Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Semiconducting (mostly p-doped) single crystals of the 6H-polytype of α-SiC(0001) were implanted with 57Fe ions with a nominal dose of 1.0 × 1016, 2.0 × 1016, 3.0 × 1016 or 2.0 × 1017 cm−2 (high-dose sample phd) at 100 or 200 keV ion energy in order to produce diluted magnetic semiconductors (DMSs). After implantation all samples (except p-hd) were subject to rapid thermal annealing at 1000 ◦C for 2 min. The structure was investigated by x-ray diffraction, high-resolution cross-sectional transmission electron microscopy and sputter-Auger depth profiling. The magnetic properties were obtained from superconducting quantum interference device (SQUID) magnetometry and 57Fe conversion electron M¨ossbauer spectroscopy (CEMS) at room temperature (RT) and 4.2 K. Our combined results obtained by several techniques prove unambiguously that ferromagnetism in 57Fe-implanted SiC for Fe concentrations above 3%originatesmostly from epitaxial superparamagnetic Fe3Si (and possibly a small fraction of Fe nanoparticles) in the SiC matrix. We find a wide range of blocking temperatures, TB, which start from 400 K for a dose of 2.0 ×1016 cm−2, and shift downwards to ∼220 K for 3.0× 1016 cm−2. For the lowest dose of 1.0 × 1016 cm−2 at 200 keV, we find evidence of ferromagnetism below 20 K via weak magnetic hyperfine interaction. Our measurements suggest that for a maximum Fe concentration in the range of 1–3%, which corresponds to this lowest Fe dose, the possibility exists to obtain a DMS in Fe-implanted SiC, prepared at lower or equal implantation doses.

This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Rossendorf. At present FELBE delivers pulses with typical durations of 0.9–5 ps in the wavelength range 4–22 µm, which soon will be extended to 150 µm. Furthermore we report on recent experiments using FELBE, namely the study of phonon resonances in ferroelectric domains using a newly designed scattering scanning near-field optical microscope (s-SNOM), as well as pump-probe spectroscopy on doped semiconductor superlattices. The pump-probe signal reflects, apart from a component due to the bleaching of the interminiband transition, the temperature of the miniband electrons on a picosecond timescale.

The Greifswald NPP was operated between 1973 and 1990. The units are of Russian WWER-440-230 type. Now trepans from the RPV were gained to investigate the post mortem properties of the material.
The paper describes the results of weld metal originating from the critical weld of the RPV of unit 1. The RPV of this unit was annealed after 14 years of operation, followed by two additional years of operation.
The neutron dosimetry was based on fluence calculations as well as retrospective Nb dosimetry. Both approaches are shortly described. A decrease of 60% through the thickness of the RPV was found by both methods.
The material test results comprise Charpy-V, tensile and fracture toughness parameters. The main interest is focussed on the comparison of assessment codes applied in Russia and other European countries where WWER-440 reactors are operated. An additional aspect is the comparison of results determined on sub-size Charpy specimens immediately after the annealing procedure.
The first results show, that the material properties are near the predicted values.

Zur Untersuchung der Materialeigenschaften wurden aus dem Reaktordruckbehälter des Blockes 1 des ehemaligen KKW Greifswald Materialproben entnommen. Die interessierenden Eigenschaften werden durch die während des Betriebes auftretende Neutronenstrahlung bestimmt.
Im Beitrag wird dargestellt, wie durch Messungen der Nb-Aktivität die Neutronenfluenz bestimmt wurde. Niob ist im im untersuchten Material nur als Spurenmetall erhalten. Die vorgenommenen Trennverfahren zur Isolation von Nb werden dargestellt.Die Messergebnisse werden mit Rechenergebnissen verglichen.

Hydrodynamic couplings are being used for torque transfer in heavy duty systems, such as naval vessels, power plants, locomotives or other transport vehicles. A hydrodynamic coupling essentially consists of two rotating bladed wheels, the pump and the turbine wheel, which are placed inside a metal enclosure. In operation the coupling is partially filled with a fluid and this fluid realises the momentum transfer from the driving side (pump) to the load side (turbine). The flow conditions in the coupling determine its operational behaviour. A known problem of such devices is the sudden change of slip during a continuous increase or decrease of either load or angular velocity of the pump. To investigate the behaviour of a hydrodynamic coupling the flow structure inside the coupling must be disclosed. But there only few measurement techniques which are applicable. Thus, the flow inside the pump is a heavily turbulent two-phase flow that is hardly accessible to optical or other measurement techniques. Gamma ray tomography provides a convenient method to measure the time integrated phase distribution within such a coupling. We performed such measurements in the past with the help of a low resolution gamma ray tomography system. Now we continued to use a high resolution gamma ray tomograph for that purpose. The measurements were carried out using a Cs-137 isotopic source and a detector arc with 2 mm spatial resolution. The test coupling mostly consists of aluminium and has an outer diameter of approximately 500 mm. For the measurement we employed the angle resolved data acquisition scheme that allows us to image rotating distributions with a fixed tomography setup. In the paper we will discuss the application of gamma ray tomography to this particular industrial problem.

We applied gamma ray tomography to the problem of phase fraction measurement in chemical reactors. Therefore, we used a new tomography device that is operated with a Cs-137 source and a high resolution gamma ray detector. One application example is the reconstruction of the fluid distribution and the measurement of radial gas fraction profiles in a laboratory scale stirred vessel. The tomograph was used to obtain radiographic projections of the averaged gamma ray attenuation for different stirrer speeds along the height of the vessel. With tomographic reconstruction techniques we calculated the angularly averaged radial distribution of the attenuation coefficient for as many as 150 single cross-sectional planes and synthesised from this data set the axial and radial fluid distribution pattern. Further, we exemplarily reconstructed the radial gas fraction distributions induced by the stirrer in the area of the stirrer blades. In a second application the gamma ray measurement system was used to visualise gas inclusions in a water cleaning column that is used to remove hazardous heavy metal species from water.

Im Beitrag werden der aktuelle Stand und die Potenziale der Wasserkraftnutzung in Ostdeutschland beschrieben. Ausgehend von der historischen Entwicklung im letzten Jahrhundert wird insbesondere die Reaktivierung von Wasserkraftanlagen nach der Wiedervereinigung diskutiert. Die bestehenden Wasserkraftanlagen und die ausbauwürdigen Potenziale liegen vor allem an den Nebenflüssen der Elbe, die Leistung übersteigt nur bei wenigen Anlagen 1 MW. Das bis zum Jahr 2010 nutzbare Potenzial liegt bei 650 GWh/a, eine Nutzung des größeren Potenzials der Elbe (1 TWh/a) ist gegenwärtig nicht absehbar.

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We have observed a very inhomogeneous dissociation of stoichiometric and non-stoichiometric thin SiO2 layers (thermally grown on Si substrates) during high temperature annealing at a low partial pressure of oxygen. During this process some silicon of the (100)Si substrate and, in case of Si ion implantation, additionally excess Si is consumed. The SiO2 dissociation has been studied by electron microscopy and Rutherford backscattering spectrometry. Large holes (>1µm) in non-implanted oxide layers have been observed which evolve probably from defects located at the Si/SiO2 interface. For Si implanted SiO2 additionally the formation of voids within the oxide during annealing has been observed preferably at the position of the implanted Si excess. Oxygen vacancies are possibly emitted from Si/SiO2 interfaces into the oxide and migrate through SiO2 with long-range distortions of the oxide network. In that way the hole and void formation in the oxide can be explained by oxygen-vacancy formation, migration and silicon-monoxide (SiO) emanation. As a driving force for growth of the large holes we identified oxygen diffusion from the Si/SiO2 interface to the bare Si surface. This surface is a sink of oxygen diffusion due to the emanation of volatile SiO, whereas the Si/SiO2 interface serves as an oxygen source. The predicted mechanism is consistent with the geometry of the holes in the SiO2 layer.

The free electron laser (FEL) facility at the electron linear accelerator ELBE of the Forschungszentrum Rossendorf, Dresden, Germany, provides an optical laboratory which is suitable for spectroscopic investigations in actinide research. For the first time a great number of actinide elements which are currently in the focus of scientific work in the field of radioecology can now be investigated with laser spectroscopic techniques using infrared FEL radiation. The facility is also open for external users. In this work we present our first results of vibrational spectroscopic experiments for the identification of actinide molecule complexes by Photothermal Beam Deflection (PTBD) spectroscopy using an FEL as a coherent pulsed pump source which can be tuned throughout a broad wavelength range of interest. We demonstrate that reliable absorption spectra of test samples containing uranyl and neptunyl compounds can be obtained which was verified by conventional FT-IR spectroscopy. A prominent feature of photothermal techniques is the capability of detection of low absorptions. Therefore we tried to evaluate the minimum content of actinide ions which can still be detected by our setup of the vibrational PTBD spectroscopic experiment. It was found that the limit is obviously given by the background absorption of the hygroscopic KBr matrix of the samples which is originated by residual water. Furthermore, we present an overview about the technical equipment of the laboratory.

Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in a 43 µm thick living multispecies biofilm grown on biotite plates. These particles differ between 1-7 µm in diameter and were located at the bottom of the biofilm in the boundary region of high and low bacterial density. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415 to 475 nm, indicative for uranium(V), or in the range of 480 to 560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilm. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron was involved.

Material science has taken a key position for new technical developments, and is therefore strongly supported by industry and governments. It has nowadays a position between physics, chemistry and engineering and extends from basic science in physics and chemistry on atomic scale to large scale applications in industry. An increasing number of material science study courses at
universities underlines the present and future importance of understanding and developing materials for the future. Looking at
the industry with one of the fastest development at present, the communication industry, it is obvious that a large part of the actual research for future materials is devoted to the understanding of materials to be used in devises developed on the nanometer (nm) scale.

The contributions to this book grew out of the lectures given at the Heraeus Ferien Kurs on materials for today, tomorrow and beyond, held at the University of Technology Chemnitz in October 2004. As the lectures were given to students of different origin (physics, chemistry, material science), the articles not only contain our todays knowledge in each of the fields, but make reference also to basic facts needed for their understanding. Thus the articles combine a presentation of the present research in the field with some basis information on a text book level; they bridge the gap between specialized reviews and study books. In addition, lectures on material simulation, a very fast advancing discipline, are combined with lectures on experimental research in material science, and the techniques used in both of these disciplines.

