Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Cathodoexcitation in the study of silicon dioxide films on silicon substrate has evealed many interesting properties of luminescence centers. The main luminescent enters in SiO2 films are the red luminescence R (1.85 eV) of the non-bridging oxygen hole enter (NBOHC) and the twofold- coordinated (divalent) silicon with a blue B (2.7 eV) and a UV band (4.4 eV). Especially the latter ones are produced under irradiation, but from existing precursors.
Morimoto et al. concluded that the blue luminescence (B) is related to interstitial oxygen. Therefore, in the present paper we want to compare a direct oxygen implantation with a direct silicon implantation into SiO2 layers producing an oxygen surplus in the first case and an oxygen deficit in the second case, respectively.
Thermally grown SiO2 layers of thicknesses d = 500 nm have been implanted by Si+ and O+ ions of energy 150 and 100 keV, respectively, and a uniform implantation dose of Di = 5 . 1016 ions/cm2. Thus the implantation profiles are expected with a concentration maximum of nearly 4 at% at the half depth dm 250 nm of the SiO2 layers. After thermal annealing to 900 oC for 1 hour in vacuum the typical red and blue luminescence bands are increased.
Generally we may state: Implanting oxygen increases the red band R (? =650 nm) but does not affect the blue band B (? = 460 nm). Silicon surplus increases the amplitude of the blue (B) luminescence, but reduces the amplitude of the red (R) one.
Studying the irradiation dose dependence of these blue and red bands we have established defect kinetics in SiO2 including six main defects and precursors, so the non-bridging oxygen hole center (NBOHC) for the red luminescence, the twofold coordinated silicon as the oxygen deficient center ODC2 for the blue luminescence and the mobile oxygen as the main transmitter between precursors and the radiation induced defects. The kinetics is described by a set of eight differential equations which predict the dose dependence of the cathodoluminescence. The experimental CL dose dependences of the red (R) and blue (B) luminescence intensities are in a good agreement with the calculated ones according to the model.

The increasing interest in low-dimensional materials is based on both fundamental and technological issues. Recently, Sn nanoclusters have been proposed as potential candidates for charge storage. However, a better understanding of formation and properties of nanocrystals is required for their technological applications. Sn nanoclusters have been formed in thin SiO2 films by ion implantation (80 KeV, 1x1016 cm-2) and annealing at different temperatures. The high brilliance of third generation sources at high energies makes it feasible to perform Sn K edge spectroscopy on these systems in which the Sn concentration is at the detection limit for XAS. In particular, we have used fluorescence - detected XAS at the GILDA beamline of the ESRF to probe the local structure of the implanted Sn atoms. Complementary structural information have been obtained by 119Sn Conversion Electron Mössbauer Spectroscopy (CEMS) and Transmission Electron Microscopy (TEM). XAS has provided unique information on the local environment of Sn nanoclusters in the SiO2 with respect to different annealing conditions. Sn ions are fully oxidized in the as-implanted state, while after annealing also the ß-Sn phase is found.
By comparing XAS data with CEMS and TEM we concluded that the metallic ß-Sn phase is related to the bigger crystalline nanoclusters formed after annealing, while the oxidized Sn is present in the matrix as dissolved SnO or as small oxide precipitates.

The ion beam synthesis (IBS) of nanoparticles in amorphous matrix has received great attention in the last years as a promising technique for nanocrystal formation in insulating layers. Metallic and semiconducting nanoclusters embedded in SiO2 have been recognized as potential materials for the production of memory devices and optoelectronic components. Sn nanoclusters has been proposed, together with Si and Ge nanoclusters, as potential candidates for charge storage. One of the critical point for the technological application of nanocrystals is that they must be isolated and similar in size. In addition, their position and spacing, their structure and stability after formation should be controllable.
In this work we address the formation of Sn nanoclusters by ion implantation and thermal treatments in thin SiO2 films (< 100 nm), where the cluster formation mechanism is not well understood yet. The local structure of Sn in SiO2 has been addressed by 119 Sn CEMS and EXAFS. EXAFS and CEMS analyses provided unique information on the local atomic and electronic environment of Sn in SiO2.
Sn 2+ and Sn 4+ oxidized phases or the Sn 0 metallic phase have been found under different annealing conditions. By comparing these data with TEM and RBS analyses we concluded that metallic beta-Sn phase is related to big Sn crystalline clusters formed after annealing, while the oxidized Sn is due to atoms dissolved in the matrix or in small precipitates of SnO2 or SnOx. In addition, the formation mechanism of Sn nanoclusters may be influenced by H2O absorption in the highly damaged SiO2 film after ion implantation, and by in-diffusion of moisture during the annealing. Low energy ion implantation (10–15 keV) showed the possibility for a better control of the cluster size distribution and positioning inside the SiO2 films. This may be relevant for the application of this kind of nanoclusters for charge storage applications in memory devices. Preliminary electrical characterization confirmed the memory effects in MOS capacitors with Sn nanocrystals embedded in the gate oxide.

The aim of this work is to predict the influence of the external magnetic field on the solidification process of two-component material. Based on the continuum model of two-phase flow a mathematical model for the directional solidification of a binary alloy in an applied magnetic field is presented. The model includes mass, momentum, energy and species conservation equations and additional relationships describing the temperature-solute coupling. The geometry under study is a cylindrical mold with adiabatic walls and cooled bottom. The macroscale transport in the solidification of alloys is governed by the progress of the two-phase mushy zone which is treated by means of a porous medium approach.
The results of calculation are compared with experimental data. The experiments as well as the calculations showed that by rotation of the liquid phase caused by the Lorentz force, the solidifcation front has a non-linear surface.

The lateral resolution of energy dispersive X-ray analysis (EDX) and cathodoluminescence (CL) mapping in a scanning electron microscope (SEM) can be extended to depth analysis by means of varying the electron beam energy, Eo, and thus the excitation range R(E).Comparing the Ge atom profiles nGe(x) shift with those of the CL center profiles nCL(x) after thermal annealing a much smaller displacement of the Ge atom concentration with respect to the profile shift of the luminescent centers towards the surface was detected.

Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+, Si+, and O+ ions of energy 350, 150, and 100 keV, respectively, and a uniform implantation dose of Di = 5E16 ions/cm2. Thus the implantation profiles are expected with a concentration maximum of nearly 4 at% at the half-depth dm = 250 nm of the SiO2 layers. After thermal annealing to 900 °C for 1 h in dry nitrogen or vacuum the typical violet luminescence band (at 400 nm) of the Ge+ implanted centers is increased more than 200-fold and the Ge luminescent center depth profile is shifted from about 250 to 170 nm towards the surface as determined by cathodoluminescence (CL) depth profiling. Implanting oxygen increases the red band ( at 650 nm) but does not affect the blue band (at 460 nm). Silion surplus increases the amplitude of the blue (B) luminescence, but reduces the amplitude of the red (R) one.
Studying the irradiation dose dependence of these blue and red bands we have established defect kinetics in SiO2 including six main defects and precursors, including the non-bridging oxygen hole center for the red luminescence, the twofold-coordinated silicon as the oxygen deficient center ODC(2) for the blue luminescence and the mobile oxygen as the main transmitter between precursors and the radiation induced defects. The kinetics are described by a set of eight differential equations which predict the dose dependence of the CL.

For investigation of luminescent center profile cathodoluminescence measurements are used under variation of the primary electron energy Eo = 2..30 keV. Applying a constant incident power regime (Eo x Io = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx.
Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses (0.5-5)E16 ion/cm2. Thus Ge profiles with a concentration maximum (0.4-4)at% at the depth of dm = 240 nm are expected. Afterwards the layers have been partially annealed up to Ta = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (at 400 nm) of the Ge centers is strongly increased but also the luminescence center profiles are shifted from about 250 nm to 170 nm depth towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm.

Silicon nanocrystal (NC) based nonvolatile memories are currently an active subject of study. In order to synthesize NCs in the gate oxide, ion implantation followed by annealing is the most compatible method with the current CMOS technology. Although, the process of phase separation during annealing and the influence of the very close Si/SiO₂ interface is not completely understood.


In this contribution, binary collision simulations of highfluence Si implantation are combined with kinetic 3D lattice Monte Carlo simulations of NC formation by phase separation during annealing. For low concentrations of implanted Si, NCs form via nucleation, growth and Ostwald ripening, whereas for high concentrations Si separates from SiO₂ by spinodal decomposition. In both regimes, the close Si/SiO₂ interface has substantial influence on the NC formation. Specifically, it leads to a self-adjusted NC-free tunneling oxide at the interface, which has the just right thickness (2 .. 4 nm) to act as barrier for NC charging by direct electron tunneling. However, the evolution of NCs during annealing differs in the two regimes. It is shown that a constant tunneling distance and a constant mean NC diameter can be achieved in the nucleation regime at high NC densities ( > 1x10¹² cm^-2). This is not the case for spinodal decomposition. Thus, it is predicted that the technological demands on the NC synthesis for nonvolatile memories are fulfilled best in the nucleation regime.

