Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Aqueous uranyl carbonate complexes play an important role in the hydrogeology of uranium mining areas and nuclear waste disposals. Many publications are available for the stability of uranyl carbonate complexes, but thermodynamical data like the enthalpy or entropy are rare. We determined thermodynamical data from spectroscopic studies for the uranyl carbonate complex UO2(CO3)34- in the temperature range from 5°C to 70°C. We found for the reaction enthalpy the value 36.25 ± 4.31 kJ/mol and for the reaction entropy a value of 297.082 ± 13.839 J/(K∙mol).

Verfahren zum Bestimmen der Materialzusammensetzung einer Strahlung abstrahlenden Materialprobe (12) mit den folgenden Verfahrensschritten: Aufnehmen (P2) eines Spektrums der in einem Detektormaterial durch die Strahlung deponierten Energie; Bestimmen einer in einem ersten Energiebereich deponierten ersten Energie (F1), einer in einem zweiten Energiebereich deponierten zweiten Energie (F2) und einer in einem dritten Energiebereich deponierten dritten Energie (F3); Zuordnen (P4) eines ersten Farbparameters (F1) zu der ersten deponierten Energie, eines zweiten Farbparameters (F2) zu der zweiten deponierten Energie und eines dritten Farbparameters (F3) zu der dritten deponierten Energie und Vergleichen (P5) der zugeordneten Farbparameter (F1, F2, F3) mit vorgegebenen Werten für die Farbparameter (R1, R2, R3), wobei die vorgegebenen Werte (R1, R2, R3) typischen Farbparametern einer vorbestimmten Materialzusammensetzung entsprechen.

Detektoranordnung (1) zur winkelauflösenden Detektion von Strahlung mit mindestens einem Detektorelement (2), welches eine Vorderseite (3) und eine Rückseite (4), ein erstes Detektormaterial und ein zweites Detektormaterial zwischen der Vorderseite (3) und der Rückseite (4) aufweist, wobei ein Raum zwischen der Vorderseite (3) und der Rückseite (4) des Detektorelementes (2) von mehreren Bereichen (6) aus dem ersten Detektormaterial und mindestens einem Bereich (5) aus dem zweiten Detektormaterial ausgefüllt ist und jeder Bereich die Vorderseite (3) mit der Rückseite (4) des Detektorelementes (2) verbindet und wobei eine Kollimation von durch die Vorderseite (3) in das Detektorelement (2) eintretender Strahlung (γ) durch die Detektormaterialien erfolgt.

The long-term safety assessment of nuclear waste disposals requires detailed knowledge of the transport and interaction behavior of actinides within the technical, geotechnical and geological barriers. Humic substances, ubiquitous in natural environments, are able to influence the migration of actinides due to their ability for complex and colloid formation and their redox properties. It is known, that especially their carboxylic and phenolic OH groups are able to complex metal ions. In addition to these oxygen containing functional groups, humic substances also offer sulfur and nitrogen containing functionalities.
The aim of this work is to determine the influence of various sulfur and nitrogen containing functional groups on the uranium(VI) complexation and to evaluate their contribution in comparison to oxygen containing functional groups. For this, simple organic model ligands that can occur as building blocks for humic substances are used in the first instance with the objective to transfer the results to humic substances.
In this study, results are presented for the uranium(VI) complexation by the organic ligands benzenesulfonic and 4-hydroxybenzenesulfonic acid as well as for nicotinic and anthranilic acid. The complex formation constants for the uranium(VI) complexation were determined applying UV-vis absorption spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS) as a function of pH.
Interestingly, we did not see any interaction of the uranyl ion with benzenesulfonic acid (BSA). In contrast, for the uranium(VI) complexation by 4-hydroxybenzenesulfonic acid (HBSA) the formation of a 1:1 complex was detected. The stability constant for this complex of the type MpHqLr was determined with log ß101 = 3.9 ± 0.03.

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Peptidoglycan (PGN) forms the main part of the outer membrane of Gram-positive bacteria. We investigated the interaction of the uranyl cation (UO22+) with PGN from Bacillus subtilis by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH range (2.4 – 9) and at environmentally relevant low uranium concentrations (10-4 – 10-5 M). The PGN polymer contains a high density of functional groups for metal ion binding, like carboxyl, amino and hydroxyl groups.
With potentiometric titration the dissociation constants of the functional groups and the corresponding site densities could be detected. We found four functional groups, which can be dedicated to two different carboxyl functionalities, amino and hydroxyl groups. Using the same technique, two different uranyl PGN complexes could be identified, one complex with a carboxyl ligand (R-COO-UO2+) and a second complex with additional hydroxyl coordination (R-COO-UO2+-HO-R). The complex stability constants were determined to be log beta = 5.16 ± 0.13 for the first, and log beta = 13.00 ± 0.05 for the second complex, respectively.
TRLFS measurements show from pH 2.4 to 4.5 a red shift of the peak maxima of about 8 – 10 nm, in comparison to the free uranyl ion, connected with an increase of the luminescence intensity. Over pH 4.5 up to pH 9 the luminescence intensity decreases. The time resolved measurements show beneath the lifetimes of the free uranyl ion (1800 ± 200 ns) and the known uranyl hydroxides only one additional lifetime (224 ± 54 ns) which can be dedicated to a uranyl PGN complex species. From these we conclude that the two uranyl PGN complex species found by potentiometry can also be identified with TRLFS. The first complex (R-COO-UO2+) shows luminescence activity, but the second complex (R-COO-UO2+-HO-R) not. Complex stability constants for these two complexes were determined using the computer program SPECFIT. They are in good accordance to those calculated from potentiometric titrations.

The influence of external homogeneous magnetic fields during electrochemical metal deposition in cuboid cells is shortly reviewed. By analytical means, supported by numerical simulations, it is shown that a simplified two-dimensional approach is often misleading and has to be replaced by a more complex three-dimensional treatment as only the solenoidal part of the Lorentz force can cause convection.

Conformational substates of B-DNA have been reported to be involved in DNA recognition by proteins [1]. BI and BII substates, that co-exist in B-DNA, differ in the phosphate backbone conformation about the C3'-O3'-P segment related to the variability of the dihedral e and z angles (see figure left [2]). Typical IR marker bands have previously been identified which allow assessing the relative population of BI and BII conformers by FTIR spectroscopy for DNA from salmon testes, poly(dG-dC) and the d(CGCGAATTCGCG)2 dodecamer [3]. So far, BI/BII dynamics studies were restricted to static FTIR spectroscopy under isothermal relaxation at low temperatures . We have attempted to monitor the BI/BII transition under defined native-like conditions using rapid scan FTIR-difference-spectroscopy at a time resolution of 70 ms. An ATR-cell accessory was designed that allows both, the application of flashes to induce small temperature jumps and the adjustment of constant humidity of the sample. The latter is critical to address the role of backbone hydration in the dynamics of the BI/BII transition.

The Taylor coefficients of flavor diagonal and off-diagonal susceptibilities as well as baryon number, isovector and electric charge susceptibilities are considered within a phenomenological quasiparticle model of the quark-gluon plasma and successfully compared with lattice QCD data for two degenerate quark flavors. These susceptibility coefficients represent sensible probes of baryon density effects in the equation of state. The baryon charge is carried, in our model, by quark-quasiparticle excitations for hard momenta.

Activation of G protein-coupled receptors (GPCRs) orginates in ligand-induced structural changes that are transmitted across the plasma membrane to the cytosolic receptor surface. In rhodopsin-like class-1GPCRs, protonation of a carboxylic acid (Glu134 in rhodopsin) in the conserved cytosolic D(E)RY motif in transmembrane helix 3 (TM3) is coupled to receptor activation. Here, we have investigated the proton-sensitivity of the structure of synthetic peptides consisting of 30amino acids derived from TM3 of bovine rhodopsin (rho) and the chemokine receptor CCR3. ATR- Fourier-transform-infrared (FTIR) spectroscopy reveals a helical structure of the rho-TM3 peptide in PC vesicles and detergent micelles, where Glu134 exchanges protons with the solvent at a pKa of 5.5-6.0 as determined from the pH sensitivity of the COO- stretching mode. The amide I modes reveal a proton-induced helical turn formation in rho-TM3 and CCR3-TM3. The conformational change in the ERY motif is affects also the Tyr136 fluorescence which exhibits a strong pH sensitivity (pKa of 6) which is abolished upon replacement of Glu134 by Gln in rho-TM3. Förster-Resonance-Energy-transfer from a C-terminal Trp to DANSYL-labelled lipids in mixed micelles and lipid vesicles evidences that the D(E)RY motif constitutes an autonomous proton-driven conformational switch which couples protonation to helical turn formation and probably helix insertion depth. We propose that the protonation-controlled hydrophobicity profile at the cytosolic end of TM3 provides a pH-sensitive module that couples helix packing in the active receptor conformation of class I GPCRs to proton exchange reactions with the cytosol.

