Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The report gives an overview on the activities of the Institute ofBioinorganic and Radiopharmaceutical Chemistry in 2003.

The remediation of former uranium mining and milling sites of Saxony and Thuringia requires, amongst others, the purification of uranium contaminated seepage and mine waters. For this, predominantly conventional water treatment methods (precipitation, flocculation) are applied.
We developed an alternative method for the separation of uranium(VI) from aqueous solution. For this, a uranophile calix[6]arene (p-tert-butyl-calix[6]arene hexacarboxylic acid) is permanently immobilized onto textile material (polyethylene terephthalate fabric) via spacer groups [1]. Calixarenes are macrocyclic molecules formed by 4, 6 or 8 para-substituted phenolic units linked by methylene bridges ortho-positioned to the OH functions. Thus, molecules of various ring sizes are formed. The substitution of calix[6]arenes on the hydroxyl group by carboxylic and hydroxamic groups, respectively, leads to ligands that are able to bind uranium(VI) selectively.
In the present work, the uranium(VI) binding onto the calixarene modified textile is studied as a function of pH value and initial uranium concentration in the absence and presence of competing ions by means of batch experiments. Furthermore, the kinetics of the uranium binding is studied as well as the possibility for remobilization of the bound uranium.
The results have shown, that the calixarene modified textile is suitable for the separation of uranium(VI) from aqueous solution at pH values higher than 4. Maximal 7.6x10-7 mol uranium per 1 g of the calixarene modified textile is bound at pH 5. The influence of competing ions (sodium, potassium, calcium, magnesium, carbonate and sulfate) on the uranium separation at pH 5 is very small. At pH 7 in carbonate rich waters calcium ions have a competing effect. Under environmentally relevant pH conditions (near-neutral pH range) the uranium is strongly bound to the calixarene modified textile and cannot be mobilized. Under acidic conditions an almost complete regeneration of the calixarene modified textile is feasible. The regenerated textile filter material can be utilized for further uranium separation cycles.
In dependence on the specific requirements on-site the textile filter material can be used in batch or column operation. Especially for smaller remediation objects and for objects with lower contamination levels ([UO22+] = 1×10-6 M) this method provides a lower cost alternative to conventional water treatment methods. The applicability of this separation principle to further actinides is expected.

[1]Schmeide, K., Heise, K.H., Bernhard, G., Keil, D., Jansen, K., Praschak, D.: Uranium(VI) separation from aqueous solution by calix[6]arene modified textiles. J. Radioanal. Nucl. Chem. 261 (1), 61-67 (2004).

Recently, a plasma with energetic deuterons has been produced in the Gas Dynamic Trap (GDT) experiment under skew injection of 4 MW, 15-17 keV deuterium neutral beams. The GDT is a long, axially symmetric magnetic mirror device with a high mirror ratio. The deuterium neutral beams have been injected at the midplane of the device under 45o to the axis. High anisotropy of the fast ion angular distribution results in a strong peaking of the fast ion density at the turning points near the end mirrors. The axial profile of DD fusion product fluxes has been measured and found to be strongly peaked in the same regions. The characteristics of the profiles are consistent with the classical mechanism of fast ion relaxation caused by two-body Coulomb collisions with plasma particles. This observation validates an approach used in a GDT based neutron source, in which the regions of high neutron flux would be surrounded by the testing zones for fusion material irradiations.

This paper is concerned with laboratory studies using liquid metals with Tmelt £ 300°C to model realistic processes. Considering three selected examples the main features of such cold models are described. In the first instance we examine an aluminium alloy investment casting process. The request to reduce the high flow velocities was served by the installation of a d.c. magnetic field. Local velocity measurements as well as integrated flow rate determination have been carried out utilizing eutectic InGaSn (Tmelt = 10°C). As a second example, model experiments on the electromagnetic stirring of liquid metals have been performed in a cylindrical cavity. We applied a rotating (RMF) and a travelling magnetic field, and recorded flow maps by means of the ultrasonic Doppler velocimetry. With the goal of an efficient 3D-mixing first measurements with promising results were done for the combination of both field types. Third, we report on systematic studies of the impact exerted by a RMF on the solidification of a PbSn alloy. Directional solidification experiments demonstrate the influence of the electromagnetically driven convection on the resulting microstructure.

Magnetic fields provide an attractive possibility of a tailored flow control for metallurgical and crystal growth processes. The following examples will be presented:

-the application of a specially shaped steady magnetic field in the melt extraction process of thin metallic fibers,
-the control of the flow filling process in the investment casting of aluminum alloys,
-the stabilization of electromagnetically levitated droplets,
-the magnetic field control of the Czochralski growth of single crystals of silicon.
The role of model experiments and the development of velocity measuring techniques for metallic melts will be stressed.

This study presents a numerical stability analysis of a flow of electrically conducting liquid driven by a rotating magnetic field in a cylindrical container. The aim of the work is to investigate the previously often neglected effect of the strength of the rotating magnetic field on the stability of the flow driven by the field. Linear hydrodynamic stability analysis has been carried out by Chebyshev-tau and Galerkin spectral numerical methods. We find that the strength of the rotating magnetic field has a stabilizing effect on the flow. The obtained results may be of practical relevance for certain semiconductor growth technologies from the melt.

For an MRI experiment with some liquid metal the possibilities for velocity measurements should be taken into account from the beginning. We present a summary of such measuring techniques, mainly focussing on local potential probes and the ultrasonic Doppler velocimetry. The latter is especially attractive as it provides a full velocity profile along the ultrasonic beam. The possibility of a full 3D velocity tomography, recently shown in a demo experiment, will also be discussed.

The mould filling process of aluminum investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. Several types of filters are already in use for the purpose of inclusion filtering but velocity reduction, too.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical calculations were performed to simulate the filling process and the effect of the magnetic field. The free surface problem which occurs in the riser of the casting unit was taken into account by a Volume-of-Fluids Method. 3d transient calculations using the commercial finite- element code FIDAP (FLUENT Inc.) were carried out for a simplified model system as well as for the real aluminum casting unit. The term for the electromagnetic force was implemented into the code via a user defined subroutine, and an additional equation for the electrical potential was solved. End effects due to the limited size of the magnet poles were taken into account. In that way, results from three-dimensional transient simulations of the filling process were obtained.
Parallel to the simulations model experiments have been performed using the low melting eutectic InGaSn. The casting unit was modelled by a plexiglas model [1]. The ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model [2]. Such measurements delivered the basis to validate the numerical calculations. A comparison between numerical and experimental results showed an excellent agreement, allowing scaling up the simulations to the realistic aluminium casting process.
Real tests have been performed at an industrial investment caster with molten aluminium. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly shown. In a second set of experiments the amplitude of the DC field was tuned during the process. At the beginning the maximum braking force was applied, whereas the field strength was reduced with increasing fluid level in the casting unit. In this regime, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time.

REFERENCES

[1] S. Eckert, G. Gerbeth, A. Cramer, B. Willers, W. Witke, V. Galindo, Liquid metal model experiments on casting and solidification processes, Proc. Int. Symposium on liquid metal processing and casting, Eds.: P.D. Lee, A. Mitchell, J.-P. Bellot, A. Jardy, (2003), 333-343.
[2] S. Eckert, G. Gerbeth, T. Gundrum, F. Stefani, W. Witke, New approaches to determine the velocity field in metallic melts, EPM 2003, Lyon, Proceedings PL13 (2003).

For compensation of transverse emittance in normal conducting RF photoelectron guns a static magnetic field is applied. In superconducting RF guns the application of a static magnetic field is impossible. Therefore we put instead of a static field a magnetic RF field (TE-mode) together with the corresponding accelerating mode into the superconducting cavity of the RF gun. For a 3-cell cavity of the superconducting gun with frequencies f = 1.3 GHz for the accelerating mode and f = 3.9 GHz for the magnetic mode an a bunch charge of 1 nC a transversal emittance of 0.5 mm mrad has been obtained. In this case the maximal field strength on the axis were Ez = 50 MV/m for the accelerating mode and Bz = 0.34 T for the magnetic mode (this corresponds to Bs(max) = 0.22 T on the surface of the cavity). Possibilities for the technical realization (input of RF power for the TE mode, tuning of two frequencies in one cavity, phase stability) are discussed.

After sucessful tests of an SRF gun with a superconducting half-cell cavity (*), a new SRF photo-injector for CW operation at the ELBE linac has been designed. In this report the design layout of the SRF photo-injector, the parameters of the superconducting cavity and the expected electron beam parameters are presented. The SRF gun has a 3 1/2-cell niobium cavity working at 1.3 MHz and will be operated at 2 K. The three full cells have TESLA-like shapes. In the half cell the photocathode is situated which will be cooled by liquid nitrogen.

Measurements carried out in an original-size VVER-1000 mock-up (V-1000 facility, Kurchatov Institute Moscow) were used for the validation of three-dimensional neutron-kinetic codes, designed for VVER safety calculations. The significant neutron flux tilt measured in the V-1000 core, which is caused only by radial-reflector asymmetries, was successfully modeled. A good agreement between calculated and measured steady-state powers has been achieved, for relative assembly powers and inner-assembly pin power distributions. Calculated effective multiplication factors exceed unity in all cases. The time behaviour of local powers, measured during two transients that were initiated by control rod moving in a slightly super-critical core, has been well simulated by the neutron-kinetic codes.

Carbon nitride (CNx) thin films were grown at different substrate temperatures by low-energy (<100 eV) ion beam assistance deposition (LE-IBAD) in order to discern possible formation mechanisms of a fullerene-like (FL) microstructure. The samples were characterized by elastic recoil detection analysis, Raman spectroscopy, spectroscopic ellipsometry, and high-resolution transmission electron microscopy. The results are compared to those of well-structured FL-CNx films synthesized by reactive magnetron sputtering (MS). The comparison yields similar trends for both techniques, such as limitation of the nitrogen content at 20-25 at. %, dominance of sp2 hybrids, as well as thermally activated chemical desorption of CxNy species from the substrate during growth. However, CNx films produced by LE-IBAD are amorphous and, thus, lack FL features. This result correlates with a lower sp2 clustering, attributed to the promotion of nitrile groups. Therefore, low-energy ion bombardment is shown not to be a sufficient condition for the FL microstructure formation. An important difference in the film-forming fluxes between both techniques is the contribution of pre-formed CxNy species from the sputtering target in MS. These species may play a determinant role, serving as precursors for the introduction of FL arrangements during growth.

Hydrogen uptake can potentially enhances the neutron embrittlement of reactor pressure vessel (RPV) steels. This suggests that irradiation defects act as hydrogen traps. The evidence of hydrogen trapping was investigated using the small angle neutron scattering (SANS) method on four RPV steels. The samples were examined in the unirradiated and irradiated state and both in the as-received condition and after hydrogen precharging. Despite the low bulk content of hydrogen achieved after precharging with low current densities, an enrichment of hydrogen in small microstructural defects could be identified. Preferential traps were the microstructural defects in the size range of approx. > 10 nm in the unirradiated as well as in the irradiated samples. However, the results do not show any evidence for hydrogen trapping in irradiation defects.

Cluster production is investigated in central collisions of Ca+Ca, Ni+Ni, ⁹⁶Zr+⁹⁶Zr, ⁹⁶Ru+⁹⁶Ru, Xe+CsI and Au+Au reactions at 0.4 AGeV incident energy. We find that the multiplicity of clusters with charge Z >= 3 grows quadratically with the system's total charge and is associated with a mid-rapidity source with increasing transverse velocity fluctuations. When reduced to the same number of available charges, an increase of cluster production by about a factor of 5.5 is observed in the mid-rapidity region between the lightest system (Ca+Ca) and the heaviest one (Au+Au). The results, as well as simulations using Quantum Molecular Dynamics, suggest a collision process where droplets, i.e. nucleon clusters, are created in an expanding, gradually cooling, nucleon gas. Within this picture, expansion dynamics, collective radial flow and cluster formation are closely linked as a result of the combined action of nucleon-nucleon scatterings and the mean fields.

