Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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.

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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.

Nanocrystalline thin Nb films loaded with hydrogen were studied in the present work. Thin Nb films were prepared on (100) Si substrates at room temperature by cathode beam sputtering. Microstructure observations by transmission elec tron mi cros copy (TEM) revealed that the films exhibit elon gated col umnlike grains. The width of the columns is smaller than 100 nm. Two “generations” of grains can be distinguished in the columns: (i) “first generation” grains at tached directly to the Si substrate, and (ii) “second generation” grains which grow on top of the “first generation” grains. X-ray diffraction (XRD) studies revealed that the Nb films are characterized by a strong (110) texture. However, the lateral orientation of grains (i.e. in the plane of the substrate) is random. Defect studies were performed by variable energy positron annihilation spectroscopy (VEPAS) with measurement of Doppler broadening (DB) of the an ni hi la tion line. The shape of the annihilation line was characterized by the S parameter which represents a frac tion of positrons annihilating with low-momentum electrons. It was found that the virgin Nb films (i.e. free of hy dro gen) con tain a high den sity of defects. Nanocrystalline grain size leads to a sig nif i cant volume frac tion of grain bound aries con tain ing open volume vacancy-like defects. Thus, most of positrons annihilate from a trapped state in the open volume defects at grain boundaries. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free standing bulk metals, the lattice expansion is highly anisotropic in thin films. The inplane expansion is prevented because the films are clamped to an elastically hard substrate. On the other hand, the out-of-plane expansion is substantially larger than in the bulk samples. Moreover, an enhanced hydrogen solubility in the a-phase in the nanocrystalline Nb films is found. Formation of the b-phase (NbH) starts at a hydrogen concentration of xH = 0.25 [H/Nb atomic ra tio], i.e. it is » 4 times higher than in bulk Nb. Using VEPAS it was found that hydrogen is trapped in vacancy-like de fects at grain bound aries. Hydrogen trapping leads to a local increase of the electron density in these defects and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. Subsequently, when the hydrogen concentration exceeds xH = 0.02 [H/Nb], all available traps at grain bound aries are already filled with hydrogen and the S parameter does not change any more. Formation of the b-phase particles leads to an introduction of new de fects, which is reflected by an increase of the S parameter at xH > 0.25 [H/Nb].

The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO wafer grown by pressurized melt growth with nitrogen ions. The authors found the commonly observed donorlike defects E1 and E3 and two acceptorlike defects A2 and A3, as well as a broad acceptorlike defect band. The thermal activation energies of A2 and A3, were determined to be about 150 and 280 meV, respectively.

We present a numerical analysis of the liquid metal flow and its 3D linear stability in a spherical droplet spinning in an alternating magnetic field. The applied magnetic field is uniform and the droplet spins around an axis parallel to the field. The droplet is assumed to be small so that its deformation by both electromagnetic and centrifugal forces is negligible. We find that a sufficiently fast spinning suppresses and so stabilizes the internal flow in the droplet. However, there is a narrow range of rotation rates corresponding to an Ekman number of E » 10-2 where the spinning can destabilize the internal flow. Our results can be useful for the assessment of melt flow conditions in certain material processing technologies using electromagnetic levitation melting techniques.

The Performance Ratio (PR) is the most frequently used figure to characterize the quality of design and components of a photovoltaic power plant (PVP). It is usually calculated from the measured irradiation in the generator plane and the generated photovoltaic energy (final yield). Unfortunately, at the most PVPs no irradiation sensor is available.
The paper presents a simple approach to estimate the performance ratio from daily energy measurements and terrestrial irradiation measurements in the neighbourhood of the PVP. The approach is verified in Saxony, based on irradiance ground data collected by the Saxon agro-meteorological measuring network.

