Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The interaction of high-intensity, ultra-short laser pulses with matter is based on the well-understood physics of classical electromagnetics. In order to design, analyse and optimize laser-driven radiation sources, understanding the microscopic dynamics of electrons and ions interacting with strong laser fields is vital. These complex dynamics are both hard to resolve in experiment and hard to describe by analytic models. Here, realistic simulations based on the fundamental physical laws which govern the interaction can provide new and valuable insights. So-called computer experiments can bridge the gap between experiment and analytic theory and thus advance our understanding of the underlying plasma dynamics. Today, newest high performance computing technology makes it possible to incorporate all relevant physical processes in the simulation. With this, detailed modelling of experiments has entered the stage and will guide the way to new laser-driven radiation sources.

At FZD the combination of ultra-short high-power Lasers and ultra-brilliant electron accelerators allows to provide unique sources for ions, electrons and photons. In combination, these sources will allow to probe the structure of matter in a new way, from applications in material science, the detection of strong magnetic fields, as a tool to study short-time-scale plasma dynamics and as a possible future source for medical applications. This talk presents some of the recent results and developments at FZD concerning new targets for ion beams, short-pulse x-ray sources and intense electron beams.

Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches at a best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs.

Introduction: Among the presolar grains in meteorites, nanodiamonds are still the most enigmatic. Partly this is due their small size, which would render results from single grain analyses - even if they were possible – of limited value. Another reason is the low abundance of trace elements [1]. In acid resistant residues that also contain “impurities” of presolar silicon carbide, the trace element pattern is dominated by the SiC contribution for many elements, in particular in the REE range [2]. The most distinctive isotopic patterns linking the diamonds to a supernova have been observed in the noble gases, in particular xenon [3, 4]. This has been supplemented by large effects observed in tellurium [5], and smaller not so telling effects in a few other elements (Sr, Ba, Pd: [6, 7]).
Experimental: We have been continuing our search for isotopic effects in platinum. As in [8], we use accelerator mass spectrometry, which eliminates molecular interferences, a problem encountered in our multi-grain multi-element study by ICP-MS [2]. AMS is also able in principle to distinguish between true isobars, but this has not been necessary in our case. Ignoring low-abundant ¹⁹⁰Pt and ¹⁹²Pt, the only interfering isobars are at masses 196 and 198 from volatile Hg, which is not present in the beam when using negative ions. Measurements were performed at the Vienna Environmental Research Accelerator (VERA) [9] using similar methods as in our previous work at TU Munich [8]. VERA has recently been optimized for heavy ion detection, resulting in improved precision and background suppression.
Results: We observed enhancements in ¹⁹⁸Pt/¹⁹⁵Pt by ~6% in two diamond residues from Allende, AKL and AMW, which were prepared by different dissolution techniques [8]. Analyses were run in two different analytical sessions and the effect was reproduced. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly could be identified in a third Allende diamond sample.
Interpretation: Enhanced ¹⁹⁸Pt/¹⁹⁵Pt is predicted by both the neutron burst model [10] and the rapid r-process separation scenario [11]. However, the latter also predicts a strong negative anomaly in ¹⁹⁴Pt/¹⁹⁵Pt, which is not observed. Thus, the Pt results seem to favor the neutron burst model. This is in contrast to the situation in tellurium (and xenon, to some extent) and adds to the enigma of the nanodiamonds.
References: [1] Lewis R. S. et al. 1991. Meteoritics 26:363-364. [2] Yin Q.-Z. et al. 2006. Astrophysical Journal 647:676-684. [3] Lewis R. S. et al. 1987. Nature 326:160-162. [4] Huss G. R. & Lewis R. S. 1994. Meteoritics 29:791-810. [5] Richter S. et al. 1998. Nature 391:261-263. [6] Lewis R. S. et al. 1991. 22nd Lunar and Planetary Science Conference. pp. 807-808. [7] Maas R. et al. 2001. Meteoritics & Planetary Science 36:849-858. [8] Merchel S. et al. 2003. Geochimica et Cosmochimica Acta 67:4949-4960. [9] Wallner A. 2010. Nuclear Instruments and Methods in Physics Research B268: 1277-1282. [10] Meyer B.S. et al. 2000. Astrophysical Journal Letters 540:L49-L52. [11] Ott U. 1996. Astrophysical Journal 463:344-348.