Das Verhalten einer 3-Punkt-Biegeprobe mit Anriss unter Belastung kann mittels eines Finite-Element-Modells nachgebildet werden. Das Modell ermöglicht die Berücksichtigung von elastisch-plastischem Materialverhalten entsprechend der jeweiligen materialspezifischen Spannungs-Dehnungs-Kurve, welche mit dem Ansatz der multilinearen kinematischen Verfestigung (MKIN) umgesetzt wird. Weiterhin gestattet das Modell die Einbeziehung der realen Rollenkinematik beim Biegevorgang. Für die Beschreibung des Bruchkriteriums wird ein spezielles Damage-Modell verwendet, mit dem man in der Lage ist, das Risswachstums in geeigneter Weise wiederzugeben.
Mit diesem Modell lässt sich auch das Teilentlastungs-Compliance-Verfahren nachbilden. Diese Simulation ermöglicht die Einschätzung von Korrekturansätzen zur experimentellen Risslängenbestimmung über die Compliance-Methode.

The paper deals with the problematic of determination of the crack initiation for three point bend specimens during fracture toughness test of materials in the upper transition and upper shelf region. In the presented study various published methods as Double Clip Gauge Method, Strain Near to Crack Tip Measurement method, Double Displacement Method, Compliance Changing Rate Method, Stretch Width Zone measurement were applied together with the methods using the crack extension vs. crack mouth opening displacement and force vs. displacement for the crack initiation determination. Blunting line based evaluations were also performed and all results were compared. The investigation was carried out on five different steels.

Objective: In an in vitro biosensor model (PCT/ET 97/05212), the interplay between different lipoproteins in arteriosclerotic nanoplaque formation, as well as aqueous garlic extract (0.2-5.0 g/l from LI 111 powder) as a possible candidate drug against arterio/atherosclerosis were tested within the frame of a high throughput screening. Methods: The processes described below were studied by ellipsometric techniques quantifying the adsorbed amount (nanoplaque formation) and layer thickness (nanoplaque size). A thorough description of the experimental setup has been given previously. Results: Proteoheparan sulfate (HS-PG) absorption to hydrophobic silica was monoexponential and after approximately 30 min constant. The addition of 2.52 mmol/l Ca²⁺ led to a further increase in HS-PG adsorption because Ca²⁺ was bound to the polyanionic glycosaminoglycan (GAG) chains thus screening their negative fixed charges and turning the whole molecule more hydrophobic. Incubation with 0.2 g/l aqueous garlic extract (GE) for 30 min did not change the adsorption of HS-PG. However, the following addition of Ca²⁺ ions reduced the increase in adsorption by 50.8 % within 40 min. The adsorption of a second Ca²⁺ step to 10.08 mmol/l was reduced by even 82.1 % within the next 40 min. Having detected this inhibition of receptor calcification, it could be expected that the build-up of the ternary nanoplaque complex is also affected by garlic. The LDL plasma fraction (100 mg/dl) from a healthy probationer showed beginning arteriosclerotic nanoplaque formation already at a normal blood Ca²⁺ concentration, with a strong increase at higher Ca²⁺ concentration. GE, preferably in a concentration of 1 g/l, applied acutely in the experiment, markedly slowed down this process of ternary aggregational nanoplaque complexation at all Ca²⁺ concentrations used. In a normal blood Ca²⁺ concentration of 2.52 mmol/l, the garlic induced reduction of nanoplaque formation and molecular size amounted to 14.8 % and 3.9 %, respectively, as compared to the controls. Furthermore, after ternary complex build-up. GE similar to HLD, was able to reduce nanoplaque formation and size. The incubation time for HDL and garlic was only 30 min each in these experiments. Nevertheless, after this short time the deposition of the ternary complex decreased by 6.2 % resp. 16.5 %, i.e. the complex aggregates were basically resolvable. Conclusions: These experiments clearly proved that garlic extract strongly inhibits Ca²⁺ binding to HS-PG. In consequence, the formation of the ternary HS-PG/LDL/Ca²⁺ complex, initially responsible for the nanoplaque´composition and ultimately for the arteriosclerotic plaque generation, is decisively blunted.

Colloid-borne Heavy Metals in the Drainage Gallery of an Abandoned Zn-Pb-Ag Mine (in German). The colloid inventories and the colloid-borne heavy metals in the Rothschönberger Stolln adit, the main drainage gallery of the Freiberg, Germany, mining district, were investigated. This adit runs from Freiberg to the village of Rothschönberg, where it flows into the river Triebisch, a tributary of the river Elbe. The water of the adit is a typical mine water from a flooded ore mine. The main reason for choosing the Rothschönberger Stolln adit for colloid investigations was that ample knowledge concerning the origin of the water and the geology of its catchment area exists. The aim was to characterize the colloids at the mouth of the adit and to elucidate if important contaminants occur in a colloid-borne form. A colloid concentration of about 1 mg/L was found. The particles have a size of 50 to 150 nm. They primarily consist of iron and aluminum oxyhydroxide and carry trace elements such as Pb, As, Cu, Y, La. The contaminants Pb and As are almost entirely colloid-borne. Colloids can have both a retarding and a stimulating influence on the transport of contaminants. The existence of colloids should be taken into account if mine waters flow to the biosphere or if mine waters are to be purified by permeable reactive barriers.

The core baffle of a PWR is loaded by the pressure difference between bypass and core and by temperature profiles originating from gamma and neutron heating and heat transfer into the coolant. Strain, deformation and gaps between the core baffle sheets resulting from this load are determined considering the effect of neutron irradiation induced creep of the core baffle bolts. The finite element code ANSYS® is applied for the thermal and mechanical analyses. The FE-model comprises a complete 45° sector of the core baffle structure including the core barrel, the formers, the core baffle sheets and about 230 bolt connections with non-linear contact between the single components and the effect of friction. The complete analysis requires three major steps:

· Evaluation of the three dimensional distribution of neutron flux and gamma induced internal heating
· Calculation of the temperature distribution in the core baffle
· Calculation of time dependent deformation, stresses and strains
The results show the equalizing effect of redistribution of bolt loads from high flux to lower flux exposure locations in a self controlled process, keeping the mechanical and geometrical stability of the core baffle structure and leaving the gaps between sheet edges unaffected.

In Eulerian-Eulerian modeling of multiphase flow, closure models are needed for interfacial forces. The present work was concentrated on the non-drag forces, namely the lift, virtual mass, turbulent dispersion and wall lubrication force. They are reported to be mainly responsible for the gas volume fraction distribution in a vertical bubbly flow. Different models were proposed in the literature for each of these forces. In this work, we implemented a number of non-drag force models in the Eulerian multiphase flow package of the commercial code CFX-5.6 in order to enhance its application range. Extensive numerical experiments were carried out in order to examine their numerical properties (convergence characteristics, grid dependence of the results) and to
evaluate their validity. The evaluation was based on the experimental database for upward air-water flows in a vertical pipe established at Forschungszentrum Rossendorf (FZR) using the fast wiremesh sensor measurement technique. In all simulations a zero-equation model was used for the dispersed phase whereas two different turbulence models, namely the $k$-$\varepsilon$ and SST model, were investigated for the liquid phase. The bubble induced turbulence was taken into account by the Sato model. Fairly good agreements were observed between the numerical solutions and measurements for all test cases when the SST model was chosen together with the Tomiyama correlations for the lift and wall lubrication force and the {Favr\'e}-Averaged Drag (FAD) model for the turbulent dispersion force due to Burns (2001). The results clearly show the advantage of the FAD model over the widely applied model by Lopez de Bertodano et al.(1994). In addition, the investigation also indicates that further efforts in multiphase phase flow turbulence modeling and in near-wall treatment are very necessary.

A comparative study of clustering of sp² -bonded atoms in the as-deposited and annealed diamond-like amorphous carbon (DLC) films is presented. The as-deposited DLC with a grown-in compressive stress of ~10 GPa is modelled using amorphous networks generated by ion-beam film deposition simulations with a modified hydrocarbon potential of Brenner. The DLC networks were annealed in the temperature range of 600-2000 K, using molecular-dynamics with the same interatomic potential. The size and type of the sp² clusters were analysed as a function of the annealing temperature and simulation parameters. An essential finding of this study is that at the density less than 3.0 g/cm³ the structure of DLC can become unstable with respect to formation of large sp² clusters. In particular, molecular-dynamics simulations show how the small sp² clusters coalesce, forming the large ones. The influence of the sp² clustering on the mechanical properties of DLC is also discussed.

The hypothetical scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a light water Reactor Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the containment. To obtain an improved understanding and knowledge of the melt pool convection thermal loads, the vessel creep, and vessel failure modes occurring during the late phase of a core melt down accident the FOREVER-experiments have been performed at the Royal Institute of Technology, Stockholm. These experiments simulated the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurised vessel scenario.
Due to the multi-axial creep deformation of the vessel with prototypic non-uniform temperature field these experiments are on the one hand an excellent source of data to validate numerical creep models that are developed on the basis of uniaxial creep tests and on the other hand they provide reasonably accurate insights into the course of a prototypic accident in which vessel failure may occur.
A Finite Element model was developed simulating melt pool convection and calculating the temperature field within the melt pool and within the vessel wall. The transient structural mechanical calculations are then performed applying a creep model, which takes into account the large temperature, stress and strain variations.
After performing successful pre- and post-test calculations, a discussion about the lessons learned from the experiments and the analyses led to the idea of providing a vessel support and an external water-flooding device.

Amorphous carbon (a-C) film deposition was studied theoretically by molecular-dynamics simulations in the temperature range of 100-873 K. For each temperature the simulations yield a mixture of sp² and sp³ hybrids, which allows for the sp² and sp³ fractions, and size and type of the sp² clusters to be calculated. In parallel, the bonding structure of a-C thin films prepared by filtered cathodic vacuum arc (FCVA) at different substrate temperatures was analysed by x-ray absorption near edge spectroscopy (XANES) and Raman techniques. In addition, the optical properties of these films were determined from spectroscopic ellipsometry (SE).

Both, theory and experiment, show a transition from diamond-like to graphite-like films as the substrate temperature exceeds a certain threshold, in agreement with previous observations. The evolution of the sp² clusters, as defined by the number of consecutive sp² atoms, and of sp² sites rings with substrate temperature was computed from the simulated films. The results indicate an increase of sp² clustering with temperature and a pronounced promotion of six to ten membered rings for substrate temperatures above the transition threshold. The further formation of these rings above the transition temperature does not correlate with the sp² content and suggests an in-situ sp² rearrangement process during deposition. The evolution of the sp² networks predicted by the simulations will be contrasted with the data from the XANES and Raman investigations. Finally, the correlation of sp² arrangement and of observed optical properties will be discussed.

Neutron and gamma fluence calculation results of participants of the REDOS project for the VVER-1000 mock-up at the LR0-reactor in Rez had been compared between themselves and with measured data. 11 fluence spectrum integrals and neutron and gamma DPA-values obtained independently by 6 participants from 4 countries were included into the comparison. For fast neutrons mostly excellent agreement between participants results and with experimental data was reached. For thermal neutrons and photons the agreement was much worse.

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An analysis of experimental data consisting of isotopically resolved spallation products from 1 GeV proton-necleus interactions with targets from Fe to Cd is presented. It was found that the yield ratios of isotopes classified by the difference of the neutron numbers are compatible with relations derived in the grand canonical approach. The independence of isotopic temperatures on the target mass was demonstrated for spallation products. An 'unified' isoscaling is proposed which takes into account different nucleonic compositions of the emitting sources. Modified isoscaling parameters are proposed and their physical meaning is discussed.

Using symmetric ¹¹²Sn + ¹¹²Sn, ¹²⁴Sn + ¹²⁴Sn collision as references, we probe isospin diffusion in peripheral asymmetric ¹¹²Sn + ¹²⁴Sn, ¹²⁴Sn + ¹¹²Sn systems at incident energy of E/A = 50 MeV. Isoscalic analyses imply that the quasi-projectile and quasi-target in these collisions do not achieve isospin equilibrum, permitting an assesment of the isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical obstacles, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.