Motivated by the high application potential of carbon nanotubes, the search for other quasi one-dimensional nanostructures has been pursued both by theoretical and experimental approaches. The investigations soon concentrated on layered inorganic materials, which may be exfoliated and rolled up to tubular and scroll-type forms. The present chapter reviews the basic design principles, which govern the search for novel inorganic nanostructures on the basis of energy- and strain-related stability criteria.
These principles are then applied to the prediction and characterisation of the properties of non-carbon, elemental and binary nanotubes derived from layered boride, nitride, and sulfide bulk phases. Finally, the present chapter introduces examples, where one-dimensional nanostructures such as tubes and scrolls have successfully been constructed from non-layered materials, especially from oxides. Examples for the experimental verification of the predicted structures are given throughout the discussion and impressively underline the predictive power of today's materials modelling.

The proper treatment of defects is one of the major tasks in materials design, because defects are responsible for the either desirable or detrimental deviations between the characteristics of the material to be tuned and the well-known properties of an ideal crystal. Microelectronic devices work because of clever point defect engineering, line defects govern plastic deformation processes, and interfaces determine the mechanical stability of composite materials. Especially interfaces gain importance with the current trend towards nanoscale materials; first, the surface-to-volume ratio is strongly increased in nanocrystalline material, and, second, stable arrangements of point or line defects require a minimum crystallite size, which can be larger than the actual nanocrystallites. Thus, the present chapter gives an introduction into the most common approaches for modeling interface properties. We introduce the basic concepts of interface symmetry, structure and analysis with a strong focus on the theoretical methods and give an overview of currently available techniques for the modeling and simulation of the interface properties at an atomic-scale level. Two fundamentally different interface types are distinguished: The discussion of the homophase boundary properties is focussed on oxide grain boundaries, which we studied extensively in comparison with amply available experimental observations. For the heterophase boundaries examples of non-reactive, reactively doped, and inherently reactive boundaries are presented. A special focus lies on the interfaces between metals and oxides where the discrepancy of the material properties across the interface is most prominent and all three bonding situations can occur: weak adhesion between inert fragments, activated adhesion upon doping, and strong adhesion.

Atomic and electronic properties of the Mo6S8 cluster are investigated using DFT band structure calculations with pseudopotentials and a plane-wave basis set. The calculations showed that these clusters can be well bound on the surface in a potential well with degenerate local energy minima, despite a negligible net electron transfer between the two subsystems. The cluster may move freely inside this well on the surface. The cluster-surface binding is via S-Au bonds, with additional contributions of the Mo atom in the vicinity of the surface.

Amadori products are formed in the early stage of the so-called Maillard reaction between reducing sugars and amino acids or proteins. Such nonenzymatic glycosylation may occur during the heating or storage of foods, but also under physiological conditions. N-epslion-fructoselysine is formed via this reaction between the epsilon-amino group of peptide-bound lysine and glucose. Despite the fact that, in certain heated foods, up to 50% of lysyl moieties may be modified to such lysine derivatives, up to now, very little is known about the metabolic fate of alimentary administered Amadori compounds. In the present study, N-succinimidyl-4-[¹⁸F]fluorobenzoate was used to modify N-epsilon-fructoselysine at the a-amino group of the lysyl moiety. The in vitro stability of the resulting 4-[¹⁸F]fluorobenzoylated derivative was tested in different tissue homogenates. Furthermore, the 4-[¹⁸F]fluorobenzoylated N-epsilon-fructoselysine was used in positron emission tomography studies, as well as in studies concerning biodistribution and catabolism. The results show that the 4-[¹⁸F]fluorobenzoylated N-epsilon-fructoselysine is phosphorylated in vitro, as well as in vivo. This phosphorylation is caused by fructosamine 3-kinases and occurs in vivo, particularly in the kidneys. Despite the action of these enzymes, it was shown that a large part of the intravenously applied radiolabeled N-epsilon-fructoselysine was excreted nearly unchanged in the urine. Therefore, it was concluded that the predominant part of peptide-bound lysine that was fructosylated during food processing is not available for nutrition.

The Rossendorf Beamline with its X-ray absorption spectroscopy (XAS) station dedicated to actinide research was the first of its kind at a European synchrotron. Since its opening in 1999, it serves for about 30 experiments each year. An overview on the current status of operation modes, the technical details and on access conditions is presented.

Application of small angle neutron scattering to RPV steels had to be reconsidered, when it was discovered by Atom Probe investigations that irradiation-induced clusters in RPV steels do contain Fe. It was no longer justified in general to determine the total volume fraction of clusters, as long as the magnetic moment of the Fe atoms inside the clusters is not known for sure. The aim of the talk is to compile ways out from this dilemma. The first part is devoted to selected SANS results obtained assuming non-magnetic clusters. The second part is a compilation of 5 ways to solve the questions that arise, if this assumption is not justified. In the third part it will be analyzed, which conclusions remain valid and which have to be modified. If the magnetic character of scatterers is not known in advance, SANS and 3DAP can be combined synergistically: 3DAP yields cluster composition, but sensitivity to vacancies is low. SANS (A-ratio) is particularly sensitive to the vacancy fraction.

Alcanivorax borkumensis is a ubiquitous marine petroleum oil-degrading bacterium with an unusual physiology specialized for alkane metabolism. This “hydrocarbonoclastic” bacterium degrades an exceptionally broad range of alkane hydrocarbons but few other substrates. The proteomic analysis presented here reveals metabolic features of the hydrocarbonoclastic lifestyle. Specifically, hexadecane-grown and pyruvate-grown cells differed in the expression of 97 cytoplasmic and membrane-associated proteins whose genes appeared to be components of 46 putative operon structures. Membrane proteins up-regulated in alkane-grown cells included three enzyme systems able to convert alkanes via terminal oxidation to fatty acids, namely, enzymes encoded by the well-known alkB1 gene cluster and two new alkane hydroxylating systems, a P450 cytochrome monooxygenase and a putative flavin-binding monooxygenase, and enzymes mediating -oxidation of fatty acids. Cytoplasmic proteins up-regulated in hexadecane-grown cells reflect a central metabolism based on a fatty acid diet, namely, enzymes of the glyoxylate bypass and of the gluconeogenesis pathway, able to provide key metabolic intermediates, like phosphoenolpyruvate, from fatty acids. They also include enzymes for synthesis of riboflavin and of unsaturated fatty acids and cardiolipin, which presumably reflect membrane restructuring required for membranes to adapt to perturbations induced by the massive influx of alkane oxidation enzymes. Ancillary functions up-regulated included the lipoprotein releasing system (Lol), presumably associated with biosurfactant release, and polyhydroxyalkanoate synthesis enzymes associated with carbon storage under conditions of carbon surfeit. The existence of three different alkane-oxidizing systems is consistent with the broad range of oil hydrocarbons degraded by A. borkumensis and its ecological success in oil-contaminated marine habitats.

AAlcanivorax borkumensis is a cosmopolitan marine bacterium that uses oil hydrocarbons as its exclusive source of carbon and energy. Although barely detectable in unpolluted environments, A. borkumensis becomes the dominant microbe in oil-polluted waters. A. borkumensis SK2 has a streamlined genome with a paucity of mobile genetic elements and energy generation–related genes, but with a plethora of genes accounting for its wide hydrocarbon substrate range and efficient oil-degradation capabilities. The genome further specifies systems for scavenging of nutrients, particularly organic and inorganic nitrogen and oligo-elements, biofilm formation at the oil-water interface, biosurfactant production and niche-specific stress responses. The unique combination of these features provides A. borkumensis SK2 with a competitive edge in oil-polluted environments. This genome sequence provides the basis for the future design of strategies to mitigate the ecological damage caused by oil spills.

The partial waveguide resonator of the U100-FEL at FZ-Rossendorf and its peculiarities are ilustrated.

The ELBE electron beam at Forschungszentrum Rossendorf, Dresden, with energies up to 40 MeV, will be used to produce intense neutron beams. The neutron radiator consists of a liquid lead circuit where bremsstrahlung photons created by the electrons produce neutrons in (gamma,n) reactions. The short beam pulses (5 ps) provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about 1 % with a flight path of 4 m. The neutron beam is shaped by a 2.4 m long collimator. The usable energy range is from 50 keV up to 10 MeV when ELBE delivers a beam repetition rate of 0.5 MHz. In this energy interval, there is a need for neutron cross section measurements relevant for the transmutation of minor actinides in nuclear waste, as well as for applications to fission and fusion reactors. The neutron flux at the sample position is 10^7 cm^-2 s^-1. Different detector types are being developed. For neutron capture gamma rays, a BaF2 scintillation detector array of 42 crystals is being constructed, whereas for neutron detection, an up to 1 m^2 large plastic scintillator wall consisting of 1 cm thick scintillation panels is being built.

In this paper we present a time domain analysis of a short pulse partial-waveguide FEL oscillator employing toroidal mirrors and a hole outcoupling. The use of toroidal mirrors with optimized radius of curvature helps to reduce cavity losses arising from the mismatch of the free space propagating optical field into a waveguided one. We introduce semi-analytical expressions for the calculation of the scattering matrix elements describing the loss and mode coupling mechanism as well as the amount of the extracted power from the cavity. The formulation is implemented in a time domain FEL code based on modal expansion approach. The described model is applied to a partial waveguide FEL system and simulation results are compared with measurements.

Epitaxial Pr–Co films with a nominal composition of Pr2Co17 have been prepared on a Cr buffered MgO (110) substrate. Pole figures and magnetic measurements reveal that these Pr–Co films crystallize in a metastable disordered hexagonal PrCo7 phase (TbCu7 type) rather than an ordered rhombohedral Pr2Co17 phase (Th2Zn17 type). Consequently high uniaxial anisotropy at room temperature is observed instead of the planar anisotropy expected for the rhombohedral phase. The energy density obtained in the nonequilibrium Pr–Co films is (BH)max=277 kJ/m3, which exceeds the (BH)max values of single phase Sm–Co films and Sm–Co/Fe and Pr–Co/Co multilayers.

