonon transition probability indicate a lower confin!
ement barrier compared to other systems containing nc-Si and additional migration effects of the excitons between the nanocrystals. A separation of quantum confinement and migration effects on the PL signal is possible due to the very narrow size distribution of the nc-Si and detailed time and temperature dependent investigations of the photoluminescence.

InP single crystals implanted with 1.2 MeV As-ions and InP/InGaAsP superlattices were studied with RBS/c and high resolution X-ray diffraction (HRXRD). The principal advantage of HRXRD is the determination of interplanar spacing with an accuracy of 10(-5). One should be aware of a variety of pitfalls inherently involved with the nature of X-ray diffraction. These are primarily due to the ambiguity of X-ray rocking curves evaluation. Additional peaks appearing in X-ray rocking curves after ion implantation are usually attributed to regions with distinct lattice parameter. Calculations using damage profiles measured by RBS/c indicated that they could result from X-ray interference effects. For quaternary compounds where HRXRD can hardly detect local change of composition RBS was applied for this purpose. The great accuracy of HRXRD is also advantageous for the RBS analysis: determination of lattice spacing allows the layer density determination hence, the depth scale can be expressed in linear units and stopping power data can be adjusted accurately.

The hydrodynamics of a rectangular bubble column operating in the dispersed bubbly regime has been experimentally and numerically investigated. The bubble column was locally aerated using a sparger located in the center of the bottom plate. The experimental studies involve wire-mesh tomography measurements for void fraction and bubble size distributions and digital image rocessing of high speed camera images for estimation of bubble velocities, size distributions and flow patterns. Experiments were performed for various aspect ratios (height of water column to width ratio) and superficial gas velocities. Computational fluid dynamic calculations of transient flow for the above bubble column were performed using an Eulerian-Eulerian two fluid model. Turbulence in the liquid phase was accounted for, using the k-epsilon turbulence model. The effect of the gas phase on turbulence in the continuous phase was modeled using Sato’s eddy viscosity model for bubble-induced turbulence. A systematic analysis of the interfacial momentum transfer terms has been conducted. It was found that the non-drag bubble forces play a very prominent role in the predicting the correct flow pattern and void fraction distributions. In the calculations, the lift force and the wall force were considered. A ‘wall peak’ in the time averaged void fraction distribution has been experimentally observed and this cannot be predicted without including these non-drag forces in the numerical calculations. In this paper, experimental data are compared with the results of the numerical simulations.

The H-3,4(Lambda) and H-4(Lambda) hypernuclear bound states have been observed for the first time in kaon electroproduction on He-3,He-4 targets. The production cross sections have been determined at Q(2)=0.35 GeV2 and W=1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the He-3,He-4(e,e(')K(+))(Lambda)H-3,H-4 processes to the elementary cross section H-1(e,eK(+))Lambda on the free proton, measured during the same experiment.

Due to the reduced dimension, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range from 5 - 150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Similar effects can also be observed using Ga+ ion irradiation, which is the common ion source in focused ion beam lithography.

Examples for ion induced modifications of magnetic anisotropies and exchange coupling are presented. This review is limited to radiation induced structural changes giving rise to a modification of magnetic parameters. Ion implantation is discussed only in special cases.

Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may have an applied interest. The main patterning technique is homogeneous ion irradiation through masks. Focused ion beam and ion projection lithography are commonly only relevant for larger ion masses. The creation of magnetic feature sizes below 50 nm is shown. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic leading to new phenomena at their mutual interface.

Most of the material systems discussed here are important for technological applications. The main areas are magnetic data storage applications, such as, hard magnetic media with a large perpendicular magnetic anisotropy or patterned media with an improved signal to noise ratio, and magnetic sensor elements. It will be shown that light-ion irradiation has many advantages for design of new material properties and the fabrication technology of actual devices.

The Project on Ex-Vessel Core Melt Stabilization Research (ECOSTAR) started in January 2000 and to be concluded by end of 2003. The project is performed by 14 partner institutions from 5 European countries and involves a large number of experiments with low and high temperature simulant melts and real corium at different scales. Model development and scaling analysis allows application of the research results to existing and to future LWRs in the area of reactor design and accident mitigation.
The project is oriented toward the analysis and mitigation of severe accident sequences that could occur in the ex-vessel phase of a postulated core melt accident. The issues are: (1) the release of melt form the pressure vessel, (2) the transfer and spreading of the melt on the basement, (3) the analysis of the physical-chemical processes that are important for corium behavior especially during concrete erosion with onset of solidification, and (4) stabilization of the melt by cooling through direct water contact.
The results achieved so far, resolve a number of important issues: The amount of melt that could be transferred at RPV failure from the RPV into the containment can be substantially reduced by lowering the residual pressure in the primary circuit. It is found that melt dispersion is also strongly depending on the location of the RPV failure, and that lateral failure results in substantially less melt dispersion. During melt release, the impinging melt jet could erode parts of the upper basement surface. Jet experiments and a derived heat transfer relation allow estimation of its contribution to concrete erosion. Spreading of the corium melt on the available basement surface is an important process, which defines the initial conditions for concrete attack or for the efficiency of cooling in case of water contact, respectively. Validation of the spreading codes based on a large-scale benchmark experiment, is underway and will allow determination of the initial conditions, for which a corium melt can be assumed to spread homogeneously over the available surface. Experiments with UO2-based corium melts highlight the role of phase segregation during onset of melt solidification and during concrete erosion. To cool the spread corium melt, the efficacy of top flooding and bottom flooding is investigated in small scale and in large-scale experiments, supported by model developments. Project assessment is continuing to apply the results to present and future reactors.