Hafnium oxynitride films are deposited from a Hf target employing direct current magnetron sputtering in an Ar-O₂-N₂ atmosphere. It is shown that the presence of N₂ allows for the stabilization of the transition zone between the metallic and the compound sputtering mode enabling deposition of films at well defined conditions of target coverage by varying the O₂ partial pressure. Plasma analysis reveals that this experimental strategy facilitates control over the flux of the O- ions which are generated at the oxidized target surface and accelerated by the negative target potential towards the growing film. An arrangement that enables film growth without O- ion bombardment is also implemented. Moreover, stabilization of the transition sputtering zone and control of the O- ion flux without N₂ addition is achieved employing high power pulse magnetron sputtering. Structural characterization of the deposited films unambiguously proves that the phase formation of hafnium oxide and hafnium oxynitride films with the crystal structure of HfO₂ is independent from the O- bombardment conditions. Experimental and theoretical data indicate that the presence of vacancies and/or the substitution of O by N atoms in the non-metal sublattice favor the formation of the cubic and/or the tetragonal HfO₂ crystal structure at the expense of the monoclinic HfO₂ one.

Cell shape and architecture are determined by cell-extracellular matrix interactions and have profound effects on cellular behavior, chromatin condensation, and tumor cell resistance to radiotherapy and chemotherapy. To evaluate the role of chromatin condensation for radiation cell survival, tumor cells grown in three-dimensional (3D) cell cultures as xenografts and monolayer cell cultures were compared. Here, we show that increased levels of heterochromatin in 3D cell cultures characterized by histone H3 deacetylation and induced heterochromatin protein 1α expression result in increased radiation survival and reduced numbers of DNA double strand breaks (DSB) and lethal chromosome aberrations. Intriguingly, euchromatin to heterochromatin–associated DSBs were equally distributed in irradiated 3D cell cultures and xenograft tumors, whereas irradiated monolayer cultures showed a 2:1 euchromatin to heterochromatin DSB distribution. Depletion of histone deacetylase (HDAC) 1/2/4 or application of the class I/II pharmacologic HDAC inhibitor LBH589 induced moderate or strong chromatin decondensation, respectively, which was translated into cell line–dependent radiosensitization and, in case of LBH589, into an increased number of DSBs. Neither growth conditions nor HDAC modifications significantly affected the radiation-induced phosphorylation of the important DNA repair protein ataxia telangiectasia mutated. Our data show an interrelation between cell morphology and cellular radiosensitivity essentially based on chromatin organization. Understanding the molecular mechanisms by which chromatin structure influences the processing of radiation-induced DNA lesions is of high relevance for normal tissue protection and optimization of cancer therapy.

The influence of the high temperature annealing ambient (N₂ or Ar) on size controlled Si nanocrystals (NCs) in SiO₂ ranging from ~2 to ~6 nm has been investigated in detail. Generally, N₂ annealing is beneficial as the dangling bond density (Pb-defects at the NC/SiO2 interface) is about half accompanied by a doubled PL intensity. The N-related PL blueshift was found to be pronounced only for the small NCs whereas it appears to be insignificant for larger NCs. The origin of this N-blueshift was previously attributed to NC growth suppression by the presence of N. However, no evidence for this assumption is found by time-resolved PL, as the luminescence decay times are similar despite considerable N-blueshift. The exact location of the N incorporated during annealing was investigated by ToF-SIMS and ESR: Besides the distinct N-enrichment in the NC-layer, the K⁰-center (•Si≡N₃) was detected indicating the formation of an interfacial N layer at the NC/SiO₂ interface. ERD analysis enabled the quantification of the incorporated N as well as the excess Si. Combined with TEM analysis (determination of NC size) the calculation of the NC-density per superlattice layer and the thickness of the interfacial N-layer were achieved. It turns out that ~ 5×10¹⁴ N-atoms cm^-2 exist at the NC, which is well in accordance to the optimum value of the bulk Si/SiO₂ interface. These results support our recently suggested explanation for the N-blueshift that is based on the influence of the polarity of the surface terminating groups on the bandgap of the NC.

The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI), neptunium(V) and selenium(VI) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, iron, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy.
Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.

A resistive plate counter for timing purposes in the high-rate environment of the Compressed Baryonic Matter Experiment has been developed at the Forschungszentrum Dresden-Rossendorf. The detector electrodes are made of a ceramics composite.
Detector tests have been performed with minimum ionizing single electrons, delivered by the electron accelerator ELBE with a time accuracy of few picoseconds. The ceramics RPC shows an all-time high-rate capability for electron fluxes up to 2.7x10E5 /s/cm².

In order to validate newly developed multiphase flow models in the code ANSYS CFX, a CFD simulation of the counter-current two-phase flow of 1/3rd scale model of the hot leg of a German Konvoi Pressurized Water Reactor with rectangular cross section was performed. A selected air-water Counter-current flow limitation (CCFL) experiment of Forschungszentrum Dresden-Rossendorf (FZD) at 0.153 MPa and room temperature was simulated with three-dimensional two-fluid Euler-Euler models of computer code CFX 12.0 (ANSYS CFX). The calculation was carried out in fully transient manner using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model. In the simulation, the drag coefficient was approached by the Algebraic Interfacial Area Density (AIAD) model. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. Next, a comparison with the high-speed video observations shows also a good qualitative agreement.