Since the pioneering studies on oxidative modification of proteins exposed to ionizing radiation by swallow, Garrison, Schuessler, and colleagues and on oxidative inactivation of enzymes by metal-catalyzed oxidation systems by Earl Stadtman's group and colleagues, recent progresses in life sciences have led to the development of a range of excellent methods and experimental approaches and procedures that enable an always more detailed investigation and evaluation of the phenomenon of Protein Oxidation at both the micro- and macrostructural level under physiological and pathophysiological conditions, respectively. In this line, this volume "Protein Oxidation and Disease" assesses critically recent evidence that underpins the argument that oxidative damage to proteins is a significant causative or associated factor in aging as well as the etiology, progression, and manifestation of various human diseases.

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Reaction pathways of a novel method to fabricate nanowires (NWs) using focused ion beams (FIBs) are presented. This investigation is based on an extension of TRIM simulations to realistic FIB profiles and on kinetic Monte Carlo simulations by which post-implantation phase separation is described. A focused ion implantation along a straight line leads to local supersaturation of the implanted species in the substrate. During post-implantation annealing, NWs embedded in the substrate form along the implantation trace if the ion fluence was sufficiently high. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. During long-term thermal annealing, NWs disintegrate into regular chains of nanoparticles (Rayleigh instability). Thus, regular chains of metallic nanoparticles can be fabricated which are applicable as surface-plasmon-polariton (SPP) waveguides. Even complex structures involving several NWs, e.g. T- or X-junctions, may be obtained. Crossing points, corners and ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors may be realized where an isolated nanocluster is located in a tunnel distance from several NW contacts. Moreover, multi-gate NW field effect transistors are predicted to form by crossing FIB traces of different ion fluences.

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Single-crystals of chromium doped with 10E16 119Sn ions per cm2 and energies ranging between 45 keV and 190 keV were investigated with conversion electron Mössbauer spectroscopy (CEMS), Auger electron spectroscopy (AES), grazing angle X-ray diffraction (GAXRD), and scanning electron microscopy (SEM). The Mössbauer spectra were found to be significantly different than those of the bulk. Both the maximum and the average hf. field values were higher by a factor of ~ 3 than the corresponding quantities for the bulk. The overall shape of the spectra is also different. GAXRD study has revealed that the near-surface zone of the investigated samples has a nanocrystalline structure with the average size of grains ranging between ~ 20 nm and ~ 40 nm. The latter seems to be the main reason for the observed enhancement of the spin-density and its distortion.

It is well known that under certain conditions, low and medium energy (typically 0.1 – 100 keV) ion sputtering can induce the formation of self-organized patterns on the irradiated surface [1]. Periodic ripple patterns and hexagonally ordered dot arrays form for oblique and normal ion incidence, respectively. The periodicity of the patterns depends on the sputtering conditions and ranges from some ten nanometres up to several microns. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [2]. The first attempt to describe the formation process was made by Bradley and Harper and led to a continuum model based on sputter theory [3].
In this framework, the patterns result from the interplay between curvature dependent sputter yield and diffusion.
To investigate the process of pattern formation, semiconductor surfaces are eroded by sub-keV Ar ions. The topography of the sputtered surfaces is studied by ex-situ atomic force microscopy (AFM).
Off-normal ion erosion of Si creates ripple patterns with a wavelength ranging from 20 nm to 60 nm and amplitude of approximately 2 nm. By means of normal incidence bombardment, well ordered dot arrays are fabricated on GaSb. These arrays exhibit hexagonal symmetry and a periodicity of the order of 40 nm. The amplitude is of the same magnitude as the periodicity. The formation process will be discussed in detail and recent results of our studies on pattern evolution and the influence of boundary conditions are presented.
As a promising application, erosion induced surface patterns can be used as templates in further processes such as molecular beam epitaxy or sputter deposition. The morphological anisotropy of the surface can influence the process significantly. Recent findings of investigations on ripple induced anisotropies in metallic thin films are presented.

[1]M. Navez, D. Chaperot and C. Sella, C. R. Acad. Sci. 254, 240 (1962)
[2]U. Valbusa, C. Boragno and F. Buatier de Mongeot, J. Phys.: Condens. Matter 14, 8153 (2002)
[3]R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)

Es wurde eine Methode entwickelt, Multinuklidproben, wie Pb-210 / Bi-210 / Po-210 oder Ra-226 / U-233 / Np-237, in nur einem Flüssigszintillations (LS)-Spektrum zu bestimmen. Zunächst werden durch a/b-Diskriminierung die a- und b-Spektren getrennt. Im Anschluss daran werden die a- bzw. b-strahlenden Nuklide mittels Pekfitting entfaltet. Die a-Peaks lassen sich am besten mit einer speziellen Peakfittingfunktion beschreiben, die auf der niederenergetischen Seite von der reinen Gaussform abweicht und durch einen exponentiellen Term ersetzt wird. b-Peaks mit geringer Halbwertsbreite werden auch mit dieser Peakfittingfunktion entfaltet, Peaks mit großer Halbwertsbreite durch eine Bi-Gauss-Funktion.
Im System Pb-210 / Bi-210 / Po-210 ist der Spektrenauswertung mit einem a-Strahler Po-210, und zwei b-Strahlern Pb-210 und Bi-210, deren Spektren sich nur geringfügig überlappen recht einfach. Schwieriger ist das im System Ra-226 / U-233 / Np-237, deren Peaks so nah beieinander liegen (4,8 MeV), dass sie durch Peakfitting nicht separiert werden können. Die Bestimmung erfolgt über die b-Tochter von Np-237: Pa-233 und die a-Töchter von Ra-226: Rn-222, Po-218 and Po-214. Als erstes wird Np-237 über Pa-233 bestimmt (Aktivitäten im Gleichgewicht: 1 zu 1, allerdings müssen die b-Töchter von Ra-226 berücksichtigt werden). 5-6 Wochen nach der Probenpräparation, wenn Ra-226 im Gleichgewicht mit den kurzlebigen a-Töchtern ist, wird die Probe erneut gemessen. Aus dem einzeln stehenden Po-214 Peak bei 7.7 MeV wird der Ra-226-Gehalt bestimmt. Zuletzt wird U-233 aus der Differenz Gesamtpeak (bei 4.8 MeV) minus Np-237 und Ra-226 ermittelt.

In this letter, the authors report the correlation between the magnetic and the structural properties of 200 keV Kr and 50 keV Ar ion irradiated Co/Pt bilayer samples at different temperatures and fluences. They observe irradiation induced formation of stable Co–Pt phases, which appears to be more prominent at higher irradiation temperatures. A large shape anisotropy in the hysteresis loop is also observed when irradiated at higher temperatures, which could be indicative of a magnetization reversal. A CoPt ordered/disordered phase formation leads to the enhancement in the coercivity. The sequence of phase formations is predicted by the heat of formation rule.

We investigate the effects of room-temperature irradiation of Au and Ge nanoislands grown on Si. Our studies show the formation of Au-Ge alloy phase within the islands and wetting of the substrate. High-resolution transmission electron microscopy along with synchrotron radiation-based x-ray reflectivity and grazing incidence x-ray diffraction measurements were performed to characterize the irradiation-induced changes brought into the sequentially deposited Au and Ge island thin films. The results are attributed to the recoil implantation and the transient melting of the nanoislands followed by the formation of crystalline alloy phase.

The amorphous-to-crystalline transition in 4H-SiC has been studied using molecular dynamics (MD) methods, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Two nanosized amorphous layers, one with the normal of the a-c interfaces along the [-12-10] direction and the other along the [-1010] direction, were created within a crystalline cell to study epitaxial recrystallization and the formation of secondary phases. The recovery of bond defects at the interfaces is an important process driving the epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interface normal along the [-12-10] direction can be completely recrystallized at temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. On the other hand, the recrystallization process for the a-c interface normal along the [-1010] direction is hindered by the nucleation of polycrystalline phases, and these secondary phases are stable for longer simulation times. A general method to calculate activation energy spectra is employed to analyze the MD annealing simulations, and the recrystallization mechanism in SiC consists of multiple stages with activation energies ranging from 0.8 to 1.7 eV.

Rate theory (RT) is a mean-field approach focussed on the long-term evolution of precipitates or clusters of defects and/or solute atoms in the present case. Interactions between any one particular cluster and particular cluster-forming species are replaced by average interactions. Therefore, any space variables drop out and the temporal evolution of the size distribution is at the centre of interest. On the one hand, the assumptions may not be completely valid in the case of displacement cascades and special attention has to be paid to the initial conditions and to the source term. On the other hand, RT allows the evolution of the cluster size distribution to be followed over time intervals corresponding to the operation of a reactor pressure vessel up to end-of-life within reasonable computation time. As a second advantage, cluster size distributions measured by means of small-angle neutron scattering (SANS) are well suited for the experimental validation of RT models.

Application of RT to three particular systems exposed to neutron irradiation will be considered in the presentation:

• the coupled evolution of the concentrations of single vacancies and single self-interstitial atoms (SIAs) in Fe,
• the evolution of the size distribution of vacancy clusters in Fe,
• and the evolution of pure coherent Cu clusters in dilute Fe-Cu.
Special emphasis will be placed on the aspect of experimental validation using SANS results obtained for low-Cu and Cu-enriched Fe-based model alloys. The problem of multi-component clusters will be touched in the outlook.

The first maximum at cluster sizes of about 0.3 nm is caused by the direct generation of small clusters due to neutron irradiation. After some ten days of irradiation a second peak appears, which becomes more and more dominant. It is observed that:

• the shape of the size distribution is rather independent of the model parameters,
• the rate of cluster growth is essentially influenced by sink strength for vacancies and interstitials only,
• and the volume fraction at a given instant of time is influenced by both sink strength and surface tension of Fe.

From these findings a strategy that allows for fitting the calculated size distribution to SANS data is worked out. However, it turns out that even in low-Cu Fe-based alloys except pure Fe the average cluster detected by means of SANS is not a pure vacancy cluster. Comparability is therefore limited and a concept to deal with two- or multi-component clusters is required.

It is known that fast neutron irradiation induces nanometre-sized defects in reactor pressure vessel (RPV) steels. SANS can detect changes of microstructure on such a small size scale and operates as volume integrating measuring method, i.e. statistically reliable mean values can be determined.