Piezoresistive deflection sensing is a promising approach for massively parallel AFM cantilever arrays. It is well known, that p-type Si exhibits piezoresistivity [1]. We have fabricated boron-doped piezoresistors in n-type Si with pn-junction depths down to 10-20 nm. For p-type Si layers below 10 nm it is known, that the piezoresistive coefficient in <110> direction is much larger than for bulk p-type Si due to quantum confinement effects [2]. This was achieved by a sophisticated process technology called point defect engineering (PDE). Using 400 keV Si+ ion irradiation a vacancy-rich layer near the wafer surface was created [3]. A 10nm thick boron layer was deposited as a solid source for subsequent diffusion using Rapid Thermal Annealing (RTA) at temperatures between 900°C and 1000°C. Secondary ion mass spectrometry (SIMS) analyses were carried out to obtain and compare the boron atomic concentration profiles. These show, that the transient enhanced diffusion of boron can be retarded by this fabrication method, and pn-junction depths of about 10-20 nm can be achieved. In comparison, pn-junctions were fabricated using low energy ion implantation of 1 keV B+ ions and subsequent RTA. SIMS profile analyses show, that the pn-junction depth is larger, but still in the range of <100 nm.
The sheet resistance of the fabricated ultra-thin p-doped layers were measured using a dedicated layout, which allows extracting the sheet resistance using conventional two-point probe measurements of U-I-characteristics. These measurements show, that the PDE fabricated layers exhibit a lower sheet resistance than the B+ implanted layers, even though the conducting layer thickness is smaller. This shows, that the PDE process not only yields very shallow pn-junctions, but also that the boron activation during RTA is improved compared to the ion implanted samples.
Finally we present sensitivity measurements for the completed cantilever chip, which show excellent sub-nm sensitivity.

[1] C. S. Smith, Phys. Rev. 94 (1954) 42
[2] T. Ivanov, PhD Thesis (2004), University of Kassel
[3] K.-H. Heinig and H.-U. Jäger, Proc. of 1st workshop of ENDEASD (European Network on Defect Engin. of Advanced Semiconductor Devices), C. Claeys, (ed.), Santorini, Greece, April 1999, p. 294

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The mobility and availability of the toxic metalloid selenium in the environment is largely controlled by sorption and redox reactions, which may proceed at temporal scales similar to that of subsurface water movement at saturated or unsaturated conditions. Since such waters are often anaerobic and rich in Fe2+, we investigated the long-term (£ 1 month) kinetics of selenite (Se(IV)O3-) sorption to montmorillonite in the presence of Fe2+ at anoxic condition. A synthetic montmorillonite was used to eliminate the influence of structural Fe. In the absence of aqueous Fe2+, selenite was sorbed as outer-sphere sorption complex, covering only part of the positive edge sites, as verified by a structure-based MUSIC model and Se K-edge X-ray absorption spectroscopy. When selenite was added to montmorillonite equilibrated with Fe2+ solution, however, slow reduction of Se and formation of a solid phase was observed with Se K-edge XANES (x-ray absorption near-edge spectroscopy) and EXAFS (extended x-ray absorption fine-structure) spectroscopy. Iterative transformation factor analysis of XANES and EXAFS spectra suggested that only one Se reaction product formed, which was identified as nano-particulate Se(0). Even after one month, only 75 % of the initially sorbed Se(IV) was reduced to this solid species.
Moessbauer spectrometry revealed that before and after addition and reduction of Se, 5 % of total sorbed Fe occurred as Fe(III) species on edge sites of montmorillonite (» 2 mmol kg-1). The only change observed after addition of Se was the formation of a new Fe(II) species (15 %) with d =
1.37 mm s-1 and DEQ = 3.76 mm s-1. The large quadrupolar splitting may indicate formation of an outer-sphere Fe(II)-Se sorption complex. The combined Moessbauer and XAS results hence clearly suggest that the Se and Fe redox reactions are not directly coupled. Based on the results of a companion paper, we hypothesize that the electrons produced in the absence of Se by oxidation of sorbed Fe(II) are stored, e.g. by formation of surface
H2 species, and are then available for the later Se(IV) reduction. The slow reaction rate indicates a diffusion controlled process. Homogeneous precipitation of an iron selenite was thermodynamically predicted and experimentally observed only in the absence of clay. Interestingly, half of Fe was oxidized in this precipitate (Moessbauer). Since DFT calculations predicted the oxidation of Fe at the water-Se solid interface only and not in the bulk phase, the average particle size of this precipitate would not exceed 2 nm. A comparison with the Moessbauer and XAS spectra of the clay samples demonstrates that such homogenous precipitation can be excluded as mechanism for the observed slow Se reduction, emphasizing the role of abiotic, heterogeneous precipitation and reduction for the removal of Se from subsurface waters.

