Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Energy and polarization dependent Diffraction Anomalous Fine Structure (DAFS) also known as Anisotropic Anomalous Scattering (AAS) can be employed in addition to X-ray Absorption Fine Structure (XAFS) to study electronic transitions from core states to unoccupied states. Here, we present results from resonant X-ray diffraction experiments on TiO2 rutile, space group (136) P42/mnm. For this model structure, site symmetry information was extracted from determination of the structure factor tensor by refining elements of Ti atomic scattering factor tensors. Influences of oxygen vacancies on the anomalous scattering contributions have been studied on a series of rutile wafers of different oxygen concentration. Samples investigated were 10 × 10 × 1 mm³ single crystal wafers and experiments were carried out at DESY/HASYLAB beamlines C and E2 using a Si (111) double crystal monochromator in the vicinity of the Ti-K absorption edge. Considered reflections include the ‘forbidden’ 001 and allowed 111 reflection.

Strontium titanate (SrTiO3) is an oxide crystallizing with cubic perovskite-type of structure that exhibits a high tunability of dielectric, electric, mechanical and optical properties by means of defects. Apart from dopants, also intrinsic oxygen vacancies or ordered stacking faults, e.g. Ruddlesden-Popper (RP) phases SrO(SrTiO3)n, may influence these properties.
We have investigated the surface energy, relaxation and electronic properties of such RP surfaces up to n = 3 in comparison to ’pure’ SrTiO3 by means of density-functional theory for ⟨ 001⟩ and ⟨ 100⟩ directions and with all possible perfect crystal terminations. We find a significant influence of the surface-near SrO-OSr stacking fault on surface energies and rumpling. Migrating surface states decrease the band gap of TiO2 terminations but all terminations show insulating character. A detailed discussion of surface-near relaxations will be presented.

In coordination chemistry, the nature and strength of the metal-ligand interaction has attracted much interest. Metal-sulfur complexes, in particular in comparison with their oxygen-based analogues, are intriguing as the sulfur atoms are polarized more easily. The use of specifically tailored sulfur-based ligands allows for tuning the complex functional properties. Among them, electronic properties are very sensitive to changes in the sulfur coordination sphere, suggesting potential uses as molecular switches in optoelectronic devices. Metal dithiocarbamates [R2NCS2]lM have been extensively studied by IR and UV-vis. spectroscopy, ESR and to a limited extent XPS and UPS. Here, we present experimental and theoretical studies investigating the electronic properties of a series of dithiocarbamates of Pd(II) and Pt(II): the pyrrolidine-based one and the 1-pyrrolidinecarbodithioate methyl ester (PyDTM). MX2(PyDTM) (M=Pt/Pd; X=Cl/Br) were analyzed by XPS and by FT-IR spectroscopy. DFT calculations yielded details on the electronic structure and allowed for unambiguous assignment of the IR spectral features. Ionization energies were evaluated with the asymptotically correct LB94 potential and the two components ZORA.

The influence of helium on the mechanical properties of reduced-activation ferritic/martensitic Cr-steels under fusion-relevant irradiation conditions is still a concern. While the fact that He can influence the mechanical properties is well established [1,2], the underlying mechanisms are not fully understood [1,2]. In this work the effect of He and displacements per atom (dpa) on the irradiation-induced hardening of Eurofer97 at 300°C was studied. Self-ion irradiation was applied to simulate the neutron-irradiation-induced damage. Helium was implanted prior to (pre-implantation), simultaneously (dual-beam irradiation) or following the (post-implantation) self-ion irradiation to investigate the He effect. Nanoindentation was used in order to characterize the damage layer. Under the present conditions (300°C, 1 dpa, 10 appmHe) the observed hardening increased in the following order: single-beam Fe-ion irradiation/pre-implantation < simultaneous implantation < post-implantation. We conclude, that there is a significant interaction between damage and He.
Additionally, Eurofer97 and ODS-Eurofer were irradiated with Fe ions up to 1 and 10 dpa to study the effect of the oxide particles on the irradiation-induced hardening. We have found a higher irradiation-induced hardening at 1 dpa for ODS-Eurofer but a steeper hardness increase per dpa up to 10 dpa for Eurofer97.

Hyperon production in the threshold region was studied in the reaction pp -> K+ Lambda p using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the three different beam momenta of pbeam = 2.95, 3.20 and 3.30GeV/c, corresponding to excess energies of epsilon = 204, 285 and 316MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9 ± 0.8 ± 2.0 μb, 28.4 ± 1.3 ± 2.2 μb and 35.0 ± 1.3 ± 3.0 μb. Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N(1650)-resonance at pbeam = 2.95GeV/c, whereas for the higher momenta an increasing relative contribution of the N(1710)- and/or of the N(1720)- resonance was observed. In addition, the p Lambda-final-state interaction turned out to have a significant influence on the Dalitz plot distribution

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW caldera and cone sites, whose geology, permeability, vent fluid compositions, mineralogy and ore forming conditions are in stark contrast to each other. The NW caldera site strikes for ~600 m in a SW-NE direction with chimneys occurring over a ~145 m depth interval, between ~1,690 and 1,545 m. At least 100 dead and active sulfide chimney spires occur in this field, as seen during manned submersible dives, and are typically 2-3 m in height, although locally reach 6-7 m. Their ages fall into three groups: 0-4 years (at time of sampling), 23 and 35 years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. More rare are massive sulfide crusts up to 2-3 m thick. Two main types of chimney predominate: Cu-rich chimneys (with parts up to 28.5 wt.% Cu) and more commonly, Zn-rich chimneys (up to 43.8 wt.% Zn). Geochemical results indicate a "magmatic" suite of elements associated with the Cu mineralization, including up to 91 ppm Au, and an ‘epithermal’ suite of elements with the dominant Zn-rich chimneys. The cone site comprises the Upper cone site atop the summit of the recent (main) dacite cone, and the Lower cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower cone site, in complete contrast to venting at both the Upper cone and NW caldera sites. Individual vents are marked by low relief (≤0.5 m) mounds comprised predominately of native sulfur with bacterial mats. Vent fluids of the NW caldera field are focused, hot (≤300°C), acidic (pH ≥ 2.8), metal-rich and relatively gas-poor. Calculated end-member fluids from various NW caldera vents indicate phase-separation has occurred with Cl values ranging from 93% to 137% seawater values. By contrast, vent fluids for the cone site are diffuse, noticeably cooler (≤122°C), very acidic (to pH = 1.86), relatively metal-poor and very gas-rich. Higher-than-seawater values of SO4 and Mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Three year old Fe-oxide crusts covering the main cone summit appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO2 (e.g., 206 mM/kg at the cone site), high CO2/³He values, negative δD and δ18OH2O values for vent fluids, negative δ34S values for sulfides (to -4.6‰), sulfur (to -10.2‰) and δ15N2 (to -3.5‰), vent fluid pH values to -1.9 and mineral assemblages of chalcopyrite, bornite, chalcocite, covelllite and euhedral grains of hematite. Changing physio-chemical conditions at the Brothers hydrothermal system, and especially the cone site, occur over months to hundreds of years, as shown by interlayed Cu/Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions between vents, similar shifts in 3He/4He values for both cone and NW caldera sites, and overprinting of "magmatic" mineral assemblages by water/rock dominated ones. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (~2.5 km long), narrow (~300 m diameter) "pipes", consistent with evidence of vent fluids forming at higher than hydrostatic pressures, at relatively shallow depths. The NW caldera and cone sites are considered to represent stages along a continuum between magmatic-hydrothermal and water/rock-dominated end-members.

Eine Übersicht über das Forschungszentrum und die Abteilung Magnetohydrodynamik soll die Zuhörer auf die Aufgaben für die Prozessautomation in der Forschung einstimmen. Die Prozessautomation bei Modellexperimenten mit Flüssigmetallen ist mannigfaltig und weicht durch die Versuchsanordnung stark von einer industriellen Prozessautomation ab. Hardwareseitig werden PC's und ADSP Systeme eingesetzt. Angepasst an vorhandenes Know-How werden die Systeme mit Fortran, C++, LabView und AdBasic programmiert. Anhand des Rigaer Dynamo Experimentes, der kontaklosen Strömungstomografie (CIFT) und der Strangguss-Modellanlage (LIMMCAST) wird der Herangehensweise und Ergebnisse erleutert.

In nanostructured materials spatial confinement effects lead to structure-dependent deviations from the bulk transport properties. Such modifications may in part be accounted for by classical transport simulations, but a microscopically more detailed and mostly parameter-free picture is obtained from quantum-mechanical density-functional theory (DFT). DFT calculations yield the atom arrangement and electronic structure of nanotubes and nanowires in the electronic ground state. Additionally, an extension by a Green’s function formalism leads to the determination and analysis of electronic transport through contacted nanostructures. A combination of both approaches allows to correlate structural and transport properties of nanostructures. The applicability of this approach will be demonstrated for a mechanically triggered metal-insulator transition in nanowires.
Kibsgaard et al. Nano Lett 8 (2008) 3928; [2] Popov et al. Nano Lett 8 (2008) 4093.

Brine channels are formed in sea ice under certain constraints and represent a habitat of different microorganisms. The complex system depends on a number of various quantities as salinity, density, pH-value or temperature. Each quantity governs the process of brine channel formation. There exists a strong link between bulk salinity and the presence of brine drainage channels in growing ice with respect to both the horizontal and vertical planes. We develop a suitable phenomenological model for the formation of brine channels both referring to the Ginzburg-Landau-theory of phase transitions as well as to the chemical basis of morphogenesis according to Turing. It is possible to conclude from the critical wavenumber on the size of the structure and the critical parameters. The theoretically deduced transition rates have the same magnitude as the experimental values. The model creates channels of similar size as observed experimentally. An extension of the model towards channels with different sizes is possible. The microstructure of ice determines the albedo feedback and plays therefore an important role for large-scale global circulation models (GCMs).

Thermodynamic equilibration of complex systems like spin glasses or (degenerate) anisotropic spin crystals by numerical methods can be challenging due to the presence of multiple minima on the potential energy surface. This problem becomes pronounced especially at low temperature, where the system remains mainly in few states. We employ the anisotropic Heisenberg model in two dimensions to simulate and analyze the domain formation and the domain structure of multiferroic oxides. In particular, we discuss various techniques to improve the low-temperature equilibration behavior by means of a trigonal antiferromagnet with single-ion anisotropy. Furthermore, we present a localized sampling method for the Metropolis algorithm, which increases the acceptance ratio significantly.

A systematic study of the production of omega-mesons in proton-proton-collisions was carried out in a kinematically complete experiment at three excess energies (epsilon= 92, 128, 173 MeV). Both protons were detected using the large-acceptance COSY-TOF spectrometer at an external beam line at the Cooler Synchrotron COSY at Forschungszentrum J¨ulich. The total cross section, angular distributions of both omega-mesons and protons were measured and presented in various reference frames such as the overall CMS, helicity and Jackson frame. In addition, the orientation of the omega-spin and invariant mass spectra were determined. We observe !-production to take place dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and, additionally, in Sd at epsilon = 173 MeV. No obvious indication of resonant omega-production via N*- resonances was found, as proton angular distributions are almost isotropic and invariant mass spectra are compatible with phase space distributions. A dominant role of 3P1 and 1S0 initial partial waves for omega-production was concluded from the orientation of the decay plane of the !-meson. Although the Jackson angle distributions in the omega-p-Jackson frame are anisotropic we argue that this is not an indication of a resonance but rather a kinematical effect reflecting the anisotropy of the omega angular distribution. The helicity angle distribution in the omega-p-helicity frame shows an anisotropy which probably reflects effects of the omega angular momenta in the final state; this observable may be, in addition to the orientation of the omega decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.

A series of complexes of formula Tp(R,R')CoL, where Tp(R,R'-) = hydrotris(3-R,5-R'-pyrazol-1-yl)borate ("scorpionate") anion (R = tert-butyl, R' = H, Me, 2'-thienyl (Tn), L = Cl-, NCS-, NCO-, N-3(-)), has been characterized by electronic absorption spectroscopy in the visible and near-infrared (near-IR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR). Reported here are also crystal structures of seven members of the series that have not been reported previously: R' = H, L = NCO-, N-3(-); R' = Me, L = Cl-, NCS-, NCO-, N-3(-); R' = Tn, L = Cl-, NCS-. These include a structure for Tp(t-Bu,me)CoCl different from that previously reported. All of the investigated complexes contain a four-coordinate cobalt(II) ion (3d(7)) with approximate C-3v point group symmetry about the metal ion and exhibit an S = 3/2 high-spin ground state. The use of HFEPR allows extraction of the full set of intrinsic S = 3/2 spin Hamiltonian parameters (D, E, and g values)!The axial zero-field splitting parameter, D, for all investigated Tp(R,R')CoL complexes is always positive, a fact not easily determined by other methods. However, the magnitude of this parameter varies widely: 2.4 cm(-1)<= D<= 12.7 cm(-1), indicating the extreme sensitivity of this parameter to environment. The spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-near-IR spectra to yield ligand-field parameters for these complexes following the angular overlap model (AOM). This description of electronic structure and bonding in pseudotetrahedral cobalt(II) complexes can enhance the understanding of similar sites in metalloproteins, specifically cobalt-substituted zinc enzymes.