Purpose of the talk is to describe preparation, measuring procedure and raw-data treatment of a SANS experiment as well as data interpretation considering as example the analysis of irradiation-induced defect/solute clusters in RPV steels and iron alloys. Preparation covers not only preparation and transport of radioactive specimen but also to submit a scientific proposal to get access to a SANS facility. Part of the measuring procedure and data treatment are absolute calibration, background correction etc.

A particular example for the application of SANS in the field of RPV steels is sketched below. More examples will be outlined in the presentation. Fig. 1 shows a SANS image recorded by an two-dimensional position-sensitive detector consisting of 64x64 cells with a size of 1x1 cm^2. It was obtained for a Fe-based alloy placed in a saturation magnetic field. The scattering vector, Q, is proportional to the scattering angle. The anisotropic scattering pattern is caused by the magnetic field and can be used to separate magnetic and nuclear scattering contributions.

The measured dependence of the scattered intensity on scattering vector (also called scattering curve) is presented in Fig. 2 for an RPV steel in two different irradiation conditions and the unirradiated reference state. An increase of the scattered intensity is observed in the range Q > 0.5 nm^-1. This increase is caused by irradiation-induced defect/solute clusters. The size distribution of these clusters is obtained by Fourier transformation of the scattering curve. The underlying assumptions will be discussed in the talk. The calculated size distribution of the irradiation-induced clusters is shown in Fig. 3.

The basic findings of this experiment are a volume fraction of clusters, which increases with neutron fluence and a mean cluster radius of about 1 nm independent of neutron fluence.

At present, the GDT experimental facility of the Budker Institute Novosibirsk is upgraded. The construction of the hot ion plasmoid experiment is one part of the upgrade. First experiments with low parameters were carried out and compared with the results of pre-calculations. The paper gives an overview on the present stage of the experiment and on next research activities. The main results are: - The maximal fast ion density was three times greater than the warm ion density. - No evidence of MHD or micro-instabilities was observed, therefore, it can be concluded that the fast ion confinement is fully controlled by Coulomb collisions and charge-exchange. - The feasibility of ambipolar plugging in gas dynamic traps was demonstrated.

The role of monoatomic steps at the mutual interface between a ferromagnetic and an antiferromagnetic layer in a Ni81Fe19/Fe50Mn50 exchange bias system is enlightened. As a result of the reduced coordination at the step edges a strong uniaxial anisotropy is induced in the polycrystalline Ni81Fe19 layer, which is fixed in its orientation. By means of different field annealing cycles the direction of the induced unidirectional anisotropy can be chosen. For all mutual orientations both anisotropy contributions are superimposed independently and the angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model with one parameter set. In addition it is demonstrated that not only the magnitude of the uniaxial anisotropy contribution but also that of the unidirectional one scales with the step density of the substrate, which is in full agreement with theoretical predictions.

We report on in-situ investigations of a recrystallization process of an ion beam-induced rip-pled silicon. The one dimensional ripple structure was created by 40Ar+ ion irradiation with dose of ~5x1017 ions/cm2 under an angle 60° with respect to the surface normal at an energy of 60 keV. At the surface the induced ripples have a period and an amplitude of about 915nm and 80nm, respectively. Structure and morphology of ripples were studied by two x-ray grazing in-cidence scattering methods, transmission electron microscopy and atomic force microscopy. X-ray grazing-incidence amorphous scattering pattern were recorded in-situ in a range from 250°C to 750°C. Up to about 500°C mainly we found a single broad scattering maximum cor-responding to the Si(111) inter-planar distances. At higher temperature these peaks becomes sharp and intense indicating the onset of a re-crystallization process in the amorphous top layer.
Two processes were found, a formation of crystalline islands at the top of amorphous surface ripples and a growth of polycrystalline twins close to the former amorphous-crystalline inter-face.

Der Block 8 des Kernkraftwerkes Greifswald ist ein Druckwasserreaktor russischer Bauart vom Typ WWER-440-213, dessen Reaktordruckbehälter (RDB) vom SKODA-Konzern in der früheren Tschechoslowakischen Republik Ende der 70er Jahre hergestellt worden ist. Dieser Reaktorblock wurde nicht in Betrieb genommen und der RDB beim Rückbau zerlegt. Im Forschungszentrum Rossendorf sind Grundwerkstoff 15Kh2MFA und Schweißgut 10KhMFT dieses RDB untersucht worden. An Proben aus unterschiedlichen Schmiederingen und Schweißnähten sind Charpy-V-, Bruchzähigkeits- und Zugversuche durchgeführt worden, wobei der Schwerpunkt auf der Ermittlung von Bruchzähigkeiten nach ASTM E1921 und E1820 lag.
Die auf dem “Master-Curve” (MC)-Konzept basierende ASTM-Prüfvorschrift E1921 ist für die Ermittlung einer Referenztemperatur T0 homogener Stähle mit einer kubisch-raumzentrierten Grundstruktur konzipiert. Die Referenztemperatur T0 wird aus einem Datensatz von Bruchzähigkeiten KJc berechnet, die im unteren spröd-duktilen-Übergangsbereich beim Einsatz von Spaltbruch gemessen werden. Insbesondere große und dickwandige Schmiederinge für RDB sind makroskopisch oft nicht homogen. Aus diesem Grund wurden auf dem MC-Konzept basierende Verfahren entwickelt, mit denen sich Referenztemperaturen von Stähle ermitteln lassen, die makroskopisch inhomogen sind. Die SINTAP-Prozedur enthält eine solche Modifikation, die es erlaubt, eine konservative untere Grenzkurve der MC zu bestimmen, welche den spröden Bestandteil widerspiegelt. Mit zwei neuen Erweiterungen des Master-Curve-Ansatzes können Datensätze ausgewertet werden, welche zwei unterschiedliche Bestandteile (bimodal) und zufällig verteilte (random) Inhomogenitäten enthalten.
Mit Proben aus RDB-Grundwerkstoff 15Kh2MFA und Schweißgut 10KhMFT gemessene KJc-Werte sind nach der Standard MC-Methode und den modifizierten MC-Ansätzen ausgewertet worden. Während die KJc- Werte des Schweißgutes nahezu vollständig von der 5%-Fractilen eingehüllt werden, zeigen die KJc-Werte der Grundwerkstoffe ein große Streuung. Dabei liegen deutlich mehr als 5% der KJc-Werte unterhalb der 5%-Fraktilen. Metallographische und fraktographische Untersuchungen zeigen, dass der untersuchte RDB-Grundwerkstoff makroskopisch inhomogen ist und ca. 15 bis 20% interkristalline Spaltflächen in der Bruchfläche zeigt. Die Datensätze der Grundwerkstoffe wurden mit dem Random-MC-Ansatz ausgewertet. Mit diesem Ansatz konnte eine Referenztemperatur T0 und 5%-und 95%-Fraktile berechnet werden, welche die KJc-Datensätze dieser inhomogenen Grundwerkstoffe gut wiedergeben.
Mit dem hier vorgestellten Beispiel wird gezeigt, dass eine kritische Bewertung von nach ASTM E1921 ermittelten Referenztemperaturen notwendig ist. Insbesondere bei kleinen Datensätzen wird eine fraktographische Validierung der Prüfergebnisse für notwendig erachtet.
The Master Curve (MC) approach used to measure the transition temperature, T0, was standardized first-time in the ASTM Standard Test Method E1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred cubic (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
Charpy size SE(B) specimens of base and weld metal from the WWER-440 Greifswald Unit 8 RPV were tested according to the ASTM test standard E1921-05. The measured fracture toughness values at brittle failure (KJc) of the specimens show a large scatter. In general the KJc values of the RPV weld and base metal follow the trend of the MC. For two base metals more than 5% of the KJc values lie below the 5% fracture probability line. It is therefore suspected that the investigated WWER-440 RPV base material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data and the nature of inhomogeneity was investigated.

Computed tomography is for a long time no being a valuable tool for human medical diagnostics. It has also found applications in non-destructive testing and process diagnostics. Whereas for NDT applications systems with high spatial resolution, three dimensional imaging capability and a high dynamic range of photon energies are required, the challenging parameters for process diagnostics are temporal resolution, costs and flexibility. Many groups have dedicated past and current research to the establishment of tomography imaging modilities which fullfil such requirements. However, the search has not yet been finished. The presentation gives an overview on the past and recent developments in gamma ray and X-ray tomography and discusses their potentials and drawbacks in process diagnostics.

Zur Zeit werden weltweit über 440 Kernkraftwerke im kommerziellen Leistungsbetrieb eingesetzt. Die überwiegende Mehrheit sind sogenannte Leichtwasserreaktoren (LWR). Das Risiko, dass es beim Betrieb von LWR der heutigen Generation zu einem schweren Unfall (engl. Severe Accident, SA) mit partiellem oder vollständigem Abschmelzen des Reaktorkerns kommt, ist gering. Es lässt sich aber trotz umfangreicher Sicherheitsvorkehrungen nicht vollständig ausschließen.
Bei der Entwicklung und Auslegung von Kernkraftwerken wurde von Beginn an ein erhöhtes Sicherheits- beziehungsweise Schutzkonzept verfolgt, weil bekannt war, dass das radioaktive Inventar, das aus den während des Betriebs entstehenden Spalt- und Aktivierungsprodukten besteht, nicht unkontrolliert freigesetzt werden darf. Es wurde daher von vornherein ein sogenanntes Mehrstufenkonzept („defence-in-depth“) eingeführt, um die in jeder technischen Anlage auftretenden Störungen innerhalb des Kraftwerks zu beherrschen und Unfälle auszuschließen.
Das Mehrstufenkonzept besteht heute aus 4 Ebenen. Die Ebenen 1 bis 3 – Normalbetrieb, Betriebsstörungen und Auslegungsstörfälle – wurden bereits bei der Reaktorauslegung berücksichtigt und dienen der Störfallverhinderung beziehungsweise der Störfallvermeidung. Zur Vermeidung und Begrenzung von schweren Unfällen ist mit dem sogenannten „anlageninternen Notfallschutz“ nachträglich die 4. Ebene eingeführt worden.
Die Wirksamkeit des Defence-in-Depth wird zum einen durch die technische Auslegung sichergestellt. Zum anderen durch die Umsetzung der sogenannten Sicherheitskultur. Die Sicherheitskultur stellt die Gesamtheit der Eigenschaften und Einstellungen von Personen und Organisationen dar, die dafür sorgt, dass dem sicheren Anlagenbetrieb die höchste Priorität zukommt.
Ein Pfeiler der Sicherheitskultur ist die Sicherheitsforschung. In diesem Vortrag werden zwei Beispiele der aktuellen Arbeiten im Forschungszentrum Rossendorf zu sicherheitsrelevanten Fragestellungen behandelt: die sogenannten Borverdünnungstransienten und die Kernschmelzerückhaltung im Reaktordruckbehälter.
Ein kurzer Überblick über die Historie der verschiedenen Kernkraftwerksgenerationen und die Erläuterung der wesentlichen Eigenschaften der aktuell in Bau befindlichen dritten Generation sowie der heute in der internationalen Forschung betrachteten zukünftigen Reaktortypen (Generation IV) schließen den Vortrag ab.