[no abstract]

Phosphorus depth profiles in Si obtained by 140 keV implantation into the [001] axial channel direction and into a direction 7⁰ off axis are investigated at two different doses (5x10¹³ and 5x10¹⁵ cm^-2)for implantation temperatures of 350 ⁰C and room temperature (RT). At low dose and at channeling incidence, the penetration depth of implanted ions is higher at RT than at 350 ⁰C This behavior is caused by the dechanneling of lattice vibrations. At high dose, the temperature dependence of the shape of the implantation profiles is opposite that at low dose, due to the enhanced dechanneling by defect accumulation at RT. On the other hand, damage buildup does not occur at elevated temperature. The temperature dependence of the profiles obtained by tilted implantation is much less than for the channeled implants. The P profiles measured can be reproduced very well by atomistic simulations which take into account both lattice vibrations and defect accumulation during ion bombardment.

As device geometries scale, there is an increasing trend for high energy CMOS well implants to migrate to small incidence angles (near zero degree), and therefore avoid the well spacing limitations caused by shadowing and encroachments of the ion beam by the photoresist mask. However, this transition results in the replacement of traditional de-channeling profiles by channeled dopant profiles. From a device engineering perspective, accurate models of channeled profiles are becoming more important. The degree of channeling is dependent on the acceptance angle, incident angle, dopant species, energy, dose and extent of damage induced in the crystal. This paper discusses both experimental and simulation results that shed light on the contribution of these factors. In addition, the control requirements on ion implantation parameters from a channeling perspective will also be discussed.

The catalytic hydrogenation of aromatic nitro compounds is a complex exothermic process influenced by the competing effects of the mass transfer and the kinetics. In reaction calorimeters, several methods were applied to determine the parameters of kinetics and mass transfer under different process conditions. It was found that a bad quality of the aromatic nitro compound and disadvantageous process conditions can cause an accumulation of intermediates which probably deactivate the catalyst and lead to low reaction rates.

A novel technique for the determination of the thermodynamic and kinetic parameters of the Grignard reagent formation is described. Instead of operating under the spontaneous exothermic initiation of Grignard reactions, the calorimetric measurement was carried out in a closed reactor pressure vessel. In that way, the increase of the reactor temperature and the pressure can be used for detecting the initiation of the Grignard-reagent formation as shown by comparison with the on-line profiles of the concentration of the Grignard reagent measured by FTIR-spectroscopy simultaneously. Results showed that the molar reaction enthalpy of a Grignard reagent could be determined by a closed reactor vessel more accurately than under reflux conditions.

The beta decay of 100In, the one proton hole and one neutron particle neighbor to 100Sn, was investigated at the GSI on-line mass separator by using germanium
detectors and a NaI total-absorption spectrometer. On the basis of bgg coincidences, the 100In decay scheme was established for the first time. The ground-state spin and parity for 100In are discussed by investigating beta feeding of levels in 100Cd and beta-delayed proton emission to 99Ag. The half-life was remeasured and found to be 5.9(2) s. The Q-EC value was determined from the measured EC/beta+ ratio for the beta-delayed protons to be 10.08(23) MeV. The main fraction of the
beta feeding was established to populate the region of 6 MeV excitation energy, which corresponds
to a total Gamow-Teller (GT) strength of 3.9(9) and a centroid at 6.4 MeV. Large-scale shell-model calculations employing a realistic interaction are used to a
ssign configurations to states in 100In and 100Cd. The GT beta-decay strength distribution measured in the total absorption experiment is compared to shell-model
predictions. The deduced overall hindrance of the GT strength agrees with the values predicted for the 100Sn GT decay.

A monitoring system based on adaptive heat balances has been developed for early fault detection in exothermic reactions. Its efficiency could experimentally be proven for a homogeneous esterification reaction in the laboratory reactor and pilot plant scale.
Experiments under normal and several faulty conditions were carried out in different reactor scales to prove the adaptation of the monitoring technique to various scales of chemical batch reactors. Results of the on-line testing in the pilot plant showed that the monitoring system was able to recognise undesired faults correctly.

QCD sum rules predict that the change of the strange quark condensate ‹ss› in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from Φ- meson decays.
Due to the expansion of hadron matter in heavy-ion collisions, the Φ peak suffers a smearing governed by the interval of density in the expanding fireball, which appears as effective broadening of the di-electron spectrum in the Φ region. The width of the emerging broadening is sensitive to in-medium change of ‹ss›. This allows to probe directly in-medium modifications of ‹ss› via di-electron spectra in heavy-ion collisions at SIS energies with HADES.

Im Rahmen des Teilvorhabens wurde ein Online-Monitoring-System für stark exotherme Reaktionen entwickelt, das das Bedienungspersonal bei der optimalen und umweltgerechten Prozessführung von komplexen oder sicherheitstechnisch schwierigen Semibatch-Prozessen in Rührkesselreaktoren (Batch-Reaktoren) unterstützen soll. Das Monitoring-System (MoSys) basiert auf dimensionslosen Stoff- und Wärmebilanzen mit adaptiven Komponenten. MoSys muss zuerst mit den Prozessdaten von normalen und unerwünschten Batch-Verläufen angelernt werden, die im Miniplant unter den Bedingungen des Industrieprozesses durchgeführt wurden. Die Adaption der Bilanzmodelle an die Zielanlage erfolgt durch zweischichtige Perceptron-Netze. Um eine vollständige Maßstabsübertragung zu gewährleisten, sollte MoSys mit Prozessdaten von mindestens einem normalen Batch-Verlauf in der Chemieanlage angepasst und validiert werden. MoSys wurde sowohl für eine homogene exotherme Veresterungsreaktion als auch für einen komplexen heterogenen exothermen Hydrierprozess konzipiert. Experimentelle Tests wurden für die Veresterung in einer Pilotanlage und für die Hydrierung in einer industriellen Chemieanlage durchgeführt. Zur Industrieerprobung wurde MoSys in ein Batch-Informations-Management-System (BIMS) integriert, das auch entwickelt und in das Prozessleitsystem (PLS) einer Mehrzweckanlage im Feinchemie-Werk Radebeul (Degussa AG) implementiert wurde. Dadurch konnten die MoSys-Ausgaben simultan mit wichtigen Prozesssignalen auf den Terminals des PLS visualisiert werden. Zum Beispiel werden der Hydrierungsfortschritt, das vorhergesagte Reaktionsende und die Konzentrationsverläufe des Edukts, Zwischenprodukts und Produkts auf den Terminals der Operatorstationen angezeigt. Wenn unerwünschte Betriebszustände auftreten, wird das Bedienungspersonal frühzeitig alarmiert und Anweisungen für Gegenmaßnahmen, die nur vom Operator ausgeführt werden dürfen, werden auf den Terminals angezeigt. Die Leistungsfähigkeit von MoSys/BIMS konnte während zweier Hydrierungs-Produktionskampagnen nachgewiesen werden.

The on-line monitoring system (MoSys) for complex hydrogenation processes has been developed to support the operator in decision making. For industrial testing, the MoSys prototype was embedded in a newly developed batch-information-management system (BIMS) coupled to the process control system of the chemical plant. In this paper, the working principles of MoSys and BIMS are described. Furthermore, the optimisation and the verification of MoSys in the laboratory reactor are discussed. First results from on-line testing in a chemical plant of the Degussa AG are also presented.

An on-line monitoring system (MoSys) based on dimensionless mass and heat balances with adaptive functions was developed to support the operational personnel during the optimal and environmentally compatible process control of the complex multiphase hydrogenation in stirred tank reactors. For industrial testing, MoSys was integrated in a batch-information-management system (BIMS) which was also developed and implemented in the process control system (PSC) of a multipurpose reactor installation. As a result, the outputs of MoSys, such as the progress of hydrogenation, the predictive end of reaction and concentration profiles, can simultaneously be visualised with important process signals on terminals of PCS. The efficiency of BIMS/MoSys could be proven during two industrial hydrogenation campaigns.

no abstract delivered from author

The core baffle of a PWR is loaded by the pressure difference between bypass and core and by temperature profiles developing from gamma heating and heat transfer into the coolant. Strain, deformation and gaps between the sheets resulting from this load are determined con-sidering the effect of neutron irradiation induced creep of the core baffle bolts. The finite ele-ment code ANSYSÒ 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:

1. Evaluation of the three dimensional distribution of neutron flux and gamma induced in-ternal heating with the Monte Carlo code MCNP®. These calculations are based on pin wise power distributions at the core edge for typical loading patterns.
2. Calculation of the temperature distribution in the core baffle for different operational conditions and core loading patterns, considering heat conduction in the components with internal heat sources (gamma heating, step 1) and convectional boundary condi-tions (heat transfer coefficients and bulk temperature of the coolant).
3. Calculation of time dependent deformation, stresses and strains taking into account weight, pressure loads, temperature fields for different load situations (step 2), prestress-ing, irradiation induced creep of the bolts as correlated to neutron flux (step 1).

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.

The coupling of Bloch oscillations to longitudinal optical phonons is investigated in a narrow-well InGaAs/InAlAs superlattice. A strong increase of coherent phonon amplitudes is observed when the Bloch oscillations are subsequently tuned into resonance with different optical phonon modes. The rapid dephasing of the Bloch oscillations due to field induced tunneling from the weakly bound miniband into above-barrier continuum states leads to an additional and new excitation process of coherent phonons in superlattices at high electric fields. Polarization dependent measurements confirm their generation via Coulomb interaction excluding any contribution through impulsively stimulated Raman scattering.

