Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Introduction:

Radiolabelled particles are an attractive tool in the therapy of malignancies of the liver. We consider particles manufactured from denatured human serum albumin (HSAM) as useful carriers of therapeutic radionuclides, e.g. Y-90.

Experimental:

Two batches of HSAM (ROTOP Pharmaka GmbH; diameter: 20 – 30 μm) with smooth or rough surface, as determined by REM, were used for our studies. HSAM were functionalized by coupling DOTA via its isothiocyanate derivative in aqueous solution at pH 8.5 to lysine ε-amino groups on the surface of the spheres. Stability of Y-86 labelled DOTA-HSAM was investigated both in vitro (DTPA challenge) and in vivo (i. v. injection into the tail vein of healthy Wistar rats).

Results and Discussion:

Approximately 25 DOTA molecules per molecule HSA could be attached as estimated from elemental analysis of DOTA-HSAM. Y-86 labelling was performed under optimized conditions in 96 ± 1 % yield. No significant differences between smooth- and rough-surfaced HSAM were found for both, DOTA coupling and Y-86-labelling. In DTPA challenge experiments 98 ± 0 % of the radioactivity were still particle-associated after 24 hours incubation at 37 °C. In the in vivo experiments radiolabelled smooth and rough microspheres were completely trapped in the lungs. After 48 h the two batches differed significantly in their biodistribution pattern. For the clearance of radioactivity from the lungs decay-corrected half-lives of 85 h (rough microspheres) and 187 h (smooth microspheres) were calculated.

Conclusion:

For the preparation of HSA-derived microspheres for radiotherapeutic application smooth-surfaced spheres are superior to rough spheres due to their higher in vivo stability.

The introduction of mammography screening programs in some countries initiated a continuous discussion about the benefit or possible accompanied risk of the used radiation qualities. Contributing to this discussion we used different methods, such as clonogenic survival and the analysis of chromosomal aberrations by FISH, to study biological effects with the human mammary epithelial cell line 184A1, which is of interest especially for the induction of breast cancer. Radiation qualities applied were 10 and 25 kV soft X-rays and a 200 kV X-ray tube as reference radiation source. Furthermore, we develop these methods and investigate the repair kinetics of DNA double strand breaks (DSB) with cell line 184A1 to learn more about the underlying processes.
The DNA damage response, following irradiation, includes an efficient DSB recognition system as well as different DSB repair mechanisms. Important contributions to these processes are the phosphorylation of histone H2AX (gH2AX) and the localization and phosphorylation of the p53 binding protein 1 (53BP1) at the sides of DNA DSBs. Both molecules are essential for the recognition of DNA DSBs and hence for the induction of repair processes. Using appropriate antibodies, the phosphorylated molecules can be visualized as nuclear foci and their time-dependent formation can be followed after irradiation.
The time-dependent formation of gH2AX- and 53BP1-foci was used in the present work to investigate the induction and rejoining of DNA DSBs up to 48 hours after irradiation. Two different antibodies were used to visualize and quantify the foci induced by two different doses of 0.25 and 2 Gy of 25 and 200 kV X-rays, respectively.
The kinetics obtained after irradiations with 2 Gy show a similar shape and therefore energy independence for both energies, which can be explained by the same underlying repair processes. Shortly after irradiation the number of foci per cell shows a steep increase, resulting in a maximum after 2 hours and a subsequent 2-phase decrease. Although the position of the maximum is the same, the number of foci per cell differs for 25 kV and 200 kV X-rays, being 7.99 ± 0.12 and 6.19 ± 0.10, respectively. The rejoining of DSBs, deduced by the decrease of number of foci per cell can be divided in a first phase, which seems to be faster, and a slower second one. During the first phase, the number of foci per cell is reduced to about 50 % of the maximum and in the second phase they are reduced to the control level, whereas for 25 kV a significant number of foci per cell remain. These results implicate that, on the one hand, the number of the induced DNA DSBs is significantly higher for 25 kV X-rays and, that on the other hand, some DSBs remain unrepaired. These DSBs can influence the genomic integrity and can result in chromosomal aberrations.
First experiments for the irradiation with 0.25 Gy of 25 kV show the same shape as that with higher dose, but the maximum is derived at 30 minutes after irradiation. The maximum number of foci per cell was 4.03, which is about the half compared to a dose of 2 Gy with the same energy.

Lead-bismuth alloys are under intense consideration as target material of spallation sources. The thermohydraulic design of such a target or related coolant systems requires a reliable data basis regarding the temperature dependent physical properties of such alloys. We present new measurements of the electrical conductivity and the thermoelectric power up to about one hundred degree above the melting point for various alloy compositions. For the eutectic alloy the measurements were performed up to a temperature of 1000 K including, in addition, viscosity, thermal conductivity and surface tension. A comparison with data and scaling relations available in literature will be given. New temperature scaling relations will be derived for each of those properties, which we recommend as input for thermohydraulic simulations.

The objective of the European 6th framework project EUROTRANS, is to demonstrate the technical feasibility of transmutation of high level nuclear waste using Accelerator Driven Systems (ADS). Within this objective the design of a European experimental ADS (XT-ADS) should demonstrate the technical feasibilities to transmute a sizeable amount of waste and to operate an ADS safely. The XT-ADS will be a subcritical reactor system having liquid lead-bismuth eutectic (LBE) as coolant.
This liquid LBE is also intended to serve as target material for the spallation reaction which forms a crucial part to the subcritical reactor core. Since LBE is used as core coolant and spallation material, knowledge of the thermal hydraulic behaviour of LBE is essential.
Within the DEMETRA domain of the EUROTRANS project, basic thermal hydraulic studies in order to support the design and safety analysis of XT-ADS components and the development of measurement techniques have been started. In particular, the work focuses on:
• Characterisation of the free surface flow for the windowless spallation target design.
Validated numerical methods are needed to predict the LBE heat removal capability in the windowless spallation target configuration. For this purpose, computational fluid dynamics (CFD) simulation methods are most appropriate. CFD methods allow to capture the specific three-dimensional local effects of the LBE free surface including the heat deposition.
Various methods are assessed and first promising results have been obtained for the simulation of an isothermal windowless spallation target. For the improvement and validation of the developed numerical models, an experimental campaign has started. This campaign exists of experiments in a water-loop and in an LBE loop.
• The interaction of LBE with water as secondary coolant.
Since the XT-ADS design foresees the presence of steam generator modules placed inside the main vessel in direct contact with the lead-bismuth and the probability of a steam generator tube rupture is not negligible, the consequences of such an accident have to be assessed. Experimental campaigns aim at assessing the physical effects and possible consequences related to the interaction of LBE and water in representative conditions for the XT-ADS design. The experimental data are also used for the validation of the SIMMER code. First experimental campaigns have been performed successfully. Simulation of the experimental data with the SIMMER code showed a good agreement.
• The development of measurement techniques for heavy liquid metal (HLM) flows.
Measurement techniques are developed for different purposes (i.e. thermal-hydraulics experiments and operational techniques for large facilities in relation to the development of the XT-ADS) and tested within the laboratories of FZD (Germany), FZK (Germany), and SCK•CEN (Belgium). The focus is on local velocity meters, integral flow meters, and free surface level sensors. The various methods studied are briefly described.

Finally, the links with the DESIGN domain of the EUROTRANS project, with the European Commission Integrated Infrastructure Initiative VELLA (Virtual European Lead LAboratory), and with the European Commission Specific Targeted Research Project ELSY (European Lead-cooled System) are also addressed.

Objective:

To investigate the role of magnetic resonance imaging (MRI) of bone metastases in nonseminomatous germ cell tumors.

Methods and Materials:

There were 5 consecutive patients with bone metastases from nonseminomatous germ cell tumors treated
between 2003 and 2006 who underwent imaging studies, including MRI. The characteristic imaging findings are discussed in the light of the clinical course.

Results:

Of the 5 patients, 3 had symptoms related to bone involvement at diagnosis. All patients received conventional x-ray of their bony lesions, but only 1 of them was considered abnormal. Skeletal MRI was obtained in all patients. A bone scan was available in 3 cases with spinal involvement. It was normal in 1 case and detected only a minority of the lesions visible on MRI in the other 2 cases. Follow-up MRIs were available in all patients. A partial resolution of bone involvement during chemotherapy was observed in only 1 of them. In 2 cases, there was a slight progression of a diffuse alteration of the bone marrow during treatment. In 1 patient, severe spinal bone marrow
changes were visible on MRI 2 years after cessation of treatment without evidence of disease recurrence.

Conclusions:

MRI may disclose bone metastases in nonseminomatous germ cell tumors, which otherwise may be missed. MRI findings of bone lesions during treatment do not directly reflect the course of the disease and have to be interpreted with caution using clinical information.

Administration of ionizing radiation for diagnostic purposes can be associated with a risk for the induction of tumors. Therefore, particularly with regard to general screening programs, e.g. with mammography, cost-benefit considerations must be discussed including risk estimation depending upon the radiation quality administered. The present study was initiated to investigate the in vitro X-ray energy dependence for the induction of chromosomal aberrations in the two mammary epithelial cell lines, 184A1 and MCF-12A. The induced excess fragments, dicentric chromosomes and centric rings were analyzed and the relative biological effectiveness (RBE) was determined for 10 and 25 kV X-rays relative to 200 kV X-rays. The assumed energy dependence with higher values for 10 kV X-rays was confirmed for the excess fragments, with RBEM values of 1.92 +/- A 0.26 and 1.40 +/- A 0.12 for 10 kV X-rays and 1.17 +/- A 0.12 and 0.97 +/- A 0.10 for 25 kV photons determined for cell lines 184A1!
and MCF-12A, respectively. Meaningful results for the induction of dicentric chromosomes and centric rings were obtained only for higher doses with RBE values of 1.31 +/- A 0.21 and 1.70 +/- A 0.29 for 184A1 and 1.08 +/- A 0.08 and 1.43 +/- A 0.12 for MCF-12A irradiated with 25 and 10 kV X-rays, respectively.

Die Anwendung dynamischer Betriebsweisen bei abwärts durchströmten Festbettreaktoren zur Erhöhung der Phaseninteraktion und zur Steigerung der Katalysatoreffektivität wurde experimentell bereits erfolgreich nachgewiesen. Aufgrund der komplexen Zusammenhänge erfordern Modellierung und Simulation dynamisch betriebener Festbettreaktoren ein umfangreiches Wissen über makroskopische und mikroskopische Vorgänge und deren Kopplung. Bisherige Reaktormodelle vernachlässigen die Vorgänge im Katalysatorpartikel nahezu komplett oder verzichten auf die Kopplung mit Reaktormodellen.
Das entwickelte mehrskalige isotherme Modell setzt sich aus dem axialen Dispersionsmodell im Reaktormaßstab und einem Partikelmodell zur Berücksichtigung von dynamischen intrapartikulären Konzentrationsprofilen und Akkumulationen zusammen. Zusätzlich zur veränderlichen Teilbenetzung der Katalysatoroberfläche wird ein Verteilungsfaktor eingeführt, der die Morphologie der Flüssigkeit auf der Katalysatoroberfläche als Maß für die Gleichmäßigkeit der Verteilung beschreibt.
Das quasi-3D-Modell wurde in COMSOL MultiphysicsTM 3.2 umgesetzt und ermöglicht die Simulation ausgewählter dynamischer Zustände, die Ableitung günstiger Betriebsparameter zur Leistungssteigerung bei Festbettreaktoren und die Analyse optimaler Katalysatorkonfigurationen ohne aufwendige experimentelle Parameterstudien. Die Simulationsergebnisse für die Hydrierung eines organischen Lösungsmittels werden mit experimentellen Daten verglichen.