The presenation gives an overview on flow models for capillary flow with emphasize on reactive two-phase flows in chemical engineering problems and describes measurement methods that can be used to visualize the flow and measure certain parameters, such as void fraction, film thickness and flow velocity.

We report the direct investigation of the vortex-antivortex interaction by imaging the magnetic excitation spectrum of a single cross-tie wall by means of x-ray magnetic circular dichroism - photoemission electron microscopy (XMCD-PEEM). The 10 × 6 μm2 Permalloy rectangle of 20 nm thickness was excited by a short magnetic in plane pulse with a maximum field value of about 20 Oe. The high temporal and lateral resolution allows a detailed quantitative analysis of the magnetodynamic excitations. We find new eigenmodes in the frequency domain which are characteristic for the vortex-antivortex interaction in a single cross-tie wall. We discuss our experiment in the light of micromagnetic simulations.

For the investigation of multiphase or multicomponent flows, which are of interest for instance in the oil extraction and processing or in the chemical engineering, there are only few suitable measuring techniques. This presentation gives an overview about the recent efforts of your group in applying high-speed complex impedance measurements for the investigation of dynamic fluid flow. We present a new developed high-speed complex permittivity needle probe as well as a feasibility study for the development of a complex impedance wire-mesh sensor.

We introduce first results of a void fraction distribution measurement in boiling water reactor fuel element bundles. We employed a recently developed high resolution gamma ray tomography system with a collimated Cs137 isotopic source and a 320 element detector arc. The average spatial resolution of the system is 3 mm in plane and 8 mm axial. We performed transversal scans in six axial planes, with approximately 25 minutes recording time for each scan. To determine void fraction calibration measurements have been recorded at zero and one hundred percent void fraction respectively. Image reconstruction was performed with standard filtered back projection algorithms.

Using MgO nanowires as a reactive template, we fabricated for the first time single-crystal MgAl2O4 spinel nanotubes through an interfacial solid-state reaction of MgO–Al2O3 core–shell nanowires. Single-crystal MgO nanowires are coated with a conformal thin layer of amorphous Al2O3 via atomic layer deposition. Subsequent annealing at 700 °C activates the interfacial reaction between MgO and Al2O3, transforming the alumina shell into a spinel shell. Finally, after etching away the remaining MgO core in ammonia sulfuric solution, MgAl2O4 spinel nanotubes are obtained. As a transition from conventional planar spinel layers via thin-film interface reactions, our result might open a window for the fabrication of a wide variety of MgO-based spinel one-dimensional nanostructures.

The measurement of void fraction distribution in electrically heated fuel element bundles suffers from the problem of structure shifts due to thermal expansion and magnetic pinching of the constructive elements during heating. To cope with such displacement problems for subchannel void fraction determination we developed special image processing algorithms. The core feature of these algorithms is a precise tracking of the rods in the images by means of a pattern recognition algorithm. In this way rod displacements can be determined automatically. This allows us to automatically generate a sub-channel integration mask that is subsequently used to determine the void fraction values in the unaffected sub-channel areas.

The electron beam is commonly used as a unique tool for welding of metal parts, curing and polishing of product surfaces, or sterilisation of goods. In such cases the energy of the beam is used to modify a material. A sideproduct of is X-ray radiation which is considered a hazardous side effect of the processing. However, the X-ray radiation generated by an electromagnetically steered electron beam can also be used for X-ray imaging. Thus, a sophisticated imaging technique is electron beam X-ray computed tomography that has now for more than 20 years been used in cardiac diagnostics. Our group at Institute of Safety Research at FZ Rossendorf uses this technique to perform tomography on multi phase flows. The presentation will introduce the concept that is behind this technique and demonstrate its application on industrially relevant applications.

The presentation gives an overview on the methods and applications of X-ray and gamma ray tomography in industrial flow measurement problems. Special emphasize will be given on recent results of system development and industrial applications at the Institute of Safety Research at FZ Rossendorf.

The presentation gives an overview over advanced multi-phase flow measurement and imaging techbniques, including conductivity and impedance needle probes and wire mesh sensors, gamma and X-ray tomography as well as optical technqiues. Industrial and scientific applications are being discussed.

Recently, we developed a high resolution gamma ray tomography system that is operated with a Cs-137 source and comprises a detector arc with 320 small scintillation detector elements. With this system different flow diagnostic applications have been investigated, such as the measurement of phase distributions in water-steam two-phase flows and hydrodynamics in stirred and trickle-bed type chemical reactors. The presentation introduces the application of a high resolution gamma ray tomography technique to the measurement of phase fractions and liquid hold-up in industrial multi-phase flow systems.

We developed a high-resolution gamma ray detection system and associated fast read-out electronics to image rapidly rotating multi-phase distributions in stirred chemical reactors and hydrodynamic machines. The detector arc is made of 320 small scintillation detector elements comprising LYSO scintillation crystals with an active area of 2 mm x 8 mm coupled to large area avalanche photodiodes. Pulse processing electronics is made of charge sensitive pre-amplifier, pulse shaper, gain adjustable amplifier, energy discrimination stage, and binary pulse counters. The counter stage is implemented in FPGA architecture. For fast measurements on rotating objects a fast read-out scheme with 6 bit counter depth and 40 µs read-out interval has been implemented. This enables acquisition of 500 full radiographic projections of objects rotating at 3000 rpm.

Katalytische Gas-Flüssig-Reaktionen spielen in der chemischen Industrie eine bedeutende Rolle. Ein weit verbreiteter Dreiphasenreaktor ist der Trickle-Bed-Reaktor, der durch eine abwärts gerichtete Strömung der fluiden Phasen durch ein regellos gepacktes Katalysatorbett gekennzeichnet ist. Die Reaktorleistung ist dabei wesentlich von der komplexen Zweiphasenströmung in der unregelmäßigen porösen Schüttung abhängig. Aufgrund des niedrigen Flüssigkeitsdurchsatzes ist die Benetzung der Schüttung ein bedeutender Faktor für die Stofftransportprozesse (gas-flüssig, gas-fest und flüssig-fest). Der Katalysatorbenetzungsgrad wie auch der Zweiphasendruckverlust werden vom Flüssigkeits-Holdup (Flüssigkeitsanteil im Reaktorvolumen) beeinflusst. Der Flüssigkeits-Holdup und die Benetzung sind somit wichtige Größen zur Modellierung und Auslegung von Trickle-Bed-Reaktoren. Röntgenbasierte Messverfahren eignen sich besonders zur nichtinvasiven Untersuchung der Hydrodynamik (z. B. Phasenverteilung, Holdup) in Trickle-Bed-Reaktoren.

Katalytische Gas-Flüssig-Reaktionen spielen in der chemischen Industrie eine bedeutende Rolle. Ein weit verbreiteter Dreiphasenreaktor ist der Trickle-Bed-Reaktor, der durch eine abwärts gerichtete Strömung der fluiden Phasen durch ein regellos gepacktes Katalysatorbett gekennzeichnet ist. Die Reaktorleistung ist dabei wesentlich von der komplexen Zweiphasenströmung in der unregelmäßigen porösen Schüttung abhängig. Aufgrund des niedrigen Flüssigkeitsdurchsatzes ist die Benetzung der Schüttung ein bedeutender Faktor für die Stofftransportprozesse (gas-flüssig, gas-fest und flüssig-fest). Der Katalysatorbenetzungsgrad wie auch der Zweiphasendruckverlust werden vom Flüssigkeits-Holdup (Flüssigkeitsanteil im Reaktorvolumen) beeinflusst. Der Flüssigkeits-Holdup und die Benetzung sind somit wichtige Größen zur Modellierung und Auslegung von Trickle-Bed-Reaktoren. Röntgenbasierte Messverfahren eignen sich besonders zur nichtinvasiven Untersuchung der Hydrodynamik (z. B. Phasenverteilung, Holdup) in Trickle-Bed-Reaktoren.

Multiphase flows exist in many areas of commerce such as manufacture of petroleum-based products and fuels, the production of commodity and specialty chemicals, pharmaceuticals and pollution abatement (Al-Dahhan et al., 1997). Especially, randomly packed beds operated in gas-liquid concurrent down-flow mode in the trickling regime are widely used (e.g. catalytic hydrogenations and oxidations). The reactor behavior is very complex and depends strongly on the hydrodynamics as fundamental criteria for the selection and productivity of multiphase reactors and safety of processes (Krishna and Sie, 1994). Most important hydrodynamic aspects are the liquid holdup and the cross sectional liquid distribution. Two phase flow in randomly packed beds is difficult to visualize, characterize and quantify due to opaque systems, irregular nature and internal objects and structures. X-ray computed radiography (CR) and computed tomography (CT) is used to explore two phase flow in randomly packed beds.