Since 1997 in-beam PET is successfully used to monitor the precision of dose application in highly conformal carbon ion tumour therapy at the experimental facility at the Gesellschaft f\"ur Schwerionenforschung Darmstadt (GSI), Germany.
The potential of the method for the monitoring of proton therapy is currently under investigation.
In our first experiment, three monoenergetic proton beams were stopped in targets of organic plastics placed in the centre of the field of view of the in-beam PET scanner at GSI. The beta^{+}-activity was found to be three times higher than that induced by carbon ions at the same range and applied dose. The reconstructed beta^{+}-activity distributions were rather well reproduced by model calculations. The possible extraction of valuable clinical information from the comparison between measured and calculated beta^{+}-activity distributions is discussed.
Despite the weaker spatial correlation between beta^{+}-activity and dose depth-profiles in the proton case, the presented analysis strongly supports the feasibility and clinical usefulness of in-beam PET for the monitoring of proton therapy.

A thin Si3N4 surface layer is formed by implantation of 60 keV 15N nitrogen ions into single-crystalline silicon <100> with a fluence of 5.6x1017 ions/cm2 and subsequent annealing (1295°C, 15 min) under high vacuum conditions. The 15N depth distribution is measured with the resonant nuclear reaction 15N(p,alpha-gamma)12C. The formation of Si-N bonds is proven by Fourier transform infrared spectroscopy using samples implanted with 14N ions and 15N ions, respectively. The crystallinity of the Si3N4 surface layer is studied by X-ray diffraction and transmission electron microscopy. The annealing process leads to the formation of a polycrystalline alpha-Si3N4 surface layer with a thickness of 90 nm. The analysis of high resolution TEM micrographs shows that the layer is split into two sublayers both consisting of single alpha-Si3N4 crystals with lateral extension up to 500 nm.

Obwohl zur Anwendung von Magnetfeldern bei der Erstarrung, z. B. beim Stranggießen von Al-Legierungen oder Stahl und bei der Kristallzüchtung, bereits Erkenntnisse vorliegen, befindet sich dieses Gebiet erst am Anfang seiner Entwicklung. Die Beeinflussung des Temperaturfeldes durch magnetfeldinduzierte Strömungen beim Phasenübergang flüssig/fest läßt wegen der Auswirkungen auf Keimbildungs- und - Kornwachstumsreaktionen ein bisher kaum beachtetes Entwicklungspotential für Werkstoffe und Technologien erwarten. Zielstellung der Arbeiten ist die Erzeugung eines feinkörnigen, globulitischen Gefüges bereits in Folge des Erstarrungsprozesses, analog dem, welches in Knetlegierungen nach einer Umformung und Wärmebehandlung vorliegt. Zu klären ist, inwieweit die bei herkömmlicher Erstarrung auftretenden Konzentrations- und Eigenschaftsgradienten sowie die Lunkerbildung unterdrückt werden können. Ferner soll untersucht werden, inwieweit durch die Dauer und Intensität magnetfeldinduzierter Strömungsvorgänge speziell im Zweiphasengebiet flüssig/fest Einfluß auf die Entstehung und den Aufbau des Endgefüges genommen werden kann.
Vorgestellt werden experimentelle Arbeiten zur Untersuchung der gerichteten Erstarrung von PbSn-Legierungen in einem rotierenden Magnetfeld. Gemessen werden Abkühlungskurven und Geschwindigkeitsmessungen während des Erstarrungsprozesses.

Due to significant differences in material properties such as density or surface tension the behaviour of gas bubbles reveals some peculiarities in liquid metal applications as compared with ordinary water flows. Moreover, questions about the wetting of solid surfaces or the role of impurities which have a minor importance in water systems, however, show a more dominant influence in metallic melts.
In view of the production of metallic foams the control of the properties of liquid metal two-phase flows by electromagnetic forces in a contactless way would be very attractive. Some examples of magnetic field applications will be presented with respect to the bubble generation process, the dispersion of gas bubbles or the momentum and heat transfer properties of liquid metal bubbly flows.
If gas bubbles are injected into a liquid metal characterised by a large surface tension one should take care to get a good wetting between the fluid and the surface of the gas injector. Otherwise, the gas would try to spread out along this interface to form gas layers. A control of the bubble size and formation rate becomes difficult. The comparison between experiment and theoretical models describing bubble formation processes requires an ideally wetted gas injector. The bubble formation in mercury and the eutectic alloy InGaSn has been studied by means of several methods of gas injection, for instance through single orifices or injectors made from sintered metals with a mean porosity of a few microns. X-ray measurements have been used to directly observe the resulting gas bubbles rising in the liquid metal. In the case of a single orifice the influence of electromagnetic forces on the bubble frequency has been demonstrated.
The transport properties of small argon bubbles have been studied in turbulent upwards channel flows of sodium and mercury. The bubbles were injected by a single orifice located in the centre of the channel cross section. After a distinct distance the local void fraction and the bubble velocity have been measured by means of electrical resistivity probes. The flow has been exposed to external magnetic fields directed transverse or longitudinal to the mean flow direction. Experimental results showing the effect of the magnetic field on the horizontal gas distribution and the ratio between gas and liquid velocity will be presented.
The variety of standard measuring techniques to characterise liquid metal flows is limited due to the nature of metallic melts. However, the availability of diagnostic methods to get information about the structure of liquid metal two-phase flows is a crucial point. A selection of measuring techniques which have been developed in our group to determine flow parameters such as the phase velocities, the void fraction or the bubble size will be discussed with respect to their capabilities and restrictions in various applications.

Constitutive models for the interaction between the gaseous and the liquid phase are needed for application of CFD codes on two-phase flow phenomena as they occur in many scenarios concerning safety analysis of nuclear reactor systems. For the bubble flow and slug flow regime this especially concerns the forces acting on a bubble in the liquid flow field and bubble coalescence and break-up. Vertical pipe flow is an appropriate situation to investigate these effects. This is done experimentally by using new measuring techniques, which allow measurements with a high resolution in space an time. The experimental results show, that besides local effects also the bubble size distribution has an important influence of the development of the flow. A simplified model was developed to test and improve the constitutive laws. To ensure the transferability of the models experiments for vertical pipes with an inner diameter of up to 200 mm are planned, using our new test facility TOPFLOW.

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

no abstract

no abstract

no abstract

no abstract

no abstract

kein Abstract -Poster-

kein Abstract -Poster-

Especially in Saxony and Thuringia the intense uranium mining and milling causes a wide variety of contaminated waters. These seepage and mine waters contain besides uranium several inorganic and organic complex forming agents [1, 2].
Heavy metals in the aquatic environment are normally transported as a complexed species. Knowledge about the complex formation is therefore an essential constituent in prediction of the migration of these elements.
Spectroscopic methods have the advantage to be non-invasive and non-destructive. The high intensity of laser light sources allows the excitation of all species in the illuminated volume. Therefore laser based methods reach low detection limits.
At higher concentrations uranium forms often poly-nuclear complexes. Therefore studies of the complex formation should be carried out at concentrations which are relevant to those of the contaminated sites. Also the direct determination of the species formed in the mining related waters is essential for the selection of effective cleaning methods.
As uranium(VI) shows fluorescence properties (except carbonate species) time-resolved laser-induced fluorescence spectroscopy enables the detection of species up to detection limits of 10-8 M. Besides the study of the complex formation (sulfate, phosphate, arsenate) we determined the formed species in several mining related waters as function of pH. The change in the speciation of uranium(VI) is shown to be in agreement with calculations, if also the formation of formerly unknown species is included.
Carbonate species are dominating the uranium(VI) speciation in the neutral pH range. As mentioned above these species do not emit fluorescence. Uranium(IV) does not show fluorescence properties. In these cases only the absorption spectra can be used for the direct determination of these species. However the concentration of uranium in the natural environment is much lower than the detection limit of conventional UV-VIS spectroscopy. Using laser-induced photoacoustic spectroscopy the detection limit can be decreased by about three orders of magnitude. Studies of the complex formation of uranium(IV) with phosphate and arsenate will be presented [3], demonstrating the advantage of direct speciation methods.

[1] G. Geipel, G. Bernhard, M. Rutsch, V. Brendler, H. Nitsche; Speciation in Water Released from Mining and Milling Facilities In T.E. Baca and T. Florkowski (eds.), The environmental Challenges of Nuclear Disarmament, Kluwer Academic Publishers, 2000, p. 323-332
[2] G. Bernhard, G. Geipel, V. Brendler, H. Nitsche; Speciation of Uranium in Seepage Waters from a Mine Tailing Pile Studied by Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS); Radiochimica Acta, 74, 87, (1996)

The nuclear microprobe at the 5 MV tandem accelerator of the Central Institute for Nuclear Research at Rossendorf is realized by object diaphragms of 50, 70 and
100-mu-m and a magnetic quadrupole triplet. The proton microbeam with a spot size of about 4-mu-m is used for NRA. Depth profiles for oxygen in zirconium
alloys and for fluorine in human teeth were measured by scanning the beam linearly over cross sections of the samples using the resonant proton backscattering at 4.5
MeV and the nuclear reaction F-19(p, alpha(0))O-16 at 3 MeV, respectively.