Defects in a nitrogen implanted and thermally annealed zinc oxide thin film (n-type conducting) and reference samples were studied. Space charge regions realised by fabrication of semitransparent palladium Schottky contacts enabled the application of capacitance spectroscopic methods and photo - current measurements. We report on the formation of a deep level, in the following labelled TN1. It is 580 meV below the conduction band edge, probably related to nitrogen, and must be distinguished from the well known intrinsic deep level E4 at almost equal energetical depth. Capacitance measurements in combination with optical excitation, conducted at different temperatures, as well as photo-current measurements revealed the existence of two states approximately 60 meV and 100 meV above the valence band edge for the nitrogen implanted sample. These states cause an acceptor compensation degree larger than 0.9. The thermal emission of holes from these states into the valence band was observed by optical deep level transient spectroscopy.

This paper considers three variants of MHD induction pumps a centrifugal magnetovortex pump, a transformer type pump with magnetic asymmetry and a travelling field pump All these pumps have a flat channel placed between the poles of one or several ferromagnetic cores inducing an alternating magnetic field directed normally to the channel plane To describe electromagnetic forces generated in the pump channel, a mathematical model is proposed The results of numerical and physical experiments ale presented.

Recently, research on diluted magnetic semiconductors (DMS) became very popular due to their large potential in future spintronics devices like spin valves or current-induced magnetic switches. Mostly, transition metal doped classical semiconductors like Si, Ge or GaAs as well as oxides have been investigated. The research faces, however, serious difficulties due to the appearance of tiny magnetic secondary phases, spinodal decomposition or magnetically active defects in the semiconductor induced by the implantation/oversaturation. It was found that those effects lead to ferromagnetic as well as magneto-transport properties which, by mistake, could be interpreted as intrinsic DMS. In this paper, I will focus on the discussion of pitfalls during magnetic and structural analysis, especially on element-specific analysis methods for the identification of the source of the ferromagnetic signal. Moreover, possibilities to overcome those difficulties will be presented.

Durch den Uranbergbau entstanden in Sachsen und Thüringen eine Vielzahl von Gruben, Abfallhalden und Absetzanlagen, aus denen beispielsweise über Sickerwasser das Schwermetall in die Umwelt gelangen konnte. Böden wurden kontaminiert und das Actinoid kann von Pflanzen aufgenommen werden. Um Erkenntnisse über die Migration und Wirkung des Urans gewinnen zu können, ist es notwendig die Wechselwirkung mit einzelnen Pflanzenstoffen zu untersuchen.
Im Mittelpunkt dieser Arbeit stand die Untersuchung von in vitro-Wechselwirkungen des in Pflanzen weitverbreiteten Flavonoids Quercetin mit Uranverbindungen. Insbesondere sollte überprüft werden, ob eine Reduktion des Uranyl zu Uran(IV) stattfindet. Im Allgemeinen besitzt vierwertiges Uran gegenüber dem sechswertigen Uran eine sehr geringe Löslichkeit, dies führt zu einer Immobilisierung des Urans.
Zur Charakterisierung des Reduktionsvermögens wurde das Redoxpotential des Polyphenols in Abhängigkeit vom pH-Wert in dem für die nachfolgenden Versuche verwendeten Lösungsmittel (50 % Methanol) bestimmt. Hierbei wurde ein linearer Zusammenhang zwischen pH 3,3 und 8,3 festgestellt: E = (-69 ± 3) mV * pH + (616 ± 7) mV bestimmt gegen Silber-Silberchlorid-Elektrode. Somit weist Quercetin bei steigendem pH-Wert ein zunehmendes Reduktionsvermögen auf.
Es erfolgte zudem die Bestimmung der Stabilitätskonstante des Komplexes zwischen Uran(IV) und Quercetin bei einem pH-Wert von 5,8 in 50 % Methanol im carbonatfreien System unter Inertgasbedingungen (Modellkomplexierung). Die Stabilitätskonstante wurde mittels UV/Vis-Spektroskopie zu log10β1:3:1 = 20,36 ± 0,18 bestimmt. Durch diese starke Komplexbildung wird auch die Löslichkeit der sonst schwerer löslichen Uran(IV)-Spezies erhöht. Dieser Komplex ist zudem stabiler als der Uranyl-Quercetin-Komplex (log10β1:3:1 = 13,8 [1]). Dies bedeutet, dass durch die Komplexbildung eine Erhöhung des Redoxpotentials des Redoxpaares U(VI)│U(IV) vorliegt und somit bei der Koordination des Uranyls mit Quercetin eine Reduktion des Metall-Ions leichter möglich ist.
Es galt weiterhin zu prüfen, ob ein Redoxprozess zwischen Quercetin und Uranyl in vitro bei pH 5,8 bzw. pH 7,0 in 50 % Methanol unter Inertgasbedingungen stattfindet. Eine Reduktion des Uranyl-Ions führt zur Bildung von Uran(IV), der stabilsten reduzierten Oxidationsstufe des Urans. Vierwertiges Uran konnte mittels laserinduzierter photoakustischer Spektroskopie (LIPAS), durch die Komplexbildung mit Arsenazo III bzw. durch die Extraktion mit 2-Thenoyltrifluoraceton (TTA) nachgewiesen werden. Es wurde mithilfe der genannten Methoden bestimmt, dass der Umsatz von Uranyl zu Uran(IV) durch das Reduktionsmittel Quercetin im Prozentbereich liegt.

[1] Viehweger, K. & Geipel, G. (2009) Report FZD-511 p. 41

In this work we report on the synthesis of Ni:SiO2 nanogranular films with different metal fraction 0.10 < x < 0.68 and a homogeneous distribution of Ni particles by atom beam sputtering technique and on the study of their microstructure, electrical transport, magnetic properties, and on the observation of extraordinary Hall effect (EHE). Films with the Ni fraction x above percolation threshold x > 0.58 > xp as revealed by resistivity versus temperature measurements have a large Ni particle size, pronounced ferromagnetic characteristics, and appreciable extraordinary Hall resistivity at 300 K. Furthermore, films above percolation have a relatively low, nearly temperature independent Ohmic resistivity smaller than 10E−3 Ohm cm and may be useful for Hall sensor applications. On the other hand, films below percolation threshold x < 0.54 < xp have a small Ni particle size, superparamagnetic behavior, and do not show EHE at 300 K. However, at 5 K all films show ferromagnetic characteristics with an enhanced EHE.

The static and time-dependent magnetic properties of Bi(Fe0.95Co0.05)O3 have been investigated by dc and ac magnetization measurements. Cluster spin glass has been confirmed to be the ground state due to the frustration of the interaction between the ferromagnetic clusters by canted antiferromagnetically arranged Fe spins (Tc > 350 K) and by ferrimagnetically arranged Co and Fe spins (Tc ~ 250 K). Two freezing temperatures Tf of about 260 K and 100 K have been clearly identified from the abrupt change in magnetization relaxation. The higher Tf is related to the canted antiferromagnetically arranged Fe spins, and the lower Tf is related to the ferrimagnetically arranged Co and Fe spins. The cluster spin glass behavior with two freezing temperatures has been confirmed by ac susceptibility measurements.

In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 10¹⁸ to 2.1$\times$10²⁰ cm^-3, the latter being the highest reported so far. Based on the magneto-transport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.

We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by pulsed laser annealing. Benefiting from the short time annealing, the hole concentration in Mn-implanted Ge has been increased by two orders of magnitude from 10¹⁸ to over 10²⁰ cm⁻³. Likely due to the high hole concentration, we observe that the longitudinal and Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated ferromagnetism.

The nucleus ¹⁸⁷ Ir has been populated up to high spin using the reaction ¹⁸⁶ W(7 Li, 6n) at a beam energy of 59 MeV. A comprehensive extension of its level scheme has been proposed comprising 116 newly established excited states connected by 194 transitions which have been observed for the first time. All known rotational bands have been extended up to higher spin and in particular the band crossing region of the h9/2 band has been revised. A number of new intrinsic high-K states has been identified and for some of them multi-quasiparticle configurations have been tentatively assigned. The three-quasiparticle state with spin 29/2- and an excitation energy of 2487 keV is isomeric with a half-live of T_1/2 = 1.8(5) µs. On top of this state a rich level scheme reaching up to spin (59/2-) and excitation energies around 7 MeV has been established. Of particular interest is a new structure built on the 31/2-, maximum spin three-quasiparticle state with {11/2-[505]} {11/2+[615],9/2+[624]} configuration at 2755 keV. Arguments have been presented which indicate a vibrational character of these states similar to the proposed vibration-plus-quasiparticle coupling suggested for the structure built on the 11/2- h11/2 proton 1qp state.

In dieser Arbeit wird die Wirkung des elektromagnetischen Rührens der Restschmelze bei der gerichteten Erstarrung einer Al-Si-Legierung untersucht. Dabei werden neue Methoden zum elektromagnetischen Rühren unter Nutzung eines zeitlich modulierten rotierenden Magnetfeldes (RMF) und eines wandernden Magnetfeldes (TMF) vorgestellt. Beim elektromagnetischen Rühren mit kontinuierlich wirkenden Feldern treten oft strömungsinduzierte Entmischungen im Gefüge auf. Mit der Strategie der Nutzung zeitmodulierter Felder sollen diese bekannten Nachteile vermieden werden. Die Ergebnisse zeigen, dass das Rühren unter Anwendung eines modulierten magnetischen Feldes Möglichkeiten zur effizienten Kontrolle des Strömungsfeldes vor der Erstarrungsfront bietet.

Der Einsatz elektromagnetischer Felder zum Rühren metallischer Schmelzen stellt eine elegante Möglichkeit einer völlig kontaktlosen Strömungskontrolle in erstarrenden Metalllegierungen dar, wobei die Strömungsintensität über die elektrischen Regelgrößen Strom und Frequenz gesteuert werden kann.
Trotz der nachweislichen Verbesserung der Gefügeeigenschaften, wie Kornfeinung und Vergrößerung des equiaxialen Erstarrungsbereiches durch eine intensive Strömung im Bereich der Erstarrungsfront, ist der Einsatz des elektromagnetischen Rührens auch problembehaftet, da die Strömung negative Auswirkungen wie strömungsinduzierte Porosität oder Gefügeinhomogenitäten (z. B. weiße Bänder beim Stahlguss) hervorrufen kann. Diese Nachteile erschweren eine industrielle Anwendung des Verfahrens im Strangguss.
Der Einsatz maßgeschneiderter, zeitmodulierter Magnetfelder bietet die Perspektive, die oben genannten, nachteiligen Effekte zu vermeiden. Mit dem Konzept der maßgeschneiderten Magnetfelder werden geeignete Strömungen erzeugt, welche die für die Herausbildung vorteilhafter Gefüge notwendigen Temperatur- und Konzentrationsfelder in der erstarrenden Schmelze liefern. Dies erfordert jedoch ein genaues Verständnis der Wechselwirkung von Magnetfeld, induzierter Strömung und Erstarrungsvorgang.
In diesem Vortrag wird die Wirkung des elektromagnetischen Rührens der Restschmelze mittels zeitmodulierter Magnetfelder bei der gerichteten Erstarrung einer binären Al-Si-Legierung untersucht. Für eine erfolgreiche Anwendung dieses Verfahrens sind geeignete Kombinationen der Magnetfeldparameter zu ermitteln. Zu diesem Zweck wurden Strömungsmessungen in einer isothermen Modellschmelze unter dem Einfluss modulierter Magnetfelder durchgeführt. Aufbauend auf den gewonnenen Erkenntnissen zur zeitlichen Entwicklung der Strömungsstruktur wurden geeignete Strategien für eine gezielte Beeinflussung der Gefügemerkmale durch den Einsatz maßgeschneiderter Magnetfelder abgeleitet. Die Erstarrungsversuche demonstrieren, dass es möglich ist, mit Hilfe zeitmodulierter magnetischer Felder korngefeinte, equiaxiale Gefüge unter Vermeidung der Herausbildung makroskopischer Gefügeinhomogenitäten herzustellen.
Die Ergebnisse veranschaulichen das große Potenzial des elektromagnetischen Rührens zur Verbesserung der Materialeigenschaften der erstarrten Struktur und einer Optimierung der Prozesskontrolle.

In free-electron lasers (FEL) optical gain and stimulated emission are provided by relativistic electrons, wiggling through a periodic magnetic-field arrangement. Since the emitted wavelength only depends on the energy of the electrons and the magnetic field strength, an in principle arbitrary lasing wavelength may be achieved. Thus FELs are mostly used in spectral ranges, where conventional lasers with reasonably high power hardly exist. This is true, among others, for the long-wavelength infrared and terahertz (THz) range and represents the motivation to build such bulky THz sources.

Here I will discuss the operation principle of an FEL and then describe the THz FEL at FZD in Dresden. This FEL, called FELBE, was first operated in 2004 and covers now a wavelength range of nearly two spectral decades (3-300 µm or 1-100 THz). The key feature which distinguishes FELBE from other FEL user facilities is the possibility of delivering a continuous train of (micro)pulses, made possible by the superconducting accelerator cavities. The FEL thus provides picosecond optical pulses at a repetition rate of 13 MHz.

In order to pinpoint interesting scientific experiments using the FEL, one has to focus on its unique features, which are high peak power (up to 1 MW), high average power (tens of Watts), and short pulses (1-20 ps, depending on the wavelength). These features lend themselves to nonlinear optical experiments, near-field microscopy, and time resolved pump-probe studies, respectively. I will present experiments belonging to each of these three classes, namely

(1) pumping the intra-excitonic 1s-2p transition in semiconductor quantum wells, which leads to THz sideband generation and the observation of the AC Stark effect;
(2) near-field micro-spectroscopy of ferroelectrics, which allows imaging of ferroelectric domains in BaTiO3 purely due to their optical contrast resulting from a slight anisotropy of the dielectric function;
(3) carrier relaxation in semiconductor quantum dots. Here the relaxation time varies by three orders of magnitude (2 ps to 1.5 ns), if the energy level spacing is changed by only a factor of two (30 meV to 15 meV).