In multi-phase flow diagnostics there is a strong interest in ultra fast computed tomography technologies. Such imaging modalities are of ultimate value, for instance in chemical reactor design, optimisation of nuclear fuel element assemblies and mineral oil processing. However, the required time resolution for typical flow measurements is in the range of more than 1000 images per second, thus classical X-ray or gamma ray computed tomography devices with mechanical rotation of object or measurement system are not applicable. Scanned electron beam X-ray tomography, however, is a promising technology. It has been introduced in medicine two decades ago were it is mainly used for cardiovascular diagnostics. However, medical systems are still too slow and too expensive for technical flow diagnostic problems. For this reason we have started to develop a flexible scanned electron beam X-ray apparatus that offers a number of different measurement features including linear scan limited angle tomography, full angle tomography, multi-plane tomography and phase velocity measurement.
The principle setup of a prospective scanned electron beam X-ray CT system for flow measurements is shown in figure 1. Essential components are a fast X-ray detector and an electron beam generator similar to those devices used in electron beam welding. The gun produces an electron beam of at least 150 kV acceleration voltage and a few milliampere beam current. The beam is focussed onto a tungsten or molybdenum target. An x-y-deflection system periodically sweeps the beam on the target along a well defined path, thus producing a focussed moving X-ray source. In front of the target there is the object of investigation, which may be for example a pipeline with a liquid-gas flow or a small chemical reactor. The X-ray arc detector records the X-ray intensity behind the object in synchronisation with the source deflection signal. In that way we obtain radiographic projections from different viewing angles which may then be algorithmically processed to cross-sectional images by means of a computer. Tomography can be done in different ways. Conventional tomography would require moving the X-ray source approximately 210° about the object. Medical EBT scanner work this way. The detector in that case must be annular and arranged with some axial offset to the focal spot path. In many cases such an arrangement is not possible due to constructive constraints. Then still a limited angle linear scan CT may be applicable where the X-ray source is only linearly moved on one side of the object. Multiple targets or a step target thereby allows us to perform tomography in different planes, which is useful for flow velocity measurement.
Primary tests of a limited angle linear scan ultra fast X-ray tomography have been carried out in a conventional electron beam welding box. Therefore we have employed a fast 64 element X-ray detector and operated the equipment within the evacuated chamber of the welding box. We scanned static phantoms as well as a dynamic phantom consisting of moving pearls in an aluminium cup (figure 2). The image rate we achieved was 1000 images per second. Currently we are about to build a fast X-ray tomography scanner which comprises a special electron beam generator with wide angle scanning capability and a 512 element ultra fast CZT X-ray detector. The electron beam unit (figure 3) is operated at acceleration voltages up to 150 kV and 33 mA beam current. The sweeping range is ±15° at 10 kHz large signal deflection frequency in two dimensions. As a target we use a water cooled tungsten block with a multiple step structure. As in a conventional X-ray tube a proper X-ray window made of a 100 µm steel film allows radiation exit to the environment. The whole system will be operated in a lead cabin for radiation protection.

On the way to a flexible ultra fast X-ray tomography system with a scanned electron beam we have proceeded to develop and build major system components. These are a fast 512 element CZT X-ray detector with 1 MHz channel sampling rate and a 150 kV / 33 mA electron beam unit with two-dimensional deflection capability (15° deflection angle, 10 kHz deflection rate). Furthermore, we developed a special tungsten target for tomography including water cooling for high electron current operation.

We developed and tested an optical tomograph for the investigation of single and two phase flows in pipes or bubble columns. The device works similar to a conventional CT with 256 light emitters and 32 light receivers arranged about the object’s cross-section. The light emitters are sequentially flashed while the light receiver intensities are recorded synchronously. Primary area of application is single phase flows with dye tracers. Another potential application is the investigation of bubbly two phase flows at low gas fractions. Principle tests have been made for both problems.

Abstract wird nachgereicht

In laboratory column experiments, ion exchange resins and the corresponding non-functionalized copolymers were compared in order to investigate the uptake mechanisms of organics during the water demineralization process. To improve the detection limit, C-14-labeled model substances (ß-alanine, starch, synthetic humic acid type M42) were used. These compounds are supposed to represent the TOC fractions of polysaccharides, neutrals/amphiphilics and humics following the LC-OCD method. The uptake was investigated depending on the salinity and pH, the concentration of the organics, and the loading temperature. The main results are:

• At neutral pH, a near 100 % removal of ß-alanine and starch by ion exchange and/or adsorption was observed, whereas humic acid was taken up by ion exchange to an extent of about 10 %.
• In acidic conditions, ß-alanine and starch were completely removed up to the breakthrough point of the sulfate ions. Those elute the organics. Humic acid will be removed owing to precipitation.
• The last mechanism allows the removal of humic acid by the copolymers too. These are inefficient in regard to the uptake of ß-alanine and starch.
• The variation in the concentration of the organics as well as that in the loading temperature have only a subordinate influence on the uptake.

Die sich ständig und stark verändernden Bedingungen der Wirtschaftsprozesse in vielen entwickelten Industrieländern werden zu den entscheidenden Bedingungen sowohl für den Verlauf der Unternehmenstätigkeit als auch für den Unternehmenserfolg. Eine der Analysen über die Ursachen erfolgloser Unternehmen zeigte auf, dass die Human Ressources nicht vernachlässigt werden dürfen. Vor diesem Hintergrund stehen oft folgende Schlüsselprobleme: Versagen in der Unternehmungsführung, Mangel an Fach- und Persönlichkeitsqualität, niedrige Koordination und anpassungsfähigkeit der Bildungsprozesse, niedrige Partizipation der Arbeitgeber an der fachlichen Bildung sowie auch schlechte Moral der Gesellschaft. Dies gibt Hinweise auf die Art der Unternehmensführung; die Wahrnehmung der Führung durch Mitarbeiter ist Gegenstand dieses Beitrages.

Die Gebiete in Sachsen und Thüringen, in denen die sowjetisch-deutsche Aktiengesellschaft "Wismut" mehr als 40 Jahre tätig war, sind durch die rücksichtslose Gewinnung und Verarbeitung von Uranerzen stark beeinfluss. Als der Uranerzbergbau Ende 1990 abrupt eingestellt wurde, hinterließ er tiefgreifende Schädigungen der Umwelt.
Zurückgeblieben waren u. a. 1400 km offene Grubenbaue, 311 Mio m³ haldenmaterial und 160 Mio m³ radioaktive Schlämme in dicht besiedelten Gebieten.
...
Ein Teil [der Aufgabe des Instituts für Radiochemie] ist es, auch das in der Natur vorkommende Sekundärmineral Compreignacit zum einen spektroskopisch zu untersuchen und somit zur besseren Identifizierung anderer Uranverbindungen einzusetzen, und zum anderen bei Vorlage genügend großer Substanzmengen dessen Löslichkeit zu bestimmen.

The dynamics of magnetic vortices in thin permalloy disks comprising artificial point defects at
different locations within the disk has been investigated by means of frequency-domain spatially
resolved ferromagnetic resonance. It is found that the vortex core can be effectively trapped by
a point defect. Consequently the commonly observed gyrotropic vortex motion in an applied microwave
field of 1 mT is suppressed. However, if in addition a static magnetic field of at least 4.3
mT is applied, the vortex core is unpinned from the artificial point defect and a modified gyrotropic
motion starts again.

In der vorliegenden Diplomarbeit sollte die Eignung bakterieller Hüllproteine zur Reinigung von uranhaltigen Wässern untersucht werden. Dazu wurden die drei Haldenisolate Bacillus sphaericus JG-A12, Bacillus sp. JG-B7 und Bacillus sp. JG-B12 sowie deren Referenzstämme B. sphaericus NCTC 9602, B. fusiformis DSM 2898 und B. mycoides DSM 2048 kultiviert und sowohl die pH- als auch die Urantoleranz der sechs Stämme untersucht. Dabei zeigte sich, dass das Paar JG-B12/B. mycoides DSM 2048 azidotoleranter als die beiden anderen Paare ist. Für keines der Isolate konnte beim pH-Wert, der dem ihres Isolationsortes entsprach, Wachstum festgestellt werden, da sie zum Zeitpunkt der Probennahme vermutlich größtenteils als Sporen im Haldenboden existierten. Die Urantoleranz wurde nur von zwei Paaren bestimmt. Im Falle des B. sphaericus-Paares wurde eine minimale inhibierende Urankonzentration von 15 mM ermittelt, für das Paar Bacillus sp. JG-B7/B. fusiformis DSM 2898 konnte dagegen keine bestimmt werden. Die Hüllproteine des Paares Bacillus sp. JG-B7/B. fusiformis DSM 2898 wurden isoliert und ihre Eigenschaften mit denen der Hüllproteine des B. sphaericus-Paares verglichen. Während die Hüllproteine beider B. sphaericus-Stämme eine tetragonale Symmetrie aufweisen, wurde für das Isolat JG-B7 eine schräge Symmetrie ermittelt. Bei B. fusiformis DSM reichten die erhaltenen Daten zur Bestimmung der Symmetrie nicht aus. In Hinblick auf mögliche funktionelle Gruppen zur Bindung von Metallen wurden posttranslationale Modifikationen der Hüllproteine untersucht. Alle vier Hüllproteine sind nicht glykosyliert, weisen aber einen Gehalt von ungefähr 1-2,5 mol Phosphat pro mol Hüllprotein auf.
Zur Bestimmung der uranbindenden Eigenschaften von intakten Bakterienzellen und isolierten Hüllproteinen wurden Bindungsversuche mit synthetischen Uranlösungen und natürlichen Heilwässern durchgeführt. Es konnte dabei ein entscheidender Einfluss des pH-Wertes nachgewiesen werden. Mit Ausnahme eines Falles wurden die höchsten Bindungskapazitäten aus synthetischen Lösungen bei pH 6 ermittelt. In Bindungsversuchen mit Hüllproteinen in Lösungen mit 10-4-10-6 M Uran zeigte sich, dass die prozentuale Uranentfernung mit sinkender Ausgangskonzentration zunahm und das Actinid bei 1 und 5 µM fast vollständig gebunden wurde. Die Bindung von Uran an die Hüllproteine der untersuchten Bacillus-Stämme ist daher eine spezifische Reaktion. Der Großteil dieser Bindung erfolgt über Carboxylgruppen, nur ein kleiner Teil des Urans ist an Phosphatgruppen gebunden. Aus natürlichen Heilwässern konnten nur die isolierten Hüllproteine Uran binden, intakte Zellen nicht. Es zeigte sich aber auch, dass die Uranbindung aus diesen Wässern durch eine Vielzahl von Ionen gehemmt wird. Unterschiede zwischen den uranbindenden Eigenschaften der Haldenisolate und ihren Referenzstämmen konnten nur für die Hüllproteine bei hohen Urankonzentrationen und leicht sauren pH-Werten festgestellt werden.
Die Untersuchungen dieser Arbeit führen letztendlich zu dem Schluss, dass die untersuchten Hüllproteine zwar grundsätzlich für die Reinigung uranhaltiger Wässer geeignet sind, ihre großtechnische Anwendung als Bestandteil von neuartigen Filtermaterialien auf Basis der erhaltenen Daten aber nicht sinnvoll erscheint.