For studying deuterium depth profiles in surfaces of JET (Joint European Torus) limiters, a new deuterium profiling method was developed and used. A smooth
10-degrees slope plane on the specimen was produced by ion beam slope cutting using a 10 keV Kr ion beam. To detect deuterium the nuclear reaction H-2(C-12,
p)C-13 was used at E(C-12(3+) = 7.5 MeV. The very narrow proton peak could be clearly separated from the background of the spectra. For measuring the
lateral and vertical deuterium distribution the C-12 beam of the Rossendorf 5 MV tandem accelerator was focussed to about 6-mu-m and scanned across the
specimen. The preliminary results show a deuterium distribution up to a depth of about 5-mu-m in a carbon limiter

The fluorine concentration of chemically enriched hydroxylapatite (Ca10(PO4)6(OH)2) was measured by means of PIGE using the nuclear reactions F-19(p, p'
gamma)F-19 and F-19(p, alpha-gamma)O-16. The experiments were done in-two runs with 1.68 and 2.15 MeV proton incidence. The results determined with
inelastic scattering are in good agreement in the two runs. The samples are suitable as new fluorine standards in the ppm region to study the fluorine content in tooth
enamel.

kein Abstrakt

no abstract delivered from author

For measuring hydrogen concentrations up to a depth of several tens of micrometers we propose the use of a special sample preparation method - ion beam slope
cutting. The principle and the experimental arrangement are described. The depth profiles are obtained by line scans of the nuclear microbeam over the slope planes.
The nuclear reactions (H(15N, alpha0)C)-H-1-C-12 and (H(B, alpha)2alpha)-H-1-B-11 were investigated and proved suitable for hydrogen analysis with the
microbeam detecting the alpha-particles at backward angles.

no abstract delivered from author

kein Abstrakt

SiO(x)N(y) layers in the thickness range from 4 to 20 nm are grown by rapid thermal processing (RTP) using NH3 and N2O as nitridants. I-V measurements,
investigation of the time-dependent breakdown, and post-stress C-V display significant distinctions between the layers according to their growth conditions. For the
explanation of the electrical behaviour, the compositional structure was examined by means of AES, SIMS, and NRA.

Bone structures, represented in the form of so-called lines of arrested growth, were observed in medieval human femur. Because process and causes of line
formation are not yet understood multielement analysis on a cross section of a femoral bone was carried out by micro PIXE using the Rossendorf nuclear
microprobe. A series of line profiles across the bone lines, elemental maps and point analyses on a line and beside it show reproducibly increased concentrations of
the trace elements Mn, Fe, Zn, Pb and Sr on the bone lines.

Siliconoxynitride layers with thicknesses between 5 and 10 nm were grown on (100) oriented silicon by rapid thermal processing (RTP) using either N20 or NH3 as nitridant. In order to study the trapping behaviour at the interface and in die insulator bulk, capacitance-voltage (CV) and current-voltage (IV) measurements have been performed combined with different magnitudes of Fowler-Nordheim stress. In addition, Deep Level Transient Spectroscopy (DLTS) has been applied for interface state detection. Auger Electron Spectroscopy (AES) has been used to obtain depth profiles for Si, N, 0 and C. The deconvolution of die AES signal displays significant peak contributions related to intermedium oxidation states. Nuclear Reaction Analysis (NRA) was successfully applied for hydrogen detection in buried SiOXNY thin films.

Titanium oxides are considered as blood compatible surfaces, however, it may be possible to improve the compatibility to the inner lining cells of blood vessels by addition of Ag which modifies the electronic properties of this oxide. Therefore, Ti–Ag–O films with the thickness of 200–350 nm have been deposited on Si substrates using an ion beam assisted deposition (IBAD) system which has two evaporators to allow a simultaneous deposition of Ti and Ag. The evaporation rates of Ti and Ag, as well as the flow rate of O2 have varied. For physicochemical analysis of the films, glancing incidence X-ray diffraction (GIXRD) analysis, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were performed. The formed phases in Ti–Ag–O films consist of TiO2, AgO, Ag2O, Ag, TiAg, AgTi3, and low valent titanium oxides. The bovine aortic endothelial cell line GM07373 was grown on these surfaces in a medium with 10% fetal bovine serum. The toxicity of the layers was rated by the release of lactate dehydrogenase (LDH) from the cells and are found to be below the detection limit; the cell adhesion was investigated by fluorescent staining of the adhesion molecule vinculin and the cytoskeleton protein filamentary actin; the cell nuclei were counterstained with DAPI, showing good cell adherence, good compatibility to endothelial cells, and no indication of apoptotic cell death.

Three effects have been observed in wet-thermally grown SiO2/Si structures under bombardement with energetic N-15 ions:

(1) Out-diffusion of H from the SiO2/Si system through the surface,
(2) Accumulation of H at the SiO2/Si interface,
(3) Changes in the optical fingerprint spectra of Psi and Delta in dependence on lambda (wavelength) obtained by ellipsometric measurements.

The coolant mixing is significant for safety assessment of boron dilution and cold water transients. For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM was constructed. ROCOM is a 1:5 scaled Plexiglas model of the PWR Konvoi disposing of four loops with fully controllable coolant pumps. Mixing of both overcooled and de-borated water is investigated by adding a tracer salt solution, performing conductivity measurements by wire mesh sensors and velocity measurements by the LDA technique. The tracer concentration fields established by coolant mixing under steady-state and transient flow conditions were investigated. The experiments aimed at the validation of CFD codes. CFD calculations were carried out with the code CFX-4. In case of running pumps, ROCOM measurements provided a tracer concentration maximum in the core sector below the inlet nozzle of the loop with tracer injection, while the maximum reaches more than 90% of the simulated overcooling in the corresponding loop. This situation is typical for a cold water transient due to main steam line break. During start-up of the first pump being relevant for boron dilution transients, the maximum of the tracer concentration appears at the core inlet at positions opposite of the loop with injection, while the maximum boron dilution strongly depends on slug size, slug initial position and mass flow ramp. A good agreement was achieved between measuring results and CFD calculations.

A semi-analytical perturbation reconstruction model (SAPR) has been developed allowing the description of the coolant mixing inside the reactor pressure vessel of PWRs by superposition of response functions on nearly Dirac-shaped perturbations, which can be determined experimentally or from CFD calculations. SAPR provides realistic time-dependent boron concentration fields at the core inlet for the analysis of a hypothetical boron dilution event after start-up of the first main coolant pump in a generic four-loop PWR. Core calculations were performed with the 3D reactor dynamics code DYN3D. By varying the initial slug volume it was found, that for the given core loading pattern slugs of less than 20 m3 do not lead to re-criticality of the shut-off reactor. Calculations with the bounding slug volume of 36 m3 show, that the corresponding reactivity insertion does not result in core damage.

In the Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, electrode-mesh sensors were developed, which allow the measurement of the electrical conductivity distribution in a flow duct with a rate of up to 10 000 frames per second. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Beside a description of the working principle, this lecture focuses on different applications of the method, which will be illustrated by digital image sequences obtained by electrode-mesh sensors.
The sensor consists of two planes of wire grids placed into the flow in a short distance behind each other. The angle between the wires of both grids is 90 deg. The wires of the first plane (transmitter plane) are supplied with pulses of a driving voltage. During the measuring cycle, they are activated by a multiplex circuit in a successive order. After an analogue/digital conversion the receiver signals are recorded by a data acquisition computer connected to AD converters and stored for each receiver electrode separately. This procedure is repeated for all transmitter electrodes. In this way the distribution of the electrical conductivity over the cross section occupied by the sensor is obtained row by row. This data is used for slow-motion visualization of transient flows and for quantitative measurements of gas fractions and their profiles, bubble sizes and velocities.
Special attention was given to achieve a DC free excitation of the electrodes in order to suppress the imaginary part of the measured impedance. Measures were taken to suppress cross-talk between parallel electrodes. The first generation device allowed measurements in a grid of 16 x 16 measuring points distributed over the cross section of the flow duct with a rate of 1200 frames per second.
The high spatial and time resolution of the wire-mesh sensor allows to calculate bubble size distributions from the sequence of frames. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. After assigning the local instantaneous gas fractions (pixels) to bubbles by a bubble recognition algorithm, the volume of each identified bubble is obtained by adding the local values belonging to the selected bubble. Capabilities and accuracy of this method were investigated using a sensor, which was built into a transparent perspex channel. Combined visualizations using the frames of a high-speed video camera together with the measuring sequences of the wire-mesh sensor have shown that the sensor acts as a bubble fragmenting obstacle. It could nevertheless be proven, that the sensor signal represents the bubble geometry present in the upstream flow, i.e. before the disturbance, with a good accuracy.
In the first application the sensor was used to study the evolution of the flow pattern in an upwards air-water flow. The visualization shows the result of an air injection through wall orifices of 4 mm diameter (pipe diameter 51.2 mm) and the evolution of the flow pattern from L/D = 0.6 to L/D = 60. Large primary bubbles are observed, which are both coalescing and fragmenting in the direction of the flow. Large bubbles tend to travel towards the center of the pipe. At the end of the test section a slug flow is established. Another wire-mesh sensor was used by the University of Munich, Germany, to visualize the effect of a globe valve to the flow regime in a horizontal pipe. The image sequence shows the initial slug flow through the open globe valve and the transition of the flow pattern during closing of the glob valve.
Beside air-water flows the sensor can also be applied to measure the void fraction in steam-water mixtures. The sensor is used to study natural circulation instabilities in a boiling water reactors. For this purpose, two wire-mesh sensors are installed at the CIRCUS test facility of the U...