Metallorganische Verbindungen, wie beispielsweise Grignard-Reagenzien, haben große Bedeutung als Zwischenprodukte für organische Synthesen in der Feinchemie und der pharmazeutischen Industrie. Auf Grund des spezifischen Prozessverhaltens der stark exothermen Bildungsreaktionen und der hohen Reaktivität der Grignard-Reagenzien besitzen Grignard-Reaktionen ein hohes Gefahrenpotential. Von großer Bedeutung für die Prozesssicherheit ist deshalb die Entwicklung industriell anwendbarer Methoden für eine objektive Detektion des Reaktionsstarts und für die Online-Verfolgung von Edukt-Akkumulationen im Reaktionsgemisch des Rührkessel-Reaktors. Hierfür wurde eine wärmebilanzbasierte Online-Überwachungsmethode entwickelt und anhand von Experimenten im Miniplant getestet. Neben der Ermittlung von Konzentrationsverläufen ist mit der Methode eine Abschätzung von sicherheitsrelevanten Parametern realisierbar (on-line worst case calculations). Die Ergebnisse ermöglichen den Einsatz sicherheitsorientierter Regelungsstrategien für Grignard-Reaktionen. Gleichzeitig können derartige Systeme zu einer Erhöhung der Effizienz durch Steigerung der Raum-Zeit-Ausbeute sowie zur Realisierung einer inhärenten Prozesssicherheit beitragen. Durch Einbindung in ein komplexes Batch Information Management System (BIMS) können die Ergebnisse des Monitoring Systems chargenweise zusammen mit den Prozess-, Anlagen- und Analysedaten gespeichert und archiviert werden und dienen somit einer späteren Prozessanalyse und –optimierung.

There is no abstract provided.

Low-energy (<100eV) ion bombardment has been shown to be a key parameter in the production of hard and elastic carbon nitride (CNx) thin films with fullerene-like (FL) structure [1]. The production of FL-CNx is mostly reported for reactive magnetron sputtering but still the growth mechanisms are not clear [2]. In this way, the growth by ion beam assisted deposition (IBAD) would provide a better understanding since the source of neutrals and ions are independent. In this work we study the growth of CNx films produced by e-beam evaporation of graphite and simultaneous low-energy N2 ion assistance at different substrate temperatures. The low-energy ions were provided by an End-Hall ion source. The samples were characterized by spectroscopic ellipsometry, elastic recoil detection analysis (ERDA), Raman and high resolution transmission electron microscopy (HRTEM). Despite the low-energy ions, a high thermal-activated re-sputtering of the deposited films has been observed, indicating its chemical origin. In addition, the maximum nitrogen content in the films is limited to ~25 at.%, which should be related to the re-sputtering process. The Raman spectra and the optical properties indicate the dominance of sp2 hybrids. However, the results differ from those of FL-CNx, indicating that the sp2 hybrids are not arranged in a FL microstructure. This is also corroborated by HRTEM, where the samples were found to be mainly amorphous. Therefore, our results suggest that low-energy ion bombardment is not the main driving force for the promotion of FL arrangements, although this condition may be necessary to avoid damage on the growing microstructure. In this sense, the incorporation of neutrals, such as CxNy species formed during magnetron sputtering, may play a dominant role for the growth of FL-CNx [3].
1. Sjöstrom et al. Phys. Rev. Lett. 75 (1995) 1336. 2. Hultman et al. MRS Bulletin 28/3 (2003) 194. 3. Neidhardt et al. J. Appl. Phys. (in press).

Thermal treatment of indium tin oxide (ITO) is often used as a method to decrease its resistivity. The amorphous-to-crystalline transition is often assumed as the reason for this improvement due to a Sn donor activation at elevated temperatures (Frank-Koestlin model), but the physical mechanisms behind the experimental observation are not clear. In present work, ITO thin films produced by reactive middle frequency magnetron sputtering were annealed in vacuum in two ways: 1) annealing within the temperature range Ta=20-330 °C at a constant heating rate of 5 °C/min, 2) isothermal annealing at Ta=210 and 240 °C. The amorphous layers and films with a small crystalline fraction have been investigated. This study is focused on in situ spectroscopic ellipsometry (SE) monitoring of the film properties during annealing. The SE data were reduced by using the Drude-Lorentz parameterization of ITO optical constants. In separate experiments, the films were investigated by in situ four point probe resistivity measurement technique and the in situ X-ray diffraction (XRD) in Bragg-Brentano geometry.
The observed temperature dependences of the ellipsometry parameters and resistivity indicate several stages (typically four) in contrast to the simpler two-stage behavior of these characteristics obtained during isothermal annealing. Even in the XRD-amorphous state, the film resistivity significantly decreases with increasing temperature due to a free-electron density enhancement as shown by SE. The increase of the free-electron density in this case can be attributed to the creation of oxygen vacancies due to relaxation of distorted In-O bonds in the amorphous phase. Since Sn is known not to be electrically active in amorphous ITO and does not affect the free-electron density, any creation of substitutional Sn in the amorphous film can be neglected. Tin donor activation gives significant contribution to a free electron density only at temperatures above 250 °C which agrees with the crystallization onset suggested by in situ XRD. The crystallization kinetics is analyzed by using the Kolmogorov–Johnson–Mehl-Avrami equation which yielded a kinetic exponent of the process of approximately 3. Under the condition that the coherently diffracting domain size is smaller than the film thickness, this kinetic exponent indicates a three-dimensional crystallization process. The refractive index decreases at increasing annealing temperature above 150 °C. An even stronger decrease is observed above Ta=250 °C, both processes are related to the enhancement of the free electron density.

The report summarizes the most important technical developments realized in 2003/2004 at the Materials Research end-station. There are described new programs which simplify the visualisation and analysis of a large amount of data. These data are collected by a linear position sensitive detector (PSD) and a multi-channel analyzer. Additionally, an electronic stepperrmotor controller switch had been developed. It allows to use two different types of stepper motor controllers to control four of the axes of a 6-circle HUBER-diffractometrer by two different instrumentation systems.

Tag des offenen Labors, FZD

A new multi-element detector with higher energy resolution was aqcuired which is instrumented with a high-rate digital multi-analysis spectrometer from X-ray Instrumentation Associates (XIA) which is particularly well suited for EXAFS with multi-element detectors. The installation of this new detector involved not only electronic instrumentation and software development, but - due to the complex radiochemical safety system at the Radochemistry end-station -also mechanical engineering.

A tin liquid metal ion source (LMIS) containing ~ 13% Pb has been studied. From a careful examination of the mass spectra of the source it is concluded that post-ionisation is a most probable mechanism for the formation of Pb++ ions. In the case of tin, however both Sn+ and Sn++ appear to form by direct field-evaporation. This view is supported by energy deficit measurements on the Sn+ and Sn++ beams . Our results for Pb++/Pb+ agree with those of Komuro (1983) with a pure Pb source. The reason for this is understandable and is related to the similarity between the evaporation fields of Sn and Pb. For the sake of completeness we also present measurements of the energy spread of the Sn++ and Sn+ beams.

Focused ion beam applications using ions other than Gallium are of increasing interest during the previous years. A promising candidate is Germanium due to its compatibility to the semiconductor technology, i.e. for local doping of SixGe1-x structures. The energy spread ΔE½ of the source, which, through the chromatic aberrations of the system, determines the final spot size at the target and the peak energy deficit (PED) as well as the mass spectra emitted from an eutectic Au73Ge27 (m.p.=366°C) alloy liquid metal ion source were investigated as a function of the emitter temperature. ΔE½, measured with a retarding field analyser, is expressed as the full width of the distribution at half its maximum height (FWHM). Doubly-charged ions achieve double of energy, compared to singly-charged ions, which is taken into account for analysis. Furthermore, Ge shows a much more abundant in the doubly-charged state, following Brandon`s criterion. Due to the analysis of PED we think Ge++ as well as Au+ and Ge+ are directly field-evaporated in the doubly- and singly-charged state, respectively. Au++ should be post-ionized from the singly-charged state.
Due to the regular expected behaviour of the surface tension dependence on temperature shows in contrast to Si containing metallic glass alloys, like AuSi or AuGeSi, that the ion emission is enhanced with increasing temperature, obtained from a field of I-V-characteristics. The slope of this change also depends on the volume of the source reservoir, which is demonstrated for a drop volume of 0.5 and 3.4 mm3, respectively, in the temperature range from 400 to 1000 °C. The mass spectra, measured with an E x B analyser are evaluated with respect to the emission intensity for the main ion species Au+ and Au++, Ge+ and Ge++ and for various molecular ions and clusters, formed by droplet disintegration. The ratio of doubly-charged to singly-charged monomer species is given as a function of temperature in the emission current range of 1 to 30 µA.

NV-centres are commonly known as good candidates for spintronic and optical quantum computer applications. These centres have already been used to construct single photon sources .
We present a set up to position / implant single atoms with nm resolution into diamond surface. An atomic force microscope (AFM) tip and a focused ion beam (FIB) set up form the core of our set up. High precision positioning of atoms requires cooled atom handling. An accuracy of more than 5nm requires ion energies below 1keV. Otherwise single ion impact detection becomes impossible at these low energies. We discuss these requirements and challenges and present a suitable solution based on an AFM tip acting as a collimator diaphragm.

The article describes the most important technical improvments which had been performed at the beamline ROBL in 2005 and 2006. These are new systems such a cryostat and a sample holder which unifies the adjustment of samples in the glove box. Additionally, there was an update of electronics and basic software to enhance the compatibility with the standard equipment used at ESRF beamlines (migration from OS9 to Linux operating systems, new instrumentation of beamposition monitors.) There was also a SMS-based warning system installed to inform the responsible beamline scientist in case of problems during unattended experiments.

We propose a method for deterministic implantation of single atoms into solids which relies on a linear ion trap as an ion source. Our approach allows a deterministic control of the number of implanted atoms and a spatial resolution of less than 1 nm. Furthermore, the method is expected to work for almost all chemical elements. The deterministic implantation of single phosphor or nitrogen atoms is interesting for the realization of scalable solid state quantum computers, in particular for silicon and diamond based schemes. A wide range of further applications is expected for the fabrication of nano-electric devices.

The generation of surface plasmon polaritons (SPPs) at isolated nanoholes in 100 nm thick Au films is studied using near-field scanning optical microscopy. Finite-difference time-domain calculations,some explicitly including a model of the scanning tip, are used to interpret the results. We find the holes act as point-like sources of SPPs and demonstrate that the interference between the SPP and a directly transmitted wave allows determination of the wavelength, phase, and decay length of the SPP. The near-field intensity patterns can be manipulated by varying the angle and polarization of the incident beam.

Der Messplatz des Instituts für Radiochemie am Synchrotron der ESRF in Grenoble/Frankreich wird aus der Sicht der elektronischen Instrumentierung beschrieben. Der Schwerpunkt liegt auf dem benutzten Messprinzip und der gewählten Hard- und insbesondere Softwarestruktur. Insbesonder wird auf das benutzte Messprogramm "xatros", das eine messplatzspezifische ROBL-Eigenentwicklung ist, eingegangen.

Significant progress in the synthesis and isolation of trimetallic-nitride (TNT) clusterfullerenes has been achieved in the recent years, with a variety of M₃N (M=Sc, Y, Gd-Lu) being encapsulated in various C_2n (n=34-44) cages (see Ref.[1] for review and references therein). However, structural information for many of the new structures remains limited because of the low available amounts, which often appear insufficient for X-ray crystallographic or ¹³C NMR spectroscopic studies. IR and Raman spectroscopy, which require substantially smaller amounts of the material, have been extensively used in our group for characterization of new clusterfullerenes.[2] In this work we develop the general methodology allowing elucidation of molecular structures of new clusterfullerenes based on the vibrational spectroscopy and DFT computations.

Laboratory experiments were carried out to study the phenomena related to open-eye formation in ladle treatment. Ga-In-Sn alloy with a melting temperature of 283 K was used to simulate the liquid steel, while MgCl2-Glycerol(87%) solution as well as HCl solution were used to simulate the ladle slag. No open-eye was formed at lower gas flow rates, but, occurred when gas flow reached a critical rate. This critical gas flow rate was found to depend significantly on the height of the top liquid. No noticeable amount of top liquid was observed in any of the samples taken from the metal bulk during gas stirring. To confirm this aspect, samples of slag-metal interface were taken around the open-eye in an industrial gas stirred steel ladle. No entrapped slag droplet was found in the solidified steel within the region between the interface and 2 cm from the interface. The accordance of the laboratory and industrial results suggests that the entrainment of slag into the steel bulk around the open-eye cannot be considered as the major contribution to inclusion formation.

For experiments at the superconducting electron accelerator ELBE, where neutrons in the kinetic energy region from some tens of keV to a few MeV will be produced by bremsstrahlung, neutron-time-of-flight detectors have been developed. These detectors are made from the plastic scintillator material EJ-200. Efficiency calibration showed more than 10% efficiency for kinetic energies down to 30 keV. The calibration was done at the “accelerator facility for fast neutron research” at Physikalisch-Technische Bundesanstalt in Braunschweig, using pulsed quasi-monoenergetic neutron fields with a well-determined fluence. The low detection threshold was obtained by coincident readout of two Hamamatsu R2059-01 photomultiplier tubes per scintillator and by triggering just below the single-photo-electron peak of these photomultiplier tubes, which additionally gives a well-reproduceable detection threshold.