We report on the generation of impulsive terahertz (THz) radiation with 36 kV/cm vacuum electric field (1.5 mW average thermal power) at 250 kHz repetition rate and a high NIR-to-THz conversion efficiency of 2×10⁻³. This is achieved by photoexciting biased large-area photoconductive emitter with NIR fs pulses of μJ pulse energy. We demonstrate focussing of the THz beam by tailoring the pulse front of the exciting laser beam without any focussing element for the THz beam. A high dynamic range of 104 signal-to-noise is obtained with an amplifier based system.

Biosorption of uranium(VI) by the green alga Chlorella vulgaris was studied at varying uranium concentrations from 5 µM to 1 mM, and in the environmentally relevant pH range of 4.4 to 7.0. Living cells bind in a 0.1 mM uranium solution at pH 4.4 within 5 min 14.3 ± 5.5 mg U/g dry biomass and dead cells 28.3 ± 0.6 mg U/g dry biomass which corresponds to 45% and 90% of total uranium in solution, respectively. During 96 h of incubation with uranium initially living cells died off and with 26.6 ± 2.1 mg U/g dry biomass bound similar amounts of uranium compared to dead cells, binding 27.0 ± 0.7 mg U/g dry biomass. In both cases, these amounts correspond to around 85 % of the initially applied uranium. Interestingly, at a lower and more environmentally relevant uranium concentration of 5 µM, living cells firstly bind with 1.3±0.2 mg U/g dry biomass to 1.4±0.1 mg U/g dry biomass almost all uranium within the first 5 min of incubation. But then algal cells again mobilize up to 80% of the bound uranium during ongoing incubation in the time from 48 h to 96 h. The release of metabolism related substances is suggested to cause this mobilization of uranium. As potential leachates for algal-bound uranium oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound uranium within 24 h. Differences in complexation of uranium by active and inactive algae cells were investigated with a combination of time-resolved laser-induced fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure (EXAFS) spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Obtained results demonstrated an involvement of carboxylic and organic/inorganic phosphate groups in the uranium complexation with varying contributions dependent on cell status, uranium concentration and pH.

In the present study we propose new coalescence and breakup closures for the inhomogeneous MUltiple bubble Size Group (MUSIG) model. The major purpose is to consider bubble coalescence and breakup due to different mechanisms in turbulent gas-liquid mixtures and to develop a generally applicable constitutive model for CFD applications. For bubble coalescence the new model includes coalescence due to turbulence, laminar shear, wake entrainment and eddy capture. Bubble breakup mechanisms encompass turbulent fluctuation, laminar shear and interfacial slip velocity. The new model was implemented in the commercial CFD software (CFX-12.0) and applied to the case of turbulent air-water mixtures in a large vertical pipe (DN200). Simulation results for the evolution of bubble size distributions were compared to the standard closure model of Luo and Svendsen (1996), Prince and Blanch (1990) as well as the experimental data of TOPFLOW test facility. Better prediction is accomplished by the proposed new model.

In poly-disperse bubbly flows, bubble coalescence and breakup are important local events, which determines the evolution of the flow as well as the transition to slug flow. On the other hand side, the characterization of bubble coalescence and breakup is still one weak point in the CFD simulation of poly-disperse bubbly flows, since the transferability of available models is limited. A generalized model was proposed in our previous work, which takes into account all mechanisms of interest for bubble coalescence and breakup. Turbulence is one major mechanism in a turbulent bubbly flow. In other word, the performance of models for bubble coalescence and breakup relies on the accuracy of turbulence modeling. However, two-phase turbulence modeling is still one open issue.

In the current work, air-water bubbly flow in a vertical pipe (DN200) was investigated. The experimental data were obtained from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The inhomogeneous MUSIG approach in CFD code CFX with a new closure model for bubble coalescence and breakup was used for the simulation. Influence of various two-phase turbulence models was studied. The results of bubble size distribution, radial gas volume fraction, air/water axial velocity, Sauter mean bubble diameter as well as turbulent parameters were compared for each model.
In general, a good agreement with the experimental data has been achieved. The new model for bubble coalescence and breakup was shown as capable of predicting the flow evolution. The influence of two-phase turbulence modeling is considerable. Bubble-induced turbulence can be modeled by additional source term for turbulence transport equations instead of additional viscosity term.

Die skalenübergreifende Modellierung der strahleninduzierten Schädigung von RDB-Stahl von den Primärschäden auf der atomaren Skala bis zu den Änderungen der mechanischen Eigenschaften auf der Makroskala trägt wesentlich zu einem ver¬besserten Verständnis des Phänomens der Neutronenversprödung bei. Sie kann sich zukünftig zu einem Bestandteil der Sicherheitsbewertung des RDB entwickeln. Der gewählte zweistufige Modellierungsansatz beruht auf der Kopplung eines ratentheoretischen Moduls zur Voraussage der Größenverteilung der strahlen¬induzierten Defekt-Fremdatom-Cluster mit einem Härtungs-Modul zur Voraussage der strahleninduzierten Streckgrenzenerhöhung. Gegenstand der Untersuchungen sind die Weiterentwicklung und Validierung entsprechender Software-Komponenten. Die Validierung erfolgt durch Gegenüberstellung der Berechnungsergebnisse mit Resultaten von Neutronenkleinwinkelstreumessungen und Zugversuchen an neutronenbestrahlten RDB-Stählen.

Der entwickelte ratentheoretische Modul ermöglicht es, die Größe, Konzentration und Zusammensetzung gemischter Cu-Leerstellen-Cluster über die für RDB-Stähle relevanten Größenbereiche von bis zu 10000 Atomen und Zeitbereiche von bis zu mehreren 10 Jahren zu verfolgen. Die Verbindung der Ratentheorie zur Härtungs¬modellierung beruht auf der Übergabe von berechneten mittleren Hindernis¬abständen und -stärken. Die Validierung der numerischen Werkzeuge hat ergeben, dass wesentliche Tendenzen der strahleninduzierten Streckgrenzenerhöhung von Cu-haltigen und Cu-armen RDB-Stählen richtig wiedergegeben werden. Erste Ansätze zur Erfassung des Einflusses des Legierungselements Nickel im Rahmen der Ratentheorie und der Härtungsmodellierung wurden verwirklicht.

Experiments were done at the TOPFLOW facility of the Forschungszentrum Dresden-Rossendorf to establish a CFD-grade database on the condensation of steam bubbles injected into sub-cooled upwards vertical pipe flow. Bubble condensation has to be considered in Nuclear Reactor Safety Research, e.g. if sub-cooled boiling or bubble entrainment caused by ECC injection occurs. Bubble size distributions are important, since the condensation rate is proportional to the interfacial area density. To develop and validate closure models for CFD codes experimental data with high resolution in space and time are required. The steam was injected via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Pressure, steam and water flow rates and the sub-cooling were also varied. Measurements are done using wire-mesh sensors and thermocouples. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are available.

Pressurized Thermal Shock (PTS) has been identified as one of the most important industrial needs related to nuclear reactor safety. The PTS analysis requires the simulation of the thermal mixing of cold Emergency Core Cooling (ECC) water injected to the cold leg and flowing to the downcomer with the hot coolant, which is present in the primary circuit. The simulation of single-phase and two-phase PTS situations including e.g. stratification of the flow and direct contact condensation is a challenge for CFD methods and requires careful validation against experimental data. In the frame of the NURISP project attempts are made to improve the CFD modelling for two-phase PTS situations. For this purpose, two reference cases with and without mass transfer due the condensation were defined, which are related to the TOPLOW PTS experiments. The present paper focuses on numerical investigations of thermal mixing process in the cold leg and the downcomer using homogeneous and inhomogeneous models for the resolution of momentum equations. Numerical simulations were performed by using the commercial CFD code ANSYS CFX 12.0.

This paper focuses on the evaluation of a multichannel-plate photomultiplier tube (MCP-PMT) as a candidate detector, suitable for positron lifetime studies. Several properties of MCP-PMTs, such as their fast time response, compact size, low susceptibility to magnetic fields, relatively high gain and the low power consumption make them attractive for the positron lifetime spectroscopy. The preliminary tests were performed with the 85001-501 Burle Planacon$^{TM}$ photomultiplier tube assembly. Initial measurements were conducted with a pulsed Picosecond Injection Laser (PiLas) system. The engineering sample of the 85001 exhibits a transit-time-spread (TTS) of 110 ps (FWHM). Further timing experiments showing the suitability of the device as Cherenkov detector are presented. For the first time, a conventional positron lifetime spectrum of Cz-Si probe measured with a spectrometer, where a MCP-PMT detector is incorporated has been demonstrated.

The AMS business is booming: Many low-energy (< 1 MV) facilities, which are fully dedicated for ¹⁴C-analysis, are under construction or in funding status. Additionally, medium-energy accelerators such as the British 5 MV-NEC machine at “SUERC” Glasgow, the French 5 MV-HVEE-machine “ASTER” at Aix-en-Provence [2] and the two German 6 MV-HVEE-machines “DREAMS” at Dresden [3] and “Cologne AMS” at Cologne [4] have been recently installed or are still in testing mode in Central Europe. Of course, these bigger machines need not only experienced physicists and technicians to get them running. It also seems to be advisable to have some experienced scientists around, who knows how to prepare AMS targets for ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, and ¹²⁹I measurements.
In contrast to the ¹⁴C-community, where e.g. round-robin exercises are routine business, the idea of quality assurance and traceable standards has only been brought up lately for the other cosmogenic radionuclides measurable at medium-energy AMS facilities. Thus, world-wide accepted standards issued by metrology institutes are rare: NIST is selling two kinds of ¹²⁹I/¹²⁷I-standards, and the Institute for Reference Materials and Measurements (IRMM) provides one set of ⁴¹Ca/⁴⁰Ca solutions having eight different ratios [5]. Unfortunately, the most commonly used ¹⁰Be/⁹Be standard provided by NIST has been recently sold-out and will not be reissued. Other primary standard-type materials (²⁶Al,³⁶Cl), which are not commercially available, have been prepared by diluting certified activities and subsequent analysis within round-robin exercises [6-8]. After production of big quantities of in-house secondary standards for all nuclides (Tab. 1), cross-calibration versus primary standard-type materials has to be performed [2].

Table 1: Primary and secondary AMS standards in use at ASTER and DREAMS.
Primary standards Secondary (in-house) standards
¹⁰Be NIST SRM 4325 (sold-out) NIST SRM 4325 (ASTER)
¹⁰Be via ⁹Be(n_th,gamma)¹⁰Be (DREAMS)
²⁶Al MB04-A,B,C,D [6] SM-Al-10,11,12,13 [2]
³⁶Cl SM-Cl-11,12,13 [7,8] SM-Cl-11,12,13 [7,8]
⁴¹Ca IRMM ERM^®-AE701 [5] SM-Ca-10,11,12 [2]
--> SM-Ca-P9,11,13 [2]
¹²⁹I NIST SRM 3231, Level II SM-I-9,10,11,12

Finally, as commercial ⁹Be contains intrinsic ¹⁰Be up to a level of 4x10^-14 [9] sophisticated production of in-house carriers, used as machine blanks and for samples, from Be-containing minerals such as Be₂SiO₄ originating from deep mines, is needed. After production and measurement of all these materials, the AMS facility is ready for routine measurements.

Acknowledgments: We are grateful to U. Herpers & E. Strub for providing ²⁶Al-activity, to A. Wallner & M. Bichler for performing the neutron-irradiation of ⁹Be, to C. Varajão for providing Be₂SiO₄ crystals, and to R.C. Finkel, L. Benedetti, W. Möller, HVEE, the FZD-operator- & AMS-team for great cooperation.

References: [1] S. Freeman et al., NIM B 259 (2007) 66. [2] M. Arnold et al., doi: 10.1016/ j.nimb.2010.02.107. [3] Sh. Akhmadaliev et al., this meeting. [4] M. Klein et al., this meeting. [5] C. Hennessy et al., NIM B 229 (2005) 281. [6] S. Merchel, W. Bremser, NIM B 223–224 (2004) 393. [7] S. Merchel et al. Geochim. Cosmochim. Acta 73 (2009) A871. [8] S. Merchel et al., in prep. for NIM B. [9] S. Merchel et al., NIM B 266 (2008) 4921.

Results on Lambda p femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76A~GeV, the reaction Ar+KCl was studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. A high-statistics and high-purity Lambda sample was collected, allowing for the investigation of Lambda p correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the Lambda p emission source. The Lambda p source radius is found slightly smaller than the pp correlation radius for a similar collision system. The present Lambda p radius is significantly smaller than that found for Au+Au/Pb+Pb collisions in the AGS, SPS and RHIC energy domains, but larger than that observed for electroproduction from He. Taking into account all available data, we find the Lambda p source radius to increase almost linearly with the number of participants to the power of one-third.

Die Komplexierung zwischen Uran(VI) und Huminsäure (HA) in Gegenwart von Carbonat wurde mittels abgeschwächter Totalreflexion Fourier-Transform Infrarotspektroskopie (ATR FT-IR) und zeitaufgelöster laserinduzierter Fluoreszenzspektroskopie bei tiefen Temperaturen untersucht. Die Bildung eines ternären U(VI)-Carbonato-Humat Komplexes konnte spektroskopisch nach gewiesen werden. Die in dieser Arbeit bestimmten Komplexbildungskonstanten von log K(I=0,1M) = 2,69 ± 0,47 (cryo-TRLFS) und log K(I=0,1M) = 3,14 ± 0,70 (ATR FT-IR) zeigen eine sehr gute Übereinstimmung.