Damages in pipeline systems are often ascribed to water hammer and cavitational hammer. The resulting leakage can cause considerable damages to mankind and environment. To control these pressure surges, Fraunhofer UMSICHT and Forschungszentrum Rossendorf have conducted experiments whose results are used to develop new methods for the prevention of water hammer and cavitational hammer. The fast-acting valve is equipped with an innovative hydraulic braking system ("ABS-Armatur") and is combined with a check valve to suppress the water hammer. Since the described system does not need any additional energy source and adapts automatically to changes of the pipe system parameters, it is also regarded as particularily suitable for already existing plants.

High-spin states in ¹²³Xe were populated in the
¹¹⁰Pd(¹⁸O,5n)
reaction at 75 MeV and gamma-ray coincidences were measured with
the GASP spectrometer.
A new rotational sequence of enhanced dipole transitions was established.
This band, as well as a similar band in ¹²⁴Xe, may be described
within the framework of the tilted axis cranking model as bands for
which comparable amounts of angular momentum are generated by
magnetic and collective rotation, respectively.

Thin films of Ba3Ca1.18Nb1.82O8.73, prepared in a sol-gel process by multiple dip-coating on silicon wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressure and temperature. The hydrogen content was determined ex situ at room temperature using nuclear resonance reaction analysis. From the resulting water vapour pressure-composition isotherms the absorption enthalpies Delta(empty set)H(o), Delta(empty set)H(t) and the absorption entropy Delta(empty set)S were calculated, using a two-site model, based on Fermi-Dirac statistics. On Ba3Ca1.18Nb1.82O8.73 bulk material also impedance spectroscopy, concentration and fuel-cell measurements as well as neutron diffraction were performed. From these data, taken together, the proton diffusion coefficient D-H could be evaluated and compared to quasielastic neutron scattering results.

The nucleus ⁷⁰Se was studied using the ⁴⁰Ca(⁴⁰Ca, 2α) reaction at a beam energy of 185 MeV. Gamma rays were measured with the EUROBALL III spectrometer. The known positive-parity bands have been extended and one new band of positive parity and two of negative parity have been identified.
These bands are interpreted in terms of the cranked Nilsson-Strutinsky approach. Calculations suggest that the two negative-parity bands, which have the same signature, are both based on a configuration with two protons and three neutrons lifted from the fp shell to the g _9/2 orbital, but at different nuclear shapes. This represents a shape coexistence at high spin.

kein Abstrakt

Deuterium inventories have been measured in plasma facing components of ASDEX Upgrade. Nearly 60% of the total D-inventory was observed in the lower inner divertor target plate in redeposited layers of low-Z material. The outer divertor, however, was found to be dominated by erosion processes and correspondingly retained a much lower amount of deuterium. The D-inventory at the main chamber plasma facing components can be explained by a model employing implantation of charge-exchange neutrals, which yields very good agreement with the experimental findings for all surfaces not exposed to direct ion fluxes.

no abstract delivered from author

Raman spectroscopy, spreading resistance probe (SRP) analysis, scanning electron microscopy (SEM) and elastic recoil detection analysis (ERDA) studies were carried out on H-plasma treated and annealed p-type Czochralski (Cz) Si. The formation of voids filled with hydrogen molecules was observed by Raman spectroscopy after plasma hydrogenation. The Raman and ERDA measurements show that molecular hydrogen can be released from nanovoids at 600 °C which leads to the formation of empty voids. ERDA and SEM investigations show that after the hydrogen plasma treatment the formation of voids filled by hydrogen occurs at a depth of about 400 nm. SRP measurements show, that at 400 °C post-hydrogenation annealing for 10-60 min a fast diffusion of hydrogen into the bulk occurs. This leads to the hydrogen enhanced thermal donor formation and therefore to a carrier profiles modification up to a depth of a few hundred microns. The Raman measurements show that the molecular hydrogen can not be released from nanovoids at 400°C which is in good agreement with ERDA data. Our investigations give a method for the low-temperature, low-cost modification of die Cz Si substrates which leads to die formation of a carrier gradient in die bulk, to surface structuring and to voids formation in the subsurface region.

A Distributed Electron Cyclotron Resonance plasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit ta-C:H (Diamond-Like Carbon, DLC) thin films at RT. A graphite sputtering target immersed in an argon plasma was used as carbon source. The Ar plasma density was about 5 exp(10) cm-3. Single crystalSi substrates were RF biased to a negative voltage of -80 V. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H ---> 12C +4He + Gamma, elastic recoil detection analysis (ERDA) and Rutherford backscattering (RBS) were used to investigate the early phase of the growth. The morphology of the films grown at low pressure (0.3 mTorr) is shown to be dominated by stress-mediated nucleation leading to formation of basket-like clusters of circular hillocks 20 nm high surrounded by a planar, mostly sp2 bonded film ~8 nm thick. With increasing plasma pressure the spatial frequency of the hillocks becomes random and the growth is dominated by the Stranski-Krastanov mode. The XPS data taken at decreasing emergence angles show that the structure of the hillocks is dominated by sp3 bonded carbon. The XPS argon signal disappears at 10° emergence angle indicating that integration of argon occurs mainly within the sp2 bonded regions. The NRA and ERDA analysis show that the amount of integrated hydrogen decreases with increasing substrate current density. RBS data indicate that increasing bias enhances argon integration.

A distributed electron cyclotron resonance (DECR) plasma reactor powered by a microwave generator operating at 2.45 GHz (800 W) was used to deposit (t)a-C:H thin films at RT on <100> Si substrates RF biased within the range 25 < |Vo| < 600 V. C2H2 was used as precursor. The plasma pressure was varied within the range 0. 1 < P < 1 .5 mTorr. The films were analysed using spectroscopic ellipsometry (SE) and Fourier transform infrared (FTIR) spectroscopy. The hydrogen content NH and the density of the films were determined from nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H ---> 12C + 4He + Gamma. Positron annihilation spectroscopy was used to detect the porosity. The evolutions of NH as a function of the substrate ion current density n+ and as a function of Vo show that the hydrogen incorporation results from the competition between chemisorption and deposited energy density related effects. The increase of the hydrogen incorporation leads to a decrease in the film density and a lower deposition rate. The porosity of the films deposited at low pressure (~ 0. 1 mTorr) with Vo = - 80 V has been detected. The comparison between results of SRIM-2000 simulations and the evolution of NH as a function of Vo shows that the porosity and the hydrogen content are not correlated. The absorption of oxygen and nitrogen for the low density films has been detected from the observation of the 3250-4000 cm-1 infrared (IR) band.

Until recently, the existence of oscillatory mean-field dynamos of the alpha^2-type with spherically symmetric and isotropic alpha was an open question. We find such dynamos by means of an evolutionary strategy, and we illustrate the spectral properties of the corresponding dynamo operators.

Alloying by high dose ion implantation of iron into magnesium and aluminum

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

The encapsulation of active centres is a widespread principle used in biological systems. So, enzymes may wrap certain substrates leading to the complete shielding from the environment. Currently, dendrimers are considered to be applicable as artificial encapsulating systems which can effectively bind guest molecules. In principle, dendrimers can accommodate different kind of guests, such as anionic species, metal ions, and neutral substrates. Furthermore there is the possibility to graft biomolecules on the periphery of dendrimers, by which in particular the biodistribution can be influenced. These unique structural features and properties make dendrimers attractive as candidates for imaging and therapeutic purposes. In this nexus, the encapsulation of radionuclides by dendritic boxes^[1] (I) and the fixation by dendrons^[2] (II) seems to be promising concepts.

We report on preliminary results of binding pertechnetate and perrhenate by polypropyleneamine dendrimers. Lipophilic urea-containing dendrimers are efficient carriers for these anions. We could shown that the polyamine skeleton is suitable for binding some anions inside of the dendrimer.
The concept of dendritic encapsulation in view of the development of highly stable metallodendrimers is discussed. Some examples for potential copper- and rhenium-containing dendrimers are presented.