Several newly proposed superconducting linacs are designed to use TESLA technology operating CW rather than pulsed for which the system was developed. It must therefore be demonstrated that CW operation is feasible. Here we describe a series of CW tests with the TTF-III power coupler to determine the average power limit. These tests were performed on a coupler test stand both at room temperature at the FZ Rossendorf and under cryogenic operating conditions in BESSY’s HOBICAT[1] facility. An extrapolation of the measurements suggests that the coupler can handle 5 kW CW standing wave. It was also demonstrated that even higher power levels are feasible if the cooling of the inner conductor is modified.

Ziel/Aim:

Für den Transport von Acetylcholin in die präsynaptischen Vesikel im Hirn ist der vesikuläre Acetylcholintransporter (VAChT) verantwortlich. Zur Diagnose cholinerger Läsionen im Gehirn und deren Visualisierung mit Hilfe von PET sind insbesondere F-18-Radioliganden von großem Interesse, die spezifisch an den VAChT binden. Solche Tracer leiten sich von der Struktur des Vesamicols ab. Auf Basis von Untersuchungen zur Strukturoptimierung potentiell neuer Radiotracer werden Radiosynthesen ausgewählter bicyclischer Vesamicol-Derivate vorgestellt.

Methodik/Methods:

Zur Verbesserung der pharmakologischen Eigenschaften gegenüber Benzyloxyvesamicol-Derivaten wurden Verbindungen des 6-(4-Phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-7-ols abgeleitet. Im Ergebnis von detaillierten Bindungsstudien wurden als Derivate [F-18]F-acetyl- ([F-18]VL115), 4-[F-18]F-benzoyl- ([F-18]VL112), 4-[F-18]F-benzyl- ([F-18]VL64) und [F-18]F-propyl für erste Radiosynthesen ausgewählt, wobei für [F-18]VL115 ein Br-, für [F-18]VL112 ein Nitro-Präkursor verfügbar war und für [F-18]VL64 eine Aufbausynthese mit 4-[F-18]Fluorbenzylbromid (FBBr) angestrebt wurde.

Ergebnisse/Results:

Die Synthese von [F-18]VL115 erfolgt durch nukleophile Radiofluorierung des Präkursors in DMF (145-155°C, 15 min) und nachfolgende Abtrennung des Zielproduktes durch SPE und anschließende HPLC. Das Endprodukt wurde mittels TLC, Radio-HPLC und GC charakterisiert: Radiochemische Reinheit 99,0 %, spezifische Aktivität: 34-100 GBq/#mikro#mol. Die Synthese konnte auf einen Automaten (TRACERlab, Fa. GE/Healthcare) übertragen werden (Synthesezeit ca. 1,6 h, Ausbeute 23 %). Zentraler Schritt der Synthese von [F-18]VL112 ist die nukleophile Substitution der Nitrogruppe durch nicht konventionelles Erhitzen mit Mikrowellen in DMF (150 Watt, 150-156°C, 15 min). Das Produktgemisch enthält noch Reste an nicht-abtrennbarem Präkursor. Die Separation gelingt nach Reduktion mit Pd/Ammoniumformiat in MeOH. Nach Feinreinigung mit SPE und HPLC ist der Radiotracer in hoher Reinheit und spez. Aktivität erhältlich (98,5 % bzw. 35-150 GBq/#mikro#mol), jedoch nur in moderater Ausbeute (≤15 %). Als Voraussetzung für die Darstellung von [F-18]VL64 wurde [F-18]FBBr in ausreichender Menge in einem verbesserten Verfahren erhalten. In ersten Versuchen wurden signifikante Unterschiede im Reaktionsverhalten zwischen nicht-radioaktiven Reaktionspartnern zum Umsatz mit [F-18]FBBr bei analoger Reaktionsführung festgestellt.

Schlussfolgerungen/Conclusions:

Die vorgestellten Radiosynthesen ermöglichen eine sichere reproduzierbare Herstellung der Radiotracer [F-18]VL115, [F-18]VL112 und deren Formulierung als sterile ethanolische Lösung. Zur Herstellung von [F-18]VL115 wurde eine automatisierte Synthese unter Nutzung eines kommerziellen Synthesemoduls entwickelt.

Cosmic magnetic fields are not only passive by-products of the hydromagnetic dynamo effect, they also play an active role in the formation of stars and black holes by virtue of the Magnetorotational Instability (MRI). By destabilizing Keplerian flows which are hydrodynamically stable due to Rayleighs criterion, the MRI enables outward transport of angular momentum in accretion discs. The effort to investigate the MRI in a liquid metal experiment can be dramatically reduced if the purely axial magnetic field is replaced by a helical magnetic field. We present results of a Taylor-Couette experiment with the liquid metallic alloy GaInSn under the influence of helical magnetic fields that show typical features of MRI at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10.

Grundlagen der Ionenstrahlphysik und der verdünnten magnetischen Halbleiter

The stability, the structural and the electronic properties of elongated titanium silicide nanostructures have been investigated by density-functional-based tight-binding calculations. Our results show that the strain energy in tubular form does not follow the trends observed for other layered materials; tubes from TiSi2 are more stable than the flat monolayer, because in nanotubes free valences of Ti and Si atoms can be saturated for geometric reasons. Multi-layered tubes are energetically favoured and exhibit a tendency towards facetting. All such nanostructures are metallic with a density of Ti(3d) states at the Fermi level, which is considerably higher than that of the bulk compound. Thus, nanostructured TiSi2 may exhibit a better conductivity than the bulk phase along the tube direction.

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Imaging of regional glucose metabolism in small animals by dynamic PET Imaging of regional glucose metabolism in small animals by dynamic PET studies using 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) provides the unique possibility to study normal physiology and pathophysiological situations in various disease models in vivo. However, plasma glucose levels and other factors influence 18F-FDG PET studies. Therefore, we examined and compared the tissue-specific 18F-FDG uptake and kinetics in rats without and with a glucose challenge. 18F-FDG kinetics was studied for one hour in anesthetized rats using a dedicated small animal PET system. The animals were injected intravenously with 18F-FDG without (control) or simultaneously with glucose (270 mg/kg body weight). PET images were reconstructed and three-dimensional regions of interest were determined for subsequent data analysis. The plasma glucose concentrations one hour after injection were similar in the control and post challenge group. Tissue-specific 18F-FDG uptake, e.g., in brain, heart and liver, tends to be lower in the post challenge group as compared to the controls. Only with increasing body weight (>250 g) post challenge plasma glucose increased. However, in the post challenge group the kinetics of 18F-FDG was different only in the first 15 min after injection when compared to the controls, but subsequently converged to control kinetics within the following 45 min. In summary, glucose challenge did not influence the tissue-specific distribution pattern of 18F-FDG due to the high glycolysis rate of the rat. On the other hand, in diabetic models, older or larger animals the effects of increased plasma glucose levels should be taken into account for interpretation of PET data.

Adipose tissue (AT) plays a crucial role in the pathogenesis of the metabolic syndrome. In this line, for investigation of AT biology and disorder rodent models gain increasing importance. However, non-invasive differentiation and characterization of AT deposits in rodents in vivo is a current challenge. In the present study, high resolution magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques were applied for quantitative in vivo evaluation of various brown adipose tissue (BAT) and white adipose tissue (WAT) deposits in mice. Experiments were carried out in NMRI and nude mice, respectively. Morphological differentiation between various AT deposits was obtained by ¹H-MRI at 7 Tesla. Images were obtained with high spatial resolution of 156 microns. Furthermore, ¹H-MRS has been performed to quantify in vivo different lipid patterns in BAT and WAT deposits using a volume selective PRESS sequence on 3 to 8 mm3 voxels. In both NMRI and nude mice various BAT and WAT deposits were clearly distinguished from the non-AT tissue with excellent contrast by T1-weighted MSME MRI sequences. High resolution spectra obtained at 7 Tesla allow identification of at least 9 different proton resonances specific for lipids, and, thus, for exact calculation of mono- to polyunsaturated fatty acid ratio in vivo. In this study, nude mice showed, e.g., a 4-fold higher degree of polyunsaturation of triglyceride fatty acids in BAT when compared to NMRI mice. High-resolution MRI and MRS are potentially useful tools for studying the biology of different BAT and WAT deposits non-invasively in rodent models in vivo.

Aims:

We wanted to study factors influencing the size of LDL particles.

Material and methods:

752 persons (330 males, 422 females) have been studied. We performed an OGTT (plasma glucose, insulin, proinsulin). Triglycerides (TG), total cholesterol (TC) and protein (in whole plasma, in VLDL, in LDL) and HDL cholesterol have been measured. The size of the LDL particles has been estimated using a gel electrophoresis
(in LDL subclasses 1 – 3, mean LDL particle diameter, affiliation to phenotypes A or B). Probands have been subdivided into those with normal glucose tolerance (n 540), with an impaired glucose tolerance (n 137), with a newly discovered or known diabetes (n 51), or with a diabetes mellitus which was treated by insulin (n 24). The
Metabolic Syndrome (MS) has been defined according to the NCEP criteria.

Results:

In 29 % of all probands a MS was observed. These probands had a significantly smaller mean LDL particle diameter (25.5 nm) than those persons without a MS (26.2 nm). In univariate analysis (partially adjusted for fasting plasma glucose, proinsulin, insulin, gender, age, body mass index) the mean LDL diameter showed significant
correlations with the VLDL TG, plasma TG, VLDL cholesterol, VLDL proteins and HDL cholesterol. In a linear stepwise regression analysis in the different groups of glucose tolerance different independent factors of influence were seen. Conclusions: The data obtained show the significance of TG levels, of glucose intolerance and the presence of the MS for the formation of atherogenic small dense LDL particles.

Data concerning the role of circulating glycated (glycLDL) and glycoxidized LDL (glycoxLDL) in atherogenesis and other pathologies are scarce. One reason for this is the lack of suitable radiolabeling methods for direct assessment of metabolic pathways of modified LDL in vivo. We report a novel approach for specific labeling of human native LDL (nLDL), glycLDL, and glycoxLDL with the positron emitter fluorine-18 (¹⁸F) by either N-succinimidyl-4-[¹⁸F]fluorobenzoate or N-[6-(4-[¹⁸F]fluorobenzylidene)-aminooxyhexyl]maleimide (radiochemical yields, 15-40%; specific radioactivity, 150-400 GBq/µmol). Radiolabeling itself caused neither additional oxidative structural modifications of LDL constituents nor adverse alterations of their biological activity and functionality in vitro. The approach was evaluated with respect to binding and uptake of ¹⁸F-nLDL, ¹⁸F-glycLDL, and ¹⁸F-glycoxLDL in cells overexpressing various lipoprotein-recognizing receptors. The metabolic fate of ¹⁸F-labeled nLDL, glycLDL, and glycoxLDL in vivo was delineated by dynamic small animal PET studies in rats. Dynamic PET data demonstrated a significantly delayed catabolism of glycLDL when compared with nLDL. In contrast, glycoxLDL showed an enhanced catabolism when compared with nLDL. The in vivo distribution and kinetics of nLDL, glycLDL, and glycoxLDL correlated well with the anatomical localization and functional expression of LDL receptors, scavenger receptors, and receptors for advanced glycation end products. The study shows that LDL modification in part or fully blocks binding to the LDL receptor, and reroutes modified LDL to various tissue-specific pathways. In this line, ¹⁸F-labeling of LDL and the use of small animal PET provide a valuable tool for imaging and functional characterization of these pathways in animal models in vivo.

Hydration and water exchange mechanism of the UO22+ ion was studied by the B3LYP calculations. Relative Gibbs energies in aqueous phase of the 4-, 5-, and 6-fold uranyl(VI) hydrates were compared. A model with a complete first hydration shell and one water in the second shell was used (which is called "n+1" model) to compare the energy of the UO22+ ion with different hydration number. The "n+1" model tends to overestimate the overall stability of the complex, and this type of model should be carefully used for the determination of the coordination number or the coordination mode such as unidentate or bidentate. A stable 5-fold uranyl(VI) hydrate go through a very rapid water exchange process via an associative (A-) mechanism keeping the 5-fold uranyl(VI) being dominant species.