Codes for reactor core calculations use few-group cross sections (XS) which depend on local burnup, given in terms of the energy produced per fuel mass (MWd/kgHM). However, a certain burnup value can be reached under different spectral conditions depending on moderator density and other local parameters. Neglecting these spectral effects, i.e. applying the summary-burnup value only, can cause considerable errors in the calculated power density.
This paper describes a way to take into account spectral-history effects. It is shown that the respective XS correction linearly depends on the actual Pu-239 concentration. The applicability of the method was proved not only for usual uranium oxide fuel, but also for mixed uranium/plutonium oxide (MOX) and fuel assemblies with burnable absorber. The code DYN3D was extended by new subroutines which calculate the actual distribution of Pu-239 in the core and apply a spectral-history correction for the XS.

The behavior of minor hysteresis loops in perpendicular anisotropy [Co/Pt]- and [Co/Pd]-multilayers has been investigated. Upon applying a succession of identical magnetic field cycles, we observe a very substantial cumulative growth of the minor loop area. For the [Co/Pt] multilayers this effect only saturates near complete magnetization reversal, while the behavior is slightly more limited for [Co/Pd] multilayers. We also find this cumulative growth to occur even if the minor loop field cycles are made asymmetric by means of a positive bias field. The cumulative behavior persists up to a sample dependent threshold value above which this effect disappears. In all samples, the cumulative minor loop growth is correlated with a small reduction of the maximum magnetization value in each cycle. Magneto-optical Kerr microscopy studies correlate the minor-loop growth with the memory and cumulative expansion of lateral domain cycling. All experimental observations can be consistently explained as an accumulation of small nucleation domains that aid subsequent reversals and facilitate the cumulative minor loop growth.

Currently, gas phase chemistry experiments with heaviest elements are usually performed with the gasjet technique with the disadvantage that all reaction products are collected in a gas-filled thermalisation chamber adjacent to the target. The incorporation of a physical preseparation device between target and collection chamber opens up the perspective to perform new chemical studies. But this approach requires detailed knowledge of the stopping force (STF) of the heaviest elements in various materials. Measurements of the energy loss of mercury (Hg), radon (Rn), and nobelium (No) in Mylar and argon (Ar) were performed at low kinetic energies of around (40–270) keV per nucleon. The experimentally obtained values were compared with STF calculations of the commonly used program for calculating stopping and ranges of ions in matter (SRIM). Using the obtained data points an extrapolation of the STF up to element 114, eka-lead, in the same stopping media was carried out. These estimations were applied to design and to perform a first chemical experiment with a superheavy element behind a physical preseparator using the nuclear fusion reaction 244Pu(48Ca; 3n)289114. One decay chain assigned to an atom of 285112, the adecay product of 289114, was observed.

The intermetallic compounds RIn3 and RTIn5 (R = rare earth, T = transition metal) have attracted great interest for their large variety of anomalous ground states. Among these are the well-known heavy-fermion superconductors CeCoIn₅ and CeIrIn₅. We present here a dHvA study of YbCoIn₅ and LuCoIn₅, performed by use of a capacitive torque cantilever technique at temperatures down to 0.4 K in magnetic fields up to 13 T. In addition, one single crystal of LuCoIn₅ has been measured in magnetic field up to 34 T. Besides their angular-dependent Fermi-surface topologies, we have also determined the effective masses of the different bands by following the temperature-dependent amplitude changes of the dHvA oscillations. A large number of different dHvA frequencies has been observed for the main crystallographic directions. In contrast to CeCoIn₅ and CeIrIn₅, the cyclotron effective masses for these compounds are in the range from 0.7 to 2.0 m₀.

Tb₅Ge₃ is a weak antiferromagnet, which orders at 83 K. It crystallizes in Mn₅Si₃-type hexagonal structure with two different positions for the Tb³⁺ ions. The hexagonal ab-plane is the easy plane of magnetization. Magnetization and magnetostriction measurements have been done on a single crystal in static fields up to 30 T and in pulsed fields up to 50 T. In addition to the antiferromagnetic phase, three more phases were found in fields in the ab-plane at low temperatures. Surprisingly, the measurements along the b-axis do not resemble the a-axis properties which indicates an anisotropy in the hexagonal plane. Initial model calculations reveal the anisotropy of the magnetic exchange, which is dominant over the crystal electric field effect, as cause. The hard c-axis shows only one phase transition at 5 T followed by a nearly linear magnetization and magnetostriction slope which is attributed to a steady-going rotation of the moment.