The paper compares two different high-resolution imaging techniques for the investigation of the hydrodynamics in a laboratory packed bed reactor operating at different stationary states and with two different particle packings. The wire-mesh sensor offers cross-sectional liquid holdup distribution imaging at ultra high speed of 10,000 frames per second and good spatial resolution. It is therefore a very useful imaging tool for transient and periodic flow conditions. But yet its influence on the flow in a packed bed was never analyzed. Gamma-ray computed tomography uses 662 keV gamma photons to obtain cross-sectional phase distribution images. It offers as well a good spatial resolution of 2 mm and does not influence the flow. But it needs rather long scanning times. As a non-invasive technique gamma-ray tomography has been used as a reference modality to evaluate the wire-mesh sensor measurements. Data from both imaging modalities are compared utilizing different analyzing models and showed good agreement. For the wire mesh sensor only marginal intrusive effects with respect to the flow dynamics were found.

Die Herstellung von Holzfaserstoffen im Druckrefiner stellt einen hoch komplexen Prozess dar, dessen Wirkungsweise und entsprechende physikalische Zusammenhänge bisher Zeitpunkt nur in geringem Maße beschrieben sind. Momentan werden Holzfaserstoffe in ausreichender Qualität unter enormem Energieeinsatz produziert, wobei sich jedoch eine gezielte Einstellung und Messung der Faserqualität als schwierig gestaltet. Das Potential, dass die umfassende theoretische Durchdringung des Zerfaserungsprozesses und die sich daraus ergebenden Optimierungsmöglichkeiten hinsichtlich Einstellung einer definierten Faserqualität und Energieeinsparung bietet, wird nicht ausgeschöpft. Die vorliegende Arbeit befasst sich daher mit der Ist-Stand-Analyse des thermomechanischen Faserstoffaufschlusses und macht die Abbildung der thermodynamischen Prozesse, des Materialflusses und der Energieaufnahme während der Zerfaserung möglich.

Im Vortrag werden Ergebnisse zur spektroskopischen Bestimmung von Stabilitätskonstanten für die Am(III)-Komplexierung durch organische Modellliganden sowie zur temperaturabhängigen Untersuchung der U(VI)-Humat-Komplexierung präsentiert. Desweiteren wird der Einflusses von Schwefelfunktionalitäten auf die Np(V)-Reduktion durch Huminsäuren diskutiert. Weiterhin werden neue Erkenntnisse zur pH-abhängigen U(VI)-Sorption an Opalinuston unter anaeroben und aeroben Bedingungen vorgestellt.

We summarize and critically evaluate the available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. We also discuss opportunities for further increasing the precision of key rates, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to Reviews of Modern Physics 70 (1998) 1265.

An electrically driven silicon light emitting diode with two distributed Bragg reflectors is reported. The active material is a Si pn-junction fabricated by boron ion implantation into an n-type silicon-on-insulator wafer. The cavity with a thickness of a few wavelengths is formed by amorphous Si/SiO2 multilayer stacks. A strong narrowing and enhancement of the electroluminescence at a resonant wavelength of lambda=1146 nm is observed with a quality factor of Q=143 and a finesse of F=11.

A conductance Wire Mesh Sensor system has been employed on a vertical 67 mm diameter pipe with the up flow of air and water mixtures. The measuring system provides time and cross-sectionally resolved information about the spatial distribution of the phases. Statistical information can be extracted and used to identify flow patterns. The fully resolved data has revealed a hitherto unreported structure has been seen in churn flow which could be linked to the wisps in wispy-annular flow.

Nuclear plant operators must demonstrate that the structural integrity of a nuclear reactor pressure vessel (RPV) is assured during routine operations or under postulated accident conditions. The aging of the RPV steels is controlled with surveillance program results. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response. A chance is given now with the investigation of RPV material from the decommissioned Greifswald NPP (WWER-440/230).
The Greifswald RPVs represent different material conditions such as irradiated, irradiated and annealed and irradiated, annealed and re-irradiated. A region covering ±0.70 m above and below the circumferential core weld was recovery annealed at 475° for about 150 hours. The working program is focused on the characterisation of the RPV steels (base and weld metal) through the RPV wall. It comprises chemical analysis, microstructure investigations (by means of metallography, electron microscopy and SANS) and mechanical testing (hardness measurements, tensile, Charpy-V), and fracture mechanics testing. The key part of the testing is focussed on the determination of the reference temperature T0 following the ASTM test standard E1921-09 to determine the facture toughness, and how it degrades under neutron irradiation.
The paper presents test results measured on trepans of the welding seam and base metal located in the reactor core region. The test results comprise Charpy-V, tensile and fracture toughness parameters. An additional aspect is the comparison of results determined on sub-size Charpy specimens machined of templates taken after the annealing from the uncladded inner RPV wall.

1. Introduction:

Prostate cancer is the most frequently diagnosed cancer in men over the age of 40 years in Europe and the USA and its early detection is crucial for prognosis and outcome of the disease. Besides the established radiotracers based on ¹¹C- and ¹⁸F-labeled choline [¹¹C]acetate is used for the early detection of prostate cancer and its recurrence. 2-[¹⁸F]Fluoroacetate has been proposed as alternative to [¹¹C]acetate offering the advantage of longer half-life which facilitates synthesis, shipping and allowing longer imaging protocols. A few radiosyntheses of the radiotracer have been published in the past, mainly based on trapping of the 2-[¹⁸F]fluoroacetate ethylester on C18 cartridges (Oasis HLB), followed by acidic hydrolysis [1-3]. Our approach is the fully automated synthesis of 2-[¹⁸F]fluoroacetate with a Tracerlab_FXN synthesizer including separation of the radiotracer via anion exchange cartridges in alkaline solution.

2. Materials and methods:

The radiolabeling with [¹⁸F]fluoride was performed with 2-methanesulfonyl-acetic acid t-butyl-ester as precursor in acetonitrile at 100°C. After hydrolysis with 1M HCl and addition of 1M NaOH the alkaline reaction mixture was diluted with 20mL of water and passed through a combination of two anion exchange cartridges where 2-[¹⁸F]fluoroacetate was trapped. The 2-[¹⁸F]fluoroacetate was recovered by elution with NaHCO₃ and excess [¹⁸F]fluoride was removed by alumina N cartridges to provide radiochemical pure sodium 2-[¹⁸F]fluoroacetate (radio-TLC, RP18, acetonitrile/water=85/15; R_f=0.59).

3. Results:

The radiosynthesis of sodium 2-[¹⁸F]fluoroacetate was accomplished with a TracerlabFXN synthesizer by a fully automated procedure. The purification of the product was performed by anion exchange cartridges and gave the radiotracer in 27-30% yield (decay-corrected) and 99% radiochemical purity within 30 min total synthesis time.

4. Discussion/Conclusion:

The modified approach of radiosynthesis and purification delivers sodium 2-[¹⁸F]fluoroacetate in high radiochemical purity and good radiochemical yield. The improved radio-TLC method using RP18 plates represents an easy system to distinguish [¹⁸F]fluoride from 2-[¹⁸F]fluoroacetate. Further optimization of this new method utilising a new precursor and a modified separation system is in progress. The conformation of the process to GMP requirements will be performed in the near future.

References:

[1] Sun LQ, Mori T, Dence CS, Ponde DE, Welch MJ, Furukawa T, Yonekura Y, Fujibayashi Y, [2006], Nucl.Med.Biol., 33:153-158
[2] Ponde DE, Dence CS, Oyama N, Kim J, Tai YC, Laforest R, Siegel BA, Welch MJ, [2007], J.Nucl.Med., 48(3): 420-428
[3] Marik J, Ogasawara A, McNulty BM, Ross J, Flores JE, Gill HS, Tinianow JN, Vanderbilt AN, Nishimura M, Peale F, Pastuskovas C, Greve JM, van Bruggen N, Williams SP, [2009], J.Nucl.Med., 50(6): 982-990

We report on the irradiation of in vitro tumour cells with laser-accelerated proton pulses showing dose dependent biological damage. This experiment, paving the way for future radiobiological studies with laser-accelerated protons, demonstrates for the first time the simultaneous and reliable availability of all components indispensable for systematic radiobiological studies: A laser-plasma accelerator providing stable proton spectra with maximum energy exceeding 15 MeV and applicable doses of a few Gy within few minutes, a beam transport and filtering system, an in-air irradiation site, a dedicated dosimetry system providing both online dose monitoring and a precise absolute dose information applied to the cell sample, and the full infrastructure for analysing radiation induced damage in cells.

Nanocoatings have the potential to improve the surface characteristics of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. Our research activity focuses on self-lubricating and hard cabon-based nanocoatings (C:TM and taC films) investigated by atomic-scale simulations. We will present morphological as well as tribological properties of the studied systems. Support by the European Union and the Freistaat Sachsen via SAB project 13857/2379 within the ECEMP initiative is gratefully acknowledged.

Surface erosion of a strained Si_0.8Ge_0.2 epilayer by 500 eV Ar⁺ ions with a fluence of 4 x10¹⁷ ions/cm² and the transformation from crystalline ripples to elongated Ge islands are reported by aligning the beam from 69° to 50° from the surface normal. Crystalline nature and the near surface Ge enrichment in such ripple structures are revealed by transmission electron microscopy. Moreover, ion beam induced decomposition of the SiGe network and the appearance of dislocation bands by suppressing the near-bandgap emission are manifested by u-Raman and photoluminescence studies, respectively.

Ziel/Aim:

Bedingt durch die bestehende Knappheit an 99m-Technetium wurden vermehrte Skelettszintigraphien mit 18F-Natriumfluorid (18F-NaF) am PET-Scanner (Siemens HR+) durchgeführt. Es sollte untersucht werden, wie flexibel die Einwirkzeit des 18F-NaF in der Routine gehandhabt werden kann, ohne die Bildqualität negativ zu beeinflussen.

Methodik/Methods:

Der PET-Scan wurde in 3D-Listmode-Technik aufgenommen, 360 MBq 18F-NaF, Emissionsdauer von 4 min pro Bettposition, keine Schwächungskorrektur. Der Abstand von Injektion von 18F-NaF zum Untersuchungssbeginn betrug in der ersten Gruppe 40-60 min, in der 2. Gruppe 60-80 min, in der 3.Gruppe 80-120 min. Bislang wurden 10 Patienten pro Gruppe ausgewertet. Es wurden standardisierte Regions of interest über Lunge und LWK1 (bzw LWK 2 oder BWK 12 gelegt, falls bei LWK 1 eine pathologische Mehranreicherung erkennen ließ) und Quotienten aus Anreicherung in LWK und Lunge gebildet.

Ergebnisse/Results:

Qualitativ konnten alle Patienten ausgewertet werden. Der Mittelwert der Quotienten aus LWK/Lunge betrug für die Gruppe 40-60 min p.i. 2,4; für die Gruppe 60-80 min p.i. 2,3 und für die Gruppe 80-120 min p.i. 3,0. Zwischen Gruppe 1 und 2 bestand hinsichtlich der LWK/Lunge-Quotienten kein wesentlicher Unterschied. Der Mittelwert für die Gruppe 3 lag mit 3,0 etwas höher, unterschied sich jedoch statistisch nicht signifikant von Gruppe 1 und 2.

Schlussfolgerungen/Conclusions:

Nach 40 min ist ohne weiteres eine Aufnahme mit 18F-Fluorid mit guter Bildqualität möglich. Unsere Berechnungen haben ergeben, dass bei einer Einwirkzeit zwischen 40 -80 min keine wesentlichen Qualitätsunterschiede zu erwarten sind. Dadurch fügt sich die Skelettaufnahme am PET flexibel in den Tagesablauf ein. Einen möglichen Gewinn an Bildqualität nach 80-120 min sollte man sich bei adipösen Patienten zu nutze machen.

Ziel/Aim:

Die Berücksichtigung hypoxischer Tumorsubvolumina anhand von FMISO-Daten zur Strahlentherapieplanung ist aufgrund des geringen Signal-zu-Rausch-Verhältnisses schwierig, weil die Konturen nicht eindeutig definiert sind. Ziel dieser Untersuchung war darzustellen, wie weit sich die Schwerpunkte Wie weit wandern die Schwerpunkte hypoxischer Tumorsubvolumina unter kombinierter Radiochemotherapie bewegen.

Methodik/Methods:

14 Patienten (2@, medianes Alter 55 Jahre) mit Plattenepithelkarzinomen des HNO-Traktes wurden vor kombinierter Radiochemotherapie (RCT) mit FDG sowie vor und nach 10Gy, 20Gy und 60Gy unter RCT mit FMISO untersucht (56 Untersuchungen). Mit der Rover-Software (ABX, Radeberg) wurde anhand der co-registrierten Daten Kontrast-basiert in jeder Untersuchung ein hypoxisches Tumorsubvolumen definiert und dessen Schwerpunkt im Koordinatensystem bestimmt. Die Bewegung dieses Schwerpunktes im Raum wurde unter RCT vermessen.

Ergebnisse/Results:

Im Mittel bewegen sich die Tumoren von der ersten zur zweiten Untersuchung um 5.6 mm, von der zweiten zur dritten Untersuchung um 5.5 mm und von der dritten zur vierten Untersuchung um 8 mm. Zwischen erster und vierter Untersuchung bewegten sich die Tumoren um 8.8 mm am weitesten. Die durchschnittliche Verschiebung des Schwerpunktes unter RCT lag bei 6.4 mm.