Ziel/Aim:

Radiolabelled fatty acids displaying efficient myocardial uptake and adequate retention are attractive candidates for the clinical evaluation of regional discrepancies in the cardiac metabolism and energy turnover (1). The aim of this work is the substitution of the accelerator produced radiolabel I-123 for FA against the low price generator radionuclide Tc-99m (2).

Methodik/Methods:

Synthesis and physico-chemical characterization of the new Tc-99m labelled FA derivatives were followed by in vitro and in vivo experiments for their biological evaluation. Experiments on isolated perfused rat hearts provide a simple and well reproducible approach to detect promising Tc-99m compounds for biodistribution experiments. Biodistribution and metabolism studies in male Wistar rats after a single intravenous injection of various Tc-99m-labelled FA were investigated (3).

Ergebnisse/Results:

A very rapid disappearance of Tc-99m tracer concentration from the blood circulation was observed for all compounds. C11S FA showed the highest uptake with 2.0% ID/g tissue (alternatively 3.6% by addition of Tween 80) in the rat heart. Liver and kidneys are mainly responsible for fast removal of Tc-99m derivatives from the circulation. At 5 min after injection, approximately 50% of the injected dose is liver-associated. A substantial fraction is cleared by the kidneys and approximately 6% of the injected dose is kidney-associated at 5 min p.i. Overall, fast systemic clearance of Tc-99m species after injection of Tc-99m labelled FA in the rat is explained by the rapid hepatobiliary and renal elimination of Tc-99m species. On the other hand, the low mean accumulation of Tc-99m compounds in the thyroid gland (<0.07 %ID at 5 min; <0.07 %ID at 60 min) and the stomach (<1.7 %ID at 5 min; < 3.9% at 60 min), respectively, which express the sodium-iodide transporter is indicative of a very low abundance of pertechnetate in vivo.

Schlussfolgerungen/Conclusions:

Experiments on isolated perfused rat hearts showed very high ventricular extraction rates of the FA complexes, being in the order C11 compound (26.6% ± 3.7, n= 12), C12 (24.4% ± 4.9, n= 5), and C11S (23.4% ± 4.9, n= 5). These extraction rates exceed considerably those achieved with the established iodinated FA [I-123]IPPA (15.5% ± 1.1).The metabolic in vivo studies reveal the complete ß-oxidation within one hour. Condition precedent for the use of the described Tc-FA in heart imaging are the improvement of the heart : liver ratio of 0.25±0.1 at 5 min p.i., which may be achieved by alterations of the FA binding mode to the “4+1” chelate unit and variations of the chelate position in the FA chain.

Literatur/References:

(1) Knapp, F. F. Jr., Kropp, J. (1995) Eur. J. Nucl. Med. 22(4), 361-381.
(2) Mach, R. H., Kung, H. F., Jungwiwattanaporn, (1991) Nucl. Med. Biol. 18, 215-226.
(3) M. Walther, C. M. Jung, R. Bergmann, (2006) Bioconjugate Chem. submitted

Ziel:

Die vorliegende Arbeit untersucht das Potenzial von C-11-Azetat-Positronen-Emissions-Tomographie (PET) zur Darstellung von Nierentumoren am Menschen, da das Staging von Nierentumoren mit FDG-PET unzufriedenstellend ist.

Methodik:

Einundzwanzig Patienten mit Verdacht auf einen Nierentumor im CT/MRT wurden nach Injektion von 820±430 MBq C-11-Azetat dynamisch über 30 min untersucht (ECAT EXACT HR+, Siemens/CTI, Knoxville, USA). Die Azetat-Aufnahme wurde qualitativ auf einer 5-Punkte-Skala eingeschätzt. Die Aufnahme-Kinetik von Nierenparenchym und Tumor wurde qualitativ verglichen. Bei 18/21 Patienten erfolgte eine Operation und histologische Klassifizierung.

Ergebnisse:

Die Azetat-Aufnahme in die Tumore war geringer (n = 11), gleich (n = 8) oder höher (n = 2) als das umgebende Nierenparenchym. Bei den letztgenannten Tumoren zeigte die kinetische Analyse eine Radiotracerzunahme bis zur 10. min gefolgt von einer langsamen Tracerabnahme über den Untersuchungszeitraum. Die übrigen Tumore zeigten eine dem Nierenparenchym ähnlich Kinetik bei teilweise initial verminderter Traceraufnahme. Die Nierenfunktion war bei allen Patienten nur gering bis mäßig beeinträchtigt. Histologisch lagen klarzellige Nierenkarzinome (n = 14), zwei papilläre und zwei onkozytäre Nierentumore vor, was einer typischen Verteilung entspricht. Nur die beiden Onkozytome zeigten eine gesteigerte Azetat-Aufnahme. Diese Ergebnisse stehen im Widerspruch zur Untersuchung von Shreve et al. (1995), in der 3/3 klarzelligen Nierenkarzinomen eine erhöhte Azetat-Aufnahme aufwiesen.

Schlussfolgerungen:

Die meisten untersuchten Nierentumore zeigten keine gegenüber dem umgebenden Nierenparenchym erhöhte C-11-Azetat-Aufnahme. Die geringe C-11-Azetat-Aufnahme war nicht messtechnisch durch zu späte Akquisitionen bedingt. Auch Spätbilder zeigten keine wesentliche Kontrastzunahme. Daher kann C-11-Azetat-PET nicht routinemäßig zum Primärstaging von Nierentumoren empfohlen werden. Die Bedeutung von C-11-Azetat-PET für den Nachweis von Lymphknoten-, Fernmetastasen oder Rezidiven von Nierentumoren muß noch weiter untersucht werden.

Literatur:

Shreve P et al., J Nucl Med 36 (1995):1595-601

Ziel/Aim:

Die Mehrzahl maligner Tumore weisen einen erhöhten Glukosestoffwechsel auf, ein Mechanismus der bei der Positronen-Emissions-Tomographie mit F-18-FDG in der Onkologie diagnostisch genutzt wird. Ziel dieser Untersuchung war es, die unterschiedlichen Einflüsse von Tumorhypoxie und Proliferation auf die intratumorale FDG-Aufnahme in 2 menschlichen Tumormodellen auf Nacktmäusen zu untersuchen.

Methodik/Methods:

Je 10 Nacktmäusen mit transplantiertem menschlichen Plattenepithel-Carcinom Fadu oder humanem Adeno-Carcinom HT29 wurden mit FDG und PET (MicroPET P4, CTI Molecular Imaging, gemessenen Transmission, 8 MBq FDG i.v., Untersuchung 30-60min p.i.) untersucht (Tumorvolumina 0,4 ± 0,2cc). Aus den PET-Aufnahmen wurde der SUVmax der Tumore bestimmt. Vor dem PET wurde den Mäusen Pimonidazol (Pimo) und Bromdesoxyuridin (BrdU) injiziert, die Mäuse wurden unmittelbar nach der PET getötet, die Tumore entnommen, tiefgefroren, serielle Schnitte von 20 µm angefertigt und die intratumorale FDG-Verteilung per Autoradiographie (BAS 5000, Fuji) bestimmt. Leberschnitte von 20µm dienten als Referenzgewebe. Anschließend erfolgte die Färbung der Schnitte mit Hämatoxylin/Eosin, Antikörper gegen Pimonidazol, BrdU oder Ki-67. Die Tumorschnitte wurden mit einer digitalen Kamera gescannt und per Bildanalyse wurden Masken für vitalen Tumor, Nekrose und funktionelle Färbungen (Pimo, BrdU, Ki-67) angefertigt. Die digitalen Histologien wurden mit der korrespondierenden Autoradiographie koregistriert und die quantitative FDG-Aufnahme in den definierten Tumorarealen bestimmt.

Ergebnisse/Results:

Der SUVmax in Fadu (1,55 ± 0,26) lag etwas höher als in HT29 (1,30 ± 0,17; p=0,03). Fadu bildet größere hypometabole Bereich aus, die sich in der Histologie als Nekrose identifizieren liessen. Bei ähnlicher Größe der Pimo-positiven Areale in Fadu und HT29 fand sich nur in Fadu eine signifikant höhere FDG-Aufnahme in den hypoxischen Arealen im Vergleich zu vitalem Pimo-negativem Tumorgewebe (Fadu: 3,1 ± 0,2 versus 2,2 ± 0,2 %ID/g, p=0,002, HT29: 2,4 ± 0,2 versus 2,2 ± 0,2%ID/g, p=0,4). In beiden Tumormodellen fand sich keine regional erhöhte FDG-Aufnahme in Tumorregionen mit proliferativer Aktivität im Vergleich zu nicht in Teilung begriffenen vitalen Tumorarealen.

Schlussfolgerungen/Conclusions:

In den zwei untersuchten Tumormodellen war nur bei dem Plattenepithel-Ca Fadu ein Einfluß der Hypoxie auf die FDG-Aufnahme zu erkennen, die höhere FDG-Aufnahme in Hypoxiearealen könnte sich in dem höheren SUVmax im Vergleich zum Adeno-Ca HT29 widerspiegeln. Weder in Fadu noch in HT29 fand sich eine Korrelation zwischen Proliferation (BrdU, Ki-67) und Intensität der FDG-Aufnahme.

Die Daten wurden im Rahmen des 6.Rahmenprogrammes der EU, Projekt Biocare, proposal Nr. 505785, erhoben.

Ziel/Aim:

Ziel war die Bestimmung des Einflusses von Kopfbewegungen während einer dynamischen Untersuchung auf die Kompartmentmodell-gestützte Quantifizierung des FDOPA Uptakes durch den Vergleich von Auswertungen der bewegungskorrigierten und der unkorrigierten Daten.

Methodik/Methods:

Retrospektiv wurden Daten von 57 Patienten (32 m, 25 w, mittleres Alter 58,8 Jahre) analysiert, welche im Rahmen der Parkinson-Diagnostik mit F-18-FDOPA eine PET-Untersuchung (EXACT HR+, Siemens) erhielten. Die Messung erfolgte im Listmode, daraus wurde eine dynamische Studie von 21 Frames erstellt. Parallel zur Aufnahme wurde die Kopfbewegung mit einem Motion-Tracking-System (A.R.T.,München) aufgezeichnet. Die Bewegungsdaten wurden detailliert analysiert und zur Korrektur der Emissionsbilder verwendet. Dopamin-Einstromraten für die korrigierten und unkorrigierten Studien wurden mittels grafischer Patlak-Analyse sowohl für 8 manuell positionierte striatale VOIs (0,35ml, Software: ROVER, abx biochemicals) als auch voxelweise quantifiziert (Referenzregion okzipitaler Cortex, Regression 15-60min) und verglichen.

Ergebnisse/Results:

Bei 2 Patienten wurde ein Versagen der Bewegungskorrektur festgestellt, was auf eine ungenügende Fixierung des Targets für die Bewegungsmessung am Patientenkopf zurückgeführt wurde. Über das Kollektiv betrachtet sind die Bewegungen klein: Median und Quantilen (10%-90%) Translationen in mm für x;y;z 1,6 (0,8-3,4); 1,8 (1,0-4,7); 2,8 (1,0-8,0); Rotation in Grad um x;y;z-Achse 2,2 (1,2-4,9); 0,8 (0,4-1,7); 0,6 (0,3-1,7). Daraus ergeben sich maximale Voxelverschiebungen innerhalb des Gehirns von: weniger als 4mm bei 24 Patienten, zwischen 4 und 8mm bei 20 Patienten und 10mm bei einem Patienten. Die Verteilung des prozentualen Unterschiedes der Einstromraten ohne und mit Korrektur für die 440 VOIs hat einen Median von 1%. 80% der Werte liegen zwischen -4% und 13,6%. Bei 11 Patienten finden sich Abweichungen von mehr als 20% (Absolutbetrag), wobei bei 3 Patienten mehr als 3 VOIs betroffen sind. Dies sind Patienten, welche sich insbesondere in z-Richtung stark bewegt haben (>11mm). Kopfbewegung während der Aufnahme führt meist zu einer Überschätzung der Einstromraten, was sich auch in den Histogrammen der voxelweise korrelierten parametrischen Bilder zeigt. Artefakte in den parametrischen Bildern sind am ehesten in den kortikalen Bereichen erkennbar.

Schlussfolgerungen/Conclusions:

Bei der Quantifizierung der Dopamin-Einstromraten sollte eine Bewegungskorrektur angestrebt werden. Die hier angewandte framebasierte Methode ist einfach und schnell anwendbar, weitere Verbesserungen sollten durch eventbasierte Korrektur der Emission und Einrechnung von korrigierten Transmissionsdaten erreichbar sein.