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Rh₁₇S₁₅ is a 4d-electron metal which becomes superconducting below T_c = 5.4 K at zero field. The upper critical field is 19.2 T at T = 0.07 K. Above T_c, Rh₁₇S₁₅ is a paramagnet. The crystallographic structure (Pm3m) of Rh₁₇S₁₅ features a nearest-neighbor Rh-Rh distance even less than in elementary (fcc) Rh, possibly resulting in a high density of 4d-electron states at the Fermi level. Using a polycrystalline sample, we measured the specific heat, resistivity, magnetization, and magnetostriction in fields up to 14 T as well as the magnetic susceptibility in fields up to 20 T. Our data allow us to present the complete superconducting phase diagram. The assumption of narrow 4d band states (and thus of strong electronic correlations not providing magnetic correlations) is supported by the moderately enhanced electronic contribution to the specific heat of 107 mJ/molK² and favors the existence of a strong superconducting interaction. Together with the remarkably high upper critical field (exceeding the Pauli limit by a factor of two), our findings make Rh₁₇S₁₅ a likely candidate for unconventional superconductivity.

The rare-earth nickel borocarbides show an intriguing competition between magnetism and superconductivity. For HoNi₂B₂C, this leads to a rich phase diagram with superconducting and magnetic phase transitions. Besides these competing electronic interactions, also the nuclear magnetic moment of Holmium may influence the superconducting state due to an expected strong hyperfine-enhanced nuclear polarization. In order to study this in more detail, we performed high-resolution specific-heat measurements by use of a continuous relaxation-time method. While the superconducting transition at about 8 K results in a very small, but resolvable specific-heat jump, at lower temperatures there are at least three independent magnetic-ordering transitions. One of these shows a lambda-like anomaly with a small hysteresis indicating a first-order phase transition. Additionally, the increasing specific heat below 1 K can be taken as evidence for a pronounced hyperfine contribution.

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The results of investigations of the point defect generation, redistribution and interaction with impurities in the Si–SiO₂ system during the process of its formation by means of electron paramagnetic resonance (EPR) and nucleus magnetic resonance (NMR) techniques are presented. The type and density of the point defect that are generated in the Si surface layer during thermal oxidation depend on the oxidation condition: temperature, cooling rate, oxidation time, and impurity content. The interaction between the point defects with extended defects and impurities affects the properties of the Si–SiO₂ interface. The influence of the point defects may be diminished and the interface properties improved by an appropriate choice of the oxidation conditions. The difference between the interface properties of n- and p-type wafers may be connected with the different position of the Fermi level at the interface and different point defects density in the volume near the interface.

A joint experimental and theoretical investigation of the spin 1/2 system Cu₂(PO₃)₂CH₂ suggests a description of this compound as coupled alternating antiferromagnetic Heisenberg chains. Magnetic susceptibility, specific heat, nuclear magnetic resonance, nuclear quadrupole resonance, and high-field magnetization measurements evidence a spin gap of about 25 K. Surprisingly, the leading antiferromagnetic exchange of about 75 K can be assigned by density-functional band-structure calculations to a coupling between the structural Cu₂O₆ dimers, whereas the coupling within these dimers is strongly reduced due to sizable ferromagnetic contributions. The coupling within the structural dimers competes with a number of long-range couplings. The present available experimental data can be consistently described in a scenario of coupled alternating chains. The proposed model should be considered as a minimal model for an appropriate description of this compound.

Tm₂Co₁₇ is a ferrimagnet with T_C = 1170 K and, at 4.2 K, has a spontaneous magnetic moment M_s =13.4 mu_B/ f.u. Magnetization curves were measured on a Tm₂Co₁₇ single crystal along the principal axes in pulsed magnetic fields up to 70 T at 4.2 K. The curve along the easy [001] direction exhibits a distinct anomaly at mu₀H_cr = 39 T, where the magnetization exhibits a stepwise rise from M_s to M_flip = 40.6 mu_B/ f.u. The observed transition from the ferrimagnetic ground state (with M_s = 17mu_Co − 2mu_Tm) to a saturated spin-flip state with parallel orientation of the sublattice moments and M_flip = 17mu_Co + 2mu_Tm is unusual for 3d-4f intermetallics because it does not proceed via an intermediate angled-sublattice state. Rather, a collinear remagnetization of the Tm sublattice takes place: as the applied magnetic field grows, the Tm moments disorder at first, reaching a fully disordered paramagnetic state at H = H_cr, then they order magnetically in the opposite sense.