Technetium-labelled fatty acids intended for myocardial metabolism imaging and the respective rhenium model complexes were synthesized according to the “4+1” mixed-ligand approach and investigated in vitro and in vivo. In “4+1” mixed-ligand Tc(III) and Re(III) complexes the metal is coordinated by both a tripodal tetradentate thiolato ligand and by a monodentate isocyano ligand bearing the biomolecule. High heart extraction in perfused heart studies (up to 26% ID) and noticeable heart uptake of the ^99mTc tracer in vivo being in the order of 2% ID/g at 5 min p.i., accompanied by a good heart to blood ratio of 8, confirms that the new Tc-compounds are mimics of fatty acids.

Neurotensin(8-13) analogs containing a glycine or 5-aminovaleroyl spacer were labeled with fluorescein through formation of a N-terminal thiourea function. The receptor binding was measured in HT-29 cell cultures and showed a substantial decrease in affinity, especially for the metabolically stabilized[MeArg⁹, Tle¹¹] analog. Using fluorescence microscopy, the internalization of the fluorescent neurotensin analogs into HT-29 cells was observed.

Hydration of uranyl(VI) ion has been a subject of both theoretical and experimental interests for many years. Most of recent publications from both theory and experimental sides agree that the uranyl(VI) ion in aqueous solution exists as 5-fold UO2(H2O)52+. In this work, we studied the hydration of uranyl(VI, V) and neptunyl(VI) ions in further accurate way by optimizing structures of AnO2(H2O)n2+/+ (n = 4, 5, 6) clusters at the DFT level in aqueous solution using polarizable continuum model (PCM); with special focus on the conformation of coordinating water molecules. A stable energy minimum with no imaginary vibrational frequency was found for UO2(H2O)52+ having U-Oax distance of 1.756 and 1.757Å, and U-Oeq distance of 2.428, 2.436, 2.441, 2.441, and 2.443Å. Three water planes stay perpendicular to the equatorial plane, while two water planes stay parallel to the equatorial plane. Structures and energies of 4-, and 5-fold uranyl(VI,V) and neptunyl(VI) hydrates were studied and compared with recent experimental data some of which suggest presence of 4-fold actinyl hydrates.

Irradiation of reactor pressure vessel (RPV) steels induces a degradation of the mechanical properties caused by the formation of nano-scale defect-solute clusters. Impurity Cu plays the major role in cluster formation, whereas the effect of the alloying element Ni depends on the Cu level and is not yet well understood.
The present experiment was devoted to the Ni effect. The SANS results for a Fe-3%Ni alloy, pure Fe and model alloys were reported.

Flammenpyrolytische Oberflächenvorbehandlung von beschichteten Halbzeugen vor dem Kleben

Nanotechnologie gilt als Zukunftstechnologie schlechthin. Auch die Biologie kann hier einen bedeutenden Beitrag leisten, zumal die wichtigsten "Bioobjekte" (DNA, Proteine ...) Nanoobjekte sind und damit die Biologie selbst höchst erfolgreich im Nanobereich "agiert".
Insbesondere die Hüllstrukturen vieler Bakterien, sogenannte S-Layer, bieten aufgrund ihrer Fähigkeit zur Selbstassemblierung und zur Ausbildung monolagiger hochgeordneter Gitterstrukturen neue Möglichkeiten zur Herstellung kleinster metallischer und halbleitender Nanocluster, Nanostrukturen und damit zur Entwicklung neuartiger (Biokomposit-)Materialien.