Ziel/Aim:

Die Integration der PET in die Bestrahlungsplanung ist für die Strahlentherapie von zunehmendem Interesse. Folgende Voraussetzungen sind hierfür zu erfüllen: 1) adäquate DICOM-Integration der PET (Herstellerseitig für neuere Geräte i.w. erfüllt), 2) volumetrisch korrekte und routinefähige 3D ROI-Abgrenzung in den PET-Daten, 3) Transfer der 3D-ROIs in den DICOM-RT Standard, 4) Koregistrierung PET vs. Bestrahlungsplanungs-CT. Ziel dieser Arbeit war die vollständige Implementierung eines routinefähigen Workflows unter Nutzung existierender und neu entwickelter Methoden.

Methodik/Methods:

Die genutzten Verfahren zur benutzerunabhängigen 3D-ROI-Definition und Koregistrierung wurden anderweitig bereits vorgestellt (1-3). Umgesetzt wurde nunmehr die fehlende Übersetzung der resultierenden 3D-ROIs in den DICOM-RT Standard als Voraussetzung für den Import der ROIs in die Bestrahlungsplanungssysteme sowie die Kombination der verschiedenen Arbeitsschritte in einen routinefähigen Ablauf unter Nutzung einer eigenen DICOM-Schnittstelle. Das gesamte Verfahren wurde an verschiedenen Bestrahlungsplanungssystemen getestet.

Ergebnisse/Results:

Die PET-Information konnte in Planungssysteme verschiedenerer Hersteller integriert werden, wobei der Integrations-Workflow teilweise an das jeweilige Planungssystem angepasst werden musste. Unser Verfahren erlaubt insbesondere auch die Kombination der PET-ROIs und die Planungs-CT Konturen, was die Handhabung der kombinierten Information auf den Planungssystemen erleichtert. Der durch die Integration verursachte zusätzliche zeitliche Aufwand bei der Auswertung der PET-Aufnahmen ist vernachlässigbar.

Schlussfolgerungen/Conclusions:

Die vorgestellte Methode erlaubt eine routinemäßige Integration der PET-Information in die Bestrahlungsplanung.

Literatur/References:

1. C. Pötzsch;F. Hofheinz;J. van den Hoff; Nuklearmedizin (2005) 44 p. A16
2. C. Pötzsch;F. Hofheinz;J. van den Hoff; Nuklearmedizin (2006) 45 p. A42
3. F. Hofheinz;C. Pötzsch;J. van den Hoff; Nuklearmedizin (2005) 44 p. A162

Ziel/Aim:

Die kardiale PET zeichnet sich gegenüber der SPECT u. a. durch die Möglichkeit der absolut quantifizierenden Messung der myokardialen Perfusion aus. In der Diagnostik der KHK wird zunehmend eine Kombination von SPECT oder PET mit einer morphologischen Darstellung der Koronargefäße durch eine CT-Angiographie eingesetzt. Auch bei Einsatz von Hybridgeräten machen Unterschiede in der Datenakquisition und die Thoraxbewegung bei der Atmung eine Koregistrierung der Datensätze erforderlich. Von Seiten der Gerätehersteller wird derzeit jedoch nur eine Koregistrierung statischer Datensätze unterstützt. Der wesentliche Vorteil der PET, die Einschätzung einer koronaren 3-Gefäßerkrankung durch Beurteilung der absoluten Flusswerte, geht dadurch verloren. Ziel war daher die Koregistierung von CT und funktionellem PET-Datensatz.

Methodik/Methods:

Verwendet wurden dynamische PET-Studien mit N-13-Ammoniak und CT-Angiographien der Koronargefäße, die an unabhängigen Geräten akquiriert wurden. Die Koregistrierung von CT und PET erfolgte anhand des rekonstruierten CT-Datensatzes und des PET-Uptake-Bildes (letztes Frame der dynamischen Studie, 9.-16. Minute). Die Koregistrierung erfolgte manuell sowie durch automatische Detektion von Grenzflächen über Schwellenwerte. Im Rahmen der Kompartmentmodellierung dynamischer PET-Datensätze findet eine Reorientierung entsprechend der Herzachsen statt und die funktionellen Parameter können nur für Volumenelemente innerhalb des Myokards bestimmt werden. Daher gehen die ursprüngliche Orientierung der Datensätze und weitergehende anatomische Informationen zunächst verloren. Für eine kombinierte Darstellung der Morphologie der Koronargefäße und der quantitativen Flussinformation wurde daher in einem nächsten Schritt eine Rückprojektion der Flussinformation in die anatomisch korrekte Lokalisation durchgeführt.

Ergebnisse/Results:

Mit der vorliegenden Methode ist es möglich, quantitative Flussinformationen aus der PET mit CT-Angiographien der Koronargefäße zu koregistrieren und somit im Kontext anatomischer Daten darzustellen. Dies bedeutet für die klinische Anwendung, dass es im Vergleich zur myokardialen SPECT/CT möglich ist, relevante Hauptstammstenosen zu erkennen und auch bei koronarer Mehrgefäßerkrankung nicht nur die funktionelle Relevanz der führenden, sondern aller Stenosen zu beurteilen.

Schlussfolgerungen/Conclusions:

Die Weiterentwicklung von Software, die eine Koregistrierung von morphologischen Daten aus der CT und funktionellen Daten aus der PET ohne Informationsverluste ermöglicht, ist insbesondere im Hinblick auf die zunehmende Häufigkeit von Hybridgeräten dringend erforderlich.

In this article we present the first experimental results of in-beam PET measurements during high energy photon phantom irradiation. An inhomogeneous phantom was irradiated with pulsed 34 MV bremsstrahlung. The measurements have been conducted with a dedicated double head photon camera. A high material contrast could be achieved and furthermore production rates of C-11 and O-15 were derived from the time dependent activity.

Caffeine is among the most frequently consumed alkaloidal compounds and is omnipresent in many plants. The traditional significant sources of caffeine in daily life are coffee, black tea and cocoa. Actually, the alkaloid is an ingredient of Cola beverages and energy drinks. Many analgesics sold-over-the-counter contain also caffeine. Because of the wide range of applications and the potential of new analytical tools caffeine is currently gathering an increasing attention. Recently, we reported the synthesis of functionalized triphenylene ketals which represent the rigid C3v symmetric scaffold of our novel receptors (1). The cleft like structure exhibits a high affinity to caffeine and does not interfere with the alkyl groups of the oxopurine system leading to a novel concept for the molecular recognition of caffeine and related compounds. Based on this concept several methods for the detection of caffeine in real life samples have been established. With extraction studies using ¹⁴C-labelled caffeine the potential of this receptor systems and their binding action could be elucidated. This is a key prerequisite for the further development of caffeine detection systems on a dip-stick model. Furthermore, first experiments were done in view of the development of controlled release systems for caffeine in aqueous media.

The utilization of a pulsed rotating magnetic field (RMF) is presented as an auspicious method to obtain an intensive stirring and mixing in a pool of liquid metal. The RMF pulses within a sequence have been applied with constant or alternating direction, respectively. The resulting flow structure in a cylindrical liquid metal column has been explored by numerical simulations and by model experiments using the ternary alloy GaInSn. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the vertical velocity. The numerical results as well as the velocity measurements demonstrate the capability of the proposed stirring regimes to overcome the limited mixing character of conventional rotary stirring. The application of a time-modulated RMF offers a considerable potential to provide optimal flow pattern in a solidifying melt for reasons of a well-aimed modification of casting properties.

Cyclooxygenase-2 (COX-2) is an enzyme induced during inflammation by various stimuli, but overexpression of COX-2 has been observed also in oncogenesis in a variety of tumors. Although several COX-2 inhibitors have recently been radiolabeled with isotopes for positron emission tomography (PET), their potential for tumor imaging has not been explored extensively. Herein we report the synthesis and radiopharmacological evaluation of 1-(4-[¹¹C]methoxyphenyl)-2-(4-methylsulfonylphenyl)-1-cyclopentene as novel ¹¹C-labelled radiotracer for PET imaging of COX-2.

Methods:

The radiolabeling was performed via a ¹¹C-methylation reaction of the corresponding desmethyl precursor using [¹¹C]MeI in a TRACERLab FXC module.
Biodistribution studies were performed in normal Wistar rats. Small animal PET studies were performed using xenografted HT-29 and FaDu tumors in mice using a micro-PET^® P4 scanner.

Results:

The radiolabeling was achieved by the reaction of 1-(4-hydroxyphenyl)-2-(4-methylsulfonylphenyl)-1-cyclopentene at 60°C in DMF/aqueous NaOH with [¹¹C]CH₃I. After semi-preparative HPLC purification and solid phase extraction the ¹¹C-labelled COX-2 inhibitor was obtained in 12-14 % decay-corrected radiochemical yield at a specific activity of 30 GBq/µmol at the end-of-synthesis. The radiochemical purity exceeded 97%. Biodistribution in normal rats showed high radioactivity accumulation in the liver, adrenals and brown adipose tissue, reaching 0.6±0.1, 0.7±0.2 and 0.8±0.1 %ID/g after 1 h post injection, respectively. Tumor-to-muscle ratios of 1.7±0.2 and 2.1±0.3, respectively, were determined with small animal PET-studies of xenografted HT-29 and FaDu tumors in mice after 1 h post injection.

Our group previously synthesized ^99mTc-labeled fatty acids suitable for myocardial metabolism and flow imaging. In this set of experiments 28 new analogues were synthesized according to the “4+1” mixed ligand approach with some specific differences. Conventional “4+1” ^99mTc-fatty acids are built in the sequence Tc-chelate, alkyl chain and carboxylic group. We developed compounds with a new design with the sequence carboxylic group, alkyl chain, Tc-chelate, and lipophilic tail. Therefore the ^99mTc-chelate was transferred to a more central position of the compound, aiming towards an improved myocardial profile and an accelerated liver clearance. In this context several functional groups incorporated in the lipophilic tail section were tested to evaluate their influence on the compound’s character. In addition to biodistribution studies in vivo the myocardial first-pass extraction of the compounds was tested in an isolated Langendorff rat heart model. A satisfactory myocardial uptake up to 20% of the injected dose (% ID) in the perfused heart and a fast liver clearance in vivo with only 0.29% ID/g at 60 min post injection demonstrates that the induced molecular modifications affect the kinetics of ^99mTc-radiolabeled fatty acid compounds favorably. From the data set rules for estimating the biodistribution of fatty acids tracers are deduced.

Introduction:

⁶⁴Cu (t_1/2 = 12.7 h; ß⁺ 0.653 MeV, 17.4%; ß^-: 0.578 MeV, 39%) [1,2] is the most used copper isotope in nuclear medicine due to its favorable decay characteristics and its ability to be produced with high specific activity. Bispidines and azamacrocycles containing pyridine pendant arms form thermodynamically stable complexes with copper(II) [1,2]. These chelating agents – possessing an additional linker group – provide an attractive lead for labelling biomolecules with copper radionuclides.

Experimental:

First experiments to adapt the described ⁶⁴Cu-production process [3,4] at a biomedical cyclotron CYCLONE 18/9 were performed. A bombarding energy of 10 MeV and a proton beam current of 10 µA for 15 to 60 min were used. The yields of the ⁶⁴Ni(p,n)⁶⁴Cu reaction were comparable to reference values [179-331 MBq/µA/h versus 185-248 MBq/µA/h [3,4]].
Two novel ligands with carboxylic groups – a hexadentate bispidine 1 and a derivative of 1,4,7-triazacyclononane (TACN) 2 [5] were prepared. Labelling experiments of these ligands indicated the rapid formation of stable ⁶⁴Cu-complexes under mild conditions. The bioconjugates 3 and 4 were obtained by coupling the bombesin (BBN) derivate βAla-βAla-[Cha¹³, Nle¹⁴]BBN(7-14) [6] to the ligands 1 and 2 (HBTU, DIPEA, DMF, r.t.).

Results and Discussion:
The bioconjugation of 1 and 2 to a bombesin derivative was successfully achieved via amide coupling to give 3 and 4. The free ligands and the bioconjugates were labelled with ⁶⁴Cu and the resulting complexes were found to be stable in the presence of a large excess of competing ligands such as cyclam and even in rat plasma.