It has been proposed to investigate the magnetorotational instability at a large scale liquid sodium facility. This sort of laboratory astrophysics is encouraged by the recent successful dynamo experiments. We report on our experiences with the Riga dynamo experiment where magnetic field self-exciation is achieved in a cylindrical vessel filled with approximately 2 qm of liquid sodium which can reach flow velocities up to 20 m/s. The main experimental results on the kinematic and the saturation regime are compared with numerical modelling. Some focus is also laid on the technical design of the facility and the measurement instrumentation.

The experimental demonstration of MRI in a liquid sodium Taylor-Couette experiment might be hampered by sealing problems at the two end plates whose sophisticated design could be crucial to avoid non-linear instabilities. Thus motivated, we consider alternative flow configurations with respect to their suitability to show MRI. First results for flows that are driven by azimuthal pressure gradients (Dean flows) and for combinations with Couette flows (Taylor-Dean flows) are presented. The influence of an axial magnetic field on the stability of Dean and Taylor-Dean flows with arbitrary gap spacing between the cylinders is considered. For Dean flows with magnetic Prandtl number equal to one it is found that, similar to the result for the Taylor-Couette flow, a significant decrease of the critical Reynolds number occurs for intermediate Hartmann numbers. This MRI is more pronounced for small values of the ratio of the radii of the inner and outer cylinder. For Taylor-Dean flows the onset of the instability in dependence on the ratio of azimuthal pressure gradient and cylinder rotation is investigated.

High-spin states of ⁹⁵Ru have been populated using the ³⁵Cl+ ⁶⁴Zn reaction at a beam energy of 135 MeV. In a recoil-distance Doppler-shift experiment, the lifetimes or lifetime limits of 26 high-spin states have been measured, giving information on a total of 49 reduced transition strengths. The results are compared with shell-model calculations with different model spaces and residual interactions. Several families of states with defined proton and neutron seniorities are proposed. The M1 strengths in the negative-parity yrast sequence show a pronounced staggering which is reproduced by the shell-model calculations.

Momentum and mass transfer during copper electrolysis in a small cell can be significantly influenced by Lorentz forces. Depending on the magnetic field configurations, a multitude of flow fields with an accordingly large range of mass transfer conditions can be arranged. The moderate magnetic field of simple permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. The interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10−6 M U(VI) showed one silicon atom at a USi distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O)2UO2, on the silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO4, resulting in surface material similar to amorphous silica gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex.

Apart from chemical and physical factors influencing mobility of radionuclides, microbial metabolism also plays a decisive role in enhancing or retarding migration effects. Bacteria are able to reduce or oxidize metals and also to accumulate and bind them. In this work biosorption of U by cells, spores and S-layers of a U mining waste pile isolate Bacillus sphaericus JG-A12 was investigated. Furthermore, these three bacterial structures were used for construction of porous biocomponent-silicate hybrids referred to as biological ceramics (biocers) for bioremediation. The results show the highest binding capacity for the spores followed by the cells and the S-layer sheets. The silicate matrix itself binds only small amounts of U. Sol-gel encapsulation does not affect the U binding properties of the cells or the S-layer sheets but strongly reduces the binding capacity of the spores. Spectroscopic analyses of the U complexes demonstrate that U is bound to phosphate and carboxyl groups of the biocomponents and to silanol groups of the silicate matrix.

This work deals with on-line monitoring of exothermic chemical processes in stirred tank reactors. To support the personnel in the efficient and safe operation of batch processes, the monitoring system (MoSys) based on heat/mass balancing was developed. A model was implemented for estimating concentrations from heat/mass balances. Dimensionless balances with adaptive parameters were used to adapt the heat/mass balances to the chemical target reactor and to realise the scale-up. For industrial testing, MoSys was integrated in a batch-information-management system (BIMS), which was also developed and implemented in the process control system of a multipurpose reactor installation. As a result, the outputs of MoSys can simultaneously be visualised with important process signals on terminals of the process control system. Operational experiences in monitoring an industrial hydrogenation process are represented.

The HADES dielectron spectrometer has recently launched its physics program at the heavy ion synchrotron SIS at GSI Darmstadt. The spectroscopy of vector mesons in heavy ion collisions via their dielectron decay channels makes great demands on the HADES tracking system regarding acceptance and spatial resolution. It is formed out of 24 low-mass, trapezoidal multi-layer drift chambers providing about 30 m² of active area. Low multiple scattering in total four planes of drift chambers before and after the magnetic field is ensured by using Helium-based gas mixtures and aluminum cathode and field wires. First in-beam performance results will be contrasted with expectations from simulations. Emphasis is placed on the energy loss information, exploring its relevance regarding track recognition.

Monte Carlo methods are actually the best tools to perform the detailed dosimetric and radiobiological calculations required in conformal radiotherapy. In this work we focus our attention on the FLUKA simulation program and on the electronic stopping power calculationsfor protons and alpha particles in materials of interest for therapy. We discovered large inaccuracies (>10%) with respect to the values suggested by ICRU (standard reference) for protons in compounds and alpha particles both in elements and compounds below 1 MeV/amu. These deviations, due to the standard approach based on additivity and scaling rules, could indeed affect radiobiological evaluations for primary charged hadron and neutron beams. Therefore we developed new algorithms based on proper parametric formulae and inserted them in the FLUKA code. The new approach allows an agreement with ICRU data much better than 1% in the entire energy range 1 keV-100 MeV/amu spanned by the old one.

The PGE content of liquid magmatic Ni-Cu(-PGE) sulfide mineralization in the Lusatian anticline has been known since the early 20th century. The mineralization occurs only in vein- or stock-like intrusive bodies of gabbroic, dioritic or noritic composition. Mineralization consisting mainly of pyrrhotite, pentlandite and chalcopyrite probably results from gravity segregation of an exsolved sulfide melt. Sulfides occur in general near the contacts of the intrusions. Different types of ore textures can be distinguished. Besides extensive fieldwork at numerous exposures, microscopic, geochemical, and semiquantitative microanalysis was carried out to characterize the sulfide mineralization and the PGE phases. These contain, beside Pt and Pd, remarkable amounts of Sb, Te, Hg and As. The Lusatian Ni-Cu(-PGE) mineralization is genetically similar to Norilsk-Talnakh-type ore deposits.

We present a unique parameterization of the equation of state of strongly interacting matter in the temperature interval 0.6 T_c \cdots 3 T_c at \mu = 0 within a quasi-particle model based on quark and gluon degrees of freedom.
The extension to non-vanishing baryon-chemical potential is discussed.

The production of the light vector mesons V =ρωφ in the reactions πN → V N and N N → V N N near threshold is studied. The subsequent electromagnetic decay V → γ^* → e^+ e^- is particularly suited for exploring subthreshold ωN resonances.

Nanostructuring of metallic and semiconductor surfaces in the sub-100 nm range is a key point in the development of future technologies. In this work we describe a simple and low-cost method for metal nanostructuring with 50 nm lateral and 6 nm vertical resolutions based on metal film deposition on a silane-derivatized nanostructured silicon master. The silane monolayer anti-sticking properties allow nanopattern transfer from the master to the deposited metal films as well as easy film detachment. The method is non-destructive, allowing the use of the derivatized master several times without damaging. Potential applications of the method are in the field of high-density data storage, heterogeneous catalysis and electrocatalysis, microanalysis (sensors and biosensors) and new optical devices.

The β decay of ⁹⁴Ag, a nucleus with three proton and three neutron holes with respect on ¹⁰⁰Sn, was investigated at the GSI on-line mass spectrometer by using an array of germanium and silicon detectors. On the basis of an β γ γ coincidence measurement, the previously reported decay scheme has been considerably improved and evidence is presented for a spin-gap isomer with a spin-parity assignment of (21⁺), i. e., the highest spin ever observed in β decay. The half-life of the low spin-spin isomer (7⁺) was remeasured to be 0.59(2) s, whereas the half-life of the high-spin isomer was determined as 0.47(8) S. For the states in ⁹⁴Ag and ⁹⁴Pd, large-scale shell-model calculations that include up to 4p-4h excitations across the N = Z = 50 shell gap and employ a realistic interaction were carried out. These core excitations play a crucial role in generating the E4 isomerism required for the interpretation of th long half-life of the (21⁺) state in ⁹⁴Ag.

To perform transient analysis for Molten Salt Reactors (MSR), the reactor dynamics code DYN3D developed in FZR was modified for MSR applications. The MSR as a liquid fuel system can serve simultaneously as an actinide burner and a thorium breeder. The specifics of the reactor dynamics of MSR consist in the fact, that there is direct influence of the fuel velocity to the reactivity, which is caused by the delayed neutrons drift. This drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit. This leads to the reactivity loss due to the fuel acceleration or to the reactivity increase in the case of deceleration.
For the first analyses, a 1D modified version DYN1D-MSR of the code has been developed. By means of the DYN1D-MSR, several transients typical for the liquid fuel system were analyzed. Transients due to the overcooling of fuel at the core inlet, due to the reactivity insertion, and the fuel pump trip have been considered. The results of all transient studies have shown that the dynamic behavior of MSR is stable when the coefficients of thermal feedback are negative.
For studying space-dependent effects like e.g. local blockages of fuel channels, a 3D code version DYN3D-MSR will be developed. The nodal expansion method used in DYN3D for hexagonal fuel element geometry of VVER can be applied considering MSR design with hexagonal graphite channels.

Computation of the shape of etch pits needs to know the varying track etch rate along the particle trajectories. Experiments with alpha particles and 7-Li ions entering CR-39 detectors under different angles showed that this function is not affected by the inclination of the particle trajectory with respect to the normal on the detector surface. Track formation for oblique particle incidence can, therefore, be simulated using the track etch rates determined for perpendicular incidence. 3D computation of the track shape was performed applying a model recently described in literature. A special programm has been written for computing the x, y, z coordinates of points on the etch pit walls. In addition, the etch pit profiles in sagittal sections as well as the contours of the etch pit openings on the detector surface have been determined experimentally. Computed and experimental results were in good agreement confirming the applicability of the 3D computational model in combination with the functions for the depth-dependent track etch rates determined experimentally.

The project aims at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity. Measurement data from a set of mixing experiments, gained by using advanced measurement techniques with enhanced resolution in time and space help to improve the basic understanding of turbulent mixing and to provide data for Computational Fluid Dynamics (CFD) code validation. Slug mixing tests simulating the start-up of the first main circulation pump are performed with two 1:5 scaled facilities: The Rossendorf coolant mixing model ROCOM and the VATTENFALL test facility, modelling a German Konvoi type and a Westinghouse type three-loop PWR, respectively. Additional data on slug mixing in a VVER-1000 type reactor gained at a 1:5 scaled metal mock-up at EDO Gidropress are provided. Experimental results on mixing of fluids with density differences obtained at ROCOM and the FORTUM PTS test facility are made available.
Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests (Sizewell-B for PWRs, Loviisa and Paks for VVERs) are used together with the data from the ROCOM facility as a basis for the flow distribution studies. The test matrix on flow distribution and steady state mixing performed at ROCOM comprises experiments with various combinations of running pumps and various mass flow rates in the working loops.
Computational fluid dynamics calculations are accomplished for selected experiments with two different CFD codes (CFX-5, FLUENT). The applicability of various turbulence modelling techniques is studied for transient and steady state flow. Best practice guidelines (BPG) are referenced in all CFD work when choosing computational grid, time step, turbulence models, modelling of internal geometry, boundary conditions, numerical schemes and convergence criteria. The strategy of code validation based on the BPG and a matrix of CFD code validation calculations have been elaborated. The computational grid generation for the test facilities and first calculations on the benchmark tests have been performed.