There is an ongoing discussion on the relative biological effectiveness (RBE) of low-energy X-rays below about 50 keV. Considering their wide application in diagnostic radiology and particularly in mammography, RBE has to be determined for an appropriate biological object. Further, the dependence on the photon energy distribution of the radiation sources has to be considered.
We have determined the effectiveness of low-energy X-rays by X-ray tube irradiation for two human mammary epithelial cell lines, MCF-12A and 184A1. For the soft X-ray irradiation, a tungsten-anode X-ray tube operated at either 10 kV (no filtration) or 25 kV (0.3 mm Al filter) was used. The reference radiation source was a 200 kV X-ray tube filtered with 0.5 mm Cu. The dose rate for all irradiations was 0.3 -1.9 Gy/min, and doses in the range 0.5 - 5 Gy were applied. The cytokinesis-block micronucleus (MN) test was used to assess chromosomal damage in the cell line MCF-12A. The fraction of binucleated cells (BNC) with MN, the number of MN per BNC and the number of MN per BNC with MN were determined for all radiation qualities. Additionally, chromosomal aberrations were studied by conventional Giemsa-staining in both cell lines. Dicentrics, rings and excess acentric fragments were assessed. In addition, first results will be presented on stable chromosome aberrations studied by whole-chromosome FISH painting of chromosomes 1, 8 and 17 for the cell line 184A1.
All data has been fitted to the linear-quadratic model. The soft X-rays were observed to be more effective in inducing radiation damage, RBE increasing with decreasing photon energy. Whereas the RBE for 25 kV X-rays determined by the MN test resulted in a value of 1.1 - 1.4, values of up to 3 were obtained for the 10 kV X-rays for the cell line MCF-12A. The chromosomal aberration data for both cell lines resulted in an RBE value of up to 2 for both soft X-ray radiation qualities.
The data obtained in the present work confirm the observations of other authors for the photon energy dependence of RBE in this energy range. However, the study of the detailed RBE dependence on photon energy is possible only at a monochromatic X-ray source. The progress in the installation of a quasi-monochromatic channelling radiation source at the ELBE accelerator at Forschungszentrum Rossendorf will be presented.

Two 4-substituted aromatic iodosyl compounds were investigated with regard to their solubility, stability and chromatographic behaviour. 1-Iodosyl-4-methoxy- and 1-iodosyl-4-nitro-benzene are soluble in methanol and provide acceptable ¹H and ¹³C NMR spectra; however, gradual oxidation of the solvent was observed. LC-MS analyses suggest that unlike the parent substance, iodosylbenzene, which has a polymeric structure, both compounds rather exist in the monomeric form.

The lecture is divided in two parts. First, as introduction on the subject, in part I a brief overview is given on the actual state in the area of transmutation of radioactive nuclear waste by means of reactors and driven sub-critical systems. In part II the application of the GDT-based neutron source as driver in a sub-critical system dedicated to the transmutation of minor actinides is discussed. This GDT driven minor actinide burner is compared with the corresponding accelerator driven system, which is presently considered as the favored option.

The properties of pentavalent uranium have not been well understood yet, although a large number of studies have been performed and reported concerning the uranium chemistry up to now, because it is very unstable due to its disproportionation reaction to U(IV) and U(VI). At the moment, the uranyl tricarbonate complex, [UO2(CO3)3]n-, is the only known species that can be stabilized as U(V) in aqueous solution. In order to elucidate the properties of this complex in detail, we performed electrochemical (cyclic voltammetry) and spectroscopic (UV-visible absorption and XAFS) measurement.
From the electrochemical study, it was found that the UVO2+-carbonate complex was stable only in the limited concentration range of 0.8 M < [Na2CO3] < 1.4 M, and a Pt- or Au working electrode is more efficient to reduce UVIO22+ to UVO2+ than a glassy carbon electrode. Therefore, the UVO2+ samples for XAFS measurements were prepared in 1.4 M-Na2CO3 solution by using a Pt-mesh working electrode. The UVO2+ solution was transferred to a glass cuvette that was completely sealed by hot melting to avoid the possibility of any O2-penetration in the cuvette during sample transportation and measurement. The results of XAFS measurement indicated that both uranyl(V) and uranyl(VI) ions form the tricarbonate complex, [UO2(CO3)3]n- (n = 5 for uranyl(V) and 4 for uranyl(VI)). The coordination occurs in a bidentate manner and, in general, all bond lengths for the uranyl(V) complex were longer than those for the uranyl(VI) complex. Additionally, a chemical shift was also observed in the U LI- and LIII-XANES spectra.