Conclusion:

The bispidine ligand 1, the TACN derivative 2 and their bombesin bioconjugates 3 and 4 are able to form complexes with high stability. These bifunctional chelating agents may be attractive candidates for the development of new copper radiopharmaceuticals for diagnosis (⁶⁴Cu) and therapy (⁶⁷Cu). Preliminary studies on the bio-distribution of ⁶⁴Cu-complexes of 3 and 4 are currently underway [5].

[1] C. Bleiholder et al., Inorg. Chem. 2005, 44, 8145-8155.
[2] G. A. McLachlan et al., Inorg. Chem. 1994, 33, 4663-4668.
[3] F. Szelecsényi et al., Appl. Radiat. Isotopes 1993, 44, 575-580.
[4] D. W. McCarthy et al., Nucl. Med. Biol. 1997, 24, 35–43.
[5] G. Gasser et al., Bioconjugate Chemistry, 2007, in prep.
[6] E. Garcia Garayoa et al., Nucl. Med. Biol. 2007, 34, 17-28.

A superconducting radio-frequency photo electron injector (SRF gun) is currently under construction by a collaboration of BESSY, DESY, FZR and MBI. The project aims at the design and setup of a CW SRF gun including a diagnostics beamline for the ELBE FEL and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development serving a multitude of operation settings ranging from low-charge (77pC), low-emittance (1 mm mrad) mode to high-charge (2.5nC) operation of the gun. For these operation modes beam dynamics simulations are resulting in boundary conditions for the beam instrumentation. Proven and mature technology is projected wherever possible, for example for current and beam position monitoring. The layout of the beam profile and emittance measurement systems is described. For the bunch length, which varies between 5 ps and 50 ps, two schemes using electro-optical sampling and Cherenkov radiation are detailed. The beam energy and energy spread is measured with a 180o spectrometer.

We present new measurements of the 7Besp,gd8B cross section from Ec.m.=116 to 2460 keV (where c.m. means center-of-mass), which incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17s0d=22.1±0.6sexptd±0.6stheord eV b based on data from Ec.m.=116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low-energy data. We compare our results to other S17s0d values extracted from both direct f7Besp,gd8Bg and indirect (Coulomb-dissociation and heavy-ion reaction) measurements, and show that the results of these three types of experiments are not mutually compatible. We recommend a “best” value, S17s0d=21.4±0.5sexptd±0.6stheord eV b, based on the mean of all modern direct measurements below the 1+ resonance. We also present S factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S17s20d =21.4±0.6sexptd±0.6stheord eV b, and the recommended value is S17s20d=20.6±0.5sexptd±0.6stheord eV b.

We present new measurements of the 7Besp,gd8B cross section from Ec.m.=116 to 2460 keV (where c.m. means center-of-mass), which incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17s0d=22.1±0.6sexptd±0.6stheord eV b based on data from Ec.m.=116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low-energy data. We compare our results to other S17s0d values extracted from both direct f7Besp,gd8Bg and indirect (Coulomb-dissociation and heavy-ion reaction) measurements, and show that the results of these three types of experiments are not mutually compatible. We recommend a “best” value, S17s0d=21.4±0.5sexptd±0.6stheord eV b, based on the mean of all modern direct measurements below the 1+ resonance. We also present S factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S17s20d =21.4±0.6sexptd±0.6stheord eV b, and the recommended value is S17s20d=20.6±0.5sexptd±0.6stheord eV b.

Fission spectrum neutron irradiation of pure Fe at irradiation temperatures of about 300 °C gives rise to the formation of two populations of defects: planar dislocation loops and spherical vacancy-type clusters. Knowledge of the type and size distributions of these populations is important for the purpose of multi-scale modelling of the mechanical behaviour of Fe-based alloys. Among the experimental techniques with nanometer size resolution, transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) allow to gain information on both nature and size distribution of particular types of defects. Furthermore, positron annihilation spectroscopy (PAS) is sensitive to sub-nanometer size open-volume defects. However, there is no single experimental technique capable of providing the full set of information required for calibration and validation of advanced models. The complementarity between the three techniques to identify and quantify the defects created by irradiation in pure Fe is emphasised in the paper. It is shown that while TEM allows direct size-resolved evidence of dislocation loops, PAS a qualitative appreciation of the existing sub-nanometer size vacancy-type clusters, SANS yields indirect size-resolved evidence of vacancy-type clusters, which form a sound basis for the quantification of the size distributions.

The spallation residues produced in the bombardment of 56Fe at 1.5A, 1.0A, 0.75A, 0.5A, and 0.3A GeV on a liquid-hydrogen target have been measured using the reverse kinematics technique and the fragment separator at GSI (Darmstadt). This technique has permitted the full identification in charge and mass of all isotopes produced with cross sections larger than 10−2 mb down to Z = 8. Their individual production cross sections and recoil velocities at the five energies are presented. Production cross sections are compared with previously existing data and with empirical parametric formulas, often used in cosmic-ray astrophysics. The experimental data are also extensively compared with the results of different combinations of intranuclear cascade and deexcitation models. It is shown that the yields of the lightest isotopes cannot be accounted for by standard evaporation models. The GEMINI model, which includes an asymmetric fission decay mode, gives an overall good agreement with the data. These experimental data can be directly used for the estimation of composition modifications and damages in materials containing iron in spallation sources. They are also useful for improving high-precision cosmic-ray measurements.

In the search for Si- and C-based crystalline phases in low-energy ion implanted and electron-beam annealed Si surface layers, X-ray diffraction (XRD) measurements were performed at grazing incidence on samples of large SiC nanocrystals grown on a 90 nm thick Si layer containing C atoms. Diffraction patterns and reciprocal space maps did not reveal XRD patterns originating from the nanocrystals or the implanted layer, but did show that distortions of the Si crystal structure were introduced into the implanted layer. After annealing, the strain in the implanted layer is reduced, possibly by carbon atoms that have moved to locations close to dislocations and dislocation loops. This investigation underpins the growth theory of the SiC nanocrystals on Si, with carbon atoms migrating to form the nanostructures.

Ni-Ti SMA are smart materials undergoing first order martensitic transformations driven by temperature and/or stress. In the form of film they are very attractive candidates for microelectro-mechanical system (MEMS) applications. Future directions include the production of functionally graded films by changing deliberately the ratio Ti/Ni across their thickness. However, for the successful development of this type of films, it is important to characterize, model and control the variations in composition, crystalline structure and transformation temperatures. Our approach is in-situ XRD study of the actual growth of the films of varying composition along the thickness carried out using a deposition chamber installed at a synchrotron radiation beamline. These studies were complemented with ex-situ analysis techniques. The results achieved on a Ni-Ti film co-sputtered from Ni-Ti and Ti targets on a TiN buffer layer are presented in this paper. The deposition started by using optimised parameters for a near equiatomic composition. After 1 h (≈330 nm thick film), the Ti power was increased from 20 to 25 W, leading to the precipitation of Ti2Ni. The evolution of the lattice parameter values of the B2 phase, calculated from the corresponding XRD data, is clearly linked with the increase of the Ti power. The depth profile of the atomic concentrations determined by Auger Electron Spectroscopy (AES) is in agreement with the in situ XRD results. The temperature dependence of the electrical resistivity was used to monitor phase transformations, Scanning Electron Microscopy (SEM) has shown the presence of twinned martensite on the film’s surface at room temperature.

Ni-Ti Shape Memory Alloy thin films are suitable materials for microelectromechanical devices. During the deposition of Ni-Ti thin films on Si substrates, there exist interfacial diffusion and chemical interactions at the interface due to the high temperature processing necessary to crystallize the film. For the present study, Ni-Ti thin films were prepared by magnetron cosputtering from Ni-Ti and Ti targets in a specially designed chamber mounted on the 6-circle goniometer of the ROssendorf BeamLine (ROBL-CRG) at ESRF, Grenoble (France). The objective of this study has been to investigate the interfacial structure resulting from depositions (at a temperature of ≈ 470°C) on different substrates: naturally oxidized Si(100), Si(111) and poly-Si substrates. A detailed High-Resolution TEM analysis of the interfacial structure has been performed. When Ni-Ti is deposited on Si(100) substrate, a considerable diffusion of Ni into the substrate takes place, resulting in the growth of semi-octaeder A-NiSi2 silicide. In the case of Ni-Ti deposited on Si(111), there appears an uniform thickness plate, due to the alignment between substrate orientation and the [111]-growth front. For Ni-Ti deposited on poly-Si, the diffusion is inhomogeneous. Preferential diffusion is found along the columnar grains of poly-Si, which are favourably aligned for Ni diffusion. These results show that for the Ni-Ti/Si system, the morphology of the diffusion interface is strongly dependent on the type of substrates.

Research on experiments using real photons from bremsstrahlung production at ELBE is presented in an invited talk at the annual spring meeting of the german physical society.

Optical tomography is a potential technique for the visualisation of fast transient phenomena in multiphase flows. It can be applied for liquid-liquid, gas-liquid and gas-solid flows as long as the flow consists of a major transparent component/phase, such as a liquid or gas, and a minor component/phase that alters the intensity or light ray propagation path, such as solid particles or gas bubbles. The technique is also applicable in single phase flows with dye tracer marked fluid volumes. Recently we have built a fast optical tomography system that achieves frame rates up to 5 kfps and can be applied to study bubbly two-phase flows in pipes with an inner diameter of two inches. High frame rate at high spatial resolution in the range of 3 mm is obtained by application of a specially developed fully parallel 64 channel data logger with 1MSample simultaneous sampling frequency. The tomography system works similar to an X-ray computed tomography system. As radiation emitters we use 256 LEDs and as detector elements 32 avalanche photo diodes which are optically connected to the tomographic cross section be means of plastic optical fibres. For image reconstruction we use conventional CT algorithms. These algorithms, however, suffer to some degree from the non-linear attenuation of the light at phase boundaries due to total reflection or refraction. Therefore, we currently develop improved image reconstruction algorithms which use a binary reconstruction scheme together with a-priori information on the gas phase. With the new fast optical tomograph we have investigated different two and single phase flow phenomena and compared different image reconstruction algorithms concerning their quantitative accuracy. Especially for lower void fractions in bubble flow or lower particle numbers in liquids we get reliable high resolution images of the cross section at very high temporal resolution.

The plasma enhanced chemical vapor deposition of a-C:H films using methane and acetylene as precursors was studied. Non-invasive in-situ techniques were used to analyze the plasma processes with respect to the self-bias voltage, the displacement currents to the grounded electrode, the neutral gas composition, the optical sheath thickness as well as current and energy of the ions hitting the powered electrode. The a-C:H films were characterized for their deposition rate, surface roughness, hardness, mass density and hydrogen content. Ion mean free paths, suitable for low pressure RF sheaths, have been quantified for both precursors. The film with the highest hardness of 25 GPa was formed in the C2H2 discharge when the mean energy per deposited carbon atom was about 50 eV. The hardness obtained with the CH4 discharge was lower at 17 GPa and less sensitive to changes in the process parameters. It was found that the creation of hard (hardness > 15 GPa) a-C:H films from both precursors is possible if the mean energy per deposited carbon atom exceeds only ~ 15 eV. Further film characteristics like surface roughness and hydrogen content show the interplay of ion flux and deposition from radicals to form the a-C:H structure and properties.

The green algae Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 40 % of the uranium was bound by the algal cells. The uranium removal is almost complete at pH 5 and 6 under the given experimental conditions. Scanning electron microscopy and laser-induced fluorescence spectroscopy were used to characterize formed uranyl species in the selected pH range. Thus demonstrating the regular distribution of U(VI) on the cell surface. Fluorescence spectroscopic investigations of formed complexes outside/inside the cells indicate, the binding of U(VI) to carboxyl groups plays a dominating role at pH 3. Whereas a minor impact of organic phosphate compounds on the U(VI) sorption can not be excluded. In contrast the phosphate groups are mainly responsible for the removal and immobilization of U (VI) at pH 5 and 6 by formation of organic or/and inorganic uranyl phosphates.

The synthesis and characterisation of the new endohedral clusterfullerene Sc₃CH@C₈₀ is reported. The encapsulation of the first hydrocarbon cluster inside a fullerene was achieved by the arc burning method in a reactive CH₄ atmosphere. The extensive characterisation by MS, HPLC, Sc-NMR, ESR, UV-Vis-NIR and Raman spectroscopy provided the experimental evidence for the caging of the five-atomic Sc₃CH cluster inside the C₈₀ cage isomer with icosahedral symmetry. The proposed new structure was confirmed by DFT calculations, which gave a closed shell and large energy gap structure. Thus a pyramidal Sc₃CH cluster and the I_h-C₈₀ cage were shown to be the most stable configuration for Sc₃CH@C₈₀ whereas alternative structures give a smaller bonding energy as well as a smaller energy gap.