Large single crystals (∼6 mm in diameter and 35-50 mm in length) of spin dimer system Sr₃Cr₂O₈ have been grown in a four-mirror type optical floating-zone furnace under different atmospheres. Single crystals were characterized by polarized optical microscopy, energy dispersive X-ray analysis, X-ray powder diffraction, X-ray, and neutron Laue measurements, etc. Crystals were grown under an optimized growth atmosphere of flowing (6-8 L/min) synthetic air found to be free of any impurities and excellent in quality. Characteristics of the magnetic susceptibility and magnetization along different crystallographic axes are also shown.

We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn₅, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu₂Si₂, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition.

We report results on ultrasound studies of the frustrated magnet CdCr₂O₄. This compound demonstrates an antiferromagnetic ordering at T_N = 7.8 K and a metamagnetic phase transition at 28 T followed by a wide magnetization plateau with one half of the full moment of S = 3/2 of Cr³⁺ ions. A longitudinal acoustic mode in the [111] crystallographic direction exhibits pronounced effects both in the temperature and magnetic-field dependencies. Pulsed-field measurements show a drastic change in the sound velocity just below and above the 1/2 magnetization plateau. Our results suggest a large spin-strain coupling and give evidence for a pronounced interplay between spin and lattice degrees of freedom in CdCr₂O₄.

Abstract We report on results of sound velocity and sound-attenuation measurements performed on the antiferromagnetic (T_N = 48 K) UCuGe. The measurements have been done on a UCuGe single crystal at different frequencies for longitudinal ultrasound waves propagating along the [001] direction in static (up to 18 T) and pulsed (up to 60 T) magnetic fields applied along the same direction. The temperature dependences of the sound velocity and attenuation display a pronounced anomaly at T_N, which is evidence for a strong magneto-elastic interaction. The pulse-field measurements at 4.2 K show a minimum in the sound velocity followed by a jump-like anomaly at 37 T, and another kink-like anomaly at 48–49 T. These anomalies are due to field-induced spin rearrangements as measured in magnetization studies. In the paramagnetic state (T > T_N), both acoustic characteristics show large frequency-dependent changes revealing the presence of an unusual relaxation mechanism which might be due to vacancy dynamics.

The 14N(p,gamma)15O reaction is the slowest reaction of the carbon-nitrogen-oxygen cycle of hydrogen burning in stars. As a consequence, it determines the rate of the cycle. The 15N(p, alpha gamma)12C reaction is frequently used in inverse kinematics for hydrogen depth profiling in materials. The 14N(p,gamma)15O and 15N(p, alpha gamma)12C reactions have been studied simultaneously, using titanium nitride targets of natural isotopic composition and a proton beam. The strengths of the resonances at Ep = 1058 keV in 14N(p,gamma)15O and at Ep = 897 and 430 keV in 15N(p, alpha gamma)12C have been determined with improved precision, relative to the well-known resonance at Ep = 278 keV in 14N(p,gamma)15O. The new recommended values are omega gamma = 0.353 ± 0.018, 362 ± 20, and 21.9 ± 1.0 eV for their respective strengths. In addition, the branching ratios for the decay of the Ep = 1058 keV resonance in 14N(p,gamma)15O have been redetermined. The data reported here should facilitate future studies of off-resonant capture in the 14N(p,gamma)15O reaction that are needed for an improved R-matrix extrapolation of the cross section. In addition, the data on the 430 keV resonance in 15N(p, alpha gamma)12C may be useful for hydrogen depth profiling.

Summary
Measurement of multiphase flow rates, for example in gas-liquid two-phase flow, is a challenging issue in many industrial applications. While current solutions are based on upstream phase separation or combination of different methods (e.g. densitometry and Venturi tube flow meter), the target of our new sensor is to allow an inline measurement of multiphase flow rates at lower cost and space requirements. Starting with flow rate measurements in gas-liquid systems, the sensor principle is to subdivide the gas-liquid flow into partial streams of alternating gas and liquid fractions (also called Taylor flow) in a grid of small tubes. This allows contactless instantaneous phase detection and time-resolved detection of subsequent phase transitions using a capacitance sensing principle based only on the dielectric properties of the flu-ids. The sensor design will be discussed in detail, a prototype introduced and simulation and experimental results presented. Further, application requirements and limitations of the measurement principle will be discussed. The performance of the multiphase flow meter was evaluated from experiments in a gas-liquid flow loop.
Motivation
Multiphase flows, whether wanted or not, are encountered in very different industrial areas, e.g. oil explo-ration, fueling of petrol or in milk floats, chemical production units, etc. However, they have in common, that they often require quantitative measurement or at least qualitative detection of multiple phases. Con-ventional measurement systems typically require expensive phase separation units to allow the applica-tion of well-established single phase measurement equipment. Alternatively, transmission-based systems that are costly and require stringent safety regulations may be combined with measurement devices that reveal mixture velocity by cross-correlation methods. However, measurement accuracy decreases clearly if the flow deviates from a-priori assumed well-defined regimes and if phases separate locally. To summarize, economic and space saving sensor concepts would be highly appreciated.
Results
The development of the new sensor concept makes use of preferable flow conditions (superficial gas and liquid flow rates), such as the Taylor flow regime, which allows sharp discrimination of phase transitions at intermitted liquid and gas fractions. As a preliminary study such gas-liquid flow scenarios were ob-served in a transparent sensor model using a high speed camera (see Fig. 1). Important design specifications for a high functionality of the sensor concept (prevention of micro bubbles or single-phase formations) were derived. Furthermore, characteristic flow behavior was studied and findings of earlier studies confirmed.
At Taylor flow conditions, phase transition can be detected at two positions with an axial offset (see Fig. 2) and velocity of the corresponding fraction can be determined by cross-correlation. As a detection principle we use local capacitance measurement due to its conceptual simplicity and capability of discriminating many different fluids. An optimized electrode configuration was chosen by performing field simulations on the fluid layers. (see Fig. 3)