We present a layer resolved magnetic soft x-ray microscopy study of a RKKY coupled Ni81Fe19/Ru/Co90Fe10 layered system where magnetic patterns were imprinted by using a 60 keV fine focused Co ion beam so as to change the coupling from antiferromagnetic to ferromagnetic on a micron scale. Thereby artificial structures in form of stripes with locally varying interlayer exchange coupling are generated. Utilizing the elemental specificity of high-resolution full field soft x-ray microscopy at the Co L3 and the Ni L3 edges we determined the magnetic domain configuration during full magnetization reversal processes locally and layer resolved. In addition to the locally varying interlayer exchange coupling across the Ru layer our data verify a direct exchange coupling within each ferromagnetic layer in the magnetically patterned structure. We conclude that the magnetization reversal behaviour of the irradiated
stripes is largely influenced by the surrounding magnetic film for both, the Permalloy and the Co90Fe10 layer.

Self-organized ripple formation during ion erosion of a Si wafer is used to create a template system with a well defined roughness of uniaxial symmetry. By using special buffer layers subsequent thin magnetic film deposition by molecular beam epitaxy leads to a periodically modulated magnetic thin film with drastically modified magnetic properties with respect to a nominally “flat” film of the same thickness. In the case of Permalloy thin films, an enhancement of the uniaxial in-plane anisotropy by approximately a factor of 20 is observed (see Fig. 2). The enhancement can be explained by a combination of step induced dipolar and magnetocrystalline surface anisotropy contributions.
If a ferromagnet/antiferromagnet-bilayer is deposited a superposition of ripple-induced uniaxial anisotropy and exchange coupling induced unidirectional anisotropy is observed. Since the direction of the unidirectional anisotropy depends only on the magnetic field direction during a field cooling procedure any angle between both anisotropy contributions can be set. The observed angular dependence of the magnetization reversal behavior is in perfect agreement with simulations based on the Stoner-Wolfarth coherent rotation model.

A review about the influence of the substrate, buffer layers and the substrate morphology on the magnetic properties of ultrathin films is presented.

The influence of assisting low energy (~150 eV) ion bombardment during the deposition of evaporated C60 on the composition and bonding structure is investigated. Thin films were grown on Si (100) substrates by evaporation of C60 with assisting low-energy (~150 eV) N or Ar ion bombardment at different ion to molecule arrival ratios Iion/Imolecule (4-10) and substrate temperatures (RT-300°C). The film composition and areal density was analysed using elastic recoil detection analysis, while the obtained chemical bond structure was analysed by Raman spectroscopy. Spectroscopic ellipsometry was used to determine the film thickness. Raman spectra of the films grown without ion assistance show similar features as the Raman spectrum of initial C60 powder. The additional N or Ar assistance results in a decomposition of the C60 molecules independent of the ion type and Iion/Imolecule, resulting in a bonding structure similar to that observed in a-C or a-CNx. The N and Ar atomic ratios in the films (16-27 at. % for N and 2-4 at.% for Ar) are proportional to Iion/Imolecule and no saturation limit was reached under the present working conditions. The amount of deposited material decreases with increasing Iion/Imolecule for a given substrate temperature for both type of ions. Besides, it is observed that ion bombardment results in a densification of the films compared to the films obtained without ion assistance. The results are discussed on the basis of ion induced displacements of C atoms in the fullerene molecules resulting in a decomposition of the initial fullerene structure.

The effect of Ge deposition rate on the morphology and structural properties of self-assembled Ge/Si(001) islands was studied. Ge/Si(001) layers were grown by solid-source molecular-beam epitaxy at 500 ◦C. We adjusted the Ge coverage, 6 monolayers (ML), and varied the Ge growth rate by a factor of 100, R = 0.02–2 ML s−1, to produce films consisting of hut-shaped Ge islands. The samples were characterized by scanning tunnelling microscopy, Raman spectroscopy, and Rutherford backscattering measurements. The mean lateral size of Ge nanoclusters decreases from 14.1 nm at R = 0.02 ML s−1 to 9.8 nm at R = 2 ML s−1. The normalized width of the size distribution shows non-monotonic behaviour as a function of R and has a
minimum value of 19% at R = 2 ML s−1. Ge nanoclusters fabricated at the highest deposition rate demonstrate the best structural quality and the highest Ge content (∼0.9).