Plasma immersion ion implantation (PIII) has been used to modify the surface properties of 304 austenitic stainless steel (AISI). The influence of working gas pressure, 0.2 - 1.0 Pa, and substrate temperature, 300 - 500 oC, on the microstructure, treating rate, nitrogen/carbon concentration depth profile, and surface microhardness was investigated. A gas composition of 25 % C2H2, 75 % N2, rf plasma power input of 350 W, and a negatively biased potential of 30 kV were fixed during the experiment. The experimental results show that the substrate temperature and the diffusion process of nitrogen and carbon depend on gas pressure inside the plasma chamber. The thickness of the modified layer has been found to be more than 30 µm after 60 minutes plasma processing time. The results provide recent values of diffusion coefficient and surface microhardness are 3.4 x 10-1 µm2/sec and 1880 kg/mm2 respectively.

Colloids of some nanometers in size are interesting for the transport of contaminants in natural waters because of their high specific surface. Optical and acoustic detection of plasmas induced by laser pulses on individual particles allows determining of size and concentration of smallest colloids in the ppt-range. The apparatus for laser induced breakdown detection established in the Institute of Radiochemistry at FZR is described. First results of measurements on particle standards, de-ionized waters and nearly colloid-free environmental samples are presented.

Poster - kein Abstract

Bacteria, ubiquitous in all aquatic and soil systems, can interact in many ways with actinides. They can mobilize or immobilize actinides in the environment, leading to their dissolution or precipitation. Knowledge of bacteria-actinide interactions is important for understanding the migration behaviour of the latter in the biogeosphere. In this work, a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared (IR) spectroscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) was used to conduct a molecular and atomic analysis of the uranium complexes formed by different bacterial strains isolated from uranium mining waste piles. EXAFS analysis showed that the cells of Stenotrophomonas maltophilia JG-2, Pseudomonas rhodesiae R5 and Myxococcus xanthus precipitate U(VI) as autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, in the case of B. sphaericus JG-A12 the uranium bonding was consistent with the formation of a ternary complex with phosphate and carboxylate. These results are in agreement with those found by Infrared measurements. TEM and EDS analysis showed strain-specific extracellularl and/or intracellularl uranium accumulation to varying degrees. In B. sphaericus JG-A12 the uranium is located at the cell wall, while the cells of S. maltophilia JG-2 and P. rhodesiea R5 accumulate uranium both extracellularly on the cell surface and intracellularly as electron-dense granules.

Zur Dimensionierung von Schutzeinrichtungen und nachgeschalteten Anlagenteilen von Rührkesselreaktoren sowie für die sicherheitstechnische Bewertung unerwünschter Betriebszustände ist die Kenntnis der bei Druckentlastungen ablaufenden hydro- und thermodynamischen sowie reaktionskinetischen Prozesse unabdingbar. Die Qualität der Simulationsergebnisse existierender Computercodes (z. B. SAFIRE/ Vent, BRICK) ist von der Genauigkeit der Untermodelle zur Berücksichtigung von Wärme- und Stofftransport, Reaktionskinetik, Mischphasenthermodynamik sowie Aufwall- und Schaumverhalten abhängig. Reaktionskinetische Modelle zur Simulation von Druckentlastungsprozessen wurden bisher meist auf der Grundlage von Experimenten in adiabatischen Kalorimetern ermittelt. Wie eigene Untersuchungen unter isothermen Bedingungen zeigen, geben diese Formalkinetiken den thermischen Reaktionsverlauf oft nur unzureichend wieder.

Ziel der Arbeiten ist eine Verbesserung der Modellierung der Einzelphänomene unter Berücksichtigung der spezifischen Prozessbedingungen der Druckentlastung. Die Modelle werden in den am FZ Rossendorf entwickelten 1D-Code BRICK eingebunden. Hierdurch soll eine Ertüchtigung des Codes für die Simulation von Druckentlastungsprozessen siedend aufwallender bzw. schäumender reaktiver Stoffsysteme erfolgen.

Als Modellprozess wurde die Veresterung von Essigsäureanhydrid mit Methanol gewählt. Die Modellbildung bzw. –auswahl erfolgt auf der Grundlage isothermer und isoperiboler Experimente im Reaktionskalorimeter RC1, wobei zur Erfassung der Konzentrationsverläufe während der Reaktion, Messungen mit einem In-Situ-FTIR-Spektrometer erfolgen. Die Ausdehnung des Gültigkeitsbereiches der Modelle erfolgt anschließend durch ergänzende Experimente im adiabatischen Kalorimeter PhiTecII. Gleichzeitig werden zur Berücksichtigung thermodynamischer Einflüsse Mischungsenthalpien und Mischleistungsverläufe im RC1 gemessen, modelliert und in das Prozessmodell integriert.
Zur Bewertung von Druckentlastungsprozessen hinsichtlich des Gefährdungspotenzials, verursacht durch aus dem Reaktor austretende Substanzen, ist die quantitative Zusammensetzung des bei der Druckentlastung austretenden Stoffgemisches von entscheidender Bedeutung. Darüber hinaus ist die Kenntnis der Konzentrationen hilfreich zur Validierung der Simulationssoftware und zur Charakterisierung des thermodynamische Zustandes des Reaktionsgemisches zum Zeitpunkt der Druckentlastung. Die Konzentrationsmessungen erfolgen mittels Offline-FTIR, wobei die Gemischzusammensetzungen der ausgetragenen Substanzen unmittelbar nach der Duckentlastung und die Konzentrationen der im Reaktor verbliebenen Gemische ermittelt werden. Hierzu erfolgen Druckentlastungsexperimente im PhiTecII, wobei zum Abstoppen der Reaktion die ausgetretenen Substanzen in ein mit flüssigem Stickstoff gekühltes Quench-Gefäß eingeleitet werden.

Es werden die unter isothermen, isoperibolen und adiabatischen Bedingungen experimentell ermittelten thermischen Reaktionsverläufe und die Konzentrationsverläufe im Vergleich zu den mittels Literaturdaten berechneten und den auf Grundlage des entwickelten Prozessmodells unter Einfluß der Mischungsenthalpie simulierten Daten dargestellt und diskutiert. Weiterhin werden die Methodiken für die Konzentrationsmessungen bei den Druckentlastungsexperimenten vorgestellt und die Messergebnisse diskutiert.

Indium tin oxide films produced by reactive middle frequency dual magnetron sputtering were annealed in vacuum at a constant rate of the temperature enhancement. The film electrical and optical properties have been studied in situ along with direct characterization of the structure. Even in amorphous state the film resistivity significantly decreases at increasing temperature due to a free electron density enhancement likely by oxygen vacancies creation. The rapid crystallization within the temperature range 250-280 °C leads to further decrease of the resistivity due to a Sn donor activation. The resistivity and optical properties depend non-linearly on the crystalline fraction.

In the framework of the EU project VALCO, measurements at the V-1000 test facility of the Russian Research Centre 'Kurtschatov Institute' are used for the validation of three-dimensional neutronic calculations. Experimental results of steady states and kinetic experiments are available for comparisons with calculations. Respective DYN3D calculations have been performed by using the cross section libraries generated with the codes HELIOS, CASMO and WIMS.
Results obtained by the DYN3D code are compared with steady-state measurements for two different configurations of the V-1000 facility. Pin-power distributions measured within one fuel assembly are compared to the results of the pin power reconstruction implemented in DYN3D.
Two kinetic experiments performed in the V-1000 facility were simulated by the DYN3D code. Comparisons of the calculated results with the measurements at the in-core detector positions are given. The calculated fast flux of the nodes, situated near to the ionisation chambers of the two reactimeters, is compared with the detector signal. The results of the relative detector rates coincide with the measurements. The dynamical reactivities are obtained from the core-averaged flux by inverse point kinetics. It is compared with reactivity curves, provided by the two reactimeters.

Die Bibliothek ist die zentrale Stelle für wissenschaftliche Literatur- und Fachinformation des Forschungszentrums Rossendorf. Mit ihren spezifischen Leistungen unterstützt sie die Forschung und trägt damit zur Sicherung der Attraktivität des Forschungsstandortes Rossendorf im internationalen Standortwettbewerb bei. Davon ausgehend werden die neuesten elektronischen Informationsservices dargestellt: Zugang zum "Web of Knowledge" und zu einer Vielzahl elektronischer Zeitschriften im Volltext. Durch Umbau der ehemaligen Buchbinderei im Haus der Bibliothek konnte ein IT-Schulungsraum eingerichtet werden.

Al supersaturated SiC layers (5x10^20 Al cm-3) were produced by multi-energy, high dose ion implantation into 6H- and 4H-SiC. Several implantation schemes with varying implantation sequence and temperature were investigated. In dependence on the implantation conditions damaged single-crystalline, amorphous or nanocrystalline layers were formed. The layer morphology and Al distribution in the as-implanted state as well as structural changes and related Al redistribution after high temperature annealing (1500-1700°C) were characterized by XTEM, RBS/C, AFM and SIMS analysis. Remarkable Al redistribution effects have been found after annealing of Al supersaturated SiC. During high temperature annealing Al atoms in excess to the solid solubility (2x1020 Al cm-3) tend to precipitate in single crystalline SiC whereas they diffuse out in amorphous or nanocrystalline SiC. Redistribution of Al with concentration below the solid solubility is governed by transient enhanced diffusion which can be controlled by the annealing scheme. Amorphization of SiC is advantageous in the case of Al doping to levels higher than the solid solubility because it prevents Al precipitation during annealing and helps to form box-like Al profiles with smooth plateau and abrupt edge.

wird nachgereicht

The application of surface complexation models (SCM) towards real-world problems requires not only a reliable parameter database but also information about the chemical structure of surface species and the crystallographic location of binding sites. This study focused on the sorption behavior the uranyl cation UO₂ ²⁺ on aluminol and silanol groups in model substances for clays, namely gibbsite: γ-Al(OH)₃.
Batch sorption experiments were carried out at an ionic strength of 0.1 M NaClO)₄ and at different pH values with a stepping of 0.5 from 3.5 to 9.5 under air. After a contact time of 2 days in the overhead shaker gibbsite was separated by centrifugation and the uranium contend in the separated solution was measured by ICP-MS. The concentration of uranium adsorbed on gibbsite was calculated in accounting for uranium sorbed on the container wall. The sorption curve indicates a maximum sorption between pH 5.5 and 7.5.
For the spectroscopic investigations with TRLIF (Time-resolved laser-induced fluorescence) the gibbsite from the batch experiments was re-suspended in a solution with pH and ionic strength being identical to the original solution. So it was guaranteed, that the fluorescence signals were only caused from uranium sorbed on the gibbsite, and not from uranium in solution. After a second centrifugation the solution was also measured to ensure the absence of dissolved uranyl species.
The TRLIF spectra, excluding the wavelength range between 525 and 540 nm influenced by the laser dispersion peak, were integrated and then fitted to a sum of exponential decay terms. The best approximation for the fluorescence decay gave a bi-exponential decay function yielding two fluorescence decay times: t)₁. in a range between 200 and 450 ns (this indicates the formation of UO)₂.(OH))³⁺) and t)₂. between 3200 and 7900 ns (indicates UO)₂.(OH))₂.).
The peak maxima (at approximately 498, 521, 543 and 557 nm) differ slightly at varying pH, but do not show systematic shifts. The uranium surface species are therefore assumed to be similar throughout the investigated pH range. They should have identical numbers of hydroxyl groups in their first coordination sphere and differ only in the respective water content. This is valid both for the short lived and the long lived species.

Niedriglegierte ferritische Stähle gelten ebenso wie die hochlegierten austentischen Stähle als anfällig gegen Wasserstoffversprödung. Im Kernreaktor können Korrosion oder Radiolyse zur Bildung von atomaren Wasserstoff an der inneren Oberfläche des Reaktordruckbehälters und folglich zur Wasserstoffaufnahme während des Reaktor-betriebes führen. Werden die als Folge der Bestrahlung entstehenden Strukturdefek-te auch als Wasserstoff-Traps wirksam, sind sicherheitsgefährdende Synergismen zwischen dem Phänomen der Strahlen- und Wasserstoffversprödung nicht auszu-schließen. Frühere Untersuchungen haben gezeigt, dass Wasserstoffgehalte > 2,5 ... 4 ppm eine deutliche Zähigkeitsabnahme bewirken und vor allem hochfeste Zustän-de in diesem Fall bei Raumtemperatur vollständig verspröden.