Actinides have been and will be introduced into shallow and deep groundwater environments via various human activities. The process of interaction between naturally occurring chelating substances and metals may influence the migration behavior of hazardous actinides in the environment once they have been released. Siderophores are chelating substances produced by microorganisms under iron-deficient conditions. For example, Powell et al. [1] demonstrated the occurrence of hydroxamate siderophores produced by microorganisms in concentrations ranging from 10-7 to 10-8 M in a variety of soils. In general catechol and hydroxamate groups in siderophores are the main functional groups involved in binding with actinides. As an example, Pseudomonas species are ubiquitous soil and groundwater bacteria that synthesize bacterial pyoverdin-type [2-5] and hydroxamate siderophores [6]. The observed mobilization effects of siderophore molecules on radionuclides probably due to the formation of strong soluble species motivated detailed investigation of their complexation characteristics, using a radionuclide suitable for spectroscopic methods.
To overcome the lack of information about actinide(III) siderophore interactions, we thus present findings regarding the complexation of curium(III) with pyoverdins (PYO) and desferrioxamine B (DFO), obtained using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The excellent luminescence properties of curium(III) were used to explore its complexation behavior with the two different bioligands at environmentally relevant curium(III) concentrations.
(A) PYO: Pseudomonas fluorescens (CCUG 32456) cells isolated from the granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden, secreted a pyoverdin mixture containing 4 main components [5].
(B) DFO: Desferrioxamine B (DFO) is a microbial produced trihydroxamate siderophore which is commercially available and could occur naturally in soils. Recently Essen et al. [6] could show the production of desferrioxamine siderophors by Pseudomonas stutzeri (CCUG 36651). This strain was also isolated at the Äspö Hard Rock Laboratory.

We explored the unknown luminescence properties, lifetimes and individual luminescence emission spectra of the formed Cm(III) species. The strength of the complex formation of the two bioligands will be discussed on the basis of the spectroscopic properties obtained in their individual systems. The results of this study increase our understanding of the mobilization of actinides by siderophores secreted by resident bacteria in a natural environment.

[1] Powell, P.E., et al., Nature 287 (1980) 833-834.
[2] Budzikiewicz H., Fortschr. Chem. Org. Naturst. 87 (2004) 83-237 .
[3] Kalinowski B.E., et al., Geomicrobiol. J. 23 (2006) 157-164.
[4] Moll, H., et al., BioMetals 21 (2008) 219-228.
[5] Moll, H., et al., Geomicrobiol. J. 25 (2008) 157-166.
[6] Essen, S.A., et al., Appl. Environ. Microbiol. 73 (2007) 5857-5864.

no abstract available

Natural and synthetic crystalline α-quartz, as well as synthetic SiO₂ glass, were irradiated with different doses of 8.8 MeV He²⁺ ions. The irradiation-induced alteration was characterised using Raman and cathodoluminescence (CL) spectroscopy, optical microscopy, transmission electron microscopy (TEM) and CL and electron microscope imaging. The initially dull bluishviolet CL colour of the two α-quartz samples was found to be transformed to bright yellow in the irradiated areas. The emission maximum was observed 45 μm below the surface, which corresponds well with correlated helium trajectory lengths and defect density distribution. Both, total intensity and radial intensity distribution of the CL emission change with the irradiation dose. Observations suggest a nonlinear, approximately logarithmic increase of the CL intensity depending on the alpha dose. Significant broadening of Raman bands is only observed near the far end of helium trajectories. This broadening is not only caused by the structural radiation damage but also by strain between strongly and lowly damaged areas.

Aureoles surrounding radioactive inclusions – so called radiohaloes – are a common feature often observed in several rock-forming minerals. These alterations are caused by the action of alpha-particles (i.e. He²⁺ ions) emitted into the host mineral.
While in some cases (e.g. biotite, cordierite) the most striking feature of radiohaloes is a strongly enhanced absorption of light, there are commonly no visible changes found in quartz. In this mineral, alpha irradiation leads to a marked change in the emission behaviour, which can be very well observed using cathodoluminescence (CL) imaging.
In the present study several micro- and nano-techniques [i.e., Raman spectroscopy, CL spectroscopy, and transmission electron microscopy (TEM)] were used to study the alteration in synthetic radiohaloes, produced by artificial alpha irradiation of various SiO₂ samples. Alpha-quartz of natural and synthetic origin as well as synthetic SiO₂ glass were implanted with different doses of 8.8 MeV He²⁺ ions (fluences in the range from 10¹³ to 10¹⁷ ions/cm²).
The initially dull bluish-violet CL colour of the crystalline quartz samples was found to be transformed to bright yellow in irradiated areas. Monte Carlo simulations predicted that the observed depth of alteration is in very good agreement with the calculated range of alpha particles in quartz. Both, total intensity and radial intensity distribution of the CL emission change with the irradiation dose. Observations suggest a non-linear, approximately logarithmic increase of the CL intensity depending on the alpha dose. In contrast, no significant change in CL emission was observed in the case of He-irradiated amorphous SiO₂.
The changed emission behaviour of He-irradiated areas in alpha-quartz is accompanied by structural damage, caused by the impact of the alpha particles. Significant broadening of Raman bands is only observed near the far end of helium trajectories. This broadening is not only caused by the structural radiation damage but also by strain, inter alia due to (locally heterogeneous) volume expansion of irradiated micro-areas.
Restricted to the end of the helium trajectories, there is a clearly defined, lense-shaped zone, characterised by changed optical and BSE behaviour. The structural state of this region, as investigated by TEM, will be discussed.

Sandstone is one of the most important host rocks for uranium ore deposits, e.g. in Germany (Königstein) or the Czech Republic (Pribram). Any remediation efforts of respective mining legacies thus require a detailed understanding of this system. Namely the sorption in this complex rock is not well enough investigated yet.
One widely accepted approach (Component Additivity – CA, cf. [1]) to describe the sorption is based on the assumption that the surface of a complex mineral assemblage is composed of a mixture of one or more phases whose surface properties are known from independent studies. An internally consistent SCM database can be developed that describes the adsorption reactions of solutes to each phase. The fitting of data of the complex system is not necessary.
We predicted the sorption of uranium(VI) on sandstone using the results of the surface characterization of the assemblage and published data for adsorption onto the pure mineral constituents. The results were compared with batch sorption experiments using natural and synthetic sandstone (mixture of the main components quartz, muscovite, and hematite).
The sorption of U(VI) on natural and two synthetic sandstone (I and II) was investigated in batch sorption experiments (air atmosphere, 0.1M NaClO4, pH 3-11, [U(VI)] 10^-9-10^-3M). We had to consider the natural uranium concentration dissolved from the sandstone at low concentrations.
The synthetic sandstone was a mixture of quartz with muscovite and hematite. The surface area (N₂-BET) of quartz was 0.047 m²/g, of muscovite 0.88 m²/g, of hematite 0.89 m²/g and of natural sandstone (mainly quartz) 0.69 m²/g.
The pH dependence shows a maximal sorption between pH 6 and 7. The U(VI) sorption varies between 95% (10^-9M) and 7% (10^-4) on natural sandstone, and between 80% (10^-9M) and 2% (10^-4M) on synthetic sandstone.
The modeling of U(VI) sorption on sandstone was performed using the CA approach. We assumed just one type of surface sites and applied a model with simple electrostatics, the Diffuse Double Layer Model (DDLM). For the modeling the code MINTEQA2 (Version 4.03, US EPA, May 2006) was used. The aqueous species were taken from the NEA-TDB [2].
As surface reactions we considered the protolysis of quartz, hematite, muscovite, the U(VI) surface complexes of quartz, hematite, muscovite (monomer, dimer) and the ternary U(VI) surface complexes of quartz and hematite with carbonate. The surface area was considered according to the mineral fraction. Despite of a slight shift of the predicted curve to lower pH in both systems, a good accordance with experimental values were found. Obviously, the sorption is strongly influenced by the small amount (0.5%) of hematite.
For the sorption behavior at varying U(VI) initial concentration, a precipitation of schoepite was predicted. As schoepite is an aged mineral, it is unlikely to be formed within the experimental duration of five days. A subsequent exclusion from the list of allowed phases led to a predicted precipitation of both soddyite and metaschoepite.
[1] Davis, J.A. et al. (1998) Application of the surface complexation concept to complex mineral assemblages. Environ. Sci. Technol. 32, 2820-2828.
[2] Guillaumont, R. et al. (2003) Update on the chemical thermodynamics of U, Np, Pu, Am, Tc. Elsevier, Amsterdam.

The generation of the highest laser peak intensities at a high degree of system compactness can be achieved by combining modern diode-pump technologies with the chirped pulse amplification technique. In principle, the spectroscopic properties of the gain medium determine the scaling laws of both high output pulse energy and short pulse duration. Here we introduce a novel criterion classifying laser materials with respect to their ability to generate pulses of highest peak power in a diode-pumped solid state laser system. Furthermore, amplified spontaneous emission as well as laser damage issues affecting the efficiency and compactness of a laser amplifier system are discussed.

An output pulse energy of 17.3 mJ has been achieved with a diodepumped Yb:CaF₂) regenerative laser amplifier. The bandwidth of the output pulse spectrum was 7.3 nm, being seeded with femtosecond pulses stretched to 2.2 ns. In cw operation a tuning range of 80 nm has been observed. A maximum pulse energy of 44mJ at a repetition rate of 1 Hz has been obtained in Q-switched mode. The laser damage threshold of a Yb:CaF₂) crystal has been determined at a wavelength of 1064 nm and a pulse duration of 10 ns.

Characterized by the interplay of Lorentz forces, flow and concentration distributions, magnetoelectrochemical processes are typically quite complex. We aim to show that flow field and concentration measurements by means of Particle Image Velocimetry (PIV) and the relatively new technique Background Oriented Schlieren (BOS) are a valuable aid in understanding the observed phenomena. Two examples, the flow field in a cylindrical cell and the concentration distribution near a circular millielectrode, will be discussed in detail.