Prior to their restoration, the porcelain bodies of broken pieces from 31 authentic Meissen objects of the early 18th century were investigated by proton-beam analysis. Attention was paid so that the proton beam probed only the bare porcelain paste areas of fractures. Thus, contributions to the measured X-ray and γ-ray spectra from adjacent surface glaze were prevented. The chemical compositions, obtained by simultaneous detection of elements with Z ≥ 13 (X-rays) and lighter elements Z ≤ 14 (γ-rays), represent rather consistent mixtures of paste ingredients. This result highlights the durable recipes and raw materials used in early Meissen porcelain production in the years 1725–50. Mean concentration values of element oxides, deduced from the detailed measurements, prove suitable for use as a database for Meissen porcelain paste identification. Material authentication of intact objects, without access to the bare porcelain body, is demonstrated by inspection of the white glaze. Unique museum objects are examined in atmosphere and without sampling. A low proton-beam intensity and a short irradiation time ensure non-destructive analysis. Simultaneous radiation and backscattered particle detection allow complete composition analysis, using the established ion beam techniques of particle-induced X-ray emission (PIXE), particle-induced gamma-ray emission (PIGE) and Rutherford backscattering spectrometry (RBS).

The deuteron breakup reaction pd→{pp}sn, where {pp}s is a fast proton pair emitted in forward direction with small excitation energy Epp<3  MeV, has been studied at proton beam energies of 0.5–2.0  GeV using the ANKE spectrometer at COSY-Jülich. The differential c.m. cross sections are measured in complete kinematics and provide angular distributions of the neutron emission angle in the range θn=168°–180°, the dependence on beam energy at θn=180°, angular distributions of the direction of the proton in the pp rest frame, and distributions of the excitation energy Epp of the proton pair. The obtained data are analyzed on the basis of theoretical models previously developed for the pd→dp process in a similar kinematics and properly modified for the diproton channel in pd→{pp}sn. It is shown that the measured observables are highly sensitive to the short-range part of the nucleon-nucleon interaction.

Nuclear astrophysics strives for a comprehensive picture of the nuclear reactions responsible for synthesizing the chemical elements and for powering the stellar evolution engine. Deep underground in the Gran Sasso laboratory the cross sections of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The salient features of underground nuclear astrophysics are summarized here. The main results obtained by LUNA in the last twenty years are reviewed, and their influence on the comprehension of the properties of the neutrino, of the Sun and of the Universe itself are discussed. Future directions of underground nuclear astrophysics towards the study of helium and carbon burning and of stellar neutron sources in stars are pointed out.

The speciation of Zn in contaminated soils depends on soil pH, clay content, and other soil properties. However, it is currently unclear how the type of Zn-bearing contaminant itself influences the Zn species newly formed in soils upon contamination. Therefore, we conducted a soil incubation study in which four soils (pH 4.2 to 7.7) were spiked either with ZnO (zincite) or ZnS (sphalerite) to a total Zn concentration of 2000 mg/kg and then incubated under aerated conditions near field capacity. The extractability and speciation of Zn were assessed after 1, 2, and 4 years of incubation using extractions with 0.01 M CaCl2 and Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy, respectively. ZnO was dissolved most rapidly in the acidic soils, and in all soils more than 90% of the added ZnO were dissolved after four years. Fast dissolution of ZnO presumably results in elevated pH and high local Zn concentrations around dissolving ZnO particles, favoring the formation of Zn-LDH, and to a lesser degree Zn-phyllosilicates besides adsorbed Zn species. In contrast, ZnS dissolved much more slowly, reaching only 25 to 97% of the added ZnS after four years, with lower dissolution rates in the acidic soils. The resulting Zn speciation after 4 years was markedly different, with Zn-LDH only occurring in the neutral and alkaline soils. In both cases, adsorbed Zn was mainly octahedrally coordinated Zn bound as outer-sphere complex or Zn bound to HIM in the acidic soils, whereas tetrahedrally coordinated Zn sorbed as inner-sphere complex was found to be more important at higher soil pH. These results show that the type of Zn-bearing contaminant and its influence on local chemical conditions in addition to bulk soil properties control the types of Zn species forming in contaminated soil.