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This paper reports on the new control program CORA for the ROMA detection device. It was developed as part of the HITGAS apparatus for the study of seaborgium (Z=106) as oxide hydroxide.

CORA runs under Win9x and Win NT. It is object oriented, programmed with Borland C++ Builder. Its main features are high flexibility for various experiment modes, hardware independence to a large extent, and an easy-to-understand user interface.

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The speciation of 1 mM uranium(VI) in carbonate-free aqueous solutions of 50 mM protocatechuic acid (PCA, 3,4-dihydroxybenzoic acid) was studied in the pH range of 4.0 to 6.8 using EXAFS spectroscopy. The uranium LIII-edge EXAFS spectra were analyzed using a newly developed computer algorithm for iterative transformation factor analysis (FA). Two structural different uranium(VI) complexes were observed. The speciation in the pH range of 4.0 to 4.8 is dominated by a 1:2 or 1:3 uranium(VI)/PCA complex with bidentate coordination of the carboxyl group to the uranium(VI) moiety. Already at pH 4.6 significant amounts of a second species are formed. This uranium(VI) species contains two PCA ligands that are bound to the uranium via their neighboring phenolic hydroxyl groups under formation of five-member rings.

The radiation source ELBE (Electron Linear accelerator with high Brilliance and low Emittance) at Forschungszentrum Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to Ie- = 1 mA at energies up to Ee- = 40 MeV can be delivered with a pulse width of less than 10 ps.
With these parameters the electron beam allows to generate sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and producing neutrons by bremsstrahlung photons through (gamma,n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n,gamma), (n,n'gamma), (n,p), (n,alpha), and (n,f) at a time-of-flight arrangement with a short flight path of only a few meters it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons, which would broaden the neutron pulses. It is the primary physics objective of this neutron source to measure neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select materials with low activation cross sections, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. Furthermore experiments can be performed which address problems of nuclear astrophysics.
The power deposition of the electron beam in the small neutron radiator volume of 1 cm³ reaches up to 25 kW. This is such a high power density that any solid high Z number material would melt. Therefore, the neutron radiator consists of liquid lead circulated by an electromagnetic pump. The heating power introduced by the electrons is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are between 1 m/s and 5 m/s in the radiator section. From the thermal and mechanical point of view, molybdenum turned out to be the most suited target wall material in the region where the electrons impinge on the neutron radiator.
To reduce the radiation background at the measurement position, the neutrons are decoupled from the radiator at an angle of about 90° with respect to the impinging electrons. Particle transport calculations using the Monte Carlo codes MCNP and FLUKA predict a neutron source strength in the range of 7.9E12 n/s to 2.7E13 n/s for electron energies between Ee- = 20 and 40 MeV. At the measuring place 3.9 m away from the radiator, a neutron flux of about 1.5E7 n/(cm² s) will be obtained. The short beam pulses allow for a neutron energy resolution of better than 1 % for neutron energies between En = 50 keV and 5 MeV. The usable energies range up to about 10 MeV.

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Intracrystalline organic compounds, enclosed within in situ–precipitated marine microcrystalline calcite (automicrite), might represent either an inclusion or the catalyst of such precipitation. We use evidence from a Lower Cretaceous deep-water carbonate mound to show (1) the original source, (2) the degree of condensation, (3) the redox conditions involved, and (4) the catalytic role of natural organic matter for the precipitation of automicrite. Fluorescence spectrometry of the intracrystalline organic fraction extracted from these carbonates identifies a marine fulvic acid–like organic compound with a low degree of polycondensation. This finding points to a temporal correlation of the initial stage of geopolymer formation with the precipitation of automicrite. Furthermore, the rare earth element (REE) distribution patterns in the mineral show a consistent positive Ce anomaly, suggesting an episode of reductive dissolution of iron-manganese oxyhydroxides during automicrite formation. In general, a relative enrichment of middle-weight REEs is observed, resulting in a convex distribution pattern typical for, e.g., phosphate concretions or humic acid material. By merging the results of spectrometry and REE geochemistry we thus conclude that the marine calcite precipitation was catalyzed by marine fulvic acid–like compounds during the early stages of humification under suboxic conditions. This indicates that humification, driven by the presence of a benthic biomass, is more important for calcite authigenesis than any site-specific microbial metabolism. The Neoproterozoic rise of carbonate mounds supports this hypothesis; there is molecular evidence for early metazoan divergence then, but not for a major evolutionary episode of microorganisms.

The redox–sensitive fission product technetium–99 has been investigated in systems containing different reducing solid phases (pyrite, magnetite, ironsulphide and Gorleben sand) on the one hand and Gorleben groundwater, which contains a high amount of humic substances, on the other hand. Initially, technetium–99 was added to these systems as pertechnetate (Tc(VII)), which was reduced in presence and absence of humic substances with the aid of the different reducing surfaces (neutral to alkaline pH). Both in absence and presence of humic substances, Tc concentrations were observed which exceeded the TcO2 solubility limit, whereby the presence of humic substances had a 100 fold higher Tc concentration compared to its absence. Using the La–precipitation method, it was shown that Tc(IV) inorganic colloids and organic colloids were quantitatively precipitated. It was demonstrated for the first time by a combination of chemical speciation methods (La–precipitation method and gel permeation chromatography) and XANES spectroscopy of the humic substance containing supernatant solutions, that Tc(IV) species were formed in these systems, indicating an association between Tc(IV) and humic substances.

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We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca₂UO₂(CO₃)₃(aq.), in uranium mining related waters [1]. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA^4-.

Slope analysis of the log (fluorescence intensity) versus log[Ca²⁺] with both methods have shown that two calcium ions are bound to form the complex Ca₂UO₂(CO₃)₃(aq.).
The formation constants determined from the two independent methods are:
i) logβ°213=30.45±0.35 and
ii) logβ°213=30.77±0.25.

A bathochrome shift of 0.35 nm between the UO₂(CO₃)₃ ^4- complex and the Ca₂UO₂(CO₃)₃(aq.) complex is observed in the laser-induced photoacoustic spectrum (LIPAS), giving additional evidence for the formation of the calcium uranyl carbonate complex.

EXAFS spectra at the LII and LIII-edges of uranium in uranyl carbonate solutions with and without calcium do not differ significantly. A somewhat better fit to the EXAFS of the Ca₂UO₂(CO₃)₃(aq.)complex is obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca₂UO₂(CO₃)₃(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.

This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.

Different charge exchange canals and alkali metals were tested at the Rossendorf 3 MV Tandetron to install an additional injector for negative He ions. The results of these investigations and the construction of the new injector are reported.

Single crystal X-ray diffraction (XRD), high-resolution electron holography and density functional calculations (DFT) are employed to investigate single-crystalline BaTiO3 in the non-centrosymmetric tetragonal phase. From XRD and DFT the structure parameters, the electron density and corresponding properties, like atomic charges and the dipole moment are determined. For this purpose the maximum-entropy method was utilized to get accurate electron densities in the case of XRD, whereas all-electron calculations were performed in the framework of DFT. A comparison of experimental results and density functional calculations yield a rather good agreement. The electron density distributions are used to determine the ‘natural’ unit cell corresponding to the neutral boundary cells of the whole crystal and its dipole moment, providing the boundary conditions necessary for calculating the Electrostatic potential within the unit cell through the Poisson equation. The Electrostatic potential was then utilized to perform electron scattering simulations within the framework of the Multislice formalism, resembling unique features of experimentally recorded electron holograms. It is shown that the phase wedge in the scattered wave, which is due to the polarization field within the specimen, is essential for the image reconstruction. This essential feature has not been included in simulations before.

The actual technical equipment of the Rossendorf beamline will presented. It includes a high-throughput/high energy resolution 13-element solid state Ge detector (100 mm2 LEGes)with XIA digital x-ray spectrometer (DXP-2X4T-M, 4-channel, 40 MHz, timing model), a closed cycle He-cryostate for low temerature measurements, a goniometer for polarization dependent measurements and a spectroelectrochemical cell including electrodes for electrolysis and analysis of the solution (T, Eh, pH).

The presentation gives an introduction in spectroelectrochemistry, cyclic volatammetry and electrolysis, as well as its combination with XAFS. The technical background and several examples will be discussed.

Recently 3D neutron kinetics core models have been coupled to advanced thermal hydraulic system codes. These coupled codes can be used for the analysis of the whole reactor system. In the framework of the international association „Atomic Energy Research“ (AER) on VVER Reactor Physics and Reactor Safety, two benchmarks for these code systems were defined. The reference reactor is the Russian VVER-440. The response of the reactor core to a symmetric and an asymmetric main steam line break should be investigated. So, different aspects of the coupling could be tested. As an additional feature, the participants had to use own nuclear data.

Each of these benchmarks was calculated by five different code systems. The comparison of the received solutions for the symmetric case shows a good agreement in the evolution of the thermal hydraulics. When the core power re-establishes after re-criticality, differences between the single solutions are developing, mainly connected with the use of the different nuclear data. Due to the increased complexity of the calculations, in the second benchmark differences between the thermal hydraulic behaviour in the single calculations were observed, additionally. These differences have their main origin in the behaviour of the secondary side.

The results of both benchmarks show the safety potential of the VVER-440 reactor. Even under very conservative conditions no fuel rod failure was observed in the calculations and the reactor was transferred into a sub-critical final state.

For the measurement of sub-channel void distributions and dry-out effects in electrically heated fuel element bundles at the thermal hydraulic test loop KATHY (AREVA NP GmbH, Germany) we have recently developed a high-resolution gamma ray tomograph. This device enables a non-invasive measurement of cross-sectional void fraction profiles through the pressure vessel for fuel element bundles under typical nuclear reaction conditions. The gamma ray tomography system consists of a collimated Cs137 isotopic source and a 320 element detector arc. The average spatial resolution of the system is 3 mm in plane and 8 mm axial. With a special gantry vertical positioning and continuous rotation of the measurement setup is realised. Performing transversal scans takes approximately 25 minutes recording time. To measure void fraction calibration measurements have been recorded at zero and one hundred percent void fraction respectively. Image reconstruction was performed with standard filtered back projection algorithms.