The incorporation of hydrogen within ultrananocrystalline diamond/amorphous carbon composite films has been investigated by nuclear reaction analysis (NRA) and Fourier transform infrared spectroscopy (FTIR). The film bulk contains ca. 7.5-8 % H (for a deposition temperature of 600°C), while the H concentration in the surface region is considerably higher. FTIR measurements show that the hydrogen-rich surface is formed right at the beginning of the deposition process and grows outward as the film thickness increases. It can thus be concluded that surface hydrogen species play an active role in the formation of ultrananocrystalline diamond/amorphous carbon films.

We report the results of an experiment in which we studied the near-yrast states in selenium isotopes approaching N = 50 following their population in multinucleon transfer reactions between a 82Se beam and a 192Os target. The level schemes for 80,82Se derived from the current work are compared with restricted-basis shell-model calculations and pair-truncated shell-model calculations. These provide a good description of the yrast sequences in these nuclei using a basis space limited to excitations in the (p3/2 , p1/2 , g9/2 ) and (f5/2 , p3/2 , p1/2 ) orbitals.

The evolution of nanoscale ripple patterns during sub-keV ion sputtering of thermally grown, fused, and single crystalline SiO2 surfaces has been investigated by means of atomic force microscopy. For all three materials, different dependencies of the ripple wavelength and the surface roughness on the ion fluence have been found. Within the Bradley-Harper model of pattern formation, the observed differences are consistent with different amounts of surface and near-surface mass transport by ion-enhanced viscous flow which might result from different surface energies of the SiO2 specimens.

At the heavy ion therapy facility at the Gesellschaft für Schwerionenforschung Darmstadt, Germany, an in-beam PET scanner is operated for quality assurance monitoring simultaneously to the therapeutic irradiation. The PET scanner, which is completely integrated into the treatment facility, registers the annihilation γ - rays following the decay of minor amounts of β+ radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. We investigate how reconstruction of in-beam PET data can profit from the time of flight (TOF) information taking into account specific issues of in-beam PET system, namely, a very low counting statistics and the dual head geometry of the PET scanner which results in missing ray sums in certain directions. We simulated β+-activity distributions based on real treatment plans and generated events measured with a timing resolution 1.2 ns FWHM. We further reconstructed the data via list mode MLEM algorithm and via randomly filled subsets expectation maximization (RFS-EM) algorithm (a modification of OSEM adapted for in-beam PET). Two irradiation situations were evaluated: a relatively small field in the head and neck region (clivus chondrosarcoma) and a large field in the pelvic region (prostate carcinoma). Root mean square error is reduced by 20 % for head and neck field and by 36 % for pelvic field for TOF included reconstructions. Also a significant reduction of specific reconstruction artifacts (in particular, elongation of the images caused by the dual head geometry of the scanner) is observed in TOF included reconstructions versus non-TOF ones for both irradiation cases.

Zusammenfassung über die Arbeiten zur Bestimmung des RBW von weicher Röntgenstrahlung

No abstract available.

The contributions of the Forschungszentrum Dresden-Rossendorf (FZD)/Institute of Radiochemistry (IRC) within the microbe project as part of the international co-operation of the Äspö HRL (Sweden) with the BMWi (Germany) are concentrated in a project addressing the indirect interaction mechanism of a mobilization of actinides by released bioligands in the aquifer system from relevant Äspö bacteria. The ongoing study is focused on: (i) isolation and characterization of microbial ligands produced from a subsurface strain of Pseudomonas fluorescens isolated at Äspö, (ii) interaction of U(VI), Np(V), and Cm(III) with the microbial ligands including compounds simulating the functionality of the microbial ligands and the surface of the bacteria and (iii) spectroscopic characterization of the formed actinide complexes/compounds. The formation constants determined will be used directly in speciation and transport models. This project should help to identify the dominating process of the interaction between actinides and microbes (direct or indirect ones). The research performed in our project improves the understanding of the behavior of colloids and microbes and their respective interaction with radionuclides.
The activities in 2007 were concentrated on (a) complexation studies of U(VI) with the secreted bioligand mixture of P. fluorescens found at Äspö HRL, (b) complexation studies of Cm(III) with relevant pyoverdin model compounds, and (c) complexation studies of U(VI) and Cm(III) with model molecules simulating the functionality of bacterial cell envelopes to explain the interactions of actinides in biologically systems on a molecular level. Selected results of the topics (a) and (b) will be reported here.

Harmonic and transient eddy currents in the eutectic liquid metal alloy GaInSn positioned above an excitation coil are determined by measuring the corresponding voltage drop in an electric potential probe. The resulting spatio-temporal eddy current field is compared with the corresponding analytical expressions for a conducting half-space. Further, a deformation of the eddy current distribution due to a non-conducting torus immersed into the liquid metal is measured and compared with numerical results. The method can be generalized to arbitrary geometries, and might help to validate numerical models for non-destructive testing and magnetic inductance tomography.

New workable aluminium-based light alloys are a key issue in current materials science. In this work, thermophysical properties (density, viscosity and electrical conductivity) of liquid Al96Cu4, Al80Cu20, Al70Cu30, and AlCu4TiMg (wt.%) alloys have been measured in a wide temperature range.
The anomalies with respect to the concentration dependence of the electrical conductivity are explained in terms of the s–d hybridization model. A comparison with data and scaling relations being available in the literature is given.

Oriented multiwalled carbon nanotubes have been synthesized by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition. Elastic recoil detection analysis measurements on multiwalled carbon nanotubes are reported here for the first time. On the basis of the recorded depth profiles, we have developed a simple model to estimate the surface densities of as-grown nanotubes. Besides, nitrogen and hydrogen contents into MWNT, typically less than 6.5 and 8 atom %, respectively, have been characterized as a function of the chemical nature of the catalyst, the synthesis temperature, and the hydrogen carrying diluent gas. These results are discussed with respect to the structural characterization performed by electron energy loss spectroscopy measurements, transmission electron microscopy and X-ray photoelectron spectroscopy.

This presentation reports about a new experimental series on air-water upwards pipe flow. The generated database is suitable for investigations on bubble coalescence and fragmentation.

Der Vortrag gibt eine Einführung in die Problematik der Borverdünnungstransienten in Druckwasserreaktoren. An einem konkreten Fall werden die Möglichkeiten gekoppelter neutronenkinetisch/thermohydraulischer Rechenprogramme, diese Art von Transienten zu berechnen, gezeigt.

Im Vortrag wird ein Überblick zu den durchgeführten Experimenten an der TOPFLOW-Anlage sowie der Nutzung der gewonnen Daten für die CFD-Code-Entwicklung und -validierung gegeben.

We present a numerical analysis of the free surface liquid metal flow and its three-dimensional linear stability. The flow is driven by an alternating magnetic field in a spinning cylindrical container. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface. The hydrodynamic equations are solved by a spectral collocation method, and the alternating magnetic field distribution is found by a boundary-integral method. The flow stability is analyzed for various magnetohydrodynamic interaction parameter and Ekman numbers assuming a flat free surface. We find that only a sufficiently fast spinning suppresses and stabilizes the flow, but a moderate spinning can significantly destabilize it.

ZnO(0001) single crystals annealed in high vacuum have been investigated with respect to their magnetic properties. Annealing at mild temperatures up to 773 K leads to ferromagnetic properties without any transition metal doping. Fe ion implantation at low temperatures leads to similar results. However, no evidence for the relevance of the Fe magnetic moment for the generation of ferromagnetism was observed. Nevertheless, the degradation of the magnetization with time is much less pronounced for the implanted crystals with respect to the purely annealed samples.

Hydroxamate-type siderophores like desferrioxamine B (DFO) are the most common siderophores ubiquitously found in the environment. These naturally occurring chelating substances have the potential to enhance the solubility and mobility of actinides by forming soluble complexes. The unknown interaction between curium(III) and the aqueous DFO species is the subject of this paper. The interaction between soluble species of curium(III) and DFO was studied at trace curium(III) concentrations (3 x 10-7 M) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm3+ - DFO species, MpHqLr, could be identified from the luminescence spectra, CmH2DFO2+, CmHDFO+, and CmDFB, having emission maxima at 599, 611, and 614 nm, respectively. The as well large formation constants, log β121 = 31.62 ± 0.23, log β111 = 25.70 ± 0.17, and log β101 = 16.80 ± 0.40, compared to those of other chelating agents illustrate the unique complexation properties of hydroxamate-type siderophores. An indirect excitation mechanism for the curium(III) luminescence was observed in the presence of the DFO molecules.