The synthesis of PuCrO3 compound starting from metallic or sesquioxide chromium and PuO2 powder mixtures in stoichiometric ratios has been studied at different temperatures under atmospheres with a varying oxygen potential (Ar, Ar + 5% H2, Ar + 5% H2 + 850 ppm H2O). The structure of the polycrystalline perovskite compound PuCrO3 was investigated by X-ray powder pattern fitting. A Rietveld analysis was performed using the computer program JANA 2000. PuCrO3 crystallizes in the orthorhombic space group Pbnm with a = 543±2 Å, b = 549±2 Å and c = 771±2 Å. A XAS study gave oxidation states +III for both chromium and plutonium. The heat capacity of PuCrO3 was measured by means of a differential scanning calorimeter (DSC) in the temperature range of 373–1373 K. Debye temperature as well as electronic defect energies have been fitted from these measurements. Enthalpy increment, entropy and free energy function of PuCrO3 have been calculated from the measured heat capacity and estimated data as a function of temperature.

In this paper we propose a new procedure for fast evaluation of the potential of periodic operations in trickle-bed reactors, based on empirical modeling. Step response experiments, with different input amplitudes, were performed on a laboratory trickle-bed reactor, in order to derive a simple nonlinear dynamic model. α-methylstyrene (AMS) hydrogenation was used as a test reaction and the feed AMS concentration was used as the modulated input. An empirical nonlinear model was postulated and used for simulation of periodic operations. The simulation of a periodic operation with sinusoidal modulation of the inlet AMS concentration with 40 % amplitude resulted with up to 35% higher time averaged conversion than the corresponding steady-state one.

Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.

We report on the development of measurements techniques for flows in lead-bismuth eutectic alloys (LBE). This paper covers the test results of newly developed contact-less flow rate sensors as well as the development and test of the LIDAR technique for operational free surface level detection. The flow rate sensors are based on the flow-induced disturbance of an externally applied AC magnetic field which manifests itself by a modified amplitude or a modified phase of the AC field. Another concept of a force-free contactless flow meter uses a single cylindrical permanent magnet. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. The operation of those sensors has been demonstrated at liquid metal test loops for which comparative flow rate measurements are available, as well as at the LBE loops THESYS at KIT and WEBEXPIR at SCK-CEN. For the level detection a commercial LIDAR system was successfully tested at the WEBEXPIR facility in Mol and the THEADES loop in Karlsruhe.

In this paper we present the new experimental facility LIMMCAST for modeling the continuous casting process of steel by using the low melting point alloy SnBi. The facility operates at temperatures of 200°C-400°C. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. First experimental results will be presented which have been obtained using a small-scale preliminary set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied.

Cryogenic techniques in laser spectroscopy are currently used in scanning tunnelling microscopy (STM) and single molecule spectroscopy. Recently such cryogenic devices have also been adapted to time resolved laser-induced fluorescence spectroscopy (TRLFS) systems applied to uranium. We used TRLFS at low temperatures (cryo-TRLFS) as an experimental technique to investigate the uranium(VI) complexation with a variety of organic ligands (glucose, citric acid, oxalic acid). For the first time, luminescence properties were determined for a uranium(VI) glucose complex [1], uranium(VI) citrate [2] and uranium(VI) oxalate [2] species by cryo-TRLFS at 153 K. The emission signals are bathochromic shifted in comparison to the emission maxima of the uncomplexed uranyl(VI) cation. Using the spectroscopic data, the corresponding complex formation constants were calculated. This is a great improvement towards TRLFS measurements at room temperature, where emission signals of the complex species are not detectable. Our TRLFS investigation at low temperature opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encountered at room temperature condition are suppressed. In addition we used cryo-TRLFS technique for studying uranium(VI) speciation in natural samples. The uranium(VI) speciation in urine and in mineral water [3] could be thus investigated. Samples with an uranium concentration of < 0.1 μg/L could be analyzed unproblematically. The complexation of uranium(VI) with carbonate in commercial mineral waters could be verified. In urine, it was found that the uranium(VI) speciation strongly depends on the pH, with the latter varied between 5 and 7 as observed in human samples. Up to pH value of 6 the uranium(VI) speciation is defined mostly by organic ligands. At higher pH the uranium(VI) speciation should be dominated by inorganic phosphate complexes or carbonate complexes. The fluorescence spectroscopic analysis showed a mixture of complexation by citrate and phosphate at lower pH (< 6) and at higher pH (> 6) an dominance of complexation by carbonate. This results are in a very good correspondence with model calculation of the uranium(VI) speciation in urine.