The warranty of the high safety standards of existing nuclear power plants requires the assessment and characterization of the actual material state changing during service, e.g. embrittlement due to irradiation. In the brittle and brittle-ductile transition region, ferritic steels fail due to transcrystalline or intercrystalline cleavage fracture starting at flaws resulting from microplastic deformations. The large scatter of fracture mechanical properties in the transition region originating from statistically distributed flaws can be described by Weibull theory. Using the Beremin local approach model, the probability of cleavage fracture at a certain load state can be quantified.
In the small-punch-testing, a quadratical specimen lying on a die is loaded centrically and deformed vertically by a spherical punch, hence starting at plate-like bending and ending in a deep drawing process. Large parts of the specimen are exposed to a biaxial stress state, making the test rather suitable to represent the actual stress state observed in pressure vessel steels in service than other miniaturized methods such as tension or bending tests. Due to the tiny specimen size, material remnants of ongoing surveillance programs (slices of Charpy-specimen) can be used. A special small-punch device was manufactured to be installed into a testing machine in hot cells. To enable testing at temperatures down to -185°C, a cooling system based on liquid nitrogen is used. Neural networks are used to solve the inverse problem of finding material parameters from measured load-displacement-curves. Having identified the parameters describing hardening, Weibull-parameters are determined from both experimental data, e.g. displacement of the punch at fracture, and calculated stress distribution inside the specimen, obtained from FE calculations using the identified plastic properties. The reactor vessel steel A508 (IAEA JFL) is characterized at different levels of irradiation and different temperatures, covering brittle and brittle-ductile transition region of the steel.

This paper presents a method for the identification of hardening parameters in the brittle-ductile transition region and the determination of WEIBULL parameters in the brittle region. A small-punch-test device is developed for hot cells, where a miniaturised disk-like specimen is manufactured and deformed by a spherical punch. Its load-displacement-curve is analysed regarding its information about the material behaviour. Using Neural Networks, an identification routine is presented, which avoids time-consuming calculations with FEM during an optimisation algorithm. Identified material properties are compared with data from tensile tests. WEIBULL parameters are calculated for temperatures at which cleavage fracture occurs using the identified hardening parameters.

Photoluminescence (PL) from CdS nanoclusters formed in the matrix of a Langmuir-Blodgett film and from the same clusters with the matrix removed has been studied. The PL spectrum of clusters in the matrix has the form of a broad band (full width at half-maximum (FWHM) ∼ 0.6 eV) peaked at 2.4 eV. After removing the matrix with hexane, the PL spectrum consists of a high-energy band at 2.9 eV (FWHM ∼ 0.2 eV) and two low-energy bands at 2.4 and 2.0 eV (FWHM ∼ 0.5 eV). The high-energy band is attributed to exciton recombination in the nanoclusters, and the bands at 2.4 and 2.0 eV, to recombination via levels related to defects in the bulk of the matrix and at the nanocluster-matrix interface, respectively.

6H-SiC samples were amorphised by multiple Al implantations at room temperature, in order to study the annealing process. The paper deals with the influence of specific annealing conditions, such as furnace atmosphere and heating rate, on SiC reordering and Al profile. Below a certain deposited nuclear energy, solid phase epitaxy is possible and leads to recrystallisation under precise conditions (high heating rate, silicon partial pressure prescribed). Above it, material etching and dopant losses are observed, even though annealing has proven to be efficient for avoiding surface impairment (due to a specific cleaning process).

The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Trepans taken from the whole RPV wall enable a comprehensive material characterisation. The paper describes the trepanning technology applied to the decommissioned WWER-440/230 RPVs of the Greifswald NPP. The Greifswald RPVs represent different material conditions such as irradiated, irradiated and recovery annealed and irradiated, recovery annealed and re-irradiated. The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations. In a first step the material of the core welding seam was investigated. It could be shown that the Master Curve approach as adopted in E1921 is applicable to the investigated original RPV weld metal. The weld metal located in a distance of about 22 mm from the inner surface of the RPV wall yielded a T0 of 50°C which is about 40K higher than T0 close to the inner surface. This outcome is important for the assessment of results retrieved from so called boat samples taken directly from the RPV surface after the recovery annealing. It shows that boat samples do not represent the material with the lowest toughness.

The influence of hydrostatic compression on the implantation-induced synthesis of Ge nanocrystals in SiO2 host was studied. It is found that high-temperature annealing under pressure leads to retardation of Ge diffusion in SiO2. It is shown that unstressed Ge nanocrystals are formed as a result of conventional annealing (under atmospheric pressure). Annealing under pressure is accompanied by formation of hydrostatically stressed Ge nanocrystals. The stress in Ge nanocrystals was determined from optical-phonon frequencies in the Raman spectra. The shift of Raman resonance energy (E 1, E 1 + Δ1) corresponds to the quantization of the ground-state energy for a two-dimensional exciton at the critical point M 1 of germanium. It is ascertained that a photoluminescence band peaked at 520 nm is observed only in the spectra of the films which contain stressed Ge nanocrystals.

Pyoverdins, bacterial siderophores produced by ubiquitous fluorescent Pseudomonas species, have great potential to bind and thus transport actinides in the environment. Therefore, the influence of pyoverdins secreted by microbes on the migration processes of actinides must be taken into account in strategies for the risk assessment of potential nuclear waste disposal sites. The unknown interaction between curium(III) and the pyoverdins released by Pseudomonas fluorescens (CCUG 32456) isolated from the granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden, is the subject of this paper.
The interaction between soluble species of curium(III) and pyoverdins was studied at trace curium(III) concentrations (3  10 -7 M) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm3+  P. fluorescens (CCUG 32456) pyoverdin species, MpHqLr, could be identified from the fluorescence emission spectra, CmH2L+, CmHL, and CmL-, having peak maxima at 601, 607, and 611 nm, respectively. The large formation constants, log β121 = 32.50 ± 0.06, log β111 = 27.40 ± 0.11, and log β101 = 19.30 ± 0.17, compared to those of other chelating agents illustrate the unique complexation properties of pyoverdin-type siderophores. An indirect excitation mechanism for the curium(III) fluorescence was observed in the presence of the pyoverdin molecules.

Silver nanoparticle formation in poly(vinyl alcohol) thin films is analyzed in real time by spectroscopic ellipsometry. Modeling the data using the Maxwell-Garnett theory shows that the silver content predicted by the model depends of the film thickness. This is conjectured to be due to the absence of plasmon resonances in very small particles affecting the model. The size dependence of the free electron relaxation frequency is used to analyze the particle size during nucleation and growth. Evaporation of the polymer matrix is also monitored by real time ellipsometry and the plasmon resonance is observed to shift from 3.0 to 2.2 eV as the particles are liberated from the polymer. The particle density on the surface can be controlled by the silver concentration and the initial polymer thickness. The exposed particles are easily imaged with scanning electron microscopy, and the particle sizes are compared to the parameters predicted from the Maxwell-Garnett theory.

The present work is concerned with the metallurgical process of melt extraction. Certain industrial requirements, e.g. high purity and small cross-sectional area of the extracted fibres, require a geometrically strictly confined melt volume that is not in contact with any other material being a potential source of pollution. Hitherto, the pending drop method is embodied on small scale facilities. It suffers from low productivity because only one edge can be used to tear a filament out off the molten droplet forming at the tip of a heated rod. Here, a modification is proposed that uses extraction from a pending molten edge at the lower end of a metal sheet. Being a trivial task by all appearances, closer examination shows that it is not. Almost any embodiment of the pending drop technique makes use of locally confined sources of heat, i.e. an acetylene-oxygen torch, or, in the case of high valued materials, laser or electron beams. As attempts to employ induction heating to a single drop did not work even there, it is all the more difficult to melt a sheet along its entire edge rather than between the two opposing branches of an inductor. Tailoring of the induction heating magnetic field, the basic feature of which is the same direction of the electric current in both branches of the inductor, solved the problem. A proper choice of geometry, electrical conductivities of both extraction and substrate material, and the frequency of the alternating magnetic field have proven to be essential for the extraction process. Melting a platinum sheet at the edge and extraction of fibres only 25 micron in effective cross-section from a tin sheet was successfully demonstrated in model experiments.

Magnetization measurements in pulsed magnetic fields up to 47 T were utilized to estimate the average Ru moment in polycrystalline RuSr₂GdCu₂O₈. A NbSr₂GdCu₂O₈ sample was used as reference. The extracted Ru moment of about 1.8µ_B at 4.2 K and 47 T is indicative of a mixed-valence state of Ru involving Ru⁵⁺ and Ru⁴⁺ ions with magnetic moments of 2µ_B/Ru⁵⁺ and 0.9µ_B/Ru⁴⁺. The estimated ratio of Ru⁵⁺:Ru⁴⁺≈ 87%:13% corresponds to a hole concentration p≈0.065 in the CuO₂ planes suggesting an underdoped nature of the superconducting state. We propose that the magnetic structure of the Ru moments corresponds to an antiferromagnetic phase, involving only Ru⁵⁺ ions, interrupted by ferromagnetic stripes, where charge transfer between Ru⁴⁺and Ru⁵⁺ ions takes place.

The formation of Ti2AlN by solid state reaction between layers of wurtzite-AlN and alpha-Ti was characterized by in situ x-ray scattering. The sequential deposition of these layers by dual magnetron sputtering onto Al2O3 (0001) at 200°C yielded smooth, heteroepitaxial (0001) oriented films, with abrupt AlN/Ti interfaces as shown by x-ray reflectivity and Rutherford backscattering spectroscopy. Annealing at 400°C led to AlN decomposition and diffusion of released Al and N into the Ti layers, with formation of Ti3AlN. Further annealing at 500°C resulted in a phase transformation into Ti2AlN(0001) after only 5 min.

The capabilities of plasma doping (PLAD) and flash lamp annealing (FLA) for use in ultra-shallow junction (USJ) fabrication have been evaluated. Silicon wafers have been doped in a BF3 plasma using wafer biases ranging from 0.6 to 1 kV and a dose of 4 × 1015 cm−2. The wafers so implanted have been heat-treated by FLA using pre-heating temperatures in the range of 500–700 °C, peak temperatures of 1100–1350 °C, and effective anneal times of 20 and 3 ms. Secondary ion mass spectrometry (SIMS) and sheet resistance measurements have been undertaken to determine the junction depth and the sheet resistance, respectively. Optimum processing conditions have been identified under which both high electrical activation and insignificant dopant diffusion occur compared to the as-implanted state. In this way, one can obtain combinations of junction depth and sheet resistance that meet the 45 nm technology node requirements.

A growing interest in the development of dual modality PET/CT scanners prompts the comparative study of numerous scintillators to select the best one, which could be used simultaneously in PET detectors working in the pulsing mode and in the CT detectors working in the current mode. In the comparative measurements, done in the same experimental conditions, various samples of BGO, GSO, GSO:Ce,Zr, LGSO, LSO, LYSO, MLS, LaCl3, LaBr3 and CWO scintillators were tested. The measurements covered a determination of the light output, energy resolution, non-proportionality of the light yield, decay times of the light pulses and for the selected crystals their time resolution for 511 keV annihilation quanta. Moreover, a comparative study of afterglow, induced by 60 keV gamma-rays from a strong 241-Am source (13.9 GBq), was done in the second range of time. The LSO-like crystals are best in the PET scanners application. However, they do not fit to the CT requirements, due to a high afterglow. The studies conclude that besides of the well known BGO, only GSO:Ce and most likely LaBr3 might be considered for the simultaneous PET/CT detectors.

The properties of germanium implanted into the SiO2 layers in the vicinity of the bonding interface of silicon-on-insulator structures are studied. It is shown that, under conditions of high-temperature (1100 degrees C) annealing, germanium nanocrystals are not formed, while the implanted Ge atoms segregate at the Si/SiO2 bonding interface. It is established that, in this case, Ge atoms are found at sites that are coherent with the lattice of the top silicon layer. In this situation, the main type of traps is the positive-charge traps; their effect is interpreted in the context of an increase in the surface-state density due to the formation of weaker Ge-O bonds. It is found that the slope of the drain-gate characteristics of the back MIS transistors increases; this increase is attributed to an increased mobility of holes due to the contribution of an intermediate germanium layer formed at the Si/SiO2 interface.