Schlussfolgerungen/Conclusions:

Unter Berücksichtigung der Registrierungsgenauigkeit von 2 mm und der maximalen Schwerpunktsbewegung von 9 mm erfasst der Strahlentherapieplan am Ende der Therapie das mit FMISO primär geplante Zielvolumen noch vollständig, wenn die üblichen Sicherheitsabstände berücksichtigt werden.

Ziel/Aim:

Die F-18-Misonidazol-PET (FMISO) zur Detektion hypoxischer Tumorsubvolumina weist ein vergleichsweise geringes Signal-zu-Rausch-Verhältnis auf. Üblicherweise werden neben der Dynamik Aufnahmen nach 2h und 4h p.i. angefertigt. Ziel dieser Untersuchung war es zu entscheiden, welche der beiden Spätaufnahmen den besten Kontrast hat und damit am besten für Volumenanalysen geeignet ist.

Methodik/Methods:

25 Patienten (3@, medianes Alter 55 Jahre) mit Plattenepithelkarzinomen des HNO-Traktes wurden vor kombinierter Radiochemotherapie (RCT) mit FDG sowie vor und nach 10Gy, 20Gy und 60Gy unter RCT mit FMISO untersucht (66 Untersuchungen). Mit der Rover-Software (ABX, Radeberg) wurde nach Co-Registrierung der PETs mit dem halbautomatischen Source-to-Background-Algorithmus anhand der FDG-Daten das Tumorgesamtvolumen definiert und in die FMISO kopiert. In diesem Tumorvolumen wurde die MISO-Aktivität bestimmt. Zusätzlich wurde in jeder FMISO ein 5-10 ml großes Referenzvolumen zur Definition des Hintergrundsignals von MISO in der Halsmuskulatur als definiert. Der Kontrast wurde mit dem Verhältnis MISO-Aktivität im Tumor zu MISO-Aktivität im Hintergrund bestimmt. Der statistische Vergleich erfolgte mit dem Wilcoxon-matched-pairs Test.

Ergebnisse/Results:

Der mittlere SUVmax im Tumor nach 2h war 1.9, nach 4h 2.3, der mittlere SUVmean in der Halsmuskulatur nach 2h war 1.2 und nach 4h 1.1. Der Mittelwert±Standardabweichung für den Kontrast nach 2h war 1.33±0.28 und nach 4h 1.41±0.32. Mediane, Minima und Maxima für den Kontrast lagen nach 2h bei 1.29, 0.81 und 2.06 und nach 4h bei 1.38, 0.90 und 2.33. Der Wilcoxon-matched-pairs Test ergab einen hoch signifikanten Unterschied für die Kontraste zwischen diesen beiden Untersuchungszeitpunkten (p = 0.000052).

Schlussfolgerungen/Conclusions:

Für Volumenanalysen von FMISO, z. B. für die Strahlentherapieplanung sind 4h-Daten besser geeignet als 2h-Daten.

We have conducted two sets of laser-ion acceleration experiments at the LANL 200 TW Trident short-pulse laser at ~1020 W/cm² (1 μm, 80-100 J and ~600 fs) at high (>1010) and low (>108) contrast, comparing regular size flat foils (~2 mm by 2 mm), reduced mass targets (200 μm to 500 μm diameter) and new Cu micro-cone targets in three separate geometries (flat-top or pizza-top, funnel, and snub-nose) to elucidate the production of hot electrons [1] and ions in these targets.
Results from the latest experiment show proton energies in excess of ~65 MeV for the pizza-top cones, compared to ~55 MeV for reduced mass targets and ~45 MeV for regular flat foils for high contrast. Data from a Cu Kα 2D imaging crystal, an X-ray single hit CCD, proton beam images on RCF film stacks, and an electron/proton spectrometer are presented and compared, showing the importance of not just generating hot electrons, but in the case of ion acceleration, efficiently propagating these hot electrons to the accelerating “tip”, where they can then be efficiently converted to ion energy, as well as the importance of the micro-cones’ supporting foil size.

Ziel/Aim:

Zur Optimierung/Individualisierung der Strahlentherapie könnte die Detektion und Berücksichtigung hypoxischer Tumorsubvolumina im Therapieverlauf wichtig sein. Ziel dieser Untersuchung war darzustellen, wie sich in Tumoren die Hypoxie im Vergleich zum nicht im primären Zielvolumen gelegenen Normalgewebe verändert.

Methodik/Methods:

25 Patienten (3@, medianes Alter 55 Jahre) mit Plattenepithelkarzinomen des HNO-Traktes wurden vor kombinierter Radiochemotherapie (RCT) mit FDG sowie vor und nach 10Gy, 20Gy und 60Gy unter RCT mit FMISO untersucht (66 Untersuchungen). Mit der Rover-Software (ABX, Radeberg) wurde nach Co-Registrierung der PETs mit dem halbautomatischen Source-to-Background-Algorithmus anhand der FDG-Daten das Tumorgesamtvolumen definiert und in die FMISO kopiert. In diesem Tumorvolumen wurde die MISO-Aktivität bestimmt. Zusätzlich wurde in jeder FMISO ein 5-10 ml großes Referenzvolumen zur Definition des Hintergrundsignals von MISO in der Halsmuskulatur definiert. Bestimmt wurden im Verlauf der SUVmax, das hypoxische Volumen ("total lesion hypoxia (TLH)" = SUVmean x Volumen) und der Kontrast in Abhängigkeit von der MISO-Aktivität im Hintergrund.

Ergebnisse/Results:

Der gemittelte SUVmax±sd vor, nach 10Gy, nach 20Gy und nach 60Gy lag bei: 2.6±0.6, 2.6±0.7, 2.1±0.6 und 1.6±04. Der SUVmax sank im Mittel auf 64% des Ausgangswertes. Die TLH [ml] vor, nach 10Gy, nach 20Gy und nach 60Gy lag bei: 93.3 ml, 79.6 ml, 77.3 ml und 55.3 ml. Der Kontrast vor, nach 10Gy, nach 20Gy und nach 60Gy lag bei: 1.6±0.3, 1.6±3.9, 1.4±02 und 1.1±0.2. Der Kontrast sank im Mittel auf 71% des Ausgangswertes.

Schlussfolgerungen/Conclusions:

Unter kombinierter Radiochemotherapie sinkt sowohl das Tumorvolumen (erkennbar an den morphologischen CT-Daten) als auch die hypoxische Aktivität der HNO-Tumoren. Da nach 60 Gy der Kontrast in den FMISO-Untersuchungen nahe 1 liegt, lässt sich anhand der aufgenommenen Daten keine Planung für einen Strahlentherapieboost erstellen.

Ziel/Aim:

(-)-F-18-Norchloro-fluoro-homoepibatidin (-)-NCFHEB) ist ein neuer vielversprechender Tracer für die Darstellung von alpha4beta2 nikotinischen Acetylcholinrezeptoren bei neuropsychiatrischen Erkrankungen mit PET. Um die Strahlenexposition durch die Applikation des Tracers abzuschätzen, wurde CD1 Mäusen (-)-NCFHEB appliziert. Es wurden die Biodistribution und die resultierenden Organdosen (OD) sowie die effektive Dosis (ED) bestimmt.

Methodik/Methods:

27 weiblichen CD1 Mäusen (Gewicht: 28,2 ± 2,1g) wurden 0,75± 0,334MBq (-)-F-18-NCFHEB [1] über die V. caudata lateralis appliziert. Nach 5, 15, 30, 45, 60, 90, 120, 180 und 240 min p.i. wurden die Tiere getötet (n=3 pro Zeitpunkt). Die Organe (Hirn, Herz, Lunge, Magen, Dünndarm, Dickdarm, Leber, Nieren, Harnblase, Milz, Thymus, Bauchspeicheldrüse, Nebennieren, Ovarien, Blut, Haut, Muskel, Skelett) wurden isoliert, gewogen und ihr Aktivitätsgehalt in einem g-Counter bestimmt. Die Massen von Skelett und Muskel wurden aus Gewebeproben extrapoliert [2]. Die Zeit- und Massenskalen wurden an die menschlichen Skalen angepasst [3]. Die Aktivitätsanteile in Quellorganen wurden als Fraktionen der injizierten Aktivitätsmenge [%ID] pro Gramm bzw. Organ dargestellt. Mit trapezoiden und exponentiellen Anpassungen an diese Daten wurden Zeit-Aktivitätskurven für jedes Organ bzw. Kompartiment abgeleitet. Die kumulierte Aktivität in den Quellorganen wurden bestimmt und ODs und die ED wurden mit OLINDA abgeschätzt.

Ergebnisse/Results:

Die Harnblase erhält die höchste OD mit 104,0 μSv/MBq, gefolgt von den Nieren (24,2 μSv/MBq), dem Uterus (14,1 μSv/MBq), der Leber (14,0 μSv/MBq) und der Bauchspeicheldrüse (14,0 μSv/MBq). Den höchsten Beitrag zur ED leistet die Harnblase (5,2μSv/MBq) gefolgt von den Ovarien (2,1μSv/MBq), dem Dickdarm (1,5μSv/MBq) und dem roten Knochenmark (1,3 μSv/MBq). Mit diesen Daten ergibt sich die ED durch i.v. Applikation von (-)-F-18-NCFHEB zu 14,2 μSv/MBq.

Schlussfolgerungen/Conclusions:

Die ED durch i.v. Applikation von etwa 370 MBq (-)-F-18-NCFHEB am Menschen ergibt sich zu 5,3 mSv. Dies liegt im Bereich der Strahlenexposition, welche durch andere F-18-markierte Radioliganden erzeugt wird. Diese vorklinischen inkorporationsdosimetrischen Ergebnisse bestärken die weitere Entwicklung von (-)-F-18-NCFHEB in klinischen Studienphasen am Menschen und seine weitere Entwicklung als klinischer Hirn-PET-Tracer.

Literatur/References:

[1] Brust P et. al.: In vivo measurement of nicotinic acetylcholine receptors with [18F]norchloro-fluoro-homoepibatidine (NCFHEB). Synapse 62, 205-218.
[2] Lindstedt SL, Schaeffer PJ.: Use of allometry in predicting anatomical and physiological parameters of mammals Laboratory Animals (2002) 36, 1–19
[3] Stabin MJ: Fundamentals of Nuclear Medicine Dosimetry, Springer 2008, ISBN 978-0-387-74578-7, 237P Diese Studie wird durch das Bundesministerium für Bildung und Forschung unterstützt. (Nr. 01EZ0820)

Fast ignition fusion requires transporting a large amount of energy into the compressed ICF capsule in a short period of time. One metthod for efficiently transporting laser energy into a compressed fusion capsule is to use a cone situated near or in the capsule, decreasing the distance to the core, improing laser conversion efficiency and concentrating charged particle flow. Results from recent experiments performed at the LANL 200 TW Trident short-pulse laser at ~10²⁰ W/cm² (80-100 J and ~600 fs) are presented.

Ziel/Aim:

Die zentralen SERT lassen sich mittels SPECT-Radiotracern in SERT-reichen Gehirnarealen und mit PET-Markern wie [¹¹C]DASB hochselektiv im gesamten Gehirn darstellen. Die kortikale Test-Retest-Reliabilität von [¹¹C]DASB PET ist lediglich moderat, eine Quantifizierung endogenen Serotonins gelingt mit dieser Methode nicht. Möglicherweise können Tracer mit längerlebigen Nukliden diese Mängel beseitigen helfen. Ziel unserer Studie war die erstmalige Applikation eines Fluor-18-markierten SERT-Radiotracers im Menschen.

Methodik/Methods:

In Anlehnung an (1) wurde die Synthese von [¹⁸F]FMe-McN 5652 unter GMP-Bedingungen in einem modifizierten Synthesemodul "TRACERlab FxF-N” als 2-Stufen-2-Topf-Reaktion adaptiert: Stufe 1: Synthese von [¹⁸F]Fluormethylbromid durch nukleophile [¹⁸F]Fluorierung von Dibrommethan und nachfolgende Reinigung mittels Silicagel-Kartuschen (2). Stufe 2: [¹⁸F]Fluormethylierung eines entsprechenden Thiolat-Präkursors. Da [¹⁸F]FMe-McN 5652 in wässriger Lösung nicht stabil ist, wurde eine HPLC-Reinigung unter Verwendung eines ethanolischen Eluenten entwickelt, in deren Produktfraktion der Tracer stabil ist. Die PET-Datensätze, erhoben bei 5 gesunden Probanden (2 weiblich, Alter 39±10 Jahre) als dynamische Akquisition über 120 Min. nach i.v. 90-Sek.-Bolusinjektion von 298±57 MBq [¹⁸F]FMe-McN 5652 sowie statische Aufnahmen über 30 Min, wurden mit dem individuellen MRT koregistriert (PMOD) und mittels VOI analysiert (Target-/Background-Ratios, TB-R, Background=Zerebellum).

Ergebnisse/Results:

Die TB-R für den frontalen Kortex (FC) betragen 1,02±0,04 für rechts und 1,01±0,03 für links, für die Kaudatuskopfregion (Kaud) 1,46±0,16 (rechts) und 1,50±0,15 (links) und für die RaphÈ-Region 2,04±0,11. Vergleichsweise finden sich bei gesunden Probanden, die mittels [¹¹C]DASB-PET untersucht wurden (N=21, 11 weiblich, 38±8 Jahre), entsprechende TB-R von 1,10±0,07 (FC rechts, t-Test: n.s.), 1,08±0,78 (FC links, n.s.), 2,14±0,21 (Kaud rechts, n.s.), 2,06±0,19 (Kaud links, n.s.) und 2,23±0,39 (RaphÈ, n.s.) bei insgesamt visuell besserer Bildqualität des neuen Tracers.