Mit dem einachsigen Zugversuch wurden die mechanischen Eigenschaften verschie-dener unbestrahlter und vor allem bestrahlter, mit Wasserstoff beladener RDB-Stähle bestimmt. Das Ziel der Untersuchungen bestand darin, einen potenziellen Zusam-menhang von Versprödungseffekten infolge Neutronenbestrahlung und Wasserstoff aufzudecken. Fraktografische Untersuchungen der Bruchflächen ergänzten das Pro-gramm. Mit SANS-Untersuchungen sollte überprüft werden, ob die Strahlendefekte als Haftstellen für den Wasserstoff wirksam werden.
Für die mechanischen Untersuchungen standen T3-Kleinzugproben der RDB-Stähle A 533 B cl.1, A 508 cl.3 und 15Kh2MFA (KAB, Skoda) im bestrahlten und unbestrahl-ten Zustand zur Verfügung. Die Proben wurden elektrolytisch im simulierten Reak-tordruckwasser bis zur Sättigung mit Wasserstoff beladen. Die Zugversuche wurden bei RT und 250°C und verschiedenen Dehnraten durchgeführt.

Das Verformungsverhalten der bis zu hohen Neutronenfluenzen und bei reak-torbetriebsnahen Temperaturen bestrahlten RDB-Stahlmarken bzw. –chargen des Untersuchungsprogrammes wird nicht signifikant durch eine Wasserstoff-vorbeladung beeinflusst. In Übereinstimmung damit liefern auch SANS-Messungen keinen Hinweis auf eine Wechselwirkung zwischen dem strukturellen Strahlendefekt und den Wasserstoffatomen. Die SANS-Methode erwies sich aber als geeignet, Wasserstoffeinlagerungen in RDB-Stählen zu detektieren.
Ein deutlicher Versprödungseffekt der Wasserstoffvorbeladung tritt nach Bestrahlung bei niedrigerer Temperatur auf. Das Ergebnis zeigt, dass der Typ der Strahlendefek-te entscheidend für die Effektivität der Defekt-Wasserstoff-Wechselwirkung ist. Die bisherigen Ergebnisse haben sich vorzugsweise auf Proben konzentriert, bei denen die Strahlendefekte vor allem mit dem Typ der Cu-reichen Ausscheidungen identifi-ziert werden müssen. Im weiteren werden Proben mit Strahlendefekten des sog. Matrixtyps (Leerstellenkomplexe) untersucht, um die Frage zu beantworten, ob unter bestimmten Bestrahlungsbedingungen ein sicherheitsrelevanter Versprödungseffekt von Wasserstoff nicht auszuschließen ist.

The synthesis of a single monolayer of nanocrystals (NCs) with a maximum density but no in-plane electrical percolation paths is a challenging task. Such layers are required for the fabrica-tion of multi-dot nonvolatile memories. Here, compared to the conventional nonvolatile memory, the floating gate is replaced by a layer of Si NCs allowing for distributed charge storage and, therefore, lower operation voltages, faster programming, etc. These advantages are lost at too high NC densities when NC’s charge can spread over neighboring NCs by electron tun-neling, i.e. due to electrical in-plane percolation paths.
In this contribution, studies on the synthesis of Si NCs by low energy Si+ implantation into thin gate oxides of NC memories are presented. Using a kinetic 3D lattice Monte Carlo code, the nucleation, growth and Ostwald ripening of the Si NCs in Si supersaturation is simulated. On the basis of these simula-tions, the dependence of the Si NC density, the distribution of the NC spacing as well as the threshold for extended electron tunneling paths are predicted. Thus, process conditions could be identified, where NCs align in a thin layer at high density but sufficient electrical isolation.

The results of classical molecular-dynamics simulations of amorphous carbon films are reviewed. An analytic interatomic potential of Brenner was adopted, but with an increased C-C interaction range. Deposition of films with a thickness of up to 10 nm was simulated for ion energies E_ion=10-80 eV and for a wide range of substrate temperatures. The thermodynamically favoured structural transformations in these films during post-deposition annealing at low temperatures (less than ~600 °C) were carefully examined. The approach used describes quite accurately the properties of highly tetrahedral amorphous carbon (ta-C) films, overestimating, however, density of graphitic films, since the potential does not account for the long-range repulsion between non-bonded pi-orbitals.

The film deposition simulations revealed a short-term temperature-dependent relaxation stage (t~70-1000 fs), where the film formation is considerably influenced by substrate temperature T_s. During this stage, depending on T_s, the carbon atoms coming to rest at metastable highly coordinated sites can relax to either three- or fourfold coordinated positions. In agreement with experiment the molecular-dynamics simulations predict a sharp (within the range of about 50 K) transition from ta-C to graphitic carbon as T_s exceeds a critical temperature T_c. The as-deposited ta-C films contain many small clusters (mostly pairs) of sp² bonded atoms, but some extended sp² networks are also found in the films. The ring statistics within these networks will be presented.

During low-temperature annealing the potential energy and stress of the as-deposited ta-C films are released with only minor changes in the short-range order and density. It is demonstrated that as a result of annealing the volumes of sp³ atoms decrease, which is consistent with experiment. The change of potential energy with annealing time can be fit by an exponential function, which enables to analyse the relaxation kinetics in ta-C, in particular, to obtain the dependence of the relaxation time on annealing temperature.

We investigated for the first time the complex formation of curium(III) with adenosine 5’-triphosphate (ATP) by time-resolved laser fluorescence spectroscopy (TRLFS). The interaction between soluble species of curium(III) with ATP was studied at trace Cm(III) concentrations (10-7 M), at different concentrations of ATP and at different pH using 0.154 M NaCl as background electrolyte. Predominant 1:1 complex formation reactions were observed. Taking the dissociation of H4ATP into consideration, we found evidence for the existence of three Cm – ATP species: CmH2ATP+, CmHATP and CmATP-.

Based on the oxidation of phenolic compounds (e.g., hydroquinone, catechol) we developed synthetic HA model substances with pronounced redox functionalities in order to study the redox behavior of HA and the redox stability of actinide humate complexes. In the present work we studied the redox stability of U(VI) humate complexes applying these synthetic HA in comparison to purified natural HA from Aldrich.

The volatility of plutonium oxides in the O2-H2O(g)/SiO2(s) system has been studied by thermo-chromatography in the temperature range 1475 to 600 K. Oxides of thorium, protactinium, uranium, neptunium, and americium in trace amounts have been studied for comparison. Oxide samples containing 105 – 1016 actinide atoms were heated in the starting position of the ther-mochromatographic silica columns. Mixtures of helium, oxygen and water vapor were applied as reactive mobile gas phase. Resulting from thermochromatography the volatile actinide spe-cies are deposited in the column downstream, thus creating inner chromatograms along a temperature gradient. At the end of each experiment the actinide chromatograms were meas-ured by alpha spectrometry. Gamma spectrometry was used to measure protactinium.
Plutonium was found to be volatile in humid oxygen at temperatures above 1300 K. The Pu volatility is lower than that of uranium, but higher as one would expect for stable Pu(IV) which is nonvolatile under the applied experimental conditions. The Pu volatility is assigned to PuO2(OH)2(g). The experimental results give evidence of the oxidation of PuO2 and NpO2 to higher oxides by moist oxygen.

Clay minerals are main components of many soils, sediments, pelitic rocks, as well as fracture filling material in crystalline rocks. Furthermore, clays are used in geo-engineering, particularly to design hydraulic and geochemical barriers in contaminated sites, landfills or underground repositories for toxic or nuclear wastes. Due to the low permeability of clay molecular diffusion is the main transport mechanism of dissolved or colloidal substances at natural hydraulic gradients. This process has to be studied to assess the long-term behavior of geoengineered barrier systems.
In order to determine effective transport parameters in kaolinite diffusion experiments with a conservative tracer were performed. Kaolinite from Hirschau (Germany) was filled in a diffusion cell (cross sectional area 78.6 cm2, layer thickness 1.8 cm), compacted to a dry density of 1.1 g cm-3 and fixed between two filter plates. The through-diffusion of tritiated water (HTO) was observed applying a tracer reservoir with a starting activity of 4·105 Bq in 100 mL. The tracer activities of the high and the low concentration side were measured in intervals by liquid scintillation counting.
An analytical solution of the one dimensional transport equation was developed to determine the diffusion coefficient and the effective porosity. Two variable boundary conditions accounted for the changing concentrations in the transient phase.
A diffusion coefficient of De = 3.2·10-10 m2s-1 and an effective porosity of e = 0.6 were determined from the measured concentration versus time. These results are compared with stationary diffusion experiments using reactive tracers (Cu2+, Zn2+ Pb2+, AsO43-) and natural sealing material (loess loam) and kaolinite (Hamad, 2003). For instance, in loess loam De was found to be 2.47, 3.04, and 4.14·10-10 m2s-1 for Cu, Pb, and Zn, respectively. These results indicate that the diffusion parameters in the natural and the engineered barrier material are in the same order of magnitude.

Data from KEK on subthreshold bar{p} as well as on π^± and K^±production in pC, dC and αC reactions at energies between 3.5 and 12.0~AGeV are described for the first time within a unified approach. We use a model which considers a nuclear reaction as an incoherent sum over collisions of varying numbers of projectile and target nucleons. It samples complete events and thus allows for the simultaneous consideration of all final particles including the decay products of the nuclear residues. The enormous enhancement of the bar{p} cross section as well as the moderate increase of meson production in dC and αC compared to pC~reactions is well reproduced. In our approach, the observed enhancement near the production threshold is mainly due to the contributions from the interactions of few-nucleon groups.

New results on nuclear collective flow are presented for central and semi-central Ru + Ru collisions at 400 AMeV measured with the FOPI detector at GSI Darmstadt. The source shape parameters, flow angle and aspect rations, are extracted from Gaussian fits to in-plane and out-of-plane momentum distributions. The orientation and the shape of the source exhibit different trends according to the investigated phase space region. The shape parameters of the participant source are studied as a function of the particle mass and collision centrality. The flow angle is found to be independent of the particle mass. Both the flow angle and the aspect ratios depend sensitively on the impact parameter. Detailed comparisons with the predictions of the Isospin Quantum Molecular Dynamics model are performed. It is shown in particular that the source shape parameters permit to extract information on the in-medium nucleon-nucleon cross section.

The CFD package CFX-5 has been used to predict the development of upward directed gas-liquid flows in a vertical pipe. Under the assumption of monodisperse bubbles the dilute gas-liquid flow has been predicted using the Eulerian framework of multiphase flow modeling. The capabilities of the CFX-5 flow solver have been extended by taking into account additional non-drag forces like lift, turbulent dispersion and wall lubrication forces. Range of applicability and accuracy of the numerical model have been validated against measured gas void fraction profiles obtained at the MT-Loop test facility of the Forschungszentrum Rossendorf (FZR) in the bubbly flow regime. Best agreement of numerical results with experimental data could be obtained for a wide range of experimental conditions, if Menter s k-w Shear Stress Transport (SST) turbulence model has been used in combination with the Favre averaged drag (FAD) turbulent dispersion force model as derived by Burns [1]. Furthermore results of extensive numerical experiments [2] for the examination and comparison of different model formulations for the wall lubrication and turbulent dispersion forces are presented in this paper.

The investigation of insulation debris generation, transport and sedimentation gains importance regarding the reactor safety research for PWR and BWR considering all types of LOCA as well as short and long term behavior of emergency core coolant systems.
A common project in cooperation with IPM-Zittau deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow (see ref. 1). The activities are funded by the German Federal Ministry of Economy and Technology. While experiments are performed at the IPM-Zittau, theoretical work is concentrated at Forschungszentrum Rossendorf.
In the present paper the basic concepts are described and first feasibility studies are shown. During the ongoing work further results are expected.