We report thermal annealing and 100 MeV Si8+ swift heavy ion irradiation effects on the structural and magnetic properties of Ni-implanted HfO2 thin films. At low Ni doping concentration (1%), HfO2 thin films show ferromagnetic behavior. We clearly demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization vs. temperature data. Rutherford backscattering spectrometry is used to estimate the film thickness and to establish that Ni-ions are placed in the HfO2 matrix. By comparing the results for the annealed and swift heavy ion irradiated samples, it is concluded that the enhancement in magnetic signal is closely related to the dispersion/diffusion of implanted Ni and defect creation such as oxygen vacancies. The results of magnetic force microscopy supported the observation of room temperature ferromagnetism in Ni-implanted HfO2 films.

Introduction
Carbon nanotubes (CNTs) are structurally well-defined, chemically inert and electrically conducting or semi-conducting fibers which have extensively been explored for medical applications as active components such as antibacterial agents or electric conductors, as templates for cell growth, drugs and magnetic probes or as sensors. Recently, the enhanced antibacterial activity of dispersed single-wall CNTs was successfully related to the piercing of the bacterial cell membranes by the CNTs [1]. Solution-spun composite fibers from CNTs and DNA have proven their suitability as electrically conducting scaffolds, which target muscle or nerve repair [2]. Regularly aligned CNTs are efficient and inert templates for the growth and proliferation of human osteoblasts [3]. Cancer treatment relies on the ability of CNTs to specifically deliver anti-cancer agents and on the hyperthermal effect induced by magnetically doped CNTs in an oscillating magnetic field [4] CNT-based sensors exhibit an exceptional specificity for measuring electronic properties of small biological structures [5]. Here we focus on the functionalization of CNTs by DNA molecules; we present an analysis of the nanoscale CNT-DNA interactions and the immobilization of such aggregates on oxidic surfaces.

Materials and Methods
Carbon nanotubes embedded in single-stranded DNA (CNT@DNA) were investigated by self-consistent density-functional-based tight-binding calculations (DFTB). A phenomenological model for the stability was derived, which gives the CNT-DNA interaction energy as a function of the nanotube radii and the number of DNA chains [6]. To study anchoring such aggregates on scaffold materials we analyze the interactions which bond the nucleotide to oxidized surfaces by DFTB calculations [7].

Results and Discussion
Single CNTs are readily complexed by DNA, but for CNT bundles an essential energy gain is only obtained, if multiple DNA chains wrap around the tubes. Hence, the destruction of the CNT bundles, e.g. by sonication, can promote the CNT@DNA complex formation. Pyrimidine-based homopolymeric DNA more effectively wraps the CNT, whereas purine-based DNA exhibits a larger radius selectivity. The CNT-DNA interaction is not a genuine van-der-Waals interaction. The electronic structure of most aggregates is close to a superposition of the electronic states of the “free” DNA and CNT fragments. However, within a small structural window there exist several very strongly bonding systems which are characterized by combined electronic states. Hence, magic matching occurs in conjunction with a remarkable charge transfer (Fig. 1).
While the DNA-CNT interaction involves the aromatic part of the DNA immobilization of suchsystems on oxidic surfaces occurs mainly via the phosphate group. The preferred anchoring on titania and alumina [7,8] relies on bonding two oxygen atoms of the phosphate group to the surface by esterification. The resulting structures are stable against solvatation.

YFeMnO5 crystallizes in the structure type of the orthorhombic RMn2O5 class of oxides. These show a series of antiferromagnetic phases with propagation vectors (1/2-δ, 0, 1/4+є) below TN ≈ 45 K. For several of these phases, magnetism coexists with ferroelectricity. In YFeMnO5, only one commensurable ferrimagnetic phase was found below TN = 165 K, and ferroelectricity is absent. We apply crystallographic and quantum chemical methods to compare the Fe-substituted and the mangenese-only compounds. Diffraction experiments show slight displacements of the atom sites with increasing Fe content. The largest effects are related to crystal-field repulsion acting on the local metal 3d orbitals. The interaction between the magnetic metal ions is studied using DFT calculations starting with a bias magnetization of the atoms.

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)