Bestrahlung der Brustdrüsenepithelzellinie MCF-12A mit Röntgenstrahlung aus konventionellen Röntgenröhren und Bestimmung der Dosis-Effekt-Kurve

Boron 10 is a strong thermal neutron absorber. As boric acid solved in the coolant of PWRs, it is used to compensate the excess reactivity of the reactor especially at the beginning of the fuel cycle. Therefore, an inadvertent or even unavoidable reduction of the boron concentration means an increase of reactivity that might result in a power excursion, a so called boron dilution transient.
The reactivity increase depends on the of mixing of the underborated water with the coolant inventory in the downcomer (DC) and lower plenum (LP) where the boron concentration is still on the normal high level.
After introducing the different boron dilution scenarios, results of the latest PKL (Primärkreislauf test facility at FANP) experiments will be presented aiming at the assessment of the maximum slug volume for the different safety injection cases. Moreover, the ROCOM (Rossendorf Coolant Mixing) tests will be discussed that were performed to study mixing phenomena inside the reactor pressure vessel (RPV) and which provided typical boron concentration profiles at the core entrance for the different flow regimes. These experiments are used to develop and validate calculation models for boron mixing. Such models are needed to get information about realistic time dependent boron concentration profiles over the cross section of the core entrance. The obtained concentration profiles are used as boundary conditions for coupled neutronic / thermal-hydraulic core calculations to show whether recriticality of the shut down reactor is reached and how high the maximum power peak can be. The results of such calculations will be presented proving that these deborated slugs can cause prompt criticality. Nevertheless, due to the fast Doppler feedback no core damage occurs even with the maximum slug volume of 36m³ .

The presentation starts from sustainability considerations of different energy carries like oil, hoard cool, or nuclear energy.
It is highlighted, that in terms of sustainability nuclear energy suffers from the danger of proliferation of weapons grade material, the maximum damage of a conceivable severe accident, and the extremely long isolation period of the nuclear waste in the final disposal. Discussing the safety analysis of so called boron dilution transients in PWRs, the behaviour of the reactor pressure vessel during a severe core melt accident, and the possibilities of the transmutation of long lived radio-nuclides it is shown how modern nuclear safety research can contribute to improved sustainability performance of nuclear energy.

The presentation starts from sustainability considerations of different energy carries like oil, hoard cool, or nuclear energy.
It is highlighted, that in terms of sustainability nuclear energy suffers from the danger of proliferation of weapons grade material, the maximum damage of a conceivable severe accident, and the extremely long isolation period of the nuclear waste in the final disposal. Discussing the safety analysis of so called boron dilution transients in PWRs, the behaviour of the reactor pressure vessel during a severe core melt accident, and the possibilities of the transmutation of long lived radio-nuclides it is shown how modern nuclear safety research can contribute to improved sustainability performance of nuclear energy.

Small self-interstitial clusters play an important role in the evolution of radiation damage in Si during post-implantation annealing. These small clusters can be formed by two different processes: (i) fast relaxation of highly disordered cascade regions immediately after ion impact and (ii) clustering of diffusing self-interstitials in the first stage of the annealing process.
The structure and energetics of the small self-interstitial clusters have been investigated by different theoretical methods. However, there are only few data on their mobility and migration mechanisms. They have been mainly obtained by static potential energy calculations. This work presents results of a systematic molecular dynamics study of the migration of di- and tri-interstitials. A classical potential approach is employed since it allows the investigation of defect migration under relatively realistic conditions, by considering large computational cells, long periods and different initial conditions. The di- and tri-interstitial configurations with the lowest formation energies are determined, and the results are compared with literature data. Then, the migration of di- and tri-interstitials is followed for 10 – 30 ns, at temperatures between 800 and 1600 K. Defect diffusivity and self-diffusion coefficient per defect are obtained by the Wigner-Seitz cell analysis and the Guinan method as well as from the mean square displacements of all atoms. The effective migration energies are determined and compared with the data from literature. The elementary migration mechanisms are discussed in detail by the analysis of movies and snapshots of defect trajectories and atomic rearrangements.