Lithium tantalate (LT) single crystals are very promising substrates for constructing highly sophisticated photonics devices. The used
procedure for fabricating optical waveguides in them was annealed proton exchange (APE). Here we have used Rutherford backscattering
spectrometry (RBS) – channeling analysis, X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA) to study changes in
the surface of the LT wafers caused by the APE treatment and to determine the concentration depth profiles of hydrogen atoms. The
measurements were taken for both virgin (untreated) and APE:LT samples fabricated using various experimental conditions. We have
found that the incorporation of hydrogen during the first step, i.e. the PE procedure (proton exchange), leads to modifications of the
structure of the LT single crystal, which gradually relaxed towards the structure of the original LT during the post-proton-exchange
annealing (A). This study also revealed a substantial dependence of sample behaviour on the crystallographic orientation of the pertinent
substrate wafers (commonly used X-(h1120i) and Z-(h0001i) cuts).

Crystalline Ge nanospheres embedded in SiO2 where irradiated at room temperature with fluences from 1x1015 to 4x1015 cm-2 of energetic J7+ ions. The spheres transform into amorphous oblate-like Ge nanoparticles, with the short axis aligned to the ion beam direction. This ion beam shaping is similar to that of free silica spheres, but differs from the prolate-like ion beam shaping of Au spheres embedded in SiO2.

The local lattice plane curvature of semiconductor disk laser devices were determined by a newly devel-oped X-ray spot mapping technique using white beam synchrotron radiation. This method is suited for in-situ studies of the dependence of both parameters on device temperature and on local heating by optical pumping. The influence of different device mounting procedures on the structural and optical device pa-rameters was investigated as well. This knowledge was used for device optimisation.

In this work a defect induced formation of CoSi2 nanoparticles and nanowires is investigated and discussed. The results show that the defects created in silicon by FIB irradiation can getter Co atoms, solved in the sample before the ion beam treatment. Nanowires and nanoparticles are formed in the defect regions and are stabilized by following Ostwald ripening and can grow due to diffusion of the Co atoms during annealing. The nanowires are oriented in the <110> crystalline directions energetically favored for CoSi2 growth. Presumably this process is initiated by the formation of the well known {311}-extended rod-like defects elongated in those <110> directions.

We investigate the temporal distribution of polarity reversals of the geomagnetic field. In spite of the commonly assumption that the reversal sequence can be modeled as a realization of a renewal Poisson process with a variable rate, we show that the polarity reversals strongly depart from a local Poisson statistics. The origin of this failure can be attributed to the presence of temporal clustering. We also show that a Lévy function is able to reproduce the distribution of polarity persistence times, thus suggesting the presence of long-range correlations in the underlying dynamo process. In this framework we compare our results with the behavior of some toy models that describe the time evolution of the reversals and with MHD geodynamo numerical simulations.

Cobalt implantation with a focused ion beam (FIB) was applied to study ion beam synthesis of cobalt disilicide nanowires in silicon. Two mechanisms of CoSi2 nanowire formation were investigated: (a) conventional synthesis by Co++ FIB implantation at elevated temperatures into silicon along in-plane <110> Si crystal direction and subsequent annealing, and (b) self-aligned CoSi2 nanowire growth in Co supersaturated silicon on FIB-induced defects at RT during subsequent annealing. The obtained CoSi2 nanowires are 20-100 nm in diameter and several micrometers long.

Untersucht wurde die Aufnahme C-14-markierter Modellsubstanzen (beta-Alanin, Stärke und synthetische Huminsäure M42) durch Anionenaustauscher und ihre korrespondierenden nichtfunktionalisierten Copolymere. Die Modellsubstanzen stehen für die TOC-Fraktionen der Neutralstoffe / Amphiphile, Polysaccharide und Huminstoffe enstprechender der LC-OCD-Methode von HUBER. Variiert wurden der Salzgehalt resp. der pH-Wert und die Temperatur bei der Beladung...