Schlussfolgerungen/Conclusions:

Die zerebrale [¹⁸F]FMe-McN 5652-Aufnahme entspricht der Verteilung der SERT auch beim Menschen, so dass der Radiotracer einen geeigneten Marker für SERT darstellen könnte. Trotz der tendenziell geringeren TB-R im Vergleich mit den [¹¹C]DASB-PET-Daten könnte sich die geringere Standardabweichung bei der Untersuchung der Test-Retest-Reliabilität mit größeren Fallzahlen als Vorteil erweisen. Zudem soll mit Verdrängungsstudien die Sensivitität des neuen Markers, insbesondere in den kortikalen Arealen und hinsichtlich der Quantifizierung endogenen Serotonins, eingeschätzt werden.

Literatur/References:

(1) Zessin J, Eskola O, Brust P et al. Nucl Med Biol 2001; 28: 857-863.
(2) Iwata R, Pascali C, Bogni A et al. Appl Radiat Isot 2002; 57: 347-352

Ziel/Aim:

Neurotensin (NT) und seine Rezeptoren werden in verschiedenen humanen Tumoren (Brust-, Prostata-, Lungen-, duktale Pankreas- und Hypophysentumore) überexprimiert, insbesondere stehen sie im Zusammenhang mit der Tumorprogression und dem Übergang zu aggressiveren Tumorphänotypen. Deshalb kommt der quantitativen in vivo-Bildgebung der funktionellen Neurotensin-Rezeptor-Expression, sowohl in der Forschung, als auch in Diagnostik und Therapie besondere Bedeutung zu. Deshalb sollte ein in vivo stabiles Neurotensin-Analogon entwickelt werden, das sowohl zur Bildgebung, als auch für therapeutische Zwecke eingesetzt werden kann.

Methodik/Methods:

Durch manuelle Festphasensynthese auf Merrifield-Resin mit anschließender DOTA-Konjugation wurde DOTA-ArgΨ(CH2NH)ArgProDmtTleLeu-OH synthetisiert. Die Markierung des Peptides (3 pmol) mit Cu-64 erfolgte in Ammoniumacetat-Lösung 0,1 M, pH 5.5 über 15 min bei 50&inf;C. Der IC50 wurde an HT-29-Zellen bestimmt. Zellaufnahme und Internalisierung wurden an HT-29- und PC3-Zellen untersucht. Die Bioverteilung des Radiotracers wurde bei HT-29- tumortragenden NMRI-Nacktmäusen sowohl durch Organentnahme (je 4 Tiere pro Zeitpunkt), als auch mit Kleintier-PET (insgesamt 8 Tiere) untersucht. Die Dynamik der Metabolisierung wurde bei Ratten bestimmt.

Ergebnisse/Results:

Die Bindungsaffinität des Peptides an HT-29-Membranen, mit Neurotensin-Rezeptor 1 betrug 7 nM (4-12 nM, 95% Konfidenzintervall). Das Peptid konnte mit einer radiochemischen Reinheit größer 92% in einem Schritt mit Cu-64 markiert werden. Nach einmaliger intravenöser Injektion stieg die Konzentration im Tumor schnell an (0,8±0,1 SUV, 5 min p.i.) und verringerte sich dann auf 0,3±0,1 SUV (60 min p.i.). Daraus ergaben sich Tumor zu Organ-Verhältnisse von 2,8±0,7 im Blut, 5,2±0,9 im Muskel, 4,2±0,6 im Pankreas, 0,6±0,5 in Leber und 0,4±0,4 in Nieren. Das Peptid wurde schnell von den Nieren (3,7±0,6 SUV, 5 min p.i.; 0,8±0,1 SUV 60 min p.i. ) aufgenommen und in den Urin (60±6%ID im Urin nach 1 h) eliminiert . In der PET konnten die xenotransplantierten Tumore deutlich dargestellt werden. Bei gleichzeitiger Injektion von Neurotensin verringerte sich die Tumoraufnahme des Tracers auf 27% der Kontrolle. Nach 1 h lagen noch 33% der Aktivität im Blutplasma der Ratte als Originalsubstanz vor.

Schlussfolgerungen/Conclusions:

Das Cu-64-Neurotensin-Analogon erlaubt auf Grund seiner Stabilität, Affinität und Spezifität die bildgebende Darstellung der funktionellen Expression von Neurotensin-Rezeptoren in vivo. Die Daten lassen erwarten, dass ähnliche Ergebnisse auch mit Radionukliden für SPECT (In-111) oder therapeutische Anwendungen (Cu-67, Lu-177, Y-90) erreicht werden können.

Literatur/References:

Das Projekt wurde partiell durch das EU-Projekt GIPIO (Grant Agreement Nr. 223057) gefördert.

Ziel/Aim:

Intraarteriell applizierbare Partikel, markiert mit therapeutisch wirksamen Radionukliden (Y-90, Lu-177, Re-188) sind eine Alternative zur Behandlung von Lebertumoren und Lebermetastasen. Ga-68 markierte Partikel könnten zur Blutflussdarstellung und zur Lungenperfusion verwendet werden. In unserer Untersuchung verwendeten wir 20μm HSA Mikrosphären (MS). Es wurde untersucht, unter welchen Bedingungen sich DOTA modifizierte MS markieren lassen und wie stabil die Markierungen in vitro und in vivo sind.

Methodik/Methods:

Markiert wurde 1mg MS in 0,5M Azetatpuffer bei pH5, Reaktion 15min bei 95&inf;C unter Schütteln mit 0,1-0,5GBq Ga-68, 0,1-7,2GBq Y-90 und 1,8GBq Lu-177. Die Ausbeuten und die in vitro Stabilität wurden mit ITLC und nach Zentrifugieren bestimmt. Nach Zugabe von 1ml 0,1M DTPA Lösung (Challenge), 20mg Ascorbinsäure (Radikalfänger) und Stehenlassen der Suspension bestimmten wir die in vitro Stabilität der Produkte nach einigen Stunden bis Tagen in Gegenwart von DTPA/Ascorbinsäure bzw. Plasma und die in vivo Stabilität der Y-90 DOTA-MS nach intravenöser Injektion in Wistar-Ratten.

Ergebnisse/Results:

Die Markierungsausbeuten betrugen bei allen Nukliden >90%. Zur Bestimmung der in vitro Stabilitäten wurde das Produkt zentrifugiert und der Überstand abgenommen und/oder nach Aufschütteln eine Dünnschichtchromatografie durchgeführt. Nach 3h Inkubation in Humanplasma wurde 5% Ga-68 im Überstand gefunden. Nach Ascorbinsäurezugabe zum Reaktionsansatz fanden sich 18% freies Lu-177 nach 7d. Bei Y-90 DOTA MS wurden in Gegenwart von Ascorbinsäure bei Markierungen im GBq-Bereich im Überstand der Partikelsuspension unmittelbar nach Markierung bereits >10% der Radioaktivität nachgewiesen. Dabei handelt es sich wahrscheinlich um Y-90 DOTA-Thioharnstoffderivate, die vermutlich in Folge von Radiolyse und erhöhter Temperatur von den Partikeln abgespalten werden. Die Halbwertszeit von Y-90 DOTA-MS in der Lunge nach i.v. Injektion der Partikel in Wistarratten beträgt 3,5d.

Schlussfolgerungen/Conclusions:

Die Stabilität der Ga-68 markierten MS ist ausreichend für in vivo Anwendungen. Y-90 markierte Albumin-MS sind radiolytisch instabil und werden in vivo relativ rasch abgebaut. Sie sind deshalb kein Alternative zu den Re-188 markierten MS, die wir regelmäßig zur i.a. Therapie verwenden [1]. Dementsprechend ist auch eine Lu-177 Markierung dieser biologisch abbaubaren Partikeln nicht sinnvoll.

Literatur/References:

1] Wunderlich, G., Drews, A., Kotzerke, J. A kit for labelling of Re-188 HSA Mikrosphären for therapeutic use in nuclear medicine. Appl Radiat Isot 62 (2005) 915-918

Ferromagnetic semiconductors with high Curie temperatures and large coercivity are very promising materials for spintronic applications. An approach to fabricate ferromagnetic GaMnAs is Mn ion implantation into GaAs followed by pulsed laser annealing (PLA) [1]. Magnetic Mn ions which occupy the Ga sublattice sites form acceptor centers and pro-vide free holes for the mediation of the parallel align-ment of the magnetic moments of the Mn ions. For a strong ferromagnetic interaction, activation of the Mn acceptor dopants over their thermodynamic equilib-rium solubility is necessary. Long time, rapid thermal, and also flash lamp annealing processes take too long to realize a large enough free hole concentration by activation of Mn acceptor dopants. From a thermody-namical point of view, the PLA process is beside the more expensive LT-MBE process the best route to fabricate oversaturated ferromagnetic GaMnAs.
We investigated the influence of the implanted Mn concentration and PLA conditions on the structural and magnetic properties of GaMnAs thin films. We per-formed heatflow calculations to visualize the fast tem-peratue quenching during the PLA process [2]. Using SQUID magnetometry, we reveal a strong decrease of the saturation magnetization with increasing number of laser pulses during PLA (Fig. 1). However, the crystal-line quality is improved after several laser pulses. This has been verified by RBS (Fig. 2) and XRD measure-ments. The decrease of saturation magnetization after several laser pulses may be caused by the continuous Mn cluster formation during each PLA cycle.
[1] M. A. Scarpulla. et al. APL 82 (2003) 1251
[2] D. Bürger et al. PRB 81 115202 (2010)

The incorporation of transition metals dopants in semiconductors over their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Dietl et al. [1] calculated the Curie temperatures for various semiconductors doped with 5 at% Mn. A lot of experimental effort was focused on the fabrication of diluted magnetic semiconductors. Unfortunately, such metastable alloys try to reach their thermodynamical equilibrium by the diffusion of the incorporated dopants. The equilibrium state at room temperature for semiconductors with a low solubility of magnetic dopant atoms is characterized by unwanted secondary phases. We present the results from combined random walk simulations and heatflow calculations and explain the successful fabrication of GaAs:Mn and the impossibility to produce Si:Mn. The clustering process is simulated under the assumption that neighbouring magnetic atoms stick together. This is a general approach for the growth of clusters in supersaturated materials [2]. With the knowledge of the diffusion coefficient our modelling can be used to predict the thermodynamical limit at room temperature and the producibility by pulsed laser annealing of diluted magnetic semiconductors.
[1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000)
[2] P. Meakin, Fractals, scaling and growth far from equilibrium (Cambridge University Press, 1998)

The 14N(p,gamma)15O reaction controls the rate of the hydrogen burning CNO cycle. The solar CNO neutrino flux which may be detected e.g. in Borexino and SNO+ can in principle be used to measure the carbon and nitrogen abundance at the center of the Sun, thus addressing the "solar abundance problem". However this requires more precise nuclear data. Updated results from the experimental study performed at the LUNA facility (Gran Sasso National Laboratories, Italy) in the energy range E_p = 0.36 - 0.4 MeV and from the high-current FZD Tandetron (Dresden) in the range E_p = 0.6 - 2.0 MeV are presented.

The 14N(p,gamma)15O reaction controls the rate of the hydrogen burning CNO cycle. By detecting solar CNO neutrinos (e.g. in Borexino, SNO+) one can in principle measure directly the carbon and nitrogen abundance at the center of the Sun. However this requires more precise nuclear data. Updated experimental results on capture to various excited states (as well as to the ground state) in 15O are shown, together with improved branching ratios obtained for the E_p = 278 keV resonance.

The field of underground accelerator physics to study rare nuclear reaction events has greatly expanded over the last decade. Consequently, there is an increasing need to put ion accelerators in underground laboratories, making use of overlying rock to suppress cosmic-ray induced background. Here we show data from a feasibility study on such a laboratory in the Dresden Felsenkeller.

An escape-suppressed, composite high-purity germanium detector of the Clover type has been installed at the Laboratory for Underground Nuclear Astrophysics (LUNA) facility, deep underground in the Gran Sasso Laboratory, Italy. The laboratory gamma-ray background of the Clover detector has been studied underground at LUNA and, for comparison, also in an overground laboratory. Spectra have been recorded both for the single segments and for the virtual detector formed by online addition of all four segments. The effect of the escape-suppression shield has been studied as well. Despite their generally higher intrinsic background, escape-suppressed detectors are found to be well suited for underground nuclear astrophysics studies. As an example for the advantage of using a composite detector deep underground, the weak ground state branching of the Ep = 223 keV resonance in the 24Mg(p,gamma)25Al reaction is determined with improved precision.

The NeuLAND detector at the R$^3$B experiment at the future FAIR facility in Darmstadt aims to detect fast neutrons (0.2-1.0\,GeV) with high time and spatial resolutions ($\sigma_{\rm t}$$<$100\,ps, $\sigma_{\rm x,y,z}$$<$1\,cm). The detector will consist of about 60 subsequent MRPC stacks containing a 4\,mm thick anode made of iron converter material, with an additional 4\,mm of converter material between two stacks. The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPC's.

Prototypes for the NeuLAND detector have been built at FZD and GSI and then studied using the 32\,MeV pulsed electron beam at the superconducting electron accelerator ELBE in Dresden, Germany. Owing to the new, single-electron per bunch mode of operation, a rapid validation of the design criteria ($\geq$90\% efficiency for minimum ionizing particles, $\sigma$ $\leq$ 100\,ps time resolution) was possible.

Tested properties of the prototypes include glass thickness, spacing of the central anode, and a comparison of single-ended and differential readout. Tested frontend electronics schemes include FOPI (single-ended), PADI-based (both single-ended and differential mode tested), and ALICE (differential). --- Supported by BMBF (06DR9058I) and GSI FuE.