Die ENSO Strom AG ist der ostsächsische Regionalversorger. Das Netzgebiet reicht von Riesa im Westen bis zur polnischen Grenze im Osten und vom Erzgebirge im Süden bis zur Landesgrenze zu Brandenburg. Die ENSO Strom AG betreibt seit 1998 eine eigene PV-Anlage und veranstaltet seit dieser Zeit jährlich im Frühjahr einen „Solartag“, der zur Information und zum Erfahrungsaustausch der Anlagenbetreiber genutzt wird.
Im ENSO-Netzgebiet wurde 1990 die erste PV-Anlage der damaligen DDR in Betrieb genommen. Größere Zuwächse waren an die folgenden Förderprogramme gebunden. Mit dem 1000-Dächer-Programm erfolgte der erste wesentliche Schritt, nach einer Phase geringen Wachstums begann ab 2000 mit dem 100000-Dächer-Programm und dem EEG ein steiler Aufschwung. Das Leistungsspektrum der Anlagen reicht von 1 kW bis zu 1 MW, die durchschnittliche Leistung der etwa 1100 Anlagen lag Ende 2006 bei knapp 8 kW.
Die Netzintegration der meist kleinen Anlagen gestaltet sich unproblematisch, nur in Ausnahmefällen (Stichleitungen in ländlichen Netzen) waren Netzberechnungen und gegebenenfalls Festlegung anderer Verknüpfungspunkte erforderlich.
Die Ertragsentwicklung der PV-Anlagen im ENSO-Netzgebiet wird seit einigen Jahren verfolgt und auf den genannten Solartagen ausgewertet. Zwei Hauptergebnisse werden hier detailliert vorgestellt. Zum einen wird seit einigen Jahren der Zusammenhang zwischen der Einstrahlung im Netzgebiet und den Standorten der ertragsstärksten Anlagen untersucht. Diese Anlagen sind per se optimal ausgelegt und ausgerichtet. Es ist deutlich, dass zwischen den Standorten der besten Anlagen (Erträge 2006 > 1080 kWh/kW) und den vom DWD ermittelten Gebieten mit unterschiedlicher Einstrahlung kein nachweisbarer Zusammenhang besteht.
Dies deutet darauf hin, dass die den Ertrag bestimmenden technischen Unterschiede zwischen den einzelnen Anlagen größer sind als die Einstrahlungsdifferenzen im Netzgebiet.
Ein zweites interessantes Ergebnis ist die Ertragsentwicklung der besten Anlagen im Verlauf der letzten 4 Jahre. Seit 2003 wurden jährlich die jeweils besten 20 Anlagen ermittelt und deren gemittelter Ertrag (in kWh/kW) mit den entsprechenden Werten der Vorjahre verglichen. Es zeigte sich, dass in den Folgejahren jeweils neu errichtete Anlagen die älteren „Spitzenanlagen“ übertrafen: Das höheren Erträge neu errichteter Anlagen spiegeln offensichtlich technische Fortschritte in Komponentenqualität und Auslegung wider. Die Erträge erreichen Werte, die bisher nur von Anlagen aus dem süddeutschen Raum bekannt wurden.

Grignard reagents are of vital importance as intermediate products of numerous organic syntheses in the fine-chemical and pharmaceutical industry. They are commonly prepared by reactions between organic halides and magnesium. These so-called Grignard reactions possess considerable hazard potentials due to the spontaneous heat release during the strongly exothermic initiation stage and the high reactivity of the Grignard compounds. From process safety point of view, it is of vital importance to establish industrially applicable methods for an objective real-time detection of the reaction start-up and for educt accumulations in the reaction mixture of the stirred tank reactor during the semi-batch process.
To avoid the use of fragile and expensive on-line analytics, a balance-based on-line monitoring approach for Grignard processes was developed and tested. By solving a set of energy/ mass balances in real-time, concentration profiles of reactants and products can be calculated based on process signals, substance data and plant parameters. Instead of operating under reflux conditions which are commonly used to control the spontaneous exothermic initiation of Grignard reactions, a pressurised vessel process regime is preferred when the on-line monitoring method is applied. In such a way, the accuracy of the calculation can be considerably increased.
Additionally, the approach provides an estimation of the hazard potential due to the reactivity of the organic halide accumulated in the reaction mixture. Assuming an adiabatic behaviour as the worst case, the Maximum Temperature of the Synthesis Reaction (MTSR) and the related pressure in the case of a runaway can be estimated as time-dependent functions and compared with pre-defined thresholds. Furthermore, these safety-relevant parameters enable the optimisation of the process regime. Thus, the reaction can be carried out as a non-stop semi-batch process to increase the space-time yield.
The real-time estimation of safety-relevant parameters, like MTSR courses and corresponding maximum reactor pressure profiles, enables application of advanced control strategies up to the point of a safety-oriented fully automatic control of Grignard reactions.

Between 1973 and 1990 4 units of the Russian NPP type WWER-440/230 were operated in Greifswald (former GDR). The operation was stopped after the German reunification, because the units did not completely follow western nuclear safety standards. Material probes from the pressure vessels were gained in the frame of the ongoing decommissioning procedure.
The investigations of this material started with material from the circumferential core weld of unit 1. This weld was annealed after 13 cycles and operated further for 2 cycles. Additionally, starting with cycle 11, dummy assemblies were inserted to reduce the neutron fluence in the RPV wall.
Firstly this paper presents results of the RPV fluence calculations depending on different loading schemes and on the axial weld position based on the Monte Carlo code TRAMO. The results show, that the use of the dummy assemblies reduces the flux by a factor of 2 – 5 depending on the azimuthal position. The fluence increase is reduced to 1/6 at the position of the maximum fluence.
The neutron fluence at the different circumferential welds is closely related to their distance to the core. The circumferential core weld (SN0.1.4) received a fluence of 2.4•1019 neutrons/cm² at the inner surface, it decreases to 0.8•1019 neutrons/cm² at the outer surface. The neutron fluences at the both other welds are 2 resp. 4 orders of magnitude smaller according to their distances to the core. It should be mentioned that in this cases the fluence gradient can be negative through the wall.
The first material investigations were done using a trepan from the circumferential core weld. Master Curve and Charpy V-notch testing were applied. Specimens from 7 locations through the thickness of the welding seam were tested according to ASTM E1921-05. The reference temperature T0 was calculated with the measured fracture toughness values, KJc, at brittle failure of the specimen. Generally the KJc values measured on pre-cracked and side-grooved Charpy size SE(B) specimens of the investigated weld metal follows the course of the Master Curve. The KJc values show a remarkable scatter. More values than expected lie below the 5% fractile. In addition the MC SINTAP procedure was applied to determine T0SINTAP of the brittle fraction of the data set. There are remarkable differences between T0 and T0SINTAP indicating macroscopic inhomogeneous weld metal. The highest T0 was about 50°C at a distance of 22 mm from the inner surface of the weld. It is 40 K higher compared with T0 at the inner surface. This is important for the assessment of ductile-to-brittle temperatures measured with sub size Charpy specimens made of weld metal from the inner RPV wall. This material does not represent the most conservative condition. Nevertheless, the Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.
The VERLIFE procedure prepared for the integrity assessment of WWER RPV was applied on the measured results. It enables the determination of a reference temperature, RTT0 to index a lower bound fracture toughness curve. This curve agrees with the MC 5% fractile as specified in ASTM E1921-05. The measured KJc values are not enveloped by this lower bound curve. However, the VERLIFE lower bound curve indexed with the SINTAP reference temperature RTT0SINTAP envelops the KJc values. Therefore for a conservative integrity assessment the fracture toughness curve indexed with a RT representing the brittle fraction of a dataset of measured KJc values has to be applied.

The sorption characteristics of U(VI) on bentonite and montmorillonite were investigated in batch experiments for understanding the near-field behaviour in geological nuclear repositories. Sorption parameters were determined in batch tests. The sorption on bentonite (KWK) was studied at different dry bulk densities of the clay (1.3, 1.6, 1.9 g/cm³) at pH 8 for the U(VI) concentration dependence (10^-4 to 10^-9 m). The sorption on the pure mineral montmorillonite (SWy-1) in 0.1 M NaClO₄ was determined for the concentration dependence at pH 5.5, and pH dependence between pH 3 and 11). A scientifically founded description of sorption processes at the mineral-liquid surface is possible with the surface complexation models (SCM), the ion adsorption on surface sites as complexation reaction. We use the diffuse double layer model (DDL) to predict the sorption with the code MINTEQA2 (Version 4.03, US EPA May 2006), thermodynamic data of aqueous and solid species from the NEA-TDB [1], the mineral characterization and the respective protolysis data [2] and surface complex constants from [3].
The prediction of U(VI) sorption on montmorillonite at the pH dependence was very good. The modelling of the sorption on montmorillonite and bentonite versus U(VI) concentration shows a good agreement of measured and predicted values.

[1] Guillaumont, R. et al. (2003) “Update on the chemical thermodynamics of U, Np, Pu, Am, Tc. Chemical Thermo-dynamics”, Vol. 5 (OECD Nuclear Energy Agency, ed.), Elsevier, Amsterdam.
[4] Pabalan, R.T. et al. (1997) Aquat. Geochem. 2, 203-226.
[3] Pabalan, R.T. et al. (1998) in: Adsorption of metals by geomedia. Variables, mechanisms, and model applications; Jenne EA (Ed.), Academic Press; San Diego.

Funding by the European Commission (NF-PRO C2-ST-C-01) is gratefully acknowledged.

Experiments were done on co-current and counter-current flows of air-water and also steam-water for a flat geometry reflecting a hot leg and steam generator inlet chamber of a Pressurized Water Reactor. The focus of the experiments was on the phenomenon of Counter-Current Flow Limitation. For air-water flows the flooding curve was obtained for this special geometry. The main aim of the experiments is however to provide a detailed database for CFD code validation. For this reason a model of a part of the hot leg and the steam generator inlet chamber was equipped with large glass windows to enable high speed camera observations. To use this measuring technique also for steam-water flows a new technology, the so-called pressure tank technology was used for the first time. The test section itself is built-in into a large pressure tank which can be operated for pressures up to 5 MPa. A condenser at the end of the test section guarantees the pressure equilibrium between the inside of the test section and the tank atmosphere. This enables to manufacture the test section from thin materials and to use large glass windows. For the first time steam-water co-current and counter-current flows were observed by high speed video observations at a pressure of 1.5 MPa. Further experiments with pressure up to 5 MPa will follow.