[1] J. F. G. A. Jansen, E. W. Meijer, E. M. M. de Brabander-van den Berg: The dendritic box: Shape-selective liberation of encapsulated guests, J. Am. Chem. Soc. 1995, 117, 4417-18.
[2] S. Hecht, J.M.J. Frechet: Dendritic encapsulation of function: Applying nature's site isolation principle from biomimetics to materials science, Angew. Chem. Int. Ed. Engl. 2001, 40, 74-91.

no abstract delivered from author

Diamond-like carbon is a system of rather high disorder as it has a wide optical absorption tail and a high density of paramagnetic defects. The defect density
remains high even in DLCs containing 30-60% hydrogen, so hydrogen does not appear to passivate defects well unlike in a-Si:H. To investigate the role of hydrogen
on the disorder in DLCs we have investigated the effect of low concentrations of hydrogen on the disorder in ta-C, by introducing 10(-6)-10(-3) mbar hydrogen into
the deposition of ta-C by filtered cathodic vacuum are (FCVA), which corresponds to 0.1-15 at.% hydrogen in the films. Higher pressures of hydrogen reduces the
ionisation leading to sp(2) bonding, and ultimately the thermalisation of the plasma leads to nanotubes and fullerenes. The deposited ta-C:H films were investigated by
electron energy loss spectroscopy (EELS), Raman spectroscopy, optical measurements, electronic transport and N-15 resonant nuclear reaction analysis. Plasma
characterisation with a retarding field analyser showed that the ion current density remains nearly unchanged in the pressure range used to deposit the films. Raman
measurements indicate the onset of clustering of sp(2) sites when the hydrogen pressure exceeds 2 x 10(-4) mbar. We find that small amounts of hydrogen increase
the optical gap up to 2X10(-6) mbar hydrogen pressure, and then the band gap decreases continuously. The absorption tail sharpens by the addition of hydrogen, as
measured by photothermal deflection spectroscopy (PDS) and thus confirms the Raman measurements that suggest that the order in the material increases with
increasing hydrogen content. (C) 2001 Elsevier Science B.V. All rights reserved.

Hüllproteinschichten (S-Layer) sind Protein- oder Glykoproteinschichten auf der Oberfläche vieler Bakterien und Archaea. Sie können als Gitter mit schräger, tetragonaler oder hexagonaler Symmetrie vorliegen. Die Funktion dieser äußersten Zellwandkomponente ist nicht einheitlich und nur teilweise näher untersucht. So können diese zum Beispiel als Schutzhülle, Molekularsieb oder Ionenfalle fungieren oder der Formerhaltung dienen. In neueren Arbeiten konnte gezeigt werden, dass die Hüllproteinschichten verschiedene Metalle binden und in einigen Fällen die Bildung von Nanoclustern ermöglichen. Unter den Aspekten der Wechselwirkungen von Hüllproteinen mit Schwermetallen und der Entwicklung möglicher Bioremediationsverfahren auf der Basis immobilisierter Biokomponenten wurden Hüllproteine von Bakterien untersucht, die von Schwermetall und Radionuklid belasteten Umgebungen isoliert wurden. Dazu wurde ein Hüll-protein eines Bakteriums aus einer Uranabfallhalde isoliert und strukturell sowie molekularbiologisch analysiert.
Im Rahmen der vorgelegten Arbeit wurden mehrere Haldenisolate der Gattung Bacillus hinsichtlich der Existenz von Hüllproteinen untersucht. Dies erfolgte mit Hilfe einer neu entwickelten Methode zum schnellen Nachweis von Hüllproteinen auf Gram-positiven Bakterien. Dabei wird das Peptidoglycan der Zellwand mit Lysozym verdaut und auf diese Weise die Proteinschicht von der Zellwand gelöst. Die freien Schichten können somit im Transmissionselektronenmikroskop oder Atomkraftmikroskop direkt nachgewiesen werden. Es wurde gefunden, dass nur das Isolat Bacillus sphaericus JG-A12 eine Hüllproteinschicht mit tetragonaler Symmetrie und einer Gitterkonstante von 12,5 nm besitzt. Die (135±5) kDa schweren Hüllproteinmonomere sind nicht glykosyliert, weisen aber zwei verschieden stabil gebundene Phosphorspezies auf. Mittels molekularbiologischer Analysen konnten Teile der Hüllproteingene von B. sphaericus JG-A12 (Base 1 bis 1497 des strukturkodierenden Teils des Gens) und des nächst verwandten Referenzstamms B. sphaericus NCTC 9602 (Base 1 bis 579 des strukturellen Teils des Gens) entschlüsselt werden. Beide Hüllproteine besitzen N-terminal drei S-Layer homologe Domänen und weisen in den Aminosäuren 1-182 nur sehr geringe Identitäten zu bereits entschlüsselten Hüllproteinen anderer B. sphaericus Stämme auf. Dem gegenüber ergeben sich hohe Identitäten für die Aminosäuren 183-320 für Hüllproteine mit tetragonaler Symmetrie (Hüllproteine der B. sphaericus Stämme P-1 und CCM 2177) und sehr niedrige für das Hüllprotein mit schräger Symmetrie (Hüllprotein von B. sphaericus WHO 2362).

Im Hinblick auf katalytische Anwendungen oder der Entwicklung von Bioremediationsverfahren auf der Basis immobilisierter Biokomponenten wurden die Wechselwirkungen von Hüllproteinen mit verschiedenen Metallen untersucht. Es konnten direkte Wechselwirkungen von Palladium, Platin und Uran mit den Hüllproteinen von B. sphaericus JG-A12 und NCTC 9602 nachgewiesen werden. Die Ergebnisse zeigen für beide Proteine eine Komplexierung von Platin über CO- und NH-Gruppen der Peptidbindungen und über COOH- und OH-Gruppen. Das Hüllprotein von B. sphaericus JG-A12 komplexiert Palladium über NH-Gruppen der Peptidbindung und COOH-Gruppen, während das von B. sphaericus NCTC 9602 Palladium sowohl über CO-Gruppen der Peptidbindungen als auch über COOH- und OH-Gruppen bindet. Die Komplexierung von Uran erfolgt vorrangig über NH-Gruppen der Peptidbindungen aber auch über OH- sowie zwei verschiedene PO4-Gruppen. Um eine Anwendung der metallbindenden Eigenschaften von Hüllproteinen im Rahmen von Bioremediationsprozessen zu ermöglichen, wurden diese mittels Sol-Gel-Technik in einer SiO2-Matrix immobilisiert und die Sorption und Desorption von Uran und Kupfer untersucht. Zum Vergleich wurden intakte Zellen und Sporen immobilisiert und in die Untersuchungen mit einbezogen. Die biologisierten Keramiken (Biocere) binden 2,7-42fach mehr Uran und Kupfer als andere zur Sanierun...

Energiereiche Neutronenstrahlung verursacht in Materialien Schädigungen, die zum Verlust ihrer mechanischen Festigkeit führen. Ein solcher Effekt ist die Neutronenversprödung. Für Komponenten, die sich innerhalb bzw. nahe des Kerns eines Spaltreaktors befinden, ist sie der wichtigste Schädigungsmechanismus. Für den Druckbehälter ist sie von besonderer Sicherheitsrelevanz. Da sich die Schädigung mit fortlaufender Bestrahlung akkumuliert, ergibt sich aus Sicherheitsgründen für eine Komponente eine maximal zulässige Strahlungsfluenz, der sie ausgesetzt werden darf. Bei vielen Druckwasserreaktoren ist der Materialzustand des Druckbehälters sogar entscheidend für die zulässige Betriebsdauer des Reaktors. Daher ist einerseits die Monitorierung der Strahlungsbelastung für sicherheitsrelevante Komponenten mit Hilfe geeigneter Messungen und Berechnungen eine notwendige Voraussetzung für den sicheren Betrieb eines Kernreaktors und andererseits die Entwicklung und Verifikation solcher Mess- und Berechnungsmethoden eine wichtige Aufgabe der Reaktorsicherheitsforschung. Die möglichst zuverlässige Bestimmung der Strahlungsbelastung für kernnahe Komponenten, darunter insbesondere des Druckbehälters, zu ermöglichen, ist das Ziel des Fachgebiets "Reaktordosimetrie". Seine Bearbeitung auf hohem wissenschaftlich-technischen Niveau ist daher eine notwendige Voraussetzung für zuverlässige Integritätsbewertung und Gewährleistung von Komponentensicherheit.

Nach dem Zusammenbruch des Ostblocks ist die Sicherheitsproblematik der Druckbehälter der russischen Kernreaktoren vom Typ WWER weltweit ins Blickfeld der Öffentlichkeit gerückt und zum Gegenstand zahlreicher Forschungsprojekte geworden. Da in diesem Falle die Strahlenschädigung im Vergleich zu anderen Effekten wesentlich größer ist, hat insbesondere die Reaktordosimetrie dadurch neue Impulse erfahren. Mit der Neugründung des Forschungszentrums Rossendorf aus dem ehemaligen ZfK Rossendorf wurde auch ein Teil der reaktordosimetrischen Arbeiten zu WWER-Reaktoren übernommen und im Institut für Sicherheitsforschung parallel zur entsprechenden Materialforschung fortgeführt. Bisher wurden hier die wichtigsten Teilgebiete bearbeitet: Fluenzmessung, Fluenzberechnung und Spektrumsjustierung. Im Vortrag werden der erreichte Stand dargelegt, dieser mit dem internationalen Niveau verglichen und Ansätze für Weiterentwicklungen aufgezeigt.