Die Rate des Bethe-Weizsäcker-Zyklus des Wasserstoffbrennens wird von der langsamsten Reaktion, ^{14}N(p,gamma)^{15}O, bestimmt. Diese Reaktion ist kürzlich u. a. bei LUNA im Energiebereich unterhalb 0.5\,MeV gründlich neu untersucht worden. Allerdings spielen auch höherenergetische Daten eine Rolle bei der Extrapolation des Wirkungsquerschnitts zu extrem niedrigen, unmessbaren Energien. Die Reaktion wurde jetzt am FZD-Tandetron im Energiebereich von 0.6-2.0\,MeV neu untersucht. --- Unterstützt von der Herbert-Quandt-Stiftung (Stipendium f\"ur T.S.) und der Europäischen Union (FP6 AIM RITA 025646).

The NeuLAND detector at the R$^3$B experiment at the future FAIR facility in Darmstadt aims to detect fast neutrons (0.2-1.0\,GeV) with high time and spatial resolutions ($\sigma_{\rm t}$$<$100\,ps, $\sigma_{\rm x,y,z}$$<$1\,cm). The detector will consist of about 60 subsequent MRPC stacks containing a 4\,mm thick anode made of iron converter material, with an additional 4\,mm of converter material between two stacks. The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPC's.

As part of the ongoing development effort, a number of prototypes for this detector have been developed and built at GSI, FZD, and SINP. By testing some prototypes from GSI and FZD in experiments with picosecond electrons at ELBE (Dresden, Germany) and with 175 MeV quasi-monochromatic neutrons at TSL (Uppsala, Sweden) it was shown that the working principle is sound.

Precisely known nuclear cross sections are an essential ingredient for the modeling of nuclear processes in our Sun, in stars, and in the Big Bang. Uncertainties due to theoretical extrapolations can be avoided if experimental data are available directly at astrophysically relevant energies. Since such energies are typically far below the Coulomb barrier, this entails cross section measurements in the picobarn range.

The Laboratory for Underground Nuclear Astrophysics (LUNA) inside the Gran Sasso mountain in Italy takes up this challenge by combining accelerator-based experiments with low-background measurement techniques. Using this approach, in recent years several reactions relevant to hydrogen burning have been studied, e.g. $^3$He($\alpha$,$\gamma$)$^7$Be and $^{14}$N(p,$\gamma$)$^{15}$O. The implications of the data range from an independent lower limit on the age of the universe to a precise solar thermometer.

Based on this progress, currently there are efforts in several countries to construct new underground accelerators. The exciting science that can be probed with these new facilities will be highlighted.

First studies have been carried out in stalactite-like biofilms from the uranium mine Königstein (Germany), where the mining activities had been stopped in 1990 and the uranium mine has been partially flooded for remediation. In the acidic, sulphate-rich waters with high concentration of heavy metals and radionuclides (uranium) as contaminants, biofilms are formed and occur as gelatinous filaments, and as stalactite-like snotites. The analyses of the bacterial diversity of these biofilms showed a dominance of Ferrovum myxofaciens, an acidophilic, autotrophic, iron oxidizing bacteria, which belongs to the Betaproteobacteria. Ferrous iron is oxidized strongly catalyzed by Fe(II)-oxidizing bacteria with the consequence of producing oxidizing conditions within the biofilm with high oxygen concentration. Fiber-optic oxgyen microprofiles, carried out in these snotites are in a good agreement with electro-chemical measurements. The oxygen concentration is decreasing slowly from the edge versus center of the snotite biofilm. Electrochemical redox potential micoprofilings were carried out in these snottite-biofilms by a miniaturized platinum redox electrode with a tip diameter of 10 µm, too. In the bulk solution a redox potential of 728 mV +- 9.5 mV was measured in comparison to an increased redox potential of 834.5 mV +- 10.21 mV within the snottite-biofilm. We guess that the different geochemical conditions are due to the oxidation of ferrous iron catalyzed by Fe(II) oxidizing bacteria and that they will have an influence on the uranium speciations. A pH-Eh diagram for the U-S-O-H-C system at 15 °C was constructed using the geochemical speciation code “Geochemist´s Workbench” Version 8.0.8 / ACT2 Version 8.0.8 and the most recent NEA database for Uranyl Silicates and solid Uranates (Guillaumont et al., 2003), supplemented with solubility data for Uranophane (Nguyen et al., 1992) and CaU2O7.3H2O(s) (Altmaier et al., 2006) and the analytical data of the bulk water for the calculation of the field stability boundaries of different uranium species. The plotting of the measured pH and Eh values into this diagram showed that the theoretical stability fields of U species are defined in areas characterized by higher pH or lower Eh. The measured values indicate that aqueous Uranium(VI) Sulfate Complexations were formed in the biofilm as well as in the bulk solution. Only the changing of the local conditions (e.g. closure of the underground galleries) will lead to substantial changes and the formation of solid uranium(IV) species.

To compare the applicability of an electrochemical and a laser-based fiber-optical microsensor for oxygen determination in biofilm samples, microprofiling measurements in uranium free biofilms and in biofilms exposed to ecologically relevant uranium concentration were performed. For our studies we used a commercial available Clark-type microelectrode and a custom fiber-optic instrument, which was optimized for tip probes < 10 µm (optodes) by use of a diode laser and the so-called two frequency phase modulation technique, to mask interfering background fluorescence.
The data obtained from both microsensor methods in uranium free and uranium contaminated biofilms were in good agreement. Fiber-optic and electrochemical microsensor measurements showed high concentrations of oxygen over the total thickness of the uranium free biofilms. In contrast, biofilms exposed to uranium revealed a much lower oxygen concentration in the upper layers of the biofilm. At a biofilm depth of approximately 750 µm no oxygen was detectable at all.

Ion-beam eroded self-organized nanostructures on semiconductors offer new ways for the fabrication of high density memory and optoelectronic devices. It is known that wavelength and amplitude of noble gas ion-induced rippled structures tune with the ion energy and the fluence depending on the energy range, ion type and substrate. The linear theory by Makeev [1] predicts a linear dependence of the ion energy on the wavelength for low temperatures. For Ar+ and Xe+ it was observed by different groups [2] that the wavelength grows with increasing fluence after being constant up to an onset fluence and before saturation. In this coarsening regime power-law or exponential behavior of the wavelength with the fluence was monitored. So far, investigations for Xe ions on silicon surfaces mainly concentrated on energies below 1keV. We found a linear dependence of both the ion energy and the fluence on the wavelength and amplitude of rippled structures over a wide range of the Xe+ ion energy between 5 and 70keV. Moreover, we estimated the ratio of wavelength to amplitude to be constant meaning a shape stability when a threshold fluence of 2x1017cm−2 was exceeded.

A strong decrease of the carrier mobility of the nanometer thick silicon films imposes limitation on the application of SOI structures in the current silicon planar CMOS technology. The formation of heterostructures-on-insulator is a way to increase carrier mobility in the nanometer scale layers.

In the past the lack of stable native germanium oxide for surface passivation and gate dielectrics as well as the inability to epitaxially grow sufficiently thick defect-free germanium layers on silicon hindered the integration of germanium into the mainstream Si-based technology. Recent developments, such as high-k dielectrics and germanium-on-insulator substrates have made germanium a promising candidate for future high mobility devices. Therefore electrical doping of germanium by ion implantation and subsequent annealing has drawn a renewed interest. Investigations on the formation of ultra shallow junctions by ion beam processing have shown that p+-doping using B yields junctions that meet the requirements for the 22 nm technology node, whereas the formation of n+-junctions by P or As is complicated by the high diffusivity and the low solubility of the dopants. Recently, the concentration-dependent diffusion of n-dopants like P, As and Sb has been explored, and it has been found that doubly negatively charged vacancies are the mobile species responsible for the migration of the dopant atoms. The application of conventional rapid thermal annealing (RTA) with durations of some seconds and temperatures above about 500 °C leads to the activation of the n-dopants but their fast concentration-dependent diffusion can generally not be prevented. On the other hand it has been shown that both the diffusion and the activation of the dopants does not depend significantly on the implantation damage, i.e. using the defect engineering schemes known from Si technology seems not to be promising. Therefore, in order to control junction depth and dopant activation ultra-short annealing by flash lamps or lasers are currently under investigation.
The present work deals with the application of millisecond flash lamp annealing (FLA) to samples containing an implanted surface layer of about 100 nm thickness. P or As ions were implanted at an energy of 30 or 90 keV, respectively, and a fluence of 3x1015 cm-2. The investigations are focused on solid phase epitaxial recrystallization, dopant redistribution and dopant activation. The dependence of these effects on the heat transfer to the sample during FLA as well as on pre-amorphization and pre-annealing treatment is discussed. The results are compared to typical data achievable by RTA. Different characterization methods were employed. Channeling Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy (XTEM) were used to monitor the recrystallization of the amorphous layers formed during implantation. The depth distributions of P and As were measured by secondary ion mass spectrometry. In order to determine the sheet resistance variable probe spacing and micro four point probe measurements were utilized. Selected samples were studied by XTEM to search for precipitates and end-of-range defects. While in RTA the concentration dependent dopant diffusion hinders the formation of ultra-shallow n+ layers, FLA does not cause any diffusion. The maximum activation obtained by FLA is about 6x1019 and 2x1019 cm-3 for P and As, respectively. This is about 3-4 times higher than under typical RTA conditions. However, the activation and the sheet resistance achieved by FLA do not yet fulfill the ITRS requirements for the 22 nm technology node. Possible mechanisms responsible for dopant deactivation are discussed.

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We report on ESR, magnetization, and specific-heat studies of [Cu(pyz)₂(HF₂)]PF₆ single crystals, identified as a quasi-twodimensional spin-1/2 Heisenberg antiferromagnet. Our measurements revealed J_inter/J_intrainter,J_intra, J are the interplane, intraplane and mean exchange interactions, respectively, and A is the anisotropy constant. It is argued that the magnetic properties of this material are strongly affected by two-dimensional spin fluctuations, despite of the onset of 3D long-range magnetic ordering at T_N ≈ 4.4 K. The temperature-field phase diagram and ESR magnetic excitation spectrum in the 3D ordered phase of [Cu(pyz)₂(HF₂)]PF₆ will be discussed in detail.

We survey some prospects of identifying furhter in-medium modifications of hadrons in a strongly interacting medium with respect to ongoing experiment series of the HADES Collaboration and planned experiments of the CBM Collaboration at FAIR. Di-electrons, strange and charm mesons are considered and their potential for signalling imprints of chiral restoration is highlighted.

Using a backward-wave-oscillator-based setup in a Mach-Zehnder interferometer arrangement, we have measured the temperature and frequency-dependent transmission and phase-shift spectra of LuNi₂B₂C films on MgO substrates in the range 200 GHz - 1.4 THz. From the measured spectra, we have directly calculated the complex optical conductivity. We observe a clear signature of the superconducting energy gap in the spectra. In the talk, a comparison of the experimentally obtained spectra with theoretical predictions for a multi-band superconductor will be given.

Ba₃Cr₂O₈ is a system of three-dimensionally coupled dimers, exhibiting a field-induced phase transition from a quantum-disordered to a long-range antiferromagnetically ordered state at H_c1 = 12.5 T. We report tunable-frequency electron spin resonance (ESR) studies of Ba₃Cr₂O₈ single crystals performed in a frequency range between 50 and 700 GHz in fields up to 25 T (applied along the c axis). Two gaps in the magnetic excitation spectrum, Δ1 = 564 GHz and Δ2 = 400 GHz, were observed directly, confirming the spin-singlet ground state of Ba₃Cr₂O₈ below H_c1. The observation of singlet-triplet ESR transitions, which are normally forbidden in spin-1/2 dimer systems by selection rules, indicates the break-down of the axial symmetry in this compound. Details of the ESR excitation spectrum of Ba₃Cr₂O₈ across different regions of its phase diagram will be discussed.

We report recent discoveries of superconductivity in Ga-doped germanium fabricated by ion implantation and subsequent flash-lamp or oven annealing. Tuning the preparation parameters allows for varying both charge-carrier and Ga concentration in the resulting roughly 100 nm thin nano- or single-crystalline layers. Transport measurements on systematically prepared samples reveal that besides a needed charge-carrier concentration of more than 0.4 atom%, superconductivity occurs to be sensitive on the implanted Ga content which may also be attributed to a change in the phonon properties. Onset transition temperatures up to 1.4 K have been found for almost 10 atom% Ga. Further, we observe in-plane critical fields exceeding 1 T and being close to the Pauli-Clogston limit. An exceptionally low Cooper-pair density of around 10¹⁵ cm⁻³ turns out the extreme type-II character of superconductivity. Finally, our work adds to our previous report [1] and may help to understand superconductivity in doped elemental semiconductors in general.

Today's available strong magnets allow to study distinct magnetic effects in various electrochemical systems. Lorentz forces and also magnetic gradient forces can be utilized to tailor convection and mass transfer in electrolytic cells, thereby influencing for example the morphology and the structure of the electrodeposits. The presentation will give an overview on recent results of numerical simulations and experimental findings in lab-scale electrochemical systems and will discuss potential applications. Whereas Lorentz forces are often known to enhance mass transfer, new results show that the convection pattern found in simple geometries can already be quite complex. A deeper understanding is required for improved applications. Recently, also magnetic gradient forces gained attention, e.g. for their potential in preparing micro-structured deposits. A detailed discussion of recent results will give further insight. Finally, new investigations of cyclic operation modes or time-dependent magnetic fields are presented which allow for a broad range of new phenomena.