Functional imaging for radiotherapy is expected to provide diagnostic as well as prognostic information, to monitor treatment, to help stratification of patients for specific therapeutic interventions and to guide dose-painting. During the last years radiotracer-based functional imaging with positron emission tomography (PET), mainly using the glucose analogue [¹⁸F]2-fluoro-2-deoxy-D-glucose ([¹⁸F]FDG), has been widely implemented in radiotherapy for a more accurate staging and an improved target volume definition in a variety of tumor types [1, 2, 4]. While the technology for integration of functional imaging into clinical radiotherapy is increasingly available, the biological implications for radiation response are poorly understood [6]. Importantly, biomarker development needs to account for the specific parameters known to determine the results of curative radiotherapy. Clinical as well as preclinical studies are necessary to exploit the potential of functional imaging to improve outcome after radiotherapy. In the following sections recent findings from experimental studies using xenotransplanted tumors in nude mice carried out in our laboratories are briefly summarized.

The investigation of insulation debris generation, transport and sedimentation becomes more important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core coolant systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are for example the particle load on strainers and corresponding pressure drop, the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow. A joint research project on such questions is being performed in cooperation with the University of Applied Science Zittau/Görlitz. The project deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While the experiments are performed at the University Zittau, the theoretical work is concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.

In the present study, the model ligands citric acid and glutaric acid as well as mandelic acid and glycolic acid were chosen for the uranium(IV) complexation. These ligands stand for a variety of organic ligands in aqueous systems. The complex formation constants for the uranium(IV) complexation were determined applying UV-Vis absorption spectroscopy. Thereby, the hydrogen ion concentration and the ionic strength were varied.
For instance, the complexation of uranium(IV) with citric acid has been investigated in dependence on hydrogen ion concentration (1 M, 0.5 M, 0.1 M and 0.05 M). Thereby, the formation of 1:1 and 1:2 complexes was detected in the citrate media. The stability constants for 1:1 and 1:2 uranium(IV) citrate complexes of the type MpHqLr were determined with log ß101 = 13.5 ± 0.2 and log ß102 = 25.1 ± 0.2. The obtained log ß fit well in the known series of log ß determined for the complexation of further tetravalent actinides (e.g., Pu(IV), Np(IV), Th(IV)) by citric acid.

For the very improbable scenario of a severe accident with core meltdown and for-mation of a melt pool in the lower plenum of a Light Water Reactor (LWR) Pressure Vessel (RPV) computer codes are developed to assess the thermal and mechanical behaviour of the RPV wall. If the RPV wall fails within the lower head region, the melt is discharged into the reactor pit, which can result in severe thermal and mechanical loads for the containment. One accident management strategy could be to stabilize the in-vessel debris or melt pool configuration in the RPV via external flooding.
Based on the successful simulation and analysis work of the FOREVER-experiments (cf. Fig. 1 and [1]) coupled thermo-mechanical models have been developed further to simulate the prototypical scenario of an In-Vessel-Retention in large PWRs [2]. According to the recent publication “An Effective Convectivity Model (ECM) for Simulation of In-Vessel Core Melt Progression in a Boiling Water Reactor” by Tran and Dinh [3] the thermal part of the FE-model developed at FZD is now improved to be able to apply the new ECM approach.

The paper describes the modelling and evaluation of a pressurized thermal shock (PTS) scenario in a VVER-440 reactor pressure vessel due to an emergency case. An axially oriented semi-elliptical crack is assumed to be located in the core welding seam. Two variants of fracture mechanical evaluation are performed: the analysis of a sub-cladding crack and of a surface crack. Three-dimensional finite element (FE) models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. Within the subsequent postprocessing using the j integral technique the stress intensity factors KI along the crack front are obtained. The FE results are compared to analytical calculations proposed in the VERLIFE code. The stress intensity factors are compared to the fracture toughness curve for the weld material.

This paper concerns the model of a polydispersed bubble population in the frame of an ensemble averaged two-phase flow formulation. The ability of the moment density approach to represent bubble population size distribution within a multi-dimensional CFD code based on the two-fluid model is studied. Two different methods describing the polydispersion are presented: (i) a moment density method, developed at IRSN, to model the bubble size distribution function and (ii) a population balance method considering several different velocity fields of the gaseous phase. The first method is implemented in the NEPTUNE_CFD code whereas the second method is implemented in the CFD code ANSYS/CFX. Both methods consider coalescence and break-up phenomena and momentum inter-phase transfers related to drag and lift forces.
Air-water bubbly flows in a vertical pipe with obstacle of the TOPFLOW experiments series performed at FZD are then used as simulations test cases. The numerical results, obtained with NEPTUNE_CFD and with ANSYS/CFX, allow attesting the validity of the approaches. Perspectives concerning the improvement of the models, their validation, as well as the extension of their applicability range are discussed.

The talk presents our parametrization of a theoretical calculation of nuceon - nucleon Bremsstrahlung, done by L. Kaptari and B. Kaempfer, that is to be implemented in the PLUTO somulation framework

The talk presents recent results from our investigations of new nanocomposite materials for the construction of resistive plate counters. This counters are forseen as timing detectors for the upcomming Compressed Baryonic Matter (CBM) experiment at FAIR. These tests where performed at the electron beam of ELBE.

Übersicht über die Anwendung des in-beam PET bei der Schwerionentherapie.

Übersicht über die Anwendung von in-beam PET bei harten Photonen

Ionenstrahlen bieten aufgrund ihrer besonderen physikalischen und biologischen Eigenschaften die Möglichkeit einer präzisen Tumorbestrahlung mit geringer Belastung für das umliegende gesunde Gewebe. Dadurch können auch tief sitzende Tumoren in der Nähe von Risikoorganen bestrahlt werden, die mit konventioneller Strahlung nur eingeschränkt therapierbar sind.
Im Dezember 1997 begann die Behandlung von Krebspatienten mit Kohlenstoffionen an der Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. An dieser europaweit ersten Schwerionentherapie-Pilotanlage sind bis heute ca. 400 Patienten mit Kopf- und Beckentumoren bestrahlt worden.
Da die durch die Ionenstrahlen deponierte Dosisverteilung äußerst empfindlich auf Veränderungen in der Ionen-Reichweite reagiert, ist eine Verifikation der Bestrahlungsfeldposition unabhängig von der Strahlapplikation wünschenswert. Hierzu wurde am Forschungszentrum Dresden-Rossendorf eine Methode entwickelt, die auf der Detektion von Annihilationsphotonen mit PET (Positronen-Emissions-Tomographie) und einem Vergleich der gemessenen, rekonstruierten Aktivität mit Vorhersagen aus der Bestrahlungsplanung beruht. Die Positronen emittierenden Nuklide entstehen während der Bestrahlung durch Kernreaktionen zwischen den Atomkernen des Gewebes und den Ionen des Therapiestrahls. Dieses so genannte in-beam PET-Verfahren ist die zurzeit einzige bekannte Methode zur in-situ und in-vivo Verifikation der Dosisapplikation bei der Bestrahlung mit Ionen. Das Verfahren kam bei nahezu allen an der GSI behandelten Patienten zum Einsatz und führte zu einer Verbesserung des verwendeten Strahlenmodells. Ferner werden sporadische Abweichungen zwischen geplanter und realisierter Teilchenreichweite nachgewiesen. Diese Abweichungen können ihre Ursachen z. B. in temporären anatomischen Veränderungen im durchstrahlten Volumen, in geringfügigen Bewegungen des Patienten während der Bestrahlung oder in Fehlern bei der Patientenpositionierung haben.
Die gewebeabhängige Kinetik des metabolisch verursachten Abtransportes der Aktivität aus dem bestrahlten Volumen ist bisher nur unzureichend bekannt und steht einer quantitativen Berechnung der Dosis aus der gemessenen Aktivitätsverteilung entgegen. Hier kommt ein interaktives Verfahren zur Anwendung, das die Identifikation der Ursachen von auftretenden Abweichungen ermöglicht.

2-[¹⁸F]Fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) as the most important PET radiotracer is available in almost every PET center. However, there are only very few examples using [¹⁸F]FDG as a building block for the synthesis of ¹⁸F-labeled compounds. The present study describes the use of [¹⁸F]FDG as building block for the synthesis of ¹⁸F-labeled peptides and proteins. [¹⁸F]FDG was converted into [¹⁸F]FDG-maleimidehexyloxime ([¹⁸F]FDG-MHO), a novel [¹⁸F]FDG-based prosthetic group for the mild and thiol group-specific ¹⁸F labeling of peptides and proteins. The reaction was performed at 100°C for 15 min in a sealed vial containing [¹⁸F]FDG and N-(6-aminoxy-hexyl)maleimide in 80% ethanol. [¹⁸F]FDG-MHO was obtained in 45-69% radiochemical yield (based upon [¹⁸F]FDG) after HPLC purification in a total synthesis time of 45 min. Chemoselecetive conjugation of [¹⁸F]FDG-MHO to thiol groups was investigated by the reaction with the tripeptide glutathione (GSH) and the single cysteine containing protein annexin A5 (anxA5). Radiolabeled annexin A5 ([¹⁸F]FDG-MHO-anxA5) was obtained in 43-58% radiochemical yield (based upon [¹⁸F]FDG-MHO, n=6), and [¹⁸F]FDG-MHO-anxA5 was used for a pilot small animal PET study to assess in vivo biodistribution and kinetics in a HT-29 murine xenograft model.

The synthesis and crystal structure of a new 34-membered N6O4-donor macrocycle 2 is reported. Solvent extraction experiments (water/chloroform) indicated that 2 acts as an efficient extractant towards silver(I) and zinc(II) at pH values beyond 6 while the extraction of iodide and chromate occurs below this pH. A competitive metal extraction experiment at pH 7.2 in which the perchlorate salts of cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) were present together in the aqueous phase led to the following order of increasing extraction efficiency: cobalt(II) o nickel(II) o zinc(II) o copper(II) B cadmium(II). A substantial synergistic enhancement of zinc(II) salt extraction was observed for a dual-host extraction system using the macrocycle 2 as cation binder and the tripodal thiourea ligand 3 as anion receptor; in particular, a notable extraction of zinc(II) sulfate was obtained.