Bubbly flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. The presence of a second phase, re-circulating flow, instabilities of the gas plume and turbulence, complicate the hydrodynamics of bubble column reactors. This paper describes experimental and numerical results obtained in a rectangular bubble column with a cross-sectional area of 20 cm2. Images obtained from a high speed camera have been processed to calculate bubble velocities, bubble turbulence parameters and bubble size distributions. Gas disengagement technique was used to obtain the volume averaged gas fraction over a range of superficial gas velocities. A wire mesh sensor was applied, to measure the local volume fraction. Numerical calculations were performed with an Eulerian-Eulerian two-fluid model approach using the commercial code CFX.
The paper details the effect of various two-fluid model interfacial momentum transfer terms on the numerical results. The inclusion of a lift force was found to be necessary to obtain a global circulation pattern and local void distribution that was consistent with the experimental measurements. The nature of the drag force formulation was found to have significant effect on the quantitative volume averaged void fraction predictions.

The usual method to treat kinematic dynamos numerically is to solve the induction equation. For celestial bodies of spherical shape, like the Earth and the Sun, the boundary conditions for the magnetic field can be formulated separately for every degree and order of the spherical harmonics. However, there are a number of aspherical dynamos as, e.g., galactic dynamos and the laboratory dynamos in Riga, Karlsruhe and Cadarache, for which the correct handling of the non-local boundary conditions is a notorious problem. Several methods have been used to deal with this problem, including the use of simplified local boundary conditions, the embedding of the very dynamo region into a spherical region with lower conductivity, or the full solution of the Laplace equation in the exterior.
An alternative way to implement the correct boundary conditions is based on Biot-Savart's law. We present the general formulation of the integral equation approach to both steady and time-dependent dynamos. For spherical dynamos we show the numerical equivalence of this approach with the differential equation approach. The suitability of the method to cope with dynamo problems in arbitrary finite domains is exemplified by the treatment of mean-field dynamos in rectangular boxes.
For flows with small magnetic Reynolds numbers, that are exposed to an external magnetic field, the integral equation approach can be cast into a linear inverse problem for the determination of the flow velocity from externally measured induced magnetic fields. This inverse problem is the basis of the "Contactless Inductive Flow Tomography" (CIFT) which has been demonstrated in a recent experiment. In a cylindrical vessel filled with InGaSn a flow is produced by a motor driven propeller. The moving liquid is exposed alternately to an axial and an transversal magnetic field. The two corresponding sets of induced magnetic fields measured at 49 external Hall sensors are processed in an inverse problems solver to give a rough, but reliable, picture of the flow.

The incorporation of nitrogen into thin (10 nm) Ta layers using plasma immersion ion implantation (PIII) have been studied. PIII was carried out using a low-pressure (0.3 Pa) plasma and ion energies between 6 and 25 keV. The depth distributions of nitrogen were measured by Auger Electron Spectroscopy and compared with those obtained by numerical simulations (Profile Code). The experimental profiles do not show a maximum at the projected range of the implanted ions, but a high nitrogen concentration at the surface decreasing into depth. The influence of implantation parameters such as high-voltage pulse rise and fall times, voltage amplitude, and plasma pulsing on the shape of the nitrogen profile is investigated and discussed.

Abandoned uranium mines which underwent or just undergo flooding may represent a severe source of radioactive contaminants against groundwater, surface water, and the atmosphere. The uranium mines operated until 1990 in Saxony and Thuringia left a total void volume of more than 100 million m³ to be flooded. Prognosis of radionuclide emission via the water path needs detailed knowledge about the hydrological regime of the mine and the speciation of the contaminants. The adsorption of radionuclides on colloidal phases may stimulate or delay their transport and migration. Neglecting the colloidal phases may have the following consequences on environmental hazard prognosis:

a) The radionuclide is fully mobile, i.e. it is not adsorbed onto solid phases: colloidal transport is irrelevant and the model description is correct.
b) The radionuclide is regarded as fully mobile in the model, but it adsorbs on colloids which aggregate and settle (‘natural attenuation’): the prognosis is too pessimistic.
c) The radionuclide is regarded as immobile in the model due to adsorption on the host rock, but in part it adsorbs on colloids which are transported: the prognosis is too optimistic.
Based on their chemical and colloidal composition, mine waters usually range between the following water types:
i) Type ‘acid pore water’ (acid rock or mine drainage, sometimes called ‘yellow boy’): Very acidic (pH 1-3) and usually anoxic waters with a high salt loading.
ii) Type ‘bulk water’: Near-neutral, oxic or suboxic waters with a moderate salt loading, typically represented by gallery or adit water.
Mine flooding is accompanied with a transition of type (i) into type (ii) water, which is crucial for colloid-chemical processes changing the partitioning of heavy metals and radionuclides. Due to pH increase and access of oxygen, colloids of Fe(III) and Al compounds are formed known to adsorb trace metals.
To assess the uranium migration in the stage of flooding and afterwards, we performed neutralization experiments by mixing acid floodwater from an uranium mine with oxic groundwater from an aquifer above the mine and studied the formation and composition of colloids as well as the adsorption of uranium onto these colloids by using spectroscopic methods.

The paper presents the general strategy and an example for the current blind predictive capabilities of surface complexation models (SCM) and the respective database RES3T - the "Rossendorf Expert System for Surface and Sorption Thermodynamics"[1]. The approach for the elucidation of numerical data includes the collection of the mineral surface characteristics, the selection of reliable data records, the extrapolation to infinite dilution, the normalization to a reference site density and the averaging of selected thermodynamic data records.
The copper(II) sorption onto goethite was chosen as system illustrating the blind predictive capabilities. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected accounting for electrostatics. The calculations were performed with FITEQL code [2].
The model prediction represents the experimental values for the adsorbed amount of Cu(II), expressed as conventional distribution coefficients KD as required by most performance assessment software, within one order of magnitude or better.

Scalability and performance of current flash memories can be improved substantially by novel devices based on Multi-Dot Floating Gate MOSFETs. The multi-dot layer in the very thin gate oxide can be fabricated CMOS-compatibly by ion beam synthesis (IBS). Here, we present both experimental and theoretical studies on IBS of multi-dot layers consisting of Si nanocrystals (NCs). The NCs are produced by ultra low energy Si ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this su-persaturation leads to phase separation of the excess Si from the SiO₂. Till now, the study of this phase separation suffered from the weak z contrast between Si and SiO₂ phases in Transmission Electron Microscopy (TEM). Here, this imaging problem is solved by Energy Filtered Scanning Transmission Electron Microscopy (EFSTEM). Additionally, kinetic lattice Monte Carlo simula-tions of Si phase separation have been performed and compared with EFSTEM images. It has been predicted theoretically that the morphology of the multi-dot Si floating gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These pat-tern agree remarkably with EFSTEM images. However, the predicted fluence for spinodal pattern is lower than the experimental one. Because oxidants of the ambient atmosphere penetrate into the as-implanted SiO₂, a substantial fraction of the implanted Si is lost due to oxidation.

Electromagnetic, i.e. Lorentz forces, may be used to influence the flow of electrically conducting fluids. The present paper investigates the application of time periodic Lorentz forces to the control of the suction side flow on a NACA 0015 hydrofoil.
Experimental results, consisting of flow visualizations and force measurements, characterizing the control effect in the low Reynolds number range of 10^4 < Re < 10^5, are presented. A comparison of the forcing effect with stationary Lorentz forces on one hand and conventional oscillatory blowing on the other hand is given as well.

It is well-known that several shear flows become turbulent far below their linear stability limit. The transition to turbulence is triggered by unavoidable finite-amplitude disturbances. Although all infinitesimal disturbances eventually decay, their amplitude can grow temporarily. The lower limit of the control parameter when the amplitude of disturbances can grow initially is called limit of energetical instability [1]. As a rule, this limit considerably underestimates the threshold when the transition to turbulence is observed experimentally in various shear flows. Only recently certain clues of theoretical prediction of the phenomenon of non-linear non-normal transition have been found [2]. However, a routine method to predict this so-called non-normal non-linear transition is still a challenge.
We consider the flow of an electrically conducting melt driven by a rotating magnetic field (RMF) in a cylindrical cavity. Our numerical analysis evidenced that the intermittency route may take place also for this example of a rotating flow [3]. A pronounced flow sensitivity and additional unstable saddle type steady solutions have been detected at control parameters several times below the critical value for the onset of linear axisymmetric instability. The presence of such additional solutions is a sign of a possible non-linear non-normal transition due to finite perturbations despite the linear stability of the basic flow.
We present experimental and numerical results for the transition to turbulence in the RMF driven flow in a cylindrical cavity. The experimental approach is based on a non-invasive examination of the sensitive flow field by hanging the cavity on a torsion wire [4]. Under carefully prepared, clean conditions the occurrence of first flow oscillations was observed at a control parameter close to the linear stability threshold. If an artificial perturbation like a thermocouple was installed at the inner cavity wall, the transition was observed at a considerably lower forcing in the linearly stable parameter range. Examples of the typically intermittent onset of transition will be given. The numerical results will comprise the linear stability analysis based on a highly accurate spectral method and, in particular, the investigation of additional unstable steady solutions. Current evidence suggests that the lowest possible control parameter for the non-linear transition may be reasonably associated with the first bifurcation of such solutions. Indeed, a good quantitative agreement was found between experiments and numeric for the value of this global stability threshold.
Further results will be presented for the linear as well as global stability limits if the RMF driven flow in the cylinder is additionally exposed to a heating from below or a superimposed steady magnetic field. The latter typically delays the transition. The stability analysis of such flows is of particular interest in crystal growth technologies from the melt, for which the occurrence of a turbulent flow should often be prevented.

[1] D. D. Joseph, Stability of Fluid Motions Vol. I, Springer, Berlin, 1976.
[2] S. Grossmann, The onset of shear flow turbulence, Rev. Mod. Phys. 72, 603, 2000.
[3] I. Grants, G. Gerbeth, Stability of axially symmetric flow driven by a rotating magnetic field in a cylindrical cavity, J. Fluid Mech. 431, 407, 2000.
[4] I. Grants, G. Gerbeth, Experimetal study of non-normal nonlinear transition to turbulence in a rotating magnetic field driven flow, Phys. Fluids 15, 2803, 2003.

This study is dedicated to a better understanding of the processes occurring under ion bombardment of ultra-thin ZrO2/SiO2/Si gate dielectric stacks. Complex-shaped depth profiles were obtained by using TOF-SIMS with dual beam (500 eV for sputtering and 10 keV for analysis) Ar+ ions. The SIMS intensities of all the elements depend critically on the amount of oxygen at any moment of the sputtering process. Increased intensity is observed at the surface and at the ZrO2/SiO2 interface. A long tail of the Zr signal is present in the Si substrate, even after the second (SiO2/Si) interface, and a double bump structure in the ⁹⁰Zr and ZrO dimer is observed, which is more pronounced with increasing thickness of the interfacial SiO2 layer.

Computer simulations using the dynamic Monte Carlo code (TRIDYN) are performed in order to distinguish the ion-bombardment-induced effects from changes in the ionization degree. The original code is extended with simple models for the ionization mechanism and for the molecular yield during sputtering. Oxygen preferential sputtering at the surface and ballistic transport of Zr towards and through the interface are clearly demonstrated, but there is also evidence that due to recoil implantation oxygen gets piled-up near the ZrO2/SiO2 interface.

TiN coatings were deposited on Al substrates using the plasma immersion ion implantation and deposition (PIIIAD) technique, employing a filtered Ti cathodic arc in a nitrogen atmosphere. Negative pulsed bias voltages between 0 to –4.0 kV were applied with varying duty cycles, at a constant time-averaged bias. Stress measurements using X-ray diffraction reveal an increase and then a decrease in the intrinsic compressive stress at increasing on-time bias. A bias dependent preferred orientation of TiN is observed i.e., {111}, {200} and {220} at low bias and predominantly {200} at higher bias. The hardness reduces from 29 GPa at lower bias to 20 GPa at higher bias. Thus, the time averaged energy of ion bombardment does not uniquely determine the properties of the growing coating, which can be adjusted by the on-time substrate bias applied for very short durations. A subplantation model of stress development is applied to explain the results.