SIMOX (separation by implanted oxygen) process was studied using cross section scanning spreading resistance microscopy (SSRM). Firstly, open volume defects, nanocavities, have been introduced by He+ ion implantation in the region, where SiO2 precipitates were subsequently formed. Secondly, dual (simultaneous) oxygen (O+) and silicon (Si+) implantation was used to modify SiO2 reaction kinetics too. The results show that the He-induced nanocavities enhance the SiO2 formation presumably releasing excess strain associated with Si oxidation, while the use of a dual O+/Si+ beam do not influence significantly the oxidation kinetics in the initial state of the SIMOX process in our samples. Overall, SSRM was shown to be a suitable method for observation of the early stage of buried oxide formation in Si, since it measures the local resistivity, the main functional parameter of a SIMOX structure.

We present an investigation of magnetic ordering in the two-dimensional S=1/2 quantum magnet Cu(Pz)₂(ClO)₄)₂ using specific heat and zero-field muon-spin relaxation (µ+SR). The magnetic contribution to the specific heat is consistent with an exchange strength of 17.7(3) K. We find unambiguous evidence for a transition to a state of three-dimensional long-range order below a critical temperature T_N=4.21(1) K using µ+SR even though there is no feature in the specific heat at that temperature. The absence of a specific heat anomaly at T_N is consistent with recent theoretical predictions. The ratio of T_N/J=0.24 corresponds to a ratio of intralayer to interlayer exchange constants of |J´ /J| =6.8x10⁻⁴, indicative of excellent two-dimensional isolation. The scaled magnetic specific heat of [Cu(Pz)₂(HF₂)]BF₄, a compound with an analogous structure, is very similar to that of Cu(Pz)₂(ClO)₄)₂ although both differ slightly from the predicted value for an ideal 2D S=1/2 Heisenberg antiferromagnet.

Low-temperature ESR studies of copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and the Dzyaloshinskii–Moriya interaction, are presented. The ESR linewidth and g-factor shift are investigated as function of temperature. The data are interpreted in frame of a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82 (1999) 5136] and applied for precise calculations of the ESR parameters in S ¼ 1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained.

BaCuSi₂O₆ can be regarded as an almost ideal realization of an S = 1/2 system of weakly interacting spin dimers with spin-singlet ground state and gapped excitation spectrum. We argue that the fine structure observed in low-temperature EPR spectra of BaCuSi₂O₆ is a fingerprint of triplet excitations (excitons). Analyzing the angular dependence of the exciton modes allows us to precisely calculate the zero-field splitting within the triplet states and, correspondingly, the anisotropy parameter, D = 0.07cm^-1. The proposed procedure can be applied for studying anisotropy effects in a large number of S = 1/2 gapped quantum antiferromagnets with dimerized or alternating spin structure.

A nonconventional x-ray source based on the production of electron channeling radiation in a diamond crystal has been installed at the Radiation source ELBE. The brilliant electron beam with an average current up to 100 microA available in the radiation physics cave allows to reach photon rates of quasi-monochromatic channeling radiation of the order of 10^(11) s^(-1) per 10% bandwidth. On-line x-ray monitoring was realised using a Compton spectrometer. The photon energy can be tuned by variation of the beam energy. Monochromisation of channeling radiation and bremsstrahlung background reduction have been investigated applying x-ray diffraction on a HOPG crystal.

We report on the Fermi surface in the correlated half-Heusler compounds Ce1xLaxBiPt. In CeBiPt, as well as in Ce0:95La0:05BiPt, we find a temperature-dependent Fermi-surface topology. In addition, we observe a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above 25 T, in a simple one band picture, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikov-de Haas (SdH) signal disappears at the same field. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4f electrons. Electronic band–structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.

In this short review some basic concepts of phase transitions at non-zero and zero temperature are highlighted. For that the critical behavior of classical, thermodynamically driven magnetic phase transitions is exemplified for conventional universality classes as well as for systems reflecting chiral order. Finally the quantum critical phenomena for two magnetic-field-driven phase transitions are presented.

Interlayer-resistivity measurements have been performed on a variety of single crystals of the quasi-two-dimensional organic superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br. These crystals, which have been synthesized along two somewhat different routes, reveal strongly sample-dependent resistivity profiles: while the majority of samples shows a more or less pronounced r(T) maximum around 90 K with a semiconducting behaviour above, some crystals remain metallic at all temperatures T 300 K. In the absence of significant differences in the crystals’ structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis [C. Strack et al., Phys. Rev. B 72 (2005) 054511], these results indicate that real structure phenomena, i.e. disorder and/or defects, may strongly affect the inelastic scattering. Comparative resistivity measurements under He-gas pressure on two crystals with strongly differing r(T) profiles indicate that these additional, sample-dependent scattering contributions are characterized by an extraordinarily strong pressure response which is highly non-monotonous as a function of temperature. No correlations have been found between the strength of these scattering contributions and other characteristic properties such as the glass transition at Tg ¼ 77 K, the temperature T*z40 K, where the temperature dependence of the resistivity changes rather abruptly, or the superconducting transition temperature Tc.

Based on the identification of actin as a target protein for the flavonol quercetin, the binding affinities of quercetin and structurally related flavonoids were determined by flavonoid-dependent quenching of tryptophan fluorescence from actin. Irrespective of differences in the hydroxyl pattern, similar Kd values in the 20 µM range were observed for six flavonoids encompassing members of the flavonol, isoflavone, flavanone, and flavane group. The potential biological relevance of the flavonoid/actin interaction in the cytoplasm and the nucleus was addressed using an actin polymerization and a transcription assay, respectively. In contrast to the similar binding affinities, the flavonoids exert distinct and partially opposing biological effects: while flavonols inhibit actin functions, the structurally related flavane epigallocatechin promotes actin activity in both test systems. Infrared spectroscopic evidence reveals flavonoid-specific conformational changes in actin which may mediate the different biological effects. Docking studies provide models of flavonoid binding to the known small molecule-binding sites in actin. Among these, the mostly hydrophobic tetramethylrhodamine-binding site is a prime candidate for flavonoid binding and rationalizes the high efficiency of quenching of the two closely located fluorescent tryptophans. The experimental and theoretical data consistently indicate the importance of hydrophobic, rather than H-bond-mediated actin-flavonoid interactions. Depending on the rigidity of the flavonoid structures, different functionally relevant conformational changes are evoked through an induced fit.

Oscillating Lorentz forces are used to control transition in a flat-plate boundary layer.

Oscillating Lorentz forces are used to control the development of Tollmien-Schlichting waves in a flat-plate boundary layer

Lorentz forces originating from surface-mounted actuators of permanent magnets and electrodes in weakly conducting fluids like seawater provide a convenient tool for separation control at hydrofoils. A well-known actuator design of alternating stripes of permanent magnets and externally fed electrodes is considered which creates a mainly streamwise Lorentz force that is exponentially decaying in wall-normal direction. Separation control by steady forcing at the suction side and by oscillatory forcing near the leading edge of a symmetric foil is investigated numerically, mostly in the post-stall regime. The results are based on direct numerical simulations in the laminar flow regime in order to reveal basic control phenomena as well as on simulations using turbulence modelling at higher Reynolds numbers which are closer to possible naval application.
By applying a strong enough steady control, separation can always be completely suppressed. The scaling behaviour of the maximum lift gain Delta C_L^{max} in the turbulent regime nicely agrees with experimental results. - Oscillatory forcing always has to compete with the natural shedding process, lock-in behavior may occur. Lift-optimum control for strong amplitudes is found in a frequency band around the natural shedding frequency. In terms of the momentum coefficient describing the control effort, appropriate excitation frequencies in relation to the natural vortex shedding frequency allow for a more effective lift control than steady forcing for small lift gains; for large lift enhancement the energetic effort seems to approach the level of steady control.

A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. Simulating a poly-dispersed gaseous liquid two phase flow along with the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation and the momentum exchange of bubble size dependent bubble forces have to be considered. Particularly the lift force has been proved to play an important role establishing a certain flow regime.
The derived model has been validated against experimental data from the TOPFLOW test facility at the Forschungszentrum Dresden (FZD). The wire mesh measuring technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid was applied. Numerous tests investigating air water flow and steam water flow at saturation conditions in vertical pipes having a length up to 8 m and a diameter up to 200 mm were performed and used for model validation. To check the model framework for a more complex flow situation in further experiments on the flow field around a half moon shaped asymmetric obstacle were performed and simulated by applying the inhomogeneous MUSIG model.
The paper describes the main concepts of the model approach and presents model validation and application cases. The inhomogeneous MUSIG model approach was shown to be able to describe of bubbly flow with higher gas content. Particularly the separation phenomenon of small and large bubbles which was proven to be a key phenomenon for the establishment of the corresponding flow regime is well described. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated.

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

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

This study, carried out at Institut de Radioprotection et de Sûreté Nucléaire, concerns the model of a polydispersed bubble population in the frame of an ensemble averaged two-phase flow formulation. We consider the ability of the moment density approach, e.g. Kamp et al. (2001), to represent bubble population size distribution within a multi-dimensional CFD code based on the two-fluid model. Special attention is given to the closure issue of the method. We consider in particular the influence of the polydispersion on (i) coalescence and break-up phenomena and on (ii) momentum inter-phase transfers related to drag and lift forces. A first approach formulation is developed allowing to represent a full spectrum of bubble size with a very reduced number of parameters. The latter property constitutes one of the main advantages of the moment density method with regard to alternative methods for polydispersion representation like population balance. The system of transport equations and corresponding main closure terms are derived in the case of adiabatic flows with spherical bubbles of an incompressible fluid that is immiscible in the continuous phase. Air-water polydispersed bubbly flows in a vertical pipe with obstacle of the TOPFLOW experiments series performed at FZD, e.g. Prasser et al. (2006), are then used as simulations test cases. The numerical results, obtained with NEPTUNE_CFD, e.g. Guelfi et al. (2005), allow to attest the validity of the approach. Perspectives concerning the improvement of the model, its validation, as well as the extension of its applicability range are discussed.

A numerical investigation of insulation debris transport and sedimentation is being performed as part of a joint research project with the Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau. The study considers the impact of the transport of insulation wool debris on the long-term behaviour of emergency core coolant systems during all types of LOCA that occur in PWR and BWR. In order to implement models into computational fluid dynamic codes (CFD), the models that characterize insulation debris (particle buoyancy, drag, turbulent dispersion and the fluid-particle mixture viscosity) must be tested. Experimental investigations are being performed at the IPM-Zittau to provide detailed information with which the numerical models can be validated.

The transport of mineral wool insulation debris, which is generated during all types of loss of coolant accidents (LOCA) could impede the long-term operation of emergency core coolant systems (ECCS) in nuclear power plants. Therefore, a combined experimental and numerical investigation of mineral wool fibers is being pursued to improve the understanding of how ECCS can be undermined by the transport, sedimentation and resuspension of mineral wool fibers.
The application of the Eulerian-Eulerian multiphase flow model to the transport of the fibers is discussed here with regard to the transport of fibers in a racetrack type channel. The study examines the application of closure models such as the Favre-Averaged turbulence dispersion force and the mixture viscosity and the impact that they have on fiber transport. The intention of the study is to aid the experimental part of the study by determining which parameters influence the particle forces and which conditions can be used in analyzing the parameters for further model development and evaluation. The phenomena observed in the calculations correspond qualitatively to preliminary experimental observations.

A population balance model was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10 (Frank et al. 2005, Krepper et al. 2007). The current paper presents the application of the model to upward flow in vertical pipes for air/water and for steam/water bubbly flow. Finally the application to a bubbly flow around a half moon shaped obstacle arranged in a 200 mm pipe is shown (see Frank et al. 2007).
Applying the inhomogeneous MUSIG approach a more deep understanding of the flow structure is possible. For upward two phase flow in vertical pipes the core peak in the cross sectional gas fraction distribution could be reproduced very well. For complex flows the general structure of the flow could be well reproduced in the simulations. This test case of the obstacle demonstrates the complicated relationship between size dependent bubble migration and bubble coalescence and break-up effects for real flows. While the closure models for bubble forces, which are responsible for the simulation of bubble migration are in agreement with the experimental observations, clear deviations occur for bubble coalescence and fragmentation. The presently applied models describing bubble fragmentation and coalescence could be proved as weak points in numerous CFD analyses of vertical upward two phase pipe flow. Further work on this topic is considered for future investigations.