We investigate nonlinear mid-infrared detection via two-photon transitions involving two bound subbands and one continuum resonance in an n-type multiple quantum well. By varying the excitation energy, we have tuned the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.

To reduce the occupancy of the large-size coordinate detectors, the high-granularity straw tracking chamber has been designed and tested. The main tasks were to improve the detector granularity and provide the best value of the detector radiation thickness. We have developed the techniques of the multiple anode production, assembling of the segmented straws and the low-mass readout by means of flat cable. Testing of the constructed prototypes has shown that these techniques can be applied to build the high-granularity straw detectors.

The NURESIM Integrated Project of the 6th European Framework Program was envisaged to initiate the development of the next-generation common European Standard Software Platform for simulating nuclear reactors. The overall objective of NURESIM Thermalhydraulic sub-project is to improve the understanding and the predictive capabilities of the simulation tools for key two-phase flow thermal-hydraulic processes such as the Critical Heat Flux (CHF). A multi-scale analysis of reactor thermalhydraulics is envisaged and two-phase CFD is developed to allow some zoom on local processes when the resolution of system codes is not sufficient.
Current industrial methods for CHF mainly use the sub-channel analysis and empirical CHF correlations based on large scale experiments having the real geometry of the reactor assembly. The NURESIM-TH activities regarding CHF aim at using two-phase CFD as a tool for understanding boiling flow processes, in order to subsequently help new fuel assembly design and to develop better CHF predictions in both PWR and BWR. A “Local Predictive Approach” may be envisaged for the long term where CHF empirical correlations would be based on local T/H parameters provided by CFD.
This paper presents a review of existing experimental data bases which can be used for validation of the two-phase CFD application to Critical Heat Flux (CHF) investigations with respect to nuclear reactors. The phenomenology of DNB and Dry-Out are detailed identifying all basic flow processes which require a specific modeling in CFD tool. The resulting program of work is given and the current state of the art of the modeling is presented.

This paper reports activities regarding the simulation of Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. Some Loss of Coolant Accident (LOCA) scenarios for Pressurized Water Reactors (PWR) may cause Emergency Core Coolant injection into the cold leg and thus lead to PTS situations. They imply the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. The present paper, in the area of fluid dynamics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. It summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase flow sub-phenomena are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance is still limited. In the near term, one may envisage a simplified treatment of two-phase PTS transients by neglecting some effects which are not yet well controlled, leading to slightly conservative predictions.

In the DEBORA experiments subcooled boiling is investigated heating up Dichlorodifluoromethane (R12) in a side wall heated tube. Radial profiles for gas volume fraction, gas velocity, liquid temperatures and bubble sizes were measured at the end of the heated length. This enables the validation not only of the wall boiling model but also of the models for liquid/gas momentum, heat and mass transfers.
The report describes the model simulating the wall boiling preliminary implemented in CFX-11 which is also implemented in the NEPTUNE code. These approaches are based on the proposal of Kurul and Podowski (1990). Specific model developments concerning the near wall phenomena are described in the report. Furthermore the momentum exchange models used in the CFX simulations are described.
The same parameters for the model correlations adjusted for water/steam flow were applied simulating the fluid R12. To investigate the influence on the results, essential boiling model parameters were varied and the sensitivity of the results is shown. The need of further model development and of further experiments can be confirmed. The validation applying for the different models shows the state and the limits of the present modelling.
The simulations are intended for the comparison to other CFD models e.g. to the NURESIM-CFD platform.

The Master Curve (MC) approach as standardised in the ASTM Standard Test Method E 1921-05 was applied on weld metal of the reactor pressure vessel (RPV) core welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the Master Curve. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behaviour, respectively.

The synthesis, structure and properties of fullerene-like alloyed carbon films are reviewed. The term fullerene-like describes extended structures consisting of curved basal planes, which are stacked perpendicular to the basal planes. Fullerene-like structures can be observed in layered materials like graphitic carbon, carbon nitride, hexagonal boron nitride or tungsten disulfide. They can be characterized by extension, curvature and cross-linking of basal planes. Their structure results in an exceptional combination of mechanical properties such as high hardness, high elastic recovery, high wear resistance and low coefficient of friction.

In carbon based fullerene-like structures, these properties result from stiff (sigma pi)-bonds within the basal graphitic planes, fullerene-like structure assuring the presence of their 3D network due to the curvature and cross-linking. The fullerene-like structure of pure carbon can be further stabilized by alloying with nitrogen. Different nitrogen incorporation routes result in different local carbon-nitrogen bonding arrangements which then determine the extension, curvature and cross-linking of basal planes. Since both elements – carbon and nitrogen – can form sp1, sp2 and sp3 bonds, the nanostructure is determined by the relative concentration of local chemical environments such as nitrile-like, pyridine-like or graphite-substitutional. The former two configurations are terminating, thus hindering the extension of basal planes The latter induces buckling in the planes due to stabilization of pentagon rings or due to the difference between C-N and C-C bonds which locally shrinks the network.

An alternative way to produce fullerene-like structures is carbon alloying with metallic elements. The metal atoms segregate into the nanoparticles which act as catalytic sites for the six-fold-ring clustering of carbon atoms. Different metal incorporation routes determine the shape of metal nanoparticles ranging from completely spherical to nanorod-like. This significantly affects the graphitization of carbon as the so-formed graphitic planes follow the boundaries of the metal nanoparticles resulting in partially wrapped metal nanocolumns or completely encapsulated metal nanoparticles. These fullerene-like nanostructures might be used for applications as low-friction, self-lubrication, wear resistant coatings, as 2D network of tunnel junctions, as nanocontainers for foreign materials, or for encapsulation of ferromagnetic nanoparticles in non-magnetic media.

Usually, the slug flow regime is characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry a significant amount of liquid with high kinetic energy. It is potentially hazardous to the structure of a system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs. Because slug flow cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space.

Thanks to the optical access of the test channels built at Forschungszentrum Dresden-Rossendorf, it is possible to study detailed local stratified air/water flow phenomena. These experimental results give an important input for two-phase flow CFD model validation (i.e. interfacial momentum transfer, turbulent profiles of each phase). For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built (Fig. 1). Its inlet device provides defined inlet boundary conditions for code comparison. The channel allows in particular the study of air/water slug flow under atmospheric pressure. A flow pattern map (Fig. 2) was arranged constructed on the basis of a visual observation of the flow structure at different combinations of the gas and liquid superficial velocities. Parallel to the experiments, CFD calculations were carried out. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made (Figs. 3 and 4). The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value.

The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments like pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.

The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the cold leg and downcomer of a Pressurised Water Reactor (PWR) was analyzed at the ROssendorf COolant Mixing (ROCOM) test facility. This paper presents a matrix of ROCOM experiments in which water with the same or higher density was injected into a cold leg of the reactor model with already established natural circulation conditions at different low mass flow rates. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the cold leg, upper and lower part of the downcomer. A transition matrix from momentum to buoyancy-driven flow experiments was selected for validation of the CFD software ANSYS CFX. A mesh with 4 million control volumes was used for the calculations. The turbulence models usually applied in such cases assume that turbulence is isotropic, whilst buoyancy actually induces anisotropy. Thus, in this paper, higher order turbulence models have been developed which take into account for that anisotropy. Buoyancy generated source and dissipation terms were proposed and introduced into the balance equations for the turbulent kinetic energy. The results of the experiments and of the numerical calculations show that mixing strongly depends on buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation with lower mass flow rates and/or higher density differences. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWR and should be also considered in Pressurized Thermal Shock (PTS) scenarios. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.

In order to study valve characteristics, experiments of the Institut für Strömungsmechanik at the Technical University Hamburg-Haburg (TUHH) were used to validate the CFD-code ANSYS CFX. Due to the constant improvement of the physical models and numerics of the code it is now possible to simulate very complex flows through valves. This includes phenomena like jets, flow around obstacles, flow separation effects, stagnant regions and partly zones with high mach numbers. The geometric details of the safety valve internals have a strong influence on the flow field. Therefore, an exact representation of the inlet region, the seat and disc region and the shape of the valve body were necessary. The computational grid contains one million nodes. For code validation purposes experiments were taken with different fluids and mixtures and the influence of the different hubs was studied. In all cases a good agreement between measurements and numerical results could be achieved with existing models of the CFD code.

kein Abstract verfügbar

kein Abstract verfügbar

The visualization of an exceptional point in a PT-symmetric directional coupler (DC) is demonstrated. In such a system the exceptional point can be probed by varying only a single parameter. Using the Rayleigh-Schrödinger perturbation theory we prove that the spectrum is real as long as the radius of convergence has not been reached. We also show how one can use a PT-symmetric DC to measure the radius of convergence for non PT-symmetric structures. For such systems the physical meaning of the rather mathematical term `radius of convergence´ is exemplified.

Nach einem kurzen Überblick über die Forschung an meinem Institut möchte ich zwei Themengebiete näher diskutieren:

(1) Lichtemitter auf Basis von Silizium MOS Strukturen als möglicher Weg zu einer integrierten Silizium-Optoelektronik
(2) Infrarot-Nahfeldmikroskopie als Methode zur Untersuchung von oberflächennahen Nanostrukturen, hier demonstriert an ferroelektrischen Domänen in BaTiO3.