For gamma ray tomography measurements of void fraction distributions in fuel rod bundles of boiling water reactors a new high resolution tomography system has been designed and built. Particular objectives of this application are the measurement of sub-channel void distribution and the investigation of dry-out effects in electrically heated fuel rod bundles. The application requires a robust tomography system that works in an industrial environment. In particular it was necessary to develop a high-resolution gamma radiation detector that is unsusceptible to strong magnetic fields, ambient temperature changes, and vibration forces. The developed detector is made of avalanche photodiodes (APD) coupled to small lutetium yttrium orthosilicate scintillation crystals (LYSO). Together with a special data processing unit and either a Cs137 or a Co60 source it can be operated as a tomography device for diverse diagnostic problems in science and engineering.

We present a modular gamma ray detector design for gamma ray tomography applications. As a key electronic component we use the APD array S8550 of Hamamatsu Corp. with 4 x 8 single APD elements each of 1.6 mm x 1.6 mm size. For this APD array we tested and evaluated different configurations of 2 mm wide lutetium yttrium orthosilicate scintillation crystals. Emphasize was given to high counting efficiency and low dead time in order to secure applicability of the detector to tomography of objects with highly attenuating materials. For electronic processing we designed a low-cost low-power charge sensitive preamplifier circuit using commercially available operational amplifier ICs. The modular design of the detectors allows us to build up larger line or arc detectors.

In the German practice of considering boron dilution transients (BDT) in safety analysis reports (SAR), a strongly conservative approach is applied,. The approach is based on recommendations of the German Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) and the technical expert organizations (TÜV) and accepted by the Reactor Safety Commission (RSK) and is currently followed by the industries and the facilities. No final recommendation and guidelines exist, because the item is subject of comprehensive discussions and research in Germany currently.

This conservative approach is based on a combination of analytical and experimental steps. In the first step, the bounding scenarios which lead to maximum realistic volumes of the lower-borated coolant which can be transported to the reactor core by re-establishing circulation in the primary circuit are determined in a series of thermal hydraulic system code calculations. These are mainly small break loss of coolant accidents (SBLOCA), during which the decay heat is removed from the core in the reflux-condenser regime. The position and maximum size of lower-borated slugs are identified, and the circulation re-start conditions are determined. The main SBLOCA scenarios are verified on experiments at large scale test facilities (e.g. PKL in Germany). While in the integral tests, the formation and transport of the slugs in the loops is assessed, the mixing is investigated in detail in dedicated mixing test facilities using the boundary conditions either from the integral tests or from the system code calculations. In this way, the minimum boron concentration at the core inlet, which is reached during the transient, is estimated. Additionally, the minimum boron concentration is calculated by using computational fluid dynamics (CFD) codes. The critical boron concentration of a reactor core should be lower than this minimum boron concentration. This approach contains a high amount of conservatism, because it is assumed that the boron concentration is uniform in the whole reactor core. The spatial and temporal distribution of the boron concentration in the reactor core, available from the detailed analyses, is not taken into account.

A different approach based on best-estimate calculations has been developed at FZR and was applied to generic studies of BDT scenarios connected with start-up of the first MCP for German KONVOI type reactors. This approach starts with the definition of a bounding scenario which covers all possible BDT scenarios with respect to reactivity consequences (maximum reactivity insertion). This is followed by a reactivity initiated accident (RIA) analysis using appropriate best-estimate tools (coupled 3D neutron kinetics/thermal hydraulic codes). Best-estimate boundary conditions for the boron concentration at the core inlet are applied. These are time-dependent boron concentration at the core inlet determined from experiments or CFD calculations. The final goal of the analysis is to show the integrity of the fuel rods. Usual acceptance limits with respect to maximum fuel temperature, maximum cladding temperature, radially averaged enthalpy deposited in the fuel and maximum cladding oxide layer thickness for RIA are applied.

The use of this best estimate approach, which should be accompanied by an uncertainty analysis, can help to make the design of future reactor cores more flexible and economically not decreasing the safety level of the nuclear installations.

Zum ersten Mal wird über die direkte spektroskopische Bestimmung der Bindungsform des Urans bei niedrigsten originalen Konzentrationen in Mineralwasserproben berichtet.
Zu diesem Zweck wurde ein spezielles laserinduziertes Fluoreszenzspektroskopiesystem eingesetzt und die Proben bei tiefen Temperaturen vermessen. Exemplarisch werden die Ergebnisse der spektroskopischen Bestimmung der Bindungsform des Urans in einer Mineralwasserprobe (Urankonzentration 3,56 μg/L) und im Wasser einer Heilquelle (Urankonzentration 467,0 μg/L) vorgestellt. Die Speziation wird im Mineralwasser durch den Komplex Ca2UO2(CO3)3 und im Heilwasser durch eine Mischung aus den Komplexen Ca2UO2(CO3)3 und UO2 (CO3)34- dominiert. Die Mobilität und Toxizität des Urans sind stark abhängig von seiner Bindungsform.

The the U27-FEL of the ELBE radiation source allows to choose between five mirrors with different outcoupling holes. This allows to adapt the optical resonator to the required wavelength range to ensure the needed laser gain and to optimize the outcoupled laser power. Another parameter which influences the achievable laser gain and output power is the detuning length of the optical cavity. While for CW operation often the minimum detuning point is choosen which maximizes the outcoupled power, for pulsed-mode operation about one wavelength of cavity detuning maximizes the laser gain and yields best stability of the laser. To gain some insight into the behavior of the optical resonator we have measured the round-trip losses and the net laser gain and compare both to calulations. For the measurements we have used a fast-readout MCT detector to measure the decay and rise-time of the outcoupled infrared beam caused by a 10μs break in the electron beam micro-pulse train. We show gain and loss for 5, 10 and 20μm wavelength with the typical detuning curves of an FEL.

The radiation source ELBE is the central research facility in the Forschungszentrum Rossendorf. The machine is based on a 40 MeV superconducting RF Linac wich can be operated up to 1mA in cwmode. After commissioning the Bremsstrahlung and the X-ray facilities in 2002, and 2003 respectively, and the first lasing of the mid- IR FEL (4-22 um) in 2004 about 7000 hours user beam-time have been provided. At present a second FEL for long IR waves (15-150 um) using a partial waveguide is under commissioning. Besides in-house users especially the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. In this talk the fundamental features of the ELBE IR FEL’s and the parameters demanded by users are displayed. In addition, an overview about user experimental work and important machine date like availability are shown. Future projects like the combination of the new High Magnetic Field lab with the ELBE-IR beams will be described.

We present the designs and report on the progress in construction and testing of the cryomodule and the tuning system for the
SRF gun. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a high average current CW photo injector at the ELBE linac with a Nb cavity. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from ELBE module. A cooling and support systemfor the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with stepmotors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment.

At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is nearly finished. One of the main attentionwas focussed at the treatment of the cavity. Their RF properties were measured at room temperature. The warm tuning was carried out considering pre-stressing and tuning range of both tuners (half cell and full cells). The adjusted field profiles and pass band frequencies of the four fundamental modes met the requirements. An external Q study of the main coupler yielded to an optimal antenna length and showed very good agreement between simulation and measurement. Furthermore the characteristics of the choke filter and both HOM filters were simulated, measured and tuned at the pi-mode frequency. The preparation (etching and rinsing) and the cold test were successfully done at DESY. The poster presents the setup for the measurements as well as a comparison of the simulated and measured results.

The RF system for the ELBE accelerator was originally designed for CW mode. Although this works problem-free tests have shown that it is possible to reach higher gradients in the TESLA cavities with a pulsed RF system. The new RF system will be presented together with measurements of the achievable gradients. Roughly 30% higher gradients could now be used in pulsed mode. As positive side effects the radiation by field emission is reduced by the duty cycle and an easy in situ RF conditioning of cavities and coupler windows is possible.

The driver LINAC of the ELBE radiation source is built for cw operation. However, in some cases a pulsed-mode operation was desired to extend the otherwise stringent gradient limits. The main restriction results from field emission that decreases the Q of the cavities which was evaluated from measurements of the liquid helium consumption. After pulsed-mode operation with gradients exceeding the maximum cw accelerating gradients by 30–40\% a significant reduction in the field emission was observed. This in turn allows higher accelerating gradients to be used in cw as well. We attribute this behaviour to an rf-processing of the cavity surface which burns off field emitters.

In a collaboration between BESSY, DESY, FZR, MBI and BINP a 3-1/2 cell superconducting RF electron gun is under development at the FZ - Rossendorf. The status of the project and the progress obtained in the last year is reported on this conference. The motivation for the design of a new gun cavity, presented in this paper, is the new FEL project at BESSY. This FEL is designed for a bunch charge of 2.5 nC and the transverse emittance should be comparable with that of the current SRF gun project. In order to compensate the high bunch charge a high electric field on the cavity axis is necessary. In the present paper we will present the design of a 1-1/2 cell cavity for a superconducting RF gun. The active length of the cavity (without beam tube) is 14.4 cm. For the magnetic peak field the conservative value of 130 mT is assumed. The obtained particle energy is 6.6 MeV, corresponding to an accelerating field strength of 45.6 MV/m . In the TESLA cavity the same magnetic peak field is connected with an accelerating field strength of approximately 31 MV/m. Tracking calculation of electron bunches are in progress and will be also reported.

In this paper we report the status and the progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 10 MeV electron energy. The cavity consists of three cells with TESLA geometry, a special designed half-cell in which the photo cathode will be inserted and a choke filter, which prevents the leakage of RF power by the coaxial line between the cathode and the cavity cell. A double tuner allows the tuning of the half-cell and the TESLA cells separately. In 2005 the fabrication of two cavities with RRR300 and RRR40 was finished. We present the results of the field measurement and the warm tuning of the cavity cells as well as the tuning and performance measurement of the choke filter. The fabrication of the double tuner has been also finished. In a test bench we measured the properties of the tuner (tuning range, resolution) at LN2 temperature. Further activities concern the diagnostic beam line of the gun, the new cathode preparation and cathode transfer system, the driver laser and the LHe transfer line.