The sorption of neptunium(V) onto granite and its main mineral constituents quartz, orthoclase, albite, biotite, and muscovite is studied under anaerobic conditions as a function of pH in a series of batch equilibrium experiments. Furthermore, the effect of humic acid on the neptunium(V) sorption is studied applying a 14C-labeled synthetic humic acid (type M42) for the experiments. The data suggest that the neptunium sorption onto granite is affected by both the pH and the presence of organic material. In the absence of humic acid, the neptunium sorption starts between pH 7 and pH 8 and increases with increasing pH value. Due to addition of humic acid the neptunium sorption onto granite is decreased in the neutral to alkaline pH range, which is attributed to complexation of neptunium by humic acid in solution. Thus, in this pH range the neptunium mobility is increased by humic substances. The neptunium(V) sorption onto granite and onto its mineral constituent biotite is nearly equal, suggesting that the sorption of neptunium(V) is controlled by the minor amount of biotite which, however, is reactive.

We have studied the trapping of negative and positive charge in Si-implanted SiO2 layers of Al/SiO2/Si-based devices during high-field electron injection from the Si substrate under conditions typically used for obtaining electroluminescence. The location, capture cross-section and concentration of negatively and positively charged traps have been determined in dependence on the time of heat treatment by rapid thermal annealing (RTA). A comparison between the results obtained from Si- and Ge-implanted oxide layers has been made. It has been shown that in the case of Si-rich oxides an increase in the RTA time leads to the formation of hole and electron traps of high concentration, both of which are located within the oxide. For Ge-rich oxide layers, however, the hole traps are found primarily in the vicinity of the SiO2/Si interface while the electron traps are present within the oxide. The nature of these traps has been discussed.

Objectives: PET imaging of cardiac reporter gene expression holds promise for noninvasive monitoring of gene therapy. Two approaches based on herpesviral thymidine kinase gene(HSV1-tk) habe been applied. Wild-type HSV1-tk was imaged with 2´-fluoro-2´-deoxy-5[¹²⁴I]-iodo-arabinofuranosyluracil([¹²⁴I]FIAU), and mutant HSV1-sr39tk was imaged with 9-[4-[¹⁸F]-fluoro-3-(hydroxymethylbutyl)guanine([¹⁸F]FHBG).
Methods: Adenovirus expressing wild-type HSV1-tk(Ad_tk), mutant HSV1-sr39tk (Ad_sr39tk), or control gene (Ad_LacZ) were directly injected into myocarcardium of 24 rats and 8 pigs. Two days later, dynamic PET imaging was performed for 120 min after injection of [¹²⁴I]FIAU or [¹⁸F]FHBG with a clinical scanner. Imaging with [¹³N]-ammonia was performed to identify cardiac regions of interest. Pig hearts were sliced into 5 short-axis slices for ex vivo imaging, and regional tracer uptake was analyzed.
Results: For [¹²⁴I]FIAU, the largest difference of cardiac uptake between Ad_tk rats and controls was found at 10-30 min after injection (1.7±0.25 vs 0.87±0.22 %dose/ml, p=0.035). No difference was observed at later imaging times due to [¹²⁴I]FIAU washout. For [¹⁸F]FHBG, difference between Ad_sr39tk rats and controls continuously increased over time and was largest at 105-120 min (1.45±0.45 vs 0.35±0.05 %dose/ml, P=0.0066). Global cardiac reporter probe kinetics in rats was confirmed by regional myocardial analysis in pigs. Transgene expression was specifically visualized by both approaches. Highest target/background ratio of [¹²⁴I]FIAU in Ad_tk infected myocardium was 1.50±0.20 vs 2.64±0.49 for [¹⁸F]FHBG in Ad_sr39tk infected areas (P=0.01). In vivo results of rats were confirmed by ex vivo counting and autoradiography. In vivo segmental reporter probe uptake in pigs correlated well with those in ex vivo images.
Conclusions: Both combinations were feasible for PET of cardiac transgene expression in different species. Specific probe kinetics suggests different myocardial handling of pyrimidine ([¹²⁴I]FIAU) and acycloguanosine ([¹⁸F]FHBG) derivatives. Results are in favour of [¹⁸F]FHBG because of continuous accumulation over time and higher imaging contrast.

Background: Coexpression of a reporter gene and therapeutic gene may allow for non-invasive monitoring of cardiac gene therapy. We sought to evaluate the usefulness of an adenoviral vector expressing mutant herpesviral thymidine kinase reporter gene(HSV1-sr39tk) and VEGF₁₂₁ in independent expression cassettes(Ad4tk).
Methods and Results: Accumulation of [¹⁴C]FIAU and [¹⁸F] FHBG as reporter probes, and VEGF secretion into medium were determined for Ad4tk-infected H9c2 rat cardiac cells in vitro. Tracer uptake increased with increasing vector concentration and over time, and was comparable to cells infected with adenovirus expressing only wild-type HSV1-tk(reporter probe: [¹⁴C]FIAU) or mutant HSV1-sr39tk(reporter probe: [¹⁸F]FHBG). No significant uptake was observed in uninfected cells or cells infected with adenovirus expressing VEGF alone. With increasing vector concentration, Ad4tk-infected cells increasingly released VEGF into medium. VEGF production correlated significantly with cellular reporter uptake (r=.98). In an initial in vivo experiment, Ad4tk and control vector were injected directly into two separate myocardial areas of a healthy pig following thoracotomy. Two days later, PET imaging was performed using [¹²⁴I]FIAU, allowing for specific visualization of the area of Ad4tk injection. Identification of regional reporter gene expression was accompanied by significant increase of plasma VEGF concentration.
Conclusion: The usefulness of a vector coexpressing HSV1-tk and VEGF for noninvasive imaging of the expression of a therapeutic transgene has been demonstrated for the first time. This approach may allow for in vivo monitoring of cardiac angiogenesis gene therapy in the future.
Condensed Abstract: Usefulness of an adenoviral vector(Ad4tk) expressing mutant herpesviral thymidine kinase reporter gene and VEGF₁₂₁ was evaluated. Accumulation of radiolabelled reporter probes increased for Ad4tk-infected rat cardiac cells with increading vector concentration and over time, and was comparabel to cells expressing reporter gene alone. No significant uptake was observed in cells expressing VEGF alone. VEGF production after Ad4tk-infecion correlated significantly with reporter probe uptake in vitro. In vivo, PET yielded specific visualization of Ad4tk injection area in a pig. This approach may allow for noninvasive monitoring of cardiac angiogenesis gene therapy.

Background: PET imaging of reporter gene expression holds promise for noninvasive monitoring of gene therapy. Previously, two approaches based on the herpes simplex virus type 1 thymidine kinase gene(HSV1-tk) have been applied to the heart. Wild-type HSV1-tk was imaged with [¹²⁴I]-fluoro-deoxy-iodo-arabinofuranosyluracil(FIAU) and mutant HSV1-sr39tk with [¹⁸F]-fluoro-hydroxymethylbutyl-guanine(FHBG), but a direct comparison has not yet been performed.
Methods and Results: In H9c2 cardiac cells, in vitro FIAU accumulation was superior to FHBG following infection with adenovirus expressing wild-type HSV1-tk(Ad_tk), while FHBG uptake was superior to FIAU using adenovirus expressing mutant HSV1-sr39tk(Ad_tk). Subsequent in vivo studies employed dynamic PET two days after intramyocardial vector injection. FIAU was used after Ad_tk infection. Highest cardiac uptake compared to negative controls occurred at 10-30min after tracer injection. Specific uptake disappeared at later times due to FIAU washout. FHBG was used after Ad_sr39tk infection. Specific tracer uptake continuously increased over time and was highest vs controls at latest imaging times(105-120min). Global cardiac reporter probe kinetics in rats were confirmed by regional analyses in pigs. Transgene expression was specifically visualized by both approaches. Highest traget/backgrounde ratio of FIAU in Ad_tk infected pig myocardium was 1.50±0.20 vs 2.64±0.49 for FHBG in Ad_sr39tk infected areas(P=0.01). In vivo results were confirmed by ex vivo counting and autoradiography.
Conclusions: Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression in different species. Specific probe kinetics suggest different myocardial handling of pyrimidine(FIAU) and acycloguanosine(FHBG) derivatives. Results are in favour of FHBG and mutant HSV1-sr39tk because of continuous accumulation over time and higher imaging contrast.
Condensed Abstract: Two approaches for PET imaging of cardiac reporter gene expression based on herpesviral thymidine kinase gene (HSV1-tk) were compared in small and large animals. Using wild-type HSV1-tk, dynamically imaged with [¹²⁴I]-fluoro-deoxy-iodo-arabinofuranosyluracil (FIAU), highest myocardial FIAU uptake occurred early after injection, but tracer washout was observed at later times. Using mutant HSV1-sr39tk, imaged with [¹⁸F]-fluoro-hydroxymethylbutyl-guanine (FHBG), specific uptake increased over time and was highest at late imaging. Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression, but results are in favour of FHBG because of continuous accumulation over time and higher imaging contrast.

To evaluate the influence of humic substances upon the extent of neptunium(V) sorption by granite, the sorption of neptunium(V) on granite in the absence and presence of humic acid was studied under anaerobic conditions as a function of pH in a series of batch equilibrium experiments. The neptunium and humic acid sorption onto the mineral constituents of granite (quartz, orthoclase, albite, biotite, and muscovite) was also studied to identify the mineral component which dominates the sorption of neptunium and humic acid on granite. The study showed that the neptunium sorption is affected by both the pH and the presence of humic acid. An increased mobility of neptunium was found between pH 7 and pH 11 in the presence of humic acid. As dominating mineral phase in the granite for the neptunium sorption, biotite was identified.

We report on the formation of thick 3C-SiC films on 3C-SiC/Si substrates which were produced by flash lamp processing (FLP). Employing a three step process, firstly a 35nm thick 3C-SiC film on a <100>-Si substrate is deposited which is followed, secondly by FLP. This leads to a melting of the SiC/Si interface region within 20ms followed by epitaxial solidification. Then, in a third step, this film is used as a seed for the deposition of a second, 3 µm thick, 3C-SiC layer. This newly developed process including FLP is called FLASiC (Flash LAmp supported deposition of Silicon Carbide). Compared with standard 3 µm thick layers directly grown on silicon, both transmission electron microscopy and low temperature photoluminescence evidence improvement of the re-grown material.

The formation of SiC on Insulator (SiCOI) using a tool wet sacrificial oxidation is studied. The wet oxidation in 3C-SiC is very anisotropic strongly depended on the defect density, especially the inversion domain boundaries (IDBs). The SiCOI structure was realized by depositing of 35 nm thick 3C-SiC film on (100)-Si substrate by APCVD subsequently the film was annealed by flash lamps. The flash lamp annealing system consists of Xe lamps powered by discharging capacitors producing pulses of 20 ms. After radiation two zones can be distinguished, upper and lower, exhibiting high and low defect density, respectively. The highly defected upper zone was etched by wet sacrificial oxidation at 1150°C for 16 min. forming a 50nm thick oxide layer on the top of a good quality, 20nm thick, 3C-SiC film. In parallel, a buried oxide layer having a mean thickness of 44nm was formed by oxidation of the Si substrate through existing channels created in the SiC by the preferential wet oxidation of the IDBs which touch the SiC/Si interface. Through the oxided channels the Si substrate is oxided fast forming a continuous buried oxide layer realizing the SiCOI structure.

The production of cubic SiC (3C-SiC) layers in device quality through the epitaxial growth on (100)-Si wafers has remained a challenging task yet. Recently, it was demonstrated that the use of Flash Lamp Processing (FLP) can support the production of high quality 3C-SiC layers in a promising manner. The FLASiC team organized within a project of the V. Framework of the European Community is currently extending this early work as a broader approach with the following main aspects: a) Development of the epitaxial process including FLP, b) Development of a prototype equipment for the FLP, and c) Demonstrating the improved quality at dedicated devices. In this talk a short overview will be given regarding the latest advancements of this new approach.