Die Koordinationschemie von Uran(VI) hat in den letzten Jahren vielfältiges Interesse gefunden. Ursachen dafür sind sowohl dessen Bedeutung im Rahmen der Kernenergiegewinnung als auch Probleme bei der Aufarbeitung sowie Lagerung von verbrauchten Kernbrennstoffen. Weitere Fragestellungen beziehen sich auf die Umweltrelevanz von U(VI) als Folge seiner natürlichen Verbreitung sowie bergbaulicher Altlasten. Schließlich werden auch potentielle Anwendungsoptionen von spezifischen Komplexverbindungen des Urans diskutiert.
Wir haben einige Imin-Liganden synthetisiert und drei neue Komplexverbindungen mit UO2(NO3)2 strukturell charakterisiert. Zum Vergleich wurden auch die strukturanalogen Aminderivate in die Untersuchungen einbezogen. Extraktionsexperimente mit den genannten Liganden zeigen differenzierte Extraktionseigenschaften gegenüber U(VI) mit einer ausgeprägten Selektivität gegenüber Eu(III).

Kelvin probe force microscopy (KPFM) is used for the nanoscale characterization of semiconductors. Quantitative dopant profiling by means of KPFM measurements is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions after Mn implantation [2].
In addition, it will be shown that due to surface state formation and charge trapping in a thin native oxide layer the Kelvin bias probed above differently doped regions strongly depends on the measurement frequency [3]. Therefore, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, H. Schmidt, submitted.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

Control over the morphology and spatial correlations at the nanoscale is one of the major challenge of the nowadays nanoscience and nanotechnology. Bottom-up approaches to nanostructured material synthesis are based on self-organization processes to precisely define ordered nanostructures on a large scale. Self-organization occurs via the interplay between two factors - an external constraint acting on internal system processes. During the thin film growth this is translated into the interplay between thermodynamic driving forces and kinetic constraints. In this talk I will summarize the recent research activities of our group on the phase separation during the growth of carbontransition metal thin films. Different processes can be ’switched off/on’ by external control of the experimental parameters such as temperature, substrate type, matrix/dispersed phase chemical affinity or incoming particle energy. This results in a large variety of lateral or vertical composition modulations, such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays. Such self-organization process is versatile as different carbontransition metal systems show this effect. The observed tendencies will be discussed on the basis of the interplay of thermal and energetic ion induced phenomena.

Actinide redox chemistry plays a crucial role in nuclear technology like fuel reprocessing and nuclear waste disposal aspects including predicting of actinide mobility in the environment. Hydrolysis and complex formation of the early actinides are strongly related with their redox behavior in aqueous and nonaqueous solutions. We are interested in understanding the complexation of actinide compounds under controlled redox conditions in presence of inorganic oxo ligands and organic ligands with carboxylic groups.
This study is mainly focused on the use of EXAFS spectroscopy in combination with other supporting methods. The information from EXAFS spectroscopy is restricted to a pair distribution function providing coordination numbers and distances of the next neighbors. Two pathways were used to relate this information to the spatial arrangement of the ligands: (i) EXAFS was combined with DFT calculations which introduce constraints of molecular characteristics [1], and (ii) individual solution species were preserved in crystal structures and determined with single crystal diffraction. EXAFS was used subsequently to quantify differences or identify agreement between the coordination of complex structures in solution and solid state [2-4]. EXAFS is furthermore not very sensitive to differentiate between individual solution species, especially in not a single sample. This problem was solved in the following manner: (i) combination of EXAFS with other more species sensitive techniques, e.g. like UV-Vis spectroscopy [5] and (ii) by using sample series with broad variation of species distribution and subsequent application of statistical analysis techniques to separate the scattering contribution of individual solution species [6]. Finally, we investigated the correlation between the formal redox potential and the stability range of solution species [7].

[1] Hennig et al. The sulfate coordination of Np(IV), Np(V) and Np(VI) in aqueous solution. Inorg. Chem. 48 (2009) 5350-5360.
[2] Hennig et al. Comparative investigation of the solution species [U(CO3)5]6 and the crystal structure of Na6[U(CO3)5]•12H2O. Dalton Trans. 39 (2010) 3744–3750.
[3] Takao et al. First hexanuclear UIV and ThIV formate complexes – structure and stability range in solution. Eur. J. Inorg. Chem. (2009) 4771-4775.
[4] Hennig et al. Coordination of a uranium(IV) monomer in aqueous solution and in solid state. Inorg. Chem. 47 (2008) 1634-1638.
[5] Hennig et al. The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution. Radiochim. Acta 96 (2008) 607-611.
[6] Hennig et al. Species distribution and coordination of uranyl chloro complexes in acetonitrile. Inorg. Chem. 47 (2008) 2987-2993.
[7] Takao et al. Complex formation and molecular structure of neptunyl(VI) and –(V) acetates. Inorg. Chem. 48 (2009) 8803-8810.

The aim of this paper is to present the validation of a new methodology implemented in ANSYS CFX (ANSYS, 2009), that extends the standard capabilities of the inhomogeneous MUltiple-SIze Group model (MUSIG) by additionally accounting for bubble size changes due to heat and mass transfer. Bubble condensation plays an important role in sub-cooled boiling or steam injection into pools among many other applications of interest in the Nuclear Reactor Safety (NRS) area and other engineering areas. Since the mass transfer rate between phases is proportional to the interfacial area density, a polydisperse modelling approach considering different bubble sizes is of main importance, because an accurate prediction of the bubble diameter distribution is required.
The standard MUSIG approach is an inhomogeneous one with respect to bubble velocities, which combines the size classes into different so-called velocity groups to precisely capture the different behaviour of the bubbles depending on their size. In the framework of collaboration between ANSYS and the Forschungszentrum Dresden-Rossendorf (FZD) an extension of the MUSIG model was developed, which allows to take into account the effect of mass transfer due to evaporation and condensation on the bubble size distribution changes in addition to breakup and coalescence effects.
After the successful verification of the model, the next step was the validation of the new developed model against experimental data. For this purpose an experiment was chosen, which was investigated in detail at the TOPFLOW test facility at FZD. It consists of a steam bubble condensation case at 2MPa pressure in 3.9K sub-cooled water at a large diameter (DN200) vertical pipe. Sub-cooled water flows into the 195.3 mm wide and 8 m height pipe, were steam is injected at z=0.0 m and is recondensing. The experimental results are published in (Lucas, et al., 2007). Using a wire-mesh sensor technique the main characteristics of the two-phase flow were measured, i.e. radial steam volume fraction distribution and bubble
diameter distribution at different heights and cross-sections.
ANSYS CFX 12.0 was used for the numerical prediction. A 60 degrees pipe sector was modelled in order to save computational time, discretized into a mesh containing about 260.000 elements refined towards the pipe wall and towards the location of the steam injection nozzles. Interfacial forces due to drag, lift, turbulent dispersion and wall lubrication force were considered. The numerical results were compared to the experimental data. The agreement is highly satisfactory, proving the capability of the new MUSIG model extension to accurately predict such complex two-phase flow.

The objective of this work has been to study the mechanisms governing flow and phase distributions in developing gas/liquid two phase flows in general, and the evolution of different size bubbles in an adiabatic vertical pipe in particular. Flow regimes from bubbly to churn-turbulent have been accounted for. The main emphasis of the work has been on the modeling of various interfacial forces between the dispersed bubbles and the continuous liquid, as well as of bubble/bubble interactions (coalescence and breakup).
The proposed modeling concept uses a complete set of transport equations for each field, such as the continuous liquid and dispersed bubble fields. The overall model has been implemented in a state-of-the-art computational multiphase fluid dynamics code, NPHASE–CMFD. This three-dimensional four-field model, including the continuous liquid field and three dispersed gas fields representing bubbles of different sizes, has been carefully tested for numerical convergence and accuracy, and then validated against the TOPFLOW experimental results.
The NPHASE-CMFD simulations were aimed at demonstrating the capability of the proposed modeling concepts to predict the evolution of bubble concentration from channel inlet to near-equilibrium (fully-developed) conditions downstream. Along with several interfacial closure laws, the effect of elevation on air density has also been included in the model.

In the first part of the contribution, a rather simple design of a conventional, magnetically guided, continuous positron beam will be presented. The moderator is a tungsten mesh and the energy selection is realized using a bent tube. The sample is on ground potential. Further details will be presented during the talk.
In the second part of the talk, the recent progress of the EPOS project at the Research Center Dresden-Rossendorf will be demonstrated. EPOS consists of a pulsed monoenergetic positron beam (MePS), a conventional lifetime/Doppler spectrometer (CoPS), and a setup for gamma-induced positron annihilation spectroscopy (GiPS). While CoPS and GiPS systems are available for user operation, the MePS system is still under construction. First positrons were moderated and fed into the positron lab. At the moment, the chopper/buncher/accelerator system is under construction.

We report on the nature of vacancy complexes and voids involved in H ion-induced splitting of free standing fs-GaN. The fs-GaN wafers were subjected to room temperature implantation with 50 keV H ions at a fluence of 2x10¹⁷ H cm^-2. After implantation, the wafers were annealed at different temperatures ranging from 100 to 600 °C. Variable energy Doppler broadening spectroscopy (VEDBS) was used in order to probe open-volume defects and their thermoevolution. Pulsed low energy positron lifetime spectroscopy (PLEPLS) was employed to qualitively characterize H ion-induced vacancy complexes and to observe their subtle changes during the thermally activated splitting of GaN thin layer. The decomposition of the lifetime spectra of as-implanted and annealed samples up to a temperature of 450 °C resulted in the detection of two vacancy defects: divacancies (260-282 ps) and vacancy clusters (470-650 ps). With increasing temperature, we have noted in addition the existence of other kind of vacancy-type defects, namely, monovacancies (220-236 ps) and a long lifetime which is attributed to positronium. From the values of positronium lifetime equal to 1 ns, 2.2 ns and 3.8 ns, it was possible to estimate the corresponding wall spacing according to the Tao-Eldrup model to be 0.2 nm to 0.4 nm. The fact that positron annihilation spectroscopy can give information about the wall spacing in GaN, leads us to say that this technique is able to predict the phenomenon of splitting in wide band gap semiconductors.

Kinematic simulations of the induction equation are carried out for different setups suitable for the von-Karman-Sodium (VKS) dynamo experiment. Material properties of the flow driving impellers are considered by means of high conducting and high permeability disks that are present in a cylindrical volume filled with a conducting fluid. Two entirely different numerical codes are mutually validated by showing quantitative agreement on Ohmic decay and kinematic dynamo problems using various configurations and physical parameters. Field geometry and growth rates are strongly modified by the material properties of the disks even if the high permeability/high conductivity material is localized within a quite thin region. In contrast the influence of external boundary conditions remains small.

Utilizing a VKS like mean fluid flow and high permeability disks yields a reduction of the critical magnetic Reynolds number for the onset of dynamo action of the simplest non-axisymmetric field mode. However this decrease is not sufficient to become relevant in the VKS experiment. Furthermore, the reduction of Rm_c is essentially influenced by tiny changes in the flow configuration so that the result is not very robust against small modifications of setup and properties of turbulence.

Particle Image Velocimetry (PIV) is a powerful measurement technique, suitable for the study of complex flow fields encountered in single- or two-phase flow phenomena. Air entrainment is a widely studied phenomenon, which is encountered in multiple industrial applications, as well as in nature. Results from the successful application of PIV to both impinging region and recirculation zone are presented. Both instantaneous and time-averaged flow fields were obtained. The turbulent kinetic energy is estimated from the averaged velocity fields in the recirculation zone. Simulations of the phenomenon are performed with ANSYS-CFX. The turbulence was modelled using the k-epsilon model. Experimental results were compared with the simulation and showed good agreement.

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We report on measurements of the magnetization up to 7 T, of the specific heat and electrical resistivity in fields up to 14 T, and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh₁₇S₁₅. Our data allow us to complement the superconducting phase diagram. The existence of narrow 4 d-band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the moderately high electronic contribution to the specific heat of about 107 mJ/molK², favoring the existence of a strong superconducting interaction. This fact, and the remarkably high upper critical field (exceeding the simple Pauli limit by a factor of two), give evidence of the uncommon nature of the superconductivity in Rh₁₇S₁₅.

The transverse acoustic wave propagating along the [100] axis of the cubic paramagnet Tb₃Ga₅O₁₂ (TGG) exhibits amplitude oscillations as a function of magnetic field applied in the direction of propagation. This magneto-acoustic Faraday effect shows a linear frequency dependence contrary to theoretical expectation which demands a quadratic frequency dependence. The c₄₄ mode demonstrates also a strong softening of 6% up to 19 T, the magnetic field where an energy level of the CEF triplet branch starts to cross the quasi-doublet branch. This softening has the same origin, the magneto-elastic coupling, as the anomalies in the temperature dependence of the elastic constants and the magneto-acoustic Faraday effect.

We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice spin-1/2 antiferromagnet Cs₂CuCl₄ (T_N = 0.6 K), in external magnetic fields up to 14 T, applied along the b axis, and at temperatures down to 300 mK. The results are analyzed with a quasi-two-dimensional hard-core boson theory based on exchange-striction coupling. There is a good qualitative agreement between theoretical and experimental results.

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area from 90 × 90 μm down to 20 × 20 μm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. MHPs were intensively tested in static (up to 14 T) and pulsed magnetic fields and shown to be appropriate for various applications in the temperature range 2–300 K and in pulsed magnetic fields up to 87 T. The latest version of these probes, with overall cross-section thickness-width dimensions of 150 × 750 μm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged or unpackaged sensors.