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There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of preocessing in the millisecond or nanosecond range. This was driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This paper reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with the Mattson group and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that the basic principle of short time thermal processing, i.e. surface heating on a colder bulk, features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century.

Der gekoppelte Programmkomplex DYN3D/ATHLET wurde im Rahmen der Arbeiten zum Projekt weiterentwickelt. Dabei wurde das in der externen Kopplung von DYN3D und ATHLET verfügbare Modell für die Beschreibung der Kühlmittelvermischung auf weitere Szenarien erweitert und in die anderen beiden Kopplungsoptionen implementiert. Des Weiteren wurde ein spezielles Modell zur Vermeidung der numerischen Diffusion beim Bortransport innerhalb des Reaktorkerns, das für DYN3D entwickelt worden war, in das Thermohydraulikprogramm ATHLET übertragen.
Für die Analyse von heterogenen Borverdünnungsstörfällen wurde eine Methodik bestehend aus stationären und transienten Rechnungen entwickelt. Durch die Implementierung des o.g. Modells zur realistischen Beschreibung der Kühlmittelvermischung in den gekoppelten Programmkomplex DYN3D/ATHLET war es möglich, eine neue Qualität in der Analyse von Borverdünnungsstörfällen zu erreichen. Die Methodik wurde auf zwei verschiedene Borverdünnungsstörfalle angewandt. Wesentliches Ergebnis ist, dass entsprechend den Rechenergebnissen selbst bei Vorgabe einer aus konservativen Abschätzungen stammenden maximalen Pfropfengröße für beide Szenarien die Integrität des Brennstoffs nicht gefährdet ist. Die entsprechenden Studien zeigten die großen Reserven, die beim konsequenten Abbau von Konservativitäten freigesetzt werden können. Der entscheidende Beitrag zu diesem Abbau ist dabei auf die realistische Modellierung der Vermischung der deborierten Pfropfen innerhalb des Reaktordruckbehälters zurückzuführen. Von Vorteil erwies sich hier der Einsatz der verschiedenen Kopplungsoptionen. Die damit verbundene Anwendung unterschiedlicher Thermohydraulikmodelle auf ein und dieselbe Störfalltransiente erhöht das Vertrauen in die erzielten Ergebnisse.
Die Untersuchungen zur Borverdünnung während des Nachkühlbetriebes wurden in einem gesonderten Bericht ausführlich dargestellt. Dieser Bericht wird derzeit im Rahmen eines Genehmigungsverfahrens eingesetzt.
Erstmals wurde das Programm DYN3D/ATHLET auf eine ATWS-Transiente angewandt. Am Beispiel der Transiente: „Ausfall der Hauptspeisewasserversorgung“ wurde der Einfluss verschiedener thermohydraulischer und neutronenkinetischer Randbedingungen auf die Ergebnisse untersucht. Der wichtigste Sicherheitsparameter bei der betrachteten Transiente ist der Druck im Primärkreislauf. Im Bereich der thermohydraulischen Variationen hat die Effektivität der Entlastungs- und Sicherheitsventile den größten Einfluss auf diesen Parameter. Der berechnete Maximaldruck hängt auch stark von der Kernbeladung ab. So wurde gezeigt, dass mit Erhöhung der Anzahl der MOX-Brennelemente das berechnete Druckmaximum deutlich niedriger ausfällt. Weiterhin wurden die Rückkopplungsparameter einer generischen Kernbeladung einer statistischen Unsicherheits- und Sensitivitätsanalyse unterzogen, in deren Verlauf 100 Variationsrechnungen durchgeführt wurden. Diese Analyse ergab, dass dabei bei identischer relativer Variationsbreite der Rückkopplungskoeffizient der Moderatordichte einen doppelt so großen Einfluss auf den berechneten Maximaldruck hat wie der Koeffizient der Brennstofftemperatur.
Mit dem Programmkomplex DYN3D/ATHLET steht ein anwendungsbereites Werkzeug mit einer breiten Validierungsbasis für die Analyse von Störfällen zur Verfügung, in denen die enge Kopplung von Neutronenkinetik und Thermohydraulik unter Berücksichtigung des Einflusses der Anlagenkomponenten von Bedeutung ist. Es kann für konkrete Nachweisrechnungen einschließlich der Quantifizierung von Unsicherheiten auf Basis deterministischer oder statistischer Ansätze eingesetzt werden.

hat nicht vorgelegen

hat nicht vorgelegen

We studied the sorption of Am(III), Np(V) and U(VI) onto kaolinite under aerobic and anaerobic conditions as a function of pH, ionic strength and actinide concentration in a series of batch equilibrium experiments. These actinides were selected as representatives of actinides in different oxidation states. Furthermore, we studied the influence of humic acid on the actinide sorption.

An artificial humic substance-kaolinite-associate was synthesized as a model substance for natural clays containing organic matter in clay formations, soils, and sediments. The U(VI) sorption onto this model substance was studied in batch experiments as a function of pH and compared to the U(VI) sorption onto kaolinite in absence and presence of separately added humic acid (HA).
The humic substance-kaolinite-associate has a TOC content of 4.9 mg/g. It was found that the humic matter associated with kaolinite exhibits an immobilizing as well as an mobilizing effect on U(VI). Between pH 3 and 5, humic matter causes an increase in the U(VI) sorption onto kaolinite, whereas at pH above 5 the release of humic matter from the associate in the solution and the formation of dissolved uranyl humate complexes reduces the U(VI) sorption. The U(VI) sorption onto the synthetic humic substance-kaolinite-associate differs from that of U(VI) in the system U(VI)-HA-kaolinite with comparable amounts of separately added HA. Separately added HA causes a stronger mobilizing effect on U(VI) than humic matter present in the humic substance-kaolinite-associate. This can be attributed to structural and functional dissimilarities of the humic substances.

Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in a living multispecies biofilm grown on biotite plates. Anaysis of amplified 16S rRNA fragments and fluorescence in situ hybridization were used to characterize the biofilm communities. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilms. Concentration profiles of oxygen versus biofilm depths were measured in the biofilms by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed that the vertical profiles of the O2 concentration within the biofilms are affected by the presence as well as by the concentration of U(VI) in the culture media. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration.

Since bulk WS2 forms layered structures similar to bulk graphite, this material might also built up stable cage-like fullerene structures. Large graphite-like structures (multiwall fullerenes, nanotubes) have been found in TEM experiments, but so far no anorganic fullerenes have been detected in the size regime of C60. Thus, we started a search for WS2 fullerenes by combining gas phase and deposition experiments. In the gas phase, we identified a variety of different structures (nanowires, nanoplatelets) in the size regime up to 30 metal atoms [1-3]. To investigate the suitability as building blocks, in a first attempt small size-selected WnSm-clusters were soft-landed on Ag- and Si substrates at ultrahigh vacuum conditions. These samples were analysed via HREELS and XPS. The HREELS spectra are different for the different cluster sizes indicating that these clusters survived the soft landing on the substrate and do not coalesce to bulk-like structures.
[1] S. Gemming, J. Tamuliene, G. Seifert, N. Bertram, Y.D. Kim, and G. Ganteför, Appl. Phys. 82, 161 (2006)
[2] N. Bertram, Y.D. Kim, G. Ganteför, Q. Sun, P. Jena, J. Tamuliene, and G. Seifert, Chem. Phys. Lett. 396, 341 (2004)
[3] N. Bertram, J. Cordes, Y.D. Kim, G. Ganteför, S. Gemming, and G. Seifert, Chem. Phys. Lett. 418, 36 (2006)

The present study describes an approach for the scale-bridging modelling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterised by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straighforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism. In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides.

The functionality of standard silicon-based semiconductor devices is achieved by careful point defect engineering, hence tremendous efforts have been made to arrive at a quantitative understanding of the underlying interactions. Germanium has distinct advantages over silicon, for instance the lower energy gap between occupied and empty electronic states and the resultant lower carrier injection barriers. However, point defect engineering in germanium has not yet reached a level of sophistication comparable with the one in silicon. Thus, both theoretical and experimental investigations were carried out to study the interaction of point defects in germanium.
Conductivity measurements of phosphorus-implanted germanium indicate that not all dopant atoms are electronically active. Therefore density-functional calculations were carried out to study the properties of Ge vacancies, substitutional phosphorus defects and their interaction. Stable defect clusters are obtained, and in the limit of high dopant concentration an electrically inactive form of the P dopant is predicted.

The Burton-Cabrera-Frank (BCF) model describes the structural evolution of vicinal surfaces in terms of an incoming particle flux and concentration-dependent desorption and surface diffusion terms. A continuum formulation of the BCF scheme given by a phase-field implementation for the moving-boundary problem yields the long-term evolution of the step structure during a step-flow growth mode. A particle-based Ising-type approach with a Metropolis-Monte-Carlo kinetics additionally provides nucleation processes in a temperature-controlled manner and on a shorter time and length scale. We have integrated both approaches in a hybrid algorithm, which describes adsorption, nucleation, and structure evolution processes at solid-liquid and solid-gas interfaces on both time and length scales. The short term nucleation is resolved by the Monte-Carlo generated dynamics of an anisotropic Ising model, whose interaction parameters stem from first-principles calculations. The long-term microstructure dynamics is calculated by the phase-field method. Several growth modes are distinguished: In addition to step-flow growth the nucleation processes on the terraces can lead to roughening or an epitaxial layer-by-layer growth controlled by temperature and by flux.

no abstract for this publication

no abstract for this publication

no abstract for this publication

Trace amounts of oxidic plutonium species were studied by thermochromatography in silica glass columns in comparison to oxidic species of Th, Pa, U, Np, and Am. Humid oxygen was used as reactive admixture to the carrier gas helium. The thermochromatographic behavior of plutonium provides evidence for the oxidation of Pu(IV) to Pu(VI) with humid oxygen. The gas chromatographic transport of U, Np, and Pu is governed by the surface reaction
MO2(OH)2(g) = MO3(ads) + H2O(g)
with M = U, Np, and Pu in the hexavalent state and competitive reactions of the actinide oxides with silica to nonvolatile compounds or solid solutions. There is good agreement with earlier volatility studies and the reported oxidation of PuO2 with water. The oxidation to PuO4 as claimed by Domanov could not be confirmed.