The formation of 3C-SiC epitaxially grown on Si wafers is still a considerable problem. Due to the 20% misfit between Si and 3C-SiC the defect density in the film is very high. the partial melting and subsequent recrystallization of the film by the flash lamp process can improve the quality of the thin 3C-SiC films. In this paper the microstructure of the annealed and partially recrystallized 35 nm thick films is studied by transmission electron microscopy. The films were grown by APCVD using Silane and Propane. The flash lamp annealing system consists of Xe lamps powered by discharging capacitors producing pulses of 20 ms. After irradiation almost free of defects 3C-SiC trapezoidal protrusions (TPs) are formed at the lower part of the film. In the uppermost part of the film the defect density was also reduced. The good quality of the TPs is shown by high resolution cross-section TEM observations. The good quality of the films was also confirmed by Plane View TEM observations of the moiré patterns in the as grown and annealed films. Moiré patterns are formed when the electron beam penetrates both the Si and the SiC lattices and are very sensitive to any lattice distortion or defects.

Embedded Si or Ge nanoclusters in SiO2 films might be a future alternative to conventional floating gate memories. Si or Ge implanted 20nm SiO2 layers were annealed to generate nanoclusters with sizes of 3-4 nm. The charge storage of the implanted layers was studied by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM). Local charge injections were accomplished by a biased conductive tip.
The amount of the injected charge was estimated from the shifts of the local dC/dV curves acquired with scanning capacitance spectroscopy (SCS). The SCS data were compared with CV-measurements on planar MOS structures. The decay of the SCM- and EFM-contrasts was monitored and the retention time was determined.

Mittels Kapazitästransientenspektroskopie (DLTS) wurde die Umladung von Grenzflächen- und Isolatorzuständen in MOS-Strukturen mit eingebetteten Ge-Nanoclustern untersucht. Die Clusterbildung in den 20 nm dicken SiO2-Schichten erfolgte durch Ionenstrahlsynthese, wobei Ge mit verschiedenen Dosen (5x10^15, 1.5x10^16 cm^-2) und Energien (12, 18 keV) implantiert wurde und die Proben bei 950°C/1050°C in N2-Atmosphäre getempert wurden. TEM-Messungen zeigen die Bildung und Verteilung der Nanocluster im SiO2. Die DLTS-Messungen ergaben eine signifkante Abhängigkeit der Zustandsdichte an der Si-SiO2-Grenzfläche von den Ausheilparametern. Ein Trapniveau ~0.32 eV oberhalb der Valenzbandkante des Siliziums wurde in allen implantierten Proben gefunden. Durch Variation der elektrischen Anregungspulse kann der Beitrag der langsam relaxierenden grenzflächennahen Oxidzustände separiert und die für die Clusterumladung relevante Tunneloxidschicht an der Interface charakterisiert werden.

Semiconductor nanoclusters (NCs) embedded in thin gate dielectrics are of fundamental interest for future integrated memory concepts. In this contribution we compare the properties of Ge and Si NCs embedded in thin SiO2 films (d = 20 nm) with respect to their charge storage behaviour. Those NCs were prepared by ion beam synthesis combining low energy ion implantation (6-18 keV, 5x1015-2x1016cm-2) with subsequent rapid thermal processing (950 or 1050°C, 30-120 s) choosing identical ion ranges and peak concentrations for both elements. Electrical characterization based on CV, IU, pulsed Ct and It measurements were performed at MOS capacitors. The investigations reveal significant differences for Ge and Si NC containing gate oxides. Ge NCs near the Si/SiO2 interface are characterized by fast charging / decharging and a flatband voltage shift of several volts. In contrast, Si implanted oxides show memory effects with a smaller flatband voltage shift, but considerably improved data retention. In both cases charging is possible for electrical field strength of 4-6 MV/cm, well below the Fowler-Nordheim tunnelling region. The varying electrical properties correlate with differences in the spatial distribution of ion beam synthesized Ge and Si NC in thin SiO2 films, which were investigated by XTEM and RBS. The change of spatial distribution during annealing is due to different thermodynamics of NC evolution and chemical processes especially in thin SiO2 films.

Studies of semiconductor nanocrystals (NC’s) in the MOS gate oxide received much interest due to their potential application in non-volatile memory devices. However, the detailed charge storage mechanism is still under discussion. Defect-based charge trapping at NC surfaces is hard to distinguish from storage in the conduction band of NC’s. For metal NC’s in SiO2 the situation is different. Charge traps at the Au/SiO2 interface are assumed to be negligible at first sight. In this contribution, Au NC’s serve as a model system for the charge storage phenomena in NC containing gate oxides with a thickness of less than 40 nm. For the present study, Au NC’s were synthesized by low-energy ion implantation followed by annealing. The formation of well-separated NCs (4..5 nm diameter) were observed by X-TEM studies. Additionally, a zone denuded of NC’s forms at the interface. Thus, the formed NC-layer has the right distance from the Si/SiO2 interface for charging by direct electron tunneling. On prepared MOS capacitor structures, charge storage behavior was successfully demonstrated by capacitance-voltage measurements.

In the present work the influence of HA on the interaction of tetravalent actinides onto quartz sand was investigated in batch and column experiments. HA can affect the sorption of actinides onto mineral surface as a complexing ligand for cations in solutions, and as an adsorbent by modifying the properties of the mineral surface.
Batch experiments were performed with Th(IV) as stable tetravalent actinide element. Column experiments were carried out with uranium which is less stable in the tetravalent state under laboratory conditions. Results of the U(IV) migration were compared to the U(VI) migration.
HA shows a pH-dependent influence on the Th(IV) sorption onto quartz sand. At pH < 4 HA may immobilize Th(IV) due to HA sorption and/or precipitation onto the surface. Between pH 4 and pH 5 the Th(IV) sorption is decreased in the presence of HA which can be attributed to the formation of dissolved Th(IV)-humate complexes. For higher pH values a comparable effect is assumed. The experimental proof was not possible by the performed batch experiments.
From the column experiments it can be concluded that HA affects the migration of both U(IV) and U(VI). In the presence of HA U(VI) is significantly mobilized. A similar effect is supposed for U(IV). This is in accordance with the results of the batch experiments.

The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt. The most prominent properties of this strain are reversible and selective binding of U, Cu, Pb, Al and Cd and the presence of a surface layer protein as outermost cell wall component. Mass spectroscopical, colorimetric and phosphor specific staining methods showed phosphorylation of the S-layer protein. EXAFS analysis and Infrared spectroscopy of the uranium complexes formed by the cells and S-layer of this bacterium demonstrated that this metal is coordinated to carboxyl and phosphate groups. In this work we present analysis of Pd nanoclusters formed on the cells of B. sphaericus JG-A12 in the presence of H2 as a reducing agent. These nanoclusters are interesting for the development of bionanocatalysts and biosensors. Further, by embedding cells, spores or S-layers using sol-gel techniques bioceramics particles were produced. These bioceramics can be used for bioremediation of heavy metal contaminated waters.

Contamination of soils with heavy metals and radionuclides is a severe environmental problem. Bacteria are involved in migration and detoxification of a large number of toxic metals due to their ability to interact with and to biotransform them. Total DNA was extracted from soils of one uranium mining waste pile near the town of Johanngeorgenstadt (Germany) and of one uranium mill tailings near Shiprock, NM in the USA. Universal bacterial, archael and also Geobacter-specific primers were used to construct 16S rDNA libraries. We found that natural microbial communities at the two uranium wastes differed significantly. Alpha-Proteobacteria and representatives of the Holophaga/Acidobacterium phylum were predominant in the U mining waste pile, whereas the Shiprock U mill tailings was occupied mainly by Bacillales, Gamma-Proteobacteria and Green non-sulfur bacteria. The most related sequences to ours in the GenBank were those of not yet cultured bacteria or archaea. Representatives of the genus Geobacter were identified in the U waste pile by using Geobacter-specific primers and in the U mill tailings by both Geobacter-specific and universal primers. Because these bacteria are able to reduce and immobilize a large number of heavy metals, we are performing a quantification of them via Real time PCR. Efforts to cultivate some bacterial isolates from the U wastes are in progress in our laboratory.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig

Bacterial diversity was studied in water samples collected at depths of 290 to 324 m from the Siberian deep-well radioactive waste disposal site S15 near the Russian city of Tomsk by using the 16S rDNA retrieval. Bacterial clone libraries were constructed for the DNA isolated from the biomass collected on filters with a pore size of 0.45µm and 0.22µm. Comparative analyses of the two libraries revealed significant differences in the predominant bacterial groups and in the species composition. In the 0.45µm clone library a dominance of Dechlorosoma spp. was found, whereas in the 0.22µm library populations of Chrysobacterium spp. belonging to Cytophaga/Flavobacterium/ Bacteroides (CFB) group were predominant. Many of the identified 16S rDNA sequences were affiliated to uncultured members of different bacterial lineages. Effort to culture some of them is in progress in our laboratory.
In addition, using CFB-specific primers and applying semi-nested PCR a clone library was generated for the total DNA extracted from the same site. Our previous study of this DNA, applying universal bacterial primers, indicated a presence of relatively small CFB population there. The estimation of the real amount and the significance of this bacterial group via real-time PCR is also in progress.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig

Cells of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 are capable of selective and reversible accumulation of heavy metals.
The cells of B. sphaericus JG-A12 are enveloped by a surface-layer (S-layer). S-layers, which are composed of identical protein monomers with the ability to self-assemble into two-dimensional crystalline arrays, are one of the most commonly observed surface structures of archaea and bacteria.
In case of the strain JG-A12 our analyses showed that the S-layer is capable of binding metals. Thus, it is probable that the S-layer contributes to heavy metal resistance.
Sequence analyses showed, that the S-layer proteins of B. sphaericus JG-A12 and its closest relative, B. sphaericus NCTC9602, possess an unusual high identity of the N-terminus and the central domain, whereas the C-terminal parts differ significantly between the two strains. Further, both strains contain a second truncated S-layer gene-like copy which is possibly encoded by large plasmids. These results indicate a horizontal transfer of parts of the gene between different strains.
The S-layer proteins show a high content of aspartate and glutamate, especially in the C-terminal part. IR analyses demonstrated that the carboxylgroups of these residues are involved in Pd-binding.

VAAM 2004
Braunschweig 28.03.-31.03.2004

As a consequence of the averaging process constitutive models for the interaction between the phases are required in the multi-fluid modelling. For the simulation of bubbly flows this concerns models for the forces acting on bubbles. Detailed experimental data for vertical pipe flow, obtained by an advanced wire-mesh sensor, were used to assess such models for a wide range of combinations of superficial velocities. A simplified one-dimensional model, which considers a number of bubble classes is used for the prediction of radial gas fraction profiles from a given (measured) bubble size distribution. A comparison of these profiles with the measurements allows the evaluation of the models for the non-drag forces. In contrast to common CFD codes the simplified model also allows to consider the extension of the bubbles. This is important, if large bubbles or slugs occur. A good agreement is achieved for liquid superficial velocities up to 1 m/s using the lift- and wall force models from Tomiyama and the Favre averaged drag model for the turbulent dispersion force. For larger liquid superficial velocities an intermediate peak occur in the measured radial gas fraction profile, which cannot be reproduced by the available models.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern ermöglicht. In Anrege-Abfrage Experimenten ist damit die Zeitskala zugänglich, in der sich wichtige elementare Wechselwirkungen abspielen. In Halbleiter Quantenstrukturen können durch fs-Laserpulse z. B. kohärente elektronische Wellenpakete präpariert werden, deren Untersuchung die Überprüfung elementarer Vorhersagen zur Existenz von Bloch Oszillationen erlaubt. Desweiteren werde ich auf Beiträge zur technologischen Weiterentwicklung des Feldes, wie die Realisierung des kompaktesten fs-Lasers auf Festkörperbasis, und dessen Anwendungen eingehen.