Focused Ion beam (FIB) systems employing liquid metal ion sources (LMISs) have become of increasing importance in the microelectronics research and industry [1]. Applications of LMISs include IC analysis and modification, maskless ion implantation, secondary ion mass spectroscopy, scanning ion microscopy and ion beam lithography [2-3].
Alloy LMISs are the basis of mass separated FIB systems applying a variety of ion species which can be focused into diameters smaller than 10nm with current densities of several A/cm2 [4].
In this work a Ga38Bi62 alloy liquid metal ion source (Tmelt = 222°C), prepared on a mechanical treated Ta - emitter has been studied, which allows to implant in the case of a silicon substrate shallow donor ions (Bi) as well as acceptors (Ga) in the sub micron range without changing the source. A detailed analysis of the mass spectra as a function of emission current, obtained from this source, shown in Fig. 1, was used to investigate the mechanism for the production of single and double-charged ions. The transition metals in the mass spectra result from the re-sputtered extractor stainless steal material. Moreover, we represent the intensity of cluster ions extracted by the source, as function of emission current. Theoretical modeling support the experimental results.
[1]P.D. Prewett, G.L.R. Mair, Focused Ion Beams from Liquid Metal Ion Sources,
Taunton, Somerset, UK: Research Studies Press, 1991, Chap. 2.
[2]J. Orloff et al, High Resolution Focused Ion Beams – FIB and Its Applications,
Kluwer Academic / Plenum Publishers, 2002, Chap. 6.
[3]L. Bischoff, J. Teichert, S. Hausmann, Th. Ganetsos and GLR. Mair, Microelectronic Engineering, 53 (2000) 613.
[4]L. Bischoff, Ultramicroscopy, 103 (2005) 59.

Planar channeling radiation from 32 MeV electrons channeled in quartz has for the first time been measured at the radiation source ELBE. The theory of channeling radiation was applied for the assignment of the observed spectra to the crystal planes. Calculations of the continuum potentials, transverse electron states, transition energies, and radiation intensities have been performed for selected planes of quartz. Specific properties of the hexagonal binary quartz crystal influencing the generation of channeling radiation are discussed.

We present results of a numerical computer simulation based on the extended dynamical classical over the barrier model (EDCOB). To get an energy balance for the transferred potential energy of the highly charged ions (HCIs) to the solid surface, we apply an additional extension of the model evaluating the energy loss of Auger electrons which are generated during the relaxation of the HCI. From the results of the simulation we can distinguish between the potential energy deposited in the nuclear system due to image charge acceleration of the incoming HCI and the potential energy which is released over Auger processes. Further, we break down this energy into that which is deposited in the solid and that which is re-emitted due to escaping secondary electrons.

First deep sub-threshold production of the Sigma(1385) hyperon resonance is presented. The measurement was performed in Al+Al collisions at a beam energy of 1.9A GeV with the FOPI detector at GSI-Darmstadt. The result is found to be in relatively good agreement with the statistical model prediction. It allows to better understand strangeness sub-threshold production by leading information on the strangeness exchange reaction which is the dominant process for K^- production below and close-to threshold.

Self-assembled thin films of gold nanoparticles of 4-5 nm, prepared on glass using aliphatic dithiols of different hydrocarbon chain lengths as interparticle linker molecules, have been studied by x-ray methods and dc conductivity. X-ray data revealed small spacer-dependent cluster size variations in the films. Conductivity, in the temperature range of 4.2-300 K, showed a strong relation with spacer length, indicating that different mechanisms of conduction from metal-like through hopping to tunneling dominate, depending on temperature range and particle spacing. The results demonstrate that the electronic and optical properties of such films can be precisely controlled by interparticle distance.

Nitrogen Plasma Íon Implantation of Al Alloy in the High Voltage Glow Discharge Mode

Plasma Immersion Ion Implantation with a 4 kV/10kHz Compact High Voltage Pulser

Implantação Iônica por Imersão em Plasma de Nitrogênio Usando Baixa Energia

Hybrid Processing of Ti-6Al-4V Using Plasma Immersion Ion
Implantation Combined with Plasma Nitriding

A Traveling Magnetic Field (TMF) is attractive for melt crystal growth as it offers a direct flow driving mechanism. We present numerical and experimental results on the TMF driven flow in an isothermal model fluid. The TMF is generated by a system of six equidistant coils, which are fed by a three phase current power supply to create an up- or downward directed traveling field. Special attention is focused on the description of the electromagnetic fields for varying field frequency, and its influence on the resulting melt velocity.