The effect of uranium added in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by confocal laser fluorescence microscopy (CLSM). The microsensor profile measurements in the stable multispecies biofilms exposed to uranium showed that the oxygen concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the oxygen consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 68 nmol cm-3s-1 in the top layer (0 - 70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer. Analysis of the amplified 16S rRNA gene fragments showed that the addition of uranium in ecological relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms and is therefore not responsible for the different oxygen profiles in the biofilms. The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilms zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm air interface which triggers redox processes leading to a precipitation of uranium(IV) solids and consequently to a removal of uranium from the aqueous phase.

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Darstellung von ausgewählten Methoden zur Bestimmung der chemischen Speziation von Uran(IV) im System Boden-Pflanze

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A correlation of the nitrogen concentration on graphitic sheets with structural deformations is presented using the density functional based tight binding method (DFTB). Graphite sheets of various sizes were doped by nitrogen at different sites; either a local deviation from planarity or negative curvature is obtained. In addition, we derive a formula for constructing two sets of isomer series namely methylene cyclopentadiene and benzene to study nitrogen's role in positive curvature formation. Comparing these structures, the exact energy difference to convert a fully hexagonal network to a pentagon centered hexagonal network can be predicted systematically for infinitely large structures. (c) 2007 Elsevier B.V. All rights reserved.

Intersubband transitions (ISBT) in semiconductor quantum wells have been attracting much attention for infrared optoelectronic device applications such as quantum cascade lasers and quantum well infrared detectors. There is also considerable interest to extend ISBT to short wavelengths (< 2 μm), for devices applications such as fast switching and modulators, due to ultrafast intersubband relaxation in the picosecond and subpicosecond regime. Therefore attentions were driven to heterosystem with large conduction band offsets (> 1 eV).
On the other hand, to achieve short wavelengths thin quantum wells (< 3 nm) are required, where the first excited state inside the QW may lie higher than some state related to indirect valleys. Examples for such material systems are strained InGaAs/AlAs or lattice matched InGaAs/AlAsSb, both grown on InP.
We have studied the intersubband relaxation dynamics in multi QWs of both material systems by femtosecond pump-probe measurements using an optical parametric oscillator. By the transient transmission as a function of the pump-probe delay we observe that some long living states are present in our systems, showing that more than two levels might be involved in the relaxation dynamics. This can be caused by transfer of electrons to X- or L-states in the QWs or the barriers. To investigate the origin of such long living states and the involved relaxation time constants, we have studied samples with different QW thicknesses, containing doping impurities localized either inside the QW or at the barriers. The experimental results are compared to simulations based on rate equations.

The magnetorotational instability (MRI) plays an essential role in the formation of stars and black holes. By destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs which is necessary for the mass accumulation of central objects.
In order to examine the MRI we applied helical magnetic fields to a Taylor-Couette experiment with the liquid alloy GaInSn [1,2,3]. The low velocities of the liquid metal in the experiment are measured using an ultrasonic Doppler velocimeter.
The results show typical predicted features of MRI at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10. Particular focus is laid on new results with an improved experiment in which split end caps are used to minimize the effect of Ekman pumping.

This paper presents the results from a severe accident analysis performed with ASTEC V1.3.0 code for a nuclear power plant with a VVER-1000/V-320 reactor. The purpose of this analysis is to assess the ASTEC code behaviour in modelling of main severe accident phenomena in the primary and secondary circuit arising during a hypothetical severe accident. The performed analyses cover a station blackout (SBO) sequence with passive safety injection systems (hydro-accumulators), in order to investigate the capabilities of ASTEC to model the physical phenomena during the in-vessel phase of such a transient.

An investigation on a SBO scenario with primary side depressurization has been carried out. The code results show delayed RPV failure by depressurization of the primary side, as slowing the core damage would allow more time for systems to be recovered to mitigate or terminate the accident. This would give more time and different possibilities for operator interventions.

Die kombinierte Implantation von Fluor und Silizium in die Werkstoffoberfläche von TiAl-Legierungen kann deren Oxidationsbestähigkeit im Temperaturbereich von 750 bis 1100°C an Luft gegenüber unbehandelten TiAl-Legierungen deutlich erhöhen. Die Implantation kann durch verschiedene Verfahren, einmal die Beamline-Ionenimplantation (BLII) oder die Plasma-lmmersion-Ionenimplantation(PlII,PI3), erfolgen. Entgegen dem bisherigen Kenntnisstand, wo nur reine Halogene imlantiert wurden, lassen sich durch die Kombination von Fluor und Silizium bessere Ergebnisse als bei reiner Fluorimplantation erzielen.

Hydrophilic oxybathophenanthroline dendrons (generation 1 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding bromo-functionalized etheraryl branching units containing triethylene glycol monomethyl end groups. Radiotracer experiments using ⁶⁴Cu prove the rapid formation of stable copper(II) complexes in aqueous solution. These ⁶⁴Cu complexes remain unchanged even upon addition of a high excess of glutathion as competing ligand, thus demonstrating the high stability of the formed copper(II) complexes. Electronic and EPR spectroscopy indicate the formation of [Cu(L)₂(OH₂)₂]²⁺ (L = Ligand) complexes in aqueous solution, confirmed by time-resolved laser fluorescence spectroscopy and supported by molecular mechanics modeling.

The antiproliferative activity screening on human tumor cell lines of a series of modified uracil and cytosine bases as well as some corresponding acyclonucleotides, and comparison of structure-activity relationship revealed the importance of chemical reactivity of the substituent attached to the C5-position of uracil for the activity of studied compounds. Namely, the results obtained for the most active compounds, 5-(chloroacetylamino)uracil (2) and its acyclic sugar analogue 18, suggest that formation of a covalent bond between reactive substituent and several possible targets within the thymidylate synthase mechanism (sulphur of the cysteine residue, basic part of the enzyme, N,N-methylene tetrahydrofolate or its reactive iminium forms) is the most probable mode of action. In addition, novel C5-substituted uracil derivative 6 (5-[bis-(2-p-methoxybenzylthioethyl)amine]-acetylaminouracil) exhibited high antiproliferative activity against HeLa and MiaPaCa-2 cell lines, by an as yet unknown mechanism.

Ion implantation in Ge is studied at energies and doses relevant for application to advanced modern devices, such as CMOS transistors. Shallow donors like P typically have high diffusivity and low activity in view of the formation of shallow, low-resistance junctions. Similarly to the Si case, co-doping with non-dopant elements (N in this study) and advanced annealing techniques, such as FLA annealing, can provide a viable route to significantly improve the trade-off of n-type Ge junctions.
Residual implant-induced defectivity, which can be a source of enhanced diffusion and generation currents in Ge diodes, seems to remain up to temperatures (≥ 500 oC) important for activation of dopants in Ge.
However, once the thermal budget is optimized for implant damage removal, the Ge diode leakage may be dominated by surface generation currents, due to a high density of surface states, not efficiently reduced by current passivation schemes.

Seventy years ago Meyer and Neldel investigated four polycrystalline n-type conducting ZnO rods [W. Meyer and H. Neldel, Z. Tech. Phys. (Leipzig) 12, 588 (1937)]. The specific conductivity increased exponentially with temperature. A linear relationship between the thermal activation energy for the specific conductivity and the logarithm of the prefactor was observed. Since then thermally activated processes revealing this behavior are said to follow the Meyer-Neldel (MN) rule. We show that the emission of charge carriers from deep electron traps in ZnO follows the MN rule with the isokinetic temperature amounting to 226±4 K.

There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of preocessing in the millisecond or nanosecond range. This was recently driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This talk reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with other groups and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that short time thermal processing features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century - as a completely different world of materials processing!

This presentation show an overview about the research at the IRC, in particular about the investigations of the biochemical interactions of actinides with microorganisms and plants.

Changes in the archaeal community of a uranium mining waste pile, called Haberland caused by the addition of uranyl or sodium nitrate were investigated by using the 16S rRNA gene retrieval. The natural archaeal diversity in studied environment was limited to only a few lineages of mesophilic Crenarchaeota, predominantly of subgroup 1.1a. Addition of and subsequent incubation with uranyl nitrate for 4 weeks resulted in a significant shifting of the archaeal populations to the soil/sediment cluster 1.1b of Crenarchaeota. The proliferation of the latter populations occurred independently of the amount of the added uranium and the aeration conditions during the incubation. The same shifting of the archaeal populations was also observed in the parallel control samples which were supplemented with sodium nitrate.
Efforts to culture members of the 1.1b Crenarchaeota resulted in their enrichment together with representatives of Firmicutes, mainly of Clostridium spp. Clostridia can effectively interact with uranium and they can also fermentatively reduce nitrate to ammonium. Because an ammonia oxidizing activity was deduced on the basis of meta-genomic analyses of the closest relative to the stimulated in our case 1.1b populations, we speculate that the clostridia possibly supply the crenarchaeal members of the recovered synergetic consortium with ammonia.