Early evidence that small technetium compounds may be subject to active transport processes was provided by the historical serependipitous finding that pertechnetate was handled by the sodium-iodide symporter in the thyroid gland. The pertechnetate ion can mimic the iodide ion, despite its different nature and geometry.
Starting from this observation ^99mTc radiotracers are designed for probing and imaging a distinct biochemical reaction of diagnostic relevance. Such biochemical reactions are transmembrane processes, binding reactions, enzymatic conversions, possibly redox reactions, etc., and key proteins or enzymes are the targets of the ^99mTc diagnostic agents. "Bioactivity" is therefore required in the sense of the ^99mTc species being able to participate in the biochemical reaction of interest, being bound or processed.
Keeping the artificiality of technetium in the human body in mind, the feasibility of biochemical Tc-99m probes can only be based on imperfection of the target specificity, on the tolerance of the target molecule towards a substrate mimic that accidentally fits the target molecule to some extent, despite its different chemical nature. This will be examplified by the development of ^99mTc ligands for brain receptors.
The possibility of using biochemical ^99mTc probes for various CNS receptors is due to the tolerance of the target molecules towards metal-based mimics. As the high in-vitro affinities to various neuroreceptors in the nanomolar and subnanomolar range indicate, molecular recognition of complex technetium molecules has become possible.
However, one main issue in developing CNS receptor imaging agents remains the very low or totally absent brain uptake. After two decades of research into brain ^99mTc perfusion agents it has now become feasible for certain technetium complexes to cross the blood-brain barrier. In contrast, a suitable combination of a high receptor affinity with a sufficient brain uptake was not achieved. Systematic studies of model technetium compounds with various logP and pKa values provided rules for selected homologous series of complexes but did not really help to tackle the problem. Since a wide variety of chemically diverse compounds, among them lipophilic cations such as ^99mTc MIBI, ^99mTc tetrofosmin or Q-series compounds, may be actively transported out of the cell by P-glycoprotein, it might also affect the transport of potentially receptor-binding ^99mTc agents.

To conclude, approaches to specific small technetium radiopharmaceutical tracers have not changed much in recent years. From a coordination chemistry point of view, the design of new ^99mTc radiopharmaceuticals starts conceptually with the modification of the coordination environment around the metal with a variety of chelators. Diversity of the chelate unit is needed, and considerable research has consequently been devoted to designing improved and new chelate types, resulting in a flourishing technetium chemistry. New impetus has come in particular from the progress made in technetium(I) chemistry.
Although this knowledge explosion in the technetium chemistry has been translated into targeted radiopharmaceutical research activity the number of newly launched Tc-99m radiopharmaceuticals is stagnant, at least in a short-term perspective. The development of biochemically specific, small technetium and rhenium complexes remains therefore a challenging, rewarding and often frustrating activity.

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

Inhalt

• Material: Halbleiter-Heterostrukturen aus SiC in Si, Diamant in SiC, SiC in Diamant
• Ionenstrahlsynthese: Ionenverteilung im Material, Strahlenschäden, Temperatur-behandlung bei und nach Implantation
• Bedeutung der Synchrotronstrahlung für die Materialforschung, Rossendorfer Beamline an der ESRF Grenoble
• Materialcharakterisierung wie Phasen-bildung, Kristallitgröße und -orientierung, Gitterdeformation in Matrix und Kristallit mittels diverser Röntgenmethoden
• Ausblick: simultane Doppelimplantation

CFD codes are more and more used for practical applications as the design and optimization of technical facilities, e.g. in process industry or in nuclear power plants. For most cases this limited to single phase flows. To qualify CFD codes for two-phase flows, they have to be equipped with constitutive laws describing the interaction between the gaseous and the liquid phases. In the case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. To obtain detailed experimental data, an electrode wire-mesh sensor was used, which enables the measurement of the phase distribution with high reso-lution in space and in time. Air-water flow at ambient conditions in a vertical pipe (51.2 mm inner diameter) is investigated to have well defined boundary condi-tions. Local bubble size distributions are calculated from the data. The measure-ments were done in different distances from the gas injection device. As a result the development of bubble size distributions and the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe.

Oxidized LDL (oxLDL) is a key mediator in atherogenesis and a marker of coronary artery disease (CAD). Type 2 diabetes is associated with excessive cardiovascular morbidity and mortality. Because atherogenesis starts before diabetes is diagnosed, we investigated whether circulating oxLDL levels are increased in impaired glucose tolerance (IGT). OxLDL levels were measured in 376 subjects with normal glucose tolerance (NGT), 113 patients with IGT, and 54 patients with newly diagnosed type 2 diabetes. After correction for age and BMI, serum levels of oxLDL were significantly increased in IGT versus NGT subjects (P = 0.002). OxLDL levels were not associated with the following parameters of the oxidative/antioxidative balance in the blood: total antioxidant capacity, urate-to-allantoin ratio, and circulating phagocyte oxygenation activity. In stepwise multivariate analysis, LDL cholesterol (P < 0.0005) and triglycerides (P < 0.0005) were the strongest predictors of circulating oxLDL levels, followed by HDL cholesterol (P = 0.003), 2-h postchallenge C-peptide (P = 0.011), fasting free fatty acids (P = 0.013), and serum paraoxonase activity (P = 0.035). The strong correlation of oxLDL with LDL cholesterol and triglycerides indicates that LDL oxidation in IGT is preferentially associated with dyslipidemia. OxLDL increase may explain the high atherogenic potency of dyslipidemia in the prediabetic

The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite) and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80% diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence.
A more detailed analysis shows that several stages should be considered corresponding to different dominating processes on very different time scales. For investigation of the film growth in the short time impact stage molecular dynamics was used. For this purpose the empirical interaction potential of Brenner was modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) was quantitatively analysed in dependence on particle energy and temperature.
The results of the impact stage represent the input data for the long time diffusion stage. Based on continuum mechanics a simplified model for the further film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.

Range distributions of carbon ions deposited onto tetrahedral amorphous carbon films at kinetic energies between 22 eV and 692 eV are measured utilizing high-resolution elastic recoil detection. These data are compared to range calculations based on binary collision approximation as well as to classical molecular dynamics simulations. Asymmetric range profiles, differences in mean ion ranges and increased range straggling compared to theories are attributed due to self diffusion during thermal spike and have to be considered in subplantation growth models.

The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite) and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80% diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence.
To understand the film growth on a quantitative level molecular dynamics has been used. For this purpose the empirical interaction potential of Brenner has been modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) has been quantitatively analyzed in dependence on particle energy and temperature.
Based on these fundamental studies a simplified model for the film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.

The corrosion of metals is associated both with a release of ions and changes in optical surface properties. In this study these two effects were correlated by a potentiodynamic corrosion test and in situ probing of the surface by ellipsometry. The studies were carried out with stainless steel AISI 304 and 316 in phosphate buffered saline (PBS) and in Dulbecco's Modified Minimal Essential Medium (DMEM) at pH 7.4. In both media 304 steel is more susceptible to corrosion than 316 grade. The 316 steel shows higher corrosion potential and higher corrosion current density in PBS than in DMEM, for 304 steel this behavior is vice versa. Ellipsometry demonstrated a higher sensitivity than potentiodynamics to surface modification in the cathodic area. In DMEM the removal of a surface layer at negative voltage and a further repassivation with increasing voltage was characteristic. In PBS a surface layer started to grow immediately. X-ray photoelectron spectra of this layer formed in PBS are consistent with iron phosphate. Its formation is inhibited in DMEM; the presence of aminoacids is discussed as the reason.

The morphological evolution of nanostructures on semiconductor surfaces eroded by low-energy ion beams has gained particular interest recently as a possible way to generate regular, ordered, and highly dense quantum dots. Generally, the erosion by ion beams increases the surface roughness, which under certain sputter conditions can turn to periodic surface structures. At normal incidence of the ion beam hexagonally arranged dot patterns appear on the eroded surface. The diameter of these structures is in the range of 15 - 80 nm depending on ion energy with a density up to 2x10^11cm^-2.
After an initial stage of irradiation the temporal evolution of the dot pattern can be described by a stochastic continuum equation. In the case of crystalline semiconductor surfaces rapid amorphization and variation in stoichiometry takes place. As the erosion process proceeds nanoscale dot structures appear at the surface, which are remarkable well ordered and grow up to an aspect ratio of nearly unity. We present the temporal evolution of dot pattern formation on GaSb (100) surfaces during Ar+ ion sputtering. The characteristic length of the dot pattern is determined as a function of ion energy, ion current density, and sample temperature.

Ion beam deposition of carbon films was studied by molecular-dynamics simulations. Using an analytic hydrocarbon potential of Brenner with an increased C-C interaction cutoff value, deposition of films with a thickness of up to 10 nm was simulated for ion energies E_ion =10-80 eV, and for substrate temperatures T_s ranging from 100 to 900 K. The bulk properties of the computed tetrahedral amorphous carbon (ta-C) films as well as structure and roughness of their sp² -rich surface layers agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp³ fraction in the films increases with ion energy, resulting in a highly sp³ -bonded ta-C with a high compressive stress for E_ion >30 eV. This trend remains also at room temperature, however with lower sp³ content and stress.
In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as T_s exceeds a critical temperature T_c . The calculated transition temperature T_c is a bit too low (T_c ~100 ^oC for E_ion =40 eV). For the ion energies E_ion ≤ 80 eV, the incidence atom is predicted to come to rest in the sp² -rich surface layer. A time-resolved analysis of the film formation shows that atom subplantation leads generally to a highly tetrahedral structure, but above T_c the kinetic energy of the atoms is sufficiently large to overcome the barrier in cohesive energy between ta-C and the more stable graphite-like films.