The bacterial strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. The cells of this strain are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters [1]. Further, they are enveloped by a surface layer (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date [2]. The highly ordered crystalline S-layers are one of the most common cell envelope structures of bacteria and archaea [3]. They are composed of protein monomers which possess the ability to self-assemble into two-dimensional paracrystalline lattices. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for different metals and nucleation sites for the formation of metal nanoclusters or minerals.
EXAFS and IR analyses of the interactions of purified and recrystallised S-layer with Pd(II) demonstrated, that Pd(II) is bound to the carboxyl groups of the protein. In accordance to these results the C-terminal domain of the protein was found to contain aspartate and glutamate rich stretches which we assume to be responsible for the deposition of Pd in the pores of the protein lattices. Interestingly, the Laser Induced Infrared spectroscopic analysis showed that the deposition of the Pd complexes stabilizes the structure of the protein. The bound Pd(II) is reduced to metallic Pd nanoclusters in the presence of reducing agents which is in agreement with previous studies on another S-layer [4]. In addition, Pd nanoclusters are formed on the intact cells of B. sphaericus JG-A12 via a two step process consisting of biosorption (I) and of consequent metal reduction (II) in the presence of molecular H2 as an electron donor. The metallic nature of the clusters was confirmed by EXAFS and their size was estimated to be about 9-10 Ǻ. TEM analysis showed that the clusters are localised at specific sites of the bacterial cell wall, indicating the primary role of the S-layer in their formation.
The Pd nanoclusters formed on S-layer and bacterial cell templates are highly interesting for technical applications, e. g for the development of novel catalysts. Genetic engineering of the S-layer is applied for optimising its capability to form Pd nanoclusters with increased catalytic activity and also in order to extend its binding capacity to other metals of industrial interest.

1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67.
2. Raff, J. (2002) “Wechselwirkungen der Hüllproteine von Bakterien aus Uranabfallhalden mit Schwermetallen“ PhD Thesis, FZR-Report No. 358.
3. Sleytr, U. et al. (1997) FEMS Microbiol. Rev. 20, 47-97.
4. Wahl et al. (2001) Advanced Materials 13, 736-740.

Uranium is a long-living radionuclide that represents ecological and human health hazards. The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive waste. It is critical that the uranium in these wastes has to be effectively immobilized and removed away in order to prevent ground water contamination. Microbial biosorption of U(VI) was proposed as one of the methods for uranium immobilization. In this paper, we describe the isolation of bacterial strains from water and soil samples collected from different uranium contaminated environments. Phylogenetic analysis of these strains revealed that they are related to Stenotrophomonas maltophilia, Bacillus sphaericus, Microbacterium oxydans, Pseudomonas rhodesiae etc. As estimated by using ICP-MS these natural isolates possess a high ability to accumulate uranium and other heavy metals such as Cd, Pb, Ni and Ag. The bacterial uranium tolerance was studied using flow cytometry techniques. X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate phase) at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, at pH 2 the uranium bonding was consistent with the formation of complexes with organic bound phosphate of the cell surface. These results are in agreement with those found by infrared measurements.Transmission electron microscope and energy dispersive X-ray analysis showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees.

Uranium is a long-living radionuclide that represents ecological and human health hazards. The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive waste. It is critical that the uranium in these wastes has to be effectively immobilized and removed away in order to prevent ground water contamination. Microbial biosorption of U(VI) was proposed as one of the methods for uranium immobilization. In this paper, we describe the isolation of bacterial strains from water and soil samples collected from different uranium contaminated environments. Phylogenetic analysis of these strains revealed that they are related to Stenotrophomonas maltophilia, Bacillus sphaericus, Microbacterium oxydans, Pseudomonas rhodesiae etc. As estimated by using ICP-MS these natural isolates possess a high ability to accumulate uranium and other heavy metals such as Cd, Pb, Ni and Ag. The bacterial uranium tolerance was studied using flow cytometry techniques. X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate phase) at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, at pH 2 the uranium bonding was consistent with the formation of complexes with organic bound phosphate of the cell surface. These results are in agreement with those found by infrared measurements.Transmission electron microscope and energy dispersive X-ray analysis showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees.

Atomic-scale computer simulations, both molecular dynamics (MD) and the nudged-elastic band methods, have been applied to investigate long-range migration of point defects in cubic SiC (3C-SiC) over the temperature range from 0.36Tm to 0.95Tm (melting temperature). The point defect diffusivities, activation energies, and defect correlation factors have been obtained. Stable C split interstitials can migrate via the first- or second-nearest-neighbor sites, but the relative probability for the latter mechanism is very low. Si interstitials migrate directly from one tetrahedral position to another neighboring equivalent position by a kick-in/kick-out process via a split-interstitial configuration. Both C and Si vacancies jump to one of their equivalent sites through a direct migration mechanism. The migration barriers obtained for C and Si interstitials are consistent with the activation energies observed experimentally for two distinct recovery stages in irradiated SiC. Also, energy barriers for C interstitial and vacancy diffusion are in reasonable agreement with ab initio data.