The complexation of uranium(VI) by humic and fulvic acids was studied to obtain information on the binding of uranium(VI) onto functional groups of humic substances. For this, various natural and synthetic humic acids were chemically modified resulting in humic acids with blocked phenolic OH groups. Both from the original and from the modified humic substances, solid uranyl humate complexes were prepared at pH 2. FTIR and extended X-ray absorption fine structure (EXAFS) spectroscopy were applied to study the chemical modification process of humic substances, to study the structure of uranyl humate complexes and to evaluate the effect of individual functional groups of humic substances (carboxylic and phenolic OH groups) on the complexation of uranyl ions. The results confirmed the predominant blocking of phenolic OH groups in the modified humic acids. These modified humic acids are suitable model substances to study the role of phenolic OH groups of humic acids in dependence on pH. By EXAFS spectroscopy, identical structural parameters were determined for all uranyl humates. Axial U-O bond distances of 1.78 Å were determined. In the equatorial plane approximately five oxygen atoms were found at a mean distance of 2.39 Å. The blocking of phenolic OH groups of humic acids did not change the near-neighbor surrounding of uranium(VI) in uranyl humate complexes. Thus, the results confirmed that predominantly humic acid carboxylate groups are responsible for binding of uranyl ions and that the influence of phenolic OH groups is insignificant under the applied experimental conditions. The carboxylate groups are monodentate coordinated to uranyl ions.

The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar.
The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.

A combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X -ray (EDX) was used to conduct a molecular and atomic analysis of the uranium complexes formed by A. ferrooxidans. The results demonstrated that this bacterium accumulates uranium as phosphate compounds. We hypothesize that the poly P-bodies of A. ferrooxidans may play a role in detoxification of those part of uranium which is uptaken by the cells.

BACKGROUND: Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade. METHODS: Titanium oxide films were produced by metal plasma deposition and implantation in form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the electronic band gap of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples. RESULTS: The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces. CONCLUSION: Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

This work reports the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: (i) conventional method of doping by implanting with N into an ion beam synthesized SiC layer and (ii) a novel method based on pre-doping (with N and P) of the Si wafers before the ion beam synthesis of SiC. For the N implantation the electrical data show a p-type overcompensation of the SiC layers for both doping methods used. The structural (XRD) and in-depth (SIMS, Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N ion implantation damage, and therefore, the need for further optimization of their thermal processing. In contrast, the P-doped SiC layers always show n-type conductivity. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the undoped material. Our electrical data, together with the absence of additional stress related to P-implant suggest that this technique could be suitable to avoid effects related to the ion implantation damage in the SiC lattice, although the electrical activation of P in the SiC is about one order of magnitude lower than in Si.

This work reports preliminary data on the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: i) doping by ion implantation (with N) of ion beam synthesized SiC layers and ii) ion beam synthesis of SiC in previously doped (with P) Si wafers. In the first case, the electrical data show a p-type overcompensation of the SiC layer in the range of temperatures between -50°C and 125 °C. The structural (XRD) and in-depth (SIMS; Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N-ion implantation damage, and therefore the need for further optimization of their thermal processing. In contrast, the p-doped SiC layers always show n-type doping. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the not doped material. Electrical activation of P in the SiC lattice is about one order of magnitude lower than in Si. These data constitute, to our knowledge, the first results reported on the doping of ion beam synthesized SiC layers.

Benchmark calculations for the validation of the coupled neutron kinetics/thermohydraulic code complex DYN3D-ATHLET are described. Two benchmark problems concerning hypothetical accident scenarios with leaks in the steam system for a VVER-440 type reactor and the TMI-1 PWR have been solved. The first benchmark task has been defined by FZR in the frame of the international association "Atomic Energy Research" (AER), the second exercise has been organised under the auspices of the OECD. While in the first benchmark the break of the main steam collector in the sub-critical hot zero power state of the reactor was considered, the break of one of the two main steam lines at full reactor power was assumed in the OECD benchmark. Therefore, in this exercise the mixing of the coolant from the intact and the defect loops had to be considered, while in the AER benchmark the steam collector break causes a homogeneous overcooling of the primary circuit. In the AER benchmark, each participant had to use its own macroscopic cross section libraries. In the OECD benchmark, the cross sections were given in the benchmark definition. The main task of both benchmark problems was to analyse the re-criticality of the scrammed reactor due to the overcooling.
For both benchmark problems, a good agreement of the DYN3D-ATHLET solution with the results of other codes was achieved. Differences in the time of re-criticality and the height of the power peak between various solutions of the AER benchmark can be explained by the use of different cross section data. Significant differences in the thermohydraulic parameters (coolant temperature, pressure) occurred only at the late stage of the transient during the emergency injection of highly borated water. In the OECD benchmark, a broader scattering of the thermohydraulic results can be observed, while a good agreement between the various 3D reactor core calculations with given thermohydraulic boundary conditions was achieved. Reasons for the differences in the thermohydraulics were assumed in the difficult modelling of the vertical once-through steam generator with steam superheating.
Sensitivity analyses which considered the influence of the nodalisation and the impact of the coolant mixing model were performed for the DYN3D-ATHLET solution of the OECD benchmark. The solution of the benchmarks essentially contributed to the qualification of the code complex DYN3D-ATHLET as an advanced tool for the accident analysis for both VVER type reactors and Western PWRs.

VALCO is an EU FP5 project on transient analysis code validation for VVER type reactors that continues the work of the former EU Phare project SRR1/95. Twelve organisations from nine East and West European countries are participating. For the validation of coupled neutronic / thermal-hydraulic codes that are used in VVER safety analyses, five measured transients from different VVER-440 and VVER-1000 plants have been documented. Two of them have been chosen for validation calculations. First results of an ATHLET / DYN3D calculations for a MCP trip measured in the Kozloduy-6 VVER-1000 are presented. Uncertainty analysis applying the SUSA methodology developed at GRS to coupled-code calculations for VVER will be performed. To validate the stand-alone three-dimensional neutronic codes together with the applied two-group diffusion parameters independently from thermohydraulic feedback, the analysis of measurements in the V-1000 zero-power facility (KI Moscow), which is a full-scale VVER-1000 mock-up, is going to be performed. Preliminary results of DYN3D steady-state calculations using a HELIOS two-group data library and albedo coefficients calculated by the transport code MARIKO are compared to measurement data.

Thin films of semiconducting iron disilicide (ß-FeSi2)with up to 8 at.% Cr addition grown on Si(001) and Si(111) substrates were studied by spectroscopic ellipsometry as well as transmission and reflection measurements at room temperature. The dielectric function was deduced in the interband spectral range. In molecular beam epitaxy (MBE) preparation part of the Fe atoms were substituted by Cr during deposition. For a low Cr amount in the doping range up to about 0.4 at.%, Cr was found to modify epitaxial growth on Si(111) substrates with a change in dominating ß-FeSi2 grain orientation. Higher amounts of Cr lead to the precipitation of CrSi2, which was detected optically and confirmed by x-ray diffraction measurements and a deterioration of film morphology. Furthermore, ß-FeSi2 thin films were implanted with Cr and subsequently annealed at varios temperatures. In these samples also CrSi2 was detected. The results suggest that it is impossible to produce ß-(Fe(1-x)Cr(x))Si2 alloys by MBE or ion implantation.

Diamondlike amorphous carbon (DLC) is a transparent hard material approaching crystalline diamond in hardness and elastic modulus. The main issue restricting applications of this very promising material is a high compressive stress in DLC films after growth. I present recent results of atomic scale calculations of growth and mechanical properties of DLC films performed in collaboration with H.-U. Jaeger. The following topics are discussed:

- the nature of intrinsic stresses in DLC films;
- the dependence on the intrinsic stresses on the film deposition parameters;
- the effect of the intrinsic stresses on the second-order elastic constants of amorphous carbon.

The atomic models of DLC films are prepared by direct molecular dynamics simulation of ion-beam deposition. Similar to real as-deposited films, the simulated films have a high content of tetrahedrally coordinated atoms and large intrinsic compressive stresses in the region of steady-state growth. The stress in the region of steady-state growth is calculated as an average of atomic-level stresses derived from an empirical interatomic potential. The origin of the intrinsic stress in DLC films is discussed on the basis of the structural changes due to thermal annealing simulated by molecular dynamics method. We propose that the high stress in DLC films can be
related to local defects in amorphous carbon networks. The dependence of the second-order elastic contants of amorphous carbon on the intrinsic stress is examined by the method of homogeneous deformation. We nonlinear effects are shown to become appreciable at the stress values typical of as-deposited DLC films.